Provided by: gcc-11_11.4.0-1ubuntu1~22.04_amd64 bug

NAME

       gcc - GNU project C and C++ compiler

SYNOPSIS

       gcc [-c|-S|-E] [-std=standard]
           [-g] [-pg] [-Olevel]
           [-Wwarn...] [-Wpedantic]
           [-Idir...] [-Ldir...]
           [-Dmacro[=defn]...] [-Umacro]
           [-foption...] [-mmachine-option...]
           [-o outfile] [@file] infile...

       Only the most useful options are listed here; see below for the remainder.  g++ accepts mostly the same
       options as gcc.

DESCRIPTION

       When you invoke GCC, it normally does preprocessing, compilation, assembly and linking.  The "overall
       options" allow you to stop this process at an intermediate stage.  For example, the -c option says not to
       run the linker.  Then the output consists of object files output by the assembler.

       Other options are passed on to one or more stages of processing.  Some options control the preprocessor
       and others the compiler itself.  Yet other options control the assembler and linker; most of these are
       not documented here, since you rarely need to use any of them.

       Most of the command-line options that you can use with GCC are useful for C programs; when an option is
       only useful with another language (usually C++), the explanation says so explicitly.  If the description
       for a particular option does not mention a source language, you can use that option with all supported
       languages.

       The usual way to run GCC is to run the executable called gcc, or machine-gcc when cross-compiling, or
       machine-gcc-version to run a specific version of GCC.  When you compile C++ programs, you should invoke
       GCC as g++ instead.

       The gcc program accepts options and file names as operands.  Many options have multi-letter names;
       therefore multiple single-letter options may not be grouped: -dv is very different from -d -v.

       You can mix options and other arguments.  For the most part, the order you use doesn't matter.  Order
       does matter when you use several options of the same kind; for example, if you specify -L more than once,
       the directories are searched in the order specified.  Also, the placement of the -l option is
       significant.

       Many options have long names starting with -f or with -W---for example, -fmove-loop-invariants, -Wformat
       and so on.  Most of these have both positive and negative forms; the negative form of -ffoo is -fno-foo.
       This manual documents only one of these two forms, whichever one is not the default.

       Some options take one or more arguments typically separated either by a space or by the equals sign (=)
       from the option name.  Unless documented otherwise, an argument can be either numeric or a string.
       Numeric arguments must typically be small unsigned decimal or hexadecimal integers.  Hexadecimal
       arguments must begin with the 0x prefix.  Arguments to options that specify a size threshold of some sort
       may be arbitrarily large decimal or hexadecimal integers followed by a byte size suffix designating a
       multiple of bytes such as "kB" and "KiB" for kilobyte and kibibyte, respectively, "MB" and "MiB" for
       megabyte and mebibyte, "GB" and "GiB" for gigabyte and gigibyte, and so on.  Such arguments are
       designated by byte-size in the following text.  Refer to the NIST, IEC, and other relevant national and
       international standards for the full listing and explanation of the binary and decimal byte size
       prefixes.

OPTIONS

   Option Summary
       Here is a summary of all the options, grouped by type.  Explanations are in the following sections.

       Overall Options
           -c   -S   -E   -o  file -dumpbase dumpbase  -dumpbase-ext auxdropsuf -dumpdir dumppfx  -x language -v
           -###  --help[=class[,...]]  --target-help  --version -pass-exit-codes  -pipe   -specs=file   -wrapper
           @file     -ffile-prefix-map=old=new   -fplugin=file    -fplugin-arg-name=arg   -fdump-ada-spec[-slim]
           -fada-spec-parent=unit  -fdump-go-spec=file

       C Language Options
           -ansi   -std=standard   -fgnu89-inline   -fpermitted-flt-eval-methods=standard   -aux-info   filename
           -fallow-parameterless-variadic-functions   -fno-asm   -fno-builtin   -fno-builtin-function   -fgimple
           -fhosted   -ffreestanding  -fopenacc   -fopenacc-dim=geom  -fopenmp   -fopenmp-simd   -fms-extensions
           -fplan9-extensions        -fsso-struct=endianness      -fallow-single-precision       -fcond-mismatch
           -flax-vector-conversions -fsigned-bitfields  -fsigned-char -funsigned-bitfields  -funsigned-char

       C++ Language Options
           -fabi-version=n   -fno-access-control  -faligned-new=n   -fargs-in-order=n   -fchar8_t    -fcheck-new
           -fconstexpr-depth=n    -fconstexpr-cache-depth=n   -fconstexpr-loop-limit=n   -fconstexpr-ops-limit=n
           -fno-elide-constructors     -fno-enforce-eh-specs      -fno-gnu-keywords      -fno-implicit-templates
           -fno-implicit-inline-templates     -fno-implement-inlines     -fmodule-header[=kind]    -fmodule-only
           -fmodules-ts      -fmodule-implicit-inline       -fno-module-lazy       -fmodule-mapper=specification
           -fmodule-version-ignore        -fms-extensions        -fnew-inheriting-ctors       -fnew-ttp-matching
           -fno-nonansi-builtins    -fnothrow-opt    -fno-operator-names    -fno-optional-diags     -fpermissive
           -fno-pretty-templates -fno-rtti  -fsized-deallocation -ftemplate-backtrace-limit=n -ftemplate-depth=n
           -fno-threadsafe-statics     -fuse-cxa-atexit   -fno-weak    -nostdinc++   -fvisibility-inlines-hidden
           -fvisibility-ms-compat         -fext-numeric-literals          -flang-info-include-translate[=header]
           -flang-info-include-translate-not  -flang-info-module-cmi[=module] -stdlib=libstdc++,libc++ -Wabi-tag
           -Wcatch-value     -Wcatch-value=n    -Wno-class-conversion     -Wclass-memaccess    -Wcomma-subscript
           -Wconditionally-supported    -Wno-conversion-null     -Wctad-maybe-unsupported    -Wctor-dtor-privacy
           -Wno-delete-incomplete    -Wdelete-non-virtual-dtor      -Wdeprecated-copy     -Wdeprecated-copy-dtor
           -Wno-deprecated-enum-enum-conversion  -Wno-deprecated-enum-float-conversion -Weffc++  -Wno-exceptions
           -Wextra-semi     -Wno-inaccessible-base     -Wno-inherited-variadic-ctor      -Wno-init-list-lifetime
           -Winvalid-imported-macros   -Wno-invalid-offsetof    -Wno-literal-suffix   -Wno-mismatched-new-delete
           -Wmismatched-tags  -Wmultiple-inheritance   -Wnamespaces   -Wnarrowing  -Wnoexcept    -Wnoexcept-type
           -Wnon-virtual-dtor  -Wpessimizing-move   -Wno-placement-new  -Wplacement-new=n -Wrange-loop-construct
           -Wredundant-move      -Wredundant-tags       -Wreorder        -Wregister       -Wstrict-null-sentinel
           -Wno-subobject-linkage   -Wtemplates  -Wno-non-template-friend  -Wold-style-cast -Woverloaded-virtual
           -Wno-pmf-conversions -Wsign-promo -Wsized-deallocation  -Wsuggest-final-methods -Wsuggest-final-types
           -Wsuggest-override   -Wno-terminate     -Wuseless-cast     -Wno-vexing-parse    -Wvirtual-inheritance
           -Wno-virtual-move-assign  -Wvolatile  -Wzero-as-null-pointer-constant

       Objective-C and Objective-C++ Language Options
           -fconstant-string-class=class-name       -fgnu-runtime        -fnext-runtime       -fno-nil-receivers
           -fobjc-abi-version=n  -fobjc-call-cxx-cdtors   -fobjc-direct-dispatch   -fobjc-exceptions   -fobjc-gc
           -fobjc-nilcheck                           -fobjc-std=objc1                           -fno-local-ivars
           -fivar-visibility=[public|protected|private|package]  -freplace-objc-classes  -fzero-link  -gen-decls
           -Wassign-intercept     -Wno-property-assign-default    -Wno-protocol   -Wobjc-root-class   -Wselector
           -Wstrict-selector-match -Wundeclared-selector

       Diagnostic Message Formatting Options
           -fmessage-length=n      -fdiagnostics-plain-output      -fdiagnostics-show-location=[once|every-line]
           -fdiagnostics-color=[auto|never|always]                        -fdiagnostics-urls=[auto|never|always]
           -fdiagnostics-format=[text|json]      -fno-diagnostics-show-option        -fno-diagnostics-show-caret
           -fno-diagnostics-show-labels        -fno-diagnostics-show-line-numbers      -fno-diagnostics-show-cwe
           -fdiagnostics-minimum-margin-width=width -fdiagnostics-parseable-fixits  -fdiagnostics-generate-patch
           -fdiagnostics-show-template-tree       -fno-elide-type      -fdiagnostics-path-format=[none|separate-
           events|inline-events]                 -fdiagnostics-show-path-depths                 -fno-show-column
           -fdiagnostics-column-unit=[display|byte] -fdiagnostics-column-origin=origin

       Warning Options
           -fsyntax-only  -fmax-errors=n  -Wpedantic -pedantic-errors  -w   -Wextra   -Wall   -Wabi=n  -Waddress
           -Wno-address-of-packed-member   -Waggregate-return  -Walloc-size-larger-than=byte-size   -Walloc-zero
           -Walloca    -Walloca-larger-than=byte-size   -Wno-aggressive-loop-optimizations    -Warith-conversion
           -Warray-bounds     -Warray-bounds=n    -Wno-attributes     -Wattribute-alias=n   -Wno-attribute-alias
           -Wno-attribute-warning     -Wbool-compare      -Wbool-operation     -Wno-builtin-declaration-mismatch
           -Wno-builtin-macro-redefined    -Wc90-c99-compat    -Wc99-c11-compat   -Wc11-c2x-compat  -Wc++-compat
           -Wc++11-compat   -Wc++14-compat   -Wc++17-compat  -Wc++20-compat  -Wcast-align    -Wcast-align=strict
           -Wcast-function-type     -Wcast-qual    -Wchar-subscripts    -Wclobbered     -Wcomment   -Wconversion
           -Wno-coverage-mismatch        -Wno-cpp       -Wdangling-else        -Wdate-time       -Wno-deprecated
           -Wno-deprecated-declarations                -Wno-designated-init              -Wdisabled-optimization
           -Wno-discarded-array-qualifiers    -Wno-discarded-qualifiers   -Wno-div-by-zero    -Wdouble-promotion
           -Wduplicated-branches      -Wduplicated-cond    -Wempty-body     -Wno-endif-labels     -Wenum-compare
           -Wenum-conversion  -Werror   -Werror=*   -Wexpansion-to-defined   -Wfatal-errors   -Wfloat-conversion
           -Wfloat-equal       -Wformat      -Wformat=2     -Wno-format-contains-nul      -Wno-format-extra-args
           -Wformat-nonliteral         -Wformat-overflow=n        -Wformat-security          -Wformat-signedness
           -Wformat-truncation=n        -Wformat-y2k         -Wframe-address       -Wframe-larger-than=byte-size
           -Wno-free-nonheap-object    -Wno-if-not-aligned      -Wno-ignored-attributes     -Wignored-qualifiers
           -Wno-incompatible-pointer-types    -Wimplicit     -Wimplicit-fallthrough     -Wimplicit-fallthrough=n
           -Wno-implicit-function-declaration   -Wno-implicit-int  -Winit-self   -Winline    -Wno-int-conversion
           -Wint-in-bool-context      -Wno-int-to-pointer-cast       -Wno-invalid-memory-model     -Winvalid-pch
           -Wjump-misses-init   -Wlarger-than=byte-size  -Wlogical-not-parentheses   -Wlogical-op    -Wlong-long
           -Wno-lto-type-mismatch   -Wmain   -Wmaybe-uninitialized  -Wmemset-elt-size   -Wmemset-transposed-args
           -Wmisleading-indentation    -Wmissing-attributes     -Wmissing-braces    -Wmissing-field-initializers
           -Wmissing-format-attribute     -Wmissing-include-dirs     -Wmissing-noreturn     -Wno-missing-profile
           -Wno-multichar  -Wmultistatement-macros  -Wnonnull  -Wnonnull-compare -Wnormalized=[none|id|nfc|nfkc]
           -Wnull-dereference       -Wno-odr       -Wopenmp-simd       -Wno-overflow        -Woverlength-strings
           -Wno-override-init-side-effects -Wpacked  -Wno-packed-bitfield-compat  -Wpacked-not-aligned  -Wpadded
           -Wparentheses           -Wno-pedantic-ms-format         -Wpointer-arith          -Wno-pointer-compare
           -Wno-pointer-to-int-cast    -Wno-pragmas     -Wno-prio-ctor-dtor     -Wredundant-decls     -Wrestrict
           -Wno-return-local-addr     -Wreturn-type    -Wno-scalar-storage-order     -Wsequence-point   -Wshadow
           -Wshadow=global  -Wshadow=local  -Wshadow=compatible-local -Wno-shadow-ivar -Wno-shift-count-negative
           -Wno-shift-count-overflow      -Wshift-negative-value     -Wno-shift-overflow      -Wshift-overflow=n
           -Wsign-compare   -Wsign-conversion -Wno-sizeof-array-argument -Wsizeof-array-div -Wsizeof-pointer-div
           -Wsizeof-pointer-memaccess     -Wstack-protector      -Wstack-usage=byte-size       -Wstrict-aliasing
           -Wstrict-aliasing=n   -Wstrict-overflow   -Wstrict-overflow=n -Wstring-compare -Wno-stringop-overflow
           -Wno-stringop-overread                                                       -Wno-stringop-truncation
           -Wsuggest-attribute=[pure|const|noreturn|format|malloc]  -Wswitch  -Wno-switch-bool  -Wswitch-default
           -Wswitch-enum  -Wno-switch-outside-range    -Wno-switch-unreachable    -Wsync-nand   -Wsystem-headers
           -Wtautological-compare   -Wtrampolines   -Wtrigraphs  -Wtsan  -Wtype-limits   -Wundef -Wuninitialized
           -Wunknown-pragmas       -Wunsuffixed-float-constants        -Wunused       -Wunused-but-set-parameter
           -Wunused-but-set-variable    -Wunused-const-variable    -Wunused-const-variable=n   -Wunused-function
           -Wunused-label   -Wunused-local-typedefs   -Wunused-macros   -Wunused-parameter    -Wno-unused-result
           -Wunused-value    -Wunused-variable  -Wno-varargs   -Wvariadic-macros  -Wvector-operation-performance
           -Wvla   -Wvla-larger-than=byte-size   -Wno-vla-larger-than  -Wvolatile-register-var   -Wwrite-strings
           -Wzero-length-bounds

       Static Analyzer Options
           -fanalyzer      -fanalyzer-call-summaries      -fanalyzer-checker=name      -fno-analyzer-feasibility
           -fanalyzer-fine-grained   -fanalyzer-state-merge    -fanalyzer-state-purge    -fanalyzer-transitivity
           -fanalyzer-verbose-edges  -fanalyzer-verbose-state-changes -fanalyzer-verbosity=level -fdump-analyzer
           -fdump-analyzer-stderr            -fdump-analyzer-callgraph            -fdump-analyzer-exploded-graph
           -fdump-analyzer-exploded-nodes    -fdump-analyzer-exploded-nodes-2   -fdump-analyzer-exploded-nodes-3
           -fdump-analyzer-feasibility             -fdump-analyzer-json              -fdump-analyzer-state-purge
           -fdump-analyzer-supergraph            -Wno-analyzer-double-fclose           -Wno-analyzer-double-free
           -Wno-analyzer-exposure-through-output-file   -Wno-analyzer-file-leak   -Wno-analyzer-free-of-non-heap
           -Wno-analyzer-malloc-leak      -Wno-analyzer-mismatching-deallocation     -Wno-analyzer-null-argument
           -Wno-analyzer-null-dereference                                   -Wno-analyzer-possible-null-argument
           -Wno-analyzer-possible-null-dereference                            -Wno-analyzer-shift-count-negative
           -Wno-analyzer-shift-count-overflow                                  -Wno-analyzer-stale-setjmp-buffer
           -Wno-analyzer-tainted-array-index                                              -Wanalyzer-too-complex
           -Wno-analyzer-unsafe-call-within-signal-handler                          -Wno-analyzer-use-after-free
           -Wno-analyzer-use-of-pointer-in-stale-stack-frame            -Wno-analyzer-use-of-uninitialized-value
           -Wno-analyzer-write-to-const -Wno-analyzer-write-to-string-literal

       C and Objective-C-only Warning Options
           -Wbad-function-cast     -Wmissing-declarations     -Wmissing-parameter-type      -Wmissing-prototypes
           -Wnested-externs  -Wold-style-declaration   -Wold-style-definition -Wstrict-prototypes  -Wtraditional
           -Wtraditional-conversion -Wdeclaration-after-statement  -Wpointer-sign

       Debugging Options
           -g  -glevel  -gdwarf  -gdwarf-version -ggdb  -grecord-gcc-switches  -gno-record-gcc-switches  -gstabs
           -gstabs+       -gstrict-dwarf       -gno-strict-dwarf      -gas-loc-support       -gno-as-loc-support
           -gas-locview-support  -gno-as-locview-support -gcolumn-info  -gno-column-info   -gdwarf32   -gdwarf64
           -gstatement-frontiers                -gno-statement-frontiers               -gvariable-location-views
           -gno-variable-location-views   -ginternal-reset-location-views     -gno-internal-reset-location-views
           -ginline-points     -gno-inline-points    -gvms     -gxcoff    -gxcoff+    -gz[=type]   -gsplit-dwarf
           -gdescribe-dies       -gno-describe-dies      -fdebug-prefix-map=old=new        -fdebug-types-section
           -fno-eliminate-unused-debug-types      -femit-struct-debug-baseonly       -femit-struct-debug-reduced
           -femit-struct-debug-detailed[=spec-list]                          -fno-eliminate-unused-debug-symbols
           -femit-class-debug-always      -fno-merge-debug-strings       -fno-dwarf2-cfi-asm      -fvar-tracking
           -fvar-tracking-assignments

       Optimization Options
           -faggressive-loop-optimizations  -falign-functions[=n[:m:[n2[:m2]]]]  -falign-jumps[=n[:m:[n2[:m2]]]]
           -falign-labels[=n[:m:[n2[:m2]]]]          -falign-loops[=n[:m:[n2[:m2]]]]         -fno-allocation-dce
           -fallow-store-data-races  -fassociative-math   -fauto-profile   -fauto-profile[=path]  -fauto-inc-dec
           -fbranch-probabilities  -fcaller-saves  -fcombine-stack-adjustments   -fconserve-stack -fcompare-elim
           -fcprop-registers    -fcrossjumping   -fcse-follow-jumps     -fcse-skip-blocks     -fcx-fortran-rules
           -fcx-limited-range     -fdata-sections     -fdce     -fdelayed-branch    -fdelete-null-pointer-checks
           -fdevirtualize    -fdevirtualize-speculatively   -fdevirtualize-at-ltrans    -fdse   -fearly-inlining
           -fipa-sra      -fexpensive-optimizations      -ffat-lto-objects    -ffast-math     -ffinite-math-only
           -ffloat-store   -fexcess-precision=style  -ffinite-loops   -fforward-propagate    -ffp-contract=style
           -ffunction-sections -fgcse  -fgcse-after-reload  -fgcse-las  -fgcse-lm  -fgraphite-identity -fgcse-sm
           -fhoist-adjacent-loads    -fif-conversion  -fif-conversion2   -findirect-inlining  -finline-functions
           -finline-functions-called-once   -finline-limit=n  -finline-small-functions   -fipa-modref   -fipa-cp
           -fipa-cp-clone  -fipa-bit-cp   -fipa-vrp   -fipa-pta  -fipa-profile  -fipa-pure-const -fipa-reference
           -fipa-reference-addressable     -fipa-stack-alignment       -fipa-icf       -fira-algorithm=algorithm
           -flive-patching=level       -fira-region=region        -fira-hoist-pressure       -fira-loop-pressure
           -fno-ira-share-save-slots      -fno-ira-share-spill-slots       -fisolate-erroneous-paths-dereference
           -fisolate-erroneous-paths-attribute    -fivopts    -fkeep-inline-functions    -fkeep-static-functions
           -fkeep-static-consts       -flimit-function-alignment       -flive-range-shrinkage       -floop-block
           -floop-interchange         -floop-strip-mine        -floop-unroll-and-jam        -floop-nest-optimize
           -floop-parallelize-all     -flra-remat     -flto      -flto-compression-level     -flto-partition=alg
           -fmerge-all-constants      -fmerge-constants       -fmodulo-sched       -fmodulo-sched-allow-regmoves
           -fmove-loop-invariants      -fno-branch-count-reg     -fno-defer-pop      -fno-fp-int-builtin-inexact
           -fno-function-cse    -fno-guess-branch-probability    -fno-inline    -fno-math-errno    -fno-peephole
           -fno-peephole2  -fno-printf-return-value   -fno-sched-interblock  -fno-sched-spec   -fno-signed-zeros
           -fno-toplevel-reorder     -fno-trapping-math     -fno-zero-initialized-in-bss    -fomit-frame-pointer
           -foptimize-sibling-calls       -fpartial-inlining         -fpeel-loops         -fpredictive-commoning
           -fprefetch-loop-arrays         -fprofile-correction         -fprofile-use          -fprofile-use=path
           -fprofile-partial-training  -fprofile-values  -fprofile-reorder-functions  -freciprocal-math    -free
           -frename-registers                -freorder-blocks               -freorder-blocks-algorithm=algorithm
           -freorder-blocks-and-partition               -freorder-functions               -frerun-cse-after-loop
           -freschedule-modulo-scheduled-loops            -frounding-math             -fsave-optimization-record
           -fsched2-use-superblocks      -fsched-pressure     -fsched-spec-load      -fsched-spec-load-dangerous
           -fsched-stalled-insns-dep[=n]             -fsched-stalled-insns[=n]           -fsched-group-heuristic
           -fsched-critical-path-heuristic          -fsched-spec-insn-heuristic           -fsched-rank-heuristic
           -fsched-last-insn-heuristic      -fsched-dep-count-heuristic    -fschedule-fusion    -fschedule-insns
           -fschedule-insns2       -fsection-anchors       -fselective-scheduling        -fselective-scheduling2
           -fsel-sched-pipelining   -fsel-sched-pipelining-outer-loops  -fsemantic-interposition   -fshrink-wrap
           -fshrink-wrap-separate    -fsignaling-nans    -fsingle-precision-constant     -fsplit-ivs-in-unroller
           -fsplit-loops     -fsplit-paths    -fsplit-wide-types     -fsplit-wide-types-early     -fssa-backprop
           -fssa-phiopt    -fstdarg-opt     -fstore-merging     -fstrict-aliasing    -fthread-jumps     -ftracer
           -ftree-bit-ccp  -ftree-builtin-call-dce  -ftree-ccp  -ftree-ch -ftree-coalesce-vars  -ftree-copy-prop
           -ftree-dce    -ftree-dominator-opts   -ftree-dse    -ftree-forwprop    -ftree-fre     -fcode-hoisting
           -ftree-loop-if-convert          -ftree-loop-im        -ftree-phiprop         -ftree-loop-distribution
           -ftree-loop-distribute-patterns   -ftree-loop-ivcanon     -ftree-loop-linear     -ftree-loop-optimize
           -ftree-loop-vectorize    -ftree-parallelize-loops=n    -ftree-pre    -ftree-partial-pre    -ftree-pta
           -ftree-reassoc   -ftree-scev-cprop   -ftree-sink   -ftree-slsr   -ftree-sra  -ftree-switch-conversion
           -ftree-tail-merge  -ftree-ter  -ftree-vectorize  -ftree-vrp  -funconstrained-commons -funit-at-a-time
           -funroll-all-loops     -funroll-loops    -funsafe-math-optimizations     -funswitch-loops    -fipa-ra
           -fvariable-expansion-in-unroller     -fvect-cost-model     -fvpt    -fweb    -fwhole-program    -fwpa
           -fuse-linker-plugin -fzero-call-used-regs --param name=value -O  -O0  -O1  -O2  -O3  -Os  -Ofast  -Og

       Program Instrumentation Options
           -p   -pg    -fprofile-arcs    --coverage    -ftest-coverage   -fprofile-abs-path   -fprofile-dir=path
           -fprofile-generate    -fprofile-generate=path   -fprofile-info-section    -fprofile-info-section=name
           -fprofile-note=path -fprofile-prefix-path=path  -fprofile-update=method  -fprofile-filter-files=regex
           -fprofile-exclude-files=regex             -fprofile-reproducible=[multithreaded|parallel-runs|serial]
           -fsanitize=style     -fsanitize-recover      -fsanitize-recover=style     -fasan-shadow-offset=number
           -fsanitize-sections=s1,s2,...            -fsanitize-undefined-trap-on-error            -fbounds-check
           -fcf-protection=[full|branch|return|none|check]       -fstack-protector         -fstack-protector-all
           -fstack-protector-strong    -fstack-protector-explicit     -fstack-check   -fstack-limit-register=reg
           -fstack-limit-symbol=sym    -fno-stack-limit     -fsplit-stack     -fvtable-verify=[std|preinit|none]
           -fvtv-counts                             -fvtv-debug                           -finstrument-functions
           -finstrument-functions-exclude-function-list=sym,sym,...
           -finstrument-functions-exclude-file-list=file,file,...

       Preprocessor Options
           -Aquestion=answer -A-question[=answer] -C  -CC  -Dmacro[=defn] -dD  -dI  -dM   -dN   -dU  -fdebug-cpp
           -fdirectives-only      -fdollars-in-identifiers     -fexec-charset=charset     -fextended-identifiers
           -finput-charset=charset   -flarge-source-files  -fmacro-prefix-map=old=new  -fmax-include-depth=depth
           -fno-canonical-system-headers     -fpch-deps     -fpch-preprocess   -fpreprocessed    -ftabstop=width
           -ftrack-macro-expansion -fwide-exec-charset=charset  -fworking-directory -H  -imacros file   -include
           file  -M   -MD   -MF   -MG   -MM   -MMD   -MP  -MQ  -MT -Mno-modules -no-integrated-cpp  -P  -pthread
           -remap -traditional  -traditional-cpp  -trigraphs -Umacro  -undef -Wp,option  -Xpreprocessor option

       Assembler Options
           -Wa,option  -Xassembler option

       Linker Options
           object-file-name  -fuse-ld=linker  -llibrary -nostartfiles   -nodefaultlibs   -nolibc   -nostdlib  -e
           entry    --entry=entry  -pie   -pthread   -r   -rdynamic  -s   -static   -static-pie   -static-libgcc
           -static-libstdc++  -static-libasan   -static-libtsan    -static-liblsan    -static-libubsan   -shared
           -shared-libgcc  -symbolic -T script  -Wl,option  -Xlinker option -u symbol  -z keyword

       Directory Options
           -Bprefix   -Idir   -I-  -idirafter  dir  -imacros file  -imultilib dir -iplugindir=dir  -iprefix file
           -iquote  dir   -isysroot  dir   -isystem  dir  -iwithprefix   dir    -iwithprefixbefore   dir   -Ldir
           -no-canonical-prefixes  --no-sysroot-suffix -nostdinc  -nostdinc++  --sysroot=dir

       Code Generation Options
           -fcall-saved-reg       -fcall-used-reg      -ffixed-reg       -fexceptions      -fnon-call-exceptions
           -fdelete-dead-exceptions       -funwind-tables      -fasynchronous-unwind-tables      -fno-gnu-unique
           -finhibit-size-directive   -fcommon   -fno-ident  -fpcc-struct-return   -fpic   -fPIC   -fpie   -fPIE
           -fno-plt -fno-jump-tables  -fno-bit-tests  -frecord-gcc-switches  -freg-struct-return   -fshort-enums
           -fshort-wchar     -fverbose-asm      -fpack-struct[=n]     -fleading-underscore     -ftls-model=model
           -fstack-reuse=reuse_level               -ftrampolines                 -ftrapv                 -fwrapv
           -fvisibility=[default|internal|hidden|protected] -fstrict-volatile-bitfields  -fsync-libcalls

       Developer Options
           -dletters    -dumpspecs    -dumpmachine    -dumpversion   -dumpfullversion   -fcallgraph-info[=su,da]
           -fchecking   -fchecking=n   -fdbg-cnt-list     -fdbg-cnt=counter-value-list   -fdisable-ipa-pass_name
           -fdisable-rtl-pass_name          -fdisable-rtl-pass-name=range-list          -fdisable-tree-pass_name
           -fdisable-tree-pass-name=range-list -fdump-debug  -fdump-earlydebug -fdump-noaddr   -fdump-unnumbered
           -fdump-unnumbered-links       -fdump-final-insns[=file]       -fdump-ipa-all        -fdump-ipa-cgraph
           -fdump-ipa-inline        -fdump-lang-all        -fdump-lang-switch         -fdump-lang-switch-options
           -fdump-lang-switch-options=filename     -fdump-passes    -fdump-rtl-pass     -fdump-rtl-pass=filename
           -fdump-statistics        -fdump-tree-all        -fdump-tree-switch         -fdump-tree-switch-options
           -fdump-tree-switch-options=filename -fcompare-debug[=opts]  -fcompare-debug-second -fenable-kind-pass
           -fenable-kind-pass=range-list   -fira-verbose=n   -flto-report    -flto-report-wpa   -fmem-report-wpa
           -fmem-report   -fpre-ipa-mem-report   -fpost-ipa-mem-report   -fopt-info    -fopt-info-options[=file]
           -fprofile-report  -frandom-seed=string   -fsched-verbose=n  -fsel-sched-verbose  -fsel-sched-dump-cfg
           -fsel-sched-pipelining-verbose   -fstats    -fstack-usage     -ftime-report     -ftime-report-details
           -fvar-tracking-assignments-toggle     -gtoggle    -print-file-name=library    -print-libgcc-file-name
           -print-multi-directory     -print-multi-lib     -print-multi-os-directory    -print-prog-name=program
           -print-search-dirs   -Q  -print-sysroot   -print-sysroot-headers-suffix  -save-temps  -save-temps=cwd
           -save-temps=obj  -time[=file]

       Machine-Dependent Options
           AArch64  Options  -mabi=name    -mbig-endian    -mlittle-endian   -mgeneral-regs-only   -mcmodel=tiny
           -mcmodel=small     -mcmodel=large    -mstrict-align     -mno-strict-align   -momit-leaf-frame-pointer
           -mtls-dialect=desc       -mtls-dialect=traditional      -mtls-size=size       -mfix-cortex-a53-835769
           -mfix-cortex-a53-843419    -mlow-precision-recip-sqrt     -mlow-precision-sqrt    -mlow-precision-div
           -mpc-relative-literal-loads    -msign-return-address=scope     -mbranch-protection=none|standard|pac-
           ret[+leaf   +b-key]|bti  -mharden-sls=opts  -march=name   -mcpu=name   -mtune=name  -moverride=string
           -mverbose-cost-dump         -mstack-protector-guard=guard          -mstack-protector-guard-reg=sysreg
           -mstack-protector-guard-offset=offset -mtrack-speculation -moutline-atomics

           Adapteva   Epiphany  Options  -mhalf-reg-file   -mprefer-short-insn-regs  -mbranch-cost=num   -mcmove
           -mnops=num  -msoft-cmpsf -msplit-lohi  -mpost-inc  -mpost-modify  -mstack-offset=num  -mround-nearest
           -mlong-calls     -mshort-calls     -msmall16   -mfp-mode=mode    -mvect-double    -max-vect-align=num
           -msplit-vecmove-early  -m1reg-reg

           AMD GCN Options -march=gpu -mtune=gpu -mstack-size=bytes

           ARC  Options  -mbarrel-shifter   -mjli-always  -mcpu=cpu   -mA6   -mARC600   -mA7   -mARC700   -mdpfp
           -mdpfp-compact   -mdpfp-fast   -mno-dpfp-lrsr  -mea   -mno-mpy   -mmul32x16  -mmul64  -matomic -mnorm
           -mspfp  -mspfp-compact  -mspfp-fast  -msimd  -msoft-float  -mswap -mcrc  -mdsp-packa  -mdvbf   -mlock
           -mmac-d16   -mmac-24   -mrtsc   -mswape  -mtelephony   -mxy   -misize   -mannotate-align   -marclinux
           -marclinux_prof   -mlong-calls    -mmedium-calls    -msdata     -mirq-ctrl-saved    -mrgf-banked-regs
           -mlpc-width=width    -G   num   -mvolatile-cache   -mtp-regno=regno  -malign-call   -mauto-modify-reg
           -mbbit-peephole  -mno-brcc -mcase-vector-pcrel  -mcompact-casesi   -mno-cond-exec   -mearly-cbranchsi
           -mexpand-adddi   -mindexed-loads   -mlra   -mlra-priority-none  -mlra-priority-compact mlra-priority-
           noncompact   -mmillicode  -mmixed-code   -mq-class   -mRcq   -mRcw    -msize-level=level   -mtune=cpu
           -mmultcost=num     -mcode-density-frame    -munalign-prob-threshold=probability    -mmpy-option=multo
           -mdiv-rem  -mcode-density  -mll64  -mfpu=fpu  -mrf16  -mbranch-index

           ARM  Options  -mapcs-frame   -mno-apcs-frame  -mabi=name  -mapcs-stack-check    -mno-apcs-stack-check
           -mapcs-reentrant     -mno-apcs-reentrant    -mgeneral-regs-only   -msched-prolog    -mno-sched-prolog
           -mlittle-endian  -mbig-endian -mbe8   -mbe32  -mfloat-abi=name  -mfp16-format=name  -mthumb-interwork
           -mno-thumb-interwork    -mcpu=name     -march=name     -mfpu=name    -mtune=name    -mprint-tune-info
           -mstructure-size-boundary=n  -mabort-on-noreturn  -mlong-calls    -mno-long-calls   -msingle-pic-base
           -mno-single-pic-base   -mpic-register=reg  -mnop-fun-dllimport  -mpoke-function-name  -mthumb   -marm
           -mflip-thumb -mtpcs-frame  -mtpcs-leaf-frame -mcaller-super-interworking  -mcallee-super-interworking
           -mtp=name    -mtls-dialect=dialect   -mword-relocations    -mfix-cortex-m3-ldrd    -munaligned-access
           -mneon-for-64bits    -mslow-flash-data    -masm-syntax-unified    -mrestrict-it   -mverbose-cost-dump
           -mpure-code -mcmse -mfix-cmse-cve-2021-35465 -mfdpic

           AVR   Options   -mmcu=mcu    -mabsdata    -maccumulate-args    -mbranch-cost=cost    -mcall-prologues
           -mgas-isr-prologues    -mint8   -mdouble=bits   -mlong-double=bits   -mn_flash=size   -mno-interrupts
           -mmain-is-OS_task  -mrelax  -mrmw  -mstrict-X   -mtiny-stack  -mfract-convert-truncate  -mshort-calls
           -nodevicelib  -nodevicespecs -Waddr-space-convert  -Wmisspelled-isr

           Blackfin         Options        -mcpu=cpu[-sirevision]        -msim         -momit-leaf-frame-pointer
           -mno-omit-leaf-frame-pointer       -mspecld-anomaly        -mno-specld-anomaly        -mcsync-anomaly
           -mno-csync-anomaly       -mlow-64k       -mno-low64k       -mstack-check-l1       -mid-shared-library
           -mno-id-shared-library  -mshared-library-id=n  -mleaf-id-shared-library   -mno-leaf-id-shared-library
           -msep-data    -mno-sep-data    -mlong-calls   -mno-long-calls  -mfast-fp   -minline-plt   -mmulticore
           -mcorea  -mcoreb  -msdram -micplb

           C6X Options -mbig-endian  -mlittle-endian  -march=cpu -msim  -msdata=sdata-type

           CRIS Options -mcpu=cpu  -march=cpu  -mtune=cpu  -mmax-stack-frame=n  -metrax4   -metrax100   -mpdebug
           -mcc-init   -mno-side-effects  -mstack-align  -mdata-align  -mconst-align -m32-bit  -m16-bit  -m8-bit
           -mno-prologue-epilogue -melf  -maout  -sim  -sim2 -mmul-bug-workaround  -mno-mul-bug-workaround

           CR16 Options -mmac -mcr16cplus  -mcr16c -msim  -mint32  -mbit-ops -mdata-model=model

           C-SKY  Options  -march=arch   -mcpu=cpu  -mbig-endian    -EB    -mlittle-endian    -EL   -mhard-float
           -msoft-float   -mfpu=fpu   -mdouble-float   -mfdivdu  -mfloat-abi=name  -melrw   -mistack  -mmp  -mcp
           -mcache  -msecurity   -mtrust  -mdsp   -medsp   -mvdsp  -mdiv   -msmart   -mhigh-registers   -manchor
           -mpushpop     -mmultiple-stld     -mconstpool    -mstack-size    -mccrt   -mbranch-cost=n    -mcse-cc
           -msched-prolog -msim

           Darwin Options -all_load   -allowable_client   -arch   -arch_errors_fatal  -arch_only   -bind_at_load
           -bundle     -bundle_loader   -client_name    -compatibility_version    -current_version   -dead_strip
           -dependency-file  -dylib_file  -dylinker_install_name -dynamic   -dynamiclib   -exported_symbols_list
           -filelist  -flat_namespace  -force_cpusubtype_ALL -force_flat_namespace  -headerpad_max_install_names
           -iframework -image_base  -init  -install_name  -keep_private_externs -multi_module  -multiply_defined
           -multiply_defined_unused  -noall_load   -no_dead_strip_inits_and_terms -nofixprebinding  -nomultidefs
           -noprebind  -noseglinkedit -pagezero_size   -prebind   -prebind_all_twolevel_modules  -private_bundle
           -read_only_relocs  -sectalign -sectobjectsymbols  -whyload  -seg1addr -sectcreate  -sectobjectsymbols
           -sectorder       -segaddr       -segs_read_only_addr       -segs_read_write_addr      -seg_addr_table
           -seg_addr_table_filename    -seglinkedit   -segprot    -segs_read_only_addr     -segs_read_write_addr
           -single_module   -static   -sub_library   -sub_umbrella  -twolevel_namespace   -umbrella   -undefined
           -unexported_symbols_list     -weak_reference_mismatches    -whatsloaded     -F     -gused      -gfull
           -mmacosx-version-min=version -mkernel  -mone-byte-bool

           DEC   Alpha   Options   -mno-fp-regs   -msoft-float  -mieee   -mieee-with-inexact   -mieee-conformant
           -mfp-trap-mode=mode  -mfp-rounding-mode=mode -mtrap-precision=mode  -mbuild-constants  -mcpu=cpu-type
           -mtune=cpu-type  -mbwx  -mmax  -mfix  -mcix -mfloat-vax  -mfloat-ieee -mexplicit-relocs  -msmall-data
           -mlarge-data -msmall-text  -mlarge-text -mmemory-latency=time

           eBPF Options -mbig-endian -mlittle-endian -mkernel=version -mframe-limit=bytes -mxbpf

           FR30 Options -msmall-model  -mno-lsim

           FT32 Options -msim  -mlra  -mnodiv  -mft32b  -mcompress  -mnopm

           FRV Options -mgpr-32  -mgpr-64  -mfpr-32  -mfpr-64 -mhard-float  -msoft-float -malloc-cc   -mfixed-cc
           -mdword    -mno-dword  -mdouble   -mno-double  -mmedia   -mno-media   -mmuladd   -mno-muladd  -mfdpic
           -minline-plt    -mgprel-ro    -multilib-library-pic   -mlinked-fp     -mlong-calls     -malign-labels
           -mlibrary-pic    -macc-4    -macc-8   -mpack   -mno-pack   -mno-eflags   -mcond-move   -mno-cond-move
           -moptimize-membar  -mno-optimize-membar -mscc  -mno-scc   -mcond-exec   -mno-cond-exec  -mvliw-branch
           -mno-vliw-branch  -mmulti-cond-exec   -mno-multi-cond-exec   -mnested-cond-exec -mno-nested-cond-exec
           -mtomcat-stats -mTLS  -mtls -mcpu=cpu

           GNU/Linux Options -mglibc  -muclibc  -mmusl  -mbionic  -mandroid -tno-android-cc  -tno-android-ld

           H8/300 Options -mrelax  -mh  -ms  -mn  -mexr  -mno-exr  -mint32  -malign-300

           HPPA   Options   -march=architecture-type   -mcaller-copies    -mdisable-fpregs    -mdisable-indexing
           -mfast-indirect-calls    -mgas    -mgnu-ld     -mhp-ld  -mfixed-range=register-range  -mjump-in-delay
           -mlinker-opt     -mlong-calls    -mlong-load-store      -mno-disable-fpregs     -mno-disable-indexing
           -mno-fast-indirect-calls   -mno-gas  -mno-jump-in-delay   -mno-long-load-store  -mno-portable-runtime
           -mno-soft-float   -mno-space-regs    -msoft-float    -mpa-risc-1-0    -mpa-risc-1-1     -mpa-risc-2-0
           -mportable-runtime   -mschedule=cpu-type   -mspace-regs   -msio   -mwsio  -munix=unix-std   -nolibdld
           -static  -threads

           IA-64  Options  -mbig-endian   -mlittle-endian   -mgnu-as   -mgnu-ld   -mno-pic   -mvolatile-asm-stop
           -mregister-names       -msdata       -mno-sdata      -mconstant-gp       -mauto-pic      -mfused-madd
           -minline-float-divide-min-latency    -minline-float-divide-max-throughput    -mno-inline-float-divide
           -minline-int-divide-min-latency       -minline-int-divide-max-throughput       -mno-inline-int-divide
           -minline-sqrt-min-latency       -minline-sqrt-max-throughput      -mno-inline-sqrt       -mdwarf2-asm
           -mearly-stop-bits  -mfixed-range=register-range  -mtls-size=tls-size -mtune=cpu-type  -milp32  -mlp64
           -msched-br-data-spec      -msched-ar-data-spec      -msched-control-spec      -msched-br-in-data-spec
           -msched-ar-in-data-spec      -msched-in-control-spec    -msched-spec-ldc     -msched-spec-control-ldc
           -msched-prefer-non-data-spec-insns                              -msched-prefer-non-control-spec-insns
           -msched-stop-bits-after-every-cycle                               -msched-count-spec-in-critical-path
           -msel-sched-dont-check-control-spec                                     -msched-fp-mem-deps-zero-cost
           -msched-max-memory-insns-hard-limit  -msched-max-memory-insns=max-insns

           LM32   Options  -mbarrel-shift-enabled   -mdivide-enabled   -mmultiply-enabled  -msign-extend-enabled
           -muser-enabled

           M32R/D Options -m32r2  -m32rx   -m32r  -mdebug  -malign-loops   -mno-align-loops  -missue-rate=number
           -mbranch-cost=number       -mmodel=code-size-model-type       -msdata=sdata-type      -mno-flush-func
           -mflush-func=name -mno-flush-trap  -mflush-trap=number -G num

           M32C Options -mcpu=cpu  -msim  -memregs=number

           M680x0 Options -march=arch  -mcpu=cpu  -mtune=tune -m68000  -m68020  -m68020-40  -m68020-60   -m68030
           -m68040  -m68060  -mcpu32  -m5200  -m5206e  -m528x  -m5307  -m5407 -mcfv4e  -mbitfield  -mno-bitfield
           -mc68000  -mc68020 -mnobitfield  -mrtd  -mno-rtd  -mdiv  -mno-div  -mshort  -mno-short   -mhard-float
           -m68881     -msoft-float     -mpcrel    -malign-int     -mstrict-align    -msep-data    -mno-sep-data
           -mshared-library-id=n      -mid-shared-library      -mno-id-shared-library     -mxgot       -mno-xgot
           -mlong-jump-table-offsets

           MCore  Options  -mhardlit   -mno-hardlit   -mdiv   -mno-div  -mrelax-immediates -mno-relax-immediates
           -mwide-bitfields   -mno-wide-bitfields  -m4byte-functions    -mno-4byte-functions    -mcallgraph-data
           -mno-callgraph-data   -mslow-bytes   -mno-slow-bytes   -mno-lsim -mlittle-endian  -mbig-endian  -m210
           -m340  -mstack-increment

           MeP Options -mabsdiff  -mall-opts  -maverage  -mbased=n  -mbitops -mc=n  -mclip  -mconfig=name  -mcop
           -mcop32  -mcop64  -mivc2 -mdc  -mdiv  -meb  -mel  -mio-volatile  -ml  -mleadz  -mm   -mminmax  -mmult
           -mno-opts  -mrepeat  -ms  -msatur  -msdram  -msim  -msimnovec  -mtf -mtiny=n

           MicroBlaze  Options  -msoft-float   -mhard-float   -msmall-divides  -mcpu=cpu -mmemcpy  -mxl-soft-mul
           -mxl-soft-div  -mxl-barrel-shift -mxl-pattern-compare  -mxl-stack-check   -mxl-gp-opt   -mno-clearbss
           -mxl-multiply-high   -mxl-float-convert   -mxl-float-sqrt -mbig-endian  -mlittle-endian  -mxl-reorder
           -mxl-mode-app-model -mpic-data-is-text-relative

           MIPS Options -EL  -EB  -march=arch  -mtune=arch -mips1  -mips2  -mips3   -mips4   -mips32   -mips32r2
           -mips32r3    -mips32r5   -mips32r6   -mips64   -mips64r2   -mips64r3   -mips64r5   -mips64r6  -mips16
           -mno-mips16   -mflip-mips16  -minterlink-compressed    -mno-interlink-compressed   -minterlink-mips16
           -mno-interlink-mips16  -mabi=abi   -mabicalls   -mno-abicalls  -mshared  -mno-shared  -mplt  -mno-plt
           -mxgot  -mno-xgot -mgp32  -mgp64   -mfp32   -mfpxx   -mfp64   -mhard-float   -msoft-float  -mno-float
           -msingle-float  -mdouble-float -modd-spreg  -mno-odd-spreg -mabs=mode  -mnan=encoding -mdsp  -mno-dsp
           -mdspr2   -mno-dspr2  -mmcu   -mmno-mcu  -meva   -mno-eva  -mvirt   -mno-virt  -mxpa   -mno-xpa -mcrc
           -mno-crc   -mginv    -mno-ginv   -mmicromips    -mno-micromips   -mmsa     -mno-msa    -mloongson-mmi
           -mno-loongson-mmi  -mloongson-ext   -mno-loongson-ext  -mloongson-ext2  -mno-loongson-ext2 -mfpu=fpu-
           type  -msmartmips   -mno-smartmips  -mpaired-single   -mno-paired-single   -mdmx   -mno-mdmx  -mips3d
           -mno-mips3d    -mmt   -mno-mt   -mllsc   -mno-llsc  -mlong64   -mlong32   -msym32   -mno-sym32  -Gnum
           -mlocal-sdata  -mno-local-sdata -mextern-sdata  -mno-extern-sdata  -mgpopt  -mno-gopt -membedded-data
           -mno-embedded-data  -muninit-const-in-rodata    -mno-uninit-const-in-rodata   -mcode-readable=setting
           -msplit-addresses  -mno-split-addresses -mexplicit-relocs  -mno-explicit-relocs -mcheck-zero-division
           -mno-check-zero-division  -mdivide-traps   -mdivide-breaks  -mload-store-pairs  -mno-load-store-pairs
           -mmemcpy   -mno-memcpy   -mlong-calls    -mno-long-calls   -mmad    -mno-mad    -mimadd    -mno-imadd
           -mfused-madd    -mno-fused-madd    -nocpp   -mfix-24k    -mno-fix-24k   -mfix-r4000    -mno-fix-r4000
           -mfix-r4400  -mno-fix-r4400 -mfix-r5900  -mno-fix-r5900 -mfix-r10000   -mno-fix-r10000   -mfix-rm7000
           -mno-fix-rm7000  -mfix-vr4120  -mno-fix-vr4120 -mfix-vr4130  -mno-fix-vr4130  -mfix-sb1  -mno-fix-sb1
           -mflush-func=func     -mno-flush-func    -mbranch-cost=num     -mbranch-likely     -mno-branch-likely
           -mcompact-branches=policy   -mfp-exceptions    -mno-fp-exceptions  -mvr4130-align   -mno-vr4130-align
           -msynci    -mno-synci   -mlxc1-sxc1    -mno-lxc1-sxc1     -mmadd4     -mno-madd4    -mrelax-pic-calls
           -mno-relax-pic-calls  -mmcount-ra-address -mframe-header-opt  -mno-frame-header-opt

           MMIX   Options   -mlibfuncs    -mno-libfuncs    -mepsilon    -mno-epsilon   -mabi=gnu  -mabi=mmixware
           -mzero-extend    -mknuthdiv    -mtoplevel-symbols   -melf    -mbranch-predict     -mno-branch-predict
           -mbase-addresses -mno-base-addresses  -msingle-exit  -mno-single-exit

           MN10300  Options  -mmult-bug   -mno-mult-bug  -mno-am33   -mam33   -mam33-2   -mam34  -mtune=cpu-type
           -mreturn-pointer-on-d0 -mno-crt0  -mrelax  -mliw  -msetlb

           Moxie Options -meb  -mel  -mmul.x  -mno-crt0

           MSP430 Options -msim  -masm-hex  -mmcu=  -mcpu=  -mlarge  -msmall  -mrelax -mwarn-mcu  -mcode-region=
           -mdata-region=    -msilicon-errata=     -msilicon-errata-warn=   -mhwmult=    -minrt    -mtiny-printf
           -mmax-inline-shift=

           NDS32 Options -mbig-endian  -mlittle-endian -mreduced-regs  -mfull-regs -mcmov  -mno-cmov  -mext-perf
           -mno-ext-perf -mext-perf2  -mno-ext-perf2 -mext-string  -mno-ext-string -mv3push  -mno-v3push -m16bit
           -mno-16bit  -misr-vector-size=num  -mcache-block-size=num -march=arch -mcmodel=code-model -mctor-dtor
           -mrelax

           Nios II Options -G num  -mgpopt=option  -mgpopt   -mno-gpopt  -mgprel-sec=regexp   -mr0rel-sec=regexp
           -mel   -meb  -mno-bypass-cache  -mbypass-cache -mno-cache-volatile  -mcache-volatile -mno-fast-sw-div
           -mfast-sw-div -mhw-mul  -mno-hw-mul  -mhw-mulx  -mno-hw-mulx  -mno-hw-div   -mhw-div  -mcustom-insn=N
           -mno-custom-insn  -mcustom-fpu-cfg=name  -mhal  -msmallc  -msys-crt0=name  -msys-lib=name -march=arch
           -mbmx  -mno-bmx  -mcdx  -mno-cdx

           Nvidia PTX Options -m64  -mmainkernel  -moptimize

           OpenRISC Options -mboard=name  -mnewlib  -mhard-mul  -mhard-div -msoft-mul   -msoft-div  -msoft-float
           -mhard-float  -mdouble-float -munordered-float -mcmov  -mror  -mrori  -msext  -msfimm  -mshftimm

           PDP-11  Options  -mfpu   -msoft-float  -mac0  -mno-ac0  -m40  -m45  -m10 -mint32  -mno-int16  -mint16
           -mno-int32 -msplit  -munix-asm  -mdec-asm  -mgnu-asm  -mlra

           picoChip Options -mae=ae_type  -mvliw-lookahead=N -msymbol-as-address  -mno-inefficient-warnings

           PowerPC Options See RS/6000 and PowerPC Options.

           PRU Options -mmcu=mcu  -minrt  -mno-relax  -mloop -mabi=variant

           RISC-V Options -mbranch-cost=N-instruction -mplt  -mno-plt -mabi=ABI-string -mfdiv   -mno-fdiv  -mdiv
           -mno-div        -march=ISA-string        -mtune=processor-string       -mpreferred-stack-boundary=num
           -msmall-data-limit=N-bytes -msave-restore  -mno-save-restore -mshorten-memrefs   -mno-shorten-memrefs
           -mstrict-align       -mno-strict-align     -mcmodel=medlow      -mcmodel=medany     -mexplicit-relocs
           -mno-explicit-relocs -mrelax  -mno-relax  -mriscv-attribute   -mmo-riscv-attribute  -malign-data=type
           -mbig-endian     -mlittle-endian    +-mstack-protector-guard=guard    -mstack-protector-guard-reg=reg
           +-mstack-protector-guard-offset=offset

           RL78 Options -msim  -mmul=none   -mmul=g13   -mmul=g14   -mallregs  -mcpu=g10   -mcpu=g13   -mcpu=g14
           -mg10  -mg13  -mg14 -m64bit-doubles  -m32bit-doubles  -msave-mduc-in-interrupts

           RS/6000  and PowerPC Options -mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model -mpowerpc64 -maltivec
           -mno-altivec  -mpowerpc-gpopt   -mno-powerpc-gpopt  -mpowerpc-gfxopt    -mno-powerpc-gfxopt   -mmfcrf
           -mno-mfcrf   -mpopcntb   -mno-popcntb   -mpopcntd  -mno-popcntd -mfprnd  -mno-fprnd -mcmpb  -mno-cmpb
           -mhard-dfp  -mno-hard-dfp -mfull-toc    -mminimal-toc   -mno-fp-in-toc   -mno-sum-in-toc  -m64   -m32
           -mxl-compat    -mno-xl-compat    -mpe   -malign-power    -malign-natural  -msoft-float   -mhard-float
           -mmultiple         -mno-multiple        -mupdate         -mno-update        -mavoid-indexed-addresses
           -mno-avoid-indexed-addresses     -mfused-madd      -mno-fused-madd     -mbit-align     -mno-bit-align
           -mstrict-align      -mno-strict-align      -mrelocatable     -mno-relocatable       -mrelocatable-lib
           -mno-relocatable-lib -mtoc  -mno-toc  -mlittle  -mlittle-endian  -mbig  -mbig-endian -mdynamic-no-pic
           -mswdiv   -msingle-pic-base -mprioritize-restricted-insns=priority -msched-costly-dep=dependence_type
           -minsert-sched-nops=scheme -mcall-aixdesc  -mcall-eabi   -mcall-freebsd  -mcall-linux   -mcall-netbsd
           -mcall-openbsd    -mcall-sysv     -mcall-sysv-eabi    -mcall-sysv-noeabi   -mtraceback=traceback_type
           -maix-struct-return   -msvr4-struct-return   -mabi=abi-type    -msecure-plt    -mbss-plt   -mlongcall
           -mno-longcall   -mpltseq   -mno-pltseq -mblock-move-inline-limit=num -mblock-compare-inline-limit=num
           -mblock-compare-inline-loop-limit=num -mno-block-ops-unaligned-vsx  -mstring-compare-inline-limit=num
           -misel    -mno-isel   -mvrsave   -mno-vrsave  -mmulhw   -mno-mulhw  -mdlmzb   -mno-dlmzb  -mprototype
           -mno-prototype -msim  -mmvme  -mads  -myellowknife  -memb  -msdata  -msdata=opt   -mreadonly-in-sdata
           -mvxworks    -G   num   -mrecip    -mrecip=opt   -mno-recip   -mrecip-precision  -mno-recip-precision
           -mveclibabi=type  -mfriz  -mno-friz -mpointers-to-nested-functions  -mno-pointers-to-nested-functions
           -msave-toc-indirect   -mno-save-toc-indirect  -mpower8-fusion   -mno-mpower8-fusion   -mpower8-vector
           -mno-power8-vector   -mcrypto    -mno-crypto    -mhtm    -mno-htm   -mquad-memory    -mno-quad-memory
           -mquad-memory-atomic  -mno-quad-memory-atomic -mcompat-align-parm  -mno-compat-align-parm  -mfloat128
           -mno-float128    -mfloat128-hardware    -mno-float128-hardware   -mgnu-attribute   -mno-gnu-attribute
           -mstack-protector-guard=guard  -mstack-protector-guard-reg=reg  -mstack-protector-guard-offset=offset
           -mprefixed   -mno-prefixed   -mpcrel   -mno-pcrel   -mmma  -mno-mmma  -mrop-protect  -mno-rop-protect
           -mprivileged -mno-privileged

           RX   Options   -m64bit-doubles     -m32bit-doubles     -fpu     -nofpu    -mcpu=    -mbig-endian-data
           -mlittle-endian-data   -msmall-data   -msim    -mno-sim   -mas100-syntax   -mno-as100-syntax  -mrelax
           -mmax-constant-size=  -mint-register=  -mpid  -mallow-string-insns    -mno-allow-string-insns   -mjsr
           -mno-warn-multiple-fast-interrupts -msave-acc-in-interrupts

           S/390  and  zSeries  Options  -mtune=cpu-type  -march=cpu-type -mhard-float  -msoft-float  -mhard-dfp
           -mno-hard-dfp  -mlong-double-64   -mlong-double-128   -mbackchain    -mno-backchain    -mpacked-stack
           -mno-packed-stack  -msmall-exec  -mno-small-exec  -mmvcle  -mno-mvcle -m64  -m31  -mdebug  -mno-debug
           -mesa    -mzarch   -mhtm    -mvx     -mzvector    -mtpf-trace     -mno-tpf-trace     -mtpf-trace-skip
           -mno-tpf-trace-skip -mfused-madd  -mno-fused-madd -mwarn-framesize  -mwarn-dynamicstack  -mstack-size
           -mstack-guard -mhotpatch=halfwords,halfwords

           Score Options -meb  -mel -mnhwloop -muls -mmac -mscore5  -mscore5u  -mscore7  -mscore7d

           SH  Options  -m1   -m2   -m2e  -m2a-nofpu   -m2a-single-only   -m2a-single   -m2a -m3  -m3e -m4-nofpu
           -m4-single-only  -m4-single  -m4 -m4a-nofpu  -m4a-single-only   -m4a-single   -m4a   -m4al  -mb   -ml
           -mdalign   -mrelax  -mbigtable   -mfmovd   -mrenesas   -mno-renesas   -mnomacsave  -mieee   -mno-ieee
           -mbitops  -misize   -minline-ic_invalidate   -mpadstruct  -mprefergot   -musermode   -multcost=number
           -mdiv=strategy    -mdivsi3_libfunc=name     -mfixed-range=register-range   -maccumulate-outgoing-args
           -matomic-model=atomic-model -mbranch-cost=num  -mzdcbranch  -mno-zdcbranch -mcbranch-force-delay-slot
           -mfused-madd  -mno-fused-madd  -mfsca  -mno-fsca  -mfsrra  -mno-fsrra -mpretend-cmove  -mtas

           Solaris 2 Options -mclear-hwcap  -mno-clear-hwcap  -mimpure-text  -mno-impure-text -pthreads

           SPARC Options -mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model -mmemory-model=mem-model -m32   -m64
           -mapp-regs   -mno-app-regs  -mfaster-structs   -mno-faster-structs  -mflat  -mno-flat -mfpu  -mno-fpu
           -mhard-float   -msoft-float  -mhard-quad-float    -msoft-quad-float   -mstack-bias    -mno-stack-bias
           -mstd-struct-return   -mno-std-struct-return  -munaligned-doubles  -mno-unaligned-doubles -muser-mode
           -mno-user-mode -mv8plus  -mno-v8plus  -mvis  -mno-vis -mvis2   -mno-vis2   -mvis3   -mno-vis3  -mvis4
           -mno-vis4  -mvis4b  -mno-vis4b -mcbcond  -mno-cbcond  -mfmaf  -mno-fmaf  -mfsmuld  -mno-fsmuld -mpopc
           -mno-popc  -msubxc  -mno-subxc -mfix-at697f  -mfix-ut699  -mfix-ut700  -mfix-gr712rc -mlra  -mno-lra

           System V Options -Qy  -Qn  -YP,paths  -Ym,dir

           TILE-Gx Options -mcpu=CPU  -m32  -m64  -mbig-endian  -mlittle-endian -mcmodel=code-model

           TILEPro Options -mcpu=cpu  -m32

           V850  Options  -mlong-calls   -mno-long-calls   -mep  -mno-ep -mprolog-function  -mno-prolog-function
           -mspace -mtda=n   -msda=n   -mzda=n  -mapp-regs   -mno-app-regs  -mdisable-callt   -mno-disable-callt
           -mv850e2v3   -mv850e2   -mv850e1   -mv850es  -mv850e   -mv850  -mv850e3v5 -mloop -mrelax -mlong-jumps
           -msoft-float -mhard-float -mgcc-abi -mrh850-abi -mbig-switch

           VAX Options -mg  -mgnu  -munix

           Visium  Options  -mdebug   -msim   -mfpu    -mno-fpu    -mhard-float    -msoft-float   -mcpu=cpu-type
           -mtune=cpu-type  -msv-mode  -muser-mode

           VMS Options -mvms-return-codes  -mdebug-main=prefix  -mmalloc64 -mpointer-size=size

           VxWorks Options -mrtp  -non-static  -Bstatic  -Bdynamic -Xbind-lazy  -Xbind-now

           x86   Options   -mtune=cpu-type    -march=cpu-type   -mtune-ctrl=feature-list    -mdump-tune-features
           -mno-default   -mfpmath=unit   -masm=dialect    -mno-fancy-math-387    -mno-fp-ret-in-387     -m80387
           -mhard-float   -msoft-float  -mno-wide-multiply  -mrtd  -malign-double -mpreferred-stack-boundary=num
           -mincoming-stack-boundary=num -mcld  -mcx16  -msahf  -mmovbe  -mcrc32  -mmwait  -mrecip   -mrecip=opt
           -mvzeroupper   -mprefer-avx128   -mprefer-vector-width=opt  -mmmx   -msse   -msse2   -msse3   -mssse3
           -msse4.1  -msse4.2  -msse4  -mavx -mavx2  -mavx512f  -mavx512pf  -mavx512er   -mavx512cd   -mavx512vl
           -mavx512bw   -mavx512dq   -mavx512ifma   -mavx512vbmi   -msha   -maes  -mpclmul   -mfsgsbase  -mrdrnd
           -mf16c   -mfma   -mpconfig   -mwbnoinvd  -mptwrite   -mprefetchwt1   -mclflushopt   -mclwb   -mxsavec
           -mxsaves  -msse4a   -m3dnow   -m3dnowa   -mpopcnt   -mabm  -mbmi  -mtbm  -mfma4  -mxop -madx  -mlzcnt
           -mbmi2  -mfxsr  -mxsave  -mxsaveopt  -mrtm  -mhle  -mlwp -mmwaitx  -mclzero  -mpku  -mthreads  -mgfni
           -mvaes  -mwaitpkg -mshstk -mmanual-endbr -mforce-indirect-call  -mavx512vbmi2  -mavx512bf16  -menqcmd
           -mvpclmulqdq   -mavx512bitalg  -mmovdiri  -mmovdir64b  -mavx512vpopcntdq -mavx5124fmaps  -mavx512vnni
           -mavx5124vnniw   -mprfchw   -mrdpid  -mrdseed   -msgx  -mavx512vp2intersect  -mserialize   -mtsxldtrk
           -mamx-tile    -mamx-int8    -mamx-bf16   -muintr   -mhreset   -mavxvnni   -mcldemote   -mms-bitfields
           -mno-align-stringops  -minline-all-stringops -minline-stringops-dynamically   -mstringop-strategy=alg
           -mkl       -mwidekl      -mmemcpy-strategy=strategy       -mmemset-strategy=strategy      -mpush-args
           -maccumulate-outgoing-args       -m128bit-long-double      -m96bit-long-double       -mlong-double-64
           -mlong-double-80   -mlong-double-128 -mregparm=num  -msseregparm -mveclibabi=type  -mvect8-ret-in-mem
           -mpc32    -mpc64    -mpc80   -mdaz-ftz   -mstackrealign   -momit-leaf-frame-pointer     -mno-red-zone
           -mno-tls-direct-seg-refs -mcmodel=code-model  -mabi=name  -maddress-mode=mode -m32  -m64  -mx32  -m16
           -miamcu   -mlarge-data-threshold=num  -msse2avx  -mfentry  -mrecord-mcount  -mnop-mcount  -m8bit-idiv
           -minstrument-return=type   -mfentry-name=name   -mfentry-section=name   -mavx256-split-unaligned-load
           -mavx256-split-unaligned-store            -malign-data=type             -mstack-protector-guard=guard
           -mstack-protector-guard-reg=reg                                 -mstack-protector-guard-offset=offset
           -mstack-protector-guard-symbol=symbol           -mgeneral-regs-only            -mcall-ms2sysv-xlogues
           -mindirect-branch=choice   -mfunction-return=choice  -mindirect-branch-register   -mharden-sls=choice
           -mindirect-branch-cs-prefix -mneeded

           x86  Windows  Options -mconsole  -mcygwin  -mno-cygwin  -mdll -mnop-fun-dllimport  -mthread -municode
           -mwin32  -mwindows  -fno-set-stack-executable

           Xstormy16 Options -msim

           Xtensa    Options    -mconst16     -mno-const16    -mfused-madd     -mno-fused-madd    -mforce-no-pic
           -mserialize-volatile    -mno-serialize-volatile  -mtext-section-literals   -mno-text-section-literals
           -mauto-litpools  -mno-auto-litpools  -mtarget-align   -mno-target-align  -mlongcalls   -mno-longcalls
           -mabi=abi-type

           zSeries Options See S/390 and zSeries Options.

   Options Controlling the Kind of Output
       Compilation  can  involve  up  to  four  stages: preprocessing, compilation proper, assembly and linking,
       always in that order.  GCC is capable of preprocessing and compiling several files  either  into  several
       assembler  input  files,  or  into  one  assembler input file; then each assembler input file produces an
       object file, and linking combines all the object files (those newly  compiled,  and  those  specified  as
       input) into an executable file.

       For any given input file, the file name suffix determines what kind of compilation is done:

       file.c
           C source code that must be preprocessed.

       file.i
           C source code that should not be preprocessed.

       file.ii
           C++ source code that should not be preprocessed.

       file.m
           Objective-C  source  code.   Note  that you must link with the libobjc library to make an Objective-C
           program work.

       file.mi
           Objective-C source code that should not be preprocessed.

       file.mm
       file.M
           Objective-C++ source code.  Note that you must link with the libobjc library to make an Objective-C++
           program work.  Note that .M refers to a literal capital M.

       file.mii
           Objective-C++ source code that should not be preprocessed.

       file.h
           C, C++, Objective-C or Objective-C++ header file to be turned into a precompiled header (default), or
           C, C++ header file to be turned into an Ada spec (via the -fdump-ada-spec switch).

       file.cc
       file.cp
       file.cxx
       file.cpp
       file.CPP
       file.c++
       file.C
           C++ source code that must be preprocessed.  Note that in .cxx, the last  two  letters  must  both  be
           literally x.  Likewise, .C refers to a literal capital C.

       file.mm
       file.M
           Objective-C++ source code that must be preprocessed.

       file.mii
           Objective-C++ source code that should not be preprocessed.

       file.hh
       file.H
       file.hp
       file.hxx
       file.hpp
       file.HPP
       file.h++
       file.tcc
           C++ header file to be turned into a precompiled header or Ada spec.

       file.f
       file.for
       file.ftn
           Fixed form Fortran source code that should not be preprocessed.

       file.F
       file.FOR
       file.fpp
       file.FPP
       file.FTN
           Fixed form Fortran source code that must be preprocessed (with the traditional preprocessor).

       file.f90
       file.f95
       file.f03
       file.f08
           Free form Fortran source code that should not be preprocessed.

       file.F90
       file.F95
       file.F03
       file.F08
           Free form Fortran source code that must be preprocessed (with the traditional preprocessor).

       file.go
           Go source code.

       file.brig
           BRIG files (binary representation of HSAIL).

       file.d
           D source code.

       file.di
           D interface file.

       file.dd
           D documentation code (Ddoc).

       file.ads
           Ada  source  code  file  that  contains  a  library  unit  declaration  (a  declaration of a package,
           subprogram, or generic, or a generic instantiation),  or  a  library  unit  renaming  declaration  (a
           package, generic, or subprogram renaming declaration).  Such files are also called specs.

       file.adb
           Ada  source  code file containing a library unit body (a subprogram or package body).  Such files are
           also called bodies.

       file.s
           Assembler code.

       file.S
       file.sx
           Assembler code that must be preprocessed.

       other
           An object file to be fed straight into linking.  Any file name with no recognized suffix  is  treated
           this way.

       You can specify the input language explicitly with the -x option:

       -x language
           Specify  explicitly  the  language  for  the  following input files (rather than letting the compiler
           choose a default based on the file name suffix).  This option applies to all  following  input  files
           until the next -x option.  Possible values for language are:

                   c  c-header  cpp-output
                   c++  c++-header  c++-system-header c++-user-header c++-cpp-output
                   objective-c  objective-c-header  objective-c-cpp-output
                   objective-c++ objective-c++-header objective-c++-cpp-output
                   assembler  assembler-with-cpp
                   ada
                   d
                   f77  f77-cpp-input f95  f95-cpp-input
                   go
                   brig

       -x none
           Turn  off  any  specification  of a language, so that subsequent files are handled according to their
           file name suffixes (as they are if -x has not been used at all).

       If you only want some of the stages of compilation, you can use -x (or filename  suffixes)  to  tell  gcc
       where  to  start,  and  one  of  the  options  -c, -S, or -E to say where gcc is to stop.  Note that some
       combinations (for example, -x cpp-output -E) instruct gcc to do nothing at all.

       -c  Compile or assemble the source files, but do not link.  The linking stage simply is  not  done.   The
           ultimate output is in the form of an object file for each source file.

           By  default, the object file name for a source file is made by replacing the suffix .c, .i, .s, etc.,
           with .o.

           Unrecognized input files, not requiring compilation or assembly, are ignored.

       -S  Stop after the stage of compilation proper; do not assemble.   The  output  is  in  the  form  of  an
           assembler code file for each non-assembler input file specified.

           By  default,  the assembler file name for a source file is made by replacing the suffix .c, .i, etc.,
           with .s.

           Input files that don't require compilation are ignored.

       -E  Stop after the preprocessing stage; do not run the compiler proper.  The output is  in  the  form  of
           preprocessed source code, which is sent to the standard output.

           Input files that don't require preprocessing are ignored.

       -o file
           Place  the  primary  output in file file.  This applies to whatever sort of output is being produced,
           whether it be an executable file, an object file, an assembler file or preprocessed C code.

           If -o is not specified, the default is to put an executable  file  in  a.out,  the  object  file  for
           source.suffix   in   source.o,  its  assembler  file  in  source.s,  a  precompiled  header  file  in
           source.suffix.gch, and all preprocessed C source on standard output.

           Though -o names only the primary output, it also affects the naming of auxiliary  and  dump  outputs.
           See the examples below.  Unless overridden, both auxiliary outputs and dump outputs are placed in the
           same directory as the primary output.  In auxiliary outputs, the suffix of the input file is replaced
           with that of the auxiliary output file type; in dump outputs, the suffix of the dump file is appended
           to  the input file suffix.  In compilation commands, the base name of both auxiliary and dump outputs
           is that of the primary output; in compile and link commands,  the  primary  output  name,  minus  the
           executable  suffix,  is  combined  with  the  input  file  name.   If  both share the same base name,
           disregarding the suffix, the result of the  combination  is  that  base  name,  otherwise,  they  are
           concatenated, separated by a dash.

                   gcc -c foo.c ...

           will  use  foo.o  as  the  primary output, and place aux outputs and dumps next to it, e.g., aux file
           foo.dwo for -gsplit-dwarf, and dump file foo.c.???r.final for -fdump-rtl-final.

           If a non-linker output file is explicitly specified, aux and dump files by default take the same base
           name:

                   gcc -c foo.c -o dir/foobar.o ...

           will name aux outputs dir/foobar.* and dump outputs dir/foobar.c.*.

           A linker output will instead prefix aux and dump outputs:

                   gcc foo.c bar.c -o dir/foobar ...

           will  generally  name  aux  outputs  dir/foobar-foo.*  and   dir/foobar-bar.*,   and   dump   outputs
           dir/foobar-foo.c.* and dir/foobar-bar.c.*.

           The one exception to the above is when the executable shares the base name with the single input:

                   gcc foo.c -o dir/foo ...

           in which case aux outputs are named dir/foo.* and dump outputs named dir/foo.c.*.

           The  location  and  the names of auxiliary and dump outputs can be adjusted by the options -dumpbase,
           -dumpbase-ext, -dumpdir, -save-temps=cwd, and -save-temps=obj.

       -dumpbase dumpbase
           This option sets the base name for auxiliary and dump output files.  It does not affect the  name  of
           the  primary output file.  Intermediate outputs, when preserved, are not regarded as primary outputs,
           but as auxiliary outputs:

                   gcc -save-temps -S foo.c

           saves the (no longer) temporary preprocessed file in foo.i, and then compiles to the (implied) output
           file foo.s, whereas:

                   gcc -save-temps -dumpbase save-foo -c foo.c

           preprocesses to in save-foo.i, compiles to save-foo.s (now an intermediate, thus  auxiliary  output),
           and then assembles to the (implied) output file foo.o.

           Absent this option, dump and aux files take their names from the input file, or from the (non-linker)
           output  file,  if  one  is  explicitly specified: dump output files (e.g. those requested by -fdump-*
           options) with the input name suffix, and aux output files (those requested by other non-dump options,
           e.g. "-save-temps", "-gsplit-dwarf", "-fcallgraph-info") without it.

           Similar suffix differentiation of dump and aux outputs can be attained for explicitly-given -dumpbase
           basename.suf by also specifying -dumpbase-ext .suf.

           If dumpbase is explicitly specified with any directory component,  any  dumppfx  specification  (e.g.
           -dumpdir or -save-temps=*) is ignored, and instead of appending to it, dumpbase fully overrides it:

                   gcc foo.c -c -o dir/foo.o -dumpbase alt/foo \
                     -dumpdir pfx- -save-temps=cwd ...

           creates auxiliary and dump outputs named alt/foo.*, disregarding dir/ in -o, the ./ prefix implied by
           -save-temps=cwd, and pfx- in -dumpdir.

           When  -dumpbase  is  specified  in a command that compiles multiple inputs, or that compiles and then
           links, it may be combined with dumppfx, as specified  under  -dumpdir.   Then,  each  input  file  is
           compiled  using the combined dumppfx, and default values for dumpbase and auxdropsuf are computed for
           each input file:

                   gcc foo.c bar.c -c -dumpbase main ...

           creates foo.o and bar.o as primary outputs, and avoids overwriting the auxiliary and dump outputs  by
           using the dumpbase as a prefix, creating auxiliary and dump outputs named main-foo.*  and main-bar.*.

           An  empty  string  specified as dumpbase avoids the influence of the output basename in the naming of
           auxiliary and dump outputs during compilation, computing default values :

                   gcc -c foo.c -o dir/foobar.o -dumpbase " ...

           will name aux outputs dir/foo.* and dump outputs dir/foo.c.*.  Note how  their  basenames  are  taken
           from the input name, but the directory still defaults to that of the output.

           The empty-string dumpbase does not prevent the use of the output basename for outputs during linking:

                   gcc foo.c bar.c -o dir/foobar -dumpbase " -flto ...

           The  compilation  of  the  source files will name auxiliary outputs dir/foo.* and dir/bar.*, and dump
           outputs dir/foo.c.* and dir/bar.c.*.  LTO recompilation during linking will use  dir/foobar.  as  the
           prefix for dumps and auxiliary files.

       -dumpbase-ext auxdropsuf
           When  forming  the  name  of an auxiliary (but not a dump) output file, drop trailing auxdropsuf from
           dumpbase before appending any suffixes.  If not specified, this option defaults to the  suffix  of  a
           default  dumpbase,  i.e.,  the  suffix of the input file when -dumpbase is not present in the command
           line, or dumpbase is combined with dumppfx.

                   gcc foo.c -c -o dir/foo.o -dumpbase x-foo.c -dumpbase-ext .c ...

           creates dir/foo.o as the main output, and generates auxiliary  outputs  in  dir/x-foo.*,  taking  the
           location  of  the  primary output, and dropping the .c suffix from the dumpbase.  Dump outputs retain
           the suffix: dir/x-foo.c.*.

           This option is disregarded if it does not match the suffix of a  specified  dumpbase,  except  as  an
           alternative  to  the  executable  suffix  when  appending  the linker output base name to dumppfx, as
           specified below:

                   gcc foo.c bar.c -o main.out -dumpbase-ext .out ...

           creates main.out as the primary output, and avoids overwriting the  auxiliary  and  dump  outputs  by
           using  the  executable name minus auxdropsuf as a prefix, creating auxiliary outputs named main-foo.*
           and main-bar.* and dump outputs named main-foo.c.* and main-bar.c.*.

       -dumpdir dumppfx
           When forming the name of an auxiliary or dump output file, use dumppfx as a prefix:

                   gcc -dumpdir pfx- -c foo.c ...

           creates foo.o as the primary output, and auxiliary  outputs  named  pfx-foo.*,  combining  the  given
           dumppfx  with  the default dumpbase derived from the default primary output, derived in turn from the
           input name.  Dump outputs also take the input name suffix: pfx-foo.c.*.

           If dumppfx is to be used as a directory name, it must end with a directory separator:

                   gcc -dumpdir dir/ -c foo.c -o obj/bar.o ...

           creates obj/bar.o as the primary output, and auxiliary outputs named dir/bar.*, combining  the  given
           dumppfx  with  the default dumpbase derived from the primary output name.  Dump outputs also take the
           input name suffix: dir/bar.c.*.

           It defaults to the location of the output file, unless  the  output  file  is  a  special  file  like
           "/dev/null". Options -save-temps=cwd and -save-temps=obj override this default, just like an explicit
           -dumpdir option.  In case multiple such options are given, the last one prevails:

                   gcc -dumpdir pfx- -c foo.c -save-temps=obj ...

           outputs  foo.o,  with auxiliary outputs named foo.* because -save-temps=* overrides the dumppfx given
           by the earlier -dumpdir option.  It does not matter that =obj is the  default  for  -save-temps,  nor
           that the output directory is implicitly the current directory.  Dump outputs are named foo.c.*.

           When  compiling  from  multiple  input files, if -dumpbase is specified, dumpbase, minus a auxdropsuf
           suffix, and a dash are appended to (or override, if containing any directory components) an  explicit
           or  defaulted  dumppfx, so that each of the multiple compilations gets differently-named aux and dump
           outputs.

                   gcc foo.c bar.c -c -dumpdir dir/pfx- -dumpbase main ...

           outputs auxiliary dumps to dir/pfx-main-foo.* and dir/pfx-main-bar.*, appending dumpbase- to dumppfx.
           Dump  outputs  retain  the  input  file  suffix:  dir/pfx-main-foo.c.*    and   dir/pfx-main-bar.c.*,
           respectively.  Contrast with the single-input compilation:

                   gcc foo.c -c -dumpdir dir/pfx- -dumpbase main ...

           that,  applying  -dumpbase  to  a  single source, does not compute and append a separate dumpbase per
           input file.  Its auxiliary and dump outputs go in dir/pfx-main.*.

           When compiling and then linking from multiple  input  files,  a  defaulted  or  explicitly  specified
           dumppfx  also  undergoes  the dumpbase- transformation above (e.g. the compilation of foo.c and bar.c
           above, but without -c).  If neither -dumpdir nor -dumpbase are given, the linker  output  base  name,
           minus  auxdropsuf,  if  specified, or the executable suffix otherwise, plus a dash is appended to the
           default dumppfx instead.  Note, however, that unlike earlier cases of linking:

                   gcc foo.c bar.c -dumpdir dir/pfx- -o main ...

           does not append the output name main to dumppfx, because -dumpdir is explicitly specified.  The  goal
           is that the explicitly-specified dumppfx may contain the specified output name as part of the prefix,
           if  desired;  only  an  explicitly-specified  -dumpbase  would be combined with it, in order to avoid
           simply discarding a meaningful option.

           When compiling and then linking from a single input file, the linker output base name  will  only  be
           appended  to  the  default  dumppfx as above if it does not share the base name with the single input
           file name.  This has been covered in single-input linking cases  above,  but  not  with  an  explicit
           -dumpdir that inhibits the combination, even if overridden by -save-temps=*:

                   gcc foo.c -dumpdir alt/pfx- -o dir/main.exe -save-temps=cwd ...

           Auxiliary  outputs  are  named  foo.*,  and dump outputs foo.c.*, in the current working directory as
           ultimately requested by -save-temps=cwd.

           Summing it all up for an intuitive though slightly imprecise data flow: the primary  output  name  is
           broken  into a directory part and a basename part; dumppfx is set to the former, unless overridden by
           -dumpdir or -save-temps=*, and dumpbase is set to the latter,  unless  overriden  by  -dumpbase.   If
           there  are multiple inputs or linking, this dumpbase may be combined with dumppfx and taken from each
           input file.  Auxiliary output names for each input are formed by combining  dumppfx,  dumpbase  minus
           suffix, and the auxiliary output suffix; dump output names are only different in that the suffix from
           dumpbase is retained.

           When  it  comes  to  auxiliary  and  dump  outputs created during LTO recompilation, a combination of
           dumppfx and dumpbase, as given or as derived from the linker output name but not from inputs, even in
           cases in which this combination would not otherwise be used as such, is passed down with  a  trailing
           period replacing the compiler-added dash, if any, as a -dumpdir option to lto-wrapper; being involved
           in linking, this program does not normally get any -dumpbase and -dumpbase-ext, and it ignores them.

           When  running  sub-compilers, lto-wrapper appends LTO stage names to the received dumppfx, ensures it
           contains a directory component so that it overrides any -dumpdir, and passes  that  as  -dumpbase  to
           sub-compilers.

       -v  Print  (on standard error output) the commands executed to run the stages of compilation.  Also print
           the version number of the compiler driver program and of the preprocessor and the compiler proper.

       -###
           Like -v except the commands are not executed and  arguments  are  quoted  unless  they  contain  only
           alphanumeric  characters or "./-_".  This is useful for shell scripts to capture the driver-generated
           command lines.

       --help
           Print (on the standard output) a description of the command-line options understood by gcc.   If  the
           -v option is also specified then --help is also passed on to the various processes invoked by gcc, so
           that  they  can  display  the  command-line options they accept.  If the -Wextra option has also been
           specified (prior to the  --help  option),  then  command-line  options  that  have  no  documentation
           associated with them are also displayed.

       --target-help
           Print  (on  the standard output) a description of target-specific command-line options for each tool.
           For some targets extra target-specific information may also be printed.

       --help={class|[^]qualifier}[,...]
           Print (on the standard output) a description of the command-line options understood by  the  compiler
           that fit into all specified classes and qualifiers.  These are the supported classes:

           optimizers
               Display all of the optimization options supported by the compiler.

           warnings
               Display all of the options controlling warning messages produced by the compiler.

           target
               Display  target-specific  options.   Unlike  the  --target-help  option  however, target-specific
               options of the linker and assembler are not displayed.   This  is  because  those  tools  do  not
               currently support the extended --help= syntax.

           params
               Display the values recognized by the --param option.

           language
               Display  the  options  supported for language, where language is the name of one of the languages
               supported in this version of GCC.  If an option is supported  by  all  languages,  one  needs  to
               select common class.

           common
               Display the options that are common to all languages.

           These are the supported qualifiers:

           undocumented
               Display only those options that are undocumented.

           joined
               Display  options taking an argument that appears after an equal sign in the same continuous piece
               of text, such as: --help=target.

           separate
               Display options taking an argument that appears as a separate word following the original option,
               such as: -o output-file.

           Thus for example to display all the undocumented target-specific switches supported by the  compiler,
           use:

                   --help=target,undocumented

           The  sense  of  a  qualifier  can be inverted by prefixing it with the ^ character, so for example to
           display all binary warning options (i.e., ones that are either on or off and  that  do  not  take  an
           argument) that have a description, use:

                   --help=warnings,^joined,^undocumented

           The argument to --help= should not consist solely of inverted qualifiers.

           Combining  several classes is possible, although this usually restricts the output so much that there
           is nothing to display.  One case where it does work, however, is when one of the classes  is  target.
           For example, to display all the target-specific optimization options, use:

                   --help=target,optimizers

           The  --help=  option can be repeated on the command line.  Each successive use displays its requested
           class of options, skipping those that have already been  displayed.   If  --help  is  also  specified
           anywhere on the command line then this takes precedence over any --help= option.

           If  the  -Q  option  appears on the command line before the --help= option, then the descriptive text
           displayed by --help= is changed.  Instead of describing the displayed options, an indication is given
           as to whether the option is enabled, disabled or set to a specific value (assuming that the  compiler
           knows this at the point where the --help= option is used).

           Here is a truncated example from the ARM port of gcc:

                     % gcc -Q -mabi=2 --help=target -c
                     The following options are target specific:
                     -mabi=                                2
                     -mabort-on-noreturn                   [disabled]
                     -mapcs                                [disabled]

           The  output  is  sensitive  to  the  effects  of  previous command-line options, so for example it is
           possible to find out which optimizations are enabled at -O2 by using:

                   -Q -O2 --help=optimizers

           Alternatively you can discover which binary optimizations are enabled by -O3 by using:

                   gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
                   gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
                   diff /tmp/O2-opts /tmp/O3-opts | grep enabled

       --version
           Display the version number and copyrights of the invoked GCC.

       -pass-exit-codes
           Normally the gcc program exits with the code of 1 if any phase of the compiler returns a  non-success
           return  code.   If you specify -pass-exit-codes, the gcc program instead returns with the numerically
           highest error produced by any phase returning an error indication.  The C,  C++,  and  Fortran  front
           ends return 4 if an internal compiler error is encountered.

       -pipe
           Use  pipes  rather  than temporary files for communication between the various stages of compilation.
           This fails to work on some systems where the assembler is unable to read from a  pipe;  but  the  GNU
           assembler has no trouble.

       -specs=file
           Process  file  after the compiler reads in the standard specs file, in order to override the defaults
           which the gcc driver program uses when determining what switches to pass to  cc1,  cc1plus,  as,  ld,
           etc.   More  than  one  -specs=file  can  be specified on the command line, and they are processed in
           order, from left to right.

       -wrapper
           Invoke all subcommands under a wrapper program.  The name of the wrapper program and  its  parameters
           are passed as a comma separated list.

                   gcc -c t.c -wrapper gdb,--args

           This  invokes  all  subprograms of gcc under gdb --args, thus the invocation of cc1 is gdb --args cc1
           ....

       -ffile-prefix-map=old=new
           When compiling files residing in directory old, record any references to them in the  result  of  the
           compilation  as  if the files resided in directory new instead.  Specifying this option is equivalent
           to specifying all the individual -f*-prefix-map options.  This  can  be  used  to  make  reproducible
           builds that are location independent.  See also -fmacro-prefix-map and -fdebug-prefix-map.

       -fplugin=name.so
           Load  the  plugin code in file name.so, assumed to be a shared object to be dlopen'd by the compiler.
           The base name of the shared object file is used to identify the plugin for the purposes  of  argument
           parsing  (See  -fplugin-arg-name-key=value  below).  Each plugin should define the callback functions
           specified in the Plugins API.

       -fplugin-arg-name-key=value
           Define an argument called key with a value of value for the plugin called name.

       -fdump-ada-spec[-slim]
           For C and C++ source and include files, generate corresponding Ada specs.

       -fada-spec-parent=unit
           In conjunction with -fdump-ada-spec[-slim] above, generate Ada specs as child units of parent unit.

       -fdump-go-spec=file
           For input files in any language, generate corresponding Go declarations in file.  This  generates  Go
           "const",  "type",  "var",  and  "func"  declarations  which may be a useful way to start writing a Go
           interface to code written in some other language.

       @file
           Read command-line options from file.  The options read are inserted in place of  the  original  @file
           option.   If  file  does not exist, or cannot be read, then the option will be treated literally, and
           not removed.

           Options in file are separated by whitespace.  A whitespace character may be included in an option  by
           surrounding  the  entire  option  in  either  single  or  double  quotes.  Any character (including a
           backslash) may be included by prefixing the character to be included with a backslash.  The file  may
           itself contain additional @file options; any such options will be processed recursively.

   Compiling C++ Programs
       C++  source  files  conventionally  use  one of the suffixes .C, .cc, .cpp, .CPP, .c++, .cp, or .cxx; C++
       header files often use .hh, .hpp, .H, or (for shared template code) .tcc; and preprocessed C++ files  use
       the suffix .ii.  GCC recognizes files with these names and compiles them as C++ programs even if you call
       the compiler the same way as for compiling C programs (usually with the name gcc).

       However,  the use of gcc does not add the C++ library.  g++ is a program that calls GCC and automatically
       specifies linking against the C++ library.  It treats .c, .h and .i files as C++ source files instead  of
       C  source  files unless -x is used.  This program is also useful when precompiling a C header file with a
       .h extension for use in C++ compilations.  On many systems, g++ is also installed with the name c++.

       When you compile C++ programs, you may specify many of the same command-line options  that  you  use  for
       compiling  programs  in  any language; or command-line options meaningful for C and related languages; or
       options that are meaningful only for C++ programs.

   Options Controlling C Dialect
       The following options control the dialect of C (or languages derived from C, such as C++, Objective-C and
       Objective-C++) that the compiler accepts:

       -ansi
           In C mode, this is equivalent to -std=c90. In C++ mode, it is equivalent to -std=c++98.

           This turns off certain features of GCC that are incompatible with ISO C90 (when compiling C code), or
           of standard C++ (when compiling C++ code), such as the "asm" and "typeof"  keywords,  and  predefined
           macros  such as "unix" and "vax" that identify the type of system you are using.  It also enables the
           undesirable and rarely used ISO trigraph feature.  For the C compiler, it disables recognition of C++
           style // comments as well as the "inline" keyword.

           The alternate keywords "__asm__", "__extension__", "__inline__" and  "__typeof__"  continue  to  work
           despite  -ansi.   You  would not want to use them in an ISO C program, of course, but it is useful to
           put them in header files  that  might  be  included  in  compilations  done  with  -ansi.   Alternate
           predefined macros such as "__unix__" and "__vax__" are also available, with or without -ansi.

           The  -ansi  option does not cause non-ISO programs to be rejected gratuitously.  For that, -Wpedantic
           is required in addition to -ansi.

           The macro "__STRICT_ANSI__" is predefined when the -ansi option  is  used.   Some  header  files  may
           notice  this  macro  and refrain from declaring certain functions or defining certain macros that the
           ISO standard doesn't call for; this is to avoid interfering with any programs that  might  use  these
           names for other things.

           Functions that are normally built in but do not have semantics defined by ISO C (such as "alloca" and
           "ffs") are not built-in functions when -ansi is used.

       -std=
           Determine the language standard.   This option is currently only supported when compiling C or C++.

           The  compiler  can  accept  several  base  standards, such as c90 or c++98, and GNU dialects of those
           standards, such as gnu90 or gnu++98.  When a base standard is specified,  the  compiler  accepts  all
           programs  following  that  standard  plus  those using GNU extensions that do not contradict it.  For
           example, -std=c90 turns off certain features of GCC that are incompatible with ISO C90, such  as  the
           "asm" and "typeof" keywords, but not other GNU extensions that do not have a meaning in ISO C90, such
           as omitting the middle term of a "?:" expression. On the other hand, when a GNU dialect of a standard
           is specified, all features supported by the compiler are enabled, even when those features change the
           meaning  of  the  base  standard.  As a result, some strict-conforming programs may be rejected.  The
           particular standard is used by -Wpedantic to identify which features are GNU  extensions  given  that
           version  of  the standard. For example -std=gnu90 -Wpedantic warns about C++ style // comments, while
           -std=gnu99 -Wpedantic does not.

           A value for this option must be provided; possible values are

           c90
           c89
           iso9899:1990
               Support all ISO C90 programs (certain GNU extensions that conflict with ISO  C90  are  disabled).
               Same as -ansi for C code.

           iso9899:199409
               ISO C90 as modified in amendment 1.

           c99
           c9x
           iso9899:1999
           iso9899:199x
               ISO  C99.   This  standard  is substantially completely supported, modulo bugs and floating-point
               issues (mainly but not entirely relating to optional C99 features from Annexes  F  and  G).   See
               <http://gcc.gnu.org/c99status.html>  for  more  information.   The names c9x and iso9899:199x are
               deprecated.

           c11
           c1x
           iso9899:2011
               ISO C11, the 2011 revision of the ISO C standard.   This  standard  is  substantially  completely
               supported,  modulo  bugs, floating-point issues (mainly but not entirely relating to optional C11
               features from Annexes F and G) and the optional Annexes  K  (Bounds-checking  interfaces)  and  L
               (Analyzability).  The name c1x is deprecated.

           c17
           c18
           iso9899:2017
           iso9899:2018
               ISO  C17,  the 2017 revision of the ISO C standard (published in 2018).  This standard is same as
               C11 except for corrections of defects (all of which are also applied with  -std=c11)  and  a  new
               value of "__STDC_VERSION__", and so is supported to the same extent as C11.

           c2x The next version of the ISO C standard, still under development.  The support for this version is
               experimental and incomplete.

           gnu90
           gnu89
               GNU dialect of ISO C90 (including some C99 features).

           gnu99
           gnu9x
               GNU dialect of ISO C99.  The name gnu9x is deprecated.

           gnu11
           gnu1x
               GNU dialect of ISO C11.  The name gnu1x is deprecated.

           gnu17
           gnu18
               GNU dialect of ISO C17.  This is the default for C code.

           gnu2x
               The  next  version  of  the  ISO  C  standard, still under development, plus GNU extensions.  The
               support for this version is experimental and incomplete.

           c++98
           c++03
               The 1998 ISO C++ standard plus the 2003 technical corrigendum and some additional defect reports.
               Same as -ansi for C++ code.

           gnu++98
           gnu++03
               GNU dialect of -std=c++98.

           c++11
           c++0x
               The 2011 ISO C++ standard plus amendments.  The name c++0x is deprecated.

           gnu++11
           gnu++0x
               GNU dialect of -std=c++11.  The name gnu++0x is deprecated.

           c++14
           c++1y
               The 2014 ISO C++ standard plus amendments.  The name c++1y is deprecated.

           gnu++14
           gnu++1y
               GNU dialect of -std=c++14.  The name gnu++1y is deprecated.

           c++17
           c++1z
               The 2017 ISO C++ standard plus amendments.  The name c++1z is deprecated.

           gnu++17
           gnu++1z
               GNU dialect of -std=c++17.  This is the default for C++ code.  The name gnu++1z is deprecated.

           c++20
           c++2a
               The 2020 ISO C++ standard  plus  amendments.   Support  is  experimental,  and  could  change  in
               incompatible ways in future releases.  The name c++2a is deprecated.

           gnu++20
           gnu++2a
               GNU  dialect  of  -std=c++20.   Support is experimental, and could change in incompatible ways in
               future releases.  The name gnu++2a is deprecated.

           c++2b
           c++23
               The next revision of the ISO C++ standard, planned for 2023.  Support is highly experimental, and
               will almost certainly change in incompatible ways in future releases.

           gnu++2b
           gnu++23
               GNU dialect of -std=c++2b.  Support is highly experimental, and will almost certainly  change  in
               incompatible ways in future releases.

       -fgnu89-inline
           The  option -fgnu89-inline tells GCC to use the traditional GNU semantics for "inline" functions when
           in C99 mode.

           Using this option is roughly equivalent to adding the "gnu_inline" function attribute to  all  inline
           functions.

           The  option  -fno-gnu89-inline explicitly tells GCC to use the C99 semantics for "inline" when in C99
           or gnu99 mode (i.e., it specifies the default behavior).  This option is not supported in -std=c90 or
           -std=gnu90 mode.

           The preprocessor macros "__GNUC_GNU_INLINE__" and "__GNUC_STDC_INLINE__" may be used to  check  which
           semantics are in effect for "inline" functions.

       -fpermitted-flt-eval-methods=style
           ISO/IEC TS 18661-3 defines new permissible values for "FLT_EVAL_METHOD" that indicate that operations
           and  constants  with a semantic type that is an interchange or extended format should be evaluated to
           the precision and range of that type.  These new values are  a  superset  of  those  permitted  under
           C99/C11,  which does not specify the meaning of other positive values of "FLT_EVAL_METHOD".  As such,
           code conforming to C11 may not have been written expecting the possibility of the new values.

           -fpermitted-flt-eval-methods  specifies  whether  the  compiler  should  allow  only  the  values  of
           "FLT_EVAL_METHOD"  specified  in  C99/C11,  or  the  extended  set  of values specified in ISO/IEC TS
           18661-3.

           style is either "c11" or "ts-18661-3" as appropriate.

           The   default   when   in    a    standards    compliant    mode    (-std=c11    or    similar)    is
           -fpermitted-flt-eval-methods=c11.   The  default  when  in  a  GNU dialect (-std=gnu11 or similar) is
           -fpermitted-flt-eval-methods=ts-18661-3.

       -aux-info filename
           Output to the given filename prototyped declarations for all functions declared and/or defined  in  a
           translation  unit,  including those in header files.  This option is silently ignored in any language
           other than C.

           Besides declarations, the file indicates, in comments, the origin of each  declaration  (source  file
           and  line),  whether  the declaration was implicit, prototyped or unprototyped (I, N for new or O for
           old, respectively, in the first character after the line number and the colon), and whether  it  came
           from  a  declaration or a definition (C or F, respectively, in the following character).  In the case
           of function definitions, a K&R-style list  of  arguments  followed  by  their  declarations  is  also
           provided, inside comments, after the declaration.

       -fallow-parameterless-variadic-functions
           Accept variadic functions without named parameters.

           Although  it  is possible to define such a function, this is not very useful as it is not possible to
           read the arguments.  This is only supported for C as this construct is allowed by C++.

       -fno-asm
           Do not recognize "asm", "inline" or "typeof" as a keyword, so  that  code  can  use  these  words  as
           identifiers.   You  can  use  the  keywords  "__asm__", "__inline__" and "__typeof__" instead.  -ansi
           implies -fno-asm.

           In C++, this switch only affects  the  "typeof"  keyword,  since  "asm"  and  "inline"  are  standard
           keywords.  You may want to use the -fno-gnu-keywords flag instead, which has the same effect.  In C99
           mode  (-std=c99  or  -std=gnu99),  this  switch  only  affects the "asm" and "typeof" keywords, since
           "inline" is a standard keyword in ISO C99.

       -fno-builtin
       -fno-builtin-function
           Don't recognize built-in functions that do not begin with __builtin_ as prefix.

           GCC normally generates special code to  handle  certain  built-in  functions  more  efficiently;  for
           instance, calls to "alloca" may become single instructions which adjust the stack directly, and calls
           to  "memcpy"  may become inline copy loops.  The resulting code is often both smaller and faster, but
           since the function calls no longer appear as such, you cannot set a breakpoint on  those  calls,  nor
           can  you change the behavior of the functions by linking with a different library.  In addition, when
           a function is recognized as a built-in function, GCC may use information about that function to  warn
           about problems with calls to that function, or to generate more efficient code, even if the resulting
           code  still  contains  calls to that function.  For example, warnings are given with -Wformat for bad
           calls to "printf" when "printf" is built in and "strlen" is known not to modify global memory.

           With the -fno-builtin-function option only the built-in function function is disabled.  function must
           not begin with __builtin_.  If a function is named that is not built-in in this version of GCC,  this
           option is ignored.  There is no corresponding -fbuiltin-function option; if you wish to enable built-
           in functions selectively when using -fno-builtin or -ffreestanding, you may define macros such as:

                   #define abs(n)          __builtin_abs ((n))
                   #define strcpy(d, s)    __builtin_strcpy ((d), (s))

       -fgimple
           Enable  parsing of function definitions marked with "__GIMPLE".  This is an experimental feature that
           allows unit testing of GIMPLE passes.

       -fhosted
           Assert that compilation targets a hosted environment.  This implies -fbuiltin.  A hosted  environment
           is  one  in  which the entire standard library is available, and in which "main" has a return type of
           "int".  Examples are nearly everything except a kernel.  This is equivalent to -fno-freestanding.

       -ffreestanding
           Assert  that  compilation  targets  a  freestanding  environment.   This  implies  -fno-builtin.    A
           freestanding  environment is one in which the standard library may not exist, and program startup may
           not necessarily be at "main".  The most obvious example is an  OS  kernel.   This  is  equivalent  to
           -fno-hosted.

       -fopenacc
           Enable  handling of OpenACC directives "#pragma acc" in C/C++ and "!$acc" in Fortran.  When -fopenacc
           is  specified,  the  compiler  generates  accelerated  code  according  to  the  OpenACC  Application
           Programming Interface v2.6 <https://www.openacc.org>.  This option implies -pthread, and thus is only
           supported on targets that have support for -pthread.

       -fopenacc-dim=geom
           Specify  default compute dimensions for parallel offload regions that do not explicitly specify.  The
           geom value is a triple of ':'-separated sizes, in order 'gang', 'worker' and, 'vector'.  A  size  can
           be omitted, to use a target-specific default value.

       -fopenmp
           Enable handling of OpenMP directives "#pragma omp" in C/C++ and "!$omp" in Fortran.  When -fopenmp is
           specified, the compiler generates parallel code according to the OpenMP Application Program Interface
           v4.5  <https://www.openmp.org>.   This option implies -pthread, and thus is only supported on targets
           that have support for -pthread. -fopenmp implies -fopenmp-simd.

       -fopenmp-simd
           Enable handling of OpenMP's SIMD directives with "#pragma omp" in C/C++ and "!$omp" in Fortran. Other
           OpenMP directives are ignored.

       -fgnu-tm
           When the option -fgnu-tm is specified, the compiler generates code for the Linux variant  of  Intel's
           current  Transactional  Memory  ABI  specification  document  (Revision 1.1, May 6 2009).  This is an
           experimental feature whose  interface  may  change  in  future  versions  of  GCC,  as  the  official
           specification changes.  Please note that not all architectures are supported for this feature.

           For more information on GCC's support for transactional memory,

           Note   that   the   transactional   memory   feature   is  not  supported  with  non-call  exceptions
           (-fnon-call-exceptions).

       -fms-extensions
           Accept some non-standard constructs used in Microsoft header files.

           In C++ code, this allows member names in structures to be similar to previous types declarations.

                   typedef int UOW;
                   struct ABC {
                     UOW UOW;
                   };

           Some cases of unnamed fields in structures and unions are only accepted with this option.

           Note that this option is off for all targets except for x86 targets using ms-abi.

       -fplan9-extensions
           Accept some non-standard constructs used in Plan 9 code.

           This enables -fms-extensions, permits  passing  pointers  to  structures  with  anonymous  fields  to
           functions  that  expect  pointers  to  elements  of  the  type of the field, and permits referring to
           anonymous fields declared using a typedef.    This is only supported for C, not C++.

       -fcond-mismatch
           Allow conditional expressions with mismatched types in the second and third arguments.  The value  of
           such an expression is void.  This option is not supported for C++.

       -flax-vector-conversions
           Allow  implicit  conversions  between  vectors with differing numbers of elements and/or incompatible
           element types.  This option should not be used for new code.

       -funsigned-char
           Let the type "char" be unsigned, like "unsigned char".

           Each kind of machine has a default for what "char" should be.  It is either like "unsigned  char"  by
           default or like "signed char" by default.

           Ideally, a portable program should always use "signed char" or "unsigned char" when it depends on the
           signedness of an object.  But many programs have been written to use plain "char" and expect it to be
           signed,  or  expect it to be unsigned, depending on the machines they were written for.  This option,
           and its inverse, let you make such a program work with the opposite default.

           The type "char" is always a distinct type from each of "signed char" or "unsigned char", even  though
           its behavior is always just like one of those two.

       -fsigned-char
           Let the type "char" be signed, like "signed char".

           Note  that  this  is equivalent to -fno-unsigned-char, which is the negative form of -funsigned-char.
           Likewise, the option -fno-signed-char is equivalent to -funsigned-char.

       -fsigned-bitfields
       -funsigned-bitfields
       -fno-signed-bitfields
       -fno-unsigned-bitfields
           These options control whether a bit-field is signed or unsigned, when the declaration  does  not  use
           either  "signed"  or "unsigned".  By default, such a bit-field is signed, because this is consistent:
           the basic integer types such as "int" are signed types.

       -fsso-struct=endianness
           Set the default scalar storage order of structures and  unions  to  the  specified  endianness.   The
           accepted values are big-endian, little-endian and native for the native endianness of the target (the
           default).  This option is not supported for C++.

           Warning:  the -fsso-struct switch causes GCC to generate code that is not binary compatible with code
           generated without it if the specified endianness is not the native endianness of the target.

   Options Controlling C++ Dialect
       This section describes the command-line options that are only meaningful for C++ programs.  You can  also
       use  most  of  the GNU compiler options regardless of what language your program is in.  For example, you
       might compile a file firstClass.C like this:

               g++ -g -fstrict-enums -O -c firstClass.C

       In this example, only -fstrict-enums is an option meant only for C++ programs;  you  can  use  the  other
       options with any language supported by GCC.

       Some options for compiling C programs, such as -std, are also relevant for C++ programs.

       Here is a list of options that are only for compiling C++ programs:

       -fabi-version=n
           Use version n of the C++ ABI.  The default is version 0.

           Version 0 refers to the version conforming most closely to the C++ ABI specification.  Therefore, the
           ABI obtained using version 0 will change in different versions of G++ as ABI bugs are fixed.

           Version 1 is the version of the C++ ABI that first appeared in G++ 3.2.

           Version  2  is the version of the C++ ABI that first appeared in G++ 3.4, and was the default through
           G++ 4.9.

           Version 3 corrects an error in mangling a constant address as a template argument.

           Version 4, which first appeared in G++ 4.5, implements a standard mangling for vector types.

           Version 5, which first appeared in G++ 4.6, corrects the  mangling  of  attribute  const/volatile  on
           function  pointer types, decltype of a plain decl, and use of a function parameter in the declaration
           of another parameter.

           Version 6, which first appeared in G++ 4.7, corrects the promotion behavior of C++11 scoped enums and
           the mangling of template argument packs, const/static_cast, prefix ++  and  --,  and  a  class  scope
           function used as a template argument.

           Version  7, which first appeared in G++ 4.8, that treats nullptr_t as a builtin type and corrects the
           mangling of lambdas in default argument scope.

           Version 8, which first appeared in G++ 4.9, corrects the substitution behavior of function types with
           function-cv-qualifiers.

           Version 9, which first appeared in G++ 5.2, corrects the alignment of "nullptr_t".

           Version 10, which first appeared in G++ 6.1, adds mangling of attributes that affect  type  identity,
           such as ia32 calling convention attributes (e.g. stdcall).

           Version  11,  which  first  appeared  in  G++  7,  corrects the mangling of sizeof... expressions and
           operator names.  For multiple entities with the same name within a function,  that  are  declared  in
           different  scopes,  the  mangling  now changes starting with the twelfth occurrence.  It also implies
           -fnew-inheriting-ctors.

           Version 12, which first appeared in G++ 8, corrects the calling conventions for empty classes on  the
           x86_64  target and for classes with only deleted copy/move constructors.  It accidentally changes the
           calling convention for classes with a deleted copy constructor and a trivial move constructor.

           Version 13, which first appeared in G++ 8.2, fixes the accidental change in version 12.

           Version 14, which first appeared in G++ 10, corrects the mangling of the nullptr expression.

           Version 15, which first appeared in G++ 11, changes the mangling of "__alignof__" to be distinct from
           that of "alignof", and dependent operator names.

           See also -Wabi.

       -fabi-compat-version=n
           On targets that support strong aliases, G++ works around mangling changes by creating an  alias  with
           the  correct  mangled  name  when  defining  a  symbol  with  an incorrect mangled name.  This switch
           specifies which ABI version to use for the alias.

           With -fabi-version=0 (the default), this defaults to  11  (GCC  7  compatibility).   If  another  ABI
           version  is explicitly selected, this defaults to 0.  For compatibility with GCC versions 3.2 through
           4.9, use -fabi-compat-version=2.

           If this option is not provided but -Wabi=n is, that version is used for  compatibility  aliases.   If
           this  option is provided along with -Wabi (without the version), the version from this option is used
           for the warning.

       -fno-access-control
           Turn off all access checking.  This switch is mainly useful for working around  bugs  in  the  access
           control code.

       -faligned-new
           Enable  support  for  C++17  "new"  of  types  that  require  more  alignment  than "void* ::operator
           new(std::size_t)" provides.  A numeric argument such as "-faligned-new=32" can be used to specify how
           much alignment (in bytes) is provided by that function, but few  users  will  need  to  override  the
           default of "alignof(std::max_align_t)".

           This flag is enabled by default for -std=c++17.

       -fchar8_t
       -fno-char8_t
           Enable  support  for  "char8_t"  as adopted for C++20.  This includes the addition of a new "char8_t"
           fundamental type, changes to the types of UTF-8 string and character  literals,  new  signatures  for
           user-defined   literals,   associated   standard   library   updates,  and  new  "__cpp_char8_t"  and
           "__cpp_lib_char8_t" feature test macros.

           This option enables functions to be overloaded for ordinary and UTF-8 strings:

                   int f(const char *);    // #1
                   int f(const char8_t *); // #2
                   int v1 = f("text");     // Calls #1
                   int v2 = f(u8"text");   // Calls #2

           and introduces new signatures for user-defined literals:

                   int operator""_udl1(char8_t);
                   int v3 = u8'x'_udl1;
                   int operator""_udl2(const char8_t*, std::size_t);
                   int v4 = u8"text"_udl2;
                   template<typename T, T...> int operator""_udl3();
                   int v5 = u8"text"_udl3;

           The change to the types of UTF-8 string and character literals introduces incompatibilities with  ISO
           C++11  and  later  standards.  For example, the following code is well-formed under ISO C++11, but is
           ill-formed when -fchar8_t is specified.

                   char ca[] = u8"xx";     // error: char-array initialized from wide
                                           //        string
                   const char *cp = u8"xx";// error: invalid conversion from
                                           //        `const char8_t*' to `const char*'
                   int f(const char*);
                   auto v = f(u8"xx");     // error: invalid conversion from
                                           //        `const char8_t*' to `const char*'
                   std::string s{u8"xx"};  // error: no matching function for call to
                                           //        `std::basic_string<char>::basic_string()'
                   using namespace std::literals;
                   s = u8"xx"s;            // error: conversion from
                                           //        `basic_string<char8_t>' to non-scalar
                                           //        type `basic_string<char>' requested

       -fcheck-new
           Check that the pointer returned by "operator new" is non-null before attempting to modify the storage
           allocated.  This check is normally unnecessary because the C++ standard specifies that "operator new"
           only returns 0 if it is declared "throw()", in which case the compiler always checks the return value
           even without this option.  In all  other  cases,  when  "operator  new"  has  a  non-empty  exception
           specification, memory exhaustion is signalled by throwing "std::bad_alloc".  See also new (nothrow).

       -fconcepts
       -fconcepts-ts
           Below  -std=c++20,  -fconcepts  enables  support  for  the  C++  Extensions  for  Concepts  Technical
           Specification, ISO 19217 (2015).

           With -std=c++20 and above, Concepts are part of the language standard, so -fconcepts defaults to  on.
           But the standard specification of Concepts differs significantly from the TS, so some constructs that
           were allowed in the TS but didn't make it into the standard can still be enabled by -fconcepts-ts.

       -fconstexpr-depth=n
           Set  the  maximum  nested  evaluation depth for C++11 constexpr functions to n.  A limit is needed to
           detect endless recursion during  constant  expression  evaluation.   The  minimum  specified  by  the
           standard is 512.

       -fconstexpr-cache-depth=n
           Set the maximum level of nested evaluation depth for C++11 constexpr functions that will be cached to
           n.   This  is  a  heuristic  that  trades  off  compilation  speed  (when  the  cache avoids repeated
           calculations) against memory consumption (when the cache  grows  very  large  from  highly  recursive
           evaluations).   The  default  is 8.  Very few users are likely to want to adjust it, but if your code
           does heavy constexpr calculations you might want to experiment to find which  value  works  best  for
           you.

       -fconstexpr-loop-limit=n
           Set the maximum number of iterations for a loop in C++14 constexpr functions to n.  A limit is needed
           to detect infinite loops during constant expression evaluation.  The default is 262144 (1<<18).

       -fconstexpr-ops-limit=n
           Set  the  maximum  number  of  operations  during a single constexpr evaluation.  Even when number of
           iterations of a single loop is limited with the above limit, if there are several  nested  loops  and
           each of them has many iterations but still smaller than the above limit, or if in a body of some loop
           or  even  outside  of  a  loop  too  many  expressions  need to be evaluated, the resulting constexpr
           evaluation might take too long.  The default is 33554432 (1<<25).

       -fcoroutines
           Enable support for the C++ coroutines extension (experimental).

       -fno-elide-constructors
           The C++ standard allows an implementation  to  omit  creating  a  temporary  that  is  only  used  to
           initialize  another  object of the same type.  Specifying this option disables that optimization, and
           forces G++ to call the copy constructor in all cases.  This option also causes G++  to  call  trivial
           member functions which otherwise would be expanded inline.

           In  C++17,  the compiler is required to omit these temporaries, but this option still affects trivial
           member functions.

       -fno-enforce-eh-specs
           Don't generate code to check for violation of exception specifications  at  run  time.   This  option
           violates  the  C++ standard, but may be useful for reducing code size in production builds, much like
           defining "NDEBUG".  This does not give user code permission to throw exceptions in violation  of  the
           exception  specifications;  the  compiler still optimizes based on the specifications, so throwing an
           unexpected exception results in undefined behavior at run time.

       -fextern-tls-init
       -fno-extern-tls-init
           The C++11 and OpenMP standards allow "thread_local" and "threadprivate"  variables  to  have  dynamic
           (runtime)  initialization.   To  support  this,  any  use  of  such a variable goes through a wrapper
           function that performs any necessary initialization.  When the use and definition of the variable are
           in the same translation unit, this overhead can be optimized away, but when the use is in a different
           translation unit there is significant overhead even if the variable  doesn't  actually  need  dynamic
           initialization.  If the programmer can be sure that no use of the variable in a non-defining TU needs
           to trigger dynamic initialization (either because the variable is statically initialized, or a use of
           the  variable in the defining TU will be executed before any uses in another TU), they can avoid this
           overhead with the -fno-extern-tls-init option.

           On targets that support symbol aliases, the default is -fextern-tls-init.  On  targets  that  do  not
           support symbol aliases, the default is -fno-extern-tls-init.

       -fno-gnu-keywords
           Do not recognize "typeof" as a keyword, so that code can use this word as an identifier.  You can use
           the  keyword  "__typeof__"  instead.   This  option is implied by the strict ISO C++ dialects: -ansi,
           -std=c++98, -std=c++11, etc.

       -fno-implicit-templates
           Never emit code for non-inline templates that are instantiated implicitly (i.e. by  use);  only  emit
           code  for explicit instantiations.  If you use this option, you must take care to structure your code
           to include all the necessary explicit instantiations to avoid getting undefined symbols at link time.

       -fno-implicit-inline-templates
           Don't emit code for implicit instantiations of inline templates, either.  The default  is  to  handle
           inlines  differently  so  that  compiles  with and without optimization need the same set of explicit
           instantiations.

       -fno-implement-inlines
           To  save  space,  do  not  emit  out-of-line  copies  of  inline  functions  controlled  by  "#pragma
           implementation".   This  causes  linker errors if these functions are not inlined everywhere they are
           called.

       -fmodules-ts
       -fno-modules-ts
           Enable support for C++20 modules   The -fno-modules-ts is usually not needed, as that is the default.
           Even though this is a C++20 feature, it  is  not  currently  implicitly  enabled  by  selecting  that
           standard version.

       -fmodule-header
       -fmodule-header=user
       -fmodule-header=system
           Compile a header file to create an importable header unit.

       -fmodule-implicit-inline
           Member functions defined in their class definitions are not implicitly inline for modular code.  This
           is  different  to traditional C++ behavior, for good reasons.  However, it may result in a difficulty
           during code porting.  This option makes such function definitions implicitly inline.  It does however
           generate an ABI incompatibility, so you must use it everywhere or nowhere.  (Such definitions outside
           of a named module remain implicitly inline, regardless.)

       -fno-module-lazy
           Disable lazy module importing and module mapper creation.

       -fmodule-mapper=[hostname]:port[?ident]
       -fmodule-mapper=|program[?ident] args...
       -fmodule-mapper==socket[?ident]
       -fmodule-mapper=<>[inout][?ident]
       -fmodule-mapper=<in>out[?ident]
       -fmodule-mapper=file[?ident]
           An oracle to query for module name  to  filename  mappings.   If  unspecified  the  CXX_MODULE_MAPPER
           environment variable is used, and if that is unset, an in-process default is provided.

       -fmodule-only
           Only emit the Compiled Module Interface, inhibiting any object file.

       -fms-extensions
           Disable  Wpedantic  warnings about constructs used in MFC, such as implicit int and getting a pointer
           to member function via non-standard syntax.

       -fnew-inheriting-ctors
           Enable the P0136 adjustment to the semantics of C++11 constructor inheritance.  This is part of C++17
           but also considered to be a Defect Report against C++11 and C++14.  This flag is enabled  by  default
           unless -fabi-version=10 or lower is specified.

       -fnew-ttp-matching
           Enable  the  P0522  resolution to Core issue 150, template template parameters and default arguments:
           this allows a template with default template  arguments  as  an  argument  for  a  template  template
           parameter with fewer template parameters.  This flag is enabled by default for -std=c++17.

       -fno-nonansi-builtins
           Disable built-in declarations of functions that are not mandated by ANSI/ISO C.  These include "ffs",
           "alloca", "_exit", "index", "bzero", "conjf", and other related functions.

       -fnothrow-opt
           Treat  a  "throw()"  exception  specification  as  if it were a "noexcept" specification to reduce or
           eliminate the text size overhead relative to a function with  no  exception  specification.   If  the
           function  has  local  variables  of  types  with non-trivial destructors, the exception specification
           actually makes the function smaller because the EH cleanups for  those  variables  can  be  optimized
           away.   The  semantic  effect  is  that  an exception thrown out of a function with such an exception
           specification results in a call to "terminate" rather than "unexpected".

       -fno-operator-names
           Do not treat the operator name keywords "and", "bitand", "bitor", "compl", "not", "or" and  "xor"  as
           synonyms as keywords.

       -fno-optional-diags
           Disable  diagnostics  that  the standard says a compiler does not need to issue.  Currently, the only
           such diagnostic issued by G++ is the one for a name having multiple meanings within a class.

       -fpermissive
           Downgrade  some  diagnostics  about  nonconformant  code  from  errors  to  warnings.   Thus,   using
           -fpermissive allows some nonconforming code to compile.

       -fno-pretty-templates
           When an error message refers to a specialization of a function template, the compiler normally prints
           the signature of the template followed by the template arguments and any typedefs or typenames in the
           signature  (e.g.  "void  f(T)  [with  T  =  int]" rather than "void f(int)") so that it's clear which
           template is involved.  When an error message refers to a specialization  of  a  class  template,  the
           compiler  omits  any  template arguments that match the default template arguments for that template.
           If either of these behaviors make it harder to understand the error message rather than  easier,  you
           can use -fno-pretty-templates to disable them.

       -fno-rtti
           Disable  generation  of  information about every class with virtual functions for use by the C++ run-
           time type identification features ("dynamic_cast" and "typeid").  If you don't use those parts of the
           language, you can save some space by using this flag.  Note that exception  handling  uses  the  same
           information,  but G++ generates it as needed. The "dynamic_cast" operator can still be used for casts
           that do not require run-time type information, i.e. casts to "void *" or to unambiguous base classes.

           Mixing code compiled with -frtti with that compiled  with  -fno-rtti  may  not  work.   For  example,
           programs  may  fail to link if a class compiled with -fno-rtti is used as a base for a class compiled
           with -frtti.

       -fsized-deallocation
           Enable the built-in global declarations

                   void operator delete (void *, std::size_t) noexcept;
                   void operator delete[] (void *, std::size_t) noexcept;

           as introduced in C++14.  This is useful for user-defined replacement deallocation functions that, for
           example, use the size of the object to make deallocation faster.  Enabled by default under -std=c++14
           and above.  The flag -Wsized-deallocation warns about places that might want to add a definition.

       -fstrict-enums
           Allow the compiler to optimize using the assumption that a value of enumerated type can only  be  one
           of  the  values  of  the  enumeration (as defined in the C++ standard; basically, a value that can be
           represented in the minimum number of bits needed to represent all the enumerators).  This  assumption
           may  not  be valid if the program uses a cast to convert an arbitrary integer value to the enumerated
           type.

       -fstrong-eval-order
           Evaluate member access, array  subscripting,  and  shift  expressions  in  left-to-right  order,  and
           evaluate  assignment  in  right-to-left  order,  as  adopted  for  C++17.   Enabled  by  default with
           -std=c++17.   -fstrong-eval-order=some  enables  just  the  ordering  of  member  access  and   shift
           expressions, and is the default without -std=c++17.

       -ftemplate-backtrace-limit=n
           Set  the  maximum  number  of  template  instantiation notes for a single warning or error to n.  The
           default value is 10.

       -ftemplate-depth=n
           Set the maximum instantiation depth for template classes to n.  A limit on the template instantiation
           depth is needed to detect endless recursions  during  template  class  instantiation.   ANSI/ISO  C++
           conforming programs must not rely on a maximum depth greater than 17 (changed to 1024 in C++11).  The
           default  value  is  900,  as  the  compiler  can  run  out of stack space before hitting 1024 in some
           situations.

       -fno-threadsafe-statics
           Do not emit  the  extra  code  to  use  the  routines  specified  in  the  C++  ABI  for  thread-safe
           initialization  of  local statics.  You can use this option to reduce code size slightly in code that
           doesn't need to be thread-safe.

       -fuse-cxa-atexit
           Register destructors for objects with static storage duration with the "__cxa_atexit" function rather
           than the "atexit" function.  This option is required for fully standards-compliant handling of static
           destructors, but only works if your C library supports "__cxa_atexit".

       -fno-use-cxa-get-exception-ptr
           Don't use the "__cxa_get_exception_ptr" runtime routine.  This causes "std::uncaught_exception" to be
           incorrect, but is necessary if the runtime routine is not available.

       -fvisibility-inlines-hidden
           This switch declares that the user does not attempt  to  compare  pointers  to  inline  functions  or
           methods where the addresses of the two functions are taken in different shared objects.

           The effect of this is that GCC may, effectively, mark inline methods with "__attribute__ ((visibility
           ("hidden")))"  so  that  they  do  not  appear  in the export table of a DSO and do not require a PLT
           indirection when used within the DSO.  Enabling this option can have a dramatic effect  on  load  and
           link  times  of  a  DSO as it massively reduces the size of the dynamic export table when the library
           makes heavy use of templates.

           The behavior of this switch is not quite the same as marking the methods as hidden directly,  because
           it  does  not  affect static variables local to the function or cause the compiler to deduce that the
           function is defined in only one shared object.

           You may mark a method as having a visibility explicitly to negate the effect of the switch  for  that
           method.   For  example,  if  you do want to compare pointers to a particular inline method, you might
           mark it as having default visibility.  Marking the enclosing class with explicit  visibility  has  no
           effect.

           Explicitly instantiated inline methods are unaffected by this option as their linkage might otherwise
           cross a shared library boundary.

       -fvisibility-ms-compat
           This flag attempts to use visibility settings to make GCC's C++ linkage model compatible with that of
           Microsoft Visual Studio.

           The flag makes these changes to GCC's linkage model:

           1.  It sets the default visibility to "hidden", like -fvisibility=hidden.

           2.  Types, but not their members, are not hidden by default.

           3.  The  One Definition Rule is relaxed for types without explicit visibility specifications that are
               defined in more than one shared object: those declarations are permitted if  they  are  permitted
               when this option is not used.

           In  new code it is better to use -fvisibility=hidden and export those classes that are intended to be
           externally visible.  Unfortunately it is possible for code to  rely,  perhaps  accidentally,  on  the
           Visual Studio behavior.

           Among  the  consequences of these changes are that static data members of the same type with the same
           name but defined in different shared objects are different, so  changing  one  does  not  change  the
           other;  and  that  pointers  to  function members defined in different shared objects may not compare
           equal.  When this flag is given, it is a violation of the ODR to define  types  with  the  same  name
           differently.

       -fno-weak
           Do  not  use  weak  symbol  support, even if it is provided by the linker.  By default, G++ uses weak
           symbols if they are available.  This option exists only for testing, and should not be used  by  end-
           users;  it  results  in  inferior  code  and has no benefits.  This option may be removed in a future
           release of G++.

       -fext-numeric-literals (C++ and Objective-C++ only)
           Accept imaginary, fixed-point, or machine-defined literal number suffixes as  GNU  extensions.   When
           this  option is turned off these suffixes are treated as C++11 user-defined literal numeric suffixes.
           This is on by default for all pre-C++11 dialects and  all  GNU  dialects:  -std=c++98,  -std=gnu++98,
           -std=gnu++11, -std=gnu++14.  This option is off by default for ISO C++11 onwards (-std=c++11, ...).

       -nostdinc++
           Do  not  search for header files in the standard directories specific to C++, but do still search the
           other standard directories.  (This option is used when building the C++ library.)

       -flang-info-include-translate
       -flang-info-include-translate-not
       -flang-info-include-translate=header
           Inform of include translation events.  The first will note accepted include translations, the  second
           will  note  declined  include  translations.   The  header  form  will inform of include translations
           relating to that specific header.  If header is of the form "user" or "<system>" it will be  resolved
           to a specific user or system header using the include path.

       -flang-info-module-cmi
       -flang-info-module-cmi=module
           Inform  of  Compiled  Module  Interface  pathnames.  The first will note all read CMI pathnames.  The
           module form will not reading a specific module's CMI.  module may be a named module or a  header-unit
           (the  latter indicated by either being a pathname containing directory separators or enclosed in "<>"
           or "").

       -stdlib=libstdc++,libc++
           When G++ is configured to support this option, it  allows  specification  of  alternate  C++  runtime
           libraries.  Two options are available: libstdc++ (the default, native C++ runtime for G++) and libc++
           which  is  the  C++  runtime  installed on some operating systems (e.g. Darwin versions from Darwin11
           onwards).  The option switches G++ to use  the  headers  from  the  specified  library  and  to  emit
           "-lstdc++" or "-lc++" respectively, when a C++ runtime is required for linking.

       In addition, these warning options have meanings only for C++ programs:

       -Wabi-tag (C++ and Objective-C++ only)
           Warn  when  a  type  with  an  ABI tag is used in a context that does not have that ABI tag.  See C++
           Attributes for more information about ABI tags.

       -Wcomma-subscript (C++ and Objective-C++ only)
           Warn about uses of a comma expression within a subscripting expression.  This usage was deprecated in
           C++20.  However, a comma expression wrapped in "( )" is not deprecated.  Example:

                   void f(int *a, int b, int c) {
                       a[b,c];     // deprecated
                       a[(b,c)];   // OK
                   }

           Enabled by default with -std=c++20.

       -Wctad-maybe-unsupported (C++ and Objective-C++ only)
           Warn when performing class template argument deduction (CTAD) on a type with  no  explicitly  written
           deduction  guides.   This warning will point out cases where CTAD succeeded only because the compiler
           synthesized the implicit deduction guides, which might not be what the programmer intended.   Certain
           style guides allow CTAD only on types that specifically "opt-in"; i.e., on types that are designed to
           support CTAD.  This warning can be suppressed with the following pattern:

                   struct allow_ctad_t; // any name works
                   template <typename T> struct S {
                     S(T) { }
                   };
                   S(allow_ctad_t) -> S<void>; // guide with incomplete parameter type will never be considered

       -Wctor-dtor-privacy (C++ and Objective-C++ only)
           Warn  when  a  class  seems  unusable  because  all the constructors or destructors in that class are
           private, and it has neither friends nor public static member functions.  Also warn if  there  are  no
           non-private  methods,  and  there's  at least one private member function that isn't a constructor or
           destructor.

       -Wdelete-non-virtual-dtor (C++ and Objective-C++ only)
           Warn when "delete" is used to destroy an instance of a class that  has  virtual  functions  and  non-
           virtual destructor. It is unsafe to delete an instance of a derived class through a pointer to a base
           class if the base class does not have a virtual destructor.  This warning is enabled by -Wall.

       -Wdeprecated-copy (C++ and Objective-C++ only)
           Warn that the implicit declaration of a copy constructor or copy assignment operator is deprecated if
           the  class  has  a user-provided copy constructor or copy assignment operator, in C++11 and up.  This
           warning is enabled by -Wextra.  With -Wdeprecated-copy-dtor, also deprecate if the class has a  user-
           provided destructor.

       -Wno-deprecated-enum-enum-conversion (C++ and Objective-C++ only)
           Disable  the  warning  about  the  case when the usual arithmetic conversions are applied on operands
           where one is of enumeration type and the other is of a different enumeration type.   This  conversion
           was deprecated in C++20.  For example:

                   enum E1 { e };
                   enum E2 { f };
                   int k = f - e;

           -Wdeprecated-enum-enum-conversion is enabled by default with -std=c++20.  In pre-C++20 dialects, this
           warning can be enabled by -Wenum-conversion.

