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gcc(1)                                GNU                               gcc(1)




NAME

       gcc - GNU project C and C++ compiler


SYNOPSIS

       gcc [-c|-S|-E] [-std=standard]
           [-g] [-pg] [-Olevel]
           [-Wwarn...] [-pedantic]
           [-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.

       In Apple's version of GCC, both cc and gcc are actually symbolic links
       to the llvm-gcc compiler.  Similarly, c++ and g++ are links to
       llvm-g++.

       Note that Apple's GCC includes a number of extensions to standard GCC
       (flagged below with "APPLE ONLY"), and that not all generic GCC options
       are available or supported on Darwin / Mac OS X.  In particular, Apple
       does not currently support the compilation of Fortran, Ada, or Java,
       although there are third parties who have made these work.


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

       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.

       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 would be
       -fno-foo.  This manual documents only one of these two forms, whichever
       one is not the default.


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  -combine  -no-canonical-prefixes -pipe
           -pass-exit-codes -ObjC (APPLE ONLY) -ObjC++ (APPLE ONLY) -arch arch
           (APPLE ONLY) -Xarch_arch option (APPLE ONLY) -fsave-repository=file
           -x language  -v  -###  --help  --target-help  --version @file

       C Language Options
           -ansi  -std=standard  -fgnu89-inline -aux-info filename -faltivec
           (APPLE ONLY) -fasm-blocks (APPLE ONLY) -fno-asm -fno-blocks
           -fno-builtin  -fno-builtin-function -fhosted  -ffreestanding
           -fopenmp -fms-extensions -trigraphs  -no-integrated-cpp
           -traditional  -traditional-cpp -fallow-single-precision
           -fcond-mismatch -flax-vector-conversions -fconstant-cfstrings
           (APPLE ONLY) -fnon-lvalue-assign (APPLE ONLY) -fno-nested-functions
           -fpch-preprocess (APPLE ONLY) -fsigned-bitfields  -fsigned-char
           -Wno-#warnings (APPLE ONLY) -Wextra-tokens (APPLE ONLY)
           -Wnewline-eof (APPLE ONLY) -Wno-altivec-long-deprecated (APPLE
           ONLY) -fglobal-alloc-prefer-bytes (APPLE ONLY)
           -fno-global-alloc-prefer-bytes (APPLE ONLY) -funsigned-bitfields
           -funsigned-char  -fwritable-strings

       C++ Language Options
           -fabi-version=n  -fno-access-control  -fcheck-new -fconserve-space
           -ffriend-injection -fno-elide-constructors -fno-enforce-eh-specs
           -ffor-scope  -fno-for-scope  -fno-gnu-keywords
           -fno-implicit-templates -fno-implicit-inline-templates
           -fno-implement-inlines  -fms-extensions -fno-nonansi-builtins
           -fno-operator-names -fno-optional-diags  -fpermissive -frepo
           -fno-rtti  -fstats  -ftemplate-depth-n -fno-threadsafe-statics
           -fuse-cxa-atexit  -fno-weak  -nostdinc++ -fno-default-inline
           -fvisibility-inlines-hidden -fvisibility-ms-compat -Wabi
           -Wctor-dtor-privacy -Wnon-virtual-dtor  -Wreorder -Weffc++
           -Wno-deprecated  -Wstrict-null-sentinel -Wno-non-template-friend
           -Wold-style-cast -Woverloaded-virtual  -Wno-pmf-conversions
           -Wsign-promo

       Objective-C and Objective-C++ Language Options
           -fconstant-string-class=class-name -fgnu-runtime  -fnext-runtime
           -fno-nil-receivers -fobjc-call-cxx-cdtors -fobjc-direct-dispatch
           -fobjc-sjlj-exceptions -fobjc-gc -freplace-objc-classes -fzero-link
           -gen-decls -Wassign-intercept -Wno-protocol  -Wselector
           -Wno-property-assign-default -Wstrict-selector-match
           -Wundeclared-selector

       Language Independent Options
           -fmessage-length=n -fdiagnostics-show-location=[once|every-line]
           -fdiagnostics-show-option

       Warning Options
           -fsyntax-only  -pedantic  -pedantic-errors -w  -Wextra  -Wall
           -Waddress  -Waggregate-return -Wno-attributes -Wc++-compat
           -Wcast-align  -Wcast-qual  -Wchar-subscripts  -Wcomment
           -Wconversion  -Wno-deprecated-declarations -Wdisabled-optimization
           -Wno-div-by-zero  -Wno-endif-labels -Werror  -Werror=*
           -Werror-implicit-function-declaration -Wfatal-errors  -Wfloat-equal
           -Wno-format  -Wformat=2 -Wno-format-extra-args -Wformat-nonliteral
           -Wno-format-security  -Wformat-y2k -Wglobal-constructors -Wimplicit
           -Wimplicit-function-declaration  -Wimplicit-int -Wimport
           -Wno-import  -Winit-self  -Winline -Wno-int-to-pointer-cast
           -Wno-invalid-offsetof  -Winvalid-pch -Wlarger-than-len
           -Wunsafe-loop-optimizations  -Wlong-long -Wmain  -Wmissing-braces
           -Wmissing-field-initializers -Wmissing-format-attribute
           -Wmissing-include-dirs -Wmissing-noreturn -Wmissing-prototypes
           -Wmost (APPLE ONLY) -Wno-multichar  -Wnonnull  -Wno-overflow
           -Woverlength-strings  -Wpacked  -Wpadded -Wparentheses
           -Wpointer-arith  -Wno-pointer-to-int-cast -Wredundant-decls
           -Wreturn-type  -Wsequence-point  -Wshadow -Wsign-compare
           -Wstack-protector -Wstrict-aliasing -Wstrict-aliasing=2
           -Wstrict-overflow -Wstrict-overflow=n -Wswitch  -Wswitch-default
           -Wswitch-enum -Wsystem-headers  -Wtrigraphs  -Wundef
           -Wuninitialized -Wunknown-pragmas  -Wno-pragmas -Wunreachable-code
           -Wunused  -Wunused-function  -Wunused-label  -Wunused-parameter
           -Wunused-value  -Wunused-variable  -Wvariadic-macros
           -Wvolatile-register-var  -Wwrite-strings

       C-only Warning Options
           -Wbad-function-cast  -Wmissing-declarations -Wnested-externs
           -Wold-style-definition -Wstrict-prototypes  -Wtraditional
           -Wdeclaration-after-statement -Wno-discard-qual -Wno-pointer-sign

       Debugging Options
           -dletters  -dumpspecs  -dumpmachine  -dumpversion -fdump-noaddr
           -fdump-unnumbered  -fdump-translation-unit[-n]
           -fdump-class-hierarchy[-n] -fdump-ipa-all -fdump-ipa-cgraph
           -fdump-tree-all -fdump-tree-original[-n] -fdump-tree-optimized[-n]
           -fdump-tree-inlined[-n] -fdump-tree-cfg -fdump-tree-vcg
           -fdump-tree-alias -fdump-tree-ch -fdump-tree-ssa[-n]
           -fdump-tree-pre[-n] -fdump-tree-ccp[-n] -fdump-tree-dce[-n]
           -fdump-tree-gimple[-raw] -fdump-tree-mudflap[-n]
           -fdump-tree-dom[-n] -fdump-tree-dse[-n] -fdump-tree-phiopt[-n]
           -fdump-tree-forwprop[-n] -fdump-tree-copyrename[-n] -fdump-tree-nrv
           -fdump-tree-vect -fdump-tree-sink -fdump-tree-sra[-n]
           -fdump-tree-salias -fdump-tree-fre[-n] -fdump-tree-vrp[-n]
           -ftree-vectorizer-verbose=n -fdump-tree-storeccp[-n]
           -flimit-debug-info -feliminate-dwarf2-dups
           -feliminate-unused-debug-types -feliminate-unused-debug-symbols
           -femit-class-debug-always -fmem-report -fopt-diary -fprofile-arcs
           -frandom-seed=string -fsched-verbose=n -ftest-coverage
           -ftime-report -fvar-tracking -g  -glevel  -gcoff -gdwarf-2 -ggdb
           -gstabs  -gstabs+  -gvms  -gxcoff  -gxcoff+ -p  -pg
           -print-file-name=library  -print-libgcc-file-name
           -print-multi-directory  -print-multi-lib -print-prog-name=program
           -print-search-dirs  -Q -mllvm string -save-temps  -time

       Optimization Options
           -falign-functions=n  -falign-jumps=n -falign-labels=n
           -falign-loops=n -falign-loops-max-skip=n -falign-jumps-max-skip=n
           -fbounds-check -fmudflap -fmudflapth -fmudflapir
           -fbranch-probabilities -fprofile-values -fvpt
           -fbranch-target-load-optimize -fbranch-target-load-optimize2
           -fbtr-bb-exclusive -fcaller-saves  -fcprop-registers
           -fcreate-profile -fcse-follow-jumps -fcse-skip-blocks
           -fcx-limited-range  -fdata-sections -fdelayed-branch
           -fdelete-null-pointer-checks -fearly-inlining
           -fexpensive-optimizations  -ffast-math  -ffloat-store -fforce-addr
           -ffunction-sections -fgcse  -fgcse-lm  -fgcse-sm  -fgcse-las
           -fgcse-after-reload -fcrossjumping  -fif-conversion
           -fif-conversion2 -finline-functions  -finline-functions-called-once
           -finline-limit=n  -fkeep-inline-functions -fkeep-static-consts
           -flocal-alloc (APPLE ONLY) -fmerge-constants  -fmerge-all-constants
           -fmodulo-sched -fno-branch-count-reg -fno-default-inline
           -fno-defer-pop -fmove-loop-invariants -fno-function-cse
           -fno-guess-branch-probability -fno-inline  -fno-math-errno
           -fno-peephole  -fno-peephole2 -funsafe-math-optimizations
           -funsafe-loop-optimizations  -ffinite-math-only
           -fno-toplevel-reorder -fno-trapping-math
           -fno-zero-initialized-in-bss -mstackrealign -fomit-frame-pointer
           -foptimize-register-move -foptimize-sibling-calls
           -fprefetch-loop-arrays -fprofile-generate -fprofile-use -fregmove
           -frename-registers -freorder-blocks  -freorder-blocks-and-partition
           -freorder-functions -frerun-cse-after-loop -frounding-math
           -frtl-abstract-sequences -fschedule-insns  -fschedule-insns2
           -fno-sched-interblock  -fno-sched-spec  -fsched-spec-load
           -fsched-spec-load-dangerous -fsched-stalled-insns=n
           -fsched-stalled-insns-dep=n -fsched2-use-superblocks
           -fsched2-use-traces -fsee -freschedule-modulo-scheduled-loops
           -fsection-anchors  -fsignaling-nans  -fsingle-precision-constant
           -fstack-protector  -fstack-protector-all -fstrict-aliasing
           -fstrict-overflow  -ftracer  -fthread-jumps -funroll-all-loops
           -funroll-loops  -fpeel-loops -fsplit-ivs-in-unroller
           -funswitch-loops -fvariable-expansion-in-unroller -ftree-pre
           -ftree-ccp  -ftree-dce -ftree-loop-optimize -ftree-loop-linear
           -ftree-loop-im -ftree-loop-ivcanon -fivopts -ftree-dominator-opts
           -ftree-dse -ftree-copyrename -ftree-sink -ftree-ch -ftree-sra
           -ftree-ter -ftree-lrs -ftree-fre -ftree-vectorize
           -ftree-vect-loop-version -ftree-salias -fuse-profile -fipa-pta
           -fweb -ftree-copy-prop -ftree-store-ccp -ftree-store-copy-prop
           -fwhole-program --param name=value (APPLE ONLY) -O  -O0  -O1  -O2
           -O3 (APPLE ONLY) -Os -Oz (APPLE ONLY) -fast (APPLE ONLY)

       Preprocessor Options
           -Aquestion=answer -A-question[=answer] -C  -dD  -dI  -dM  -dN
           -Dmacro[=defn]  -E  -H -idirafter dir -include file  -imacros file
           -iprefix file  -iwithprefix dir -iwithprefixbefore dir  -isystem
           dir -imultilib dir -isysroot dir -iwithsysroot (APPLE ONLY) dir -M
           -MM  -MF  -MG  -MP  -MQ  -MT  -nostdinc -P  -fworking-directory
           -remap -trigraphs  -undef  -Umacro  -Wp,option -Xpreprocessor
           option

       Assembler Option
           -Wa,option  -Xassembler option

       Linker Options
           object-file-name  -llibrary -nostartfiles  -nodefaultlibs
           -nostdlib -pie -rdynamic -s  -static  -static-libgcc  -shared
           -shared-libgcc  -symbolic -Wl,option  -Xlinker option -u symbol

       Directory Options
           -Bprefix  -Idir  -iquotedir  -Ldir -specs=file  -I- --sysroot=dir

       Target Options
           -V version  -b machine

       Machine Dependent Options
           ARM Options -mapcs-frame  -mno-apcs-frame -mabi=name
           -mapcs-stack-check  -mno-apcs-stack-check -mapcs-float
           -mno-apcs-float -mapcs-reentrant  -mno-apcs-reentrant
           -msched-prolog  -mno-sched-prolog -mlittle-endian  -mbig-endian
           -mwords-little-endian -mfloat-abi=name  -msoft-float  -mhard-float
           -mfpe -mthumb-interwork  -mno-thumb-interwork -mcpu=name
           -march=name  -mfpu=name -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
           -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns
           -mpoke-function-name -mthumb  -marm -mtpcs-frame  -mtpcs-leaf-frame
           -mcaller-super-interworking  -mcallee-super-interworking -mtp=name
           -mms-bitfields -mno-ms-bitfields

           CRX Options -mmac -mpush-args

           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  -force_load
           -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 -miphoneos-version-min=version
           -mpascal-strings (APPLE ONLY) -mkernel -mone-byte-bool -Xarch_arch

           i386 and x86-64 Options -mtune=cpu-type  -march=cpu-type
           -mfpmath=unit -masm=dialect  -mno-fancy-math-387 -mno-fp-ret-in-387
           -msoft-float  -msvr3-shlib -mno-wide-multiply  -mrtd
           -malign-double -mpreferred-stack-boundary=num -mmmx  -msse  -msse2
           -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -msse4a -mthreads
           -mno-align-stringops  -minline-all-stringops -mpush-args
           -maccumulate-outgoing-args  -m128bit-long-double
           -m96bit-long-double  -mregparm=num  -msseregparm -mstackrealign
           -momit-leaf-frame-pointer  -mno-red-zone -mno-tls-direct-seg-refs
           -mcmodel=code-model -m32  -m64 -mlarge-data-threshold=num
           -mms-bitfields -mno-ms-bitfields

           PowerPC Options See RS/6000 and PowerPC Options.

           RS/6000 and PowerPC Options -mcpu=cpu-type -mtune=cpu-type -mpower
           -mno-power  -mpower2  -mno-power2 -mpowerpc  -mpowerpc64
           -mno-powerpc -maltivec  -mno-altivec -mpim-altivec -mno-pim-altivec
           -mpowerpc-gpopt  -mno-powerpc-gpopt -mpowerpc-gfxopt
           -mno-powerpc-gfxopt -mmfcrf  -mno-mfcrf  -mpopcntb  -mno-popcntb
           -mfprnd  -mno-fprnd -mnew-mnemonics  -mold-mnemonics -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 -mstring
           -mno-string  -mupdate  -mno-update -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  -maltivec  -mswdiv
           -mprioritize-restricted-insns=priority
           -msched-costly-dep=dependence_type -minsert-sched-nops=scheme
           -mcall-sysv  -mcall-netbsd -maix-struct-return
           -msvr4-struct-return -mabi=abi-type -msecure-plt -mbss-plt -misel
           -mno-isel -misel=yes  -misel=no -mspe -mno-spe -mspe=yes  -mspe=no
           -mvrsave -mno-vrsave -mmulhw -mno-mulhw -mdlmzb -mno-dlmzb
           -mfloat-gprs=yes  -mfloat-gprs=no -mfloat-gprs=single
           -mfloat-gprs=double -mprototype  -mno-prototype -msim  -mmvme
           -mads  -myellowknife  -memb  -msdata -msdata=opt  -mvxworks
           -mwindiss  -G num  -pthread -mms-bitfields -mno-ms-bitfields

       Code Generation Options
           -fcall-saved-reg  -fcall-used-reg -ffixed-reg  -fexceptions
           -fnon-call-exceptions  -funwind-tables -fasynchronous-unwind-tables
           -finhibit-size-directive  -finstrument-functions -fno-common
           -fno-ident -fpcc-struct-return  -fpic  -fPIC -fpie -fPIE
           -fno-jump-tables -freg-struct-return  -fshort-enums -fshort-double
           -fshort-wchar -fverbose-asm  -fpack-struct[=n]  -fstack-check
           -fstack-limit-register=reg  -fstack-limit-symbol=sym
           -fargument-alias  -fargument-noalias -fargument-noalias-global
           -fargument-noalias-anything -fleading-underscore  -ftls-model=model
           -fwrapv  -fbounds-check -fvisibility

   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 which must be preprocessed.

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

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

       file.h
           C, C++, Objective-C or Objective-C++ header file to be turned into
           a precompiled header.

       file.cc
       file.cp
       file.cxx
       file.cpp
       file.CPP
       file.c++
       file.C
           C++ source code which 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.hh
       file.H
           C++ header file to be turned into a precompiled header.

       file.f
       file.for
       file.FOR
           Fixed form Fortran source code which should not be preprocessed.

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

       file.f90
       file.f95
           Free form Fortran source code which should not be preprocessed.

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

       file.ads
           Ada source code file which 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.  Apple's version of GCC runs the preprocessor on
           these files as well as those ending in .S.

       file.S
           Assembler code which 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  c-cpp-output
                   c++  c++-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
                   f95  f95-cpp-input
                   java
                   treelang

       -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).

       -ObjC
       -ObjC++
           These are similar in effect to -x objective-c and -x objective-c++,
           but affect only the choice of compiler for files already identified
           as source files.  (APPLE ONLY)

       -arch arch
           Compile for the specified target architecture arch.  The allowable
           values are i386, x86_64, ppc and ppc64.  Multiple options work, and
           direct the compiler to produce "universal" binaries including
           object code for each architecture specified with -arch.  This
           option only works if assembler and libraries are available for each
           architecture specified.  (APPLE ONLY)

       -Xarch_arch option
           Apply option to the command line for architecture arch.  This is
           useful for specifying an option that should only apply to one
           architecture when building a "universal" binary.  (APPLE ONLY)

       -fsave-repository=file
           Save debug info in separate object file.  This is available only
           while building PCH in -gfull mode.

       -pass-exit-codes
           Normally the gcc program will exit 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 will instead return with
           numerically highest error produced by any phase that returned an
           error indication.  The C, C++, and Fortran frontends return 4, if
           an internal compiler error is encountered.

       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 which don't require preprocessing are ignored.

       -o file
           Place output in file file.  This applies regardless 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.

       -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 all command
           arguments are quoted.  This is useful for shell scripts to capture
           the driver-generated command lines.

       -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.

       -combine
           If you are compiling multiple source files, this option tells the
           driver to pass all the source files to the compiler at once (for
           those languages for which the compiler can handle this).  This will
           allow intermodule analysis (IMA) to be performed by the compiler.
           Currently the only language for which this is supported is C.  If
           you pass source files for multiple languages to the driver, using
           this option, the driver will invoke the compiler(s) that support
           IMA once each, passing each compiler all the source files
           appropriate for it.  For those languages that do not support IMA
           this option will be ignored, and the compiler will be invoked once
           for each source file in that language.  If you use this option in
           conjunction with -save-temps, the compiler will generate multiple
           pre-processed files (one for each source file), but only one
           (combined) .o or .s file.

       --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 will also be passed on to the various processes invoked by
           gcc, so that they can display the command line options they accept.
           If the -Wextra option is also specified then command line options
           which have no documentation associated with them will also be
           displayed.

       --target-help
           Print (on the standard output) a description of target specific
           command line options for each tool.

       -no-canonical-prefixes
           Do not expand any symbolic links, resolve references to /../ or
           /./, or make the path absolute when generating a relative prefix.

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

       @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 or .H; 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 treats .c, .h and .i files as C++ source files
       instead of C source files unless -x is used, and automatically
       specifies linking against the C++ library.  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, support all ISO C90 programs.  In C++ mode, remove GNU
           extensions that conflict with ISO C++.

           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, -pedantic 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 which would normally be built in but do not have
           semantics defined by ISO C (such as "alloca" and "ffs") are not
           built-in functions with -ansi is used.

