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GCC(1)				   GNU Tools				GCC(1)

       gcc, g++ - GNU project C and C++ Compiler (v2.7)

       gcc [ option | filename ]...
       g++ [ option | filename ]...

       The information in this man page is an extract from the full documenta‐
       tion of the GNU C compiler, and	is  limited  to	 the  meaning  of  the

       This  man  page	is  not kept up to date except when volunteers want to
       maintain it.  If you find a discrepancy between the man	page  and  the
       software,  please check the Info file, which is the authoritative docu‐

       If we find that the things in this man page that are out of date	 cause
       significant  confusion or complaints, we will stop distributing the man
       page.  The alternative, updating the man page when we update  the  Info
       file,  is impossible because the rest of the work of maintaining GNU CC
       leaves us no time for that.  The GNU project regards man pages as obso‐
       lete and should not let them take time away from other things.

       For complete and current documentation, refer to the Info file `gcc' or
       the manual Using and Porting GNU CC (for version 2.0).  Both  are  made
       from the Texinfo source file gcc.texinfo.

       The  C  and  C++	 compilers  are	 integrated.  Both process input files
       through one or more of four stages: preprocessing, compilation,	assem‐
       bly,  and  linking.   Source filename suffixes identify the source lan‐
       guage, but which name you use for the compiler governs default  assump‐

       gcc    assumes  preprocessed (.i) files are C and assumes C style link‐

       g++    assumes preprocessed (.i) files are C++ and  assumes  C++	 style

       Suffixes	 of  source  file names indicate the language and kind of pro‐
       cessing to be done:

       .c    C source; preprocess, compile, assemble
       .C    C++ source; preprocess, compile, assemble
       .cc   C++ source; preprocess, compile, assemble
       .cxx  C++ source; preprocess, compile, assemble
       .m    Objective-C source; preprocess, compile, assemble
       .i    preprocessed C; compile, assemble
       .ii   preprocessed C++; compile, assemble
       .s    Assembler source; assemble
       .S    Assembler source; preprocess, assemble
       .h    Preprocessor file; not usually named on command line

       Files with other suffixes are  passed  to  the  linker.	 Common	 cases

       .o    Object file
       .a    Archive file

       Linking	is  always the last stage unless you use one of the -c, -S, or
       -E options to avoid it (or unless compilation  errors  stop  the	 whole
       process).   For	the  link  stage, all .o files corresponding to source
       files, -l libraries, unrecognized filenames (including named .o	object
       files and .a archives) are passed to the linker in command-line order.

       Options must be separate: `-dr' is quite different from `-d -r '.

       Most  `-f'  and	`-W'  options  have  two  contrary  forms:  -fname and
       -fno-name (or -Wname and -Wno-name).  Only the  non-default  forms  are
       shown here.

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

       Overall Options
	      -c -S -E -o file -pipe -v -x language

       Language Options
	      -ansi -fall-virtual -fcond-mismatch -fdollars-in-identifiers
	      -fenum-int-equiv -fexternal-templates -fno-asm -fno-builtin
	      -fno-strict-prototype -fsigned-bitfields -fsigned-char
	      -fthis-is-variable -funsigned-bitfields -funsigned-char
	      -fwritable-strings -traditional -traditional-cpp -trigraphs

       Warning Options
	      -fsyntax-only -pedantic -pedantic-errors -w -W -Wall
	      -Waggregate-return -Wcast-align -Wcast-qual -Wchar-subscript
	      -Wcomment -Wconversion -Wenum-clash -Werror -Wformat
	      -Wid-clash-len -Wimplicit -Winline -Wmissing-prototypes
	      -Wmissing-declarations -Wnested-externs -Wno-import
	      -Wparentheses -Wpointer-arith -Wredundant-decls -Wreturn-type
	      -Wshadow -Wstrict-prototypes -Wswitch -Wtemplate-debugging
	      -Wtraditional -Wtrigraphs -Wuninitialized -Wunused

       Debugging Options
	      -a -dletters -fpretend-float -g -glevel -gcoff -gxcoff -gxcoff+
	      -gdwarf -gdwarf+ -gstabs -gstabs+ -ggdb -p -pg -save-temps
	      -print-file-name=library -print-libgcc-file-name

       Optimization Options
	      -fcaller-saves -fcse-follow-jumps -fcse-skip-blocks
	      -fdelayed-branch -felide-constructors -fexpensive-optimizations
	      -ffast-math -ffloat-store -fforce-addr -fforce-mem
	      -finline-functions -fkeep-inline-functions -fmemoize-lookups
	      -fno-default-inline -fno-defer-pop -fno-function-cse -fno-inline
	      -fno-peephole -fomit-frame-pointer -frerun-cse-after-loop
	      -fschedule-insns -fschedule-insns2 -fstrength-reduce
	      -fthread-jumps -funroll-all-loops -funroll-loops -O -O2