       -Wno-deprecated-enum-float-conversion (C++ and Objective-C++ only)
           Disable  the  warning  about  the  case when the usual arithmetic conversions are applied on operands
           where one is of enumeration type and the other is of a  floating-point  type.   This  conversion  was
           deprecated in C++20.  For example:

                   enum E1 { e };
                   enum E2 { f };
                   bool b = e <= 3.7;

           -Wdeprecated-enum-float-conversion  is  enabled  by  default with -std=c++20.  In pre-C++20 dialects,
           this warning can be enabled by -Wenum-conversion.

       -Wno-init-list-lifetime (C++ and Objective-C++ only)
           Do not warn about uses of "std::initializer_list" that are likely to  result  in  dangling  pointers.
           Since  the  underlying array for an "initializer_list" is handled like a normal C++ temporary object,
           it is easy to inadvertently keep a pointer to the array past the end of the  array's  lifetime.   For
           example:

           *   If a function returns a temporary "initializer_list", or a local "initializer_list" variable, the
               array's  lifetime  ends  at the end of the return statement, so the value returned has a dangling
               pointer.

           *   If a new-expression creates an "initializer_list", the array only lives  until  the  end  of  the
               enclosing full-expression, so the "initializer_list" in the heap has a dangling pointer.

           *   When  an  "initializer_list"  variable  is  assigned  from a brace-enclosed initializer list, the
               temporary array created for the right side of the assignment only lives  until  the  end  of  the
               full-expression, so at the next statement the "initializer_list" variable has a dangling pointer.

                       // li's initial underlying array lives as long as li
                       std::initializer_list<int> li = { 1,2,3 };
                       // assignment changes li to point to a temporary array
                       li = { 4, 5 };
                       // now the temporary is gone and li has a dangling pointer
                       int i = li.begin()[0] // undefined behavior

           *   When  a  list  constructor  stores the "begin" pointer from the "initializer_list" argument, this
               doesn't extend the lifetime of the array, so if a class variable is constructed from a  temporary
               "initializer_list",  the  pointer  is  left  dangling  by  the  end  of  the variable declaration
               statement.

       -Winvalid-imported-macros
           Verify all imported macro definitions are valid at the end of compilation.  This is  not  enabled  by
           default,  as it requires additional processing to determine.  It may be useful when preparing sets of
           header-units to ensure consistent macros.

       -Wno-literal-suffix (C++ and Objective-C++ only)
           Do not warn when a string or character literal is followed by a ud-suffix which does not  begin  with
           an  underscore.  As a conforming extension, GCC treats such suffixes as separate preprocessing tokens
           in  order  to  maintain  backwards  compatibility  with  code  that  uses  formatting   macros   from
           "<inttypes.h>".  For example:

                   #define __STDC_FORMAT_MACROS
                   #include <inttypes.h>
                   #include <stdio.h>

                   int main() {
                     int64_t i64 = 123;
                     printf("My int64: %" PRId64"\n", i64);
                   }

           In this case, "PRId64" is treated as a separate preprocessing token.

           This  option  also  controls warnings when a user-defined literal operator is declared with a literal
           suffix identifier that doesn't begin with an underscore. Literal suffix identifiers that don't  begin
           with an underscore are reserved for future standardization.

           These warnings are enabled by default.

       -Wno-narrowing (C++ and Objective-C++ only)
           For  C++11  and  later  standards, narrowing conversions are diagnosed by default, as required by the
           standard.  A narrowing conversion from a constant produces an error, and a narrowing conversion  from
           a non-constant produces a warning, but -Wno-narrowing suppresses the diagnostic.  Note that this does
           not  affect the meaning of well-formed code; narrowing conversions are still considered ill-formed in
           SFINAE contexts.

           With -Wnarrowing in C++98, warn when a narrowing conversion prohibited by C++11 occurs  within  {  },
           e.g.

                   int i = { 2.2 }; // error: narrowing from double to int

           This flag is included in -Wall and -Wc++11-compat.

       -Wnoexcept (C++ and Objective-C++ only)
           Warn when a noexcept-expression evaluates to false because of a call to a function that does not have
           a non-throwing exception specification (i.e. "throw()" or "noexcept") but is known by the compiler to
           never throw an exception.

       -Wnoexcept-type (C++ and Objective-C++ only)
           Warn  if  the  C++17  feature making "noexcept" part of a function type changes the mangled name of a
           symbol relative to C++14.  Enabled by -Wabi and -Wc++17-compat.

           As an example:

                   template <class T> void f(T t) { t(); };
                   void g() noexcept;
                   void h() { f(g); }

           In C++14, "f" calls "f<void(*)()>", but in C++17 it calls "f<void(*)()noexcept>".

       -Wclass-memaccess (C++ and Objective-C++ only)
           Warn when the destination of a call to a raw memory function such  as  "memset"  or  "memcpy"  is  an
           object  of  class  type,  and  when writing into such an object might bypass the class non-trivial or
           deleted constructor or copy  assignment,  violate  const-correctness  or  encapsulation,  or  corrupt
           virtual  table  pointers.   Modifying  the  representation  of  such  objects  may violate invariants
           maintained by member functions of the class.  For example, the call to "memset"  below  is  undefined
           because  it modifies a non-trivial class object and is, therefore, diagnosed.  The safe way to either
           initialize or clear the storage of objects of such types is by using the appropriate  constructor  or
           assignment operator, if one is available.

                   std::string str = "abc";
                   memset (&str, 0, sizeof str);

           The -Wclass-memaccess option is enabled by -Wall.  Explicitly casting the pointer to the class object
           to  "void  *"  or  to  a  type  that can be safely accessed by the raw memory function suppresses the
           warning.

       -Wnon-virtual-dtor (C++ and Objective-C++ only)
           Warn when a class has virtual functions and an accessible non-virtual  destructor  itself  or  in  an
           accessible polymorphic base class, in which case it is possible but unsafe to delete an instance of a
           derived  class  through  a  pointer to the class itself or base class.  This warning is automatically
           enabled if -Weffc++ is specified.

       -Wregister (C++ and Objective-C++ only)
           Warn on uses of the "register" storage class specifier, except when it is part of  the  GNU  Explicit
           Register  Variables extension.  The use of the "register" keyword as storage class specifier has been
           deprecated in C++11 and removed in C++17.  Enabled by default with -std=c++17.

       -Wreorder (C++ and Objective-C++ only)
           Warn when the order of member initializers given in the code does not match the order in  which  they
           must be executed.  For instance:

                   struct A {
                     int i;
                     int j;
                     A(): j (0), i (1) { }
                   };

           The compiler rearranges the member initializers for "i" and "j" to match the declaration order of the
           members, emitting a warning to that effect.  This warning is enabled by -Wall.

       -Wno-pessimizing-move (C++ and Objective-C++ only)
           This  warning  warns  when a call to "std::move" prevents copy elision.  A typical scenario when copy
           elision can occur is when returning in a function with a class return type, when the expression being
           returned is the name of a non-volatile automatic object, and is not a function parameter, and has the
           same type as the function return type.

                   struct T {
                   ...
                   };
                   T fn()
                   {
                     T t;
                     ...
                     return std::move (t);
                   }

           But in this example, the "std::move" call prevents copy elision.

           This warning is enabled by -Wall.

       -Wno-redundant-move (C++ and Objective-C++ only)
           This warning warns about redundant calls to "std::move"; that is, when a move  operation  would  have
           been  performed  even  without  the "std::move" call.  This happens because the compiler is forced to
           treat the object as if it were an rvalue in certain situations such as returning  a  local  variable,
           where copy elision isn't applicable.  Consider:

                   struct T {
                   ...
                   };
                   T fn(T t)
                   {
                     ...
                     return std::move (t);
                   }

           Here, the "std::move" call is redundant.  Because G++ implements Core Issue 1579, another example is:

                   struct T { // convertible to U
                   ...
                   };
                   struct U {
                   ...
                   };
                   U fn()
                   {
                     T t;
                     ...
                     return std::move (t);
                   }

           In  this example, copy elision isn't applicable because the type of the expression being returned and
           the function return type differ, yet G++ treats the return value as  if  it  were  designated  by  an
           rvalue.

           This warning is enabled by -Wextra.

       -Wrange-loop-construct (C++ and Objective-C++ only)
           This  warning warns when a C++ range-based for-loop is creating an unnecessary copy.  This can happen
           when the range declaration is not a reference, but probably should be.  For example:

                   struct S { char arr[128]; };
                   void fn () {
                     S arr[5];
                     for (const auto x : arr) { ... }
                   }

           It does not warn when the type being copied is a trivially-copyable type whose size is less  than  64
           bytes.

           This warning also warns when a loop variable in a range-based for-loop is initialized with a value of
           a different type resulting in a copy.  For example:

                   void fn() {
                     int arr[10];
                     for (const double &x : arr) { ... }
                   }

           In  the  example  above, in every iteration of the loop a temporary value of type "double" is created
           and destroyed, to which the reference "const double &" is bound.

           This warning is enabled by -Wall.

       -Wredundant-tags (C++ and Objective-C++ only)
           Warn about redundant class-key and enum-key in references to class  types  and  enumerated  types  in
           contexts where the key can be eliminated without causing an ambiguity.  For example:

                   struct foo;
                   struct foo *p;   // warn that keyword struct can be eliminated

           On the other hand, in this example there is no warning:

                   struct foo;
                   void foo ();   // "hides" struct foo
                   void bar (struct foo&);  // no warning, keyword struct is necessary

       -Wno-subobject-linkage (C++ and Objective-C++ only)
           Do  not warn if a class type has a base or a field whose type uses the anonymous namespace or depends
           on a type with no linkage.  If a type A depends on a type B with no or internal linkage, defining  it
           in multiple translation units would be an ODR violation because the meaning of B is different in each
           translation  unit.   If  A  only  appears  in  a single translation unit, the best way to silence the
           warning is to give it internal linkage by putting it in an anonymous namespace as well.  The compiler
           doesn't give this warning for types defined in the main .C  file,  as  those  are  unlikely  to  have
           multiple definitions.  -Wsubobject-linkage is enabled by default.

       -Weffc++ (C++ and Objective-C++ only)
           Warn  about  violations  of the following style guidelines from Scott Meyers' Effective C++ series of
           books:

           *   Define a copy constructor and an  assignment  operator  for  classes  with  dynamically-allocated
               memory.

           *   Prefer initialization to assignment in constructors.

           *   Have "operator=" return a reference to *this.

           *   Don't try to return a reference when you must return an object.

           *   Distinguish between prefix and postfix forms of increment and decrement operators.

           *   Never overload "&&", "||", or ",".

           This  option also enables -Wnon-virtual-dtor, which is also one of the effective C++ recommendations.
           However, the check is extended to warn about the  lack  of  virtual  destructor  in  accessible  non-
           polymorphic bases classes too.

           When  selecting  this  option,  be  aware  that the standard library headers do not obey all of these
           guidelines; use grep -v to filter out those warnings.

       -Wno-exceptions (C++ and Objective-C++ only)
           Disable the warning about the case when an exception handler is shadowed by  another  handler,  which
           can point out a wrong ordering of exception handlers.

       -Wstrict-null-sentinel (C++ and Objective-C++ only)
           Warn  about  the use of an uncasted "NULL" as sentinel.  When compiling only with GCC this is a valid
           sentinel, as "NULL" is defined to "__null".  Although it is a null pointer  constant  rather  than  a
           null  pointer,  it  is  guaranteed to be of the same size as a pointer.  But this use is not portable
           across different compilers.

       -Wno-non-template-friend (C++ and Objective-C++ only)
           Disable warnings when non-template friend functions are declared within  a  template.   In  very  old
           versions  of  GCC  that  predate  implementation of the ISO standard, declarations such as friend int
           foo(int), where the name of the friend is an unqualified-id, could be  interpreted  as  a  particular
           specialization  of a template function; the warning exists to diagnose compatibility problems, and is
           enabled by default.

       -Wold-style-cast (C++ and Objective-C++ only)
           Warn if an old-style (C-style) cast to a non-void type is used within a C++ program.   The  new-style
           casts  ("dynamic_cast",  "static_cast",  "reinterpret_cast", and "const_cast") are less vulnerable to
           unintended effects and much easier to search for.

       -Woverloaded-virtual (C++ and Objective-C++ only)
           Warn when a function declaration hides virtual functions from a base class.  For example, in:

                   struct A {
                     virtual void f();
                   };

                   struct B: public A {
                     void f(int);
                   };

           the "A" class version of "f" is hidden in "B", and code like:

                   B* b;
                   b->f();

           fails to compile.

       -Wno-pmf-conversions (C++ and Objective-C++ only)
           Disable the diagnostic for converting a bound pointer to member function to a plain pointer.

       -Wsign-promo (C++ and Objective-C++ only)
           Warn when overload resolution chooses a promotion from unsigned or enumerated type to a signed  type,
           over  a  conversion to an unsigned type of the same size.  Previous versions of G++ tried to preserve
           unsignedness, but the standard mandates the current behavior.

       -Wtemplates (C++ and Objective-C++ only)
           Warn when a primary template declaration is encountered.  Some coding rules disallow  templates,  and
           this  may be used to enforce that rule.  The warning is inactive inside a system header file, such as
           the STL, so one can still use the STL.  One may also instantiate or specialize templates.

       -Wno-mismatched-new-delete (C++ and Objective-C++ only)
           Warn for mismatches between calls to "operator new" or "operator delete" and the  corresponding  call
           to  the allocation or deallocation function.  This includes invocations of C++ "operator delete" with
           pointers returned from either mismatched forms of  "operator  new",  or  from  other  functions  that
           allocate  objects  for  which the "operator delete" isn't a suitable deallocator, as well as calls to
           other deallocation functions with pointers returned from "operator new" for  which  the  deallocation
           function isn't suitable.

           For  example, the "delete" expression in the function below is diagnosed because it doesn't match the
           array form of the "new" expression the pointer argument was returned from.  Similarly,  the  call  to
           "free" is also diagnosed.

                   void f ()
                   {
                     int *a = new int[n];
                     delete a;   // warning: mismatch in array forms of expressions

                     char *p = new char[n];
                     free (p);   // warning: mismatch between new and free
                   }

           The  related  option  -Wmismatched-dealloc diagnoses mismatches involving allocation and deallocation
           functions other than "operator new" and "operator delete".

           -Wmismatched-new-delete is enabled by default.

       -Wmismatched-tags (C++ and Objective-C++ only)
           Warn for declarations of structs, classes, and class  templates  and  their  specializations  with  a
           class-key  that  does  not  match  either the definition or the first declaration if no definition is
           provided.

           For example, the declaration of "struct Object" in the argument list of "draw" triggers the  warning.
           To  avoid  it, either remove the redundant class-key "struct" or replace it with "class" to match its
           definition.

                   class Object {
                   public:
                     virtual ~Object () = 0;
                   };
                   void draw (struct Object*);

           It is not wrong to declare a class with the class-key "struct"  as  the  example  above  shows.   The
           -Wmismatched-tags  option  is  intended to help achieve a consistent style of class declarations.  In
           code that is intended to be portable to Windows-based compilers the warning helps prevent  unresolved
           references  due to the difference in the mangling of symbols declared with different class-keys.  The
           option can be used either on its own or in conjunction with -Wredundant-tags.

       -Wmultiple-inheritance (C++ and Objective-C++ only)
           Warn when a class is defined with multiple direct base classes.  Some coding rules disallow  multiple
           inheritance,  and  this  may  be  used to enforce that rule.  The warning is inactive inside a system
           header file, such as the STL, so one can still use  the  STL.   One  may  also  define  classes  that
           indirectly use multiple inheritance.

       -Wvirtual-inheritance
           Warn  when  a class is defined with a virtual direct base class.  Some coding rules disallow multiple
           inheritance, and this may be used to enforce that rule.  The warning  is  inactive  inside  a  system
           header  file,  such  as  the  STL,  so  one  can still use the STL.  One may also define classes that
           indirectly use virtual inheritance.

       -Wno-virtual-move-assign
           Suppress warnings about inheriting from a virtual base  with  a  non-trivial  C++11  move  assignment
           operator.  This is dangerous because if the virtual base is reachable along more than one path, it is
           moved  multiple  times,  which  can  mean  both  objects end up in the moved-from state.  If the move
           assignment operator is written to avoid  moving  from  a  moved-from  object,  this  warning  can  be
           disabled.

       -Wnamespaces
           Warn  when  a namespace definition is opened.  Some coding rules disallow namespaces, and this may be
           used to enforce that rule.  The warning is inactive inside a system header file, such as the STL,  so
           one can still use the STL.  One may also use using directives and qualified names.

       -Wno-terminate (C++ and Objective-C++ only)
           Disable the warning about a throw-expression that will immediately result in a call to "terminate".

       -Wno-vexing-parse (C++ and Objective-C++ only)
           Warn  about the most vexing parse syntactic ambiguity.  This warns about the cases when a declaration
           looks like a variable definition, but the C++ language requires it to be interpreted  as  a  function
           declaration.  For instance:

                   void f(double a) {
                     int i();        // extern int i (void);
                     int n(int(a));  // extern int n (int);
                   }

           Another example:

                   struct S { S(int); };
                   void f(double a) {
                     S x(int(a));   // extern struct S x (int);
                     S y(int());    // extern struct S y (int (*) (void));
                     S z();         // extern struct S z (void);
                   }

           The  warning  will  suggest options how to deal with such an ambiguity; e.g., it can suggest removing
           the parentheses or using braces instead.

           This warning is enabled by default.

       -Wno-class-conversion (C++ and Objective-C++ only)
           Do not warn when a conversion function converts an object to the same type, to a base class  of  that
           type, or to void; such a conversion function will never be called.

       -Wvolatile (C++ and Objective-C++ only)
           Warn  about  deprecated  uses of the "volatile" qualifier.  This includes postfix and prefix "++" and
           "--" expressions of "volatile"-qualified types, using simple assignments where the left operand is  a
           "volatile"-qualified non-class type for their value, compound assignments where the left operand is a
           "volatile"-qualified  non-class type, "volatile"-qualified function return type, "volatile"-qualified
           parameter type, and structured bindings of a "volatile"-qualified type.  This usage was deprecated in
           C++20.

           Enabled by default with -std=c++20.

       -Wzero-as-null-pointer-constant (C++ and Objective-C++ only)
           Warn when a literal 0 is used as null pointer  constant.   This  can  be  useful  to  facilitate  the
           conversion to "nullptr" in C++11.

       -Waligned-new
           Warn   about   a   new-expression   of   a   type   that   requires   greater   alignment   than  the
           "alignof(std::max_align_t)" but uses an allocation function without an explicit alignment  parameter.
           This option is enabled by -Wall.

           Normally  this  only  warns about global allocation functions, but -Waligned-new=all also warns about
           class member allocation functions.

       -Wno-placement-new
       -Wplacement-new=n
           Warn about placement new expressions with undefined behavior, such as constructing  an  object  in  a
           buffer  that is smaller than the type of the object.  For example, the placement new expression below
           is diagnosed because it attempts to construct an array of 64 integers  in  a  buffer  only  64  bytes
           large.

                   char buf [64];
                   new (buf) int[64];

           This warning is enabled by default.

           -Wplacement-new=1
               This  is  the  default warning level of -Wplacement-new.  At this level the warning is not issued
               for some strictly undefined constructs that GCC  allows  as  extensions  for  compatibility  with
               legacy  code.   For  example,  the following "new" expression is not diagnosed at this level even
               though it has undefined behavior according to the C++ standard because it writes past the end  of
               the one-element array.

                       struct S { int n, a[1]; };
                       S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]);
                       new (s->a)int [32]();

           -Wplacement-new=2
               At  this  level, in addition to diagnosing all the same constructs as at level 1, a diagnostic is
               also issued for placement new expressions  that  construct  an  object  in  the  last  member  of
               structure  whose type is an array of a single element and whose size is less than the size of the
               object being constructed.  While the previous example would be diagnosed, the following construct
               makes use of the flexible member array extension to avoid the warning at level 2.

                       struct S { int n, a[]; };
                       S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]);
                       new (s->a)int [32]();

       -Wcatch-value
       -Wcatch-value=n (C++ and Objective-C++ only)
           Warn about catch handlers that do not catch via reference.  With  -Wcatch-value=1  (or  -Wcatch-value
           for  short)  warn  about polymorphic class types that are caught by value.  With -Wcatch-value=2 warn
           about all class types that are caught by value. With -Wcatch-value=3 warn about all  types  that  are
           not caught by reference. -Wcatch-value is enabled by -Wall.

       -Wconditionally-supported (C++ and Objective-C++ only)
           Warn for conditionally-supported (C++11 [intro.defs]) constructs.

       -Wno-delete-incomplete (C++ and Objective-C++ only)
           Do  not  warn  when  deleting  a  pointer  to  incomplete type, which may cause undefined behavior at
           runtime.  This warning is enabled by default.

       -Wextra-semi (C++, Objective-C++ only)
           Warn about redundant semicolons after in-class function definitions.

       -Wno-inaccessible-base (C++, Objective-C++ only)
           This option controls warnings when a base class is inaccessible in a class derived  from  it  due  to
           ambiguity.   The warning is enabled by default.  Note that the warning for ambiguous virtual bases is
           enabled by the -Wextra option.

                   struct A { int a; };

                   struct B : A { };

                   struct C : B, A { };

       -Wno-inherited-variadic-ctor
           Suppress warnings about use of C++11 inheriting constructors when the base class inherited from has a
           C variadic constructor; the warning is on by default because the ellipsis is not inherited.

       -Wno-invalid-offsetof (C++ and Objective-C++ only)
           Suppress warnings from applying the "offsetof" macro to a non-POD type.  According to  the  2014  ISO
           C++  standard,  applying  "offsetof"  to  a  non-standard-layout  type is undefined.  In existing C++
           implementations, however, "offsetof" typically gives meaningful results.  This flag is for users  who
           are  aware  that  they  are  writing  nonportable code and who have deliberately chosen to ignore the
           warning about it.

           The restrictions on "offsetof" may be relaxed in a future version of the C++ standard.

       -Wsized-deallocation (C++ and Objective-C++ only)
           Warn about a definition of an unsized deallocation function

                   void operator delete (void *) noexcept;
                   void operator delete[] (void *) noexcept;

           without a definition of the corresponding sized deallocation function

                   void operator delete (void *, std::size_t) noexcept;
                   void operator delete[] (void *, std::size_t) noexcept;

           or vice versa.  Enabled by -Wextra along with -fsized-deallocation.

       -Wsuggest-final-types
           Warn about types with virtual methods where code quality would be improved if the type were  declared
           with  the  C++11  "final" specifier, or, if possible, declared in an anonymous namespace. This allows
           GCC to more aggressively devirtualize the polymorphic calls. This  warning  is  more  effective  with
           link-time optimization, where the information about the class hierarchy graph is more complete.

       -Wsuggest-final-methods
           Warn  about virtual methods where code quality would be improved if the method were declared with the
           C++11 "final" specifier, or, if possible, its type were declared in an anonymous  namespace  or  with
           the  "final"  specifier.   This  warning  is  more  effective  with link-time optimization, where the
           information about the class hierarchy graph is more complete. It is  recommended  to  first  consider
           suggestions of -Wsuggest-final-types and then rebuild with new annotations.

       -Wsuggest-override
           Warn about overriding virtual functions that are not marked with the "override" keyword.

       -Wuseless-cast (C++ and Objective-C++ only)
           Warn when an expression is casted to its own type.

       -Wno-conversion-null (C++ and Objective-C++ only)
           Do  not  warn  for  conversions between "NULL" and non-pointer types. -Wconversion-null is enabled by
           default.

   Options Controlling Objective-C and Objective-C++ Dialects
       (NOTE: This manual does not describe the Objective-C and Objective-C++ languages themselves.

       This  section  describes  the  command-line  options  that  are  only  meaningful  for  Objective-C   and
       Objective-C++  programs.   You  can  also use most of the language-independent GNU compiler options.  For
       example, you might compile a file some_class.m like this:

               gcc -g -fgnu-runtime -O -c some_class.m

       In this example, -fgnu-runtime is an option meant only for Objective-C and  Objective-C++  programs;  you
       can use the other options with any language supported by GCC.

       Note  that  since  Objective-C  is  an extension of the C language, Objective-C compilations may also use
       options specific to the C front-end (e.g., -Wtraditional).  Similarly, Objective-C++ compilations may use
       C++-specific options (e.g., -Wabi).

       Here is a list of options that are only for compiling Objective-C and Objective-C++ programs:

       -fconstant-string-class=class-name
           Use class-name as the name of the class to instantiate for each literal  string  specified  with  the
           syntax  "@"..."".  The default class name is "NXConstantString" if the GNU runtime is being used, and
           "NSConstantString" if the NeXT runtime is being used (see below).  The  -fconstant-cfstrings  option,
           if also present, overrides the -fconstant-string-class setting and cause "@"..."" literals to be laid
           out as constant CoreFoundation strings.

       -fgnu-runtime
           Generate  object  code compatible with the standard GNU Objective-C runtime.  This is the default for
           most types of systems.

       -fnext-runtime
           Generate output compatible with the NeXT runtime.   This  is  the  default  for  NeXT-based  systems,
           including  Darwin  and  Mac  OS  X.  The macro "__NEXT_RUNTIME__" is predefined if (and only if) this
           option is used.

       -fno-nil-receivers
           Assume that all Objective-C message dispatches ("[receiver message:arg]") in  this  translation  unit
           ensure that the receiver is not "nil".  This allows for more efficient entry points in the runtime to
           be used.  This option is only available in conjunction with the NeXT runtime and ABI version 0 or 1.

       -fobjc-abi-version=n
           Use  version  n  of the Objective-C ABI for the selected runtime.  This option is currently supported
           only for the NeXT runtime.  In that case, Version 0 is the traditional (32-bit) ABI  without  support
           for  properties  and other Objective-C 2.0 additions.  Version 1 is the traditional (32-bit) ABI with
           support for properties and other Objective-C 2.0 additions.  Version 2 is the  modern  (64-bit)  ABI.
           If  nothing is specified, the default is Version 0 on 32-bit target machines, and Version 2 on 64-bit
           target machines.

       -fobjc-call-cxx-cdtors
           For each Objective-C class, check if any of its instance variables is a C++ object with a non-trivial
           default constructor.  If so, synthesize a special "- (id) .cxx_construct" instance method which  runs
           non-trivial  default  constructors  on any such instance variables, in order, and then return "self".
           Similarly, check if any instance variable is a C++ object with a non-trivial destructor, and  if  so,
           synthesize  a  special  "-  (void)  .cxx_destruct" method which runs all such default destructors, in
           reverse order.

           The "- (id) .cxx_construct" and "- (void) .cxx_destruct" methods thusly  generated  only  operate  on
           instance  variables  declared  in  the  current  Objective-C  class,  and  not  those  inherited from
           superclasses.  It is the responsibility of the Objective-C runtime to invoke all such methods  in  an
           object's  inheritance  hierarchy.   The  "-  (id)  .cxx_construct" methods are invoked by the runtime
           immediately after a new object instance is  allocated;  the  "-  (void)  .cxx_destruct"  methods  are
           invoked immediately before the runtime deallocates an object instance.

           As  of this writing, only the NeXT runtime on Mac OS X 10.4 and later has support for invoking the "-
           (id) .cxx_construct" and "- (void) .cxx_destruct" methods.

       -fobjc-direct-dispatch
           Allow fast jumps to the message dispatcher.  On Darwin this is accomplished via the comm page.

       -fobjc-exceptions
           Enable syntactic support for structured exception handling in Objective-C, similar to what is offered
           by C++.  This option is required to use the Objective-C keywords @try, @throw, @catch,  @finally  and
           @synchronized.   This  option  is  available  with both the GNU runtime and the NeXT runtime (but not
           available in conjunction with the NeXT runtime on Mac OS X 10.2 and earlier).

       -fobjc-gc
           Enable garbage collection (GC) in Objective-C  and  Objective-C++  programs.   This  option  is  only
           available  with  the  NeXT runtime; the GNU runtime has a different garbage collection implementation
           that does not require special compiler flags.

       -fobjc-nilcheck
           For the NeXT runtime with version 2 of the ABI, check for a nil receiver in method invocations before
           doing the actual method call.  This is the default and  can  be  disabled  using  -fno-objc-nilcheck.
           Class  methods  and super calls are never checked for nil in this way no matter what this flag is set
           to.  Currently this flag does nothing when the GNU runtime, or an older version of the  NeXT  runtime
           ABI, is used.

       -fobjc-std=objc1
           Conform  to  the  language  syntax of Objective-C 1.0, the language recognized by GCC 4.0.  This only
           affects the Objective-C additions to the C/C++ language; it does  not  affect  conformance  to  C/C++
           standards,  which is controlled by the separate C/C++ dialect option flags.  When this option is used
           with the Objective-C or Objective-C++ compiler, any Objective-C syntax that is not recognized by  GCC
           4.0  is rejected.  This is useful if you need to make sure that your Objective-C code can be compiled
           with older versions of GCC.

       -freplace-objc-classes
           Emit a special marker instructing ld(1) not to statically link in  the  resulting  object  file,  and
           allow  dyld(1)  to  load  it  in  at run time instead.  This is used in conjunction with the Fix-and-
           Continue debugging mode, where the object file in question may be recompiled and dynamically reloaded
           in the course of program execution, without the need to restart the program itself.  Currently,  Fix-
           and-Continue  functionality  is  only available in conjunction with the NeXT runtime on Mac OS X 10.3
           and later.

       -fzero-link
           When compiling for the NeXT runtime, the compiler ordinarily replaces calls to "objc_getClass("...")"
           (when the name of the class is  known  at  compile  time)  with  static  class  references  that  get
           initialized  at  load  time,  which  improves  run-time performance.  Specifying the -fzero-link flag
           suppresses this behavior and causes calls to "objc_getClass("...")"  to be retained.  This is  useful
           in  Zero-Link  debugging  mode,  since  it allows for individual class implementations to be modified
           during program execution.  The GNU runtime currently always retains calls to  "objc_get_class("...")"
           regardless of command-line options.

       -fno-local-ivars
           By  default  instance  variables  in Objective-C can be accessed as if they were local variables from
           within the methods of the class they're declared in.  This can lead  to  shadowing  between  instance
           variables and other variables declared either locally inside a class method or globally with the same
           name.   Specifying  the -fno-local-ivars flag disables this behavior thus avoiding variable shadowing
           issues.

       -fivar-visibility=[public|protected|private|package]
           Set the default instance variable visibility to the  specified  option  so  that  instance  variables
           declared outside the scope of any access modifier directives default to the specified visibility.

       -gen-decls
           Dump interface declarations for all classes seen in the source file to a file named sourcename.decl.

       -Wassign-intercept (Objective-C and Objective-C++ only)
           Warn whenever an Objective-C assignment is being intercepted by the garbage collector.

       -Wno-property-assign-default (Objective-C and Objective-C++ only)
           Do not warn if a property for an Objective-C object has no assign semantics specified.

       -Wno-protocol (Objective-C and Objective-C++ only)
           If  a class is declared to implement a protocol, a warning is issued for every method in the protocol
           that is not implemented by the class.  The default behavior is to issue a warning  for  every  method
           not  explicitly  implemented  in  the  class,  even  if a method implementation is inherited from the
           superclass.  If you use the -Wno-protocol option, then methods  inherited  from  the  superclass  are
           considered to be implemented, and no warning is issued for them.

       -Wobjc-root-class (Objective-C and Objective-C++ only)
           Warn if a class interface lacks a superclass. Most classes will inherit from "NSObject" (or "Object")
           for  example.   When  declaring classes intended to be root classes, the warning can be suppressed by
           marking their interfaces with "__attribute__((objc_root_class))".

       -Wselector (Objective-C and Objective-C++ only)
           Warn if multiple methods of different types for the same selector are found during compilation.   The
           check  is  performed on the list of methods in the final stage of compilation.  Additionally, a check
           is performed for each selector appearing in  a  "@selector(...)"   expression,  and  a  corresponding
           method  for  that  selector  has been found during compilation.  Because these checks scan the method
           table only at the end of compilation,  these  warnings  are  not  produced  if  the  final  stage  of
           compilation  is not reached, for example because an error is found during compilation, or because the
           -fsyntax-only option is being used.

       -Wstrict-selector-match (Objective-C and Objective-C++ only)
           Warn if multiple methods with differing argument and/or return types are found for a  given  selector
           when  attempting  to  send a message using this selector to a receiver of type "id" or "Class".  When
           this flag is off (which is the default behavior), the compiler omits such warnings if any differences
           found are confined to types that share the same size and alignment.

       -Wundeclared-selector (Objective-C and Objective-C++ only)
           Warn if a "@selector(...)" expression referring to an undeclared selector is found.   A  selector  is
           considered  undeclared  if  no  method  with  that name has been declared before the "@selector(...)"
           expression, either explicitly in  an  @interface  or  @protocol  declaration,  or  implicitly  in  an
           @implementation  section.   This  option  always  performs  its  checks as soon as a "@selector(...)"
           expression is found, while -Wselector only performs its checks in the  final  stage  of  compilation.
           This  also  enforces  the  coding style convention that methods and selectors must be declared before
           being used.

       -print-objc-runtime-info
           Generate C header describing the largest structure that is passed by value, if any.

   Options to Control Diagnostic Messages Formatting
       Traditionally, diagnostic messages have been formatted irrespective of the output device's  aspect  (e.g.
       its  width,  ...).   You  can  use  the  options  described below to control the formatting algorithm for
       diagnostic messages, e.g. how many characters per line, how often source location information  should  be
       reported.  Note that some language front ends may not honor these options.

       -fmessage-length=n
           Try  to format error messages so that they fit on lines of about n characters.  If n is zero, then no
           line-wrapping is done; each error message appears on a single line.  This  is  the  default  for  all
           front ends.

           Note  - this option also affects the display of the #error and #warning pre-processor directives, and
           the deprecated function/type/variable attribute.  It does not however affect the pragma  GCC  warning
           and pragma GCC error pragmas.

       -fdiagnostics-plain-output
           This  option  requests  that  diagnostic  output  look as plain as possible, which may be useful when
           running dejagnu or other utilities that need to parse diagnostics output and prefer  that  it  remain
           more  stable over time.  -fdiagnostics-plain-output is currently equivalent to the following options:
           -fno-diagnostics-show-caret       -fno-diagnostics-show-line-numbers        -fdiagnostics-color=never
           -fdiagnostics-urls=never  -fdiagnostics-path-format=separate-events In the future, if GCC changes the
           default appearance of its diagnostics, the corresponding option to disable the new behavior  will  be
           added to this list.

       -fdiagnostics-show-location=once
           Only  meaningful  in  line-wrapping  mode.  Instructs the diagnostic messages reporter to emit source
           location information once; that is, in case the message is too long to fit on a single physical  line
           and  has  to  be  wrapped,  the source location won't be emitted (as prefix) again, over and over, in
           subsequent continuation lines.  This is the default behavior.

       -fdiagnostics-show-location=every-line
           Only meaningful in line-wrapping mode.  Instructs the diagnostic messages reporter to emit  the  same
           source location information (as prefix) for physical lines that result from the process of breaking a
           message which is too long to fit on a single line.

       -fdiagnostics-color[=WHEN]
       -fno-diagnostics-color
           Use  color  in diagnostics.  WHEN is never, always, or auto.  The default depends on how the compiler
           has been configured, it can be any of the above WHEN options or also never if GCC_COLORS  environment
           variable  isn't  present  in the environment, and auto otherwise.  auto makes GCC use color only when
           the  standard  error  is  a  terminal,  and  when  not  executing  in  an  emacs  shell.   The  forms
           -fdiagnostics-color   and  -fno-diagnostics-color  are  aliases  for  -fdiagnostics-color=always  and
           -fdiagnostics-color=never, respectively.

           The colors are defined by the environment variable GCC_COLORS.  Its value is a  colon-separated  list
           of  capabilities  and  Select Graphic Rendition (SGR) substrings. SGR commands are interpreted by the
           terminal or terminal emulator.  (See the section in the  documentation  of  your  text  terminal  for
           permitted values and their meanings as character attributes.)  These substring values are integers in
           decimal representation and can be concatenated with semicolons.  Common values to concatenate include
           1  for  bold,  4 for underline, 5 for blink, 7 for inverse, 39 for default foreground color, 30 to 37
           for foreground colors, 90 to 97 for 16-color mode foreground colors, 38;5;0 to 38;5;255 for  88-color
           and  256-color  modes  foreground  colors,  49  for default background color, 40 to 47 for background
           colors, 100 to 107 for 16-color mode background colors, and  48;5;0  to  48;5;255  for  88-color  and
           256-color modes background colors.

           The default GCC_COLORS is

                   error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\
                   quote=01:path=01;36:fixit-insert=32:fixit-delete=31:\
                   diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\
                   type-diff=01;32

           where  01;31  is  bold red, 01;35 is bold magenta, 01;36 is bold cyan, 32 is green, 34 is blue, 01 is
           bold, and 31 is red.  Setting GCC_COLORS to the empty string disables colors.  Supported capabilities
           are as follows.

           "error="
               SGR substring for error: markers.

           "warning="
               SGR substring for warning: markers.

           "note="
               SGR substring for note: markers.

           "path="
               SGR   substring   for   colorizing   paths   of    control-flow    events    as    printed    via
               -fdiagnostics-path-format=,  such  as  the  identifiers of individual events and lines indicating
               interprocedural calls and returns.

           "range1="
               SGR substring for first additional range.

           "range2="
               SGR substring for second additional range.

           "locus="
               SGR substring for location information, file:line or file:line:column etc.

           "quote="
               SGR substring for information printed within quotes.

           "fixit-insert="
               SGR substring for fix-it hints suggesting text to be inserted or replaced.

           "fixit-delete="
               SGR substring for fix-it hints suggesting text to be deleted.

           "diff-filename="
               SGR substring for filename headers within generated patches.

           "diff-hunk="
               SGR substring for the starts of hunks within generated patches.

           "diff-delete="
               SGR substring for deleted lines within generated patches.

           "diff-insert="
               SGR substring for inserted lines within generated patches.

           "type-diff="
               SGR substring for highlighting mismatching types within template arguments in the C++ frontend.

       -fdiagnostics-urls[=WHEN]
           Use escape sequences to embed URLs in diagnostics.  For example, when -fdiagnostics-show-option emits
           text showing the command-line option controlling a diagnostic, embed a URL for documentation of  that
           option.

           WHEN is never, always, or auto.  auto makes GCC use URL escape sequences only when the standard error
           is  a  terminal, and when not executing in an emacs shell or any graphical terminal which is known to
           be incompatible with this feature, see below.

           The default depends on how the compiler has been configured.   It  can  be  any  of  the  above  WHEN
           options.

           GCC  can  also  be  configured (via the --with-diagnostics-urls=auto-if-env configure-time option) so
           that the default is affected by environment variables.  Under such a configuration, GCC  defaults  to
           using  auto  if  either  GCC_URLS or TERM_URLS environment variables are present and non-empty in the
           environment of the compiler, or never if neither are.

           However,  even  with  -fdiagnostics-urls=always  the  behavior  is  dependent  on  those  environment
           variables:  If  GCC_URLS is set to empty or no, do not embed URLs in diagnostics.  If set to st, URLs
           use ST escape sequences.  If set to bel, the default, URLs use BEL escape sequences.  Any other  non-
           empty  value  enables the feature.  If GCC_URLS is not set, use TERM_URLS as a fallback.  Note: ST is
           an ANSI escape sequence, string terminator ESC \, BEL is an  ASCII  character,  CTRL-G  that  usually
           sounds like a beep.

           At  this  time  GCC  tries  to  detect  also  a few terminals that are known to not implement the URL
           feature, and have bugs or at least had bugs in some versions that are still in  use,  where  the  URL
           escapes  are  likely  to  misbehave,  i.e.  print  garbage  on  the  screen.   That list is currently
           xfce4-terminal, certain known to be buggy gnome-terminal versions,  the  linux  console,  and  mingw.
           This check can be skipped with the -fdiagnostics-urls=always.

       -fno-diagnostics-show-option
           By  default,  each  diagnostic emitted includes text indicating the command-line option that directly
           controls the diagnostic (if such an option is known to the  diagnostic  machinery).   Specifying  the
           -fno-diagnostics-show-option flag suppresses that behavior.

       -fno-diagnostics-show-caret
           By  default,  each  diagnostic emitted includes the original source line and a caret ^ indicating the
           column.  This option suppresses this information.  The source line is truncated to n  characters,  if
           the  -fmessage-length=n  option  is  given.   When  the  output is done to the terminal, the width is
           limited to the width given by the COLUMNS environment variable or, if not set, to the terminal width.

       -fno-diagnostics-show-labels
           By default, when printing source code (via -fdiagnostics-show-caret), diagnostics can label ranges of
           source code with pertinent information, such as the types of expressions:

                       printf ("foo %s bar", long_i + long_j);
                                    ~^       ~~~~~~~~~~~~~~~
                                     |              |
                                     char *         long int

           This option suppresses the printing of these labels (in the example above, the vertical bars and  the
           "char *" and "long int" text).

       -fno-diagnostics-show-cwe
           Diagnostic  messages  can  optionally  have an associated @url{https://cwe.mitre.org/index.html, CWE}
           identifier.  GCC itself only provides such metadata for some  of  the  -fanalyzer  diagnostics.   GCC
           plugins may also provide diagnostics with such metadata.  By default, if this information is present,
           it will be printed with the diagnostic.  This option suppresses the printing of this metadata.

       -fno-diagnostics-show-line-numbers
           By  default,  when  printing  source  code  (via -fdiagnostics-show-caret), a left margin is printed,
           showing line numbers.  This option suppresses this left margin.

       -fdiagnostics-minimum-margin-width=width
           This option controls the minimum width of the left margin printed by -fdiagnostics-show-line-numbers.
           It defaults to 6.

       -fdiagnostics-parseable-fixits
           Emit fix-it hints in a machine-parseable format, suitable for consumption by IDEs.  For each  fix-it,
           a  line  will  be  printed  after  the  relevant diagnostic, starting with the string "fix-it:".  For
           example:

                   fix-it:"test.c":{45:3-45:21}:"gtk_widget_show_all"

           The location is expressed as a half-open range, expressed as a count of bytes, starting at byte 1 for
           the initial column.  In the above example, bytes 3 through 20 of  line  45  of  "test.c"  are  to  be
           replaced with the given string:

                   00000000011111111112222222222
                   12345678901234567890123456789
                     gtk_widget_showall (dlg);
                     ^^^^^^^^^^^^^^^^^^
                     gtk_widget_show_all

           The  filename  and  replacement string escape backslash as "\\", tab as "\t", newline as "\n", double
           quotes as "\"", non-printable characters as octal (e.g. vertical tab as "\013").

           An empty replacement string indicates that the given range is to be removed.  An  empty  range  (e.g.
           "45:3-45:3") indicates that the string is to be inserted at the given position.

       -fdiagnostics-generate-patch
           Print fix-it hints to stderr in unified diff format, after any diagnostics are printed.  For example:

                   --- test.c
                   +++ test.c
                   @ -42,5 +42,5 @

                    void show_cb(GtkDialog *dlg)
                    {
                   -  gtk_widget_showall(dlg);
                   +  gtk_widget_show_all(dlg);
                    }

           The  diff  may  or  may  not  be  colorized,  following  the  same  rules  as  for  diagnostics  (see
           -fdiagnostics-color).

       -fdiagnostics-show-template-tree
           In the C++ frontend, when printing diagnostics showing mismatching template types, such as:

                     could not convert 'std::map<int, std::vector<double> >()'
                       from 'map<[...],vector<double>>' to 'map<[...],vector<float>>

           the -fdiagnostics-show-template-tree flag enables printing a tree-like structure showing  the  common
           and differing parts of the types, such as:

                     map<
                       [...],
                       vector<
                         [double != float]>>

           The parts that differ are highlighted with color ("double" and "float" in this case).

       -fno-elide-type
           By  default when the C++ frontend prints diagnostics showing mismatching template types, common parts
           of the types are printed as "[...]" to simplify the error message.  For example:

                     could not convert 'std::map<int, std::vector<double> >()'
                       from 'map<[...],vector<double>>' to 'map<[...],vector<float>>

           Specifying the -fno-elide-type flag suppresses that behavior.  This flag also affects the  output  of
           the -fdiagnostics-show-template-tree flag.

       -fdiagnostics-path-format=KIND
           Specify  how  to  print paths of control-flow events for diagnostics that have such a path associated
           with them.

           KIND is none, separate-events, or inline-events, the default.

           none means to not print diagnostic paths.

           separate-events means to print a separate "note" diagnostic for each  event  within  the  diagnostic.
           For example:

                   test.c:29:5: error: passing NULL as argument 1 to 'PyList_Append' which requires a non-NULL parameter
                   test.c:25:10: note: (1) when 'PyList_New' fails, returning NULL
                   test.c:27:3: note: (2) when 'i < count'
                   test.c:29:5: note: (3) when calling 'PyList_Append', passing NULL from (1) as argument 1

           inline-events  means  to  print  the  events  "inline" within the source code.  This view attempts to
           consolidate the events into runs of sufficiently-close  events,  printing  them  as  labelled  ranges
           within the source.

           For example, the same events as above might be printed as:

                     'test': events 1-3
                       |
                       |   25 |   list = PyList_New(0);
                       |      |          ^~~~~~~~~~~~~
                       |      |          |
                       |      |          (1) when 'PyList_New' fails, returning NULL
                       |   26 |
                       |   27 |   for (i = 0; i < count; i++) {
                       |      |   ~~~
                       |      |   |
                       |      |   (2) when 'i < count'
                       |   28 |     item = PyLong_FromLong(random());
                       |   29 |     PyList_Append(list, item);
                       |      |     ~~~~~~~~~~~~~~~~~~~~~~~~~
                       |      |     |
                       |      |     (3) when calling 'PyList_Append', passing NULL from (1) as argument 1
                       |

           Interprocedural control flow is shown by grouping the events by stack frame, and using indentation to
           show how stack frames are nested, pushed, and popped.

           For example:

                     'test': events 1-2
                       |
                       |  133 | {
                       |      | ^
                       |      | |
                       |      | (1) entering 'test'
                       |  134 |   boxed_int *obj = make_boxed_int (i);
                       |      |                    ~~~~~~~~~~~~~~~~~~
                       |      |                    |
                       |      |                    (2) calling 'make_boxed_int'
                       |
                       +--> 'make_boxed_int': events 3-4
                              |
                              |  120 | {
                              |      | ^
                              |      | |
                              |      | (3) entering 'make_boxed_int'
                              |  121 |   boxed_int *result = (boxed_int *)wrapped_malloc (sizeof (boxed_int));
                              |      |                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                              |      |                                    |
                              |      |                                    (4) calling 'wrapped_malloc'
                              |
                              +--> 'wrapped_malloc': events 5-6
                                     |
                                     |    7 | {
                                     |      | ^
                                     |      | |
                                     |      | (5) entering 'wrapped_malloc'
                                     |    8 |   return malloc (size);
                                     |      |          ~~~~~~~~~~~~~
                                     |      |          |
                                     |      |          (6) calling 'malloc'
                                     |
                       <-------------+
                       |
                    'test': event 7
                       |
                       |  138 |   free_boxed_int (obj);
                       |      |   ^~~~~~~~~~~~~~~~~~~~
                       |      |   |
                       |      |   (7) calling 'free_boxed_int'
                       |
                   (etc)

       -fdiagnostics-show-path-depths
           This  option  provides  additional  information  when  printing  control-flow paths associated with a
           diagnostic.

           If this is option is provided then the stack depth will be printed for  each  run  of  events  within
           -fdiagnostics-path-format=separate-events.

           This  is  intended  for  use  by GCC developers and plugin developers when debugging diagnostics that
           report interprocedural control flow.

       -fno-show-column
           Do not print column numbers in diagnostics.  This may be necessary if diagnostics are  being  scanned
           by a program that does not understand the column numbers, such as dejagnu.

       -fdiagnostics-column-unit=UNIT
           Select  the  units  for  the  column number.  This affects traditional diagnostics (in the absence of
           -fno-show-column), as well as JSON format diagnostics if requested.

           The default UNIT, display, considers the number of display columns occupied by each character.   This
           may  be  larger  than  the  number  of  bytes  required  to  encode the character, in the case of tab
           characters, or it may be smaller, in the case of multibyte characters.  For  example,  the  character
           "GREEK  SMALL  LETTER  PI  (U+03C0)" occupies one display column, and its UTF-8 encoding requires two
           bytes; the character "SLIGHTLY SMILING FACE (U+1F642)" occupies two display columns,  and  its  UTF-8
           encoding requires four bytes.

           Setting  UNIT  to  byte  changes  the  column  number  to  the  raw  byte  count in all cases, as was
           traditionally output by GCC prior to version 11.1.0.

       -fdiagnostics-column-origin=ORIGIN
           Select the origin for column numbers, i.e. the column number  assigned  to  the  first  column.   The
           default  value  of  1  corresponds  to  traditional  GCC  behavior  and to the GNU style guide.  Some
           utilities may perform better with an origin of 0; any non-negative value may be specified.

       -fdiagnostics-format=FORMAT
           Select a different format for printing diagnostics.  FORMAT is text or json.  The default is text.

           The json format consists  of  a  top-level  JSON  array  containing  JSON  objects  representing  the
           diagnostics.

           The  JSON  is  emitted  as  one  line, without formatting; the examples below have been formatted for
           clarity.

           Diagnostics can have child diagnostics.  For example, this error and note:

                   misleading-indentation.c:15:3: warning: this 'if' clause does not
                     guard... [-Wmisleading-indentation]
                      15 |   if (flag)
                         |   ^~
                   misleading-indentation.c:17:5: note: ...this statement, but the latter
                     is misleadingly indented as if it were guarded by the 'if'
                      17 |     y = 2;
                         |     ^

           might be printed in JSON form (after formatting) like this:

                   [
                       {
                           "kind": "warning",
                           "locations": [
                               {
                                   "caret": {
                                       "display-column": 3,
                                       "byte-column": 3,
                                       "column": 3,
                                       "file": "misleading-indentation.c",
                                       "line": 15
                                   },
                                   "finish": {
                                       "display-column": 4,
                                       "byte-column": 4,
                                       "column": 4,
                                       "file": "misleading-indentation.c",
                                       "line": 15
                                   }
                               }
                           ],
                           "message": "this \u2018if\u2019 clause does not guard...",
                           "option": "-Wmisleading-indentation",
                           "option_url": "https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wmisleading-indentation",
                           "children": [
                               {
                                   "kind": "note",
                                   "locations": [
                                       {
                                           "caret": {
                                               "display-column": 5,
                                               "byte-column": 5,
                                               "column": 5,
                                               "file": "misleading-indentation.c",
                                               "line": 17
                                           }
                                       }
                                   ],
                                   "message": "...this statement, but the latter is ..."
                               }
                           ]
                           "column-origin": 1,
                       },
                       ...
                   ]

           where the "note" is a child of the "warning".

           A diagnostic has a "kind".  If this is "warning", then  there  is  an  "option"  key  describing  the
           command-line option controlling the warning.

           A diagnostic can contain zero or more locations.  Each location has an optional "label" string and up
           to  three  positions  within  it:  a "caret" position and optional "start" and "finish" positions.  A
           position is described by a "file" name, a "line"  number,  and  three  numbers  indicating  a  column
           position:

           *   "display-column" counts display columns, accounting for tabs and multibyte characters.

           *   "byte-column" counts raw bytes.

           *   "column"  is  equal  to  one  of  the  previous two, as dictated by the -fdiagnostics-column-unit
               option.

           All three columns are relative to the  origin  specified  by  -fdiagnostics-column-origin,  which  is
           typically  equal  to 1 but may be set, for instance, to 0 for compatibility with other utilities that
           number columns from 0.  The column origin is recorded in the JSON output in the "column-origin"  tag.
           In the remaining examples below, the extra column number outputs have been omitted for brevity.

           For example, this error:

                   bad-binary-ops.c:64:23: error: invalid operands to binary + (have 'S' {aka
                      'struct s'} and 'T' {aka 'struct t'})
                      64 |   return callee_4a () + callee_4b ();
                         |          ~~~~~~~~~~~~ ^ ~~~~~~~~~~~~
                         |          |              |
                         |          |              T {aka struct t}
                         |          S {aka struct s}

           has  three  locations.   Its primary location is at the "+" token at column 23.  It has two secondary
           locations, describing the left and right-hand sides of the expression, which have labels.   It  might
           be printed in JSON form as:

                       {
                           "children": [],
                           "kind": "error",
                           "locations": [
                               {
                                   "caret": {
                                       "column": 23, "file": "bad-binary-ops.c", "line": 64
                                   }
                               },
                               {
                                   "caret": {
                                       "column": 10, "file": "bad-binary-ops.c", "line": 64
                                   },
                                   "finish": {
                                       "column": 21, "file": "bad-binary-ops.c", "line": 64
                                   },
                                   "label": "S {aka struct s}"
                               },
                               {
                                   "caret": {
                                       "column": 25, "file": "bad-binary-ops.c", "line": 64
                                   },
                                   "finish": {
                                       "column": 36, "file": "bad-binary-ops.c", "line": 64
                                   },
                                   "label": "T {aka struct t}"
                               }
                           ],
                           "message": "invalid operands to binary + ..."
                       }

           If  a  diagnostic  contains fix-it hints, it has a "fixits" array, consisting of half-open intervals,
           similar to the output  of  -fdiagnostics-parseable-fixits.   For  example,  this  diagnostic  with  a
           replacement fix-it hint:

                   demo.c:8:15: error: 'struct s' has no member named 'colour'; did you
                     mean 'color'?
                       8 |   return ptr->colour;
                         |               ^~~~~~
                         |               color

           might be printed in JSON form as:

                       {
                           "children": [],
                           "fixits": [
                               {
                                   "next": {
                                       "column": 21,
                                       "file": "demo.c",
                                       "line": 8
                                   },
                                   "start": {
                                       "column": 15,
                                       "file": "demo.c",
                                       "line": 8
                                   },
                                   "string": "color"
                               }
                           ],
                           "kind": "error",
                           "locations": [
                               {
                                   "caret": {
                                       "column": 15,
                                       "file": "demo.c",
                                       "line": 8
                                   },
                                   "finish": {
                                       "column": 20,
                                       "file": "demo.c",
                                       "line": 8
                                   }
                               }
                           ],
                           "message": "\u2018struct s\u2019 has no member named ..."
                       }

           where  the  fix-it  hint suggests replacing the text from "start" up to but not including "next" with
           "string"'s value.  Deletions are expressed via an empty value  for  "string",  insertions  by  having
           "start" equal "next".

           If  the  diagnostic  has  a  path of control-flow events associated with it, it has a "path" array of
           objects representing the events.  Each event object has a "description" string, a "location"  object,
           along  with  a  "function"  string  and a "depth" number for representing interprocedural paths.  The
           "function" represents the current function at that event, and the "depth" represents the stack  depth
           relative to some baseline: the higher, the more frames are within the stack.

           For  example,  the  intraprocedural example shown for -fdiagnostics-path-format= might have this JSON
           for its path:

                       "path": [
                           {
                               "depth": 0,
                               "description": "when 'PyList_New' fails, returning NULL",
                               "function": "test",
                               "location": {
                                   "column": 10,
                                   "file": "test.c",
                                   "line": 25
                               }
                           },
                           {
                               "depth": 0,
                               "description": "when 'i < count'",
                               "function": "test",
                               "location": {
                                   "column": 3,
                                   "file": "test.c",
                                   "line": 27
                               }
                           },
                           {
                               "depth": 0,
                               "description": "when calling 'PyList_Append', passing NULL from (1) as argument 1",
                               "function": "test",
                               "location": {
                                   "column": 5,
                                   "file": "test.c",
                                   "line": 29
                               }
                           }
                       ]

   Options to Request or Suppress Warnings
       Warnings are diagnostic messages that report constructions that are not inherently erroneous but that are
       risky or suggest there may have been an error.

       The following language-independent options do not enable specific  warnings  but  control  the  kinds  of
       diagnostics produced by GCC.

       -fsyntax-only
           Check the code for syntax errors, but don't do anything beyond that.

       -fmax-errors=n
           Limits the maximum number of error messages to n, at which point GCC bails out rather than attempting
           to  continue processing the source code.  If n is 0 (the default), there is no limit on the number of
           error messages produced.  If -Wfatal-errors is also specified, then -Wfatal-errors  takes  precedence
           over this option.

       -w  Inhibit all warning messages.

       -Werror
           Make all warnings into errors.

       -Werror=
           Make  the  specified  warning  into  an  error.  The specifier for a warning is appended; for example
           -Werror=switch turns the warnings controlled by -Wswitch into errors.  This switch takes  a  negative
           form,  to  be  used  to  negate  -Werror  for  specific warnings; for example -Wno-error=switch makes
           -Wswitch warnings not be errors, even when -Werror is in effect.

           The warning message for each controllable warning includes the  option  that  controls  the  warning.
           That  option  can  then  be  used with -Werror= and -Wno-error= as described above.  (Printing of the
           option in the warning message can be disabled using the -fno-diagnostics-show-option flag.)

           Note that specifying -Werror=foo automatically implies -Wfoo.  However, -Wno-error=foo does not imply
           anything.

       -Wfatal-errors
           This option causes the compiler to abort compilation on the first error occurred rather  than  trying
           to keep going and printing further error messages.

       You  can request many specific warnings with options beginning with -W, for example -Wimplicit to request
       warnings on implicit declarations.  Each of these specific warning  options  also  has  a  negative  form
       beginning  -Wno- to turn off warnings; for example, -Wno-implicit.  This manual lists only one of the two
       forms, whichever is not the default.  For further language-specific options also  refer  to  C++  Dialect
       Options  and  Objective-C  and  Objective-C++  Dialect  Options.   Additional warnings can be produced by
       enabling the static analyzer;

       Some options, such as -Wall and -Wextra, turn on other options, such  as  -Wunused,  which  may  turn  on
       further  options, such as -Wunused-value. The combined effect of positive and negative forms is that more
       specific options have priority over less specific ones, independently of their position in  the  command-
       line.  For  options  of  the same specificity, the last one takes effect. Options enabled or disabled via
       pragmas take effect as if they appeared at the end of the command-line.

       When an unrecognized warning option is  requested  (e.g.,  -Wunknown-warning),  GCC  emits  a  diagnostic
       stating  that the option is not recognized.  However, if the -Wno- form is used, the behavior is slightly
       different: no diagnostic  is  produced  for  -Wno-unknown-warning  unless  other  diagnostics  are  being
       produced.   This allows the use of new -Wno- options with old compilers, but if something goes wrong, the
       compiler warns that an unrecognized option is present.

       The  effectiveness  of  some  warnings  depends  on  optimizations  also  being  enabled.   For   example
       -Wsuggest-final-types  is  more  effective with link-time optimization and -Wmaybe-uninitialized does not
       warn at all unless optimization is enabled.

       -Wpedantic
       -pedantic
           Issue all the warnings demanded by strict ISO C and ISO C++; reject all programs that  use  forbidden
           extensions,  and  some  other  programs that do not follow ISO C and ISO C++.  For ISO C, follows the
           version of the ISO C standard specified by any -std option used.

           Valid ISO C and ISO C++ programs should compile properly with or without this option (though  a  rare
           few  require -ansi or a -std option specifying the required version of ISO C).  However, without this
           option, certain GNU extensions and traditional C and C++ features are supported as well.   With  this
           option, they are rejected.

           -Wpedantic  does  not  cause warning messages for use of the alternate keywords whose names begin and
           end with __.  This alternate format can also be used to disable warnings for  non-ISO  __intN  types,
           i.e.  __intN__.   Pedantic warnings are also disabled in the expression that follows "__extension__".
           However, only system header files should use these escape routes; application programs  should  avoid
           them.

           Some users try to use -Wpedantic to check programs for strict ISO C conformance.  They soon find that
           it  does  not  do quite what they want: it finds some non-ISO practices, but not all---only those for
           which ISO C requires a diagnostic, and some others for which diagnostics have been added.

           A feature to report any failure to conform to ISO C might be useful  in  some  instances,  but  would
           require  considerable  additional  work  and would be quite different from -Wpedantic.  We don't have
           plans to support such a feature in the near future.

           Where the standard specified with -std represents a GNU extended dialect  of  C,  such  as  gnu90  or
           gnu99, there is a corresponding base standard, the version of ISO C on which the GNU extended dialect
           is based.  Warnings from -Wpedantic are given where they are required by the base standard.  (It does
           not  make  sense  for such warnings to be given only for features not in the specified GNU C dialect,
           since by definition the GNU dialects of C include all features the compiler supports with  the  given
           option, and there would be nothing to warn about.)

       -pedantic-errors
           Give  an error whenever the base standard (see -Wpedantic) requires a diagnostic, in some cases where
           there is undefined behavior at compile-time and in some other cases that do not  prevent  compilation
           of  programs  that  are  valid according to the standard. This is not equivalent to -Werror=pedantic,
           since there are errors enabled by this option and not enabled by the latter and vice versa.

       -Wall
           This enables all the warnings about constructions that some users consider questionable, and that are
           easy to avoid (or modify to prevent the warning), even in conjunction with macros.  This also enables
           some language-specific warnings described in C++ Dialect Options and  Objective-C  and  Objective-C++
           Dialect Options.

           -Wall turns on the following warning flags:

           -Waddress   -Warray-bounds=1   (only   with   -O2)   -Warray-parameter=2  (C  and  Objective-C  only)
           -Wbool-compare -Wbool-operation -Wc++11-compat  -Wc++14-compat -Wcatch-value (C++  and  Objective-C++
           only)  -Wchar-subscripts -Wcomment -Wduplicate-decl-specifier (C and Objective-C only) -Wenum-compare
           (in  C/ObjC;  this  is  on  by  default  in  C++)  -Wformat   -Wformat-overflow   -Wformat-truncation
           -Wint-in-bool-context  -Wimplicit  (C  and  Objective-C only) -Wimplicit-int (C and Objective-C only)
           -Wimplicit-function-declaration   (C   and   Objective-C   only)   -Winit-self   (only    for    C++)
           -Wlogical-not-parentheses  -Wmain  (only  for C/ObjC and unless -ffreestanding) -Wmaybe-uninitialized
           -Wmemset-elt-size    -Wmemset-transposed-args    -Wmisleading-indentation    (only     for     C/C++)
           -Wmissing-attributes -Wmissing-braces (only for C/ObjC) -Wmultistatement-macros -Wnarrowing (only for
           C++)  -Wnonnull  -Wnonnull-compare  -Wopenmp-simd  -Wparentheses  -Wpessimizing-move  (only  for C++)
           -Wpointer-sign   -Wrange-loop-construct   (only   for   C++)   -Wreorder   -Wrestrict   -Wreturn-type
           -Wsequence-point    -Wsign-compare    (only    in    C++)   -Wsizeof-array-div   -Wsizeof-pointer-div
           -Wsizeof-pointer-memaccess  -Wstrict-aliasing  -Wstrict-overflow=1  -Wswitch   -Wtautological-compare
           -Wtrigraphs   -Wuninitialized   -Wunknown-pragmas   -Wunused-function  -Wunused-label  -Wunused-value
           -Wunused-variable    -Wvla-parameter    (C    and    Objective-C    only)     -Wvolatile-register-var
           -Wzero-length-bounds

           Note  that  some  warning flags are not implied by -Wall.  Some of them warn about constructions that
           users generally do not consider questionable, but which occasionally you might  wish  to  check  for;
           others  warn  about  constructions that are necessary or hard to avoid in some cases, and there is no
           simple way to modify the code to suppress the warning. Some of them are enabled by -Wextra  but  many
           of them must be enabled individually.

       -Wextra
           This  enables  some extra warning flags that are not enabled by -Wall. (This option used to be called
           -W.  The older name is still supported, but the newer name is more descriptive.)

           -Wclobbered -Wcast-function-type -Wdeprecated-copy (C++ only) -Wempty-body -Wenum-conversion (C only)
           -Wignored-qualifiers -Wimplicit-fallthrough=3  -Wmissing-field-initializers  -Wmissing-parameter-type
           (C  only)  -Wold-style-declaration  (C only) -Woverride-init -Wsign-compare (C only) -Wstring-compare
           -Wredundant-move (only for C++) -Wtype-limits -Wuninitialized  -Wshift-negative-value  (in  C++11  to
           C++17    and    in    C99   and   newer)   -Wunused-parameter   (only   with   -Wunused   or   -Wall)
           -Wunused-but-set-parameter (only with -Wunused or -Wall)

           The option -Wextra also prints warning messages for the following cases:

           *   A pointer is compared against integer zero with "<", "<=", ">", or ">=".

           *   (C++ only) An enumerator and a non-enumerator both appear in a conditional expression.

           *   (C++ only) Ambiguous virtual bases.

           *   (C++ only) Subscripting an array that has been declared "register".

           *   (C++ only) Taking the address of a variable that has been declared "register".

           *   (C++ only) A base class is not initialized in the copy constructor of a derived class.

       -Wabi (C, Objective-C, C++ and Objective-C++ only)
           Warn about code affected by ABI changes.  This includes code that may  not  be  compatible  with  the
           vendor-neutral C++ ABI as well as the psABI for the particular target.

           Since  G++  now defaults to updating the ABI with each major release, normally -Wabi warns only about
           C++ ABI compatibility problems if there is a check added later in a release series for an  ABI  issue
           discovered  since  the  initial  release.   -Wabi  warns about more things if an older ABI version is
           selected (with -fabi-version=n).

           -Wabi can also be used with an explicit version number to warn about C++  ABI  compatibility  with  a
           particular -fabi-version level, e.g. -Wabi=2 to warn about changes relative to -fabi-version=2.

           If  an  explicit  version  number  is provided and -fabi-compat-version is not specified, the version
           number from this option is used for compatibility aliases.  If no explicit version number is provided
           with this option, but -fabi-compat-version is specified, that version number  is  used  for  C++  ABI
           warnings.

           Although an effort has been made to warn about all such cases, there are probably some cases that are
           not  warned  about,  even  though G++ is generating incompatible code.  There may also be cases where
           warnings are emitted even though the code that is generated is compatible.

           You should rewrite your code to avoid these warnings if you are concerned about the  fact  that  code
           generated by G++ may not be binary compatible with code generated by other compilers.

           Known incompatibilities in -fabi-version=2 (which was the default from GCC 3.4 to 4.9) include:

           *   A template with a non-type template parameter of reference type was mangled incorrectly:

                       extern int N;
                       template <int &> struct S {};
                       void n (S<N>) {2}

               This was fixed in -fabi-version=3.

           *   SIMD vector types declared using "__attribute ((vector_size))" were mangled in a non-standard way
               that does not allow for overloading of functions taking vectors of different sizes.

               The mangling was changed in -fabi-version=4.

           *   "__attribute ((const))" and "noreturn" were mangled as type qualifiers, and "decltype" of a plain
               declaration was folded away.

               These mangling issues were fixed in -fabi-version=5.

           *   Scoped  enumerators  passed  as  arguments  to  a  variadic  function  are promoted like unscoped
               enumerators, causing "va_arg" to complain.  On most targets this does  not  actually  affect  the
               parameter passing ABI, as there is no way to pass an argument smaller than "int".

               Also,  the  ABI  changed  the  mangling  of template argument packs, "const_cast", "static_cast",
               prefix increment/decrement, and a class scope function used as a template argument.

               These issues were corrected in -fabi-version=6.

           *   Lambdas in default argument scope were mangled incorrectly, and the ABI changed the  mangling  of
               "nullptr_t".

               These issues were corrected in -fabi-version=7.

           *   When  mangling  a  function  type with function-cv-qualifiers, the un-qualified function type was
               incorrectly treated as a substitution candidate.

               This was fixed in -fabi-version=8, the default for GCC 5.1.

           *   "decltype(nullptr)" incorrectly had an alignment of 1, leading to unaligned accesses.  Note  that
               this  did  not  affect  the  ABI of a function with a "nullptr_t" parameter, as parameters have a
               minimum alignment.

               This was fixed in -fabi-version=9, the default for GCC 5.2.

           *   Target-specific attributes that affect the identity of a type, such as ia32  calling  conventions
               on  a  function  type  (stdcall, regparm, etc.), did not affect the mangled name, leading to name
               collisions when function pointers were used as template arguments.

               This was fixed in -fabi-version=10, the default for GCC 6.1.

           This option also enables warnings about psABI-related changes.  The known psABI changes at this point
           include:

           *   For SysV/x86-64, unions with "long double" members are passed in memory as  specified  in  psABI.
               Prior to GCC 4.4, this was not the case.  For example:

                       union U {
                         long double ld;
                         int i;
                       };

               "union U" is now always passed in memory.

       -Wchar-subscripts
           Warn  if  an  array subscript has type "char".  This is a common cause of error, as programmers often
           forget that this type is signed on some machines.  This warning is enabled by -Wall.

       -Wno-coverage-mismatch
           Warn if feedback profiles do not match when using the -fprofile-use option.   If  a  source  file  is
           changed  between compiling with -fprofile-generate and with -fprofile-use, the files with the profile
           feedback can fail to match the source file and GCC cannot use the profile feedback  information.   By
           default,  this  warning is enabled and is treated as an error.  -Wno-coverage-mismatch can be used to
           disable the warning or -Wno-error=coverage-mismatch can be used to disable the error.  Disabling  the
           error  for  this  warning  can result in poorly optimized code and is useful only in the case of very
           minor changes such as bug fixes to an existing code-base.  Completely disabling the  warning  is  not
           recommended.

       -Wno-cpp
           (C, Objective-C, C++, Objective-C++ and Fortran only) Suppress warning messages emitted by "#warning"
           directives.

       -Wdouble-promotion (C, C++, Objective-C and Objective-C++ only)
           Give  a  warning when a value of type "float" is implicitly promoted to "double".  CPUs with a 32-bit
           "single-precision" floating-point unit  implement  "float"  in  hardware,  but  emulate  "double"  in
           software.  On such a machine, doing computations using "double" values is much more expensive because
           of the overhead required for software emulation.

           It  is  easy  to  accidentally  do  computations  with  "double"  because floating-point literals are
           implicitly of type "double".  For example, in:

                   float area(float radius)
                   {
                      return 3.14159 * radius * radius;
                   }

           the compiler performs the entire computation with "double" because the floating-point  literal  is  a
           "double".

       -Wduplicate-decl-specifier (C and Objective-C only)
           Warn  if  a  declaration  has duplicate "const", "volatile", "restrict" or "_Atomic" specifier.  This
           warning is enabled by -Wall.

       -Wformat
       -Wformat=n
           Check calls to "printf" and "scanf", etc., to make  sure  that  the  arguments  supplied  have  types
           appropriate  to  the format string specified, and that the conversions specified in the format string
           make sense.  This includes standard functions, and others specified  by  format  attributes,  in  the
           "printf", "scanf", "strftime" and "strfmon" (an X/Open extension, not in the C standard) families (or
           other  target-specific  families).  Which functions are checked without format attributes having been
           specified depends on the standard  version  selected,  and  such  checks  of  functions  without  the
           attribute specified are disabled by -ffreestanding or -fno-builtin.

           The formats are checked against the format features supported by GNU libc version 2.2.  These include
           all ISO C90 and C99 features, as well as features from the Single Unix Specification and some BSD and
           GNU  extensions.   Other  library  implementations  may  not support all these features; GCC does not
           support warning about features that go  beyond  a  particular  library's  limitations.   However,  if
           -Wpedantic  is  used  with  -Wformat,  warnings  are  given about format features not in the selected
           standard version (but not for "strfmon" formats, since  those  are  not  in  any  version  of  the  C
           standard).

           -Wformat=1
           -Wformat
               Option  -Wformat is equivalent to -Wformat=1, and -Wno-format is equivalent to -Wformat=0.  Since
               -Wformat also checks for null format arguments  for  several  functions,  -Wformat  also  implies
               -Wnonnull.   Some  aspects  of  this  level  of  format  checking can be disabled by the options:
               -Wno-format-contains-nul,  -Wno-format-extra-args,  and  -Wno-format-zero-length.   -Wformat   is
               enabled by -Wall.

           -Wformat=2
               Enable   -Wformat   plus   additional   format   checks.    Currently   equivalent   to  -Wformat
               -Wformat-nonliteral -Wformat-security -Wformat-y2k.

       -Wno-format-contains-nul
           If -Wformat is specified, do not warn about format strings that contain NUL bytes.

       -Wno-format-extra-args
           If -Wformat is specified, do not warn  about  excess  arguments  to  a  "printf"  or  "scanf"  format
           function.  The C standard specifies that such arguments are ignored.

           Where  the  unused  arguments  lie  between  used  arguments that are specified with $ operand number
           specifications, normally warnings are still given, since the implementation could not know what  type
           to  pass  to  "va_arg"  to  skip the unused arguments.  However, in the case of "scanf" formats, this
           option suppresses the warning if the unused  arguments  are  all  pointers,  since  the  Single  Unix
           Specification says that such unused arguments are allowed.

       -Wformat-overflow
       -Wformat-overflow=level
           Warn  about  calls  to  formatted  input/output functions such as "sprintf" and "vsprintf" that might
           overflow the destination buffer.  When the exact number of bytes written by a format directive cannot
           be determined at compile-time it is estimated based on heuristics that depend on the  level  argument
           and  on  optimization.   While  enabling  optimization will in most cases improve the accuracy of the
           warning, it may also result in false positives.

           -Wformat-overflow
           -Wformat-overflow=1
               Level 1 of -Wformat-overflow enabled by -Wformat employs a conservative approach that warns  only
               about  calls  that  most  likely overflow the buffer.  At this level, numeric arguments to format
               directives with unknown values are assumed to have the value  of  one,  and  strings  of  unknown
               length  to be empty.  Numeric arguments that are known to be bounded to a subrange of their type,
               or string arguments whose output is bounded either by their directive's precision or by a  finite
               set  of  string  literals,  are assumed to take on the value within the range that results in the
               most bytes on output.  For example, the call to "sprintf" below is diagnosed  because  even  with
               both  a and b equal to zero, the terminating NUL character ('\0') appended by the function to the
               destination buffer will be written past its end.  Increasing the size of the buffer by  a  single
               byte is sufficient to avoid the warning, though it may not be sufficient to avoid the overflow.

                       void f (int a, int b)
                       {
                         char buf [13];
                         sprintf (buf, "a = %i, b = %i\n", a, b);
                       }

           -Wformat-overflow=2
               Level  2  warns  also about calls that might overflow the destination buffer given an argument of
               sufficient length or magnitude.  At level 2, unknown numeric arguments are assumed  to  have  the
               minimum  representable  value  for  signed types with a precision greater than 1, and the maximum
               representable value otherwise.  Unknown string arguments whose length cannot  be  assumed  to  be
               bounded  either  by  the  directive's  precision,  or by a finite set of string literals they may
               evaluate to, or the character array they may point to, are assumed to be 1 character long.

               At level 2, the call in the example above is again diagnosed, but this time because with a  equal
               to  a 32-bit "INT_MIN" the first %i directive will write some of its digits beyond the end of the
               destination buffer.  To make the call safe regardless of the values of  the  two  variables,  the
               size  of the destination buffer must be increased to at least 34 bytes.  GCC includes the minimum
               size of the buffer in an informational note following the warning.

               An alternative to increasing the size of the destination buffer is  to  constrain  the  range  of
               formatted  values.   The  maximum  length  of  string  arguments can be bounded by specifying the
               precision in the format directive.  When numeric arguments of format directives can be assumed to
               be bounded by less than the precision of their type, choosing an appropriate length  modifier  to
               the  format  specifier  will  reduce  the  required  buffer size.  For example, if a and b in the
               example above can be assumed to be within the precision of the "short int" type then using either
               the %hi format directive or casting the argument to "short" reduces the maximum required size  of
               the buffer to 24 bytes.

                       void f (int a, int b)
                       {
                         char buf [23];
                         sprintf (buf, "a = %hi, b = %i\n", a, (short)b);
                       }

       -Wno-format-zero-length
           If -Wformat is specified, do not warn about zero-length formats.  The C standard specifies that zero-
           length formats are allowed.

       -Wformat-nonliteral
           If  -Wformat  is  specified,  also warn if the format string is not a string literal and so cannot be
           checked, unless the format function takes its format arguments as a "va_list".

       -Wformat-security
           If -Wformat is specified, also warn about uses of format functions that represent  possible  security
           problems.   At  present,  this  warns  about calls to "printf" and "scanf" functions where the format
           string is not a string literal and there are no format arguments, as in "printf (foo);".  This may be
           a security hole if the format string came from untrusted input and contains %n.  (This is currently a
           subset  of  what  -Wformat-nonliteral  warns  about,  but  in  future  warnings  may  be   added   to
           -Wformat-security that are not included in -Wformat-nonliteral.)

       -Wformat-signedness
           If  -Wformat  is  specified,  also  warn  if  the format string requires an unsigned argument and the
           argument is signed and vice versa.

       -Wformat-truncation
       -Wformat-truncation=level
           Warn about calls to formatted input/output functions such as "snprintf" and  "vsnprintf"  that  might
           result  in output truncation.  When the exact number of bytes written by a format directive cannot be
           determined at compile-time it is estimated based on heuristics that depend on the level argument  and
           on optimization.  While enabling optimization will in most cases improve the accuracy of the warning,
           it  may  also  result  in false positives.  Except as noted otherwise, the option uses the same logic
           -Wformat-overflow.

           -Wformat-truncation
           -Wformat-truncation=1
               Level 1 of -Wformat-truncation enabled by -Wformat employs a  conservative  approach  that  warns
               only  about  calls  to  bounded  functions whose return value is unused and that will most likely
               result in output truncation.

           -Wformat-truncation=2
               Level 2 warns also about calls to bounded functions whose return value is  used  and  that  might
               result in truncation given an argument of sufficient length or magnitude.

       -Wformat-y2k
           If -Wformat is specified, also warn about "strftime" formats that may yield only a two-digit year.

       -Wnonnull
           Warn about passing a null pointer for arguments marked as requiring a non-null value by the "nonnull"
           function attribute.

           -Wnonnull is included in -Wall and -Wformat.  It can be disabled with the -Wno-nonnull option.

       -Wnonnull-compare
           Warn  when comparing an argument marked with the "nonnull" function attribute against null inside the
           function.

           -Wnonnull-compare is included in -Wall.  It can be disabled with the -Wno-nonnull-compare option.

       -Wnull-dereference
           Warn if the compiler detects paths that trigger erroneous or undefined behavior due to  dereferencing
           a  null  pointer.   This  option is only active when -fdelete-null-pointer-checks is active, which is
           enabled by optimizations in most targets.  The precision of the warnings depends on the  optimization
           options used.

       -Winit-self (C, C++, Objective-C and Objective-C++ only)
           Warn  about  uninitialized variables that are initialized with themselves.  Note this option can only
           be used with the -Wuninitialized option.

           For example, GCC warns about "i" being uninitialized in the following snippet only  when  -Winit-self
           has been specified:

                   int f()
                   {
                     int i = i;
                     return i;
                   }

           This warning is enabled by -Wall in C++.

       -Wno-implicit-int (C and Objective-C only)
           This option controls warnings when a declaration does not specify a type.  This warning is enabled by
           default in C99 and later dialects of C, and also by -Wall.

       -Wno-implicit-function-declaration (C and Objective-C only)
           This option controls warnings when a function is used before being declared.  This warning is enabled
           by  default  in C99 and later dialects of C, and also by -Wall.  The warning is made into an error by
           -pedantic-errors.

       -Wimplicit (C and Objective-C only)
           Same as -Wimplicit-int and -Wimplicit-function-declaration.  This warning is enabled by -Wall.

       -Wimplicit-fallthrough
           -Wimplicit-fallthrough is the same as -Wimplicit-fallthrough=3 and -Wno-implicit-fallthrough  is  the
           same as -Wimplicit-fallthrough=0.

       -Wimplicit-fallthrough=n
           Warn when a switch case falls through.  For example:

                   switch (cond)
                     {
                     case 1:
                       a = 1;
                       break;
                     case 2:
                       a = 2;
                     case 3:
                       a = 3;
                       break;
                     }

           This  warning does not warn when the last statement of a case cannot fall through, e.g. when there is
           a  return   statement   or   a   call   to   function   declared   with   the   noreturn   attribute.
           -Wimplicit-fallthrough=  also takes into account control flow statements, such as ifs, and only warns
           when appropriate.  E.g.

                   switch (cond)
                     {
                     case 1:
                       if (i > 3) {
                         bar (5);
                         break;
                       } else if (i < 1) {
                         bar (0);
                       } else
                         return;
                     default:
                       ...
                     }

           Since there are occasions where a switch case fall through is desirable, GCC provides  an  attribute,
           "__attribute__  ((fallthrough))",  that  is  to  be used along with a null statement to suppress this
           warning that would normally occur:

                   switch (cond)
                     {
                     case 1:
                       bar (0);
                       __attribute__ ((fallthrough));
                     default:
                       ...
                     }

           C++17 provides a standard way to suppress the -Wimplicit-fallthrough warning using "[[fallthrough]];"
           instead of the GNU attribute.  In C++11 or C++14 users can use "[[gnu::fallthrough]];",  which  is  a
           GNU  extension.   Instead  of  these  attributes, it is also possible to add a fallthrough comment to
           silence the warning.  The whole body of the C or C++ style comment should  match  the  given  regular
           expressions listed below.  The option argument n specifies what kind of comments are accepted:

           *<-Wimplicit-fallthrough=0 disables the warning altogether.>
           *<-Wimplicit-fallthrough=1 matches ".*" regular>
               expression, any comment is used as fallthrough comment.

           *<-Wimplicit-fallthrough=2 case insensitively matches>
               ".*falls?[ \t-]*thr(ough|u).*" regular expression.

           *<-Wimplicit-fallthrough=3 case sensitively matches one of the>
               following regular expressions:

               *<"-fallthrough">
               *<"@fallthrough@">
               *<"lint -fallthrough[ \t]*">
               *<"[ \t.!]*(ELSE,? |INTENTIONAL(LY)? )?FALL(S | |-)?THR(OUGH|U)[ \t.!]*(-[^\n\r]*)?">
               *<"[ \t.!]*(Else,? |Intentional(ly)? )?Fall((s | |-)[Tt]|t)hr(ough|u)[ \t.!]*(-[^\n\r]*)?">
               *<"[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?fall(s | |-)?thr(ough|u)[ \t.!]*(-[^\n\r]*)?">
           *<-Wimplicit-fallthrough=4 case sensitively matches one of the>
               following regular expressions:

               *<"-fallthrough">
               *<"@fallthrough@">
               *<"lint -fallthrough[ \t]*">
               *<"[ \t]*FALLTHR(OUGH|U)[ \t]*">
           *<-Wimplicit-fallthrough=5 doesn't recognize any comments as>
               fallthrough comments, only attributes disable the warning.

           The  comment needs to be followed after optional whitespace and other comments by "case" or "default"
           keywords or by a user label that precedes some "case" or "default" label.

                   switch (cond)
                     {
                     case 1:
                       bar (0);
                       /* FALLTHRU */
                     default:
                       ...
                     }

           The -Wimplicit-fallthrough=3 warning is enabled by -Wextra.

       -Wno-if-not-aligned (C, C++, Objective-C and Objective-C++ only)
           Control if warnings triggered  by  the  "warn_if_not_aligned"  attribute  should  be  issued.   These
           warnings are enabled by default.

       -Wignored-qualifiers (C and C++ only)
           Warn  if  the  return type of a function has a type qualifier such as "const".  For ISO C such a type
           qualifier has no effect, since the value returned by a function is  not  an  lvalue.   For  C++,  the
           warning is only emitted for scalar types or "void".  ISO C prohibits qualified "void" return types on
           function definitions, so such return types always receive a warning even without this option.

           This warning is also enabled by -Wextra.

       -Wno-ignored-attributes (C and C++ only)
           This  option controls warnings when an attribute is ignored.  This is different from the -Wattributes
           option in that it warns whenever the compiler decides to drop an attribute, not that the attribute is
           either unknown, used in a wrong place, etc.  This warning is enabled by default.

       -Wmain
           Warn if the type of "main" is suspicious.   "main"  should  be  a  function  with  external  linkage,
           returning  int,  taking  either  zero  arguments, two, or three arguments of appropriate types.  This
           warning is enabled by default in C++ and is enabled by either -Wall or -Wpedantic.

       -Wmisleading-indentation (C and C++ only)
           Warn when the indentation of the code does not reflect the block structure.  Specifically, a  warning
           is  issued  for  "if",  "else", "while", and "for" clauses with a guarded statement that does not use
           braces, followed by an unguarded statement with the same indentation.

           In the following example, the call to "bar" is misleadingly indented as if it  were  guarded  by  the
           "if" conditional.

                     if (some_condition ())
                       foo ();
                       bar ();  /* Gotcha: this is not guarded by the "if".  */

           In  the  case  of  mixed  tabs and spaces, the warning uses the -ftabstop= option to determine if the
           statements line up (defaulting to 8).

           The warning is not issued for code involving multiline  preprocessor  logic  such  as  the  following
           example.

                     if (flagA)
                       foo (0);
                   #if SOME_CONDITION_THAT_DOES_NOT_HOLD
                     if (flagB)
                   #endif
                       foo (1);

           The  warning  is  not  issued after a "#line" directive, since this typically indicates autogenerated
           code, and no assumptions can be made about the layout of the file that the directive references.

           This warning is enabled by -Wall in C and C++.

       -Wmissing-attributes
           Warn when a declaration of a function is missing one or more attributes that a  related  function  is
           declared with and whose absence may adversely affect the correctness or efficiency of generated code.
           For  example,  the  warning is issued for declarations of aliases that use attributes to specify less
           restrictive requirements than  those  of  their  targets.   This  typically  represents  a  potential
           optimization  opportunity.  By contrast, the -Wattribute-alias=2 option controls warnings issued when
           the alias is more restrictive than the  target,  which  could  lead  to  incorrect  code  generation.
           Attributes  considered include "alloc_align", "alloc_size", "cold", "const", "hot", "leaf", "malloc",
           "nonnull", "noreturn", "nothrow", "pure", "returns_nonnull", and "returns_twice".

           In C++, the warning is issued when an explicit specialization of a  primary  template  declared  with
           attribute   "alloc_align",  "alloc_size",  "assume_aligned",  "format",  "format_arg",  "malloc",  or
           "nonnull" is declared without it.  Attributes  "deprecated",  "error",  and  "warning"  suppress  the
           warning..

           You  can  use  the  "copy"  attribute to apply the same set of attributes to a declaration as that on
           another declaration without explicitly enumerating the attributes. This attribute can be  applied  to
           declarations of functions, variables, or types.

           -Wmissing-attributes is enabled by -Wall.

           For example, since the declaration of the primary function template below makes use of both attribute
           "malloc" and "alloc_size" the declaration of the explicit specialization of the template is diagnosed
           because it is missing one of the attributes.

                   template <class T>
                   T* __attribute__ ((malloc, alloc_size (1)))
                   allocate (size_t);

                   template <>
                   void* __attribute__ ((malloc))   // missing alloc_size
                   allocate<void> (size_t);

       -Wmissing-braces
           Warn  if  an  aggregate  or  union initializer is not fully bracketed.  In the following example, the
           initializer for "a" is not fully bracketed, but that for "b" is fully bracketed.

                   int a[2][2] = { 0, 1, 2, 3 };
                   int b[2][2] = { { 0, 1 }, { 2, 3 } };

           This warning is enabled by -Wall.

       -Wmissing-include-dirs (C, C++, Objective-C and Objective-C++ only)
           Warn if a user-supplied include directory does not exist.

       -Wno-missing-profile
           This option controls warnings if feedback profiles are missing when using the  -fprofile-use  option.
           This  option diagnoses those cases where a new function or a new file is added between compiling with
           -fprofile-generate and with -fprofile-use, without regenerating the profiles.  In  these  cases,  the
           profile  feedback  data  files  do  not  contain any profile feedback information for the newly added
           function or file respectively.  Also, in the case when profile count data (.gcda) files are  removed,
           GCC  cannot  use any profile feedback information.  In all these cases, warnings are issued to inform
           you that a profile generation step is due.  Ignoring the warning can result in poorly optimized code.
           -Wno-missing-profile can be used to disable the warning, but this is not recommended  and  should  be
           done only when non-existent profile data is justified.

       -Wno-mismatched-dealloc
           Warn  for  calls  to  deallocation  functions  with  pointer arguments returned from from allocations
           functions for which the former isn't a suitable deallocator.  A pair of functions can  be  associated
           as  matching  allocators  and  deallocators  by  use  of  attribute "malloc".  Unless disabled by the
           -fno-builtin option the standard functions "calloc", "malloc", "realloc", and "free", as well as  the
           corresponding forms of C++ "operator new" and "operator delete" are implicitly associated as matching
           allocators  and  deallocators.   In the following example "mydealloc" is the deallocator for pointers
           returned from "myalloc".

                   void mydealloc (void*);

                   __attribute__ ((malloc (mydealloc, 1))) void*
                   myalloc (size_t);

                   void f (void)
                   {
                     void *p = myalloc (32);
                     // ...use p...
                     free (p);   // warning: not a matching deallocator for myalloc
                     mydealloc (p);   // ok
                   }

           In C++, the related option -Wmismatched-new-delete diagnoses mismatches  involving  either  "operator
           new" or "operator delete".

           Option -Wmismatched-dealloc is enabled by default.

       -Wmultistatement-macros
           Warn  about  unsafe  multiple  statement  macros  that appear to be guarded by a clause such as "if",
           "else", "for", "switch", or "while", in which only the first statement is actually guarded after  the
           macro is expanded.

           For example:

                   #define DOIT x++; y++
                   if (c)
                     DOIT;

           will  increment  "y"  unconditionally, not just when "c" holds.  The can usually be fixed by wrapping
           the macro in a do-while loop:

                   #define DOIT do { x++; y++; } while (0)
                   if (c)
                     DOIT;

           This warning is enabled by -Wall in C and C++.

       -Wparentheses
           Warn if parentheses are omitted in certain contexts, such as when there is an assignment in a context
           where a truth value is expected, or when operators are  nested  whose  precedence  people  often  get
           confused about.

           Also  warn if a comparison like "x<=y<=z" appears; this is equivalent to "(x<=y ? 1 : 0) <= z", which
           is a different interpretation from that of ordinary mathematical notation.

           Also warn for dangerous uses of the GNU extension to "?:"  with  omitted  middle  operand.  When  the
           condition  in  the  "?":  operator  is  a  boolean  expression, the omitted value is always 1.  Often
           programmers expect it to be a value computed inside the conditional expression instead.

           For C++ this also warns for some cases of unnecessary parentheses in declarations, which can indicate
           an attempt at a function call instead of a declaration:

                   {
                     // Declares a local variable called mymutex.
                     std::unique_lock<std::mutex> (mymutex);
                     // User meant std::unique_lock<std::mutex> lock (mymutex);
                   }

           This warning is enabled by -Wall.

       -Wsequence-point
           Warn about code that may have undefined semantics because of violations of sequence  point  rules  in
           the C and C++ standards.

           The  C  and  C++  standards define the order in which expressions in a C/C++ program are evaluated in
           terms of sequence points, which represent a partial ordering between the execution of  parts  of  the
           program:  those  executed  before the sequence point, and those executed after it.  These occur after
           the evaluation of a full expression (one which is  not  part  of  a  larger  expression),  after  the
           evaluation  of the first operand of a "&&", "||", "? :" or "," (comma) operator, before a function is
           called (but after the evaluation of its arguments and the expression denoting the  called  function),
           and  in  certain  other  places.   Other  than as expressed by the sequence point rules, the order of
           evaluation of subexpressions of an expression is not specified.  All  these  rules  describe  only  a
           partial  order  rather than a total order, since, for example, if two functions are called within one
           expression with no sequence point between them, the order in which the functions are  called  is  not
           specified.  However, the standards committee have ruled that function calls do not overlap.

           It  is not specified when between sequence points modifications to the values of objects take effect.
           Programs whose behavior depends on this have undefined behavior; the C and C++ standards specify that
           "Between the previous and next sequence point an object shall have its stored value modified at  most
           once  by  the  evaluation  of  an  expression.   Furthermore,  the  prior value shall be read only to
           determine the value to be stored.".  If a program breaks these rules, the results on  any  particular
           implementation are entirely unpredictable.

           Examples  of  code  with  undefined behavior are "a = a++;", "a[n] = b[n++]" and "a[i++] = i;".  Some
           more complicated cases are not diagnosed by this option, and it may give an occasional false positive
           result, but in general it has been found fairly effective  at  detecting  this  sort  of  problem  in
           programs.

           The  C++17  standard  will define the order of evaluation of operands in more cases: in particular it
           requires that the right-hand side of an assignment be evaluated before the  left-hand  side,  so  the
           above  examples  are no longer undefined.  But this option will still warn about them, to help people
           avoid writing code that is undefined in C and earlier revisions of C++.

           The standard is worded confusingly, therefore there is some debate over the precise  meaning  of  the
           sequence point rules in subtle cases.  Links to discussions of the problem, including proposed formal
           definitions, may be found on the GCC readings page, at <http://gcc.gnu.org/readings.html>.

           This warning is enabled by -Wall for C and C++.

       -Wno-return-local-addr
           Do  not  warn about returning a pointer (or in C++, a reference) to a variable that goes out of scope
           after the function returns.

       -Wreturn-type
           Warn whenever a function is defined with a return type that defaults to "int".  Also warn  about  any
           "return"  statement  with  no return value in a function whose return type is not "void" (falling off
           the end of the function body is considered returning without a value).

           For C only, warn about a "return" statement with an expression in a function  whose  return  type  is
           "void",  unless  the expression type is also "void".  As a GNU extension, the latter case is accepted
           without a warning unless -Wpedantic is used.  Attempting to use the  return  value  of  a  non-"void"
           function other than "main" that flows off the end by reaching the closing curly brace that terminates
           the function is undefined.

           Unlike  in  C,  in  C++,  flowing  off  the end of a non-"void" function other than "main" results in
           undefined behavior even when the value of the function is not used.

           This warning is enabled by default in C++ and by -Wall otherwise.

       -Wno-shift-count-negative
           Controls warnings if a shift count is negative.  This warning is enabled by default.

       -Wno-shift-count-overflow
           Controls warnings if a shift count is greater than or equal to the  bit  width  of  the  type.   This
           warning is enabled by default.

       -Wshift-negative-value
           Warn  if  left  shifting a negative value.  This warning is enabled by -Wextra in C99 (and newer) and
           C++11 to C++17 modes.

       -Wno-shift-overflow
       -Wshift-overflow=n
           These options control warnings about left shift overflows.

           -Wshift-overflow=1
               This is the warning level of -Wshift-overflow and is enabled by default in C99  and  C++11  modes
               (and  newer).   This  warning  level  does  not  warn  about  left-shifting  1 into the sign bit.
               (However, in C, such an overflow  is  still  rejected  in  contexts  where  an  integer  constant
               expression  is required.)  No warning is emitted in C++20 mode (and newer), as signed left shifts
               always wrap.

           -Wshift-overflow=2
               This warning level also warns about left-shifting 1 into the sign  bit,  unless  C++14  mode  (or
               newer) is active.

       -Wswitch
           Warn whenever a "switch" statement has an index of enumerated type and lacks a "case" for one or more
           of  the  named codes of that enumeration.  (The presence of a "default" label prevents this warning.)
           "case" labels outside the enumeration range also provoke warnings when this option is used  (even  if
           there is a "default" label).  This warning is enabled by -Wall.

       -Wswitch-default
           Warn whenever a "switch" statement does not have a "default" case.

       -Wswitch-enum
           Warn whenever a "switch" statement has an index of enumerated type and lacks a "case" for one or more
           of  the  named  codes  of that enumeration.  "case" labels outside the enumeration range also provoke
           warnings when this option is used.  The only difference between -Wswitch and this option is that this
           option gives a warning about an omitted enumeration code even if there is a "default" label.

       -Wno-switch-bool
           Do not warn when a "switch" statement has an index of boolean type and the case  values  are  outside
           the  range  of  a  boolean  type.  It is possible to suppress this warning by casting the controlling
           expression to a type other than "bool".  For example:

                   switch ((int) (a == 4))
                     {
                     ...
                     }

           This warning is enabled by default for C and C++ programs.

       -Wno-switch-outside-range
           This option controls warnings when a "switch" case has a value that is outside of its respective type
           range.  This warning is enabled by default for C and C++ programs.

       -Wno-switch-unreachable
           Do not warn when a "switch" statement contains statements between the controlling expression and  the
           first case label, which will never be executed.  For example:

                   switch (cond)
                     {
                      i = 15;
                     ...
                      case 5:
                     ...
                     }

           -Wswitch-unreachable  does not warn if the statement between the controlling expression and the first
           case label is just a declaration:

                   switch (cond)
                     {
                      int i;
                     ...
                      case 5:
                      i = 5;
                     ...
                     }

           This warning is enabled by default for C and C++ programs.

       -Wsync-nand (C and C++ only)
           Warn when "__sync_fetch_and_nand" and "__sync_nand_and_fetch" built-in  functions  are  used.   These
           functions changed semantics in GCC 4.4.

       -Wunused-but-set-parameter
           Warn whenever a function parameter is assigned to, but otherwise unused (aside from its declaration).

           To suppress this warning use the "unused" attribute.

           This warning is also enabled by -Wunused together with -Wextra.

       -Wunused-but-set-variable
           Warn  whenever  a  local  variable is assigned to, but otherwise unused (aside from its declaration).
           This warning is enabled by -Wall.

           To suppress this warning use the "unused" attribute.

           This warning is also enabled by -Wunused, which is enabled by -Wall.

       -Wunused-function
           Warn whenever a static function is declared but not  defined  or  a  non-inline  static  function  is
           unused.  This warning is enabled by -Wall.

       -Wunused-label
           Warn whenever a label is declared but not used.  This warning is enabled by -Wall.

           To suppress this warning use the "unused" attribute.

       -Wunused-local-typedefs (C, Objective-C, C++ and Objective-C++ only)
           Warn when a typedef locally defined in a function is not used.  This warning is enabled by -Wall.

       -Wunused-parameter
           Warn whenever a function parameter is unused aside from its declaration.

           To suppress this warning use the "unused" attribute.

       -Wno-unused-result
           Do  not  warn  if  a caller of a function marked with attribute "warn_unused_result" does not use its
           return value. The default is -Wunused-result.

       -Wunused-variable
           Warn whenever a local or static variable is unused aside from its declaration.  This  option  implies
           -Wunused-const-variable=1 for C, but not for C++. This warning is enabled by -Wall.

           To suppress this warning use the "unused" attribute.

       -Wunused-const-variable
       -Wunused-const-variable=n
           Warn    whenever   a   constant   static   variable   is   unused   aside   from   its   declaration.
           -Wunused-const-variable=1 is enabled by -Wunused-variable for C, but not for C++. In C this  declares
           variable storage, but in C++ this is not an error since const variables take the place of "#define"s.

           To suppress this warning use the "unused" attribute.

           -Wunused-const-variable=1
               This is the warning level that is enabled by -Wunused-variable for C.  It warns only about unused
               static const variables defined in the main compilation unit, but not about static const variables
               declared in any header included.

           -Wunused-const-variable=2
               This  warning  level also warns for unused constant static variables in headers (excluding system
               headers).  This is the warning level of -Wunused-const-variable and must be explicitly  requested
               since in C++ this isn't an error and in C it might be harder to clean up all headers included.

       -Wunused-value
           Warn  whenever  a  statement  computes a result that is explicitly not used. To suppress this warning
           cast the unused expression to "void". This includes an expression-statement or the left-hand side  of
           a  comma expression that contains no side effects. For example, an expression such as "x[i,j]" causes
           a warning, while "x[(void)i,j]" does not.

           This warning is enabled by -Wall.

       -Wunused
           All the above -Wunused options combined.

           In order to get a warning about an  unused  function  parameter,  you  must  either  specify  -Wextra
           -Wunused (note that -Wall implies -Wunused), or separately specify -Wunused-parameter.

       -Wuninitialized
           Warn  if  an  object  with  automatic  or  allocated  storage  duration  is  used without having been
           initialized.  In C++, also warn if a non-static reference or non-static "const" member appears  in  a
           class without constructors.

           In  addition,  passing  a  pointer  (or  in  C++,  a  reference)  to  an  uninitialized  object  to a
           "const"-qualified argument of a built-in function known to read the object is also diagnosed by  this
           warning.  (-Wmaybe-uninitialized is issued for ordinary functions.)

           If  you  want  to  warn  about  code  that  uses  the  uninitialized value of the variable in its own
           initializer, use the -Winit-self option.

           These warnings occur for individual uninitialized elements of structure, union or array variables  as
           well as for variables that are uninitialized as a whole.  They do not occur for variables or elements
           declared  "volatile".  Because these warnings depend on optimization, the exact variables or elements
           for which there are warnings depend on the precise optimization options and version of GCC used.

           Note that there may be no warning about a variable that is used only to compute a value  that  itself
           is never used, because such computations may be deleted by data flow analysis before the warnings are
           printed.

       -Wno-invalid-memory-model
           This  option  controls  warnings  for  invocations of __atomic Builtins, __sync Builtins, and the C11
           atomic generic functions with a memory consistency argument that is either invalid for the  operation
           or  outside  the  range  of  values  of  the  "memory_order"  enumeration.   For  example,  since the
           "__atomic_store" and "__atomic_store_n" built-ins are only defined  for  the  relaxed,  release,  and
           sequentially consistent memory orders the following code is diagnosed:

                   void store (int *i)
                   {
                     __atomic_store_n (i, 0, memory_order_consume);
                   }

           -Winvalid-memory-model is enabled by default.

       -Wmaybe-uninitialized
           For  an object with automatic or allocated storage duration, if there exists a path from the function
           entry to a use of the object that is initialized, but there exist some  other  paths  for  which  the
           object  is  not  initialized, the compiler emits a warning if it cannot prove the uninitialized paths
           are not executed at run time.

           In addition,  passing  a  pointer  (or  in  C++,  a  reference)  to  an  uninitialized  object  to  a
           "const"-qualified  function  argument  is also diagnosed by this warning.  (-Wuninitialized is issued
           for built-in functions known to read the object.)  Annotating the  function  with  attribute  "access
           (none)" indicates that the argument isn't used to access the object and avoids the warning.

           These warnings are only possible in optimizing compilation, because otherwise GCC does not keep track
           of the state of variables.

           These warnings are made optional because GCC may not be able to determine when the code is correct in
           spite of appearing to have an error.  Here is one example of how this can happen:

                   {
                     int x;
                     switch (y)
                       {
                       case 1: x = 1;
                         break;
                       case 2: x = 4;
                         break;
                       case 3: x = 5;
                       }
                     foo (x);
                   }

           If  the  value of "y" is always 1, 2 or 3, then "x" is always initialized, but GCC doesn't know this.
           To suppress the warning, you need to provide a default case with assert(0) or similar code.

           This option also warns when a  non-volatile  automatic  variable  might  be  changed  by  a  call  to
           "longjmp".   The  compiler  sees  only the calls to "setjmp".  It cannot know where "longjmp" will be
           called; in fact, a signal handler could call it at any point in the code.  As a result, you may get a
           warning even when there is in fact no problem because "longjmp" cannot in fact be called at the place
           that would cause a problem.

           Some spurious warnings can be avoided if you declare all the functions you use that never  return  as
           "noreturn".

           This warning is enabled by -Wall or -Wextra.

       -Wunknown-pragmas
           Warn  when  a "#pragma" directive is encountered that is not understood by GCC.  If this command-line
           option is used, warnings are even issued for unknown pragmas in system header files.  This is not the
           case if the warnings are only enabled by the -Wall command-line option.

       -Wno-pragmas
           Do not warn about misuses of pragmas, such as incorrect  parameters,  invalid  syntax,  or  conflicts
           between pragmas.  See also -Wunknown-pragmas.

       -Wno-prio-ctor-dtor
           Do  not  warn  if  a  priority  from  0  to  100  is  used for constructor or destructor.  The use of
           constructor and destructor attributes allow you to assign a priority to the constructor/destructor to
           control its order of execution before "main" is called or after it returns.  The priority values must
           be greater than 100 as the compiler reserves priority values between 0--100 for the implementation.

       -Wstrict-aliasing
           This option is only active when -fstrict-aliasing is active.  It warns about code  that  might  break
           the  strict  aliasing  rules that the compiler is using for optimization.  The warning does not catch
           all cases, but does attempt to catch the more common pitfalls.  It  is  included  in  -Wall.   It  is
           equivalent to -Wstrict-aliasing=3

       -Wstrict-aliasing=n
           This  option  is  only active when -fstrict-aliasing is active.  It warns about code that might break
           the strict aliasing rules that the compiler is using for optimization.  Higher levels  correspond  to
           higher  accuracy  (fewer  false positives).  Higher levels also correspond to more effort, similar to
           the way -O works.  -Wstrict-aliasing is equivalent to -Wstrict-aliasing=3.

           Level 1: Most aggressive, quick, least accurate.  Possibly useful when higher levels do not warn  but
           -fstrict-aliasing  still  breaks  the code, as it has very few false negatives.  However, it has many
           false positives.  Warns for all pointer conversions between  possibly  incompatible  types,  even  if
           never dereferenced.  Runs in the front end only.

           Level  2:  Aggressive,  quick,  not too precise.  May still have many false positives (not as many as
           level 1 though), and few false negatives (but possibly more than level 1).  Unlike level 1,  it  only
           warns when an address is taken.  Warns about incomplete types.  Runs in the front end only.

           Level  3  (default  for  -Wstrict-aliasing):  Should  have  very  few  false  positives and few false
           negatives.  Slightly slower than levels 1 or 2 when optimization  is  enabled.   Takes  care  of  the
           common  pun+dereference  pattern in the front end: "*(int*)&some_float".  If optimization is enabled,
           it also runs in the back end, where it deals  with  multiple  statement  cases  using  flow-sensitive
           points-to  information.   Only warns when the converted pointer is dereferenced.  Does not warn about
           incomplete types.

       -Wstrict-overflow
       -Wstrict-overflow=n
           This option is only active when signed overflow  is  undefined.   It  warns  about  cases  where  the
           compiler  optimizes  based  on the assumption that signed overflow does not occur.  Note that it does
           not warn about all cases where the code might overflow: it only warns about cases where the  compiler
           implements some optimization.  Thus this warning depends on the optimization level.

           An  optimization  that assumes that signed overflow does not occur is perfectly safe if the values of
           the variables involved are such that overflow never does, in fact, occur.  Therefore this warning can
           easily give a false positive: a warning about code that is not actually a problem.  To help focus  on
           important  issues,  several  warning  levels  are  defined.   No  warnings  are issued for the use of
           undefined signed overflow when estimating how many iterations a loop  requires,  in  particular  when
           determining whether a loop will be executed at all.

           -Wstrict-overflow=1
               Warn  about  cases  that  are  both  questionable  and  easy  to avoid.  For example the compiler
               simplifies "x + 1 > x" to 1.  This level of -Wstrict-overflow is enabled by -Wall; higher  levels
               are not, and must be explicitly requested.

           -Wstrict-overflow=2
               Also  warn  about  other cases where a comparison is simplified to a constant.  For example: "abs
               (x) >= 0".  This can only be simplified when signed integer overflow is undefined,  because  "abs
               (INT_MIN)" overflows to "INT_MIN", which is less than zero.  -Wstrict-overflow (with no level) is
               the same as -Wstrict-overflow=2.

           -Wstrict-overflow=3
               Also  warn  about  other  cases  where  a  comparison is simplified.  For example: "x + 1 > 1" is
               simplified to "x > 0".

           -Wstrict-overflow=4
               Also warn about other simplifications not covered by the above cases.  For example: "(x *  10)  /
               5" is simplified to "x * 2".

           -Wstrict-overflow=5
               Also  warn  about  cases  where  the  compiler  reduces the magnitude of a constant involved in a
               comparison.  For example: "x + 2 > y" is simplified to "x + 1 >= y".  This is  reported  only  at
               the  highest  warning  level  because  this  simplification  applies to many comparisons, so this
               warning level gives a very large number of false positives.

       -Wstring-compare
           Warn for calls to "strcmp" and "strncmp" whose result is determined to be either zero or non-zero  in
           tests  for such equality owing to the length of one argument being greater than the size of the array
           the other argument is stored in (or the bound in  the  case  of  "strncmp").   Such  calls  could  be
           mistakes.   For  example,  the  call to "strcmp" below is diagnosed because its result is necessarily
           non-zero irrespective of the contents of the array "a".

                   extern char a[4];
                   void f (char *d)
                   {
                     strcpy (d, "string");
                     ...
                     if (0 == strcmp (a, d))   // cannot be true
                       puts ("a and d are the same");
                   }

           -Wstring-compare is enabled by -Wextra.

       -Wno-stringop-overflow
       -Wstringop-overflow
       -Wstringop-overflow=type
           Warn for calls to string manipulation functions such as "memcpy" and "strcpy" that are determined  to
           overflow  the  destination buffer.  The optional argument is one greater than the type of Object Size
           Checking to perform to determine the size of the destination.  The argument is  meaningful  only  for
           functions  that  operate  on  character  arrays  but not for raw memory functions like "memcpy" which
           always make use of Object Size type-0.  The option also warns for calls that specify a size in excess
           of the largest possible object or at most "SIZE_MAX / 2" bytes.  The option produces the best results
           with optimization enabled but can detect a small subset  of  simple  buffer  overflows  even  without
           optimization  in  calls  to the GCC built-in functions like "__builtin_memcpy" that correspond to the
           standard functions.  In any case, the option warns about just a subset of buffer  overflows  detected
           by  the  corresponding overflow checking built-ins.  For example, the option issues a warning for the
           "strcpy" call below because it copies  at  least  5  characters  (the  string  "blue"  including  the
           terminating NUL) into the buffer of size 4.

                   enum Color { blue, purple, yellow };
                   const char* f (enum Color clr)
                   {
                     static char buf [4];
                     const char *str;
                     switch (clr)
                       {
                         case blue: str = "blue"; break;
                         case purple: str = "purple"; break;
                         case yellow: str = "yellow"; break;
                       }

                     return strcpy (buf, str);   // warning here
                   }

           Option -Wstringop-overflow=2 is enabled by default.

           -Wstringop-overflow
           -Wstringop-overflow=1
               The  -Wstringop-overflow=1  option  uses type-zero Object Size Checking to determine the sizes of
               destination objects.  At this setting the option does  not  warn  for  writes  past  the  end  of
               subobjects  of  larger  objects  accessed  by pointers unless the size of the largest surrounding
               object is known.  When the destination may be one of several objects it  is  assumed  to  be  the
               largest  one  of them.  On Linux systems, when optimization is enabled at this setting the option
               warns for the same code as when the "_FORTIFY_SOURCE" macro is defined to a non-zero value.

           -Wstringop-overflow=2
               The -Wstringop-overflow=2 option uses type-one Object Size Checking to  determine  the  sizes  of
               destination objects.  At this setting the option warns about overflows when writing to members of
               the  largest complete objects whose exact size is known.  However, it does not warn for excessive
               writes to the same members of unknown objects referenced by pointers  since  they  may  point  to
               arrays containing unknown numbers of elements.  This is the default setting of the option.

           -Wstringop-overflow=3
               The  -Wstringop-overflow=3  option  uses  type-two Object Size Checking to determine the sizes of
               destination objects.  At this setting the option warns about overflowing the smallest  object  or
               data  member.  This is the most restrictive setting of the option that may result in warnings for
               safe code.

           -Wstringop-overflow=4
               The -Wstringop-overflow=4 option uses type-three Object Size Checking to determine the  sizes  of
               destination  objects.   At  this setting the option warns about overflowing any data members, and
               when the destination is one of several objects it uses the size of the largest of them to  decide
               whether  to  issue  a warning.  Similarly to -Wstringop-overflow=3 this setting of the option may
               result in warnings for benign code.

       -Wno-stringop-overread
           Warn for calls to string manipulation functions such as "memchr", or "strcpy" that are determined  to
           read past the end of the source sequence.

           Option -Wstringop-overread is enabled by default.

       -Wno-stringop-truncation
           Do  not  warn  for  calls  to bounded string manipulation functions such as "strncat", "strncpy", and
           "stpncpy" that may either truncate the copied string or leave the destination unchanged.

           In the following example, the call to "strncat" specifies a bound that is less than the length of the
           source string.  As a result, the copy of the source will be truncated and so the call  is  diagnosed.
           To avoid the warning use "bufsize - strlen (buf) - 1)" as the bound.

                   void append (char *buf, size_t bufsize)
                   {
                     strncat (buf, ".txt", 3);
                   }

           As  another  example,  the  following call to "strncpy" results in copying to "d" just the characters
           preceding the terminating NUL, without appending  the  NUL  to  the  end.   Assuming  the  result  of
           "strncpy"  is  necessarily a NUL-terminated string is a common mistake, and so the call is diagnosed.
           To avoid the warning when the result is not expected to be NUL-terminated, call "memcpy" instead.

                   void copy (char *d, const char *s)
                   {
                     strncpy (d, s, strlen (s));
                   }

           In the following example, the call to "strncpy" specifies the size of the destination buffer  as  the
           bound.   If  the  length of the source string is equal to or greater than this size the result of the
           copy will not be NUL-terminated.  Therefore, the call is  also  diagnosed.   To  avoid  the  warning,
           specify "sizeof buf - 1" as the bound and set the last element of the buffer to "NUL".

                   void copy (const char *s)
                   {
                     char buf[80];
                     strncpy (buf, s, sizeof buf);
                     ...
                   }

           In  situations  where  a character array is intended to store a sequence of bytes with no terminating
           "NUL" such an array may be annotated with attribute "nonstring" to avoid this warning.  Such  arrays,
           however,  are  not  suitable  arguments  to  functions that expect "NUL"-terminated strings.  To help
           detect accidental misuses of such arrays GCC issues warnings unless it can  prove  that  the  use  is
           safe.

       -Wsuggest-attribute=[pure|const|noreturn|format|cold|malloc]
           Warn  for  cases  where adding an attribute may be beneficial. The attributes currently supported are
           listed below.

           -Wsuggest-attribute=pure
           -Wsuggest-attribute=const
           -Wsuggest-attribute=noreturn
           -Wmissing-noreturn
           -Wsuggest-attribute=malloc
               Warn about functions that might be candidates for attributes "pure",  "const"  or  "noreturn"  or
               "malloc".  The  compiler  only  warns for functions visible in other compilation units or (in the
               case of "pure" and "const") if it cannot prove that the function  returns  normally.  A  function
               returns normally if it doesn't contain an infinite loop or return abnormally by throwing, calling
               "abort" or trapping.  This analysis requires option -fipa-pure-const, which is enabled by default
               at -O and higher.  Higher optimization levels improve the accuracy of the analysis.

           -Wsuggest-attribute=format
           -Wmissing-format-attribute
               Warn  about  function  pointers that might be candidates for "format" attributes.  Note these are
               only possible candidates, not absolute ones.  GCC guesses that function  pointers  with  "format"
               attributes  that  are  used in assignment, initialization, parameter passing or return statements
               should have a corresponding "format" attribute in the resulting type.  I.e. the left-hand side of
               the assignment or initialization, the type of the parameter variable, or the return type  of  the
               containing function respectively should also have a "format" attribute to avoid the warning.

               GCC  also  warns  about  function  definitions  that might be candidates for "format" attributes.
               Again, these are only possible  candidates.   GCC  guesses  that  "format"  attributes  might  be
               appropriate for any function that calls a function like "vprintf" or "vscanf", but this might not
               always  be  the case, and some functions for which "format" attributes are appropriate may not be
               detected.

           -Wsuggest-attribute=cold
               Warn about functions that might be candidates for "cold" attribute.   This  is  based  on  static
               detection and generally only warns about functions which always leads to a call to another "cold"
               function such as wrappers of C++ "throw" or fatal error reporting functions leading to "abort".

       -Walloc-zero
           Warn  about  calls  to  allocation  functions decorated with attribute "alloc_size" that specify zero
           bytes, including those to the built-in forms of the functions  "aligned_alloc",  "alloca",  "calloc",
           "malloc",  and  "realloc".   Because  the  behavior  of  these functions when called with a zero size
           differs among implementations (and in the case of "realloc" has been deprecated) relying  on  it  may
           result in subtle portability bugs and should be avoided.

       -Walloc-size-larger-than=byte-size
           Warn  about calls to functions decorated with attribute "alloc_size" that attempt to allocate objects
           larger than the specified number of bytes, or where the result of the size computation in an  integer
           type   with   infinite   precision   would   exceed   the   value   of  PTRDIFF_MAX  on  the  target.
           -Walloc-size-larger-than=PTRDIFF_MAX is enabled by default.  Warnings controlled by the option can be
           disabled either by specifying byte-size of SIZE_MAX or more or by -Wno-alloc-size-larger-than.

       -Wno-alloc-size-larger-than
           Disable     -Walloc-size-larger-than=     warnings.      The     option     is     equivalent      to
           -Walloc-size-larger-than=SIZE_MAX or larger.

       -Walloca
           This option warns on all uses of "alloca" in the source.

       -Walloca-larger-than=byte-size
           This  option  warns on calls to "alloca" with an integer argument whose value is either zero, or that
           is not bounded by a controlling predicate that limits its value to at most byte-size.  It also  warns
           for  calls  to  "alloca"  where  the  bound  value  is  unknown.   Arguments of non-integer types are
           considered unbounded even if they appear to be constrained to the expected range.

           For example, a bounded case of "alloca" could be:

                   void func (size_t n)
                   {
                     void *p;
                     if (n <= 1000)
                       p = alloca (n);
                     else
                       p = malloc (n);
                     f (p);
                   }

           In the above example, passing "-Walloca-larger-than=1000" would not issue a warning because the  call
           to  "alloca"  is known to be at most 1000 bytes.  However, if "-Walloca-larger-than=500" were passed,
           the compiler would emit a warning.

           Unbounded uses, on the other hand, are uses of "alloca" with no  controlling  predicate  constraining
           its integer argument.  For example:

                   void func ()
                   {
                     void *p = alloca (n);
                     f (p);
                   }

           If  "-Walloca-larger-than=500"  were passed, the above would trigger a warning, but this time because
           of the lack of bounds checking.

           Note, that even seemingly correct code involving signed integers could cause a warning:

                   void func (signed int n)
                   {
                     if (n < 500)
                       {
                         p = alloca (n);
                         f (p);
                       }
                   }

           In the above example, n could be negative, causing a larger than expected argument to  be  implicitly
           cast into the "alloca" call.

           This option also warns when "alloca" is used in a loop.

           -Walloca-larger-than=PTRDIFF_MAX is enabled by default but is usually only effective  when -ftree-vrp
           is active (default for -O2 and above).

           See also -Wvla-larger-than=byte-size.

       -Wno-alloca-larger-than
           Disable -Walloca-larger-than= warnings.  The option is equivalent to -Walloca-larger-than=SIZE_MAX or
           larger.

       -Warith-conversion
           Do warn about implicit conversions from arithmetic operations even when conversion of the operands to
           the   same   type   cannot   change   their   values.    This  affects  warnings  from  -Wconversion,
           -Wfloat-conversion, and -Wsign-conversion.

                   void f (char c, int i)
                   {
                     c = c + i; // warns with B<-Wconversion>
                     c = c + 1; // only warns with B<-Warith-conversion>
                   }

       -Warray-bounds
       -Warray-bounds=n
           This option is only active when -ftree-vrp is active (default for -O2  and  above).  It  warns  about
           subscripts to arrays that are always out of bounds. This warning is enabled by -Wall.

           -Warray-bounds=1
               This  is  the warning level of -Warray-bounds and is enabled by -Wall; higher levels are not, and
               must be explicitly requested.

           -Warray-bounds=2
               This warning level also warns about out of bounds access for arrays at the end of  a  struct  and
               for  arrays  accessed  through  pointers.  This  warning  level may give a larger number of false
               positives and is deactivated by default.

       -Warray-parameter
       -Warray-parameter=n
           Warn about redeclarations of functions involving arguments of array or pointer types of  inconsistent
           kinds  or  forms,  and  enable the detection of out-of-bounds accesses to such parameters by warnings
           such as -Warray-bounds.

           If the first function declaration uses the array form the bound specified in the array is assumed  to
           be  the  minimum  number of elements expected to be provided in calls to the function and the maximum
           number of elements accessed by it.  Failing to provide arguments of sufficient size or accessing more
           than the maximum number of elements may be diagnosed by warnings such as -Warray-bounds.  At level  1
           the  warning  diagnoses  inconsistencies  involving array parameters declared using the "T[static N]"
           form.

           For example, the warning triggers for the following redeclarations because the first  one  allows  an
           array  of  any size to be passed to "f" while the second one with the keyword "static" specifies that
           the array argument must have at least four elements.

                   void f (int[static 4]);
                   void f (int[]);           // warning (inconsistent array form)

                   void g (void)
                   {
                     int *p = (int *)malloc (4);
                     f (p);                  // warning (array too small)
                     ...
                   }

           At level 2 the warning also triggers for redeclarations involving any other inconsistency in array or
           pointer argument forms denoting array sizes.  Pointers and arrays of unspecified bound are considered
           equivalent and do not trigger a warning.

                   void g (int*);
                   void g (int[]);     // no warning
                   void g (int[8]);    // warning (inconsistent array bound)

           -Warray-parameter=2 is included in -Wall.  The -Wvla-parameter option triggers warnings  for  similar
           inconsistencies involving Variable Length Array arguments.

       -Wattribute-alias=n
       -Wno-attribute-alias
           Warn  about  declarations  using the "alias" and similar attributes whose target is incompatible with
           the type of the alias.

           -Wattribute-alias=1
               The default warning level of the -Wattribute-alias option diagnoses incompatibilities between the
               type of the alias declaration and that of  its  target.   Such  incompatibilities  are  typically
               indicative of bugs.

           -Wattribute-alias=2
               At  this  level  -Wattribute-alias  also  diagnoses  cases  where  the  attributes  of  the alias
               declaration are more restrictive than the attributes applied to its target.  These mismatches can
               potentially result in incorrect code generation.  In other cases they may be benign and could  be
               resolved  simply  by  adding  the  missing  attribute  to  the  target.   For comparison, see the
               -Wmissing-attributes option, which controls  diagnostics  when  the  alias  declaration  is  less
               restrictive than the target, rather than more restrictive.

               Attributes  considered  include  "alloc_align",  "alloc_size",  "cold",  "const",  "hot", "leaf",
               "malloc", "nonnull", "noreturn", "nothrow", "pure", "returns_nonnull", and "returns_twice".

           -Wattribute-alias is equivalent to -Wattribute-alias=1.  This is the default.  You can disable  these
           warnings with either -Wno-attribute-alias or -Wattribute-alias=0.

       -Wbool-compare
           Warn  about  boolean  expression  compared  with an integer value different from "true"/"false".  For
           instance, the following comparison is always false:

                   int n = 5;
                   ...
                   if ((n > 1) == 2) { ... }

           This warning is enabled by -Wall.

       -Wbool-operation
           Warn about suspicious operations on expressions of a boolean type.  For instance, bitwise negation of
           a boolean is very likely a bug in the program.  For C, this warning also warns about incrementing  or
           decrementing a boolean, which rarely makes sense.  (In C++, decrementing a boolean is always invalid.
           Incrementing a boolean is invalid in C++17, and deprecated otherwise.)

           This warning is enabled by -Wall.

       -Wduplicated-branches
           Warn when an if-else has identical branches.  This warning detects cases like

                   if (p != NULL)
                     return 0;
                   else
                     return 0;

           It  doesn't  warn  when  both  branches  contain  just  a null statement.  This warning also warn for
           conditional operators:

                     int i = x ? *p : *p;

       -Wduplicated-cond
           Warn about duplicated conditions in an if-else-if chain.  For instance, warn for the following code:

                   if (p->q != NULL) { ... }
                   else if (p->q != NULL) { ... }

       -Wframe-address
           Warn when the __builtin_frame_address or __builtin_return_address is called with an argument  greater
           than 0.  Such calls may return indeterminate values or crash the program.  The warning is included in
           -Wall.

       -Wno-discarded-qualifiers (C and Objective-C only)
           Do  not  warn if type qualifiers on pointers are being discarded.  Typically, the compiler warns if a
           "const char *" variable is passed to a function that takes a "char *" parameter.  This option can  be
           used to suppress such a warning.

       -Wno-discarded-array-qualifiers (C and Objective-C only)
           Do  not  warn if type qualifiers on arrays which are pointer targets are being discarded.  Typically,
           the compiler warns if a "const int (*)[]" variable is passed to a function that takes a  "int  (*)[]"
           parameter.  This option can be used to suppress such a warning.

       -Wno-incompatible-pointer-types (C and Objective-C only)
           Do  not  warn when there is a conversion between pointers that have incompatible types.  This warning
           is for cases not covered by -Wno-pointer-sign, which warns for pointer argument passing or assignment
           with different signedness.

       -Wno-int-conversion (C and Objective-C only)
           Do not warn about incompatible integer to pointer and pointer to integer conversions.   This  warning
           is  about  implicit  conversions;  for explicit conversions the warnings -Wno-int-to-pointer-cast and
           -Wno-pointer-to-int-cast may be used.

       -Wzero-length-bounds
           Warn about accesses to elements of zero-length array members that might overlap other members of  the
           same  object.   Declaring  interior  zero-length  arrays  is discouraged because accesses to them are
           undefined.  See

           For example, the first two stores in function "bad" are diagnosed because the array elements  overlap
           the  subsequent  members  "b"  and "c".  The third store is diagnosed by -Warray-bounds because it is
           beyond the bounds of the enclosing object.

                   struct X { int a[0]; int b, c; };
                   struct X x;

                   void bad (void)
                   {
                     x.a[0] = 0;   // -Wzero-length-bounds
                     x.a[1] = 1;   // -Wzero-length-bounds
                     x.a[2] = 2;   // -Warray-bounds
                   }

           Option -Wzero-length-bounds is enabled by -Warray-bounds.

       -Wno-div-by-zero
           Do not warn about compile-time integer division by zero.  Floating-point  division  by  zero  is  not
           warned about, as it can be a legitimate way of obtaining infinities and NaNs.

       -Wsystem-headers
           Print warning messages for constructs found in system header files.  Warnings from system headers are
           normally suppressed, on the assumption that they usually do not indicate real problems and would only
           make  the  compiler output harder to read.  Using this command-line option tells GCC to emit warnings
           from system headers as if they occurred in user code.  However, note that using -Wall in  conjunction
           with  this option does not warn about unknown pragmas in system headers---for that, -Wunknown-pragmas
           must also be used.

       -Wtautological-compare
           Warn if a self-comparison always evaluates to true or false.  This warning detects  various  mistakes
           such as:

                   int i = 1;
                   ...
                   if (i > i) { ... }

           This  warning  also  warns  about  bitwise  comparisons  that  always  evaluate to true or false, for
           instance:

                   if ((a & 16) == 10) { ... }

           will always be false.

           This warning is enabled by -Wall.

       -Wtrampolines
           Warn about trampolines generated for pointers to nested functions.  A trampoline is a small piece  of
           data or code that is created at run time on the stack when the address of a nested function is taken,
           and is used to call the nested function indirectly.  For some targets, it is made up of data only and
           thus  requires  no special treatment.  But, for most targets, it is made up of code and thus requires
           the stack to be made executable in order for the program to work properly.

       -Wfloat-equal
           Warn if floating-point values are used in equality comparisons.

           The idea behind this is that sometimes it is convenient (for the programmer)  to  consider  floating-
           point  values  as approximations to infinitely precise real numbers.  If you are doing this, then you
           need to compute (by analyzing the code, or in some other way) the maximum  or  likely  maximum  error
           that  the  computation  introduces,  and allow for it when performing comparisons (and when producing
           output, but that's a different problem).  In particular, instead of testing for equality, you  should
           check  to  see  whether the two values have ranges that overlap; and this is done with the relational
           operators, so equality comparisons are probably mistaken.

       -Wtraditional (C and Objective-C only)
           Warn about certain constructs that behave differently in traditional and ISO C.  Also warn about  ISO
           C  constructs  that  have  no  traditional C equivalent, and/or problematic constructs that should be
           avoided.

           *   Macro parameters that appear within string literals in the macro body.  In  traditional  C  macro
               replacement takes place within string literals, but in ISO C it does not.

           *   In  traditional  C,  some  preprocessor directives did not exist.  Traditional preprocessors only
               considered a line to be a directive if the #  appeared  in  column  1  on  the  line.   Therefore
               -Wtraditional  warns  about  directives  that traditional C understands but ignores because the #
               does not appear as the first character on the line.  It also suggests you  hide  directives  like
               "#pragma" not understood by traditional C by indenting them.  Some traditional implementations do
               not recognize "#elif", so this option suggests avoiding it altogether.

           *   A function-like macro that appears without arguments.

           *   The unary plus operator.

           *   The  U  integer  constant suffix, or the F or L floating-point constant suffixes.  (Traditional C
               does support the L suffix on integer constants.)  Note, these suffixes appear in  macros  defined
               in  the system headers of most modern systems, e.g. the _MIN/_MAX macros in "<limits.h>".  Use of
               these macros in user code might normally lead to  spurious  warnings,  however  GCC's  integrated
               preprocessor has enough context to avoid warning in these cases.