       -std=
           Determine the language standard.  This option is currently only
           supported when compiling C or C++.  A value for this option must be
           provided; possible values are

           c89
           iso9899:1990
               ISO C90 (same as -ansi).

           iso9899:199409
               ISO C90 as modified in amendment 1.

           c99
           c9x
           iso9899:1999
           iso9899:199x
               ISO C99.  Note that this standard is not yet fully supported;
               see <http://gcc.gnu.org/gcc-4.2/c99status.html> for more
               information.  The names c9x and iso9899:199x are deprecated.

           gnu89
               Default, ISO C90 plus GNU extensions (including some C99
               features).

           gnu99
           gnu9x
               ISO C99 plus GNU extensions.  When ISO C99 is fully implemented
               in GCC, this will become the default.  The name gnu9x is
               deprecated.

           c++98
               The 1998 ISO C++ standard plus amendments.

           gnu++98
               The same as -std=c++98 plus GNU extensions.  This is the
               default for C++ code.

           Even when this option is not specified, you can still use some of
           the features of newer standards in so far as they do not conflict
           with previous C standards.  For example, you may use "__restrict__"
           even when -std=c99 is not specified.

           The -std options specifying some version of ISO C have the same
           effects as -ansi, except that features that were not in ISO C90 but
           are in the specified version (for example, // comments and the
           "inline" keyword in ISO C99) are not disabled.

       -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.

           This option is accepted by GCC versions 4.1.3 and up.  In GCC
           versions /* APPLE LOCAL extern inline */ prior to 4.3 (4.2 for
           Apple's gcc), C99 inline semantics are not supported, and thus this
           option is effectively assumed to be present regardless of whether
           or not it is specified; the only effect of specifying it explicitly
           is to disable warnings about using inline functions in C99 mode.
           Likewise, the option -fno-gnu89-inline is not supported in versions
           of /* APPLE LOCAL extern inline */ GCC before 4.3 (4.2 for Apple's
           gcc).  It is supported only in C99 or gnu99 mode, not in C89 or
           gnu89 mode.

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

       -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.

       -faltivec
           This flag is provided for compatibility with Metrowerks CodeWarrior
           and MrC compilers as well as previous Apple versions of GCC.  It
           causes the -mpim-altivec option to be turned on.

       -fasm-blocks
           Enable the use of blocks and entire functions of assembly code
           within a C or C++ file.  The syntax follows that used in
           CodeWarrior.  This option is not supported for ARM targets.  (APPLE
           ONLY)

       -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-blocks
           Disable the use of blocks.  In -std=c99 mode, blocks are turned off
           by default.  -fblocks can be used to re-enable the feature, if off.
           Runtime support for blocks first appeared in Mac OS X 10.6.  When
           targeting 10.6 (see -mmacosx-version-min) and later, the extension
           is on by default.

       -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 that 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 this 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))

       -fhosted
           Assert that compilation takes place in 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 takes place in 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.

       -fopenmp
           "!$omp" in Fortran.  When -fopenmp is specified, the compiler
           generates parallel code according to the OpenMP Application Program
           Interface v2.5 <http://www.openmp.org/>.

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

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

       -trigraphs
           Support ISO C trigraphs.  The -ansi option (and -std options for
           strict ISO C conformance) implies -trigraphs.

       -no-integrated-cpp
           Performs a compilation in two passes: preprocessing and compiling.
           This option allows a user supplied "cc1", "cc1plus", or "cc1obj"
           via the -B option.  The user supplied compilation step can then add
           in an additional preprocessing step after normal preprocessing but
           before compiling.  The default is to use the integrated cpp
           (internal cpp)

           The semantics of this option will change if "cc1", "cc1plus", and
           "cc1obj" are merged.

       -traditional
       -traditional-cpp
           Formerly, these options caused GCC to attempt to emulate a pre-
           standard C compiler.  They are now only supported with the -E
           switch.  The preprocessor continues to support a pre-standard mode.
           See the GNU CPP manual for details.

       -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++.

       -fno-nested-functions
           Disable nested functions.  This option is not supported for C++ or
           Objective-C++.  On Darwin, nested functions are disabled by
           default.

       -fpch-preprocess
           Enable PCH processing even when -E or -save-temps is used.

       -fnon-lvalue-assign
           C and C++ forbid the use of casts and conditional expressions as
           lvalues, e.g.:

                   float *p, q, r;
                   ((int *)p)++;
                   (cond ? q : r) = 3.0;

           As a transitional measure, the Apple version of GCC 4.0 allows
           casts and conditional expressions to be used as lvalues in certain
           situations.  This is accomplished via the -fnon-lvalue-assign
           switch, which is on by default.  Whenever an lvalue cast or an
           lvalue conditional expression is encountered, the compiler will
           issue a deprecation warning and then rewrite the expression as
           follows:

                   (type)expr                ---becomes--->      *(type *)&expr
                   cond ? expr1 : expr2      ---becomes--->      *(cond ? &expr1 : &expr2)

           To disallow lvalue casts and lvalue conditional expressions
           altogether, specify -fno-non-lvalue-assign; lvalue casts and lvalue
           conditional expressions will be disallowed in future versions of
           Apple's GCC.

       -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.

       -fconstant-cfstrings
           Enable the automatic creation of a CoreFoundation-type constant
           string whenever a special builtin
           "__builtin__CFStringMakeConstantString" is called on a literal
           string.  (APPLE ONLY)

       -Wnonportable-cfstrings
           Warn if constant CFString objects contain non-portable characters
           (default behavior)

       -fglobal-alloc-prefer-bytes
       -fno-global-alloc-prefer-bytes
           For the x86_32 architecture, prefer byte or short values to word
           values during global register allocation.  Some of the registers on
           this target can't be used with values smaller than a 32-bit word;
           allocating these values earlier increases the chance they will get
           a byte-capable (or short-capable) register.  Ignored for other
           targets.  Defaults on with global register allocation ("-Os",
           "-O2", or "-O3").  (APPLE ONLY)

       -fwritable-strings
           Store string constants in the writable data segment and don't
           uniquize them.  This is for compatibility with old programs which
           assume they can write into string constants.

           Writing into string constants is a very bad idea; "constants"
           should be constant.

           This option is deprecated.

   Options Controlling C++ Dialect
       This section describes the command-line options that are only
       meaningful for C++ programs; but 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 -frepo -O -c firstClass.C

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

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

       -fabi-version=n
           Use version n of the C++ ABI.  Version 2 is the version of the C++
           ABI that first appeared in G++ 3.4.  Version 1 is the version of
           the C++ ABI that first appeared in G++ 3.2.  Version 0 will always
           be the version that conforms most closely to the C++ ABI
           specification.  Therefore, the ABI obtained using version 0 will
           change as ABI bugs are fixed.

           The default is version 2.

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

       -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" will only return 0 if it is declared throw(), in
           which case the compiler will always check 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).

       -fconserve-space
           Put uninitialized or runtime-initialized global variables into the
           common segment, as C does.  This saves space in the executable at
           the cost of not diagnosing duplicate definitions.  If you compile
           with this flag and your program mysteriously crashes after "main()"
           has completed, you may have an object that is being destroyed twice
           because two definitions were merged.

           This option is no longer useful on most targets, now that support
           has been added for putting variables into BSS without making them
           common.

       -ffriend-injection
           Inject friend functions into the enclosing namespace, so that they
           are visible outside the scope of the class in which they are
           declared.  Friend functions were documented to work this way in the
           old Annotated C++ Reference Manual, and versions of G++ before 4.1
           always worked that way.  However, in ISO C++ a friend function
           which is not declared in an enclosing scope can only be found using
           argument dependent lookup.  This option causes friends to be
           injected as they were in earlier releases.

           This option is for compatibility, and may be removed in a future
           release of G++.

       -fno-elide-constructors
           The C++ standard allows an implementation to omit creating a
           temporary which 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.

       -fno-enforce-eh-specs
           Don't generate code to check for violation of exception
           specifications at runtime.  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 will still optimize based on the specifications, so
           throwing an unexpected exception will result in undefined behavior.

       -ffor-scope
       -fno-for-scope
           If -ffor-scope is specified, the scope of variables declared in a
           for-init-statement is limited to the for loop itself, as specified
           by the C++ standard.  If -fno-for-scope is specified, the scope of
           variables declared in a for-init-statement extends to the end of
           the enclosing scope, as was the case in old versions of G++, and
           other (traditional) implementations of C++.

           The default if neither flag is given to follow the standard, but to
           allow and give a warning for old-style code that would otherwise be
           invalid, or have different behavior.

       -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.  -ansi implies -fno-gnu-keywords.

       -fno-implicit-templates
           Never emit code for non-inline templates which are instantiated
           implicitly (i.e. by use); only emit code for explicit
           instantiations.

       -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 will need the same set of
           explicit instantiations.

       -fno-implement-inlines
           To save space, do not emit out-of-line copies of inline functions
           errors if these functions are not inlined everywhere they are
           called.

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

       -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.

       -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 will allow some nonconforming
           code to compile.

       -frepo
           Enable automatic template instantiation at link time.  This option
           also implies -fno-implicit-templates.

       -fno-rtti
           Disable generation of information about every class with virtual
           functions for use by the C++ runtime 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 it will generate
           it as needed. The dynamic_cast operator can still be used for casts
           that do not require runtime type information, i.e. casts to "void
           *" or to unambiguous base classes.

       -fstats
           Emit statistics about front-end processing at the end of the
           compilation.  This information is generally only useful to the G++
           development team.

       -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.

       -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 will only work if your C library supports
           "__cxa_atexit".

       -fno-use-cxa-get-exception-ptr
           Don't use the "__cxa_get_exception_ptr" runtime routine.  This will
           cause "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 methods where the addresses of the two functions
           were 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 behaviour 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 will have 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 which are defined in
           more than one different shared object: those declarations are
           permitted if they would have been permitted when this option was
           not used.

           This option is discouraged, rather, it is preferable for types to
           be explicitly exported as desired on a per-class basis.
           Unfortunately because Visual Studio can't compare two different
           hidden types as unequal for the purposes of type_info and exception
           handling, users are able to write code that relies upon this
           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 will be different, so changing one will
           not change the other; and that pointers to function members defined
           in different shared objects will 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++ will use weak symbols if they are
           available.  This option exists only for testing, and should not be
           used by end-users; it will result in inferior code and has no
           benefits.  This option may be removed in a future release of G++.

       -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.)

       In addition, these optimization, warning, and code generation options
       have meanings only for C++ programs:

       -fno-default-inline
           Do not assume inline for functions defined inside a class scope.
             Note that these functions will have linkage like inline
           functions; they just won't be inlined by default.

       -Wabi (C++ only)
           Warn when G++ generates code that is probably not compatible with
           the vendor-neutral C++ ABI.  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 will be 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.

           The known incompatibilities at this point include:

           o   Incorrect handling of tail-padding for bit-fields.  G++ may
               attempt to pack data into the same byte as a base class.  For
               example:

                       struct A { virtual void f(); int f1 : 1; };
                       struct B : public A { int f2 : 1; };

               In this case, G++ will place "B::f2" into the same byte
               as"A::f1"; other compilers will not.  You can avoid this
               problem by explicitly padding "A" so that its size is a
               multiple of the byte size on your platform; that will cause G++
               and other compilers to layout "B" identically.

           o   Incorrect handling of tail-padding for virtual bases.  G++ does
               not use tail padding when laying out virtual bases.  For
               example:

                       struct A { virtual void f(); char c1; };
                       struct B { B(); char c2; };
                       struct C : public A, public virtual B {};

               In this case, G++ will not place "B" into the tail-padding for
               "A"; other compilers will.  You can avoid this problem by
               explicitly padding "A" so that its size is a multiple of its
               alignment (ignoring virtual base classes); that will cause G++
               and other compilers to layout "C" identically.

           o   Incorrect handling of bit-fields with declared widths greater
               than that of their underlying types, when the bit-fields appear
               in a union.  For example:

                       union U { int i : 4096; };

               Assuming that an "int" does not have 4096 bits, G++ will make
               the union too small by the number of bits in an "int".

           o   Empty classes can be placed at incorrect offsets.  For example:

                       struct A {};

                       struct B {
                         A a;
                         virtual void f ();
                       };

                       struct C : public B, public A {};

               G++ will place the "A" base class of "C" at a nonzero offset;
               it should be placed at offset zero.  G++ mistakenly believes
               that the "A" data member of "B" is already at offset zero.

           o   Names of template functions whose types involve "typename" or
               template template parameters can be mangled incorrectly.

                       template <typename Q>
                       void f(typename Q::X) {}

                       template <template <typename> class Q>
                       void f(typename Q<int>::X) {}

               Instantiations of these templates may be mangled incorrectly.

       -Wctor-dtor-privacy (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.

       -Wnon-virtual-dtor (C++ only)
           Warn when a class appears to be polymorphic, thereby requiring a
           virtual destructor, yet it declares a non-virtual one.  This
           warning is also enabled if -Weffc++ is specified.

       -Wreorder (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 will rearrange 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.

       The following -W... options are not affected by -Wall.

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

           o   Item 11:  Define a copy constructor and an assignment operator
               for classes with dynamically allocated memory.

           o   Item 12:  Prefer initialization to assignment in constructors.

           o   Item 14:  Make destructors virtual in base classes.

           o   Item 15:  Have "operator=" return a reference to *this.

           o   Item 23:  Don't try to return a reference when you must return
               an object.

           Also warn about violations of the following style guidelines from
           Scott Meyers' More Effective C++ book:

           o   Item 6:  Distinguish between prefix and postfix forms of
               increment and decrement operators.

           o   Item 7:  Never overload "&&", "||", or ",".

           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-deprecated (C++ only)
           Do not warn about usage of deprecated features.

       -Wstrict-null-sentinel (C++ only)
           Warn also 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 not a
           null pointer, it is guaranteed to of the same size as a pointer.
           But this use is not portable across different compilers.

       -Wno-non-template-friend (C++ only)
           Disable warnings when non-templatized friend functions are declared
           within a template.  Since the advent of explicit template
           specification support in G++, if the name of the friend is an
           unqualified-id (i.e., friend foo(int)), the C++ language
           specification demands that the friend declare or define an
           ordinary, nontemplate function.  (Section 14.5.3).  Before G++
           implemented explicit specification, unqualified-ids could be
           interpreted as a particular specialization of a templatized
           function.  Because this non-conforming behavior is no longer the
           default behavior for G++, -Wnon-template-friend allows the compiler
           to check existing code for potential trouble spots and is on by
           default.  This new compiler behavior can be turned off with
           -Wno-non-template-friend which keeps the conformant compiler code
           but disables the helpful warning.

       -Wold-style-cast (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++ 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();

           will fail to compile.

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

       -Wsign-promo (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++ would try to
           preserve unsignedness, but the standard mandates the current
           behavior.

                   struct A {
                     operator int ();
                     A& operator = (int);
                   };

                   main ()
                   {
                     A a,b;
                     a = b;
                   }

           In this example, G++ will synthesize a default A& operator = (const
           A&);, while cfront will use the user-defined operator =.

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

       This section describes the command-line options that are only
       meaningful for Objective-C and Objective-C++ programs, but 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, will
           override 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 (e.g., "[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.  Currently, this option is only available in
           conjunction with the NeXT runtime on Mac OS X 10.3 and later.

       -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 that
           will run 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 that will run all such default destructors,
           in reverse order.

           The "- (id) .cxx_construct" and/or "- (void) .cxx_destruct" methods
           thusly generated will 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 will be invoked by the runtime
           immediately after a new object instance is allocated; the "- (void)
           .cxx_destruct" methods will be 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-sjlj-exceptions
           Enable syntactic support for structured exception handling in
           Objective-C, similar to what is offered by C++ and Java.  This
           option is unavailable in conjunction with the NeXT runtime on Mac
           OS X 10.2 and earlier.  This option is on by default with the NeXT
           runtime.

                     @try {
                       ...
                          @throw expr;
                       ...
                     }
                     @catch (AnObjCClass *exc) {
                       ...
                         @throw expr;
                       ...
                         @throw;
                       ...
                     }
                     @catch (AnotherClass *exc) {
                       ...
                     }
                     @catch (id allOthers) {
                       ...
                     }
                     @finally {
                       ...
                         @throw expr;
                       ...
                     }

           The @throw statement may appear anywhere in an Objective-C or
           Objective-C++ program; when used inside of a @catch block, the
           @throw may appear without an argument (as shown above), in which
           case the object caught by the @catch will be rethrown.

           Note that only (pointers to) Objective-C objects may be thrown and
           caught using this scheme.  When an object is thrown, it will be
           caught by the nearest @catch clause capable of handling objects of
           that type, analogously to how "catch" blocks work in C++ and Java.
           A "@catch(id ...)" clause (as shown above) may also be provided to
           catch any and all Objective-C exceptions not caught by previous
           @catch clauses (if any).

           The @finally clause, if present, will be executed upon exit from
           the immediately preceding "@try ... @catch" section.  This will
           happen regardless of whether any exceptions are thrown, caught or
           rethrown inside the "@try ... @catch" section, analogously to the
           behavior of the "finally" clause in Java.

           There are several caveats to using the new exception mechanism:

           o   Although currently designed to be binary compatible with
               "NS_HANDLER"-style idioms provided by the "NSException" class,
               the new exceptions can only be used on Mac OS X 10.3 (Panther)
               and later systems, due to additional functionality needed in
               the (NeXT) Objective-C runtime.

           o   As mentioned above, the new exceptions do not support handling
               types other than Objective-C objects.   Furthermore, when used
               from Objective-C++, the Objective-C exception model does not
               interoperate with C++ exceptions at this time.  This means you
               cannot @throw an exception from Objective-C and "catch" it in
               C++, or vice versa (i.e., "throw ... @catch").

           The -fobjc-sjlj-exceptions switch also enables the use of
           synchronization blocks for thread-safe execution:

                     @synchronized (ObjCClass *guard) {
                       ...
                     }

           Upon entering the @synchronized block, a thread of execution shall
           first check whether a lock has been placed on the corresponding
           "guard" object by another thread.  If it has, the current thread
           shall wait until the other thread relinquishes its lock.  Once
           "guard" becomes available, the current thread will place its own
           lock on it, execute the code contained in the @synchronized block,
           and finally relinquish the lock (thereby making "guard" available
           to other threads).

           Unlike Java, Objective-C does not allow for entire methods to be
           marked @synchronized.  Note that throwing exceptions out of
           @synchronized blocks is allowed, and will cause the guarding object
           to be unlocked properly.

       -fobjc-gc
           Enable garbage collection (GC) in Objective-C and Objective-C++
           programs.  The resulting binary requires additional runtime support
           which is present on Mac OS X Version 10.5 (Leopard) and later.  All
           Objective-C objects are presumed to be garbage collected. To aid in
           this effort, compiler implements assignments of Objective-C object
           pointers via runtime support functions. These functions work
           correctly in non-GC environments as well, in case this code is used
           as part of a library.  Assignments of objects into instance
           variables of other objects are intercepted, so are assignments to
           global object variables. In general, assignments through pointers
           to objects are intercepted. Additionally, assignments of objects as
           fields within structures are intercepted.

           In addition, other pointer variables may be marked with the
           __strong storage class modifier to indicate to the compiler that
           these assignments need to use the assignment runtime functions as
           well, allowing the memory referenced by these pointers to be
           allocated from the collector. A __weak storage class modifier for
           pointers is also introduced to indicate a zero-ing weak reference.
           This is permitted only for instance variables of an object or
           globals.  The compiler arranges for all reads as well as writes to
           these variables to occur via runtime support functions.  Under
           garbage collection these variables are not consulted when
           determining what is not garbage and they are set to nil (zero) if
           the memory they reference is deemed garbage and is collected.

                     __strong void *p;  // assignments to 'p' will have runtime support calls
                     int *q;            // assignments to 'q' ordinarly will not
                       ...
                     (__strong int *)q = 0;   // this assignment will call a runtime support function

           Conversely, the "__weak" type qualifier may be used to call weak
           runtime functions.

                     __weak id q;      // assignments to 'q' will have the '__weak' semantics
                     id p;             // assignments to 'p' will have the "__strong' semantics
                       ...
                     (__weak id)p = 0;   // Fall back to '__weak' semantics in this assignment.

       -fobjc-gc-only
           Use this option to indicate that the Objective-C program supports
           garbage collection (GC) only - that is, it does not contain
           retain/release logic.  This flag implies -fobjc-gc as well. With
           this flag, framework is marked as not honoring retain/release.

       -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.

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

       -Wassign-intercept
           Warn whenever an Objective-C assignment is being intercepted by the
           garbage collector.

       -Wno-protocol
           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.

       -Wselector
           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.

       -Wproperty-assign-default
           Warn if no "assign", "retain", or "copy" attribute is specified on
           a property of pointer to object type. Property is then assumed to
           be "assign" by default.

       -Wdirect-ivar-access
           Warn if ivar of pointer to object type is directly accessed in non-
           gc mode, instead of using property syntax access.

       -Wstrict-selector-match
           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
           will omit such warnings if any differences found are confined to
           types which share the same size and alignment.

       -Wundeclared-selector
           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, ...).  The options
       described below can be used to control the diagnostic messages
       formatting algorithm, e.g. how many characters per line, how often
       source location information should be reported.  Right now, only the
       C++ front end can honor these options.  However it is expected, in the
       near future, that the remaining front ends would be able to digest them
       correctly.