       Preprocessor Options
	      -Aassertion -C -dD -dM -dN -Dmacro[=defn] -E -H -idirafter dir
	      -include file -imacros file -iprefix file -iwithprefix dir -M
	      -MD -MM -MMD -nostdinc -P -Umacro -undef

       Assembler Option

       Linker Options
	      -llibrary -nostartfiles -nostdlib -static -shared -symbolic
	      -Xlinker option -Wl,option -u symbol

       Directory Options
	      -Bprefix -Idir -I- -Ldir

       Target Options
	      -b  machine -V version

       Configuration Dependent Options
	      M680x0 Options
	      -m68000 -m68020 -m68020-40 -m68030 -m68040 -m68881 -mbitfield
	      -mc68000 -mc68020 -mfpa -mnobitfield -mrtd -mshort -msoft-float

	      VAX Options
	      -mg -mgnu -munix

	      SPARC Options
	      -mepilogue -mfpu -mhard-float -mno-fpu -mno-epilogue
	      -msoft-float -msparclite -mv8 -msupersparc -mcypress

	      Convex Options
	      -margcount -mc1 -mc2 -mnoargcount

	      AMD29K Options
	      -m29000 -m29050 -mbw -mdw -mkernel-registers -mlarge -mnbw
	      -mnodw -msmall -mstack-check -muser-registers

	      M88K Options
	      -m88000 -m88100 -m88110 -mbig-pic -mcheck-zero-division
	      -mhandle-large-shift -midentify-revision
	      -mno-check-zero-division -mno-ocs-debug-info
	      -mno-ocs-frame-position -mno-optimize-arg-area
	      -mno-serialize-volatile -mno-underscores -mocs-debug-info
	      -mocs-frame-position -moptimize-arg-area -mserialize-volatile
	      -mshort-data-num -msvr3 -msvr4 -mtrap-large-shift
	      -muse-div-instruction -mversion-03.00 -mwarn-passed-structs

	      RS6000 Options
	      -mfp-in-toc -mno-fop-in-toc

	      RT Options
	      -mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs
	      -mfull-fp-blocks -mhc-struct-return -min-line-mul
	      -mminimum-fp-blocks -mnohc-struct-return

	      MIPS Options
	      -mcpu=cpu type -mips2 -mips3 -mint64 -mlong64 -mlonglong128
	      -mmips-as -mgas -mrnames -mno-rnames -mgpopt -mno-gpopt -mstats
	      -mno-stats -mmemcpy -mno-memcpy -mno-mips-tfile -mmips-tfile
	      -msoft-float -mhard-float -mabicalls -mno-abicalls -mhalf-pic
	      -mno-half-pic -G num -nocpp

	      i386 Options
	      -m486 -mno-486 -msoft-float -mno-fp-ret-in-387

	      HPPA Options
	      -mpa-risc-1-0 -mpa-risc-1-1 -mkernel -mshared-libs
	      -mno-shared-libs -mlong-calls -mdisable-fpregs
	      -mdisable-indexing -mtrailing-colon

	      i960 Options
	      -mcpu-type -mnumerics -msoft-float -mleaf-procedures
	      -mno-leaf-procedures -mtail-call -mno-tail-call -mcomplex-addr
	      -mno-complex-addr -mcode-align -mno-code-align -mic-compat
	      -mic2.0-compat -mic3.0-compat -masm-compat -mintel-asm
	      -mstrict-align -mno-strict-align -mold-align -mno-old-align

	      DEC Alpha Options
	      -mfp-regs -mno-fp-regs -mno-soft-float -msoft-float

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

       Code Generation Options
	      -fcall-saved-reg -fcall-used-reg -ffixed-reg
	      -finhibit-size-directive -fnonnull-objects -fno-common
	      -fno-ident -fno-gnu-linker -fpcc-struct-return -fpic -fPIC
	      -freg-struct-return -fshared-data -fshort-enums -fshort-double
	      -fvolatile -fvolatile-global -fverbose-asm

       -x language
	      Specify  explicitly  the	language for the following input files
	      (rather than choosing a default based on the file name suffix) .
	      This  option applies to all following input files until the next
	      `-x' option.  Possible  values  of  language  are	 `c',  `objec‐
	      tive-c',	`c-header', `c++', `cpp-output', `assembler', and `as‐

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

       If you want only some of the four stages (preprocess,  compile,	assem‐
       ble,  link),  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 com‐
	      piler  output  is	 an  object  file corresponding to each source

	      By default, GCC makes the object file name for a source file  by
	      replacing	 the suffix `.c', `.i', `.s', etc., with `.o'.	Use -o
	      to select another name.