           *   A function declared external in one block and then used after the end of the block.

           *   A "switch" statement has an operand of type "long".

           *   A  non-"static"  function  declaration follows a "static" one.  This construct is not accepted by
               some traditional C compilers.

           *   The ISO type of an integer constant has a different width  or  signedness  from  its  traditional
               type.  This warning is only issued if the base of the constant is ten.  I.e. hexadecimal or octal
               values, which typically represent bit patterns, are not warned about.

           *   Usage of ISO string concatenation is detected.

           *   Initialization of automatic aggregates.

           *   Identifier conflicts with labels.  Traditional C lacks a separate namespace for labels.

           *   Initialization  of  unions.   If  the  initializer is zero, the warning is omitted.  This is done
               under the assumption that  the  zero  initializer  in  user  code  appears  conditioned  on  e.g.
               "__STDC__"  to avoid missing initializer warnings and relies on default initialization to zero in
               the traditional C case.

           *   Conversions by prototypes between fixed/floating-point values and vice  versa.   The  absence  of
               these  prototypes when compiling with traditional C causes serious problems.  This is a subset of
               the possible conversion warnings; for the full set use -Wtraditional-conversion.

           *   Use of ISO C style function definitions.  This warning intentionally is not issued for  prototype
               declarations  or  variadic  functions because these ISO C features appear in your code when using
               libiberty's traditional C compatibility macros, "PARAMS" and "VPARAMS".   This  warning  is  also
               bypassed  for  nested  functions  because  that  feature  is already a GCC extension and thus not
               relevant to traditional C compatibility.

       -Wtraditional-conversion (C and Objective-C only)
           Warn if a prototype causes a type conversion that is different from what would  happen  to  the  same
           argument  in  the  absence  of a prototype.  This includes conversions of fixed point to floating and
           vice versa, and conversions changing the width or signedness of a fixed-point  argument  except  when
           the same as the default promotion.

       -Wdeclaration-after-statement (C and Objective-C only)
           Warn  when  a declaration is found after a statement in a block.  This construct, known from C++, was
           introduced with ISO C99 and is by default allowed in GCC.  It is not supported by ISO C90.

       -Wshadow
           Warn whenever a local variable or type declaration shadows another variable, parameter,  type,  class
           member  (in  C++), or instance variable (in Objective-C) or whenever a built-in function is shadowed.
           Note that in C++, the compiler warns if a local variable shadows an explicit typedef, but not  if  it
           shadows  a  struct/class/enum.   If  this warning is enabled, it includes also all instances of local
           shadowing.  This means that  -Wno-shadow=local  and  -Wno-shadow=compatible-local  are  ignored  when
           -Wshadow is used.  Same as -Wshadow=global.

       -Wno-shadow-ivar (Objective-C only)
           Do not warn whenever a local variable shadows an instance variable in an Objective-C method.

       -Wshadow=global
           Warn for any shadowing.  Same as -Wshadow.

       -Wshadow=local
           Warn when a local variable shadows another local variable or parameter.

       -Wshadow=compatible-local
           Warn  when a local variable shadows another local variable or parameter whose type is compatible with
           that of the shadowing variable.  In C++, type compatibility here means  the  type  of  the  shadowing
           variable  can  be converted to that of the shadowed variable.  The creation of this flag (in addition
           to -Wshadow=local) is based  on  the  idea  that  when  a  local  variable  shadows  another  one  of
           incompatible  type,  it  is  most  likely  intentional,  not a bug or typo, as shown in the following
           example:

                   for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i)
                   {
                     for (int i = 0; i < N; ++i)
                     {
                       ...
                     }
                     ...
                   }

           Since  the  two  variable  "i"  in  the  example  above  have  incompatible  types,   enabling   only
           -Wshadow=compatible-local  does  not  emit  a  warning.   Because  their types are incompatible, if a
           programmer accidentally uses one in place of the other, type checking is expected to catch  that  and
           emit  an error or warning.  Use of this flag instead of -Wshadow=local can possibly reduce the number
           of warnings triggered by intentional shadowing.  Note that this also means that shadowing "const char
           *i" by "char *i" does not emit a warning.

           This warning is also enabled by -Wshadow=local.

       -Wlarger-than=byte-size
           Warn whenever an object is  defined  whose  size  exceeds  byte-size.   -Wlarger-than=PTRDIFF_MAX  is
           enabled by default.  Warnings controlled by the option can be disabled either by specifying byte-size
           of SIZE_MAX or more or by -Wno-larger-than.

           Also  warn  for calls to bounded functions such as "memchr" or "strnlen" that specify a bound greater
           than the largest possible object, which is PTRDIFF_MAX bytes by default.  These warnings can only  be
           disabled by -Wno-larger-than.

       -Wno-larger-than
           Disable -Wlarger-than= warnings.  The option is equivalent to -Wlarger-than=SIZE_MAX or larger.

       -Wframe-larger-than=byte-size
           Warn  if the size of a function frame exceeds byte-size.  The computation done to determine the stack
           frame size is approximate and not conservative.  The actual requirements may be somewhat greater than
           byte-size even if you do not get a warning.  In addition, any space allocated via "alloca", variable-
           length arrays, or related constructs is not included by the compiler when determining whether or  not
           to  issue  a warning.  -Wframe-larger-than=PTRDIFF_MAX is enabled by default.  Warnings controlled by
           the  option  can  be  disabled  either  by  specifying  byte-size  of  SIZE_MAX   or   more   or   by
           -Wno-frame-larger-than.

       -Wno-frame-larger-than
           Disable  -Wframe-larger-than=  warnings.  The option is equivalent to -Wframe-larger-than=SIZE_MAX or
           larger.

       -Wno-free-nonheap-object
           Warn when attempting to deallocate an object that was either not allocated on the heap, or by using a
           pointer that was not returned from a prior  call  to  the  corresponding  allocation  function.   For
           example,  because  the call to "stpcpy" returns a pointer to the terminating nul character and not to
           the begginning of the object, the call to "free" below is diagnosed.

                   void f (char *p)
                   {
                     p = stpcpy (p, "abc");
                     // ...
                     free (p);   // warning
                   }

           -Wfree-nonheap-object is enabled by default.

       -Wstack-usage=byte-size
           Warn if the stack usage of a function might exceed byte-size.  The computation done to determine  the
           stack  usage  is  conservative.  Any space allocated via "alloca", variable-length arrays, or related
           constructs is included by the compiler when determining whether or not to issue a warning.

           The message is in keeping with the output of -fstack-usage.

           *   If the stack usage is fully static but exceeds the specified amount, it's:

                         warning: stack usage is 1120 bytes

           *   If the stack usage is (partly) dynamic but bounded, it's:

                         warning: stack usage might be 1648 bytes

           *   If the stack usage is (partly) dynamic and not bounded, it's:

                         warning: stack usage might be unbounded

           -Wstack-usage=PTRDIFF_MAX is enabled by default.  Warnings controlled by the option can  be  disabled
           either by specifying byte-size of SIZE_MAX or more or by -Wno-stack-usage.

       -Wno-stack-usage
           Disable -Wstack-usage= warnings.  The option is equivalent to -Wstack-usage=SIZE_MAX or larger.

       -Wunsafe-loop-optimizations
           Warn if the loop cannot be optimized because the compiler cannot assume anything on the bounds of the
           loop indices.  With -funsafe-loop-optimizations warn if the compiler makes such assumptions.

       -Wno-pedantic-ms-format (MinGW targets only)
           When used in combination with -Wformat and -pedantic without GNU extensions, this option disables the
           warnings  about  non-ISO  "printf"  /  "scanf"  format width specifiers "I32", "I64", and "I" used on
           Windows targets, which depend on the MS runtime.

       -Wpointer-arith
           Warn about anything that depends on the "size of" a function type or of "void".  GNU C assigns  these
           types  a size of 1, for convenience in calculations with "void *" pointers and pointers to functions.
           In C++, warn also when an arithmetic operation involves "NULL".  This  warning  is  also  enabled  by
           -Wpedantic.

       -Wno-pointer-compare
           Do  not  warn  if  a pointer is compared with a zero character constant.  This usually means that the
           pointer was meant to be dereferenced.  For example:

                   const char *p = foo ();
                   if (p == '\0')
                     return 42;

           Note that the code above is invalid in C++11.

           This warning is enabled by default.

       -Wtsan
           Warn about unsupported features in ThreadSanitizer.

           ThreadSanitizer does not support "std::atomic_thread_fence" and can report false positives.

           This warning is enabled by default.

       -Wtype-limits
           Warn if a comparison is always true or always false due to the limited range of the data type, but do
           not warn for constant expressions.  For example, warn if an unsigned  variable  is  compared  against
           zero with "<" or ">=".  This warning is also enabled by -Wextra.

       -Wabsolute-value (C and Objective-C only)
           Warn  for  calls  to  standard  functions  that compute the absolute value of an argument when a more
           appropriate standard function is available.  For example, calling "abs(3.14)"  triggers  the  warning
           because  the  appropriate  function  to  call  to  compute the absolute value of a double argument is
           "fabs".  The option also triggers warnings when the argument in a call to  such  a  function  has  an
           unsigned  type.   This warning can be suppressed with an explicit type cast and it is also enabled by
           -Wextra.

       -Wcomment
       -Wcomments
           Warn whenever a comment-start sequence /* appears in a /* comment, or  whenever  a  backslash-newline
           appears in a // comment.  This warning is enabled by -Wall.

       -Wtrigraphs
           Warn if any trigraphs are encountered that might change the meaning of the program.  Trigraphs within
           comments are not warned about, except those that would form escaped newlines.

           This  option  is  implied  by  -Wall.   If  -Wall  is  not given, this option is still enabled unless
           trigraphs are enabled.  To get  trigraph  conversion  without  warnings,  but  get  the  other  -Wall
           warnings, use -trigraphs -Wall -Wno-trigraphs.

       -Wundef
           Warn  if  an  undefined identifier is evaluated in an "#if" directive.  Such identifiers are replaced
           with zero.

       -Wexpansion-to-defined
           Warn whenever defined is encountered in the expansion of a macro (including the case where the  macro
           is  expanded  by  an  #if  directive).   Such usage is not portable.  This warning is also enabled by
           -Wpedantic and -Wextra.

       -Wunused-macros
           Warn about macros defined in the main file that are unused.  A macro is used if  it  is  expanded  or
           tested  for  existence  at least once.  The preprocessor also warns if the macro has not been used at
           the time it is redefined or undefined.

           Built-in macros, macros defined on the command line, and macros defined  in  include  files  are  not
           warned about.

           Note: If a macro is actually used, but only used in skipped conditional blocks, then the preprocessor
           reports  it  as  unused.   To  avoid  the  warning in such a case, you might improve the scope of the
           macro's definition by, for example, moving it into the first skipped block.  Alternatively, you could
           provide a dummy use with something like:

                   #if defined the_macro_causing_the_warning
                   #endif

       -Wno-endif-labels
           Do not warn whenever an "#else" or an "#endif" are followed by text.  This sometimes happens in older
           programs with code of the form

                   #if FOO
                   ...
                   #else FOO
                   ...
                   #endif FOO

           The second and third "FOO" should be in comments.  This warning is on by default.

       -Wbad-function-cast (C and Objective-C only)
           Warn when a function call is cast to a non-matching type.  For example, warn if a call to a  function
           returning an integer type is cast to a pointer type.

       -Wc90-c99-compat (C and Objective-C only)
           Warn  about features not present in ISO C90, but present in ISO C99.  For instance, warn about use of
           variable length arrays, "long long" type, "bool" type, compound  literals,  designated  initializers,
           and  so  on.   This  option  is  independent  of  the  standards  mode.  Warnings are disabled in the
           expression that follows "__extension__".

       -Wc99-c11-compat (C and Objective-C only)
           Warn about features not present in ISO C99, but present in ISO C11.  For instance, warn about use  of
           anonymous  structures  and unions, "_Atomic" type qualifier, "_Thread_local" storage-class specifier,
           "_Alignas" specifier, "Alignof" operator, "_Generic" keyword, and so on.  This option is  independent
           of the standards mode.  Warnings are disabled in the expression that follows "__extension__".

       -Wc11-c2x-compat (C and Objective-C only)
           Warn  about  features  not  present  in  ISO  C11,  but present in ISO C2X.  For instance, warn about
           omitting the string in "_Static_assert", use of [[]] syntax for attributes, use of decimal  floating-
           point  types, and so on.  This option is independent of the standards mode.  Warnings are disabled in
           the expression that follows "__extension__".

       -Wc++-compat (C and Objective-C only)
           Warn about ISO C constructs that are outside of the common subset of ISO C and ISO C++, e.g.  request
           for implicit conversion from "void *" to a pointer to non-"void" type.

       -Wc++11-compat (C++ and Objective-C++ only)
           Warn  about  C++  constructs  whose  meaning  differs  between  ISO  C++ 1998 and ISO C++ 2011, e.g.,
           identifiers in ISO C++ 1998 that are keywords in ISO C++ 2011.  This warning turns on -Wnarrowing and
           is enabled by -Wall.

       -Wc++14-compat (C++ and Objective-C++ only)
           Warn about C++ constructs whose meaning differs between ISO C++ 2011 and ISO C++ 2014.  This  warning
           is enabled by -Wall.

       -Wc++17-compat (C++ and Objective-C++ only)
           Warn  about C++ constructs whose meaning differs between ISO C++ 2014 and ISO C++ 2017.  This warning
           is enabled by -Wall.

       -Wc++20-compat (C++ and Objective-C++ only)
           Warn about C++ constructs whose meaning differs between ISO C++ 2017 and ISO C++ 2020.  This  warning
           is enabled by -Wall.

       -Wcast-qual
           Warn  whenever a pointer is cast so as to remove a type qualifier from the target type.  For example,
           warn if a "const char *" is cast to an ordinary "char *".

           Also warn when making a cast that introduces a type qualifier in an unsafe way.  For example, casting
           "char **" to "const char **" is unsafe, as in this example:

                     /* p is char ** value.  */
                     const char **q = (const char **) p;
                     /* Assignment of readonly string to const char * is OK.  */
                     *q = "string";
                     /* Now char** pointer points to read-only memory.  */
                     **p = 'b';

       -Wcast-align
           Warn whenever a pointer is cast such that the required alignment of the  target  is  increased.   For
           example,  warn if a "char *" is cast to an "int *" on machines where integers can only be accessed at
           two- or four-byte boundaries.

       -Wcast-align=strict
           Warn whenever a pointer is cast such that the required alignment of the  target  is  increased.   For
           example, warn if a "char *" is cast to an "int *" regardless of the target machine.

       -Wcast-function-type
           Warn  when  a  function  pointer  is  cast  to an incompatible function pointer.  In a cast involving
           function types with a variable argument list only the types of initial arguments  that  are  provided
           are  considered.   Any  parameter  of  pointer-type  matches  any  other  pointer-type.   Any  benign
           differences in integral types are ignored, like "int" vs. "long" on  ILP32  targets.   Likewise  type
           qualifiers are ignored.  The function type "void (*) (void)" is special and matches everything, which
           can be used to suppress this warning.  In a cast involving pointer to member types this warning warns
           whenever the type cast is changing the pointer to member type.  This warning is enabled by -Wextra.

       -Wwrite-strings
           When  compiling C, give string constants the type "const char[length]" so that copying the address of
           one into a non-"const" "char *" pointer produces a warning.  These warnings help you find at  compile
           time  code that can try to write into a string constant, but only if you have been very careful about
           using "const" in declarations and prototypes.  Otherwise, it is just a nuisance. This is why  we  did
           not make -Wall request these warnings.

           When  compiling  C++,  warn  about  the deprecated conversion from string literals to "char *".  This
           warning is enabled by default for C++ programs.

       -Wclobbered
           Warn for variables that might be changed by "longjmp" or "vfork".  This warning is  also  enabled  by
           -Wextra.

       -Wconversion
           Warn  for  implicit  conversions  that  may alter a value. This includes conversions between real and
           integer, like "abs (x)" when "x" is "double"; conversions between signed and unsigned, like "unsigned
           ui = -1"; and conversions to smaller types, like "sqrtf (M_PI)". Do not warn for explicit casts  like
           "abs  ((int)  x)"  and "ui = (unsigned) -1", or if the value is not changed by the conversion like in
           "abs (2.0)".  Warnings about conversions between signed and unsigned  integers  can  be  disabled  by
           using -Wno-sign-conversion.

           For  C++,  also  warn for confusing overload resolution for user-defined conversions; and conversions
           that never use a type conversion operator: conversions to "void", the same type, a base  class  or  a
           reference  to  them.  Warnings about conversions between signed and unsigned integers are disabled by
           default in C++ unless -Wsign-conversion is explicitly enabled.

           Warnings about conversion from arithmetic on a small type back to  that  type  are  only  given  with
           -Warith-conversion.

       -Wdangling-else
           Warn  about  constructions  where  there  may  be  confusion to which "if" statement an "else" branch
           belongs.  Here is an example of such a case:

                   {
                     if (a)
                       if (b)
                         foo ();
                     else
                       bar ();
                   }

           In C/C++, every "else" branch belongs to the innermost possible "if" statement, which in this example
           is "if (b)".  This is often not what the programmer expected, as illustrated in the above example  by
           indentation  the  programmer  chose.   When  there  is the potential for this confusion, GCC issues a
           warning when this flag is specified.  To eliminate  the  warning,  add  explicit  braces  around  the
           innermost  "if"  statement  so  there  is  no  way  the "else" can belong to the enclosing "if".  The
           resulting code looks like this:

                   {
                     if (a)
                       {
                         if (b)
                           foo ();
                         else
                           bar ();
                       }
                   }

           This warning is enabled by -Wparentheses.

       -Wdate-time
           Warn when macros "__TIME__", "__DATE__" or "__TIMESTAMP__" are encountered as they might prevent bit-
           wise-identical reproducible compilations.

       -Wempty-body
           Warn if an empty body occurs in an "if", "else" or  "do  while"  statement.   This  warning  is  also
           enabled by -Wextra.

       -Wno-endif-labels
           Do not warn about stray tokens after "#else" and "#endif".

       -Wenum-compare
           Warn  about  a  comparison  between  values  of  different  enumerated types.  In C++ enumerated type
           mismatches in conditional expressions are also diagnosed and the warning is enabled by default.  In C
           this warning is enabled by -Wall.

       -Wenum-conversion
           Warn when a value of enumerated type is implicitly converted to a different  enumerated  type.   This
           warning is enabled by -Wextra in C.

       -Wjump-misses-init (C, Objective-C only)
           Warn  if  a  "goto"  statement  or  a "switch" statement jumps forward across the initialization of a
           variable, or jumps backward to a label after the variable has  been  initialized.   This  only  warns
           about  variables  that  are initialized when they are declared.  This warning is only supported for C
           and Objective-C; in C++ this sort of branch is an error in any case.

           -Wjump-misses-init is included in -Wc++-compat.  It can be disabled  with  the  -Wno-jump-misses-init
           option.

       -Wsign-compare
           Warn  when a comparison between signed and unsigned values could produce an incorrect result when the
           signed value is converted to unsigned.  In C++, this warning is also enabled by -Wall.  In C,  it  is
           also enabled by -Wextra.

       -Wsign-conversion
           Warn  for  implicit conversions that may change the sign of an integer value, like assigning a signed
           integer expression to an unsigned integer variable. An explicit cast silences the warning. In C, this
           option is enabled also by -Wconversion.

       -Wfloat-conversion
           Warn for implicit conversions that reduce the precision of a real value.  This  includes  conversions
           from  real to integer, and from higher precision real to lower precision real values.  This option is
           also enabled by -Wconversion.

       -Wno-scalar-storage-order
           Do not warn on suspicious constructs involving reverse scalar storage order.

       -Wsizeof-array-div
           Warn about divisions of two sizeof operators when the first one  is  applied  to  an  array  and  the
           divisor does not equal the size of the array element.  In such a case, the computation will not yield
           the number of elements in the array, which is likely what the user intended.  This warning warns e.g.
           about

                   int fn ()
                   {
                     int arr[10];
                     return sizeof (arr) / sizeof (short);
                   }

           This warning is enabled by -Wall.

       -Wsizeof-pointer-div
           Warn  for  suspicious divisions of two sizeof expressions that divide the pointer size by the element
           size, which is the usual way to compute the array size but won't work out  correctly  with  pointers.
           This  warning  warns  e.g.  about  "sizeof  (ptr)  / sizeof (ptr[0])" if "ptr" is not an array, but a
           pointer.  This warning is enabled by -Wall.

       -Wsizeof-pointer-memaccess
           Warn for suspicious length parameters to certain string and memory built-in functions if the argument
           uses "sizeof".  This warning triggers for example for "memset (ptr, 0, sizeof (ptr));"  if  "ptr"  is
           not  an  array,  but  a  pointer,  and  suggests  a possible fix, or about "memcpy (&foo, ptr, sizeof
           (&foo));".  -Wsizeof-pointer-memaccess also warns about calls to bounded string copy  functions  like
           "strncat"  or  "strncpy"  that  specify  as the bound a "sizeof" expression of the source array.  For
           example, in the following function the call to "strncat" specifies the size of the source  string  as
           the bound.  That is almost certainly a mistake and so the call is diagnosed.

                   void make_file (const char *name)
                   {
                     char path[PATH_MAX];
                     strncpy (path, name, sizeof path - 1);
                     strncat (path, ".text", sizeof ".text");
                     ...
                   }

           The -Wsizeof-pointer-memaccess option is enabled by -Wall.

       -Wno-sizeof-array-argument
           Do  not  warn  when the "sizeof" operator is applied to a parameter that is declared as an array in a
           function definition.  This warning is enabled by default for C and C++ programs.

       -Wmemset-elt-size
           Warn for suspicious calls to the "memset" built-in function, if  the  first  argument  references  an
           array,  and the third argument is a number equal to the number of elements, but not equal to the size
           of the array in memory.  This indicates that the user has omitted a  multiplication  by  the  element
           size.  This warning is enabled by -Wall.

       -Wmemset-transposed-args
           Warn for suspicious calls to the "memset" built-in function where the second argument is not zero and
           the third argument is zero.  For example, the call "memset (buf, sizeof buf, 0)" is diagnosed because
           "memset  (buf,  0,  sizeof  buf)"  was  meant  instead.   The diagnostic is only emitted if the third
           argument is a literal zero.  Otherwise, if it is an expression that is folded to zero, or a  cast  of
           zero  to  some  type, it is far less likely that the arguments have been mistakenly transposed and no
           warning is emitted.  This warning is enabled by -Wall.

       -Waddress
           Warn about suspicious uses of memory addresses. These include using the address of a  function  in  a
           conditional  expression,  such  as  "void  func(void); if (func)", and comparisons against the memory
           address of a string literal, such as "if (x == "abc")".  Such uses typically  indicate  a  programmer
           error:  the  address  of  a  function always evaluates to true, so their use in a conditional usually
           indicate that the programmer forgot the parentheses in  a  function  call;  and  comparisons  against
           string  literals  result  in unspecified behavior and are not portable in C, so they usually indicate
           that the programmer intended to use "strcmp".  This warning is enabled by -Wall.

       -Wno-address-of-packed-member
           Do not warn when the address of packed member of struct or union is taken, which usually  results  in
           an unaligned pointer value.  This is enabled by default.

       -Wlogical-op
           Warn  about  suspicious  uses  of  logical  operators  in  expressions.   This includes using logical
           operators in contexts where a bit-wise operator is likely  to  be  expected.   Also  warns  when  the
           operands of a logical operator are the same:

                   extern int a;
                   if (a < 0 && a < 0) { ... }

       -Wlogical-not-parentheses
           Warn about logical not used on the left hand side operand of a comparison.  This option does not warn
           if  the  right operand is considered to be a boolean expression.  Its purpose is to detect suspicious
           code like the following:

                   int a;
                   ...
                   if (!a > 1) { ... }

           It is possible to suppress the warning by wrapping the LHS into parentheses:

                   if ((!a) > 1) { ... }

           This warning is enabled by -Wall.

       -Waggregate-return
           Warn if any functions that return structures or unions are defined or called.   (In  languages  where
           you can return an array, this also elicits a warning.)

       -Wno-aggressive-loop-optimizations
           Warn  if in a loop with constant number of iterations the compiler detects undefined behavior in some
           statement during one or more of the iterations.

       -Wno-attributes
           Do not warn if an unexpected "__attribute__" is  used,  such  as  unrecognized  attributes,  function
           attributes  applied  to  variables,  etc.   This  does not stop errors for incorrect use of supported
           attributes.

       -Wno-builtin-declaration-mismatch
           Warn if a built-in function is declared with an incompatible signature or as a non-function, or  when
           a  built-in  function declared with a type that does not include a prototype is called with arguments
           whose promoted types do not match those expected by the function.  When -Wextra  is  specified,  also
           warn  when  a  built-in  function  that  takes  arguments  is  declared  without  a  prototype.   The
           -Wbuiltin-declaration-mismatch warning is enabled by default.   To  avoid  the  warning  include  the
           appropriate header to bring the prototypes of built-in functions into scope.

           For  example,  the  call to "memset" below is diagnosed by the warning because the function expects a
           value of type "size_t" as its argument but the type of 32 is "int".  With -Wextra, the declaration of
           the function is diagnosed as well.

                   extern void* memset ();
                   void f (void *d)
                   {
                     memset (d, '\0', 32);
                   }

       -Wno-builtin-macro-redefined
           Do not warn if certain built-in macros are redefined.  This suppresses warnings for  redefinition  of
           "__TIMESTAMP__", "__TIME__", "__DATE__", "__FILE__", and "__BASE_FILE__".

       -Wstrict-prototypes (C and Objective-C only)
           Warn  if  a  function  is  declared  or defined without specifying the argument types.  (An old-style
           function definition is permitted without a warning if preceded by a declaration  that  specifies  the
           argument types.)

       -Wold-style-declaration (C and Objective-C only)
           Warn  for  obsolescent  usages,  according  to the C Standard, in a declaration. For example, warn if
           storage-class specifiers like "static" are not the first things in a declaration.   This  warning  is
           also enabled by -Wextra.

       -Wold-style-definition (C and Objective-C only)
           Warn  if  an  old-style  function definition is used.  A warning is given even if there is a previous
           prototype.  A definition using () is not considered an old-style definition in C2X mode,  because  it
           is equivalent to (void) in that case, but is considered an old-style definition for older standards.

       -Wmissing-parameter-type (C and Objective-C only)
           A function parameter is declared without a type specifier in K&R-style functions:

                   void foo(bar) { }

           This warning is also enabled by -Wextra.

       -Wmissing-prototypes (C and Objective-C only)
           Warn  if  a  global  function  is  defined without a previous prototype declaration.  This warning is
           issued even if the definition itself  provides  a  prototype.   Use  this  option  to  detect  global
           functions  that  do  not  have a matching prototype declaration in a header file.  This option is not
           valid for C++ because all function declarations provide prototypes  and  a  non-matching  declaration
           declares an overload rather than conflict with an earlier declaration.  Use -Wmissing-declarations to
           detect missing declarations in C++.

       -Wmissing-declarations
           Warn  if  a  global function is defined without a previous declaration.  Do so even if the definition
           itself provides a prototype.  Use this option to detect global functions that  are  not  declared  in
           header  files.   In C, no warnings are issued for functions with previous non-prototype declarations;
           use -Wmissing-prototypes to detect missing prototypes.  In C++, no warnings are issued  for  function
           templates, or for inline functions, or for functions in anonymous namespaces.

       -Wmissing-field-initializers
           Warn  if  a  structure's initializer has some fields missing.  For example, the following code causes
           such a warning, because "x.h" is implicitly zero:

                   struct s { int f, g, h; };
                   struct s x = { 3, 4 };

           This option does not warn about designated initializers,  so  the  following  modification  does  not
           trigger a warning:

                   struct s { int f, g, h; };
                   struct s x = { .f = 3, .g = 4 };

           In C this option does not warn about the universal zero initializer { 0 }:

                   struct s { int f, g, h; };
                   struct s x = { 0 };

           Likewise, in C++ this option does not warn about the empty { } initializer, for example:

                   struct s { int f, g, h; };
                   s x = { };

           This  warning  is  included  in -Wextra.  To get other -Wextra warnings without this one, use -Wextra
           -Wno-missing-field-initializers.

       -Wno-multichar
           Do not warn if a multicharacter constant ('FOOF') is used.  Usually  they  indicate  a  typo  in  the
           user's code, as they have implementation-defined values, and should not be used in portable code.

       -Wnormalized=[none|id|nfc|nfkc]
           In  ISO  C  and ISO C++, two identifiers are different if they are different sequences of characters.
           However, sometimes when characters outside the basic ASCII character set are used, you can  have  two
           different  character  sequences  that look the same.  To avoid confusion, the ISO 10646 standard sets
           out some normalization rules which when applied ensure that two sequences  that  look  the  same  are
           turned  into  the  same  sequence.   GCC can warn you if you are using identifiers that have not been
           normalized; this option controls that warning.

           There are four levels of warning supported by GCC.  The  default  is  -Wnormalized=nfc,  which  warns
           about  any  identifier that is not in the ISO 10646 "C" normalized form, NFC.  NFC is the recommended
           form for most uses.  It is equivalent to -Wnormalized.

           Unfortunately, there are some characters allowed in identifiers by ISO  C  and  ISO  C++  that,  when
           turned  into  NFC,  are  not allowed in identifiers.  That is, there's no way to use these symbols in
           portable ISO C or C++ and have all your identifiers in NFC.  -Wnormalized=id suppresses  the  warning
           for  these characters.  It is hoped that future versions of the standards involved will correct this,
           which is why this option is not the default.

           You can switch the warning off for all characters by writing  -Wnormalized=none  or  -Wno-normalized.
           You  should  only  do  this  if  you  are  using  some other normalization scheme (like "D"), because
           otherwise you can easily create bugs that are literally impossible to see.

           Some characters in ISO 10646 have distinct meanings but look  identical  in  some  fonts  or  display
           methodologies,  especially  once  formatting  has  been applied.  For instance "\u207F", "SUPERSCRIPT
           LATIN SMALL LETTER N", displays just like a regular "n" that has been placed in a  superscript.   ISO
           10646  defines  the  NFKC normalization scheme to convert all these into a standard form as well, and
           GCC warns if your code is not in NFKC if you use -Wnormalized=nfkc.  This warning  is  comparable  to
           warning about every identifier that contains the letter O because it might be confused with the digit
           0,  and  so  is  not  the  default, but may be useful as a local coding convention if the programming
           environment cannot be fixed to display these characters distinctly.

       -Wno-attribute-warning
           Do not warn about usage of functions declared with "warning" attribute.  By default, this warning  is
           enabled.   -Wno-attribute-warning  can be used to disable the warning or -Wno-error=attribute-warning
           can be used to disable the error when compiled with -Werror flag.

       -Wno-deprecated
           Do not warn about usage of deprecated features.

       -Wno-deprecated-declarations
           Do not warn about uses of  functions,  variables,  and  types  marked  as  deprecated  by  using  the
           "deprecated" attribute.

       -Wno-overflow
           Do not warn about compile-time overflow in constant expressions.

       -Wno-odr
           Warn about One Definition Rule violations during link-time optimization.  Enabled by default.

       -Wopenmp-simd
           Warn  if  the  vectorizer  cost  model  overrides  the  OpenMP  simd  directive  set  by  user.   The
           -fsimd-cost-model=unlimited option can be used to relax the cost model.

       -Woverride-init (C and Objective-C only)
           Warn if an initialized field without side effects is overridden when using designated initializers.

           This warning is included in -Wextra.  To get other -Wextra warnings without  this  one,  use  -Wextra
           -Wno-override-init.

       -Wno-override-init-side-effects (C and Objective-C only)
           Do  not  warn  if  an  initialized  field  with  side  effects  is  overridden  when using designated
           initializers.  This warning is enabled by default.

       -Wpacked
           Warn if a structure is given the packed attribute, but the packed attribute  has  no  effect  on  the
           layout  or  size  of  the  structure.   Such  structures  may be mis-aligned for little benefit.  For
           instance, in this code, the variable "f.x" in "struct bar" is misaligned  even  though  "struct  bar"
           does not itself have the packed attribute:

                   struct foo {
                     int x;
                     char a, b, c, d;
                   } __attribute__((packed));
                   struct bar {
                     char z;
                     struct foo f;
                   };

       -Wnopacked-bitfield-compat
           The  4.1, 4.2 and 4.3 series of GCC ignore the "packed" attribute on bit-fields of type "char".  This
           was fixed in GCC 4.4 but the change can lead to differences in the structure layout.  GCC informs you
           when the offset of such a field has changed in GCC 4.4.  For example  there  is  no  longer  a  4-bit
           padding between field "a" and "b" in this structure:

                   struct foo
                   {
                     char a:4;
                     char b:8;
                   } __attribute__ ((packed));

           This warning is enabled by default.  Use -Wno-packed-bitfield-compat to disable this warning.

       -Wpacked-not-aligned (C, C++, Objective-C and Objective-C++ only)
           Warn  if  a  structure  field  with  explicitly  specified  alignment  in a packed struct or union is
           misaligned.  For example, a warning will be issued on "struct S",  like,  "warning:  alignment  1  of
           'struct S' is less than 8", in this code:

                   struct __attribute__ ((aligned (8))) S8 { char a[8]; };
                   struct __attribute__ ((packed)) S {
                     struct S8 s8;
                   };

           This warning is enabled by -Wall.

       -Wpadded
           Warn  if  padding is included in a structure, either to align an element of the structure or to align
           the whole structure.  Sometimes when this happens it is possible  to  rearrange  the  fields  of  the
           structure to reduce the padding and so make the structure smaller.

       -Wredundant-decls
           Warn  if  anything  is  declared  more  than  once  in  the  same scope, even in cases where multiple
           declaration is valid and changes nothing.

       -Wrestrict
           Warn  when  an  object  referenced   by   a   "restrict"-qualified   parameter   (or,   in   C++,   a
           "__restrict"-qualified parameter) is aliased by another argument, or when copies between such objects
           overlap.   For  example,  the  call to the "strcpy" function below attempts to truncate the string by
           replacing its initial  characters  with  the  last  four.   However,  because  the  call  writes  the
           terminating NUL into "a[4]", the copies overlap and the call is diagnosed.

                   void foo (void)
                   {
                     char a[] = "abcd1234";
                     strcpy (a, a + 4);
                     ...
                   }

           The  -Wrestrict  option  detects some instances of simple overlap even without optimization but works
           best at -O2 and above.  It is included in -Wall.

       -Wnested-externs (C and Objective-C only)
           Warn if an "extern" declaration is encountered within a function.

       -Winline
           Warn if a function that is declared as inline cannot be inlined.  Even with this option, the compiler
           does not warn about failures to inline functions declared in system headers.

           The compiler uses a variety of heuristics to determine whether or not  to  inline  a  function.   For
           example,  the  compiler  takes  into account the size of the function being inlined and the amount of
           inlining that has already been done in the  current  function.   Therefore,  seemingly  insignificant
           changes in the source program can cause the warnings produced by -Winline to appear or disappear.

       -Wint-in-bool-context
           Warn  for  suspicious  use  of  integer values where boolean values are expected, such as conditional
           expressions (?:) using non-boolean integer constants in boolean context, like "if (a <= b ? 2 :  3)".
           Or  left  shifting of signed integers in boolean context, like "for (a = 0; 1 << a; a++);".  Likewise
           for all kinds of multiplications regardless of the data type.  This warning is enabled by -Wall.

       -Wno-int-to-pointer-cast
           Suppress warnings from casts to pointer type of an integer of a different size. In C++, casting to  a
           pointer type of smaller size is an error. Wint-to-pointer-cast is enabled by default.

       -Wno-pointer-to-int-cast (C and Objective-C only)
           Suppress warnings from casts from a pointer to an integer type of a different size.

       -Winvalid-pch
           Warn if a precompiled header is found in the search path but cannot be used.

       -Wlong-long
           Warn  if  "long long" type is used.  This is enabled by either -Wpedantic or -Wtraditional in ISO C90
           and C++98 modes.  To inhibit the warning messages, use -Wno-long-long.

       -Wvariadic-macros
           Warn if variadic macros are used in ISO C90 mode, or if the GNU alternate syntax is used in  ISO  C99
           mode.   This  is enabled by either -Wpedantic or -Wtraditional.  To inhibit the warning messages, use
           -Wno-variadic-macros.

       -Wno-varargs
           Do not warn upon questionable usage of the macros used to handle variable arguments like  "va_start".
           These warnings are enabled by default.

       -Wvector-operation-performance
           Warn if vector operation is not implemented via SIMD capabilities of the architecture.  Mainly useful
           for  the  performance  tuning.  Vector operation can be implemented "piecewise", which means that the
           scalar operation is performed on every vector element; "in parallel", which  means  that  the  vector
           operation  is  implemented using scalars of wider type, which normally is more performance efficient;
           and "as a single scalar", which means that vector fits into a scalar type.

       -Wvla
           Warn if a variable-length array is used in the code.  -Wno-vla prevents the -Wpedantic warning of the
           variable-length array.

       -Wvla-larger-than=byte-size
           If this option is used, the compiler warns for declarations of variable-length arrays whose  size  is
           either  unbounded,  or  bounded  by an argument that allows the array size to exceed byte-size bytes.
           This is similar to how -Walloca-larger-than=byte-size works, but with variable-length arrays.

           Note that GCC may optimize small variable-length arrays of a known value into plain arrays,  so  this
           warning may not get triggered for such arrays.

           -Wvla-larger-than=PTRDIFF_MAX  is  enabled by default but is typically only effective when -ftree-vrp
           is active (default for -O2 and above).

           See also -Walloca-larger-than=byte-size.

       -Wno-vla-larger-than
           Disable -Wvla-larger-than= warnings.  The  option  is  equivalent  to  -Wvla-larger-than=SIZE_MAX  or
           larger.

       -Wvla-parameter
           Warn  about  redeclarations  of  functions  involving  arguments  of  Variable  Length Array types of
           inconsistent kinds or forms, and enable the detection of out-of-bounds accesses to such parameters by
           warnings such as -Warray-bounds.

           If the first function declaration uses the VLA form the bound specified in the array is assumed to be
           the minimum number of elements expected to be provided in calls  to  the  function  and  the  maximum
           number of elements accessed by it.  Failing to provide arguments of sufficient size or accessing more
           than the maximum number of elements may be diagnosed.

           For  example,  the  warning triggers for the following redeclarations because the first one allows an
           array of any size to be passed to "f" while the second one specifies that  the  array  argument  must
           have  at  least  "n"  elements.   In addition, calling "f" with the assotiated VLA bound parameter in
           excess of the actual VLA bound triggers a warning as well.

                   void f (int n, int[n]);
                   void f (int, int[]);     // warning: argument 2 previously declared as a VLA

                   void g (int n)
                   {
                       if (n > 4)
                         return;
                       int a[n];
                       f (sizeof a, a);     // warning: access to a by f may be out of bounds
                     ...
                   }

           -Wvla-parameter is included in -Wall.  The -Warray-parameter option  triggers  warnings  for  similar
           problems involving ordinary array arguments.

       -Wvolatile-register-var
           Warn  if  a  register  variable  is  declared  volatile.   The volatile modifier does not inhibit all
           optimizations that may eliminate reads and/or writes to register variables.  This warning is  enabled
           by -Wall.

       -Wdisabled-optimization
           Warn  if  a  requested  optimization pass is disabled.  This warning does not generally indicate that
           there is anything wrong with your code; it merely indicates  that  GCC's  optimizers  are  unable  to
           handle  the  code  effectively.   Often, the problem is that your code is too big or too complex; GCC
           refuses to optimize programs when the optimization itself is likely to  take  inordinate  amounts  of
           time.

       -Wpointer-sign (C and Objective-C only)
           Warn  for  pointer  argument  passing  or  assignment with different signedness.  This option is only
           supported for C and Objective-C.  It is implied by -Wall and by -Wpedantic,  which  can  be  disabled
           with -Wno-pointer-sign.

       -Wstack-protector
           This  option  is only active when -fstack-protector is active.  It warns about functions that are not
           protected against stack smashing.

       -Woverlength-strings
           Warn about string constants that are longer than the "minimum maximum"  length  specified  in  the  C
           standard.  Modern compilers generally allow string constants that are much longer than the standard's
           minimum limit, but very portable programs should avoid using longer strings.

           The  limit applies after string constant concatenation, and does not count the trailing NUL.  In C90,
           the limit was 509 characters; in C99, it was raised to 4095.  C++98  does  not  specify  a  normative
           minimum maximum, so we do not diagnose overlength strings in C++.

           This option is implied by -Wpedantic, and can be disabled with -Wno-overlength-strings.

       -Wunsuffixed-float-constants (C and Objective-C only)
           Issue  a  warning  for  any  floating  constant that does not have a suffix.  When used together with
           -Wsystem-headers it warns about such constants in system header  files.   This  can  be  useful  when
           preparing  code  to  use  with  the  "FLOAT_CONST_DECIMAL64"  pragma  from the decimal floating-point
           extension to C99.

       -Wno-lto-type-mismatch
           During the link-time optimization, do not warn about type  mismatches  in  global  declarations  from
           different compilation units.  Requires -flto to be enabled.  Enabled by default.

       -Wno-designated-init (C and Objective-C only)
           Suppress  warnings  when  a  positional  initializer  is used to initialize a structure that has been
           marked with the "designated_init" attribute.

   Options That Control Static Analysis
       -fanalyzer
           This option enables an static analysis of program flow which looks for "interesting"  interprocedural
           paths through the code, and issues warnings for problems found on them.

           This analysis is much more expensive than other GCC warnings.

           Enabling this option effectively enables the following warnings:

           -Wanalyzer-double-fclose        -Wanalyzer-double-free        -Wanalyzer-exposure-through-output-file
           -Wanalyzer-file-leak                -Wanalyzer-free-of-non-heap                -Wanalyzer-malloc-leak
           -Wanalyzer-mismatching-deallocation                                 -Wanalyzer-possible-null-argument
           -Wanalyzer-possible-null-dereference       -Wanalyzer-null-argument       -Wanalyzer-null-dereference
           -Wanalyzer-shift-count-negative     -Wanalyzer-shift-count-overflow    -Wanalyzer-stale-setjmp-buffer
           -Wanalyzer-tainted-array-index -Wanalyzer-unsafe-call-within-signal-handler -Wanalyzer-use-after-free
           -Wanalyzer-use-of-pointer-in-stale-stack-frame                              -Wanalyzer-write-to-const
           -Wanalyzer-write-to-string-literal

           This option is only available if GCC was configured with analyzer support enabled.

       -Wanalyzer-too-complex
           If -fanalyzer is enabled, the analyzer uses various heuristics to attempt to explore the control flow
           and data flow in the program, but these can be defeated by sufficiently complicated code.

           By  default,  the  analysis  silently  stops if the code is too complicated for the analyzer to fully
           explore and it reaches an internal limit.  The -Wanalyzer-too-complex option warns if this occurs.

       -Wno-analyzer-double-fclose
           This warning requires -fanalyzer, which enables it; use -Wno-analyzer-double-fclose to disable it.

           This diagnostic warns for paths through the code in which a "FILE *" can have "fclose" called  on  it
           more than once.

       -Wno-analyzer-double-free
           This warning requires -fanalyzer, which enables it; use -Wno-analyzer-double-free to disable it.

           This  diagnostic warns for paths through the code in which a pointer can have a deallocator called on
           it more than once, either "free", or a deallocator referenced by attribute "malloc".

       -Wno-analyzer-exposure-through-output-file
           This warning requires -fanalyzer, which enables it; use -Wno-analyzer-exposure-through-output-file to
           disable it.

           This diagnostic warns for paths through the code in which a security-sensitive value is written to an
           output file (such as writing a password to a log file).

       -Wno-analyzer-file-leak
           This warning requires -fanalyzer, which enables it; use -Wno-analyzer-file-leak to disable it.

           This diagnostic warns for paths through the code in which a "<stdio.h>" "FILE  *"  stream  object  is
           leaked.

       -Wno-analyzer-free-of-non-heap
           This warning requires -fanalyzer, which enables it; use -Wno-analyzer-free-of-non-heap to disable it.

           This  diagnostic  warns  for  paths  through the code in which "free" is called on a non-heap pointer
           (e.g. an on-stack buffer, or a global).

       -Wno-analyzer-malloc-leak
           This warning requires -fanalyzer, which enables it; use -Wno-analyzer-malloc-leak to disable it.

           This diagnostic warns for paths through the code in which a pointer allocated  via  an  allocator  is
           leaked: either "malloc", or a function marked with attribute "malloc".

       -Wno-analyzer-mismatching-deallocation
           This  warning  requires  -fanalyzer,  which enables it; use -Wno-analyzer-mismatching-deallocation to
           disable it.

           This diagnostic warns for paths through the code in which the wrong deallocation function  is  called
           on  a  pointer value, based on which function was used to allocate the pointer value.  The diagnostic
           will warn about mismatches between "free", scalar "delete" and vector "delete[]", and those marked as
           allocator/deallocator pairs using attribute "malloc".

       -Wno-analyzer-possible-null-argument
           This warning requires -fanalyzer,  which  enables  it;  use  -Wno-analyzer-possible-null-argument  to
           disable it.

           This  diagnostic  warns  for  paths  through  the  code in which a possibly-NULL value is passed to a
           function argument marked with "__attribute__((nonnull))" as requiring a non-NULL value.

       -Wno-analyzer-possible-null-dereference
           This warning requires -fanalyzer, which enables it;  use  -Wno-analyzer-possible-null-dereference  to
           disable it.

           This diagnostic warns for paths through the code in which a possibly-NULL value is dereferenced.

       -Wno-analyzer-null-argument
           This warning requires -fanalyzer, which enables it; use -Wno-analyzer-null-argument to disable it.

           This  diagnostic  warns  for  paths through the code in which a value known to be NULL is passed to a
           function argument marked with "__attribute__((nonnull))" as requiring a non-NULL value.

       -Wno-analyzer-null-dereference
           This warning requires -fanalyzer, which enables it; use -Wno-analyzer-null-dereference to disable it.

           This diagnostic warns for paths through the code in which a value known to be NULL is dereferenced.

       -Wno-analyzer-shift-count-negative
           This warning requires -fanalyzer, which enables it; use -Wno-analyzer-shift-count-negative to disable
           it.

           This diagnostic warns for paths through the code in which a shift is attempted with a negative count.
           It is analogous to the -Wshift-count-negative diagnostic implemented in the C/C++ front ends, but  is
           implemented  based  on  analyzing  interprocedural paths, rather than merely parsing the syntax tree.
           However, the analyzer does not prioritize detection of such paths, so false negatives are more likely
           relative to other warnings.

       -Wno-analyzer-shift-count-overflow
           This warning requires -fanalyzer, which enables it; use -Wno-analyzer-shift-count-overflow to disable
           it.

           This diagnostic warns for paths through the code in which a shift is attempted with a  count  greater
           than  or equal to the precision of the operand's type.  It is analogous to the -Wshift-count-overflow
           diagnostic implemented in the C/C++ front ends, but is implemented based on analyzing interprocedural
           paths, rather than merely parsing the  syntax  tree.   However,  the  analyzer  does  not  prioritize
           detection of such paths, so false negatives are more likely relative to other warnings.

       -Wno-analyzer-stale-setjmp-buffer
           This  warning requires -fanalyzer, which enables it; use -Wno-analyzer-stale-setjmp-buffer to disable
           it.

           This diagnostic warns for paths through the code  in  which  "longjmp"  is  called  to  rewind  to  a
           "jmp_buf" relating to a "setjmp" call in a function that has returned.

           When  "setjmp" is called on a "jmp_buf" to record a rewind location, it records the stack frame.  The
           stack frame becomes invalid when the function containing the "setjmp" call  returns.   Attempting  to
           rewind  to it via "longjmp" would reference a stack frame that no longer exists, and likely lead to a
           crash (or worse).

       -Wno-analyzer-tainted-array-index
           This  warning  requires  both   -fanalyzer   and   -fanalyzer-checker=taint   to   enable   it;   use
           -Wno-analyzer-tainted-array-index to disable it.

           This  diagnostic  warns for paths through the code in which a value that could be under an attacker's
           control is used as the index of an array access without being sanitized.

       -Wno-analyzer-unsafe-call-within-signal-handler
           This       warning       requires       -fanalyzer,        which        enables        it;        use
           -Wno-analyzer-unsafe-call-within-signal-handler to disable it.

           This  diagnostic warns for paths through the code in which a function known to be async-signal-unsafe
           (such as "fprintf") is called from a signal handler.

       -Wno-analyzer-use-after-free
           This warning requires -fanalyzer, which enables it; use -Wno-analyzer-use-after-free to disable it.

           This diagnostic warns for paths through the code in which a pointer is used after  a  deallocator  is
           called on it: either "free", or a deallocator referenced by attribute "malloc".

       -Wno-analyzer-use-of-pointer-in-stale-stack-frame
           This        warning        requires        -fanalyzer,        which       enables       it;       use
           -Wno-analyzer-use-of-pointer-in-stale-stack-frame to disable it.

           This diagnostic warns for paths through the code in which a pointer is dereferenced that points to  a
           variable in a stale stack frame.

       -Wno-analyzer-write-to-const
           This warning requires -fanalyzer, which enables it; use -Wno-analyzer-write-to-const to disable it.

           This  diagnostic  warns  for paths through the code in which the analyzer detects an attempt to write
           through a pointer to a "const" object.  However, the analyzer does not prioritize detection  of  such
           paths, so false negatives are more likely relative to other warnings.

       -Wno-analyzer-write-to-string-literal
           This  warning  requires  -fanalyzer,  which  enables it; use -Wno-analyzer-write-to-string-literal to
           disable it.

           This diagnostic warns for paths through the code in which the analyzer detects an  attempt  to  write
           through  a  pointer to a string literal.  However, the analyzer does not prioritize detection of such
           paths, so false negatives are more likely relative to other warnings.

       Pertinent parameters for controlling the  exploration  are:  --param  analyzer-bb-explosion-factor=value,
       --param   analyzer-max-enodes-per-program-point=value,  --param  analyzer-max-recursion-depth=value,  and
       --param analyzer-min-snodes-for-call-summary=value.

       The following options control the analyzer.

       -fanalyzer-call-summaries
           Simplify interprocedural analysis by computing the effect of certain calls, rather than exploring all
           paths through the function from callsite to each possible return.

           If enabled, call summaries are only used for functions with more than one call  site,  and  that  are
           sufficiently complicated (as per --param analyzer-min-snodes-for-call-summary=value).

       -fanalyzer-checker=name
           Restrict the analyzer to run just the named checker, and enable it.

           Some  checkers  are  disabled  by  default  (even  with -fanalyzer), such as the "taint" checker that
           implements -Wanalyzer-tainted-array-index, and this option is required to enable them.

       -fno-analyzer-feasibility
           This option is intended for analyzer developers.

           By default the analyzer verifies that there is a feasible control flow path for  each  diagnostic  it
           emits:  that  the conditions that hold are not mutually exclusive.  Diagnostics for which no feasible
           path can be found are rejected.  This filtering can be suppressed with -fno-analyzer-feasibility, for
           debugging issues in this code.

       -fanalyzer-fine-grained
           This option is intended for analyzer developers.

           Internally the analyzer builds an "exploded graph" that combines control flow graphs with  data  flow
           information.

           By  default,  an  edge in this graph can contain the effects of a run of multiple statements within a
           basic block.  With -fanalyzer-fine-grained, each statement gets its own edge.

       -fanalyzer-show-duplicate-count
           This option is intended for analyzer developers: if multiple diagnostics have been detected as  being
           duplicates  of  each  other, it emits a note when reporting the best diagnostic, giving the number of
           additional diagnostics that were suppressed by the deduplication logic.

       -fno-analyzer-state-merge
           This option is intended for analyzer developers.

           By default the analyzer attempts to simplify analysis by merging sufficiently similar states at  each
           program  point as it builds its "exploded graph".  With -fno-analyzer-state-merge this merging can be
           suppressed, for debugging state-handling issues.

       -fno-analyzer-state-purge
           This option is intended for analyzer developers.

           By default the analyzer attempts to simplify analysis by purging aspects of state at a program  point
           that  appear  to  no  longer  be relevant e.g. the values of locals that aren't accessed later in the
           function and which aren't relevant to leak analysis.

           With -fno-analyzer-state-purge this purging of state can be suppressed, for debugging  state-handling
           issues.

       -fanalyzer-transitivity
           This option enables transitivity of constraints within the analyzer.

       -fanalyzer-verbose-edges
           This  option is intended for analyzer developers.  It enables more verbose, lower-level detail in the
           descriptions of control flow within diagnostic paths.

       -fanalyzer-verbose-state-changes
           This option is intended for analyzer developers.  It enables more verbose, lower-level detail in  the
           descriptions of events relating to state machines within diagnostic paths.

       -fanalyzer-verbosity=level
           This  option  controls  the  complexity  of  the  control  flow  paths  that are emitted for analyzer
           diagnostics.

           The level can be one of:

           0   At this level, interprocedural call  and  return  events  are  displayed,  along  with  the  most
               pertinent  state-change  events  relating  to  a  diagnostic.   For  example, for a double-"free"
               diagnostic, both calls to "free" will be shown.

           1   As per the previous level, but also show events for the entry to each function.

           2   As per the previous level, but also show events relating to control flow that are significant  to
               triggering the issue (e.g. "true path taken" at a conditional).

               This level is the default.

           3   As per the previous level, but show all control flow events, not just significant ones.

           4   This  level  is  intended  for  analyzer  developers;  it  adds various other events intended for
               debugging the analyzer.

       -fdump-analyzer
           Dump internal details about what  the  analyzer  is  doing  to  file.analyzer.txt.   This  option  is
           overridden by -fdump-analyzer-stderr.

       -fdump-analyzer-stderr
           Dump  internal  details  about  what  the  analyzer  is  doing  to  stderr.   This  option  overrides
           -fdump-analyzer.

       -fdump-analyzer-callgraph
           Dump a representation of the call graph suitable for viewing with GraphViz to file.callgraph.dot.

       -fdump-analyzer-exploded-graph
           Dump a representation of the "exploded graph" suitable for  viewing  with  GraphViz  to  file.eg.dot.
           Nodes are color-coded based on state-machine states to emphasize state changes.

       -fdump-analyzer-exploded-nodes
           Emit diagnostics showing where nodes in the "exploded graph" are in relation to the program source.

       -fdump-analyzer-exploded-nodes-2
           Dump a textual representation of the "exploded graph" to file.eg.txt.

       -fdump-analyzer-exploded-nodes-3
           Dump  a  textual representation of the "exploded graph" to one dump file per node, to file.eg-id.txt.
           This is typically a large number of dump files.

       -fdump-analyzer-feasibility
           Dump internal details about the analyzer's search for feasible paths.  The details are written  in  a
           form suitable for viewing with GraphViz to filenames of the form file.*.fg.dot and file.*.tg.dot.

       -fdump-analyzer-json
           Dump  a  compressed  JSON representation of analyzer internals to file.analyzer.json.gz.  The precise
           format is subject to change.

       -fdump-analyzer-state-purge
           As per -fdump-analyzer-supergraph, dump a representation of the  "supergraph"  suitable  for  viewing
           with  GraphViz,  but  annotate  the graph with information on what state will be purged at each node.
           The graph is written to file.state-purge.dot.

       -fdump-analyzer-supergraph
           Dump representations of the "supergraph" suitable for viewing with  GraphViz  to  file.supergraph.dot
           and  to  file.supergraph-eg.dot.   These  show  all  of  the control flow graphs in the program, with
           interprocedural edges for calls and returns.  The second dump contains annotations showing  nodes  in
           the "exploded graph" and diagnostics associated with them.

   Options for Debugging Your Program
       To  tell GCC to emit extra information for use by a debugger, in almost all cases you need only to add -g
       to your other options.

       GCC allows you to use -g with -O.  The shortcuts taken by optimized code may occasionally be  surprising:
       some  variables  you  declared  may  not exist at all; flow of control may briefly move where you did not
       expect it; some statements may not be executed because they compute constant results or their values  are
       already  at  hand;  some  statements  may execute in different places because they have been moved out of
       loops.  Nevertheless it is possible to debug optimized output.  This  makes  it  reasonable  to  use  the
       optimizer for programs that might have bugs.

       If  you  are  not using some other optimization option, consider using -Og with -g.  With no -O option at
       all, some compiler passes that collect information useful for debugging do not run at all,  so  that  -Og
       may result in a better debugging experience.

       -g  Produce debugging information in the operating system's native format (stabs, COFF, XCOFF, or DWARF).
           GDB can work with this debugging information.

           On  most  systems  that use stabs format, -g enables use of extra debugging information that only GDB
           can use; this extra information makes debugging work better in GDB but probably makes other debuggers
           crash or refuse to read the program.  If you want to control for  certain  whether  to  generate  the
           extra information, use -gstabs+, -gstabs, -gxcoff+, -gxcoff, or -gvms (see below).

       -ggdb
           Produce debugging information for use by GDB.  This means to use the most expressive format available
           (DWARF,  stabs,  or the native format if neither of those are supported), including GDB extensions if
           at all possible.

       -gdwarf
       -gdwarf-version
           Produce debugging information in DWARF format (if that is supported).  The value of  version  may  be
           either  2,  3,  4 or 5; the default version for most targets is 5 (with the exception of VxWorks, TPF
           and Darwin/Mac OS X, which default to version 2, and AIX, which defaults to version 4).

           Note that with DWARF Version 2, some ports require  and  always  use  some  non-conflicting  DWARF  3
           extensions in the unwind tables.

           Version  4 may require GDB 7.0 and -fvar-tracking-assignments for maximum benefit. Version 5 requires
           GDB 8.0 or higher.

           GCC no longer supports DWARF Version 1, which is substantially different than Version  2  and  later.
           For  historical  reasons,  some  other  DWARF-related  options  such as -fno-dwarf2-cfi-asm) retain a
           reference to DWARF Version 2 in their names, but apply to all currently-supported versions of DWARF.

       -gstabs
           Produce debugging information in stabs format (if that is supported), without GDB  extensions.   This
           is  the  format  used by DBX on most BSD systems.  On MIPS, Alpha and System V Release 4 systems this
           option produces stabs debugging output that is not understood by DBX.  On System V Release 4  systems
           this option requires the GNU assembler.

       -gstabs+
           Produce debugging information in stabs format (if that is supported), using GNU extensions understood
           only  by the GNU debugger (GDB).  The use of these extensions is likely to make other debuggers crash
           or refuse to read the program.

       -gxcoff
           Produce debugging information in XCOFF format (if that is supported).  This is the format used by the
           DBX debugger on IBM RS/6000 systems.

       -gxcoff+
           Produce debugging information in XCOFF format (if that is supported), using GNU extensions understood
           only by the GNU debugger (GDB).  The use of these extensions is likely to make other debuggers  crash
           or  refuse  to  read the program, and may cause assemblers other than the GNU assembler (GAS) to fail
           with an error.

       -gvms
           Produce debugging information in Alpha/VMS debug format (if that is supported).  This is  the  format
           used by DEBUG on Alpha/VMS systems.

       -glevel
       -ggdblevel
       -gstabslevel
       -gxcofflevel
       -gvmslevel
           Request  debugging information and also use level to specify how much information.  The default level
           is 2.

           Level 0 produces no debug information at all.  Thus, -g0 negates -g.

           Level 1 produces minimal information, enough for making backtraces in parts of the program  that  you
           don't plan to debug.  This includes descriptions of functions and external variables, and line number
           tables, but no information about local variables.

           Level  3  includes extra information, such as all the macro definitions present in the program.  Some
           debuggers support macro expansion when you use -g3.

           If you use multiple -g options, with or without level numbers, the last such option is the  one  that
           is effective.

           -gdwarf  does  not accept a concatenated debug level, to avoid confusion with -gdwarf-level.  Instead
           use an additional -glevel option to change the debug level for DWARF.

       -fno-eliminate-unused-debug-symbols
           By default, no debug information is produced for symbols that are not actually used. Use this  option
           if you want debug information for all symbols.

       -femit-class-debug-always
           Instead  of  emitting  debugging  information for a C++ class in only one object file, emit it in all
           object files using the class.  This option should be used only with  debuggers  that  are  unable  to
           handle  the  way  GCC  normally  emits  debugging  information  for classes because using this option
           increases the size of debugging information by as much as a factor of two.

       -fno-merge-debug-strings
           Direct the linker to not merge together strings in the debugging information that  are  identical  in
           different  object  files.   Merging is not supported by all assemblers or linkers.  Merging decreases
           the size of the debug information in the output file at the cost of increasing link processing  time.
           Merging is enabled by default.

       -fdebug-prefix-map=old=new
           When  compiling  files  residing in directory old, record debugging information describing them as if
           the files resided in directory new instead.  This can be used to replace a build-time  path  with  an
           install-time  path  in  the debug info.  It can also be used to change an absolute path to a relative
           path by using . for new.  This can give more reproducible builds, which are location independent, but
           may require an extra command to tell GDB where to find the source files. See also -ffile-prefix-map.

       -fvar-tracking
           Run variable tracking pass.  It computes where variables are stored at each position in code.  Better
           debugging  information  is  then  generated  (if  the  debugging  information  format  supports  this
           information).

           It  is enabled by default when compiling with optimization (-Os, -O, -O2, ...), debugging information
           (-g) and the debug info format supports it.

       -fvar-tracking-assignments
           Annotate assignments to user variables early in the compilation and attempt to carry the  annotations
           over  throughout  the  compilation all the way to the end, in an attempt to improve debug information
           while optimizing.  Use of -gdwarf-4 is recommended along with it.

           It can be enabled even if var-tracking is  disabled,  in  which  case  annotations  are  created  and
           maintained, but discarded at the end.  By default, this flag is enabled together with -fvar-tracking,
           except when selective scheduling is enabled.

       -gsplit-dwarf
           If  DWARF debugging information is enabled, separate as much debugging information as possible into a
           separate output file with the extension .dwo.  This option allows the build system to  avoid  linking
           files  with debug information.  To be useful, this option requires a debugger capable of reading .dwo
           files.

       -gdwarf32
       -gdwarf64
           If DWARF debugging information is enabled, the -gdwarf32 selects the  32-bit  DWARF  format  and  the
           -gdwarf64  selects  the  64-bit  DWARF format.  The default is target specific, on most targets it is
           -gdwarf32 though.  The 32-bit DWARF format is smaller, but can't support  more  than  2GiB  of  debug
           information  in  any  of the DWARF debug information sections.  The 64-bit DWARF format allows larger
           debug information and might not be well supported by all consumers yet.

       -gdescribe-dies
           Add description attributes to some DWARF DIEs  that  have  no  name  attribute,  such  as  artificial
           variables, external references and call site parameter DIEs.

       -gpubnames
           Generate DWARF ".debug_pubnames" and ".debug_pubtypes" sections.

       -ggnu-pubnames
           Generate  ".debug_pubnames" and ".debug_pubtypes" sections in a format suitable for conversion into a
           GDB index.  This option is only useful with a linker that can produce GDB index version 7.

       -fdebug-types-section
           When using DWARF Version 4 or higher, type DIEs can be put  into  their  own  ".debug_types"  section
           instead  of  making  them  part  of the ".debug_info" section.  It is more efficient to put them in a
           separate comdat section since the linker can then remove duplicates.  But  not  all  DWARF  consumers
           support  ".debug_types"  sections  yet  and on some objects ".debug_types" produces larger instead of
           smaller debugging information.

       -grecord-gcc-switches
       -gno-record-gcc-switches
           This switch causes the command-line options  used  to  invoke  the  compiler  that  may  affect  code
           generation  to  be  appended  to  the  DW_AT_producer  attribute in DWARF debugging information.  The
           options are concatenated with spaces separating them from each other and from the  compiler  version.
           It is enabled by default.  See also -frecord-gcc-switches for another way of storing compiler options
           into the object file.

       -gstrict-dwarf
           Disallow  using  extensions  of  later DWARF standard version than selected with -gdwarf-version.  On
           most targets using non-conflicting DWARF extensions from later standard versions is allowed.

       -gno-strict-dwarf
           Allow using extensions of later DWARF standard version than selected with -gdwarf-version.

       -gas-loc-support
           Inform the compiler that the assembler supports ".loc" directives.  It may  then  use  them  for  the
           assembler to generate DWARF2+ line number tables.

           This  is  generally  desirable, because assembler-generated line-number tables are a lot more compact
           than those the compiler can generate itself.

           This option will be enabled by default if, at GCC configure time, the assembler was found to  support
           such directives.

       -gno-as-loc-support
           Force  GCC to generate DWARF2+ line number tables internally, if DWARF2+ line number tables are to be
           generated.

       -gas-locview-support
           Inform the compiler that the assembler supports "view" assignment and  reset  assertion  checking  in
           ".loc" directives.

           This  option will be enabled by default if, at GCC configure time, the assembler was found to support
           them.

       -gno-as-locview-support
           Force GCC to assign view numbers internally, if -gvariable-location-views are explicitly requested.

       -gcolumn-info
       -gno-column-info
           Emit location column information into DWARF debugging information, rather than just  file  and  line.
           This option is enabled by default.

       -gstatement-frontiers
       -gno-statement-frontiers
           This  option  causes  GCC  to  create  markers  in  the  internal  representation at the beginning of
           statements, and to keep them roughly in place throughout compilation, using them to guide the  output
           of  "is_stmt"  markers  in  the  line  number  table.  This is enabled by default when compiling with
           optimization (-Os, -O, -O2, ...), and outputting DWARF 2 debug information at the normal level.

       -gvariable-location-views
       -gvariable-location-views=incompat5
       -gno-variable-location-views
           Augment variable location lists with progressive view numbers implied from  the  line  number  table.
           This  enables  debug information consumers to inspect state at certain points of the program, even if
           no instructions associated with the corresponding source locations are present at that point.  If the
           assembler lacks support for view numbers in line number tables, this will cause the compiler to  emit
           the  line  number table, which generally makes them somewhat less compact.  The augmented line number
           tables and location lists are fully backward-compatible, so they can be consumed by debug information
           consumers that are not aware of these augmentations, but they won't  derive  any  benefit  from  them
           either.

           This  is enabled by default when outputting DWARF 2 debug information at the normal level, as long as
           there is assembler support, -fvar-tracking-assignments is enabled and -gstrict-dwarf  is  not.   When
           assembler  support  is  not  available,  this  may  still be enabled, but it will force GCC to output
           internal line number tables, and if -ginternal-reset-location-views is not enabled,  that  will  most
           certainly lead to silently mismatching location views.

           There is a proposed representation for view numbers that is not backward compatible with the location
           list  format  introduced  in  DWARF  5, that can be enabled with -gvariable-location-views=incompat5.
           This option may be removed in the future, is only provided  as  a  reference  implementation  of  the
           proposed  representation.   Debug  information  consumers  are  not expected to support this extended
           format, and they would be rendered unable to decode location lists using it.

       -ginternal-reset-location-views
       -gno-internal-reset-location-views
           Attempt to determine location views that can be omitted from location view lists.  This requires  the
           compiler  to  have very accurate insn length estimates, which isn't always the case, and it may cause
           incorrect view lists to be generated silently when using an assembler that does not support  location
           view  lists.   The  GNU assembler will flag any such error as a "view number mismatch".  This is only
           enabled on ports that define a reliable estimation function.

       -ginline-points
       -gno-inline-points
           Generate extended debug information for  inlined  functions.   Location  view  tracking  markers  are
           inserted  at  inlined  entry  points,  so that address and view numbers can be computed and output in
           debug information.  This can be enabled independently of location  views,  in  which  case  the  view
           numbers  won't  be  output, but it can only be enabled along with statement frontiers, and it is only
           enabled by default if location views are enabled.

       -gz[=type]
           Produce compressed debug sections in DWARF format, if that is supported.  If type is not  given,  the
           default  type  depends on the capabilities of the assembler and linker used.  type may be one of none
           (don't compress debug sections), zlib (use zlib compression in ELF gABI  format),  or  zlib-gnu  (use
           zlib  compression in traditional GNU format).  If the linker doesn't support writing compressed debug
           sections, the option is rejected.  Otherwise, if the assembler does not support them, -gz is silently
           ignored when producing object files.

       -femit-struct-debug-baseonly
           Emit debug information for struct-like types only when the base name of the compilation  source  file
           matches the base name of file in which the struct is defined.

           This  option  substantially  reduces  the size of debugging information, but at significant potential
           loss in type information to the debugger.  See  -femit-struct-debug-reduced  for  a  less  aggressive
           option.  See -femit-struct-debug-detailed for more detailed control.

           This option works only with DWARF debug output.

       -femit-struct-debug-reduced
           Emit  debug  information for struct-like types only when the base name of the compilation source file
           matches the base name of file in which the type is defined,  unless  the  struct  is  a  template  or
           defined in a system header.

           This option significantly reduces the size of debugging information, with some potential loss in type
           information  to  the  debugger.   See -femit-struct-debug-baseonly for a more aggressive option.  See
           -femit-struct-debug-detailed for more detailed control.

           This option works only with DWARF debug output.

       -femit-struct-debug-detailed[=spec-list]
           Specify the struct-like types for which the compiler generates debug information.  The intent  is  to
           reduce duplicate struct debug information between different object files within the same program.

           This  option  is  a detailed version of -femit-struct-debug-reduced and -femit-struct-debug-baseonly,
           which serves for most needs.

           A specification has the syntax[dir:|ind:][ord:|gen:](any|sys|base|none)

           The optional first word limits the specification to structs that are used  directly  (dir:)  or  used
           indirectly  (ind:).   A  struct  type  is  used  directly  when it is the type of a variable, member.
           Indirect uses arise through pointers to structs.  That is, when use of an incomplete struct is valid,
           the use is indirect.  An example is struct one direct; struct two * indirect;.

           The optional second word limits the specification to  ordinary  structs  (ord:)  or  generic  structs
           (gen:).   Generic  structs  are  a  bit  complicated  to  explain.   For  C++, these are non-explicit
           specializations of template classes, or non-template classes within  the  above.   Other  programming
           languages have generics, but -femit-struct-debug-detailed does not yet implement them.

           The  third word specifies the source files for those structs for which the compiler should emit debug
           information.  The values none and any have the normal meaning.  The value base means that the base of
           name of the file in which the type declaration appears must match the base of the name  of  the  main
           compilation  file.  In practice, this means that when compiling foo.c, debug information is generated
           for types declared in that file and foo.h, but not other header files.  The  value  sys  means  those
           types satisfying base or declared in system or compiler headers.

           You may need to experiment to determine the best settings for your application.

           The default is -femit-struct-debug-detailed=all.

           This option works only with DWARF debug output.

       -fno-dwarf2-cfi-asm
           Emit  DWARF  unwind  info  as  compiler  generated  ".eh_frame" section instead of using GAS ".cfi_*"
           directives.

       -fno-eliminate-unused-debug-types
           Normally, when producing DWARF output, GCC avoids producing debug symbol output for  types  that  are
           nowhere  used  in  the source file being compiled.  Sometimes it is useful to have GCC emit debugging
           information for all types declared in a compilation unit, regardless  of  whether  or  not  they  are
           actually  used in that compilation unit, for example if, in the debugger, you want to cast a value to
           a type that is not actually used in your program  (but  is  declared).   More  often,  however,  this
           results in a significant amount of wasted space.

   Options That Control Optimization
       These options control various sorts of optimizations.

       Without  any  optimization  option,  the compiler's goal is to reduce the cost of compilation and to make
       debugging produce the expected results.  Statements are independent: if  you  stop  the  program  with  a
       breakpoint  between  statements,  you  can  then assign a new value to any variable or change the program
       counter to any other statement in the function and get exactly the results you  expect  from  the  source
       code.

       Turning  on  optimization flags makes the compiler attempt to improve the performance and/or code size at
       the expense of compilation time and possibly the ability to debug the program.

       The compiler performs optimization based on the knowledge it has  of  the  program.   Compiling  multiple
       files  at once to a single output file mode allows the compiler to use information gained from all of the
       files when compiling each of them.

       Not all optimizations are controlled directly by a flag.  Only optimizations that have a flag are  listed
       in this section.

       Most  optimizations are completely disabled at -O0 or if an -O level is not set on the command line, even
       if individual optimization flags are specified.  Similarly, -Og suppresses many optimization passes.

       Depending on the target and how GCC was configured, a slightly different  set  of  optimizations  may  be
       enabled  at  each  -O level than those listed here.  You can invoke GCC with -Q --help=optimizers to find
       out the exact set of optimizations that are enabled at each level.

       -O
       -O1 Optimize.  Optimizing compilation takes somewhat more time,  and  a  lot  more  memory  for  a  large
           function.

           With  -O,  the  compiler  tries  to  reduce  code  size  and  execution  time, without performing any
           optimizations that take a great deal of compilation time.

           -O turns on the following optimization flags:

           -fauto-inc-dec -fbranch-count-reg -fcombine-stack-adjustments -fcompare-elim -fcprop-registers  -fdce
           -fdefer-pop  -fdelayed-branch  -fdse  -fforward-propagate  -fguess-branch-probability -fif-conversion
           -fif-conversion2   -finline-functions-called-once   -fipa-modref    -fipa-profile    -fipa-pure-const
           -fipa-reference       -fipa-reference-addressable       -fmerge-constants      -fmove-loop-invariants
           -fomit-frame-pointer   -freorder-blocks   -fshrink-wrap   -fshrink-wrap-separate   -fsplit-wide-types
           -fssa-backprop -fssa-phiopt -ftree-bit-ccp -ftree-ccp -ftree-ch -ftree-coalesce-vars -ftree-copy-prop
           -ftree-dce  -ftree-dominator-opts  -ftree-dse  -ftree-forwprop  -ftree-fre  -ftree-phiprop -ftree-pta
           -ftree-scev-cprop -ftree-sink -ftree-slsr -ftree-sra -ftree-ter -funit-at-a-time

       -O2 Optimize even more.  GCC performs nearly all supported optimizations that do  not  involve  a  space-
           speed  tradeoff.   As compared to -O, this option increases both compilation time and the performance
           of the generated code.

           -O2 turns on all optimization flags specified by -O.  It also turns  on  the  following  optimization
           flags:

           -falign-functions    -falign-jumps   -falign-labels    -falign-loops  -fcaller-saves  -fcode-hoisting
           -fcrossjumping  -fcse-follow-jumps   -fcse-skip-blocks  -fdelete-null-pointer-checks   -fdevirtualize
           -fdevirtualize-speculatively     -fexpensive-optimizations     -ffinite-loops    -fgcse     -fgcse-lm
           -fhoist-adjacent-loads -finline-functions -finline-small-functions  -findirect-inlining  -fipa-bit-cp
           -fipa-cp   -fipa-icf -fipa-ra  -fipa-sra  -fipa-vrp -fisolate-erroneous-paths-dereference -flra-remat
           -foptimize-sibling-calls          -foptimize-strlen          -fpartial-inlining           -fpeephole2
           -freorder-blocks-algorithm=stc           -freorder-blocks-and-partition           -freorder-functions
           -frerun-cse-after-loop   -fschedule-insns    -fschedule-insns2    -fsched-interblock     -fsched-spec
           -fstore-merging      -fstrict-aliasing      -fthread-jumps     -ftree-builtin-call-dce     -ftree-pre
           -ftree-switch-conversion  -ftree-tail-merge -ftree-vrp

           Please note the warning under -fgcse about invoking -O2 on programs that use computed gotos.

           NOTE: In Ubuntu 8.10 and later versions, -D_FORTIFY_SOURCE=2 is set by default, and is activated when
           -O is set to 2 or higher.  This enables additional compile-time and run-time checks for several  libc
           functions.  To disable, specify either -U_FORTIFY_SOURCE or -D_FORTIFY_SOURCE=0.

       -O3 Optimize  yet  more.  -O3 turns on all optimizations specified by -O2 and also turns on the following
           optimization flags:

           -fgcse-after-reload    -fipa-cp-clone    -floop-interchange    -floop-unroll-and-jam     -fpeel-loops
           -fpredictive-commoning  -fsplit-loops  -fsplit-paths  -ftree-loop-distribution  -ftree-loop-vectorize
           -ftree-partial-pre -ftree-slp-vectorize -funswitch-loops -fvect-cost-model  -fvect-cost-model=dynamic
           -fversion-loops-for-strides

       -O0 Reduce compilation time and make debugging produce the expected results.  This is the default.

       -Os Optimize for size.  -Os enables all -O2 optimizations except those that often increase code size:

           -falign-functions      -falign-jumps     -falign-labels      -falign-loops     -fprefetch-loop-arrays
           -freorder-blocks-algorithm=stc

           It also enables -finline-functions, causes the compiler to tune for code size rather  than  execution
           speed, and performs further optimizations designed to reduce code size.

       -Ofast
           Disregard  strict  standards  compliance.   -Ofast  enables  all  -O3 optimizations.  It also enables
           optimizations that are not valid for all  standard-compliant  programs.   It  turns  on  -ffast-math,
           -fallow-store-data-races  and  the  Fortran-specific  -fstack-arrays,  unless -fmax-stack-var-size is
           specified, and -fno-protect-parens.

       -Og Optimize debugging experience.  -Og should be the optimization level of choice for the standard edit-
           compile-debug cycle, offering a reasonable level of optimization while maintaining  fast  compilation
           and  a  good  debugging  experience.   It  is  a better choice than -O0 for producing debuggable code
           because some compiler passes that collect debug information are disabled at -O0.

           Like -O0, -Og completely disables  a  number  of  optimization  passes  so  that  individual  options
           controlling  them  have no effect.  Otherwise -Og enables all -O1 optimization flags except for those
           that may interfere with debugging:

           -fbranch-count-reg        -fdelayed-branch       -fdse        -fif-conversion        -fif-conversion2
           -finline-functions-called-once   -fmove-loop-invariants    -fssa-phiopt   -ftree-bit-ccp   -ftree-dse
           -ftree-pta  -ftree-sra

       If you use multiple -O options, with or without level numbers, the last such option is the  one  that  is
       effective.

       Options of the form -fflag specify machine-independent flags.  Most flags have both positive and negative
       forms; the negative form of -ffoo is -fno-foo.  In the table below, only one of the forms is listed---the
       one you typically use.  You can figure out the other form by either removing no- or adding it.

       The  following  options  control  specific optimizations.  They are either activated by -O options or are
       related to ones that are.  You can use the following flags  in  the  rare  cases  when  "fine-tuning"  of
       optimizations to be performed is desired.

       -fno-defer-pop
           For  machines that must pop arguments after a function call, always pop the arguments as soon as each
           function returns.  At levels -O1 and higher, -fdefer-pop is the default; this allows the compiler  to
           let arguments accumulate on the stack for several function calls and pop them all at once.

       -fforward-propagate
           Perform  a forward propagation pass on RTL.  The pass tries to combine two instructions and checks if
           the result can be simplified.  If loop unrolling is active, two passes are performed and  the  second
           is scheduled after loop unrolling.

           This option is enabled by default at optimization levels -O, -O2, -O3, -Os.

       -ffp-contract=style
           -ffp-contract=off   disables   floating-point  expression  contraction.   -ffp-contract=fast  enables
           floating-point expression contraction such as forming of fused multiply-add operations if the  target
           has  native  support  for  them.   -ffp-contract=on  enables floating-point expression contraction if
           allowed by  the  language  standard.   This  is  currently  not  implemented  and  treated  equal  to
           -ffp-contract=off.

           The default is -ffp-contract=fast.

       -fomit-frame-pointer
           Omit  the  frame pointer in functions that don't need one.  This avoids the instructions to save, set
           up and restore the frame pointer; on many targets it also makes an extra register available.

           On some targets this flag has no effect because the standard calling sequence  always  uses  a  frame
           pointer, so it cannot be omitted.

           Note  that  -fno-omit-frame-pointer  doesn't  guarantee  the  frame pointer is used in all functions.
           Several targets always omit the frame pointer in leaf functions.

           Enabled by default at -O and higher.

       -foptimize-sibling-calls
           Optimize sibling and tail recursive calls.

           Enabled at levels -O2, -O3, -Os.

       -foptimize-strlen
           Optimize various standard C  string  functions  (e.g.  "strlen",  "strchr"  or  "strcpy")  and  their
           "_FORTIFY_SOURCE" counterparts into faster alternatives.

           Enabled at levels -O2, -O3.

       -fno-inline
           Do  not expand any functions inline apart from those marked with the "always_inline" attribute.  This
           is the default when not optimizing.

           Single functions can be exempted from inlining by marking them with the "noinline" attribute.

       -finline-small-functions
           Integrate functions into their callers when their body is smaller than expected  function  call  code
           (so  overall  size  of program gets smaller).  The compiler heuristically decides which functions are
           simple enough to be worth integrating in this way.  This inlining  applies  to  all  functions,  even
           those not declared inline.

           Enabled at levels -O2, -O3, -Os.

       -findirect-inlining
           Inline  also  indirect  calls  that  are  discovered  to  be known at compile time thanks to previous
           inlining.   This  option  has  any  effect  only  when  inlining  itself  is   turned   on   by   the
           -finline-functions or -finline-small-functions options.

           Enabled at levels -O2, -O3, -Os.

       -finline-functions
           Consider  all  functions  for  inlining,  even  if  they  are  not  declared  inline.   The  compiler
           heuristically decides which functions are worth integrating in this way.

           If all calls to a given function are integrated, and the function  is  declared  "static",  then  the
           function is normally not output as assembler code in its own right.

           Enabled at levels -O2, -O3, -Os.  Also enabled by -fprofile-use and -fauto-profile.

       -finline-functions-called-once
           Consider  all  "static"  functions  called  once  for inlining into their caller even if they are not
           marked "inline".  If a call to a given function is integrated, then the function  is  not  output  as
           assembler code in its own right.

           Enabled at levels -O1, -O2, -O3 and -Os, but not -Og.

       -fearly-inlining
           Inline  functions  marked by "always_inline" and functions whose body seems smaller than the function
           call overhead early before doing -fprofile-generate instrumentation and real inlining pass.  Doing so
           makes profiling significantly cheaper and usually inlining faster on programs having large chains  of
           nested wrapper functions.

           Enabled by default.

       -fipa-sra
           Perform   interprocedural  scalar  replacement  of  aggregates,  removal  of  unused  parameters  and
           replacement of parameters passed by reference by parameters passed by value.

           Enabled at levels -O2, -O3 and -Os.

       -finline-limit=n
           By default, GCC limits the size of functions that can be inlined.  This flag allows coarse control of
           this limit.  n is the size of functions that can be inlined in number of pseudo instructions.

           Inlining is actually controlled by a number of parameters, which may  be  specified  individually  by
           using --param name=value.  The -finline-limit=n option sets some of these parameters as follows:

           max-inline-insns-single
               is set to n/2.

           max-inline-insns-auto
               is set to n/2.

           See  below for a documentation of the individual parameters controlling inlining and for the defaults
           of these parameters.

           Note: there may be no value to -finline-limit that results in default behavior.

           Note: pseudo  instruction  represents,  in  this  particular  context,  an  abstract  measurement  of
           function's  size.  In no way does it represent a count of assembly instructions and as such its exact
           meaning might change from one release to an another.

       -fno-keep-inline-dllexport
           This is a more fine-grained version of -fkeep-inline-functions, which applies only to functions  that
           are declared using the "dllexport" attribute or declspec.

       -fkeep-inline-functions
           In  C,  emit "static" functions that are declared "inline" into the object file, even if the function
           has been inlined into all of its callers.  This switch does not affect functions  using  the  "extern
           inline" extension in GNU C90.  In C++, emit any and all inline functions into the object file.

       -fkeep-static-functions
           Emit "static" functions into the object file, even if the function is never used.

       -fkeep-static-consts
           Emit  variables  declared  "static  const"  when  optimization isn't turned on, even if the variables
           aren't referenced.

           GCC enables this option by default.  If you want to force the compiler to  check  if  a  variable  is
           referenced,  regardless  of whether or not optimization is turned on, use the -fno-keep-static-consts
           option.

       -fmerge-constants
           Attempt  to  merge  identical  constants  (string  constants  and  floating-point  constants)  across
           compilation units.

           This  option  is  the  default for optimized compilation if the assembler and linker support it.  Use
           -fno-merge-constants to inhibit this behavior.

           Enabled at levels -O, -O2, -O3, -Os.

       -fmerge-all-constants
           Attempt to merge identical constants and identical variables.

           This option implies -fmerge-constants.  In addition to -fmerge-constants  this  considers  e.g.  even
           constant  initialized arrays or initialized constant variables with integral or floating-point types.
           Languages like C or C++ require each variable, including multiple instances of the same  variable  in
           recursive calls, to have distinct locations, so using this option results in non-conforming behavior.

       -fmodulo-sched
           Perform  swing  modulo  scheduling  immediately before the first scheduling pass.  This pass looks at
           innermost loops and reorders their instructions by overlapping different iterations.

       -fmodulo-sched-allow-regmoves
           Perform more aggressive SMS-based modulo scheduling with register moves  allowed.   By  setting  this
           flag  certain anti-dependences edges are deleted, which triggers the generation of reg-moves based on
           the life-range analysis.  This option is effective only with -fmodulo-sched enabled.

       -fno-branch-count-reg
           Disable the optimization pass that scans for opportunities to use "decrement and branch" instructions
           on a count register instead of instruction sequences that decrement a register,  compare  it  against
           zero,  and  then  branch based upon the result.  This option is only meaningful on architectures that
           support  such  instructions,  which  include  x86,  PowerPC,  IA-64  and  S/390.    Note   that   the
           -fno-branch-count-reg  option doesn't remove the decrement and branch instructions from the generated
           instruction stream introduced by other optimization passes.

           The default is -fbranch-count-reg at -O1 and higher, except for -Og.

       -fno-function-cse
           Do not put function addresses in registers; make each instruction  that  calls  a  constant  function
           contain the function's address explicitly.

           This  option  results  in less efficient code, but some strange hacks that alter the assembler output
           may be confused by the optimizations performed when this option is not used.

           The default is -ffunction-cse

       -fno-zero-initialized-in-bss
           If the target supports a BSS section, GCC by default puts variables that are initialized to zero into
           BSS.  This can save space in the resulting code.

           This option turns off this behavior because some programs explicitly rely on variables going  to  the
           data  section---e.g.,  so that the resulting executable can find the beginning of that section and/or
           make assumptions based on that.

           The default is -fzero-initialized-in-bss.

       -fthread-jumps
           Perform optimizations that check to see if a jump branches to a  location  where  another  comparison
           subsumed  by  the first is found.  If so, the first branch is redirected to either the destination of
           the second branch or a point immediately following it, depending on whether the condition is known to
           be true or false.

           Enabled at levels -O2, -O3, -Os.

       -fsplit-wide-types
           When using a type that occupies multiple registers, such as "long long" on a 32-bit system, split the
           registers apart and allocate them independently.  This  normally  generates  better  code  for  those
           types, but may make debugging more difficult.

           Enabled at levels -O, -O2, -O3, -Os.

       -fsplit-wide-types-early
           Fully   split   wide  types  early,  instead  of  very  late.   This  option  has  no  effect  unless
           -fsplit-wide-types is turned on.

           This is the default on some targets.

       -fcse-follow-jumps
           In common subexpression elimination (CSE), scan through jump instructions when the target of the jump
           is not reached by any other path.  For example, when CSE encounters an "if" statement with an  "else"
           clause, CSE follows the jump when the condition tested is false.

           Enabled at levels -O2, -O3, -Os.

       -fcse-skip-blocks
           This  is  similar  to -fcse-follow-jumps, but causes CSE to follow jumps that conditionally skip over
           blocks.  When CSE encounters a simple "if" statement with no else  clause,  -fcse-skip-blocks  causes
           CSE to follow the jump around the body of the "if".

           Enabled at levels -O2, -O3, -Os.

       -frerun-cse-after-loop
           Re-run common subexpression elimination after loop optimizations are performed.

           Enabled at levels -O2, -O3, -Os.

       -fgcse
           Perform  a global common subexpression elimination pass.  This pass also performs global constant and
           copy propagation.

           Note: When compiling a program using computed gotos, a GCC extension, you  may  get  better  run-time
           performance  if  you  disable the global common subexpression elimination pass by adding -fno-gcse to
           the command line.

           Enabled at levels -O2, -O3, -Os.

       -fgcse-lm
           When -fgcse-lm is enabled, global common subexpression elimination attempts to move  loads  that  are
           only  killed  by  stores  into themselves.  This allows a loop containing a load/store sequence to be
           changed to a load outside the loop, and a copy/store within the loop.

           Enabled by default when -fgcse is enabled.

       -fgcse-sm
           When -fgcse-sm is enabled, a store motion pass is run after global common subexpression  elimination.
           This  pass  attempts  to  move  stores  out of loops.  When used in conjunction with -fgcse-lm, loops
           containing a load/store sequence can be changed to a load before the loop and a store after the loop.

           Not enabled at any optimization level.

       -fgcse-las
           When -fgcse-las is enabled, the global common subexpression  elimination  pass  eliminates  redundant
           loads that come after stores to the same memory location (both partial and full redundancies).

           Not enabled at any optimization level.

       -fgcse-after-reload
           When  -fgcse-after-reload  is  enabled,  a redundant load elimination pass is performed after reload.
           The purpose of this pass is to clean up redundant spilling.

           Enabled by -fprofile-use and -fauto-profile.

       -faggressive-loop-optimizations
           This option tells the loop optimizer to use language constraints to derive bounds for the  number  of
           iterations  of a loop.  This assumes that loop code does not invoke undefined behavior by for example
           causing signed integer overflows or out-of-bound array  accesses.   The  bounds  for  the  number  of
           iterations  of  a loop are used to guide loop unrolling and peeling and loop exit test optimizations.
           This option is enabled by default.

       -funconstrained-commons
           This option tells the compiler that variables declared in common blocks (e.g. Fortran) may  later  be
           overridden  with  longer  trailing arrays. This prevents certain optimizations that depend on knowing
           the array bounds.

       -fcrossjumping
           Perform cross-jumping transformation.  This transformation unifies equivalent  code  and  saves  code
           size.  The resulting code may or may not perform better than without cross-jumping.

           Enabled at levels -O2, -O3, -Os.

       -fauto-inc-dec
           Combine  increments  or decrements of addresses with memory accesses.  This pass is always skipped on
           architectures that do not have instructions to support this.  Enabled by default at -O and higher  on
           architectures that support this.

       -fdce
           Perform dead code elimination (DCE) on RTL.  Enabled by default at -O and higher.

       -fdse
           Perform dead store elimination (DSE) on RTL.  Enabled by default at -O and higher.

       -fif-conversion
           Attempt  to  transform  conditional  jumps  into  branch-less  equivalents.   This  includes  use  of
           conditional moves, min, max, set flags and abs instructions,  and  some  tricks  doable  by  standard
           arithmetics.   The  use  of  conditional  execution  on  chips where it is available is controlled by
           -fif-conversion2.

           Enabled at levels -O, -O2, -O3, -Os, but not with -Og.

       -fif-conversion2
           Use  conditional  execution  (where  available)  to  transform  conditional  jumps  into  branch-less
           equivalents.

           Enabled at levels -O, -O2, -O3, -Os, but not with -Og.

       -fdeclone-ctor-dtor
           The  C++  ABI  requires  multiple  entry  points  for  constructors  and  destructors: one for a base
           subobject, one for a complete object, and one for a virtual destructor  that  calls  operator  delete
           afterwards.   For  a  hierarchy  with virtual bases, the base and complete variants are clones, which
           means two copies of the function.  With this option, the base and complete variants are changed to be
           thunks that call a common implementation.

           Enabled by -Os.

       -fdelete-null-pointer-checks
           Assume that programs cannot safely dereference null pointers,  and  that  no  code  or  data  element
           resides  at  address  zero.   This  option  enables  simple  constant  folding  optimizations  at all
           optimization levels.  In addition, other optimization passes in GCC use this flag to  control  global
           dataflow  analyses that eliminate useless checks for null pointers; these assume that a memory access
           to address zero always results in a trap, so that if a pointer is checked after it has  already  been
           dereferenced, it cannot be null.

           Note    however    that    in    some    environments    this    assumption   is   not   true.    Use
           -fno-delete-null-pointer-checks to disable  this  optimization  for  programs  that  depend  on  that
           behavior.

           This  option  is  enabled  by  default on most targets.  On Nios II ELF, it defaults to off.  On AVR,
           CR16, and MSP430, this option is completely disabled.

           Passes that use the dataflow information are enabled independently at different optimization levels.

       -fdevirtualize
           Attempt to convert calls to virtual functions to direct calls.  This is done both within a  procedure
           and interprocedurally as part of indirect inlining (-findirect-inlining) and interprocedural constant
           propagation (-fipa-cp).  Enabled at levels -O2, -O3, -Os.

       -fdevirtualize-speculatively
           Attempt  to convert calls to virtual functions to speculative direct calls.  Based on the analysis of
           the type inheritance graph, determine for a given call the set of  likely  targets.  If  the  set  is
           small,  preferably of size 1, change the call into a conditional deciding between direct and indirect
           calls.  The speculative calls enable more optimizations, such as inlining.  When  they  seem  useless
           after further optimization, they are converted back into original form.

       -fdevirtualize-at-ltrans
           Stream  extra information needed for aggressive devirtualization when running the link-time optimizer
           in local transformation mode.  This option enables more devirtualization but significantly  increases
           the size of streamed data. For this reason it is disabled by default.

       -fexpensive-optimizations
           Perform a number of minor optimizations that are relatively expensive.

           Enabled at levels -O2, -O3, -Os.

       -free
           Attempt  to  remove  redundant  extension  instructions.   This  is especially helpful for the x86-64
           architecture, which implicitly zero-extends in 64-bit registers after writing to their  lower  32-bit
           half.

           Enabled for Alpha, AArch64 and x86 at levels -O2, -O3, -Os.

       -fno-lifetime-dse
           In  C++  the value of an object is only affected by changes within its lifetime: when the constructor
           begins, the object has an indeterminate value, and any changes during the lifetime of the object  are
           dead  when  the object is destroyed.  Normally dead store elimination will take advantage of this; if
           your code relies on the value of the object storage persisting beyond the lifetime of the object, you
           can use this flag to disable this optimization.  To preserve stores  before  the  constructor  starts
           (e.g.  because  your operator new clears the object storage) but still treat the object as dead after
           the destructor, you can use -flifetime-dse=1.  The default behavior can be explicitly  selected  with
           -flifetime-dse=2.  -flifetime-dse=0 is equivalent to -fno-lifetime-dse.

       -flive-range-shrinkage
           Attempt  to  decrease  register  pressure through register live range shrinkage.  This is helpful for
           fast processors with small or moderate size register sets.

       -fira-algorithm=algorithm
           Use the specified coloring algorithm for the integrated register allocator.  The  algorithm  argument
           can  be  priority,  which  specifies  Chow's priority coloring, or CB, which specifies Chaitin-Briggs
           coloring.  Chaitin-Briggs coloring is not implemented for all architectures, but  for  those  targets
           that do support it, it is the default because it generates better code.

       -fira-region=region
           Use  specified  regions  for the integrated register allocator.  The region argument should be one of
           the following:

           all Use all loops as register allocation regions.  This can give the best results for machines with a
               small and/or irregular register set.

           mixed
               Use all loops except for loops with small register pressure as the regions.  This  value  usually
               gives  the  best results in most cases and for most architectures, and is enabled by default when
               compiling with optimization for speed (-O, -O2, ...).

           one Use all functions as a single region.  This typically results in the smallest code size,  and  is
               enabled by default for -Os or -O0.

       -fira-hoist-pressure
           Use  IRA  to evaluate register pressure in the code hoisting pass for decisions to hoist expressions.
           This option usually results in smaller code, but it can slow the compiler down.

           This option is enabled at level -Os for all targets.

       -fira-loop-pressure
           Use IRA to evaluate register pressure in loops for decisions to move loop  invariants.   This  option
           usually results in generation of faster and smaller code on machines with large register files (>= 32
           registers), but it can slow the compiler down.

           This option is enabled at level -O3 for some targets.

       -fno-ira-share-save-slots
           Disable  sharing of stack slots used for saving call-used hard registers living through a call.  Each
           hard register gets a separate stack slot, and as a result function stack frames are larger.

       -fno-ira-share-spill-slots
           Disable sharing of stack slots allocated for pseudo-registers.  Each pseudo-register  that  does  not
           get a hard register gets a separate stack slot, and as a result function stack frames are larger.

       -flra-remat
           Enable  CFG-sensitive  rematerialization  in  LRA.  Instead of loading values of spilled pseudos, LRA
           tries to rematerialize (recalculate) values if it is profitable.

           Enabled at levels -O2, -O3, -Os.

       -fdelayed-branch
           If supported for the target machine, attempt to reorder instructions  to  exploit  instruction  slots
           available after delayed branch instructions.

           Enabled at levels -O, -O2, -O3, -Os, but not at -Og.

       -fschedule-insns
           If  supported  for  the target machine, attempt to reorder instructions to eliminate execution stalls
           due to required data being unavailable.  This helps machines that have slow floating point or  memory
           load  instructions  by  allowing  other  instructions  to  be  issued until the result of the load or
           floating-point instruction is required.

           Enabled at levels -O2, -O3.

       -fschedule-insns2
           Similar to -fschedule-insns, but requests an additional pass of instruction scheduling after register
           allocation has been done.  This is especially useful on machines with a relatively  small  number  of
           registers and where memory load instructions take more than one cycle.

           Enabled at levels -O2, -O3, -Os.

       -fno-sched-interblock
           Disable  instruction scheduling across basic blocks, which is normally enabled when scheduling before
           register allocation, i.e.  with -fschedule-insns or at -O2 or higher.

       -fno-sched-spec
           Disable speculative motion of non-load instructions, which is normally enabled when scheduling before
           register allocation, i.e.  with -fschedule-insns or at -O2 or higher.

       -fsched-pressure
           Enable register pressure sensitive insn scheduling before register allocation.  This only makes sense
           when scheduling before register allocation is enabled,  i.e.  with  -fschedule-insns  or  at  -O2  or
           higher.   Usage  of  this  option  can improve the generated code and decrease its size by preventing
           register pressure increase above the number of available hard  registers  and  subsequent  spills  in
           register allocation.

       -fsched-spec-load
           Allow  speculative  motion  of  some load instructions.  This only makes sense when scheduling before
           register allocation, i.e. with -fschedule-insns or at -O2 or higher.

       -fsched-spec-load-dangerous
           Allow speculative motion of more load instructions.  This only makes  sense  when  scheduling  before
           register allocation, i.e. with -fschedule-insns or at -O2 or higher.

       -fsched-stalled-insns
       -fsched-stalled-insns=n
           Define  how  many  insns  (if  any) can be moved prematurely from the queue of stalled insns into the
           ready list during the second scheduling pass.  -fno-sched-stalled-insns means that no insns are moved
           prematurely, -fsched-stalled-insns=0 means there is no limit on how many queued insns  can  be  moved
           prematurely.  -fsched-stalled-insns without a value is equivalent to -fsched-stalled-insns=1.

       -fsched-stalled-insns-dep
       -fsched-stalled-insns-dep=n
           Define  how  many  insn  groups  (cycles)  are  examined for a dependency on a stalled insn that is a
           candidate for premature removal from the queue of stalled insns.  This has an effect only during  the
           second  scheduling  pass, and only if -fsched-stalled-insns is used.  -fno-sched-stalled-insns-dep is
           equivalent to -fsched-stalled-insns-dep=0.  -fsched-stalled-insns-dep without a value  is  equivalent
           to -fsched-stalled-insns-dep=1.

       -fsched2-use-superblocks
           When  scheduling  after  register  allocation,  use superblock scheduling.  This allows motion across
           basic block boundaries, resulting in faster schedules.  This  option  is  experimental,  as  not  all
           machine  descriptions  used  by GCC model the CPU closely enough to avoid unreliable results from the
           algorithm.

           This only makes sense when scheduling after register allocation, i.e. with  -fschedule-insns2  or  at
           -O2 or higher.

       -fsched-group-heuristic
           Enable the group heuristic in the scheduler.  This heuristic favors the instruction that belongs to a
           schedule group.  This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or
           -fschedule-insns2 or at -O2 or higher.

       -fsched-critical-path-heuristic
           Enable  the  critical-path  heuristic  in  the  scheduler.  This heuristic favors instructions on the
           critical path.  This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns  or
           -fschedule-insns2 or at -O2 or higher.

       -fsched-spec-insn-heuristic
           Enable  the  speculative  instruction  heuristic in the scheduler.  This heuristic favors speculative
           instructions with greater dependency weakness.   This  is  enabled  by  default  when  scheduling  is
           enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2 or higher.

       -fsched-rank-heuristic
           Enable  the  rank  heuristic  in the scheduler.  This heuristic favors the instruction belonging to a
           basic block with greater size or frequency.  This is enabled by default when scheduling  is  enabled,
           i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2 or higher.

       -fsched-last-insn-heuristic
           Enable  the  last-instruction heuristic in the scheduler.  This heuristic favors the instruction that
           is less dependent on the last instruction scheduled.  This is enabled by default when  scheduling  is
           enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher.

       -fsched-dep-count-heuristic
           Enable  the  dependent-count  heuristic in the scheduler.  This heuristic favors the instruction that
           has more instructions depending on it.  This is enabled by default when scheduling is  enabled,  i.e.
           with -fschedule-insns or -fschedule-insns2 or at -O2 or higher.

       -freschedule-modulo-scheduled-loops
           Modulo  scheduling  is performed before traditional scheduling.  If a loop is modulo scheduled, later
           scheduling passes may change its schedule.  Use this option to control that behavior.

       -fselective-scheduling
           Schedule instructions using selective scheduling algorithm.  Selective scheduling runs instead of the
           first scheduler pass.

       -fselective-scheduling2
           Schedule instructions using selective scheduling algorithm.  Selective scheduling runs instead of the
           second scheduler pass.

       -fsel-sched-pipelining
           Enable software pipelining of innermost loops during selective scheduling.  This option has no effect
           unless one of -fselective-scheduling or -fselective-scheduling2 is turned on.

       -fsel-sched-pipelining-outer-loops
           When pipelining loops during selective scheduling, also pipeline outer loops.   This  option  has  no
           effect unless -fsel-sched-pipelining is turned on.

       -fsemantic-interposition
           Some  object  formats, like ELF, allow interposing of symbols by the dynamic linker.  This means that
           for symbols exported from the DSO, the compiler cannot perform interprocedural propagation,  inlining
           and  other  optimizations in anticipation that the function or variable in question may change. While
           this feature is  useful,  for  example,  to  rewrite  memory  allocation  functions  by  a  debugging
           implementation,  it  is expensive in the terms of code quality.  With -fno-semantic-interposition the
           compiler assumes that if interposition happens for  functions  the  overwriting  function  will  have
           precisely  the  same semantics (and side effects).  Similarly if interposition happens for variables,
           the constructor of the variable will be the same. The flag has no  effect  for  functions  explicitly
           declared  inline  (where  it  is never allowed for interposition to change semantics) and for symbols
           explicitly declared weak.

       -fshrink-wrap
           Emit function prologues only before parts of the function that need it, rather than at the top of the
           function.  This flag is enabled by default at -O and higher.

       -fshrink-wrap-separate
           Shrink-wrap separate parts of the prologue and epilogue separately, so  that  those  parts  are  only
           executed  when  needed.  This option is on by default, but has no effect unless -fshrink-wrap is also
           turned on and the target supports this.

       -fcaller-saves
           Enable allocation of values to registers that are clobbered by  function  calls,  by  emitting  extra
           instructions  to save and restore the registers around such calls.  Such allocation is done only when
           it seems to result in better code.

           This option is always enabled by default on certain machines,  usually  those  which  have  no  call-
           preserved registers to use instead.

           Enabled at levels -O2, -O3, -Os.

       -fcombine-stack-adjustments
           Tracks stack adjustments (pushes and pops) and stack memory references and then tries to find ways to
           combine them.

           Enabled by default at -O1 and higher.

       -fipa-ra
           Use  caller save registers for allocation if those registers are not used by any called function.  In
           that case it is not necessary to save and restore them around calls.  This is only possible if called
           functions are part of same compilation unit as current function and they are compiled before it.

           Enabled at levels -O2,  -O3,  -Os,  however  the  option  is  disabled  if  generated  code  will  be
           instrumented  for  profiling (-p, or -pg) or if callee's register usage cannot be known exactly (this
           happens on targets that do not expose prologues and epilogues in RTL).

       -fconserve-stack
           Attempt to minimize stack usage.  The compiler attempts to use less stack space, even if  that  makes
           the  program  slower.   This  option  implies  setting the large-stack-frame parameter to 100 and the
           large-stack-frame-growth parameter to 400.

       -ftree-reassoc
           Perform reassociation on trees.  This flag is enabled by default at -O and higher.

       -fcode-hoisting
           Perform code hoisting.  Code hoisting tries to move the evaluation of  expressions  executed  on  all
           paths  to  the  function  exit  as  early  as  possible.   This  is  especially useful as a code size
           optimization, but it often helps for code speed as well.  This flag is enabled by default at -O2  and
           higher.

       -ftree-pre
           Perform  partial  redundancy  elimination (PRE) on trees.  This flag is enabled by default at -O2 and
           -O3.

       -ftree-partial-pre
           Make partial redundancy elimination (PRE) more aggressive.  This flag is enabled by default at -O3.

       -ftree-forwprop
           Perform forward propagation on trees.  This flag is enabled by default at -O and higher.

       -ftree-fre
           Perform full redundancy elimination (FRE) on trees.  The difference between FRE and PRE is  that  FRE
           only considers expressions that are computed on all paths leading to the redundant computation.  This
           analysis  is  faster than PRE, though it exposes fewer redundancies.  This flag is enabled by default
           at -O and higher.

       -ftree-phiprop
           Perform hoisting of loads from conditional pointers on trees.  This pass is enabled by default at  -O
           and higher.

       -fhoist-adjacent-loads
           Speculatively  hoist  loads  from  both  branches  of  an if-then-else if the loads are from adjacent
           locations in the same structure and the target architecture has a conditional move instruction.  This
           flag is enabled by default at -O2 and higher.

       -ftree-copy-prop
           Perform copy propagation on trees.  This pass eliminates unnecessary copy operations.  This  flag  is
           enabled by default at -O and higher.

       -fipa-pure-const
           Discover which functions are pure or constant.  Enabled by default at -O and higher.

       -fipa-reference
           Discover  which  static  variables  do not escape the compilation unit.  Enabled by default at -O and
           higher.

       -fipa-reference-addressable
           Discover read-only, write-only and non-addressable static variables.  Enabled by default  at  -O  and
           higher.

       -fipa-stack-alignment
           Reduce stack alignment on call sites if possible.  Enabled by default.

       -fipa-pta
           Perform  interprocedural  pointer  analysis  and interprocedural modification and reference analysis.
           This option can cause excessive memory and compile-time usage on large compilation units.  It is  not
           enabled by default at any optimization level.

       -fipa-profile
           Perform  interprocedural  profile  propagation.   The  functions  called only from cold functions are
           marked as cold. Also functions executed once (such as  "cold",  "noreturn",  static  constructors  or
           destructors)  are  identified. Cold functions and loop less parts of functions executed once are then
           optimized for size.  Enabled by default at -O and higher.

       -fipa-modref
           Perform interprocedural mod/ref analysis.  This optimization analyzes the side effects  of  functions
           (memory  locations  that  are  modified  or  referenced)  and  enables better optimization across the
           function call boundary.  This flag is enabled by default at -O and higher.

       -fipa-cp
           Perform interprocedural constant propagation.  This optimization analyzes the  program  to  determine
           when  values passed to functions are constants and then optimizes accordingly.  This optimization can
           substantially increase performance if the application has constants passed to functions.   This  flag
           is enabled by default at -O2, -Os and -O3.  It is also enabled by -fprofile-use and -fauto-profile.

       -fipa-cp-clone
           Perform  function  cloning  to  make  interprocedural  constant  propagation stronger.  When enabled,
           interprocedural constant propagation performs function cloning when externally visible  function  can
           be  called  with  constant  arguments.   Because  this  optimization  can  create  multiple copies of
           functions, it may significantly increase code size (see --param ipa-cp-unit-growth=value).  This flag
           is enabled by default at -O3.  It is also enabled by -fprofile-use and -fauto-profile.

       -fipa-bit-cp
           When enabled, perform interprocedural bitwise constant propagation. This flag is enabled  by  default
           at -O2 and by -fprofile-use and -fauto-profile.  It requires that -fipa-cp is enabled.

       -fipa-vrp
           When enabled, perform interprocedural propagation of value ranges. This flag is enabled by default at
           -O2. It requires that -fipa-cp is enabled.

       -fipa-icf
           Perform  Identical Code Folding for functions and read-only variables.  The optimization reduces code
           size and may disturb unwind stacks by replacing a function by equivalent one with a  different  name.
           The optimization works more effectively with link-time optimization enabled.

           Although  the  behavior  is similar to the Gold Linker's ICF optimization, GCC ICF works on different
           levels and thus the optimizations are not same - there are equivalences that are found  only  by  GCC
           and equivalences found only by Gold.

           This flag is enabled by default at -O2 and -Os.

       -flive-patching=level
           Control GCC's optimizations to produce output suitable for live-patching.

           If  the  compiler's  optimization  uses  a  function's body or information extracted from its body to
           optimize/change another function, the latter is called an impacted function  of  the  former.   If  a
           function is patched, its impacted functions should be patched too.

           The  impacted functions are determined by the compiler's interprocedural optimizations.  For example,
           a caller is impacted when inlining a function into its caller, cloning a function  and  changing  its
           caller  to call this new clone, or extracting a function's pureness/constness information to optimize
           its direct or indirect callers, etc.

           Usually, the more IPA optimizations enabled, the larger the number of  impacted  functions  for  each
           function.   In  order to control the number of impacted functions and more easily compute the list of
           impacted function, IPA optimizations can be partially enabled at two different levels.

           The level argument should be one of the following:

           inline-clone
               Only enable inlining and cloning optimizations, which includes inlining, cloning, interprocedural
               scalar replacement of aggregates and partial inlining.  As a result, when  patching  a  function,
               all its callers and its clones' callers are impacted, therefore need to be patched as well.

               -flive-patching=inline-clone   disables   the   following   optimization  flags:  -fwhole-program
               -fipa-pta   -fipa-reference    -fipa-ra   -fipa-icf    -fipa-icf-functions    -fipa-icf-variables
               -fipa-bit-cp    -fipa-vrp   -fipa-pure-const   -fipa-reference-addressable  -fipa-stack-alignment
               -fipa-modref

           inline-only-static
               Only enable inlining of static functions.  As a result, when patching a static function, all  its
               callers are impacted and so need to be patched as well.

               In     addition    to    all    the    flags    that    -flive-patching=inline-clone    disables,
               -flive-patching=inline-only-static  disables  the  following   additional   optimization   flags:
               -fipa-cp-clone  -fipa-sra  -fpartial-inlining  -fipa-cp

           When -flive-patching is specified without any value, the default value is inline-clone.

           This flag is disabled by default.

           Note that -flive-patching is not supported with link-time optimization (-flto).

       -fisolate-erroneous-paths-dereference
           Detect  paths  that  trigger  erroneous  or  undefined  behavior due to dereferencing a null pointer.
           Isolate those paths from the main control flow and turn the statement  with  erroneous  or  undefined
           behavior  into  a  trap.   This  flag  is  enabled  by  default  at  -O2  and  higher  and depends on
           -fdelete-null-pointer-checks also being enabled.

       -fisolate-erroneous-paths-attribute
           Detect paths that trigger erroneous or undefined behavior due to a null value being  used  in  a  way
           forbidden  by  a "returns_nonnull" or "nonnull" attribute.  Isolate those paths from the main control
           flow and turn the statement with erroneous or undefined behavior into a trap.  This is not  currently
           enabled, but may be enabled by -O2 in the future.

       -ftree-sink
           Perform forward store motion on trees.  This flag is enabled by default at -O and higher.

       -ftree-bit-ccp
           Perform  sparse  conditional  bit  constant  propagation  on  trees  and  propagate pointer alignment
           information.  This pass only operates on local scalar variables and is enabled by default at -O1  and
           higher, except for -Og.  It requires that -ftree-ccp is enabled.

       -ftree-ccp
           Perform  sparse  conditional  constant  propagation (CCP) on trees.  This pass only operates on local
           scalar variables and is enabled by default at -O and higher.

       -fssa-backprop
           Propagate information about uses of a value  up  the  definition  chain  in  order  to  simplify  the
           definitions.   For  example,  this  pass strips sign operations if the sign of a value never matters.
           The flag is enabled by default at -O and higher.

       -fssa-phiopt
           Perform pattern matching on SSA PHI nodes to optimize conditional code.   This  pass  is  enabled  by
           default at -O1 and higher, except for -Og.

       -ftree-switch-conversion
           Perform  conversion  of  simple  initializations  in a switch to initializations from a scalar array.
           This flag is enabled by default at -O2 and higher.

       -ftree-tail-merge
           Look for identical code sequences.  When  found,  replace  one  with  a  jump  to  the  other.   This
           optimization  is  known as tail merging or cross jumping.  This flag is enabled by default at -O2 and
           higher.  The compilation time in this pass can be limited using max-tail-merge-comparisons  parameter
           and max-tail-merge-iterations parameter.

       -ftree-dce
           Perform dead code elimination (DCE) on trees.  This flag is enabled by default at -O and higher.

       -ftree-builtin-call-dce
           Perform  conditional dead code elimination (DCE) for calls to built-in functions that may set "errno"
           but are otherwise free of side effects.  This flag is enabled by default at -O2 and higher if -Os  is
           not also specified.

       -ffinite-loops
           Assume that a loop with an exit will eventually take the exit and not loop indefinitely.  This allows
           the  compiler  to  remove loops that otherwise have no side-effects, not considering eventual endless
           looping as such.

           This option is enabled by default at -O2 for C++ with -std=c++11 or higher.

       -ftree-dominator-opts
           Perform a variety of simple scalar cleanups (constant/copy propagation, redundancy elimination, range
           propagation and expression simplification) based on a dominator tree traversal.  This  also  performs
           jump threading (to reduce jumps to jumps). This flag is enabled by default at -O and higher.

       -ftree-dse
           Perform  dead  store elimination (DSE) on trees.  A dead store is a store into a memory location that
           is later overwritten by another store without any intervening loads.  In this case the earlier  store
           can be deleted.  This flag is enabled by default at -O and higher.

       -ftree-ch
           Perform  loop  header  copying on trees.  This is beneficial since it increases effectiveness of code
           motion optimizations.  It also saves one jump.  This flag is enabled by default at -O and higher.  It
           is not enabled for -Os, since it usually increases code size.

       -ftree-loop-optimize
           Perform loop optimizations on trees.  This flag is enabled by default at -O and higher.

       -ftree-loop-linear
       -floop-strip-mine
       -floop-block
           Perform loop nest optimizations.  Same as -floop-nest-optimize.  To use this code transformation, GCC
           has to be configured with --with-isl to enable the Graphite loop transformation infrastructure.

       -fgraphite-identity
           Enable the identity  transformation  for  graphite.   For  every  SCoP  we  generate  the  polyhedral
           representation  and transform it back to gimple.  Using -fgraphite-identity we can check the costs or
           benefits of the GIMPLE -> GRAPHITE -> GIMPLE transformation.  Some  minimal  optimizations  are  also
           performed by the code generator isl, like index splitting and dead code elimination in loops.

       -floop-nest-optimize
           Enable  the  isl based loop nest optimizer.  This is a generic loop nest optimizer based on the Pluto
           optimization algorithms.  It calculates a loop structure optimized for data-locality and parallelism.
           This option is experimental.

       -floop-parallelize-all
           Use the Graphite data dependence analysis to identify loops that can  be  parallelized.   Parallelize
           all  the  loops that can be analyzed to not contain loop carried dependences without checking that it
           is profitable to parallelize the loops.

       -ftree-coalesce-vars
           While transforming the program out of the SSA representation, attempt to reduce copying by coalescing
           versions of different user-defined  variables,  instead  of  just  compiler  temporaries.   This  may
           severely limit the ability to debug an optimized program compiled with -fno-var-tracking-assignments.
           In  the negated form, this flag prevents SSA coalescing of user variables.  This option is enabled by
           default if optimization is enabled, and it does very little otherwise.

       -ftree-loop-if-convert
           Attempt to transform conditional jumps in the innermost loops to branch-less equivalents.  The intent
           is to remove control-flow  from  the  innermost  loops  in  order  to  improve  the  ability  of  the
           vectorization pass to handle these loops.  This is enabled by default if vectorization is enabled.

       -ftree-loop-distribution
           Perform  loop  distribution.   This  flag  can improve cache performance on big loop bodies and allow
           further loop optimizations, like parallelization or vectorization, to take place.  For  example,  the
           loop

                   DO I = 1, N
                     A(I) = B(I) + C
                     D(I) = E(I) * F
                   ENDDO

           is transformed to

                   DO I = 1, N
                      A(I) = B(I) + C
                   ENDDO
                   DO I = 1, N
                      D(I) = E(I) * F
                   ENDDO

           This flag is enabled by default at -O3.  It is also enabled by -fprofile-use and -fauto-profile.

       -ftree-loop-distribute-patterns
           Perform  loop distribution of patterns that can be code generated with calls to a library.  This flag
           is enabled by default at -O2 and higher, and by -fprofile-use and -fauto-profile.

           This pass distributes the initialization loops and generates a call to memset zero.  For example, the
           loop

                   DO I = 1, N
                     A(I) = 0
                     B(I) = A(I) + I
                   ENDDO

           is transformed to

                   DO I = 1, N
                      A(I) = 0
                   ENDDO
                   DO I = 1, N
                      B(I) = A(I) + I
                   ENDDO

           and the initialization loop is transformed into a call to memset  zero.   This  flag  is  enabled  by
           default at -O3.  It is also enabled by -fprofile-use and -fauto-profile.

       -floop-interchange
           Perform  loop  interchange outside of graphite.  This flag can improve cache performance on loop nest
           and allow further loop optimizations, like vectorization, to take place.  For example, the loop

                   for (int i = 0; i < N; i++)
                     for (int j = 0; j < N; j++)
                       for (int k = 0; k < N; k++)
                         c[i][j] = c[i][j] + a[i][k]*b[k][j];

           is transformed to

                   for (int i = 0; i < N; i++)
                     for (int k = 0; k < N; k++)
                       for (int j = 0; j < N; j++)
                         c[i][j] = c[i][j] + a[i][k]*b[k][j];

           This flag is enabled by default at -O3.  It is also enabled by -fprofile-use and -fauto-profile.

       -floop-unroll-and-jam
           Apply unroll and jam transformations on feasible loops.  In a loop nest this unrolls the  outer  loop
           by some factor and fuses the resulting multiple inner loops.  This flag is enabled by default at -O3.
           It is also enabled by -fprofile-use and -fauto-profile.

       -ftree-loop-im
           Perform  loop  invariant motion on trees.  This pass moves only invariants that are hard to handle at
           RTL level  (function  calls,  operations  that  expand  to  nontrivial  sequences  of  insns).   With
           -funswitch-loops  it also moves operands of conditions that are invariant out of the loop, so that we
           can use just trivial invariantness analysis in  loop  unswitching.   The  pass  also  includes  store
           motion.

       -ftree-loop-ivcanon
           Create  a  canonical  counter  for  number  of  iterations  in  loops for which determining number of
           iterations requires complicated analysis.  Later optimizations then may determine the number  easily.
           Useful especially in connection with unrolling.

       -ftree-scev-cprop
           Perform  final  value  replacement.  If a variable is modified in a loop in such a way that its value
           when exiting the loop can be determined  using  only  its  initial  value  and  the  number  of  loop
           iterations, replace uses of the final value by such a computation, provided it is sufficiently cheap.
           This  reduces  data dependencies and may allow further simplifications.  Enabled by default at -O and
           higher.

       -fivopts
           Perform  induction  variable  optimizations  (strength  reduction,  induction  variable  merging  and
           induction variable elimination) on trees.

       -ftree-parallelize-loops=n
           Parallelize  loops, i.e., split their iteration space to run in n threads.  This is only possible for
           loops whose iterations are independent and can be arbitrarily reordered.  The  optimization  is  only
           profitable on multiprocessor machines, for loops that are CPU-intensive, rather than constrained e.g.
           by  memory  bandwidth.  This option implies -pthread, and thus is only supported on targets that have
           support for -pthread.

       -ftree-pta
           Perform function-local points-to analysis on trees.  This flag is  enabled  by  default  at  -O1  and
           higher, except for -Og.

       -ftree-sra
           Perform  scalar  replacement  of aggregates.  This pass replaces structure references with scalars to
           prevent committing structures to memory too early.  This flag  is  enabled  by  default  at  -O1  and
           higher, except for -Og.

       -fstore-merging
           Perform merging of narrow stores to consecutive memory addresses.  This pass merges contiguous stores
           of  immediate  values  narrower  than  a  word  into  fewer  wider  stores  to  reduce  the number of
           instructions.  This is enabled by default at -O2 and higher as well as -Os.

       -ftree-ter
           Perform temporary expression  replacement  during  the  SSA->normal  phase.   Single  use/single  def
           temporaries  are replaced at their use location with their defining expression.  This results in non-
           GIMPLE code, but gives the expanders much more complex trees to  work  on  resulting  in  better  RTL
           generation.  This is enabled by default at -O and higher.

       -ftree-slsr
           Perform  straight-line  strength  reduction  on trees.  This recognizes related expressions involving
           multiplications and replaces them by less expensive calculations when possible.  This is  enabled  by
           default at -O and higher.

       -ftree-vectorize
           Perform  vectorization  on trees. This flag enables -ftree-loop-vectorize and -ftree-slp-vectorize if
           not explicitly specified.

       -ftree-loop-vectorize
           Perform loop vectorization on trees. This flag is enabled by default at -O3 and by  -ftree-vectorize,
           -fprofile-use, and -fauto-profile.

       -ftree-slp-vectorize
           Perform  basic  block  vectorization  on  trees.  This  flag  is  enabled  by  default  at -O3 and by
           -ftree-vectorize, -fprofile-use, and -fauto-profile.

       -fvect-cost-model=model
           Alter the cost model used for vectorization.  The model argument should be one of unlimited, dynamic,
           cheap or very-cheap.  With the unlimited model the vectorized code-path is assumed to  be  profitable
           while  with  the  dynamic model a runtime check guards the vectorized code-path to enable it only for
           iteration counts that will likely execute faster than when executing the original scalar  loop.   The
           cheap  model disables vectorization of loops where doing so would be cost prohibitive for example due
           to required runtime checks for data dependence or alignment but otherwise is  equal  to  the  dynamic
           model.   The very-cheap model only allows vectorization if the vector code would entirely replace the
           scalar code that is being vectorized.  For example, if each iteration of a vectorized loop would only
           be able to handle exactly four iterations of the scalar loop, the very-cheap model would  only  allow
           vectorization if the scalar iteration count is known to be a multiple of four.

           The default cost model depends on other optimization flags and is either dynamic or cheap.

       -fsimd-cost-model=model
           Alter  the  cost  model  used  for vectorization of loops marked with the OpenMP simd directive.  The
           model argument should be one of unlimited, dynamic, cheap.  All values of model have the same meaning
           as described in -fvect-cost-model and by default a cost model defined with -fvect-cost-model is used.

       -ftree-vrp
           Perform Value Range Propagation on trees.  This is similar to  the  constant  propagation  pass,  but
           instead of values, ranges of values are propagated.  This allows the optimizers to remove unnecessary
           range  checks like array bound checks and null pointer checks.  This is enabled by default at -O2 and
           higher.  Null pointer check elimination is only done if -fdelete-null-pointer-checks is enabled.

       -fsplit-paths
           Split paths  leading  to  loop  backedges.   This  can  improve  dead  code  elimination  and  common
           subexpression elimination.  This is enabled by default at -O3 and above.

       -fsplit-ivs-in-unroller
           Enables  expression  of  values of induction variables in later iterations of the unrolled loop using
           the value in the first iteration.  This breaks long dependency chains, thus improving  efficiency  of
           the scheduling passes.

           A  combination  of -fweb and CSE is often sufficient to obtain the same effect.  However, that is not
           reliable in cases where the loop body is more complicated than a single basic block.   It  also  does
           not work at all on some architectures due to restrictions in the CSE pass.

           This optimization is enabled by default.

       -fvariable-expansion-in-unroller
           With this option, the compiler creates multiple copies of some local variables when unrolling a loop,
           which can result in superior code.

           This optimization is enabled by default for PowerPC targets, but disabled by default otherwise.

       -fpartial-inlining
           Inline  parts of functions.  This option has any effect only when inlining itself is turned on by the
           -finline-functions or -finline-small-functions options.

           Enabled at levels -O2, -O3, -Os.

       -fpredictive-commoning
           Perform predictive commoning optimization, i.e., reusing computations (especially  memory  loads  and
           stores) performed in previous iterations of loops.

           This option is enabled at level -O3.  It is also enabled by -fprofile-use and -fauto-profile.

       -fprefetch-loop-arrays
           If  supported  by  the  target  machine,  generate  instructions  to  prefetch  memory to improve the
           performance of loops that access large arrays.

           This option may generate better or worse code; results are highly dependent on the structure of loops
           within the source code.

           Disabled at level -Os.

       -fno-printf-return-value
           Do not substitute constants for known return value of formatted output functions such  as  "sprintf",
           "snprintf",  "vsprintf", and "vsnprintf" (but not "printf" of "fprintf").  This transformation allows
           GCC to optimize or even eliminate branches based on the known return value of these functions  called
           with  arguments  that  are  either  constant,  or  whose values are known to be in a range that makes
           determining the exact return value possible.  For example, when -fprintf-return-value is  in  effect,
           both  the  branch and the body of the "if" statement (but not the call to "snprint") can be optimized
           away when "i" is a 32-bit or smaller integer because the return value is guaranteed to be at most 8.

                   char buf[9];
                   if (snprintf (buf, "%08x", i) >= sizeof buf)
                     ...

           The -fprintf-return-value option relies on other optimizations and yields best results with  -O2  and
           above.   It  works  in  tandem  with  the  -Wformat-overflow  and  -Wformat-truncation  options.  The
           -fprintf-return-value option is enabled by default.

       -fno-peephole
       -fno-peephole2
           Disable any machine-specific  peephole  optimizations.   The  difference  between  -fno-peephole  and
           -fno-peephole2  is  in  how  they are implemented in the compiler; some targets use one, some use the
           other, a few use both.

           -fpeephole is enabled by default.  -fpeephole2 enabled at levels -O2, -O3, -Os.

       -fno-guess-branch-probability
           Do not guess branch probabilities using heuristics.

           GCC uses heuristics to guess branch probabilities if they are  not  provided  by  profiling  feedback
           (-fprofile-arcs).    These  heuristics  are  based  on  the  control  flow  graph.   If  some  branch
           probabilities are specified by "__builtin_expect", then the  heuristics  are  used  to  guess  branch
           probabilities  for  the  rest  of  the  control  flow  graph, taking the "__builtin_expect" info into
           account.  The interactions between the heuristics and "__builtin_expect" can be complex, and in  some
           cases,  it  may  be  useful  to  disable the heuristics so that the effects of "__builtin_expect" are
           easier to understand.

           It   is   also   possible   to   specify   expected    probability    of    the    expression    with
           "__builtin_expect_with_probability" built-in function.

           The default is -fguess-branch-probability at levels -O, -O2, -O3, -Os.

       -freorder-blocks
           Reorder basic blocks in the compiled function in order to reduce number of taken branches and improve
           code locality.

           Enabled at levels -O, -O2, -O3, -Os.

       -freorder-blocks-algorithm=algorithm
           Use  the specified algorithm for basic block reordering.  The algorithm argument can be simple, which
           does not increase code size (except sometimes due to secondary effects like alignment), or  stc,  the
           "software trace cache" algorithm, which tries to put all often executed code together, minimizing the
           number of branches executed by making extra copies of code.

           The default is simple at levels -O, -Os, and stc at levels -O2, -O3.

       -freorder-blocks-and-partition
           In  addition  to reordering basic blocks in the compiled function, in order to reduce number of taken
           branches, partitions hot and cold basic blocks into separate sections of the assembly and  .o  files,
           to improve paging and cache locality performance.

           This  optimization is automatically turned off in the presence of exception handling or unwind tables
           (on targets using setjump/longjump or target specific scheme), for linkonce sections,  for  functions
           with  a  user-defined section attribute and on any architecture that does not support named sections.
           When -fsplit-stack is used this option is not enabled by default (to avoid linker errors), but may be
           enabled explicitly (if using a working linker).

           Enabled for x86 at levels -O2, -O3, -Os.

       -freorder-functions
           Reorder functions in the object file in order to improve code locality.  This is implemented by using
           special subsections ".text.hot" for most  frequently  executed  functions  and  ".text.unlikely"  for
           unlikely  executed  functions.   Reordering  is done by the linker so object file format must support
           named sections and linker must place them in a reasonable way.