       -fmessage-length=n
           Try to format error messages so that they fit on lines of about n
           characters.  The default is 72 characters for g++ and 0 for the
           rest of the front ends supported by GCC.  If n is zero, then no
           line-wrapping will be done; each error message will appear on a
           single line.

       -fdiagnostics-show-location=once
           Only meaningful in line-wrapping mode.  Instructs the diagnostic
           messages reporter to emit once source location information; 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-show-option
           This option instructs the diagnostic machinery to add text to each
           diagnostic emitted, which indicates which command line option
           directly controls that diagnostic, when such an option is known to
           the diagnostic machinery.

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

       You can request many specific warnings with options beginning -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.

       The following options control the amount and kinds of warnings produced
       by GCC; for further, language-specific options also refer to C++
       Dialect Options and Objective-C and Objective-C++ Dialect Options.

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

       -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 will 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.

           -pedantic does not cause warning messages for use of the alternate
           keywords whose names begin and end with __.  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 -pedantic 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 -pedantic.  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 gnu89 or gnu99, there is a corresponding base
           standard, the version of ISO C on which the GNU extended dialect is
           based.  Warnings from -pedantic are given where they are required
           by the base standard.  (It would 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
           Like -pedantic, except that errors are produced rather than
           warnings.

       -w  Inhibit all warning messages.

       -Wno-import
           Inhibit warning messages about the use of #import.

       -Wno-#warnings
           Inhibit warning messages issued by #warning.

       -Wextra-tokens
           Warn about extra tokens at the end of prepreprocessor directives.
           (APPLE ONLY)

       -Wnewline-eof
           Warn about files missing a newline at the end of the file.  (APPLE
           ONLY)

       -Wno-altivec-long-deprecated
           Do not warn about the use of the deprecated 'long' keyword in
           AltiVec data types.  (APPLE ONLY)

       -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.

       -Wcomment
           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.

       -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.

       -Wno-format
           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
           -pedantic is used with -Wformat, warnings will be 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).

           Since -Wformat also checks for null format arguments for several
           functions, -Wformat also implies -Wnonnull.

           -Wformat is included in -Wall.  For more control over some aspects
           of format checking, the options -Wformat-y2k,
           -Wno-format-extra-args, -Wno-format-zero-length,
           -Wformat-nonliteral, -Wformat-security, and -Wformat=2 are
           available, but are not included in -Wall.

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

       -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 will suppress the warning if
           the unused arguments are all pointers, since the Single Unix
           Specification says that such unused arguments are allowed.

       -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".

       -Wno-format-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=2
           Enable -Wformat plus format checks not included in -Wformat.
           Currently equivalent to -Wformat -Wformat-nonliteral
           -Wformat-security -Wformat-y2k.

       -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.

       -Wglobal-constructors
           Warn about namespace scope data that requires construction or
           destruction, or functions that use the constructor attribute or the
           destructor attribute.  Additionally warn if the Objective-C GNU
           runtime is used to initialize various metadata.

       -Winit-self (C, C++, Objective-C and Objective-C++ only)
           Warn about uninitialized variables which are initialized with
           themselves.  Note this option can only be used with the
           -Wuninitialized option, which in turn only works with -O1 and
           above.

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

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

       -Wimplicit-int
           Warn when a declaration does not specify a type.  This warning is
           enabled by -Wall.

       -Wimplicit-function-declaration
       -Werror-implicit-function-declaration
           Give a warning (or error) whenever a function is used before being
           declared.  The form -Wno-error-implicit-function-declaration is not
           supported.  This warning is enabled by -Wall (as a warning, not an
           error).

       -Wimplicit
           Same as -Wimplicit-int and -Wimplicit-function-declaration.  This
           warning is enabled by -Wall.

       -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 -Wall.

       -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.

       -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.  Only the warning for an assignment used
           as a truth value is supported when compiling C++; the other
           warnings are only supported when compiling C.

           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 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, 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 will issue 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" could
           belong to the enclosing "if".  The resulting code would look like
           this:

                   {
                     if (a)
                       {
                         if (b)
                           foo ();
                         else
                           bar ();
                       }
                   }

           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 defines 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 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++.

       -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".

           For C, also warn if the return type of a function has a type
           qualifier such as "const".  Such a type qualifier has no effect,
           since the value returned by a function is not an lvalue.  ISO C
           prohibits qualified "void" return types on function definitions, so
           such return types always receive a warning even without this
           option.

           For C++, a function without return type always produces a
           diagnostic message, even when -Wno-return-type is specified.  The
           only exceptions are main and functions defined in system headers.

           This warning is enabled by -Wall.

       -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.  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.

       -Wtrigraphs
           Warn if any trigraphs are encountered that might change the meaning
           of the program (trigraphs within comments are not warned about).
           This warning 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-parameter
           Warn whenever a function parameter is unused aside from its
           declaration.

           To suppress this warning use the unused attribute.

       -Wunused-variable
           Warn whenever a local variable or non-constant static variable is
           unused aside from its declaration.  This warning is enabled by
           -Wall.

           To suppress this warning use the unused attribute.

       -Wunused-value
           Warn whenever a statement computes a result that is explicitly not
           used.  This warning is enabled by -Wall.

           To suppress this warning cast the expression to void.

       -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 automatic variable is used without first being
           initialized or if a variable may be clobbered by a "setjmp" call.

           These warnings are possible only in optimizing compilation, because
           they require data flow information that is computed only when
           optimizing.  If you do not specify -O, you will not get these
           warnings. Instead, GCC will issue a warning about -Wuninitialized
           requiring -O.

           If you want to warn about code which uses the uninitialized value
           of the variable in its own initializer, use the -Winit-self option.

           These warnings occur for individual uninitialized or clobbered
           elements of structure, union or array variables as well as for
           variables which are uninitialized or clobbered 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 will 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.

           These warnings are made optional because GCC is not smart enough to
           see all the reasons why the code might be correct despite 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.  Here is another common
           case:

                   {
                     int save_y;
                     if (change_y) save_y = y, y = new_y;
                     ...
                     if (change_y) y = save_y;
                   }

           This has no bug because "save_y" is used only if it is set.

           This option also warns when a non-volatile automatic variable might
           be changed by a call to "longjmp".  These warnings as well are
           possible only in optimizing compilation.

           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 which 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.

       -Wunknown-pragmas
           understood by GCC.  If this command line option is used, warnings
           will even be issued for unknown pragmas in system header files.
           This is not the case if the warnings were 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.

       -Wstrict-aliasing
           This option is only active when -fstrict-aliasing is active.  It
           warns about code which 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.

       -Wstrict-aliasing=2
           This option is only active when -fstrict-aliasing is active.  It
           warns about code which might break the strict aliasing rules that
           the compiler is using for optimization.  This warning catches more
           cases than -Wstrict-aliasing, but it will also give a warning for
           some ambiguous cases that are safe.

       -Wstrict-overflow
       -Wstrict-overflow=n
           This option is only active when -fstrict-overflow is active.  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 which 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 which 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 will require, in particular when determining whether a loop
           will be executed at all.

           -Wstrict-overflow=1
               Warn about cases which are both questionable and easy to avoid.
               For example: "x + 1 > x"; with -fstrict-overflow, the compiler
               will simplify this 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 -fstrict-overflow is in effect, 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" will be simplified to "x > 0".

           -Wstrict-overflow=4
               Also warn about other simplifications not covered by the above
               cases.  For example: "(x * 10) / 5" will be 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" will be 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 will give a
               very large number of false positives.

       -Wall
           All of the above -W options combined.  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.

       -Wmost
           This is equivalent to -Wall -Wno-parentheses.  (APPLE ONLY)

       The following -W... options 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.

       -Wextra
           (This option used to be called -W.  The older name is still
           supported, but the newer name is more descriptive.)  Print extra
           warning messages for these events:

           o   A function can return either with or without a value.  (Falling
               off the end of the function body is considered returning
               without a value.)  For example, this function would evoke such
               a warning:

                       foo (a)
                       {
                         if (a > 0)
                           return a;
                       }

           o   An expression-statement or the left-hand side of a comma
               expression contains no side effects.  To suppress the warning,
               cast the unused expression to void.  For example, an expression
               such as x[i,j] will cause a warning, but x[(void)i,j] will not.

           o   An unsigned value is compared against zero with < or >=.

           o   Storage-class specifiers like "static" are not the first things
               in a declaration.  According to the C Standard, this usage is
               obsolescent.

           o   If -Wall or -Wunused is also specified, warn about unused
               arguments.

           o   A comparison between signed and unsigned values could produce
               an incorrect result when the signed value is converted to
               unsigned.  (But don't warn if -Wno-sign-compare is also
               specified.)

           o   An aggregate has an initializer which does not initialize all
               members.  This warning can be independently controlled by
               -Wmissing-field-initializers.

           o   An initialized field without side effects is overridden when
               using designated initializers.  This warning can be
               independently controlled by -Woverride-init.

           o   A function parameter is declared without a type specifier in
               K&R-style functions:

                       void foo(bar) { }

           o   An empty body occurs in an if or else statement.

           o   (C++ only) An empty body occurs in a while or for statement
               with no whitespacing before the semicolon. This warning can be
               independently controlled by -Wempty-body.

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

           o   A variable might be changed by longjmp or vfork.

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

           o   (C++ only) A non-static reference or non-static const member
               appears in a class without constructors.

           o   (C++ only) Ambiguous virtual bases.

           o   (C++ only) Subscripting an array which has been declared
               register.

           o   (C++ only) Taking the address of a variable which has been
               declared register.

           o   (C++ only) A base class is not initialized in a derived class'
               copy constructor.

       -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 will not warn about unknown pragmas
           in system headers---for that, -Wunknown-pragmas must also be used.

       -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 would 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.

       -Wfour-char-constants
           Warn about four char constants, e.g. OSType 'APPL'.  This warning
           is disabled by default.

       -Wtraditional (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 which
           should be avoided.

           o   Macro parameters that appear within string literals in the
               macro body.  In traditional C macro replacement takes place
               within string literals, but does not in ISO C.

           o   In traditional C, some preprocessor directives did not exist.
               Traditional preprocessors would only consider 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 would ignore because the # does not appear as
               the first character on the line.  It also suggests you hide
               indenting them.  Some traditional implementations would not
               recognize #elif, so it suggests avoiding it altogether.

           o   A function-like macro that appears without arguments.

           o   The unary plus operator.

           o   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.

           o   A function declared external in one block and then used after
               the end of the block.

           o   A "switch" statement has an operand of type "long".

           o   A non-"static" function declaration follows a "static" one.
               This construct is not accepted by some traditional C compilers.

           o   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.

           o   Usage of ISO string concatenation is detected.

           o   Initialization of automatic aggregates.

           o   Identifier conflicts with labels.  Traditional C lacks a
               separate namespace for labels.

           o   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.

           o   Conversions by prototypes between fixed/floating point values
               and vice versa.  The absence of these prototypes when compiling
               with traditional C would cause serious problems.  This is a
               subset of the possible conversion warnings, for the full set
               use -Wconversion.

           o   Use of ISO C style function definitions.  This warning
               intentionally is not issued for prototype declarations or
               variadic functions because these ISO C features will 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.

       -Wdeclaration-after-statement (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 and was
           not supported by GCC versions before GCC 3.0.

       -Wno-discard-qual
           This flag allows user to suppress warning that is issued when
           qualification is discarded in situations like, initialization,
           assignment and argument passing.

       -Wundef
           Warn if an undefined identifier is evaluated in an #if directive.

       -Wno-endif-labels
           Do not warn whenever an #else or an #endif are followed by text.

       -Wshadow
           Warn whenever a local variable shadows another local variable,
           parameter or global variable or whenever a built-in function is
           shadowed.

       -Wlarger-than-len
           Warn whenever an object of larger than len bytes is defined.

       -Wunsafe-loop-optimizations
           Warn if the loop cannot be optimized because the compiler could not
           assume anything on the bounds of the loop indices.  With
           -funsafe-loop-optimizations warn if the compiler made such
           assumptions.

       -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.

       -Wbad-function-cast (C only)
           Warn whenever a function call is cast to a non-matching type.  For
           example, warn if "int malloc()" is cast to "anything *".

       -Wc++-compat
           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.

       -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 *".

       -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.

       -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 will get a warning; when compiling C++, warn about
           the deprecated conversion from string literals to "char *".  This
           warning, by default, is enabled for C++ programs.  These warnings
           will 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 will
           just be a nuisance; this is why we did not make -Wall request these
           warnings.

       -Wconversion
           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.

           Also, warn if a negative integer constant expression is implicitly
           converted to an unsigned type.  For example, warn about the
           assignment "x = -1" if "x" is unsigned.  But do not warn about
           explicit casts like "(unsigned) -1".

       -Wshorten-64-to-32
           Warn if a value is implicitly converted from a 64 bit type to a 32
           bit type.

       -Wempty-body
           Warn if an empty body occurs in an if or else statement.
           Additionally, in C++, warn when an empty body occurs in a while or
           for statement with no whitespacing before the semicolon.  This
           warning is also enabled by -Wextra.

       -Wsign-compare
           Warn when a comparison between signed and unsigned values could
           produce an incorrect result when the signed value is converted to
           unsigned.  This warning is also enabled by -Wextra; to get the
           other warnings of -Wextra without this warning, use -Wextra
           -Wno-sign-compare.

       -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.

       -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-attributes
           Do not warn if an unexpected "__attribute__" is used, such as
           unrecognized attributes, function attributes applied to variables,
           etc.  This will not stop errors for incorrect use of supported
           attributes.

       -Wstrict-prototypes (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 which specifies the
           argument types.)

       -Wold-style-definition (C only)
           Warn if an old-style function definition is used.  A warning is
           given even if there is a previous prototype.

       -Wmissing-prototypes
           Warn if a global function is defined without a previous prototype
           declaration.  This warning is issued even if the definition itself
           provides a prototype.  The aim is to detect global functions that
           fail to be declared in header files.

       -Wmissing-declarations (C only)
           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.

       -Wmissing-field-initializers
           Warn if a structure's initializer has some fields missing.  For
           example, the following code would cause 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 would not trigger a warning:

                   struct s { int f, g, h; };
                   struct s x = { .f = 3, .g = 4 };

           This warning is included in -Wextra.  To get other -Wextra warnings
           without this one, use -Wextra -Wno-missing-field-initializers.

       -Wmissing-noreturn
           Warn about functions which might be candidates for attribute
           "noreturn".  Note these are only possible candidates, not absolute
           ones.  Care should be taken to manually verify functions actually
           do not ever return before adding the "noreturn" attribute,
           otherwise subtle code generation bugs could be introduced.  You
           will not get a warning for "main" in hosted C environments.

       -Wmissing-format-attribute
           Warn about function pointers which might be candidates for "format"
           attributes.  Note these are only possible candidates, not absolute
           ones.  GCC will guess 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 will also warn about function definitions which might be
           candidates for "format" attributes.  Again, these are only possible
           candidates.  GCC will guess 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.

       -Wno-multichar
           Do not warn if a multicharacter constant ('FOO') 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.  This flag does not control warning for a constant with four
           characters, use -Wfour-char-constants instead.

       -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 which have not been normalized; this option
           controls that warning.

           There are four levels of warning that GCC supports.  The default is
           -Wnormalized=nfc, which warns about any identifier which is not in
           the ISO 10646 "C" normalized form, NFC.  NFC is the recommended
           form for most uses.

           Unfortunately, there are some characters which ISO C and ISO C++
           allow in identifiers that when turned into NFC aren't allowable as
           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.  You would only want to do this if you were
           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", will display just like a regular "n" which
           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 will warn 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
           is unable to be fixed to display these characters distinctly.

       -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.

       -Woverride-init
           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.

       -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" will be
           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;
                   };

       -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.

       -Wnested-externs (C only)
           Warn if an "extern" declaration is encountered within a function.

       -Wunreachable-code
           Warn if the compiler detects that code will never be executed.

           This option is intended to warn when the compiler detects that at
           least a whole line of source code will never be executed, because
           some condition is never satisfied or because it is after a
           procedure that never returns.

           It is possible for this option to produce a warning even though
           there are circumstances under which part of the affected line can
           be executed, so care should be taken when removing apparently-
           unreachable code.

           For instance, when a function is inlined, a warning may mean that
           the line is unreachable in only one inlined copy of the function.

           This option is not made part of -Wall because in a debugging
           version of a program there is often substantial code which checks
           correct functioning of the program and is, hopefully, unreachable
           because the program does work.  Another common use of unreachable
           code is to provide behavior which is selectable at compile-time.

       -Winline
           Warn if a function can not be inlined and it was declared as
           inline.  Even with this option, the compiler will 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.

       -Wno-invalid-offsetof (C++ only)
           Suppress warnings from applying the offsetof macro to a non-POD
           type.  According to the 1998 ISO C++ standard, applying offsetof to
           a non-POD type is undefined.  In existing C++ implementations,
           however, offsetof typically gives meaningful results even when
           applied to certain kinds of non-POD types. (Such as a simple struct
           that fails to be a POD type only by virtue of having a
           constructor.)  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.

       -Wno-int-to-pointer-cast (C only)
           Suppress warnings from casts to pointer type of an integer of a
           different size.

       -Wno-pointer-to-int-cast (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 can't
           be used.

       -Wlong-long
           Warn if long long type is used.  This is default.  To inhibit the
           warning messages, use -Wno-long-long.  Flags -Wlong-long and
           -Wno-long-long are taken into account only when -pedantic flag is
           used.

       -Wvariadic-macros
           Warn if variadic macros are used in pedantic ISO C90 mode, or the
           GNU alternate syntax when in pedantic ISO C99 mode.  This is
           default.  To inhibit the warning messages, use
           -Wno-variadic-macros.

       -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.

       -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 were unable to
           handle the code effectively.  Often, the problem is that your code
           is too big or too complex; GCC will refuse to optimize programs
           when the optimization itself is likely to take inordinate amounts
           of time.

       -Wpointer-sign
           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 -pedantic, which can be disabled with
           -Wno-pointer-sign.

       -Werror
           Make all warnings into errors.

       -Werror=
           Make the specified warning into an errors.  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.  You can use the
           -fdiagnostics-show-option option to have each controllable warning
           amended with the option which controls it, to determine what to use
           with this option.

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

       -Wstack-protector
           This option is only active when -fstack-protector is active.  It
           warns about functions that will not be protected against stack
           smashing.

       -Woverlength-strings
           Warn about string constants which are longer than the "minimum
           maximum" length specified in the C standard.  Modern compilers
           generally allow string constants which 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 C89, 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 -pedantic, and can be disabled with
           -Wno-overlength-strings.

   Options for Debugging Your Program or GCC
       GCC has various special options that are used for debugging either your
       program or GCC:

       -g  Produce debugging information in the operating system's native
           format (stabs, COFF, XCOFF, or DWARF 2).  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 will probably make other
           debuggers crash or refuse to read the program.  If you want to
           control for certain whether to generate the extra information, use
           -gstabs+ or -gstabs (see below).

           GCC allows you to use -g with -O.  The shortcuts taken by optimized
           code may occasionally produce surprising results: 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 were already
           at hand; some statements may execute in different places because
           they were moved out of loops.

           Nevertheless it proves possible to debug optimized output.  This
           makes it reasonable to use the optimizer for programs that might
           have bugs.

           The following options are useful when GCC is generated with the
           capability for more than one debugging format.

       -ggdb
           Produce debugging information for use by GDB.  This means to use
           the most expressive format available (DWARF 2, stabs, or the native
           format if neither of those are supported), including GDB extensions
           if at all possible.

       -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 which is not understood
           by DBX or SDB.  On System V Release 4 systems this option requires
           the GNU assembler.

       -flimit-debug-info
           Limit debug information produced to reduce size of debug binary.

       -feliminate-unused-debug-symbols
           Produce debugging information in stabs format (if that is
           supported), for only symbols that are actually used.

       -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 will increase the size of debugging
           information by as much as a factor of two.

       -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.

       -gdwarf-2
           Produce debugging information in DWARF version 2 format (if that is
           supported).  This is the format used by DBX on IRIX 6.  With this
           option, GCC uses features of DWARF version 3 when they are useful;
           version 3 is upward compatible with version 2, but may still cause
           problems for older debuggers.

           (Other debug formats, such as -gcoff, are not supported in Darwin
           or Mac OS X.)

       -glevel
       -ggdblevel
       -gstabslevel
           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, but no
           information about local variables and no line numbers.

           Level 3 includes extra information, such as all the macro
           definitions present in the program.  Some debuggers support macro
           expansion when you use -g3.

           -gdwarf-2 does not accept a concatenated debug level, because GCC
           used to support an option -gdwarf that meant to generate debug
           information in version 1 of the DWARF format (which is very
           different from version 2), and it would have been too confusing.
           That debug format is long obsolete, but the option cannot be
           changed now.  Instead use an additional -glevel option to change
           the debug level for DWARF2.