	      GCC ignores any unrecognized input files (those that do not  re‐
	      quire compilation or assembly) with the -c option.

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

	      By  default, GCC makes the assembler file name for a source file
	      by replacing the suffix `.c', `.i', etc., with `.s'.  Use -o  to
	      select another name.

	      GCC ignores any input files that don't require compilation.

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

	      GCC ignores input files which don't require preprocessing.

       -o file
	      Place  output in file file.  This applies regardless to whatever
	      sort of output GCC is producing, whether	it  be	an  executable
	      file, an object file, an assembler file or preprocessed C code.

	      Since  only  one	output file can be specified, it does not make
	      sense to use `-o' when compiling more than one input  file,  un‐
	      less you are producing an executable file as output.

	      If  you do not specify `-o', 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', and all prepro‐
	      cessed 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

       -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 cannot read from a pipe; but the GNU
	      assembler has no trouble.

       The following options control the dialect of C that  the	 compiler  ac‐

       -ansi  Support all ANSI standard C programs.

	      This  turns  off certain features of GNU C that are incompatible
	      with ANSI C, such as the asm, inline 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 ANSI trigraph feature, and disallows `$' as part of

	      The alternate keywords __asm__,  __extension__,  __inline__  and
	      __typeof__ continue to work despite `-ansi'.  You would not want
	      to use them in an ANSI 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-ANSI programs to be re‐
	      jected gratuitously.  For that, `-pedantic' is required in addi‐
	      tion to `-ansi'.

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

	      Do not recognize asm, inline or  typeof  as  a  keyword.	 These
	      words  may  then	be  used as identifiers.  You can use __asm__,
	      __inline__ and __typeof__ instead.  `-ansi' implies `-fno-asm'.

	      Don't recognize built-in functions that do not  begin  with  two
	      leading  underscores.  Currently, the functions affected include
	      _exit, abort, abs, alloca, cos, exit, fabs, labs,	 memcmp,  mem‐
	      cpy, sin, sqrt, strcmp, strcpy, and strlen.

	      The  `-ansi' option prevents alloca and _exit from being builtin

	      Treat a function declaration with no arguments, such as `int foo
	      ();',  as C would treat it—as saying nothing about the number of
	      arguments or their types (C++ only).  Normally, such a  declara‐
	      tion in C++ means that the function foo takes no arguments.

	      Support  ANSI  C	trigraphs.   The `-ansi' option implies `-tri‐

	      Attempt to support some aspects of traditional C compilers.  For
	      details,	see the GNU C Manual; the duplicate list here has been
	      deleted so that we won't get complaints when it is out of date.

	      But one note about C++ programs only  (not  C).	`-traditional'
	      has one additional effect for C++: assignment to this is permit‐
	      ted.  This is the same as the effect of `-fthis-is-variable'.

	      Attempt to support some aspects of traditional C	preprocessors.
	      This includes the items that specifically mention the preproces‐
	      sor above, but none of the other effects of `-traditional'.

	      Permit the use of `$' in identifiers (C++ only).	You  can  also
	      use  `-fno-dollars-in-identifiers' to explicitly prohibit use of
	      `$'.  (GNU C++ allows `$' by default on some target systems  but
	      not others.)

	      Permit  implicit conversion of int to enumeration types (C++ on‐
	      ly).  Normally GNU C++ allows conversion of enum to int, but not
	      the other way around.

	      Produce  smaller	code  for template declarations, by generating
	      only a single copy of each template function where it is defined
	      (C++ only).  To use this option successfully, you must also mark
	      all files that use templates with	 either	 `#pragma  implementa‐
	      tion' (the definition) or `#pragma interface' (declarations).

	      When your code is compiled with `-fexternal-templates', all tem‐
	      plate instantiations are external.  You  must  arrange  for  all
	      necessary	 instantiations	 to appear in the implementation file;
	      you can do this with a typedef that references  each  instantia‐
	      tion needed.  Conversely, when you compile using the default op‐
	      tion `-fno-external-templates', all template instantiations  are
	      explicitly internal.

	      Treat all possible member functions as virtual, implicitly.  All
	      member functions (except for constructor functions  and  new  or
	      delete member operators) are treated as virtual functions of the
	      class where they appear.