           This option isn't effective unless you  either  provide  profile  feedback  (see  -fprofile-arcs  for
           details) or manually annotate functions with "hot" or "cold" attributes.

           Enabled at levels -O2, -O3, -Os.

       -fstrict-aliasing
           Allow  the compiler to assume the strictest aliasing rules applicable to the language being compiled.
           For C (and C++), this activates optimizations based on the type of expressions.   In  particular,  an
           object  of  one type is assumed never to reside at the same address as an object of a different type,
           unless the types are almost the same.  For example, an "unsigned int" can alias an "int", but  not  a
           "void*" or a "double".  A character type may alias any other type.

           Pay special attention to code like this:

                   union a_union {
                     int i;
                     double d;
                   };

                   int f() {
                     union a_union t;
                     t.d = 3.0;
                     return t.i;
                   }

           The  practice  of reading from a different union member than the one most recently written to (called
           "type-punning") is common.  Even with -fstrict-aliasing, type-punning is allowed, provided the memory
           is accessed through the union type.  So, the code above works  as  expected.     However,  this  code
           might not:

                   int f() {
                     union a_union t;
                     int* ip;
                     t.d = 3.0;
                     ip = &t.i;
                     return *ip;
                   }

           Similarly,  access  by taking the address, casting the resulting pointer and dereferencing the result
           has undefined behavior, even if the cast uses a union type, e.g.:

                   int f() {
                     double d = 3.0;
                     return ((union a_union *) &d)->i;
                   }

           The -fstrict-aliasing option is enabled at levels -O2, -O3, -Os.

       -falign-functions
       -falign-functions=n
       -falign-functions=n:m
       -falign-functions=n:m:n2
       -falign-functions=n:m:n2:m2
           Align the start of functions to the next power-of-two greater than or equal to n, skipping up to  m-1
           bytes.   This  ensures  that  at  least  the  first m bytes of the function can be fetched by the CPU
           without crossing an n-byte alignment boundary.

           If m is not specified, it defaults to n.

           Examples: -falign-functions=32 aligns functions to the next  32-byte  boundary,  -falign-functions=24
           aligns  to  the  next  32-byte  boundary  only  if  this  can  be  done by skipping 23 bytes or less,
           -falign-functions=32:7 aligns to the next 32-byte boundary only if this can be  done  by  skipping  6
           bytes or less.

           The    second   pair   of   n2:m2   values   allows   you   to   specify   a   secondary   alignment:
           -falign-functions=64:7:32:3 aligns to the next 64-byte boundary if this can be  done  by  skipping  6
           bytes  or less, otherwise aligns to the next 32-byte boundary if this can be done by skipping 2 bytes
           or less.  If m2 is not specified, it defaults to n2.

           Some assemblers only support this flag when n is a power of two; in that case, it is rounded up.

           -fno-align-functions and -falign-functions=1 are equivalent and mean that functions are not aligned.

           If n is not specified or is zero, use a machine-dependent default.   The  maximum  allowed  n  option
           value is 65536.

           Enabled at levels -O2, -O3.

       -flimit-function-alignment
           If  this  option  is  enabled,  the  compiler tries to avoid unnecessarily overaligning functions. It
           attempts to instruct the assembler to align by the amount specified by -falign-functions, but not  to
           skip more bytes than the size of the function.

       -falign-labels
       -falign-labels=n
       -falign-labels=n:m
       -falign-labels=n:m:n2
       -falign-labels=n:m:n2:m2
           Align all branch targets to a power-of-two boundary.

           Parameters  of  this  option  are  analogous  to the -falign-functions option.  -fno-align-labels and
           -falign-labels=1 are equivalent and mean that labels are not aligned.

           If -falign-loops or -falign-jumps are applicable and are greater than this value, then  their  values
           are used instead.

           If  n  is  not  specified  or  is zero, use a machine-dependent default which is very likely to be 1,
           meaning no alignment.  The maximum allowed n option value is 65536.

           Enabled at levels -O2, -O3.

       -falign-loops
       -falign-loops=n
       -falign-loops=n:m
       -falign-loops=n:m:n2
       -falign-loops=n:m:n2:m2
           Align loops to a power-of-two boundary.  If the loops are executed many times, this makes up for  any
           execution of the dummy padding instructions.

           If -falign-labels is greater than this value, then its value is used instead.

           Parameters  of  this  option  are  analogous  to  the -falign-functions option.  -fno-align-loops and
           -falign-loops=1 are equivalent and mean that loops are not aligned.  The  maximum  allowed  n  option
           value is 65536.

           If n is not specified or is zero, use a machine-dependent default.

           Enabled at levels -O2, -O3.

       -falign-jumps
       -falign-jumps=n
       -falign-jumps=n:m
       -falign-jumps=n:m:n2
       -falign-jumps=n:m:n2:m2
           Align  branch  targets  to  a power-of-two boundary, for branch targets where the targets can only be
           reached by jumping.  In this case, no dummy operations need be executed.

           If -falign-labels is greater than this value, then its value is used instead.

           Parameters of this option are  analogous  to  the  -falign-functions  option.   -fno-align-jumps  and
           -falign-jumps=1 are equivalent and mean that loops are not aligned.

           If  n  is  not  specified  or is zero, use a machine-dependent default.  The maximum allowed n option
           value is 65536.

           Enabled at levels -O2, -O3.

       -fno-allocation-dce
           Do not remove unused C++ allocations in dead code elimination.

       -fallow-store-data-races
           Allow the compiler to perform optimizations that may introduce new  data  races  on  stores,  without
           proving  that  the  variable  cannot  be  concurrently  accessed  by  other threads.  Does not affect
           optimization of local data.  It is safe to use this option if it is known that global data  will  not
           be accessed by multiple threads.

           Examples of optimizations enabled by -fallow-store-data-races include hoisting or if-conversions that
           may  cause a value that was already in memory to be re-written with that same value.  Such re-writing
           is safe in a single threaded context but may be unsafe in a multi-threaded  context.   Note  that  on
           some processors, if-conversions may be required in order to enable vectorization.

           Enabled at level -Ofast.

       -funit-at-a-time
           This   option   is   left   for   compatibility   reasons.  -funit-at-a-time  has  no  effect,  while
           -fno-unit-at-a-time implies -fno-toplevel-reorder and -fno-section-anchors.

           Enabled by default.

       -fno-toplevel-reorder
           Do not reorder top-level functions, variables, and "asm" statements.  Output them in the  same  order
           that  they appear in the input file.  When this option is used, unreferenced static variables are not
           removed.  This option is intended to support existing code that relies on a particular ordering.  For
           new code, it is better to use attributes when possible.

           -ftoplevel-reorder is the default at -O1  and  higher,  and  also  at  -O0  if  -fsection-anchors  is
           explicitly requested.  Additionally -fno-toplevel-reorder implies -fno-section-anchors.

       -fweb
           Constructs  webs  as  commonly  used  for register allocation purposes and assign each web individual
           pseudo register.  This allows the register allocation pass to operate on pseudos directly,  but  also
           strengthens  several  other  optimization  passes,  such as CSE, loop optimizer and trivial dead code
           remover.  It can, however, make debugging impossible, since variables  no  longer  stay  in  a  "home
           register".

           Enabled by default with -funroll-loops.

       -fwhole-program
           Assume  that  the  current  compilation unit represents the whole program being compiled.  All public
           functions  and  variables  with  the  exception   of   "main"   and   those   merged   by   attribute
           "externally_visible"  become  static  functions  and  in  effect  are  optimized more aggressively by
           interprocedural optimizers.

           This option should not be used in combination with -flto.  Instead relying on a linker plugin  should
           provide safer and more precise information.

       -flto[=n]
           This  option  runs  the  standard  link-time  optimizer.  When invoked with source code, it generates
           GIMPLE (one of GCC's internal representations) and writes it to special ELF sections  in  the  object
           file.   When  the  object  files are linked together, all the function bodies are read from these ELF
           sections and instantiated as if they had been part of the same translation unit.

           To use the link-time optimizer, -flto and optimization options should be specified  at  compile  time
           and  during  the  final  link.  It is recommended that you compile all the files participating in the
           same link with the same options and also specify those options at link time.  For example:

                   gcc -c -O2 -flto foo.c
                   gcc -c -O2 -flto bar.c
                   gcc -o myprog -flto -O2 foo.o bar.o

           The first two invocations to GCC save a bytecode representation of GIMPLE into special  ELF  sections
           inside  foo.o and bar.o.  The final invocation reads the GIMPLE bytecode from foo.o and bar.o, merges
           the two files into a single internal image, and compiles the result as usual.  Since both  foo.o  and
           bar.o  are merged into a single image, this causes all the interprocedural analyses and optimizations
           in GCC to work across the two files as if they were a single one.  This means, for example, that  the
           inliner is able to inline functions in bar.o into functions in foo.o and vice-versa.

           Another (simpler) way to enable link-time optimization is:

                   gcc -o myprog -flto -O2 foo.c bar.c

           The  above  generates  bytecode  for  foo.c  and  bar.c,  merges  them  together into a single GIMPLE
           representation and optimizes them as usual to produce myprog.

           The important thing to keep in mind is that to enable link-time optimizations you need to use the GCC
           driver to perform the link step.  GCC automatically performs link-time optimization  if  any  of  the
           objects  involved  were  compiled  with  the  -flto command-line option.  You can always override the
           automatic decision to do link-time optimization by passing -fno-lto to the link command.

           To make whole program  optimization  effective,  it  is  necessary  to  make  certain  whole  program
           assumptions.   The  compiler  needs to know what functions and variables can be accessed by libraries
           and runtime outside of the link-time optimized unit.  When supported by the linker, the linker plugin
           (see -fuse-linker-plugin) passes information to  the  compiler  about  used  and  externally  visible
           symbols.   When  the  linker  plugin  is  not  available, -fwhole-program should be used to allow the
           compiler to make these assumptions, which leads to more aggressive optimization decisions.

           When a file is compiled with -flto without -fuse-linker-plugin, the generated object file  is  larger
           than  a  regular  object  file  because  it  contains  GIMPLE bytecodes and the usual final code (see
           -ffat-lto-objects).  This means that object files with LTO information can be linked as normal object
           files; if -fno-lto is passed to the linker, no interprocedural optimizations are applied.  Note  that
           when  -fno-fat-lto-objects  is  enabled the compile stage is faster but you cannot perform a regular,
           non-LTO link on them.

           When producing the final binary, GCC only applies link-time optimizations to those files that contain
           bytecode.  Therefore, you can mix and match object files and  libraries  with  GIMPLE  bytecodes  and
           final  object code.  GCC automatically selects which files to optimize in LTO mode and which files to
           link without further processing.

           Generally, options specified at link time override those specified at compile time, although in  some
           cases GCC attempts to infer link-time options from the settings used to compile the input files.

           If  you  do  not  specify  an  optimization  level  option -O at link time, then GCC uses the highest
           optimization level used when compiling the object files.  Note that it is  generally  ineffective  to
           specify  an  optimization  level  option  only at link time and not at compile time, for two reasons.
           First, compiling without optimization suppresses compiler passes that gather information  needed  for
           effective optimization at link time.  Second, some early optimization passes can be performed only at
           compile time and not at link time.

           There  are  some code generation flags preserved by GCC when generating bytecodes, as they need to be
           used during the final link.  Currently, the following options and their settings are taken  from  the
           first  object  file  that  explicitly  specifies them: -fcommon, -fexceptions, -fnon-call-exceptions,
           -fgnu-tm and all the -m target flags.

           The following options -fPIC, -fpic, -fpie and -fPIE are combined based on the following scheme:

                   B<-fPIC> + B<-fpic> = B<-fpic>
                   B<-fPIC> + B<-fno-pic> = B<-fno-pic>
                   B<-fpic/-fPIC> + (no option) = (no option)
                   B<-fPIC> + B<-fPIE> = B<-fPIE>
                   B<-fpic> + B<-fPIE> = B<-fpie>
                   B<-fPIC/-fpic> + B<-fpie> = B<-fpie>

           Certain ABI-changing flags are required to match in all compilation units,  and  trying  to  override
           this   at   link  time  with  a  conflicting  value  is  ignored.   This  includes  options  such  as
           -freg-struct-return and -fpcc-struct-return.

           Other   options   such   as   -ffp-contract,    -fno-strict-overflow,    -fwrapv,    -fno-trapv    or
           -fno-strict-aliasing  are  passed through to the link stage and merged conservatively for conflicting
           translation units.  Specifically -fno-strict-overflow, -fwrapv and -fno-trapv  take  precedence;  and
           for  example  -ffp-contract=off  takes  precedence over -ffp-contract=fast.  You can override them at
           link time.

           Diagnostic options such as -Wstringop-overflow are passed through to the link stage and their setting
           matches that of  the  compile-step  at  function  granularity.   Note  that  this  matters  only  for
           diagnostics  emitted  during  optimization.   Note  that code transforms such as inlining can lead to
           warnings being enabled or disabled for regions if code not consistent with  the  setting  at  compile
           time.

           When  you  need  to  pass options to the assembler via -Wa or -Xassembler make sure to either compile
           such translation units  with  -fno-lto  or  consistently  use  the  same  assembler  options  on  all
           translation units.  You can alternatively also specify assembler options at LTO link time.

           To  enable debug info generation you need to supply -g at compile time.  If any of the input files at
           link time were built with debug info generation enabled the link will enable debug info generation as
           well.  Any elaborate debug info settings like  the  dwarf  level  -gdwarf-5  need  to  be  explicitly
           repeated  at  the linker command line and mixing different settings in different translation units is
           discouraged.

           If LTO encounters objects with C linkage declared with incompatible  types  in  separate  translation
           units  to  be linked together (undefined behavior according to ISO C99 6.2.7), a non-fatal diagnostic
           may be issued.  The behavior is still undefined at run time.  Similar diagnostics may be  raised  for
           other languages.

           Another feature of LTO is that it is possible to apply interprocedural optimizations on files written
           in different languages:

                   gcc -c -flto foo.c
                   g++ -c -flto bar.cc
                   gfortran -c -flto baz.f90
                   g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran

           Notice  that the final link is done with g++ to get the C++ runtime libraries and -lgfortran is added
           to get the Fortran runtime libraries.  In general, when mixing languages in LTO mode, you should  use
           the same link command options as when mixing languages in a regular (non-LTO) compilation.

           If  object  files  containing  GIMPLE  bytecode  are stored in a library archive, say libfoo.a, it is
           possible to extract and use them in an LTO link if you are using a linker with  plugin  support.   To
           create static libraries suitable for LTO, use gcc-ar and gcc-ranlib instead of ar and ranlib; to show
           the symbols of object files with GIMPLE bytecode, use gcc-nm.  Those commands require that ar, ranlib
           and  nm  have  been  compiled with plugin support.  At link time, use the flag -fuse-linker-plugin to
           ensure that the library participates in the LTO optimization process:

                   gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo

           With the linker plugin enabled, the linker extracts the needed GIMPLE files from libfoo.a and  passes
           them on to the running GCC to make them part of the aggregated GIMPLE image to be optimized.

           If  you  are  not using a linker with plugin support and/or do not enable the linker plugin, then the
           objects inside libfoo.a are extracted and linked as usual, but they do not  participate  in  the  LTO
           optimization process.  In order to make a static library suitable for both LTO optimization and usual
           linkage, compile its object files with -flto -ffat-lto-objects.

           Link-time  optimizations do not require the presence of the whole program to operate.  If the program
           does not require any symbols to be exported, it is possible to combine -flto and  -fwhole-program  to
           allow  the  interprocedural  optimizers to use more aggressive assumptions which may lead to improved
           optimization opportunities.  Use of -fwhole-program is not needed when linker plugin is  active  (see
           -fuse-linker-plugin).

           The  current  implementation  of  LTO  makes no attempt to generate bytecode that is portable between
           different types of hosts.  The bytecode files are versioned and there is a strict version  check,  so
           bytecode files generated in one version of GCC do not work with an older or newer version of GCC.

           Link-time  optimization  does not work well with generation of debugging information on systems other
           than those using a combination of ELF and DWARF.

           If you specify the optional n, the optimization and code generation done at link time is executed  in
           parallel using n parallel jobs by utilizing an installed make program.  The environment variable MAKE
           may be used to override the program used.

           You  can  also  specify  -flto=jobserver to use GNU make's job server mode to determine the number of
           parallel jobs. This is useful when the Makefile calling GCC is already executing  in  parallel.   You
           must  prepend  a + to the command recipe in the parent Makefile for this to work.  This option likely
           only works if MAKE is GNU make.  Even without the option value, GCC tries to automatically  detect  a
           running GNU make's job server.

           Use -flto=auto to use GNU make's job server, if available, or otherwise fall back to autodetection of
           the number of CPU threads present in your system.

       -flto-partition=alg
           Specify  the  partitioning  algorithm  used  by the link-time optimizer.  The value is either 1to1 to
           specify a partitioning mirroring the original source files or balanced to specify  partitioning  into
           equally  sized  chunks  (whenever  possible)  or  max  to create new partition for every symbol where
           possible.  Specifying none as an algorithm  disables  partitioning  and  streaming  completely.   The
           default  value is balanced. While 1to1 can be used as an workaround for various code ordering issues,
           the max partitioning is intended for internal testing only.  The value one specifies that exactly one
           partition should be used while the value  none  bypasses  partitioning  and  executes  the  link-time
           optimization step directly from the WPA phase.

       -flto-compression-level=n
           This  option  specifies the level of compression used for intermediate language written to LTO object
           files, and is only meaningful in conjunction with LTO mode (-flto).  GCC currently supports  two  LTO
           compression  algorithms.  For  zstd, valid values are 0 (no compression) to 19 (maximum compression),
           while zlib supports values from 0 to 9.  Values outside this range are clamped to either  minimum  or
           maximum  of the supported values.  If the option is not given, a default balanced compression setting
           is used.

       -fuse-linker-plugin
           Enables the use of a linker plugin during link-time  optimization.   This  option  relies  on  plugin
           support in the linker, which is available in gold or in GNU ld 2.21 or newer.

           This option enables the extraction of object files with GIMPLE bytecode out of library archives. This
           improves  the  quality  of  optimization  by  exposing  more  code  to the link-time optimizer.  This
           information specifies what symbols can be accessed externally (by non-LTO object  or  during  dynamic
           linking).   Resulting  code  quality  improvements  on binaries (and shared libraries that use hidden
           visibility) are similar to -fwhole-program.  See -flto for a description of the effect of  this  flag
           and how to use it.

           This  option  is enabled by default when LTO support in GCC is enabled and GCC was configured for use
           with a linker supporting plugins (GNU ld 2.21 or newer or gold).

       -ffat-lto-objects
           Fat LTO objects are object files that contain both the intermediate language  and  the  object  code.
           This  makes  them  usable for both LTO linking and normal linking. This option is effective only when
           compiling with -flto and is ignored at link time.

           -fno-fat-lto-objects improves compilation time over plain LTO, but requires the complete toolchain to
           be aware of  LTO.  It  requires  a  linker  with  linker  plugin  support  for  basic  functionality.
           Additionally,  nm,  ar  and  ranlib  need  to  support  linker plugins to allow a full-featured build
           environment (capable of building static libraries etc).  GCC provides the gcc-ar, gcc-nm,  gcc-ranlib
           wrappers  to pass the right options to these tools. With non fat LTO makefiles need to be modified to
           use them.

           Note that modern binutils provide plugin auto-load mechanism.   Installing  the  linker  plugin  into
           $libdir/bfd-plugins  has  the  same  effect as usage of the command wrappers (gcc-ar, gcc-nm and gcc-
           ranlib).

           The default is -fno-fat-lto-objects on targets with linker plugin support.

       -fcompare-elim
           After register allocation and post-register allocation  instruction  splitting,  identify  arithmetic
           instructions that compute processor flags similar to a comparison operation based on that arithmetic.
           If possible, eliminate the explicit comparison operation.

           This  pass  only applies to certain targets that cannot explicitly represent the comparison operation
           before register allocation is complete.

           Enabled at levels -O, -O2, -O3, -Os.

       -fcprop-registers
           After register allocation  and  post-register  allocation  instruction  splitting,  perform  a  copy-
           propagation pass to try to reduce scheduling dependencies and occasionally eliminate the copy.

           Enabled at levels -O, -O2, -O3, -Os.

       -fprofile-correction
           Profiles  collected  using an instrumented binary for multi-threaded programs may be inconsistent due
           to missed counter updates. When this option is specified, GCC uses heuristics to  correct  or  smooth
           out  such  inconsistencies.  By  default,  GCC emits an error message when an inconsistent profile is
           detected.

           This option is enabled by -fauto-profile.

       -fprofile-partial-training
           With "-fprofile-use" all portions of programs not executed during train run are optimized agressively
           for size rather than speed.  In some cases it is not practical to train all possible hot paths in the
           program. (For example, program may contain functions specific for a given hardware and  trianing  may
           not  cover all hardware configurations program is run on.)  With "-fprofile-partial-training" profile
           feedback will be ignored for all functions not executed during the  train  run  leading  them  to  be
           optimized  as  if  they were compiled without profile feedback. This leads to better performance when
           train run is not representative but also leads to significantly bigger code.

       -fprofile-use
       -fprofile-use=path
           Enable profile feedback-directed optimizations, and the following optimizations, many  of  which  are
           generally profitable only with profile feedback available:

           -fbranch-probabilities     -fprofile-values    -funroll-loops     -fpeel-loops     -ftracer     -fvpt
           -finline-functions   -fipa-cp   -fipa-cp-clone   -fipa-bit-cp  -fpredictive-commoning   -fsplit-loops
           -funswitch-loops        -fgcse-after-reload         -ftree-loop-vectorize        -ftree-slp-vectorize
           -fvect-cost-model=dynamic  -ftree-loop-distribute-patterns -fprofile-reorder-functions

           Before you can use this option, you must first generate profiling information.

           By default, GCC emits an error message if the feedback profiles do not match the source  code.   This
           error  can  be  turned into a warning by using -Wno-error=coverage-mismatch.  Note this may result in
           poorly optimized code.  Additionally, by default, GCC also emits a warning message  if  the  feedback
           profiles do not exist (see -Wmissing-profile).

           If  path  is  specified,  GCC  looks  at  the  path  to  find  the  profile  feedback data files. See
           -fprofile-dir.

       -fauto-profile
       -fauto-profile=path
           Enable sampling-based feedback-directed optimizations, and the following optimizations, many of which
           are generally profitable only with profile feedback available:

           -fbranch-probabilities     -fprofile-values    -funroll-loops     -fpeel-loops     -ftracer     -fvpt
           -finline-functions   -fipa-cp   -fipa-cp-clone   -fipa-bit-cp  -fpredictive-commoning   -fsplit-loops
           -funswitch-loops       -fgcse-after-reload         -ftree-loop-vectorize         -ftree-slp-vectorize
           -fvect-cost-model=dynamic  -ftree-loop-distribute-patterns -fprofile-correction

           path  is  the  name  of  a  file  containing AutoFDO profile information.  If omitted, it defaults to
           fbdata.afdo in the current directory.

           Producing an AutoFDO profile data file requires running your program  with  the  perf  utility  on  a
           supported GNU/Linux target system.  For more information, see <https://perf.wiki.kernel.org/>.

           E.g.

                   perf record -e br_inst_retired:near_taken -b -o perf.data \
                       -- your_program

           Then  use  the  create_gcov tool to convert the raw profile data to a format that can be used by GCC.
           You  must  also  supply   the   unstripped   binary   for   your   program   to   this   tool.    See
           <https://github.com/google/autofdo>.

           E.g.

                   create_gcov --binary=your_program.unstripped --profile=perf.data \
                       --gcov=profile.afdo

       The following options control compiler behavior regarding floating-point arithmetic.  These options trade
       off between speed and correctness.  All must be specifically enabled.

       -ffloat-store
           Do  not  store  floating-point  variables  in  registers, and inhibit other options that might change
           whether a floating-point value is taken from a register or memory.

           This option prevents undesirable excess precision on machines such as the 68000  where  the  floating
           registers  (of the 68881) keep more precision than a "double" is supposed to have.  Similarly for the
           x86 architecture.  For most programs, the excess precision does only good, but a few programs rely on
           the precise definition of IEEE floating point.  Use -ffloat-store for such programs, after  modifying
           them to store all pertinent intermediate computations into variables.

       -fexcess-precision=style
           This  option allows further control over excess precision on machines where floating-point operations
           occur in a format with more precision or range than the IEEE standard and interchange  floating-point
           types.   By  default, -fexcess-precision=fast is in effect; this means that operations may be carried
           out in a wider precision than the types specified in the source if that would result in faster  code,
           and  it  is  unpredictable when rounding to the types specified in the source code takes place.  When
           compiling C, if -fexcess-precision=standard is specified then  excess  precision  follows  the  rules
           specified  in  ISO C99; in particular, both casts and assignments cause values to be rounded to their
           semantic types (whereas -ffloat-store only affects assignments).  This option is enabled  by  default
           for   C   if   a   strict   conformance  option  such  as  -std=c99  is  used.   -ffast-math  enables
           -fexcess-precision=fast by default regardless of whether a strict conformance option is used.

           -fexcess-precision=standard is not implemented for languages other than C.  On the  x86,  it  has  no
           effect  if  -mfpmath=sse  or  -mfpmath=sse+387 is specified; in the former case, IEEE semantics apply
           without excess precision, and in the latter, rounding is unpredictable.

       -ffast-math
           Sets    the     options     -fno-math-errno,     -funsafe-math-optimizations,     -ffinite-math-only,
           -fno-rounding-math, -fno-signaling-nans, -fcx-limited-range and -fexcess-precision=fast.

           This option causes the preprocessor macro "__FAST_MATH__" to be defined.

           This  option is not turned on by any -O option besides -Ofast since it can result in incorrect output
           for programs that depend on an exact implementation of IEEE  or  ISO  rules/specifications  for  math
           functions.  It  may,  however,  yield  faster code for programs that do not require the guarantees of
           these specifications.

       -fno-math-errno
           Do not set "errno" after calling math functions that are executed with a  single  instruction,  e.g.,
           "sqrt".   A  program that relies on IEEE exceptions for math error handling may want to use this flag
           for speed while maintaining IEEE arithmetic compatibility.

           This option is not turned on by any -O option since it can result in incorrect  output  for  programs
           that  depend  on  an  exact implementation of IEEE or ISO rules/specifications for math functions. It
           may, however,  yield  faster  code  for  programs  that  do  not  require  the  guarantees  of  these
           specifications.

           The default is -fmath-errno.

           On  Darwin  systems,  the  math  library  never  sets  "errno".  There is therefore no reason for the
           compiler to consider the possibility that it might, and -fno-math-errno is the default.

       -funsafe-math-optimizations
           Allow optimizations for floating-point arithmetic that (a) assume  that  arguments  and  results  are
           valid  and  (b) may violate IEEE or ANSI standards.  When used at link time, it may include libraries
           or startup files that change the default FPU control word or other similar optimizations.

           This option is not turned on by any -O option since it can result in incorrect  output  for  programs
           that  depend  on  an  exact implementation of IEEE or ISO rules/specifications for math functions. It
           may, however,  yield  faster  code  for  programs  that  do  not  require  the  guarantees  of  these
           specifications.     Enables    -fno-signed-zeros,    -fno-trapping-math,    -fassociative-math    and
           -freciprocal-math.

           The default is -fno-unsafe-math-optimizations.

       -fassociative-math
           Allow re-association of operands in series of floating-point operations.  This violates the ISO C and
           C++ language standard by possibly changing computation result.  NOTE: re-ordering may change the sign
           of zero as well as ignore NaNs and inhibit or create underflow or overflow (and thus cannot  be  used
           on code that relies on rounding behavior like "(x + 2**52) - 2**52".  May also reorder floating-point
           comparisons  and  thus  may  not be used when ordered comparisons are required.  This option requires
           that both -fno-signed-zeros and -fno-trapping-math be in effect.   Moreover,  it  doesn't  make  much
           sense   with   -frounding-math.   For   Fortran   the  option  is  automatically  enabled  when  both
           -fno-signed-zeros and -fno-trapping-math are in effect.

           The default is -fno-associative-math.

       -freciprocal-math
           Allow the reciprocal of a value to be  used  instead  of  dividing  by  the  value  if  this  enables
           optimizations.   For  example "x / y" can be replaced with "x * (1/y)", which is useful if "(1/y)" is
           subject to common subexpression elimination.  Note that this loses precision and increases the number
           of flops operating on the value.

           The default is -fno-reciprocal-math.

       -ffinite-math-only
           Allow optimizations for floating-point arithmetic that assume that arguments and results are not NaNs
           or +-Infs.

           This option is not turned on by any -O option since it can result in incorrect  output  for  programs
           that  depend  on  an  exact implementation of IEEE or ISO rules/specifications for math functions. It
           may, however,  yield  faster  code  for  programs  that  do  not  require  the  guarantees  of  these
           specifications.

           The default is -fno-finite-math-only.

       -fno-signed-zeros
           Allow  optimizations  for  floating-point  arithmetic  that  ignore  the  signedness  of  zero.  IEEE
           arithmetic  specifies  the  behavior  of  distinct  +0.0  and  -0.0  values,  which  then   prohibits
           simplification  of  expressions  such  as x+0.0 or 0.0*x (even with -ffinite-math-only).  This option
           implies that the sign of a zero result isn't significant.

           The default is -fsigned-zeros.

       -fno-trapping-math
           Compile code assuming that floating-point operations cannot generate user-visible traps.  These traps
           include division by zero, overflow, underflow, inexact result and  invalid  operation.   This  option
           requires  that  -fno-signaling-nans  be  in effect.  Setting this option may allow faster code if one
           relies on "non-stop" IEEE arithmetic, for example.

           This option should never be turned on by any -O option since it can result in  incorrect  output  for
           programs  that  depend  on  an  exact  implementation  of  IEEE  or ISO rules/specifications for math
           functions.

           The default is -ftrapping-math.

       -frounding-math
           Disable transformations and optimizations that assume default floating-point rounding behavior.  This
           is round-to-zero for all floating point to integer conversions, and round-to-nearest  for  all  other
           arithmetic  truncations.   This  option  should be specified for programs that change the FP rounding
           mode dynamically, or that may be executed with a non-default rounding  mode.   This  option  disables
           constant  folding  of  floating-point  expressions at compile time (which may be affected by rounding
           mode) and arithmetic transformations that are unsafe  in  the  presence  of  sign-dependent  rounding
           modes.

           The default is -fno-rounding-math.

           This  option  is  experimental and does not currently guarantee to disable all GCC optimizations that
           are affected by rounding mode.  Future versions of GCC may provide  finer  control  of  this  setting
           using C99's "FENV_ACCESS" pragma.  This command-line option will be used to specify the default state
           for "FENV_ACCESS".

       -fsignaling-nans
           Compile  code assuming that IEEE signaling NaNs may generate user-visible traps during floating-point
           operations.  Setting this option disables optimizations that may  change  the  number  of  exceptions
           visible with signaling NaNs.  This option implies -ftrapping-math.

           This option causes the preprocessor macro "__SUPPORT_SNAN__" to be defined.

           The default is -fno-signaling-nans.

           This  option  is  experimental and does not currently guarantee to disable all GCC optimizations that
           affect signaling NaN behavior.

       -fno-fp-int-builtin-inexact
           Do not allow the built-in functions "ceil", "floor", "round" and "trunc", and their "float" and "long
           double" variants, to generate code that raises the "inexact" floating-point exception for  noninteger
           arguments.   ISO  C99  and C11 allow these functions to raise the "inexact" exception, but ISO/IEC TS
           18661-1:2014, the C bindings to IEEE 754-2008, as integrated into  ISO  C2X,  does  not  allow  these
           functions to do so.

           The default is -ffp-int-builtin-inexact, allowing the exception to be raised, unless C2X or a later C
           standard is selected.  This option does nothing unless -ftrapping-math is in effect.

           Even  if  -fno-fp-int-builtin-inexact is used, if the functions generate a call to a library function
           then the "inexact" exception may be raised if the library implementation does not follow TS 18661.

       -fsingle-precision-constant
           Treat floating-point constants as single precision instead of implicitly converting them  to  double-
           precision constants.

       -fcx-limited-range
           When  enabled,  this  option states that a range reduction step is not needed when performing complex
           division.  Also, there is no checking whether the result of a complex multiplication or  division  is
           "NaN   +   I*NaN",  with  an  attempt  to  rescue  the  situation  in  that  case.   The  default  is
           -fno-cx-limited-range, but is enabled by -ffast-math.

           This option controls the default setting of the ISO C99 "CX_LIMITED_RANGE" pragma.  Nevertheless, the
           option applies to all languages.

       -fcx-fortran-rules
           Complex multiplication and division follow Fortran rules.  Range reduction is done as part of complex
           division, but there is no checking whether the result of a complex multiplication or division is "NaN
           + I*NaN", with an attempt to rescue the situation in that case.

           The default is -fno-cx-fortran-rules.

       The following options control optimizations that may improve performance, but are not enabled by  any  -O
       options.  This section includes experimental options that may produce broken code.

       -fbranch-probabilities
           After  running  a  program  compiled  with  -fprofile-arcs,  you  can  compile it a second time using
           -fbranch-probabilities, to improve optimizations based on the number of times each branch was  taken.
           When  a  program  compiled  with -fprofile-arcs exits, it saves arc execution counts to a file called
           sourcename.gcda for each source file.  The information in this data file is  very  dependent  on  the
           structure  of  the  generated  code,  so  you must use the same source code and the same optimization
           options for both compilations.

           With -fbranch-probabilities, GCC puts a REG_BR_PROB note on each JUMP_INSN and CALL_INSN.  These  can
           be  used to improve optimization.  Currently, they are only used in one place: in reorg.c, instead of
           guessing which path a branch is most likely to take, the  REG_BR_PROB  values  are  used  to  exactly
           determine which path is taken more often.

           Enabled by -fprofile-use and -fauto-profile.

       -fprofile-values
           If  combined  with  -fprofile-arcs, it adds code so that some data about values of expressions in the
           program is gathered.

           With -fbranch-probabilities, it reads back the data gathered from profiling values of expressions for
           usage in optimizations.

           Enabled by -fprofile-generate, -fprofile-use, and -fauto-profile.

       -fprofile-reorder-functions
           Function reordering based on profile instrumentation collects first time of execution of  a  function
           and orders these functions in ascending order.

           Enabled with -fprofile-use.

       -fvpt
           If combined with -fprofile-arcs, this option instructs the compiler to add code to gather information
           about values of expressions.

           With  -fbranch-probabilities, it reads back the data gathered and actually performs the optimizations
           based on them.  Currently the optimizations include specialization of division operations  using  the
           knowledge about the value of the denominator.

           Enabled with -fprofile-use and -fauto-profile.

       -frename-registers
           Attempt  to  avoid  false  dependencies  in scheduled code by making use of registers left over after
           register allocation.  This optimization most benefits processors with lots of  registers.   Depending
           on  the  debug  information  format adopted by the target, however, it can make debugging impossible,
           since variables no longer stay in a "home register".

           Enabled by default with -funroll-loops.

       -fschedule-fusion
           Performs a target dependent pass over the instruction stream to schedule instructions  of  same  type
           together  because target machine can execute them more efficiently if they are adjacent to each other
           in the instruction flow.

           Enabled at levels -O2, -O3, -Os.

       -ftracer
           Perform tail duplication to enlarge superblock size.  This transformation simplifies the control flow
           of the function allowing other optimizations to do a better job.

           Enabled by -fprofile-use and -fauto-profile.

       -funroll-loops
           Unroll loops whose number of iterations can be determined at compile time or upon entry to the  loop.
           -funroll-loops  implies  -frerun-cse-after-loop,  -fweb  and  -frename-registers.   It  also turns on
           complete loop peeling (i.e. complete removal of loops with a small constant  number  of  iterations).
           This option makes code larger, and may or may not make it run faster.

           Enabled by -fprofile-use and -fauto-profile.

       -funroll-all-loops
           Unroll  all  loops,  even  if their number of iterations is uncertain when the loop is entered.  This
           usually  makes  programs  run  more  slowly.   -funroll-all-loops  implies  the   same   options   as
           -funroll-loops.

       -fpeel-loops
           Peels  loops  for which there is enough information that they do not roll much (from profile feedback
           or static analysis).  It also turns on complete loop peeling (i.e. complete  removal  of  loops  with
           small constant number of iterations).

           Enabled by -O3, -fprofile-use, and -fauto-profile.

       -fmove-loop-invariants
           Enables  the  loop invariant motion pass in the RTL loop optimizer.  Enabled at level -O1 and higher,
           except for -Og.

       -fsplit-loops
           Split a loop into two if it contains a condition that's always true for one  side  of  the  iteration
           space and false for the other.

           Enabled by -fprofile-use and -fauto-profile.

       -funswitch-loops
           Move  branches  with  loop  invariant conditions out of the loop, with duplicates of the loop on both
           branches (modified according to result of the condition).

           Enabled by -fprofile-use and -fauto-profile.

       -fversion-loops-for-strides
           If a loop iterates over an array with a variable stride, create another  version  of  the  loop  that
           assumes the stride is always one.  For example:

                   for (int i = 0; i < n; ++i)
                     x[i * stride] = ...;

           becomes:

                   if (stride == 1)
                     for (int i = 0; i < n; ++i)
                       x[i] = ...;
                   else
                     for (int i = 0; i < n; ++i)
                       x[i * stride] = ...;

           This  is particularly useful for assumed-shape arrays in Fortran where (for example) it allows better
           vectorization assuming contiguous accesses.  This flag is enabled by default  at  -O3.   It  is  also
           enabled by -fprofile-use and -fauto-profile.

       -ffunction-sections
       -fdata-sections
           Place  each  function  or  data  item  into its own section in the output file if the target supports
           arbitrary sections.  The name of the function or the name of the data item determines  the  section's
           name in the output file.

           Use  these  options  on  systems  where  the  linker can perform optimizations to improve locality of
           reference in the instruction space.  Most systems using the ELF object format have linkers with  such
           optimizations.   On  AIX,  the  linker  rearranges  sections  (CSECTs)  based on the call graph.  The
           performance impact varies.

           Together with a linker garbage collection (linker --gc-sections option) these  options  may  lead  to
           smaller statically-linked executables (after stripping).

           On  ELF/DWARF  systems  these  options do not degenerate the quality of the debug information.  There
           could be issues with other object files/debug info formats.

           Only use these options when there are significant benefits from doing so.   When  you  specify  these
           options,  the  assembler  and  linker  create larger object and executable files and are also slower.
           These options affect code generation.  They prevent optimizations by the compiler and assembler using
           relative locations inside a translation unit since the locations are unknown  until  link  time.   An
           example of such an optimization is relaxing calls to short call instructions.

       -fstdarg-opt
           Optimize the prologue of variadic argument functions with respect to usage of those arguments.

           NOTE:  In Ubuntu 14.10 and later versions, -fstack-protector-strong is enabled by default for C, C++,
           ObjC, ObjC++, if none of -fno-stack-protector, -nostdlib, nor -ffreestanding are found.

       -fsection-anchors
           Try to reduce the number of symbolic address calculations by using shared "anchor" symbols to address
           nearby objects.  This transformation can help to reduce the number of GOT entries and GOT accesses on
           some targets.

           For example, the implementation of the following function "foo":

                   static int a, b, c;
                   int foo (void) { return a + b + c; }

           usually  calculates  the  addresses  of  all  three  variables,  but   if   you   compile   it   with
           -fsection-anchors,  it  accesses  the  variables  from  a common anchor point instead.  The effect is
           similar to the following pseudocode (which isn't valid C):

                   int foo (void)
                   {
                     register int *xr = &x;
                     return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
                   }

           Not all targets support this option.

       -fzero-call-used-regs=choice
           Zero call-used registers at function return to increase program security by either mitigating Return-
           Oriented Programming (ROP) attacks or preventing information leakage through registers.

           The possible values of choice are the same as for the "zero_call_used_regs" attribute.   The  default
           is skip.

           You   can   control   this  behavior  for  a  specific  function  by  using  the  function  attribute
           "zero_call_used_regs".

       --param name=value
           In some places, GCC uses various constants to control the amount of optimization that is  done.   For
           example,  GCC does not inline functions that contain more than a certain number of instructions.  You
           can control some of these constants on the command line using the --param option.

           The names of specific parameters, and the meaning of the values, are tied to  the  internals  of  the
           compiler, and are subject to change without notice in future releases.

           In  order  to  get  minimal,  maximal  and  default value of a parameter, one can use --help=param -Q
           options.

           In each case, the value is an integer.  The following choices of name are recognized for all targets:

           predictable-branch-outcome
               When branch is predicted to be taken with probability lower than  this  threshold  (in  percent),
               then it is considered well predictable.

           max-rtl-if-conversion-insns
               RTL  if-conversion  tries  to  remove  conditional  branches around a block and replace them with
               conditionally executed instructions.  This parameter gives the maximum number of instructions  in
               a  block  which  should  be  considered  for  if-conversion.   The  compiler  will also use other
               heuristics to decide whether if-conversion is likely to be profitable.

           max-rtl-if-conversion-predictable-cost
               RTL if-conversion will try to remove conditional branches around a block and  replace  them  with
               conditionally  executed instructions.  These parameters give the maximum permissible cost for the
               sequence that would be generated by if-conversion depending on whether the branch  is  statically
               determined  to be predictable or not.  The units for this parameter are the same as those for the
               GCC internal seq_cost metric.  The compiler will try to provide a  reasonable  default  for  this
               parameter using the BRANCH_COST target macro.

           max-crossjump-edges
               The  maximum  number  of  incoming  edges  to  consider for cross-jumping.  The algorithm used by
               -fcrossjumping is O(N^2) in the number of edges incoming to each block.  Increasing  values  mean
               more   aggressive  optimization,  making  the  compilation  time  increase  with  probably  small
               improvement in executable size.

           min-crossjump-insns
               The minimum number of instructions that must be matched at the end of two  blocks  before  cross-
               jumping  is  performed  on them.  This value is ignored in the case where all instructions in the
               block being cross-jumped from are matched.

           max-grow-copy-bb-insns
               The maximum code size expansion factor  when  copying  basic  blocks  instead  of  jumping.   The
               expansion is relative to a jump instruction.

           max-goto-duplication-insns
               The  maximum  number  of  instructions to duplicate to a block that jumps to a computed goto.  To
               avoid O(N^2) behavior in a number of passes, GCC factors computed gotos early in the  compilation
               process,  and  unfactors  them  as  late  as possible.  Only computed jumps at the end of a basic
               blocks with no more than max-goto-duplication-insns are unfactored.

           max-delay-slot-insn-search
               The maximum number of instructions to consider when looking for an instruction to  fill  a  delay
               slot.   If  more  than  this arbitrary number of instructions are searched, the time savings from
               filling the delay slot are minimal, so stop searching.  Increasing values  mean  more  aggressive
               optimization,  making  the compilation time increase with probably small improvement in execution
               time.

           max-delay-slot-live-search
               When trying to fill delay slots, the maximum number of instructions to  consider  when  searching
               for a block with valid live register information.  Increasing this arbitrarily chosen value means
               more  aggressive optimization, increasing the compilation time.  This parameter should be removed
               when the delay slot code is rewritten to maintain the control-flow graph.

           max-gcse-memory
               The approximate maximum amount of memory in "kB" that can be allocated in order  to  perform  the
               global common subexpression elimination optimization.  If more memory than specified is required,
               the optimization is not done.

           max-gcse-insertion-ratio
               If  the ratio of expression insertions to deletions is larger than this value for any expression,
               then RTL PRE inserts or removes the expression and thus leaves partially  redundant  computations
               in the instruction stream.

           max-pending-list-length
               The  maximum  number  of pending dependencies scheduling allows before flushing the current state
               and starting over.  Large functions with few branches or calls can create excessively large lists
               which needlessly consume memory and resources.

           max-modulo-backtrack-attempts
               The maximum number of backtrack attempts the scheduler should make when modulo scheduling a loop.
               Larger values can exponentially increase compilation time.

           max-inline-insns-single
               Several parameters control the tree inliner used in GCC.  This number sets the maximum number  of
               instructions  (counted  in  GCC's  internal  representation)  in  a single function that the tree
               inliner considers for  inlining.   This  only  affects  functions  declared  inline  and  methods
               implemented in a class declaration (C++).

           max-inline-insns-auto
               When you use -finline-functions (included in -O3), a lot of functions that would otherwise not be
               considered  for inlining by the compiler are investigated.  To those functions, a different (more
               restrictive) limit compared to functions declared inline  can  be  applied  (--param  max-inline-
               insns-auto).

           max-inline-insns-small
               This is bound applied to calls which are considered relevant with -finline-small-functions.

           max-inline-insns-size
               This  is  bound  applied  to calls which are optimized for size. Small growth may be desirable to
               anticipate optimization oppurtunities exposed by inlining.

           uninlined-function-insns
               Number of instructions accounted by inliner for function overhead such as function  prologue  and
               epilogue.

           uninlined-function-time
               Extra  time  accounted  by  inliner for function overhead such as time needed to execute function
               prologue and epilogue

           inline-heuristics-hint-percent
               The scale (in percents) applied to inline-insns-single, inline-insns-single-O2, inline-insns-auto
               when inline heuristics hints that inlining is very profitable (will enable later optimizations).

           uninlined-thunk-insns
           uninlined-thunk-time
               Same as --param uninlined-function-insns  and  --param  uninlined-function-time  but  applied  to
               function thunks

           inline-min-speedup
               When  estimated  performance  improvement  of  caller + callee runtime exceeds this threshold (in
               percent), the function can be inlined regardless of the limit on --param  max-inline-insns-single
               and --param max-inline-insns-auto.

           large-function-insns
               The  limit  specifying  really  large  functions.   For  functions  larger  than this limit after
               inlining, inlining is constrained by --param large-function-growth.   This  parameter  is  useful
               primarily to avoid extreme compilation time caused by non-linear algorithms used by the back end.

           large-function-growth
               Specifies  maximal  growth  of  large  function  caused  by  inlining  in percents.  For example,
               parameter value 100 limits large function growth to 2.0 times the original size.

           large-unit-insns
               The limit specifying large translation unit.  Growth caused by inlining of units larger than this
               limit is limited by --param inline-unit-growth.  For small units this might be  too  tight.   For
               example,  consider  a  unit consisting of function A that is inline and B that just calls A three
               times.  If B is small relative to A, the growth of unit is 300\% and yet such  inlining  is  very
               sane.   For  very large units consisting of small inlineable functions, however, the overall unit
               growth limit is needed to avoid exponential explosion of code size.  Thus for smaller units,  the
               size is increased to --param large-unit-insns before applying --param inline-unit-growth.

           lazy-modules
               Maximum number of concurrently open C++ module files when lazy loading.

           inline-unit-growth
               Specifies  maximal  overall  growth  of  the  compilation  unit caused by inlining.  For example,
               parameter value 20 limits unit growth to 1.2 times the  original  size.  Cold  functions  (either
               marked cold via an attribute or by profile feedback) are not accounted into the unit size.

           ipa-cp-unit-growth
               Specifies  maximal  overall  growth  of  the  compilation unit caused by interprocedural constant
               propagation.  For example, parameter value 10 limits unit growth to 1.1 times the original size.

           ipa-cp-large-unit-insns
               The size of translation unit that IPA-CP pass considers large.

           large-stack-frame
               The limit specifying large stack frames.  While inlining the algorithm is trying to not grow past
               this limit too much.

           large-stack-frame-growth
               Specifies maximal growth of large stack frames caused by  inlining  in  percents.   For  example,
               parameter value 1000 limits large stack frame growth to 11 times the original size.

           max-inline-insns-recursive
           max-inline-insns-recursive-auto
               Specifies  the  maximum  number  of  instructions  an out-of-line copy of a self-recursive inline
               function can grow into by performing recursive inlining.

               --param max-inline-insns-recursive applies to  functions  declared  inline.   For  functions  not
               declared  inline,  recursive  inlining  happens only when -finline-functions (included in -O3) is
               enabled; --param max-inline-insns-recursive-auto applies instead.

           max-inline-recursive-depth
           max-inline-recursive-depth-auto
               Specifies the maximum recursion depth used for recursive inlining.

               --param max-inline-recursive-depth applies to  functions  declared  inline.   For  functions  not
               declared  inline,  recursive  inlining  happens only when -finline-functions (included in -O3) is
               enabled; --param max-inline-recursive-depth-auto applies instead.

           min-inline-recursive-probability
               Recursive inlining is profitable only for function having deep recursion in average and can  hurt
               for  function  having  little  recursion  depth  by increasing the prologue size or complexity of
               function body to other optimizers.

               When profile feedback is available (see -fprofile-generate) the actual  recursion  depth  can  be
               guessed  from the probability that function recurses via a given call expression.  This parameter
               limits inlining only to call expressions  whose  probability  exceeds  the  given  threshold  (in
               percents).

           early-inlining-insns
               Specify  growth  that  the early inliner can make.  In effect it increases the amount of inlining
               for code having a large abstraction penalty.

           max-early-inliner-iterations
               Limit of iterations of the early inliner.  This basically bounds the number  of  nested  indirect
               calls the early inliner can resolve.  Deeper chains are still handled by late inlining.

           comdat-sharing-probability
               Probability  (in  percent)  that  C++  inline  function  with comdat visibility are shared across
               multiple compilation units.

           modref-max-bases
           modref-max-refs
           modref-max-accesses
               Specifies the maximal number of base pointers,  references  and  accesses  stored  for  a  single
               function by mod/ref analysis.

           modref-max-tests
               Specifies  the  maxmal  number of tests alias oracle can perform to disambiguate memory locations
               using the mod/ref information.  This parameter ought to be bigger than  --param  modref-max-bases
               and --param modref-max-refs.

           modref-max-depth
               Specifies  the  maximum  depth of DFS walk used by modref escape analysis.  Setting to 0 disables
               the analysis completely.

           modref-max-escape-points
               Specifies the maximum number of escape points tracked by modref per SSA-name.

           profile-func-internal-id
               A parameter to control whether to use function internal id in profile  database  lookup.  If  the
               value  is 0, the compiler uses an id that is based on function assembler name and filename, which
               makes old profile data more tolerant to source changes such as function reordering etc.

           min-vect-loop-bound
               The minimum number of iterations under which loops are not vectorized  when  -ftree-vectorize  is
               used.   The number of iterations after vectorization needs to be greater than the value specified
               by this option to allow vectorization.

           gcse-cost-distance-ratio
               Scaling  factor  in  calculation  of  maximum  distance  an  expression  can  be  moved  by  GCSE
               optimizations.   This  is  currently  supported  only  in the code hoisting pass.  The bigger the
               ratio, the more aggressive code hoisting is with simple expressions, i.e., the  expressions  that
               have   cost   less  than  gcse-unrestricted-cost.   Specifying  0  disables  hoisting  of  simple
               expressions.

           gcse-unrestricted-cost
               Cost, roughly measured as the cost of  a  single  typical  machine  instruction,  at  which  GCSE
               optimizations  do  not  constrain  the  distance  an  expression  can  travel.  This is currently
               supported only in the code hoisting pass.  The lesser the cost, the more aggressive code hoisting
               is.  Specifying 0 allows all expressions to travel unrestricted distances.

           max-hoist-depth
               The depth of search in the dominator tree for expressions  to  hoist.   This  is  used  to  avoid
               quadratic  behavior  in hoisting algorithm.  The value of 0 does not limit on the search, but may
               slow down compilation of huge functions.

           max-tail-merge-comparisons
               The maximum amount of similar bbs to compare a bb with.  This is used to avoid quadratic behavior
               in tree tail merging.

           max-tail-merge-iterations
               The maximum amount of iterations  of  the  pass  over  the  function.   This  is  used  to  limit
               compilation time in tree tail merging.

           store-merging-allow-unaligned
               Allow the store merging pass to introduce unaligned stores if it is legal to do so.

           max-stores-to-merge
               The maximum number of stores to attempt to merge into wider stores in the store merging pass.

           max-store-chains-to-track
               The  maximum  number  of store chains to track at the same time in the attempt to merge them into
               wider stores in the store merging pass.

           max-stores-to-track
               The maximum number of stores to track at the same time in the attemt to to merge them into  wider
               stores in the store merging pass.

           max-unrolled-insns
               The  maximum  number of instructions that a loop may have to be unrolled.  If a loop is unrolled,
               this parameter also determines how many times the loop code is unrolled.

           max-average-unrolled-insns
               The maximum number of instructions biased by probabilities of their execution  that  a  loop  may
               have  to  be  unrolled.  If a loop is unrolled, this parameter also determines how many times the
               loop code is unrolled.

           max-unroll-times
               The maximum number of unrollings of a single loop.

           max-peeled-insns
               The maximum number of instructions that a loop may have to be peeled.  If a loop is peeled,  this
               parameter also determines how many times the loop code is peeled.

           max-peel-times
               The maximum number of peelings of a single loop.

           max-peel-branches
               The maximum number of branches on the hot path through the peeled sequence.

           max-completely-peeled-insns
               The maximum number of insns of a completely peeled loop.

           max-completely-peel-times
               The maximum number of iterations of a loop to be suitable for complete peeling.

           max-completely-peel-loop-nest-depth
               The maximum depth of a loop nest suitable for complete peeling.

           max-unswitch-insns
               The maximum number of insns of an unswitched loop.

           max-unswitch-level
               The maximum number of branches unswitched in a single loop.

           lim-expensive
               The minimum cost of an expensive expression in the loop invariant motion.

           min-loop-cond-split-prob
               When  FDO  profile information is available, min-loop-cond-split-prob specifies minimum threshold
               for probability of semi-invariant condition statement to trigger loop split.

           iv-consider-all-candidates-bound
               Bound on number of candidates for induction variables, below which all candidates are  considered
               for  each  use in induction variable optimizations.  If there are more candidates than this, only
               the most relevant ones are considered to avoid quadratic time complexity.

           iv-max-considered-uses
               The induction variable optimizations give up on loops that contain more induction variable uses.

           iv-always-prune-cand-set-bound
               If the number of candidates in the  set  is  smaller  than  this  value,  always  try  to  remove
               unnecessary ivs from the set when adding a new one.

           avg-loop-niter
               Average number of iterations of a loop.

           dse-max-object-size
               Maximum size (in bytes) of objects tracked bytewise by dead store elimination.  Larger values may
               result in larger compilation times.

           dse-max-alias-queries-per-store
               Maximum  number  of  queries  into  the  alias  oracle per store.  Larger values result in larger
               compilation times and may result in more removed dead stores.

           scev-max-expr-size
               Bound on size of expressions used in the scalar evolutions analyzer.  Large expressions slow  the
               analyzer.

           scev-max-expr-complexity
               Bound  on  the  complexity  of  the  expressions  in  the  scalar  evolutions  analyzer.  Complex
               expressions slow the analyzer.

           max-tree-if-conversion-phi-args
               Maximum number of arguments in a PHI supported by TREE if conversion unless the  loop  is  marked
               with simd pragma.

           vect-max-version-for-alignment-checks
               The  maximum  number  of  run-time  checks  that  can be performed when doing loop versioning for
               alignment in the vectorizer.

           vect-max-version-for-alias-checks
               The maximum number of run-time checks that can be performed when doing loop versioning for  alias
               in the vectorizer.

           vect-max-peeling-for-alignment
               The  maximum  number  of loop peels to enhance access alignment for vectorizer. Value -1 means no
               limit.

           max-iterations-to-track
               The maximum number of iterations of a loop the brute-force algorithm for analysis of  the  number
               of iterations of the loop tries to evaluate.

           hot-bb-count-fraction
               The  denominator  n of fraction 1/n of the maximal execution count of a basic block in the entire
               program that a basic block needs to at least have in order to be considered hot.  The default  is
               10000,  which  means  that a basic block is considered hot if its execution count is greater than
               1/10000 of the maximal execution count.  0 means that it is never considered hot.  Used  in  non-
               LTO mode.

           hot-bb-count-ws-permille
               The  number  of most executed permilles, ranging from 0 to 1000, of the profiled execution of the
               entire program to which the execution count of a basic block must be  part  of  in  order  to  be
               considered  hot.   The  default  is  990, which means that a basic block is considered hot if its
               execution count contributes to the upper 990 permilles, or 99.0%, of the  profiled  execution  of
               the entire program.  0 means that it is never considered hot.  Used in LTO mode.

           hot-bb-frequency-fraction
               The  denominator  n  of  fraction 1/n of the execution frequency of the entry block of a function
               that a basic block of this function needs to at least have in order to be  considered  hot.   The
               default is 1000, which means that a basic block is considered hot in a function if it is executed
               more frequently than 1/1000 of the frequency of the entry block of the function.  0 means that it
               is never considered hot.

           unlikely-bb-count-fraction
               The  denominator  n  of  fraction  1/n of the number of profiled runs of the entire program below
               which the execution count of a basic block must be in order for the basic block to be  considered
               unlikely  executed.   The  default  is  20, which means that a basic block is considered unlikely
               executed if it is executed in fewer than 1/20, or 5%, of the runs of the program.  0  means  that
               it is always considered unlikely executed.

           max-predicted-iterations
               The  maximum  number  of  loop iterations we predict statically.  This is useful in cases where a
               function contains a single loop with known bound and another loop with unknown bound.  The  known
               number  of  iterations  is predicted correctly, while the unknown number of iterations average to
               roughly 10.  This means that the loop without bounds appears artificially cold  relative  to  the
               other one.

           builtin-expect-probability
               Control  the  probability  of  the  expression having the specified value. This parameter takes a
               percentage (i.e. 0 ... 100) as input.

           builtin-string-cmp-inline-length
               The maximum length of a constant string for a builtin string cmp call eligible for inlining.

           align-threshold
               Select fraction of the maximal frequency of executions of a basic block in a  function  to  align
               the basic block.

           align-loop-iterations
               A loop expected to iterate at least the selected number of iterations is aligned.

           tracer-dynamic-coverage
           tracer-dynamic-coverage-feedback
               This  value  is  used  to  limit  superblock  formation  once  the  given  percentage of executed
               instructions is covered.  This limits unnecessary code size expansion.

               The tracer-dynamic-coverage-feedback parameter is used only when profile feedback  is  available.
               The  real  profiles (as opposed to statically estimated ones) are much less balanced allowing the
               threshold to be larger value.

           tracer-max-code-growth
               Stop tail duplication once code growth has reached given percentage.  This is a rather artificial
               limit, as most of the duplicates are eliminated later in cross jumping, so it may be set to  much
               higher values than is the desired code growth.

           tracer-min-branch-ratio
               Stop  reverse  growth  when  the reverse probability of best edge is less than this threshold (in
               percent).

           tracer-min-branch-probability
           tracer-min-branch-probability-feedback
               Stop forward growth if the best edge has probability lower than this threshold.

               Similarly to tracer-dynamic-coverage two parameters are provided.  tracer-min-branch-probability-
               feedback  is  used  for  compilation  with  profile  feedback  and  tracer-min-branch-probability
               compilation  without.   The  value  for  compilation  with  profile  feedback  needs  to  be more
               conservative (higher) in order to make tracer effective.

           stack-clash-protection-guard-size
               Specify the size of the operating system provided stack guard as 2 raised to num  bytes.   Higher
               values  may  reduce  the  number of explicit probes, but a value larger than the operating system
               provided guard will leave code vulnerable to stack clash style attacks.

           stack-clash-protection-probe-interval
               Stack clash protection involves probing stack space as it is allocated.  This param controls  the
               maximum  distance  between  probes  into  the  stack as 2 raised to num bytes.  Higher values may
               reduce the number of explicit probes, but a value larger than the operating system provided guard
               will leave code vulnerable to stack clash style attacks.

           max-cse-path-length
               The maximum number of basic blocks on path that CSE considers.

           max-cse-insns
               The maximum number of instructions CSE processes before flushing.

           ggc-min-expand
               GCC uses a garbage collector to manage its own memory allocation.  This parameter  specifies  the
               minimum  percentage  by  which  the  garbage collector's heap should be allowed to expand between
               collections.  Tuning this may improve compilation speed; it has no effect on code generation.

               The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when RAM >= 1GB.  If "getrlimit"
               is available, the notion of "RAM" is the smallest of actual RAM and "RLIMIT_DATA" or "RLIMIT_AS".
               If GCC is not able to calculate RAM on a particular platform, the lower bound  of  30%  is  used.
               Setting  this  parameter  and ggc-min-heapsize to zero causes a full collection to occur at every
               opportunity.  This is extremely slow, but can be useful for debugging.

           ggc-min-heapsize
               Minimum size of the garbage collector's heap before it begins bothering to collect garbage.   The
               first  collection  occurs  after  the  heap  expands  by ggc-min-expand% beyond ggc-min-heapsize.
               Again, tuning this may improve compilation speed, and has no effect on code generation.

               The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that tries to ensure that RLIMIT_DATA
               or RLIMIT_AS are not exceeded, but with a lower bound of 4096 (four megabytes) and an upper bound
               of 131072 (128 megabytes).  If GCC is not able to calculate RAM on  a  particular  platform,  the
               lower  bound is used.  Setting this parameter very large effectively disables garbage collection.
               Setting this parameter and ggc-min-expand to zero causes a full  collection  to  occur  at  every
               opportunity.

           max-reload-search-insns
               The  maximum  number  of  instruction  reload  should  look  backward  for  equivalent  register.
               Increasing values mean more aggressive optimization, making the compilation  time  increase  with
               probably slightly better performance.

           max-cselib-memory-locations
               The  maximum  number of memory locations cselib should take into account.  Increasing values mean
               more aggressive optimization, making the compilation time increase with probably slightly  better
               performance.

           max-sched-ready-insns
               The  maximum number of instructions ready to be issued the scheduler should consider at any given
               time during the first scheduling pass.  Increasing values mean more thorough searches, making the
               compilation time increase with probably little benefit.

           max-sched-region-blocks
               The maximum number of blocks in a region to be considered for interblock scheduling.

           max-pipeline-region-blocks
               The maximum number of blocks in a region  to  be  considered  for  pipelining  in  the  selective
               scheduler.

           max-sched-region-insns
               The maximum number of insns in a region to be considered for interblock scheduling.

           max-pipeline-region-insns
               The  maximum  number  of  insns  in  a  region  to  be considered for pipelining in the selective
               scheduler.

           min-spec-prob
               The minimum probability (in percents) of reaching  a  source  block  for  interblock  speculative
               scheduling.

           max-sched-extend-regions-iters
               The  maximum  number  of  iterations through CFG to extend regions.  A value of 0 disables region
               extensions.

           max-sched-insn-conflict-delay
               The maximum conflict delay for an insn to be considered for speculative motion.

           sched-spec-prob-cutoff
               The minimal probability of speculation success (in  percents),  so  that  speculative  insns  are
               scheduled.

           sched-state-edge-prob-cutoff
               The minimum probability an edge must have for the scheduler to save its state across it.

           sched-mem-true-dep-cost
               Minimal distance (in CPU cycles) between store and load targeting same memory locations.

           selsched-max-lookahead
               The  maximum  size  of the lookahead window of selective scheduling.  It is a depth of search for
               available instructions.

           selsched-max-sched-times
               The maximum number of times that an instruction is scheduled during selective  scheduling.   This
               is the limit on the number of iterations through which the instruction may be pipelined.

           selsched-insns-to-rename
               The maximum number of best instructions in the ready list that are considered for renaming in the
               selective scheduler.

           sms-min-sc
               The minimum value of stage count that swing modulo scheduler generates.

           max-last-value-rtl
               The maximum size measured as number of RTLs that can be recorded in an expression in combiner for
               a pseudo register as last known value of that register.

           max-combine-insns
               The maximum number of instructions the RTL combiner tries to combine.

           integer-share-limit
               Small integer constants can use a shared data structure, reducing the compiler's memory usage and
               increasing its speed.  This sets the maximum value of a shared integer constant.

           ssp-buffer-size
               The  minimum  size  of  buffers  (i.e.  arrays)  that  receive  stack  smashing  protection  when
               -fstack-protection is used.

               This default before Ubuntu 10.10 was "8".  Currently  it  is  "4",  to  increase  the  number  of
               functions protected by the stack protector.

           min-size-for-stack-sharing
               The minimum size of variables taking part in stack slot sharing when not optimizing.

           max-jump-thread-duplication-stmts
               Maximum number of statements allowed in a block that needs to be duplicated when threading jumps.

           max-fields-for-field-sensitive
               Maximum  number  of  fields  in  a  structure  treated in a field sensitive manner during pointer
               analysis.

           prefetch-latency
               Estimate on average number of instructions that  are  executed  before  prefetch  finishes.   The
               distance prefetched ahead is proportional to this constant.  Increasing this number may also lead
               to less streams being prefetched (see simultaneous-prefetches).

           simultaneous-prefetches
               Maximum number of prefetches that can run at the same time.

           l1-cache-line-size
               The size of cache line in L1 data cache, in bytes.

           l1-cache-size
               The size of L1 data cache, in kilobytes.

           l2-cache-size
               The size of L2 data cache, in kilobytes.

           prefetch-dynamic-strides
               Whether  the  loop  array prefetch pass should issue software prefetch hints for strides that are
               non-constant.  In some cases this may be beneficial, though the fact the stride  is  non-constant
               may make it hard to predict when there is clear benefit to issuing these hints.

               Set  to  1 if the prefetch hints should be issued for non-constant strides.  Set to 0 if prefetch
               hints should be issued only for strides that are known to be constant and below prefetch-minimum-
               stride.

           prefetch-minimum-stride
               Minimum constant stride, in bytes, to start using prefetch hints for.  If the stride is less than
               this threshold, prefetch hints will not be issued.

               This setting is useful for processors that have hardware prefetchers, in which case there may  be
               conflicts  between  the  hardware  prefetchers  and  the  software  prefetchers.  If the hardware
               prefetchers have a maximum stride they can handle, it should be used here to improve the  use  of
               software prefetchers.

               A  value of -1 means we don't have a threshold and therefore prefetch hints can be issued for any
               constant stride.

               This setting is only useful for strides that are known and constant.

           loop-interchange-max-num-stmts
               The maximum number of stmts in a loop to be interchanged.

           loop-interchange-stride-ratio
               The minimum ratio between stride of two loops for interchange to be profitable.

           min-insn-to-prefetch-ratio
               The minimum ratio between the number of instructions and  the  number  of  prefetches  to  enable
               prefetching in a loop.

           prefetch-min-insn-to-mem-ratio
               The  minimum  ratio  between  the  number  of instructions and the number of memory references to
               enable prefetching in a loop.

           use-canonical-types
               Whether the compiler should use the "canonical" type system.  Should always be 1,  which  uses  a
               more efficient internal mechanism for comparing types in C++ and Objective-C++.  However, if bugs
               in  the  canonical  type  system are causing compilation failures, set this value to 0 to disable
               canonical types.

           switch-conversion-max-branch-ratio
               Switch initialization conversion refuses to create arrays that are bigger than switch-conversion-
               max-branch-ratio times the number of branches in the switch.

           max-partial-antic-length
               Maximum length of the partial antic set computed during the tree partial  redundancy  elimination
               optimization  (-ftree-pre)  when  optimizing at -O3 and above.  For some sorts of source code the
               enhanced partial redundancy elimination optimization can run away, consuming all  of  the  memory
               available  on  the  host machine.  This parameter sets a limit on the length of the sets that are
               computed, which prevents the runaway behavior.  Setting a value of 0 for this parameter allows an
               unlimited set length.

           rpo-vn-max-loop-depth
               Maximum loop depth that is value-numbered optimistically.  When the limit hits the innermost rpo-
               vn-max-loop-depth loops and the outermost loop in the loop nest are value-numbered optimistically
               and the remaining ones not.

           sccvn-max-alias-queries-per-access
               Maximum number of alias-oracle queries we perform when looking for  redundancies  for  loads  and
               stores.   If  this  limit  is  hit  the search is aborted and the load or store is not considered
               redundant.  The number of queries is algorithmically limited to the number of stores on all paths
               from the load to the function entry.

           ira-max-loops-num
               IRA uses regional register allocation by default.  If a function contains  more  loops  than  the
               number  given  by  this  parameter, only at most the given number of the most frequently-executed
               loops form regions for regional register allocation.

           ira-max-conflict-table-size
               Although IRA uses a sophisticated algorithm to compress the conflict table, the table  can  still
               require  excessive  amounts  of  memory for huge functions.  If the conflict table for a function
               could be more than the size in MB given by this parameter, the register allocator instead uses  a
               faster,  simpler,  and  lower-quality  algorithm that does not require building a pseudo-register
               conflict table.

           ira-loop-reserved-regs
               IRA can be used to evaluate more accurate register pressure in loops for decisions to  move  loop
               invariants  (see  -O3).   The  number  of available registers reserved for some other purposes is
               given by this parameter.  Default of the parameter is the best found from numerous experiments.

           lra-inheritance-ebb-probability-cutoff
               LRA tries to reuse values reloaded in registers in subsequent insns.  This optimization is called
               inheritance.  EBB is used as a region to do this optimization.  The parameter defines  a  minimal
               fall-through  edge  probability  in  percentage  used  to  add BB to inheritance EBB in LRA.  The
               default value was chosen from numerous runs of SPEC2000 on x86-64.

           loop-invariant-max-bbs-in-loop
               Loop invariant motion can be very expensive, both in compilation time and  in  amount  of  needed
               compile-time  memory,  with  very  large loops.  Loops with more basic blocks than this parameter
               won't have loop invariant motion optimization performed on them.

           loop-max-datarefs-for-datadeps
               Building data dependencies is expensive for very large loops.  This parameter limits  the  number
               of  data references in loops that are considered for data dependence analysis.  These large loops
               are no handled by the optimizations using loop data dependencies.

           max-vartrack-size
               Sets a maximum number of hash table slots to use during variable tracking  dataflow  analysis  of
               any  function.  If this limit is exceeded with variable tracking at assignments enabled, analysis
               for that function is retried without it, after removing all debug insns from  the  function.   If
               the  limit is exceeded even without debug insns, var tracking analysis is completely disabled for
               the function.  Setting the parameter to zero makes it unlimited.

           max-vartrack-expr-depth
               Sets a maximum number of recursion  levels  when  attempting  to  map  variable  names  or  debug
               temporaries  to  value  expressions.   This  trades  compilation  time  for  more  complete debug
               information.  If this is set  too  low,  value  expressions  that  are  available  and  could  be
               represented  in  debug  information may end up not being used; setting this higher may enable the
               compiler to find more complex debug expressions, but compile time and memory use may grow.

           max-debug-marker-count
               Sets a threshold on the number of debug markers (e.g. begin stmt  markers)  to  avoid  complexity
               explosion at inlining or expanding to RTL.  If a function has more such gimple stmts than the set
               limit,  such  stmts  will  be  dropped  from  the  inlined  copy  of a function, and from its RTL
               expansion.

           min-nondebug-insn-uid
               Use uids starting at this parameter for  nondebug  insns.   The  range  below  the  parameter  is
               reserved  exclusively  for debug insns created by -fvar-tracking-assignments, but debug insns may
               get (non-overlapping) uids above it if the reserved range is exhausted.

           ipa-sra-ptr-growth-factor
               IPA-SRA replaces a pointer to an aggregate with one  or  more  new  parameters  only  when  their
               cumulative  size  is  less  or  equal to ipa-sra-ptr-growth-factor times the size of the original
               pointer parameter.

           ipa-sra-max-replacements
               Maximum pieces of an aggregate that IPA-SRA tracks.  As a consequence, it  is  also  the  maximum
               number of replacements of a formal parameter.

           sra-max-scalarization-size-Ospeed
           sra-max-scalarization-size-Osize
               The  two  Scalar  Reduction of Aggregates passes (SRA and IPA-SRA) aim to replace scalar parts of
               aggregates with uses of independent scalar variables.  These parameters control the maximum size,
               in storage units, of aggregate which is considered for replacement when compiling for speed (sra-
               max-scalarization-size-Ospeed) or size (sra-max-scalarization-size-Osize) respectively.

           sra-max-propagations
               The maximum number of artificial accesses that Scalar Replacement of Aggregates (SRA) will track,
               per one local variable, in order to facilitate copy propagation.

           tm-max-aggregate-size
               When making copies of thread-local variables in a transaction, this parameter specifies the  size
               in  bytes  after  which variables are saved with the logging functions as opposed to save/restore
               code sequence pairs.  This option only applies when using -fgnu-tm.

           graphite-max-nb-scop-params
               To avoid exponential effects in the Graphite loop transforms,  the  number  of  parameters  in  a
               Static  Control  Part  (SCoP)  is  bounded.   A  value  of zero can be used to lift the bound.  A
               variable whose value is unknown at compilation time and defined outside a SCoP is a parameter  of
               the SCoP.

           loop-block-tile-size
               Loop  blocking  or strip mining transforms, enabled with -floop-block or -floop-strip-mine, strip
               mine each loop in the loop nest by a given number of iterations.  The strip length can be changed
               using the loop-block-tile-size parameter.

           ipa-jump-function-lookups
               Specifies number of statements visited during jump function offset discovery.

           ipa-cp-value-list-size
               IPA-CP attempts to track all possible values and types passed to a function's parameter in  order
               to  propagate them and perform devirtualization.  ipa-cp-value-list-size is the maximum number of
               values and types it stores per one formal parameter of a function.

           ipa-cp-eval-threshold
               IPA-CP calculates its own score of cloning profitability heuristics and  performs  those  cloning
               opportunities with scores that exceed ipa-cp-eval-threshold.

           ipa-cp-max-recursive-depth
               Maximum depth of recursive cloning for self-recursive function.

           ipa-cp-min-recursive-probability
               Recursive cloning only when the probability of call being executed exceeds the parameter.

           ipa-cp-recursion-penalty
               Percentage penalty the recursive functions will receive when they are evaluated for cloning.

           ipa-cp-single-call-penalty
               Percentage  penalty functions containing a single call to another function will receive when they
               are evaluated for cloning.

           ipa-max-agg-items
               IPA-CP is also capable to propagate a number of scalar values passed in  an  aggregate.  ipa-max-
               agg-items controls the maximum number of such values per one parameter.

           ipa-cp-loop-hint-bonus
               When  IPA-CP  determines  that  a cloning candidate would make the number of iterations of a loop
               known, it adds a bonus of ipa-cp-loop-hint-bonus to the profitability score of the candidate.

           ipa-max-loop-predicates
               The maximum number of different predicates IPA will use to describe when loops in a function have
               known properties.

           ipa-max-aa-steps
               During its analysis of function bodies, IPA-CP employs alias analysis in order  to  track  values
               pointed to by function parameters.  In order not spend too much time analyzing huge functions, it
               gives  up and consider all memory clobbered after examining ipa-max-aa-steps statements modifying
               memory.

           ipa-max-switch-predicate-bounds
               Maximal number of boundary endpoints of case ranges of switch statement.   For  switch  exceeding
               this  limit,  IPA-CP will not construct cloning cost predicate, which is used to estimate cloning
               benefit, for default case of the switch statement.

           ipa-max-param-expr-ops
               IPA-CP will analyze conditional statement that references some  function  parameter  to  estimate
               benefit  for  cloning  upon  certain  constant value.  But if number of operations in a parameter
               expression exceeds ipa-max-param-expr-ops, the expression is treated as complicated one,  and  is
               not handled by IPA analysis.

           lto-partitions
               Specify desired number of partitions produced during WHOPR compilation.  The number of partitions
               should exceed the number of CPUs used for compilation.

           lto-min-partition
               Size  of  minimal  partition  for  WHOPR  (in estimated instructions).  This prevents expenses of
               splitting very small programs into too many partitions.

           lto-max-partition
               Size of max partition for WHOPR (in estimated instructions).   to  provide  an  upper  bound  for
               individual size of partition.  Meant to be used only with balanced partitioning.

           lto-max-streaming-parallelism
               Maximal number of parallel processes used for LTO streaming.

           cxx-max-namespaces-for-diagnostic-help
               The  maximum  number  of  namespaces to consult for suggestions when C++ name lookup fails for an
               identifier.

           sink-frequency-threshold
               The maximum relative execution frequency  (in  percents)  of  the  target  block  relative  to  a
               statement's  original  block to allow statement sinking of a statement.  Larger numbers result in
               more aggressive statement sinking.  A small positive adjustment is applied  for  statements  with
               memory operands as those are even more profitable so sink.

           max-stores-to-sink
               The maximum number of conditional store pairs that can be sunk.  Set to 0 if either vectorization
               (-ftree-vectorize) or if-conversion (-ftree-loop-if-convert) is disabled.

           case-values-threshold
               The  smallest  number  of  different values for which it is best to use a jump-table instead of a
               tree of conditional branches.  If the value is 0, use the default for the machine.

           jump-table-max-growth-ratio-for-size
               The maximum code size growth ratio when expanding into a jump table (in percent).  The  parameter
               is used when optimizing for size.

           jump-table-max-growth-ratio-for-speed
               The  maximum code size growth ratio when expanding into a jump table (in percent).  The parameter
               is used when optimizing for speed.

           tree-reassoc-width
               Set the maximum number of instructions executed in parallel in reassociated tree. This  parameter
               overrides target dependent heuristics used by default if has non zero value.

           sched-pressure-algorithm
               Choose  between  the  two  available  implementations  of  -fsched-pressure.   Algorithm 1 is the
               original implementation and is the more likely to  prevent  instructions  from  being  reordered.
               Algorithm 2 was designed to be a compromise between the relatively conservative approach taken by
               algorithm  1  and  the rather aggressive approach taken by the default scheduler.  It relies more
               heavily on  having  a  regular  register  file  and  accurate  register  pressure  classes.   See
               haifa-sched.c in the GCC sources for more details.

               The default choice depends on the target.

           max-slsr-cand-scan
               Set  the maximum number of existing candidates that are considered when seeking a basis for a new
               straight-line strength reduction candidate.

           asan-globals
               Enable buffer overflow detection for global objects.  This  kind  of  protection  is  enabled  by
               default  if  you  are  using -fsanitize=address option.  To disable global objects protection use
               --param asan-globals=0.

           asan-stack
               Enable buffer overflow detection for stack objects.   This  kind  of  protection  is  enabled  by
               default  when  using  -fsanitize=address.   To  disable stack protection use --param asan-stack=0
               option.

           asan-instrument-reads
               Enable buffer overflow detection for memory reads.  This kind of protection is enabled by default
               when   using   -fsanitize=address.    To   disable   memory   reads   protection   use    --param
               asan-instrument-reads=0.

           asan-instrument-writes
               Enable  buffer  overflow  detection  for  memory  writes.   This kind of protection is enabled by
               default  when  using  -fsanitize=address.   To  disable  memory  writes  protection  use  --param
               asan-instrument-writes=0 option.

           asan-memintrin
               Enable  detection  for  built-in  functions.   This kind of protection is enabled by default when
               using -fsanitize=address.  To disable built-in functions protection use --param asan-memintrin=0.

           asan-use-after-return
               Enable detection of use-after-return.  This kind of protection is enabled by default  when  using
               the -fsanitize=address option.  To disable it use --param asan-use-after-return=0.

               Note:    By   default   the   check   is   disabled   at   run   time.    To   enable   it,   add
               "detect_stack_use_after_return=1" to the environment variable ASAN_OPTIONS.

           asan-instrumentation-with-call-threshold
               If number of memory accesses in function being instrumented is greater or equal to  this  number,
               use   callbacks   instead   of   inline   checks.   E.g.  to  disable  inline  code  use  --param
               asan-instrumentation-with-call-threshold=0.

           hwasan-instrument-stack
               Enable hwasan instrumentation of  statically  sized  stack-allocated  variables.   This  kind  of
               instrumentation  is  enabled  by  default when using -fsanitize=hwaddress and disabled by default
               when  using  -fsanitize=kernel-hwaddress.   To  disable   stack   instrumentation   use   --param
               hwasan-instrument-stack=0, and to enable it use --param hwasan-instrument-stack=1.

           hwasan-random-frame-tag
               When  using stack instrumentation, decide tags for stack variables using a deterministic sequence
               beginning at a random tag for each frame.  With this parameter unset tags are  chosen  using  the
               same  sequence  but  beginning  from  1.  This is enabled by default for -fsanitize=hwaddress and
               unavailable    for    -fsanitize=kernel-hwaddress.      To     disable     it     use     --param
               hwasan-random-frame-tag=0.

           hwasan-instrument-allocas
               Enable  hwasan  instrumentation  of  dynamically  sized  stack-allocated variables.  This kind of
               instrumentation is enabled by default when using -fsanitize=hwaddress  and  disabled  by  default
               when using -fsanitize=kernel-hwaddress.  To disable instrumentation of such variables use --param
               hwasan-instrument-allocas=0, and to enable it use --param hwasan-instrument-allocas=1.

           hwasan-instrument-reads
               Enable  hwasan  checks  on memory reads.  Instrumentation of reads is enabled by default for both
               -fsanitize=hwaddress and -fsanitize=kernel-hwaddress.   To  disable  checking  memory  reads  use
               --param hwasan-instrument-reads=0.

           hwasan-instrument-writes
               Enable  hwasan checks on memory writes.  Instrumentation of writes is enabled by default for both
               -fsanitize=hwaddress and -fsanitize=kernel-hwaddress.  To  disable  checking  memory  writes  use
               --param hwasan-instrument-writes=0.

           hwasan-instrument-mem-intrinsics
               Enable  hwasan  instrumentation of builtin functions.  Instrumentation of these builtin functions
               is enabled by default for both -fsanitize=hwaddress and -fsanitize=kernel-hwaddress.  To  disable
               instrumentation of builtin functions use --param hwasan-instrument-mem-intrinsics=0.

           use-after-scope-direct-emission-threshold
               If  the size of a local variable in bytes is smaller or equal to this number, directly poison (or
               unpoison) shadow memory instead of using run-time callbacks.

           tsan-distinguish-volatile
               Emit special instrumentation for accesses to volatiles.

           tsan-instrument-func-entry-exit
               Emit instrumentation calls to __tsan_func_entry() and __tsan_func_exit().

           max-fsm-thread-path-insns
               Maximum number of instructions to copy when duplicating blocks on a finite state  automaton  jump
               thread path.

           max-fsm-thread-length
               Maximum number of basic blocks on a finite state automaton jump thread path.

           max-fsm-thread-paths
               Maximum number of new jump thread paths to create for a finite state automaton.

           parloops-chunk-size
               Chunk size of omp schedule for loops parallelized by parloops.

           parloops-schedule
               Schedule  type of omp schedule for loops parallelized by parloops (static, dynamic, guided, auto,
               runtime).

           parloops-min-per-thread
               The minimum number of iterations per thread of an  innermost  parallelized  loop  for  which  the
               parallelized  variant  is  preferred  over the single threaded one.  Note that for a parallelized
               loop nest the minimum number of iterations of the outermost loop per thread is two.

           max-ssa-name-query-depth
               Maximum depth of recursion when querying properties of SSA names in things  like  fold  routines.
               One level of recursion corresponds to following a use-def chain.

           max-speculative-devirt-maydefs
               The maximum number of may-defs we analyze when looking for a must-def specifying the dynamic type
               of an object that invokes a virtual call we may be able to devirtualize speculatively.

           max-vrp-switch-assertions
               The maximum number of assertions to add along the default edge of a switch statement during VRP.

           evrp-mode
               Specifies the mode Early VRP should operate in.

           unroll-jam-min-percent
               The  minimum  percentage  of memory references that must be optimized away for the unroll-and-jam
               transformation to be considered profitable.

           unroll-jam-max-unroll
               The  maximum  number  of  times  the  outer  loop  should  be  unrolled  by  the   unroll-and-jam
               transformation.

           max-rtl-if-conversion-unpredictable-cost
               Maximum  permissible  cost for the sequence that would be generated by the RTL if-conversion pass
               for a branch that is considered unpredictable.

           max-variable-expansions-in-unroller
               If -fvariable-expansion-in-unroller is used, the maximum  number  of  times  that  an  individual
               variable will be expanded during loop unrolling.

           tracer-min-branch-probability-feedback
               Stop  forward  growth  if  the probability of best edge is less than this threshold (in percent).
               Used when profile feedback is available.

           partial-inlining-entry-probability
               Maximum probability of the entry BB of split region (in percent  relative  to  entry  BB  of  the
               function) to make partial inlining happen.

           max-tracked-strlens
               Maximum number of strings for which strlen optimization pass will track string lengths.

           gcse-after-reload-partial-fraction
               The threshold ratio for performing partial redundancy elimination after reload.

           gcse-after-reload-critical-fraction
               The  threshold  ratio  of  critical  edges  execution  count  that  permit  performing redundancy
               elimination after reload.

           max-loop-header-insns
               The maximum number of insns in loop header duplicated by the copy loop headers pass.

           vect-epilogues-nomask
               Enable loop epilogue vectorization using smaller vector size.

           vect-partial-vector-usage
               Controls when the loop  vectorizer  considers  using  partial  vector  loads  and  stores  as  an
               alternative  to  falling  back  to  scalar  code.  0 stops the vectorizer from ever using partial
               vector loads and stores.  1 allows partial vector loads and stores if vectorization  removes  the
               need  for  the  code  to  iterate.   2  allows partial vector loads and stores in all loops.  The
               parameter only has an effect on targets that support partial vector loads and stores.

           avoid-fma-max-bits
               Maximum number of bits for which we avoid creating FMAs.

           sms-loop-average-count-threshold
               A threshold on the average loop count considered by the swing modulo scheduler.

           sms-dfa-history
               The number of cycles the swing modulo scheduler considers when checking conflicts using DFA.

           max-inline-insns-recursive-auto
               The maximum number of instructions non-inline function can grow to via recursive inlining.

           graphite-allow-codegen-errors
               Whether codegen errors should be ICEs when -fchecking.

           sms-max-ii-factor
               A factor for tuning the upper bound that swing modulo scheduler uses for scheduling a loop.

           lra-max-considered-reload-pseudos
               The max number of reload pseudos which are considered during spilling a non-reload pseudo.

           max-pow-sqrt-depth
               Maximum depth of sqrt chains to use when synthesizing exponentiation by a real constant.

           max-dse-active-local-stores
               Maximum number of active local stores in RTL dead store elimination.

           asan-instrument-allocas
               Enable asan allocas/VLAs protection.

           max-iterations-computation-cost
               Bound on the cost of an expression to compute the number of iterations.

           max-isl-operations
               Maximum number of isl operations, 0 means unlimited.

           graphite-max-arrays-per-scop
               Maximum number of arrays per scop.

           max-vartrack-reverse-op-size
               Max. size of loc list for which reverse ops should be added.

           tracer-dynamic-coverage-feedback
               The percentage of function, weighted by execution  frequency,  that  must  be  covered  by  trace
               formation.  Used when profile feedback is available.

           max-inline-recursive-depth-auto
               The maximum depth of recursive inlining for non-inline functions.

           fsm-scale-path-stmts
               Scale  factor  to  apply  to  the  number of statements in a threading path when comparing to the
               number of (scaled) blocks.

           fsm-maximum-phi-arguments
               Maximum number of arguments a PHI may have before the FSM threader will not try to thread through
               its block.

           uninit-control-dep-attempts
               Maximum number of nested calls to search for control dependencies during  uninitialized  variable
               analysis.

           sra-max-scalarization-size-Osize
               Maximum size, in storage units, of an aggregate which should be considered for scalarization when
               compiling for size.

           fsm-scale-path-blocks
               Scale factor to apply to the number of blocks in a threading path when comparing to the number of
               (scaled) statements.

           sched-autopref-queue-depth
               Hardware autoprefetcher scheduler model control flag.  Number of lookahead cycles the model looks
               into; at ' ' only enable instruction sorting heuristic.

           loop-versioning-max-inner-insns
               The  maximum  number  of instructions that an inner loop can have before the loop versioning pass
               considers it too big to copy.

           loop-versioning-max-outer-insns
               The maximum number of instructions that an outer loop can have before the  loop  versioning  pass
               considers  it  too big to copy, discounting any instructions in inner loops that directly benefit
               from versioning.

           ssa-name-def-chain-limit
               The maximum number of SSA_NAME assignments to follow in determining a property of a variable such
               as its value.  This limits the  number  of  iterations  or  recursive  calls  GCC  performs  when
               optimizing certain statements or when determining their validity prior to issuing diagnostics.

           store-merging-max-size
               Maximum size of a single store merging region in bytes.

           hash-table-verification-limit
               The number of elements for which hash table verification is done for each searched element.

           max-find-base-term-values
               Maximum number of VALUEs handled during a single find_base_term call.

           analyzer-max-enodes-per-program-point
               The  maximum  number  of exploded nodes per program point within the analyzer, before terminating
               analysis of that point.

           analyzer-max-constraints
               The maximum number of constraints per state.

           analyzer-min-snodes-for-call-summary
               The minimum number of supernodes within a function for the analyzer to consider  summarizing  its
               effects at call sites.

           analyzer-max-enodes-for-full-dump
               The  maximum  depth of exploded nodes that should appear in a dot dump before switching to a less
               verbose format.

           analyzer-max-recursion-depth
               The maximum number of times a callsite can appear in a call stack  within  the  analyzer,  before
               terminating analysis of a call that would recurse deeper.

           analyzer-max-svalue-depth
               The maximum depth of a symbolic value, before approximating the value as unknown.

           analyzer-max-infeasible-edges
               The maximum number of infeasible edges to reject before declaring a diagnostic as infeasible.

           gimple-fe-computed-hot-bb-threshold
               The number of executions of a basic block which is considered hot.  The parameter is used only in
               GIMPLE FE.

           analyzer-bb-explosion-factor
               The  maximum number of 'after supernode' exploded nodes within the analyzer per supernode, before
               terminating analysis.

           ranger-logical-depth
               Maximum depth of logical expression evaluation ranger will look through when evaluating  outgoing
               edge ranges.

           openacc-kernels
               Specify  mode  of OpenACC `kernels' constructs handling.  With --param=openacc-kernels=decompose,
               OpenACC `kernels' constructs are decomposed into parts, a sequence of  compute  constructs,  each
               then  handled  individually.   This  is work in progress.  With --param=openacc-kernels=parloops,
               OpenACC `kernels' constructs are handled by the parloops pass, en  bloc.   This  is  the  current
               default.

           The following choices of name are available on AArch64 targets:

           aarch64-sve-compare-costs
               When vectorizing for SVE, consider using "unpacked" vectors for smaller elements and use the cost
               model  to pick the cheapest approach.  Also use the cost model to choose between SVE and Advanced
               SIMD vectorization.

               Using unpacked vectors includes storing smaller  elements  in  larger  containers  and  accessing
               elements with extending loads and truncating stores.

           aarch64-float-recp-precision
               The  number of Newton iterations for calculating the reciprocal for float type.  The precision of
               division is proportional to this param when division approximation is enabled.  The default value
               is 1.

           aarch64-double-recp-precision
               The number of Newton iterations for calculating the reciprocal for double type.  The precision of
               division is propotional to this param when division approximation is enabled.  The default  value
               is 2.

           aarch64-autovec-preference
               Force an ISA selection strategy for auto-vectorization.  Accepts values from 0 to 4, inclusive.

               0   Use the default heuristics.

               1   Use only Advanced SIMD for auto-vectorization.

               2   Use only SVE for auto-vectorization.

               3   Use both Advanced SIMD and SVE.  Prefer Advanced SIMD when the costs are deemed equal.

               4   Use both Advanced SIMD and SVE.  Prefer SVE when the costs are deemed equal.

               The default value is 0.

           aarch64-loop-vect-issue-rate-niters
               The  tuning  for some AArch64 CPUs tries to take both latencies and issue rates into account when
               deciding whether a loop should be vectorized using SVE, vectorized using Advanced  SIMD,  or  not
               vectorized at all.  If this parameter is set to n, GCC will not use this heuristic for loops that
               are known to execute in fewer than n Advanced SIMD iterations.

   Program Instrumentation Options
       GCC supports a number of command-line options that control adding run-time instrumentation to the code it
       normally  generates.  For example, one purpose of instrumentation is collect profiling statistics for use
       in finding program hot spots, code coverage analysis, or profile-guided optimizations.  Another class  of
       program  instrumentation  is  adding  run-time checking to detect programming errors like invalid pointer
       dereferences or out-of-bounds array accesses, as well as  deliberately  hostile  attacks  such  as  stack
       smashing  or  C++  vtable  hijacking.   There is also a general hook which can be used to implement other
       forms of tracing or function-level instrumentation for debug or program analysis purposes.

       -p
       -pg Generate extra code to write profile information suitable for the analysis program prof (for  -p)  or
           gprof  (for  -pg).  You must use this option when compiling the source files you want data about, and
           you must also use it when linking.

           You can use the function attribute  "no_instrument_function"  to  suppress  profiling  of  individual
           functions when compiling with these options.

       -fprofile-arcs
           Add  code  so that program flow arcs are instrumented.  During execution the program records how many
           times each branch and call is executed and how many times it is taken or returns.   On  targets  that
           support  constructors with priority support, profiling properly handles constructors, destructors and
           C++ constructors (and destructors) of classes which are used as a type of a global variable.

           When the compiled program exits it saves this data to a file  called  auxname.gcda  for  each  source
           file.   The data may be used for profile-directed optimizations (-fbranch-probabilities), or for test
           coverage analysis (-ftest-coverage).  Each object file's auxname is generated from the  name  of  the
           output file, if explicitly specified and it is not the final executable, otherwise it is the basename
           of  the source file.  In both cases any suffix is removed (e.g. foo.gcda for input file dir/foo.c, or
           dir/foo.gcda for output file specified as -o dir/foo.o).

       --coverage
           This option is used to compile and link code instrumented for coverage analysis.   The  option  is  a
           synonym  for  -fprofile-arcs  -ftest-coverage  (when  compiling)  and -lgcov (when linking).  See the
           documentation for those options for more details.

           *   Compile the source files with -fprofile-arcs plus optimization and code generation options.   For
               test  coverage  analysis,  use the additional -ftest-coverage option.  You do not need to profile
               every source file in a program.

           *   Compile the source files additionally with -fprofile-abs-path to create absolute  path  names  in
               the  .gcno  files.   This  allows gcov to find the correct sources in projects where compilations
               occur with different working directories.

           *   Link your object files with -lgcov or -fprofile-arcs (the latter implies the former).

           *   Run the program on a representative workload to generate the arc profile information.   This  may
               be  repeated any number of times.  You can run concurrent instances of your program, and provided
               that the file system supports locking, the data files will be correctly updated.  Unless a strict
               ISO C dialect option is in effect, "fork" calls are detected and correctly handled without double
               counting.

           *   For profile-directed optimizations, compile the source files again with the same optimization and
               code generation options plus -fbranch-probabilities.

           *   For test coverage analysis, use gcov to produce human readable information  from  the  .gcno  and
               .gcda files.  Refer to the gcov documentation for further information.

           With -fprofile-arcs, for each function of your program GCC creates a program flow graph, then finds a
           spanning  tree  for  the graph.  Only arcs that are not on the spanning tree have to be instrumented:
           the compiler adds code to count the number of times that these arcs are executed.  When an arc is the
           only exit or only entrance to a block, the instrumentation code can be added to the block; otherwise,
           a new basic block must be created to hold the instrumentation code.

       -ftest-coverage
           Produce a notes file that the gcov code-coverage utility can use  to  show  program  coverage.   Each
           source  file's  note  file  is  called  auxname.gcno.  Refer to the -fprofile-arcs option above for a
           description of auxname and instructions on how to generate test coverage data.  Coverage data matches
           the source files more closely if you do not optimize.

       -fprofile-abs-path
           Automatically convert relative source file names to absolute path names in  the  .gcno  files.   This
           allows  gcov  to find the correct sources in projects where compilations occur with different working
           directories.

       -fprofile-dir=path
           Set the directory to search for the profile data files in to path.   This  option  affects  only  the
           profile   data   generated   by  -fprofile-generate,  -ftest-coverage,  -fprofile-arcs  and  used  by
           -fprofile-use and -fbranch-probabilities and its related options.  Both absolute and  relative  paths
           can  be used.  By default, GCC uses the current directory as path, thus the profile data file appears
           in the same directory as the object file.  In order to prevent the file name clashing, if the  object
           file name is not an absolute path, we mangle the absolute path of the sourcename.gcda file and use it
           as the file name of a .gcda file.  See similar option -fprofile-note.

           When  an  executable  is  run in a massive parallel environment, it is recommended to save profile to
           different folders.  That can be done with variables in path that are exported during run-time:

           %p  process ID.

           %q{VAR}
               value of environment variable VAR

       -fprofile-generate
       -fprofile-generate=path
           Enable options usually used for  instrumenting  application  to  produce  profile  useful  for  later
           recompilation  with  profile  feedback based optimization.  You must use -fprofile-generate both when
           compiling and when linking your program.

           The  following  options  are  enabled:  -fprofile-arcs,  -fprofile-values,  -finline-functions,   and
           -fipa-bit-cp.

           If  path  is  specified,  GCC  looks  at  the  path  to  find  the  profile  feedback data files. See
           -fprofile-dir.

           To optimize the program based on the collected profile information, use -fprofile-use.

       -fprofile-info-section
       -fprofile-info-section=name
           Register the profile information in the specified section instead of using a  constructor/destructor.
           The  section name is name if it is specified, otherwise the section name defaults to ".gcov_info".  A
           pointer to the profile information generated by -fprofile-arcs or -ftest-coverage is  placed  in  the
           specified  section  for  each  translation  unit.   This  option  disables  the  profile  information
           registration through a constructor and it disables  the  profile  information  processing  through  a
           destructor.   This  option  is  not intended to be used in hosted environments such as GNU/Linux.  It
           targets systems with limited resources which do not support constructors and destructors.  The linker
           could collect the input sections in a continuous memory block and define start and end symbols.   The
           runtime  support  could  dump  the profiling information registered in this linker set during program
           termination to a serial line for example.  A GNU linker script example which defines a linker  output
           section follows:

                     .gcov_info      :
                     {
                       PROVIDE (__gcov_info_start = .);
                       KEEP (*(.gcov_info))
                       PROVIDE (__gcov_info_end = .);
                     }

       -fprofile-note=path
           If  path  is  specified,  GCC  saves  .gcno  file into path location.  If you combine the option with
           multiple source files, the .gcno file will be overwritten.

       -fprofile-prefix-path=path
           This option can be used in combination with profile-generate=profile_dir and  profile-use=profile_dir
           to  inform GCC where is the base directory of built source tree.  By default profile_dir will contain
           files with mangled absolute paths of all object files in the built project.  This  is  not  desirable
           when  directory  used  to  build the instrumented binary differs from the directory used to build the
           binary optimized with profile feedback because  the  profile  data  will  not  be  found  during  the
           optimized  build.  In such setups -fprofile-prefix-path=path with path pointing to the base directory
           of the build can be used to strip the irrelevant part of the path and keep all file names relative to
           the main build directory.

       -fprofile-update=method
           Alter the update method for an application instrumented for profile feedback based optimization.  The
           method argument should be one of single, atomic or  prefer-atomic.   The  first  one  is  useful  for
           single-threaded  applications,  while  the second one prevents profile corruption by emitting thread-
           safe code.

           Warning: When an application does not properly join all threads (or creates an  detached  thread),  a
           profile file can be still corrupted.

           Using  prefer-atomic  would be transformed either to atomic, when supported by a target, or to single
           otherwise.  The GCC driver automatically selects  prefer-atomic  when  -pthread  is  present  in  the
           command line.

       -fprofile-filter-files=regex
           Instrument  only functions from files whose name matches any of the regular expressions (separated by
           semi-colons).

           For example, -fprofile-filter-files=main\.c;module.*\.c will instrument only main.c and all  C  files
           starting with 'module'.

       -fprofile-exclude-files=regex
           Instrument  only  functions  from  files  whose  name  does  not match any of the regular expressions
           (separated by semi-colons).

           For example, -fprofile-exclude-files=/usr/.* will prevent  instrumentation  of  all  files  that  are
           located in the /usr/ folder.

       -fprofile-reproducible=[multithreaded|parallel-runs|serial]
           Control level of reproducibility of profile gathered by "-fprofile-generate".  This makes it possible
           to rebuild program with same outcome which is useful, for example, for distribution packages.

           With  -fprofile-reproducible=serial  the  profile  gathered  by  -fprofile-generate  is  reproducible
           provided the trained program behaves the same at each invocation of the train run, it is  not  multi-
           threaded  and  profile  data streaming is always done in the same order.  Note that profile streaming
           happens at the end of program run but also before "fork" function is invoked.

           Note that it is quite common that execution counts of some part of programs depends, for example,  on
           length  of  temporary  file names or memory space randomization (that may affect hash-table collision
           rate).  Such non-reproducible part of programs may be annotated by "no_instrument_function"  function
           attribute.  gcov-dump  with  -l  can  be  used  to dump gathered data and verify that they are indeed
           reproducible.

           With -fprofile-reproducible=parallel-runs collected profile stays reproducible regardless  the  order
           of  streaming  of the data into gcda files.  This setting makes it possible to run multiple instances
           of instrumented program in parallel (such as with "make -j"). This reduces quality of gathered  data,
           in particular of indirect call profiling.

       -fsanitize=address
           Enable  AddressSanitizer,  a fast memory error detector.  Memory access instructions are instrumented
           to     detect     out-of-bounds     and     use-after-free     bugs.      The     option      enables
           -fsanitize-address-use-after-scope.  See <https://github.com/google/sanitizers/wiki/AddressSanitizer>
           for  more  details.   The  run-time  behavior  can  be  influenced using the ASAN_OPTIONS environment
           variable.  When set to "help=1", the available options are  shown  at  startup  of  the  instrumented
           program.   See <https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags> for a
           list  of  supported  options.   The   option   cannot   be   combined   with   -fsanitize=thread   or
           -fsanitize=hwaddress.   Note  that  the only target -fsanitize=hwaddress is currently supported on is
           AArch64.

       -fsanitize=kernel-address
           Enable AddressSanitizer for Linux kernel.  See <https://github.com/google/kasan> for more details.

       -fsanitize=hwaddress
           Enable Hardware-assisted AddressSanitizer, which uses a hardware ability to ignore the top byte of  a
           pointer  to  allow  the  detection  of  memory  errors  with  a  low  memory overhead.  Memory access
           instructions are instrumented to detect out-of-bounds and use-after-free bugs.   The  option  enables
           -fsanitize-address-use-after-scope.                                                               See
           <https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html> for more details.  The run-
           time behavior can be influenced using the HWASAN_OPTIONS environment variable.  When set to "help=1",
           the available options are shown at startup  of  the  instrumented  program.   The  option  cannot  be
           combined with -fsanitize=thread or -fsanitize=address, and is currently only available on AArch64.

       -fsanitize=kernel-hwaddress
           Enable   Hardware-assisted  AddressSanitizer  for  compilation  of  the  Linux  kernel.   Similar  to
           -fsanitize=kernel-address  but  using  an  alternate   instrumentation   method,   and   similar   to
           -fsanitize=hwaddress  but  with instrumentation differences necessary for compiling the Linux kernel.
           These differences are to avoid hwasan library initialization calls  and  to  account  for  the  stack
           pointer having a different value in its top byte.

           Note:  This  option  has different defaults to the -fsanitize=hwaddress.  Instrumenting the stack and
           alloca calls are not on by default but are still possible  by  specifying  the  command-line  options
           --param  hwasan-instrument-stack=1  and  --param  hwasan-instrument-allocas=1  respectively.  Using a
           random frame tag is not implemented for kernel instrumentation.

       -fsanitize=pointer-compare
           Instrument comparison operation (<, <=, >, >=) with pointer operands.  The option  must  be  combined
           with  either  -fsanitize=kernel-address  or  -fsanitize=address  The  option  cannot be combined with
           -fsanitize=thread.  Note: By default  the  check  is  disabled  at  run  time.   To  enable  it,  add
           "detect_invalid_pointer_pairs=2"     to     the     environment    variable    ASAN_OPTIONS.    Using
           "detect_invalid_pointer_pairs=1" detects invalid operation only when both pointers are non-null.

       -fsanitize=pointer-subtract
           Instrument  subtraction  with  pointer  operands.   The  option  must   be   combined   with   either
           -fsanitize=kernel-address or -fsanitize=address The option cannot be combined with -fsanitize=thread.
           Note:    By    default    the    check    is   disabled   at   run   time.    To   enable   it,   add
           "detect_invalid_pointer_pairs=2"    to    the    environment     variable     ASAN_OPTIONS.     Using
           "detect_invalid_pointer_pairs=1" detects invalid operation only when both pointers are non-null.

       -fsanitize=thread
           Enable  ThreadSanitizer,  a  fast data race detector.  Memory access instructions are instrumented to
           detect data race  bugs.   See  <https://github.com/google/sanitizers/wiki#threadsanitizer>  for  more
           details.  The  run-time  behavior  can be influenced using the TSAN_OPTIONS environment variable; see
           <https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags> for a  list  of  supported  options.
           The option cannot be combined with -fsanitize=address, -fsanitize=leak.

           Note  that  sanitized  atomic  builtins  cannot  throw  exceptions  when  operating on invalid memory
           addresses with non-call exceptions (-fnon-call-exceptions).

       -fsanitize=leak
           Enable LeakSanitizer, a memory leak detector.  This option only matters for  linking  of  executables
           and the executable is linked against a library that overrides "malloc" and other allocator functions.
           See  <https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer> for more details.  The
           run-time behavior can be influenced using the LSAN_OPTIONS environment variable.  The  option  cannot
           be combined with -fsanitize=thread.

       -fsanitize=undefined
           Enable  UndefinedBehaviorSanitizer,  a  fast  undefined  behavior detector.  Various computations are
           instrumented       to       detect       undefined       behavior       at       runtime.         See
           <https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html>   for   more  details.    The  run-time
           behavior can be influenced using the UBSAN_OPTIONS environment variable.  Current suboptions are:

           -fsanitize=shift
               This option enables checking that the result of a shift operation is not  undefined.   Note  that
               what  exactly  is considered undefined differs slightly between C and C++, as well as between ISO
               C90   and   C99,   etc.    This   option   has   two   suboptions,   -fsanitize=shift-base    and
               -fsanitize=shift-exponent.

           -fsanitize=shift-exponent
               This option enables checking that the second argument of a shift operation is not negative and is
               smaller than the precision of the promoted first argument.

           -fsanitize=shift-base
               If  the  second  argument  of a shift operation is within range, check that the result of a shift
               operation is not undefined.  Note that what exactly  is  considered  undefined  differs  slightly
               between C and C++, as well as between ISO C90 and C99, etc.

           -fsanitize=integer-divide-by-zero
               Detect integer division by zero as well as "INT_MIN / -1" division.

           -fsanitize=unreachable
               With  this option, the compiler turns the "__builtin_unreachable" call into a diagnostics message
               call instead.  When reaching the "__builtin_unreachable" call, the behavior is undefined.

           -fsanitize=vla-bound
               This option instructs the compiler to check that the size of a variable length array is positive.

           -fsanitize=null
               This option enables pointer checking.  Particularly,  the  application  built  with  this  option
               turned  on  will  issue  an  error  message  when it tries to dereference a NULL pointer, or if a
               reference (possibly an rvalue reference) is bound to a NULL pointer, or if a method is invoked on
               an object pointed by a NULL pointer.

           -fsanitize=return
               This option enables return statement checking.  Programs built with this option  turned  on  will
               issue  an error message when the end of a non-void function is reached without actually returning
               a value.  This option works in C++ only.

           -fsanitize=signed-integer-overflow
               This option enables signed integer overflow checking.  We check that the result of "+", "*",  and
               both  unary  and binary "-" does not overflow in the signed arithmetics.  Note, integer promotion
               rules must be taken into account.  That is, the following is not an overflow:

                       signed char a = SCHAR_MAX;
                       a++;

           -fsanitize=bounds
               This option enables instrumentation  of  array  bounds.   Various  out  of  bounds  accesses  are
               detected.   Flexible  array  members,  flexible  array  member-like  arrays,  and initializers of
               variables with static storage are not instrumented.

           -fsanitize=bounds-strict
               This option enables strict instrumentation of array bounds.  Most  out  of  bounds  accesses  are
               detected,  including  flexible array members and flexible array member-like arrays.  Initializers
               of variables with static storage are not instrumented.

           -fsanitize=alignment
               This option enables checking of alignment of pointers when  they  are  dereferenced,  or  when  a
               reference  is  bound to insufficiently aligned target, or when a method or constructor is invoked
               on insufficiently aligned object.

           -fsanitize=object-size
               This option enables  instrumentation  of  memory  references  using  the  "__builtin_object_size"
               function.  Various out of bounds pointer accesses are detected.

           -fsanitize=float-divide-by-zero
               Detect     floating-point     division     by    zero.     Unlike    other    similar    options,
               -fsanitize=float-divide-by-zero is not  enabled  by  -fsanitize=undefined,  since  floating-point
               division by zero can be a legitimate way of obtaining infinities and NaNs.

           -fsanitize=float-cast-overflow
               This option enables floating-point type to integer conversion checking.  We check that the result
               of     the     conversion     does    not    overflow.     Unlike    other    similar    options,
               -fsanitize=float-cast-overflow is not enabled by -fsanitize=undefined.  This option does not work
               well with "FE_INVALID" exceptions enabled.

           -fsanitize=nonnull-attribute
               This option enables instrumentation of calls, checking whether null  values  are  not  passed  to
               arguments marked as requiring a non-null value by the "nonnull" function attribute.

           -fsanitize=returns-nonnull-attribute
               This   option   enables   instrumentation   of   return   statements  in  functions  marked  with
               "returns_nonnull" function attribute, to detect returning of null values from such functions.

           -fsanitize=bool
               This option enables instrumentation of loads from bool.  If a value other than 0/1 is  loaded,  a
               run-time error is issued.

           -fsanitize=enum
               This  option enables instrumentation of loads from an enum type.  If a value outside the range of
               values for the enum type is loaded, a run-time error is issued.

           -fsanitize=vptr
               This option enables instrumentation of C++  member  function  calls,  member  accesses  and  some
               conversions between pointers to base and derived classes, to verify the referenced object has the
               correct dynamic type.

           -fsanitize=pointer-overflow
               This  option  enables  instrumentation  of  pointer  arithmetics.   If  the  pointer  arithmetics
               overflows, a run-time error is issued.

           -fsanitize=builtin
               This option enables instrumentation of arguments to selected builtin functions.   If  an  invalid
               value is passed to such arguments, a run-time error is issued.  E.g. passing 0 as the argument to
               "__builtin_ctz" or "__builtin_clz" invokes undefined behavior and is diagnosed by this option.

           While  -ftrapv  causes  traps  for  signed  overflows  to  be  emitted,  -fsanitize=undefined gives a
           diagnostic message.  This currently works only for the C family of languages.

       -fno-sanitize=all
           This option disables all previously enabled sanitizers.   -fsanitize=all  is  not  allowed,  as  some
           sanitizers cannot be used together.

       -fasan-shadow-offset=number
           This  option  forces  GCC  to  use custom shadow offset in AddressSanitizer checks.  It is useful for
           experimenting with different shadow memory layouts in Kernel AddressSanitizer.

       -fsanitize-sections=s1,s2,...
           Sanitize global variables in selected user-defined sections.  si may contain wildcards.

       -fsanitize-recover[=opts]
           -fsanitize-recover= controls error recovery mode for sanitizers mentioned in comma-separated list  of
           opts.   Enabling  this  option for a sanitizer component causes it to attempt to continue running the
           program as if no error happened.  This means multiple runtime errors can  be  reported  in  a  single
           program  run,  and  the  exit  code  of  the  program may indicate success even when errors have been
           reported.  The -fno-sanitize-recover= option can be used to  alter  this  behavior:  only  the  first
           detected error is reported and program then exits with a non-zero exit code.

           Currently   this  feature  only  works  for  -fsanitize=undefined  (and  its  suboptions  except  for
           -fsanitize=unreachable        and         -fsanitize=return),         -fsanitize=float-cast-overflow,
           -fsanitize=float-divide-by-zero,      -fsanitize=bounds-strict,     -fsanitize=kernel-address     and
           -fsanitize=address.   For  these  sanitizers  error  recovery  is  turned  on  by   default,   except
           -fsanitize=address,   for   which   this   feature   is   experimental.   -fsanitize-recover=all  and
           -fno-sanitize-recover=all is also accepted, the former  enables  recovery  for  all  sanitizers  that
           support it, the latter disables recovery for all sanitizers that support it.

           Even  if  a  recovery mode is turned on the compiler side, it needs to be also enabled on the runtime
           library  side,  otherwise  the  failures  are  still  fatal.   The  runtime   library   defaults   to
           "halt_on_error=0"  for  ThreadSanitizer  and  UndefinedBehaviorSanitizer,  while  default  value  for
           AddressSanitizer is "halt_on_error=1". This can be overridden  through  setting  the  "halt_on_error"
           flag in the corresponding environment variable.

           Syntax without an explicit opts parameter is deprecated.  It is equivalent to specifying an opts list
           of:

                   undefined,float-cast-overflow,float-divide-by-zero,bounds-strict

       -fsanitize-address-use-after-scope
           Enable sanitization of local variables to detect use-after-scope bugs.  The option sets -fstack-reuse
           to none.

       -fsanitize-undefined-trap-on-error
           The  -fsanitize-undefined-trap-on-error  option  instructs  the compiler to report undefined behavior
           using "__builtin_trap" rather than a "libubsan" library routine.  The advantage of this is  that  the
           "libubsan"  library  is  not  needed  and  is  not  linked in, so this is usable even in freestanding
           environments.

       -fsanitize-coverage=trace-pc
           Enable coverage-guided fuzzing code instrumentation.  Inserts a  call  to  "__sanitizer_cov_trace_pc"
           into every basic block.

       -fsanitize-coverage=trace-cmp
           Enable dataflow guided fuzzing code instrumentation.  Inserts a call to "__sanitizer_cov_trace_cmp1",
           "__sanitizer_cov_trace_cmp2",   "__sanitizer_cov_trace_cmp4"   or   "__sanitizer_cov_trace_cmp8"  for
           integral   comparison   with   both   operands   variable   or    "__sanitizer_cov_trace_const_cmp1",
           "__sanitizer_cov_trace_const_cmp2",               "__sanitizer_cov_trace_const_cmp4"               or
           "__sanitizer_cov_trace_const_cmp8"   for   integral   comparison   with   one    operand    constant,
           "__sanitizer_cov_trace_cmpf"  or  "__sanitizer_cov_trace_cmpd"  for  float  or double comparisons and
           "__sanitizer_cov_trace_switch" for switch statements.

       -fcf-protection=[full|branch|return|none|check]
           Enable code instrumentation of control-flow transfers to increase program security by  checking  that
           target  addresses  of  control-flow  transfer  instructions (such as indirect function call, function
           return, indirect jump) are valid.  This prevents diverting the  flow  of  control  to  an  unexpected
           target.   This  is intended to protect against such threats as Return-oriented Programming (ROP), and
           similarly call/jmp-oriented programming (COP/JOP).

           The value "branch" tells the compiler to implement checking of validity of control-flow  transfer  at
           the point of indirect branch instructions, i.e. call/jmp instructions.  The value "return" implements
           checking  of  validity  at  the point of returning from a function.  The value "full" is an alias for
           specifying both "branch" and "return". The value "none" turns off instrumentation.

           The value "check" is used for the final link with link-time optimization (LTO).  An error  is  issued
           if LTO object files are compiled with different -fcf-protection values.  The value "check" is ignored
           at the compile time.

           The  macro "__CET__" is defined when -fcf-protection is used.  The first bit of "__CET__" is set to 1
           for the value "branch" and the second bit of "__CET__" is set to 1 for the "return".

           You can also use the "nocf_check" attribute to identify which functions and calls should  be  skipped
           from instrumentation.

           Currently the x86 GNU/Linux target provides an implementation based on Intel Control-flow Enforcement
           Technology (CET) which works for i686 processor or newer.

           NOTE:  In  Ubuntu  19.10  and later versions, -fcf-protection is enabled by default for C, C++, ObjC,
           ObjC++, if none of -fno-cf-protection nor -fcf-protection=* are found.

       -fstack-protector
           Emit extra code to check for buffer overflows, such as stack  smashing  attacks.   This  is  done  by
           adding  a  guard  variable  to  functions with vulnerable objects.  This includes functions that call
           "alloca", and functions with buffers larger than or equal to 8 bytes.   The  guards  are  initialized
           when  a  function  is  entered  and then checked when the function exits.  If a guard check fails, an
           error message is printed and the program exits.  Only variables that are actually  allocated  on  the
           stack are considered, optimized away variables or variables allocated in registers don't count.

       -fstack-protector-all
           Like -fstack-protector except that all functions are protected.

       -fstack-protector-strong
           Like  -fstack-protector  but  includes additional functions to be protected --- those that have local
           array definitions, or have references to local frame addresses.  Only  variables  that  are  actually
           allocated  on  the stack are considered, optimized away variables or variables allocated in registers
           don't count.

       -fstack-protector-explicit
           Like -fstack-protector but only protects those functions which have the "stack_protect" attribute.

       -fstack-check
           Generate code to verify that you do not go beyond the boundary of the stack.  You should specify this
           flag if you are running in an environment with multiple threads, but you only rarely need to  specify
           it  in  a  single-threaded  environment  since stack overflow is automatically detected on nearly all
           systems if there is only one stack.

           Note that this switch does not actually cause checking to  be  done;  the  operating  system  or  the
           language  runtime  must  do  that.   The switch causes generation of code to ensure that they see the
           stack being extended.

           You can additionally specify a string parameter: no means no checking, generic means force the use of
           old-style checking,  specific  means  use  the  best  checking  method  and  is  equivalent  to  bare
           -fstack-check.

           Old-style  checking  is  a generic mechanism that requires no specific target support in the compiler
           but comes with the following drawbacks:

           1.  Modified allocation strategy for large objects: they are always allocated  dynamically  if  their
               size exceeds a fixed threshold.  Note this may change the semantics of some code.

           2.  Fixed  limit  on  the  size  of  the static frame of functions: when it is topped by a particular
               function, stack checking is not reliable and a warning is issued by the compiler.

           3.  Inefficiency: because of both the modified allocation strategy and  the  generic  implementation,
               code performance is hampered.

           Note  that old-style stack checking is also the fallback method for specific if no target support has
           been added in the compiler.

           -fstack-check= is designed for  Ada's  needs  to  detect  infinite  recursion  and  stack  overflows.
           specific  is  an excellent choice when compiling Ada code.  It is not generally sufficient to protect
           against stack-clash attacks.  To protect against those you want -fstack-clash-protection.

       -fstack-clash-protection
           Generate code to prevent stack clash style attacks.  When this option is enabled, the  compiler  will
           only  allocate  one  page  of  stack  space  at  a  time  and each page is accessed immediately after
           allocation.  Thus, it prevents allocations from jumping over any stack guard  page  provided  by  the
           operating system.

           Most   targets   do   not   fully   support  stack  clash  protection.   However,  on  those  targets
           -fstack-clash-protection will protect dynamic stack allocations.  -fstack-clash-protection  may  also
           provide    limited    protection    for   static   stack   allocations   if   the   target   supports
           -fstack-check=specific.

           NOTE: In Ubuntu 19.10 and later versions, -fstack-clash-protection is enabled by default for C,  C++,
           ObjC, ObjC++, unless -fno-stack-clash-protection is found.

       -fstack-limit-register=reg
       -fstack-limit-symbol=sym
       -fno-stack-limit
           Generate  code  to  ensure that the stack does not grow beyond a certain value, either the value of a
           register or the address of a symbol.  If a larger stack is required, a signal is raised at run  time.
           For  most  targets, the signal is raised before the stack overruns the boundary, so it is possible to
           catch the signal without taking special precautions.

           For instance, if the stack starts at absolute address 0x80000000 and grows downwards, you can use the
           flags -fstack-limit-symbol=__stack_limit and -Wl,--defsym,__stack_limit=0x7ffe0000 to enforce a stack
           limit of 128KB.  Note that this may only work with the GNU linker.

           You can locally override stack limit checking by using the "no_stack_limit" function attribute.

       -fsplit-stack
           Generate code to automatically split the stack before it overflows.   The  resulting  program  has  a
           discontiguous  stack  which  can  only overflow if the program is unable to allocate any more memory.
           This is most useful when running threaded programs, as it is no longer necessary to calculate a  good
           stack  size  to  use for each thread.  This is currently only implemented for the x86 targets running
           GNU/Linux.

           When code compiled with -fsplit-stack calls code compiled without -fsplit-stack,  there  may  not  be
           much  stack  space  available  for  the latter code to run.  If compiling all code, including library
           code, with -fsplit-stack is not an option, then the linker can fix up these calls so  that  the  code
           compiled without -fsplit-stack always has a large stack.  Support for this is implemented in the gold
           linker in GNU binutils release 2.21 and later.

       -fvtable-verify=[std|preinit|none]
           This   option  is  only  available  when  compiling  C++  code.   It  turns  on  (or  off,  if  using
           -fvtable-verify=none) the security feature that verifies at run time, for every  virtual  call,  that
           the  vtable  pointer  through which the call is made is valid for the type of the object, and has not
           been corrupted or overwritten.  If an invalid vtable pointer is detected at run  time,  an  error  is
           reported and execution of the program is immediately halted.

           This  option  causes  run-time  data  structures  to  be built at program startup, which are used for
           verifying the vtable pointers.  The options std and preinit control the timing  of  when  these  data
           structures  are  built.  In both cases the data structures are built before execution reaches "main".
           Using -fvtable-verify=std causes the data structures to be built after  shared  libraries  have  been
           loaded and initialized.  -fvtable-verify=preinit causes them to be built before shared libraries have
           been loaded and initialized.

           If this option appears multiple times in the command line with different values specified, none takes
           highest priority over both std and preinit; preinit takes priority over std.

       -fvtv-debug
           When  used  in conjunction with -fvtable-verify=std or -fvtable-verify=preinit, causes debug versions
           of the runtime functions for the vtable verification feature to be called.  This flag also causes the
           compiler to log information about which vtable pointers it finds for each class.  This information is
           written to a file named vtv_set_ptr_data.log in the  directory  named  by  the  environment  variable
           VTV_LOGS_DIR if that is defined or the current working directory otherwise.

           Note:  This feature appends data to the log file. If you want a fresh log file, be sure to delete any
           existing one.

       -fvtv-counts
           This   is   a   debugging   flag.    When   used   in   conjunction   with   -fvtable-verify=std   or
           -fvtable-verify=preinit, this causes the compiler to keep track of the total number of virtual  calls
           it  encounters  and  the  number  of verifications it inserts.  It also counts the number of calls to
           certain run-time library functions that it inserts and logs this  information  for  each  compilation
           unit.  The compiler writes this information to a file named vtv_count_data.log in the directory named
           by  the  environment  variable  VTV_LOGS_DIR  if  that  is  defined  or the current working directory
           otherwise.  It also counts the size of the vtable pointer  sets  for  each  class,  and  writes  this
           information to vtv_class_set_sizes.log in the same directory.

           Note:   This  feature  appends  data to the log files.  To get fresh log files, be sure to delete any
           existing ones.

       -finstrument-functions
           Generate instrumentation calls for entry and exit to functions.  Just after function entry  and  just
           before  function  exit,  the following profiling functions are called with the address of the current
           function and its call site.  (On some platforms, "__builtin_return_address" does not work beyond  the
           current  function,  so  the  call  site  information  may not be available to the profiling functions
           otherwise.)

                   void __cyg_profile_func_enter (void *this_fn,
                                                  void *call_site);
                   void __cyg_profile_func_exit  (void *this_fn,
                                                  void *call_site);

           The first argument is the address of the start of the  current  function,  which  may  be  looked  up
           exactly in the symbol table.

           This  instrumentation  is  also done for functions expanded inline in other functions.  The profiling
           calls indicate where, conceptually, the inline function is  entered  and  exited.   This  means  that
           addressable  versions  of  such  functions  must  be  available.   If all your uses of a function are
           expanded inline, this may mean an additional expansion of code size.  If you use "extern  inline"  in
           your  C  code, an addressable version of such functions must be provided.  (This is normally the case
           anyway, but if you get lucky and the optimizer always expands the functions inline,  you  might  have
           gotten away without providing static copies.)

           A function may be given the attribute "no_instrument_function", in which case this instrumentation is
           not  done.   This  can  be used, for example, for the profiling functions listed above, high-priority
           interrupt routines, and any functions from which the profiling  functions  cannot  safely  be  called
           (perhaps signal handlers, if the profiling routines generate output or allocate memory).

       -finstrument-functions-exclude-file-list=file,file,...
           Set  the  list  of  functions  that  are  excluded  from  instrumentation  (see  the  description  of
           -finstrument-functions).  If the file that contains a function definition matches with one  of  file,
           then  that function is not instrumented.  The match is done on substrings: if the file parameter is a
           substring of the file name, it is considered to be a match.

           For example:

                   -finstrument-functions-exclude-file-list=/bits/stl,include/sys

           excludes any inline function defined in files whose pathnames contain /bits/stl or include/sys.

           If, for some  reason,  you  want  to  include  letter  ,  in  one  of  sym,  write  ,.  For  example,
           -finstrument-functions-exclude-file-list=',,tmp' (note the single quote surrounding the option).

       -finstrument-functions-exclude-function-list=sym,sym,...
           This  is  similar  to  -finstrument-functions-exclude-file-list,  but  this  option  sets the list of
           function names to be excluded from instrumentation.  The function name to be  matched  is  its  user-
           visible  name,  such as "vector<int> blah(const vector<int> &)", not the internal mangled name (e.g.,
           "_Z4blahRSt6vectorIiSaIiEE").  The match is done on substrings: if the sym parameter is  a  substring
           of  the  function  name,  it  is considered to be a match.  For C99 and C++ extended identifiers, the
           function name must be given in UTF-8, not using universal character names.

       -fpatchable-function-entry=N[,M]
           Generate N NOPs right at the beginning of each function, with the function entry point before the Mth
           NOP.  If M is omitted, it defaults to 0 so the function entry points to the address just at the first
           NOP.  The NOP  instructions  reserve  extra  space  which  can  be  used  to  patch  in  any  desired
           instrumentation  at  run  time,  provided  that the code segment is writable.  The amount of space is
           controllable indirectly via the  number  of  NOPs;  the  NOP  instruction  used  corresponds  to  the
           instruction  emitted  by  the  internal  GCC  back-end interface "gen_nop".  This behavior is target-
           specific and may also depend on the architecture variant and/or other compilation options.

           For run-time identification, the starting  addresses  of  these  areas,  which  correspond  to  their
           respective function entries minus M, are additionally collected in the "__patchable_function_entries"
           section of the resulting binary.

           Note  that  the  value  of  "__attribute__  ((patchable_function_entry (N,M)))" takes precedence over
           command-line option -fpatchable-function-entry=N,M.  This can be used to increase the area size or to
           remove it completely on a single function.  If "N=0", no pad location is recorded.

           The NOP instructions are inserted at---and maybe before, depending on M---the function entry address,
           even before the prologue.

           The maximum value of N and M is 65535.

   Options Controlling the Preprocessor
       These options control the C preprocessor, which is run on each C source file before actual compilation.

       If you use the -E option, nothing is done except preprocessing.  Some of these options  make  sense  only
       together with -E because they cause the preprocessor output to be unsuitable for actual compilation.

       In addition to the options listed here, there are a number of options to control search paths for include
       files documented in Directory Options.  Options to control preprocessor diagnostics are listed in Warning
       Options.

       -D name
           Predefine name as a macro, with definition 1.

       -D name=definition
           The  contents  of definition are tokenized and processed as if they appeared during translation phase
           three in a #define directive.  In  particular,  the  definition  is  truncated  by  embedded  newline
           characters.

           If  you  are  invoking  the  preprocessor  from a shell or shell-like program you may need to use the
           shell's quoting syntax to protect characters such as spaces that have a meaning in the shell syntax.

           If you wish to define a function-like macro on  the  command  line,  write  its  argument  list  with
           surrounding  parentheses before the equals sign (if any).  Parentheses are meaningful to most shells,
           so you should quote the option.  With sh and csh, -D'name(args...)=definition' works.

           -D and -U options are processed in the order they are given on the command line.  All  -imacros  file
           and -include file options are processed after all -D and -U options.

       -U name
           Cancel any previous definition of name, either built in or provided with a -D option.

       -include file
           Process file as if "#include "file"" appeared as the first line of the primary source file.  However,
           the  first  directory  searched  for  file  is  the  preprocessor's  working directory instead of the
           directory containing the main source file.  If not found there, it is searched for in  the  remainder
           of the "#include "..."" search chain as normal.

           If  multiple  -include  options  are  given,  the  files are included in the order they appear on the
           command line.

       -imacros file
           Exactly like -include, except that any output produced by scanning file is thrown  away.   Macros  it
           defines  remain  defined.   This  allows  you  to  acquire  all the macros from a header without also
           processing its declarations.

           All files specified by -imacros are processed before all files specified by -include.

       -undef
           Do not predefine any system-specific or GCC-specific macros.  The standard predefined  macros  remain
           defined.