       -feliminate-dwarf2-dups
           Compress DWARF2 debugging information by eliminating duplicated
           information about each symbol.  This option only makes sense when
           generating DWARF2 debugging information with -gdwarf-2.

       -p  Generate extra code to write profile information suitable for the
           analysis program prof.  You must use this option when compiling the
           source files you want data about, and you must also use it when
           linking.

       -pg Generate extra code to write profile information suitable for the
           analysis program gprof.  You must use this option when compiling
           the source files you want data about, and you must also use it when
           linking.

       -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.

       -fmem-report
           Makes the compiler print some statistics about permanent memory
           allocation when it finishes.

       -fopt-diary
           Enable optimization diary entries using DWARF encoding. This option
           does nothing unless gdwarf-2 is specified.

       -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.  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.

           o   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.

           o   Link your object files with -lgcov or -fprofile-arcs (the
               latter implies the former).

           o   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.  Also "fork" calls are detected and
               correctly handled (double counting will not happen).

           o   For profile-directed optimizations, compile the source files
               again with the same optimization and code generation options
               plus -fbranch-probabilities.

           o   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 will match the source files more
           closely, if you do not optimize.

       -dletters
       -fdump-rtl-pass
           Says to make debugging dumps during compilation at times specified
           by letters.    This is used for debugging the RTL-based passes of
           the compiler.  The file names for most of the dumps are made by
           appending a pass number and a word to the dumpname.  dumpname 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. These switches may have different effects when -E is
           used for preprocessing.

           Most debug dumps can be enabled either passing a letter to the -d
           option, or with a long -fdump-rtl switch; here are the possible
           letters for use in letters and pass, and their meanings:

           -dA Annotate the assembler output with miscellaneous debugging
               information.

           -dB
           -fdump-rtl-bbro
               Dump after block reordering, to file.148r.bbro.

           -dc
           -fdump-rtl-combine
               Dump after instruction combination, to the file
               file.129r.combine.

           -dC
           -fdump-rtl-ce1
           -fdump-rtl-ce2
               -dC and -fdump-rtl-ce1 enable dumping after the first if
               conversion, to the file file.117r.ce1.  -dC and -fdump-rtl-ce2
               enable dumping after the second if conversion, to the file
               file.130r.ce2.

           -dd
           -fdump-rtl-btl
           -fdump-rtl-dbr
               -dd and -fdump-rtl-btl enable dumping after branch target load
               optimization, to file.31.btl.  -dd and -fdump-rtl-dbr enable
               dumping after delayed branch scheduling, to file.36.dbr.

           -dD Dump all macro definitions, at the end of preprocessing, in
               addition to normal output.

           -dE
           -fdump-rtl-ce3
               Dump after the third if conversion, to file.146r.ce3.

           -df
           -fdump-rtl-cfg
           -fdump-rtl-life
               -df and -fdump-rtl-cfg enable dumping after control and data
               flow analysis, to file.116r.cfg.  -df and -fdump-rtl-cfg enable
               dumping dump after life analysis, to file.128r.life1 and
               file.135r.life2.

           -dg
           -fdump-rtl-greg
               Dump after global register allocation, to file.139r.greg.

           -dG
           -fdump-rtl-gcse
           -fdump-rtl-bypass
               -dG and -fdump-rtl-gcse enable dumping after GCSE, to
               file.114r.gcse.  -dG and -fdump-rtl-bypass enable dumping after
               jump bypassing and control flow optimizations, to
               file.115r.bypass.

           -dh
           -fdump-rtl-eh
               Dump after finalization of EH handling code, to file.02.eh.

           -di
           -fdump-rtl-sibling
               Dump after sibling call optimizations, to file.106r.sibling.

           -dj
           -fdump-rtl-jump
               Dump after the first jump optimization, to file.112r.jump.

           -dk
           -fdump-rtl-stack
               Dump after conversion from registers to stack, to
               file.152r.stack.

           -dl
           -fdump-rtl-lreg
               Dump after local register allocation, to file.138r.lreg.

           -dL
           -fdump-rtl-loop2
               -dL and -fdump-rtl-loop2 enable dumping after the loop
               optimization pass, to file.119r.loop2, file.120r.loop2_init,
               file.121r.loop2_invariant, and file.125r.loop2_done.

           -dm
           -fdump-rtl-sms
               Dump after modulo scheduling, to file.136r.sms.

           -dM
           -fdump-rtl-mach
               Dump after performing the machine dependent reorganization
               pass, to file.155r.mach if that pass exists.

           -dn
           -fdump-rtl-rnreg
               Dump after register renumbering, to file.147r.rnreg.

           -dN
           -fdump-rtl-regmove
               Dump after the register move pass, to file.132r.regmove.

           -do
           -fdump-rtl-postreload
               Dump after post-reload optimizations, to file.24.postreload.

           -dr
           -fdump-rtl-expand
               Dump after RTL generation, to file.104r.expand.

           -dR
           -fdump-rtl-sched2
               Dump after the second scheduling pass, to file.150r.sched2.

           -ds
           -fdump-rtl-cse
               Dump after CSE (including the jump optimization that sometimes
               follows CSE), to file.113r.cse.

           -dS
           -fdump-rtl-sched
               Dump after the first scheduling pass, to file.21.sched.

           -dt
           -fdump-rtl-cse2
               Dump after the second CSE pass (including the jump optimization
               that sometimes follows CSE), to file.127r.cse2.

           -dT
           -fdump-rtl-tracer
               Dump after running tracer, to file.118r.tracer.

           -dV
           -fdump-rtl-vpt
           -fdump-rtl-vartrack
               -dV and -fdump-rtl-vpt enable dumping after the value profile
               transformations, to file.10.vpt.  -dV and -fdump-rtl-vartrack
               enable dumping after variable tracking, to file.154r.vartrack.

           -dw
           -fdump-rtl-flow2
               Dump after the second flow pass, to file.142r.flow2.

           -dz
           -fdump-rtl-peephole2
               Dump after the peephole pass, to file.145r.peephole2.

           -dZ
           -fdump-rtl-web
               Dump after live range splitting, to file.126r.web.

           -da
           -fdump-rtl-all
               Produce all the dumps listed above.

           -dH Produce a core dump whenever an error occurs.

           -dm Print statistics on memory usage, at the end of the run, to
               standard error.

           -dp Annotate the assembler output with a comment indicating which
               pattern and alternative was used.  The length of each
               instruction is also printed.

           -dP Dump the RTL in the assembler output as a comment before each
               instruction.  Also turns on -dp annotation.

           -dv For each of the other indicated dump files (either with -d or
               -fdump-rtl-pass), dump a representation of the control flow
               graph suitable for viewing with VCG to file.pass.vcg.

           -dx Just generate RTL for a function instead of compiling it.
               Usually used with r (-fdump-rtl-expand).

           -dy Dump debugging information during parsing, to standard error.

       -fdump-noaddr
           When doing debugging dumps (see -d option above), 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.

       -fdump-unnumbered
           When doing debugging dumps (see -d option above), suppress
           instruction numbers, line number note 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-translation-unit (C++ only)
       -fdump-translation-unit-options (C++ only)
           Dump a representation of the tree structure for the entire
           translation unit to a file.  The file name is made by appending .tu
           to the source file name.  If the -options form is used, options
           controls the details of the dump as described for the -fdump-tree
           options.

       -fdump-class-hierarchy (C++ only)
       -fdump-class-hierarchy-options (C++ only)
           Dump a representation of each class's hierarchy and virtual
           function table layout to a file.  The file name is made by
           appending .class to the source file name.  If the -options form is
           used, options controls the details of the dump as described for the
           -fdump-tree options.

       -fdump-ipa-switch
           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.  The following
           dumps are possible:

           all Enables all inter-procedural analysis dumps; currently the only
               produced dump is the cgraph dump.

           cgraph
               Dumps information about call-graph optimization, unused
               function removal, and inlining decisions.

       -fdump-tree-switch
       -fdump-tree-switch-options
           Control the dumping at various stages of processing the
           intermediate language tree to a file.  The file name is generated
           by appending a switch specific suffix to the source file name.  If
           the -options form is used, options is a list of - separated options
           that control the details of the dump.  Not all options are
           applicable to all dumps, those which are not meaningful will be
           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.

           slim
               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.

           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).

           stats
               Enable dumping various statistics about the pass (not honored
               by every dump option).

           blocks
               Enable showing basic block boundaries (disabled in raw dumps).

           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.

           all Turn on all options, except raw, slim and lineno.

           The following tree dumps are possible:

           original
               Dump before any tree based optimization, to file.original.

           optimized
               Dump after all tree based optimization, to file.optimized.

           inlined
               Dump after function inlining, to file.inlined.

           gimple
               Dump each function before and after the gimplification pass to
               a file.  The file name is made by appending .gimple to the
               source file name.

           cfg Dump the control flow graph of each function to a file.  The
               file name is made by appending .cfg to the source file name.

           vcg Dump the control flow graph of each function to a file in VCG
               format.  The file name is made by appending .vcg to the source
               file name.  Note that if the file contains more than one
               function, the generated file cannot be used directly by VCG.
               You will need to cut and paste each function's graph into its
               own separate file first.

           ch  Dump each function after copying loop headers.  The file name
               is made by appending .ch to the source file name.

           ssa Dump SSA related information to a file.  The file name is made
               by appending .ssa to the source file name.

           salias
               Dump structure aliasing variable information to a file.  This
               file name is made by appending .salias to the source file name.

           alias
               Dump aliasing information for each function.  The file name is
               made by appending .alias to the source file name.

           ccp Dump each function after CCP.  The file name is made by
               appending .ccp to the source file name.

           storeccp
               Dump each function after STORE-CCP.  The file name is made by
               appending .storeccp to the source file name.

           pre Dump trees after partial redundancy elimination.  The file name
               is made by appending .pre to the source file name.

           fre Dump trees after full redundancy elimination.  The file name is
               made by appending .fre to the source file name.

           copyprop
               Dump trees after copy propagation.  The file name is made by
               appending .copyprop to the source file name.

           store_copyprop
               Dump trees after store copy-propagation.  The file name is made
               by appending .store_copyprop to the source file name.

           dce Dump each function after dead code elimination.  The file name
               is made by appending .dce to the source file name.

           mudflap
               Dump each function after adding mudflap instrumentation.  The
               file name is made by appending .mudflap to the source file
               name.

           sra Dump each function after performing scalar replacement of
               aggregates.  The file name is made by appending .sra to the
               source file name.

           sink
               Dump each function after performing code sinking.  The file
               name is made by appending .sink to the source file name.

           dom Dump each function after applying dominator tree optimizations.
               The file name is made by appending .dom to the source file
               name.

           dse Dump each function after applying dead store elimination.  The
               file name is made by appending .dse to the source file name.

           phiopt
               Dump each function after optimizing PHI nodes into straightline
               code.  The file name is made by appending .phiopt to the source
               file name.

           forwprop
               Dump each function after forward propagating single use
               variables.  The file name is made by appending .forwprop to the
               source file name.

           copyrename
               Dump each function after applying the copy rename optimization.
               The file name is made by appending .copyrename to the source
               file name.

           nrv Dump each function after applying the named return value
               optimization on generic trees.  The file name is made by
               appending .nrv to the source file name.

           vect
               Dump each function after applying vectorization of loops.  The
               file name is made by appending .vect to the source file name.

           vrp Dump each function after Value Range Propagation (VRP).  The
               file name is made by appending .vrp to the source file name.

           all Enable all the available tree dumps with the flags provided in
               this option.

       -ftree-vectorizer-verbose=n
           This option controls the amount of debugging output the vectorizer
           prints.  This information is written to standard error, unless
           -fdump-tree-all or -fdump-tree-vect is specified, in which case it
           is output to the usual dump listing file, .vect.  For n=0 no
           diagnostic information is reported.  If n=1 the vectorizer reports
           each loop that got vectorized, and the total number of loops that
           got vectorized.  If n=2 the vectorizer also reports non-vectorized
           loops that passed the first analysis phase (vect_analyze_loop_form)
           - i.e. countable, inner-most, single-bb, single-entry/exit loops.
           This is the same verbosity level that -fdump-tree-vect-stats uses.
           Higher verbosity levels mean either more information dumped for
           each reported loop, or same amount of information reported for more
           loops: If n=3, alignment related information is added to the
           reports.  If n=4, data-references related information (e.g. memory
           dependences, memory access-patterns) is added to the reports.  If
           n=5, the vectorizer reports also non-vectorized inner-most loops
           that did not pass the first analysis phase (i.e. may not be
           countable, or may have complicated control-flow).  If n=6, the
           vectorizer reports also non-vectorized nested loops.  For n=7, all
           the information the vectorizer generates during its analysis and
           transformation is reported.  This is the same verbosity level that
           -fdump-tree-vect-details uses.

       -frandom-seed=string
           This option provides a seed that GCC uses when it would otherwise
           use random numbers.  It is used to generate 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 should be different for every file you compile.

       -fsched-verbose=n
           On targets that use instruction scheduling, this option controls
           the amount of debugging output the scheduler prints.  This
           information is written to standard error, unless -dS or -dR is
           specified, in which case it is output to the usual dump listing
           file, .sched or .sched2 respectively.  However for n greater than
           nine, the output is always printed to standard error.

           For n greater than zero, -fsched-verbose outputs the same
           information as -dRS.  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.

       -save-temps
           Store the usual "temporary" intermediate files permanently; place
           them in the current directory and name them based on the source
           file.  Thus, compiling foo.c with -c -save-temps would produce
           files foo.i and foo.s, as well as foo.o.  This creates a
           preprocessed foo.i output file even though the compiler now
           normally uses an integrated preprocessor.

           When used in combination with the -x command line option,
           -save-temps is sensible enough to avoid over writing 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.

       -mllvm string
           This option provides a way to supply llvm optimization and code
           generation debugging options to LLVM component directly. This
           option is intended for compiler developers, who are investigating
           LLVM bugs, not end users.

       -time
           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).  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.

       -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, -Oz (APPLE ONLY), ...), debugging information (-g) and the
           debug info format supports it.

       -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
           @samp{-, without spaces between multiple switches.  This is
           supposed to ease shell-processing.

       -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 will search---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 /.

       -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)---and don't do
           anything else.

       -dumpspecs
           Print the compiler's built-in specs---and don't do anything else.
           (This is used when GCC itself is being built.)

       -feliminate-unused-debug-types
           Normally, when producing DWARF2 output, GCC will emit debugging
           information for all types declared in a compilation unit,
           regardless of whether or not they are actually used in that
           compilation unit.  Sometimes this is useful, such as 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.  With this option,
           GCC will avoid producing debug symbol output for types that are
           nowhere used in the source file being compiled.

   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 would 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.  Optimization levels -O and above, in particular, enable unit-
       at-a-time mode, which allows the compiler to consider information
       gained from later functions in the file when compiling a function.
       Compiling multiple files at once to a single output file in unit-at-a-
       time 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.

       -O1 Optimize.  Optimizing compilation takes somewhat more time, and a
           lot more memory for a large function.

           With -O1, the compiler tries to reduce code size and execution
           time, without performing any optimizations that take a great deal
           of compilation time.

           -O1 turns on the following optimization flags: -fdefer-pop
           -fdelayed-branch -fguess-branch-probability -fcprop-registers
           -fif-conversion -fif-conversion2 -ftree-ccp -ftree-dce
           -ftree-dominator-opts -ftree-dse -ftree-ter -ftree-lrs -ftree-sra
           -ftree-copyrename -ftree-fre -ftree-ch -funit-at-a-time
           -fmerge-constants

           -O1 also turns on -fomit-frame-pointer on machines where doing so
           does not interfere with debugging.

       -O
       -O2 Optimize even more.  GCC performs nearly all supported
           optimizations that do not involve a space-speed tradeoff.  The
           compiler does not perform loop unrolling or function inlining when
           you specify -O2.  As compared to -O1, this option increases both
           compilation time and the performance of the generated code.

           LLVM-GCC's -O is a synonym for -O2.

           -O2 turns on all optimization flags specified by -O1.  It also
           turns on the following optimization flags: -fthread-jumps
           -fcrossjumping -foptimize-sibling-calls -fcse-follow-jumps
           -fcse-skip-blocks -fgcse  -fgcse-lm -fexpensive-optimizations
           -frerun-cse-after-loop -fcaller-saves -fpeephole2 -fschedule-insns
           -fschedule-insns2 -fsched-interblock  -fsched-spec -fregmove
           -fstrict-aliasing -fstrict-overflow -fdelete-null-pointer-checks
           -freorder-blocks  -freorder-functions -falign-functions
           -falign-jumps -falign-loops  -falign-labels -ftree-vrp -ftree-pre

           Please note the warning under -fgcse about invoking -O2 on programs
           that use computed gotos.

           -O2 doesn't turn on -ftree-vrp for the Ada compiler.  This option
           must be explicitly specified on the command line to be enabled for
           the Ada compiler.

           In Apple's version of GCC, -fstrict-aliasing, -freorder-blocks, and
           -fsched-interblock are disabled by default when optimizing.

       -O3 Optimize yet more.  -O3 turns on all optimizations specified by -O2
           and also turns on the -finline-functions, -funswitch-loops and
           -fgcse-after-reload options.

       -O0 Do not optimize.  This is the default.

       -fast
           Optimize for maximum performance. -fast changes the overall
           optimization strategy of GCC in order to produce the fastest
           possible running code for PPC7450 and G5 architectures. By default,
           -fast optimizes for G5. Programs optimized for G5 will not run on
           PPC7450. To optimize for PPC7450, add -mcpu=7450 on command line.

           -fast currently enables the following optimization flags (for G5
           and PPC7450).  These flags may change in the future.  You cannot
           override any of these options if you use -fast except by setting
           -mcpu=7450 (or -fPIC, see below).

           -O3 -falign-loops-max-skip=15 -falign-jumps-max-skip=15
           -falign-loops=16 -falign-jumps=16 -falign-functions=16
           -malign-natural (except when -fastf is specified) -ffast-math
           -fstrict-aliasing -funroll-loops -ftree-loop-linear
           -ftree-loop-memset -mcpu=G5 -mpowerpc-gpopt -mtune=G5  (unless
           -mtune=G4 is specified).  -fsched-interblock -fgcse-sm -mpowerpc64

           To build shared libraries with -fast, specify -fPIC on the command
           line as -fast turns on -mdynamic-no-pic otherwise.

           Important notes: -ffast-math results in code that is not
           necessarily IEEE-compliant.  -fstrict-aliasing is highly likely to
           break non-standard-compliant programs.  -malign-natural only works
           properly if the entire program is compiled with it, and none of the
           standard headers/libraries contain any code that changes alignment
           when this option is used.

           On Intel target, -fast currently enables the following optimization
           flags:

           -O3 -fomit-frame-pointer -fstrict-aliasing
           -momit-leaf-frame-pointer -fno-tree-pre -falign-loops

           All choices of flags enabled by -fast are subject to change without
           notice.

       -Os Optimize for size, but not at the expense of speed.  -Os enables
           all -O2 optimizations that do not typically increase code size.
           However, instructions are chosen for best performance, regardless
           of size.  To optimize solely for size on Darwin, use -Oz (APPLE
           ONLY).

           The following options are set for -O2, but are disabled under -Os:
           -falign-functions  -falign-jumps  -falign-loops -falign-labels
           -freorder-blocks  -freorder-blocks-and-partition
           -fprefetch-loop-arrays  -ftree-vect-loop-version

           When optimizing with -Os or -Oz (APPLE ONLY) on Darwin, any
           function up to 30 "estimated insns" in size will be considered for
           inlining.  When compiling C and Objective-C sourcefiles with -Os or
           -Oz on Darwin, functions explictly marked with the "inline" keyword
           up to 450 "estimated insns" in size will be considered for
           inlining.  When compiling for Apple POWERPC targets, -Os and -Oz
           (APPLE ONLY) disable use of the string instructions even though
           they would usually be smaller, because the kernel can't emulate
           them correctly in some rare cases.  This behavior is not portable
           to any other gcc environment, and will not affect most programs at
           all.  If you really want the string instructions, use -mstring.

       -Oz (APPLE ONLY) Optimize for size, regardless of performance.  -Oz
           enables the same optimization flags that -Os uses, but -Oz also
           enables other optimizations intended solely to reduce code size.
           In particular, instructions that encode into fewer bytes are
           preferred over longer instructions that execute in fewer cycles.
           -Oz on Darwin is very similar to -Os in FSF distributions of GCC.
           -Oz employs the same inlining limits and avoids string instructions
           just like -Os.

           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
       would be -fno-foo.  In the table below, only one of the forms is
       listed---the one you typically will 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-default-inline
           Do not make member functions inline by default merely because they
           are defined inside the class scope (C++ only).  Otherwise, when you
           specify -O, member functions defined inside class scope are
           compiled inline by default; i.e., you don't need to add inline in
           front of the member function name.

       -fno-defer-pop
           Always pop the arguments to each function call as soon as that
           function returns.  For machines which must pop arguments after a
           function call, the compiler normally lets arguments accumulate on
           the stack for several function calls and pops them all at once.