	      This does not mean that all calls to these member functions will
	      be  made through the internal table of virtual functions.	 Under
	      some circumstances, the compiler can determine that a call to  a
	      given  virtual function can be made directly; in these cases the
	      calls are direct in any case.

	      Allow conditional expressions with mismatched types in the  sec‐
	      ond  and	third  arguments.   The value of such an expression is

	      Permit assignment to this (C++ only).  The incorporation of  us‐
	      er-defined free store management into C++ has made assignment to
	      `this' an anachronism.  Therefore, by default it is  invalid  to
	      assign  to  this	within	a class member function.  However, for
	      backwards compatibility, you can make it valid with  `-fthis-is-

	      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

	      Ideally, a portable program should always use signed char or un‐
	      signed 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  ma‐
	      chines 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
	      and  unsigned char, even though its behavior is always just like
	      one of those two.

	      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,
	      `-fno-signed-char' is equivalent to `-funsigned-char'.




	      These options control whether a bitfield is signed or  unsigned,
	      when declared with no explicit `signed' or `unsigned' qualifier.
	      By default, such a bitfield is signed, because this  is  consis‐
	      tent: the basic integer types such as int are signed types.

	      However,	when you specify `-traditional', bitfields are all un‐
	      signed no matter what.

	      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.  `-tradition‐
	      al' also has this effect.

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

       These options control the C preprocessor, which is run on each C source
       file before actual compilation.

       If  you	use  the  `-E'	option, GCC does nothing except preprocessing.
       Some of these options make sense only together with `-E'	 because  they
       cause the preprocessor output to be unsuitable for actual compilation.

       -include file
	      Process  file as input before processing the regular input file.
	      In effect, the contents of file are compiled  first.   Any  `-D'
	      and `-U' options on the command line are always processed before
	      `-include file', regardless of the order in which they are writ‐
	      ten.  All the `-include' and `-imacros' options are processed in
	      the order in which they are written.

       -imacros file
	      Process file as input, discarding the resulting  output,	before
	      processing the regular input file.  Because the output generated
	      from file is discarded, the only effect of `-imacros file' is to
	      make  the	 macros	 defined in file available for use in the main
	      input.  The preprocessor evaluates any `-D' and `-U' options  on
	      the command line before processing `-imacrosfile', regardless of
	      the order in which they are written.   All  the  `-include'  and
	      `-imacros'  options are processed in the order in which they are

       -idirafter dir
	      Add the directory dir to the second include path.	 The  directo‐
	      ries  on the second include path are searched when a header file
	      is not found in any of the directories in the main include  path
	      (the one that `-I' adds to).

       -iprefix prefix
	      Specify  prefix  as the prefix for subsequent `-iwithprefix' op‐

       -iwithprefix dir
	      Add a directory to the second  include  path.   The  directory's
	      name  is	made by concatenating prefix and dir, where prefix was
	      specified previously with `-iprefix'.

	      Do not search the standard system directories for header	files.
	      Only  the	 directories you have specified with `-I' options (and
	      the current directory, if appropriate) are searched.

	      By using both `-nostdinc' and `-I-', you can limit the  include-
	      file search file to only those directories you specify explicit‐

	      Do not search for header files in the C++-specific standard  di‐
	      rectories,  but  do still search the other standard directories.
	      (This option is used when building `libg++'.)

       -undef Do not predefine any nonstandard macros.	 (Including  architec‐
	      ture flags).

       -E     Run  only the C preprocessor.  Preprocess all the C source files
	      specified and output the results to standard output  or  to  the
	      specified output file.

       -C     Tell  the	 preprocessor  not to discard comments.	 Used with the
	      `-E' option.

       -P     Tell the preprocessor not to generate  `#line'  commands.	  Used
	      with the `-E' option.

       -M  [ -MG ]
	      Tell  the	 preprocessor  to  output a rule suitable for make de‐
	      scribing the dependencies of each object file.  For each	source
	      file, the preprocessor outputs one make-rule whose target is the
	      object file name for that source file and whose dependencies are
	      all the files `#include'd in it.	This rule may be a single line
	      or may be continued with `\'-newline if it is long.  The list of
	      rules  is printed on standard output instead of the preprocessed
	      C program.

	      `-M' implies `-E'.

	      `-MG' says to treat missing header files as generated files  and
	      assume  they  live in the same directory as the source file.  It
	      must be specified in addition to `-M'.

       -MM  [ -MG ]
	      Like `-M' but the output mentions only the user header files in‐
	      cluded with `#include file"'.  System header files included with
	      `#include <file>' are omitted.