       -pthread
           Define  additional  macros  required for using the POSIX threads library.  You should use this option
           consistently for both compilation and linking.  This option is supported on GNU/Linux  targets,  most
           other Unix derivatives, and also on x86 Cygwin and MinGW targets.

       -M  Instead  of  outputting  the  result of preprocessing, output a rule suitable for make describing the
           dependencies of the main source file.  The preprocessor outputs one make rule containing  the  object
           file  name  for  that  source file, a colon, and the names of all the included files, including those
           coming from -include or -imacros command-line options.

           Unless specified explicitly (with -MT or -MQ), the object file name  consists  of  the  name  of  the
           source  file  with  any  suffix replaced with object file suffix and with any leading directory parts
           removed.  If there are many included files then the rule is split into several lines using \-newline.
           The rule has no commands.

           This option does not suppress the preprocessor's debug output, such as -dM.   To  avoid  mixing  such
           debug  output with the dependency rules you should explicitly specify the dependency output file with
           -MF, or use an environment variable like DEPENDENCIES_OUTPUT.  Debug output  is  still  sent  to  the
           regular output stream as normal.

           Passing -M to the driver implies -E, and suppresses warnings with an implicit -w.

       -MM Like -M but do not mention header files that are found in system header directories, nor header files
           that are included, directly or indirectly, from such a header.

           This  implies that the choice of angle brackets or double quotes in an #include directive does not in
           itself determine whether that header appears in -MM dependency output.

       -MF file
           When used with -M or -MM, specifies a file to write the dependencies to.  If no -MF switch  is  given
           the preprocessor sends the rules to the same place it would send preprocessed output.

           When used with the driver options -MD or -MMD, -MF overrides the default dependency output file.

           If file is -, then the dependencies are written to stdout.

       -MG In conjunction with an option such as -M requesting dependency generation, -MG assumes missing header
           files  are  generated  files  and  adds  them  to  the dependency list without raising an error.  The
           dependency filename is taken directly from the "#include" directive without prepending any path.  -MG
           also suppresses preprocessed output, as a missing header file renders this useless.

           This feature is used in automatic updating of makefiles.

       -Mno-modules
           Disable dependency generation for compiled module interfaces.

       -MP This option instructs CPP to add a phony target for each dependency other than the main file, causing
           each to depend on nothing.  These dummy rules work around errors make  gives  if  you  remove  header
           files without updating the Makefile to match.

           This is typical output:

                   test.o: test.c test.h

                   test.h:

       -MT target
           Change the target of the rule emitted by dependency generation.  By default CPP takes the name of the
           main  input  file,  deletes  any directory components and any file suffix such as .c, and appends the
           platform's usual object suffix.  The result is the target.

           An -MT option sets the target to be exactly the string you specify.  If you  want  multiple  targets,
           you can specify them as a single argument to -MT, or use multiple -MT options.

           For example, -MT '$(objpfx)foo.o' might give

                   $(objpfx)foo.o: foo.c

       -MQ target
           Same as -MT, but it quotes any characters which are special to Make.  -MQ '$(objpfx)foo.o' gives

                   $$(objpfx)foo.o: foo.c

           The default target is automatically quoted, as if it were given with -MQ.

       -MD -MD is equivalent to -M -MF file, except that -E is not implied.  The driver determines file based on
           whether  an  -o  option  is  given.   If it is, the driver uses its argument but with a suffix of .d,
           otherwise it takes the name of the input file, removes  any  directory  components  and  suffix,  and
           applies a .d suffix.

           If  -MD  is used in conjunction with -E, any -o switch is understood to specify the dependency output
           file, but if used without -E, each -o is understood to specify a target object file.

           Since -E is not implied, -MD can be used to generate a dependency output file as a side effect of the
           compilation process.

       -MMD
           Like -MD except mention only user header files, not system header files.

       -fpreprocessed
           Indicate to the preprocessor that the input file has  already  been  preprocessed.   This  suppresses
           things  like  macro  expansion, trigraph conversion, escaped newline splicing, and processing of most
           directives.  The preprocessor still recognizes and removes comments, so that  you  can  pass  a  file
           preprocessed  with  -C to the compiler without problems.  In this mode the integrated preprocessor is
           little more than a tokenizer for the front ends.

           -fpreprocessed is implicit if the input file has one of the extensions .i, .ii or .mi.  These are the
           extensions that GCC uses for preprocessed files created by -save-temps.

       -fdirectives-only
           When preprocessing, handle directives, but do not expand macros.

           The option's behavior depends on the -E and -fpreprocessed options.

           With -E, preprocessing is limited to the handling of directives  such  as  "#define",  "#ifdef",  and
           "#error".   Other  preprocessor  operations,  such as macro expansion and trigraph conversion are not
           performed.  In addition, the -dD option is implicitly enabled.

           With -fpreprocessed, predefinition of command line and most builtin macros is disabled.  Macros  such
           as  "__LINE__",  which are contextually dependent, are handled normally.  This enables compilation of
           files previously preprocessed with "-E -fdirectives-only".

           With both -E and -fpreprocessed, the rules for -fpreprocessed take  precedence.   This  enables  full
           preprocessing of files previously preprocessed with "-E -fdirectives-only".

       -fdollars-in-identifiers
           Accept $ in identifiers.

       -fextended-identifiers
           Accept  universal  character names and extended characters in identifiers.  This option is enabled by
           default for C99 (and later C standard versions) and C++.

       -fno-canonical-system-headers
           When preprocessing, do not shorten system header paths with canonicalization.

       -fmax-include-depth=depth
           Set the maximum depth of the nested #include. The default is 200.

       -ftabstop=width
           Set the distance between tab stops.  This helps the preprocessor report  correct  column  numbers  in
           warnings  or  errors,  even  if tabs appear on the line.  If the value is less than 1 or greater than
           100, the option is ignored.  The default is 8.

       -ftrack-macro-expansion[=level]
           Track locations of tokens across macro expansions. This allows the compiler to emit diagnostic  about
           the  current  macro  expansion stack when a compilation error occurs in a macro expansion. Using this
           option makes the preprocessor and the compiler consume more memory. The level parameter can  be  used
           to choose the level of precision of token location tracking thus decreasing the memory consumption if
           necessary.  Value  0 of level de-activates this option. Value 1 tracks tokens locations in a degraded
           mode for the sake of minimal memory overhead. In this mode all tokens resulting from the expansion of
           an argument of a function-like macro  have  the  same  location.  Value  2  tracks  tokens  locations
           completely. This value is the most memory hungry.  When this option is given no argument, the default
           parameter value is 2.

           Note that "-ftrack-macro-expansion=2" is activated by default.

       -fmacro-prefix-map=old=new
           When  preprocessing files residing in directory old, expand the "__FILE__" and "__BASE_FILE__" macros
           as if the files resided in directory new instead.  This can be used to change an absolute path  to  a
           relative  path  by  using  .  for  new which can result in more reproducible builds that are location
           independent.   This  option  also  affects   "__builtin_FILE()"   during   compilation.    See   also
           -ffile-prefix-map.

       -fexec-charset=charset
           Set  the  execution  character  set,  used for string and character constants.  The default is UTF-8.
           charset can be any encoding supported by the system's "iconv" library routine.

       -fwide-exec-charset=charset
           Set the wide execution character set, used for wide string and character constants.  The  default  is
           one of UTF-32BE, UTF-32LE, UTF-16BE, or UTF-16LE, whichever corresponds to the width of "wchar_t" and
           the  big-endian  or little-endian byte order being used for code generation.  As with -fexec-charset,
           charset can be any encoding supported by the system's "iconv" library routine; however, you will have
           problems with encodings that do not fit exactly in "wchar_t".

       -finput-charset=charset
           Set the input character set, used for translation from the character set of the  input  file  to  the
           source character set used by GCC.  If the locale does not specify, or GCC cannot get this information
           from  the locale, the default is UTF-8.  This can be overridden by either the locale or this command-
           line option.  Currently the command-line option takes precedence if there's a conflict.  charset  can
           be any encoding supported by the system's "iconv" library routine.

       -fpch-deps
           When  using  precompiled headers, this flag causes the dependency-output flags to also list the files
           from the precompiled header's dependencies.  If not specified, only the precompiled header are listed
           and not the files that were used to  create  it,  because  those  files  are  not  consulted  when  a
           precompiled header is used.

       -fpch-preprocess
           This  option  allows  use  of a precompiled header together with -E.  It inserts a special "#pragma",
           "#pragma GCC pch_preprocess "filename"" in the output to mark the place where the precompiled  header
           was  found, and its filename.  When -fpreprocessed is in use, GCC recognizes this "#pragma" and loads
           the PCH.

           This option is off by default, because the resulting preprocessed output is only really  suitable  as
           input to GCC.  It is switched on by -save-temps.

           You  should not write this "#pragma" in your own code, but it is safe to edit the filename if the PCH
           file is available in a different location.  The filename may be absolute or it  may  be  relative  to
           GCC's current directory.

       -fworking-directory
           Enable  generation  of  linemarkers in the preprocessor output that let the compiler know the current
           working directory at the time of preprocessing.  When this option is enabled, the preprocessor emits,
           after the initial linemarker, a second linemarker with the current working directory followed by  two
           slashes.   GCC  uses  this  directory,  when it's present in the preprocessed input, as the directory
           emitted as the current working directory in some  debugging  information  formats.   This  option  is
           implicitly  enabled  if  debugging information is enabled, but this can be inhibited with the negated
           form -fno-working-directory.  If the -P flag is present in the  command  line,  this  option  has  no
           effect, since no "#line" directives are emitted whatsoever.

       -A predicate=answer
           Make  an  assertion  with  the  predicate predicate and answer answer.  This form is preferred to the
           older form -A predicate(answer), which is still supported, because it  does  not  use  shell  special
           characters.

       -A -predicate=answer
           Cancel an assertion with the predicate predicate and answer answer.

       -C  Do  not discard comments.  All comments are passed through to the output file, except for comments in
           processed directives, which are deleted along with the directive.

           You should be prepared for side effects when using -C; it causes the preprocessor to  treat  comments
           as  tokens  in  their  own  right.   For  example, comments appearing at the start of what would be a
           directive line have the effect of turning that line into an ordinary source  line,  since  the  first
           token on the line is no longer a #.

       -CC Do  not  discard  comments,  including during macro expansion.  This is like -C, except that comments
           contained within macros are also passed through to the output file where the macro is expanded.

           In addition to the side effects of the -C option, the -CC option causes all C++-style comments inside
           a macro to be converted to C-style comments.  This is  to  prevent  later  use  of  that  macro  from
           inadvertently commenting out the remainder of the source line.

           The -CC option is generally used to support lint comments.

       -P  Inhibit  generation  of  linemarkers  in the output from the preprocessor.  This might be useful when
           running the preprocessor on something that is not C code, and will be sent to a program  which  might
           be confused by the linemarkers.

       -traditional
       -traditional-cpp
           Try  to imitate the behavior of pre-standard C preprocessors, as opposed to ISO C preprocessors.  See
           the GNU CPP manual for details.

           Note that GCC does not otherwise attempt to emulate a pre-standard C compiler, and these options  are
           only supported with the -E switch, or when invoking CPP explicitly.

       -trigraphs
           Support ISO C trigraphs.  These are three-character sequences, all starting with ??, that are defined
           by  ISO  C  to  stand for single characters.  For example, ??/ stands for \, so '??/n' is a character
           constant for a newline.

           The nine trigraphs and their replacements are

                   Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
                   Replacement:      [    ]    {    }    #    \    ^    |    ~

           By default, GCC ignores trigraphs, but in standard-conforming modes it converts them.  See  the  -std
           and -ansi options.

       -remap
           Enable  special code to work around file systems which only permit very short file names, such as MS-
           DOS.

       -H  Print the name of each header file used, in addition  to  other  normal  activities.   Each  name  is
           indented  to  show  how deep in the #include stack it is.  Precompiled header files are also printed,
           even if they are found to be invalid; an invalid precompiled header file is printed with ...x  and  a
           valid one with ...! .

       -dletters
           Says  to  make debugging dumps during compilation as specified by letters.  The flags documented here
           are those relevant to the preprocessor.  Other letters are interpreted by  the  compiler  proper,  or
           reserved  for  future  versions  of  GCC,  and so are silently ignored.  If you specify letters whose
           behavior conflicts, the result is undefined.

           -dM Instead of the normal output, generate a list of #define directives for all  the  macros  defined
               during  the  execution of the preprocessor, including predefined macros.  This gives you a way of
               finding out what is predefined in your version of the preprocessor.  Assuming you  have  no  file
               foo.h, the command

                       touch foo.h; cpp -dM foo.h

               shows all the predefined macros.

               If you use -dM without the -E option, -dM is interpreted as a synonym for -fdump-rtl-mach.

           -dD Like  -dM  except in two respects: it does not include the predefined macros, and it outputs both
               the #define directives and the result of preprocessing.  Both kinds of output go to the  standard
               output file.

           -dN Like -dD, but emit only the macro names, not their expansions.

           -dI Output #include directives in addition to the result of preprocessing.

           -dU Like  -dD  except  that  only  macros  that  are  expanded,  or  whose  definedness  is tested in
               preprocessor directives, are output; the output is delayed until the use or test  of  the  macro;
               and #undef directives are also output for macros tested but undefined at the time.

       -fdebug-cpp
           This  option  is  only  useful  for debugging GCC.  When used from CPP or with -E, it dumps debugging
           information about location maps.  Every token in the output is preceded by the dump of  the  map  its
           location belongs to.

           When used from GCC without -E, this option has no effect.

       -Wp,option
           You  can  use  -Wp,option  to  bypass  the  compiler  driver  and pass option directly through to the
           preprocessor.  If option contains commas, it is split into multiple options at the commas.   However,
           many  options  are  modified, translated or interpreted by the compiler driver before being passed to
           the preprocessor, and -Wp forcibly bypasses this  phase.   The  preprocessor's  direct  interface  is
           undocumented  and  subject  to  change,  so  whenever possible you should avoid using -Wp and let the
           driver handle the options instead.

       -Xpreprocessor option
           Pass option as  an  option  to  the  preprocessor.   You  can  use  this  to  supply  system-specific
           preprocessor options that GCC does not recognize.

           If you want to pass an option that takes an argument, you must use -Xpreprocessor twice, once for the
           option and once for the argument.

       -no-integrated-cpp
           Perform  preprocessing as a separate pass before compilation.  By default, GCC performs preprocessing
           as an integrated part of input tokenization and parsing.  If this option is provided, the appropriate
           language front end (cc1, cc1plus, or cc1obj for C, C++, and  Objective-C,  respectively)  is  instead
           invoked twice, once for preprocessing only and once for actual compilation of the preprocessed input.
           This  option  may  be  useful  in conjunction with the -B or -wrapper options to specify an alternate
           preprocessor or perform additional processing of the program source between normal preprocessing  and
           compilation.

       -flarge-source-files
           Adjust  GCC  to  expect  large  source  files, at the expense of slower compilation and higher memory
           usage.

           Specifically, GCC normally tracks both column numbers and line numbers within  source  files  and  it
           normally  prints  both  of  these  numbers  in diagnostics.  However, once it has processed a certain
           number of source lines, it stops tracking column numbers and only tracks line  numbers.   This  means
           that  diagnostics  for  later  lines  do not include column numbers.  It also means that options like
           -Wmisleading-indentation cease to work at that point, although the compiler prints  a  note  if  this
           happens.   Passing  -flarge-source-files  significantly increases the number of source lines that GCC
           can process before it stops tracking columns.

   Passing Options to the Assembler
       You can pass options to the assembler.

       -Wa,option
           Pass option as an option to the assembler.  If option contains commas,  it  is  split  into  multiple
           options at the commas.

       -Xassembler option
           Pass  option  as  an  option  to the assembler.  You can use this to supply system-specific assembler
           options that GCC does not recognize.

           If you want to pass an option that takes an argument, you must use -Xassembler twice,  once  for  the
           option and once for the argument.

   Options for Linking
       These  options  come into play when the compiler links object files into an executable output file.  They
       are meaningless if the compiler is not doing a link step.

       object-file-name
           A file name that does not end in a special recognized suffix is considered to name an object file  or
           library.   (Object  files  are  distinguished  from  libraries  by  the  linker according to the file
           contents.)  If linking is done, these object files are used as input to the linker.

       -c
       -S
       -E  If any of these options is used, then the linker is not run, and object file names should not be used
           as arguments.

       -flinker-output=type
           This option controls code generation of the link-time optimizer.  By default  the  linker  output  is
           automatically determined by the linker plugin.  For debugging the compiler and if incremental linking
           with a non-LTO object file is desired, it may be useful to control the type manually.

           If  type  is  exec,  code  generation produces a static binary. In this case -fpic and -fpie are both
           disabled.

           If type is dyn, code generation produces a shared library.  In this case -fpic or -fPIC is preserved,
           but not enabled automatically.  This allows to build shared  libraries  without  position-independent
           code on architectures where this is possible, i.e. on x86.

           If  type  is pie, code generation produces an -fpie executable. This results in similar optimizations
           as exec except that -fpie is not disabled if specified at compilation time.

           If type is rel, the compiler assumes that incremental  linking  is  done.   The  sections  containing
           intermediate  code  for link-time optimization are merged, pre-optimized, and output to the resulting
           object file. In addition, if -ffat-lto-objects is specified, binary code is produced for future  non-
           LTO  linking.  The  object  file  produced  by  incremental  linking is smaller than a static library
           produced from the same object files.  At link time the  result  of  incremental  linking  also  loads
           faster than a static library assuming that the majority of objects in the library are used.

           Finally  nolto-rel configures the compiler for incremental linking where code generation is forced, a
           final binary is produced, and the intermediate code for later  link-time  optimization  is  stripped.
           When multiple object files are linked together the resulting code is better optimized than with link-
           time  optimizations  disabled  (for  example, cross-module inlining happens), but most of benefits of
           whole program optimizations are lost.

           During the incremental link (by -r) the linker plugin defaults to rel. With current interfaces to GNU
           Binutils it is however not possible to incrementally link LTO objects  and  non-LTO  objects  into  a
           single  mixed  object  file.  If any of object files in incremental link cannot be used for link-time
           optimization, the linker plugin issues a warning  and  uses  nolto-rel.  To  maintain  whole  program
           optimization, it is recommended to link such objects into static library instead. Alternatively it is
           possible to use H.J. Lu's binutils with support for mixed objects.

       -fuse-ld=bfd
           Use the bfd linker instead of the default linker.

       -fuse-ld=gold
           Use the gold linker instead of the default linker.

       -fuse-ld=lld
           Use the LLVM lld linker instead of the default linker.

       -fuse-ld=mold
           Use the Modern Linker (mold) instead of the default linker.

       -llibrary
       -l library
           Search  the  library  named  library  when  linking.   (The  second alternative with the library as a
           separate argument is only for POSIX compliance and is not recommended.)

           The -l option is passed directly to the linker by GCC.  Refer to your linker documentation for  exact
           details.  The general description below applies to the GNU linker.

           The linker searches a standard list of directories for the library.  The directories searched include
           several standard system directories plus any that you specify with -L.

           Static  libraries  are archives of object files, and have file names like liblibrary.a.  Some targets
           also support shared libraries, which typically have names like liblibrary.so.   If  both  static  and
           shared libraries are found, the linker gives preference to linking with the shared library unless the
           -static option is used.

           It  makes  a difference where in the command you write this option; the linker searches and processes
           libraries and object files in the order they are specified.  Thus, foo.o -lz bar.o searches library z
           after file foo.o but before bar.o.  If bar.o refers to functions in z, those  functions  may  not  be
           loaded.

       -lobjc
           You need this special case of the -l option in order to link an Objective-C or Objective-C++ program.

       -nostartfiles
           Do  not  use  the standard system startup files when linking.  The standard system libraries are used
           normally, unless -nostdlib, -nolibc, or -nodefaultlibs is used.

       -nodefaultlibs
           Do not use the standard system libraries when linking.  Only the libraries you specify are passed  to
           the  linker,  and  options  specifying  linkage  of  the  system libraries, such as -static-libgcc or
           -shared-libgcc, are ignored.  The standard startup files are used normally, unless  -nostartfiles  is
           used.

           The  compiler  may  generate  calls to "memcmp", "memset", "memcpy" and "memmove".  These entries are
           usually resolved by entries in libc.  These entry  points  should  be  supplied  through  some  other
           mechanism when this option is specified.

       -nolibc
           Do  not  use the C library or system libraries tightly coupled with it when linking.  Still link with
           the startup files,  libgcc  or  toolchain  provided  language  support  libraries  such  as  libgnat,
           libgfortran  or libstdc++ unless options preventing their inclusion are used as well.  This typically
           removes -lc from the link command line, as well as system libraries that  normally  go  with  it  and
           become  meaningless  when  absence  of  a  C library is assumed, for example -lpthread or -lm in some
           configurations.  This is intended for bare-board targets when there is indeed no C library available.

       -nostdlib
           Do not use the standard system startup files or libraries when linking.  No startup  files  and  only
           the  libraries  you  specify  are  passed to the linker, and options specifying linkage of the system
           libraries, such as -static-libgcc or -shared-libgcc, are ignored.

           The compiler may generate calls to "memcmp", "memset", "memcpy" and  "memmove".   These  entries  are
           usually  resolved  by  entries  in  libc.   These  entry points should be supplied through some other
           mechanism when this option is specified.

           One of the standard libraries bypassed by -nostdlib and -nodefaultlibs  is  libgcc.a,  a  library  of
           internal subroutines which GCC uses to overcome shortcomings of particular machines, or special needs
           for some languages.

           In  most  cases,  you  need  libgcc.a even when you want to avoid other standard libraries.  In other
           words, when you specify -nostdlib or -nodefaultlibs you should usually specify -lgcc as  well.   This
           ensures  that  you have no unresolved references to internal GCC library subroutines.  (An example of
           such an internal subroutine is "__main", used to ensure C++ constructors are called.)

       -e entry
       --entry=entry
           Specify that the program entry point is entry.  The argument is interpreted by the  linker;  the  GNU
           linker accepts either a symbol name or an address.

       -pie
           Produce  a  dynamically  linked  position  independent  executable  on  targets that support it.  For
           predictable results, you must also specify the same set  of  options  used  for  compilation  (-fpie,
           -fPIE, or model suboptions) when you specify this linker option.

       -no-pie
           Don't produce a dynamically linked position independent executable.

       -static-pie
           Produce  a  static  position  independent  executable  on targets that support it.  A static position
           independent executable is similar to a static executable, but can be loaded at any address without  a
           dynamic  linker.   For  predictable  results,  you must also specify the same set of options used for
           compilation (-fpie, -fPIE, or model suboptions) when you specify this linker option.

       -pthread
           Link with the POSIX threads library.  This option is supported on GNU/Linux targets, most other  Unix
           derivatives,  and  also on x86 Cygwin and MinGW targets.  On some targets this option also sets flags
           for the preprocessor, so it should be used consistently for both compilation and linking.

       -r  Produce a relocatable object as output.  This is also known as partial linking.

       -rdynamic
           Pass the flag -export-dynamic to the ELF linker, on targets  that  support  it.  This  instructs  the
           linker to add all symbols, not only used ones, to the dynamic symbol table. This option is needed for
           some uses of "dlopen" or to allow obtaining backtraces from within a program.

       -s  Remove all symbol table and relocation information from the executable.

       -static
           On  systems  that  support  dynamic linking, this overrides -pie and prevents linking with the shared
           libraries.  On other systems, this option has no effect.

       -shared
           Produce a shared object which can then be linked with other objects to form an executable.   Not  all
           systems  support this option.  For predictable results, you must also specify the same set of options
           used for compilation (-fpic, -fPIC, or model suboptions) when you specify this linker option.[1]

       -shared-libgcc
       -static-libgcc
           On systems that provide libgcc as a shared library, these options force the use of either the  shared
           or  static  version,  respectively.   If  no shared version of libgcc was built when the compiler was
           configured, these options have no effect.

           There are several situations in which an application should use the  shared  libgcc  instead  of  the
           static  version.   The  most  common  of  these  is  when  the  application wishes to throw and catch
           exceptions across different shared libraries.  In that case, each of the libraries  as  well  as  the
           application itself should use the shared libgcc.

           Therefore,  the G++ driver automatically adds -shared-libgcc whenever you build a shared library or a
           main executable, because C++ programs typically use exceptions, so this is the right thing to do.

           If, instead, you use the GCC driver to create shared libraries, you may find that they are not always
           linked with the shared libgcc.  If GCC finds, at its configuration time,  that  you  have  a  non-GNU
           linker  or  a  GNU linker that does not support option --eh-frame-hdr, it links the shared version of
           libgcc into shared libraries by default.  Otherwise, it takes advantage of the linker  and  optimizes
           away  the  linking  with  the  shared version of libgcc, linking with the static version of libgcc by
           default.  This allows exceptions to  propagate  through  such  shared  libraries,  without  incurring
           relocation costs at library load time.

           However,  if  a library or main executable is supposed to throw or catch exceptions, you must link it
           using the G++ driver, or using the option -shared-libgcc, such that it  is  linked  with  the  shared
           libgcc.

       -static-libasan
           When  the  -fsanitize=address  option  is  used to link a program, the GCC driver automatically links
           against libasan.  If libasan is available as a shared library, and the -static option  is  not  used,
           then  this  links  against the shared version of libasan.  The -static-libasan option directs the GCC
           driver to link libasan statically, without necessarily linking other libraries statically.

       -static-libtsan
           When the -fsanitize=thread option is used to link a  program,  the  GCC  driver  automatically  links
           against  libtsan.   If  libtsan is available as a shared library, and the -static option is not used,
           then this links against the shared version of libtsan.  The -static-libtsan option  directs  the  GCC
           driver to link libtsan statically, without necessarily linking other libraries statically.

       -static-liblsan
           When the -fsanitize=leak option is used to link a program, the GCC driver automatically links against
           liblsan.   If liblsan is available as a shared library, and the -static option is not used, then this
           links against the shared version of liblsan.  The -static-liblsan option directs the  GCC  driver  to
           link liblsan statically, without necessarily linking other libraries statically.

       -static-libubsan
           When  the  -fsanitize=undefined  option is used to link a program, the GCC driver automatically links
           against libubsan.  If libubsan is available as a shared library, and the -static option is not  used,
           then  this links against the shared version of libubsan.  The -static-libubsan option directs the GCC
           driver to link libubsan statically, without necessarily linking other libraries statically.

       -static-libstdc++
           When the g++ program is used  to  link  a  C++  program,  it  normally  automatically  links  against
           libstdc++.   If  libstdc++ is available as a shared library, and the -static option is not used, then
           this links against the shared version of libstdc++.  That is normally fine.  However, it is sometimes
           useful to freeze the version of libstdc++ used by the program without going all the way  to  a  fully
           static  link.   The  -static-libstdc++  option  directs  the g++ driver to link libstdc++ statically,
           without necessarily linking other libraries statically.

       -symbolic
           Bind references to global  symbols  when  building  a  shared  object.   Warn  about  any  unresolved
           references  (unless  overridden  by  the  link  editor option -Xlinker -z -Xlinker defs).  Only a few
           systems support this option.

       -T script
           Use script as the linker script.  This option is supported by most systems using the GNU linker.   On
           some  targets,  such as bare-board targets without an operating system, the -T option may be required
           when linking to avoid references to undefined symbols.

       -Xlinker option
           Pass option as an option to the linker.  You can use this to supply  system-specific  linker  options
           that GCC does not recognize.

           If  you  want to pass an option that takes a separate argument, you must use -Xlinker twice, once for
           the option and once for the argument.  For example, to  pass  -assert  definitions,  you  must  write
           -Xlinker  -assert  -Xlinker  definitions.   It does not work to write -Xlinker "-assert definitions",
           because this passes the entire string as a single argument, which is not what the linker expects.

           When using the GNU linker, it is usually more convenient to pass arguments to  linker  options  using
           the  option=value  syntax  than  as  separate  arguments.   For  example,  you  can  specify -Xlinker
           -Map=output.map rather than -Xlinker -Map -Xlinker output.map.  Other linkers may  not  support  this
           syntax for command-line options.

       -Wl,option
           Pass option as an option to the linker.  If option contains commas, it is split into multiple options
           at  the  commas.   You  can  use  this  syntax  to  pass  an  argument  to  the option.  For example,
           -Wl,-Map,output.map passes -Map output.map to the linker.  When using the GNU linker,  you  can  also
           get the same effect with -Wl,-Map=output.map.

           NOTE:  In  Ubuntu 8.10 and later versions, for LDFLAGS, the option -Wl,-z,relro is used.  To disable,
           use -Wl,-z,norelro.

       -u symbol
           Pretend the symbol symbol is undefined, to force linking of library modules to define  it.   You  can
           use -u multiple times with different symbols to force loading of additional library modules.

       -z keyword
           -z  is  passed  directly  on  to  the  linker  along with the keyword keyword. See the section in the
           documentation of your linker for permitted values and their meanings.

   Options for Directory Search
       These options specify directories to search for  header  files,  for  libraries  and  for  parts  of  the
       compiler:

       -I dir
       -iquote dir
       -isystem dir
       -idirafter dir
           Add  the  directory  dir  to  the  list  of  directories  to  be  searched  for  header  files during
           preprocessing.  If dir begins with = or $SYSROOT, then the = or $SYSROOT is replaced by  the  sysroot
           prefix; see --sysroot and -isysroot.

           Directories  specified with -iquote apply only to the quote form of the directive, "#include "file"".
           Directories specified with -I, -isystem, or -idirafter apply to lookup for both the "#include "file""
           and "#include <file>" directives.

           You can specify any number or combination of these options on the command line to search  for  header
           files in several directories.  The lookup order is as follows:

           1.  For the quote form of the include directive, the directory of the current file is searched first.

           2.  For  the  quote  form  of the include directive, the directories specified by -iquote options are
               searched in left-to-right order, as they appear on the command line.

           3.  Directories specified with -I options are scanned in left-to-right order.

           4.  Directories specified with -isystem options are scanned in left-to-right order.

           5.  Standard system directories are scanned.

           6.  Directories specified with -idirafter options are scanned in left-to-right order.

           You can use -I to override  a  system  header  file,  substituting  your  own  version,  since  these
           directories are searched before the standard system header file directories.  However, you should not
           use this option to add directories that contain vendor-supplied system header files; use -isystem for
           that.

           The  -isystem  and  -idirafter options also mark the directory as a system directory, so that it gets
           the same special treatment that is applied to the standard system directories.

           If a standard system include directory, or a directory specified with  -isystem,  is  also  specified
           with  -I, the -I option is ignored.  The directory is still searched but as a system directory at its
           normal position in the system include chain.  This is to ensure that GCC's  procedure  to  fix  buggy
           system  headers and the ordering for the "#include_next" directive are not inadvertently changed.  If
           you really need to change the search order for system directories, use the -nostdinc and/or  -isystem
           options.

       -I- Split  the  include  path.   This  option  has  been  deprecated.   Please use -iquote instead for -I
           directories before the -I- and remove the -I- option.

           Any directories specified with -I options before -I- are searched only  for  headers  requested  with
           "#include "file"";  they  are  not  searched  for  "#include <file>".   If additional directories are
           specified with -I options after the -I-, those directories are searched for all #include directives.

           In addition, -I- inhibits the use of the directory of the current file directory as the first  search
           directory for "#include "file"".  There is no way to override this effect of -I-.

       -iprefix prefix
           Specify  prefix  as  the  prefix  for  subsequent  -iwithprefix  options.  If the prefix represents a
           directory, you should include the final /.

       -iwithprefix dir
       -iwithprefixbefore dir
           Append dir to the prefix specified previously with -iprefix, and add the resulting directory  to  the
           include  search  path.   -iwithprefixbefore  puts it in the same place -I would; -iwithprefix puts it
           where -idirafter would.

       -isysroot dir
           This option is like the --sysroot option, but  applies  only  to  header  files  (except  for  Darwin
           targets,  where  it  applies  to both header files and libraries).  See the --sysroot option for more
           information.

       -imultilib dir
           Use dir as a subdirectory of the directory containing target-specific C++ headers.

       -nostdinc
           Do not search the standard system directories for header  files.   Only  the  directories  explicitly
           specified  with  -I,  -iquote,  -isystem, and/or -idirafter options (and the directory of the current
           file, if appropriate) are searched.

       -nostdinc++
           Do not search for header files in the C++-specific standard directories,  but  do  still  search  the
           other standard directories.  (This option is used when building the C++ library.)

       -iplugindir=dir
           Set   the   directory   to   search   for  plugins  that  are  passed  by  -fplugin=name  instead  of
           -fplugin=path/name.so.  This option is not meant to be used by the  user,  but  only  passed  by  the
           driver.

       -Ldir
           Add directory dir to the list of directories to be searched for -l.

       -Bprefix
           This  option specifies where to find the executables, libraries, include files, and data files of the
           compiler itself.

           The compiler driver program runs one or more of the subprograms cpp, cc1, as and ld.  It tries prefix
           as a prefix for each program it tries  to  run,  both  with  and  without  machine/version/  for  the
           corresponding target machine and compiler version.

           For  each  subprogram to be run, the compiler driver first tries the -B prefix, if any.  If that name
           is not found, or if -B is not specified, the driver tries two standard  prefixes,  /usr/lib/gcc/  and
           /usr/local/lib/gcc/.   If  neither  of  those  results  in  a file name that is found, the unmodified
           program name is searched for using the directories specified in your PATH environment variable.

           The compiler checks to see if the path provided by -B refers to a directory, and if necessary it adds
           a directory separator character at the end of the path.

           -B prefixes that effectively specify directory names also apply to libraries in the  linker,  because
           the  compiler  translates  these  options into -L options for the linker.  They also apply to include
           files in the preprocessor, because the compiler translates these options into  -isystem  options  for
           the preprocessor.  In this case, the compiler appends include to the prefix.

           The  runtime support file libgcc.a can also be searched for using the -B prefix, if needed.  If it is
           not found there, the two standard prefixes above are tried, and that is all.  The file is left out of
           the link if it is not found by those means.

           Another way to specify a prefix  much  like  the  -B  prefix  is  to  use  the  environment  variable
           GCC_EXEC_PREFIX.

           As  a special kludge, if the path provided by -B is [dir/]stageN/, where N is a number in the range 0
           to 9, then it is replaced by [dir/]include.  This is to help with boot-strapping the compiler.

       -no-canonical-prefixes
           Do not expand any symbolic links, resolve references to /../ or /./, or make the path  absolute  when
           generating a relative prefix.

       --sysroot=dir
           Use  dir  as  the  logical  root  directory  for headers and libraries.  For example, if the compiler
           normally searches for headers  in  /usr/include  and  libraries  in  /usr/lib,  it  instead  searches
           dir/usr/include and dir/usr/lib.

           If you use both this option and the -isysroot option, then the --sysroot option applies to libraries,
           but the -isysroot option applies to header files.

           The  GNU  linker  (beginning  with  version 2.16) has the necessary support for this option.  If your
           linker does not support this option, the header file aspect of --sysroot still works, but the library
           aspect does not.

       --no-sysroot-suffix
           For some targets, a suffix is added to the root directory specified with --sysroot, depending on  the
           other  options  used,  so  that headers may for example be found in dir/suffix/usr/include instead of
           dir/usr/include.  This option disables the addition of such a suffix.

   Options for Code Generation Conventions
       These machine-independent options control the interface conventions used in code generation.

       Most of them have both positive and negative forms; the negative form of -ffoo is -fno-foo.  In the table
       below, only one of the forms is listed---the one that is not the default.  You can figure out  the  other
       form by either removing no- or adding it.

       -fstack-reuse=reuse-level
           This  option controls stack space reuse for user declared local/auto variables and compiler generated
           temporaries.  reuse_level can be all, named_vars, or none. all enables  stack  reuse  for  all  local
           variables  and  temporaries,  named_vars enables the reuse only for user defined local variables with
           names, and none disables stack reuse completely. The default value is all. The option is needed  when
           the  program extends the lifetime of a scoped local variable or a compiler generated temporary beyond
           the end point defined by the language.  When a lifetime of a variable ends, and if the variable lives
           in memory, the optimizing compiler has the freedom to reuse its stack space with other temporaries or
           scoped local variables whose live range does  not  overlap  with  it.  Legacy  code  extending  local
           lifetime is likely to break with the stack reuse optimization.

           For example,

                      int *p;
                      {
                        int local1;

                        p = &local1;
                        local1 = 10;
                        ....
                      }
                      {
                         int local2;
                         local2 = 20;
                         ...
                      }

                      if (*p == 10)  // out of scope use of local1
                        {

                        }

           Another example:

                      struct A
                      {
                          A(int k) : i(k), j(k) { }
                          int i;
                          int j;
                      };

                      A *ap;

                      void foo(const A& ar)
                      {
                         ap = &ar;
                      }

                      void bar()
                      {
                         foo(A(10)); // temp object's lifetime ends when foo returns

                         {
                           A a(20);
                           ....
                         }
                         ap->i+= 10;  // ap references out of scope temp whose space
                                      // is reused with a. What is the value of ap->i?
                      }

           The  lifetime  of a compiler generated temporary is well defined by the C++ standard. When a lifetime
           of a temporary ends, and if the temporary lives in memory, the optimizing compiler has the freedom to
           reuse its stack space with other temporaries or scoped local variables  whose  live  range  does  not
           overlap  with  it. However some of the legacy code relies on the behavior of older compilers in which
           temporaries' stack space is not reused, the aggressive stack reuse can lead to runtime  errors.  This
           option is used to control the temporary stack reuse optimization.

       -ftrapv
           This  option generates traps for signed overflow on addition, subtraction, multiplication operations.
           The options -ftrapv and -fwrapv override each other, so using -ftrapv  -fwrapv  on  the  command-line
           results in -fwrapv being effective.  Note that only active options override, so using -ftrapv -fwrapv
           -fno-wrapv on the command-line results in -ftrapv being effective.

       -fwrapv
           This option instructs the compiler to assume that signed arithmetic overflow of addition, subtraction
           and  multiplication  wraps  around  using  twos-complement  representation.   This  flag enables some
           optimizations and disables others.  The options -ftrapv and -fwrapv override  each  other,  so  using
           -ftrapv  -fwrapv  on  the  command-line  results  in  -fwrapv being effective.  Note that only active
           options override, so using -ftrapv -fwrapv -fno-wrapv on the command-line results  in  -ftrapv  being
           effective.

       -fwrapv-pointer
           This  option  instructs  the  compiler  to  assume  that  pointer arithmetic overflow on addition and
           subtraction wraps around using twos-complement representation.  This flag disables some optimizations
           which assume pointer overflow is invalid.

       -fstrict-overflow
           This option implies -fno-wrapv -fno-wrapv-pointer and when negated implies -fwrapv -fwrapv-pointer.

       -fexceptions
           Enable exception handling.  Generates extra code needed to propagate exceptions.  For  some  targets,
           this  implies GCC generates frame unwind information for all functions, which can produce significant
           data size overhead, although it does not affect execution.  If you do not specify  this  option,  GCC
           enables  it  by default for languages like C++ that normally require exception handling, and disables
           it for languages like C that do not normally require it.  However, you may need to enable this option
           when compiling C code that needs to interoperate properly with exception  handlers  written  in  C++.
           You  may  also  wish  to  disable  this option if you are compiling older C++ programs that don't use
           exception handling.

       -fnon-call-exceptions
           Generate code that allows trapping  instructions  to  throw  exceptions.   Note  that  this  requires
           platform-specific  runtime support that does not exist everywhere.  Moreover, it only allows trapping
           instructions to throw exceptions, i.e. memory references or floating-point instructions.  It does not
           allow exceptions to be thrown from arbitrary signal handlers such as "SIGALRM".

       -fdelete-dead-exceptions
           Consider that instructions that may throw exceptions but don't otherwise contribute to the  execution
           of  the  program  can  be optimized away.  This option is enabled by default for the Ada compiler, as
           permitted by the Ada language specification.  Optimization passes that cause dead  exceptions  to  be
           removed are enabled independently at different optimization levels.

       -funwind-tables
           Similar  to  -fexceptions,  except that it just generates any needed static data, but does not affect
           the generated code in any other way.  You normally do not need to  enable  this  option;  instead,  a
           language processor that needs this handling enables it on your behalf.

       -fasynchronous-unwind-tables
           Generate  unwind  table  in DWARF format, if supported by target machine.  The table is exact at each
           instruction boundary, so it can be used  for  stack  unwinding  from  asynchronous  events  (such  as
           debugger or garbage collector).

       -fno-gnu-unique
           On  systems  with  recent  GNU  assembler  and  C library, the C++ compiler uses the "STB_GNU_UNIQUE"
           binding to make sure that definitions of template static data members and static local  variables  in
           inline functions are unique even in the presence of "RTLD_LOCAL"; this is necessary to avoid problems
           with  a  library  used by two different "RTLD_LOCAL" plugins depending on a definition in one of them
           and therefore disagreeing with the other one about the  binding  of  the  symbol.   But  this  causes
           "dlclose"  to  be  ignored for affected DSOs; if your program relies on reinitialization of a DSO via
           "dlclose" and "dlopen", you can use -fno-gnu-unique.

       -fpcc-struct-return
           Return "short" "struct" and "union" values in memory like longer  ones,  rather  than  in  registers.
           This convention is less efficient, but it has the advantage of allowing intercallability between GCC-
           compiled files and files compiled with other compilers, particularly the Portable C Compiler (pcc).

           The precise convention for returning structures in memory depends on the target configuration macros.

           Short structures and unions are those whose size and alignment match that of some integer type.

           Warning:  code  compiled  with  the  -fpcc-struct-return  switch  is  not binary compatible with code
           compiled with the -freg-struct-return switch.  Use it to conform to a non-default application  binary
           interface.

       -freg-struct-return
           Return  "struct"  and  "union"  values  in registers when possible.  This is more efficient for small
           structures than -fpcc-struct-return.

           If you specify  neither  -fpcc-struct-return  nor  -freg-struct-return,  GCC  defaults  to  whichever
           convention  is  standard  for  the  target.   If  there  is  no  standard convention, GCC defaults to
           -fpcc-struct-return, except on targets where GCC is the principal compiler.  In those cases,  we  can
           choose the standard, and we chose the more efficient register return alternative.

           Warning:  code  compiled  with  the  -freg-struct-return  switch  is  not binary compatible with code
           compiled with the -fpcc-struct-return switch.  Use it to conform to a non-default application  binary
           interface.

       -fshort-enums
           Allocate  to an "enum" type only as many bytes as it needs for the declared range of possible values.
           Specifically, the "enum" type is equivalent to the smallest integer type that has enough room.

           Warning: the -fshort-enums switch causes GCC to generate code that is not binary compatible with code
           generated without that switch.  Use it to conform to a non-default application binary interface.

       -fshort-wchar
           Override the underlying type for "wchar_t" to be "short unsigned int" instead of the default for  the
           target.  This option is useful for building programs to run under WINE.

           Warning: the -fshort-wchar switch causes GCC to generate code that is not binary compatible with code
           generated without that switch.  Use it to conform to a non-default application binary interface.

       -fcommon
           In  C  code,  this  option controls the placement of global variables defined without an initializer,
           known as  tentative  definitions  in  the  C  standard.   Tentative  definitions  are  distinct  from
           declarations of a variable with the "extern" keyword, which do not allocate storage.

           The  default  is -fno-common, which specifies that the compiler places uninitialized global variables
           in the BSS section of the object file.  This inhibits the merging of  tentative  definitions  by  the
           linker  so  you  get a multiple-definition error if the same variable is accidentally defined in more
           than one compilation unit.

           The -fcommon places uninitialized global variables in a common block.   This  allows  the  linker  to
           resolve  all  tentative  definitions  of the same variable in different compilation units to the same
           object, or to a non-tentative definition.  This behavior  is  inconsistent  with  C++,  and  on  many
           targets  implies a speed and code size penalty on global variable references.  It is mainly useful to
           enable legacy code to link without errors.

       -fno-ident
           Ignore the "#ident" directive.

       -finhibit-size-directive
           Don't output a ".size" assembler directive, or anything else that would cause trouble if the function
           is split in the middle, and the two halves are placed at locations far apart in memory.  This  option
           is used when compiling crtstuff.c; you should not need to use it for anything else.

       -fverbose-asm
           Put  extra  commentary  information  in  the  generated assembly code to make it more readable.  This
           option is generally only of use to those who actually  need  to  read  the  generated  assembly  code
           (perhaps while debugging the compiler itself).

           -fno-verbose-asm,  the  default,  causes  the  extra  information  to  be  omitted and is useful when
           comparing two assembler files.

           The added comments include:

           *   information on the compiler version and command-line options,

           *   the  source   code   lines   associated   with   the   assembly   instructions,   in   the   form
               FILENAME:LINENUMBER:CONTENT OF LINE,

           *   hints on which high-level expressions correspond to the various assembly instruction operands.

           For example, given this C source file:

                   int test (int n)
                   {
                     int i;
                     int total = 0;

                     for (i = 0; i < n; i++)
                       total += i * i;

                     return total;
                   }

           compiling to (x86_64) assembly via -S and emitting the result direct to stdout via -o -

                   gcc -S test.c -fverbose-asm -Os -o -

           gives output similar to this:

                           .file   "test.c"
                   # GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64-pc-linux-gnu)
                     [...snip...]
                   # options passed:
                     [...snip...]

                           .text
                           .globl  test
                           .type   test, @function
                   test:
                   .LFB0:
                           .cfi_startproc
                   # test.c:4:   int total = 0;
                           xorl    %eax, %eax      # <retval>
                   # test.c:6:   for (i = 0; i < n; i++)
                           xorl    %edx, %edx      # i
                   .L2:
                   # test.c:6:   for (i = 0; i < n; i++)
                           cmpl    %edi, %edx      # n, i
                           jge     .L5     #,
                   # test.c:7:     total += i * i;
                           movl    %edx, %ecx      # i, tmp92
                           imull   %edx, %ecx      # i, tmp92
                   # test.c:6:   for (i = 0; i < n; i++)
                           incl    %edx    # i
                   # test.c:7:     total += i * i;
                           addl    %ecx, %eax      # tmp92, <retval>
                           jmp     .L2     #
                   .L5:
                   # test.c:10: }
                           ret
                           .cfi_endproc
                   .LFE0:
                           .size   test, .-test
                           .ident  "GCC: (GNU) 7.0.0 20160809 (experimental)"
                           .section        .note.GNU-stack,"",@progbits

           The  comments  are  intended  for  humans  rather  than  machines and hence the precise format of the
           comments is subject to change.

       -frecord-gcc-switches
           This switch causes the command line used to invoke the compiler to be recorded into the  object  file
           that  is  being created.  This switch is only implemented on some targets and the exact format of the
           recording is target and binary file format dependent, but it usually takes  the  form  of  a  section
           containing  ASCII  text.   This  switch  is related to the -fverbose-asm switch, but that switch only
           records information in the assembler output file as comments, so it never reaches  the  object  file.
           See also -grecord-gcc-switches for another way of storing compiler options into the object file.

       -fpic
           Generate  position-independent  code (PIC) suitable for use in a shared library, if supported for the
           target machine.  Such code accesses all constant addresses through a global offset table (GOT).   The
           dynamic  loader  resolves  the GOT entries when the program starts (the dynamic loader is not part of
           GCC; it is part of the operating system).  If the GOT  size  for  the  linked  executable  exceeds  a
           machine-specific  maximum  size,  you get an error message from the linker indicating that -fpic does
           not work; in that case, recompile with -fPIC instead.  (These maximums are 8k on the  SPARC,  28k  on
           AArch64 and 32k on the m68k and RS/6000.  The x86 has no such limit.)

           Position-independent  code  requires  special  support, and therefore works only on certain machines.
           For the x86, GCC supports PIC for System V but not for the Sun 386i.   Code  generated  for  the  IBM
           RS/6000 is always position-independent.

           When this flag is set, the macros "__pic__" and "__PIC__" are defined to 1.

       -fPIC
           If supported for the target machine, emit position-independent code, suitable for dynamic linking and
           avoiding  any  limit  on  the  size  of  the  global offset table.  This option makes a difference on
           AArch64, m68k, PowerPC and SPARC.

           Position-independent code requires special support, and therefore works only on certain machines.

           When this flag is set, the macros "__pic__" and "__PIC__" are defined to 2.

       -fpie
       -fPIE
           These options are similar to -fpic and -fPIC, but the generated position-independent code can be only
           linked into executables.  Usually these options are used to compile code that will  be  linked  using
           the -pie GCC option.

           -fpie  and  -fPIE  both  define  the macros "__pie__" and "__PIE__".  The macros have the value 1 for
           -fpie and 2 for -fPIE.

       -fno-plt
           Do not use the PLT for external function calls  in  position-independent  code.   Instead,  load  the
           callee  address  at  call  sites from the GOT and branch to it.  This leads to more efficient code by
           eliminating PLT stubs and exposing GOT loads to optimizations.  On architectures such as  32-bit  x86
           where  PLT  stubs  expect the GOT pointer in a specific register, this gives more register allocation
           freedom to the compiler.  Lazy binding requires use of the PLT; with -fno-plt  all  external  symbols
           are resolved at load time.

           Alternatively, the function attribute "noplt" can be used to avoid calls through the PLT for specific
           external functions.

           In  position-dependent code, a few targets also convert calls to functions that are marked to not use
           the PLT to use the GOT instead.

       -fno-jump-tables
           Do not use jump tables for switch statements even where it would be more efficient  than  other  code
           generation  strategies.   This  option is of use in conjunction with -fpic or -fPIC for building code
           that forms part of a dynamic linker and cannot reference the  address  of  a  jump  table.   On  some
           targets, jump tables do not require a GOT and this option is not needed.

       -fno-bit-tests
           Do  not  use  bit  tests  for switch statements even where it would be more efficient than other code
           generation strategies.

       -ffixed-reg
           Treat the register named reg as a fixed register; generated code should never  refer  to  it  (except
           perhaps as a stack pointer, frame pointer or in some other fixed role).

           reg must be the name of a register.  The register names accepted are machine-specific and are defined
           in the "REGISTER_NAMES" macro in the machine description macro file.

           This flag does not have a negative form, because it specifies a three-way choice.

       -fcall-used-reg
           Treat the register named reg as an allocable register that is clobbered by function calls.  It may be
           allocated  for  temporaries or variables that do not live across a call.  Functions compiled this way
           do not save and restore the register reg.

           It is an error to use this flag with the frame pointer or stack pointer.  Use of this flag for  other
           registers  that  have  fixed  pervasive  roles  in  the machine's execution model produces disastrous
           results.

           This flag does not have a negative form, because it specifies a three-way choice.

       -fcall-saved-reg
           Treat the register named reg as an allocable register saved by functions.  It may be  allocated  even
           for  temporaries  or variables that live across a call.  Functions compiled this way save and restore
           the register reg if they use it.

           It is an error to use this flag with the frame pointer or stack pointer.  Use of this flag for  other
           registers  that  have  fixed  pervasive  roles  in  the machine's execution model produces disastrous
           results.

           A different sort of disaster results from the use of this flag  for  a  register  in  which  function
           values may be returned.

           This flag does not have a negative form, because it specifies a three-way choice.

       -fpack-struct[=n]
           Without  a  value  specified,  pack  all  structure  members together without holes.  When a value is
           specified (which must be a small power of two), pack  structure  members  according  to  this  value,
           representing  the maximum alignment (that is, objects with default alignment requirements larger than
           this are output potentially unaligned at the next fitting location.

           Warning: the -fpack-struct switch causes GCC to generate code that is not binary compatible with code
           generated without that switch.  Additionally, it makes the code suboptimal.  Use it to conform  to  a
           non-default application binary interface.

       -fleading-underscore
           This  option  and  its  counterpart,  -fno-leading-underscore,  forcibly change the way C symbols are
           represented in the object file.  One use is to help link with legacy assembly code.

           Warning: the -fleading-underscore switch causes GCC to generate code that is  not  binary  compatible
           with  code  generated  without  that  switch.   Use it to conform to a non-default application binary
           interface.  Not all targets provide complete support for this switch.

       -ftls-model=model
           Alter the thread-local storage model to be used.  The model argument should be one of global-dynamic,
           local-dynamic, initial-exec or local-exec.  Note that the choice  is  subject  to  optimization:  the
           compiler  may  use a more efficient model for symbols not visible outside of the translation unit, or
           if -fpic is not given on the command line.

           The default without -fpic is initial-exec; with -fpic the default is global-dynamic.

       -ftrampolines
           For targets that normally need trampolines for nested functions,  always  generate  them  instead  of
           using descriptors.  Otherwise, for targets that do not need them, like for example HP-PA or IA-64, do
           nothing.

           A  trampoline is a small piece of code that is created at run time on the stack when the address of a
           nested function is taken, and is used to call the nested function indirectly.  Therefore, it requires
           the stack to be made executable in order for the program to work properly.

           -fno-trampolines is enabled by default on a language by language basis  to  let  the  compiler  avoid
           generating  them,  if  it computes that this is safe, and replace them with descriptors.  Descriptors
           are made up of data only, but the generated code must be prepared to deal  with  them.   As  of  this
           writing, -fno-trampolines is enabled by default only for Ada.

           Moreover,  code  compiled  with  -ftrampolines and code compiled with -fno-trampolines are not binary
           compatible if nested functions are present.  This option must therefore be  used  on  a  program-wide
           basis and be manipulated with extreme care.

       -fvisibility=[default|internal|hidden|protected]
           Set  the  default  ELF  image symbol visibility to the specified option---all symbols are marked with
           this unless overridden within the code.  Using this feature can very  substantially  improve  linking
           and  load  times  of  shared  object libraries, produce more optimized code, provide near-perfect API
           export and prevent symbol clashes.  It is strongly recommended  that  you  use  this  in  any  shared
           objects you distribute.

           Despite  the  nomenclature,  default  always  means public; i.e., available to be linked against from
           outside the shared object.  protected and internal are pretty useless in real-world usage so the only
           other commonly used option is hidden.  The default if -fvisibility isn't specified is default,  i.e.,
           make every symbol public.

           A  good  explanation  of  the benefits offered by ensuring ELF symbols have the correct visibility is
           given  by  "How  To  Write  Shared  Libraries"  by  Ulrich   Drepper   (which   can   be   found   at
           <https://www.akkadia.org/drepper/>)---however  a  superior  solution  made possible by this option to
           marking things hidden when the default is public is to  make  the  default  hidden  and  mark  things
           public.   This  is  the  norm  with  DLLs  on Windows and with -fvisibility=hidden and "__attribute__
           ((visibility("default")))" instead of "__declspec(dllexport)" you get almost identical semantics with
           identical syntax.  This is a great boon to those working with cross-platform projects.

           For those adding visibility support to existing code, you may find "#pragma GCC visibility"  of  use.
           This  works  by  you  enclosing  the  declarations  you wish to set visibility for with (for example)
           "#pragma GCC visibility push(hidden)" and "#pragma GCC visibility pop".  Bear  in  mind  that  symbol
           visibility should be viewed as part of the API interface contract and thus all new code should always
           specify  visibility  when it is not the default; i.e., declarations only for use within the local DSO
           should always be marked explicitly as hidden as so to avoid PLT indirection  overheads---making  this
           abundantly  clear also aids readability and self-documentation of the code.  Note that due to ISO C++
           specification  requirements,  "operator  new"  and  "operator  delete"  must  always  be  of  default
           visibility.

           Be  aware  that  headers from outside your project, in particular system headers and headers from any
           other library you use, may not be expecting to be compiled with visibility other  than  the  default.
           You  may  need  to  explicitly  say  "#pragma GCC visibility push(default)" before including any such
           headers.

           "extern" declarations are not affected by -fvisibility, so a lot  of  code  can  be  recompiled  with
           -fvisibility=hidden with no modifications.  However, this means that calls to "extern" functions with
           no  explicit  visibility  use  the  PLT,  so it is more effective to use "__attribute ((visibility))"
           and/or "#pragma GCC visibility" to tell the compiler which "extern" declarations should be treated as
           hidden.

           Note that -fvisibility does affect C++ vague linkage entities. This  means  that,  for  instance,  an
           exception  class  that is be thrown between DSOs must be explicitly marked with default visibility so
           that the type_info nodes are unified between the DSOs.

           An   overview   of   these   techniques,   their   benefits   and   how   to   use   them    is    at
           <http://gcc.gnu.org/wiki/Visibility>.

       -fstrict-volatile-bitfields
           This  option  should  be used if accesses to volatile bit-fields (or other structure fields, although
           the compiler usually honors those types anyway) should use a  single  access  of  the  width  of  the
           field's  type,  aligned  to a natural alignment if possible.  For example, targets with memory-mapped
           peripheral registers might require all such accesses to be 16 bits  wide;  with  this  flag  you  can
           declare all peripheral bit-fields as "unsigned short" (assuming short is 16 bits on these targets) to
           force GCC to use 16-bit accesses instead of, perhaps, a more efficient 32-bit access.

           If  this  option  is  disabled,  the  compiler  uses the most efficient instruction.  In the previous
           example, that might be a 32-bit load instruction, even though that accesses bytes that do not contain
           any portion of the bit-field, or memory-mapped registers unrelated to the one being updated.

           In some cases, such as when the "packed" attribute is applied to a structure field,  it  may  not  be
           possible  to  access  the  field with a single read or write that is correctly aligned for the target
           machine.  In this case GCC falls back to generating multiple accesses  rather  than  code  that  will
           fault or truncate the result at run time.

           Note:   Due  to restrictions of the C/C++11 memory model, write accesses are not allowed to touch non
           bit-field members.  It is therefore recommended to define all bits of the field's type  as  bit-field
           members.

           The  default  value  of  this option is determined by the application binary interface for the target
           processor.

       -fsync-libcalls
           This option controls whether any out-of-line instance of the "__sync" family of functions may be used
           to implement the C++11 "__atomic" family of functions.

           The default value  of  this  option  is  enabled,  thus  the  only  useful  form  of  the  option  is
           -fno-sync-libcalls.  This option is used in the implementation of the libatomic runtime library.

   GCC Developer Options
       This  section  describes command-line options that are primarily of interest to GCC developers, including
       options to support compiler testing and investigation  of  compiler  bugs  and  compile-time  performance
       problems.   This  includes  options  that  produce debug dumps at various points in the compilation; that
       print statistics such as  memory  use  and  execution  time;  and  that  print  information  about  GCC's
       configuration,  such  as  where  it  searches  for libraries.  You should rarely need to use any of these
       options for ordinary compilation and linking tasks.

       Many developer options that cause GCC to dump output to a file take an optional =filename suffix. You can
       specify stdout or - to dump to standard output, and stderr for standard error.

       If =filename is omitted, a default dump file name is constructed by  concatenating  the  base  dump  file
       name,  a  pass  number,  phase letter, and pass name.  The base dump file name is the name of output file
       produced by the compiler if explicitly specified and not an executable; otherwise it is the  source  file
       name.  The pass number is determined by the order passes are registered with the compiler's pass manager.
       This  is  generally the same as the order of execution, but passes registered by plugins, target-specific
       passes, or passes that are otherwise registered late are numbered higher than the pass named final,  even
       if  they  are  executed  earlier.  The phase letter is one of i (inter-procedural analysis), l (language-
       specific), r (RTL), or t (tree).  The files are created in the directory of the output file.

       -fcallgraph-info
       -fcallgraph-info=MARKERS
           Makes the compiler output callgraph information for the program, on  a  per-object-file  basis.   The
           information  is  generated  in  the common VCG format.  It can be decorated with additional, per-node
           and/or per-edge information, if a list of comma-separated markers is  additionally  specified.   When
           the  "su"  marker  is  specified,  the  callgraph  is  decorated  with stack usage information; it is
           equivalent to -fstack-usage.  When the "da" marker is specified,  the  callgraph  is  decorated  with
           information about dynamically allocated objects.

           When  compiling  with  -flto,  no callgraph information is output along with the object file.  At LTO
           link time, -fcallgraph-info may generate multiple callgraph information files  next  to  intermediate
           LTO output files.

       -dletters
       -fdump-rtl-pass
       -fdump-rtl-pass=filename
           Says  to  make  debugging  dumps  during compilation at times specified by letters.  This is used for
           debugging the RTL-based passes of the compiler.

           Some -dletters switches have different meaning when -E is used for preprocessing.

           Debug dumps can be enabled with a -fdump-rtl switch or some -d option letters.  Here are the possible
           letters for use in pass and letters, and their meanings:

           -fdump-rtl-alignments
               Dump after branch alignments have been computed.

           -fdump-rtl-asmcons
               Dump after fixing rtl statements that have unsatisfied in/out constraints.

           -fdump-rtl-auto_inc_dec
               Dump after auto-inc-dec discovery.  This pass is only run on architectures that have auto inc  or
               auto dec instructions.

           -fdump-rtl-barriers
               Dump after cleaning up the barrier instructions.

           -fdump-rtl-bbpart
               Dump after partitioning hot and cold basic blocks.

           -fdump-rtl-bbro
               Dump after block reordering.

           -fdump-rtl-btl1
           -fdump-rtl-btl2
               -fdump-rtl-btl1  and -fdump-rtl-btl2 enable dumping after the two branch target load optimization
               passes.

           -fdump-rtl-bypass
               Dump after jump bypassing and control flow optimizations.

           -fdump-rtl-combine
               Dump after the RTL instruction combination pass.

           -fdump-rtl-compgotos
               Dump after duplicating the computed gotos.

           -fdump-rtl-ce1
           -fdump-rtl-ce2
           -fdump-rtl-ce3
               -fdump-rtl-ce1, -fdump-rtl-ce2, and -fdump-rtl-ce3 enable dumping after the three  if  conversion
               passes.

           -fdump-rtl-cprop_hardreg
               Dump after hard register copy propagation.

           -fdump-rtl-csa
               Dump after combining stack adjustments.

           -fdump-rtl-cse1
           -fdump-rtl-cse2
               -fdump-rtl-cse1 and -fdump-rtl-cse2 enable dumping after the two common subexpression elimination
               passes.

           -fdump-rtl-dce
               Dump after the standalone dead code elimination passes.

           -fdump-rtl-dbr
               Dump after delayed branch scheduling.

           -fdump-rtl-dce1
           -fdump-rtl-dce2
               -fdump-rtl-dce1 and -fdump-rtl-dce2 enable dumping after the two dead store elimination passes.

           -fdump-rtl-eh
               Dump after finalization of EH handling code.

           -fdump-rtl-eh_ranges
               Dump after conversion of EH handling range regions.

           -fdump-rtl-expand
               Dump after RTL generation.

           -fdump-rtl-fwprop1
           -fdump-rtl-fwprop2
               -fdump-rtl-fwprop1  and  -fdump-rtl-fwprop2  enable  dumping  after  the  two forward propagation
               passes.

           -fdump-rtl-gcse1
           -fdump-rtl-gcse2
               -fdump-rtl-gcse1  and  -fdump-rtl-gcse2  enable  dumping  after   global   common   subexpression
               elimination.

           -fdump-rtl-init-regs
               Dump after the initialization of the registers.

           -fdump-rtl-initvals
               Dump after the computation of the initial value sets.

           -fdump-rtl-into_cfglayout
               Dump after converting to cfglayout mode.

           -fdump-rtl-ira
               Dump after iterated register allocation.

           -fdump-rtl-jump
               Dump after the second jump optimization.

           -fdump-rtl-loop2
               -fdump-rtl-loop2 enables dumping after the rtl loop optimization passes.

           -fdump-rtl-mach
               Dump after performing the machine dependent reorganization pass, if that pass exists.

           -fdump-rtl-mode_sw
               Dump after removing redundant mode switches.

           -fdump-rtl-rnreg
               Dump after register renumbering.

           -fdump-rtl-outof_cfglayout
               Dump after converting from cfglayout mode.

           -fdump-rtl-peephole2
               Dump after the peephole pass.

           -fdump-rtl-postreload
               Dump after post-reload optimizations.

           -fdump-rtl-pro_and_epilogue
               Dump after generating the function prologues and epilogues.

           -fdump-rtl-sched1
           -fdump-rtl-sched2
               -fdump-rtl-sched1 and -fdump-rtl-sched2 enable dumping after the basic block scheduling passes.

           -fdump-rtl-ree
               Dump after sign/zero extension elimination.

           -fdump-rtl-seqabstr
               Dump after common sequence discovery.

           -fdump-rtl-shorten
               Dump after shortening branches.

           -fdump-rtl-sibling
               Dump after sibling call optimizations.

           -fdump-rtl-split1
           -fdump-rtl-split2
           -fdump-rtl-split3
           -fdump-rtl-split4
           -fdump-rtl-split5
               These options enable dumping after five rounds of instruction splitting.

           -fdump-rtl-sms
               Dump after modulo scheduling.  This pass is only run on some architectures.

           -fdump-rtl-stack
               Dump  after  conversion  from  GCC's  "flat  register  file"  registers  to  the x87's stack-like
               registers.  This pass is only run on x86 variants.

           -fdump-rtl-subreg1
           -fdump-rtl-subreg2
               -fdump-rtl-subreg1 and -fdump-rtl-subreg2 enable dumping after the two subreg expansion passes.

           -fdump-rtl-unshare
               Dump after all rtl has been unshared.

           -fdump-rtl-vartrack
               Dump after variable tracking.

           -fdump-rtl-vregs
               Dump after converting virtual registers to hard registers.

           -fdump-rtl-web
               Dump after live range splitting.

           -fdump-rtl-regclass
           -fdump-rtl-subregs_of_mode_init
           -fdump-rtl-subregs_of_mode_finish
           -fdump-rtl-dfinit
           -fdump-rtl-dfinish
               These dumps are defined but always produce empty files.

           -da
           -fdump-rtl-all
               Produce all the dumps listed above.

           -dA Annotate the assembler output with miscellaneous debugging information.

           -dD Dump all macro definitions, at the end of preprocessing, in addition to normal output.

           -dH Produce a core dump whenever an error occurs.

           -dp Annotate the assembler output with a comment indicating which pattern and  alternative  is  used.
               The length and cost of each instruction are also printed.

           -dP Dump  the  RTL  in  the assembler output as a comment before each instruction.  Also turns on -dp
               annotation.

           -dx Just generate RTL for a function instead of compiling it.  Usually used with -fdump-rtl-expand.

       -fdump-debug
           Dump debugging information generated during the debug generation phase.

       -fdump-earlydebug
           Dump debugging information generated during the early debug generation phase.

       -fdump-noaddr
           When doing debugging dumps, suppress address output.  This makes it more  feasible  to  use  diff  on
           debugging dumps for compiler invocations with different compiler binaries and/or different text / bss
           / data / heap / stack / dso start locations.

       -freport-bug
           Collect and dump debug information into a temporary file if an internal compiler error (ICE) occurs.

       -fdump-unnumbered
           When  doing  debugging  dumps,  suppress  instruction numbers and address output.  This makes it more
           feasible to use diff  on  debugging  dumps  for  compiler  invocations  with  different  options,  in
           particular with and without -g.

       -fdump-unnumbered-links
           When  doing  debugging dumps (see -d option above), suppress instruction numbers for the links to the
           previous and next instructions in a sequence.

       -fdump-ipa-switch
       -fdump-ipa-switch-options
           Control the dumping at various stages of inter-procedural analysis language tree to a file.  The file
           name is generated by appending a switch specific suffix to the source file  name,  and  the  file  is
           created in the same directory as the output file.  The following dumps are possible:

           all Enables all inter-procedural analysis dumps.

           cgraph
               Dumps information about call-graph optimization, unused function removal, and inlining decisions.

           inline
               Dump after function inlining.

           Additionally, the options -optimized, -missed, -note, and -all can be provided, with the same meaning
           as for -fopt-info, defaulting to -optimized.

           For example, -fdump-ipa-inline-optimized-missed will emit information on callsites that were inlined,
           along with callsites that were not inlined.

           By  default, the dump will contain messages about successful optimizations (equivalent to -optimized)
           together with low-level details about the analysis.

       -fdump-lang
           Dump language-specific information.  The file name is made by appending  .lang  to  the  source  file
           name.

       -fdump-lang-all
       -fdump-lang-switch
       -fdump-lang-switch-options
       -fdump-lang-switch-options=filename
           Control  the  dumping  of language-specific information.  The options and filename portions behave as
           described in the -fdump-tree option.  The following switch values are accepted:

           all Enable all language-specific dumps.

           class
               Dump class hierarchy  information.   Virtual  table  information  is  emitted  unless  'slim'  is
               specified.  This option is applicable to C++ only.

           module
               Dump  module  information.   Options lineno (locations), graph (reachability), blocks (clusters),
               uid (serialization), alias (mergeable), asmname (Elrond), eh (mapper) & vops (macros) may provide
               additional information.  This option is applicable to C++ only.

           raw Dump the raw internal tree data.  This option is applicable to C++ only.

       -fdump-passes
           Print on stderr the list of optimization passes that are turned on and off by  the  current  command-
           line options.

       -fdump-statistics-option
           Enable  and  control  dumping  of  pass statistics in a separate file.  The file name is generated by
           appending a suffix ending in .statistics to the source file name, and the file is created in the same
           directory as the output file.  If the -option form is used, -stats causes counters to be summed  over
           the whole compilation unit while -details dumps every event as the passes generate them.  The default
           with no option is to sum counters for each function compiled.

       -fdump-tree-all
       -fdump-tree-switch
       -fdump-tree-switch-options
       -fdump-tree-switch-options=filename
           Control the dumping at various stages of processing the intermediate language tree to a file.  If the
           -options  form  is  used,  options  is a list of - separated options which control the details of the
           dump.  Not all options are applicable to all dumps; those that are not meaningful are  ignored.   The
           following options are available

           address
               Print  the  address  of each node.  Usually this is not meaningful as it changes according to the
               environment and source file.  Its primary  use  is  for  tying  up  a  dump  file  with  a  debug
               environment.

           asmname
               If  "DECL_ASSEMBLER_NAME"  has  been  set  for  a  given  decl,  use  that in the dump instead of
               "DECL_NAME".  Its primary use is ease of use working backward from mangled names in the  assembly
               file.

           slim
               When  dumping  front-end  intermediate  representations, inhibit dumping of members of a scope or
               body of a function merely because that scope has been reached.  Only dump such  items  when  they
               are directly reachable by some other path.

               When dumping pretty-printed trees, this option inhibits dumping the bodies of control structures.

               When  dumping  RTL,  print  the  RTL  in  slim  (condensed) form instead of the default LISP-like
               representation.

           raw Print a raw representation of the tree.  By default,  trees  are  pretty-printed  into  a  C-like
               representation.

           details
               Enable  more detailed dumps (not honored by every dump option). Also include information from the
               optimization passes.

           stats
               Enable dumping various statistics about the pass (not honored by every dump option).

           blocks
               Enable showing basic block boundaries (disabled in raw dumps).

           graph
               For each of the other indicated dump  files  (-fdump-rtl-pass),  dump  a  representation  of  the
               control  flow graph suitable for viewing with GraphViz to file.passid.pass.dot.  Each function in
               the file is pretty-printed as a subgraph, so that GraphViz can render them all in a single plot.

               This option currently only works for RTL dumps, and the RTL is always dumped in slim form.

           vops
               Enable showing virtual operands for every statement.

           lineno
               Enable showing line numbers for statements.

           uid Enable showing the unique ID ("DECL_UID") for each variable.

           verbose
               Enable showing the tree dump for each statement.

           eh  Enable showing the EH region number holding each statement.

           scev
               Enable showing scalar evolution analysis details.

           optimized
               Enable showing optimization information (only available in certain passes).

           missed
               Enable showing missed optimization information (only available in certain passes).

           note
               Enable other detailed optimization information (only available in certain passes).

           all Turn on all options, except raw, slim, verbose and lineno.

           optall
               Turn on all optimization options, i.e., optimized, missed, and note.

           To determine what tree dumps are available or find the dump for a pass of interest follow  the  steps
           below.

           1.  Invoke  GCC  with  -fdump-passes and in the stderr output look for a code that corresponds to the
               pass you are interested in.  For example, the codes  "tree-evrp",  "tree-vrp1",  and  "tree-vrp2"
               correspond  to  the  three  Value  Range Propagation passes.  The number at the end distinguishes
               distinct invocations of the same pass.

           2.  To enable the creation of the dump file, append the pass code to the -fdump-  option  prefix  and
               invoke GCC with it.  For example, to enable the dump from the Early Value Range Propagation pass,
               invoke  GCC  with  the -fdump-tree-evrp option.  Optionally, you may specify the name of the dump
               file.  If you don't specify one, GCC creates as described below.

           3.  Find the pass dump in a file whose name is composed of three components separated  by  a  period:
               the  name  of  the  source  file GCC was invoked to compile, a numeric suffix indicating the pass
               number followed by the letter t for tree passes (and the letter r for RTL  passes),  and  finally
               the  pass code.  For example, the Early VRP pass dump might be in a file named myfile.c.038t.evrp
               in the current working directory.  Note that the numeric codes are not stable and may change from
               one version of GCC to another.

       -fopt-info
       -fopt-info-options
       -fopt-info-options=filename
           Controls optimization dumps from various optimization passes. If the -options form is  used,  options
           is a list of - separated option keywords to select the dump details and optimizations.

           The options can be divided into three groups:

           1.  options describing what kinds of messages should be emitted,

           2.  options describing the verbosity of the dump, and

           3.  options describing which optimizations should be included.

           The  options from each group can be freely mixed as they are non-overlapping. However, in case of any
           conflicts, the later options override the earlier options on the command line.

           The following options control which kinds of messages should be emitted:

           optimized
               Print information when an optimization is successfully applied. It is up  to  a  pass  to  decide
               which  information  is  relevant. For example, the vectorizer passes print the source location of
               loops which are successfully vectorized.

           missed
               Print information about missed optimizations. Individual  passes  control  which  information  to
               include in the output.

           note
               Print  verbose  information  about  optimizations, such as certain transformations, more detailed
               messages about decisions etc.

           all Print detailed optimization information. This includes optimized, missed, and note.

           The following option controls the dump verbosity:

           internals
               By default, only  "high-level"  messages  are  emitted.  This  option  enables  additional,  more
               detailed, messages, which are likely to only be of interest to GCC developers.

           One or more of the following option keywords can be used to describe a group of optimizations:

           ipa Enable dumps from all interprocedural optimizations.

           loop
               Enable dumps from all loop optimizations.

           inline
               Enable dumps from all inlining optimizations.

           omp Enable dumps from all OMP (Offloading and Multi Processing) optimizations.

           vec Enable dumps from all vectorization optimizations.

           optall
               Enable dumps from all optimizations. This is a superset of the optimization groups listed above.

           If options is omitted, it defaults to optimized-optall, which means to dump messages about successful
           optimizations from all the passes, omitting messages that are treated as "internals".

           If  the  filename  is provided, then the dumps from all the applicable optimizations are concatenated
           into the filename.  Otherwise the dump is output onto stderr. Though multiple -fopt-info options  are
           accepted,  only  one of them can include a filename. If other filenames are provided then all but the
           first such option are ignored.

           Note that the output filename is overwritten in case of multiple translation  units.  If  a  combined
           output from multiple translation units is desired, stderr should be used instead.

           In the following example, the optimization info is output to stderr:

                   gcc -O3 -fopt-info

           This example:

                   gcc -O3 -fopt-info-missed=missed.all

           outputs missed optimization report from all the passes into missed.all, and this one:

                   gcc -O2 -ftree-vectorize -fopt-info-vec-missed

           prints information about missed optimization opportunities from vectorization passes on stderr.  Note
           that  -fopt-info-vec-missed  is  equivalent  to -fopt-info-missed-vec.  The order of the optimization
           group names and message types listed after -fopt-info does not matter.

           As another example,

                   gcc -O3 -fopt-info-inline-optimized-missed=inline.txt

           outputs information about missed optimizations as well as optimized locations from all  the  inlining
           passes into inline.txt.

           Finally, consider:

                   gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt

           Here  the  two  output  filenames vec.miss and loop.opt are in conflict since only one output file is
           allowed. In this case, only the first option takes effect and the  subsequent  options  are  ignored.
           Thus only vec.miss is produced which contains dumps from the vectorizer about missed opportunities.

       -fsave-optimization-record
           Write  a  SRCFILE.opt-record.json.gz  file  detailing  what  optimizations  were performed, for those
           optimizations that support -fopt-info.

           This option is experimental and the format of the data within the compressed JSON file is subject  to
           change.

           It is roughly equivalent to a machine-readable version of -fopt-info-all, as a collection of messages
           with source file, line number and column number, with the following additional data for each message:

           *   the  execution count of the code being optimized, along with metadata about whether this was from
               actual profile data, or just an estimate, allowing  consumers  to  prioritize  messages  by  code
               hotness,

           *   the function name of the code being optimized, where applicable,

           *   the  "inlining  chain"  for  the  code  being  optimized, so that when a function is inlined into
               several different places (which might themselves be inlined), the reader can distinguish  between
               the copies,

           *   objects  identifying  those parts of the message that refer to expressions, statements or symbol-
               table nodes, which of these categories they are, and, when available, their source code location,

           *   the GCC pass that emitted the message, and

           *   the location in GCC's own code from which the message was emitted

           Additionally, some messages are logically nested within  other  messages,  reflecting  implementation
           details of the optimization passes.

       -fsched-verbose=n
           On  targets  that use instruction scheduling, this option controls the amount of debugging output the
           scheduler prints to the dump files.

           For n greater than zero, -fsched-verbose  outputs  the  same  information  as  -fdump-rtl-sched1  and
           -fdump-rtl-sched2.   For n greater than one, it also output basic block probabilities, detailed ready
           list information and unit/insn info.  For n greater  than  two,  it  includes  RTL  at  abort  point,
           control-flow and regions info.  And for n over four, -fsched-verbose also includes dependence info.

       -fenable-kind-pass
       -fdisable-kind-pass=range-list
           This  is  a  set  of  options  that are used to explicitly disable/enable optimization passes.  These
           options are intended for use for debugging GCC.   Compiler  users  should  use  regular  options  for
           enabling/disabling passes instead.

           -fdisable-ipa-pass
               Disable  IPA  pass  pass.  pass  is the pass name.  If the same pass is statically invoked in the
               compiler multiple times, the pass name should be appended with a sequential number starting  from
               1.

           -fdisable-rtl-pass
           -fdisable-rtl-pass=range-list
               Disable  RTL  pass  pass.   pass is the pass name.  If the same pass is statically invoked in the
               compiler multiple times, the pass name should be appended with a sequential number starting  from
               1.   range-list is a comma-separated list of function ranges or assembler names.  Each range is a
               number pair separated by a colon.  The range is inclusive in both ends.  If the range is trivial,
               the number pair can be simplified as a single number.  If the function's call  graph  node's  uid
               falls  within  one  of  the specified ranges, the pass is disabled for that function.  The uid is
               shown in the function header of a dump file, and the pass names can be  dumped  by  using  option
               -fdump-passes.

           -fdisable-tree-pass
           -fdisable-tree-pass=range-list
               Disable tree pass pass.  See -fdisable-rtl for the description of option arguments.

           -fenable-ipa-pass
               Enable  IPA  pass  pass.   pass  is the pass name.  If the same pass is statically invoked in the
               compiler multiple times, the pass name should be appended with a sequential number starting  from
               1.

           -fenable-rtl-pass
           -fenable-rtl-pass=range-list
               Enable RTL pass pass.  See -fdisable-rtl for option argument description and examples.

           -fenable-tree-pass
           -fenable-tree-pass=range-list
               Enable tree pass pass.  See -fdisable-rtl for the description of option arguments.

           Here are some examples showing uses of these options.

                   # disable ccp1 for all functions
                      -fdisable-tree-ccp1
                   # disable complete unroll for function whose cgraph node uid is 1
                      -fenable-tree-cunroll=1
                   # disable gcse2 for functions at the following ranges [1,1],
                   # [300,400], and [400,1000]
                   # disable gcse2 for functions foo and foo2
                      -fdisable-rtl-gcse2=foo,foo2
                   # disable early inlining
                      -fdisable-tree-einline
                   # disable ipa inlining
                      -fdisable-ipa-inline
                   # enable tree full unroll
                      -fenable-tree-unroll

       -fchecking
       -fchecking=n
           Enable   internal   consistency  checking.   The  default  depends  on  the  compiler  configuration.
           -fchecking=2 enables further internal consistency checking that might affect code generation.

       -frandom-seed=string
           This option provides a seed that GCC uses in place of random numbers  in  generating  certain  symbol
           names  that  have  to be different in every compiled file.  It is also used to place unique stamps in
           coverage data files and the object files that produce them.  You can use the -frandom-seed option  to
           produce reproducibly identical object files.

           The  string can either be a number (decimal, octal or hex) or an arbitrary string (in which case it's
           converted to a number by computing CRC32).

           The string should be different for every file you compile.

       -save-temps
           Store the usual "temporary" intermediate files permanently; name them as auxiliary output  files,  as
           specified described under -dumpbase and -dumpdir.

           When  used  in  combination  with the -x command-line option, -save-temps is sensible enough to avoid
           overwriting an input source file with the same extension as an intermediate file.  The  corresponding
           intermediate file may be obtained by renaming the source file before using -save-temps.

       -save-temps=cwd
           Equivalent to -save-temps -dumpdir ./.

       -save-temps=obj
           Equivalent  to  -save-temps  -dumpdir  outdir/,  where  outdir/  is  the directory of the output file
           specified after the -o option, including any directory separators.  If the -o option is not used, the
           -save-temps=obj switch behaves like -save-temps=cwd.

       -time[=file]
           Report the CPU time taken by each subprocess in the compilation sequence.  For C source  files,  this
           is the compiler proper and assembler (plus the linker if linking is done).

           Without the specification of an output file, the output looks like this:

                   # cc1 0.12 0.01
                   # as 0.00 0.01

           The  first  number  on each line is the "user time", that is time spent executing the program itself.
           The second number is "system time", time spent executing operating system routines on behalf  of  the
           program.  Both numbers are in seconds.

           With the specification of an output file, the output is appended to the named file, and it looks like
           this:

                   0.12 0.01 cc1 <options>
                   0.00 0.01 as <options>

           The  "user  time"  and the "system time" are moved before the program name, and the options passed to
           the program are displayed, so that one can later tell what file was being compiled,  and  with  which
           options.

       -fdump-final-insns[=file]
           Dump  the  final  internal  representation (RTL) to file.  If the optional argument is omitted (or if
           file is "."), the name of the dump file is determined by appending ".gkd" to the dump base name,  see
           -dumpbase.

       -fcompare-debug[=opts]
           If   no  error  occurs  during  compilation,  run  the  compiler  a  second  time,  adding  opts  and
           -fcompare-debug-second to the arguments passed to the second compilation.  Dump  the  final  internal
           representation in both compilations, and print an error if they differ.

           If the equal sign is omitted, the default -gtoggle is used.

           The  environment  variable  GCC_COMPARE_DEBUG,  if defined, non-empty and nonzero, implicitly enables
           -fcompare-debug.  If GCC_COMPARE_DEBUG is defined to a string starting with a dash, then it  is  used
           for opts, otherwise the default -gtoggle is used.

           -fcompare-debug=,  with  the  equal sign but without opts, is equivalent to -fno-compare-debug, which
           disables the dumping of  the  final  representation  and  the  second  compilation,  preventing  even
           GCC_COMPARE_DEBUG from taking effect.

           To   verify   full   coverage   during   -fcompare-debug   testing,   set  GCC_COMPARE_DEBUG  to  say
           -fcompare-debug-not-overridden, which GCC rejects as an invalid  option  in  any  actual  compilation
           (rather  than  preprocessing, assembly or linking).  To get just a warning, setting GCC_COMPARE_DEBUG
           to -w%n-fcompare-debug not overridden will do.

       -fcompare-debug-second
           This  option  is  implicitly  passed  to  the  compiler  for  the  second  compilation  requested  by
           -fcompare-debug,  along with options to silence warnings, and omitting other options that would cause
           the compiler to produce output to files or to standard output as  a  side  effect.   Dump  files  and
           preserved  temporary  files  are  renamed  so as to contain the ".gk" additional extension during the
           second compilation, to avoid overwriting those generated by the first.

           When this option is passed to the compiler driver, it causes the first  compilation  to  be  skipped,
           which makes it useful for little other than debugging the compiler proper.

       -gtoggle
           Turn  off generation of debug info, if leaving out this option generates it, or turn it on at level 2
           otherwise.  The position of this argument in the command line does not matter; it takes effect  after
           all  other  options  are  processed,  and it does so only once, no matter how many times it is given.
           This is mainly intended to be used with -fcompare-debug.

       -fvar-tracking-assignments-toggle
           Toggle -fvar-tracking-assignments, in the same way that -gtoggle toggles -g.

       -Q  Makes the compiler print out each function name as it is compiled, and print  some  statistics  about
           each pass when it finishes.

       -ftime-report
           Makes the compiler print some statistics about the time consumed by each pass when it finishes.

       -ftime-report-details
           Record the time consumed by infrastructure parts separately for each pass.

       -fira-verbose=n
           Control  the  verbosity of the dump file for the integrated register allocator.  The default value is
           5.  If the value n is greater or equal to 10, the dump output is sent to stderr using the same format
           as n minus 10.

       -flto-report
           Prints a report with internal details on the workings of the link-time optimizer.   The  contents  of
           this report vary from version to version.  It is meant to be useful to GCC developers when processing
           object files in LTO mode (via -flto).

           Disabled by default.

       -flto-report-wpa
           Like -flto-report, but only print for the WPA phase of link-time optimization.

       -fmem-report
           Makes the compiler print some statistics about permanent memory allocation when it finishes.

       -fmem-report-wpa
           Makes the compiler print some statistics about permanent memory allocation for the WPA phase only.

       -fpre-ipa-mem-report
       -fpost-ipa-mem-report
           Makes  the  compiler  print  some  statistics  about  permanent  memory  allocation  before  or after
           interprocedural optimization.

       -fprofile-report
           Makes the compiler print some statistics about consistency of the (estimated) profile and  effect  of
           individual passes.

       -fstack-usage
           Makes  the  compiler  output  stack  usage information for the program, on a per-function basis.  The
           filename for the dump is made by appending .su to the auxname.  auxname is generated from the name of
           the output file, if explicitly specified and it is not an executable, otherwise it is the basename of
           the source file.  An entry is made up of three fields:

           *   The name of the function.

           *   A number of bytes.

           *   One or more qualifiers: "static", "dynamic", "bounded".

           The qualifier "static" means that the function manipulates the stack statically: a  fixed  number  of
           bytes  are  allocated  for  the  frame  on  function  entry  and  released on function exit; no stack
           adjustments are otherwise made in the function.  The second field is this fixed number of bytes.

           The qualifier "dynamic" means that the function manipulates the stack dynamically: in addition to the
           static allocation described above, stack adjustments are made  in  the  body  of  the  function,  for
           example to push/pop arguments around function calls.  If the qualifier "bounded" is also present, the
           amount  of these adjustments is bounded at compile time and the second field is an upper bound of the
           total amount of stack used by the function.  If it is not present, the amount of these adjustments is
           not bounded at compile time and the second field only represents the bounded part.

       -fstats
           Emit statistics about front-end processing at the end of the compilation.  This option  is  supported
           only by the C++ front end, and the information is generally only useful to the G++ development team.

       -fdbg-cnt-list
           Print the name and the counter upper bound for all debug counters.

       -fdbg-cnt=counter-value-list
           Set  the  internal debug counter lower and upper bound.  counter-value-list is a comma-separated list
           of name:lower_bound1-upper_bound1 [:lower_bound2-upper_bound2...] tuples which sets the name  of  the
           counter  and  list  of  closed intervals.  The lower_bound is optional and is zero initialized if not
           set.  For example, with -fdbg-cnt=dce:2-4:10-11,tail_call:10, "dbg_cnt(dce)" returns  true  only  for
           second,  third, fourth, tenth and eleventh invocation.  For "dbg_cnt(tail_call)" true is returned for
           first 10 invocations.

       -print-file-name=library
           Print the full absolute name of the library file library that would be used when linking---and  don't
           do  anything  else.  With this option, GCC does not compile or link anything; it just prints the file
           name.

       -print-multi-directory
           Print the directory name corresponding to the multilib selected by any other switches present in  the
           command line.  This directory is supposed to exist in GCC_EXEC_PREFIX.

       -print-multi-lib
           Print the mapping from multilib directory names to compiler switches that enable them.  The directory
           name  is separated from the switches by ;, and each switch starts with an @ instead of the -, without
           spaces between multiple switches.  This is supposed to ease shell processing.

       -print-multi-os-directory
           Print the path to OS libraries for the selected multilib, relative to some lib subdirectory.   If  OS
           libraries  are  present in the lib subdirectory and no multilibs are used, this is usually just ., if
           OS libraries are present in libsuffix sibling  directories  this  prints  e.g.  ../lib64,  ../lib  or
           ../lib32,  or  if OS libraries are present in lib/subdir subdirectories it prints e.g. amd64, sparcv9
           or ev6.

       -print-multiarch
           Print the path to OS libraries for the selected multiarch, relative to some lib subdirectory.

       -print-prog-name=program
           Like -print-file-name, but searches for a program such as cpp.

       -print-libgcc-file-name
           Same as -print-file-name=libgcc.a.

           This is useful when you use -nostdlib or -nodefaultlibs but you do want to link with  libgcc.a.   You
           can do:

                   gcc -nostdlib <files>... `gcc -print-libgcc-file-name`

       -print-search-dirs
           Print the name of the configured installation directory and a list of program and library directories
           gcc searches---and don't do anything else.

           This is useful when gcc prints the error message installation problem, cannot exec cpp0: No such file
           or  directory.   To  resolve this you either need to put cpp0 and the other compiler components where
           gcc expects to find them, or you can set the environment variable GCC_EXEC_PREFIX  to  the  directory
           where you installed them.  Don't forget the trailing /.

       -print-sysroot
           Print  the  target  sysroot  directory  that  is used during compilation.  This is the target sysroot
           specified either at configure time or using the --sysroot option, possibly with an extra suffix  that
           depends on compilation options.  If no target sysroot is specified, the option prints nothing.

       -print-sysroot-headers-suffix
           Print  the  suffix  added  to  the target sysroot when searching for headers, or give an error if the
           compiler is not configured with such a suffix---and don't do anything else.

       -dumpmachine
           Print the compiler's target machine (for example, i686-pc-linux-gnu)---and don't do anything else.

       -dumpversion
           Print the compiler version (for example, 3.0, 6.3.0 or 7)---and don't do anything else.  This is  the
           compiler  version  used  in  filesystem  paths  and  specs.  Depending  on  how the compiler has been
           configured it can be just a single number (major version), two numbers separated by a dot (major  and
           minor version) or three numbers separated by dots (major, minor and patchlevel version).

       -dumpfullversion
           Print  the  full  compiler  version---and  don't do anything else. The output is always three numbers
           separated by dots, major, minor and patchlevel version.

       -dumpspecs
           Print the compiler's built-in specs---and don't do anything else.  (This is used when GCC  itself  is
           being built.)

   Machine-Dependent Options
       Each  target machine supported by GCC can have its own options---for example, to allow you to compile for
       a particular processor variant or ABI,  or  to  control  optimizations  specific  to  that  machine.   By
       convention, the names of machine-specific options start with -m.

       Some  configurations  of  the  compiler  also  support  additional  target-specific  options, usually for
       compatibility with other compilers on the same platform.

       AArch64 Options

       These options are defined for AArch64 implementations:

       -mabi=name
           Generate code for the specified data model.  Permissible values are ilp32 for  SysV-like  data  model
           where int, long int and pointers are 32 bits, and lp64 for SysV-like data model where int is 32 bits,
           but long int and pointers are 64 bits.

           The  default depends on the specific target configuration.  Note that the LP64 and ILP32 ABIs are not
           link-compatible; you must compile your entire program with the same ABI, and link with  a  compatible
           set of libraries.

       -mbig-endian
           Generate big-endian code.  This is the default when GCC is configured for an aarch64_be-*-* target.

       -mgeneral-regs-only
           Generate  code  which  uses  only the general-purpose registers.  This will prevent the compiler from
           using floating-point and Advanced SIMD  registers  but  will  not  impose  any  restrictions  on  the
           assembler.

       -mlittle-endian
           Generate  little-endian  code.  This is the default when GCC is configured for an aarch64-*-* but not
           an aarch64_be-*-* target.

       -mcmodel=tiny
           Generate code for the tiny code model.  The program and its statically defined symbols must be within
           1MB of each other.  Programs can be statically or dynamically linked.

       -mcmodel=small
           Generate code for the small code model.  The program and  its  statically  defined  symbols  must  be
           within  4GB  of  each  other.  Programs can be statically or dynamically linked.  This is the default
           code model.

       -mcmodel=large
           Generate code for the large code model.  This makes no  assumptions  about  addresses  and  sizes  of
           sections.   Programs  can  be statically linked only.  The -mcmodel=large option is incompatible with
           -mabi=ilp32, -fpic and -fPIC.

       -mstrict-align
       -mno-strict-align
           Avoid or allow generating memory accesses that may not be aligned on a  natural  object  boundary  as
           described in the architecture specification.

       -momit-leaf-frame-pointer
       -mno-omit-leaf-frame-pointer
           Omit or keep the frame pointer in leaf functions.  The former behavior is the default.

       -mstack-protector-guard=guard
       -mstack-protector-guard-reg=reg
       -mstack-protector-guard-offset=offset
           Generate  stack  protection  code using canary at guard.  Supported locations are global for a global
           canary or sysreg for a canary in an appropriate system register.

           With     the     latter     choice     the      options      -mstack-protector-guard-reg=reg      and
           -mstack-protector-guard-offset=offset  furthermore  specify  which  system  register  to  use as base
           register for reading the canary, and from what offset from that base register. There  is  no  default
           register or offset as this is entirely for use within the Linux kernel.

       -mtls-dialect=desc
           Use  TLS  descriptors  as  the  thread-local storage mechanism for dynamic accesses of TLS variables.
           This is the default.

       -mtls-dialect=traditional
           Use traditional TLS as the thread-local storage mechanism for dynamic accesses of TLS variables.

       -mtls-size=size
           Specify bit size of immediate TLS offsets.  Valid values are 12, 24, 32, 48.   This  option  requires
           binutils 2.26 or newer.

       -mfix-cortex-a53-835769
       -mno-fix-cortex-a53-835769
           Enable  or  disable  the  workaround  for  the  ARM  Cortex-A53 erratum number 835769.  This involves
           inserting a NOP instruction  between  memory  instructions  and  64-bit  integer  multiply-accumulate
           instructions.

       -mfix-cortex-a53-843419
       -mno-fix-cortex-a53-843419
           Enable  or  disable  the  workaround  for  the  ARM  Cortex-A53  erratum number 843419.  This erratum
           workaround is made at link time and this will only pass the corresponding flag to the linker.

       -mlow-precision-recip-sqrt
       -mno-low-precision-recip-sqrt
           Enable or disable the reciprocal square root approximation.   This  option  only  has  an  effect  if
           -ffast-math  or  -funsafe-math-optimizations  is  used  as  well.  Enabling this reduces precision of
           reciprocal square root results to about 16 bits for single  precision  and  to  32  bits  for  double
           precision.

       -mlow-precision-sqrt
       -mno-low-precision-sqrt
           Enable  or  disable  the square root approximation.  This option only has an effect if -ffast-math or
           -funsafe-math-optimizations is used as well.  Enabling this reduces precision of square root  results
           to  about  16  bits for single precision and to 32 bits for double precision.  If enabled, it implies
           -mlow-precision-recip-sqrt.

       -mlow-precision-div
       -mno-low-precision-div
           Enable or disable the division approximation.  This option only  has  an  effect  if  -ffast-math  or
           -funsafe-math-optimizations  is used as well.  Enabling this reduces precision of division results to
           about 16 bits for single precision and to 32 bits for double precision.

       -mtrack-speculation
       -mno-track-speculation
           Enable or disable generation of additional code to track speculative  execution  through  conditional
           branches.    The  tracking  state  can  then  be  used  by  the  compiler  when  expanding  calls  to
           "__builtin_speculation_safe_copy" to permit a more efficient code sequence to be generated.

       -moutline-atomics
       -mno-outline-atomics
           Enable or disable calls to out-of-line helpers to implement atomic operations.  These  helpers  will,
           at  runtime,  determine if the LSE instructions from ARMv8.1-A can be used; if not, they will use the
           load/store-exclusive instructions that are present in the base ARMv8.0 ISA.

           This option is only applicable when compiling for the base ARMv8.0 instruction set.  If using a later
           revision, e.g. -march=armv8.1-a or -march=armv8-a+lse, the ARMv8.1-Atomics instructions will be  used
           directly.   The  same applies when using -mcpu= when the selected cpu supports the lse feature.  This
           option is on by default.

       -march=name
           Specify the name of the target architecture and, optionally, one or  more  feature  modifiers.   This
           option has the form -march=arch{+[no]feature}*.

           The  table  below  summarizes  the  permissible  values for arch and the features that they enable by
           default:

           arch value : Architecture : Includes by default
           armv8-a : Armv8-A : +fp, +simd
           armv8.1-a : Armv8.1-A : armv8-a, +crc, +lse, +rdma
           armv8.2-a : Armv8.2-A : armv8.1-a
           armv8.3-a : Armv8.3-A : armv8.2-a, +pauth
           armv8.4-a : Armv8.4-A : armv8.3-a, +flagm, +fp16fml, +dotprod
           armv8.5-a : Armv8.5-A : armv8.4-a, +sb, +ssbs, +predres
           armv8.6-a : Armv8.6-A : armv8.5-a, +bf16, +i8mm
           armv8-r : Armv8-R : armv8-r

           The value native is available on native AArch64  GNU/Linux  and  causes  the  compiler  to  pick  the
           architecture  of  the  host system.  This option has no effect if the compiler is unable to recognize
           the architecture of the host system,

           The permissible values for feature are listed in the sub-section on aarch64-feature-modifiers,,-march
           and -mcpu Feature Modifiers.  Where conflicting  feature  modifiers  are  specified,  the  right-most
           feature is used.

           GCC  uses  name to determine what kind of instructions it can emit when generating assembly code.  If
           -march is specified without either of -mtune or -mcpu also being specified,  the  code  is  tuned  to
           perform well across a range of target processors implementing the target architecture.

       -mtune=name
           Specify  the  name  of  the  target  processor for which GCC should tune the performance of the code.
           Permissible values for this option are:  generic,  cortex-a35,  cortex-a53,  cortex-a55,  cortex-a57,
           cortex-a72,  cortex-a73,  cortex-a75, cortex-a76, cortex-a76ae, cortex-a77, cortex-a65, cortex-a65ae,
           cortex-a34, cortex-a78, cortex-a78ae, cortex-a78c, ares, exynos-m1,  emag,  falkor,  neoverse-512tvb,
           neoverse-e1,  neoverse-n1,  neoverse-n2,  neoverse-v1,neoverse-v2,  qdf24xx, saphira, phecda, xgene1,
           vulcan,  octeontx,  octeontx81,   octeontx83,  octeontx2,  octeontx2t98,  octeontx2t96  octeontx2t93,
           octeontx2f95,   octeontx2f95n,   octeontx2f95mm,   a64fx,   thunderx,   thunderxt88,   thunderxt88p1,
           thunderxt81,  tsv110,  thunderxt83,   thunderx2t99,   thunderx3t110,   zeus,   cortex-a57.cortex-a53,
           cortex-a72.cortex-a53,     cortex-a73.cortex-a35,    cortex-a73.cortex-a53,    cortex-a75.cortex-a55,
           cortex-a76.cortex-a55, cortex-r82, cortex-x1, ampere1, ampere1a, native.

           The      values      cortex-a57.cortex-a53,       cortex-a72.cortex-a53,       cortex-a73.cortex-a35,
           cortex-a73.cortex-a53,  cortex-a75.cortex-a55, cortex-a76.cortex-a55 specify that GCC should tune for
           a big.LITTLE system.

           The value neoverse-512tvb specifies that GCC should tune for Neoverse cores that  (a)  implement  SVE
           and (b) have a total vector bandwidth of 512 bits per cycle.  In other words, the option tells GCC to
           tune  for Neoverse cores that can execute 4 128-bit Advanced SIMD arithmetic instructions a cycle and
           that can execute an equivalent number of SVE arithmetic instructions per cycle (2 for 256-bit SVE,  4
           for  128-bit SVE).  This is more general than tuning for a specific core like Neoverse V1 but is more
           specific than the default tuning described below.

           Additionally on native AArch64 GNU/Linux systems the value  native  tunes  performance  to  the  host
           system.   This  option has no effect if the compiler is unable to recognize the processor of the host
           system.

           Where none of -mtune=, -mcpu= or -march= are specified, the code is tuned to perform  well  across  a
           range of target processors.

           This option cannot be suffixed by feature modifiers.

       -mcpu=name
           Specify the name of the target processor, optionally suffixed by one or more feature modifiers.  This
           option  has  the  form -mcpu=cpu{+[no]feature}*, where the permissible values for cpu are the same as
           those available for -mtune.  The permissible values for feature are documented in the sub-section  on
           aarch64-feature-modifiers,,-march  and  -mcpu Feature Modifiers.  Where conflicting feature modifiers
           are specified, the right-most feature is used.

           GCC uses name to determine what kind of instructions it can emit when generating assembly code (as if
           by -march) and to determine the target processor for which to tune for performance (as if by -mtune).
           Where this option is used in conjunction with -march or -mtune, those options  take  precedence  over
           the appropriate part of this option.

           -mcpu=neoverse-512tvb  is special in that it does not refer to a specific core, but instead refers to
           all Neoverse cores that (a) implement SVE and (b) have a total vector bandwidth of 512 bits a  cycle.
           Unless overridden by -march, -mcpu=neoverse-512tvb generates code that can run on a Neoverse V1 core,
           since  Neoverse  V1  is  the first Neoverse core with these properties.  Unless overridden by -mtune,
           -mcpu=neoverse-512tvb tunes code in the same way as for -mtune=neoverse-512tvb.

       -moverride=string
           Override tuning decisions made by the  back-end  in  response  to  a  -mtune=  switch.   The  syntax,
           semantics,  and  accepted values for string in this option are not guaranteed to be consistent across
           releases.

           This option is only intended to be useful when developing GCC.

       -mverbose-cost-dump
           Enable verbose cost model dumping in the debug dump files.   This  option  is  provided  for  use  in
           debugging the compiler.

       -mpc-relative-literal-loads
       -mno-pc-relative-literal-loads
           Enable  or  disable  PC-relative  literal loads.  With this option literal pools are accessed using a
           single instruction and emitted after each function.  This limits the maximum  size  of  functions  to
           1MB.  This is enabled by default for -mcmodel=tiny.

       -msign-return-address=scope
           Select  the  function  scope on which return address signing will be applied.  Permissible values are
           none, which disables return address signing, non-leaf, which enables pointer  signing  for  functions
           which  are not leaf functions, and all, which enables pointer signing for all functions.  The default
           value is none. This option has been deprecated by -mbranch-protection.

       -mbranch-protection=none|standard|pac-ret[+leaf+b-key]|bti
           Select the branch protection features to use.  none is the default and turns off all types of  branch
           protection.   standard turns on all types of branch protection features.  If a feature has additional
           tuning options, then standard sets it to its standard level.  pac-ret[+leaf] turns on return  address
           signing  to  its  standard  level: signing functions that save the return address to memory (non-leaf
           functions will practically always do this) using the a-key.  The optional argument leaf can  be  used
           to extend the signing to include leaf functions.  The optional argument b-key can be used to sign the
           functions with the B-key instead of the A-key.  bti turns on branch target identification mechanism.

       -mharden-sls=opts
           Enable compiler hardening against straight line speculation (SLS).  opts is a comma-separated list of
           the following options:

           retbr
           blr

           In  addition,  -mharden-sls=all  enables  all  SLS hardening while -mharden-sls=none disables all SLS
           hardening.

       -msve-vector-bits=bits
           Specify the number of bits in an SVE vector register.  This option only has an  effect  when  SVE  is
           enabled.

           GCC  supports  two  forms of SVE code generation: "vector-length agnostic" output that works with any
           size of vector register and "vector-length specific" output that allows GCC to make assumptions about
           the vector length when it is useful for optimization reasons.   The  possible  values  of  bits  are:
           scalable,  128,  256, 512, 1024 and 2048.  Specifying scalable selects vector-length agnostic output.
           At present -msve-vector-bits=128 also generates vector-length agnostic output for big-endian targets.
           All other values generate vector-length specific code.  The behavior of these values  may  change  in
           future  releases and no value except scalable should be relied on for producing code that is portable
           across different hardware SVE vector lengths.

           The default is -msve-vector-bits=scalable, which produces vector-length agnostic code.

       -march and -mcpu Feature Modifiers

       Feature modifiers used with -march and -mcpu can be any of the following and their inverses nofeature:

       crc Enable CRC extension.  This is on by default for -march=armv8.1-a.

       crypto
           Enable Crypto extension.  This also enables Advanced SIMD and floating-point instructions.

       fp  Enable floating-point instructions.  This is on by default for all possible values for options -march
           and -mcpu.

       simd
           Enable Advanced SIMD instructions.  This also enables floating-point instructions.   This  is  on  by
           default for all possible values for options -march and -mcpu.

       sve Enable  Scalable  Vector  Extension instructions.  This also enables Advanced SIMD and floating-point
           instructions.

       lse Enable Large System Extension instructions.  This is on by default for -march=armv8.1-a.

       rdma
           Enable Round Double Multiply Accumulate instructions.  This is on by default for -march=armv8.1-a.

       fp16
           Enable FP16 extension.  This also enables floating-point instructions.

       fp16fml
           Enable FP16 fmla extension.  This also enables FP16 extensions and floating-point instructions.  This
           option  is  enabled  by  default for -march=armv8.4-a. Use of this option with architectures prior to
           Armv8.2-A is not supported.

       rcpc
           Enable the RcPc extension.  This does not change code generation from GCC, but is passed  on  to  the
           assembler, enabling inline asm statements to use instructions from the RcPc extension.

       dotprod
           Enable the Dot Product extension.  This also enables Advanced SIMD instructions.

       aes Enable the Armv8-a aes and pmull crypto extension.  This also enables Advanced SIMD instructions.

       sha2
           Enable the Armv8-a sha2 crypto extension.  This also enables Advanced SIMD instructions.

       sha3
           Enable  the  sha512  and sha3 crypto extension.  This also enables Advanced SIMD instructions. Use of
           this option with architectures prior to Armv8.2-A is not supported.

       sm4 Enable the sm3 and sm4 crypto extension.  This also enables Advanced SIMD instructions.  Use of  this
           option with architectures prior to Armv8.2-A is not supported.

       profile
           Enable  the  Statistical  Profiling  extension.   This  option is only to enable the extension at the
           assembler level and does not affect code generation.

       rng Enable the Armv8.5-a Random Number instructions.  This option is only to enable the extension at  the
           assembler level and does not affect code generation.

       memtag
           Enable  the  Armv8.5-a  Memory  Tagging  Extensions.   Use of this option with architectures prior to
           Armv8.5-A is not supported.

       sb  Enable the Armv8-a Speculation Barrier instruction.  This option is only to enable the  extension  at
           the  assembler  level  and  does  not  affect code generation.  This option is enabled by default for
           -march=armv8.5-a.

       ssbs
           Enable the Armv8-a Speculative Store Bypass Safe instruction.  This option  is  only  to  enable  the
           extension  at  the  assembler  level  and does not affect code generation.  This option is enabled by
           default for -march=armv8.5-a.

       predres
           Enable the Armv8-a Execution and Data Prediction Restriction instructions.  This option  is  only  to
           enable  the  extension  at  the  assembler level and does not affect code generation.  This option is
           enabled by default for -march=armv8.5-a.

       sve2
           Enable the Armv8-a Scalable Vector Extension 2.  This also enables SVE instructions.

       sve2-bitperm
           Enable SVE2 bitperm instructions.  This also enables SVE2 instructions.

       sve2-sm4
           Enable SVE2 sm4 instructions.  This also enables SVE2 instructions.

       sve2-aes
           Enable SVE2 aes instructions.  This also enables SVE2 instructions.

       sve2-sha3
           Enable SVE2 sha3 instructions.  This also enables SVE2 instructions.

       tme Enable the Transactional Memory Extension.

       i8mm
           Enable 8-bit Integer Matrix Multiply instructions.  This also enables  Advanced  SIMD  and  floating-
           point instructions.  This option is enabled by default for -march=armv8.6-a.  Use of this option with
           architectures prior to Armv8.2-A is not supported.

       f32mm
           Enable  32-bit Floating point Matrix Multiply instructions.  This also enables SVE instructions.  Use
           of this option with architectures prior to Armv8.2-A is not supported.

       f64mm
           Enable 64-bit Floating point Matrix Multiply instructions.  This also enables SVE instructions.   Use
           of this option with architectures prior to Armv8.2-A is not supported.

       bf16
           Enable  brain  half-precision  floating-point  instructions.   This  also  enables  Advanced SIMD and
           floating-point instructions.  This option is enabled by default for -march=armv8.6-a.   Use  of  this
           option with architectures prior to Armv8.2-A is not supported.

       flagm
           Enable the Flag Manipulation instructions Extension.

       pauth
           Enable the Pointer Authentication Extension.

       Feature  crypto  implies  aes,  sha2, and simd, which implies fp.  Conversely, nofp implies nosimd, which
       implies nocrypto, noaes and nosha2.

       Adapteva Epiphany Options

       These -m options are defined for Adapteva Epiphany:

       -mhalf-reg-file
           Don't allocate any register in the range "r32"..."r63".  That allows code to run on hardware variants
           that lack these registers.

       -mprefer-short-insn-regs
           Preferentially allocate registers that allow  short  instruction  generation.   This  can  result  in
           increased instruction count, so this may either reduce or increase overall code size.

       -mbranch-cost=num
           Set  the cost of branches to roughly num "simple" instructions.  This cost is only a heuristic and is
           not guaranteed to produce consistent results across releases.

       -mcmove
           Enable the generation of conditional moves.

       -mnops=num
           Emit num NOPs before every other generated instruction.

       -mno-soft-cmpsf
           For single-precision floating-point comparisons, emit an "fsub" instruction and test the flags.  This
           is faster than a software comparison, but can get incorrect results in the presence of NaNs, or  when
           two  different  small  numbers  are  compared  such that their difference is calculated as zero.  The
           default is -msoft-cmpsf, which uses slower, but IEEE-compliant, software comparisons.

       -mstack-offset=num
           Set the offset between the top of the stack and the stack pointer.  E.g., a value of 8 means that the
           eight bytes in the range "sp+0...sp+7" can be  used  by  leaf  functions  without  stack  allocation.
           Values  other than 8 or 16 are untested and unlikely to work.  Note also that this option changes the
           ABI; compiling a program with a different stack offset than the libraries  have  been  compiled  with
           generally  does  not  work.   This  option can be useful if you want to evaluate if a different stack
           offset would give you better code, but to actually use a different  stack  offset  to  build  working
           programs,  it  is recommended to configure the toolchain with the appropriate --with-stack-offset=num
           option.

       -mno-round-nearest
           Make the scheduler assume that the rounding  mode  has  been  set  to  truncating.   The  default  is
           -mround-nearest.

       -mlong-calls
           If  not otherwise specified by an attribute, assume all calls might be beyond the offset range of the
           "b" / "bl" instructions, and therefore load the function address into a register before performing  a
           (otherwise direct) call.  This is the default.

       -mshort-calls
           If  not  otherwise  specified  by an attribute, assume all direct calls are in the range of the "b" /
           "bl" instructions, so use these instructions for direct calls.  The default is -mlong-calls.

       -msmall16
           Assume addresses can be loaded as 16-bit unsigned values.  This does not apply to function  addresses
           for which -mlong-calls semantics are in effect.

       -mfp-mode=mode
           Set  the prevailing mode of the floating-point unit.  This determines the floating-point mode that is
           provided and expected at function call and  return  time.   Making  this  mode  match  the  mode  you
           predominantly  need  at  function  start  can  make  your  programs  smaller  and  faster by avoiding
           unnecessary mode switches.

           mode can be set to one the following values:

           caller
               Any mode at function entry is valid, and retained or restored when the function returns, and when
               it calls other functions.  This mode is useful for compiling libraries or other compilation units
               you might want to incorporate into different programs with different prevailing  FPU  modes,  and
               the  convenience  of being able to use a single object file outweighs the size and speed overhead
               for any extra mode switching that might be needed, compared with what would be needed with a more
               specific choice of prevailing FPU mode.

           truncate
               This is the mode used for floating-point calculations with truncating (i.e. round  towards  zero)
               rounding mode.  That includes conversion from floating point to integer.

           round-nearest
               This  is  the  mode  used  for floating-point calculations with round-to-nearest-or-even rounding
               mode.

           int This is the mode used to perform integer calculations in the  FPU,  e.g.   integer  multiply,  or
               integer multiply-and-accumulate.

           The default is -mfp-mode=caller

       -mno-split-lohi
       -mno-postinc
       -mno-postmodify
           Code  generation  tweaks  that  disable, respectively, splitting of 32-bit loads, generation of post-
           increment addresses,  and  generation  of  post-modify  addresses.   The  defaults  are  msplit-lohi,
           -mpost-inc, and -mpost-modify.

       -mnovect-double
           Change  the  preferred  SIMD  mode  to  SImode.   The  default is -mvect-double, which uses DImode as
           preferred SIMD mode.

       -max-vect-align=num
           The maximum alignment for SIMD vector mode types.  num may be 4 or 8.  The default is 8.   Note  that
           this  is an ABI change, even though many library function interfaces are unaffected if they don't use
           SIMD vector modes in places that affect size and/or alignment of relevant types.

       -msplit-vecmove-early
           Split vector moves into single word moves before reload.  In theory this  can  give  better  register
           allocation, but so far the reverse seems to be generally the case.

       -m1reg-reg
           Specify  a register to hold the constant -1, which makes loading small negative constants and certain
           bitmasks faster.  Allowable values for reg are r43 and r63, which specify use of that register  as  a
           fixed  register,  and  none,  which  means that no register is used for this purpose.  The default is
           -m1reg-none.

       AMD GCN Options

       These options are defined specifically for the AMD GCN port.

       -march=gpu
       -mtune=gpu
           Set architecture type or tuning for gpu. Supported values for gpu are

           fiji
               Compile for GCN3 Fiji devices (gfx803).

           gfx900
               Compile for GCN5 Vega 10 devices (gfx900).

           gfx906
               Compile for GCN5 Vega 20 devices (gfx906).

       -msram-ecc=on
       -msram-ecc=off
       -msram-ecc=any
           Compile binaries suitable for devices with the SRAM-ECC feature enabled, disabled,  or  either  mode.
           This  feature  can  be  enabled per-process on some devices.  The compiled code must match the device
           mode. The default is any, for devices that support it.

       -mstack-size=bytes
           Specify how many bytes of stack space will be requested for each  GPU  thread  (wave-front).   Beware
           that  there  may  be many threads and limited memory available.  The size of the stack allocation may
           also have an impact on run-time performance.  The default is 32KB when using OpenACC or  OpenMP,  and
           1MB otherwise.

       -mxnack
           Compile  binaries  suitable  for devices with the XNACK feature enabled.  Some devices always require
           XNACK and some allow the user to configure XNACK.  The compiled code must match the device mode.  The
           default is -mno-xnack.  At present this  option  is  a  placeholder  for  support  that  is  not  yet
           implemented.

       ARC Options

       The following options control the architecture variant for which code is being compiled:

       -mbarrel-shifter
           Generate  instructions  supported  by  barrel  shifter.   This  is the default unless -mcpu=ARC601 or
           -mcpu=ARCEM is in effect.

       -mjli-always
           Force to call a function using jli_s instruction.  This option is valid only for ARCv2 architecture.

       -mcpu=cpu
           Set architecture type, register usage, and instruction scheduling parameters for cpu.  There are also
           shortcut alias options available for backward compatibility and convenience.   Supported  values  for
           cpu are

           arc600
               Compile for ARC600.  Aliases: -mA6, -mARC600.

           arc601
               Compile for ARC601.  Alias: -mARC601.

           arc700
               Compile  for  ARC700.   Aliases:  -mA7,  -mARC700.   This  is  the  default  when configured with
               --with-cpu=arc700.

           arcem
               Compile for ARC EM.

           archs
               Compile for ARC HS.

           em  Compile for ARC EM CPU with no hardware extensions.

           em4 Compile for ARC EM4 CPU.

           em4_dmips
               Compile for ARC EM4 DMIPS CPU.

           em4_fpus
               Compile for ARC EM4 DMIPS CPU with the single-precision floating-point extension.

           em4_fpuda
               Compile  for  ARC  EM4  DMIPS  CPU  with  single-precision  floating-point  and   double   assist
               instructions.

           hs  Compile for ARC HS CPU with no hardware extensions except the atomic instructions.

           hs34
               Compile for ARC HS34 CPU.

           hs38
               Compile for ARC HS38 CPU.

           hs38_linux
               Compile for ARC HS38 CPU with all hardware extensions on.

           arc600_norm
               Compile for ARC 600 CPU with "norm" instructions enabled.

           arc600_mul32x16
               Compile for ARC 600 CPU with "norm" and 32x16-bit multiply instructions enabled.

           arc600_mul64
               Compile for ARC 600 CPU with "norm" and "mul64"-family instructions enabled.

           arc601_norm
               Compile for ARC 601 CPU with "norm" instructions enabled.

           arc601_mul32x16
               Compile for ARC 601 CPU with "norm" and 32x16-bit multiply instructions enabled.

           arc601_mul64
               Compile for ARC 601 CPU with "norm" and "mul64"-family instructions enabled.

           nps400
               Compile for ARC 700 on NPS400 chip.

           em_mini
               Compile for ARC EM minimalist configuration featuring reduced register set.

       -mdpfp
       -mdpfp-compact
           Generate double-precision FPX instructions, tuned for the compact implementation.

       -mdpfp-fast
           Generate double-precision FPX instructions, tuned for the fast implementation.

       -mno-dpfp-lrsr
           Disable "lr" and "sr" instructions from using FPX extension aux registers.

       -mea
           Generate  extended  arithmetic instructions.  Currently only "divaw", "adds", "subs", and "sat16" are
           supported.  Only valid for -mcpu=ARC700.

       -mno-mpy
           Do not generate "mpy"-family instructions for ARC700.  This option is deprecated.

       -mmul32x16
           Generate 32x16-bit multiply and multiply-accumulate instructions.

       -mmul64
           Generate "mul64" and "mulu64" instructions.  Only valid for -mcpu=ARC600.

       -mnorm
           Generate "norm" instructions.  This is the default if -mcpu=ARC700 is in effect.

       -mspfp
       -mspfp-compact
           Generate single-precision FPX instructions, tuned for the compact implementation.

       -mspfp-fast
           Generate single-precision FPX instructions, tuned for the fast implementation.

       -msimd
           Enable  generation  of  ARC  SIMD  instructions  via  target-specific  builtins.   Only   valid   for
           -mcpu=ARC700.

       -msoft-float
           This option ignored; it is provided for compatibility purposes only.  Software floating-point code is
           emitted  by  default,  and  this  default  can  overridden by FPX options; -mspfp, -mspfp-compact, or
           -mspfp-fast for single precision, and -mdpfp, -mdpfp-compact, or -mdpfp-fast for double precision.

       -mswap
           Generate "swap" instructions.

       -matomic
           This enables use of the locked load/store conditional extension to implement atomic  memory  built-in
           functions.  Not available for ARC 6xx or ARC EM cores.

       -mdiv-rem
           Enable "div" and "rem" instructions for ARCv2 cores.

       -mcode-density
           Enable code density instructions for ARC EM.  This option is on by default for ARC HS.

       -mll64
           Enable double load/store operations for ARC HS cores.

       -mtp-regno=regno
           Specify thread pointer register number.

       -mmpy-option=multo
           Compile ARCv2 code with a multiplier design option.  You can specify the option using either a string
           or numeric value for multo.  wlh1 is the default value.  The recognized values are:

           0
           none
               No multiplier available.

           1
           w   16x16 multiplier, fully pipelined.  The following instructions are enabled: "mpyw" and "mpyuw".

           2
           wlh1
               32x32  multiplier,  fully  pipelined  (1  stage).   The  following  instructions are additionally
               enabled: "mpy", "mpyu", "mpym", "mpymu", and "mpy_s".

           3
           wlh2
               32x32 multiplier, fully pipelined  (2  stages).   The  following  instructions  are  additionally
               enabled: "mpy", "mpyu", "mpym", "mpymu", and "mpy_s".

           4
           wlh3
               Two  16x16  multipliers,  blocking,  sequential.   The  following  instructions  are additionally
               enabled: "mpy", "mpyu", "mpym", "mpymu", and "mpy_s".

           5
           wlh4
               One 16x16 multiplier, blocking, sequential.  The following instructions are additionally enabled:
               "mpy", "mpyu", "mpym", "mpymu", and "mpy_s".

           6
           wlh5
               One 32x4 multiplier, blocking, sequential.  The following instructions are additionally  enabled:
               "mpy", "mpyu", "mpym", "mpymu", and "mpy_s".

           7
           plus_dmpy
               ARC HS SIMD support.

           8
           plus_macd
               ARC HS SIMD support.

           9
           plus_qmacw
               ARC HS SIMD support.

           This option is only available for ARCv2 cores.

       -mfpu=fpu
           Enables  support  for  specific floating-point hardware extensions for ARCv2 cores.  Supported values
           for fpu are:

           fpus
               Enables support for single-precision floating-point hardware extensions.

           fpud
               Enables support for double-precision floating-point hardware  extensions.   The  single-precision
               floating-point extension is also enabled.  Not available for ARC EM.

           fpuda
               Enables  support  for  double-precision floating-point hardware extensions using double-precision
               assist instructions.  The single-precision floating-point extension is also enabled.  This option
               is only available for ARC EM.

           fpuda_div
               Enables support for double-precision floating-point hardware  extensions  using  double-precision
               assist instructions.  The single-precision floating-point, square-root, and divide extensions are
               also enabled.  This option is only available for ARC EM.

           fpuda_fma
               Enables  support  for  double-precision floating-point hardware extensions using double-precision
               assist instructions.  The single-precision floating-point and fused  multiply  and  add  hardware
               extensions are also enabled.  This option is only available for ARC EM.

           fpuda_all
               Enables  support  for  double-precision floating-point hardware extensions using double-precision
               assist instructions.  All single-precision floating-point hardware extensions are  also  enabled.
               This option is only available for ARC EM.

           fpus_div
               Enables support for single-precision floating-point, square-root and divide hardware extensions.

           fpud_div
               Enables  support for double-precision floating-point, square-root and divide hardware extensions.
               This option includes option fpus_div. Not available for ARC EM.

           fpus_fma
               Enables  support  for  single-precision  floating-point  and  fused  multiply  and  add  hardware
               extensions.

           fpud_fma
               Enables  support  for  double-precision  floating-point  and  fused  multiply  and  add  hardware
               extensions.  This option includes option fpus_fma.  Not available for ARC EM.

           fpus_all
               Enables support for all single-precision floating-point hardware extensions.

           fpud_all
               Enables support for all single- and double-precision  floating-point  hardware  extensions.   Not
               available for ARC EM.

       -mirq-ctrl-saved=register-range, blink, lp_count
           Specifies  general-purposes  registers  that  the processor automatically saves/restores on interrupt
           entry and exit.  register-range is specified as two registers separated  by  a  dash.   The  register
           range  always  starts  with "r0", the upper limit is "fp" register.  blink and lp_count are optional.
           This option is only valid for ARC EM and ARC HS cores.

       -mrgf-banked-regs=number
           Specifies the number of registers replicated in second register bank  on  entry  to  fast  interrupt.
           Fast interrupts are interrupts with the highest priority level P0.  These interrupts save only PC and
           STATUS32  registers to avoid memory transactions during interrupt entry and exit sequences.  Use this
           option when you are using fast interrupts in an ARC V2 family processor.  Permitted values are 4,  8,
           16, and 32.

       -mlpc-width=width
           Specify  the  width  of the "lp_count" register.  Valid values for width are 8, 16, 20, 24, 28 and 32
           bits.  The default width is fixed to 32 bits.  If the width is less than 32, the  compiler  does  not
           attempt  to  transform  loops in your program to use the zero-delay loop mechanism unless it is known
           that the "lp_count" register can hold the  required  loop-counter  value.   Depending  on  the  width
           specified,  the  compiler  and  run-time library might continue to use the loop mechanism for various
           needs.  This option defines macro "__ARC_LPC_WIDTH__" with the value of width.

       -mrf16
           This option instructs the compiler to generate code  for  a  16-entry  register  file.   This  option
           defines the "__ARC_RF16__" preprocessor macro.

       -mbranch-index
           Enable use of "bi" or "bih" instructions to implement jump tables.

       The following options are passed through to the assembler, and also define preprocessor macro symbols.

       -mdsp-packa
           Passed  down to the assembler to enable the DSP Pack A extensions.  Also sets the preprocessor symbol
           "__Xdsp_packa".  This option is deprecated.

       -mdvbf
           Passed down to the assembler  to  enable  the  dual  Viterbi  butterfly  extension.   Also  sets  the
           preprocessor symbol "__Xdvbf".  This option is deprecated.

       -mlock
           Passed  down  to  the assembler to enable the locked load/store conditional extension.  Also sets the
           preprocessor symbol "__Xlock".

       -mmac-d16
           Passed down to the assembler.  Also sets the  preprocessor  symbol  "__Xxmac_d16".   This  option  is
           deprecated.

       -mmac-24
           Passed  down  to  the  assembler.   Also  sets  the preprocessor symbol "__Xxmac_24".  This option is
           deprecated.

       -mrtsc
           Passed down to the assembler to enable the 64-bit time-stamp  counter  extension  instruction.   Also
           sets the preprocessor symbol "__Xrtsc".  This option is deprecated.

       -mswape
           Passed  down  to the assembler to enable the swap byte ordering extension instruction.  Also sets the
           preprocessor symbol "__Xswape".

       -mtelephony
           Passed down to the assembler to enable dual- and single-operand  instructions  for  telephony.   Also
           sets the preprocessor symbol "__Xtelephony".  This option is deprecated.

       -mxy
           Passed  down  to  the assembler to enable the XY memory extension.  Also sets the preprocessor symbol
           "__Xxy".

       The following options control how the assembly code is annotated:

       -misize
           Annotate assembler instructions with estimated addresses.

       -mannotate-align
           Explain what alignment considerations lead to the decision to make an instruction short or long.

       The following options are passed through to the linker:

       -marclinux
           Passed through to the linker, to specify use of the "arclinux" emulation.  This option is enabled  by
           default  in  tool chains built for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when profiling
           is not requested.

       -marclinux_prof
           Passed through to the linker, to specify use  of  the  "arclinux_prof"  emulation.   This  option  is
           enabled  by default in tool chains built for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when
           profiling is requested.

       The following options control the semantics of generated code:

       -mlong-calls
           Generate calls as register indirect calls, thus providing access to the full 32-bit address range.

       -mmedium-calls
           Don't use less than 25-bit addressing  range  for  calls,  which  is  the  offset  available  for  an
           unconditional branch-and-link instruction.  Conditional execution of function calls is suppressed, to
           allow  use  of the 25-bit range, rather than the 21-bit range with conditional branch-and-link.  This
           is the default for tool chains built for "arc-linux-uclibc" and "arceb-linux-uclibc" targets.

       -G num
           Put definitions of externally-visible data in a small data section if that data is no bigger than num
           bytes.  The default value of num is 4 for any ARC configuration, or 8 when we have double  load/store
           operations.

       -mno-sdata
           Do  not  generate sdata references.  This is the default for tool chains built for "arc-linux-uclibc"
           and "arceb-linux-uclibc" targets.

       -mvolatile-cache
           Use ordinarily cached memory accesses for volatile references.  This is the default.

       -mno-volatile-cache
           Enable cache bypass for volatile references.

       The following options fine tune code generation:

       -malign-call
           Do alignment optimizations for call instructions.

       -mauto-modify-reg
           Enable the use of pre/post modify with register displacement.

       -mbbit-peephole
           Enable bbit peephole2.

       -mno-brcc
           This option disables a target-specific pass in  arc_reorg  to  generate  compare-and-branch  ("brcc")
           instructions.  It has no effect on generation of these instructions driven by the combiner pass.

       -mcase-vector-pcrel
           Use PC-relative switch case tables to enable case table shortening.  This is the default for -Os.

       -mcompact-casesi
           Enable  compact  "casesi"  pattern.  This is the default for -Os, and only available for ARCv1 cores.
           This option is deprecated.

       -mno-cond-exec
           Disable the ARCompact-specific pass to generate conditional execution instructions.

           Due to delay slot scheduling and interactions between operand  numbers,  literal  sizes,  instruction
           lengths,  and  the  support  for  conditional  execution,  the  target-independent  pass  to generate
           conditional execution is often lacking, so the ARC port has kept a special pass around that tries  to
           find   more   conditional  execution  generation  opportunities  after  register  allocation,  branch
           shortening, and delay slot scheduling have been done.  This pass generally, but not always,  improves
           performance  and code size, at the cost of extra compilation time, which is why there is an option to
           switch it off.  If you have a problem with call instructions exceeding their allowable  offset  range
           because they are conditionalized, you should consider using -mmedium-calls instead.