           Disabled at levels -O, -O2, -O3, -Os, -Oz (APPLE ONLY).

       -fforce-mem
           Force memory operands to be copied into registers before doing
           arithmetic on them.  This produces better code by making all memory
           references potential common subexpressions.  When they are not
           common subexpressions, instruction combination should eliminate the
           separate register-load. This option is now a nop and will be
           removed in 4.3.

       -fforce-addr
           Force memory address constants to be copied into registers before
           doing arithmetic on them.

       -fomit-frame-pointer
           Don't keep the frame pointer in a register for functions that don't
           need one.  This avoids the instructions to save, set up and restore
           frame pointers; it also makes an extra register available in many
           functions.  It also makes debugging impossible on some machines.

           On some machines, such as the VAX, this flag has no effect, because
           the standard calling sequence automatically handles the frame
           pointer and nothing is saved by pretending it doesn't exist.  The
           machine-description macro "FRAME_POINTER_REQUIRED" controls whether
           a target machine supports this flag.

           Enabled at levels -O, -O2, -O3, -Os, -Oz (APPLE ONLY).

       -foptimize-sibling-calls
           Optimize sibling and tail recursive calls.

           Enabled at levels -O2, -O3, -Os, -Oz (APPLE ONLY).

       -fno-inline
           Don't pay attention to the "inline" keyword.  Normally this option
           is used to keep the compiler from expanding any functions inline.
           Note that if you are not optimizing, no functions can be expanded
           inline.

       -finline-functions
           Integrate all simple functions into their callers.  The compiler
           heuristically decides which functions are simple enough to be 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 level -O3.

       -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 if -funit-at-a-time is enabled.

       -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.

       -finline-limit=n
           By default, GCC limits the size of functions that can be inlined.
           This flag allows the control of this limit for functions that are
           explicitly marked as inline (i.e., marked with the inline keyword
           or defined within the class definition in c++).  n is the size of
           functions that can be inlined in number of pseudo instructions (not
           counting parameter handling).  The default value of n is 600.
           Increasing this value can result in more inlined code at the cost
           of compilation time and memory consumption.  Decreasing usually
           makes the compilation faster and less code will be inlined (which
           presumably means slower programs).  This option is particularly
           useful for programs that use inlining heavily such as those based
           on recursive templates with C++.

           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 I<n>/2.

           max-inline-insns-auto
                is set to I<n>/2.

           min-inline-insns
                is set to 130 or I<n>/4, whichever is smaller.

           max-inline-insns-rtl
                is set to I<n>.

           See below for a documentation of the individual parameters
           controlling inlining.

           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.  This option
           has no effect in llvm-gcc.  The always_inline and noinline
           parameters are honored, but none of the other inlining parameters
           have any effect; there is no specific user control on the amount of
           inlining done.  The compiler will do less inlining at -O2 or -Os
           than at -O3.

       -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 C.  In C++, emit any and all inline
           functions into the object file.

       -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 the variable was referenced, regardless of
           whether or not optimization is turned on, use the
           -fno-keep-static-consts option.

       -flocal-alloc
           (APPLE ONLY) Enable the local (intra-basic-block) register
           allocator.

           GCC enables this option by default.  If you want to force the
           compiler to supress register allocation within a basic block, use
           the -fno-local-alloc option.  This option cannot be disabled with
           -O0, for correctness reasons.

       -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, -Oz (APPLE ONLY).

       -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 non-automatic
           variable to have distinct location, so using this option will
           result 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.

       -fno-branch-count-reg
           Do not use "decrement and branch" instructions on a count register,
           but instead generate a sequence of instructions that decrement a
           register, compare it against zero, 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.

           The default is -fbranch-count-reg.

       -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.

       -fbounds-check
           For front-ends that support it, generate additional code to check
           that indices used to access arrays are within the declared range.
           This is currently only supported by the Java and Fortran front-
           ends, where this option defaults to true and false respectively.

       -fmudflap -fmudflapth -fmudflapir
           For front-ends that support it (C and C++), instrument all risky
           pointer/array dereferencing operations, some standard library
           string/heap functions, and some other associated constructs with
           range/validity tests.  Modules so instrumented should be immune to
           buffer overflows, invalid heap use, and some other classes of C/C++
           programming errors.  The instrumentation relies on a separate
           runtime library (libmudflap), which will be linked into a program
           if -fmudflap is given at link time.  Run-time behavior of the
           instrumented program is controlled by the MUDFLAP_OPTIONS
           environment variable.  See "env MUDFLAP_OPTIONS=-help a.out" for
           its options.

           Use -fmudflapth instead of -fmudflap to compile and to link if your
           program is multi-threaded.  Use -fmudflapir, in addition to
           -fmudflap or -fmudflapth, if instrumentation should ignore pointer
           reads.  This produces less instrumentation (and therefore faster
           execution) and still provides some protection against outright
           memory corrupting writes, but allows erroneously read data to
           propagate within a program.

       -fthread-jumps
           Perform optimizations where we 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, -Oz (APPLE ONLY).

       -fcse-follow-jumps
           In common subexpression elimination, 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 will follow the jump when the condition tested is
           false.

           Enabled at levels -O2, -O3, -Os, -Oz (APPLE ONLY).

       -fcse-skip-blocks
           This is similar to -fcse-follow-jumps, but causes CSE to follow
           jumps which 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, -Oz (APPLE ONLY).

       -frerun-cse-after-loop
           Re-run common subexpression elimination after loop optimizations
           has been performed.

           Enabled at levels -O2, -O3, -Os, -Oz (APPLE ONLY).

       -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 runtime performance if you disable
           the global common subexpression elimination pass by adding
           -fno-gcse to the command line.

           Enabled at levels -O2, -O3, -Os, -Oz (APPLE ONLY).

       -fgcse-lm
           When -fgcse-lm is enabled, global common subexpression elimination
           will attempt to move loads which 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 gcse is enabled.

       -fgcse-sm
           When -fgcse-sm is enabled, a store motion pass is run after global
           common subexpression elimination.  This pass will attempt 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
           cleanup redundant spilling.

       -funsafe-loop-optimizations
           If given, the loop optimizer will assume that loop indices do not
           overflow, and that the loops with nontrivial exit condition are not
           infinite.  This enables a wider range of loop optimizations even if
           the loop optimizer itself cannot prove that these assumptions are
           valid.  Using -Wunsafe-loop-optimizations, the compiler will warn
           you if it finds this kind of loop.

       -fcrossjumping
           Perform cross-jumping transformation.  This transformation unifies
           equivalent code and save code size.  The resulting code may or may
           not perform better than without cross-jumping.

           Enabled at levels -O2, -O3, -Os, -Oz (APPLE ONLY).

       -fif-conversion
           Attempt to transform conditional jumps into branch-less
           equivalents.  This include 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 "if-conversion2".

           Enabled at levels -O, -O2, -O3, -Os, -Oz (APPLE ONLY).

       -fif-conversion2
           Use conditional execution (where available) to transform
           conditional jumps into branch-less equivalents.

           Enabled at levels -O, -O2, -O3, -Os, -Oz (APPLE ONLY).

       -fdelete-null-pointer-checks
           Use global dataflow analysis to identify and eliminate useless
           checks for null pointers.  The compiler assumes that dereferencing
           a null pointer would have halted the program.  If a pointer is
           checked after it has already been dereferenced, it cannot be null.

           In some environments, this assumption is not true, and programs can
           safely dereference null pointers.  Use
           -fno-delete-null-pointer-checks to disable this optimization for
           programs which depend on that behavior.

           Enabled at levels -O2, -O3, -Os, -Oz (APPLE ONLY).

       -fexpensive-optimizations
           Perform a number of minor optimizations that are relatively
           expensive.

           Enabled at levels -O2, -O3, -Os, -Oz (APPLE ONLY).

       -foptimize-register-move
       -fregmove
           Attempt to reassign register numbers in move instructions and as
           operands of other simple instructions in order to maximize the
           amount of register tying.  This is especially helpful on machines
           with two-operand instructions.

           Note -fregmove and -foptimize-register-move are the same
           optimization.

           Enabled at levels -O2, -O3, -Os, -Oz (APPLE ONLY).

       -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, -Oz (APPLE ONLY).

       -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, -Os, -Oz for PPC targets; ignored for
           x86 targets (APPLE ONLY).

       -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, -Oz for PPC targets; ignored for
           x86 targets (APPLE ONLY).

       -fno-sched-interblock
           Don't schedule instructions across basic blocks.  This is normally
           enabled by default when scheduling before register allocation, i.e.
           with -fschedule-insns or at -O2 or higher.

       -fno-sched-spec
           Don't allow speculative motion of non-load instructions.  This is
           normally enabled by default when scheduling before register
           allocation, i.e.  with -fschedule-insns or at -O2 or higher.

       -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=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.

       -fsched-stalled-insns-dep=n
           Define how many insn groups (cycles) will be examined for a
           dependency on a stalled insn that is candidate for premature
           removal from the queue of stalled insns.  Has an effect only during
           the second scheduling pass, and only if -fsched-stalled-insns is
           used and its value is not zero.

       -fsched2-use-superblocks
           When scheduling after register allocation, do use superblock
           scheduling algorithm.  Superblock scheduling allows motion across
           basic block boundaries resulting on 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.

       -fsched2-use-traces
           Use -fsched2-use-superblocks algorithm when scheduling after
           register allocation and additionally perform code duplication in
           order to increase the size of superblocks using tracer pass.  See
           -ftracer for details on trace formation.

           This mode should produce faster but significantly longer programs.
           Also without -fbranch-probabilities the traces constructed may not
           match the reality and hurt the performance.  This only makes sense
           when scheduling after register allocation, i.e. with
           -fschedule-insns2 or at -O2 or higher.

       -fsee
           Eliminates redundant extension instructions and move the non
           redundant ones to optimal placement using LCM.

       -freschedule-modulo-scheduled-loops
           The modulo scheduling comes before the traditional scheduling, if a
           loop was modulo scheduled we may want to prevent the later
           scheduling passes from changing its schedule, we use this option to
           control that.

       -fcaller-saves
           Enable values to be allocated in registers that will be 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 than would otherwise be
           produced.

           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, -Oz (APPLE ONLY).

       -ftree-pre
           Perform Partial Redundancy Elimination (PRE) on trees.  This flag
           is enabled by default at -O2 and -O3.

       -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 faster than PRE, though it exposes fewer redundancies.
           This flag is enabled by default at -O 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.

       -ftree-store-copy-prop
           Perform copy propagation of memory loads and stores.  This pass
           eliminates unnecessary copy operations in memory references
           (structures, global variables, arrays, etc).  This flag is enabled
           by default at -O2 and higher.

       -ftree-salias
           Perform structural alias analysis on trees.  This flag is enabled
           by default at -O and higher.

       -fipa-pta
           Perform interprocedural pointer analysis.

       -ftree-sink
           Perform forward store motion  on trees.  This flag is enabled by
           default at -O and higher.

       -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.

       -ftree-store-ccp
           Perform sparse conditional constant propagation (CCP) on trees.
           This pass operates on both local scalar variables and memory stores
           and loads (global variables, structures, arrays, etc).  This flag
           is enabled by default at -O2 and higher.

       -ftree-dce
           Perform dead code elimination (DCE) on trees.  This flag is enabled
           by default at -O and 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-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 or -Oz (APPLE ONLY), 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
           Perform linear loop transformations on tree.  This flag can improve
           cache performance and allow further loop optimizations to take
           place.  This flag is known to have bugs that cause incorrect code
           to be generated in some rare cases. Note this flag is included in
           -fast.

       -ftree-loop-im
           Perform loop invariant motion on trees.  This pass moves only
           invariants that would be 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 the loop for
           that determining number of iterations requires complicated
           analysis.  Later optimizations then may determine the number
           easily.  Useful especially in connection with unrolling.

       -fivopts
           Perform induction variable optimizations (strength reduction,
           induction variable merging and induction variable elimination) on
           trees.

       -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 -O and
           higher.

       -ftree-copyrename
           Perform copy renaming on trees.  This pass attempts to rename
           compiler temporaries to other variables at copy locations, usually
           resulting in variable names which more closely resemble the
           original variables.  This flag is enabled by default at -O and
           higher.

       -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-lrs
           Perform live range splitting during the SSA->normal phase.
           Distinct live ranges of a variable are split into unique variables,
           allowing for better optimization later.  This is enabled by default
           at -O and higher.

       -ftree-vectorize
           Perform loop vectorization on trees.

           In Apple's version of GCC, -fstrict-aliasing is enabled by default
           when loop vectorization is enabled. See -fstrict-aliasing document
           for more information.

       -ftree-vect-loop-version
           Perform loop versioning when doing loop vectorization on trees.
           When a loop appears to be vectorizable except that data alignment
           or data dependence cannot be determined at compile time then
           vectorized and non-vectorized versions of the loop are generated
           along with runtime checks for alignment or dependence to control
           which version is executed.  This option is enabled by default
           except at level -Os where it is disabled.

       -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.

       -ftracer
           Perform tail duplication to enlarge superblock size.  This
           transformation simplifies the control flow of the function allowing
           other optimizations to do better job.

       -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.  This option makes code larger, and may or
           may not make it run faster.

       -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,

       -fsplit-ivs-in-unroller
           Enables expressing 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.

           Combination of -fweb and CSE is often sufficient to obtain the same
           effect.  However in cases the loop body is more complicated than a
           single basic block, this is not reliable.  It also does not work at
           all on some of the architectures due to restrictions in the CSE
           pass.

           This optimization is enabled by default.

       -fvariable-expansion-in-unroller
           With this option, the compiler will create multiple copies of some
           local variables when unrolling a loop which can result in superior
           code.

       -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 levels -Os and -Oz (APPLE ONLY).

       -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, -Oz (APPLE ONLY).

       -fno-guess-branch-probability
           Do not guess branch probabilities using heuristics.

           GCC will use 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 will be 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.

           The default is -fguess-branch-probability at levels -O, -O2, -O3,
           -Os, -Oz (APPLE ONLY).

       -freorder-blocks
           Reorder basic blocks in the compiled function in order to reduce
           number of taken branches and improve code locality.

           Enabled 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, for linkonce sections, for functions with a
           user-defined section attribute and on any architecture that does
           not support named sections.

       -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.

           Also profile feedback must be available in to make this option
           effective.  See -fprofile-arcs for details.

           Enabled at levels -O2, -O3, -Os, -Oz (APPLE ONLY).

       -fstrict-aliasing
           Allows 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() {
                     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 will
           work as expected.  However, this code might not:

                   int f() {
                     a_union t;
                     int* ip;
                     t.d = 3.0;
                     ip = &t.i;
                     return *ip;
                   }

           Every language that wishes to perform language-specific alias
           analysis should define a function that computes, given an "tree"
           node, an alias set for the node.  Nodes in different alias sets are
           not allowed to alias.  For an example, see the C front-end function
           "c_get_alias_set".

           Enabled at levels -O2, -O3, -Os, -Oz (APPLE ONLY).

       -fstrict-overflow
           Allow the compiler to assume strict signed overflow rules,
           depending on the language being compiled.  For C (and C++) this
           means that overflow when doing arithmetic with signed numbers is
           undefined, which means that the compiler may assume that it will
           not happen.  This permits various optimizations.  For example, the
           compiler will assume that an expression like "i + 10 > i" will
           always be true for signed "i".  This assumption is only valid if
           signed overflow is undefined, as the expression is false if "i +
           10" overflows when using twos complement arithmetic.  When this
           option is in effect any attempt to determine whether an operation
           on signed numbers will overflow must be written carefully to not
           actually involve overflow.

           See also the -fwrapv option.  Using -fwrapv means that signed
           overflow is fully defined: it wraps.  When -fwrapv is used, there
           is no difference between -fstrict-overflow and
           -fno-strict-overflow.  With -fwrapv certain types of overflow are
           permitted.  For example, if the compiler gets an overflow when
           doing arithmetic on constants, the overflowed value can still be
           used with -fwrapv, but not otherwise.

           The -fstrict-overflow option is enabled at levels -O2, -O3, -Os.

       -falign-functions
       -falign-functions=n
           Align the start of functions to the next power-of-two greater than
           n, skipping up to n bytes.  For instance, -falign-functions=32
           aligns functions to the next 32-byte boundary, but
           -falign-functions=24 would align to the next 32-byte boundary only
           if this can be done by skipping 23 bytes or less.

           -fno-align-functions and -falign-functions=1 are equivalent and
           mean that functions will not be aligned.

           Some assemblers only support this flag when n is a power of two; in
           that case, it is rounded up.

           If n is not specified or is zero, use a machine-dependent default.

           Enabled at levels -O2, -O3.

       -falign-labels
       -falign-labels=n
           Align all branch targets to a power-of-two boundary, skipping up to
           n bytes like -falign-functions.  This option can easily make code
           slower, because it must insert dummy operations for when the branch
           target is reached in the usual flow of the code.

           -fno-align-labels and -falign-labels=1 are equivalent and mean that
           labels will not be 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.

           Enabled at levels -O2, -O3.

       -falign-loops-max-skip
       -falign-loops-max-skip=n
           Align loops to a power-of-two boundary, but do not skip more than n
           bytes to do so.

       -falign-loops
       -falign-loops=n
           Align loops to a power-of-two boundary, skipping up to n bytes like
           -falign-functions.  The hope is that the loop will be executed many
           times, which will make up for any execution of the dummy
           operations.

           -fno-align-loops and -falign-loops=1 are equivalent and mean that
           loops will not be aligned.

           If n is not specified or is zero, use a machine-dependent default.

           Enabled at levels -O2, -O3.

       -falign-jumps
       -falign-jumps=n
           Align branch targets to a power-of-two boundary, for branch targets
           where the targets can only be reached by jumping, skipping up to n
           bytes like -falign-functions.  In this case, no dummy operations
           need be executed.

       -falign-jumps-max-skip
       -falign-jumps-max-skip=n
           Align branch targets to a power-of-two boundary, but do not skip
           more than n bytes to do so.

           -fno-align-jumps and -falign-jumps=1 are equivalent and mean that
           loops will not be aligned.

           If n is not specified or is zero, use a machine-dependent default.

           Enabled at levels -O2, -O3.

       -funit-at-a-time
           Parse the whole compilation unit before starting to produce code.
           This allows some extra optimizations to take place but consumes
           more memory (in general).  There are some compatibility issues with
           unit-at-a-time mode:

           o   enabling unit-at-a-time mode may change the order in which
               functions, variables, and top-level "asm" statements are
               emitted, and will likely break code relying on some particular
               ordering.  The majority of such top-level "asm" statements,
               though, can be replaced by "section" attributes.  The fno-
               toplevel-reorder option may be used to keep the ordering used
               in the input file, at the cost of some optimizations.

           o   unit-at-a-time mode removes unreferenced static variables and
               functions.  This may result in undefined references when an
               "asm" statement refers directly to variables or functions that
               are otherwise unused.  In that case either the
               variable/function shall be listed as an operand of the "asm"
               statement operand or, in the case of top-level "asm" statements
               the attribute "used" shall be used on the declaration.

           o   Static functions now can use non-standard passing conventions
               that may break "asm" statements calling functions directly.
               Again, attribute "used" will prevent this behavior.

           As a temporary workaround, -fno-unit-at-a-time can be used, but
           this scheme may not be supported by future releases of GCC.

           Enabled at levels -O, -O2, -O3, -Os.

       -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 will not be removed.  This option is intended to support
           existing code which relies on a particular ordering.  For new code,
           it is better to use attributes.

       -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 will no longer stay in a
           "home register".

           Enabled by default with -funroll-loops.

       -fwhole-program
           Assume that the current compilation unit represents 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 a affect gets
           more aggressively optimized by interprocedural optimizers.  While
           this option is equivalent to proper use of "static" keyword for
           programs consisting of single file, in combination with option
           --combine this flag can be used to compile most of smaller scale C
           programs since the functions and variables become local for the
           whole combined compilation unit, not for the single source file
           itself.

       -fno-cprop-registers
           After register allocation and post-register allocation instruction
           splitting, we perform a copy-propagation pass to try to reduce
           scheduling dependencies and occasionally eliminate the copy.

           Disabled at levels -O, -O2, -O3, -Os, -Oz (APPLE ONLY).

       -fprofile-generate
           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", "-fvpt".

       -fprofile-use
           Enable profile feedback directed optimizations, and optimizations
           generally profitable only with profile feedback available.

           The following options are enabled: "-fbranch-probabilities",
           "-fvpt", "-funroll-loops", "-fpeel-loops", "-ftracer"

       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.

       -ffast-math
           Sets -fno-math-errno, -funsafe-math-optimizations,
           -fno-trapping-math, -ffinite-math-only, -fno-rounding-math,
           -fno-signaling-nans and fcx-limited-range.

           This option causes the preprocessor macro "__FAST_MATH__" to be
           defined.

           This option should never be turned on by any -O option since it can
           result in incorrect output for programs which depend on an exact
           implementation of IEEE or ISO rules/specifications for math
           functions.

       -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.

           (APPLE ONLY) The Darwin math libraries never set errno, so there is
           no point in having the compiler generate code that assumes they
           might.  Therefore, the default is -fno-math-errno on Darwin.

           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 should never be turned on by any -O option since it can
           result in incorrect output for programs which depend on an exact
           implementation of IEEE or ISO rules/specifications for math
           functions.

           The default is -fno-unsafe-math-optimizations.

       -ffinite-math-only
           Allow optimizations for floating-point arithmetic that assume that
           arguments and results are not NaNs or +-Infs.

           This option should never be turned on by any -O option since it can
           result in incorrect output for programs which depend on an exact
           implementation of IEEE or ISO rules/specifications.

           The default is -fno-finite-math-only.

       -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 implies -fno-signaling-nans.  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 which 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".

       -frtl-abstract-sequences
           It is a size optimization method. This option is to find identical
           sequences of code, which can be turned into pseudo-procedures  and
           then  replace  all  occurrences with  calls to  the  newly created
           subroutine. It is kind of an opposite of -finline-functions.  This
           optimization runs at RTL level.

       -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-honor-nans
           Allow optimizations for floating-point arithmetic that assume that
           arguments and results are not NaNs.  The default is -fhonor-nans.

       -fno-honor-infinites
           Allow optimizations for floating-point arithmetic that assume that
           arguments and results are not +-Infs.  The default is
           -fhonor-infinites.

       -fsingle-precision-constant
           Treat floating point constant as single precision constant instead
           of implicitly converting it to double precision constant.

       -fcx-limited-range
       -fno-cx-limited-range
           When enabled, this option states that a range reduction step is not
           needed when performing complex division.  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.

       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 the 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 mostly to take,
           the REG_BR_PROB values are used to exactly determine which path is
           taken more often.

       -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 and adds REG_VALUE_PROFILE notes to
           instructions for their later usage in optimizations.

           Enabled with -fprofile-generate and -fprofile-use.

       -fvpt
           If combined with -fprofile-arcs, it instructs the compiler to add a
           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 operation using
           the knowledge about the value of the denominator.

       -frename-registers
           Attempt to avoid false dependencies in scheduled code by making use
           of registers left over after register allocation.  This
           optimization will most benefit processors with lots of registers.
           Depending on the debug information format adopted by the target,
           however, it can make debugging impossible, since variables will no
           longer stay in a "home register".

           Enabled by default with -funroll-loops.

       -ftracer
           Perform tail duplication to enlarge superblock size.  This
           transformation simplifies the control flow of the function allowing
           other optimizations to do better job.

           Enabled with -fprofile-use.

       -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
           small constant number of iterations).  This option makes code
           larger, and may or may not make it run faster.

           Enabled with -fprofile-use.

       -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 the loops for that there is enough information that they do
           not roll much (from profile feedback).  It also turns on complete
           loop peeling (i.e. complete removal of loops with small constant
           number of iterations).

           Enabled with -fprofile-use.

       -fmove-loop-invariants
           Enables the loop invariant motion pass in the RTL loop optimizer.
           Enabled at level -O1

       -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).

       -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 and SPARC
           processors running Solaris 2 have linkers with such optimizations.
           AIX may have these optimizations in the future.

           Only use these options when there are significant benefits from
           doing so.  When you specify these options, the assembler and linker
           will create larger object and executable files and will also be
           slower.  You will not be able to use "gprof" on all systems if you
           specify this option and you may have problems with debugging if you
           specify both this option and -g.

       -fbranch-target-load-optimize
           Perform branch target register load optimization before prologue /
           epilogue threading.  The use of target registers can typically be
           exposed only during reload, thus hoisting loads out of loops and
           doing inter-block scheduling needs a separate optimization pass.

       -fbranch-target-load-optimize2
           Perform branch target register load optimization after prologue /
           epilogue threading.

       -fbtr-bb-exclusive
           When performing branch target register load optimization, don't
           reuse branch target registers in within any basic block.

       -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 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.

       -fstack-protector-all
           Like -fstack-protector except that all functions are protected.

       -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; }

           would usually calculate the addresses of all three variables, but
           if you compile it with -fsection-anchors, it will access 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.

       --param name=value
           In some places, GCC uses various constants to control the amount of
           optimization that is done.  For example, GCC will not inline
           functions that contain more that 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 each case, the value is an integer.  The allowable choices for
           name are given in the following table:

           salias-max-implicit-fields
               The maximum number of fields in a variable without direct
               structure accesses for which structure aliasing will consider
               trying to track each field.  The default is 5

           salias-max-array-elements
               The maximum number of elements an array can have and its
               elements still be tracked individually by structure aliasing.
               The default is 4

           sra-max-structure-size
               The maximum structure size, in bytes, at which the scalar
               replacement of aggregates (SRA) optimization will perform block
               copies.  The default value, 0, implies that GCC will select the
               most appropriate size itself.

           sra-field-structure-ratio
               The threshold ratio (as a percentage) between instantiated
               fields and the complete structure size.  We say that if the
               ratio of the number of bytes in instantiated fields to the
               number of bytes in the complete structure exceeds this
               parameter, then block copies are not used.  The default is 75.

           max-crossjump-edges
               The maximum number of incoming edges to consider for
               crossjumping.  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 compile
               time increase with probably small improvement in executable
               size.

           min-crossjump-insns
               The minimum number of instructions which must be matched at the
               end of two blocks before crossjumping will be performed on
               them.  This value is ignored in the case where all instructions
               in the block being crossjumped from are matched.  The default
               value is 5.

           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.  The default value is 8.

           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.  The default value is 8.

           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 is searched, the time savings
               from filling the delay slot will be minimal so stop searching.
               Increasing values mean more aggressive optimization, making the
               compile time increase with probably small improvement in
               executable run 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
               compile 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 that will be allocated
               in order to perform the global common subexpression elimination
               optimization.  If more memory than specified is required, the
               optimization will not be done.

           max-gcse-passes
               The maximum number of passes of GCSE to run.  The default is 1.

           max-pending-list-length
               The maximum number of pending dependencies scheduling will
               allow 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-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 will consider for inlining.  This only affects
               functions declared inline and methods implemented in a class
               declaration (C++).  The default value is 450.

           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 will be investigated.  To those functions, a
               different (more restrictive) limit compared to functions
               declared inline can be applied.  The default value is 90.

           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 backend.  This parameter is
               ignored when -funit-at-a-time is not used.  The default value
               is 2700.

           large-function-growth
               Specifies maximal growth of large function caused by inlining
               in percents.  This parameter is ignored when -funit-at-a-time
               is not used.  The default value is 100 which 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
               (consider unit consisting of function A that is inline and B
               that just calls A three time.  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 inlininable 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.  The default is 10000

           inline-unit-growth
               Specifies maximal overall growth of the compilation unit caused
               by inlining.  This parameter is ignored when -funit-at-a-time
               is not used.  The default value is 50 which limits unit growth
               to 1.5 times the original size.

           max-inline-insns-recursive
           max-inline-insns-recursive-auto
               Specifies maximum number of instructions out-of-line copy of
               self recursive inline function can grow into by performing
               recursive inlining.

               For functions declared inline --param max-inline-insns-
               recursive is taken into account.  For function not declared
               inline, recursive inlining happens only when -finline-functions
               (included in -O3) is enabled and --param max-inline-insns-
               recursive-auto is used.  The default value is 450.

           max-inline-recursive-depth
           max-inline-recursive-depth-auto
               Specifies maximum recursion depth used by the recursive
               inlining.

               For functions declared inline --param max-inline-recursive-
               depth is taken into account.  For function not declared inline,
               recursive inlining happens only when -finline-functions
               (included in -O3) is enabled and --param max-inline-recursive-
               depth-auto is used.  The default value is 450.

           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 probability that
               function will recurse via given call expression.  This
               parameter limits inlining only to call expression whose
               probability exceeds given threshold (in percents).  The default
               value is 10.

           inline-call-cost
               Specify cost of call instruction relative to simple arithmetics
               operations (having cost of 1).  Increasing this cost
               disqualifies inlining of non-leaf functions and at the same
               time increases size of leaf function that is believed to reduce
               function size by being inlined.  In effect it increases amount
               of inlining for code having large abstraction penalty (many
               functions that just pass the arguments to other functions) and
               decrease inlining for code with low abstraction penalty.  The
               default value is 16.

           max-unrolled-insns
               The maximum number of instructions that a loop should have if
               that loop is unrolled, and if the loop is unrolled, it
               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 should have if that loop is
               unrolled, and if the loop is unrolled, it 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 should have if
               that loop is peeled, and if the loop is peeled, it determines
               how many times the loop code is peeled.

           max-peel-times
               The maximum number of peelings of a single loop.

           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-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.

           iv-consider-all-candidates-bound
               Bound on number of candidates for induction variables below
               that all candidates are considered for each use in induction
               variable optimizations.  Only the most relevant candidates are
               considered if there are more candidates, 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 number of candidates in the set is smaller than this value,
               we always try to remove unnecessary ivs from the set during its
               optimization when a new iv is added to the set.

           scev-max-expr-size
               Bound on size of expressions used in the scalar evolutions
               analyzer.  Large expressions slow the analyzer.

           vect-max-version-checks
               The maximum number of runtime checks that can be performed when
               doing loop versioning in the vectorizer.  See option ftree-
               vect-loop-version for more information.

           max-iterations-to-track
               The maximum number of iterations of a loop the brute force
               algorithm for analysis of # of iterations of the loop tries to
               evaluate.

           hot-bb-count-fraction
               Select fraction of the maximal count of repetitions of basic
               block in program given basic block needs to have to be
               considered hot.

           hot-bb-frequency-fraction
               Select fraction of the maximal frequency of executions of basic
               block in function given basic block needs to have to be
               considered hot

           max-predicted-iterations
               The maximum number of loop iterations we predict statically.
               This is useful in cases where function contain single loop with
               known bound and other loop with unknown.  We predict the known
               number of iterations correctly, while the unknown number of
               iterations average to roughly 10.  This means that the loop
               without bounds would appear artificially cold relative to the
               other one.

           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 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 rather hokey argument, as most of the
               duplicates will be 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-ratio
           tracer-min-branch-ratio-feedback
               Stop forward growth if the best edge do have probability lower
               than this threshold.

               Similarly to tracer-dynamic-coverage two values are present,
               one for compilation for profile feedback and one for
               compilation without.  The value for compilation with profile
               feedback needs to be more conservative (higher) in order to
               make tracer effective.

           max-cse-path-length
               Maximum number of basic blocks on path that cse considers.  The
               default is 10.

           max-cse-insns
               The maximum instructions CSE process before flushing. The
               default is 1000.

           global-var-threshold
               Counts the number of function calls (n) and the number of call-
               clobbered variables (v).  If nxv is larger than this limit, a
               single artificial variable will be created to represent all the
               call-clobbered variables at function call sites.  This
               artificial variable will then be made to alias every call-
               clobbered variable.  (done as "int * size_t" on the host
               machine; beware overflow).

           max-aliased-vops
               Maximum number of virtual operands allowed to represent aliases
               before triggering the alias grouping heuristic.  Alias grouping
               reduces compile times and memory consumption needed for
               aliasing at the expense of precision loss in alias information.

           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
               which 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 compile time increase with
               probably slightly better performance.  The default value is
               100.

           max-cselib-memory-locations
               The maximum number of memory locations cselib should take into
               account.  Increasing values mean more aggressive optimization,
               making the compile time increase with probably slightly better
               performance.  The default value is 500.

           max-flow-memory-locations
               Similar as max-cselib-memory-locations but for dataflow
               liveness.  The default value is 100.

           reorder-blocks-duplicate
           reorder-blocks-duplicate-feedback
               Used by basic block reordering pass to decide whether to use
               unconditional branch or duplicate the code on its destination.
               Code is duplicated when its estimated size is smaller than this
               value multiplied by the estimated size of unconditional jump in
               the hot spots of the program.

               The reorder-block-duplicate-feedback is used only when profile
               feedback is available and may be set to higher values than
               reorder-block-duplicate since information about the hot spots
               is more accurate.

           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.  The default value is 100.

           max-sched-region-blocks
               The maximum number of blocks in a region to be considered for
               interblock scheduling.  The default value is 10.

           max-sched-region-insns
               The maximum number of insns in a region to be considered for
               interblock scheduling.  The default value is 100.

           min-spec-prob
               The minimum probability (in percents) of reaching a source
               block for interblock speculative scheduling.  The default value
               is 40.

           max-sched-extend-regions-iters
               The maximum number of iterations through CFG to extend regions.
               0 - disable region extension, N - do at most N iterations.  The
               default value is 0.

           max-sched-insn-conflict-delay
               The maximum conflict delay for an insn to be considered for
               speculative motion.  The default value is 3.

           sched-spec-prob-cutoff
               The minimal probability of speculation success (in percents),
               so that speculative insn will be scheduled.  The default value
               is 40.

           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.  The default is 10000.

           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's.
               The default value is 256.

           min-virtual-mappings
               Specifies the minimum number of virtual mappings in the
               incremental SSA updater that should be registered to trigger
               the virtual mappings heuristic defined by virtual-mappings-
               ratio.  The default value is 100.

           virtual-mappings-ratio
               If the number of virtual mappings is virtual-mappings-ratio
               bigger than the number of virtual symbols to be updated, then
               the incremental SSA updater switches to a full update for those
               symbols.  The default ratio is 3.

           ssp-buffer-size
               The minimum size of buffers (i.e. arrays) that will receive
               stack smashing protection when -fstack-protection is used.

           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 we will treat in a
               field sensitive manner during pointer analysis.

   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.

       -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 which GCC does not know
           how to 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.

       -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 will be 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 will need to 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.

       -undef
           Do not predefine any system-specific or GCC-specific macros.  The
           standard predefined macros remain defined.

       -I dir
           Add the directory dir to the list of directories to be searched for
           header files.  Directories named by -I are searched before the
           standard system include directories.  If the directory dir is a
           standard system include directory, the option is ignored to ensure
           that the default search order for system directories and the
           special treatment of system headers are not defeated .

       -o file
           Write output to file.  This is the same as specifying file as the
           second non-option argument to cpp.  gcc has a different
           interpretation of a second non-option argument, so you must use -o
           to specify the output file.

       -Wall
           Turns on all optional warnings which are desirable for normal code.
           At present this is -Wcomment, -Wtrigraphs, -Wmultichar and a
           warning about integer promotion causing a change of sign in "#if"
           expressions.  Note that many of the preprocessor's warnings are on
           by default and have no options to control them.

       -Wcomment
       -Wcomments
           Warn whenever a comment-start sequence /* appears in a /* comment,
           or whenever a backslash-newline appears in a // comment.  (Both
           forms have the same effect.)

       -Wtrigraphs
           Most trigraphs in comments cannot affect the meaning of the
           program.  However, a trigraph that would form an escaped newline
           (??/ at the end of a line) can, by changing where the comment
           begins or ends.  Therefore, only trigraphs that would form escaped
           newlines produce warnings inside a comment.

           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.

       -Wtraditional
           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 problematic constructs which
           should be avoided.

       -Wimport
           Warn the first time #import is used.

       -Wundef
           Warn whenever an identifier which is not a macro is encountered in
           an #if directive, outside of defined.  Such identifiers are
           replaced with zero.

       -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 will also warn 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 CPP will report 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

       -Wendif-labels
           Warn whenever an #else or an #endif are followed by text.  This
           usually happens in code of the form

                   #if FOO
                   ...
                   #else FOO
                   ...
                   #endif FOO

           The second and third "FOO" should be in comments, but often are not
           in older programs.  This warning is on by default.

       -Werror
           Make all warnings into hard errors.  Source code which triggers
           warnings will be rejected.

       -Wsystem-headers
           Issue warnings for code in system headers.  These are normally
           unhelpful in finding bugs in your own code, therefore suppressed.
           If you are responsible for the system library, you may want to see
           them.

       -w  Suppress all warnings, including those which GNU CPP issues by
           default.

       -pedantic
           Issue all the mandatory diagnostics listed in the C standard.  Some
           of them are left out by default, since they trigger frequently on
           harmless code.

       -pedantic-errors
           Issue all the mandatory diagnostics, and make all mandatory
           diagnostics into errors.  This includes mandatory diagnostics that
           GCC issues without -pedantic but treats as warnings.

       -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 basename of the source file with any suffix
           replaced with object file suffix.  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 will still be 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 will appear in -MM dependency output.  This is a slight
           change in semantics from GCC versions 3.0 and earlier.

       -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 have sent preprocessed output.

           When used with the driver options -MD or -MMD, -MF overrides the
           default dependency output file.

       -dependency-file
           Like -MF. (APPLE ONLY)

       -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.

       -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, including any
           path, deletes any file suffix such as .c, and appends the
           platform's usual object suffix.  The result is the target.

           An -MT option will set 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 take the basename of the input file 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.

       -fpch-deps
           When using precompiled headers, this flag will cause the
           dependency-output flags to also list the files from the precompiled
           header's dependencies.  If not specified only the precompiled
           header would be 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.
           "<filename>"" in the output to mark the place where the precompiled
           header was found, and its filename.  When -fpreprocessed is in use,

           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.

           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.

       -x c
       -x c++
       -x objective-c
       -x objective-c++
       -x assembler-with-cpp
           Specify the source language: C, C++, Objective-C, Objective-C++, or
           assembly.  This has nothing to do with standards conformance or
           extensions; it merely selects which base syntax to expect.  If you
           give none of these options, cpp will deduce the language from the
           extension of the source file: .c, .cc, .m, .mm, or .S.  Some other
           common extensions for C++ and assembly are also recognized.  If cpp
           does not recognize the extension, it will treat the file as C; this
           is the most generic mode.

           Note: Previous versions of cpp accepted a -lang option which
           selected both the language and the standards conformance level.
           This option has been removed, because it conflicts with the -l
           option.

       -std=standard
       -ansi
           Specify the standard to which the code should conform.  Currently
           CPP knows about C and C++ standards; others may be added in the
           future.

           standard may be one of:

           "iso9899:1990"
           "c89"
               The ISO C standard from 1990.  c89 is the customary shorthand
               for this version of the standard.

               The -ansi option is equivalent to -std=c89.

           "iso9899:199409"
               The 1990 C standard, as amended in 1994.

           "iso9899:1999"
           "c99"
           "iso9899:199x"
           "c9x"
               The revised ISO C standard, published in December 1999.  Before
               publication, this was known as C9X.

           "gnu89"
               The 1990 C standard plus GNU extensions.  This is the default.

           "gnu99"
           "gnu9x"
               The 1999 C standard plus GNU extensions.

           "c++98"
               The 1998 ISO C++ standard plus amendments.

           "gnu++98"
               The same as -std=c++98 plus GNU extensions.  This is the
               default for C++ code.

       -I- Split the include path.  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"".
           This option has been deprecated.

       -nostdinc
           Do not search the standard system directories for header files.
           Only the directories you have specified with -I 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.)

       -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.

       -idirafter dir
           Search dir for header files, but do it after all directories
           specified with -I and the standard system directories have been
           exhausted.  dir is treated as a system include directory.

       -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 Apple's version of GCC, where it applies
           to both header files and libraries and effectively replaces the
           --sysroot option.  See the --sysroot option for more information.

       -imultilib dir
           Use dir as a subdirectory of the directory containing target-
           specific C++ headers.

       -isystem dir
           Search dir for header files, after all directories specified by -I
           but before the standard system directories.  Mark it as a system
           directory, so that it gets the same special treatment as is applied
           to the standard system directories.

       -iquote dir
           Search dir only for header files requested with "#include "file"";
           they are not searched for "#include <file>", before all directories
           specified by -I and before the standard system directories.

       -fdollars-in-identifiers
           Accept $ in identifiers.

       -fextended-identifiers
           Accept universal character names in identifiers.  This option is
           experimental; in a future version of GCC, it will be enabled by
           default for C99 and C++.

       -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.

       -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.

       -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 UTF-32 or UTF-16, whichever
           corresponds to the width of "wchar_t".  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.

       -fworking-directory
           Enable generation of linemarkers in the preprocessor output that
           will let the compiler know the current working directory at the
           time of preprocessing.  When this option is enabled, the
           preprocessor will emit, after the initial linemarker, a second
           linemarker with the current working directory followed by two
           slashes.  GCC will use 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.

       -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.

       -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.

       -dCHARS
           CHARS is a sequence of one or more of the following characters, and
           must not be preceded by a space.  Other characters are interpreted
           by the compiler proper, or reserved for future versions of GCC, and
           so are silently ignored.  If you specify characters whose behavior
           conflicts, the result is undefined.

           M   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

               will show all the predefined macros.

               If you use -dM without the -E option, -dM is interpreted as a
               synonym for -fdump-rtl-mach.

           D   Like M 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.

           N   Like D, but emit only the macro names, not their expansions.

           I   Output #include directives in addition to the result of
               preprocessing.

       -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.

       -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.