       -mearly-cbranchsi
           Enable pre-reload use of the "cbranchsi" pattern.

       -mexpand-adddi
           Expand  "adddi3"  and  "subdi3"  at  RTL  generation  time  into  "add.f", "adc" etc.  This option is
           deprecated.

       -mindexed-loads
           Enable the use of indexed loads.  This can be problematic because some optimizers  then  assume  that
           indexed stores exist, which is not the case.

       -mlra
           Enable  Local  Register  Allocation.   This is still experimental for ARC, so by default the compiler
           uses standard reload (i.e. -mno-lra).

       -mlra-priority-none
           Don't indicate any priority for target registers.

       -mlra-priority-compact
           Indicate target register priority for r0..r3 / r12..r15.

       -mlra-priority-noncompact
           Reduce target register priority for r0..r3 / r12..r15.

       -mmillicode
           When optimizing for size (using -Os), prologues and epilogues that have to save or  restore  a  large
           number  of  registers  are  often  shortened  by  using call to a special function in libgcc; this is
           referred to as a millicode call.  As these calls can pose performance issues,  and/or  cause  linking
           issues  when  linking  in a nonstandard way, this option is provided to turn on or off millicode call
           generation.

       -mcode-density-frame
           This option enable the compiler to emit "enter" and "leave"  instructions.   These  instructions  are
           only valid for CPUs with code-density feature.

       -mmixed-code
           Tweak  register  allocation  to help 16-bit instruction generation.  This generally has the effect of
           decreasing the average instruction size while increasing the instruction count.

       -mq-class
           Ths option is deprecated.  Enable q instruction alternatives.  This is the default for -Os.

       -mRcq
           Enable Rcq constraint handling.  Most short code generation depends on this.  This is the default.

       -mRcw
           Enable Rcw constraint handling.  Most ccfsm condexec mostly depends on this.  This is the default.

       -msize-level=level
           Fine-tune size optimization with regards to instruction lengths and alignment.  The recognized values
           for level are:

           0   No size optimization.  This level is deprecated and treated like 1.

           1   Short instructions are used opportunistically.

           2   In addition, alignment of loops and of code after barriers are dropped.

           3   In addition, optional data alignment is dropped, and the option Os is enabled.

           This defaults to 3 when -Os is in effect.  Otherwise, the behavior when this is not set is equivalent
           to level 1.

       -mtune=cpu
           Set instruction scheduling parameters for cpu, overriding any implied by -mcpu=.

           Supported values for cpu are

           ARC600
               Tune for ARC600 CPU.

           ARC601
               Tune for ARC601 CPU.

           ARC700
               Tune for ARC700 CPU with standard multiplier block.

           ARC700-xmac
               Tune for ARC700 CPU with XMAC block.

           ARC725D
               Tune for ARC725D CPU.

           ARC750D
               Tune for ARC750D CPU.

       -mmultcost=num
           Cost to assume for a multiply instruction, with 4 being equal to a normal instruction.

       -munalign-prob-threshold=probability
           Set probability threshold for unaligning branches.  When tuning for ARC700 and optimizing for  speed,
           branches  without  filled  delay  slot  are  preferably  emitted unaligned and long, unless profiling
           indicates that the probability for the branch to be taken  is  below  probability.   The  default  is
           (REG_BR_PROB_BASE/2), i.e. 5000.

       The  following  options  are  maintained  for  backward compatibility, but are now deprecated and will be
       removed in a future release:

       -margonaut
           Obsolete FPX.

       -mbig-endian
       -EB Compile code for big-endian targets.  Use of these options is now  deprecated.   Big-endian  code  is
           supported  by  configuring GCC to build "arceb-elf32" and "arceb-linux-uclibc" targets, for which big
           endian is the default.

       -mlittle-endian
       -EL Compile code for little-endian targets.  Use of these options is now deprecated.  Little-endian  code
           is supported by configuring GCC to build "arc-elf32" and "arc-linux-uclibc" targets, for which little
           endian is the default.

       -mbarrel_shifter
           Replaced by -mbarrel-shifter.

       -mdpfp_compact
           Replaced by -mdpfp-compact.

       -mdpfp_fast
           Replaced by -mdpfp-fast.

       -mdsp_packa
           Replaced by -mdsp-packa.

       -mEA
           Replaced by -mea.

       -mmac_24
           Replaced by -mmac-24.

       -mmac_d16
           Replaced by -mmac-d16.

       -mspfp_compact
           Replaced by -mspfp-compact.

       -mspfp_fast
           Replaced by -mspfp-fast.

       -mtune=cpu
           Values  arc600,  arc601,  arc700  and  arc700-xmac for cpu are replaced by ARC600, ARC601, ARC700 and
           ARC700-xmac respectively.

       -multcost=num
           Replaced by -mmultcost.

       ARM Options

       These -m options are defined for the ARM port:

       -mabi=name
           Generate code for the specified ABI.  Permissible values are: apcs-gnu, atpcs, aapcs, aapcs-linux and
           iwmmxt.

       -mapcs-frame
           Generate a stack frame that is compliant with the ARM Procedure Call Standard for all functions, even
           if this is not strictly necessary for correct execution of the code.  Specifying -fomit-frame-pointer
           with this option causes the stack frames not to be generated for  leaf  functions.   The  default  is
           -mno-apcs-frame.  This option is deprecated.

       -mapcs
           This is a synonym for -mapcs-frame and is deprecated.

       -mthumb-interwork
           Generate code that supports calling between the ARM and Thumb instruction sets.  Without this option,
           on  pre-v5  architectures,  the two instruction sets cannot be reliably used inside one program.  The
           default is -mno-thumb-interwork, since slightly larger code is generated  when  -mthumb-interwork  is
           specified.  In AAPCS configurations this option is meaningless.

       -mno-sched-prolog
           Prevent  the reordering of instructions in the function prologue, or the merging of those instruction
           with the instructions  in  the  function's  body.   This  means  that  all  functions  start  with  a
           recognizable  set  of instructions (or in fact one of a choice from a small set of different function
           prologues), and this information can be used to locate the start of functions  inside  an  executable
           piece of code.  The default is -msched-prolog.

       -mfloat-abi=name
           Specifies which floating-point ABI to use.  Permissible values are: soft, softfp and hard.

           Specifying soft causes GCC to generate output containing library calls for floating-point operations.
           softfp  allows  the generation of code using hardware floating-point instructions, but still uses the
           soft-float calling conventions.  hard allows generation of floating-point instructions and uses  FPU-
           specific calling conventions.

           The  default  depends  on the specific target configuration.  Note that the hard-float and soft-float
           ABIs are not link-compatible; you must compile your entire program with the same ABI, and link with a
           compatible set of libraries.

       -mgeneral-regs-only
           Generate code which uses only the general-purpose registers.  This will  prevent  the  compiler  from
           using  floating-point  and  Advanced  SIMD  registers  but  will  not  impose any restrictions on the
           assembler.

       -mlittle-endian
           Generate code for a processor running in little-endian mode.  This is the default  for  all  standard
           configurations.

       -mbig-endian
           Generate  code  for  a  processor  running  in  big-endian mode; the default is to compile code for a
           little-endian processor.

       -mbe8
       -mbe32
           When linking a big-endian image select between BE8 and BE32 formats.  The option has  no  effect  for
           little-endian  images  and is ignored.  The default is dependent on the selected target architecture.
           For ARMv6 and later architectures the default is BE8, for older architectures the  default  is  BE32.
           BE32 format has been deprecated by ARM.

       -march=name[+extension...]
           This specifies the name of the target ARM architecture.  GCC uses this name to determine what kind of
           instructions  it can emit when generating assembly code.  This option can be used in conjunction with
           or instead of the -mcpu= option.

           Permissible names are: armv4t, armv5t, armv5te, armv6,  armv6j,  armv6k,  armv6kz,  armv6t2,  armv6z,
           armv6zk,  armv7,  armv7-a,  armv7ve,  armv8-a, armv8.1-a, armv8.2-a, armv8.3-a, armv8.4-a, armv8.5-a,
           armv8.6-a, armv7-r,  armv8-r,  armv6-m,  armv6s-m,  armv7-m,  armv7e-m,  armv8-m.base,  armv8-m.main,
           armv8.1-m.main, iwmmxt and iwmmxt2.

           Additionally,  the  following  architectures,  which  lack support for the Thumb execution state, are
           recognized but support is deprecated: armv4.

           Many of the architectures support extensions.  These can be added  by  appending  +extension  to  the
           architecture  name.   Extension  options  are  processed  in  order  and capabilities accumulate.  An
           extension will also enable any necessary base extensions upon which it  depends.   For  example,  the
           +crypto extension will always enable the +simd extension.  The exception to the additive construction
           is  for  extensions  that are prefixed with +no...: these extensions disable the specified option and
           any other extensions that may depend on the presence of that extension.

           For example, -march=armv7-a+simd+nofp+vfpv4 is equivalent to writing -march=armv7-a+vfpv4  since  the
           +simd option is entirely disabled by the +nofp option that follows it.

           Most  extension  names  are  generically  named,  but  have  an  effect  that  is  dependent upon the
           architecture to which it is applied.  For example, the +simd option can be applied  to  both  armv7-a
           and  armv8-a  architectures, but will enable the original ARMv7-A Advanced SIMD (Neon) extensions for
           armv7-a and the ARMv8-A variant for armv8-a.

           The table below lists the supported extensions for each architecture.  Architectures not mentioned do
           not support any extensions.

           armv5te
           armv6
           armv6j
           armv6k
           armv6kz
           armv6t2
           armv6z
           armv6zk
               +fp The VFPv2 floating-point instructions.  The extension +vfpv2 can be used as an alias for this
                   extension.

               +nofp
                   Disable the floating-point instructions.

           armv7
               The common subset of the ARMv7-A, ARMv7-R and ARMv7-M architectures.

               +fp The VFPv3 floating-point instructions, with 16  double-precision  registers.   The  extension
                   +vfpv3-d16  can  be  used  as  an  alias for this extension.  Note that floating-point is not
                   supported by the base ARMv7-M architecture, but is  compatible  with  both  the  ARMv7-A  and
                   ARMv7-R architectures.

               +nofp
                   Disable the floating-point instructions.

           armv7-a
               +mp The multiprocessing extension.

               +sec
                   The security extension.

               +fp The  VFPv3  floating-point  instructions,  with 16 double-precision registers.  The extension
                   +vfpv3-d16 can be used as an alias for this extension.

               +simd
                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions.  The extensions  +neon
                   and +neon-vfpv3 can be used as aliases for this extension.

               +vfpv3
                   The VFPv3 floating-point instructions, with 32 double-precision registers.

               +vfpv3-d16-fp16
                   The  VFPv3  floating-point  instructions,  with  16  double-precision registers and the half-
                   precision floating-point conversion operations.

               +vfpv3-fp16
                   The VFPv3 floating-point instructions, with  32  double-precision  registers  and  the  half-
                   precision floating-point conversion operations.

               +vfpv4-d16
                   The VFPv4 floating-point instructions, with 16 double-precision registers.

               +vfpv4
                   The VFPv4 floating-point instructions, with 32 double-precision registers.

               +neon-fp16
                   The  Advanced  SIMD  (Neon)  v1  and  the  VFPv3  floating-point instructions, with the half-
                   precision floating-point conversion operations.

               +neon-vfpv4
                   The Advanced SIMD (Neon) v2 and the VFPv4 floating-point instructions.

               +nosimd
                   Disable the Advanced SIMD instructions (does not disable floating point).

               +nofp
                   Disable the floating-point and Advanced SIMD instructions.

           armv7ve
               The extended version of the ARMv7-A architecture with support for virtualization.

               +fp The VFPv4 floating-point instructions, with 16  double-precision  registers.   The  extension
                   +vfpv4-d16 can be used as an alias for this extension.

               +simd
                   The  Advanced  SIMD  (Neon)  v2  and  the  VFPv4  floating-point instructions.  The extension
                   +neon-vfpv4 can be used as an alias for this extension.

               +vfpv3-d16
                   The VFPv3 floating-point instructions, with 16 double-precision registers.

               +vfpv3
                   The VFPv3 floating-point instructions, with 32 double-precision registers.

               +vfpv3-d16-fp16
                   The VFPv3 floating-point instructions, with  16  double-precision  registers  and  the  half-
                   precision floating-point conversion operations.

               +vfpv3-fp16
                   The  VFPv3  floating-point  instructions,  with  32  double-precision registers and the half-
                   precision floating-point conversion operations.

               +vfpv4-d16
                   The VFPv4 floating-point instructions, with 16 double-precision registers.

               +vfpv4
                   The VFPv4 floating-point instructions, with 32 double-precision registers.

               +neon
                   The Advanced SIMD (Neon)  v1  and  the  VFPv3  floating-point  instructions.   The  extension
                   +neon-vfpv3 can be used as an alias for this extension.

               +neon-fp16
                   The  Advanced  SIMD  (Neon)  v1  and  the  VFPv3  floating-point instructions, with the half-
                   precision floating-point conversion operations.

               +nosimd
                   Disable the Advanced SIMD instructions (does not disable floating point).

               +nofp
                   Disable the floating-point and Advanced SIMD instructions.

           armv8-a
               +crc
                   The Cyclic Redundancy Check (CRC) instructions.

               +simd
                   The ARMv8-A Advanced SIMD and floating-point instructions.

               +crypto
                   The cryptographic instructions.

               +nocrypto
                   Disable the cryptographic instructions.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic instructions.

               +sb Speculation Barrier Instruction.

               +predres
                   Execution and Data Prediction Restriction Instructions.

           armv8.1-a
               +simd
                   The ARMv8.1-A Advanced SIMD and floating-point instructions.

               +crypto
                   The cryptographic instructions.  This also  enables  the  Advanced  SIMD  and  floating-point
                   instructions.

               +nocrypto
                   Disable the cryptographic instructions.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic instructions.

               +sb Speculation Barrier Instruction.

               +predres
                   Execution and Data Prediction Restriction Instructions.

           armv8.2-a
           armv8.3-a
               +fp16
                   The  half-precision  floating-point  data  processing  instructions.   This  also enables the
                   Advanced SIMD and floating-point instructions.

               +fp16fml
                   The half-precision floating-point fmla  extension.   This  also  enables  the  half-precision
                   floating-point extension and Advanced SIMD and floating-point instructions.

               +simd
                   The ARMv8.1-A Advanced SIMD and floating-point instructions.

               +crypto
                   The  cryptographic  instructions.   This  also  enables  the Advanced SIMD and floating-point
                   instructions.

               +dotprod
                   Enable the Dot Product extension.  This also enables Advanced SIMD instructions.

               +nocrypto
                   Disable the cryptographic extension.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic instructions.

               +sb Speculation Barrier Instruction.

               +predres
                   Execution and Data Prediction Restriction Instructions.

               +i8mm
                   8-bit Integer Matrix Multiply instructions.  This also enables Advanced  SIMD  and  floating-
                   point instructions.

               +bf16
                   Brain  half-precision  floating-point  instructions.   This  also  enables  Advanced SIMD and
                   floating-point instructions.

           armv8.4-a
               +fp16
                   The half-precision floating-point  data  processing  instructions.   This  also  enables  the
                   Advanced  SIMD  and  floating-point instructions as well as the Dot Product extension and the
                   half-precision floating-point fmla extension.

               +simd
                   The ARMv8.3-A Advanced SIMD and floating-point  instructions  as  well  as  the  Dot  Product
                   extension.

               +crypto
                   The  cryptographic  instructions.   This  also  enables  the Advanced SIMD and floating-point
                   instructions as well as the Dot Product extension.

               +nocrypto
                   Disable the cryptographic extension.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic instructions.

               +sb Speculation Barrier Instruction.

               +predres
                   Execution and Data Prediction Restriction Instructions.

               +i8mm
                   8-bit Integer Matrix Multiply instructions.  This also enables Advanced  SIMD  and  floating-
                   point instructions.

               +bf16
                   Brain  half-precision  floating-point  instructions.   This  also  enables  Advanced SIMD and
                   floating-point instructions.

           armv8.5-a
               +fp16
                   The half-precision floating-point  data  processing  instructions.   This  also  enables  the
                   Advanced  SIMD  and  floating-point instructions as well as the Dot Product extension and the
                   half-precision floating-point fmla extension.

               +simd
                   The ARMv8.3-A Advanced SIMD and floating-point  instructions  as  well  as  the  Dot  Product
                   extension.

               +crypto
                   The  cryptographic  instructions.   This  also  enables  the Advanced SIMD and floating-point
                   instructions as well as the Dot Product extension.

               +nocrypto
                   Disable the cryptographic extension.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic instructions.

               +i8mm
                   8-bit Integer Matrix Multiply instructions.  This also enables Advanced  SIMD  and  floating-
                   point instructions.

               +bf16
                   Brain  half-precision  floating-point  instructions.   This  also  enables  Advanced SIMD and
                   floating-point instructions.

           armv8.6-a
               +fp16
                   The half-precision floating-point  data  processing  instructions.   This  also  enables  the
                   Advanced  SIMD  and  floating-point instructions as well as the Dot Product extension and the
                   half-precision floating-point fmla extension.

               +simd
                   The ARMv8.3-A Advanced SIMD and floating-point  instructions  as  well  as  the  Dot  Product
                   extension.

               +crypto
                   The  cryptographic  instructions.   This  also  enables  the Advanced SIMD and floating-point
                   instructions as well as the Dot Product extension.

               +nocrypto
                   Disable the cryptographic extension.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic instructions.

               +i8mm
                   8-bit Integer Matrix Multiply instructions.  This also enables Advanced  SIMD  and  floating-
                   point instructions.

               +bf16
                   Brain  half-precision  floating-point  instructions.   This  also  enables  Advanced SIMD and
                   floating-point instructions.

           armv7-r
               +fp.sp
                   The single-precision VFPv3 floating-point instructions.  The extension +vfpv3xd can  be  used
                   as an alias for this extension.

               +fp The  VFPv3  floating-point  instructions  with  16 double-precision registers.  The extension
                   +vfpv3-d16 can be used as an alias for this extension.

               +vfpv3xd-d16-fp16
                   The single-precision VFPv3 floating-point instructions with 16 double-precision registers and
                   the half-precision floating-point conversion operations.

               +vfpv3-d16-fp16
                   The VFPv3 floating-point instructions  with  16  double-precision  registers  and  the  half-
                   precision floating-point conversion operations.

               +nofp
                   Disable the floating-point extension.

               +idiv
                   The ARM-state integer division instructions.

               +noidiv
                   Disable the ARM-state integer division extension.

           armv7e-m
               +fp The single-precision VFPv4 floating-point instructions.

               +fpv5
                   The single-precision FPv5 floating-point instructions.

               +fp.dp
                   The single- and double-precision FPv5 floating-point instructions.

               +nofp
                   Disable the floating-point extensions.

           armv8.1-m.main
               +dsp
                   The DSP instructions.

               +mve
                   The M-Profile Vector Extension (MVE) integer instructions.

               +mve.fp
                   The   M-Profile   Vector   Extension   (MVE)  integer  and  single  precision  floating-point
                   instructions.

               +fp The single-precision floating-point instructions.

               +fp.dp
                   The single- and double-precision floating-point instructions.

               +nofp
                   Disable the floating-point extension.

               +cdecp0, +cdecp1, ... , +cdecp7
                   Enable the Custom Datapath Extension (CDE) on selected coprocessors according to the  numbers
                   given in the options in the range 0 to 7.

           armv8-m.main
               +dsp
                   The DSP instructions.

               +nodsp
                   Disable the DSP extension.

               +fp The single-precision floating-point instructions.

               +fp.dp
                   The single- and double-precision floating-point instructions.

               +nofp
                   Disable the floating-point extension.

               +cdecp0, +cdecp1, ... , +cdecp7
                   Enable  the Custom Datapath Extension (CDE) on selected coprocessors according to the numbers
                   given in the options in the range 0 to 7.

           armv8-r
               +crc
                   The Cyclic Redundancy Check (CRC) instructions.

               +fp.sp
                   The single-precision FPv5 floating-point instructions.

               +simd
                   The ARMv8-A Advanced SIMD and floating-point instructions.

               +crypto
                   The cryptographic instructions.

               +nocrypto
                   Disable the cryptographic instructions.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic instructions.

           -march=native causes the compiler to auto-detect the architecture of the build computer.  At present,
           this feature is only supported on GNU/Linux, and not all architectures are recognized.  If the  auto-
           detect is unsuccessful the option has no effect.

       -mtune=name
           This  option specifies the name of the target ARM processor for which GCC should tune the performance
           of the code.  For some ARM implementations better performance can be obtained by using  this  option.
           Permissible  names  are:  arm7tdmi,  arm7tdmi-s,  arm710t, arm720t, arm740t, strongarm, strongarm110,
           strongarm1100, 0strongarm1110, arm8,  arm810,  arm9,  arm9e,  arm920,  arm920t,  arm922t,  arm946e-s,
           arm966e-s,  arm968e-s,  arm926ej-s,  arm940t,  arm9tdmi,  arm10tdmi,  arm1020t,  arm1026ej-s, arm10e,
           arm1020e,  arm1022e,  arm1136j-s,  arm1136jf-s,  mpcore,  mpcorenovfp,   arm1156t2-s,   arm1156t2f-s,
           arm1176jz-s,  arm1176jzf-s,  generic-armv7-a, cortex-a5, cortex-a7, cortex-a8, cortex-a9, cortex-a12,
           cortex-a15, cortex-a17,  cortex-a32,  cortex-a35,  cortex-a53,  cortex-a55,  cortex-a57,  cortex-a72,
           cortex-a73,  cortex-a75, cortex-a76, cortex-a76ae, cortex-a77, cortex-a78, cortex-a78ae, cortex-a78c,
           ares, cortex-r4, cortex-r4f, cortex-r5, cortex-r7, cortex-r8, cortex-r52,  cortex-m0,  cortex-m0plus,
           cortex-m1,   cortex-m3,   cortex-m4,  cortex-m7,  cortex-m23,  cortex-m33,  cortex-m35p,  cortex-m55,
           cortex-x1,    cortex-m1.small-multiply,    cortex-m0.small-multiply,    cortex-m0plus.small-multiply,
           exynos-m1,  marvell-pj4,  neoverse-n1,  neoverse-n2,  neoverse-v1,  xscale,  iwmmxt, iwmmxt2, ep9312,
           fa526, fa626, fa606te, fa626te, fmp626, fa726te, xgene1.

           Additionally, this option can specify that GCC  should  tune  the  performance  of  the  code  for  a
           big.LITTLE    system.     Permissible    names   are:   cortex-a15.cortex-a7,   cortex-a17.cortex-a7,
           cortex-a57.cortex-a53,    cortex-a72.cortex-a53,    cortex-a72.cortex-a35,     cortex-a73.cortex-a53,
           cortex-a75.cortex-a55, cortex-a76.cortex-a55.

           -mtune=generic-arch  specifies  that GCC should tune the performance for a blend of processors within
           architecture arch.  The aim is to generate code that run well on the current most popular processors,
           balancing between optimizations that benefit  some  CPUs  in  the  range,  and  avoiding  performance
           pitfalls  of  other CPUs.  The effects of this option may change in future GCC versions as CPU models
           come and go.

           -mtune permits the same extension options as -mcpu, but the  extension  options  do  not  affect  the
           tuning of the generated code.

           -mtune=native  causes  the  compiler  to auto-detect the CPU of the build computer.  At present, this
           feature is only supported on GNU/Linux, and not all architectures are recognized.  If the auto-detect
           is unsuccessful the option has no effect.

       -mcpu=name[+extension...]
           This specifies the name of the target ARM processor.  GCC uses this name to derive the  name  of  the
           target  ARM architecture (as if specified by -march) and the ARM processor type for which to tune for
           performance (as if specified by -mtune).  Where this option is used in  conjunction  with  -march  or
           -mtune, those options take precedence over the appropriate part of this option.

           Many  of  the  supported  CPUs  implement  optional  architectural  extensions.  Where this is so the
           architectural extensions are normally enabled by default.  If implementations that lack the extension
           exist, then the extension syntax can be used to disable those extensions that have been omitted.  For
           floating-point and Advanced SIMD (Neon) instructions, the settings of  the  options  -mfloat-abi  and
           -mfpu  must  also  be  considered: floating-point and Advanced SIMD instructions will only be used if
           -mfloat-abi is not set to soft; and any setting of -mfpu other than auto will override the  available
           floating-point and SIMD extension instructions.

           For  example,  cortex-a9  can  be  found  in  three  major  configurations: integer only, with just a
           floating-point unit or with floating-point and Advanced SIMD.  The  default  is  to  enable  all  the
           instructions,  but  the extensions +nosimd and +nofp can be used to disable just the SIMD or both the
           SIMD and floating-point instructions respectively.

           Permissible names for this option are the same as those for -mtune.

           The following extension options are common to the listed CPUs:

           +nodsp
               Disable the DSP instructions on cortex-m33, cortex-m35p.

           +nofp
               Disables the floating-point instructions  on  arm9e,  arm946e-s,  arm966e-s,  arm968e-s,  arm10e,
               arm1020e,   arm1022e,   arm926ej-s,  arm1026ej-s,  cortex-r5,  cortex-r7,  cortex-r8,  cortex-m4,
               cortex-m7, cortex-m33 and cortex-m35p.  Disables the  floating-point  and  SIMD  instructions  on
               generic-armv7-a,  cortex-a5, cortex-a7, cortex-a8, cortex-a9, cortex-a12, cortex-a15, cortex-a17,
               cortex-a15.cortex-a7, cortex-a17.cortex-a7, cortex-a32, cortex-a35, cortex-a53 and cortex-a55.

           +nofp.dp
               Disables  the  double-precision  component  of  the  floating-point  instructions  on  cortex-r5,
               cortex-r7, cortex-r8, cortex-r52 and cortex-m7.

           +nosimd
               Disables  the SIMD (but not floating-point) instructions on generic-armv7-a, cortex-a5, cortex-a7
               and cortex-a9.

           +crypto
               Enables  the  cryptographic  instructions  on  cortex-a32,  cortex-a35,  cortex-a53,  cortex-a55,
               cortex-a57,   cortex-a72,   cortex-a73,  cortex-a75,  exynos-m1,  xgene1,  cortex-a57.cortex-a53,
               cortex-a72.cortex-a53, cortex-a73.cortex-a35, cortex-a73.cortex-a53 and cortex-a75.cortex-a55.

           Additionally the generic-armv7-a pseudo target defaults to VFPv3 with 16 double-precision  registers.
           It  supports  the following extension options: mp, sec, vfpv3-d16, vfpv3, vfpv3-d16-fp16, vfpv3-fp16,
           vfpv4-d16, vfpv4, neon, neon-vfpv3, neon-fp16, neon-vfpv4.  The meanings are  the  same  as  for  the
           extensions to -march=armv7-a.

           -mcpu=generic-arch  is  also  permissible, and is equivalent to -march=arch -mtune=generic-arch.  See
           -mtune for more information.

           -mcpu=native causes the compiler to auto-detect the CPU of the  build  computer.   At  present,  this
           feature is only supported on GNU/Linux, and not all architectures are recognized.  If the auto-detect
           is unsuccessful the option has no effect.

       -mfpu=name
           This  specifies  what  floating-point  hardware  (or  hardware emulation) is available on the target.
           Permissible  names  are:  auto,  vfpv2,  vfpv3,  vfpv3-fp16,  vfpv3-d16,   vfpv3-d16-fp16,   vfpv3xd,
           vfpv3xd-fp16,   neon-vfpv3,   neon-fp16,   vfpv4,   vfpv4-d16,   fpv4-sp-d16,  neon-vfpv4,  fpv5-d16,
           fpv5-sp-d16, fp-armv8, neon-fp-armv8 and crypto-neon-fp-armv8.   Note  that  neon  is  an  alias  for
           neon-vfpv3 and vfp is an alias for vfpv2.

           The  setting auto is the default and is special.  It causes the compiler to select the floating-point
           and Advanced SIMD instructions based on the settings of -mcpu and -march.

           If the selected floating-point hardware includes the NEON  extension  (e.g.  -mfpu=neon),  note  that
           floating-point   operations   are   not   generated   by   GCC's   auto-vectorization   pass   unless
           -funsafe-math-optimizations is also  specified.   This  is  because  NEON  hardware  does  not  fully
           implement  the  IEEE  754  standard  for floating-point arithmetic (in particular denormal values are
           treated as zero), so the use of NEON instructions may lead to a loss of precision.

           You can also set the fpu name at function level by using the "target("fpu=")" function attributes  or
           pragmas.

       -mfp16-format=name
           Specify  the  format of the "__fp16" half-precision floating-point type.  Permissible names are none,
           ieee, and alternative; the default is none, in which case the "__fp16" type is not defined.

       -mstructure-size-boundary=n
           The sizes of all structures and unions are rounded up to a multiple of the number of bits set by this
           option.  Permissible values are 8, 32 and 64.  The default value  varies  for  different  toolchains.
           For  the  COFF  targeted  toolchain  the  default  value  is 8.  A value of 64 is only allowed if the
           underlying ABI supports it.

           Specifying a larger number can produce faster, more efficient code, but can also increase the size of
           the program.  Different values are potentially incompatible.  Code compiled  with  one  value  cannot
           necessarily  expect  to  work  with  code  or libraries compiled with another value, if they exchange
           information using structures or unions.

           This option is deprecated.

       -mabort-on-noreturn
           Generate a call to the function "abort" at the end of a "noreturn" function.  It is executed  if  the
           function tries to return.

       -mlong-calls
       -mno-long-calls
           Tells  the  compiler  to  perform  function calls by first loading the address of the function into a
           register and then performing a subroutine call on this register.  This switch is needed if the target
           function lies outside of the 64-megabyte addressing range of the offset-based version  of  subroutine
           call instruction.

           Even  if this switch is enabled, not all function calls are turned into long calls.  The heuristic is
           that static functions, functions that have the "short_call" attribute, functions that are inside  the
           scope  of  a  "#pragma  no_long_calls"  directive,  and functions whose definitions have already been
           compiled within the current compilation unit are not turned into long calls.  The exceptions to  this
           rule  are  that  weak function definitions, functions with the "long_call" attribute or the "section"
           attribute, and functions that are within the scope of a "#pragma  long_calls"  directive  are  always
           turned into long calls.

           This feature is not enabled by default.  Specifying -mno-long-calls restores the default behavior, as
           does placing the function calls within the scope of a "#pragma long_calls_off" directive.  Note these
           switches  have  no  effect  on  how the compiler generates code to handle function calls via function
           pointers.

       -msingle-pic-base
           Treat the register used for PIC addressing as read-only, rather than loading it in the  prologue  for
           each  function.  The runtime system is responsible for initializing this register with an appropriate
           value before execution begins.

       -mpic-register=reg
           Specify the register to be used for PIC addressing.  For standard PIC base case, the default  is  any
           suitable  register  determined by compiler.  For single PIC base case, the default is R9 if target is
           EABI based or stack-checking is enabled, otherwise the default is R10.

       -mpic-data-is-text-relative
           Assume that the displacement between the text and data segments is fixed at static link  time.   This
           permits  using PC-relative addressing operations to access data known to be in the data segment.  For
           non-VxWorks RTP targets, this option is enabled by default.  When disabled on such targets,  it  will
           enable -msingle-pic-base by default.

       -mpoke-function-name
           Write the name of each function into the text section, directly preceding the function prologue.  The
           generated code is similar to this:

                        t0
                            .ascii "arm_poke_function_name", 0
                            .align
                        t1
                            .word 0xff000000 + (t1 - t0)
                        arm_poke_function_name
                            mov     ip, sp
                            stmfd   sp!, {fp, ip, lr, pc}
                            sub     fp, ip, #4

           When  performing  a  stack  backtrace, code can inspect the value of "pc" stored at "fp + 0".  If the
           trace function then looks at location "pc - 12" and the top 8 bits are set, then we know  that  there
           is  a  function  name  embedded  immediately  preceding  this  location  and  has length "((pc[-3]) &
           0xff000000)".

       -mthumb
       -marm
           Select between generating code that  executes  in  ARM  and  Thumb  states.   The  default  for  most
           configurations  is  to  generate  code  that executes in ARM state, but the default can be changed by
           configuring GCC with the --with-mode=state configure option.

           You can also override the ARM and Thumb mode for each function by  using  the  "target("thumb")"  and
           "target("arm")" function attributes or pragmas.

       -mflip-thumb
           Switch  ARM/Thumb  modes on alternating functions.  This option is provided for regression testing of
           mixed Thumb/ARM code generation, and is not intended for ordinary use in compiling code.

       -mtpcs-frame
           Generate a stack frame that is compliant with the Thumb Procedure  Call  Standard  for  all  non-leaf
           functions.   (A  leaf  function  is  one  that  does  not  call any other functions.)  The default is
           -mno-tpcs-frame.

       -mtpcs-leaf-frame
           Generate a stack frame that is compliant  with  the  Thumb  Procedure  Call  Standard  for  all  leaf
           functions.   (A  leaf  function  is  one  that  does  not  call any other functions.)  The default is
           -mno-apcs-leaf-frame.

       -mcallee-super-interworking
           Gives all externally visible functions in the file being compiled an ARM instruction set header which
           switches to Thumb mode before executing the rest of the function.  This allows these functions to  be
           called  from  non-interworking  code.   This  option  is  not  valid  in AAPCS configurations because
           interworking is enabled by default.

       -mcaller-super-interworking
           Allows calls via function pointers (including virtual functions) to execute correctly  regardless  of
           whether  the target code has been compiled for interworking or not.  There is a small overhead in the
           cost of executing a function pointer if this option is enabled.  This option is not  valid  in  AAPCS
           configurations because interworking is enabled by default.

       -mtp=name
           Specify  the  access  model  for  the thread local storage pointer.  The valid models are soft, which
           generates calls to "__aeabi_read_tp", cp15, which fetches the thread  pointer  from  "cp15"  directly
           (supported  in  the  arm6k  architecture),  and  auto,  which  uses the best available method for the
           selected processor.  The default setting is auto.

       -mtls-dialect=dialect
           Specify the dialect to use for accessing thread local storage.  Two dialects are supported---gnu  and
           gnu2.   The  gnu  dialect selects the original GNU scheme for supporting local and global dynamic TLS
           models.  The gnu2 dialect selects the GNU descriptor scheme, which provides  better  performance  for
           shared libraries.  The GNU descriptor scheme is compatible with the original scheme, but does require
           new  assembler, linker and library support.  Initial and local exec TLS models are unaffected by this
           option and always use the original scheme.

       -mword-relocations
           Only generate absolute relocations on word-sized values  (i.e.  R_ARM_ABS32).   This  is  enabled  by
           default  on  targets (uClinux, SymbianOS) where the runtime loader imposes this restriction, and when
           -fpic or -fPIC is specified. This option conflicts with -mslow-flash-data.

       -mfix-cortex-m3-ldrd
           Some Cortex-M3 cores can cause data corruption when "ldrd" instructions with overlapping  destination
           and  base  registers  are  used.   This  option avoids generating these instructions.  This option is
           enabled by default when -mcpu=cortex-m3 is specified.

       -munaligned-access
       -mno-unaligned-access
           Enables (or disables) reading and writing of 16- and 32- bit values from addresses that are  not  16-
           or  32-  bit aligned.  By default unaligned access is disabled for all pre-ARMv6, all ARMv6-M and for
           ARMv8-M Baseline architectures, and enabled for all other architectures.  If unaligned access is  not
           enabled then words in packed data structures are accessed a byte at a time.

           The  ARM  attribute  "Tag_CPU_unaligned_access" is set in the generated object file to either true or
           false, depending upon the  setting  of  this  option.   If  unaligned  access  is  enabled  then  the
           preprocessor symbol "__ARM_FEATURE_UNALIGNED" is also defined.

       -mneon-for-64bits
           This option is deprecated and has no effect.

       -mslow-flash-data
           Assume  loading  data  from  flash  is  slower  than fetching instruction.  Therefore literal load is
           minimized for better performance.  This option is only supported when compiling for  ARMv7  M-profile
           and off by default. It conflicts with -mword-relocations.

       -masm-syntax-unified
           Assume  inline  assembler  is  using  unified asm syntax.  The default is currently off which implies
           divided syntax.  This option has no impact on Thumb2. However, this may change in future releases  of
           GCC.  Divided syntax should be considered deprecated.

       -mrestrict-it
           Restricts  generation  of IT blocks to conform to the rules of ARMv8-A.  IT blocks can only contain a
           single 16-bit instruction from a select set of instructions. This option is on by default for ARMv8-A
           Thumb mode.

       -mprint-tune-info
           Print CPU tuning information as comment  in  assembler  file.   This  is  an  option  used  only  for
           regression  testing of the compiler and not intended for ordinary use in compiling code.  This option
           is disabled by default.

       -mverbose-cost-dump
           Enable verbose cost model dumping in the debug dump files.   This  option  is  provided  for  use  in
           debugging the compiler.

       -mpure-code
           Do  not  allow  constant  data  to  be placed in code sections.  Additionally, when compiling for ELF
           object format give all text sections the ELF processor-specific section attribute "SHF_ARM_PURECODE".
           This option is only available when generating non-pic code for M-profile targets.

       -mcmse
           Generate secure code as per the "ARMv8-M  Security  Extensions:  Requirements  on  Development  Tools
           Engineering          Specification",          which          can          be         found         on
           <https://developer.arm.com/documentation/ecm0359818/latest/>.

       -mfix-cmse-cve-2021-35465
           Mitigate against a potential security issue with the "VLLDM" instruction in  some  M-profile  devices
           when  using CMSE (CVE-2021-365465).  This option is enabled by default when the option -mcpu= is used
           with "cortex-m33", "cortex-m35p" or "cortex-m55".  The  option  -mno-fix-cmse-cve-2021-35465  can  be
           used to disable the mitigation.

       -mfdpic
       -mno-fdpic
           Select  the  FDPIC  ABI,  which  uses 64-bit function descriptors to represent pointers to functions.
           When the compiler is configured for "arm-*-uclinuxfdpiceabi" targets, this option is  on  by  default
           and  implies  -fPIE  if  none  of the PIC/PIE-related options is provided.  On other targets, it only
           enables the FDPIC-specific code generation features, and  the  user  should  explicitly  provide  the
           PIC/PIE-related options as needed.

           Note  that static linking is not supported because it would still involve the dynamic linker when the
           program self-relocates.  If such behavior is acceptable, use -static and -Wl,-dynamic-linker options.

           The opposite -mno-fdpic option is useful (and required) to build the  Linux  kernel  using  the  same
           ("arm-*-uclinuxfdpiceabi") toolchain as the one used to build the userland programs.

       AVR Options

       These options are defined for AVR implementations:

       -mmcu=mcu
           Specify Atmel AVR instruction set architectures (ISA) or MCU type.

           The default for this option is avr2.

           GCC supports the following AVR devices and ISAs:

           "avr2"
               "Classic" devices with up to 8 KiB of program memory.  mcu = "attiny22", "attiny26", "at90s2313",
               "at90s2323",   "at90s2333",  "at90s2343",  "at90s4414",  "at90s4433",  "at90s4434",  "at90c8534",
               "at90s8515", "at90s8535".

           "avr25"
               "Classic" devices with up to 8 KiB of program memory and with  the  "MOVW"  instruction.   mcu  =
               "attiny13",   "attiny13a",   "attiny24",   "attiny24a",  "attiny25",  "attiny261",  "attiny261a",
               "attiny2313",  "attiny2313a",  "attiny43u",  "attiny44",  "attiny44a",  "attiny45",   "attiny48",
               "attiny441",   "attiny461",  "attiny461a",  "attiny4313",  "attiny84",  "attiny84a",  "attiny85",
               "attiny87",  "attiny88",  "attiny828",   "attiny841",   "attiny861",   "attiny861a",   "ata5272",
               "ata6616c", "at86rf401".

           "avr3"
               "Classic" devices with 16 KiB up to 64 KiB of program memory.  mcu = "at76c711", "at43usb355".

           "avr31"
               "Classic" devices with 128 KiB of program memory.  mcu = "atmega103", "at43usb320".

           "avr35"
               "Classic"  devices  with  16  KiB up to 64 KiB of program memory and with the "MOVW" instruction.
               mcu = "attiny167", "attiny1634", "atmega8u2", "atmega16u2", "atmega32u2", "ata5505",  "ata6617c",
               "ata664251", "at90usb82", "at90usb162".

           "avr4"
               "Enhanced"  devices  with  up  to  8  KiB  of  program  memory.   mcu  = "atmega48", "atmega48a",
               "atmega48p",  "atmega48pa",  "atmega48pb",  "atmega8",  "atmega8a",   "atmega8hva",   "atmega88",
               "atmega88a",  "atmega88p",  "atmega88pa",  "atmega88pb",  "atmega8515",  "atmega8535", "ata6285",
               "ata6286", "ata6289", "ata6612c", "at90pwm1", "at90pwm2", "at90pwm2b",  "at90pwm3",  "at90pwm3b",
               "at90pwm81".

           "avr5"
               "Enhanced"  devices  with  16 KiB up to 64 KiB of program memory.  mcu = "atmega16", "atmega16a",
               "atmega16hva",  "atmega16hva2",  "atmega16hvb",  "atmega16hvbrevb",  "atmega16m1",  "atmega16u4",
               "atmega161",  "atmega162",  "atmega163",  "atmega164a", "atmega164p", "atmega164pa", "atmega165",
               "atmega165a",   "atmega165p",    "atmega165pa",    "atmega168",    "atmega168a",    "atmega168p",
               "atmega168pa", "atmega168pb", "atmega169", "atmega169a", "atmega169p", "atmega169pa", "atmega32",
               "atmega32a",   "atmega32c1",   "atmega32hvb",   "atmega32hvbrevb",   "atmega32m1",  "atmega32u4",
               "atmega32u6", "atmega323", "atmega324a", "atmega324p", "atmega324pa", "atmega325",  "atmega325a",
               "atmega325p", "atmega325pa", "atmega328", "atmega328p", "atmega328pb", "atmega329", "atmega329a",
               "atmega329p",   "atmega329pa",   "atmega3250",   "atmega3250a",   "atmega3250p",  "atmega3250pa",
               "atmega3290", "atmega3290a", "atmega3290p", "atmega3290pa", "atmega406", "atmega64", "atmega64a",
               "atmega64c1",   "atmega64hve",   "atmega64hve2",   "atmega64m1",   "atmega64rfr2",   "atmega640",
               "atmega644",    "atmega644a",    "atmega644p",   "atmega644pa",   "atmega644rfr2",   "atmega645",
               "atmega645a", "atmega645p", "atmega649", "atmega649a", "atmega649p", "atmega6450", "atmega6450a",
               "atmega6450p", "atmega6490",  "atmega6490a",  "atmega6490p",  "ata5795",  "ata5790",  "ata5790n",
               "ata5791",  "ata6613c",  "ata6614q",  "ata5782",  "ata5831", "ata8210", "ata8510", "ata5702m322",
               "at90pwm161", "at90pwm216", "at90pwm316", "at90can32", "at90can64",  "at90scr100",  "at90usb646",
               "at90usb647", "at94k", "m3000".

           "avr51"
               "Enhanced"   devices   with  128  KiB  of  program  memory.   mcu  =  "atmega128",  "atmega128a",
               "atmega128rfa1",  "atmega128rfr2",  "atmega1280",  "atmega1281",   "atmega1284",   "atmega1284p",
               "atmega1284rfr2", "at90can128", "at90usb1286", "at90usb1287".

           "avr6"
               "Enhanced"  devices  with  3-byte  PC,  i.e.  with  more  than  128 KiB of program memory.  mcu =
               "atmega256rfr2", "atmega2560", "atmega2561", "atmega2564rfr2".

           "avrxmega2"
               "XMEGA" devices with more than 8 KiB and up to 64 KiB of program  memory.   mcu  =  "atxmega8e5",
               "atxmega16a4",   "atxmega16a4u",   "atxmega16c4",  "atxmega16d4",  "atxmega16e5",  "atxmega32a4",
               "atxmega32a4u", "atxmega32c3", "atxmega32c4", "atxmega32d3", "atxmega32d4", "atxmega32e5".

           "avrxmega3"
               "XMEGA" devices with up to 64 KiB of combined program memory and RAM,  and  with  program  memory
               visible  in  the  RAM  address  space.  mcu = "attiny202", "attiny204", "attiny212", "attiny214",
               "attiny402",  "attiny404",  "attiny406",  "attiny412",  "attiny414",  "attiny416",   "attiny417",
               "attiny804",  "attiny806",  "attiny807",  "attiny814",  "attiny816",  "attiny817",  "attiny1604",
               "attiny1606", "attiny1607", "attiny1614", "attiny1616", "attiny1617", "attiny3214", "attiny3216",
               "attiny3217", "atmega808", "atmega809", "atmega1608", "atmega1609",  "atmega3208",  "atmega3209",
               "atmega4808", "atmega4809".

           "avrxmega4"
               "XMEGA"  devices with more than 64 KiB and up to 128 KiB of program memory.  mcu = "atxmega64a3",
               "atxmega64a3u",  "atxmega64a4u",  "atxmega64b1",  "atxmega64b3",  "atxmega64c3",   "atxmega64d3",
               "atxmega64d4".

           "avrxmega5"
               "XMEGA" devices with more than 64 KiB and up to 128 KiB of program memory and more than 64 KiB of
               RAM.  mcu = "atxmega64a1", "atxmega64a1u".

           "avrxmega6"
               "XMEGA" devices with more than 128 KiB of program memory.  mcu = "atxmega128a3", "atxmega128a3u",
               "atxmega128b1",  "atxmega128b3",  "atxmega128c3", "atxmega128d3", "atxmega128d4", "atxmega192a3",
               "atxmega192a3u",     "atxmega192c3",     "atxmega192d3",     "atxmega256a3",     "atxmega256a3b",
               "atxmega256a3bu",     "atxmega256a3u",     "atxmega256c3",     "atxmega256d3",    "atxmega384c3",
               "atxmega384d3".

           "avrxmega7"
               "XMEGA" devices with more than 128 KiB of program memory and more than 64  KiB  of  RAM.   mcu  =
               "atxmega128a1", "atxmega128a1u", "atxmega128a4u".

           "avrtiny"
               "TINY"  Tiny  core devices with 512 B up to 4 KiB of program memory.  mcu = "attiny4", "attiny5",
               "attiny9", "attiny10", "attiny20", "attiny40".

           "avr1"
               This ISA is implemented by the minimal  AVR  core  and  supported  for  assembler  only.   mcu  =
               "attiny11", "attiny12", "attiny15", "attiny28", "at90s1200".

       -mabsdata
           Assume  that  all  data in static storage can be accessed by LDS / STS instructions.  This option has
           only an effect on  reduced  Tiny  devices  like  ATtiny40.   See  also  the  "absdata"  AVR  Variable
           Attributes,variable attribute.

       -maccumulate-args
           Accumulate  outgoing  function  arguments  and  acquire/release  the  needed stack space for outgoing
           function arguments once in function prologue/epilogue.  Without this option, outgoing  arguments  are
           pushed before calling a function and popped afterwards.

           Popping  the arguments after the function call can be expensive on AVR so that accumulating the stack
           space might lead to smaller executables because arguments need not be removed from  the  stack  after
           such a function call.

           This  option can lead to reduced code size for functions that perform several calls to functions that
           get their arguments on the stack like calls to printf-like functions.

       -mbranch-cost=cost
           Set the branch costs for conditional branch instructions to cost.  Reasonable  values  for  cost  are
           small, non-negative integers. The default branch cost is 0.

       -mcall-prologues
           Functions  prologues/epilogues  are  expanded  as  calls  to  appropriate  subroutines.  Code size is
           smaller.

       -mdouble=bits
       -mlong-double=bits
           Set the size (in bits) of the "double" or "long double" type, respectively.  Possible values for bits
           are 32 and 64.  Whether or not a specific value for bits is allowed depends on  the  "--with-double="
           and  "--with-long-double="  configure options ("https://gcc.gnu.org/install/configure.html#avr"), and
           the same applies for the default values of the options.

       -mgas-isr-prologues
           Interrupt service routines (ISRs) may  use  the  "__gcc_isr"  pseudo  instruction  supported  by  GNU
           Binutils.   If  this  option is on, the feature can still be disabled for individual ISRs by means of
           the AVR Function Attributes,,"no_gccisr" function attribute.  This feature is activated  per  default
           if  optimization  is  on  (but  not  with -Og, @pxref{Optimize Options}), and if GNU Binutils support
           PR21683 ("https://sourceware.org/PR21683").

       -mint8
           Assume "int" to be 8-bit integer.  This affects the sizes of all types: a "char" is 1 byte, an  "int"
           is  1  byte,  a "long" is 2 bytes, and "long long" is 4 bytes.  Please note that this option does not
           conform to the C standards, but it results in smaller code size.

       -mmain-is-OS_task
           Do not save registers in "main".  The effect is  the  same  like  attaching  attribute  AVR  Function
           Attributes,,"OS_task" to "main". It is activated per default if optimization is on.

       -mn-flash=num
           Assume that the flash memory has a size of num times 64 KiB.

       -mno-interrupts
           Generated code is not compatible with hardware interrupts.  Code size is smaller.

       -mrelax
           Try  to  replace  "CALL"  resp.  "JMP" instruction by the shorter "RCALL" resp. "RJMP" instruction if
           applicable.  Setting -mrelax just adds the --mlink-relax option to the assembler's command  line  and
           the --relax option to the linker's command line.

           Jump  relaxing  is performed by the linker because jump offsets are not known before code is located.
           Therefore, the assembler code generated by the compiler is the same,  but  the  instructions  in  the
           executable may differ from instructions in the assembler code.

           Relaxing  must  be  turned  on if linker stubs are needed, see the section on "EIND" and linker stubs
           below.

       -mrmw
           Assume that the device supports the Read-Modify-Write instructions "XCH", "LAC", "LAS" and "LAT".

       -mshort-calls
           Assume that "RJMP" and "RCALL" can target the whole program memory.

           This option is used internally for multilib selection.  It is not an  optimization  option,  and  you
           don't need to set it by hand.

       -msp8
           Treat the stack pointer register as an 8-bit register, i.e. assume the high byte of the stack pointer
           is zero.  In general, you don't need to set this option by hand.

           This option is used internally by the compiler to select and build multilibs for architectures "avr2"
           and  "avr25".   These  architectures  mix devices with and without "SPH".  For any setting other than
           -mmcu=avr2 or -mmcu=avr25 the compiler driver adds or removes this option from the compiler  proper's
           command  line,  because  the  compiler  then  knows  if the device or architecture has an 8-bit stack
           pointer and thus no "SPH" register or not.

       -mstrict-X
           Use address register "X" in a way proposed by the hardware.  This means that  "X"  is  only  used  in
           indirect, post-increment or pre-decrement addressing.

           Without  this  option,  the  "X"  register  may  be  used in the same way as "Y" or "Z" which then is
           emulated by additional instructions.  For example, loading a value with "X+const" addressing  with  a
           small non-negative "const < 64" to a register Rn is performed as

                   adiw r26, const   ; X += const
                   ld   <Rn>, X        ; <Rn> = *X
                   sbiw r26, const   ; X -= const

       -mtiny-stack
           Only change the lower 8 bits of the stack pointer.

       -mfract-convert-truncate
           Allow to use truncation instead of rounding towards zero for fractional fixed-point types.

       -nodevicelib
           Don't link against AVR-LibC's device specific library "lib<mcu>.a".

       -nodevicespecs
           Don't  add  -specs=device-specs/specs-mcu  to  the  compiler  driver's  command line.  The user takes
           responsibility for supplying the sub-processes  like  compiler  proper,  assembler  and  linker  with
           appropriate  command  line  options.  This means that the user has to supply her private device specs
           file by means of -specs=path-to-specs-file.  There is no more need for option -mmcu=mcu.

           This option can also serve as a replacement for the older way of specifying custom device-specs files
           that needed -B some-path to point to a directory which contains a folder named  "device-specs"  which
           contains a specs file named "specs-mcu", where mcu was specified by -mmcu=mcu.

       -Waddr-space-convert
           Warn  about  conversions  between address spaces in the case where the resulting address space is not
           contained in the incoming address space.

       -Wmisspelled-isr
           Warn if the ISR is misspelled, i.e. without __vector prefix.  Enabled by default.

       "EIND" and Devices with More Than 128 Ki Bytes of Flash

       Pointers in the implementation are 16 bits wide.  The address of a function or label  is  represented  as
       word address so that indirect jumps and calls can target any code address in the range of 64 Ki words.

       In  order  to  facilitate  indirect  jump on devices with more than 128 Ki bytes of program memory space,
       there is a special function register called "EIND" that serves as most significant  part  of  the  target
       address when "EICALL" or "EIJMP" instructions are used.

       Indirect  jumps and calls on these devices are handled as follows by the compiler and are subject to some
       limitations:

       *   The compiler never sets "EIND".

       *   The compiler uses "EIND" implicitly in "EICALL"/"EIJMP" instructions or might read "EIND" directly in
           order to emulate an indirect call/jump by means of a "RET" instruction.

       *   The compiler assumes that "EIND" never changes during the startup code or during the application.  In
           particular, "EIND" is not saved/restored in function or interrupt service routine prologue/epilogue.

       *   For  indirect  calls  to functions and computed goto, the linker generates stubs. Stubs are jump pads
           sometimes also called trampolines. Thus, the indirect call/jump jumps  to  such  a  stub.   The  stub
           contains a direct jump to the desired address.

       *   Linker  relaxation  must  be  turned  on  so  that  the  linker  generates the stubs correctly in all
           situations. See the compiler option -mrelax and the linker option --relax.  There  are  corner  cases
           where  the  linker  is supposed to generate stubs but aborts without relaxation and without a helpful
           error message.

       *   The default linker script is arranged for code with "EIND = 0".  If code is supposed to  work  for  a
           setup  with  "EIND  != 0", a custom linker script has to be used in order to place the sections whose
           name start with ".trampolines" into the segment where "EIND" points to.

       *   The startup code from libgcc never sets "EIND".  Notice that startup code is a  blend  of  code  from
           libgcc   and  AVR-LibC.   For  the  impact  of  AVR-LibC  on  "EIND",  see  the  AVR-LibC user manual
           ("http://nongnu.org/avr-libc/user-manual/").

       *   It is legitimate for user-specific startup code to set up "EIND"  early,  for  example  by  means  of
           initialization  code  located  in section ".init3". Such code runs prior to general startup code that
           initializes RAM and calls constructors, but after the bit of startup code  from  AVR-LibC  that  sets
           "EIND" to the segment where the vector table is located.

                   #include <avr/io.h>

                   static void
                   __attribute__((section(".init3"),naked,used,no_instrument_function))
                   init3_set_eind (void)
                   {
                     __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t"
                                     "out %i0,r24" :: "n" (&EIND) : "r24","memory");
                   }

           The "__trampolines_start" symbol is defined in the linker script.

       *   Stubs are generated automatically by the linker if the following two conditions are met:

           -<The address of a label is taken by means of the "gs" modifier>
               (short for generate stubs) like so:

                       LDI r24, lo8(gs(<func>))
                       LDI r25, hi8(gs(<func>))

           -<The final location of that label is in a code segment>
               outside the segment where the stubs are located.

       *   The compiler emits such "gs" modifiers for code labels in the following situations:

           -<Taking address of a function or code label.>
           -<Computed goto.>
           -<If prologue-save function is used, see -mcall-prologues>
               command-line option.

           -<Switch/case dispatch tables. If you do not want such dispatch>
               tables you can specify the -fno-jump-tables command-line option.

           -<C and C++ constructors/destructors called during startup/shutdown.>
           -<If the tools hit a "gs()" modifier explained above.>
       *   Jumping to non-symbolic addresses like so is not supported:

                   int main (void)
                   {
                       /* Call function at word address 0x2 */
                       return ((int(*)(void)) 0x2)();
                   }

           Instead,  a  stub  has to be set up, i.e. the function has to be called through a symbol ("func_4" in
           the example):

                   int main (void)
                   {
                       extern int func_4 (void);

                       /* Call function at byte address 0x4 */
                       return func_4();
                   }

           and the application be linked with -Wl,--defsym,func_4=0x4.  Alternatively, "func_4" can  be  defined
           in the linker script.

       Handling of the "RAMPD", "RAMPX", "RAMPY" and "RAMPZ" Special Function Registers

       Some AVR devices support memories larger than the 64 KiB range that can be accessed with 16-bit pointers.
       To  access  memory  locations outside this 64 KiB range, the content of a "RAMP" register is used as high
       part of the address: The "X", "Y", "Z" address  register  is  concatenated  with  the  "RAMPX",  "RAMPY",
       "RAMPZ"  special  function  register,  respectively,  to  get  a wide address. Similarly, "RAMPD" is used
       together with direct addressing.

       *   The startup code initializes the "RAMP" special function registers with zero.

       *   If a AVR Named Address Spaces,named address space other than  generic  or  "__flash"  is  used,  then
           "RAMPZ" is set as needed before the operation.

       *   If  the device supports RAM larger than 64 KiB and the compiler needs to change "RAMPZ" to accomplish
           an operation, "RAMPZ" is reset to zero after the operation.

       *   If the device comes with a specific "RAMP" register, the ISR  prologue/epilogue  saves/restores  that
           SFR and initializes it with zero in case the ISR code might (implicitly) use it.

       *   RAM  larger than 64 KiB is not supported by GCC for AVR targets.  If you use inline assembler to read
           from locations outside the 16-bit address range and change one of  the  "RAMP"  registers,  you  must
           reset it to zero after the access.

       AVR Built-in Macros

       GCC  defines  several  built-in  macros  so  that  the  user code can test for the presence or absence of
       features.  Almost any of the following built-in macros are deduced  from  device  capabilities  and  thus
       triggered by the -mmcu= command-line option.

       For even more AVR-specific built-in macros see AVR Named Address Spaces and AVR Built-in Functions.

       "__AVR_ARCH__"
           Build-in  macro that resolves to a decimal number that identifies the architecture and depends on the
           -mmcu=mcu option.  Possible values are:

           2, 25, 3, 31, 35, 4, 5, 51, 6

           for mcu="avr2", "avr25", "avr3", "avr31", "avr35", "avr4", "avr5", "avr51", "avr6",

           respectively and

           100, 102, 103, 104, 105, 106, 107

           for mcu="avrtiny", "avrxmega2",  "avrxmega3",  "avrxmega4",  "avrxmega5",  "avrxmega6",  "avrxmega7",
           respectively.   If  mcu specifies a device, this built-in macro is set accordingly. For example, with
           -mmcu=atmega8 the macro is defined to 4.

       "__AVR_Device__"
           Setting -mmcu=device defines this built-in macro which  reflects  the  device's  name.  For  example,
           -mmcu=atmega8    defines    the    built-in   macro   "__AVR_ATmega8__",   -mmcu=attiny261a   defines
           "__AVR_ATtiny261A__", etc.

           The built-in macros' names follow the scheme "__AVR_Device__" where Device is the device name as from
           the AVR user manual. The difference between Device in the built-in macro and device  in  -mmcu=device
           is that the latter is always lowercase.

           If device is not a device but only a core architecture like avr51, this macro is not defined.

       "__AVR_DEVICE_NAME__"
           Setting   -mmcu=device  defines  this  built-in  macro  to  the  device's  name.  For  example,  with
           -mmcu=atmega8 the macro is defined to "atmega8".

           If device is not a device but only a core architecture like avr51, this macro is not defined.

       "__AVR_XMEGA__"
           The device / architecture belongs to the XMEGA family of devices.

       "__AVR_HAVE_ELPM__"
           The device has the "ELPM" instruction.

       "__AVR_HAVE_ELPMX__"
           The device has the "ELPM Rn,Z" and "ELPM Rn,Z+" instructions.

       "__AVR_HAVE_MOVW__"
           The device has the "MOVW" instruction to perform 16-bit register-register moves.

       "__AVR_HAVE_LPMX__"
           The device has the "LPM Rn,Z" and "LPM Rn,Z+" instructions.

       "__AVR_HAVE_MUL__"
           The device has a hardware multiplier.

       "__AVR_HAVE_JMP_CALL__"
           The device has the "JMP" and "CALL" instructions.  This is the case for devices with more than 8  KiB
           of program memory.

       "__AVR_HAVE_EIJMP_EICALL__"
       "__AVR_3_BYTE_PC__"
           The  device  has  the "EIJMP" and "EICALL" instructions.  This is the case for devices with more than
           128 KiB of program memory.  This also means that the program counter (PC) is 3 bytes wide.

       "__AVR_2_BYTE_PC__"
           The program counter (PC) is 2 bytes wide. This is the case for devices with up to 128 KiB of  program
           memory.

       "__AVR_HAVE_8BIT_SP__"
       "__AVR_HAVE_16BIT_SP__"
           The  stack  pointer  (SP)  register is treated as 8-bit respectively 16-bit register by the compiler.
           The definition of these macros is affected by -mtiny-stack.

       "__AVR_HAVE_SPH__"
       "__AVR_SP8__"
           The device has the SPH (high part of stack pointer) special function register or has an  8-bit  stack
           pointer,  respectively.   The  definition  of  these macros is affected by -mmcu= and in the cases of
           -mmcu=avr2 and -mmcu=avr25 also by -msp8.

       "__AVR_HAVE_RAMPD__"
       "__AVR_HAVE_RAMPX__"
       "__AVR_HAVE_RAMPY__"
       "__AVR_HAVE_RAMPZ__"
           The device has the "RAMPD", "RAMPX", "RAMPY", "RAMPZ" special function register, respectively.

       "__NO_INTERRUPTS__"
           This macro reflects the -mno-interrupts command-line option.

       "__AVR_ERRATA_SKIP__"
       "__AVR_ERRATA_SKIP_JMP_CALL__"
           Some AVR devices (AT90S8515, ATmega103) must not skip  32-bit  instructions  because  of  a  hardware
           erratum.   Skip instructions are "SBRS", "SBRC", "SBIS", "SBIC" and "CPSE".  The second macro is only
           defined if "__AVR_HAVE_JMP_CALL__" is also set.

       "__AVR_ISA_RMW__"
           The device has Read-Modify-Write instructions (XCH, LAC, LAS and LAT).

       "__AVR_SFR_OFFSET__=offset"
           Instructions that can address I/O special function registers directly like "IN", "OUT",  "SBI",  etc.
           may  use a different address as if addressed by an instruction to access RAM like "LD" or "STS". This
           offset depends on the device architecture and has to be subtracted from the RAM address in  order  to
           get the respective I/O address.

       "__AVR_SHORT_CALLS__"
           The -mshort-calls command line option is set.

       "__AVR_PM_BASE_ADDRESS__=addr"
           Some  devices  support reading from flash memory by means of "LD*" instructions.  The flash memory is
           seen in the data address space at an offset of  "__AVR_PM_BASE_ADDRESS__".   If  this  macro  is  not
           defined, this feature is not available.  If defined, the address space is linear and there is no need
           to  put ".rodata" into RAM.  This is handled by the default linker description file, and is currently
           available for "avrtiny" and "avrxmega3".  Even more convenient, there  is  no  need  to  use  address
           spaces like "__flash" or features like attribute "progmem" and "pgm_read_*".

       "__WITH_AVRLIBC__"
           The  compiler  is  configured  to  be  used together with AVR-Libc.  See the --with-avrlibc configure
           option.

       "__HAVE_DOUBLE_MULTILIB__"
           Defined if -mdouble= acts as a multilib option.

       "__HAVE_DOUBLE32__"
       "__HAVE_DOUBLE64__"
           Defined if the compiler supports 32-bit double resp. 64-bit double.  The actual layout  is  specified
           by option -mdouble=.

       "__DEFAULT_DOUBLE__"
           The  size  in bits of "double" if -mdouble= is not set.  To test the layout of "double" in a program,
           use the built-in macro "__SIZEOF_DOUBLE__".

       "__HAVE_LONG_DOUBLE32__"
       "__HAVE_LONG_DOUBLE64__"
       "__HAVE_LONG_DOUBLE_MULTILIB__"
       "__DEFAULT_LONG_DOUBLE__"
           Same as above, but for "long double" instead of "double".

       "__WITH_DOUBLE_COMPARISON__"
           Reflects        the         "--with-double-comparison={tristate|bool|libf7}"         configure option
           ("https://gcc.gnu.org/install/configure.html#avr") and is defined to 2 or 3.

       "__WITH_LIBF7_LIBGCC__"
       "__WITH_LIBF7_MATH__"
       "__WITH_LIBF7_MATH_SYMBOLS__"
           Reflects           the           "--with-libf7={libgcc|math|math-symbols}"           configure option
           ("https://gcc.gnu.org/install/configure.html#avr").

       Blackfin Options

       -mcpu=cpu[-sirevision]
           Specifies the name of the target Blackfin processor.  Currently, cpu can  be  one  of  bf512,  bf514,
           bf516,  bf518,  bf522,  bf523,  bf524, bf525, bf526, bf527, bf531, bf532, bf533, bf534, bf536, bf537,
           bf538, bf539, bf542, bf544, bf547, bf548, bf549,  bf542m,  bf544m,  bf547m,  bf548m,  bf549m,  bf561,
           bf592.

           The  optional  sirevision  specifies  the  silicon  revision  of  the target Blackfin processor.  Any
           workarounds available for the targeted silicon revision are  enabled.   If  sirevision  is  none,  no
           workarounds  are  enabled.   If  sirevision  is  any,  all workarounds for the targeted processor are
           enabled.  The "__SILICON_REVISION__" macro is defined to  two  hexadecimal  digits  representing  the
           major  and  minor numbers in the silicon revision.  If sirevision is none, the "__SILICON_REVISION__"
           is not defined.  If sirevision is any, the "__SILICON_REVISION__" is defined to be 0xffff.   If  this
           optional  sirevision  is  not  used,  GCC  assumes  the latest known silicon revision of the targeted
           Blackfin processor.

           GCC defines a preprocessor macro for the specified cpu.  For  the  bfin-elf  toolchain,  this  option
           causes the hardware BSP provided by libgloss to be linked in if -msim is not given.

           Without this option, bf532 is used as the processor by default.

           Note that support for bf561 is incomplete.  For bf561, only the preprocessor macro is defined.

       -msim
           Specifies  that  the program will be run on the simulator.  This causes the simulator BSP provided by
           libgloss to be linked in.  This option  has  effect  only  for  bfin-elf  toolchain.   Certain  other
           options, such as -mid-shared-library and -mfdpic, imply -msim.

       -momit-leaf-frame-pointer
           Don't keep the frame pointer in a register for leaf functions.  This avoids the instructions to save,
           set up and restore frame pointers and makes an extra register available in leaf functions.

       -mspecld-anomaly
           When  enabled,  the compiler ensures that the generated code does not contain speculative loads after
           jump instructions. If this option is used, "__WORKAROUND_SPECULATIVE_LOADS" is defined.

       -mno-specld-anomaly
           Don't generate extra code to prevent speculative loads from occurring.

       -mcsync-anomaly
           When enabled, the compiler  ensures  that  the  generated  code  does  not  contain  CSYNC  or  SSYNC
           instructions    too    soon    after    conditional    branches.     If    this   option   is   used,
           "__WORKAROUND_SPECULATIVE_SYNCS" is defined.

       -mno-csync-anomaly
           Don't generate extra code to prevent CSYNC or SSYNC instructions from  occurring  too  soon  after  a
           conditional branch.

       -mlow64k
           When  enabled,  the  compiler is free to take advantage of the knowledge that the entire program fits
           into the low 64k of memory.

       -mno-low64k
           Assume that the program is arbitrarily large.  This is the default.

       -mstack-check-l1
           Do stack checking using information placed into L1 scratchpad memory by the uClinux kernel.

       -mid-shared-library
           Generate code that supports shared libraries via the library ID method.  This allows for  execute  in
           place  and shared libraries in an environment without virtual memory management.  This option implies
           -fPIC.  With a bfin-elf target, this option implies -msim.

       -mno-id-shared-library
           Generate code that doesn't assume ID-based shared libraries are being used.  This is the default.

       -mleaf-id-shared-library
           Generate code that supports shared libraries via the library ID method, but assumes that this library
           or executable won't link against any other ID shared libraries.  That  allows  the  compiler  to  use
           faster code for jumps and calls.

       -mno-leaf-id-shared-library
           Do  not  assume that the code being compiled won't link against any ID shared libraries.  Slower code
           is generated for jump and call insns.

       -mshared-library-id=n
           Specifies the identification number of the ID-based shared  library  being  compiled.   Specifying  a
           value  of 0 generates more compact code; specifying other values forces the allocation of that number
           to the current library but is no more space- or time-efficient than omitting this option.

       -msep-data
           Generate code that allows the data segment to be located in a different area of memory from the  text
           segment.   This  allows  for  execute in place in an environment without virtual memory management by
           eliminating relocations against the text section.

       -mno-sep-data
           Generate code that assumes that the data segment follows the text segment.  This is the default.

       -mlong-calls
       -mno-long-calls
           Tells the compiler to perform function calls by first loading the address  of  the  function  into  a
           register and then performing a subroutine call on this register.  This switch is needed if the target
           function  lies  outside of the 24-bit addressing range of the offset-based version of subroutine call
           instruction.

           This feature is not enabled by default.  Specifying -mno-long-calls restores  the  default  behavior.
           Note  these  switches  have no effect on how the compiler generates code to handle function calls via
           function pointers.

       -mfast-fp
           Link with the fast floating-point library. This library  relaxes  some  of  the  IEEE  floating-point
           standard's rules for checking inputs against Not-a-Number (NAN), in the interest of performance.

       -minline-plt
           Enable inlining of PLT entries in function calls to functions that are not known to bind locally.  It
           has no effect without -mfdpic.

       -mmulticore
           Build  a  standalone  application for multicore Blackfin processors.  This option causes proper start
           files and link scripts supporting multicore to be used, and defines the macro "__BFIN_MULTICORE".  It
           can only be used with -mcpu=bf561[-sirevision].

           This option can  be  used  with  -mcorea  or  -mcoreb,  which  selects  the  one-application-per-core
           programming model.  Without -mcorea or -mcoreb, the single-application/dual-core programming model is
           used. In this model, the main function of Core B should be named as "coreb_main".

           If this option is not used, the single-core application programming model is used.

       -mcorea
           Build  a  standalone  application  for  Core  A  of  BF561  when  using  the one-application-per-core
           programming model. Proper start files and link scripts are used to support  Core  A,  and  the  macro
           "__BFIN_COREA" is defined.  This option can only be used in conjunction with -mmulticore.

       -mcoreb
           Build  a  standalone  application  for  Core  B  of  BF561  when  using  the one-application-per-core
           programming model. Proper start files and link scripts are used to support  Core  B,  and  the  macro
           "__BFIN_COREB"  is  defined. When this option is used, "coreb_main" should be used instead of "main".
           This option can only be used in conjunction with -mmulticore.

       -msdram
           Build a standalone application for SDRAM. Proper start files and link scripts are  used  to  put  the
           application  into SDRAM, and the macro "__BFIN_SDRAM" is defined.  The loader should initialize SDRAM
           before loading the application.

       -micplb
           Assume that ICPLBs are enabled at run time.  This has an effect on certain anomaly workarounds.   For
           Linux  targets,  the default is to assume ICPLBs are enabled; for standalone applications the default
           is off.

       C6X Options

       -march=name
           This specifies the name of the target architecture.  GCC uses this name to  determine  what  kind  of
           instructions  it  can  emit when generating assembly code.  Permissible names are: c62x, c64x, c64x+,
           c67x, c67x+, c674x.

       -mbig-endian
           Generate code for a big-endian target.

       -mlittle-endian
           Generate code for a little-endian target.  This is the default.

       -msim
           Choose startup files and linker script suitable for the simulator.

       -msdata=default
           Put small global and static data in the ".neardata" section, which is pointed to by  register  "B14".
           Put  small  uninitialized  global  and  static  data  in the ".bss" section, which is adjacent to the
           ".neardata" section.  Put small  read-only  data  into  the  ".rodata"  section.   The  corresponding
           sections used for large pieces of data are ".fardata", ".far" and ".const".

       -msdata=all
           Put  all  data, not just small objects, into the sections reserved for small data, and use addressing
           relative to the "B14" register to access them.

       -msdata=none
           Make no use of the sections reserved for small data, and use absolute addresses to access  all  data.
           Put  all  initialized global and static data in the ".fardata" section, and all uninitialized data in
           the ".far" section.  Put all constant data into the ".const" section.

       CRIS Options

       These options are defined specifically for the CRIS ports.

       -march=architecture-type
       -mcpu=architecture-type
           Generate code for the specified architecture.  The choices for architecture-type are v3, v8  and  v10
           for respectively ETRAX 4, ETRAX 100, and ETRAX 100 LX.  Default is v0.

       -mtune=architecture-type
           Tune  to architecture-type everything applicable about the generated code, except for the ABI and the
           set  of  available  instructions.   The  choices  for  architecture-type  are   the   same   as   for
           -march=architecture-type.

       -mmax-stack-frame=n
           Warn when the stack frame of a function exceeds n bytes.

       -metrax4
       -metrax100
           The options -metrax4 and -metrax100 are synonyms for -march=v3 and -march=v8 respectively.

       -mmul-bug-workaround
       -mno-mul-bug-workaround
           Work around a bug in the "muls" and "mulu" instructions for CPU models where it applies.  This option
           is active by default.

       -mpdebug
           Enable  CRIS-specific  verbose  debug-related information in the assembly code.  This option also has
           the effect of turning off the #NO_APP formatted-code indicator to the assembler at the  beginning  of
           the assembly file.

       -mcc-init
           Do  not  use  condition-code  results  from  previous  instruction;  always  emit  compare  and  test
           instructions before use of condition codes.

       -mno-side-effects
           Do not emit instructions with side effects in addressing modes other than post-increment.

       -mstack-align
       -mno-stack-align
       -mdata-align
       -mno-data-align
       -mconst-align
       -mno-const-align
           These options (no- options) arrange (eliminate arrangements) for the stack frame, individual data and
           constants to be aligned for the maximum single data access  size  for  the  chosen  CPU  model.   The
           default is to arrange for 32-bit alignment.  ABI details such as structure layout are not affected by
           these options.

       -m32-bit
       -m16-bit
       -m8-bit
           Similar  to  the  stack-  data- and const-align options above, these options arrange for stack frame,
           writable data and constants to all be 32-bit,  16-bit  or  8-bit  aligned.   The  default  is  32-bit
           alignment.

       -mno-prologue-epilogue
       -mprologue-epilogue
           With  -mno-prologue-epilogue,  the normal function prologue and epilogue which set up the stack frame
           are omitted and no return instructions or return sequences are  generated  in  the  code.   Use  this
           option only together with visual inspection of the compiled code: no warnings or errors are generated
           when call-saved registers must be saved, or storage for local variables needs to be allocated.

       -melf
           Legacy no-op option.

       -sim
           This option arranges to link with input-output functions from a simulator library.  Code, initialized
           data and zero-initialized data are allocated consecutively.

       -sim2
           Like -sim, but pass linker options to locate initialized data at 0x40000000 and zero-initialized data
           at 0x80000000.

       CR16 Options

       These options are defined specifically for the CR16 ports.

       -mmac
           Enable the use of multiply-accumulate instructions. Disabled by default.

       -mcr16cplus
       -mcr16c
           Generate code for CR16C or CR16C+ architecture. CR16C+ architecture is default.

       -msim
           Links the library libsim.a which is in compatible with simulator. Applicable to ELF compiler only.

       -mint32
           Choose integer type as 32-bit wide.

       -mbit-ops
           Generates "sbit"/"cbit" instructions for bit manipulations.

       -mdata-model=model
           Choose  a data model. The choices for model are near, far or medium. medium is default.  However, far
           is not valid with -mcr16c, as the CR16C architecture does not support the far data model.

       C-SKY Options

       GCC supports these options when compiling for C-SKY V2 processors.

       -march=arch
           Specify the C-SKY target architecture.  Valid values for arch are: ck801, ck802,  ck803,  ck807,  and
           ck810.  The default is ck810.

       -mcpu=cpu
           Specify  the C-SKY target processor.  Valid values for cpu are: ck801, ck801t, ck802, ck802t, ck802j,
           ck803, ck803h, ck803t,  ck803ht,  ck803f,  ck803fh,  ck803e,  ck803eh,  ck803et,  ck803eht,  ck803ef,
           ck803efh,  ck803ft, ck803eft, ck803efht, ck803r1, ck803hr1, ck803tr1, ck803htr1, ck803fr1, ck803fhr1,
           ck803er1,  ck803ehr1,  ck803etr1,   ck803ehtr1,   ck803efr1,   ck803efhr1,   ck803ftr1,   ck803eftr1,
           ck803efhtr1,  ck803s, ck803st, ck803se, ck803sf, ck803sef, ck803seft, ck807e, ck807ef, ck807, ck807f,
           ck810e, ck810et, ck810ef, ck810eft, ck810, ck810v, ck810f, ck810t,  ck810fv,  ck810tv,  ck810ft,  and
           ck810ftv.

       -mbig-endian
       -EB
       -mlittle-endian
       -EL Select big- or little-endian code.  The default is little-endian.

       -mfloat-abi=name
           Specifies which floating-point ABI to use.  Permissible values are: soft, softfp and hard.

           Specifying soft causes GCC to generate output containing library calls for floating-point operations.
           softfp  allows  the generation of code using hardware floating-point instructions, but still uses the
           soft-float calling conventions.  hard allows generation of floating-point instructions and uses  FPU-
           specific calling conventions.

           The  default  depends  on the specific target configuration.  Note that the hard-float and soft-float
           ABIs are not link-compatible; you must compile your entire program with the same ABI, and link with a
           compatible set of libraries.

       -mhard-float
       -msoft-float
           Select hardware or software floating-point implementations.  The default is soft float.

       -mdouble-float
       -mno-double-float
           When -mhard-float is in effect, enable generation of double-precision float  instructions.   This  is
           the default except when compiling for CK803.

       -mfdivdu
       -mno-fdivdu
           When  -mhard-float  is in effect, enable generation of "frecipd", "fsqrtd", and "fdivd" instructions.
           This is the default except when compiling for CK803.

       -mfpu=fpu
           Select the floating-point processor.  This option can only be used with -mhard-float.  Values for fpu
           are fpv2_sf (equivalent to -mno-double-float  -mno-fdivdu),  fpv2  (-mdouble-float  -mno-divdu),  and
           fpv2_divd (-mdouble-float -mdivdu).

       -melrw
       -mno-elrw
           Enable the extended "lrw" instruction.  This option defaults to on for CK801 and off otherwise.

       -mistack
       -mno-istack
           Enable interrupt stack instructions; the default is off.

           The -mistack option is required to handle the "interrupt" and "isr" function attributes.

       -mmp
           Enable multiprocessor instructions; the default is off.

       -mcp
           Enable coprocessor instructions; the default is off.

       -mcache
           Enable coprocessor instructions; the default is off.

       -msecurity
           Enable C-SKY security instructions; the default is off.

       -mtrust
           Enable C-SKY trust instructions; the default is off.

       -mdsp
       -medsp
       -mvdsp
           Enable  C-SKY  DSP,  Enhanced  DSP,  or  Vector DSP instructions, respectively.  All of these options
           default to off.

       -mdiv
       -mno-div
           Generate divide instructions.  Default is off.

       -msmart
       -mno-smart
           Generate code for Smart Mode, using only registers numbered 0-7 to allow use of 16-bit  instructions.
           This  option  is  ignored  for  CK801  where this is the required behavior, and it defaults to on for
           CK802.  For other targets, the default is off.

       -mhigh-registers
       -mno-high-registers
           Generate code using the high registers numbered 16-31.  This option is not supported on CK801, CK802,
           or CK803, and is enabled by default for other processors.

       -manchor
       -mno-anchor
           Generate code using global anchor symbol addresses.

       -mpushpop
       -mno-pushpop
           Generate code using "push" and "pop" instructions.  This option defaults to on.

       -mmultiple-stld
       -mstm
       -mno-multiple-stld
       -mno-stm
           Generate code using "stm" and "ldm" instructions.  This  option  isn't  supported  on  CK801  but  is
           enabled by default on other processors.

       -mconstpool
       -mno-constpool
           Create  constant  pools in the compiler instead of deferring it to the assembler.  This option is the
           default and required for correct code generation on  CK801  and  CK802,  and  is  optional  on  other
           processors.

       -mstack-size
       -mno-stack-size
           Emit ".stack_size" directives for each function in the assembly output.  This option defaults to off.

       -mccrt
       -mno-ccrt
           Generate code for the C-SKY compiler runtime instead of libgcc.  This option defaults to off.

       -mbranch-cost=n
           Set the branch costs to roughly "n" instructions.  The default is 1.

       -msched-prolog
       -mno-sched-prolog
           Permit  scheduling of function prologue and epilogue sequences.  Using this option can result in code
           that is not compliant with the C-SKY V2 ABI prologue requirements and  that  cannot  be  debugged  or
           backtraced.  It is disabled by default.

       -msim
           Links the library libsemi.a which is in compatible with simulator. Applicable to ELF compiler only.

       Darwin Options

       These options are defined for all architectures running the Darwin operating system.

       FSF  GCC  on  Darwin  does  not  create  "fat"  object  files;  it  creates an object file for the single
       architecture that GCC was built to target.  Apple's GCC on Darwin does create  "fat"  files  if  multiple
       -arch  options  are  used;  it  does  so by running the compiler or linker multiple times and joining the
       results together with lipo.

       The subtype of the file created (like ppc7400 or ppc970 or i686) is determined by the flags that  specify
       the  ISA  that  GCC  is targeting, like -mcpu or -march.  The -force_cpusubtype_ALL option can be used to
       override this.

       The Darwin tools vary in their behavior when presented with an ISA mismatch.   The  assembler,  as,  only
       permits  instructions  to  be  used  that  are valid for the subtype of the file it is generating, so you
       cannot  put  64-bit  instructions  in  a  ppc750  object  file.   The  linker   for   shared   libraries,
       /usr/bin/libtool,  fails  and prints an error if asked to create a shared library with a less restrictive
       subtype than its input files (for instance, trying to put a ppc970 object file  in  a  ppc7400  library).
       The  linker  for executables, ld, quietly gives the executable the most restrictive subtype of any of its
       input files.

       -Fdir
           Add the framework directory dir to the head of the list of directories  to  be  searched  for  header
           files.   These  directories  are  interleaved with those specified by -I options and are scanned in a
           left-to-right order.

           A framework directory is a directory with frameworks in it.   A  framework  is  a  directory  with  a
           Headers  and/or  PrivateHeaders directory contained directly in it that ends in .framework.  The name
           of a framework is the name of this directory excluding the .framework.  Headers associated  with  the
           framework  are  found  in  one  of  those  two  directories,  with  Headers  being searched first.  A
           subframework is a framework directory that is in a framework's  Frameworks  directory.   Includes  of
           subframework headers can only appear in a header of a framework that contains the subframework, or in
           a  sibling  subframework header.  Two subframeworks are siblings if they occur in the same framework.
           A subframework should not have the same name as a framework; a warning is issued if this is violated.
           Currently a subframework cannot have subframeworks; in the future, the mechanism may be  extended  to
           support   this.    The   standard   frameworks   can   be  found  in  /System/Library/Frameworks  and
           /Library/Frameworks.  An example include looks like "#include <Framework/header.h>", where  Framework
           denotes the name of the framework and header.h is found in the PrivateHeaders or Headers directory.

       -iframeworkdir
           Like  -F  except  the directory is a treated as a system directory.  The main difference between this
           -iframework and -F is that with -iframework the compiler does not  warn  about  constructs  contained
           within header files found via dir.  This option is valid only for the C family of languages.

       -gused
           Emit  debugging  information  for  symbols  that  are used.  For stabs debugging format, this enables
           -feliminate-unused-debug-symbols.  This is by default ON.

       -gfull
           Emit debugging information for all symbols and types.

       -mmacosx-version-min=version
           The earliest version of MacOS X that this executable will run  on  is  version.   Typical  values  of
           version include 10.1, 10.2, and 10.3.9.

           If the compiler was built to use the system's headers by default, then the default for this option is
           the  system  version  on which the compiler is running, otherwise the default is to make choices that
           are compatible with as many systems and code bases as possible.

       -mkernel
           Enable kernel development mode.  The -mkernel option sets -static, -fno-common,  -fno-use-cxa-atexit,
           -fno-exceptions,  -fno-non-call-exceptions,  -fapple-kext,  -fno-weak and -fno-rtti where applicable.
           This mode also sets -mno-altivec, -msoft-float, -fno-builtin and -mlong-branch for PowerPC targets.

       -mone-byte-bool
           Override the defaults for "bool" so that "sizeof(bool)==1".  By  default  "sizeof(bool)"  is  4  when
           compiling  for  Darwin/PowerPC  and  1 when compiling for Darwin/x86, so this option has no effect on
           x86.

           Warning: The -mone-byte-bool switch causes GCC to generate code that is not  binary  compatible  with
           code generated without that switch.  Using this switch may require recompiling all other modules in a
           program, including system libraries.  Use this switch to conform to a non-default data model.

       -mfix-and-continue
       -ffix-and-continue
       -findirect-data
           Generate  code  suitable for fast turnaround development, such as to allow GDB to dynamically load .o
           files into  already-running  programs.   -findirect-data  and  -ffix-and-continue  are  provided  for
           backwards compatibility.

       -all_load
           Loads all members of static archive libraries.  See man ld(1) for more information.

       -arch_errors_fatal
           Cause the errors having to do with files that have the wrong architecture to be fatal.

       -bind_at_load
           Causes  the  output file to be marked such that the dynamic linker will bind all undefined references
           when the file is loaded or launched.

       -bundle
           Produce a Mach-o bundle format file.  See man ld(1) for more information.

       -bundle_loader executable
           This option specifies the executable that will load the build output  file  being  linked.   See  man
           ld(1) for more information.

       -dynamiclib
           When  passed this option, GCC produces a dynamic library instead of an executable when linking, using
           the Darwin libtool command.

       -force_cpusubtype_ALL
           This causes GCC's output file to have the ALL subtype, instead of one  controlled  by  the  -mcpu  or
           -march option.

       -allowable_client  client_name
       -client_name
       -compatibility_version
       -current_version
       -dead_strip
       -dependency-file
       -dylib_file
       -dylinker_install_name
       -dynamic
       -exported_symbols_list
       -filelist
       -flat_namespace
       -force_flat_namespace
       -headerpad_max_install_names
       -image_base
       -init
       -install_name
       -keep_private_externs
       -multi_module
       -multiply_defined
       -multiply_defined_unused
       -noall_load
       -no_dead_strip_inits_and_terms
       -nofixprebinding
       -nomultidefs
       -noprebind
       -noseglinkedit
       -pagezero_size
       -prebind
       -prebind_all_twolevel_modules
       -private_bundle
       -read_only_relocs
       -sectalign
       -sectobjectsymbols
       -whyload
       -seg1addr
       -sectcreate
       -sectobjectsymbols
       -sectorder
       -segaddr
       -segs_read_only_addr
       -segs_read_write_addr
       -seg_addr_table
       -seg_addr_table_filename
       -seglinkedit
       -segprot
       -segs_read_only_addr
       -segs_read_write_addr
       -single_module
       -static
       -sub_library
       -sub_umbrella
       -twolevel_namespace
       -umbrella
       -undefined
       -unexported_symbols_list
       -weak_reference_mismatches
       -whatsloaded
           These options are passed to the Darwin linker.  The Darwin linker man page describes them in detail.

       DEC Alpha Options

       These -m options are defined for the DEC Alpha implementations:

       -mno-soft-float
       -msoft-float
           Use  (do  not  use)  the  hardware  floating-point  instructions for floating-point operations.  When
           -msoft-float is specified, functions in libgcc.a  are  used  to  perform  floating-point  operations.
           Unless  they are replaced by routines that emulate the floating-point operations, or compiled in such
           a way as to call such emulations routines, these routines issue floating-point operations.    If  you
           are  compiling  for  an  Alpha without floating-point operations, you must ensure that the library is
           built so as not to call them.

           Note that Alpha implementations without floating-point operations are required to have floating-point
           registers.

       -mfp-reg
       -mno-fp-regs
           Generate code that uses (does  not  use)  the  floating-point  register  set.   -mno-fp-regs  implies
           -msoft-float.   If the floating-point register set is not used, floating-point operands are passed in
           integer registers as if they were integers and floating-point results are passed  in  $0  instead  of
           $f0.   This  is  a  non-standard  calling sequence, so any function with a floating-point argument or
           return value called by code compiled with -mno-fp-regs must also be compiled with that option.

           A typical use of this option is building a kernel that does not use, and  hence  need  not  save  and
           restore, any floating-point registers.

       -mieee
           The  Alpha  architecture implements floating-point hardware optimized for maximum performance.  It is
           mostly compliant with the IEEE floating-point  standard.   However,  for  full  compliance,  software
           assistance  is  required.   This  option  generates  code  fully  IEEE-compliant code except that the
           inexact-flag is not maintained (see below).  If this option is  turned  on,  the  preprocessor  macro
           "_IEEE_FP"  is  defined  during  compilation.   The  resulting  code is less efficient but is able to
           correctly support  denormalized  numbers  and  exceptional  IEEE  values  such  as  not-a-number  and
           plus/minus infinity.  Other Alpha compilers call this option -ieee_with_no_inexact.

       -mieee-with-inexact
           This  is like -mieee except the generated code also maintains the IEEE inexact-flag.  Turning on this
           option causes the generated code to implement fully-compliant IEEE math.  In addition to  "_IEEE_FP",
           "_IEEE_FP_EXACT"  is  defined  as  a preprocessor macro.  On some Alpha implementations the resulting
           code may execute significantly slower than the code generated by default.  Since there is very little
           code that depends on the inexact-flag, you should normally not  specify  this  option.   Other  Alpha
           compilers call this option -ieee_with_inexact.

       -mfp-trap-mode=trap-mode
           This  option controls what floating-point related traps are enabled.  Other Alpha compilers call this
           option -fptm trap-mode.  The trap mode can be set to one of four values:

           n   This is the default (normal) setting.  The only traps that are enabled are the ones  that  cannot
               be disabled in software (e.g., division by zero trap).

           u   In addition to the traps enabled by n, underflow traps are enabled as well.

           su  Like  u,  but  the  instructions  are  marked  to  be  safe  for  software  completion (see Alpha
               architecture manual for details).

           sui Like su, but inexact traps are enabled as well.

       -mfp-rounding-mode=rounding-mode
           Selects the IEEE rounding mode.  Other Alpha compilers call this  option  -fprm  rounding-mode.   The
           rounding-mode can be one of:

           n   Normal IEEE rounding mode.  Floating-point numbers are rounded towards the nearest machine number
               or towards the even machine number in case of a tie.

           m   Round towards minus infinity.

           c   Chopped rounding mode.  Floating-point numbers are rounded towards zero.

           d   Dynamic  rounding  mode.   A  field  in  the  floating-point  control  register  (fpcr, see Alpha
               architecture reference manual) controls the rounding mode in effect.  The C  library  initializes
               this register for rounding towards plus infinity.  Thus, unless your program modifies the fpcr, d
               corresponds to round towards plus infinity.

       -mtrap-precision=trap-precision
           In  the  Alpha  architecture,  floating-point  traps  are  imprecise.   This  means  without software
           assistance it is impossible to recover from a floating trap and program execution normally  needs  to
           be  terminated.   GCC can generate code that can assist operating system trap handlers in determining
           the exact location  that  caused  a  floating-point  trap.   Depending  on  the  requirements  of  an
           application, different levels of precisions can be selected:

           p   Program  precision.   This option is the default and means a trap handler can only identify which
               program caused a floating-point exception.

           f   Function precision.  The trap handler can determine the function  that  caused  a  floating-point
               exception.

           i   Instruction  precision.   The  trap  handler  can  determine  the exact instruction that caused a
               floating-point exception.

           Other Alpha compilers provide the equivalent options called -scope_safe and -resumption_safe.

       -mieee-conformant
           This option marks the generated code as IEEE conformant.  You must not use  this  option  unless  you
           also  specify -mtrap-precision=i and either -mfp-trap-mode=su or -mfp-trap-mode=sui.  Its only effect
           is to emit the line .eflag 48 in the function prologue of the generated assembly file.

       -mbuild-constants
           Normally GCC examines a 32- or 64-bit integer constant to see if it can  construct  it  from  smaller
           constants  in  two  or  three  instructions.   If it cannot, it outputs the constant as a literal and
           generates code to load it from the data segment at run time.

           Use this option to require GCC to construct all integer constants using code, even if it  takes  more
           instructions (the maximum is six).

           You  typically use this option to build a shared library dynamic loader.  Itself a shared library, it
           must relocate itself in memory before it can find  the  variables  and  constants  in  its  own  data
           segment.

       -mbwx
       -mno-bwx
       -mcix
       -mno-cix
       -mfix
       -mno-fix
       -mmax
       -mno-max
           Indicate whether GCC should generate code to use the optional BWX, CIX, FIX and MAX instruction sets.
           The  default  is to use the instruction sets supported by the CPU type specified via -mcpu= option or
           that of the CPU on which GCC was built if none is specified.

       -mfloat-vax
       -mfloat-ieee
           Generate code that uses (does not use) VAX F and G floating-point arithmetic instead of  IEEE  single
           and double precision.

       -mexplicit-relocs
       -mno-explicit-relocs
           Older  Alpha  assemblers  provided no way to generate symbol relocations except via assembler macros.
           Use of these macros does not allow optimal instruction scheduling.  GNU binutils as of  version  2.12
           supports  a  new syntax that allows the compiler to explicitly mark which relocations should apply to
           which instructions.  This option is mostly useful for debugging, as GCC detects the  capabilities  of
           the assembler when it is built and sets the default accordingly.

       -msmall-data
       -mlarge-data
           When  -mexplicit-relocs  is  in  effect,  static  data is accessed via gp-relative relocations.  When
           -msmall-data is used, objects 8 bytes long or smaller are placed in a small data area  (the  ".sdata"
           and  ".sbss"  sections) and are accessed via 16-bit relocations off of the $gp register.  This limits
           the size of the small data area to 64KB, but allows the variables  to  be  directly  accessed  via  a
           single instruction.

           The  default is -mlarge-data.  With this option the data area is limited to just below 2GB.  Programs
           that require more than 2GB of data must use "malloc" or "mmap" to  allocate  the  data  in  the  heap
           instead of in the program's data segment.

           When generating code for shared libraries, -fpic implies -msmall-data and -fPIC implies -mlarge-data.

       -msmall-text
       -mlarge-text
           When  -msmall-text  is  used,  the  compiler  assumes  that the code of the entire program (or shared
           library) fits in 4MB, and is thus reachable with a branch instruction.  When  -msmall-data  is  used,
           the  compiler  can assume that all local symbols share the same $gp value, and thus reduce the number
           of instructions required for a function call from 4 to 1.

           The default is -mlarge-text.

       -mcpu=cpu_type
           Set the instruction set and instruction scheduling parameters for machine  type  cpu_type.   You  can
           specify  either  the  EV  style  name  or  the  corresponding  chip  number.  GCC supports scheduling
           parameters for the EV4, EV5 and EV6 family of processors and  chooses  the  default  values  for  the
           instruction set from the processor you specify.  If you do not specify a processor type, GCC defaults
           to the processor on which the compiler was built.

           Supported values for cpu_type are

           ev4
           ev45
           21064
               Schedules as an EV4 and has no instruction set extensions.

           ev5
           21164
               Schedules as an EV5 and has no instruction set extensions.

           ev56
           21164a
               Schedules as an EV5 and supports the BWX extension.

           pca56
           21164pc
           21164PC
               Schedules as an EV5 and supports the BWX and MAX extensions.

           ev6
           21264
               Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.

           ev67
           21264a
               Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.

           Native  toolchains  also support the value native, which selects the best architecture option for the
           host processor.  -mcpu=native has no effect if GCC does not recognize the processor.

       -mtune=cpu_type
           Set only the instruction scheduling parameters for machine type cpu_type.  The instruction set is not
           changed.

           Native toolchains also support the value native, which selects the best architecture option  for  the
           host processor.  -mtune=native has no effect if GCC does not recognize the processor.

       -mmemory-latency=time
           Sets  the  latency  the  scheduler  should  assume  for  typical  memory  references  as  seen by the
           application.  This number is highly dependent on the memory access patterns used by  the  application
           and the size of the external cache on the machine.

           Valid options for time are

           number
               A decimal number representing clock cycles.

           L1
           L2
           L3
           main
               The  compiler  contains  estimates of the number of clock cycles for "typical" EV4 & EV5 hardware
               for the Level 1, 2 & 3 caches (also called Dcache, Scache,  and  Bcache),  as  well  as  to  main
               memory.  Note that L3 is only valid for EV5.

       eBPF Options

       -mframe-limit=bytes
           This  specifies the hard limit for frame sizes, in bytes.  Currently, the value that can be specified
           should be less than or equal to 32767.  Defaults to whatever limit is imposed by the version  of  the
           Linux kernel targeted.

       -mkernel=version
           This  specifies  the minimum version of the kernel that will run the compiled program.  GCC uses this
           version to determine which instructions to use,  what  kernel  helpers  to  allow,  etc.   Currently,
           version can be one of 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 4.10, 4.11, 4.12, 4.13, 4.14,
           4.15, 4.16, 4.17, 4.18, 4.19, 4.20, 5.0, 5.1, 5.2, latest and native.

       -mbig-endian
           Generate code for a big-endian target.

       -mlittle-endian
           Generate code for a little-endian target.  This is the default.

       -mxbpf
           Generate  code  for an expanded version of BPF, which relaxes some of the restrictions imposed by the
           BPF architecture:

           -<Save and restore callee-saved registers at function entry and>
               exit, respectively.

       FR30 Options

       These options are defined specifically for the FR30 port.

       -msmall-model
           Use the small address space model.  This can produce smaller  code,  but  it  does  assume  that  all
           symbolic values and addresses fit into a 20-bit range.

       -mno-lsim
           Assume  that  runtime  support  has  been  provided  and so there is no need to include the simulator
           library (libsim.a) on the linker command line.

       FT32 Options

       These options are defined specifically for the FT32 port.

       -msim
           Specifies that the program will be run on the simulator.  This causes an  alternate  runtime  startup
           and  library  to  be  linked.  You must not use this option when generating programs that will run on
           real hardware; you must provide your own runtime library for whatever I/O functions are needed.

       -mlra
           Enable Local Register Allocation.  This is still experimental for FT32, so by  default  the  compiler
           uses standard reload.

       -mnodiv
           Do not use div and mod instructions.

       -mft32b
           Enable use of the extended instructions of the FT32B processor.

       -mcompress
           Compress all code using the Ft32B code compression scheme.

       -mnopm
           Do not generate code that reads program memory.

       FRV Options

       -mgpr-32
           Only use the first 32 general-purpose registers.

       -mgpr-64
           Use all 64 general-purpose registers.

       -mfpr-32
           Use only the first 32 floating-point registers.

       -mfpr-64
           Use all 64 floating-point registers.

       -mhard-float
           Use hardware instructions for floating-point operations.

       -msoft-float
           Use library routines for floating-point operations.

       -malloc-cc
           Dynamically allocate condition code registers.

       -mfixed-cc
           Do not try to dynamically allocate condition code registers, only use "icc0" and "fcc0".

       -mdword
           Change ABI to use double word insns.

       -mno-dword
           Do not use double word instructions.

       -mdouble
           Use floating-point double instructions.

       -mno-double
           Do not use floating-point double instructions.

       -mmedia
           Use media instructions.

       -mno-media
           Do not use media instructions.

       -mmuladd
           Use multiply and add/subtract instructions.

       -mno-muladd
           Do not use multiply and add/subtract instructions.

       -mfdpic
           Select  the  FDPIC  ABI, which uses function descriptors to represent pointers to functions.  Without
           any PIC/PIE-related options, it implies -fPIE.  With -fpic or -fpie, it assumes GOT entries and small
           data are within a 12-bit range from the GOT base address;  with  -fPIC  or  -fPIE,  GOT  offsets  are
           computed with 32 bits.  With a bfin-elf target, this option implies -msim.

       -minline-plt
           Enable inlining of PLT entries in function calls to functions that are not known to bind locally.  It
           has  no  effect  without  -mfdpic.  It's enabled by default if optimizing for speed and compiling for
           shared libraries (i.e., -fPIC or -fpic), or when an optimization option  such  as  -O3  or  above  is
           present in the command line.

       -mTLS
           Assume a large TLS segment when generating thread-local code.

       -mtls
           Do not assume a large TLS segment when generating thread-local code.

       -mgprel-ro
           Enable  the  use  of  "GPREL"  relocations in the FDPIC ABI for data that is known to be in read-only
           sections.  It's enabled by default, except for -fpic or -fpie: even  though  it  may  help  make  the
           global  offset  table  smaller,  it  trades  1  instruction  for 4.  With -fPIC or -fPIE, it trades 3
           instructions for 4, one of which may be shared by multiple symbols, and it avoids the need for a  GOT
           entry for the referenced symbol, so it's more likely to be a win.  If it is not, -mno-gprel-ro can be
           used to disable it.

       -multilib-library-pic
           Link  with  the  (library, not FD) pic libraries.  It's implied by -mlibrary-pic, as well as by -fPIC
           and -fpic without -mfdpic.  You should never have to use it explicitly.

       -mlinked-fp
           Follow the EABI requirement of always creating a frame pointer whenever a stack frame  is  allocated.
           This option is enabled by default and can be disabled with -mno-linked-fp.

       -mlong-calls
           Use  indirect  addressing  to  call  functions outside the current compilation unit.  This allows the
           functions to be placed anywhere within the 32-bit address space.

       -malign-labels
           Try to align labels to an 8-byte boundary by inserting NOPs into the previous  packet.   This  option
           only  has an effect when VLIW packing is enabled.  It doesn't create new packets; it merely adds NOPs
           to existing ones.

       -mlibrary-pic
           Generate position-independent EABI code.

       -macc-4
           Use only the first four media accumulator registers.

       -macc-8
           Use all eight media accumulator registers.

       -mpack
           Pack VLIW instructions.

       -mno-pack
           Do not pack VLIW instructions.

       -mno-eflags
           Do not mark ABI switches in e_flags.

       -mcond-move
           Enable the use of conditional-move instructions (default).

           This switch is mainly for debugging the compiler and will likely be removed in a future version.

       -mno-cond-move
           Disable the use of conditional-move instructions.

           This switch is mainly for debugging the compiler and will likely be removed in a future version.

       -mscc
           Enable the use of conditional set instructions (default).

           This switch is mainly for debugging the compiler and will likely be removed in a future version.

       -mno-scc
           Disable the use of conditional set instructions.

           This switch is mainly for debugging the compiler and will likely be removed in a future version.

       -mcond-exec
           Enable the use of conditional execution (default).

           This switch is mainly for debugging the compiler and will likely be removed in a future version.

       -mno-cond-exec
           Disable the use of conditional execution.

           This switch is mainly for debugging the compiler and will likely be removed in a future version.

       -mvliw-branch
           Run a pass to pack branches into VLIW instructions (default).

           This switch is mainly for debugging the compiler and will likely be removed in a future version.

       -mno-vliw-branch
           Do not run a pass to pack branches into VLIW instructions.

           This switch is mainly for debugging the compiler and will likely be removed in a future version.

       -mmulti-cond-exec
           Enable optimization of "&&" and "||" in conditional execution (default).

           This switch is mainly for debugging the compiler and will likely be removed in a future version.

       -mno-multi-cond-exec
           Disable optimization of "&&" and "||" in conditional execution.

           This switch is mainly for debugging the compiler and will likely be removed in a future version.

       -mnested-cond-exec
           Enable nested conditional execution optimizations (default).

           This switch is mainly for debugging the compiler and will likely be removed in a future version.

       -mno-nested-cond-exec
           Disable nested conditional execution optimizations.

           This switch is mainly for debugging the compiler and will likely be removed in a future version.

       -moptimize-membar
           This switch removes redundant "membar" instructions from the compiler-generated code.  It is  enabled
           by default.

       -mno-optimize-membar
           This  switch  disables  the  automatic  removal of redundant "membar" instructions from the generated
           code.

       -mtomcat-stats
           Cause gas to print out tomcat statistics.

       -mcpu=cpu
           Select the processor type for which to generate code.  Possible values are frv, fr550, tomcat, fr500,
           fr450, fr405, fr400, fr300 and simple.

       GNU/Linux Options

       These -m options are defined for GNU/Linux targets:

       -mglibc
           Use the GNU C library.  This is  the  default  except  on  *-*-linux-*uclibc*,  *-*-linux-*musl*  and
           *-*-linux-*android* targets.

       -muclibc
           Use uClibc C library.  This is the default on *-*-linux-*uclibc* targets.

       -mmusl
           Use the musl C library.  This is the default on *-*-linux-*musl* targets.

       -mbionic
           Use Bionic C library.  This is the default on *-*-linux-*android* targets.

       -mandroid
           Compile code compatible with Android platform.  This is the default on *-*-linux-*android* targets.

           When  compiling, this option enables -mbionic, -fPIC, -fno-exceptions and -fno-rtti by default.  When
           linking, this option makes the GCC driver pass Android-specific options to the linker.  Finally, this
           option causes the preprocessor macro "__ANDROID__" to be defined.

       -tno-android-cc
           Disable compilation effects of -mandroid, i.e., do not enable -mbionic,  -fPIC,  -fno-exceptions  and
           -fno-rtti by default.

       -tno-android-ld
           Disable linking effects of -mandroid, i.e., pass standard Linux linking options to the linker.

       H8/300 Options

       These -m options are defined for the H8/300 implementations:

       -mrelax
           Shorten some address references at link time, when possible; uses the linker option -relax.

       -mh Generate code for the H8/300H.

       -ms Generate code for the H8S.

       -mn Generate  code  for the H8S and H8/300H in the normal mode.  This switch must be used either with -mh
           or -ms.

       -ms2600
           Generate code for the H8S/2600.  This switch must be used with -ms.

       -mexr
           Extended registers are stored on stack before execution of function with monitor  attribute.  Default
           option is -mexr.  This option is valid only for H8S targets.

       -mno-exr
           Extended  registers  are  not  stored  on  stack before execution of function with monitor attribute.
           Default option is -mno-exr.  This option is valid only for H8S targets.

       -mint32
           Make "int" data 32 bits by default.

       -malign-300
           On the H8/300H and H8S, use the same alignment rules as for the H8/300.  The default for the  H8/300H
           and  H8S is to align longs and floats on 4-byte boundaries.  -malign-300 causes them to be aligned on
           2-byte boundaries.  This option has no effect on the H8/300.

       HPPA Options

       These -m options are defined for the HPPA family of computers:

       -march=architecture-type
           Generate code for the specified architecture.  The choices for architecture-type are 1.0 for PA  1.0,
           1.1  for PA 1.1, and 2.0 for PA 2.0 processors.  Refer to /usr/lib/sched.models on an HP-UX system to
           determine the proper architecture  option  for  your  machine.   Code  compiled  for  lower  numbered
           architectures runs on higher numbered architectures, but not the other way around.

       -mpa-risc-1-0
       -mpa-risc-1-1
       -mpa-risc-2-0
           Synonyms for -march=1.0, -march=1.1, and -march=2.0 respectively.

       -mcaller-copies
           The  caller  copies  function  arguments passed by hidden reference.  This option should be used with
           care as it is not compatible with the default 32-bit runtime.  However, only aggregates  larger  than
           eight bytes are passed by hidden reference and the option provides better compatibility with OpenMP.

       -mjump-in-delay
           This option is ignored and provided for compatibility purposes only.

       -mdisable-fpregs
           Prevent  floating-point  registers  from  being  used in any manner.  This is necessary for compiling
           kernels that perform lazy context switching of floating-point registers.  If you use this option  and
           attempt to perform floating-point operations, the compiler aborts.

       -mdisable-indexing
           Prevent  the  compiler  from  using indexing address modes.  This avoids some rather obscure problems
           when compiling MIG generated code under MACH.

       -mno-space-regs
           Generate code that assumes the target has no space registers.  This allows  GCC  to  generate  faster
           indirect calls and use unscaled index address modes.

           Such code is suitable for level 0 PA systems and kernels.

       -mfast-indirect-calls
           Generate  code  that  assumes  calls never cross space boundaries.  This allows GCC to emit code that
           performs faster indirect calls.

           This option does not work in the presence of shared libraries or nested functions.

       -mfixed-range=register-range
           Generate code treating the given register range as fixed registers.  A fixed register is one that the
           register allocator cannot use.  This is useful when compiling  kernel  code.   A  register  range  is
           specified  as two registers separated by a dash.  Multiple register ranges can be specified separated
           by a comma.

       -mlong-load-store
           Generate 3-instruction load and store sequences as sometimes required by the HP-UX 10  linker.   This
           is equivalent to the +k option to the HP compilers.

       -mportable-runtime
           Use the portable calling conventions proposed by HP for ELF systems.

       -mgas
           Enable the use of assembler directives only GAS understands.

       -mschedule=cpu-type
           Schedule  code  according to the constraints for the machine type cpu-type.  The choices for cpu-type
           are 700 7100, 7100LC, 7200, 7300 and 8000.  Refer to /usr/lib/sched.models  on  an  HP-UX  system  to
           determine the proper scheduling option for your machine.  The default scheduling is 8000.

       -mlinker-opt
           Enable the optimization pass in the HP-UX linker.  Note this makes symbolic debugging impossible.  It
           also  triggers  a bug in the HP-UX 8 and HP-UX 9 linkers in which they give bogus error messages when
           linking some programs.

       -msoft-float
           Generate output containing library calls for floating point.  Warning: the  requisite  libraries  are
           not  available  for  all HPPA targets.  Normally the facilities of the machine's usual C compiler are
           used, but this cannot be done directly in cross-compilation.  You must make your own arrangements  to
           provide suitable library functions for cross-compilation.

           -msoft-float  changes  the calling convention in the output file; therefore, it is only useful if you
           compile all of a program with this option.  In particular, you need to compile libgcc.a, the  library
           that comes with GCC, with -msoft-float in order for this to work.

       -msio
           Generate  the  predefine,  "_SIO",  for  server  IO.   The  default  is  -mwsio.   This generates the
           predefines, "__hp9000s700", "__hp9000s700__" and "_WSIO", for  workstation  IO.   These  options  are
           available under HP-UX and HI-UX.

       -mgnu-ld
           Use options specific to GNU ld.  This passes -shared to ld when building a shared library.  It is the
           default  when GCC is configured, explicitly or implicitly, with the GNU linker.  This option does not
           affect which ld is called; it only changes what parameters are passed to that ld.   The  ld  that  is
           called is determined by the --with-ld configure option, GCC's program search path, and finally by the
           user's  PATH.   The  linker  used  by GCC can be printed using which `gcc -print-prog-name=ld`.  This
           option is only available on the 64-bit HP-UX GCC, i.e. configured with hppa*64*-*-hpux*.

       -mhp-ld
           Use options specific to HP ld.  This passes -b to ld  when  building  a  shared  library  and  passes
           +Accept  TypeMismatch  to  ld  on all links.  It is the default when GCC is configured, explicitly or
           implicitly, with the HP linker.  This option does not affect which ld is called; it only changes what
           parameters are passed to that ld.  The ld that is called is determined  by  the  --with-ld  configure
           option,  GCC's  program  search  path, and finally by the user's PATH.  The linker used by GCC can be
           printed using which `gcc -print-prog-name=ld`.  This option is only available  on  the  64-bit  HP-UX
           GCC, i.e. configured with hppa*64*-*-hpux*.

       -mlong-calls
           Generate code that uses long call sequences.  This ensures that a call is always able to reach linker
           generated  stubs.  The default is to generate long calls only when the distance from the call site to
           the beginning of the function or translation unit, as the case may be, exceeds a predefined limit set
           by the branch type being used.  The  limits  for  normal  calls  are  7,600,000  and  240,000  bytes,
           respectively for the PA 2.0 and PA 1.X architectures.  Sibcalls are always limited at 240,000 bytes.

           Distances  are measured from the beginning of functions when using the -ffunction-sections option, or
           when using the -mgas and -mno-portable-runtime options together under HP-UX with the SOM linker.

           It is normally not desirable to use this option as it  degrades  performance.   However,  it  may  be
           useful in large applications, particularly when partial linking is used to build the application.

           The types of long calls used depends on the capabilities of the assembler and linker, and the type of
           code  being  generated.  The impact on systems that support long absolute calls, and long pic symbol-
           difference or pc-relative calls should be relatively small.  However, an indirect  call  is  used  on
           32-bit ELF systems in pic code and it is quite long.

       -munix=unix-std
           Generate compiler predefines and select a startfile for the specified UNIX standard.  The choices for
           unix-std  are  93, 95 and 98.  93 is supported on all HP-UX versions.  95 is available on HP-UX 10.10
           and later.  98 is available on HP-UX 11.11 and later.  The default values are 93 for HP-UX 10.00,  95
           for HP-UX 10.10 though to 11.00, and 98 for HP-UX 11.11 and later.

           -munix=93  provides the same predefines as GCC 3.3 and 3.4.  -munix=95 provides additional predefines
           for "XOPEN_UNIX" and  "_XOPEN_SOURCE_EXTENDED",  and  the  startfile  unix95.o.   -munix=98  provides
           additional  predefines  for  "_XOPEN_UNIX",  "_XOPEN_SOURCE_EXTENDED", "_INCLUDE__STDC_A1_SOURCE" and
           "_INCLUDE_XOPEN_SOURCE_500", and the startfile unix98.o.

           It is important to note that this option changes the interfaces for  various  library  routines.   It
           also  affects  the operational behavior of the C library.  Thus, extreme care is needed in using this
           option.

           Library code that is intended to operate with more than one UNIX standard must test, set and  restore
           the  variable  "__xpg4_extended_mask"  as  appropriate.   Most  GNU  software  doesn't  provide  this
           capability.

       -nolibdld
           Suppress the generation of link options to search libdld.sl when the -static option is  specified  on
           HP-UX 10 and later.

       -static
           The  HP-UX implementation of setlocale in libc has a dependency on libdld.sl.  There isn't an archive
           version of libdld.sl.  Thus, when the -static option is specified, special link options are needed to
           resolve this dependency.

           On HP-UX 10 and later, the GCC driver adds the necessary options to  link  with  libdld.sl  when  the
           -static  option  is  specified.  This causes the resulting binary to be dynamic.  On the 64-bit port,
           the linkers generate dynamic binaries by default in any case.  The -nolibdld option can  be  used  to
           prevent the GCC driver from adding these link options.

       -threads
           Add  support  for multithreading with the dce thread library under HP-UX.  This option sets flags for
           both the preprocessor and linker.

       IA-64 Options

       These are the -m options defined for the Intel IA-64 architecture.

       -mbig-endian
           Generate code for a big-endian target.  This is the default for HP-UX.

       -mlittle-endian
           Generate code for a little-endian target.  This is the default for AIX5 and GNU/Linux.

       -mgnu-as
       -mno-gnu-as
           Generate (or don't) code for the GNU assembler.  This is the default.

       -mgnu-ld
       -mno-gnu-ld
           Generate (or don't) code for the GNU linker.  This is the default.

       -mno-pic
           Generate code that does not use a global pointer register.  The result is  not  position  independent
           code, and violates the IA-64 ABI.

       -mvolatile-asm-stop
       -mno-volatile-asm-stop
           Generate (or don't) a stop bit immediately before and after volatile asm statements.

       -mregister-names
       -mno-register-names
           Generate  (or  don't)  in,  loc,  and  out  register  names for the stacked registers.  This may make
           assembler output more readable.

       -mno-sdata
       -msdata
           Disable (or enable) optimizations that use the small data section.  This may be  useful  for  working
           around optimizer bugs.

       -mconstant-gp
           Generate code that uses a single constant global pointer value.  This is useful when compiling kernel
           code.

       -mauto-pic
           Generate  code  that is self-relocatable.  This implies -mconstant-gp.  This is useful when compiling
           firmware code.

       -minline-float-divide-min-latency
           Generate code for inline divides of floating-point values using the minimum latency algorithm.

       -minline-float-divide-max-throughput
           Generate code for inline divides of floating-point values using the maximum throughput algorithm.

       -mno-inline-float-divide
           Do not generate inline code for divides of floating-point values.

       -minline-int-divide-min-latency
           Generate code for inline divides of integer values using the minimum latency algorithm.

       -minline-int-divide-max-throughput
           Generate code for inline divides of integer values using the maximum throughput algorithm.

       -mno-inline-int-divide
           Do not generate inline code for divides of integer values.

       -minline-sqrt-min-latency
           Generate code for inline square roots using the minimum latency algorithm.

       -minline-sqrt-max-throughput
           Generate code for inline square roots using the maximum throughput algorithm.

       -mno-inline-sqrt
           Do not generate inline code for "sqrt".

       -mfused-madd
       -mno-fused-madd
           Do (don't) generate code that uses the fused multiply/add  or  multiply/subtract  instructions.   The
           default is to use these instructions.

       -mno-dwarf2-asm
       -mdwarf2-asm
           Don't  (or  do) generate assembler code for the DWARF line number debugging info.  This may be useful
           when not using the GNU assembler.

       -mearly-stop-bits
       -mno-early-stop-bits
           Allow stop bits to be placed earlier than immediately preceding the instruction  that  triggered  the
           stop bit.  This can improve instruction scheduling, but does not always do so.

       -mfixed-range=register-range
           Generate code treating the given register range as fixed registers.  A fixed register is one that the
           register  allocator  cannot  use.   This  is  useful when compiling kernel code.  A register range is
           specified as two registers separated by a dash.  Multiple register ranges can be specified  separated
           by a comma.

       -mtls-size=tls-size
           Specify bit size of immediate TLS offsets.  Valid values are 14, 22, and 64.

       -mtune=cpu-type
           Tune  the  instruction  scheduling  for a particular CPU, Valid values are itanium, itanium1, merced,
           itanium2, and mckinley.

       -milp32
       -mlp64
           Generate code for a 32-bit or 64-bit environment.  The 32-bit environment sets int, long and  pointer
           to  32  bits.  The 64-bit environment sets int to 32 bits and long and pointer to 64 bits.  These are
           HP-UX specific flags.

       -mno-sched-br-data-spec
       -msched-br-data-spec
           (Dis/En)able data speculative scheduling  before  reload.   This  results  in  generation  of  "ld.a"
           instructions  and  the  corresponding  check instructions ("ld.c" / "chk.a").  The default setting is
           disabled.

       -msched-ar-data-spec
       -mno-sched-ar-data-spec
           (En/Dis)able data speculative  scheduling  after  reload.   This  results  in  generation  of  "ld.a"
           instructions  and  the  corresponding  check instructions ("ld.c" / "chk.a").  The default setting is
           enabled.

       -mno-sched-control-spec
       -msched-control-spec
           (Dis/En)able control speculative scheduling.  This feature is available only during region scheduling
           (i.e. before reload).  This results in generation of the "ld.s" instructions  and  the  corresponding
           check instructions "chk.s".  The default setting is disabled.

       -msched-br-in-data-spec
       -mno-sched-br-in-data-spec
           (En/Dis)able  speculative  scheduling  of the instructions that are dependent on the data speculative
           loads before reload.  This is effective only with -msched-br-data-spec enabled.  The default  setting
           is enabled.

       -msched-ar-in-data-spec
       -mno-sched-ar-in-data-spec
           (En/Dis)able  speculative  scheduling  of the instructions that are dependent on the data speculative
           loads after reload.  This is effective only with -msched-ar-data-spec enabled.  The  default  setting
           is enabled.

       -msched-in-control-spec
       -mno-sched-in-control-spec
           (En/Dis)able speculative scheduling of the instructions that are dependent on the control speculative
           loads.  This is effective only with -msched-control-spec enabled.  The default setting is enabled.

       -mno-sched-prefer-non-data-spec-insns
       -msched-prefer-non-data-spec-insns
           If  enabled, data-speculative instructions are chosen for schedule only if there are no other choices
           at the moment.  This makes the use of the data  speculation  much  more  conservative.   The  default
           setting is disabled.

       -mno-sched-prefer-non-control-spec-insns
       -msched-prefer-non-control-spec-insns
           If  enabled,  control-speculative  instructions  are  chosen  for schedule only if there are no other
           choices at the moment.  This makes the use of the control speculation much  more  conservative.   The
           default setting is disabled.

       -mno-sched-count-spec-in-critical-path
       -msched-count-spec-in-critical-path
           If   enabled,  speculative  dependencies  are  considered  during  computation  of  the  instructions
           priorities.  This makes the use of the speculation a bit more conservative.  The default  setting  is
           disabled.

       -msched-spec-ldc
           Use a simple data speculation check.  This option is on by default.

       -msched-control-spec-ldc
           Use a simple check for control speculation.  This option is on by default.

       -msched-stop-bits-after-every-cycle
           Place a stop bit after every cycle when scheduling.  This option is on by default.

       -msched-fp-mem-deps-zero-cost
           Assume  that  floating-point stores and loads are not likely to cause a conflict when placed into the
           same instruction group.  This option is disabled by default.

       -msel-sched-dont-check-control-spec
           Generate checks for control speculation in selective scheduling.  This flag is disabled by default.

       -msched-max-memory-insns=max-insns
           Limit on the number of memory insns per instruction group, giving lower priority to subsequent memory
           insns attempting to schedule in the same instruction group. Frequently useful to prevent  cache  bank
           conflicts.  The default value is 1.

       -msched-max-memory-insns-hard-limit
           Makes  the limit specified by msched-max-memory-insns a hard limit, disallowing more than that number
           in an instruction group.  Otherwise, the limit is "soft",  meaning  that  non-memory  operations  are
           preferred when the limit is reached, but memory operations may still be scheduled.

       LM32 Options

       These -m options are defined for the LatticeMico32 architecture:

       -mbarrel-shift-enabled
           Enable barrel-shift instructions.

       -mdivide-enabled
           Enable divide and modulus instructions.

       -mmultiply-enabled
           Enable multiply instructions.

       -msign-extend-enabled
           Enable sign extend instructions.

       -muser-enabled
           Enable user-defined instructions.

       M32C Options

       -mcpu=name
           Select the CPU for which code is generated.  name may be one of r8c for the R8C/Tiny series, m16c for
           the M16C (up to /60) series, m32cm for the M16C/80 series, or m32c for the M32C/80 series.

       -msim
           Specifies that the program will be run on the simulator.  This causes an alternate runtime library to
           be  linked  in  which  supports, for example, file I/O.  You must not use this option when generating
           programs that will run on real hardware; you must provide your own runtime library for  whatever  I/O
           functions are needed.

       -memregs=number
           Specifies the number of memory-based pseudo-registers GCC uses during code generation.  These pseudo-
           registers  are used like real registers, so there is a tradeoff between GCC's ability to fit the code
           into available registers, and the performance penalty of using memory  instead  of  registers.   Note
           that all modules in a program must be compiled with the same value for this option.  Because of that,
           you must not use this option with GCC's default runtime libraries.

       M32R/D Options

       These -m options are defined for Renesas M32R/D architectures:

       -m32r2
           Generate code for the M32R/2.

       -m32rx
           Generate code for the M32R/X.

       -m32r
           Generate code for the M32R.  This is the default.

       -mmodel=small
           Assume  all  objects live in the lower 16MB of memory (so that their addresses can be loaded with the
           "ld24" instruction), and assume all subroutines are reachable with the "bl" instruction.  This is the
           default.

           The addressability of a particular object can be set with the "model" attribute.

       -mmodel=medium
           Assume objects may be anywhere in the  32-bit  address  space  (the  compiler  generates  "seth/add3"
           instructions  to  load  their  addresses),  and  assume  all  subroutines are reachable with the "bl"
           instruction.

       -mmodel=large
           Assume objects may be anywhere in the  32-bit  address  space  (the  compiler  generates  "seth/add3"
           instructions  to  load  their  addresses),  and assume subroutines may not be reachable with the "bl"
           instruction (the compiler generates the much slower "seth/add3/jl" instruction sequence).

       -msdata=none
           Disable use of the small data area.  Variables are put into one  of  ".data",  ".bss",  or  ".rodata"
           (unless the "section" attribute has been specified).  This is the default.

           The  small data area consists of sections ".sdata" and ".sbss".  Objects may be explicitly put in the
           small data area with the "section" attribute using one of these sections.

       -msdata=sdata
           Put small global and static data in the small  data  area,  but  do  not  generate  special  code  to
           reference them.

       -msdata=use
           Put  small  global  and  static  data  in  the  small data area, and generate special instructions to
           reference them.

       -G num
           Put global and static objects less than or equal to num bytes into the small  data  or  BSS  sections
           instead  of the normal data or BSS sections.  The default value of num is 8.  The -msdata option must
           be set to one of sdata or use for this option to have any effect.

           All modules should be compiled with the same -G num value.  Compiling with different  values  of  num
           may  or  may  not  work;  if  it  doesn't  the  linker gives an error message---incorrect code is not
           generated.

       -mdebug
           Makes the M32R-specific code in the compiler display some statistics that  might  help  in  debugging
           programs.

       -malign-loops
           Align all loops to a 32-byte boundary.

       -mno-align-loops
           Do not enforce a 32-byte alignment for loops.  This is the default.

       -missue-rate=number
           Issue number instructions per cycle.  number can only be 1 or 2.

       -mbranch-cost=number
           number can only be 1 or 2.  If it is 1 then branches are preferred over conditional code, if it is 2,
           then the opposite applies.

       -mflush-trap=number
           Specifies the trap number to use to flush the cache.  The default is 12.  Valid numbers are between 0
           and 15 inclusive.

       -mno-flush-trap
           Specifies that the cache cannot be flushed by using a trap.

       -mflush-func=name
           Specifies  the  name  of  the  operating  system function to call to flush the cache.  The default is
           _flush_cache, but a function call is only used if a trap is not available.

       -mno-flush-func
           Indicates that there is no OS function for flushing the cache.

       M680x0 Options

       These are the -m options defined for M680x0 and ColdFire processors.   The  default  settings  depend  on
       which  architecture  was  selected  when  the  compiler  was configured; the defaults for the most common
       choices are given below.

       -march=arch
           Generate code for a specific M680x0 or ColdFire instruction set architecture.  Permissible values  of
           arch  for  M680x0  architectures  are:  68000, 68010, 68020, 68030, 68040, 68060 and cpu32.  ColdFire
           architectures are selected according to Freescale's ISA classification  and  the  permissible  values
           are: isaa, isaaplus, isab and isac.

           GCC  defines a macro "__mcfarch__" whenever it is generating code for a ColdFire target.  The arch in
           this macro is one of the -march arguments given above.

           When used together, -march and -mtune select code that runs on a family  of  similar  processors  but
           that is optimized for a particular microarchitecture.

       -mcpu=cpu
           Generate code for a specific M680x0 or ColdFire processor.  The M680x0 cpus are: 68000, 68010, 68020,
           68030,  68040,  68060, 68302, 68332 and cpu32.  The ColdFire cpus are given by the table below, which
           also classifies the CPUs into families:

           Family : -mcpu arguments
           51 : 51 51ac 51ag 51cn 51em 51je 51jf 51jg 51jm 51mm 51qe 51qm
           5206 : 5202 5204 5206
           5206e : 5206e
           5208 : 5207 5208
           5211a : 5210a 5211a
           5213 : 5211 5212 5213
           5216 : 5214 5216
           52235 : 52230 52231 52232 52233 52234 52235
           5225 : 5224 5225
           52259 : 52252 52254 52255 52256 52258 52259
           5235 : 5232 5233 5234 5235 523x
           5249 : 5249
           5250 : 5250
           5271 : 5270 5271
           5272 : 5272
           5275 : 5274 5275
           5282 : 5280 5281 5282 528x
           53017 : 53011 53012 53013 53014 53015 53016 53017
           5307 : 5307
           5329 : 5327 5328 5329 532x
           5373 : 5372 5373 537x
           5407 : 5407
           5475 : 5470 5471 5472 5473 5474 5475 547x 5480 5481 5482 5483 5484 5485

           -mcpu=cpu overrides -march=arch if arch is compatible with cpu.   Other  combinations  of  -mcpu  and
           -march are rejected.

           GCC  defines  the  macro  "__mcf_cpu_cpu"  when  ColdFire  target  cpu  is selected.  It also defines
           "__mcf_family_family", where the value of family is given by the table above.

       -mtune=tune
           Tune the code for a particular microarchitecture within the constraints set by -march and -mcpu.  The
           M680x0 microarchitectures are: 68000, 68010, 68020, 68030, 68040,  68060  and  cpu32.   The  ColdFire
           microarchitectures are: cfv1, cfv2, cfv3, cfv4 and cfv4e.