       -traditional-cpp
           Try to imitate the behavior of old-fashioned C preprocessors, as
           opposed to ISO C preprocessors.

       -trigraphs
           Process trigraph sequences.  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.  By default, GCC ignores
           trigraphs, but in standard-conforming modes it converts them.  See
           the -std and -ansi options.

           The nine trigraphs and their replacements are

                   Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
                   Replacement:      [    ]    {    }    #    \    ^    |    ~

       -remap
           Enable special code to work around file systems which only permit
           very short file names, such as MS-DOS.

       --help
       --target-help
           Print text describing all the command line options instead of
           preprocessing anything.

       -v  Verbose mode.  Print out GNU CPP's version number at the beginning
           of execution, and report the final form of the include path.

       -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 ...! .

       -version
       --version
           Print out GNU CPP's version number.  With one dash, proceed to
           preprocess as normal.  With two dashes, exit immediately.

   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 which GCC does not know
           how to 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.

       In addition to the options listed below, Apple's GCC also accepts and
       passes nearly all of the options defined by the linker ld and by the
       library tool libtool.  Common options include -framework, -dynamic,
       -bundle, -flat_namespace, and so forth.  See the ld and libtool man
       pages for further details.

       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.

       -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.)

           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.

           The linker searches a standard list of directories for the library,
           which is actually a file named liblibrary.a.  The linker then uses
           this file as if it had been specified precisely by name.

           The directories searched include several standard system
           directories plus any that you specify with -L.

           Normally the files found this way are library files---archive files
           whose members are object files.  The linker handles an archive file
           by scanning through it for members which define symbols that have
           so far been referenced but not defined.  But if the file that is
           found is an ordinary object file, it is linked in the usual
           fashion.  The only difference between using an -l option and
           specifying a file name is that -l surrounds library with lib and .a
           and searches several directories.

       -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 or
           -nodefaultlibs is used.

       -nodefaultlibs
           Do not use the standard system libraries when linking.  Only the
           libraries you specify will be passed to the linker.  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.

       -nostdlib
           Do not use the standard system startup files or libraries when
           linking.  No startup files and only the libraries you specify will
           be passed to the linker.  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 that
           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.  (For example, __main, used to ensure C++
           constructors will be called.)

       -pie
           Produce a position independent executable on targets which support
           it.  For predictable results, you must also specify the same set of
           options that were used to generate code (-fpie, -fPIE, or model
           suboptions) when you specify this option.

       -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 prevents linking with
           the shared libraries.  On other systems, this option has no effect.

           This option will not work on Mac OS X unless all libraries
           (including libgcc.a) have also been compiled with -static.  Since
           neither a static version of libSystem.dylib nor crt0.o are
           provided, this option is not useful to most people.

       -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
           that were used to generate code (-fpic, -fPIC, or model suboptions)
           when you specify this option.[1]

           This option is not supported on Mac OS X.

       -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++ and GCJ drivers automatically add -shared-libgcc
           whenever you build a shared library or a main executable, because
           C++ and Java 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 will not always be 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 will link the shared version of libgcc into
           shared libraries by default.  Otherwise, it will take advantage of
           the linker and optimize 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++ or GCJ driver, as
           appropriate for the languages used in the program, or using the
           option -shared-libgcc, such that it is linked with the shared
           libgcc.

       -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.

       -Xlinker option
           Pass option as an option to the linker.  You can use this to supply
           system-specific linker options which GCC does not know how to
           recognize.

           If you want to pass an option that takes an 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.

       -Wl,option
           Pass option as an option to the linker.  If option contains commas,
           it is split into multiple options at the commas.

       -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.

   Options for Directory Search
       These options specify directories to search for header files, for
       libraries and for parts of the compiler:

       -Idir
           Add the directory dir to the head of the list of directories to be
           searched for header files.  This can be used to override a system
           header file, substituting your own version, since these directories
           are searched before the 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).  If
           you use more than one -I option, the directories are scanned in
           left-to-right order; the standard system directories come after.

           If a standard system include directory, or a directory specified
           with -isystem, is also specified with -I, the -I option will be
           ignored.  The directory will still be 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.

           The option -iwithsysroot (APPLE ONLY), if specified with an
           absolute path, will prepend the system root directory (if
           applicable) to the path and add it to the beginning of the system
           search paths.  If specified with a relative path, -iwithsysroot
           will behave identically to -isystem.

       -iquotedir
           Add the directory dir to the head of the list of directories to be
           searched for header files only for the case of #include "file";
           they are not searched for #include <file>, otherwise just like -I.

       -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 each subprogram to be run, the compiler driver first tries the
           -B prefix, if any.  If that name is not found, or if -B was not
           specified, the driver tries two standard prefixes, which are
           /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 will check to see if the path provided by the -B
           refers to a directory, and if necessary it will add 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
           includes 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 run-time 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 will be replaced
           by [dir/]include.  This is to help with boot-strapping the
           compiler.

       -specs=file
           Process file after the compiler reads in the standard specs file,
           in order to override the defaults that 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.

       --sysroot=dir
           Use dir as the logical root directory for headers and libraries.
           For example, if the compiler would normally search for headers in
           /usr/include and libraries in /usr/lib, it will instead search
           dir/usr/include and dir/usr/lib.

           With Apple's version of GCC, this option is effectively replaced by
           -isysroot, which you should use instead of --sysroot.  For other
           (non-Apple) versions of GCC, if you use both this option and the
           -isysroot option, then the --sysroot option will apply to
           libraries, but the -isysroot option will apply 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 will still work, but
           the library aspect will not.

       -I- This option has been deprecated.  Please use -iquote instead for -I
           directories before the -I- and remove the -I-.  Any directories you
           specify with -I options before the -I- option are searched only for
           the case of #include "file"; they are not searched for #include
           <file>.

           If additional directories are specified with -I options after the
           -I-, these directories are searched for all #include directives.
           (Ordinarily all -I directories are used this way.)

           In addition, the -I- option inhibits the use of the current
           directory (where the current input file came from) as the first
           search directory for #include "file".  There is no way to override
           this effect of -I-.  With -I. you can specify searching the
           directory which was current when the compiler was invoked.  That is
           not exactly the same as what the preprocessor does by default, but
           it is often satisfactory.

           -I- does not inhibit the use of the standard system directories for
           header files.  Thus, -I- and -nostdinc are independent.

   Specifying Target Machine and Compiler Version
       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
       version other than the one that was installed last.  Sometimes this is
       inconvenient, so GCC provides options that will switch to another
       cross-compiler or version.

       -b machine
           The argument machine specifies the target machine for compilation.

           The value to use for machine is the same as was specified as the
           machine type when configuring GCC as a cross-compiler.  For
           example, if a cross-compiler was configured with configure arm-elf,
           meaning to compile for an arm processor with elf binaries, then you
           would specify -b arm-elf to run that cross compiler.  Because there
           are other options beginning with -b, the configuration must contain
           a hyphen.

       -V version
           The argument version specifies which version of GCC to run.  This
           is useful when multiple versions are installed.  For example,
           version might be 4.0, meaning to run GCC version 4.0.

       The -V and -b options work by running the <machine>-gcc-<version>
       executable, so there's no real reason to use them if you can just run
       that directly.

   Hardware Models and Configurations
       Earlier we discussed the standard option -b which chooses among
       different installed compilers for completely different target machines,
       such as VAX vs. 68000 vs. 80386.

       In addition, each of these target machine types can have its own
       special options, starting with -m, to choose among various hardware
       models or configurations---for example, 68010 vs 68020, floating
       coprocessor or none.  A single installed version of the compiler can
       compile for any model or configuration, according to the options
       specified.

       Some configurations of the compiler also support additional special
       options, usually for compatibility with other compilers on the same
       platform.

       ARM Options

       These -m options are defined for Advanced RISC Machines (ARM)
       architectures:

       -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 will cause the stack frames
           not to be generated for leaf functions.  The default is
           -mno-apcs-frame.

       -mapcs
           This is a synonym for -mapcs-frame.

       -mapcs-stack-check
           Generate code to check the amount of stack space available upon
           entry to every function (that actually uses some stack space).  If
           there is insufficient space available then either the function
           __rt_stkovf_split_small or __rt_stkovf_split_big will be called,
           depending upon the amount of stack space required.  The run time
           system is required to provide these functions.  The default is
           -mno-apcs-stack-check, since this produces smaller code.

       -mapcs-float
           Pass floating point arguments using the float point registers.
           This is one of the variants of the APCS.  This option is
           recommended if the target hardware has a floating point unit or if
           a lot of floating point arithmetic is going to be performed by the
           code.  The default is -mno-apcs-float, since integer only code is
           slightly increased in size if -mapcs-float is used.

       -mapcs-reentrant
           Generate reentrant, position independent code.  The default is
           -mno-apcs-reentrant.

       -mthumb-interwork
           Generate code which supports calling between the ARM and Thumb
           instruction sets.  Without this option 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.

       -mno-sched-prolog
           Prevent the reordering of instructions in the function prolog, or
           the merging of those instruction with the instructions in the
           function's body.  This means that all functions will 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 if functions inside an executable
           piece of code.  The default is -msched-prolog.

       -mhard-float
           Generate output containing floating point instructions.  This is
           the default.

       -msoft-float
           Generate output containing library calls for floating point.
           Warning: the requisite libraries are not available for all ARM
           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.

       -mfloat-abi=name
           Specifies which ABI to use for floating point values.  Permissible
           values are: soft, softfp and hard.

           soft and hard are equivalent to -msoft-float and -mhard-float
           respectively.  softfp allows the generation of floating point
           instructions, but still uses the soft-float calling conventions.

       -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.

       -mwords-little-endian
           This option only applies when generating code for big-endian
           processors.  Generate code for a little-endian word order but a
           big-endian byte order.  That is, a byte order of the form 32107654.
           Note: this option should only be used if you require compatibility
           with code for big-endian ARM processors generated by versions of
           the compiler prior to 2.8.

       -mcpu=name
           This specifies the name of the target ARM processor.  GCC uses this
           name to determine what kind of instructions it can emit when
           generating assembly code.  Permissible names are: arm2, arm250,
           arm3, arm6, arm60, arm600, arm610, arm620, arm7, arm7m, arm7d,
           arm7dm, arm7di, arm7dmi, arm70, arm700, arm700i, arm710, arm710c,
           arm7100, arm7500, arm7500fe, arm7tdmi, arm7tdmi-s, arm8, strongarm,
           strongarm110, strongarm1100, 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,
           arm1176jz-s, arm1176jzf-s, xscale, iwmmxt, ep9312.

       -mtune=name
           This option is very similar to the -mcpu= option, except that
           instead of specifying the actual target processor type, and hence
           restricting which instructions can be used, it specifies that GCC
           should tune the performance of the code as if the target were of
           the type specified in this option, but still choosing the
           instructions that it will generate based on the cpu specified by a
           -mcpu= option.  For some ARM implementations better performance can
           be obtained by using this option.

       -march=name
           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:
           armv2, armv2a, armv3, armv3m, armv4, armv4t, armv5, armv5t,
           armv5te, armv6, armv6j, iwmmxt, ep9312.

       -mfpu=name
       -mfpe=number
       -mfp=number
           This specifies what floating point hardware (or hardware emulation)
           is available on the target.  Permissible names are: fpa, fpe2,
           fpe3, maverick, vfp.  -mfp and -mfpe are synonyms for
           -mfpu=fpenumber, for compatibility with older versions of GCC.

           If -msoft-float is specified this specifies the format of floating
           point values.

       -mstructure-size-boundary=n
           The size of all structures and unions will be 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 the 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.

       -mabort-on-noreturn
           Generate a call to the function "abort" at the end of a "noreturn"
           function.  It will be 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 will lie 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 will be
           turned into long calls.  The heuristic is that static functions,
           functions which have the short-call attribute, functions that are
           whose definitions have already been compiled within the current
           compilation unit, will not be turned into long calls.  The
           exception to this rule is that weak function definitions, functions
           with the long-call attribute or the section attribute, and
           directive, will always be turned into long calls.

           This feature is not enabled by default.  Specifying -mno-long-calls
           will restore the default behavior, as will placing the function
           these switches have no effect on how the compiler generates code to
           handle function calls via function pointers.

       -mnop-fun-dllimport
           Disable support for the "dllimport" attribute.

       -msingle-pic-base
           Treat the register used for PIC addressing as read-only, rather
           than loading it in the prologue for each function.  The run-time
           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.  The default is
           R10 unless stack-checking is enabled, when R9 is used.

       -mcirrus-fix-invalid-insns
           Insert NOPs into the instruction stream to in order to work around
           problems with invalid Maverick instruction combinations.  This
           option is only valid if the -mcpu=ep9312 option has been used to
           enable generation of instructions for the Cirrus Maverick floating
           point co-processor.  This option is not enabled by default, since
           the problem is only present in older Maverick implementations.  The
           default can be re-enabled by use of the
           -mno-cirrus-fix-invalid-insns switch.

       -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
           Generate code for the 16-bit Thumb instruction set.  For ARMv7, the
           default is to use the THUMB2 instruction set. For all other
           architectures, the default is to use the 32-bit ARM instruction
           set. The ARM instruction set may be explicitly selected via
           -mno-thumb or -marm.

       -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.

       -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.

       -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.

       -mms-bitfields
           Set the default structure layout to be compatible with the
           Microsoft compiler standard. This is equivalent to adding an
           "ms_struct" attribute to each structure and union tag definition.
           The default is mno-ms-bitfields.

       Darwin Options

       These options are defined for all architectures running the Darwin
       operating system.

       FSF GCC on Darwin does not create "universal" object files; it will
       create an object file for the single architecture that it was built to
       target.  Apple's GCC on Darwin does create "universal" 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 targetting,
       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, will only permit instructions to be used
       that are valid for the subtype of the file it is generating, so you
       cannot put 64-bit instructions in an ppc750 object file.  The linker
       for shared libraries, /usr/bin/libtool, will fail and print 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, will quietly give
       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 will be
           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 effect is to not warn about constructs contained within
           header files found via dir.

       -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.

           This value can also be set with the MACOSX_DEPLOYMENT_TARGET
           environment variable.  If both the command-line option is specified
           and the environment variable is set, the command-line option will
           take precedence.

           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 which
           are compatible with as many systems and code bases as possible.

           This value is not set by default for ARM targets.

       -miphoneos-version-min=version
           The earliest version of iPhone OS that this executable will run on
           is version.

           This value can also be set with the IPHONEOS_DEPLOYMENT_TARGET
           environment variable.  If both the command-line option is specified
           and the environment variable is set, the command-line option will
           take precedence.

           On ARM targets, if not specified by the command-line option or
           environment variable, this value defaults to 2.0.

       -mkernel
           Enable kernel development mode.  The -mkernel option sets -static,
           -fno-common, -fno-builtin, -fno-cxa-atexit, -fno-exceptions,
           -fno-non-call-exceptions, -fno-asynchronous-unwind-tables,
           -fapple-kext, -fno-weak and -fno-rtti where applicable.  This mode
           also sets -mno-altivec, -msoft-float and -mlong-branch for PowerPC
           targets, -mno-red-zone on x86_64, and -mlong-branch for ARM
           targets.  Of these, only -msoft-float can be changed which is
           useful in a kext that wishes to use the hardware floating point
           unit.  -dynamic can be used to override the effects of -static on
           the assembler to enable the use of weak_import.

       -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 turn around development.  Needed to
           enable gdb to dynamically load ".o" files into already running
           programs.  -findirect-data and -ffix-and-continue are provided for
           backwards compatibility.

       -fapple-kext
       -findirect-virtual-calls
       -fterminated-vtables
           Alter vtables, destructors, and other implementation details to
           more closely resemble the GCC 2.95 ABI for PowerPC and 32-bit i386.
           This is to make kernel extensions loadable by Darwin kernels, and
           is required to build any Darwin kernel extension.  In addition,
           virtual calls are not made directly, instead, code is generated to
           always go through the virtual table, as virtual tables can be
           patched by the kernel module loader.  Vtables are altered by adding
           a zero word at the end of every vtable.  -findirect-virtual-calls
           and -fterminated-vtables are accepted for backwards compatibility
           but will be removed in the future.  Additionally implies most of
           -mkernel except for -msoft-float and -mlong-branch for PowerPC
           targets.  (APPLE ONLY)

       -mpascal-strings
           Allow Pascal-style string literals to be constructed.  This option
           implies -Wpointer-sign so that conversions between Pascal-style
           strings and C-style strings are warned about.  (APPLE ONLY)

       -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 be loading the build
           output file being linked.  See man ld(1) for more information.

       -dynamiclib
           When passed this option, GCC will produce 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.

       -force_load  library_name
           Loads all members of named static archive library.  See man ld(1)
           for more information.

       -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.

       Intel 386 and AMD x86-64 Options

       These -m options are defined for the i386 and x86-64 family of
       computers:

       -mtune=cpu-type
           Tune to cpu-type everything applicable about the generated code,
           except for the ABI and the set of available instructions.  The
           choices for cpu-type are:

           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 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, the code generated option will change to
               reflect the processors that were most common when that version
               of GCC was 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.

           native
               This selects the CPU to tune for at compilation time by
               determining the processor type of the compiling machine.  Using
               -mtune=native will produce code optimized for the local machine
               under the constraints of the selected instruction set.  Using
               -march=native will enable all instruction subsets supported by
               the local machine (hence the result might not run on different
               machines).

           i386
               Original Intel's i386 CPU.

           i486
               Intel's i486 CPU.  (No scheduling is implemented for this
               chip.)

           i586, pentium
               Intel Pentium CPU with no MMX support.

           pentium-mmx
               Intel PentiumMMX CPU based on Pentium core with MMX instruction
               set support.

           pentiumpro
               Intel PentiumPro CPU.

           i686
               Same as "generic", but when used as "march" option, PentiumPro
               instruction set will be used, so the code will run on all i686
               family chips.

           pentium2
               Intel Pentium2 CPU based on PentiumPro core with MMX
               instruction set support.

           pentium3, pentium3m
               Intel Pentium3 CPU based on PentiumPro core with MMX and SSE
               instruction set support.

           pentium-m
               Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2
               instruction set support.  Used by Centrino notebooks.

           pentium4, pentium4m
               Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set
               support.

           prescott
               Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and
               SSE3 instruction set support.

           nocona
               Improved version of Intel Pentium4 CPU with 64-bit extensions,
               MMX, SSE, SSE2 and SSE3 instruction set support.

           core2
               Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3
               and SSSE3 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
               AMD K8 core based CPUs with x86-64 instruction set support.
               (This supersets MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! 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 Winchip2 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 CPU with MMX and SSE instruction set support.  (No
               scheduling is implemented for this chip.)

           While picking a specific cpu-type will schedule things
           appropriately for that particular chip, the compiler will not
           generate any code that does not run on the i386 without the
           -march=cpu-type option being used.

       -march=cpu-type
           Generate instructions for the machine type cpu-type.  The choices
           for cpu-type are the same as for -mtune.  Moreover, specifying
           -march=cpu-type implies -mtune=cpu-type.

       -mcpu=cpu-type
           A deprecated synonym for -mtune.

       -m386
       -m486
       -mpentium
       -mpentiumpro
           These options are synonyms for -mtune=i386, -mtune=i486,
           -mtune=pentium, and -mtune=pentiumpro respectively.  These synonyms
           are deprecated.

       -mfpmath=unit
           Generate floating point arithmetics for selected unit unit.  The
           choices for unit are:

           387 Use the standard 387 floating point coprocessor present
               majority of chips and emulated otherwise.  Code compiled with
               this option will run almost everywhere.  The temporary results
               are computed in 80bit precision instead of 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 i386 compiler.

           sse Use scalar floating point instructions present in the SSE
               instruction set.  This instruction set is supported by Pentium3
               and newer chips, in the AMD line by Athlon-4, Athlon-xp and
               Athlon-mp chips.  The earlier version of SSE instruction set
               supports only single precision arithmetics, thus the double and
               extended precision arithmetics is still done using 387.  Later
               version, present only in Pentium4 and the future AMD x86-64
               chips supports double precision arithmetics too.

               For the i386 compiler, you need to 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 80bit.

               This is the default choice for the x86-64 compiler.

           sse,387
               Attempt to utilize both instruction sets at once.  This
               effectively double 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 instable
               performance.

       -masm=dialect
           Output asm instructions using selected dialect.  Supported choices
           are intel or att (the default one).  Darwin does not support intel.

       -mieee-fp
       -mno-ieee-fp
           Control whether or not the compiler uses IEEE floating point
           comparisons.  These handle correctly the case where the result of a
           comparison is unordered.

       -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
           can't 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 the default on FreeBSD, OpenBSD
           and NetBSD.  This option is overridden when -march indicates that
           the target cpu will always have an FPU and so the instruction will
           not need emulation.  As of revision 2.6.1, 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 will produce 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 will be aligned differently than the
           published application binary interface specifications for the 386
           and will not be 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 i386
           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) would prefer "long double"
           to be aligned to an 8 or 16 byte boundary.  In arrays or structures
           conforming to the ABI, this would not be possible.  So specifying a
           -m128bit-long-double will align "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 to be 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, the
           structures and arrays containing "long double" variables will
           change their size as well as function calling convention for
           function taking "long double" will be modified.  Hence they will
           not be binary compatible with arrays or structures in code compiled
           without that switch.

       -mmlarge-data-threshold=number
           When -mcmodel=medium is specified, the data greater than threshold
           are placed in large data section.  This value must be the same
           across all object linked into the binary and defaults to 65535.

       -msvr3-shlib
       -mno-svr3-shlib
           Control whether GCC places uninitialized local variables into the
           "bss" or "data" segments.  -msvr3-shlib places them into "bss".
           These options are meaningful only on System V Release 3.

       -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 will be generated for calls to those functions.

           In addition, seriously incorrect code will result 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.

       -mstackrealign
           Realign the stack at entry.  On the Intel x86, the -mstackrealign
           option will generate an alternate prologue and epilogue that
           realigns the runtime stack.  This supports mixing legacy codes that
           keep a 4-byte aligned stack with modern codes that keep a 16-byte
           stack for SSE compatibility.  The alternate prologue and epilogue
           are slower and bigger than the regular ones, and the alternate
           prologue requires an extra scratch register; this lowers the number
           of registers available if used in conjunction with the "regparm"
           attribute.  The -mstackrealign option is incompatible with the
           nested function prologue; this is considered a hard error.  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).

           On Pentium and PentiumPro, "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 will most likely misalign 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
       -mno-mmx
       -msse
       -mno-sse
       -msse2
       -mno-sse2
       -msse3
       -mno-sse3
       -mssse3
       -mno-ssse3
       -msse4.1
       -mno-sse4.1
       -msse4.2
       -mno-sse4.2
       -msse4
       -mno-sse4
       -msse4a
       -mno-sse4a
       -m3dnow
       -mno-3dnow
           These switches enable or disable the use of instructions in the
           MMX, SSE, SSE2, SSE3, SSSE3, 3Dnow, SSE4.1, SSE4.2, and SSE4A
           extended instruction sets.  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 have SSE/SSE2 instructions generated automatically from
           floating-point code (as opposed to 387 instructions), see
           -mfpmath=sse.

           These options will enable GCC to use these extended instructions in
           generated code, even without -mfpmath=sse.  Applications which
           perform runtime 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.

       -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 will be computed in the function prologue.  This is
           faster on most modern CPUs because of reduced dependencies,
           improved scheduling and reduced stack usage when 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 Mingw32.  Code that
           relies 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.

       -mno-align-stringops
           Do not align 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 destination is
           known to be aligned at least to 4 byte boundary.  This enables more
           inlining, increase code size, but may improve performance of code
           that depends on fast memcpy, strlen and memset for short lengths.

       -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-frame-pointer removes the frame pointer for all
           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 legal depends on the operating system, and whether it maps the
           segment to cover the entire TLS area.

           For systems that use GNU libc, the default is on.

       These -m switches are supported in addition to the above on AMD x86-64
       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 and generates
           code that runs on any i386 system.  The 64-bit environment sets int
           to 32 bits and long and pointer to 64 bits and generates code for
           AMD's x86-64 architecture. For darwin only the -m64 option turns
           off the -fno-pic and -mdynamic-no-pic options.

       -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 will not be 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 but symbols can be located anywhere
           in the address space.  Programs can be statically or dynamically
           linked, but building of shared libraries are not supported with the
           medium model.

       -mcmodel=large
           Generate code for the large model: This model makes no assumptions
           about addresses and sizes of sections.  Currently GCC does not
           implement this model.

       -mms-bitfields
           Set the default structure layout to be compatible with the
           Microsoft compiler standard. This is equivalent to adding an
           "ms_struct" attribute to each structure and union tag definition.
           The default is mno-ms-bitfields.

       PowerPC Options

       These are listed under

       IBM RS/6000 and PowerPC Options

       These -m options are defined for the IBM RS/6000 and PowerPC:

       -mpower
       -mno-power
       -mpower2
       -mno-power2
       -mpowerpc
       -mno-powerpc
       -mpowerpc-gpopt
       -mno-powerpc-gpopt
       -mpowerpc-gfxopt
       -mno-powerpc-gfxopt
       -mpowerpc64
       -mno-powerpc64
       -mmfcrf
       -mno-mfcrf
       -mpopcntb
       -mno-popcntb
       -mfprnd
       -mno-fprnd
           GCC supports two related instruction set architectures for the
           RS/6000 and PowerPC.  The POWER instruction set are those
           instructions supported by the rios chip set used in the original
           RS/6000 systems and the PowerPC instruction set is the architecture
           of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and the
           IBM 4xx, 6xx, and follow-on microprocessors.

           Neither architecture is a subset of the other.  However there is a
           large common subset of instructions supported by both.  An MQ
           register is included in processors supporting the POWER
           architecture.

           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.

           The -mpower option allows GCC to generate instructions that are
           found only in the POWER architecture and to use the MQ register.
           Specifying -mpower2 implies -power and also allows GCC to generate
           instructions that are present in the POWER2 architecture but not
           the original POWER architecture.

           The -mpowerpc option allows GCC to generate instructions that are
           found only in the 32-bit subset of the PowerPC architecture.
           Specifying -mpowerpc-gpopt implies -mpowerpc and also allows GCC to
           use the optional PowerPC architecture instructions in the General
           Purpose group, including floating-point square root.  Specifying
           -mpowerpc-gfxopt implies -mpowerpc and also 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 -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 -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.

           If you specify both -mno-power and -mno-powerpc, GCC will use only
           the instructions in the common subset of both architectures plus
           some special AIX common-mode calls, and will not use the MQ
           register.  Specifying both -mpower and -mpowerpc permits GCC to use
           any instruction from either architecture and to allow use of the MQ
           register; specify this for the Motorola MPC601.

       -mnew-mnemonics
       -mold-mnemonics
           Select which mnemonics to use in the generated assembler code.
           With -mnew-mnemonics, GCC uses the assembler mnemonics defined for
           the PowerPC architecture.  With -mold-mnemonics it uses the
           assembler mnemonics defined for the POWER architecture.
           Instructions defined in only one architecture have only one
           mnemonic; GCC uses that mnemonic irrespective of which of these
           options is specified.

           GCC defaults to the mnemonics appropriate for the architecture in
           use.  Specifying -mcpu=cpu_type sometimes overrides the value of
           these option.  Unless you are building a cross-compiler, you should
           normally not specify either -mnew-mnemonics or -mold-mnemonics, but
           should instead accept the default.

       -mcpu=cpu_type
           Set architecture type, register usage, choice of mnemonics, and
           instruction scheduling parameters for machine type cpu_type.
           Supported values for cpu_type are 401, 403, 405, 405fp, 440, 440fp,
           505, 601, 602, 603, 603e, 604, 604e, 620, 630, 740, 7400, 7450,
           750, 801, 821, 823, 860, 970, 8540, ec603e, G3, G4, G5, power,
           power2, power3, power4, power5, power5+, power6, common, powerpc,
           powerpc64, rios, rios1, rios2, rsc, and rs64.

           -mcpu=common selects a completely generic processor.  Code
           generated under this option will run on any POWER or PowerPC
           processor.  GCC will use only the instructions in the common subset
           of both architectures, and will not use the MQ register.  GCC
           assumes a generic processor model for scheduling purposes.

           -mcpu=power, -mcpu=power2, -mcpu=powerpc, and -mcpu=powerpc64
           specify generic POWER, POWER2, pure 32-bit PowerPC (i.e., not
           MPC601), and 64-bit PowerPC architecture machine types, with an
           appropriate, generic processor model assumed for scheduling
           purposes.

           The other options specify a specific processor.  Code generated
           under those options will run 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,
           -mnew-mnemonics, -mpopcntb, -mpower, -mpower2, -mpowerpc64,
           -mpowerpc-gpopt, -mpowerpc-gfxopt, -mstring, -mmulhw, -mdlmzb.  The
           particular options set for any particular CPU will vary 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, register usage, or
           choice of mnemonics, as -mcpu=cpu_type would.  The same values for
           cpu_type are used for -mtune as for -mcpu.  If both are specified,
           the code generated will use the architecture, registers, and
           mnemonics set by -mcpu, but the scheduling parameters set by
           -mtune.

       -mswdiv
       -mno-swdiv
           Generate code to compute division as reciprocal estimate and
           iterative refinement, creating opportunities for increased
           throughput.  This feature requires: optional PowerPC Graphics
           instruction set for single precision and FRE instruction for double
           precision, assuming divides cannot generate user-visible traps, and
           the domain values not include Infinities, denormals or zero
           denominator.

       -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.

       -mpim-altivec
       -mno-pim-altivec
           Enable (or disable) built-in compiler support for the syntactic
           extensions as well as operations and predicates defined in the
           Motorola AltiVec Technology Programming Interface Manual (PIM).
           This includes the recognition of "vector" and "pixel" as (context-
           dependent) keywords, the definition of built-in functions such as
           "vec_add", and the use of parenthesized comma expression as AltiVec
           literals.  Note that unlike the option -maltivec, the extension
           does not require the inclusion of any special header files; if
           "<altivec.h>" is included, a warning will be issued and the
           contents of the header will be ignored.  The preprocessor shall
           provide an "__APPLE_ALTIVEC__" manifest constant when -mpim-altivec
           is specified.  (APPLE ONLY)

           In addition, the -mpim-altivec option disables the inlining of
           functions containing AltiVec instructions into functions that do
           not make use of the vector unit.  Certain other optimizations, such
           as inline vectorization of "memset" and "memcpy" calls, are also
           disabled.  These adjustments make it possible to compile programs
           whose use of AltiVec instructions is preceded by a run-time check
           for the presence of AltiVec functionality, and that can therefore
           be made to run on G3 processors.  Note that all of these
           optimizations may be re-enabled by supplying the -maltivec option,
           or an -mcpu option specifying a processor that supports AltiVec
           instructions.

       -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-exec .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.

       -misel=yes/no
           This switch has been deprecated.  Use -misel and -mno-isel instead.

       -mspe
       -mno-spe
           This switch enables or disables the generation of SPE simd
           instructions.

       -mspe=yes/no
           This option has been deprecated.  Use -mspe and -mno-spe instead.

       -mfloat-gprs=yes/single/double/no
       -mfloat-gprs
           This switch enables or disables the generation of floating point
           operations on the general purpose registers for architectures that
           support it.

           The argument yes or single enables the use of single-precision
           floating point operations.

           The argument double enables the use of single and double-precision
           floating point operations.

           The argument no disables floating point operations on the general
           purpose registers.

           This option is currently only available on the MPC854x.

       -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 will allocate at least one TOC entry
           for each unique non-automatic variable reference in your program.
           GCC will also place 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 will produce 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 and -mpowerpc, 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 which
           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.

           (APPLE ONLY) While the -msoft-float option is supported, the
           libraries that do the floating point emulation are not shipped on
           Apple PowerPCs, with the effect that the emulation does not work.
           However, the option may be useful for a different reason.  Normally
           the compiler can use floating point registers in contexts where you
           might not expect it, for example, to copy data from one memory
           location to another.  The -msoft-float option will prevent it from
           doing this.

       -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 the instructions usage in little endian
           mode.

       -mstring
       -mno-string
           Generate code that uses (does not use) the load string instructions
           and the store string word instructions to save multiple registers
           and do small block moves.  These instructions are generated by
           default on POWER systems, and not generated on PowerPC systems.  Do
           not use -mstring 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 the
           instructions usage 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.

       -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 is used.

       -mmulhw
       -mno-mulhw
           Generate code that uses (does not use) the half-word multiply and
           multiply-accumulate instructions on the IBM 405 and 440 processors.
           These instructions are generated by default when targetting those
           processors.

       -mdlmzb
       -mno-dlmzb
           Generate code that uses (does not use) the string-search dlmzb
           instruction on the IBM 405 and 440 processors.  This instruction is
           generated by default when targetting 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 would be aligned to a 4 byte
           boundary and have a size of 4 bytes.  By using -mno-bit-align, the
           structure would be aligned to a 1 byte boundary and be one byte in
           size.

       -mno-strict-align
       -mstrict-align
           On System V.4 and embedded PowerPC systems do not (do) assume that
           unaligned memory references will be handled by the system.

       -mrelocatable
       -mno-relocatable
           On embedded PowerPC systems generate code that allows (does not
           allow) the program to be relocated to a different address at
           runtime.  If you use -mrelocatable on any module, all objects
           linked together must be compiled with -mrelocatable or
           -mrelocatable-lib.

       -mrelocatable-lib
       -mno-relocatable-lib
           On embedded PowerPC systems generate code that allows (does not
           allow) the program to be relocated to a different address at
           runtime.  Modules compiled with -mrelocatable-lib can be linked
           with either modules compiled without -mrelocatable and
           -mrelocatable-lib or with modules compiled with 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.

       -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 0/1/2 to assign
           no/highest/second-highest 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
           which latency >= number is costly.

       -minsert-sched-nops=scheme
           This option controls which nop insertion scheme will be 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 which 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 adheres 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
           Specify both -mcall-sysv and -meabi options.

       -mcall-sysv-noeabi
           Specify both -mcall-sysv and -mno-eabi options.

       -mcall-solaris
           On System V.4 and embedded PowerPC systems compile code for the
           Solaris operating system.

       -mcall-linux
           On System V.4 and embedded PowerPC systems compile code for the
           Linux-based GNU system.

       -mcall-gnu
           On System V.4 and embedded PowerPC systems compile code for the
           Hurd-based GNU system.

       -mcall-netbsd
           On System V.4 and embedded PowerPC systems compile code for the
           NetBSD operating system.

       -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, spe, no-spe,
           ibmlongdouble, ieeelongdouble.

       -mabi=spe
           Extend the current ABI with SPE ABI extensions.  This does not
           change the default ABI, instead it adds the SPE ABI extensions to
           the current ABI.

       -mabi=no-spe
           Disable Booke SPE ABI extensions for the current ABI.

       -mabi=ibmlongdouble
           Change the current ABI to use IBM extended precision long double.
           This is a PowerPC 32-bit SYSV ABI option.

       -mabi=ieeelongdouble
           Change the current ABI to use IEEE extended precision long double.
           This is a PowerPC 32-bit Linux ABI option.

       -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 were passed in the floating
           point registers in case the function takes a variable arguments.
           With -mprototype, only calls to prototyped variable argument
           functions will 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.

       -mwindiss
           Specify that you are compiling for the WindISS simulation
           environment.

       -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 to 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, do not call an
           initialization function from "main", and the -msdata option will
           only use "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.

       -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
       -mlong-branch
       -mno-long-branch
           By default assume that all calls are far away so that a longer more
           expensive calling sequence is required.  This is required for calls
           further than 32 megabytes (33,554,432 bytes) from the current
           location.  A short call will be generated if the compiler knows the
           call cannot be that far away.  This setting can be overridden by

           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.

           callee, L42", plus a "branch island" (glue code).  The two target
           addresses represent the callee and the "branch island".  The
           Darwin/PPC linker will prefer the first address and generate a "bl
           callee" if the PPC "bl" instruction will reach the callee directly;
           otherwise, the linker will generate "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, -mlongcall directs the compiler emit to
           the glue for every direct call, and the Darwin linker decides
           whether to use or discard it.  -mlong-branch is a synonym for
           -mlongcall.

           In the future, we may cause GCC to ignore all longcall
           specifications when the linker is known to generate glue.

       -pthread
           Adds support for multithreading with the pthreads library.  This
           option sets flags for both the preprocessor and linker.

       -mms-bitfields
           Set the default structure layout to be compatible with the
           Microsoft compiler standard. This is equivalent to adding an
           "ms_struct" attribute to each structure and union tag definition.
           The default is mno-ms-bitfields.

   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 would be -fno-foo.  In the table below, only one of the forms
       is listed---the one which is not the default.  You can figure out the
       other form by either removing no- or adding it.

       -fbounds-check
           For front-ends that support it, generate additional code to check
           that indices used to access arrays are within the declared range.
           This is currently only supported by the Java and Fortran front-
           ends, where this option defaults to true and false respectively.

       -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.  This option is enabled by
           default for the Java front-end, as required by the Java language
           specification.

       -fexceptions
           Enable exception handling.  Generates extra code needed to
           propagate exceptions.  For some targets, this implies GCC will
           generate 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 will enable it
           by default for languages like C++ which normally require exception
           handling, and disable 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".

       -funwind-tables
           Similar to -fexceptions, except that it will just generate any
           needed static data, but will not affect the generated code in any
           other way.  You will normally not enable this option; instead, a
           language processor that needs this handling would enable it on your
           behalf.

       -fasynchronous-unwind-tables
           Generate unwind table in dwarf2 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).

       -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
           will be equivalent to the smallest integer type which 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-double
           Use the same size for "double" as for "float".

           Warning: the -fshort-double 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.

       -fno-common
           In C, allocate even uninitialized global variables in the data
           section of the object file, rather than generating them as common
           blocks.  This has the effect that if the same variable is declared
           (without "extern") in two different compilations, you will get an
           error when you link them.  The only reason this might be useful is
           if you wish to verify that the program will work on other systems
           which always work this way.

       -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.

       -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 and 32k on the m68k and RS/6000.  The 386 has no such
           limit.)

           Position-independent code requires special support, and therefore
           works only on certain machines.  For the 386, 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
           the 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.

           -fPIC is the default on Darwin and Mac OS X.

       -fpie
       -fPIE
           These options are similar to -fpic and -fPIC, but generated
           position independent code can be only linked into executables.
           Usually these options are used when -pie GCC option will be used
           during linking.

       -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
           which 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.

       -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 will not save and restore the register reg.

           It is an error to used 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 will produce
           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 will save and
           restore the register reg if they use it.

           It is an error to used 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 will produce
           disastrous results.

           A different sort of disaster will result 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 will be 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.

       -finstrument-functions
           Generate instrumentation calls for entry and exit to functions.
           Just after function entry and just before function exit, the
           following profiling functions will be 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 will 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 anyways,
           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 will not be 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).

       -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 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 must do that.  The switch causes generation of
           code to ensure that the operating system sees the stack being
           extended.

       -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 the stack would grow beyond the value, a signal is
           raised.  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.

       -fargument-alias
       -fargument-noalias
       -fargument-noalias-global
       -fargument-noalias-anything
           Specify the possible relationships among parameters and between
           parameters and global data.

           -fargument-alias specifies that arguments (parameters) may alias
           each other and may alias global storage.-fargument-noalias
           specifies that arguments do not alias each other, but may alias
           global storage.-fargument-noalias-global specifies that arguments
           do not alias each other and do not alias global storage.
           -fargument-noalias-anything specifies that arguments do not alias
           any other storage.

           Each language will automatically use whatever option is required by
           the language standard.  You should not need to use these options
           yourself.

       -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".

           The default without -fpic is "initial-exec"; with -fpic the default
           is "global-dynamic".

       -fvisibility=default|internal|hidden|protected
           Set the default ELF image symbol visibility to the specified
           option---all symbols will be 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 ie;
           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 will be "hidden".  The
           default if -fvisibility isn't specified is "default", i.e., make
           every symbol public---this causes the same behavior as previous
           versions of GCC.

           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
           <http://people.redhat.com/~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 DLL's 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
           declarations you wish to set visibility for with (for example)
           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 ie; 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.
           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 will use the PLT, so it is more
           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 will be thrown
           between DSOs must be explicitly marked with default visibility so
           that the type_info nodes will be unified between the DSOs.

           An overview of these techniques, their benefits and how to use them
           is at <http://gcc.gnu.org/wiki/Visibility>.


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 that allow 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 would otherwise be
           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_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 will attempt to figure out an
           appropriate prefix to use based on the pathname it was 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 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 will search
           foo/bar where it would normally search /usr/local/lib/bar.  These
           alternate directories are searched first; the standard directories
           come next.

       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 can't 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 can't 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 will use mblen and mbtowc as defined by the default locale
           to recognize and translate multibyte characters.

       MACOSX_DEPLOYMENT_TARGET
       IPHONEOS_DEPLOYMENT_TARGET
           These variables are used to set the target OS version, as described
           for command-line options -mmacosx-version-min and
           -miphoneos-version-min.  Only one OS version can be specified per
           architecture, with MACOSX_DEPLOYMENT_TARGET taking precedence on
           non-ARM targets and IPHONEOS_DEPLOYMENT_TARGET taking precedence on
           ARM targets.

           If either command-line option -mmacosx-version-min or
           -miphoneos-version-min is specified, both of these environment
           variables are ignored.

       Some additional environments 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.


BUGS

       To report bugs to Apple, see <http://developer.apple.com/bugreporter>.


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),
       adb(1), dbx(1), sdb(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, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
       1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006 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 1.2 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-4.2.1                         2012-06-15                            gcc(1)

Mac OS X 10.8 - Generated Sun Aug 19 18:04:13 CDT 2012
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