           You can also use -mtune=68020-40 for code that needs to run relatively well on 68020, 68030 and 68040
           targets.   -mtune=68020-60  is  similar but includes 68060 targets as well.  These two options select
           the same tuning decisions as -m68020-40 and -m68020-60 respectively.

           GCC defines the macros "__mcarch" and "__mcarch__" when tuning for 680x0 architecture arch.  It  also
           defines  "mcarch" unless either -ansi or a non-GNU -std option is used.  If GCC is tuning for a range
           of architectures, as selected by -mtune=68020-40 or -mtune=68020-60, it defines the macros for  every
           architecture in the range.

           GCC also defines the macro "__muarch__" when tuning for ColdFire microarchitecture uarch, where uarch
           is one of the arguments given above.

       -m68000
       -mc68000
           Generate  output  for  a  68000.  This is the default when the compiler is configured for 68000-based
           systems.  It is equivalent to -march=68000.

           Use this option for microcontrollers with a 68000 or EC000 core, including the 68008,  68302,  68306,
           68307, 68322, 68328 and 68356.

       -m68010
           Generate  output  for  a  68010.  This is the default when the compiler is configured for 68010-based
           systems.  It is equivalent to -march=68010.

       -m68020
       -mc68020
           Generate output for a 68020.  This is the default when the compiler  is  configured  for  68020-based
           systems.  It is equivalent to -march=68020.

       -m68030
           Generate  output  for  a  68030.  This is the default when the compiler is configured for 68030-based
           systems.  It is equivalent to -march=68030.

       -m68040
           Generate output for a 68040.  This is the default when the compiler  is  configured  for  68040-based
           systems.  It is equivalent to -march=68040.

           This  option inhibits the use of 68881/68882 instructions that have to be emulated by software on the
           68040.  Use this option if your 68040 does not have code to emulate those instructions.

       -m68060
           Generate output for a 68060.  This is the default when the compiler  is  configured  for  68060-based
           systems.  It is equivalent to -march=68060.

           This  option  inhibits  the  use  of  68020  and 68881/68882 instructions that have to be emulated by
           software on the 68060.  Use  this  option  if  your  68060  does  not  have  code  to  emulate  those
           instructions.

       -mcpu32
           Generate  output  for  a  CPU32.  This is the default when the compiler is configured for CPU32-based
           systems.  It is equivalent to -march=cpu32.

           Use this option for microcontrollers with a CPU32 or CPU32+ core, including the 68330, 68331,  68332,
           68333, 68334, 68336, 68340, 68341, 68349 and 68360.

       -m5200
           Generate  output  for  a  520X ColdFire CPU.  This is the default when the compiler is configured for
           520X-based systems.  It is equivalent to -mcpu=5206, and is now deprecated in favor of that option.

           Use this option for microcontroller with a 5200 core, including the  MCF5202,  MCF5203,  MCF5204  and
           MCF5206.

       -m5206e
           Generate  output  for  a 5206e ColdFire CPU.  The option is now deprecated in favor of the equivalent
           -mcpu=5206e.

       -m528x
           Generate output for a member of the ColdFire 528X family.  The option is now deprecated in  favor  of
           the equivalent -mcpu=528x.

       -m5307
           Generate  output  for  a  ColdFire 5307 CPU.  The option is now deprecated in favor of the equivalent
           -mcpu=5307.

       -m5407
           Generate output for a ColdFire 5407 CPU.  The option is now deprecated in  favor  of  the  equivalent
           -mcpu=5407.

       -mcfv4e
           Generate  output  for  a  ColdFire  V4e  family  CPU (e.g. 547x/548x).  This includes use of hardware
           floating-point instructions.  The option is equivalent to -mcpu=547x, and is now deprecated in  favor
           of that option.

       -m68020-40
           Generate  output  for  a 68040, without using any of the new instructions.  This results in code that
           can run relatively efficiently on either a 68020/68881 or a 68030 or a  68040.   The  generated  code
           does use the 68881 instructions that are emulated on the 68040.

           The option is equivalent to -march=68020 -mtune=68020-40.

       -m68020-60
           Generate  output  for  a 68060, without using any of the new instructions.  This results in code that
           can run relatively efficiently on either a 68020/68881 or a 68030 or a  68040.   The  generated  code
           does use the 68881 instructions that are emulated on the 68060.

           The option is equivalent to -march=68020 -mtune=68020-60.

       -mhard-float
       -m68881
           Generate  floating-point  instructions.   This  is  the default for 68020 and above, and for ColdFire
           devices that have an FPU.  It defines the macro "__HAVE_68881__" on M680x0 targets  and  "__mcffpu__"
           on ColdFire targets.

       -msoft-float
           Do  not  generate  floating-point  instructions;  use library calls instead.  This is the default for
           68000, 68010, and 68832 targets.  It is also the default for ColdFire devices that have no FPU.

       -mdiv
       -mno-div
           Generate (do not generate) ColdFire hardware divide and remainder instructions.  If  -march  is  used
           without  -mcpu,  the  default  is "on" for ColdFire architectures and "off" for M680x0 architectures.
           Otherwise, the default is taken from the target CPU (either the default CPU, or the one specified  by
           -mcpu).  For example, the default is "off" for -mcpu=5206 and "on" for -mcpu=5206e.

           GCC defines the macro "__mcfhwdiv__" when this option is enabled.

       -mshort
           Consider  type  "int"  to  be 16 bits wide, like "short int".  Additionally, parameters passed on the
           stack are also aligned to a 16-bit boundary even on targets whose API mandates promotion to 32-bit.

       -mno-short
           Do not consider type "int" to be 16 bits wide.  This is the default.

       -mnobitfield
       -mno-bitfield
           Do not use the bit-field instructions.  The -m68000, -mcpu32 and -m5200 options imply -mnobitfield.

       -mbitfield
           Do use the bit-field instructions.  The -m68020 option implies -mbitfield.  This is  the  default  if
           you use a configuration designed for a 68020.

       -mrtd
           Use a different function-calling convention, in which functions that take a fixed number of arguments
           return  with  the  "rtd"  instruction,  which  pops  their arguments while returning.  This saves one
           instruction in the caller since there is no need to pop the arguments there.

           This calling convention is incompatible with the one normally used on Unix, so you cannot use  it  if
           you need to call libraries compiled with the Unix compiler.

           Also,  you must provide function prototypes for all functions that take variable numbers of arguments
           (including "printf"); otherwise incorrect code is generated for calls to those functions.

           In addition, seriously incorrect code results if  you  call  a  function  with  too  many  arguments.
           (Normally, extra arguments are harmlessly ignored.)

           The "rtd" instruction is supported by the 68010, 68020, 68030, 68040, 68060 and CPU32 processors, but
           not by the 68000 or 5200.

           The default is -mno-rtd.

       -malign-int
       -mno-align-int
           Control whether GCC aligns "int", "long", "long long", "float", "double", and "long double" variables
           on  a  32-bit  boundary  (-malign-int)  or a 16-bit boundary (-mno-align-int).  Aligning variables on
           32-bit boundaries produces code that runs somewhat faster on processors with  32-bit  busses  at  the
           expense of more memory.

           Warning:  if  you  use  the  -malign-int  switch,  GCC  aligns  structures containing the above types
           differently than most published application binary interface specifications for the m68k.

           Use the pc-relative addressing mode of the 68000 directly, instead of using a  global  offset  table.
           At  present,  this option implies -fpic, allowing at most a 16-bit offset for pc-relative addressing.
           -fPIC is not presently supported with -mpcrel, though this could be supported for  68020  and  higher
           processors.

       -mno-strict-align
       -mstrict-align
           Do not (do) assume that unaligned memory references are handled by the system.

       -msep-data
           Generate  code that allows the data segment to be located in a different area of memory from the text
           segment.  This allows for execute-in-place in an environment without virtual memory management.  This
           option implies -fPIC.

       -mno-sep-data
           Generate code that assumes that the data segment follows the text segment.  This is the default.

       -mid-shared-library
           Generate code that supports shared libraries via the library ID method.  This allows for  execute-in-
           place  and shared libraries in an environment without virtual memory management.  This option implies
           -fPIC.

       -mno-id-shared-library
           Generate code that doesn't assume ID-based shared libraries are being used.  This is the default.

       -mshared-library-id=n
           Specifies the identification number of the ID-based shared  library  being  compiled.   Specifying  a
           value  of 0 generates more compact code; specifying other values forces the allocation of that number
           to the current library, but is no more space- or time-efficient than omitting this option.

       -mxgot
       -mno-xgot
           When generating position-independent code for ColdFire, generate code that works if the GOT has  more
           than  8192  entries.   This  code  is  larger and slower than code generated without this option.  On
           M680x0 processors, this option is not needed; -fPIC suffices.

           GCC normally uses a single instruction to load  values  from  the  GOT.   While  this  is  relatively
           efficient,  it only works if the GOT is smaller than about 64k.  Anything larger causes the linker to
           report an error such as:

                   relocation truncated to fit: R_68K_GOT16O foobar

           If this happens, you should recompile your code with -mxgot.  It should then  work  with  very  large
           GOTs.   However, code generated with -mxgot is less efficient, since it takes 4 instructions to fetch
           the value of a global symbol.

           Note that some linkers, including newer versions of the GNU linker, can create multiple GOTs and sort
           GOT entries.  If you have such a linker, you should only need to use -mxgot when compiling  a  single
           object file that accesses more than 8192 GOT entries.  Very few do.

           These options have no effect unless GCC is generating position-independent code.

       -mlong-jump-table-offsets
           Use 32-bit offsets in "switch" tables.  The default is to use 16-bit offsets.

       MCore Options

       These are the -m options defined for the Motorola M*Core processors.

       -mhardlit
       -mno-hardlit
           Inline constants into the code stream if it can be done in two instructions or less.

       -mdiv
       -mno-div
           Use the divide instruction.  (Enabled by default).

       -mrelax-immediate
       -mno-relax-immediate
           Allow arbitrary-sized immediates in bit operations.

       -mwide-bitfields
       -mno-wide-bitfields
           Always treat bit-fields as "int"-sized.

       -m4byte-functions
       -mno-4byte-functions
           Force all functions to be aligned to a 4-byte boundary.

       -mcallgraph-data
       -mno-callgraph-data
           Emit callgraph information.

       -mslow-bytes
       -mno-slow-bytes
           Prefer word access when reading byte quantities.

       -mlittle-endian
       -mbig-endian
           Generate code for a little-endian target.

       -m210
       -m340
           Generate code for the 210 processor.

       -mno-lsim
           Assume  that  runtime support has been provided and so omit the simulator library (libsim.a) from the
           linker command line.

       -mstack-increment=size
           Set the maximum amount for a single stack increment operation.  Large values can increase  the  speed
           of programs that contain functions that need a large amount of stack space, but they can also trigger
           a segmentation fault if the stack is extended too much.  The default value is 0x1000.

       MeP Options

       -mabsdiff
           Enables the "abs" instruction, which is the absolute difference between two registers.

       -mall-opts
           Enables  all  the  optional  instructions---average,  multiply, divide, bit operations, leading zero,
           absolute difference, min/max, clip, and saturation.

       -maverage
           Enables the "ave" instruction, which computes the average of two registers.

       -mbased=n
           Variables of size n bytes or smaller are placed in the ".based" section by default.  Based  variables
           use the $tp register as a base register, and there is a 128-byte limit to the ".based" section.

       -mbitops
           Enables  the  bit operation instructions---bit test ("btstm"), set ("bsetm"), clear ("bclrm"), invert
           ("bnotm"), and test-and-set ("tas").

       -mc=name
           Selects which section constant data is placed in.  name may be tiny, near, or far.

       -mclip
           Enables the "clip" instruction.  Note that -mclip is not useful unless you also provide -mminmax.

       -mconfig=name
           Selects one of the built-in core configurations.  Each MeP chip has one or more modules in  it;  each
           module  has  a  core  CPU and a variety of coprocessors, optional instructions, and peripherals.  The
           "MeP-Integrator" tool, not part of GCC, provides these configurations through this option; using this
           option is the same as using all the corresponding command-line options.  The default configuration is
           default.

       -mcop
           Enables the coprocessor instructions.  By default, this is  a  32-bit  coprocessor.   Note  that  the
           coprocessor is normally enabled via the -mconfig= option.

       -mcop32
           Enables the 32-bit coprocessor's instructions.

       -mcop64
           Enables the 64-bit coprocessor's instructions.

       -mivc2
           Enables IVC2 scheduling.  IVC2 is a 64-bit VLIW coprocessor.

       -mdc
           Causes constant variables to be placed in the ".near" section.

       -mdiv
           Enables the "div" and "divu" instructions.

       -meb
           Generate big-endian code.

       -mel
           Generate little-endian code.

       -mio-volatile
           Tells the compiler that any variable marked with the "io" attribute is to be considered volatile.

       -ml Causes variables to be assigned to the ".far" section by default.

       -mleadz
           Enables the "leadz" (leading zero) instruction.

       -mm Causes variables to be assigned to the ".near" section by default.

       -mminmax
           Enables the "min" and "max" instructions.

       -mmult
           Enables the multiplication and multiply-accumulate instructions.

       -mno-opts
           Disables all the optional instructions enabled by -mall-opts.

       -mrepeat
           Enables the "repeat" and "erepeat" instructions, used for low-overhead looping.

       -ms Causes  all  variables  to  default to the ".tiny" section.  Note that there is a 65536-byte limit to
           this section.  Accesses to these variables use the %gp base register.

       -msatur
           Enables the saturation instructions.  Note that  the  compiler  does  not  currently  generate  these
           itself, but this option is included for compatibility with other tools, like "as".

       -msdram
           Link the SDRAM-based runtime instead of the default ROM-based runtime.

       -msim
           Link the simulator run-time libraries.

       -msimnovec
           Link  the simulator runtime libraries, excluding built-in support for reset and exception vectors and
           tables.

       -mtf
           Causes all functions to default to the ".far" section.  Without this option, functions default to the
           ".near" section.

       -mtiny=n
           Variables that are n bytes or smaller are allocated to the ".tiny" section.  These variables use  the
           $gp base register.  The default for this option is 4, but note that there's a 65536-byte limit to the
           ".tiny" section.

       MicroBlaze Options

       -msoft-float
           Use software emulation for floating point (default).

       -mhard-float
           Use hardware floating-point instructions.

       -mmemcpy
           Do not optimize block moves, use "memcpy".

       -mno-clearbss
           This option is deprecated.  Use -fno-zero-initialized-in-bss instead.

       -mcpu=cpu-type
           Use  features  of, and schedule code for, the given CPU.  Supported values are in the format vX.YY.Z,
           where X is a major version, YY is the minor version, and Z is compatibility code.  Example values are
           v3.00.a, v4.00.b, v5.00.a, v5.00.b, v6.00.a.

       -mxl-soft-mul
           Use software multiply emulation (default).

       -mxl-soft-div
           Use software emulation for divides (default).

       -mxl-barrel-shift
           Use the hardware barrel shifter.

       -mxl-pattern-compare
           Use pattern compare instructions.

       -msmall-divides
           Use table lookup optimization for small signed integer divisions.

       -mxl-stack-check
           This option is deprecated.  Use -fstack-check instead.

       -mxl-gp-opt
           Use GP-relative ".sdata"/".sbss" sections.

       -mxl-multiply-high
           Use multiply high instructions for high part of 32x32 multiply.

       -mxl-float-convert
           Use hardware floating-point conversion instructions.

       -mxl-float-sqrt
           Use hardware floating-point square root instruction.

       -mbig-endian
           Generate code for a big-endian target.

       -mlittle-endian
           Generate code for a little-endian target.

       -mxl-reorder
           Use reorder instructions (swap and byte reversed load/store).

       -mxl-mode-app-model
           Select application model app-model.  Valid models are

           executable
               normal executable (default), uses startup code crt0.o.

           -mpic-data-is-text-relative
               Assume that the displacement between the text and data segments is fixed  at  static  link  time.
               This  allows  data to be referenced by offset from start of text address instead of GOT since PC-
               relative addressing is not supported.

           xmdstub
               for use with Xilinx Microprocessor Debugger (XMD) based software  intrusive  debug  agent  called
               xmdstub. This uses startup file crt1.o and sets the start address of the program to 0x800.

           bootstrap
               for  applications  that are loaded using a bootloader.  This model uses startup file crt2.o which
               does not contain a processor reset vector handler. This is suitable for transferring control on a
               processor reset to the bootloader rather than the application.

           novectors
               for applications that do not require any of the MicroBlaze vectors. This option may be useful for
               applications running within a monitoring application. This model uses crt3.o as a startup file.

           Option -xl-mode-app-model is a deprecated alias for -mxl-mode-app-model.

       MIPS Options

       -EB Generate big-endian code.

       -EL Generate little-endian code.  This is the default for mips*el-*-* configurations.

       -march=arch
           Generate code that runs on arch, which can be the name of a generic  MIPS  ISA,  or  the  name  of  a
           particular  processor.   The  ISA  names are: mips1, mips2, mips3, mips4, mips32, mips32r2, mips32r3,
           mips32r5, mips32r6, mips64, mips64r2, mips64r3, mips64r5 and mips64r6.  The processor names are: 4kc,
           4km, 4kp, 4ksc, 4kec, 4kem, 4kep, 4ksd, 5kc, 5kf, 20kc,  24kc,  24kf2_1,  24kf1_1,  24kec,  24kef2_1,
           24kef1_1,  34kc,  34kf2_1,  34kf1_1,  34kn,  74kc,  74kf2_1,  74kf1_1,  74kf3_2,  1004kc,  1004kf2_1,
           1004kf1_1, i6400, i6500, interaptiv, loongson2e, loongson2f, loongson3a, gs464, gs464e, gs264e,  m4k,
           m14k,  m14kc,  m14ke,  m14kec,  m5100, m5101, octeon, octeon+, octeon2, octeon3, orion, p5600, p6600,
           r2000, r3000, r3900, r4000, r4400, r4600, r4650, r4700, r5900, r6000, r8000, rm7000, rm9000,  r10000,
           r12000, r14000, r16000, sb1, sr71000, vr4100, vr4111, vr4120, vr4130, vr4300, vr5000, vr5400, vr5500,
           xlr  and  xlp.   The special value from-abi selects the most compatible architecture for the selected
           ABI (that is, mips1 for 32-bit ABIs and mips3 for 64-bit ABIs).

           The native Linux/GNU toolchain also supports the value native, which selects  the  best  architecture
           option for the host processor.  -march=native has no effect if GCC does not recognize the processor.

           In  processor  names,  a  final  000 can be abbreviated as k (for example, -march=r2k).  Prefixes are
           optional, and vr may be written r.

           Names of the form nf2_1 refer to processors with FPUs clocked at half the rate of the core, names  of
           the  form  nf1_1 refer to processors with FPUs clocked at the same rate as the core, and names of the
           form nf3_2 refer to processors with FPUs clocked a ratio of  3:2  with  respect  to  the  core.   For
           compatibility  reasons,  nf  is  accepted  as  a  synonym  for nf2_1 while nx and bfx are accepted as
           synonyms for nf1_1.

           GCC defines two macros based on the value of this option.  The first is "_MIPS_ARCH", which gives the
           name of target architecture, as a string.  The second has the form "_MIPS_ARCH_foo", where foo is the
           capitalized value of "_MIPS_ARCH".  For  example,  -march=r2000  sets  "_MIPS_ARCH"  to  "r2000"  and
           defines the macro "_MIPS_ARCH_R2000".

           Note  that  the  "_MIPS_ARCH" macro uses the processor names given above.  In other words, it has the
           full prefix and does not abbreviate 000 as k.  In the case of from-abi, the macro names the  resolved
           architecture (either "mips1" or "mips3").  It names the default architecture when no -march option is
           given.

       -mtune=arch
           Optimize  for arch.  Among other things, this option controls the way instructions are scheduled, and
           the perceived cost of arithmetic operations.  The list of arch values is the same as for -march.

           When this option is not used, GCC optimizes for the processor specified by -march.  By  using  -march
           and  -mtune  together,  it  is  possible  to  generate  code that runs on a family of processors, but
           optimize the code for one particular member of that family.

           -mtune defines the macros "_MIPS_TUNE" and "_MIPS_TUNE_foo", which work in the same way as the -march
           ones described above.

       -mips1
           Equivalent to -march=mips1.

       -mips2
           Equivalent to -march=mips2.

       -mips3
           Equivalent to -march=mips3.

       -mips4
           Equivalent to -march=mips4.

       -mips32
           Equivalent to -march=mips32.

       -mips32r3
           Equivalent to -march=mips32r3.

       -mips32r5
           Equivalent to -march=mips32r5.

       -mips32r6
           Equivalent to -march=mips32r6.

       -mips64
           Equivalent to -march=mips64.

       -mips64r2
           Equivalent to -march=mips64r2.

       -mips64r3
           Equivalent to -march=mips64r3.

       -mips64r5
           Equivalent to -march=mips64r5.

       -mips64r6
           Equivalent to -march=mips64r6.

       -mips16
       -mno-mips16
           Generate (do not generate) MIPS16 code.  If GCC is targeting a  MIPS32  or  MIPS64  architecture,  it
           makes use of the MIPS16e ASE.

           MIPS16  code  generation  can  also  be  controlled  on a per-function basis by means of "mips16" and
           "nomips16" attributes.

       -mflip-mips16
           Generate MIPS16 code on alternating functions.  This option is provided  for  regression  testing  of
           mixed MIPS16/non-MIPS16 code generation, and is not intended for ordinary use in compiling user code.

       -minterlink-compressed
       -mno-interlink-compressed
           Require (do not require) that code using the standard (uncompressed) MIPS ISA be link-compatible with
           MIPS16 and microMIPS code, and vice versa.

           For  example,  code using the standard ISA encoding cannot jump directly to MIPS16 or microMIPS code;
           it must either use a call or an indirect  jump.   -minterlink-compressed  therefore  disables  direct
           jumps unless GCC knows that the target of the jump is not compressed.

       -minterlink-mips16
       -mno-interlink-mips16
           Aliases of -minterlink-compressed and -mno-interlink-compressed.  These options predate the microMIPS
           ASE and are retained for backwards compatibility.

       -mabi=32
       -mabi=o64
       -mabi=n32
       -mabi=64
       -mabi=eabi
           Generate code for the given ABI.

           Note  that  the  EABI has a 32-bit and a 64-bit variant.  GCC normally generates 64-bit code when you
           select a 64-bit architecture, but you can use -mgp32 to get 32-bit code instead.

           For information about the O64 ABI, see <http://gcc.gnu.org/projects/mipso64-abi.html>.

           GCC supports a variant of the o32 ABI in which floating-point registers are 64 rather  than  32  bits
           wide.   You  can  select  this  combination with -mabi=32 -mfp64.  This ABI relies on the "mthc1" and
           "mfhc1" instructions and is therefore only supported for MIPS32R2, MIPS32R3 and MIPS32R5 processors.

           The register assignments for arguments and return values remain the same, but each  scalar  value  is
           passed  in  a  single  64-bit  register  rather than a pair of 32-bit registers.  For example, scalar
           floating-point values are returned in $f0 only, not a $f0/$f1 pair.  The set of call-saved  registers
           also remains the same in that the even-numbered double-precision registers are saved.

           Two  additional  variants  of  the o32 ABI are supported to enable a transition from 32-bit to 64-bit
           registers.  These are FPXX (-mfpxx) and FP64A (-mfp64 -mno-odd-spreg).  The FPXX  extension  mandates
           that  all  code  must  execute  correctly when run using 32-bit or 64-bit registers.  The code can be
           interlinked with either FP32 or FP64, but not both.  The FP64A  extension  is  similar  to  the  FP64
           extension  but  forbids  the  use  of  odd-numbered  single-precision registers.  This can be used in
           conjunction with the "FRE" mode of FPUs in MIPS32R5 processors and allows both FP32 and FP64A code to
           interlink and run in the same process without changing FPU modes.

       -mabicalls
       -mno-abicalls
           Generate (do not generate) code that is suitable for SVR4-style dynamic objects.  -mabicalls  is  the
           default for SVR4-based systems.

       -mshared
       -mno-shared
           Generate  (do not generate) code that is fully position-independent, and that can therefore be linked
           into shared libraries.  This option only affects -mabicalls.

           All -mabicalls code has traditionally been position-independent, regardless of options like -fPIC and
           -fpic.  However, as an extension, the GNU toolchain allows executables to use absolute  accesses  for
           locally-binding  symbols.   It  can  also use shorter GP initialization sequences and generate direct
           calls to locally-defined functions.  This mode is selected by -mno-shared.

           -mno-shared depends on binutils 2.16 or higher and generates objects that can only be linked  by  the
           GNU linker.  However, the option does not affect the ABI of the final executable; it only affects the
           ABI of relocatable objects.  Using -mno-shared generally makes executables both smaller and quicker.

           -mshared is the default.

       -mplt
       -mno-plt
           Assume  (do  not assume) that the static and dynamic linkers support PLTs and copy relocations.  This
           option only affects -mno-shared -mabicalls.  For the n64 ABI,  this  option  has  no  effect  without
           -msym32.

           You  can  make  -mplt  the  default by configuring GCC with --with-mips-plt.  The default is -mno-plt
           otherwise.

       -mxgot
       -mno-xgot
           Lift (do not lift) the usual restrictions on the size of the global offset table.

           GCC normally uses a single instruction to load  values  from  the  GOT.   While  this  is  relatively
           efficient,  it only works if the GOT is smaller than about 64k.  Anything larger causes the linker to
           report an error such as:

                   relocation truncated to fit: R_MIPS_GOT16 foobar

           If this happens, you should recompile your code with  -mxgot.   This  works  with  very  large  GOTs,
           although  the  code is also less efficient, since it takes three instructions to fetch the value of a
           global symbol.

           Note that some linkers can create multiple GOTs.  If you have such a linker, you should only need  to
           use -mxgot when a single object file accesses more than 64k's worth of GOT entries.  Very few do.

           These options have no effect unless GCC is generating position independent code.

       -mgp32
           Assume that general-purpose registers are 32 bits wide.

       -mgp64
           Assume that general-purpose registers are 64 bits wide.

       -mfp32
           Assume that floating-point registers are 32 bits wide.

       -mfp64
           Assume that floating-point registers are 64 bits wide.

       -mfpxx
           Do not assume the width of floating-point registers.

       -mhard-float
           Use floating-point coprocessor instructions.

       -msoft-float
           Do  not  use  floating-point  coprocessor  instructions.  Implement floating-point calculations using
           library calls instead.

       -mno-float
           Equivalent to -msoft-float, but additionally asserts that the program being compiled does not perform
           any floating-point operations.  This option is presently  supported  only  by  some  bare-metal  MIPS
           configurations,  where  it may select a special set of libraries that lack all floating-point support
           (including, for example, the floating-point "printf" formats).   If  code  compiled  with  -mno-float
           accidentally  contains  floating-point  operations,  it  is  likely to suffer a link-time or run-time
           failure.

       -msingle-float
           Assume that the floating-point coprocessor only supports single-precision operations.

       -mdouble-float
           Assume that the  floating-point  coprocessor  supports  double-precision  operations.   This  is  the
           default.

       -modd-spreg
       -mno-odd-spreg
           Enable  the  use  of odd-numbered single-precision floating-point registers for the o32 ABI.  This is
           the default for processors that are known to support these registers.  When using the o32  FPXX  ABI,
           -mno-odd-spreg is set by default.

       -mabs=2008
       -mabs=legacy
           These  options  control  the treatment of the special not-a-number (NaN) IEEE 754 floating-point data
           with the "abs.fmt" and "neg.fmt" machine instructions.

           By default or when -mabs=legacy is used the  legacy  treatment  is  selected.   In  this  case  these
           instructions  are considered arithmetic and avoided where correct operation is required and the input
           operand might be a NaN.  A longer sequence of instructions that manipulate the sign bit of  floating-
           point datum manually is used instead unless the -ffinite-math-only option has also been specified.

           The  -mabs=2008  option  selects  the  IEEE  754-2008 treatment.  In this case these instructions are
           considered non-arithmetic and therefore operating correctly in all  cases,  including  in  particular
           where  the  input  operand is a NaN.  These instructions are therefore always used for the respective
           operations.

       -mnan=2008
       -mnan=legacy
           These options control the encoding of the special not-a-number (NaN) IEEE 754 floating-point data.

           The -mnan=legacy option selects the legacy encoding.  In this case quiet NaNs (qNaNs) are denoted  by
           the first bit of their trailing significand field being 0, whereas signaling NaNs (sNaNs) are denoted
           by the first bit of their trailing significand field being 1.

           The  -mnan=2008  option  selects  the  IEEE 754-2008 encoding.  In this case qNaNs are denoted by the
           first bit of their trailing significand field being 1, whereas sNaNs are denoted by the first bit  of
           their trailing significand field being 0.

           The default is -mnan=legacy unless GCC has been configured with --with-nan=2008.

       -mllsc
       -mno-llsc
           Use  (do  not use) ll, sc, and sync instructions to implement atomic memory built-in functions.  When
           neither option is specified, GCC uses the instructions if the target architecture supports them.

           -mllsc is useful if the runtime environment can emulate the instructions and -mno-llsc can be  useful
           when  compiling for nonstandard ISAs.  You can make either option the default by configuring GCC with
           --with-llsc and --without-llsc respectively.  --with-llsc is the default for some configurations; see
           the installation documentation for details.

       -mdsp
       -mno-dsp
           Use (do not use) revision 1 of the MIPS DSP ASE.
             This option defines the preprocessor macro "__mips_dsp".  It also defines "__mips_dsp_rev" to 1.

       -mdspr2
       -mno-dspr2
           Use (do not use) revision 2 of the MIPS DSP ASE.
             This option defines the preprocessor macros  "__mips_dsp"  and  "__mips_dspr2".   It  also  defines
           "__mips_dsp_rev" to 2.

       -msmartmips
       -mno-smartmips
           Use (do not use) the MIPS SmartMIPS ASE.

       -mpaired-single
       -mno-paired-single
           Use (do not use) paired-single floating-point instructions.
             This option requires hardware floating-point support to be enabled.

       -mdmx
       -mno-mdmx
           Use  (do  not  use)  MIPS  Digital  Media  Extension instructions.  This option can only be used when
           generating 64-bit code and requires hardware floating-point support to be enabled.

       -mips3d
       -mno-mips3d
           Use (do not use) the MIPS-3D ASE.  The option -mips3d implies -mpaired-single.

       -mmicromips
       -mno-micromips
           Generate (do not generate) microMIPS code.

           MicroMIPS code generation can also be controlled on a per-function basis by means of "micromips"  and
           "nomicromips" attributes.

       -mmt
       -mno-mt
           Use (do not use) MT Multithreading instructions.

       -mmcu
       -mno-mcu
           Use (do not use) the MIPS MCU ASE instructions.

       -meva
       -mno-eva
           Use (do not use) the MIPS Enhanced Virtual Addressing instructions.

       -mvirt
       -mno-virt
           Use (do not use) the MIPS Virtualization (VZ) instructions.

       -mxpa
       -mno-xpa
           Use (do not use) the MIPS eXtended Physical Address (XPA) instructions.

       -mcrc
       -mno-crc
           Use (do not use) the MIPS Cyclic Redundancy Check (CRC) instructions.

       -mginv
       -mno-ginv
           Use (do not use) the MIPS Global INValidate (GINV) instructions.

       -mloongson-mmi
       -mno-loongson-mmi
           Use (do not use) the MIPS Loongson MultiMedia extensions Instructions (MMI).

       -mloongson-ext
       -mno-loongson-ext
           Use (do not use) the MIPS Loongson EXTensions (EXT) instructions.

       -mloongson-ext2
       -mno-loongson-ext2
           Use (do not use) the MIPS Loongson EXTensions r2 (EXT2) instructions.

       -mlong64
           Force  "long"  types  to be 64 bits wide.  See -mlong32 for an explanation of the default and the way
           that the pointer size is determined.

       -mlong32
           Force "long", "int", and pointer types to be 32 bits wide.

           The default size of "int"s, "long"s and pointers depends on the ABI.   All  the  supported  ABIs  use
           32-bit  "int"s.   The  n64  ABI  uses  64-bit "long"s, as does the 64-bit EABI; the others use 32-bit
           "long"s.  Pointers are the same size as "long"s, or the same size as integer registers, whichever  is
           smaller.

       -msym32
       -mno-sym32
           Assume  (do  not  assume)  that all symbols have 32-bit values, regardless of the selected ABI.  This
           option is useful in combination with -mabi=64 and -mno-abicalls because it  allows  GCC  to  generate
           shorter and faster references to symbolic addresses.

       -G num
           Put definitions of externally-visible data in a small data section if that data is no bigger than num
           bytes.  GCC can then generate more efficient accesses to the data; see -mgpopt for details.

           The default -G option depends on the configuration.

       -mlocal-sdata
       -mno-local-sdata
           Extend  (do  not  extend)  the  -G  behavior  to  local  data  too, such as to static variables in C.
           -mlocal-sdata is the default for all configurations.

           If the linker complains that an application is using too much small  data,  you  might  want  to  try
           rebuilding  the  less performance-critical parts with -mno-local-sdata.  You might also want to build
           large libraries with -mno-local-sdata, so that the libraries leave more room for the main program.

       -mextern-sdata
       -mno-extern-sdata
           Assume (do not assume) that externally-defined data is in a small data section if the  size  of  that
           data is within the -G limit.  -mextern-sdata is the default for all configurations.

           If  you  compile  a  module Mod with -mextern-sdata -G num -mgpopt, and Mod references a variable Var
           that is no bigger than num bytes, you must make sure that Var is placed in a small data section.   If
           Var  is  defined by another module, you must either compile that module with a high-enough -G setting
           or attach a "section" attribute to Var's definition.  If Var is common, you must link the application
           with a high-enough -G setting.

           The easiest way of satisfying these restrictions is to compile and link every module with the same -G
           option.  However, you may wish to build a library that supports several different small data  limits.
           You can do this by compiling the library with the highest supported -G setting and additionally using
           -mno-extern-sdata to stop the library from making assumptions about externally-defined data.

       -mgpopt
       -mno-gpopt
           Use  (do  not use) GP-relative accesses for symbols that are known to be in a small data section; see
           -G, -mlocal-sdata and -mextern-sdata.  -mgpopt is the default for all configurations.

           -mno-gpopt is useful for cases where the $gp register  might  not  hold  the  value  of  "_gp".   For
           example,  if  the  code is part of a library that might be used in a boot monitor, programs that call
           boot monitor routines pass an unknown value in $gp.  (In such situations, the boot monitor itself  is
           usually compiled with -G0.)

           -mno-gpopt implies -mno-local-sdata and -mno-extern-sdata.

       -membedded-data
       -mno-embedded-data
           Allocate  variables  to  the  read-only  data  section first if possible, then next in the small data
           section if possible, otherwise in data.  This gives  slightly  slower  code  than  the  default,  but
           reduces  the  amount  of  RAM  required  when  executing, and thus may be preferred for some embedded
           systems.

       -muninit-const-in-rodata
       -mno-uninit-const-in-rodata
           Put uninitialized "const" variables in the read-only data section.  This option is only meaningful in
           conjunction with -membedded-data.

       -mcode-readable=setting
           Specify whether GCC may generate code that reads from executable sections.  There are three  possible
           settings:

           -mcode-readable=yes
               Instructions may freely access executable sections.  This is the default setting.

           -mcode-readable=pcrel
               MIPS16  PC-relative load instructions can access executable sections, but other instructions must
               not do so.  This option is useful on 4KSc and 4KSd processors when the code TLBs  have  the  Read
               Inhibit  bit  set.   It  is  also  useful  on  processors  that  can be configured to have a dual
               instruction/data SRAM interface and that, like the M4K, automatically redirect PC-relative  loads
               to the instruction RAM.

           -mcode-readable=no
               Instructions  must not access executable sections.  This option can be useful on targets that are
               configured to have a dual instruction/data SRAM interface  but  that  (unlike  the  M4K)  do  not
               automatically redirect PC-relative loads to the instruction RAM.

       -msplit-addresses
       -mno-split-addresses
           Enable (disable) use of the "%hi()" and "%lo()" assembler relocation operators.  This option has been
           superseded by -mexplicit-relocs but is retained for backwards compatibility.

       -mexplicit-relocs
       -mno-explicit-relocs
           Use  (do  not  use)  assembler  relocation  operators  when  dealing  with  symbolic  addresses.  The
           alternative, selected by -mno-explicit-relocs, is to use assembler macros instead.

           -mexplicit-relocs is the default if GCC was configured to use an assembler that  supports  relocation
           operators.

       -mcheck-zero-division
       -mno-check-zero-division
           Trap (do not trap) on integer division by zero.

           The default is -mcheck-zero-division.

       -mdivide-traps
       -mdivide-breaks
           MIPS  systems  check  for  division  by  zero  by  generating  either  a  conditional trap or a break
           instruction.  Using traps results in smaller code, but is only supported on MIPS II and later.  Also,
           some versions of the Linux kernel have a bug that prevents trap from  generating  the  proper  signal
           ("SIGFPE").   Use  -mdivide-traps  to  allow conditional traps on architectures that support them and
           -mdivide-breaks to force the use of breaks.

           The default  is  usually  -mdivide-traps,  but  this  can  be  overridden  at  configure  time  using
           --with-divide=breaks.      Divide-by-zero     checks     can    be    completely    disabled    using
           -mno-check-zero-division.

       -mload-store-pairs
       -mno-load-store-pairs
           Enable (disable) an optimization  that  pairs  consecutive  load  or  store  instructions  to  enable
           load/store  bonding.   This  option  is  enabled  by  default but only takes effect when the selected
           architecture is known to support bonding.

       -mmemcpy
       -mno-memcpy
           Force (do not force) the use of "memcpy" for non-trivial block moves.  The  default  is  -mno-memcpy,
           which allows GCC to inline most constant-sized copies.

       -mlong-calls
       -mno-long-calls
           Disable  (do  not  disable)  use  of  the  "jal"  instruction.  Calling functions using "jal" is more
           efficient but requires the caller and callee to be in the same 256 megabyte segment.

           This option has no effect on abicalls code.  The default is -mno-long-calls.

       -mmad
       -mno-mad
           Enable (disable) use of the "mad", "madu" and "mul" instructions, as provided by the R4650 ISA.

       -mimadd
       -mno-imadd
           Enable (disable) use of the "madd" and "msub"  integer  instructions.   The  default  is  -mimadd  on
           architectures  that  support  "madd" and "msub" except for the 74k architecture where it was found to
           generate slower code.

       -mfused-madd
       -mno-fused-madd
           Enable (disable) use of the floating-point multiply-accumulate instructions, when they are available.
           The default is -mfused-madd.

           On the R8000 CPU  when  multiply-accumulate  instructions  are  used,  the  intermediate  product  is
           calculated  to  infinite  precision  and  is  not subject to the FCSR Flush to Zero bit.  This may be
           undesirable in some circumstances.  On other processors the result is numerically  identical  to  the
           equivalent computation using separate multiply, add, subtract and negate instructions.

       -nocpp
           Tell the MIPS assembler to not run its preprocessor over user assembler files (with a .s suffix) when
           assembling them.

       -mfix-24k
       -mno-fix-24k
           Work  around the 24K E48 (lost data on stores during refill) errata.  The workarounds are implemented
           by the assembler rather than by GCC.

       -mfix-r4000
       -mno-fix-r4000
           Work around certain R4000 CPU errata:

           -   A double-word or a variable shift may give an incorrect  result  if  executed  immediately  after
               starting an integer division.

           -   A  double-word  or  a  variable  shift  may give an incorrect result if executed while an integer
               multiplication is in progress.

           -   An integer division may give an incorrect result if started in a delay slot of a taken branch  or
               a jump.

       -mfix-r4400
       -mno-fix-r4400
           Work around certain R4400 CPU errata:

           -   A  double-word  or  a  variable  shift may give an incorrect result if executed immediately after
               starting an integer division.

       -mfix-r10000
       -mno-fix-r10000
           Work around certain R10000 errata:

           -   "ll"/"sc" sequences may not behave atomically on revisions prior to 3.0.  They  may  deadlock  on
               revisions 2.6 and earlier.

           This  option  can  only  be  used  if  the  target  architecture supports branch-likely instructions.
           -mfix-r10000 is the default when -march=r10000 is used; -mno-fix-r10000 is the default otherwise.

       -mfix-r5900
       -mno-fix-r5900
           Do not attempt to schedule the preceding instruction into the delay  slot  of  a  branch  instruction
           placed  at  the  end  of  a  short  loop  of  six  instructions  or fewer and always schedule a "nop"
           instruction there instead.  The short loop bug under certain conditions causes loops to execute  only
           once  or  twice,  due  to  a  hardware  bug  in the R5900 chip.  The workaround is implemented by the
           assembler rather than by GCC.

       -mfix-rm7000
       -mno-fix-rm7000
           Work around the RM7000 "dmult"/"dmultu" errata.  The workarounds are  implemented  by  the  assembler
           rather than by GCC.

       -mfix-vr4120
       -mno-fix-vr4120
           Work around certain VR4120 errata:

           -   "dmultu" does not always produce the correct result.

           -   "div" and "ddiv" do not always produce the correct result if one of the operands is negative.

           The  workarounds  for  the  division errata rely on special functions in libgcc.a.  At present, these
           functions are only provided by the "mips64vr*-elf" configurations.

           Other VR4120 errata require a NOP to be inserted between certain pairs of instructions.  These errata
           are handled by the assembler, not by GCC itself.

       -mfix-vr4130
           Work around the VR4130 "mflo"/"mfhi" errata.  The workarounds are implemented by the assembler rather
           than by GCC, although GCC avoids using "mflo" and "mfhi" if the VR4130 "macc", "macchi", "dmacc"  and
           "dmacchi" instructions are available instead.

       -mfix-sb1
       -mno-fix-sb1
           Work around certain SB-1 CPU core errata.  (This flag currently works around the SB-1 revision 2 "F1"
           and "F2" floating-point errata.)

       -mr10k-cache-barrier=setting
           Specify  whether  GCC  should  insert cache barriers to avoid the side effects of speculation on R10K
           processors.

           In common with many processors, the R10K tries to predict the outcome of  a  conditional  branch  and
           speculatively  executes  instructions from the "taken" branch.  It later aborts these instructions if
           the predicted outcome is wrong.  However, on the  R10K,  even  aborted  instructions  can  have  side
           effects.

           This problem only affects kernel stores and, depending on the system, kernel loads.  As an example, a
           speculatively-executed  store may load the target memory into cache and mark the cache line as dirty,
           even if the store itself is later aborted.  If a DMA operation writes to  the  same  area  of  memory
           before  the  "dirty"  line  is  flushed,  the  cached  data overwrites the DMA-ed data.  See the R10K
           processor manual for a full description, including other potential problems.

           One workaround is to insert cache barrier instructions before  every  memory  access  that  might  be
           speculatively    executed    and    that    might    have    side    effects    even    if   aborted.
           -mr10k-cache-barrier=setting controls GCC's implementation  of  this  workaround.   It  assumes  that
           aborted accesses to any byte in the following regions does not have side effects:

           1.  the memory occupied by the current function's stack frame;

           2.  the memory occupied by an incoming stack argument;

           3.  the memory occupied by an object with a link-time-constant address.

           It  is  the  kernel's  responsibility to ensure that speculative accesses to these regions are indeed
           safe.

           If the input program contains a function declaration such as:

                   void foo (void);

           then the implementation of "foo" must allow "j foo" and "jal foo" to be executed speculatively.   GCC
           honors  this  restriction  for  functions  it compiles itself.  It expects non-GCC functions (such as
           hand-written assembly code) to do the same.

           The option has three forms:

           -mr10k-cache-barrier=load-store
               Insert a cache barrier before a load or store that might be speculatively executed and that might
               have side effects even if aborted.

           -mr10k-cache-barrier=store
               Insert a cache barrier before a store that might be speculatively executed and  that  might  have
               side effects even if aborted.

           -mr10k-cache-barrier=none
               Disable the insertion of cache barriers.  This is the default setting.

       -mflush-func=func
       -mno-flush-func
           Specifies  the  function  to  call to flush the I and D caches, or to not call any such function.  If
           called, the function must take the same arguments as the common "_flush_func", that is,  the  address
           of  the  memory  range  for  which  the cache is being flushed, the size of the memory range, and the
           number 3 (to flush both caches).  The default depends on the  target  GCC  was  configured  for,  but
           commonly is either "_flush_func" or "__cpu_flush".

       mbranch-cost=num
           Set  the cost of branches to roughly num "simple" instructions.  This cost is only a heuristic and is
           not guaranteed to produce consistent results across releases.  A zero cost  redundantly  selects  the
           default, which is based on the -mtune setting.

       -mbranch-likely
       -mno-branch-likely
           Enable  or  disable  use  of  Branch  Likely instructions, regardless of the default for the selected
           architecture.  By default, Branch Likely instructions may be generated if they are supported  by  the
           selected  architecture.   An exception is for the MIPS32 and MIPS64 architectures and processors that
           implement those architectures; for those, Branch Likely instructions are not be generated by  default
           because the MIPS32 and MIPS64 architectures specifically deprecate their use.

       -mcompact-branches=never
       -mcompact-branches=optimal
       -mcompact-branches=always
           These   options   control   which   form   of   branches   will   be   generated.    The  default  is
           -mcompact-branches=optimal.

           The -mcompact-branches=never option ensures that compact branch instructions will never be generated.

           The -mcompact-branches=always option ensures that a compact branch instruction will be  generated  if
           available.  If a compact branch instruction is not available, a delay slot form of the branch will be
           used instead.

           This option is supported from MIPS Release 6 onwards.

           The  -mcompact-branches=optimal  option will cause a delay slot branch to be used if one is available
           in the current ISA and the delay slot is successfully filled.  If the delay slot  is  not  filled,  a
           compact branch will be chosen if one is available.

       -mfp-exceptions
       -mno-fp-exceptions
           Specifies whether FP exceptions are enabled.  This affects how FP instructions are scheduled for some
           processors.  The default is that FP exceptions are enabled.

           For  instance,  on  the SB-1, if FP exceptions are disabled, and we are emitting 64-bit code, then we
           can use both FP pipes.  Otherwise, we can only use one FP pipe.

       -mvr4130-align
       -mno-vr4130-align
           The VR4130 pipeline is two-way superscalar, but can only issue two instructions together if the first
           one is 8-byte aligned.  When this option is enabled, GCC aligns pairs of instructions that it  thinks
           should execute in parallel.

           This option only has an effect when optimizing for the VR4130.  It normally makes code faster, but at
           the expense of making it bigger.  It is enabled by default at optimization level -O3.

       -msynci
       -mno-synci
           Enable  (disable)  generation  of "synci" instructions on architectures that support it.  The "synci"
           instructions (if enabled) are generated when "__builtin___clear_cache" is compiled.

           This option defaults to -mno-synci, but the  default  can  be  overridden  by  configuring  GCC  with
           --with-synci.

           When  compiling  code for single processor systems, it is generally safe to use "synci".  However, on
           many multi-core (SMP) systems, it does not invalidate the instruction caches on  all  cores  and  may
           lead to undefined behavior.

       -mrelax-pic-calls
       -mno-relax-pic-calls
           Try  to turn PIC calls that are normally dispatched via register $25 into direct calls.  This is only
           possible if the linker can resolve the destination at link time and  if  the  destination  is  within
           range for a direct call.

           -mrelax-pic-calls  is the default if GCC was configured to use an assembler and a linker that support
           the ".reloc" assembly directive and -mexplicit-relocs is in effect.  With -mno-explicit-relocs,  this
           optimization can be performed by the assembler and the linker alone without help from the compiler.

       -mmcount-ra-address
       -mno-mcount-ra-address
           Emit  (do not emit) code that allows "_mcount" to modify the calling function's return address.  When
           enabled, this option extends the usual "_mcount" interface with a new ra-address parameter, which has
           type "intptr_t *" and is passed in register $12.  "_mcount" can then modify  the  return  address  by
           doing both of the following:

           *   Returning the new address in register $31.

           *   Storing the new address in "*ra-address", if ra-address is nonnull.

           The default is -mno-mcount-ra-address.

       -mframe-header-opt
       -mno-frame-header-opt
           Enable (disable) frame header optimization in the o32 ABI.  When using the o32 ABI, calling functions
           will  allocate  16  bytes on the stack for the called function to write out register arguments.  When
           enabled, this optimization will suppress the allocation of the frame header if it can  be  determined
           that it is unused.

           This optimization is off by default at all optimization levels.

       -mlxc1-sxc1
       -mno-lxc1-sxc1
           When  applicable, enable (disable) the generation of "lwxc1", "swxc1", "ldxc1", "sdxc1" instructions.
           Enabled by default.

       -mmadd4
       -mno-madd4
           When applicable, enable  (disable)  the  generation  of  4-operand  "madd.s",  "madd.d"  and  related
           instructions.  Enabled by default.

       MMIX Options

       These options are defined for the MMIX:

       -mlibfuncs
       -mno-libfuncs
           Specify  that  intrinsic  library  functions  are being compiled, passing all values in registers, no
           matter the size.

       -mepsilon
       -mno-epsilon
           Generate floating-point comparison instructions  that  compare  with  respect  to  the  "rE"  epsilon
           register.

       -mabi=mmixware
       -mabi=gnu
           Generate  code  that  passes  function parameters and return values that (in the called function) are
           seen as registers $0 and up, as opposed to the GNU ABI which uses global registers $231 and up.

       -mzero-extend
       -mno-zero-extend
           When reading data from memory in sizes shorter than 64 bits, use (do  not  use)  zero-extending  load
           instructions by default, rather than sign-extending ones.

       -mknuthdiv
       -mno-knuthdiv
           Make  the  result  of  a  division  yielding a remainder have the same sign as the divisor.  With the
           default, -mno-knuthdiv, the sign of the remainder follows the sign of the dividend.  Both methods are
           arithmetically valid, the latter being almost exclusively used.

       -mtoplevel-symbols
       -mno-toplevel-symbols
           Prepend (do not prepend) a : to all global symbols, so  the  assembly  code  can  be  used  with  the
           "PREFIX" assembly directive.

       -melf
           Generate  an  executable  in  the  ELF  format,  rather  than the default mmo format used by the mmix
           simulator.

       -mbranch-predict
       -mno-branch-predict
           Use (do not use) the probable-branch instructions, when static branch prediction indicates a probable
           branch.

       -mbase-addresses
       -mno-base-addresses
           Generate (do not generate) code that  uses  base  addresses.   Using  a  base  address  automatically
           generates a request (handled by the assembler and the linker) for a constant to be set up in a global
           register.   The register is used for one or more base address requests within the range 0 to 255 from
           the value held in the register.  The generally leads to short  and  fast  code,  but  the  number  of
           different  data  items that can be addressed is limited.  This means that a program that uses lots of
           static data may require -mno-base-addresses.

       -msingle-exit
       -mno-single-exit
           Force (do not force) generated code to have a single exit point in each function.

       MN10300 Options

       These -m options are defined for Matsushita MN10300 architectures:

       -mmult-bug
           Generate code to avoid bugs in the multiply instructions for the MN10300  processors.   This  is  the
           default.

       -mno-mult-bug
           Do not generate code to avoid bugs in the multiply instructions for the MN10300 processors.

       -mam33
           Generate code using features specific to the AM33 processor.

       -mno-am33
           Do not generate code using features specific to the AM33 processor.  This is the default.

       -mam33-2
           Generate code using features specific to the AM33/2.0 processor.

       -mam34
           Generate code using features specific to the AM34 processor.

       -mtune=cpu-type
           Use the timing characteristics of the indicated CPU type when scheduling instructions.  This does not
           change the targeted processor type.  The CPU type must be one of mn10300, am33, am33-2 or am34.

       -mreturn-pointer-on-d0
           When  generating  a  function  that  returns  a  pointer,  return  the pointer in both "a0" and "d0".
           Otherwise, the pointer is returned only in "a0", and  attempts  to  call  such  functions  without  a
           prototype result in errors.  Note that this option is on by default; use -mno-return-pointer-on-d0 to
           disable it.

       -mno-crt0
           Do not link in the C run-time initialization object file.

       -mrelax
           Indicate  to  the  linker  that it should perform a relaxation optimization pass to shorten branches,
           calls and absolute memory addresses.  This option only has an effect when used on  the  command  line
           for the final link step.

           This option makes symbolic debugging impossible.

       -mliw
           Allow the compiler to generate Long Instruction Word instructions if the target is the AM33 or later.
           This is the default.  This option defines the preprocessor macro "__LIW__".

       -mno-liw
           Do  not  allow  the compiler to generate Long Instruction Word instructions.  This option defines the
           preprocessor macro "__NO_LIW__".

       -msetlb
           Allow the compiler to generate the SETLB and Lcc instructions if the target is  the  AM33  or  later.
           This is the default.  This option defines the preprocessor macro "__SETLB__".

       -mno-setlb
           Do  not  allow  the  compiler  to  generate  SETLB  or  Lcc  instructions.   This  option defines the
           preprocessor macro "__NO_SETLB__".

       Moxie Options

       -meb
           Generate big-endian code.  This is the default for moxie-*-* configurations.

       -mel
           Generate little-endian code.

       -mmul.x
           Generate mul.x and umul.x instructions.  This is the default for moxiebox-*-* configurations.

       -mno-crt0
           Do not link in the C run-time initialization object file.

       MSP430 Options

       These options are defined for the MSP430:

       -masm-hex
           Force assembly output to always use hex constants.  Normally such constants are signed decimals,  but
           this option is available for testsuite and/or aesthetic purposes.

       -mmcu=
           Select  the  MCU  to target.  This is used to create a C preprocessor symbol based upon the MCU name,
           converted to upper case and pre- and post-fixed with __.  This in turn is used by the msp430.h header
           file to select an MCU-specific supplementary header file.

           The option also sets the ISA to use.  If the MCU name is one that is known to only  support  the  430
           ISA then that is selected, otherwise the 430X ISA is selected.  A generic MCU name of msp430 can also
           be used to select the 430 ISA.  Similarly the generic msp430x MCU name selects the 430X ISA.

           In  addition an MCU-specific linker script is added to the linker command line.  The script's name is
           the name of the MCU with .ld appended.  Thus specifying -mmcu=xxx on the gcc command line defines the
           C preprocessor symbol "__XXX__" and cause the linker to search for a script called xxx.ld.

           The ISA and hardware multiply supported for the different MCUs is hard-coded into GCC.   However,  an
           external  devices.csv  file  can  be  used to extend device support beyond those that have been hard-
           coded.

           GCC searches for the devices.csv file using the following methods  in  the  given  precedence  order,
           where the first method takes precendence over the second which takes precedence over the third.

           Include path specified with "-I" and "-L"
               devices.csv will be searched for in each of the directories specified by include paths and linker
               library search paths.

           Path specified by the environment variable MSP430_GCC_INCLUDE_DIR
               Define  the  value  of the global environment variable MSP430_GCC_INCLUDE_DIR to the full path to
               the directory containing devices.csv, and GCC will search this  directory  for  devices.csv.   If
               devices.csv  is  found,  this  directory  will  also be registered as an include path, and linker
               library path.  Header files and linker scripts in this directory can therefore  be  used  without
               manually specifying "-I" and "-L" on the command line.

           The msp430-elf{,bare}/include/devices directory
               Finally,  GCC  will  examine msp430-elf{,bare}/include/devices from the toolchain root directory.
               This directory does not exist in a default installation, but if  the  user  has  created  it  and
               copied  devices.csv there, then the MCU data will be read.  As above, this directory will also be
               registered as an include path, and linker library path.

           If none of the above search methods find devices.csv, then the hard-coded MCU data is used.

       -mwarn-mcu
       -mno-warn-mcu
           This option enables or disables warnings about conflicts between the MCU name specified by the  -mmcu
           option  and  the ISA set by the -mcpu option and/or the hardware multiply support set by the -mhwmult
           option.  It also toggles warnings about unrecognized MCU names.  This option is on by default.

       -mcpu=
           Specifies the ISA to use.  Accepted values  are  msp430,  msp430x  and  msp430xv2.   This  option  is
           deprecated.  The -mmcu= option should be used to select the ISA.

       -msim
           Link  to  the  simulator  runtime  libraries  and linker script.  Overrides any scripts that would be
           selected by the -mmcu= option.

       -mlarge
           Use large-model addressing (20-bit pointers, 20-bit "size_t").

       -msmall
           Use small-model addressing (16-bit pointers, 16-bit "size_t").

       -mrelax
           This option is passed to the  assembler  and  linker,  and  allows  the  linker  to  perform  certain
           optimizations that cannot be done until the final link.

       mhwmult=
           Describes  the  type  of  hardware multiply supported by the target.  Accepted values are none for no
           hardware multiply, 16bit for the original 16-bit-only multiply supported by early  MCUs.   32bit  for
           the  16/32-bit  multiply supported by later MCUs and f5series for the 16/32-bit multiply supported by
           F5-series MCUs.  A value of auto can also be given.  This tells GCC to deduce the  hardware  multiply
           support  based upon the MCU name provided by the -mmcu option.  If no -mmcu option is specified or if
           the MCU name is not recognized then no hardware multiply support is assumed.  "auto" is  the  default
           setting.

           Hardware  multiplies  are  normally  performed by calling a library routine.  This saves space in the
           generated code.  When compiling at -O3 or higher however the hardware multiplier is  invoked  inline.
           This makes for bigger, but faster code.

           The  hardware  multiply routines disable interrupts whilst running and restore the previous interrupt
           state when they finish.  This makes them safe to use inside interrupt handlers as well as  in  normal
           code.

       -minrt
           Enable  the  use  of a minimum runtime environment - no static initializers or constructors.  This is
           intended for memory-constrained devices.  The compiler includes special symbols in some objects  that
           tell the linker and runtime which code fragments are required.

       -mtiny-printf
           Enable  reduced  code  size "printf" and "puts" library functions.  The tiny implementations of these
           functions are not reentrant, so must be used with caution in multi-threaded applications.

           Support for streams has been removed and the string to be printed will always be sent to  stdout  via
           the "write" syscall.  The string is not buffered before it is sent to write.

           This     option    requires    Newlib    Nano    IO,    so    GCC    must    be    configured    with
           --enable-newlib-nano-formatted-io.

       -mmax-inline-shift=
           This option takes an integer between 0 and 64 inclusive, and sets the maximum number of inline  shift
           instructions  which  should  be emitted to perform a shift operation by a constant amount.  When this
           value needs to be exceeded, an mspabi helper function is used instead.  The default value is 4.

           This only affects cases where a shift by  multiple  positions  cannot  be  completed  with  a  single
           instruction (e.g. all shifts >1 on the 430 ISA).

           Shifts of a 32-bit value are at least twice as costly, so the value passed for this option is divided
           by 2 and the resulting value used instead.

       -mcode-region=
       -mdata-region=
           These  options  tell  the  compiler  where  to  place  functions and data that do not have one of the
           "lower", "upper", "either" or "section" attributes.  Possible values are "lower",  "upper",  "either"
           or  "any".   The  first  three  behave like the corresponding attribute.  The fourth possible value -
           "any" - is the default.  It leaves placement entirely up to the linker script and how it assigns  the
           standard sections (".text", ".data", etc) to the memory regions.

       -msilicon-errata=
           This option passes on a request to assembler to enable the fixes for the named silicon errata.

       -msilicon-errata-warn=
           This  option  passes  on  a request to the assembler to enable warning messages when a silicon errata
           might need to be applied.

       -mwarn-devices-csv
       -mno-warn-devices-csv
           Warn if devices.csv is not found or there are problem parsing it (default: on).

       NDS32 Options

       These options are defined for NDS32 implementations:

       -mbig-endian
           Generate code in big-endian mode.

       -mlittle-endian
           Generate code in little-endian mode.

       -mreduced-regs
           Use reduced-set registers for register allocation.

       -mfull-regs
           Use full-set registers for register allocation.

       -mcmov
           Generate conditional move instructions.

       -mno-cmov
           Do not generate conditional move instructions.

       -mext-perf
           Generate performance extension instructions.

       -mno-ext-perf
           Do not generate performance extension instructions.

       -mext-perf2
           Generate performance extension 2 instructions.

       -mno-ext-perf2
           Do not generate performance extension 2 instructions.

       -mext-string
           Generate string extension instructions.

       -mno-ext-string
           Do not generate string extension instructions.

       -mv3push
           Generate v3 push25/pop25 instructions.

       -mno-v3push
           Do not generate v3 push25/pop25 instructions.

       -m16-bit
           Generate 16-bit instructions.

       -mno-16-bit
           Do not generate 16-bit instructions.

       -misr-vector-size=num
           Specify the size of each interrupt vector, which must be 4 or 16.

       -mcache-block-size=num
           Specify the size of each cache block, which must be a power of 2 between 4 and 512.

       -march=arch
           Specify the name of the target architecture.

       -mcmodel=code-model
           Set the code model to one of

           small
               All the data and read-only data segments must be within 512KB addressing space.  The text segment
               must be within 16MB addressing space.

           medium
               The data segment must be within 512KB  while  the  read-only  data  segment  can  be  within  4GB
               addressing space.  The text segment should be still within 16MB addressing space.

           large
               All the text and data segments can be within 4GB addressing space.

       -mctor-dtor
           Enable constructor/destructor feature.

       -mrelax
           Guide linker to relax instructions.

       Nios II Options

       These are the options defined for the Altera Nios II processor.

       -G num
           Put  global  and  static  objects less than or equal to num bytes into the small data or BSS sections
           instead of the normal data or BSS sections.  The default value of num is 8.

       -mgpopt=option
       -mgpopt
       -mno-gpopt
           Generate (do not generate) GP-relative accesses.  The following option names are recognized:

           none
               Do not generate GP-relative accesses.

           local
               Generate  GP-relative  accesses  for  small  data  objects  that  are  not  external,  weak,   or
               uninitialized  common  symbols.   Also  use  GP-relative  addressing  for  objects that have been
               explicitly placed in a small data section via a "section" attribute.

           global
               As for local, but also generate GP-relative accesses for small data objects  that  are  external,
               weak,  or  common.   If  you  use  this  option,  you  must ensure that all parts of your program
               (including libraries) are compiled with the same -G setting.

           data
               Generate GP-relative accesses for all data objects in the program.  If you use this  option,  the
               entire  data  and  BSS  segments  of  your  program must fit in 64K of memory and you must use an
               appropriate linker script to allocate them within the addressable range of the global pointer.

           all Generate GP-relative addresses for function pointers as well as data pointers.  If you  use  this
               option, the entire text, data, and BSS segments of your program must fit in 64K of memory and you
               must use an appropriate linker script to allocate them within the addressable range of the global
               pointer.

           -mgpopt is equivalent to -mgpopt=local, and -mno-gpopt is equivalent to -mgpopt=none.

           The default is -mgpopt except when -fpic or -fPIC is specified to generate position-independent code.
           Note that the Nios II ABI does not permit GP-relative accesses from shared libraries.

           You  may  need  to specify -mno-gpopt explicitly when building programs that include large amounts of
           small data, including large GOT data sections.  In this  case,  the  16-bit  offset  for  GP-relative
           addressing may not be large enough to allow access to the entire small data section.

       -mgprel-sec=regexp
           This  option  specifies additional section names that can be accessed via GP-relative addressing.  It
           is most useful in conjunction with "section" attributes on variable declarations and a custom  linker
           script.  The regexp is a POSIX Extended Regular Expression.

           This option does not affect the behavior of the -G option, and the specified sections are in addition
           to the standard ".sdata" and ".sbss" small-data sections that are recognized by -mgpopt.

       -mr0rel-sec=regexp
           This  option specifies names of sections that can be accessed via a 16-bit offset from "r0"; that is,
           in the low 32K or high 32K of the 32-bit address space.   It  is  most  useful  in  conjunction  with
           "section"  attributes  on  variable  declarations  and a custom linker script.  The regexp is a POSIX
           Extended Regular Expression.

           In contrast to the use of GP-relative addressing for  small  data,  zero-based  addressing  is  never
           generated  by default and there are no conventional section names used in standard linker scripts for
           sections in the low or high areas of memory.

       -mel
       -meb
           Generate little-endian (default) or big-endian (experimental) code, respectively.

       -march=arch
           This specifies the name of the target Nios II architecture.  GCC uses this  name  to  determine  what
           kind of instructions it can emit when generating assembly code.  Permissible names are: r1, r2.

           The  preprocessor  macro "__nios2_arch__" is available to programs, with value 1 or 2, indicating the
           targeted ISA level.

       -mbypass-cache
       -mno-bypass-cache
           Force all load and  store  instructions  to  always  bypass  cache  by  using  I/O  variants  of  the
           instructions. The default is not to bypass the cache.

       -mno-cache-volatile
       -mcache-volatile
           Volatile  memory  access  bypass the cache using the I/O variants of the load and store instructions.
           The default is not to bypass the cache.

       -mno-fast-sw-div
       -mfast-sw-div
           Do not use table-based fast divide for small numbers. The default is to use the fast  divide  at  -O3
           and above.

       -mno-hw-mul
       -mhw-mul
       -mno-hw-mulx
       -mhw-mulx
       -mno-hw-div
       -mhw-div
           Enable  or  disable  emitting  "mul",  "mulx"  and  "div" family of instructions by the compiler. The
           default is to emit "mul" and not emit "div" and "mulx".

       -mbmx
       -mno-bmx
       -mcdx
       -mno-cdx
           Enable or  disable  generation  of  Nios  II  R2  BMX  (bit  manipulation)  and  CDX  (code  density)
           instructions.   Enabling  these  instructions  also requires -march=r2.  Since these instructions are
           optional extensions to the R2 architecture, the default is not to emit them.

       -mcustom-insn=N
       -mno-custom-insn
           Each -mcustom-insn=N option enables use of a custom instruction with encoding N when generating  code
           that  uses  insn.   For  example,  -mcustom-fadds=253  generates  custom  instruction 253 for single-
           precision floating-point add operations instead of the default behavior of using a library call.

           The following values of insn are supported.  Except as otherwise noted, floating-point operations are
           expected to be implemented with normal IEEE 754 semantics and correspond directly to the C  operators
           or the equivalent GCC built-in functions.

           Single-precision floating point:

           fadds, fsubs, fdivs, fmuls
               Binary arithmetic operations.

           fnegs
               Unary negation.

           fabss
               Unary absolute value.

           fcmpeqs, fcmpges, fcmpgts, fcmples, fcmplts, fcmpnes
               Comparison operations.

           fmins, fmaxs
               Floating-point  minimum and maximum.  These instructions are only generated if -ffinite-math-only
               is specified.

           fsqrts
               Unary square root operation.

           fcoss, fsins, ftans, fatans, fexps, flogs
               Floating-point trigonometric and exponential functions.  These instructions are only generated if
               -funsafe-math-optimizations is also specified.

           Double-precision floating point:

           faddd, fsubd, fdivd, fmuld
               Binary arithmetic operations.

           fnegd
               Unary negation.

           fabsd
               Unary absolute value.

           fcmpeqd, fcmpged, fcmpgtd, fcmpled, fcmpltd, fcmpned
               Comparison operations.

           fmind, fmaxd
               Double-precision   minimum   and   maximum.    These   instructions   are   only   generated   if
               -ffinite-math-only is specified.

           fsqrtd
               Unary square root operation.

           fcosd, fsind, ftand, fatand, fexpd, flogd
               Double-precision  trigonometric and exponential functions.  These instructions are only generated
               if -funsafe-math-optimizations is also specified.

           Conversions:

           fextsd
               Conversion from single precision to double precision.

           ftruncds
               Conversion from double precision to single precision.

           fixsi, fixsu, fixdi, fixdu
               Conversion from floating point to signed or unsigned integer types, with truncation towards zero.

           round
               Conversion from single-precision floating point  to  signed  integer,  rounding  to  the  nearest
               integer  and  ties  away  from  zero.   This corresponds to the "__builtin_lroundf" function when
               -fno-math-errno is used.

           floatis, floatus, floatid, floatud
               Conversion from signed or unsigned integer types to floating-point types.

           In addition, all of the following transfer instructions for  internal  registers  X  and  Y  must  be
           provided  to use any of the double-precision floating-point instructions.  Custom instructions taking
           two double-precision source operands expect the first operand in the 64-bit register  X.   The  other
           operand (or only operand of a unary operation) is given to the custom arithmetic instruction with the
           least  significant  half  in  source  register  src1 and the most significant half in src2.  A custom
           instruction that returns a double-precision result returns  the  most  significant  32  bits  in  the
           destination  register  and  the  other  half  in  32-bit register Y.  GCC automatically generates the
           necessary code sequences to write register X and/or read register Y when  double-precision  floating-
           point instructions are used.

           fwrx
               Write src1 into the least significant half of X and src2 into the most significant half of X.

           fwry
               Write src1 into Y.

           frdxhi, frdxlo
               Read the most or least (respectively) significant half of X and store it in dest.

           frdy
               Read the value of Y and store it into dest.

           Note that you can gain more local control over generation of Nios II custom instructions by using the
           "target("custom-insn=N")" and "target("no-custom-insn")" function attributes or pragmas.

       -mcustom-fpu-cfg=name
           This  option  enables  a  predefined,  named  set  of custom instruction encodings (see -mcustom-insn
           above).  Currently, the following sets are defined:

           -mcustom-fpu-cfg=60-1 is  equivalent  to:  -mcustom-fmuls=252  -mcustom-fadds=253  -mcustom-fsubs=254
           -fsingle-precision-constant

           -mcustom-fpu-cfg=60-2  is  equivalent  to:  -mcustom-fmuls=252  -mcustom-fadds=253 -mcustom-fsubs=254
           -mcustom-fdivs=255 -fsingle-precision-constant

           -mcustom-fpu-cfg=72-3 is equivalent to: -mcustom-floatus=243 -mcustom-fixsi=244  -mcustom-floatis=245
           -mcustom-fcmpgts=246       -mcustom-fcmples=249       -mcustom-fcmpeqs=250       -mcustom-fcmpnes=251
           -mcustom-fmuls=252         -mcustom-fadds=253          -mcustom-fsubs=254          -mcustom-fdivs=255
           -fsingle-precision-constant

           -mcustom-fpu-cfg=fph2  is  equivalent  to: -mcustom-fabss=224 -mcustom-fnegs=225 -mcustom-fcmpnes=226
           -mcustom-fcmpeqs=227       -mcustom-fcmpges=228       -mcustom-fcmpgts=229       -mcustom-fcmples=230
           -mcustom-fcmplts=231   -mcustom-fmaxs=232  -mcustom-fmins=233  -mcustom-round=248  -mcustom-fixsi=249
           -mcustom-floatis=250  -mcustom-fsqrts=251  -mcustom-fmuls=252  -mcustom-fadds=253  -mcustom-fsubs=254
           -mcustom-fdivs=255

           Custom  instruction  assignments  given  by individual -mcustom-insn= options override those given by
           -mcustom-fpu-cfg=, regardless of the order of the options on the command line.

           Note that you can gain more local control  over  selection  of  a  FPU  configuration  by  using  the
           "target("custom-fpu-cfg=name")" function attribute or pragma.

           The  name  fph2 is an abbreviation for Nios II Floating Point Hardware 2 Component.  Please note that
           the custom instructions enabled by -mcustom-fmins=233 and -mcustom-fmaxs=234 are  only  generated  if
           -ffinite-math-only  is  specified.   The  custom  instruction  enabled  by -mcustom-round=248 is only
           generated  if  -fno-math-errno  is   specified.    In   contrast   to   the   other   configurations,
           -fsingle-precision-constant is not set.

       These additional -m options are available for the Altera Nios II ELF (bare-metal) target:

       -mhal
           Link  with  HAL BSP.  This suppresses linking with the GCC-provided C runtime startup and termination
           code, and is typically used in conjunction with -msys-crt0= to specify the location of the  alternate
           startup code provided by the HAL BSP.

       -msmallc
           Link with a limited version of the C library, -lsmallc, rather than Newlib.

       -msys-crt0=startfile
           startfile  is  the file name of the startfile (crt0) to use when linking.  This option is only useful
           in conjunction with -mhal.

       -msys-lib=systemlib
           systemlib is the library name of the library that provides low-level system calls required by  the  C
           library, e.g. "read" and "write".  This option is typically used to link with a library provided by a
           HAL BSP.

       Nvidia PTX Options

       These options are defined for Nvidia PTX:

       -m64
           Ignored, but preserved for backward compatibility.  Only 64-bit ABI is supported.

       -misa=ISA-string
           Generate  code  for given the specified PTX ISA (e.g. sm_35).  ISA strings must be lower-case.  Valid
           ISA strings include sm_30 and sm_35.  The default ISA is sm_35.

       -mmainkernel
           Link in code for a __main kernel.  This is for stand-alone instead of offloading execution.

       -moptimize
           Apply partitioned execution optimizations.  This is the default when any  level  of  optimization  is
           selected.

       -msoft-stack
           Generate code that does not use ".local" memory directly for stack storage. Instead, a per-warp stack
           pointer is maintained explicitly. This enables variable-length stack allocation (with variable-length
           arrays  or  "alloca"),  and  when  global memory is used for underlying storage, makes it possible to
           access automatic variables from other threads, or with  atomic  instructions.  This  code  generation
           variant  is  used  for  OpenMP  offloading,  but  the option is exposed on its own for the purpose of
           testing the compiler; to generate code suitable for linking into programs  using  OpenMP  offloading,
           use option -mgomp.

       -muniform-simt
           Switch  to code generation variant that allows to execute all threads in each warp, while maintaining
           memory state and side effects as if only one thread in each warp was active outside  of  OpenMP  SIMD
           regions.   All  atomic  operations  and  calls  to  runtime (malloc, free, vprintf) are conditionally
           executed (iff current lane index equals the master lane index), and the register  being  assigned  is
           copied via a shuffle instruction from the master lane.  Outside of SIMD regions lane 0 is the master;
           inside,  each  thread sees itself as the master.  Shared memory array "int __nvptx_uni[]" stores all-
           zeros or all-ones bitmasks for each warp, indicating current mode (0 outside of SIMD regions).   Each
           thread  can bitwise-and the bitmask at position "tid.y" with current lane index to compute the master
           lane index.

       -mgomp
           Generate code for use in OpenMP offloading: enables  -msoft-stack  and  -muniform-simt  options,  and
           selects corresponding multilib variant.

       OpenRISC Options

       These options are defined for OpenRISC:

       -mboard=name
           Configure  a  board  specific  runtime.   This  will be passed to the linker for newlib board library
           linking.  The default is "or1ksim".

       -mnewlib
           This option is ignored; it is for compatibility purposes  only.   This  used  to  select  linker  and
           preprocessor options for use with newlib.

       -msoft-div
       -mhard-div
           Select  software  or  hardware  divide  ("l.div",  "l.divu")  instructions.  This default is hardware
           divide.

       -msoft-mul
       -mhard-mul
           Select software or hardware multiply ("l.mul", "l.muli")  instructions.   This  default  is  hardware
           multiply.

       -msoft-float
       -mhard-float
           Select software or hardware for floating point operations.  The default is software.

       -mdouble-float
           When  -mhard-float  is  selected, enables generation of double-precision floating point instructions.
           By default functions from libgcc are used to perform double-precision floating point operations.

       -munordered-float
           When -mhard-float is selected, enables generation of unordered floating point compare  and  set  flag
           ("lf.sfun*")  instructions.   By default functions from libgcc are used to perform unordered floating
           point compare and set flag operations.

       -mcmov
           Enable generation of conditional move ("l.cmov") instructions.  By default  the  equivalent  will  be
           generated using set and branch.

       -mror
           Enable  generation of rotate right ("l.ror") instructions.  By default functions from libgcc are used
           to perform rotate right operations.

       -mrori
           Enable generation of rotate right with immediate ("l.rori") instructions.  By default functions  from
           libgcc are used to perform rotate right with immediate operations.

       -msext
           Enable  generation  of  sign  extension ("l.ext*") instructions.  By default memory loads are used to
           perform sign extension.

       -msfimm
           Enable generation of compare and set flag with immediate ("l.sf*i") instructions.  By  default  extra
           instructions will be generated to store the immediate to a register first.

       -mshftimm
           Enable  generation  of  shift with immediate ("l.srai", "l.srli", "l.slli") instructions.  By default
           extra instructions will be generated to store the immediate to a register first.

       PDP-11 Options

       These options are defined for the PDP-11:

       -mfpu
           Use hardware FPP floating point.  This is the default.  (FIS floating point on the PDP-11/40  is  not
           supported.)  Implies -m45.

       -msoft-float
           Do not use hardware floating point.

       -mac0
           Return floating-point results in ac0 (fr0 in Unix assembler syntax).

       -mno-ac0
           Return floating-point results in memory.  This is the default.

       -m40
           Generate code for a PDP-11/40.  Implies -msoft-float -mno-split.

       -m45
           Generate code for a PDP-11/45.  This is the default.

       -m10
           Generate code for a PDP-11/10.  Implies -msoft-float -mno-split.

       -mint16
       -mno-int32
           Use 16-bit "int".  This is the default.

       -mint32
       -mno-int16
           Use 32-bit "int".

       -msplit
           Target has split instruction and data space.  Implies -m45.

       -munix-asm
           Use Unix assembler syntax.

       -mdec-asm
           Use DEC assembler syntax.

       -mgnu-asm
           Use GNU assembler syntax.  This is the default.

       -mlra
           Use the new LRA register allocator.  By default, the old "reload" allocator is used.

       picoChip Options

       These -m options are defined for picoChip implementations:

       -mae=ae_type
           Set  the  instruction set, register set, and instruction scheduling parameters for array element type
           ae_type.  Supported values for ae_type are ANY, MUL, and MAC.

           -mae=ANY selects a completely generic AE type.  Code generated with this option runs on  any  of  the
           other  AE types.  The code is not as efficient as it would be if compiled for a specific AE type, and
           some types of operation (e.g., multiplication) do not work properly on all types of AE.

           -mae=MUL selects a MUL AE type.  This is the most useful AE  type  for  compiled  code,  and  is  the
           default.

           -mae=MAC selects a DSP-style MAC AE.  Code compiled with this option may suffer from poor performance
           of byte (char) manipulation, since the DSP AE does not provide hardware support for byte load/stores.

       -msymbol-as-address
           Enable  the compiler to directly use a symbol name as an address in a load/store instruction, without
           first loading it into a register.  Typically, the use of this option generates larger programs, which
           run faster than when the option isn't used.  However, the results vary from program to program, so it
           is left as a user option, rather than being permanently enabled.

       -mno-inefficient-warnings
           Disables warnings about the generation of inefficient code.  These warnings  can  be  generated,  for
           example,  when compiling code that performs byte-level memory operations on the MAC AE type.  The MAC
           AE has no hardware support for  byte-level  memory  operations,  so  all  byte  load/stores  must  be
           synthesized  from  word  load/store  operations.   This  is inefficient and a warning is generated to
           indicate that you should rewrite the code to avoid byte operations, or to target an AE type that  has
           the necessary hardware support.  This option disables these warnings.

       PowerPC Options

       These are listed under

       PRU Options

       These command-line options are defined for PRU target:

       -minrt
           Link  with  a  minimum runtime environment, with no support for static initializers and constructors.
           Using this option can significantly reduce the size  of  the  final  ELF  binary.   Beware  that  the
           compiler  could  still  generate  code  with  static  initializers and constructors.  It is up to the
           programmer to ensure that the source program will not use those features.

       -mmcu=mcu
           Specify the PRU MCU variant to use.  Check Newlib for the exact list of supported MCUs.

       -mno-relax
           Make GCC pass the --no-relax command-line option to the linker instead of the --relax option.

       -mloop
           Allow (or do not allow) GCC to use the LOOP instruction.

       -mabi=variant
           Specify the ABI variant to output code for.  -mabi=ti selects the unmodified TI ABI  while  -mabi=gnu
           selects  a  GNU  variant  that  copes  more  naturally  with  certain GCC assumptions.  These are the
           differences:

           Function Pointer Size
               TI ABI specifies that function (code) pointers are 16-bit, whereas GNU supports only 32-bit  data
               and code pointers.

           Optional Return Value Pointer
               Function  return  values  larger  than  64 bits are passed by using a hidden pointer as the first
               argument of the function.  TI ABI, though, mandates that the pointer can  be  NULL  in  case  the
               caller  is  not  using  the  returned  value.  GNU always passes and expects a valid return value
               pointer.

           The current -mabi=ti implementation simply raises  a  compile  error  when  any  of  the  above  code
           constructs  is  detected.   As a consequence the standard C library cannot be built and it is omitted
           when linking with -mabi=ti.

           Relaxation is a GNU feature and for safety reasons is disabled when using -mabi=ti.  The TI toolchain
           does not emit relocations for QBBx instructions, so the GNU linker cannot adjust them when shortening
           adjacent LDI32 pseudo instructions.

       RISC-V Options

       These command-line options are defined for RISC-V targets:

       -mbranch-cost=n
           Set the cost of branches to roughly n instructions.

       -mplt
       -mno-plt
           When generating PIC code, do or don't allow the use of PLTs. Ignored for  non-PIC.   The  default  is
           -mplt.

       -mabi=ABI-string
           Specify  integer  and  floating-point calling convention.  ABI-string contains two parts: the size of
           integer  types  and  the  registers  used  for  floating-point  types.   For  example  -march=rv64ifd
           -mabi=lp64d  means that long and pointers are 64-bit (implicitly defining int to be 32-bit), and that
           floating-point  values  up  to  64  bits  wide  are  passed  in  F  registers.   Contrast  this  with
           -march=rv64ifd  -mabi=lp64f,  which  still allows the compiler to generate code that uses the F and D
           extensions but only allows floating-point values up to 32 bits long to be  passed  in  registers;  or
           -march=rv64ifd -mabi=lp64, in which no floating-point arguments will be passed in registers.

           The  default  for  this  argument  is  system dependent, users who want a specific calling convention
           should specify one explicitly.  The valid calling  conventions  are:  ilp32,  ilp32f,  ilp32d,  lp64,
           lp64f,  and  lp64d.   Some calling conventions are impossible to implement on some ISAs: for example,
           -march=rv32if -mabi=ilp32d is invalid  because  the  ABI  requires  64-bit  values  be  passed  in  F
           registers, but F registers are only 32 bits wide.  There is also the ilp32e ABI that can only be used
           with the rv32e architecture.  This ABI is not well specified at present, and is subject to change.

       -mfdiv
       -mno-fdiv
           Do  or don't use hardware floating-point divide and square root instructions.  This requires the F or
           D extensions for floating-point registers.  The default is to use them if the specified  architecture
           has these instructions.

       -mdiv
       -mno-div
           Do  or  don't  use  hardware  instructions for integer division.  This requires the M extension.  The
           default is to use them if the specified architecture has these instructions.

       -march=ISA-string
           Generate code for given RISC-V ISA (e.g. rv64im).  ISA strings must be lower-case.  Examples  include
           rv64i, rv32g, rv32e, and rv32imaf.

           When -march= is not specified, use the setting from -mcpu.

           If both -march and -mcpu= are not specified, the default for this argument is system dependent, users
           who want a specific architecture extensions should specify one explicitly.

       -mcpu=processor-string
           Use  architecture  of  and  optimize  the output for the given processor, specified by particular CPU
           name.  Permissible values for  this  option  are:  sifive-e20,  sifive-e21,  sifive-e24,  sifive-e31,
           sifive-e34, sifive-e76, sifive-s21, sifive-s51, sifive-s54, sifive-s76, sifive-u54, and sifive-u74.

       -mtune=processor-string
           Optimize  the  output for the given processor, specified by microarchitecture or particular CPU name.
           Permissible values for this option are: rocket,  sifive-3-series,  sifive-5-series,  sifive-7-series,
           size, and all valid options for -mcpu=.

           When  -mtune=  is  not  specified,  use the setting from -mcpu, the default is rocket if both are not
           specified.

           The size choice is not intended for use by end-users.  This  is  used  when  -Os  is  specified.   It
           overrides  the  instruction  cost  info provided by -mtune=, but does not override the pipeline info.
           This helps reduce code size while still giving good performance.

       -mpreferred-stack-boundary=num
           Attempt  to  keep  the  stack  boundary  aligned  to  a  2  raised  to   num   byte   boundary.    If
           -mpreferred-stack-boundary is not specified, the default is 4 (16 bytes or 128-bits).

           Warning:  If  you use this switch, then you must build all modules with the same value, including any
           libraries.  This includes the system libraries and startup modules.

       -msmall-data-limit=n
           Put global and static data smaller than n bytes into a special section (on some targets).

       -msave-restore
       -mno-save-restore
           Do or don't use smaller but slower prologue and epilogue code that uses library function calls.   The
           default is to use fast inline prologues and epilogues.

       -mshorten-memrefs
       -mno-shorten-memrefs
           Do or do not attempt to make more use of compressed load/store instructions by replacing a load/store
           of  'base  register  +  large offset' with a new load/store of 'new base + small offset'.  If the new
           base gets stored in a compressed register, then the new  load/store  can  be  compressed.   Currently
           targets 32-bit integer load/stores only.

       -mstrict-align
       -mno-strict-align
           Do  not  or  do  generate  unaligned  memory  accesses.   The default is set depending on whether the
           processor we are optimizing for supports fast unaligned access or not.

       -mcmodel=medlow
           Generate code for the medium-low code model. The program and its statically defined symbols must  lie
           within  a  single  2  GiB  address  range  and must lie between absolute addresses -2 GiB and +2 GiB.
           Programs can be statically or dynamically linked. This is the default code model.

       -mcmodel=medany
           Generate code for the medium-any code model. The program and its statically defined symbols  must  be
           within any single 2 GiB address range. Programs can be statically or dynamically linked.

       -mexplicit-relocs
       -mno-exlicit-relocs
           Use  or  do  not  use  assembler  relocation  operators  when  dealing  with symbolic addresses.  The
           alternative is to use assembler macros instead, which may limit optimization.

       -mrelax
       -mno-relax
           Take advantage of linker relaxations to reduce the number of  instructions  required  to  materialize
           symbol addresses. The default is to take advantage of linker relaxations.

       -memit-attribute
       -mno-emit-attribute
           Emit  (do  not  emit)  RISC-V  attribute  to record extra information into ELF objects.  This feature
           requires at least binutils 2.32.

       -malign-data=type
           Control how GCC aligns variables and constants of array, structure, or union types.  Supported values
           for type are xlen which uses x register width as the alignment value, and natural which uses  natural
           alignment.  xlen is the default.

       -mbig-endian
           Generate  big-endian  code.   This  is  the  default  when  GCC  is configured for a riscv64be-*-* or
           riscv32be-*-* target.

       -mlittle-endian
           Generate little-endian code.  This is the default  when  GCC  is  configured  for  a  riscv64-*-*  or
           riscv32-*-* but not a riscv64be-*-* or riscv32be-*-* target.

       -mstack-protector-guard=guard
       -mstack-protector-guard-reg=reg
       -mstack-protector-guard-offset=offset
           Generate  stack  protection  code using canary at guard.  Supported locations are global for a global
           canary or tls for per-thread canary in the TLS block.

           With     the     latter     choice     the      options      -mstack-protector-guard-reg=reg      and
           -mstack-protector-guard-offset=offset  furthermore specify which register to use as base register for
           reading the canary, and from what offset from that base register. There is  no  default  register  or
           offset as this is entirely for use within the Linux kernel.

       RL78 Options

       -msim
           Links in additional target libraries to support operation within a simulator.

       -mmul=none
       -mmul=g10
       -mmul=g13
       -mmul=g14
       -mmul=rl78
           Specifies  the  type  of  hardware  multiplication  and division support to be used.  The simplest is
           "none", which uses software for both multiplication and division.  This is the  default.   The  "g13"
           value  is  for  the hardware multiply/divide peripheral found on the RL78/G13 (S2 core) targets.  The
           "g14" value selects the use of the multiplication and division instructions supported by the RL78/G14
           (S3 core) parts.  The value "rl78" is an alias for "g14" and the value "mg10" is an alias for "none".

           In addition a C preprocessor macro is defined, based upon  the  setting  of  this  option.   Possible
           values are: "__RL78_MUL_NONE__", "__RL78_MUL_G13__" or "__RL78_MUL_G14__".

       -mcpu=g10
       -mcpu=g13
       -mcpu=g14
       -mcpu=rl78
           Specifies  the  RL78  core  to target.  The default is the G14 core, also known as an S3 core or just
           RL78.  The G13 or S2 core does not have multiply or divide instructions, instead it uses  a  hardware
           peripheral  for  these  operations.   The  G10  or S1 core does not have register banks, so it uses a
           different calling convention.

           If this option is set it also selects the type of hardware multiply support to use,  unless  this  is
           overridden  by  an explicit -mmul=none option on the command line.  Thus specifying -mcpu=g13 enables
           the use of the G13 hardware multiply peripheral and specifying -mcpu=g10 disables the use of hardware
           multiplications altogether.

           Note, although the RL78/G14 core is the default target, specifying -mcpu=g14  or  -mcpu=rl78  on  the
           command  line  does  change the behavior of the toolchain since it also enables G14 hardware multiply
           support.  If these options are not  specified  on  the  command  line  then  software  multiplication
           routines  will  be  used  even  though  the  code  targets  the  RL78  core.   This  is for backwards
           compatibility with older toolchains which did not have hardware multiply and divide support.

           In addition a C preprocessor macro is defined, based upon  the  setting  of  this  option.   Possible
           values are: "__RL78_G10__", "__RL78_G13__" or "__RL78_G14__".

       -mg10
       -mg13
       -mg14
       -mrl78
           These   are   aliases  for  the  corresponding  -mcpu=  option.   They  are  provided  for  backwards
           compatibility.

       -mallregs
           Allow the compiler to use all of the  available  registers.   By  default  registers  "r24..r31"  are
           reserved  for  use  in  interrupt  handlers.  With this option enabled these registers can be used in
           ordinary functions as well.

       -m64bit-doubles
       -m32bit-doubles
           Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits (-m32bit-doubles) in  size.   The
           default is -m32bit-doubles.

       -msave-mduc-in-interrupts
       -mno-save-mduc-in-interrupts
           Specifies  that  interrupt  handler  functions  should  preserve  the  MDUC  registers.  This is only
           necessary if normal code might use the MDUC registers, for example because it performs multiplication
           and division operations.  The default is to ignore the MDUC registers as  this  makes  the  interrupt
           handlers faster.  The target option -mg13 needs to be passed for this to work as this feature is only
           available  on  the  G13  target  (S2  core).   The MDUC registers will only be saved if the interrupt
           handler performs a multiplication or division operation or it calls another function.

       IBM RS/6000 and PowerPC Options

       These -m options are defined for the IBM RS/6000 and PowerPC:

       -mpowerpc-gpopt
       -mno-powerpc-gpopt
       -mpowerpc-gfxopt
       -mno-powerpc-gfxopt
       -mpowerpc64
       -mno-powerpc64
       -mmfcrf
       -mno-mfcrf
       -mpopcntb
       -mno-popcntb
       -mpopcntd
       -mno-popcntd
       -mfprnd
       -mno-fprnd
       -mcmpb
       -mno-cmpb
       -mhard-dfp
       -mno-hard-dfp
           You use these options to specify which instructions are available on the  processor  you  are  using.
           The default value of these options is determined when configuring GCC.  Specifying the -mcpu=cpu_type
           overrides  the specification of these options.  We recommend you use the -mcpu=cpu_type option rather
           than the options listed above.

           Specifying -mpowerpc-gpopt allows GCC to use the optional PowerPC architecture  instructions  in  the
           General  Purpose group, including floating-point square root.  Specifying -mpowerpc-gfxopt allows GCC
           to use the optional PowerPC architecture instructions in the Graphics group, including floating-point
           select.

           The -mmfcrf option allows GCC  to  generate  the  move  from  condition  register  field  instruction
           implemented on the POWER4 processor and other processors that support the PowerPC V2.01 architecture.
           The  -mpopcntb option allows GCC to generate the popcount and double-precision FP reciprocal estimate
           instruction implemented on the POWER5 processor and other processors that support the  PowerPC  V2.02
           architecture.   The  -mpopcntd  option allows GCC to generate the popcount instruction implemented on
           the POWER7 processor and other processors that support the PowerPC V2.06 architecture.   The  -mfprnd
           option  allows  GCC  to  generate  the  FP  round  to integer instructions implemented on the POWER5+
           processor and other processors that support the PowerPC V2.03 architecture.  The -mcmpb option allows
           GCC to generate the  compare  bytes  instruction  implemented  on  the  POWER6  processor  and  other
           processors that support the PowerPC V2.05 architecture.  The -mhard-dfp option allows GCC to generate
           the decimal floating-point instructions implemented on some POWER processors.

           The  -mpowerpc64  option  allows GCC to generate the additional 64-bit instructions that are found in
           the full PowerPC64 architecture and to treat GPRs as 64-bit, doubleword quantities.  GCC defaults  to
           -mno-powerpc64.

       -mcpu=cpu_type
           Set  architecture  type,  register  usage,  and  instruction  scheduling  parameters for machine type
           cpu_type.  Supported values for cpu_type are 401, 403, 405,  405fp,  440,  440fp,  464,  464fp,  476,
           476fp,  505, 601, 602, 603, 603e, 604, 604e, 620, 630, 740, 7400, 7450, 750, 801, 821, 823, 860, 970,
           8540, a2, e300c2, e300c3, e500mc, e500mc64, e5500, e6500, ec603e, G3, G4, G5, titan, power3,  power4,
           power5,  power5+,  power6, power6x, power7, power8, power9, power10, powerpc, powerpc64, powerpc64le,
           rs64, and native.

           -mcpu=powerpc, -mcpu=powerpc64, and -mcpu=powerpc64le specify pure 32-bit  PowerPC  (either  endian),
           64-bit  big  endian  PowerPC  and  64-bit  little  endian PowerPC architecture machine types, with an
           appropriate, generic processor model assumed for scheduling purposes.

           Specifying native as cpu type detects and selects the architecture option  that  corresponds  to  the
           host  processor of the system performing the compilation.  -mcpu=native has no effect if GCC does not
           recognize the processor.

           The other options specify a specific processor.  Code generated under those options runs best on that
           processor, and may not run at all on others.

           The -mcpu options automatically enable or disable the following options:

           -maltivec    -mfprnd    -mhard-float    -mmfcrf    -mmultiple   -mpopcntb    -mpopcntd    -mpowerpc64
           -mpowerpc-gpopt   -mpowerpc-gfxopt -mmulhw  -mdlmzb  -mmfpgpr  -mvsx -mcrypto  -mhtm  -mpower8-fusion
           -mpower8-vector  -mquad-memory   -mquad-memory-atomic   -mfloat128   -mfloat128-hardware   -mprefixed
           -mpcrel -mmma -mrop-protect

           The particular options set for any particular CPU varies between compiler versions, depending on what
           setting  seems  to  produce  optimal  code  for  that  CPU; it doesn't necessarily reflect the actual
           hardware's capabilities.  If you wish to set an individual option to  a  particular  value,  you  may
           specify it after the -mcpu option, like -mcpu=970 -mno-altivec.

           On  AIX,  the  -maltivec  and  -mpowerpc64 options are not enabled or disabled by the -mcpu option at
           present because AIX does not have full support for these options.  You may still  enable  or  disable
           them individually if you're sure it'll work in your environment.

       -mtune=cpu_type
           Set  the instruction scheduling parameters for machine type cpu_type, but do not set the architecture
           type or register usage, as -mcpu=cpu_type does.  The same values for cpu_type are used for -mtune  as
           for  -mcpu.   If  both  are  specified, the code generated uses the architecture and registers set by
           -mcpu, but the scheduling parameters set by -mtune.

       -mcmodel=small
           Generate PowerPC64 code for the small model: The TOC is limited to 64k.

       -mcmodel=medium
           Generate PowerPC64 code for the medium model: The TOC and other static data may be up to a  total  of
           4G in size.  This is the default for 64-bit Linux.

       -mcmodel=large
           Generate PowerPC64 code for the large model: The TOC may be up to 4G in size.  Other data and code is
           only limited by the 64-bit address space.

       -maltivec
       -mno-altivec
           Generate  code  that  uses  (does  not use) AltiVec instructions, and also enable the use of built-in
           functions that allow more direct access to the AltiVec instruction set.  You may  also  need  to  set
           -mabi=altivec to adjust the current ABI with AltiVec ABI enhancements.

           When  -maltivec is used, the element order for AltiVec intrinsics such as "vec_splat", "vec_extract",
           and "vec_insert" match array element order corresponding to the endianness of the target.   That  is,
           element  zero  identifies  the  leftmost  element  in  a  vector register when targeting a big-endian
           platform, and identifies the rightmost element in a vector register when  targeting  a  little-endian
           platform.

       -mvrsave
       -mno-vrsave
           Generate VRSAVE instructions when generating AltiVec code.

       -msecure-plt
           Generate  code that allows ld and ld.so to build executables and shared libraries with non-executable
           ".plt" and ".got" sections.  This is a PowerPC 32-bit SYSV ABI option.

       -mbss-plt
           Generate code that uses a BSS ".plt" section that ld.so fills in,  and  requires  ".plt"  and  ".got"
           sections that are both writable and executable.  This is a PowerPC 32-bit SYSV ABI option.

       -misel
       -mno-isel
           This switch enables or disables the generation of ISEL instructions.

       -mvsx
       -mno-vsx
           Generate  code  that uses (does not use) vector/scalar (VSX) instructions, and also enable the use of
           built-in functions that allow more direct access to the VSX instruction set.

       -mcrypto
       -mno-crypto
           Enable the use (disable) of the built-in functions that allow  direct  access  to  the  cryptographic
           instructions that were added in version 2.07 of the PowerPC ISA.

       -mhtm
       -mno-htm
           Enable  (disable)  the  use  of  the  built-in  functions  that  allow  direct access to the Hardware
           Transactional Memory (HTM) instructions that were added in version 2.07 of the PowerPC ISA.

       -mpower8-fusion
       -mno-power8-fusion
           Generate code that keeps (does not keeps) some integer operations adjacent so that  the  instructions
           can be fused together on power8 and later processors.

       -mpower8-vector
       -mno-power8-vector
           Generate  code that uses (does not use) the vector and scalar instructions that were added in version
           2.07 of the PowerPC ISA.  Also enable the use of built-in functions that allow more direct access  to
           the vector instructions.

       -mquad-memory
       -mno-quad-memory
           Generate  code  that  uses  (does  not  use)  the  non-atomic  quad  word  memory  instructions.  The
           -mquad-memory option requires use of 64-bit mode.

       -mquad-memory-atomic
       -mno-quad-memory-atomic
           Generate  code  that  uses  (does  not  use)  the  atomic  quad  word   memory   instructions.    The
           -mquad-memory-atomic option requires use of 64-bit mode.

       -mfloat128
       -mno-float128
           Enable/disable  the  __float128  keyword  for  IEEE  128-bit  floating  point and use either software
           emulation for IEEE 128-bit floating point or hardware instructions.

           The VSX instruction set (-mvsx) must be enabled to use the IEEE 128-bit floating point support.   The
           IEEE 128-bit floating point is only supported on Linux.

           The  default  for  -mfloat128  is enabled on PowerPC Linux systems using the VSX instruction set, and
           disabled on other systems.

           If you use the ISA 3.0 instruction set (-mpower9-vector or -mcpu=power9) on a 64-bit system, the IEEE
           128-bit floating point support will also enable the generation of ISA 3.0 IEEE 128-bit floating point
           instructions.  Otherwise, if you do not specify to generate ISA 3.0 instructions or you are targeting
           a 32-bit big endian system, IEEE 128-bit floating point will be done with software emulation.

       -mfloat128-hardware
       -mno-float128-hardware
           Enable/disable using ISA 3.0 hardware instructions to support the __float128 data type.

           The default for -mfloat128-hardware is enabled on PowerPC Linux systems using the ISA 3.0 instruction
           set, and disabled on other systems.

       -m32
       -m64
           Generate code for 32-bit or 64-bit environments of Darwin and  SVR4  targets  (including  GNU/Linux).
           The  32-bit  environment  sets  int,  long and pointer to 32 bits and generates code that runs on any
           PowerPC variant.  The 64-bit environment sets int to 32 bits and long and pointer  to  64  bits,  and
           generates code for PowerPC64, as for -mpowerpc64.

       -mfull-toc
       -mno-fp-in-toc
       -mno-sum-in-toc
       -mminimal-toc
           Modify  generation  of  the TOC (Table Of Contents), which is created for every executable file.  The
           -mfull-toc option is selected by default.  In that case, GCC allocates at least  one  TOC  entry  for
           each  unique  non-automatic  variable  reference  in  your  program.   GCC also places floating-point
           constants in the TOC.  However, only 16,384 entries are available in the TOC.

           If you receive a linker error message that saying you have overflowed the available  TOC  space,  you
           can  reduce  the  amount  of  TOC  space  used  with  the -mno-fp-in-toc and -mno-sum-in-toc options.
           -mno-fp-in-toc prevents GCC from putting floating-point constants  in  the  TOC  and  -mno-sum-in-toc
           forces  GCC to generate code to calculate the sum of an address and a constant at run time instead of
           putting that sum into the TOC.  You may specify one or both of these options.   Each  causes  GCC  to
           produce very slightly slower and larger code at the expense of conserving TOC space.

           If  you  still  run  out  of  space  in  the TOC even when you specify both of these options, specify
           -mminimal-toc instead.  This option causes GCC to make only one TOC entry for every file.   When  you
           specify  this option, GCC produces code that is slower and larger but which uses extremely little TOC
           space.  You may wish to use this option only on files that contain less frequently-executed code.

       -maix64
       -maix32
           Enable 64-bit AIX  ABI  and  calling  convention:  64-bit  pointers,  64-bit  "long"  type,  and  the
           infrastructure  needed  to  support  them.   Specifying  -maix64  implies  -mpowerpc64, while -maix32
           disables the 64-bit ABI and implies -mno-powerpc64.  GCC defaults to -maix32.

       -mxl-compat
       -mno-xl-compat
           Produce code that conforms more closely to IBM XL compiler semantics when using  AIX-compatible  ABI.
           Pass  floating-point  arguments  to  prototyped  functions beyond the register save area (RSA) on the
           stack in addition to argument FPRs.  Do not assume that  most  significant  double  in  128-bit  long
           double value is properly rounded when comparing values and converting to double.  Use XL symbol names
           for long double support routines.

           The  AIX calling convention was extended but not initially documented to handle an obscure K&R C case
           of calling a function that takes the address of its arguments with  fewer  arguments  than  declared.
           IBM  XL  compilers  access  floating-point arguments that do not fit in the RSA from the stack when a
           subroutine is compiled without optimization.  Because always storing floating-point arguments on  the
           stack  is  inefficient and rarely needed, this option is not enabled by default and only is necessary
           when calling subroutines compiled by IBM XL compilers without optimization.

       -mpe
           Support IBM RS/6000 SP Parallel Environment (PE).  Link an application written to use message passing
           with special startup code to enable the application to run.  The system must have PE installed in the
           standard location (/usr/lpp/ppe.poe/), or the specs file must be overridden with the  -specs=  option
           to specify the appropriate directory location.  The Parallel Environment does not support threads, so
           the -mpe option and the -pthread option are incompatible.

       -malign-natural
       -malign-power
           On  AIX,  32-bit  Darwin, and 64-bit PowerPC GNU/Linux, the option -malign-natural overrides the ABI-
           defined alignment of larger types, such  as  floating-point  doubles,  on  their  natural  size-based
           boundary.   The  option -malign-power instructs GCC to follow the ABI-specified alignment rules.  GCC
           defaults to the standard alignment defined in the ABI.

           On 64-bit Darwin, natural alignment is the default, and -malign-power is not supported.

       -msoft-float
       -mhard-float
           Generate code that does not use (uses) the  floating-point  register  set.   Software  floating-point
           emulation is provided if you use the -msoft-float option, and pass the option to GCC when linking.

       -mmultiple
       -mno-multiple
           Generate  code  that  uses  (does not use) the load multiple word instructions and the store multiple
           word instructions.  These instructions are generated by default on POWER systems, and  not  generated
           on PowerPC systems.  Do not use -mmultiple on little-endian PowerPC systems, since those instructions
           do  not work when the processor is in little-endian mode.  The exceptions are PPC740 and PPC750 which
           permit these instructions in little-endian mode.

       -mupdate
       -mno-update
           Generate code that uses (does not use) the load or store instructions that update the  base  register
           to  the  address of the calculated memory location.  These instructions are generated by default.  If
           you use -mno-update, there is a small window between the time that the stack pointer is  updated  and
           the  address  of  the  previous  frame  is stored, which means code that walks the stack frame across
           interrupts or signals may get corrupted data.

       -mavoid-indexed-addresses
       -mno-avoid-indexed-addresses
           Generate code that tries to avoid (not avoid) the use of indexed load or  store  instructions.  These
           instructions can incur a performance penalty on Power6 processors in certain situations, such as when
           stepping  through  large  arrays  that  cross a 16M boundary.  This option is enabled by default when
           targeting Power6 and disabled otherwise.

       -mfused-madd
       -mno-fused-madd
           Generate code that uses (does not use)  the  floating-point  multiply  and  accumulate  instructions.
           These  instructions  are  generated  by  default  if  hardware  floating point is used.  The machine-
           dependent -mfused-madd option is now mapped to the machine-independent -ffp-contract=fast option, and
           -mno-fused-madd is mapped to -ffp-contract=off.

       -mmulhw
       -mno-mulhw
           Generate code that uses (does not use) the half-word multiply and multiply-accumulate instructions on
           the IBM 405, 440, 464 and 476 processors.  These instructions are generated by default when targeting
           those processors.

       -mdlmzb
       -mno-dlmzb
           Generate code that uses (does not use) the string-search dlmzb instruction on the IBM 405,  440,  464
           and 476 processors.  This instruction is generated by default when targeting those processors.

       -mno-bit-align
       -mbit-align
           On  System V.4 and embedded PowerPC systems do not (do) force structures and unions that contain bit-
           fields to be aligned to the base type of the bit-field.

           For example, by default a structure containing nothing but 8 "unsigned" bit-fields  of  length  1  is
           aligned  to  a  4-byte boundary and has a size of 4 bytes.  By using -mno-bit-align, the structure is
           aligned to a 1-byte boundary and is 1 byte in size.

       -mno-strict-align
       -mstrict-align
           On System V.4 and embedded PowerPC systems do not (do) assume that unaligned  memory  references  are
           handled by the system.

       -mrelocatable
       -mno-relocatable
           Generate code that allows (does not allow) a static executable to be relocated to a different address
           at  run time.  A simple embedded PowerPC system loader should relocate the entire contents of ".got2"
           and 4-byte locations listed in the ".fixup" section, a table of 32-bit addresses  generated  by  this
           option.   For  this  to  work,  all  objects  linked  together must be compiled with -mrelocatable or
           -mrelocatable-lib.  -mrelocatable code aligns the stack to an 8-byte boundary.

       -mrelocatable-lib
       -mno-relocatable-lib
           Like -mrelocatable, -mrelocatable-lib generates a ".fixup" section to allow static executables to  be
           relocated  at  run  time,  but  -mrelocatable-lib  does  not  use  the  smaller  stack  alignment  of
           -mrelocatable.  Objects compiled with -mrelocatable-lib may be linked with objects compiled with  any
           combination of the -mrelocatable options.

       -mno-toc
       -mtoc
           On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains a pointer to a
           global area pointing to the addresses used in the program.

       -mlittle
       -mlittle-endian
           On System V.4 and embedded PowerPC systems compile code for the processor in little-endian mode.  The
           -mlittle-endian option is the same as -mlittle.

       -mbig
       -mbig-endian
           On  System  V.4  and embedded PowerPC systems compile code for the processor in big-endian mode.  The
           -mbig-endian option is the same as -mbig.

       -mdynamic-no-pic
           On Darwin and Mac OS X systems, compile code so that it is not relocatable,  but  that  its  external
           references  are  relocatable.   The  resulting  code  is  suitable  for  applications, but not shared
           libraries.

       -msingle-pic-base
           Treat the register used for PIC addressing as read-only, rather than loading it in the  prologue  for
           each  function.  The runtime system is responsible for initializing this register with an appropriate
           value before execution begins.

       -mprioritize-restricted-insns=priority
           This option controls the priority that is assigned to dispatch-slot  restricted  instructions  during
           the  second scheduling pass.  The argument priority takes the value 0, 1, or 2 to assign no, highest,
           or second-highest (respectively) priority to dispatch-slot restricted instructions.

       -msched-costly-dep=dependence_type
           This option controls which dependences  are  considered  costly  by  the  target  during  instruction
           scheduling.  The argument dependence_type takes one of the following values:

           no  No dependence is costly.

           all All dependences are costly.

           true_store_to_load
               A true dependence from store to load is costly.

           store_to_load
               Any dependence from store to load is costly.

           number
               Any dependence for which the latency is greater than or equal to number is costly.

       -minsert-sched-nops=scheme
           This  option  controls  which  NOP  insertion  scheme is used during the second scheduling pass.  The
           argument scheme takes one of the following values:

           no  Don't insert NOPs.

           pad Pad with NOPs any dispatch group that has  vacant  issue  slots,  according  to  the  scheduler's
               grouping.

           regroup_exact
               Insert NOPs to force costly dependent insns into separate groups.  Insert exactly as many NOPs as
               needed to force an insn to a new group, according to the estimated processor grouping.

           number
               Insert NOPs to force costly dependent insns into separate groups.  Insert number NOPs to force an
               insn to a new group.

       -mcall-sysv
           On  System V.4 and embedded PowerPC systems compile code using calling conventions that adhere to the
           March 1995 draft of the System V Application Binary Interface, PowerPC processor supplement.  This is
           the default unless you configured GCC using powerpc-*-eabiaix.

       -mcall-sysv-eabi
       -mcall-eabi
           Specify both -mcall-sysv and -meabi options.

       -mcall-sysv-noeabi
           Specify both -mcall-sysv and -mno-eabi options.

       -mcall-aixdesc
           On System V.4 and embedded PowerPC systems compile code for the AIX operating system.

       -mcall-linux
           On System V.4 and embedded PowerPC systems compile code for the Linux-based GNU system.

       -mcall-freebsd
           On System V.4 and embedded PowerPC systems compile code for the FreeBSD operating system.

       -mcall-netbsd
           On System V.4 and embedded PowerPC systems compile code for the NetBSD operating system.

       -mcall-openbsd
           On System V.4 and embedded PowerPC systems compile code for the OpenBSD operating system.

       -mtraceback=traceback_type
           Select the type of traceback table. Valid values for traceback_type are full, part, and no.

       -maix-struct-return
           Return all structures in memory (as specified by the AIX ABI).

       -msvr4-struct-return
           Return structures smaller than 8 bytes in registers (as specified by the SVR4 ABI).

       -mabi=abi-type
           Extend the current ABI with a particular extension, or remove  such  extension.   Valid  values  are:
           altivec,  no-altivec,  ibmlongdouble,  ieeelongdouble,  elfv1,  elfv2,  and for AIX: vec-extabi, vec-
           default.

       -mabi=ibmlongdouble
           Change the current ABI to use IBM extended-precision long double.  This is not likely to work if your
           system defaults to using IEEE extended-precision long double.  If you change  the  long  double  type
           from IEEE extended-precision, the compiler will issue a warning unless you use the -Wno-psabi option.
           Requires -mlong-double-128 to be enabled.

       -mabi=ieeelongdouble
           Change  the  current  ABI  to use IEEE extended-precision long double.  This is not likely to work if
           your system defaults to using IBM extended-precision long double.  If you change the long double type
           from IBM extended-precision, the compiler will issue a warning unless you use the -Wno-psabi  option.
           Requires -mlong-double-128 to be enabled.

       -mabi=elfv1
           Change  the  current ABI to use the ELFv1 ABI.  This is the default ABI for big-endian PowerPC 64-bit
           Linux.  Overriding the default ABI  requires  special  system  support  and  is  likely  to  fail  in
           spectacular ways.

       -mabi=elfv2
           Change  the  current  ABI  to  use  the ELFv2 ABI.  This is the default ABI for little-endian PowerPC
           64-bit Linux.  Overriding the default ABI requires special system support and is likely  to  fail  in
           spectacular ways.

       -mgnu-attribute
       -mno-gnu-attribute
           Emit  .gnu_attribute  assembly  directives  to  set tag/value pairs in a .gnu.attributes section that
           specify ABI variations in function parameters or return values.

       -mprototype
       -mno-prototype
           On System V.4 and embedded PowerPC systems assume that all calls to variable argument  functions  are
           properly  prototyped.  Otherwise, the compiler must insert an instruction before every non-prototyped
           call to set or clear bit 6 of the condition code register ("CR") to indicate  whether  floating-point
           values  are  passed  in  the  floating-point registers in case the function takes variable arguments.
           With -mprototype, only calls to prototyped variable argument functions set or clear the bit.

       -msim
           On embedded PowerPC systems, assume that the  startup  module  is  called  sim-crt0.o  and  that  the
           standard   C  libraries  are  libsim.a  and  libc.a.   This  is  the  default  for  powerpc-*-eabisim
           configurations.

       -mmvme
           On embedded PowerPC systems, assume that the startup module is  called  crt0.o  and  the  standard  C
           libraries are libmvme.a and libc.a.

       -mads
           On  embedded  PowerPC  systems,  assume  that  the startup module is called crt0.o and the standard C
           libraries are libads.a and libc.a.

       -myellowknife
           On embedded PowerPC systems, assume that the startup module is  called  crt0.o  and  the  standard  C
           libraries are libyk.a and libc.a.

       -mvxworks
           On System V.4 and embedded PowerPC systems, specify that you are compiling for a VxWorks system.

       -memb
           On  embedded  PowerPC  systems,  set  the "PPC_EMB" bit in the ELF flags header to indicate that eabi
           extended relocations are used.

       -meabi
       -mno-eabi
           On System V.4 and embedded PowerPC systems do (do not) adhere to  the  Embedded  Applications  Binary
           Interface (EABI), which is a set of modifications to the System V.4 specifications.  Selecting -meabi
           means  that  the stack is aligned to an 8-byte boundary, a function "__eabi" is called from "main" to
           set up the EABI environment, and the -msdata option can use both "r2"  and  "r13"  to  point  to  two
           separate  small  data  areas.   Selecting  -mno-eabi  means  that  the  stack is aligned to a 16-byte
           boundary, no EABI initialization function is called from "main", and the  -msdata  option  only  uses
           "r13" to point to a single small data area.  The -meabi option is on by default if you configured GCC
           using one of the powerpc*-*-eabi* options.

       -msdata=eabi
           On  System  V.4 and embedded PowerPC systems, put small initialized "const" global and static data in
           the ".sdata2" section, which is pointed to by  register  "r2".   Put  small  initialized  non-"const"
           global  and  static  data  in the ".sdata" section, which is pointed to by register "r13".  Put small
           uninitialized global and static data in the ".sbss"  section,  which  is  adjacent  to  the  ".sdata"
           section.   The  -msdata=eabi  option is incompatible with the -mrelocatable option.  The -msdata=eabi
           option also sets the -memb option.

       -msdata=sysv
           On System V.4 and embedded PowerPC systems, put small global and static data in the ".sdata" section,
           which is pointed to by register "r13".  Put small uninitialized global and static data in the ".sbss"
           section, which is adjacent to the ".sdata" section.  The -msdata=sysv option is incompatible with the
           -mrelocatable option.

       -msdata=default
       -msdata
           On System V.4 and embedded PowerPC systems, if -meabi is used, compile code the same as -msdata=eabi,
           otherwise compile code the same as -msdata=sysv.

       -msdata=data
           On System V.4 and embedded PowerPC systems, put small global data in the ".sdata" section.  Put small
           uninitialized global data in the ".sbss" section.  Do not use register "r13" to  address  small  data
           however.  This is the default behavior unless other -msdata options are used.

       -msdata=none
       -mno-sdata
           On  embedded  PowerPC systems, put all initialized global and static data in the ".data" section, and
           all uninitialized data in the ".bss" section.

       -mreadonly-in-sdata
           Put read-only objects in the ".sdata" section as well.  This is the default.

       -mblock-move-inline-limit=num
           Inline all block moves (such as calls to "memcpy" or structure copies) less  than  or  equal  to  num
           bytes.   The minimum value for num is 32 bytes on 32-bit targets and 64 bytes on 64-bit targets.  The
           default value is target-specific.

       -mblock-compare-inline-limit=num
           Generate non-looping inline code for all block compares (such  as  calls  to  "memcmp"  or  structure
           compares)  less  than or equal to num bytes. If num is 0, all inline expansion (non-loop and loop) of
           block compare is disabled. The default value is target-specific.

       -mblock-compare-inline-loop-limit=num
           Generate an inline expansion using loop code for all block compares that are less than  or  equal  to
           num  bytes,  but  greater  than  the  limit for non-loop inline block compare expansion. If the block
           length is not constant, at most num bytes will be compared before "memcmp" is called to  compare  the
           remainder of the block. The default value is target-specific.

       -mstring-compare-inline-limit=num
           Compare  at  most num string bytes with inline code.  If the difference or end of string is not found
           at the end of the inline compare a call to "strcmp" or "strncmp" will take care of the  rest  of  the
           comparison. The default is 64 bytes.

       -G num
           On  embedded  PowerPC  systems,  put global and static items less than or equal to num bytes into the
           small data or BSS sections instead of the normal data or BSS section.  By default, num is 8.  The  -G
           num switch is also passed to the linker.  All modules should be compiled with the same -G num value.

       -mregnames
       -mno-regnames
           On  System  V.4 and embedded PowerPC systems do (do not) emit register names in the assembly language
           output using symbolic forms.

       -mlongcall
       -mno-longcall
           By default assume that all calls are far away so that a longer and more expensive calling sequence is
           required.  This is required for calls farther than 32 megabytes (33,554,432 bytes) from  the  current
           location.   A  short  call is generated if the compiler knows the call cannot be that far away.  This
           setting can be overridden by the "shortcall" function attribute, or by "#pragma longcall(0)".

           Some linkers are capable of detecting out-of-range calls and generating glue code  on  the  fly.   On
           these  systems,  long  calls  are  unnecessary and generate slower code.  As of this writing, the AIX
           linker can do this, as can the GNU linker for PowerPC/64.  It is planned to add this feature  to  the
           GNU linker for 32-bit PowerPC systems as well.

           On  PowerPC64  ELFv2  and  32-bit PowerPC systems with newer GNU linkers, GCC can generate long calls
           using an inline PLT call sequence (see -mpltseq).  PowerPC with -mbss-plt and PowerPC64  ELFv1  (big-
           endian) do not support inline PLT calls.

           On  Darwin/PPC  systems,  "#pragma longcall" generates "jbsr callee, L42", plus a branch island (glue
           code).  The two target addresses represent the callee and the branch island.  The  Darwin/PPC  linker
           prefers  the first address and generates a "bl callee" if the PPC "bl" instruction reaches the callee
           directly; otherwise, the linker generates "bl L42" to call the branch island.  The branch  island  is
           appended  to  the body of the calling function; it computes the full 32-bit address of the callee and
           jumps to it.

           On Mach-O (Darwin) systems, this option directs the compiler emit to the glue for every direct  call,
           and the Darwin linker decides whether to use or discard it.

           In the future, GCC may ignore all longcall specifications when the linker is known to generate glue.

       -mpltseq
       -mno-pltseq
           Implement  (do not implement) -fno-plt and long calls using an inline PLT call sequence that supports
           lazy linking and long calls to functions in dlopen'd shared libraries.  Inline  PLT  calls  are  only
           supported  on  PowerPC64  ELFv2 and 32-bit PowerPC systems with newer GNU linkers, and are enabled by
           default if the support is detected when configuring GCC, and, in the case of 32-bit PowerPC,  if  GCC
           is  configured  with  --enable-secureplt.   -mpltseq  code  and  -mbss-plt 32-bit PowerPC relocatable
           objects may not be linked together.

       -mtls-markers
       -mno-tls-markers
           Mark (do not mark) calls to "__tls_get_addr" with a relocation specifying the function argument.  The
           relocation allows the linker to reliably associate function call with argument setup instructions for
           TLS optimization, which in turn allows GCC to better schedule the sequence.

       -mrecip
       -mno-recip
           This option enables use of the reciprocal estimate and reciprocal square root  estimate  instructions
           with  additional  Newton-Raphson steps to increase precision instead of doing a divide or square root
           and divide for floating-point arguments.  You should use the -ffast-math option  when  using  -mrecip
           (or    at    least    -funsafe-math-optimizations,    -ffinite-math-only,    -freciprocal-math    and
           -fno-trapping-math).  Note that while the throughput of the sequence is  generally  higher  than  the
           throughput of the non-reciprocal instruction, the precision of the sequence can be decreased by up to
           2 ulp (i.e. the inverse of 1.0 equals 0.99999994) for reciprocal square roots.

       -mrecip=opt
           This  option  controls  which reciprocal estimate instructions may be used.  opt is a comma-separated
           list of options, which may be preceded by a "!" to invert the option:

           all Enable all estimate instructions.

           default
               Enable the default instructions, equivalent to -mrecip.

           none
               Disable all estimate instructions, equivalent to -mno-recip.

           div Enable the reciprocal approximation instructions for both single and double precision.

           divf
               Enable the single-precision reciprocal approximation instructions.

           divd
               Enable the double-precision reciprocal approximation instructions.

           rsqrt
               Enable the  reciprocal  square  root  approximation  instructions  for  both  single  and  double
               precision.

           rsqrtf
               Enable the single-precision reciprocal square root approximation instructions.

           rsqrtd
               Enable the double-precision reciprocal square root approximation instructions.

           So,  for example, -mrecip=all,!rsqrtd enables all of the reciprocal estimate instructions, except for
           the  "FRSQRTE",  "XSRSQRTEDP",  and  "XVRSQRTEDP"  instructions  which  handle  the  double-precision
           reciprocal square root calculations.

       -mrecip-precision
       -mno-recip-precision
           Assume  (do  not assume) that the reciprocal estimate instructions provide higher-precision estimates
           than  is  mandated  by  the  PowerPC  ABI.   Selecting  -mcpu=power6,  -mcpu=power7  or  -mcpu=power8
           automatically  selects -mrecip-precision.  The double-precision square root estimate instructions are
           not generated by default on low-precision machines, since  they  do  not  provide  an  estimate  that
           converges after three steps.

       -mveclibabi=type
           Specifies  the  ABI  type to use for vectorizing intrinsics using an external library.  The only type
           supported at present is mass, which specifies to use IBM's Mathematical Acceleration Subsystem (MASS)
           libraries for vectorizing  intrinsics  using  external  libraries.   GCC  currently  emits  calls  to
           "acosd2",  "acosf4",  "acoshd2",  "acoshf4",  "asind2",  "asinf4",  "asinhd2",  "asinhf4", "atan2d2",
           "atan2f4", "atand2", "atanf4", "atanhd2", "atanhf4", "cbrtd2", "cbrtf4", "cosd2", "cosf4",  "coshd2",
           "coshf4",  "erfcd2",  "erfcf4",  "erfd2",  "erff4",  "exp2d2", "exp2f4", "expd2", "expf4", "expm1d2",
           "expm1f4", "hypotd2", "hypotf4", "lgammad2", "lgammaf4", "log10d2", "log10f4", "log1pd2",  "log1pf4",
           "log2d2",  "log2f4",  "logd2",  "logf4",  "powd2",  "powf4",  "sind2",  "sinf4",  "sinhd2", "sinhf4",
           "sqrtd2", "sqrtf4", "tand2", "tanf4", "tanhd2", and "tanhf4" when generating code for  power7.   Both
           -ftree-vectorize  and  -funsafe-math-optimizations  must also be enabled.  The MASS libraries must be
           specified at link time.

       -mfriz
       -mno-friz
           Generate (do not generate) the "friz" instruction when the -funsafe-math-optimizations option is used
           to optimize rounding of floating-point values to 64-bit integer and  back  to  floating  point.   The
           "friz" instruction does not return the same value if the floating-point number is too large to fit in
           an integer.

       -mpointers-to-nested-functions
       -mno-pointers-to-nested-functions
           Generate  (do  not generate) code to load up the static chain register ("r11") when calling through a
           pointer on AIX and 64-bit Linux systems where a function pointer points to a 3-word descriptor giving
           the function address, TOC value to be loaded in register "r2", and static chain value to be loaded in
           register "r11".  The -mpointers-to-nested-functions is  on  by  default.   You  cannot  call  through
           pointers to nested functions or pointers to functions compiled in other languages that use the static
           chain if you use -mno-pointers-to-nested-functions.

       -msave-toc-indirect
       -mno-save-toc-indirect
           Generate  (do not generate) code to save the TOC value in the reserved stack location in the function
           prologue if the function calls through a pointer on AIX and 64-bit Linux systems.  If the  TOC  value
           is  not  saved  in  the  prologue,  it  is  saved  just  before  the  call  through the pointer.  The
           -mno-save-toc-indirect option is the default.

       -mcompat-align-parm
       -mno-compat-align-parm
           Generate (do not generate) code to pass structure parameters with a maximum alignment of 64 bits, for
           compatibility with older versions of GCC.

           Older versions of GCC (prior to 4.9.0) incorrectly did not align a structure parameter on  a  128-bit
           boundary  when  that  structure contained a member requiring 128-bit alignment.  This is corrected in
           more recent versions of GCC.  This option may be used  to  generate  code  that  is  compatible  with
           functions compiled with older versions of GCC.

           The -mno-compat-align-parm option is the default.

       -mstack-protector-guard=guard
       -mstack-protector-guard-reg=reg
       -mstack-protector-guard-offset=offset
       -mstack-protector-guard-symbol=symbol
           Generate  stack  protection  code  using  canary at guard.  Supported locations are global for global
           canary or tls for per-thread canary in the TLS block (the  default  with  GNU  libc  version  2.4  or
           later).

           With      the      latter      choice     the     options     -mstack-protector-guard-reg=reg     and
           -mstack-protector-guard-offset=offset furthermore specify which register to use as base register  for
           reading  the  canary,  and  from  what  offset  from  that base register. The default for those is as
           specified in the relevant ABI.  -mstack-protector-guard-symbol=symbol overrides  the  offset  with  a
           symbol reference to a canary in the TLS block.

       -mpcrel
       -mno-pcrel
           Generate  (do not generate) pc-relative addressing.  The -mpcrel option requires that the medium code
           model (-mcmodel=medium) and prefixed addressing (-mprefixed) options are enabled.

       -mprefixed
       -mno-prefixed
           Generate (do not generate)  addressing  modes  using  prefixed  load  and  store  instructions.   The
           -mprefixed option requires that the option -mcpu=power10 (or later) is enabled.

       -mmma
       -mno-mma
           Generate  (do  not  generate)  the  MMA  instructions.   The  -mma  option  requires  that the option
           -mcpu=power10 (or later) is enabled.

       -mrop-protect
       -mno-rop-protect
           Generate (do not generate) ROP protection instructions  when  the  target  processor  supports  them.
           Currently this option disables the shrink-wrap optimization (-fshrink-wrap).

       -mprivileged
       -mno-privileged
           Generate (do not generate) code that will run in privileged state.

       -mblock-ops-unaligned-vsx
       -mno-block-ops-unaligned-vsx
           Generate  (do  not  generate)  unaligned  vsx  loads  and stores for inline expansion of "memcpy" and
           "memmove".

       RX Options

       These command-line options are defined for RX targets:

       -m64bit-doubles
       -m32bit-doubles
           Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits (-m32bit-doubles) in  size.   The
           default  is  -m32bit-doubles.   Note RX floating-point hardware only works on 32-bit values, which is
           why the default is -m32bit-doubles.

       -fpu
       -nofpu
           Enables (-fpu) or disables (-nofpu) the use of RX floating-point hardware.  The  default  is  enabled
           for the RX600 series and disabled for the RX200 series.

           Floating-point  instructions are only generated for 32-bit floating-point values, however, so the FPU
           hardware is not used for doubles if the -m64bit-doubles option is used.

           Note If the -fpu option is enabled then -funsafe-math-optimizations is  also  enabled  automatically.
           This is because the RX FPU instructions are themselves unsafe.

       -mcpu=name
           Selects  the  type  of RX CPU to be targeted.  Currently three types are supported, the generic RX600
           and RX200 series hardware and the specific RX610 CPU.  The default is RX600.

           The only difference between RX600 and  RX610  is  that  the  RX610  does  not  support  the  "MVTIPL"
           instruction.

           The  RX200  series  does  not have a hardware floating-point unit and so -nofpu is enabled by default
           when this type is selected.

       -mbig-endian-data
       -mlittle-endian-data
           Store data (but not code) in the big-endian format.  The default  is  -mlittle-endian-data,  i.e.  to
           store data in the little-endian format.

       -msmall-data-limit=N
           Specifies the maximum size in bytes of global and static variables which can be placed into the small
           data  area.   Using  the small data area can lead to smaller and faster code, but the size of area is
           limited and it is up to the programmer to ensure that the area does  not  overflow.   Also  when  the
           small  data  area  is  used one of the RX's registers (usually "r13") is reserved for use pointing to
           this area, so it is no longer available for use by the compiler.  This could result in slower  and/or
           larger code if variables are pushed onto the stack instead of being held in this register.

           Note,  common  variables (variables that have not been initialized) and constants are not placed into
           the small data area as they are assigned to other sections in the output executable.

           The default value is zero, which disables this feature.  Note, this feature is not enabled by default
           with higher optimization levels (-O2 etc) because of the potentially detrimental effects of reserving
           a register.  It is up to the programmer to experiment and discover whether this feature is of benefit
           to their program.  See the description of the -mpid option  for  a  description  of  how  the  actual
           register to hold the small data area pointer is chosen.

       -msim
       -mno-sim
           Use the simulator runtime.  The default is to use the libgloss board-specific runtime.

       -mas100-syntax
       -mno-as100-syntax
           When  generating  assembler  output  use  a syntax that is compatible with Renesas's AS100 assembler.
           This syntax can also be handled by the GAS assembler, but it has  some  restrictions  so  it  is  not
           generated by default.

       -mmax-constant-size=N
           Specifies  the  maximum  size,  in  bytes,  of  a  constant  that  can  be used as an operand in a RX
           instruction.  Although the RX instruction set does allow constants of up to 4 bytes in length  to  be
           used  in instructions, a longer value equates to a longer instruction.  Thus in some circumstances it
           can be beneficial to restrict the size of constants that are used in  instructions.   Constants  that
           are too big are instead placed into a constant pool and referenced via register indirection.

           The value N can be between 0 and 4.  A value of 0 (the default) or 4 means that constants of any size
           are allowed.

       -mrelax
           Enable  linker  relaxation.  Linker relaxation is a process whereby the linker attempts to reduce the
           size of a program by finding shorter versions of various instructions.  Disabled by default.

       -mint-register=N
           Specify the number of registers to reserve for fast interrupt handler functions.  The value N can  be
           between  0  and  4.  A value of 1 means that register "r13" is reserved for the exclusive use of fast
           interrupt handlers.  A value of 2 reserves "r13" and "r12".  A value of 3 reserves "r13",  "r12"  and
           "r11",  and  a  value of 4 reserves "r13" through "r10".  A value of 0, the default, does not reserve
           any registers.

       -msave-acc-in-interrupts
           Specifies that interrupt handler functions should preserve the accumulator register.   This  is  only
           necessary  if  normal code might use the accumulator register, for example because it performs 64-bit
           multiplications.  The default is to ignore the accumulator  as  this  makes  the  interrupt  handlers
           faster.

       -mpid
       -mno-pid
           Enables  the  generation  of  position independent data.  When enabled any access to constant data is
           done via an offset from a base address held in a register.  This allows the location of constant data
           to be determined at run time without requiring the executable to be relocated, which is a benefit  to
           embedded  applications  with  tight memory constraints.  Data that can be modified is not affected by
           this option.

           Note, using this feature reserves a register, usually "r13", for  the  constant  data  base  address.
           This can result in slower and/or larger code, especially in complicated functions.

           The  actual  register  chosen  to  hold  the  constant  data  base  address  depends upon whether the
           -msmall-data-limit and/or  the  -mint-register  command-line  options  are  enabled.   Starting  with
           register "r13" and proceeding downwards, registers are allocated first to satisfy the requirements of
           -mint-register,  then  -mpid  and finally -msmall-data-limit.  Thus it is possible for the small data
           area register to be "r8" if both -mint-register=4 and -mpid are specified on the command line.

           By default this feature is not enabled.  The default can be restored via  the  -mno-pid  command-line
           option.

       -mno-warn-multiple-fast-interrupts
       -mwarn-multiple-fast-interrupts
           Prevents  GCC from issuing a warning message if it finds more than one fast interrupt handler when it
           is compiling a file.  The default is to issue a warning for each extra fast interrupt handler  found,
           as the RX only supports one such interrupt.

       -mallow-string-insns
       -mno-allow-string-insns
           Enables  or  disables  the  use  of  the  string manipulation instructions "SMOVF", "SCMPU", "SMOVB",
           "SMOVU", "SUNTIL" "SWHILE" and also the "RMPA" instruction.  These instructions  may  prefetch  data,
           which  is not safe to do if accessing an I/O register.  (See section 12.2.7 of the RX62N Group User's
           Manual for more information).

           The default is to allow these instructions, but it is not possible for GCC  to  reliably  detect  all
           circumstances where a string instruction might be used to access an I/O register, so their use cannot
           be   disabled   automatically.    Instead   it   is   reliant   upon   the   programmer  to  use  the
           -mno-allow-string-insns option if their program accesses I/O space.

           When the instructions are enabled GCC defines the C preprocessor symbol  "__RX_ALLOW_STRING_INSNS__",
           otherwise it defines the symbol "__RX_DISALLOW_STRING_INSNS__".

       -mjsr
       -mno-jsr
           Use  only  (or  not  only) "JSR" instructions to access functions.  This option can be used when code
           size exceeds the range of "BSR" instructions.  Note that -mno-jsr does not mean to not use "JSR"  but
           instead means that any type of branch may be used.

       Note:  The  generic GCC command-line option -ffixed-reg has special significance to the RX port when used
       with the "interrupt" function attribute.  This attribute indicates a function intended  to  process  fast
       interrupts.   GCC  ensures  that  it  only  uses  the registers "r10", "r11", "r12" and/or "r13" and only
       provided that the normal use of the corresponding registers have been restricted via the  -ffixed-reg  or
       -mint-register command-line options.

       S/390 and zSeries Options

       These are the -m options defined for the S/390 and zSeries architecture.

       -mhard-float
       -msoft-float
           Use  (do  not  use)  the  hardware  floating-point  instructions  and  registers  for  floating-point
           operations.  When -msoft-float is specified, functions in libgcc.a are used to perform floating-point
           operations.  When -mhard-float is specified, the compiler generates IEEE floating-point instructions.
           This is the default.

       -mhard-dfp
       -mno-hard-dfp
           Use  (do  not  use)  the  hardware  decimal-floating-point  instructions  for  decimal-floating-point
           operations.   When  -mno-hard-dfp  is  specified,  functions in libgcc.a are used to perform decimal-
           floating-point operations.  When -mhard-dfp is specified, the  compiler  generates  decimal-floating-
           point hardware instructions.  This is the default for -march=z9-ec or higher.

       -mlong-double-64
       -mlong-double-128
           These switches control the size of "long double" type. A size of 64 bits makes the "long double" type
           equivalent to the "double" type. This is the default.

       -mbackchain
       -mno-backchain
           Store  (do  not store) the address of the caller's frame as backchain pointer into the callee's stack
           frame.  A backchain may be needed to allow debugging using tools that do not  understand  DWARF  call
           frame  information.   When  -mno-packed-stack  is  in  effect, the backchain pointer is stored at the
           bottom of the stack frame; when -mpacked-stack is in effect, the backchain is placed into the topmost
           word of the 96/160 byte register save area.

           In general, code compiled with -mbackchain is call-compatible with code compiled with -mno-backchain;
           however, use of the backchain for debugging purposes usually requires that the whole binary is  built
           with  -mbackchain.   Note that the combination of -mbackchain, -mpacked-stack and -mhard-float is not
           supported.  In order to build a linux kernel use -msoft-float.

           The default is to not maintain the backchain.

       -mpacked-stack
       -mno-packed-stack
           Use (do not use) the packed stack layout.  When -mno-packed-stack is specified, the compiler uses the
           all fields of the 96/160 byte register save area only for their default purpose; unused fields  still
           take up stack space.  When -mpacked-stack is specified, register save slots are densely packed at the
           top of the register save area; unused space is reused for other purposes, allowing for more efficient
           use  of  the available stack space.  However, when -mbackchain is also in effect, the topmost word of
           the save area is always used to store the backchain, and the return address register is always  saved
           two words below the backchain.

           As  long  as  the  stack  frame  backchain  is  not used, code generated with -mpacked-stack is call-
           compatible with code generated with -mno-packed-stack.  Note that some non-FSF releases of  GCC  2.95
           for  S/390  or  zSeries  generated code that uses the stack frame backchain at run time, not just for
           debugging purposes.  Such code is not call-compatible with code compiled with -mpacked-stack.   Also,
           note that the combination of -mbackchain, -mpacked-stack and -mhard-float is not supported.  In order
           to build a linux kernel use -msoft-float.

           The default is to not use the packed stack layout.

       -msmall-exec
       -mno-small-exec
           Generate  (or  do  not generate) code using the "bras" instruction to do subroutine calls.  This only
           works reliably if the total executable size does not exceed 64k.  The default is to  use  the  "basr"
           instruction instead, which does not have this limitation.

       -m64
       -m31
           When  -m31  is  specified,  generate  code  compliant  to  the GNU/Linux for S/390 ABI.  When -m64 is
           specified, generate code compliant to the GNU/Linux for zSeries ABI.  This allows GCC  in  particular
           to  generate 64-bit instructions.  For the s390 targets, the default is -m31, while the s390x targets
           default to -m64.

       -mzarch
       -mesa
           When -mzarch is specified, generate code using the instructions available  on  z/Architecture.   When
           -mesa  is  specified,  generate code using the instructions available on ESA/390.  Note that -mesa is
           not possible with -m64.  When generating code compliant to the GNU/Linux for S/390 ABI,  the  default
           is -mesa.  When generating code compliant to the GNU/Linux for zSeries ABI, the default is -mzarch.

       -mhtm
       -mno-htm
           The  -mhtm  option  enables  a  set  of  builtins  making  use  of  instructions  available  with the
           transactional execution facility introduced with the IBM zEnterprise EC12  machine  generation  S/390
           System z Built-in Functions.  -mhtm is enabled by default when using -march=zEC12.

       -mvx
       -mno-vx
           When  -mvx  is  specified,  generate  code using the instructions available with the vector extension
           facility introduced with the IBM z13 machine generation.  This option changes the ABI for some vector
           type values with regard to alignment and calling conventions.  In case vector type values  are  being
           used  in  an  ABI-relevant  context  a GAS .gnu_attribute command will be added to mark the resulting
           binary with the ABI used.  -mvx is enabled by default when using -march=z13.

       -mzvector
       -mno-zvector
           The -mzvector option enables vector language extensions and  builtins  using  instructions  available
           with  the vector extension facility introduced with the IBM z13 machine generation.  This option adds
           support for vector to be used as a keyword to define vector type variables and arguments.  vector  is
           only  available  when  GNU  extensions  are  enabled.  It will not be expanded when requesting strict
           standard compliance e.g. with -std=c99.  In addition to the GCC low-level builtins -mzvector  enables
           a set of builtins added for compatibility with AltiVec-style implementations like Power and Cell.  In
           order  to  make use of these builtins the header file vecintrin.h needs to be included.  -mzvector is
           disabled by default.

       -mmvcle
       -mno-mvcle
           Generate (or do not generate) code using the  "mvcle"  instruction  to  perform  block  moves.   When
           -mno-mvcle is specified, use a "mvc" loop instead.  This is the default unless optimizing for size.

       -mdebug
       -mno-debug
           Print  (or  do  not  print) additional debug information when compiling.  The default is to not print
           debug information.

       -march=cpu-type
           Generate code that runs on cpu-type, which is the name of a system representing a  certain  processor
           type.   Possible  values  for  cpu-type  are  z900/arch5, z990/arch6, z9-109, z9-ec/arch7, z10/arch8,
           z196/arch9, zEC12, z13/arch11, z14/arch12, z15/arch13, z16/arch14, and native.

           The default is -march=z900.

           Specifying native as cpu type can be used to  select  the  best  architecture  option  for  the  host
           processor.  -march=native has no effect if GCC does not recognize the processor.

       -mtune=cpu-type
           Tune  to  cpu-type  everything applicable about the generated code, except for the ABI and the set of
           available instructions.  The list of cpu-type values is the same as for -march.  The default  is  the
           value used for -march.

       -mtpf-trace
       -mno-tpf-trace
           Generate code that adds (does not add) in TPF OS specific branches to trace routines in the operating
           system.  This option is off by default, even when compiling for the TPF OS.

       -mtpf-trace-skip
       -mno-tpf-trace-skip
           Generate  code  that  changes  (does not change) the default branch targets enabled by -mtpf-trace to
           point to specialized trace routines providing the ability  of  selectively  skipping  function  trace
           entries  for  the  TPF  OS.   This  option  is off by default, even when compiling for the TPF OS and
           specifying -mtpf-trace.

       -mfused-madd
       -mno-fused-madd
           Generate code that uses (does not use)  the  floating-point  multiply  and  accumulate  instructions.
           These instructions are generated by default if hardware floating point is used.

       -mwarn-framesize=framesize
           Emit  a warning if the current function exceeds the given frame size.  Because this is a compile-time
           check it doesn't need to be a real problem when  the  program  runs.   It  is  intended  to  identify
           functions  that most probably cause a stack overflow.  It is useful to be used in an environment with
           limited stack size e.g. the linux kernel.

       -mwarn-dynamicstack
           Emit a warning if the function calls "alloca" or uses dynamically-sized arrays.  This is generally  a
           bad idea with a limited stack size.

       -mstack-guard=stack-guard
       -mstack-size=stack-size
           If  these  options  are  provided  the  S/390  back end emits additional instructions in the function
           prologue that trigger a trap if the stack size is stack-guard bytes above  the  stack-size  (remember
           that  the stack on S/390 grows downward).  If the stack-guard option is omitted the smallest power of
           2 larger than the frame size of the compiled function is chosen.  These options are  intended  to  be
           used  to  help  debugging  stack overflow problems.  The additionally emitted code causes only little
           overhead and  hence  can  also  be  used  in  production-like  systems  without  greater  performance
           degradation.   The  given  values  have to be exact powers of 2 and stack-size has to be greater than
           stack-guard without exceeding 64k.  In order to be efficient the extra code makes the assumption that
           the stack starts at an address aligned to the value given by stack-size.  The stack-guard option  can
           only be used in conjunction with stack-size.

       -mhotpatch=pre-halfwords,post-halfwords
           If  the hotpatch option is enabled, a "hot-patching" function prologue is generated for all functions
           in the compilation unit.  The funtion label is prepended  with  the  given  number  of  two-byte  NOP
           instructions  (pre-halfwords,  maximum  1000000).   After  the  label,  2  * post-halfwords bytes are
           appended, using the largest NOP like instructions the architecture allows (maximum 1000000).

           If both arguments are zero, hotpatching is disabled.

           This option can be overridden for individual functions with the "hotpatch" attribute.

       Score Options

       These options are defined for Score implementations:

       -meb
           Compile code for big-endian mode.  This is the default.

       -mel
           Compile code for little-endian mode.

       -mnhwloop
           Disable generation of "bcnz" instructions.

       -muls
           Enable generation of unaligned load and store instructions.

       -mmac
           Enable the use of multiply-accumulate instructions. Disabled by default.

       -mscore5
           Specify the SCORE5 as the target architecture.

       -mscore5u
           Specify the SCORE5U of the target architecture.

       -mscore7
           Specify the SCORE7 as the target architecture. This is the default.

       -mscore7d
           Specify the SCORE7D as the target architecture.

       SH Options

       These -m options are defined for the SH implementations:

       -m1 Generate code for the SH1.

       -m2 Generate code for the SH2.

       -m2e
           Generate code for the SH2e.

       -m2a-nofpu
           Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way that the floating-point  unit
           is not used.

       -m2a-single-only
           Generate  code for the SH2a-FPU, in such a way that no double-precision floating-point operations are
           used.

       -m2a-single
           Generate code for the SH2a-FPU assuming the  floating-point  unit  is  in  single-precision  mode  by
           default.

       -m2a
           Generate  code  for  the  SH2a-FPU  assuming  the  floating-point unit is in double-precision mode by
           default.

       -m3 Generate code for the SH3.

       -m3e
           Generate code for the SH3e.

       -m4-nofpu
           Generate code for the SH4 without a floating-point unit.

       -m4-single-only
           Generate code for the SH4 with a floating-point unit that only supports single-precision arithmetic.

       -m4-single
           Generate code for the SH4 assuming the floating-point unit is in single-precision mode by default.

       -m4 Generate code for the SH4.

       -m4-100
           Generate code for SH4-100.

       -m4-100-nofpu
           Generate code for SH4-100 in such a way that the floating-point unit is not used.

       -m4-100-single
           Generate code for SH4-100 assuming the floating-point unit is in single-precision mode by default.

       -m4-100-single-only
           Generate code for SH4-100 in such a way that no double-precision floating-point operations are used.

       -m4-200
           Generate code for SH4-200.

       -m4-200-nofpu
           Generate code for SH4-200 without in such a way that the floating-point unit is not used.

       -m4-200-single
           Generate code for SH4-200 assuming the floating-point unit is in single-precision mode by default.

       -m4-200-single-only
           Generate code for SH4-200 in such a way that no double-precision floating-point operations are used.

       -m4-300
           Generate code for SH4-300.

       -m4-300-nofpu
           Generate code for SH4-300 without in such a way that the floating-point unit is not used.

       -m4-300-single
           Generate code for SH4-300 in such a way that no double-precision floating-point operations are used.

       -m4-300-single-only
           Generate code for SH4-300 in such a way that no double-precision floating-point operations are used.

       -m4-340
           Generate code for SH4-340 (no MMU, no FPU).

       -m4-500
           Generate code for SH4-500 (no FPU).  Passes -isa=sh4-nofpu to the assembler.

       -m4a-nofpu
           Generate code for the SH4al-dsp, or for a SH4a in such a way that  the  floating-point  unit  is  not
           used.

       -m4a-single-only
           Generate  code  for  the  SH4a,  in such a way that no double-precision floating-point operations are
           used.

       -m4a-single
           Generate code for the SH4a assuming the floating-point unit is in single-precision mode by default.

       -m4a
           Generate code for the SH4a.

       -m4al
           Same as -m4a-nofpu, except that it implicitly passes -dsp to the assembler.  GCC doesn't generate any
           DSP instructions at the moment.

       -mb Compile code for the processor in big-endian mode.

       -ml Compile code for the processor in little-endian mode.

       -mdalign
           Align doubles at 64-bit boundaries.  Note that this changes the calling conventions,  and  thus  some
           functions from the standard C library do not work unless you recompile it first with -mdalign.

       -mrelax
           Shorten some address references at link time, when possible; uses the linker option -relax.

       -mbigtable
           Use 32-bit offsets in "switch" tables.  The default is to use 16-bit offsets.

       -mbitops
           Enable the use of bit manipulation instructions on SH2A.

       -mfmovd
           Enable the use of the instruction "fmovd".  Check -mdalign for alignment constraints.

       -mrenesas
           Comply with the calling conventions defined by Renesas.

       -mno-renesas
           Comply  with  the  calling conventions defined for GCC before the Renesas conventions were available.
           This option is the default for all targets of the SH toolchain.

       -mnomacsave
           Mark the "MAC" register as call-clobbered, even if -mrenesas is given.

       -mieee
       -mno-ieee
           Control the IEEE compliance of floating-point comparisons, which affects the handling of cases  where
           the   result   of  a  comparison  is  unordered.   By  default  -mieee  is  implicitly  enabled.   If
           -ffinite-math-only is enabled -mno-ieee is implicitly set, which  results  in  faster  floating-point
           greater-equal  and  less-equal  comparisons.   The  implicit settings can be overridden by specifying
           either -mieee or -mno-ieee.

       -minline-ic_invalidate
           Inline code to invalidate instruction cache entries after setting  up  nested  function  trampolines.
           This  option  has  no effect if -musermode is in effect and the selected code generation option (e.g.
           -m4) does not allow the use of the "icbi" instruction.  If the selected code generation  option  does
           not  allow  the  use  of  the  "icbi"  instruction, and -musermode is not in effect, the inlined code
           manipulates the instruction cache address array directly with an associative write.   This  not  only
           requires privileged mode at run time, but it also fails if the cache line had been mapped via the TLB
           and has become unmapped.

       -misize
           Dump instruction size and location in the assembly code.

       -mpadstruct
           This option is deprecated.  It pads structures to multiple of 4 bytes, which is incompatible with the
           SH ABI.

       -matomic-model=model
           Sets the model of atomic operations and additional parameters as a comma separated list.  For details
           on  the  atomic  built-in  functions  see __atomic Builtins.  The following models and parameters are
           supported:

           none
               Disable compiler generated atomic sequences and emit library calls for atomic  operations.   This
               is the default if the target is not "sh*-*-linux*".

           soft-gusa
               Generate  GNU/Linux  compatible gUSA software atomic sequences for the atomic built-in functions.
               The generated atomic sequences require additional support from the  interrupt/exception  handling
               code  of  the system and are only suitable for SH3* and SH4* single-core systems.  This option is
               enabled by default when the target is "sh*-*-linux*" and SH3* or SH4*.  When the target is  SH4A,
               this  option  also partially utilizes the hardware atomic instructions "movli.l" and "movco.l" to
               create more efficient code, unless strict is specified.

           soft-tcb
               Generate software atomic sequences that use a variable in the thread control block.   This  is  a
               variation  of  the gUSA sequences which can also be used on SH1* and SH2* targets.  The generated
               atomic sequences require additional support from the interrupt/exception  handling  code  of  the
               system  and  are  only  suitable for single-core systems.  When using this model, the gbr-offset=
               parameter has to be specified as well.

           soft-imask
               Generate software atomic sequences that temporarily disable interrupts  by  setting  "SR.IMASK  =
               1111".   This  model works only when the program runs in privileged mode and is only suitable for
               single-core systems.  Additional support from the interrupt/exception handling code of the system
               is not required.  This model is enabled by default when the target is "sh*-*-linux*" and SH1*  or
               SH2*.

           hard-llcs
               Generate  hardware atomic sequences using the "movli.l" and "movco.l" instructions only.  This is
               only available on SH4A and is suitable for multi-core systems.  Since the  hardware  instructions
               support  only  32  bit  atomic  variables access to 8 or 16 bit variables is emulated with 32 bit
               accesses.  Code compiled with this option is also compatible with  other  software  atomic  model
               interrupt/exception  handling systems if executed on an SH4A system.  Additional support from the
               interrupt/exception handling code of the system is not required for this model.

           gbr-offset=
               This parameter specifies the offset in  bytes  of  the  variable  in  the  thread  control  block
               structure  that should be used by the generated atomic sequences when the soft-tcb model has been
               selected.  For other models this parameter is ignored.  The specified value must  be  an  integer
               multiple of four and in the range 0-1020.

           strict
               This  parameter  prevents mixed usage of multiple atomic models, even if they are compatible, and
               makes the compiler generate atomic sequences of the specified model only.

       -mtas
           Generate the "tas.b" opcode for "__atomic_test_and_set".  Notice that  depending  on  the  particular
           hardware  and  software  configuration  this can degrade overall performance due to the operand cache
           line flushes that are implied by the "tas.b" instruction.  On multi-core SH4A processors the  "tas.b"
           instruction  must  be  used  with  caution  since  it can result in data corruption for certain cache
           configurations.

       -mprefergot
           When generating position-independent code, emit function calls using the Global Offset Table  instead
           of the Procedure Linkage Table.

       -musermode
       -mno-usermode
           Don't allow (allow) the compiler generating privileged mode code.  Specifying -musermode also implies
           -mno-inline-ic_invalidate if the inlined code would not work in user mode.  -musermode is the default
           when  the  target  is  "sh*-*-linux*".  If the target is SH1* or SH2* -musermode has no effect, since
           there is no user mode.

       -multcost=number
           Set the cost to assume for a multiply insn.

       -mdiv=strategy
           Set the division strategy to be used for integer division operations.  strategy can be one of:

           call-div1
               Calls a library function that uses the single-step division instruction  "div1"  to  perform  the
               operation.   Division  by  zero  calculates an unspecified result and does not trap.  This is the
               default except for SH4, SH2A and SHcompact.

           call-fp
               Calls a library function  that  performs  the  operation  in  double  precision  floating  point.
               Division  by zero causes a floating-point exception.  This is the default for SHcompact with FPU.
               Specifying this for targets that do not have a double precision FPU defaults to "call-div1".

           call-table
               Calls a library function that uses a lookup table for small divisors and the  "div1"  instruction
               with case distinction for larger divisors.  Division by zero calculates an unspecified result and
               does  not  trap.   This  is  the  default  for SH4.  Specifying this for targets that do not have
               dynamic shift instructions defaults to "call-div1".

           When a division strategy has not been specified the default strategy is selected based on the current
           target.  For SH2A the default strategy is to use  the  "divs"  and  "divu"  instructions  instead  of
           library function calls.

       -maccumulate-outgoing-args
           Reserve  space  once  for  outgoing  arguments in the function prologue rather than around each call.
           Generally beneficial for performance and size.  Also needed for unwinding to avoid changing the stack
           frame around conditional code.

       -mdivsi3_libfunc=name
           Set the name of the library function used for 32-bit signed division to name.  This only affects  the
           name  used  in  the  call  division  strategies,  and  the  compiler  still  expects the same sets of
           input/output/clobbered registers as if this option were not present.

       -mfixed-range=register-range
           Generate code treating the given register range as fixed registers.  A fixed register is one that the
           register allocator cannot use.  This is useful when compiling  kernel  code.   A  register  range  is
           specified  as two registers separated by a dash.  Multiple register ranges can be specified separated
           by a comma.

       -mbranch-cost=num
           Assume num to be the cost for a branch instruction.  Higher numbers make the compiler try to generate
           more branch-free code if possible.  If not specified the value is selected depending on the processor
           type that is being compiled for.

       -mzdcbranch
       -mno-zdcbranch
           Assume (do not assume) that zero displacement conditional branch instructions "bt" and "bf" are fast.
           If -mzdcbranch is specified, the compiler prefers zero displacement branch code sequences.   This  is
           enabled  by  default  when  generating  code  for  SH4  and  SH4A.   It can be explicitly disabled by
           specifying -mno-zdcbranch.

       -mcbranch-force-delay-slot
           Force the usage of delay slots for conditional branches, which stuffs the delay slot with a "nop"  if
           a  suitable  instruction  cannot be found.  By default this option is disabled.  It can be enabled to
           work around hardware bugs as found in the original SH7055.

       -mfused-madd
       -mno-fused-madd
           Generate code that uses (does not use)  the  floating-point  multiply  and  accumulate  instructions.
           These  instructions  are  generated  by  default  if  hardware  floating point is used.  The machine-
           dependent -mfused-madd option is now mapped to the machine-independent -ffp-contract=fast option, and
           -mno-fused-madd is mapped to -ffp-contract=off.

       -mfsca
       -mno-fsca
           Allow or disallow the compiler to emit the "fsca" instruction for  sine  and  cosine  approximations.
           The  option  -mfsca  must  be used in combination with -funsafe-math-optimizations.  It is enabled by
           default when generating code for SH4A.  Using -mno-fsca disables sine and cosine approximations  even
           if -funsafe-math-optimizations is in effect.

       -mfsrra
       -mno-fsrra
           Allow  or  disallow  the  compiler  to  emit  the  "fsrra"  instruction  for  reciprocal  square root
           approximations.  The option -mfsrra must be used in combination with -funsafe-math-optimizations  and
           -ffinite-math-only.   It  is  enabled  by  default  when  generating code for SH4A.  Using -mno-fsrra
           disables  reciprocal   square   root   approximations   even   if   -funsafe-math-optimizations   and
           -ffinite-math-only are in effect.

       -mpretend-cmove
           Prefer  zero-displacement  conditional  branches for conditional move instruction patterns.  This can
           result in faster code on the SH4 processor.

       -mfdpic
           Generate code using the FDPIC ABI.

       Solaris 2 Options

       These -m options are supported on Solaris 2:

       -mclear-hwcap
           -mclear-hwcap tells the compiler to  remove  the  hardware  capabilities  generated  by  the  Solaris
           assembler.   This is only necessary when object files use ISA extensions not supported by the current
           machine, but check at runtime whether or not to use them.

       -mimpure-text
           -mimpure-text, used in addition to -shared, tells the compiler to not pass -z text to the linker when
           linking a shared object.  Using this option, you can  link  position-dependent  code  into  a  shared
           object.

           -mimpure-text  suppresses  the  "relocations  remain  against  allocatable but non-writable sections"
           linker error message.  However, the necessary  relocations  trigger  copy-on-write,  and  the  shared
           object  is  not actually shared across processes.  Instead of using -mimpure-text, you should compile
           all source code with -fpic or -fPIC.

       These switches are supported in addition to the above on Solaris 2:

       -pthreads
           This is a synonym for -pthread.

       SPARC Options

       These -m options are supported on the SPARC:

       -mno-app-regs
       -mapp-regs
           Specify -mapp-regs to generate output using the global registers 2 through 4, which  the  SPARC  SVR4
           ABI  reserves for applications.  Like the global register 1, each global register 2 through 4 is then
           treated as an allocable register that is clobbered by function calls.  This is the default.

           To be fully SVR4 ABI-compliant at the cost of some  performance  loss,  specify  -mno-app-regs.   You
           should compile libraries and system software with this option.

       -mflat
       -mno-flat
           With  -mflat,  the  compiler  does not generate save/restore instructions and uses a "flat" or single
           register window model.  This model is compatible with the regular register window model.   The  local
           registers and the input registers (0--5) are still treated as "call-saved" registers and are saved on
           the stack as needed.

           With  -mno-flat  (the  default),  the  compiler  generates save/restore instructions (except for leaf
           functions).  This is the normal operating mode.

       -mfpu
       -mhard-float
           Generate output containing floating-point instructions.  This is the default.

       -mno-fpu
       -msoft-float
           Generate output containing library calls for floating point.  Warning: the  requisite  libraries  are
           not  available  for all SPARC targets.  Normally the facilities of the machine's usual C compiler are
           used, but this cannot be done directly in cross-compilation.  You must make your own arrangements  to
           provide  suitable  library  functions  for  cross-compilation.  The embedded targets sparc-*-aout and
           sparclite-*-* do provide software floating-point support.

           -msoft-float changes the calling convention in the output file; therefore, it is only useful  if  you
           compile  all of a program with this option.  In particular, you need to compile libgcc.a, the library
           that comes with GCC, with -msoft-float in order for this to work.

       -mhard-quad-float
           Generate output containing quad-word (long double) floating-point instructions.

       -msoft-quad-float
           Generate output containing library calls for quad-word  (long  double)  floating-point  instructions.
           The functions called are those specified in the SPARC ABI.  This is the default.

           As  of  this writing, there are no SPARC implementations that have hardware support for the quad-word
           floating-point instructions.  They all invoke a trap handler for one of these instructions, and  then
           the  trap handler emulates the effect of the instruction.  Because of the trap handler overhead, this
           is much slower than calling the ABI library routines.   Thus  the  -msoft-quad-float  option  is  the
           default.

       -mno-unaligned-doubles
       -munaligned-doubles
           Assume that doubles have 8-byte alignment.  This is the default.

           With  -munaligned-doubles,  GCC assumes that doubles have 8-byte alignment only if they are contained
           in another type, or if they have an  absolute  address.   Otherwise,  it  assumes  they  have  4-byte
           alignment.   Specifying  this  option  avoids some rare compatibility problems with code generated by
           other compilers.  It is not the default because it results in  a  performance  loss,  especially  for
           floating-point code.

       -muser-mode
       -mno-user-mode
           Do  not  generate  code  that  can only run in supervisor mode.  This is relevant only for the "casa"
           instruction emitted for the LEON3 processor.  This is the default.

       -mfaster-structs
       -mno-faster-structs
           With -mfaster-structs, the compiler assumes that  structures  should  have  8-byte  alignment.   This
           enables the use of pairs of "ldd" and "std" instructions for copies in structure assignment, in place
           of  twice  as many "ld" and "st" pairs.  However, the use of this changed alignment directly violates
           the SPARC ABI.  Thus, it's intended only for use on targets where  the  developer  acknowledges  that
           their resulting code is not directly in line with the rules of the ABI.

       -mstd-struct-return
       -mno-std-struct-return
           With  -mstd-struct-return,  the compiler generates checking code in functions returning structures or
           unions to detect size mismatches between the two sides of function calls, as per the 32-bit ABI.

           The default is -mno-std-struct-return.  This option has no effect in 64-bit mode.

       -mlra
       -mno-lra
           Enable Local Register Allocation.  This is the default for SPARC since GCC 7 so -mno-lra needs to  be
           passed to get old Reload.

       -mcpu=cpu_type
           Set  the  instruction  set,  register  set,  and  instruction  scheduling parameters for machine type
           cpu_type.  Supported values for cpu_type are v7, cypress, v8, supersparc,  hypersparc,  leon,  leon3,
           leon3v7,  leon5,  sparclite, f930, f934, sparclite86x, sparclet, tsc701, v9, ultrasparc, ultrasparc3,
           niagara, niagara2, niagara3, niagara4, niagara7 and m8.

           Native Solaris and GNU/Linux toolchains also  support  the  value  native,  which  selects  the  best
           architecture option for the host processor.  -mcpu=native has no effect if GCC does not recognize the
           processor.

           Default  instruction scheduling parameters are used for values that select an architecture and not an
           implementation.  These are v7, v8, sparclite, sparclet, v9.

           Here is a list of each supported architecture and their supported implementations.

           v7  cypress, leon3v7

           v8  supersparc, hypersparc, leon, leon3, leon5

           sparclite
               f930, f934, sparclite86x

           sparclet
               tsc701

           v9  ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4, niagara7, m8

           By default (unless configured otherwise), GCC  generates  code  for  the  V7  variant  of  the  SPARC
           architecture.   With  -mcpu=cypress,  the  compiler additionally optimizes it for the Cypress CY7C602
           chip, as used in the SPARCStation/SPARCServer 3xx series.  This is also  appropriate  for  the  older
           SPARCStation 1, 2, IPX etc.

           With  -mcpu=v8, GCC generates code for the V8 variant of the SPARC architecture.  The only difference
           from V7 code is that the compiler emits the integer multiply and integer  divide  instructions  which
           exist in SPARC-V8 but not in SPARC-V7.  With -mcpu=supersparc, the compiler additionally optimizes it
           for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000 series.

           With  -mcpu=sparclite,  GCC generates code for the SPARClite variant of the SPARC architecture.  This
           adds the integer multiply, integer divide step and scan ("ffs") instructions which exist in SPARClite
           but not in SPARC-V7.  With -mcpu=f930, the compiler additionally optimizes it for the Fujitsu MB86930
           chip, which is the original SPARClite, with no  FPU.   With  -mcpu=f934,  the  compiler  additionally
           optimizes it for the Fujitsu MB86934 chip, which is the more recent SPARClite with FPU.

           With  -mcpu=sparclet,  GCC  generates  code for the SPARClet variant of the SPARC architecture.  This
           adds the integer multiply, multiply/accumulate, integer divide step  and  scan  ("ffs")  instructions
           which  exist in SPARClet but not in SPARC-V7.  With -mcpu=tsc701, the compiler additionally optimizes
           it for the TEMIC SPARClet chip.

           With -mcpu=v9, GCC generates code for the V9 variant of the SPARC  architecture.   This  adds  64-bit
           integer  and  floating-point  move instructions, 3 additional floating-point condition code registers
           and conditional move instructions.  With -mcpu=ultrasparc, the compiler additionally optimizes it for
           the Sun UltraSPARC I/II/IIi chips.  With -mcpu=ultrasparc3, the compiler  additionally  optimizes  it
           for   the   Sun  UltraSPARC  III/III+/IIIi/IIIi+/IV/IV+  chips.   With  -mcpu=niagara,  the  compiler
           additionally  optimizes  it  for  Sun  UltraSPARC  T1  chips.   With  -mcpu=niagara2,  the   compiler
           additionally optimizes it for Sun UltraSPARC T2 chips. With -mcpu=niagara3, the compiler additionally
           optimizes  it  for Sun UltraSPARC T3 chips.  With -mcpu=niagara4, the compiler additionally optimizes
           it for Sun UltraSPARC T4 chips.  With -mcpu=niagara7, the  compiler  additionally  optimizes  it  for
           Oracle SPARC M7 chips.  With -mcpu=m8, the compiler additionally optimizes it for Oracle M8 chips.

       -mtune=cpu_type
           Set  the  instruction scheduling parameters for machine type cpu_type, but do not set the instruction
           set or register set that the option -mcpu=cpu_type does.

           The same values for -mcpu=cpu_type can be used for -mtune=cpu_type, but the only  useful  values  are
           those  that select a particular CPU implementation.  Those are cypress, supersparc, hypersparc, leon,
           leon3, leon3v7, leon5, f930, f934, sparclite86x, tsc701, ultrasparc, ultrasparc3, niagara,  niagara2,
           niagara3,  niagara4,  niagara7 and m8.  With native Solaris and GNU/Linux toolchains, native can also
           be used.

       -mv8plus
       -mno-v8plus
           With -mv8plus, GCC generates code for the SPARC-V8+ ABI.  The difference from the V8 ABI is that  the
           global  and  out  registers  are  considered  64 bits wide.  This is enabled by default on Solaris in
           32-bit mode for all SPARC-V9 processors.

       -mvis
       -mno-vis
           With -mvis, GCC generates code  that  takes  advantage  of  the  UltraSPARC  Visual  Instruction  Set
           extensions.  The default is -mno-vis.

       -mvis2
       -mno-vis2
           With  -mvis2,  GCC  generates  code  that  takes  advantage  of  version 2.0 of the UltraSPARC Visual
           Instruction Set extensions.   The  default  is  -mvis2  when  targeting  a  cpu  that  supports  such
           instructions, such as UltraSPARC-III and later.  Setting -mvis2 also sets -mvis.

       -mvis3
       -mno-vis3
           With  -mvis3,  GCC  generates  code  that  takes  advantage  of  version 3.0 of the UltraSPARC Visual
           Instruction Set extensions.   The  default  is  -mvis3  when  targeting  a  cpu  that  supports  such
           instructions, such as niagara-3 and later.  Setting -mvis3 also sets -mvis2 and -mvis.

       -mvis4
       -mno-vis4
           With  -mvis4,  GCC  generates  code  that  takes  advantage  of  version 4.0 of the UltraSPARC Visual
           Instruction Set extensions.   The  default  is  -mvis4  when  targeting  a  cpu  that  supports  such
           instructions, such as niagara-7 and later.  Setting -mvis4 also sets -mvis3, -mvis2 and -mvis.

       -mvis4b
       -mno-vis4b
           With  -mvis4b,  GCC  generates  code  that  takes  advantage  of version 4.0 of the UltraSPARC Visual
           Instruction Set extensions, plus the additional VIS  instructions  introduced  in  the  Oracle  SPARC
           Architecture 2017.  The default is -mvis4b when targeting a cpu that supports such instructions, such
           as m8 and later.  Setting -mvis4b also sets -mvis4, -mvis3, -mvis2 and -mvis.

       -mcbcond
       -mno-cbcond
           With  -mcbcond,  GCC  generates  code  that  takes advantage of the UltraSPARC Compare-and-Branch-on-
           Condition  instructions.   The  default  is  -mcbcond  when  targeting  a  CPU  that  supports   such
           instructions, such as Niagara-4 and later.

       -mfmaf
       -mno-fmaf
           With  -mfmaf,  GCC generates code that takes advantage of the UltraSPARC Fused Multiply-Add Floating-
           point instructions.  The default is -mfmaf when targeting a CPU that supports such instructions, such
           as Niagara-3 and later.

       -mfsmuld
       -mno-fsmuld
           With -mfsmuld, GCC generates code that takes advantage  of  the  Floating-point  Multiply  Single  to
           Double  (FsMULd)  instruction.   The  default  is  -mfsmuld  when  targeting  a  CPU  supporting  the
           architecture versions V8 or V9 with FPU except -mcpu=leon.

       -mpopc
       -mno-popc
           With -mpopc, GCC generates code that takes advantage of the UltraSPARC Population Count  instruction.
           The  default  is -mpopc when targeting a CPU that supports such an instruction, such as Niagara-2 and
           later.

       -msubxc
       -mno-subxc
           With -msubxc, GCC generates code that takes advantage of the UltraSPARC  Subtract-Extended-with-Carry
           instruction.   The default is -msubxc when targeting a CPU that supports such an instruction, such as
           Niagara-7 and later.

       -mfix-at697f
           Enable the documented workaround for  the  single  erratum  of  the  Atmel  AT697F  processor  (which
           corresponds to erratum #13 of the AT697E processor).

       -mfix-ut699
           Enable  the documented workarounds for the floating-point errata and the data cache nullify errata of
           the UT699 processor.

       -mfix-ut700
           Enable the documented workaround for the back-to-back store errata of the UT699E/UT700 processor.

       -mfix-gr712rc
           Enable the documented workaround for the back-to-back store errata of the GR712RC processor.

       These -m options are supported in addition to the above on SPARC-V9 processors in 64-bit environments:

       -m32
       -m64
           Generate code for a 32-bit or 64-bit environment.  The 32-bit environment sets int, long and  pointer
           to 32 bits.  The 64-bit environment sets int to 32 bits and long and pointer to 64 bits.

       -mcmodel=which
           Set the code model to one of

           medlow
               The  Medium/Low  code  model:  64-bit  addresses,  programs  must be linked in the low 32 bits of
               memory.  Programs can be statically or dynamically linked.

           medmid
               The Medium/Middle code model: 64-bit addresses, programs must be linked in the  low  44  bits  of
               memory,  the  text  and  data segments must be less than 2GB in size and the data segment must be
               located within 2GB of the text segment.

           medany
               The Medium/Anywhere code model: 64-bit addresses, programs may be linked anywhere in memory,  the
               text  and data segments must be less than 2GB in size and the data segment must be located within
               2GB of the text segment.

           embmedany
               The Medium/Anywhere code model for embedded systems: 64-bit addresses, the text and data segments
               must be less than 2GB in size, both starting anywhere in memory (determined at link  time).   The
               global  register  %g4 points to the base of the data segment.  Programs are statically linked and
               PIC is not supported.

       -mmemory-model=mem-model
           Set the memory model in force on the processor to one of

           default
               The default memory model for the processor and operating system.

           rmo Relaxed Memory Order

           pso Partial Store Order

           tso Total Store Order

           sc  Sequential Consistency

           These memory models are formally defined in Appendix D of the SPARC-V9 architecture manual, as set in
           the processor's "PSTATE.MM" field.

       -mstack-bias
       -mno-stack-bias
           With -mstack-bias, GCC assumes that the stack pointer, and frame pointer if present,  are  offset  by
           -2047  which  must  be  added back when making stack frame references.  This is the default in 64-bit
           mode.  Otherwise, assume no such offset is present.

       Options for System V

       These additional options are available on System V Release 4 for compatibility with  other  compilers  on
       those systems:

       -G  Create a shared object.  It is recommended that -symbolic or -shared be used instead.

       -Qy Identify  the  versions  of  each tool used by the compiler, in a ".ident" assembler directive in the
           output.

       -Qn Refrain from adding ".ident" directives to the output file (this is the default).

       -YP,dirs
           Search the directories dirs, and no others, for libraries specified with -l.

       -Ym,dir
           Look in the directory dir to find the M4 preprocessor.  The assembler uses this option.

       TILE-Gx Options

       These -m options are supported on the TILE-Gx:

       -mcmodel=small
           Generate code for the small model.  The distance for direct  calls  is  limited  to  500M  in  either
           direction.  PC-relative addresses are 32 bits.  Absolute addresses support the full address range.

       -mcmodel=large
           Generate  code  for the large model.  There is no limitation on call distance, pc-relative addresses,
           or absolute addresses.

       -mcpu=name
           Selects the type of CPU to be targeted.  Currently the only supported type is tilegx.

       -m32
       -m64
           Generate code for a 32-bit or 64-bit environment.  The 32-bit environment sets int, long, and pointer
           to 32 bits.  The 64-bit environment sets int to 32 bits and long and pointer to 64 bits.

       -mbig-endian
       -mlittle-endian
           Generate code in big/little endian mode, respectively.

       TILEPro Options

       These -m options are supported on the TILEPro:

       -mcpu=name
           Selects the type of CPU to be targeted.  Currently the only supported type is tilepro.

       -m32
           Generate code for a 32-bit environment, which sets int, long, and pointer to 32 bits.   This  is  the
           only supported behavior so the flag is essentially ignored.

       V850 Options

       These -m options are defined for V850 implementations:

       -mlong-calls
       -mno-long-calls
           Treat  all  calls as being far away (near).  If calls are assumed to be far away, the compiler always
           loads the function's address into a register, and calls indirect through the pointer.

       -mno-ep
       -mep
           Do not optimize (do optimize) basic blocks that use the same index pointer 4 or more  times  to  copy
           pointer into the "ep" register, and use the shorter "sld" and "sst" instructions.  The -mep option is
           on by default if you optimize.

       -mno-prolog-function
       -mprolog-function
           Do  not use (do use) external functions to save and restore registers at the prologue and epilogue of
           a function.  The external functions are slower, but use less code space if  more  than  one  function
           saves the same number of registers.  The -mprolog-function option is on by default if you optimize.

       -mspace
           Try  to  make  the  code  as  small  as  possible.   At  present,  this  just  turns  on the -mep and
           -mprolog-function options.

       -mtda=n
           Put static or global variables whose size is n bytes or less into the tiny data  area  that  register
           "ep"  points  to.   The  tiny  data  area  can  hold  up  to  256  bytes in total (128 bytes for byte
           references).

       -msda=n
           Put static or global variables whose size is n bytes or less into the small data area  that  register
           "gp" points to.  The small data area can hold up to 64 kilobytes.

       -mzda=n
           Put static or global variables whose size is n bytes or less into the first 32 kilobytes of memory.

       -mv850
           Specify that the target processor is the V850.

       -mv850e3v5
           Specify  that  the  target  processor  is  the V850E3V5.  The preprocessor constant "__v850e3v5__" is
           defined if this option is used.

       -mv850e2v4
           Specify that the target processor is the V850E3V5.  This is an alias for the -mv850e3v5 option.

       -mv850e2v3
           Specify that the target processor is the  V850E2V3.   The  preprocessor  constant  "__v850e2v3__"  is
           defined if this option is used.

       -mv850e2
           Specify  that  the target processor is the V850E2.  The preprocessor constant "__v850e2__" is defined
           if this option is used.

       -mv850e1
           Specify that the target processor  is  the  V850E1.   The  preprocessor  constants  "__v850e1__"  and
           "__v850e__" are defined if this option is used.

       -mv850es
           Specify that the target processor is the V850ES.  This is an alias for the -mv850e1 option.

       -mv850e
           Specify  that the target processor is the V850E.  The preprocessor constant "__v850e__" is defined if
           this option is used.

           If neither -mv850 nor -mv850e nor -mv850e1 nor -mv850e2 nor -mv850e2v3  nor  -mv850e3v5  are  defined
           then  a  default  target  processor  is  chosen  and  the relevant __v850*__ preprocessor constant is
           defined.

           The preprocessor constants "__v850" and "__v851__" are always defined, regardless of which  processor
           variant is the target.

       -mdisable-callt
       -mno-disable-callt
           This  option suppresses generation of the "CALLT" instruction for the v850e, v850e1, v850e2, v850e2v3
           and v850e3v5 flavors of the v850 architecture.

           This option is enabled by default when the RH850 ABI is in use (see  -mrh850-abi),  and  disabled  by
           default  when  the  GCC  ABI  is  in  use.   If  "CALLT"  instructions are being generated then the C
           preprocessor symbol "__V850_CALLT__" is defined.

       -mrelax
       -mno-relax
           Pass on (or do not pass on) the -mrelax command-line option to the assembler.

       -mlong-jumps
       -mno-long-jumps
           Disable (or re-enable) the generation of PC-relative jump instructions.

       -msoft-float
       -mhard-float
           Disable (or re-enable) the generation of hardware floating point instructions.  This option  is  only
           significant  when  the  target  architecture  is  V850E2V3  or  higher.   If  hardware floating point
           instructions are being generated then the C preprocessor symbol "__FPU_OK__"  is  defined,  otherwise
           the symbol "__NO_FPU__" is defined.

       -mloop
           Enables  the use of the e3v5 LOOP instruction.  The use of this instruction is not enabled by default
           when the e3v5 architecture is selected because its use is still experimental.

       -mrh850-abi
       -mghs
           Enables support for the RH850 version of the V850 ABI.  This is the default.  With  this  version  of
           the ABI the following rules apply:

           *   Integer sized structures and unions are returned via a memory pointer rather than a register.

           *   Large structures and unions (more than 8 bytes in size) are passed by value.

           *   Functions are aligned to 16-bit boundaries.

           *   The -m8byte-align command-line option is supported.

           *   The  -mdisable-callt  command-line option is enabled by default.  The -mno-disable-callt command-
               line option is not supported.

           When this version of the ABI is enabled the C preprocessor symbol "__V850_RH850_ABI__" is defined.

       -mgcc-abi
           Enables support for the old GCC version of the V850 ABI.  With this version of the ABI the  following
           rules apply:

           *   Integer sized structures and unions are returned in register "r10".

           *   Large structures and unions (more than 8 bytes in size) are passed by reference.

           *   Functions are aligned to 32-bit boundaries, unless optimizing for size.

           *   The -m8byte-align command-line option is not supported.

           *   The -mdisable-callt command-line option is supported but not enabled by default.

           When this version of the ABI is enabled the C preprocessor symbol "__V850_GCC_ABI__" is defined.

       -m8byte-align
       -mno-8byte-align
           Enables  support  for "double" and "long long" types to be aligned on 8-byte boundaries.  The default
           is to restrict the alignment of all objects to at most 4-bytes.  When -m8byte-align is in effect  the
           C preprocessor symbol "__V850_8BYTE_ALIGN__" is defined.

       -mbig-switch
           Generate  code suitable for big switch tables.  Use this option only if the assembler/linker complain
           about out of range branches within a switch table.

       -mapp-regs
           This option causes r2 and r5 to be used in the code generated by the compiler.  This setting  is  the
           default.

       -mno-app-regs
           This option causes r2 and r5 to be treated as fixed registers.

       VAX Options

       These -m options are defined for the VAX:

       -munix
           Do  not  output  certain  jump  instructions ("aobleq" and so on) that the Unix assembler for the VAX
           cannot handle across long ranges.

       -mgnu
           Do output those jump instructions, on the assumption that the GNU assembler is being used.

       -mg Output code for G-format floating-point numbers instead of D-format.

       Visium Options

       -mdebug
           A program which performs file I/O and is destined to run on an MCM target should be linked with  this
           option.   It  causes  the libraries libc.a and libdebug.a to be linked.  The program should be run on
           the target under the control of the GDB remote debugging stub.

       -msim
           A program which performs file I/O and is destined to run on  the  simulator  should  be  linked  with
           option.  This causes libraries libc.a and libsim.a to be linked.

       -mfpu
       -mhard-float
           Generate code containing floating-point instructions.  This is the default.

       -mno-fpu
       -msoft-float
           Generate code containing library calls for floating-point.

           -msoft-float  changes  the calling convention in the output file; therefore, it is only useful if you
           compile all of a program with this option.  In particular, you need to compile libgcc.a, the  library
           that comes with GCC, with -msoft-float in order for this to work.

       -mcpu=cpu_type
           Set  the  instruction  set,  register  set,  and  instruction  scheduling parameters for machine type
           cpu_type.  Supported values for cpu_type are mcm, gr5 and gr6.

           mcm is a synonym of gr5 present for backward compatibility.

           By default (unless configured otherwise), GCC generates code  for  the  GR5  variant  of  the  Visium
           architecture.

           With  -mcpu=gr6,  GCC  generates  code  for  the  GR6  variant  of the Visium architecture.  The only
           difference from GR5 code is that the compiler will generate block move instructions.

       -mtune=cpu_type
           Set the instruction scheduling parameters for machine type cpu_type, but do not set  the  instruction
           set or register set that the option -mcpu=cpu_type would.

       -msv-mode
           Generate  code  for  the  supervisor  mode,  where there are no restrictions on the access to general
           registers.  This is the default.

       -muser-mode
           Generate code for the user mode, where the access to some general registers is forbidden: on the GR5,
           registers r24 to r31 cannot be accessed in this mode; on the GR6,  only  registers  r29  to  r31  are
           affected.

       VMS Options

       These -m options are defined for the VMS implementations:

       -mvms-return-codes
           Return  VMS  condition codes from "main". The default is to return POSIX-style condition (e.g. error)
           codes.

       -mdebug-main=prefix
           Flag the first routine whose name starts with prefix as the main routine for the debugger.

       -mmalloc64
           Default to 64-bit memory allocation routines.

       -mpointer-size=size
           Set the default size of pointers. Possible options for size are 32 or short for 32 bit  pointers,  64
           or  long  for 64 bit pointers, and no for supporting only 32 bit pointers.  The later option disables
           "pragma pointer_size".

       VxWorks Options

       The options in this section are defined for all VxWorks targets.  Options specific to the target hardware
       are listed with the other options for that target.

       -mrtp
           GCC can generate code for both VxWorks kernels and real time processes (RTPs).  This option  switches
           from the former to the latter.  It also defines the preprocessor macro "__RTP__".

       -non-static
           Link  an  RTP  executable against shared libraries rather than static libraries.  The options -static
           and -shared can also be used for RTPs; -static is the default.

       -Bstatic
       -Bdynamic
           These options are passed down to the linker.  They are defined for compatibility with Diab.

       -Xbind-lazy
           Enable lazy binding of function calls.  This option is equivalent to -Wl,-z,now and  is  defined  for
           compatibility with Diab.

       -Xbind-now
           Disable  lazy binding of function calls.  This option is the default and is defined for compatibility
           with Diab.

       x86 Options

       These -m options are defined for the x86 family of computers.

       -march=cpu-type
           Generate instructions for the machine type cpu-type.  In contrast to  -mtune=cpu-type,  which  merely
           tunes the generated code for the specified cpu-type, -march=cpu-type allows GCC to generate code that
           may  not  run  at all on processors other than the one indicated.  Specifying -march=cpu-type implies
           -mtune=cpu-type, except where noted otherwise.

           The choices for cpu-type are:

           native
               This selects the CPU to generate code for at compilation time by determining the  processor  type
               of  the  compiling machine.  Using -march=native enables all instruction subsets supported by the
               local machine (hence the result might  not  run  on  different  machines).   Using  -mtune=native
               produces  code  optimized for the local machine under the constraints of the selected instruction
               set.

           x86-64
               A generic CPU with 64-bit extensions.

           x86-64-v2
           x86-64-v3
           x86-64-v4
               These choices for cpu-type select the corresponding  micro-architecture  level  from  the  x86-64
               psABI.  On ABIs other than the x86-64 psABI they select the same CPU features as the x86-64 psABI
               documents for the particular micro-architecture level.

               Since  these  cpu-type values do not have a corresponding -mtune setting, using -march with these
               values enables generic tuning.  Specific tuning can be enabled  using  the  -mtune=other-cpu-type
               option with an appropriate other-cpu-type value.

           i386
               Original Intel i386 CPU.

           i486
               Intel i486 CPU.  (No scheduling is implemented for this chip.)

           i586
           pentium
               Intel Pentium CPU with no MMX support.

           lakemont
               Intel Lakemont MCU, based on Intel Pentium CPU.

           pentium-mmx
               Intel Pentium MMX CPU, based on Pentium core with MMX instruction set support.

           pentiumpro
               Intel Pentium Pro CPU.

           i686
               When  used  with  -march,  the  Pentium Pro instruction set is used, so the code runs on all i686
               family chips.  When used with -mtune, it has the same meaning as generic.

           pentium2
               Intel Pentium II CPU, based on Pentium Pro core with MMX instruction set support.

           pentium3
           pentium3m
               Intel Pentium III CPU, based on Pentium Pro core with MMX and SSE instruction set support.

           pentium-m
               Intel Pentium M; low-power version of Intel Pentium III CPU with MMX, SSE  and  SSE2  instruction
               set support.  Used by Centrino notebooks.

           pentium4
           pentium4m
               Intel Pentium 4 CPU with MMX, SSE and SSE2 instruction set support.

           prescott
               Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2 and SSE3 instruction set support.

           nocona
               Improved  version  of  Intel  Pentium  4  CPU  with  64-bit  extensions,  MMX, SSE, SSE2 and SSE3
               instruction set support.

           core2
               Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3 instruction set support.

           nehalem
               Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2 and  POPCNT
               instruction set support.

           westmere
               Intel  Westmere  CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT,
               AES and PCLMUL instruction set support.

           sandybridge
               Intel Sandy Bridge CPU with 64-bit extensions, MMX,  SSE,  SSE2,  SSE3,  SSSE3,  SSE4.1,  SSE4.2,
               POPCNT, AVX, AES and PCLMUL instruction set support.

           ivybridge
               Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT,
               AVX, AES, PCLMUL, FSGSBASE, RDRND and F16C instruction set support.

           haswell
               Intel  Haswell  CPU  with  64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2,
               POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2 and F16C instruction set support.

           broadwell
               Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3,  SSE4.1,  SSE4.2,
               POPCNT,  AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED ADCX and PREFETCHW
               instruction set support.

           skylake
               Intel Skylake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2,  SSE3,  SSSE3,  SSE4.1,  SSE4.2,
               POPCNT,  AVX,  AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX, PREFETCHW,
               CLFLUSHOPT, XSAVEC and XSAVES instruction set support.

           bonnell
               Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3 and SSSE3  instruction  set
               support.

           silvermont
               Intel  Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2,
               POPCNT, AES, PREFETCHW, PCLMUL and RDRND instruction set support.

           goldmont
               Intel Goldmont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3,  SSSE3,  SSE4.1,  SSE4.2,
               POPCNT,  AES,  PREFETCHW, PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT and FSGSBASE instruction
               set support.

           goldmont-plus
               Intel Goldmont Plus CPU with 64-bit extensions, MOVBE,  MMX,  SSE,  SSE2,  SSE3,  SSSE3,  SSE4.1,
               SSE4.2,  POPCNT,  AES,  PREFETCHW,  PCLMUL,  RDRND,  XSAVE,  XSAVEC,  XSAVES, XSAVEOPT, FSGSBASE,
               PTWRITE, RDPID, SGX and UMIP instruction set support.

           tremont
               Intel Tremont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2,  SSE3,  SSSE3,  SSE4.1,  SSE4.2,
               POPCNT, AES, PREFETCHW, PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT, FSGSBASE, PTWRITE, RDPID,
               SGX, UMIP, GFNI-SSE, CLWB, MOVDIRI, MOVDIR64B, CLDEMOTE and WAITPKG instruction set support.

           knl Intel  Knight's  Landing  CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1,
               SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,  BMI,  BMI2,  F16C,  RDSEED,  ADCX,
               PREFETCHW, PREFETCHWT1, AVX512F, AVX512PF, AVX512ER and AVX512CD instruction set support.

           knm Intel  Knights  Mill  CPU  with  64-bit  extensions,  MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1,
               SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,  BMI,  BMI2,  F16C,  RDSEED,  ADCX,
               PREFETCHW,  PREFETCHWT1,  AVX512F,  AVX512PF,  AVX512ER, AVX512CD, AVX5124VNNIW, AVX5124FMAPS and
               AVX512VPOPCNTDQ instruction set support.

           skylake-avx512
               Intel Skylake Server CPU with 64-bit extensions, MOVBE, MMX,  SSE,  SSE2,  SSE3,  SSSE3,  SSE4.1,
               SSE4.2, POPCNT, PKU, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
               PREFETCHW,  CLFLUSHOPT,  XSAVEC, XSAVES, AVX512F, CLWB, AVX512VL, AVX512BW, AVX512DQ and AVX512CD
               instruction set support.

           cannonlake
               Intel Cannonlake Server CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3,  SSSE3,  SSE4.1,
               SSE4.2, POPCNT, PKU, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
               PREFETCHW,   CLFLUSHOPT,   XSAVEC,  XSAVES,  AVX512F,  AVX512VL,  AVX512BW,  AVX512DQ,  AVX512CD,
               AVX512VBMI, AVX512IFMA, SHA and UMIP instruction set support.

           icelake-client
               Intel Icelake Client CPU with 64-bit extensions, MOVBE, MMX,  SSE,  SSE2,  SSE3,  SSSE3,  SSE4.1,
               SSE4.2, POPCNT, PKU, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
               PREFETCHW,   CLFLUSHOPT,   XSAVEC,  XSAVES,  AVX512F,  AVX512VL,  AVX512BW,  AVX512DQ,  AVX512CD,
               AVX512VBMI, AVX512IFMA, SHA, CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ, AVX512BITALG,
               AVX512VNNI, VPCLMULQDQ, VAES instruction set support.

           icelake-server
               Intel Icelake Server CPU with 64-bit extensions, MOVBE, MMX,  SSE,  SSE2,  SSE3,  SSSE3,  SSE4.1,
               SSE4.2, POPCNT, PKU, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX,
               PREFETCHW,   CLFLUSHOPT,   XSAVEC,  XSAVES,  AVX512F,  AVX512VL,  AVX512BW,  AVX512DQ,  AVX512CD,
               AVX512VBMI, AVX512IFMA, SHA, CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ, AVX512BITALG,
               AVX512VNNI, VPCLMULQDQ, VAES, PCONFIG and WBNOINVD instruction set support.

           cascadelake
               Intel Cascadelake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2,
               POPCNT, PKU, AVX, AVX2, AES, PCLMUL,  FSGSBASE,  RDRND,  FMA,  BMI,  BMI2,  F16C,  RDSEED,  ADCX,
               PREFETCHW,  CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, CLWB, AVX512VL, AVX512BW, AVX512DQ, AVX512CD and
               AVX512VNNI instruction set support.

           cooperlake
               Intel cooperlake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1,  SSE4.2,
               POPCNT,  PKU,  AVX,  AVX2,  AES,  PCLMUL,  FSGSBASE,  RDRND,  FMA, BMI, BMI2, F16C, RDSEED, ADCX,
               PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, CLWB,  AVX512VL,  AVX512BW,  AVX512DQ,  AVX512CD,
               AVX512VNNI and AVX512BF16 instruction set support.

           tigerlake
               Intel  Tigerlake  CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2,
               POPCNT, PKU, AVX, AVX2, AES, PCLMUL,  FSGSBASE,  RDRND,  FMA,  BMI,  BMI2,  F16C,  RDSEED,  ADCX,
               PREFETCHW,   CLFLUSHOPT,   XSAVEC,  XSAVES,  AVX512F,  AVX512VL,  AVX512BW,  AVX512DQ,  AVX512CD,
               AVX512VBMI, AVX512IFMA, SHA, CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ, AVX512BITALG,
               AVX512VNNI, VPCLMULQDQ, VAES,  PCONFIG,  WBNOINVD,  MOVDIRI,  MOVDIR64B,  AVX512VP2INTERSECT  and
               KEYLOCKER instruction set support.

           sapphirerapids
               Intel  sapphirerapids  CPU  with  64-bit  extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1,
               SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND,  F16C,  AVX2,  BMI,  BMI2,
               LZCNT,  FMA,  MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F,
               AVX512VL, AVX512BW, AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES,
               AVX512VBMI2 VPCLMULQDQ, AVX512BITALG, RDPID, AVX512VPOPCNTDQ, PCONFIG, WBNOINVD,  CLWB,  MOVDIRI,
               MOVDIR64B,  AVX512VP2INTERSECT,  ENQCMD,  CLDEMOTE, PTWRITE, WAITPKG, SERIALIZE, TSXLDTRK, UINTR,
               AMX-BF16, AMX-TILE, AMX-INT8, AVX-VNNI and AVX512BF16 instruction set support.

           alderlake
               Intel Alderlake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3,  SSE4.1,  SSE4.2,
               POPCNT, AES, PREFETCHW, PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, XSAVEOPT, FSGSBASE, PTWRITE, RDPID,
               SGX,  UMIP,  GFNI-SSE,  CLWB,  MOVDIRI, MOVDIR64B, CLDEMOTE, WAITPKG, ADCX, AVX, AVX2, BMI, BMI2,
               F16C, FMA, LZCNT, PCONFIG, PKU, VAES, VPCLMULQDQ, SERIALIZE,  HRESET,  KL,  WIDEKL  and  AVX-VNNI
               instruction set support.

           rocketlake
               Intel  Rocketlake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2,
               POPCNT, PKU, AVX, AVX2, AES, PCLMUL,  FSGSBASE,  RDRND,  FMA,  BMI,  BMI2,  F16C,  RDSEED,  ADCX,
               PREFETCHW,   CLFLUSHOPT,   XSAVEC,  XSAVES,  AVX512F,  AVX512VL,  AVX512BW,  AVX512DQ,  AVX512CD,
               AVX512VBMI, AVX512IFMA, SHA, CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ, AVX512BITALG,
               AVX512VNNI, VPCLMULQDQ, VAES instruction set support.

           k6  AMD K6 CPU with MMX instruction set support.

           k6-2
           k6-3
               Improved versions of AMD K6 CPU with MMX and 3DNow! instruction set support.

           athlon
           athlon-tbird
               AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow! and SSE prefetch instructions support.

           athlon-4
           athlon-xp
           athlon-mp
               Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow! and full SSE instruction set support.

           k8
           opteron
           athlon64
           athlon-fx
               Processors based on the AMD K8 core with  x86-64  instruction  set  support,  including  the  AMD
               Opteron,  Athlon  64,  and  Athlon  64  FX  processors.   (This supersets MMX, SSE, SSE2, 3DNow!,
               enhanced 3DNow! and 64-bit instruction set extensions.)

           k8-sse3
           opteron-sse3
           athlon64-sse3
               Improved versions of AMD K8 cores with SSE3 instruction set support.

           amdfam10
           barcelona
               CPUs based on AMD Family 10h cores with x86-64 instruction set  support.   (This  supersets  MMX,
               SSE, SSE2, SSE3, SSE4A, 3DNow!, enhanced 3DNow!, ABM and 64-bit instruction set extensions.)

           bdver1
               CPUs  based  on  AMD Family 15h cores with x86-64 instruction set support.  (This supersets FMA4,
               AVX, XOP, LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3,  SSE4.1,  SSE4.2,  ABM  and
               64-bit instruction set extensions.)

           bdver2
               AMD  Family  15h  core based CPUs with x86-64 instruction set support.  (This supersets BMI, TBM,
               F16C, FMA, FMA4, AVX, XOP, LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3,  SSE4A,  SSSE3,  SSE4.1,
               SSE4.2, ABM and 64-bit instruction set extensions.)

           bdver3
               AMD  Family  15h  core based CPUs with x86-64 instruction set support.  (This supersets BMI, TBM,
               F16C, FMA, FMA4, FSGSBASE, AVX, XOP, LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A,  SSSE3,
               SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.)

           bdver4
               AMD  Family  15h core based CPUs with x86-64 instruction set support.  (This supersets BMI, BMI2,
               TBM, F16C, FMA, FMA4, FSGSBASE, AVX, AVX2, XOP, LWP, AES, PCLMUL, CX16, MOVBE,  MMX,  SSE,  SSE2,
               SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.)

           znver1
               AMD  Family  17h core based CPUs with x86-64 instruction set support.  (This supersets BMI, BMI2,
               F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL, CX16, MOVBE, MMX,
               SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2,  ABM,  XSAVEC,  XSAVES,  CLFLUSHOPT,  POPCNT,  and
               64-bit instruction set extensions.)

           znver2
               AMD  Family  17h  core based CPUs with x86-64 instruction set support. (This supersets BMI, BMI2,
               CLWB, F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED,  MWAITX,  SHA,  CLZERO,  AES,  PCLMUL,  CX16,
               MOVBE,  MMX,  SSE,  SSE2,  SSE3,  SSE4A,  SSSE3, SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT,
               POPCNT, RDPID, WBNOINVD, and 64-bit instruction set extensions.)

           znver3
               AMD Family 19h core based CPUs with x86-64 instruction set support. (This  supersets  BMI,  BMI2,
               CLWB,  F16C,  FMA,  FSGSBASE,  AVX,  AVX2,  ADCX, RDSEED, MWAITX, SHA, CLZERO, AES, PCLMUL, CX16,
               MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3,  SSE4.1,  SSE4.2,  ABM,  XSAVEC,  XSAVES,  CLFLUSHOPT,
               POPCNT, RDPID, WBNOINVD, PKU, VPCLMULQDQ, VAES, and 64-bit instruction set extensions.)

           btver1
               CPUs  based  on  AMD  Family 14h cores with x86-64 instruction set support.  (This supersets MMX,
               SSE, SSE2, SSE3, SSSE3, SSE4A, CX16, ABM and 64-bit instruction set extensions.)

           btver2
               CPUs based on AMD Family 16h cores with x86-64 instruction  set  support.  This  includes  MOVBE,
               F16C,  BMI,  AVX,  PCLMUL, AES, SSE4.2, SSE4.1, CX16, ABM, SSE4A, SSSE3, SSE3, SSE2, SSE, MMX and
               64-bit instruction set extensions.

           winchip-c6
               IDT WinChip C6 CPU, dealt in same way as i486 with additional MMX instruction set support.

           winchip2
               IDT WinChip 2 CPU, dealt in same way as i486 with additional  MMX  and  3DNow!   instruction  set
               support.

           c3  VIA  C3  CPU with MMX and 3DNow! instruction set support.  (No scheduling is implemented for this
               chip.)

           c3-2
               VIA C3-2 (Nehemiah/C5XL) CPU with MMX  and  SSE  instruction  set  support.   (No  scheduling  is
               implemented for this chip.)

           c7  VIA  C7  (Esther)  CPU  with  MMX, SSE, SSE2 and SSE3 instruction set support.  (No scheduling is
               implemented for this chip.)

           samuel-2
               VIA Eden Samuel 2 CPU with MMX and 3DNow! instruction set support.  (No scheduling is implemented
               for this chip.)

           nehemiah
               VIA Eden Nehemiah CPU with MMX and SSE instruction set support.  (No  scheduling  is  implemented
               for this chip.)

           esther
               VIA  Eden  Esther  CPU  with  MMX, SSE, SSE2 and SSE3 instruction set support.  (No scheduling is
               implemented for this chip.)

           eden-x2
               VIA Eden X2 CPU with x86-64, MMX, SSE, SSE2 and SSE3 instruction set support.  (No scheduling  is
               implemented for this chip.)

           eden-x4
               VIA  Eden  X4  CPU  with  x86-64,  MMX,  SSE,  SSE2,  SSE3,  SSSE3,  SSE4.1, SSE4.2, AVX and AVX2
               instruction set support.  (No scheduling is implemented for this chip.)

           nano
               Generic VIA Nano CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3 instruction  set  support.   (No
               scheduling is implemented for this chip.)

           nano-1000
               VIA  Nano  1xxx  CPU  with  x86-64,  MMX, SSE, SSE2, SSE3 and SSSE3 instruction set support.  (No
               scheduling is implemented for this chip.)

           nano-2000
               VIA Nano 2xxx CPU with x86-64, MMX, SSE, SSE2, SSE3  and  SSSE3  instruction  set  support.   (No
               scheduling is implemented for this chip.)

           nano-3000
               VIA  Nano  3xxx  CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1 instruction set support.
               (No scheduling is implemented for this chip.)

           nano-x2
               VIA Nano Dual Core CPU with x86-64, MMX, SSE,  SSE2,  SSE3,  SSSE3  and  SSE4.1  instruction  set
               support.  (No scheduling is implemented for this chip.)

           nano-x4
               VIA  Nano  Quad  Core  CPU  with  x86-64,  MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1 instruction set
               support.  (No scheduling is implemented for this chip.)

           geode
               AMD Geode embedded processor with MMX and 3DNow! instruction set support.

       -mtune=cpu-type
           Tune to cpu-type everything applicable about the generated code, except for the ABI and  the  set  of
           available  instructions.   While  picking a specific cpu-type schedules things appropriately for that
           particular chip, the compiler does not generate any code that cannot run on the default machine  type
           unless  you  use  a  -march=cpu-type option.  For example, if GCC is configured for i686-pc-linux-gnu
           then -mtune=pentium4 generates code that is tuned for Pentium 4 but still runs on i686 machines.

           The choices for cpu-type are the same as for -march.  In addition, -mtune supports  2  extra  choices
           for cpu-type:

           generic
               Produce  code  optimized for the most common IA32/AMD64/EM64T processors.  If you know the CPU on
               which your code will run, then you should use the corresponding -mtune or -march  option  instead
               of -mtune=generic.  But, if you do not know exactly what CPU users of your application will have,
               then you should use this option.

               As  new  processors  are  deployed  in  the marketplace, the behavior of this option will change.
               Therefore, if you upgrade to a newer version of GCC, code generation controlled  by  this  option
               will  change  to  reflect  the processors that are most common at the time that version of GCC is
               released.

               There is no -march=generic option because -march indicates the instruction set the  compiler  can
               use,  and  there is no generic instruction set applicable to all processors.  In contrast, -mtune
               indicates the processor (or, in this case, collection  of  processors)  for  which  the  code  is
               optimized.

           intel
               Produce  code  optimized  for the most current Intel processors, which are Haswell and Silvermont
               for this version of GCC.  If you know the CPU on which your code will run, then  you  should  use
               the  corresponding  -mtune  or  -march  option  instead  of  -mtune=intel.  But, if you want your
               application performs better on both Haswell and Silvermont, then you should use this option.

               As new Intel processors are deployed in the marketplace, the behavior of this option will change.
               Therefore, if you upgrade to a newer version of GCC, code generation controlled  by  this  option
               will  change  to  reflect  the  most  current Intel processors at the time that version of GCC is
               released.

               There is no -march=intel option because -march indicates the instruction  set  the  compiler  can
               use,  and  there  is no common instruction set applicable to all processors.  In contrast, -mtune
               indicates the processor (or, in this case, collection  of  processors)  for  which  the  code  is
               optimized.

       -mcpu=cpu-type
           A deprecated synonym for -mtune.

       -mfpmath=unit
           Generate floating-point arithmetic for selected unit unit.  The choices for unit are:

           387 Use  the  standard  387  floating-point coprocessor present on the majority of chips and emulated
               otherwise.  Code compiled with this option runs almost everywhere.   The  temporary  results  are
               computed  in  80-bit  precision  instead  of  the  precision  specified by the type, resulting in
               slightly different results compared to most of other chips.  See -ffloat-store for more  detailed
               description.

               This is the default choice for non-Darwin x86-32 targets.

           sse Use  scalar floating-point instructions present in the SSE instruction set.  This instruction set
               is supported by Pentium III and newer chips, and in the AMD  line  by  Athlon-4,  Athlon  XP  and
               Athlon  MP  chips.  The earlier version of the SSE instruction set supports only single-precision
               arithmetic, thus the double and extended-precision arithmetic are still done using 387.  A  later
               version,  present  only  in  Pentium 4 and AMD x86-64 chips, supports double-precision arithmetic
               too.

               For the x86-32 compiler, you must use -march=cpu-type, -msse or -msse2  switches  to  enable  SSE
               extensions and make this option effective.  For the x86-64 compiler, these extensions are enabled
               by default.

               The resulting code should be considerably faster in the majority of cases and avoid the numerical
               instability problems of 387 code, but may break some existing code that expects temporaries to be
               80 bits.

               This is the default choice for the x86-64 compiler, Darwin x86-32 targets, and the default choice
               for x86-32 targets with the SSE2 instruction set when -ffast-math is enabled.

           sse,387
           sse+387
           both
               Attempt  to  utilize  both  instruction  sets  at  once.   This effectively doubles the amount of
               available registers, and on chips with separate execution units for 387  and  SSE  the  execution
               resources  too.  Use this option with care, as it is still experimental, because the GCC register
               allocator does not model separate functional units well, resulting in unstable performance.

       -masm=dialect
           Output assembly instructions using selected dialect.  Also affects which dialect is  used  for  basic
           "asm"  and extended "asm". Supported choices (in dialect order) are att or intel. The default is att.
           Darwin does not support intel.

       -mieee-fp
       -mno-ieee-fp
           Control whether or not the compiler uses IEEE floating-point comparisons.  These correctly handle the
           case where the result of a comparison is unordered.

       -m80387
       -mhard-float
           Generate output containing 80387 instructions for floating point.

       -mno-80387
       -msoft-float
           Generate output containing library calls for floating point.

           Warning: the requisite libraries are not part of GCC.  Normally the facilities of the machine's usual
           C compiler are used, but this cannot be done directly in cross-compilation.  You must make  your  own
           arrangements to provide suitable library functions for cross-compilation.

           On  machines  where  a  function  returns  floating-point  results  in the 80387 register stack, some
           floating-point opcodes may be emitted even if -msoft-float is used.

       -mno-fp-ret-in-387
           Do not use the FPU registers for return values of functions.

           The usual calling convention has functions return values of types "float"  and  "double"  in  an  FPU
           register, even if there is no FPU.  The idea is that the operating system should emulate an FPU.

           The option -mno-fp-ret-in-387 causes such values to be returned in ordinary CPU registers instead.

       -mno-fancy-math-387
           Some 387 emulators do not support the "sin", "cos" and "sqrt" instructions for the 387.  Specify this
           option  to avoid generating those instructions.  This option is overridden when -march indicates that
           the target CPU always has an FPU and so the instruction does not need emulation.  These  instructions
           are not generated unless you also use the -funsafe-math-optimizations switch.

       -malign-double
       -mno-align-double
           Control  whether GCC aligns "double", "long double", and "long long" variables on a two-word boundary
           or a one-word boundary.  Aligning "double" variables on a two-word boundary produces code  that  runs
           somewhat faster on a Pentium at the expense of more memory.

           On x86-64, -malign-double is enabled by default.

           Warning:  if  you  use  the  -malign-double switch, structures containing the above types are aligned
           differently than the published application binary interface specifications for the x86-32 and are not
           binary compatible with structures in code compiled without that switch.

       -m96bit-long-double
       -m128bit-long-double
           These switches control the size of "long double"  type.   The  x86-32  application  binary  interface
           specifies the size to be 96 bits, so -m96bit-long-double is the default in 32-bit mode.

           Modern  architectures  (Pentium  and  newer)  prefer  "long double" to be aligned to an 8- or 16-byte
           boundary.  In arrays or structures conforming to the  ABI,  this  is  not  possible.   So  specifying
           -m128bit-long-double  aligns "long double" to a 16-byte boundary by padding the "long double" with an
           additional 32-bit zero.

           In the x86-64 compiler, -m128bit-long-double is the default choice as its ABI  specifies  that  "long
           double" is aligned on 16-byte boundary.

           Notice  that neither of these options enable any extra precision over the x87 standard of 80 bits for
           a "long double".

           Warning: if you override the default value for your target ABI, this changes the size  of  structures
           and  arrays  containing "long double" variables, as well as modifying the function calling convention
           for functions taking "long double".  Hence they are not binary-compatible with code compiled  without
           that switch.

       -mlong-double-64
       -mlong-double-80
       -mlong-double-128
           These switches control the size of "long double" type. A size of 64 bits makes the "long double" type
           equivalent to the "double" type. This is the default for 32-bit Bionic C library.  A size of 128 bits
           makes  the  "long  double"  type  equivalent to the "__float128" type. This is the default for 64-bit
           Bionic C library.

           Warning: if you override the default value for your target ABI, this changes the size  of  structures
           and  arrays  containing "long double" variables, as well as modifying the function calling convention
           for functions taking "long double".  Hence they are not binary-compatible with code compiled  without
           that switch.

       -malign-data=type
           Control  how  GCC  aligns  variables.   Supported values for type are compat uses increased alignment
           value compatible uses GCC 4.8 and earlier, abi uses alignment value as specified by  the  psABI,  and
           cacheline uses increased alignment value to match the cache line size.  compat is the default.

       -mlarge-data-threshold=threshold
           When  -mcmodel=medium  is  specified, data objects larger than threshold are placed in the large data
           section.  This value must be the same across all objects linked into  the  binary,  and  defaults  to
           65535.

       -mrtd
           Use a different function-calling convention, in which functions that take a fixed number of arguments
           return  with  the  "ret num" instruction, which pops their arguments while returning.  This saves one
           instruction in the caller since there is no need to pop the arguments there.

           You can specify that an individual function is called with this calling sequence  with  the  function
           attribute "stdcall".  You can also override the -mrtd option by using the function attribute "cdecl".

           Warning:  this  calling  convention is incompatible with the one normally used on Unix, so you cannot
           use it if you need to call libraries compiled with the Unix compiler.

           Also, you must provide function prototypes for all functions that take variable numbers of  arguments
           (including "printf"); otherwise incorrect code is generated for calls to those functions.

           In  addition,  seriously  incorrect  code  results  if  you  call a function with too many arguments.
           (Normally, extra arguments are harmlessly ignored.)

       -mregparm=num
           Control how many registers are used to pass integer arguments.  By default, no registers are used  to
           pass  arguments,  and  at most 3 registers can be used.  You can control this behavior for a specific
           function by using the function attribute "regparm".

           Warning: if you use this switch, and num is nonzero, then you must build all modules  with  the  same
           value, including any libraries.  This includes the system libraries and startup modules.

       -msseregparm
           Use  SSE  register  passing  conventions  for  float and double arguments and return values.  You can
           control this behavior for a specific function by using the function attribute "sseregparm".

           Warning: if you use this switch then you must build all modules with the same  value,  including  any
           libraries.  This includes the system libraries and startup modules.

       -mvect8-ret-in-mem
           Return  8-byte  vectors  in memory instead of MMX registers.  This is the default on VxWorks to match
           the ABI of the Sun Studio compilers until version 12.  Only use this option if  you  need  to  remain
           compatible with existing code produced by those previous compiler versions or older versions of GCC.

       -mpc32
       -mpc64
       -mpc80
           Set  80387 floating-point precision to 32, 64 or 80 bits.  When -mpc32 is specified, the significands
           of results of floating-point operations are rounded to 24 bits (single precision); -mpc64 rounds  the
           significands  of results of floating-point operations to 53 bits (double precision) and -mpc80 rounds
           the significands of results of floating-point operations to  64  bits  (extended  double  precision),
           which  is  the default.  When this option is used, floating-point operations in higher precisions are
           not available to the programmer without setting the FPU control word explicitly.

           Setting the rounding of floating-point operations to less than the default 80  bits  can  speed  some
           programs  by  2%  or  more.   Note  that  some  mathematical libraries assume that extended-precision
           (80-bit) floating-point operations are enabled by default; routines in such  libraries  could  suffer
           significant  loss  of  accuracy,  typically  through so-called "catastrophic cancellation", when this
           option is used to set the precision to less than extended precision.

       -mdaz-ftz
           The flush-to-zero (FTZ) and denormals-are-zero (DAZ) flags in the MXCSR register are used to  control
           floating-point  calculations.SSE  and AVX instructions including scalar and vector instructions could
           benefit from enabling the FTZ and DAZ flags when -mdaz-ftz is specified. Don't set FTZ/DAZ flags when
           -mno-daz-ftz is specified.

       -mstackrealign
           Realign the stack at entry.  On the x86, the -mstackrealign option generates  an  alternate  prologue
           and  epilogue  that realigns the run-time stack if necessary.  This supports mixing legacy codes that
           keep  4-byte  stack  alignment  with  modern  codes  that  keep  16-byte  stack  alignment  for   SSE
           compatibility.  See also the attribute "force_align_arg_pointer", applicable to individual functions.

       -mpreferred-stack-boundary=num
           Attempt   to   keep   the   stack  boundary  aligned  to  a  2  raised  to  num  byte  boundary.   If
           -mpreferred-stack-boundary is not specified, the default is 4 (16 bytes or 128 bits).

           Warning:  When  generating  code  for  the  x86-64  architecture  with   SSE   extensions   disabled,
           -mpreferred-stack-boundary=3  can  be  used  to  keep  the stack boundary aligned to 8 byte boundary.
           Since x86-64 ABI require 16 byte stack alignment, this is ABI incompatible and intended to be used in
           controlled environment where stack space is important limitation.  This option leads  to  wrong  code
           when  functions compiled with 16 byte stack alignment (such as functions from a standard library) are
           called with misaligned stack.  In this case, SSE instructions may lead to  misaligned  memory  access
           traps.   In  addition,  variable  arguments  are  handled  incorrectly  for  16  byte aligned objects
           (including x87 long double and __int128), leading to wrong results.  You must build all modules  with
           -mpreferred-stack-boundary=3,  including  any  libraries.   This  includes  the  system libraries and
           startup modules.

       -mincoming-stack-boundary=num
           Assume  the  incoming  stack   is   aligned   to   a   2   raised   to   num   byte   boundary.    If
           -mincoming-stack-boundary is not specified, the one specified by -mpreferred-stack-boundary is used.

           On Pentium and Pentium Pro, "double" and "long double" values should be aligned to an 8-byte boundary
           (see  -malign-double)  or  suffer  significant  run  time performance penalties.  On Pentium III, the
           Streaming SIMD Extension (SSE) data type "__m128" may not work properly if it is not 16-byte aligned.

           To ensure proper alignment of this values on the stack, the stack boundary must be as aligned as that
           required by any value stored on the stack.  Further, every function must be generated  such  that  it
           keeps  the  stack  aligned.   Thus calling a function compiled with a higher preferred stack boundary
           from a function compiled with a lower preferred stack boundary most likely misaligns the  stack.   It
           is recommended that libraries that use callbacks always use the default setting.

           This extra alignment does consume extra stack space, and generally increases code size.  Code that is
           sensitive  to  stack  space usage, such as embedded systems and operating system kernels, may want to
           reduce the preferred alignment to -mpreferred-stack-boundary=2.

       -mmmx
       -msse
       -msse2
       -msse3
       -mssse3
       -msse4
       -msse4a
       -msse4.1
       -msse4.2
       -mavx
       -mavx2
       -mavx512f
       -mavx512pf
       -mavx512er
       -mavx512cd
       -mavx512vl
       -mavx512bw
       -mavx512dq
       -mavx512ifma
       -mavx512vbmi
       -msha
       -maes
       -mpclmul
       -mclflushopt
       -mclwb
       -mfsgsbase
       -mptwrite
       -mrdrnd
       -mf16c
       -mfma
       -mpconfig
       -mwbnoinvd
       -mfma4
       -mprfchw
       -mrdpid
       -mprefetchwt1
       -mrdseed
       -msgx
       -mxop
       -mlwp
       -m3dnow
       -m3dnowa
       -mpopcnt
       -mabm
       -madx
       -mbmi
       -mbmi2
       -mlzcnt
       -mfxsr
       -mxsave
       -mxsaveopt
       -mxsavec
       -mxsaves
       -mrtm
       -mhle
       -mtbm
       -mmwaitx
       -mclzero
       -mpku
       -mavx512vbmi2
       -mavx512bf16
       -mgfni
       -mvaes
       -mwaitpkg
       -mvpclmulqdq
       -mavx512bitalg
       -mmovdiri
       -mmovdir64b
       -menqcmd
       -muintr
       -mtsxldtrk
       -mavx512vpopcntdq
       -mavx512vp2intersect
       -mavx5124fmaps
       -mavx512vnni
       -mavxvnni
       -mavx5124vnniw
       -mcldemote
       -mserialize
       -mamx-tile
       -mamx-int8
       -mamx-bf16
       -mhreset
       -mkl
       -mwidekl
           These switches enable the use of instructions in the  MMX,  SSE,  SSE2,  SSE3,  SSSE3,  SSE4,  SSE4A,
           SSE4.1,  SSE4.2,  AVX,  AVX2,  AVX512F,  AVX512PF,  AVX512ER, AVX512CD, AVX512VL, AVX512BW, AVX512DQ,
           AVX512IFMA, AVX512VBMI, SHA, AES, PCLMUL, CLFLUSHOPT, CLWB,  FSGSBASE,  PTWRITE,  RDRND,  F16C,  FMA,
           PCONFIG,  WBNOINVD,  FMA4,  PREFETCHW,  RDPID,  PREFETCHWT1,  RDSEED, SGX, XOP, LWP, 3DNow!, enhanced
           3DNow!, POPCNT, ABM, ADX, BMI, BMI2, LZCNT, FXSR, XSAVE, XSAVEOPT, XSAVEC,  XSAVES,  RTM,  HLE,  TBM,
           MWAITX,  CLZERO, PKU, AVX512VBMI2, GFNI, VAES, WAITPKG, VPCLMULQDQ, AVX512BITALG, MOVDIRI, MOVDIR64B,
           AVX512BF16,  ENQCMD,  AVX512VPOPCNTDQ,  AVX5124FMAPS,  AVX512VNNI,  AVX5124VNNIW,  SERIALIZE,  UINTR,
           HRESET,  AMXTILE,  AMXINT8,  AMXBF16, KL, WIDEKL, AVXVNNI or CLDEMOTE extended instruction sets. Each
           has a corresponding -mno- option to disable use of these instructions.

           These extensions are also available as built-in functions: see x86 Built-in Functions, for details of
           the functions enabled and disabled by these switches.

           To generate  SSE/SSE2  instructions  automatically  from  floating-point  code  (as  opposed  to  387
           instructions), see -mfpmath=sse.

           GCC depresses SSEx instructions when -mavx is used. Instead, it generates new AVX instructions or AVX
           equivalence for all SSEx instructions when needed.

           These  options  enable  GCC  to  use  these  extended  instructions  in  generated code, even without
           -mfpmath=sse.  Applications that perform run-time CPU detection must compile separate files for  each
           supported  architecture,  using  the  appropriate  flags.  In particular, the file containing the CPU
           detection code should be compiled without these options.

       -mdump-tune-features
           This option instructs GCC to dump the names of  the  x86  performance  tuning  features  and  default
           settings. The names can be used in -mtune-ctrl=feature-list.

       -mtune-ctrl=feature-list
           This  option  is  used  to  do fine grain control of x86 code generation features.  feature-list is a
           comma separated list of feature names. See also -mdump-tune-features. When specified, the feature  is
           turned  on  if  it  is not preceded with ^, otherwise, it is turned off.  -mtune-ctrl=feature-list is
           intended to be used by GCC developers. Using it may lead to code paths not covered by testing and can
           potentially result in compiler ICEs or runtime errors.

       -mno-default
           This option instructs GCC to turn off all tunable features.  See  also  -mtune-ctrl=feature-list  and
           -mdump-tune-features.

       -mcld
           This  option  instructs  GCC to emit a "cld" instruction in the prologue of functions that use string
           instructions.  String instructions  depend  on  the  DF  flag  to  select  between  autoincrement  or
           autodecrement  mode.   While  the  ABI  specifies  the  DF flag to be cleared on function entry, some
           operating systems violate this  specification  by  not  clearing  the  DF  flag  in  their  exception
           dispatchers.   The  exception  handler  can  be  invoked  with  the DF flag set, which leads to wrong
           direction mode when string instructions are used.  This option can be enabled by  default  on  32-bit
           x86  targets  by  configuring  GCC  with  the  --enable-cld  configure  option.   Generation of "cld"
           instructions can be suppressed with the -mno-cld compiler option in this case.

       -mvzeroupper
           This option instructs GCC to emit a "vzeroupper" instruction before a transfer of control flow out of
           the function to minimize the AVX to SSE transition penalty as well as remove unnecessary  "zeroupper"
           intrinsics.

       -mprefer-avx128
           This  option instructs GCC to use 128-bit AVX instructions instead of 256-bit AVX instructions in the
           auto-vectorizer.

       -mprefer-vector-width=opt
           This option instructs GCC to use opt-bit vector width in  instructions  instead  of  default  on  the
           selected platform.

           none
               No extra limitations applied to GCC other than defined by the selected platform.

           128 Prefer 128-bit vector width for instructions.

           256 Prefer 256-bit vector width for instructions.

           512 Prefer 512-bit vector width for instructions.

       -mcx16
           This  option  enables  GCC to generate "CMPXCHG16B" instructions in 64-bit code to implement compare-
           and-exchange operations on 16-byte aligned 128-bit objects.  This is useful  for  atomic  updates  of
           data  structures exceeding one machine word in size.  The compiler uses this instruction to implement
           __sync Builtins.  However, for __atomic Builtins operating on 128-bit integers,  a  library  call  is
           always used.

       -msahf
           This  option  enables  generation  of "SAHF" instructions in 64-bit code.  Early Intel Pentium 4 CPUs
           with Intel 64 support, prior to the introduction of Pentium 4 G1 step in December  2005,  lacked  the
           "LAHF"  and "SAHF" instructions which are supported by AMD64.  These are load and store instructions,
           respectively, for certain status flags.  In 64-bit mode, the "SAHF" instruction is used  to  optimize
           "fmod", "drem", and "remainder" built-in functions; see Other Builtins for details.

       -mmovbe
           This   option   enables   use  of  the  "movbe"  instruction  to  implement  "__builtin_bswap32"  and
           "__builtin_bswap64".

       -mshstk
           The -mshstk option  enables  shadow  stack  built-in  functions  from  x86  Control-flow  Enforcement
           Technology (CET).

       -mcrc32
           This   option   enables   built-in   functions   "__builtin_ia32_crc32qi",  "__builtin_ia32_crc32hi",
           "__builtin_ia32_crc32si" and "__builtin_ia32_crc32di" to generate the "crc32" machine instruction.

       -mmwait
           This option  enables  built-in  functions  "__builtin_ia32_monitor",  and  "__builtin_ia32_mwait"  to
           generate the "monitor" and "mwait" machine instructions.

       -mrecip
           This  option enables use of "RCPSS" and "RSQRTSS" instructions (and their vectorized variants "RCPPS"
           and "RSQRTPS") with an additional Newton-Raphson step to increase precision instead  of  "DIVSS"  and
           "SQRTSS"  (and  their  vectorized  variants)  for  single-precision  floating-point arguments.  These
           instructions  are  generated  only  when  -funsafe-math-optimizations  is   enabled   together   with
           -ffinite-math-only  and -fno-trapping-math.  Note that while the throughput of the sequence is higher
           than the throughput of the non-reciprocal instruction, the precision of the sequence can be decreased
           by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).

           Note that  GCC  implements  "1.0f/sqrtf(x)"  in  terms  of  "RSQRTSS"  (or  "RSQRTPS")  already  with
           -ffast-math (or the above option combination), and doesn't need -mrecip.

           Also  note  that  GCC  emits  the  above  sequence with additional Newton-Raphson step for vectorized
           single-float division and vectorized  "sqrtf(x)"  already  with  -ffast-math  (or  the  above  option
           combination), and doesn't need -mrecip.

       -mrecip=opt
           This  option  controls  which reciprocal estimate instructions may be used.  opt is a comma-separated
           list of options, which may be preceded by a ! to invert the option:

           all Enable all estimate instructions.

           default
               Enable the default instructions, equivalent to -mrecip.

           none
               Disable all estimate instructions, equivalent to -mno-recip.

           div Enable the approximation for scalar division.

           vec-div
               Enable the approximation for vectorized division.

           sqrt
               Enable the approximation for scalar square root.

           vec-sqrt
               Enable the approximation for vectorized square root.

           So, for example, -mrecip=all,!sqrt enables all of the reciprocal approximations,  except  for  square
           root.

       -mveclibabi=type
           Specifies the ABI type to use for vectorizing intrinsics using an external library.  Supported values
           for type are svml for the Intel short vector math library and acml for the AMD math core library.  To
           use  this  option,  both  -ftree-vectorize and -funsafe-math-optimizations have to be enabled, and an
           SVML or ACML ABI-compatible library must be specified at link time.

           GCC  currently  emits  calls  to  "vmldExp2",  "vmldLn2",  "vmldLog102",   "vmldPow2",   "vmldTanh2",
           "vmldTan2",   "vmldAtan2",   "vmldAtanh2",   "vmldCbrt2",   "vmldSinh2",   "vmldSin2",  "vmldAsinh2",
           "vmldAsin2", "vmldCosh2", "vmldCos2", "vmldAcosh2", "vmldAcos2", "vmlsExp4", "vmlsLn4", "vmlsLog104",
           "vmlsPow4", "vmlsTanh4", "vmlsTan4", "vmlsAtan4", "vmlsAtanh4", "vmlsCbrt4", "vmlsSinh4", "vmlsSin4",
           "vmlsAsinh4", "vmlsAsin4", "vmlsCosh4", "vmlsCos4", "vmlsAcosh4" and  "vmlsAcos4"  for  corresponding
           function   type   when  -mveclibabi=svml  is  used,  and  "__vrd2_sin",  "__vrd2_cos",  "__vrd2_exp",
           "__vrd2_log",   "__vrd2_log2",   "__vrd2_log10",   "__vrs4_sinf",    "__vrs4_cosf",    "__vrs4_expf",
           "__vrs4_logf",  "__vrs4_log2f", "__vrs4_log10f" and "__vrs4_powf" for the corresponding function type
           when -mveclibabi=acml is used.

       -mabi=name
           Generate code for the specified calling convention.  Permissible values are sysv for the ABI used  on
           GNU/Linux  and  other systems, and ms for the Microsoft ABI.  The default is to use the Microsoft ABI
           when targeting Microsoft Windows and the SysV ABI  on  all  other  systems.   You  can  control  this
           behavior for specific functions by using the function attributes "ms_abi" and "sysv_abi".

       -mforce-indirect-call
           Force all calls to functions to be indirect. This is useful when using Intel Processor Trace where it
           generates more precise timing information for function calls.

       -mmanual-endbr
           Insert ENDBR instruction at function entry only via the "cf_check" function attribute. This is useful
           when used with the option -fcf-protection=branch to control ENDBR insertion at the function entry.

       -mcall-ms2sysv-xlogues
           Due to differences in 64-bit ABIs, any Microsoft ABI function that calls a System V ABI function must
           consider  RSI,  RDI  and  XMM6-15  as clobbered.  By default, the code for saving and restoring these
           registers  is  emitted  inline,  resulting  in  fairly  lengthy  prologues  and   epilogues.    Using
           -mcall-ms2sysv-xlogues  emits  prologues and epilogues that use stubs in the static portion of libgcc
           to perform these saves and restores, thus  reducing  function  size  at  the  cost  of  a  few  extra
           instructions.

       -mtls-dialect=type
           Generate  code  to  access  thread-local  storage  using  the  gnu  or  gnu2 conventions.  gnu is the
           conservative default; gnu2 is more efficient, but it may add compile- and run-time requirements  that
           cannot be satisfied on all systems.

       -mpush-args
       -mno-push-args
           Use PUSH operations to store outgoing parameters.  This method is shorter and usually equally fast as
           method  using  SUB/MOV  operations and is enabled by default.  In some cases disabling it may improve
           performance because of improved scheduling and reduced dependencies.

       -maccumulate-outgoing-args
           If enabled, the maximum amount of space required for outgoing arguments is computed in  the  function
           prologue.   This  is  faster on most modern CPUs because of reduced dependencies, improved scheduling
           and reduced stack usage when the preferred stack boundary is not equal  to  2.   The  drawback  is  a
           notable increase in code size.  This switch implies -mno-push-args.

       -mthreads
           Support  thread-safe  exception  handling  on  MinGW.   Programs  that  rely on thread-safe exception
           handling must compile and link all code with the -mthreads option.  When compiling, -mthreads defines
           -D_MT; when linking, it links in a special thread helper library -lmingwthrd  which  cleans  up  per-
           thread exception-handling data.

       -mms-bitfields
       -mno-ms-bitfields
           Enable/disable bit-field layout compatible with the native Microsoft Windows compiler.

           If  "packed" is used on a structure, or if bit-fields are used, it may be that the Microsoft ABI lays
           out the structure differently than the way GCC normally does.  Particularly when moving  packed  data
           between functions compiled with GCC and the native Microsoft compiler (either via function call or as
           data in a file), it may be necessary to access either format.

           This  option  is  enabled  by  default  for  Microsoft  Windows  targets.   This behavior can also be
           controlled locally by use of variable or type attributes.  For more  information,  see  x86  Variable
           Attributes and x86 Type Attributes.

           The  Microsoft  structure  layout  algorithm  is  fairly  simple  with the exception of the bit-field
           packing.  The padding and alignment of members of structures and whether a bit-field can  straddle  a
           storage-unit boundary are determine by these rules:

           1. Structure members are stored sequentially in the order in which they are
               declared: the first member has the lowest memory address and the last member the highest.

           2. Every data object has an alignment requirement.  The alignment requirement
               for  all  data  except  structures,  unions,  and  arrays is either the size of the object or the
               current packing size (specified with either  the  "aligned"  attribute  or  the  "pack"  pragma),
               whichever  is less.  For structures, unions, and arrays, the alignment requirement is the largest
               alignment requirement of its members.  Every object is allocated an offset so that:

                       offset % alignment_requirement == 0

           3. Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte allocation
               unit if the integral types are the same size and if the next  bit-field  fits  into  the  current
               allocation unit without crossing the boundary imposed by the common alignment requirements of the
               bit-fields.

           MSVC interprets zero-length bit-fields in the following ways:

           1. If a zero-length bit-field is inserted between two bit-fields that
               are normally coalesced, the bit-fields are not coalesced.

               For example:

                       struct
                        {
                          unsigned long bf_1 : 12;
                          unsigned long : 0;
                          unsigned long bf_2 : 12;
                        } t1;

               The  size  of  "t1" is 8 bytes with the zero-length bit-field.  If the zero-length bit-field were
               removed, "t1"'s size would be 4 bytes.

           2. If a zero-length bit-field is inserted after a bit-field, "foo", and the
               alignment of the zero-length bit-field is greater than the member that follows it,  "bar",  "bar"
               is aligned as the type of the zero-length bit-field.

               For example:

                       struct
                        {
                          char foo : 4;
                          short : 0;
                          char bar;
                        } t2;

                       struct
                        {
                          char foo : 4;
                          short : 0;
                          double bar;
                        } t3;

               For "t2", "bar" is placed at offset 2, rather than offset 1.  Accordingly, the size of "t2" is 4.
               For  "t3",  the zero-length bit-field does not affect the alignment of "bar" or, as a result, the
               size of the structure.

               Taking this into account, it is important to note the following:

               1. If a zero-length bit-field follows a normal bit-field, the type of the
                   zero-length bit-field may affect the alignment of the structure as whole. For  example,  "t2"
                   has  a size of 4 bytes, since the zero-length bit-field follows a normal bit-field, and is of
                   type short.

               2. Even if a zero-length bit-field is not followed by a normal bit-field, it may
                   still affect the alignment of the structure:

                           struct
                            {
                              char foo : 6;
                              long : 0;
                            } t4;

                   Here, "t4" takes up 4 bytes.

           3. Zero-length bit-fields following non-bit-field members are ignored:
                       struct
                        {
                          char foo;
                          long : 0;
                          char bar;
                        } t5;

               Here, "t5" takes up 2 bytes.

       -mno-align-stringops
           Do not align the destination of inlined  string  operations.   This  switch  reduces  code  size  and
           improves performance in case the destination is already aligned, but GCC doesn't know about it.

       -minline-all-stringops
           By  default GCC inlines string operations only when the destination is known to be aligned to least a
           4-byte boundary.  This enables more inlining and increases code size, but may improve performance  of
           code  that  depends  on  fast  "memcpy"  and  "memset"  for short lengths.  The option enables inline
           expansion of "strlen" for all pointer alignments.

       -minline-stringops-dynamically
           For string operations of unknown size, use run-time checks with inline code for small  blocks  and  a
           library call for large blocks.

       -mstringop-strategy=alg
           Override  the  internal  decision  heuristic  for the particular algorithm to use for inlining string
           operations.  The allowed values for alg are:

           rep_byte
           rep_4byte
           rep_8byte
               Expand using i386 "rep" prefix of the specified size.

           byte_loop
           loop
           unrolled_loop
               Expand into an inline loop.

           libcall
               Always use a library call.

       -mmemcpy-strategy=strategy
           Override the internal decision heuristic to decide if "__builtin_memcpy" should be inlined  and  what
           inline  algorithm  to use when the expected size of the copy operation is known. strategy is a comma-
           separated list  of  alg:max_size:dest_align  triplets.   alg  is  specified  in  -mstringop-strategy,
           max_size  specifies  the  max  byte  size  with  which inline algorithm alg is allowed.  For the last
           triplet, the max_size must be "-1". The max_size of the triplets in the list  must  be  specified  in
           increasing order.  The minimal byte size for alg is 0 for the first triplet and "max_size + 1" of the
           preceding range.

       -mmemset-strategy=strategy
           The  option  is  similar  to  -mmemcpy-strategy=  except  that  it  is  to control "__builtin_memset"
           expansion.

       -momit-leaf-frame-pointer
           Don't keep the frame pointer in a register for leaf functions.  This avoids the instructions to save,
           set up, and restore frame pointers and makes an extra register  available  in  leaf  functions.   The
           option  -fomit-leaf-frame-pointer  removes  the  frame  pointer  for leaf functions, which might make
           debugging harder.

       -mtls-direct-seg-refs
       -mno-tls-direct-seg-refs
           Controls whether TLS variables may be accessed with offsets from the TLS segment  register  (%gs  for
           32-bit,  %fs  for  64-bit), or whether the thread base pointer must be added.  Whether or not this is
           valid depends on the operating system, and whether it maps the segment to cover the entire TLS area.

           For systems that use the GNU C Library, the default is on.

       -msse2avx
       -mno-sse2avx
           Specify that the assembler should encode SSE instructions with VEX prefix.  The  option  -mavx  turns
           this on by default.

       -mfentry
       -mno-fentry
           If  profiling  is  active  (-pg),  put  the profiling counter call before the prologue.  Note: On x86
           architectures the attribute "ms_hook_prologue" isn't possible at the moment for -mfentry and -pg.

       -mrecord-mcount
       -mno-record-mcount
           If profiling is active (-pg),  generate  a  __mcount_loc  section  that  contains  pointers  to  each
           profiling call. This is useful for automatically patching and out calls.

       -mnop-mcount
       -mno-nop-mcount
           If  profiling  is active (-pg), generate the calls to the profiling functions as NOPs. This is useful
           when they should be  patched  in  later  dynamically.  This  is  likely  only  useful  together  with
           -mrecord-mcount.

       -minstrument-return=type
           Instrument function exit in -pg -mfentry instrumented functions with call to specified function. This
           only  instruments  true  returns ending with ret, but not sibling calls ending with jump. Valid types
           are none to not instrument, call to generate a call to __return__, or nop5 to generate a 5 byte nop.

       -mrecord-return
       -mno-record-return
           Generate a __return_loc section pointing to all return instrumentation code.

       -mfentry-name=name
           Set name of __fentry__ symbol called at function entry for -pg -mfentry functions.

       -mfentry-section=name
           Set name of section to record -mrecord-mcount calls (default __mcount_loc).

       -mskip-rax-setup
       -mno-skip-rax-setup
           When generating code for the x86-64 architecture with SSE extensions disabled,  -mskip-rax-setup  can
           be  used  to  skip  setting  up  RAX  register  when there are no variable arguments passed in vector
           registers.

           Warning: Since RAX register is used to avoid unnecessarily saving  vector  registers  on  stack  when
           passing  variable  arguments,  the  impacts  of  this  option are callees may waste some stack space,
           misbehave or jump to a random location.  GCC 4.4 or newer don't have those issues, regardless the RAX
           register value.

       -m8bit-idiv
       -mno-8bit-idiv
           On some processors, like Intel Atom, 8-bit unsigned integer divide is much faster than  32-bit/64-bit
           integer  divide.   This  option  generates a run-time check.  If both dividend and divisor are within
           range of 0 to 255, 8-bit unsigned integer divide is used instead of 32-bit/64-bit integer divide.

       -mavx256-split-unaligned-load
       -mavx256-split-unaligned-store
           Split 32-byte AVX unaligned load and store.

       -mstack-protector-guard=guard
       -mstack-protector-guard-reg=reg
       -mstack-protector-guard-offset=offset
           Generate stack protection code using canary at guard.  Supported  locations  are  global  for  global
           canary or tls for per-thread canary in the TLS block (the default).  This option has effect only when
           -fstack-protector or -fstack-protector-all is specified.

           With      the      latter      choice     the     options     -mstack-protector-guard-reg=reg     and
           -mstack-protector-guard-offset=offset furthermore specify which segment register (%fs or %gs) to  use
           as  base  register for reading the canary, and from what offset from that base register.  The default
           for those is as specified in the relevant ABI.

       -mgeneral-regs-only
           Generate code that uses only the general-purpose registers.  This prevents the  compiler  from  using
           floating-point, vector, mask and bound registers.

       -mindirect-branch=choice
           Convert  indirect call and jump with choice.  The default is keep, which keeps indirect call and jump
           unmodified.  thunk converts indirect call and jump to call and return thunk.   thunk-inline  converts
           indirect  call  and  jump  to inlined call and return thunk.  thunk-extern converts indirect call and
           jump to external call and return thunk provided in a separate object  file.   You  can  control  this
           behavior for a specific function by using the function attribute "indirect_branch".

           Note     that     -mcmodel=large     is     incompatible     with     -mindirect-branch=thunk     and
           -mindirect-branch=thunk-extern since the thunk function may not be reachable in the large code model.

           Note that -mindirect-branch=thunk-extern is compatible with -fcf-protection=branch since the external
           thunk can be made to enable control-flow check.

       -mfunction-return=choice
           Convert function return with choice.  The default is keep, which keeps  function  return  unmodified.
           thunk  converts  function  return to call and return thunk.  thunk-inline converts function return to
           inlined call and return thunk.  thunk-extern converts function return to  external  call  and  return
           thunk  provided  in a separate object file.  You can control this behavior for a specific function by
           using the function attribute "function_return".

           Note that -mindirect-return=thunk-extern is compatible with -fcf-protection=branch since the external
           thunk can be made to enable control-flow check.

           Note     that     -mcmodel=large     is     incompatible     with     -mfunction-return=thunk     and
           -mfunction-return=thunk-extern since the thunk function may not be reachable in the large code model.

       -mindirect-branch-register
           Force indirect call and jump via register.

       -mharden-sls=choice
           Generate  code  to mitigate against straight line speculation (SLS) with choice.  The default is none
           which disables all SLS hardening.  return enables SLS hardening for function  returns.   indirect-jmp
           enables SLS hardening for indirect jumps.  all enables all SLS hardening.

       -mindirect-branch-cs-prefix
           Add  CS  prefix  to call and jmp to indirect thunk with branch target in r8-r15 registers so that the
           call and jmp instruction length is 6 bytes to allow them to be replaced with lfence; call *%r8-r15 or
           lfence; jmp *%r8-r15 at run-time.

       These -m switches are supported in addition to the above on x86-64 processors in 64-bit environments.

       -m32
       -m64
       -mx32
       -m16
       -miamcu
           Generate code for a 16-bit, 32-bit or 64-bit environment.  The -m32 option sets  "int",  "long",  and
           pointer types to 32 bits, and generates code that runs on any i386 system.

           The -m64 option sets "int" to 32 bits and "long" and pointer types to 64 bits, and generates code for
           the  x86-64  architecture.   For  Darwin  only  the  -m64  option  also  turns  off  the -fno-pic and
           -mdynamic-no-pic options.

           The -mx32 option sets "int", "long", and pointer types to 32 bits, and generates code for the  x86-64
           architecture.

           The  -m16  option is the same as -m32, except for that it outputs the ".code16gcc" assembly directive
           at the beginning of the assembly output so that the binary can run in 16-bit mode.

           The -miamcu option generates code which conforms to Intel MCU psABI.  It requires the -m32 option  to
           be turned on.

       -mno-red-zone
           Do not use a so-called "red zone" for x86-64 code.  The red zone is mandated by the x86-64 ABI; it is
           a  128-byte area beyond the location of the stack pointer that is not modified by signal or interrupt
           handlers and therefore can be used for temporary data without adjusting the stack pointer.  The  flag
           -mno-red-zone disables this red zone.

       -mcmodel=small
           Generate  code for the small code model: the program and its symbols must be linked in the lower 2 GB
           of the address space.  Pointers are 64 bits.  Programs can be statically or dynamically linked.  This
           is the default code model.

       -mcmodel=kernel
           Generate code for the kernel code model.  The kernel runs in the negative 2 GB of the address  space.
           This model has to be used for Linux kernel code.

       -mcmodel=medium
           Generate  code  for  the  medium model: the program is linked in the lower 2 GB of the address space.
           Small symbols are also placed there.  Symbols with sizes larger than -mlarge-data-threshold  are  put
           into  large  data  or  BSS  sections  and  can  be  located above 2GB.  Programs can be statically or
           dynamically linked.

       -mcmodel=large
           Generate code for the large model.  This model makes no assumptions  about  addresses  and  sizes  of
           sections.

       -maddress-mode=long
           Generate  code for long address mode.  This is only supported for 64-bit and x32 environments.  It is
           the default address mode for 64-bit environments.

       -maddress-mode=short
           Generate code for short address mode.  This is only supported for 32-bit and x32 environments.  It is
           the default address mode for 32-bit and x32 environments.

       -mneeded
       -mno-needed
           Emit GNU_PROPERTY_X86_ISA_1_NEEDED GNU property for Linux target to indicate  the  micro-architecture
           ISA level required to execute the binary.

       x86 Windows Options

       These additional options are available for Microsoft Windows targets:

       -mconsole
           This option specifies that a console application is to be generated, by instructing the linker to set
           the  PE header subsystem type required for console applications.  This option is available for Cygwin
           and MinGW targets and is enabled by default on those targets.

       -mdll
           This option is available for Cygwin and MinGW targets.  It specifies  that  a  DLL---a  dynamic  link
           library---is to be generated, enabling the selection of the required runtime startup object and entry
           point.

       -mnop-fun-dllimport
           This  option  is available for Cygwin and MinGW targets.  It specifies that the "dllimport" attribute
           should be ignored.

       -mthread
           This option is available for MinGW targets. It specifies that MinGW-specific thread support is to  be
           used.

       -municode
           This  option  is  available  for MinGW-w64 targets.  It causes the "UNICODE" preprocessor macro to be
           predefined, and chooses Unicode-capable runtime startup code.

       -mwin32
           This option is available for Cygwin and MinGW targets.   It  specifies  that  the  typical  Microsoft
           Windows  predefined  macros  are to be set in the pre-processor, but does not influence the choice of
           runtime library/startup code.

       -mwindows
           This option is available for Cygwin and MinGW targets.  It specifies that a GUI application is to  be
           generated by instructing the linker to set the PE header subsystem type appropriately.

       -fno-set-stack-executable
           This  option is available for MinGW targets. It specifies that the executable flag for the stack used
           by nested functions isn't set. This is necessary for binaries running in  kernel  mode  of  Microsoft
           Windows, as there the User32 API, which is used to set executable privileges, isn't available.

       -fwritable-relocated-rdata
           This option is available for MinGW and Cygwin targets.  It specifies that relocated-data in read-only
           section  is  put  into  the  ".data"  section.  This is a necessary for older runtimes not supporting
           modification of ".rdata" sections for pseudo-relocation.

       -mpe-aligned-commons
           This option is available for Cygwin and MinGW targets.  It specifies that the GNU extension to the PE
           file format that permits the correct alignment of COMMON variables should  be  used  when  generating
           code.   It  is enabled by default if GCC detects that the target assembler found during configuration
           supports the feature.

       See also under x86 Options for standard options.

       Xstormy16 Options

       These options are defined for Xstormy16:

       -msim
           Choose startup files and linker script suitable for the simulator.

       Xtensa Options

       These options are supported for Xtensa targets:

       -mconst16
       -mno-const16
           Enable or disable  use  of  "CONST16"  instructions  for  loading  constant  values.   The  "CONST16"
           instruction  is currently not a standard option from Tensilica.  When enabled, "CONST16" instructions
           are always used in place of the standard "L32R" instructions.  The use of  "CONST16"  is  enabled  by
           default only if the "L32R" instruction is not available.

       -mfused-madd
       -mno-fused-madd
           Enable  or disable use of fused multiply/add and multiply/subtract instructions in the floating-point
           option.  This has no effect if the floating-point  option  is  not  also  enabled.   Disabling  fused
           multiply/add  and multiply/subtract instructions forces the compiler to use separate instructions for
           the multiply and add/subtract operations.  This may be desirable in  some  cases  where  strict  IEEE
           754-compliant  results  are  required:  the fused multiply add/subtract instructions do not round the
           intermediate result, thereby producing results with more bits of precision than specified by the IEEE
           standard.  Disabling fused multiply add/subtract instructions also ensures that the program output is
           not sensitive to the compiler's ability to combine multiply and add/subtract operations.

       -mserialize-volatile
       -mno-serialize-volatile
           When this option is enabled, GCC inserts "MEMW" instructions before "volatile" memory  references  to
           guarantee  sequential consistency.  The default is -mserialize-volatile.  Use -mno-serialize-volatile
           to omit the "MEMW" instructions.

       -mforce-no-pic
           For targets, like GNU/Linux, where all user-mode Xtensa code must be position-independent code (PIC),
           this option disables PIC for compiling kernel code.

       -mtext-section-literals
       -mno-text-section-literals
           These options control the treatment of literal pools.   The  default  is  -mno-text-section-literals,
           which  places  literals in a separate section in the output file.  This allows the literal pool to be
           placed in a data RAM/ROM, and it also allows the linker to combine literal pools from separate object
           files to remove redundant literals and improve code size.  With -mtext-section-literals, the literals
           are interspersed in the text section in order to keep them as close as possible to their  references.
           This  may  be necessary for large assembly files.  Literals for each function are placed right before
           that function.

       -mauto-litpools
       -mno-auto-litpools
           These options control the treatment of literal  pools.   The  default  is  -mno-auto-litpools,  which
           places  literals  in  a  separate  section in the output file unless -mtext-section-literals is used.
           With -mauto-litpools the literals are interspersed in the text section by  the  assembler.   Compiler
           does  not  produce  explicit  ".literal"  directives  and  loads  literals into registers with "MOVI"
           instructions instead of "L32R" to let the assembler do relaxation and place  literals  as  necessary.
           This  option  allows  assembler  to  create  several literal pools per function and assemble very big
           functions, which may not be possible with -mtext-section-literals.

       -mtarget-align
       -mno-target-align
           When this option is enabled, GCC instructs the  assembler  to  automatically  align  instructions  to
           reduce branch penalties at the expense of some code density.  The assembler attempts to widen density
           instructions  to align branch targets and the instructions following call instructions.  If there are
           not enough preceding safe density instructions to align a target,  no  widening  is  performed.   The
           default  is  -mtarget-align.   These options do not affect the treatment of auto-aligned instructions
           like "LOOP", which the assembler always  aligns,  either  by  widening  density  instructions  or  by
           inserting NOP instructions.

       -mlongcalls
       -mno-longcalls
           When  this option is enabled, GCC instructs the assembler to translate direct calls to indirect calls
           unless it can determine that the target of a direct  call  is  in  the  range  allowed  by  the  call
           instruction.   This  translation  typically  occurs  for  calls  to  functions in other source files.
           Specifically, the assembler translates a direct "CALL" instruction  into  an  "L32R"  followed  by  a
           "CALLX"  instruction.   The  default is -mno-longcalls.  This option should be used in programs where
           the call target can potentially be out of range.  This option is implemented in  the  assembler,  not
           the  compiler,  so  the assembly code generated by GCC still shows direct call instructions---look at
           the disassembled object code to see the  actual  instructions.   Note  that  the  assembler  uses  an
           indirect call for every cross-file call, not just those that really are out of range.

       -mabi=name
           Generate code for the specified ABI.  Permissible values are: call0, windowed.  Default ABI is chosen
           by the Xtensa core configuration.

       -mabi=call0
           When  this option is enabled function parameters are passed in registers "a2" through "a7", registers
           "a12" through "a15" are caller-saved, and register "a15" may be used as a frame pointer.   When  this
           version of the ABI is enabled the C preprocessor symbol "__XTENSA_CALL0_ABI__" is defined.

       -mabi=windowed
           When  this  option  is  enabled  function parameters are passed in registers "a10" through "a15", and
           called function rotates register window by 8 registers on entry so that its arguments  are  found  in
           registers  "a2"  through  "a7".   Register  "a7"  may be used as a frame pointer.  Register window is
           rotated 8 registers back upon return.  When this version of the ABI is  enabled  the  C  preprocessor
           symbol "__XTENSA_WINDOWED_ABI__" is defined.

       zSeries Options

       These are listed under

ENVIRONMENT

       This  section describes several environment variables that affect how GCC operates.  Some of them work by
       specifying directories or prefixes to use when searching for various kinds of files.  Some  are  used  to
       specify other aspects of the compilation environment.

       Note  that  you  can  also  specify  places  to  search  using options such as -B, -I and -L.  These take
       precedence over places specified using environment variables, which in turn take  precedence  over  those
       specified by the configuration of GCC.

       LANG
       LC_CTYPE
       LC_MESSAGES
       LC_ALL
           These  environment  variables control the way that GCC uses localization information which allows GCC
           to work with different national  conventions.   GCC  inspects  the  locale  categories  LC_CTYPE  and
           LC_MESSAGES  if  it  has  been  configured to do so.  These locale categories can be set to any value
           supported by your installation.  A typical value is en_GB.UTF-8 for English  in  the  United  Kingdom
           encoded in UTF-8.

           The  LC_CTYPE  environment variable specifies character classification.  GCC uses it to determine the
           character boundaries in a string; this is needed for some multibyte encodings that contain quote  and
           escape characters that are otherwise interpreted as a string end or escape.

           The LC_MESSAGES environment variable specifies the language to use in diagnostic messages.

           If  the  LC_ALL  environment  variable  is  set,  it overrides the value of LC_CTYPE and LC_MESSAGES;
           otherwise, LC_CTYPE and LC_MESSAGES default to the value of the LANG environment variable.   If  none
           of these variables are set, GCC defaults to traditional C English behavior.

       TMPDIR
           If TMPDIR is set, it specifies the directory to use for temporary files.  GCC uses temporary files to
           hold  the  output  of  one  stage  of compilation which is to be used as input to the next stage: for
           example, the output of the preprocessor, which is the input to the compiler proper.

       GCC_COMPARE_DEBUG
           Setting GCC_COMPARE_DEBUG is nearly equivalent to passing -fcompare-debug  to  the  compiler  driver.
           See the documentation of this option for more details.

       GCC_EXEC_PREFIX
           If  GCC_EXEC_PREFIX  is set, it specifies a prefix to use in the names of the subprograms executed by
           the compiler.  No slash is added when this prefix is combined with the name of a subprogram, but  you
           can specify a prefix that ends with a slash if you wish.

           If  GCC_EXEC_PREFIX  is not set, GCC attempts to figure out an appropriate prefix to use based on the
           pathname it is invoked with.

           If GCC cannot find the subprogram using the specified prefix, it tries looking in  the  usual  places
           for the subprogram.

           The  default  value of GCC_EXEC_PREFIX is prefix/lib/gcc/ where prefix is the prefix to the installed
           compiler. In many cases prefix is the value of "prefix" when you ran the configure script.

           Other prefixes specified with -B take precedence over this prefix.

           This prefix is also used for finding files such as crt0.o that are used for linking.

           In addition, the prefix is used in an unusual way in finding the directories  to  search  for  header
           files.  For each of the standard directories whose name normally begins with /usr/local/lib/gcc (more
           precisely,  with the value of GCC_INCLUDE_DIR), GCC tries replacing that beginning with the specified
           prefix to produce an alternate directory name.  Thus, with -Bfoo/, GCC searches foo/bar  just  before
           it  searches  the  standard  directory  /usr/local/lib/bar.   If a standard directory begins with the
           configured prefix then the value of prefix is replaced by GCC_EXEC_PREFIX  when  looking  for  header
           files.

       COMPILER_PATH
           The  value  of COMPILER_PATH is a colon-separated list of directories, much like PATH.  GCC tries the
           directories thus specified when searching for subprograms, if it cannot find  the  subprograms  using
           GCC_EXEC_PREFIX.

       LIBRARY_PATH
           The  value of LIBRARY_PATH is a colon-separated list of directories, much like PATH.  When configured
           as a native compiler, GCC tries the directories thus specified  when  searching  for  special  linker
           files,  if  it cannot find them using GCC_EXEC_PREFIX.  Linking using GCC also uses these directories
           when searching for ordinary libraries for the -l option  (but  directories  specified  with  -L  come
           first).

       LANG
           This  variable is used to pass locale information to the compiler.  One way in which this information
           is used is to determine the character set to be used when character  literals,  string  literals  and
           comments are parsed in C and C++.  When the compiler is configured to allow multibyte characters, the
           following values for LANG are recognized:

           C-JIS
               Recognize JIS characters.

           C-SJIS
               Recognize SJIS characters.

           C-EUCJP
               Recognize EUCJP characters.

           If LANG is not defined, or if it has some other value, then the compiler uses "mblen" and "mbtowc" as
           defined by the default locale to recognize and translate multibyte characters.

       GCC_EXTRA_DIAGNOSTIC_OUTPUT
           If  GCC_EXTRA_DIAGNOSTIC_OUTPUT  is  set to one of the following values, then additional text will be
           emitted  to   stderr   when   fix-it   hints   are   emitted.    -fdiagnostics-parseable-fixits   and
           -fno-diagnostics-parseable-fixits take precedence over this environment variable.

           fixits-v1
               Emit  parseable  fix-it  hints,  equivalent  to  -fdiagnostics-parseable-fixits.   In particular,
               columns are expressed as a count of bytes, starting at byte 1 for the initial column.

           fixits-v2
               As   "fixits-v1",    but    columns    are    expressed    as    display    columns,    as    per
               -fdiagnostics-column-unit=display.

       Some additional environment variables affect the behavior of the preprocessor.

       CPATH
       C_INCLUDE_PATH
       CPLUS_INCLUDE_PATH
       OBJC_INCLUDE_PATH
           Each  variable's  value is a list of directories separated by a special character, much like PATH, in
           which to look for header files.  The special character,  "PATH_SEPARATOR",  is  target-dependent  and
           determined  at GCC build time.  For Microsoft Windows-based targets it is a semicolon, and for almost
           all other targets it is a colon.

           CPATH specifies a list of directories to be searched as if specified with -I,  but  after  any  paths
           given  with  -I  options  on the command line.  This environment variable is used regardless of which
           language is being preprocessed.

           The remaining environment variables apply only when preprocessing the particular language  indicated.
           Each  specifies  a  list  of  directories to be searched as if specified with -isystem, but after any
           paths given with -isystem options on the command line.

           In all these variables, an empty element  instructs  the  compiler  to  search  its  current  working
           directory.   Empty elements can appear at the beginning or end of a path.  For instance, if the value
           of CPATH is ":/special/include", that has the same effect as -I. -I/special/include.

       DEPENDENCIES_OUTPUT
           If this variable is set, its value specifies how to output dependencies for Make based  on  the  non-
           system  header  files  processed  by the compiler.  System header files are ignored in the dependency
           output.

           The value of DEPENDENCIES_OUTPUT can be just a file name, in which case the Make rules are written to
           that file, guessing the target name from the source file name.  Or the value can have the  form  file
           target, in which case the rules are written to file file using target as the target name.

           In other words, this environment variable is equivalent to combining the options -MM and -MF, with an
           optional -MT switch too.

       SUNPRO_DEPENDENCIES
           This variable is the same as DEPENDENCIES_OUTPUT (see above), except that system header files are not
           ignored,  so  it  implies  -M  rather  than  -MM.   However, the dependence on the main input file is
           omitted.

       SOURCE_DATE_EPOCH
           If this variable is set, its value specifies a UNIX timestamp  to  be  used  in  replacement  of  the
           current date and time in the "__DATE__" and "__TIME__" macros, so that the embedded timestamps become
           reproducible.

           The  value of SOURCE_DATE_EPOCH must be a UNIX timestamp, defined as the number of seconds (excluding
           leap seconds) since 01 Jan 1970 00:00:00 represented in ASCII; identical to the output of "date  +%s"
           on GNU/Linux and other systems that support the %s extension in the "date" command.

           The value should be a known timestamp such as the last modification time of the source or package and
           it should be set by the build process.

BUGS

       For instructions on reporting bugs, see <file:///usr/share/doc/gcc-11/README.Bugs>.

FOOTNOTES

       1.  On  some  systems,  gcc  -shared needs to build supplementary stub code for constructors to work.  On
           multi-libbed systems, gcc -shared must select the correct support libraries to link against.  Failing
           to supply the correct flags may lead to subtle defects.  Supplying them in cases where they  are  not
           necessary is innocuous.

SEE ALSO

       gpl(7),  gfdl(7),  fsf-funding(7), cpp(1), gcov(1), as(1), ld(1), gdb(1), dbx(1) and the Info entries for
       gcc, cpp, as, ld, binutils and gdb.

AUTHOR

       See the Info entry for gcc, or <http://gcc.gnu.org/onlinedocs/gcc/Contributors.html>, for contributors to
       GCC.

COPYRIGHT

       Copyright (c) 1988-2021 Free Software Foundation, Inc.

       Permission is granted to copy, distribute and/or modify this document under the terms  of  the  GNU  Free
       Documentation  License,  Version 1.3 or any later version published by the Free Software Foundation; with
       the Invariant Sections being "GNU General Public License" and "Funding Free  Software",  the  Front-Cover
       texts  being (a) (see below), and with the Back-Cover Texts being (b) (see below).  A copy of the license
       is included in the gfdl(7) man page.

       (a) The FSF's Front-Cover Text is:

            A GNU Manual

       (b) The FSF's Back-Cover Text is:

            You have freedom to copy and modify this GNU Manual, like GNU
            software.  Copies published by the Free Software Foundation raise
            funds for GNU development.

gcc-11                                             2023-05-28                                             GCC(1)