       -MD    Like `-M' but the dependency information	is  written  to	 files
	      with  names  made	 by replacing `.o' with `.d' at the end of the
	      output file names.  This is in addition to compiling the file as
	      specified—`-MD'  does  not  inhibit ordinary compilation the way
	      `-M' does.

	      The Mach utility `md' can be used to merge the `.d' files into a
	      single  dependency  file suitable for using with the `make' com‐

       -MMD   Like `-MD' except mention only user  header  files,  not	system
	      header files.

       -H     Print  the  name	of each header file used, in addition to other
	      normal activities.

	      Assert the answer answer for question, in case it is tested with
	      a	 preprocessor  conditional  such  as  `#if #question(answer)'.
	      `-A-' disables the standard assertions  that  normally  describe
	      the target machine.

	      (answer)	Assert	the  answer answer for question, in case it is
	      tested with a  preprocessor  conditional	such  as  `#if	#ques‐
	      tion(answer)'.  `-A-' disables the standard assertions that nor‐
	      mally describe the target machine.

	      Define macro macro with the string `1' as its definition.

	      Define macro macro as defn.    All instances of `-D' on the com‐
	      mand line are processed before any `-U' options.

	      Undefine macro macro.  `-U' options are evaluated after all `-D'
	      options, but before any `-include' and `-imacros' options.

       -dM    Tell the preprocessor to output only a list of the macro defini‐
	      tions that are in effect at the end of preprocessing.  Used with
	      the `-E' option.

       -dD    Tell the preprocessor to pass all	 macro	definitions  into  the
	      output, in their proper sequence in the rest of the output.

       -dN    Like  `-dD'  except  that	 the  macro arguments and contents are
	      omitted.	Only `#define name' is included in the output.

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

       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.

	      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 GCC does a link step, these object files are used
	      as input to the linker.

	      Use the library named library when linking.

	      The  linker  searches a standard list of directories for the li‐
	      brary, which is actually a file named `liblibrary.a'.  The link‐
	      er  then uses this file as if it had been specified precisely by

	      The directories searched include several standard system	direc‐
	      tories 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 ar‐
	      chive  file by scanning through it for members which define sym‐
	      bols that have so far been referenced but not defined.  However,
	      if  the  linker  finds an ordinary object file rather than a li‐
	      brary, the object file 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 program.

	      Do not use the standard system startup files when linking.   The
	      standard libraries are used normally.

	      Don't  use  the standard system libraries and startup files when
	      linking.	Only the files you specify will be passed to the link‐

	      On  systems  that support dynamic linking, this prevents linking
	      with the shared libraries.  On other systems, this option has no

	      Produce  a shared object which can then be linked with other ob‐
	      jects to form an executable.  Only a few	systems	 support  this

	      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 GNU CC 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 argu‐
	      ment.  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.

	      Pass option as an option to the linker.  If option contains com‐
	      mas, it is split into multiple options at the commas.

       -u symbol
	      Pretend  the symbol symbol is undefined, to force linking of li‐
	      brary modules to define it.  You can  use	 `-u'  multiple	 times
	      with  different  symbols	to force loading of additional library

       These options specify directories to search for header files,  for  li‐
       braries and for parts of the compiler:

       -Idir  Append directory dir to the list of directories searched for in‐
	      clude files.

       -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' di‐
	      rectives.	 (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  directo‐
	      ries for header files.  Thus, `-I-' and `-nostdinc' are indepen‐

       -Ldir  Add directory dir to the list of directories to be searched  for

	      This  option  specifies where to find the executables, libraries
	      and data files of the compiler itself.

	      The compiler driver program runs one or more of the  subprograms
	      `cpp',  `cc1' (or, for C++, `cc1plus'), `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-lib/'.   If  neither
	      of  those	 results  in  a	 file name that is found, the compiler
	      driver searches for the unmodified program name, using  the  di‐
	      rectories specified in your `PATH' environment variable.

	      The  run-time support file `libgcc.a' is also 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.  Most of
	      the  time,  on  most machines, `libgcc.a' is not actually neces‐

	      You can get a  similar  result  from  the	 environment  variable
	      GCC_EXEC_PREFIX; if it is defined, its value is used as a prefix
	      in the same way.	If both the `-B' option and the	 GCC_EXEC_PRE‐
	      FIX  variable are present, the `-B' option is used first and the
	      environment variable value second.

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

       These options control the amount and kinds of warnings produced by  GNU

	      Check the code for syntax errors, but don't emit any output.

       -w     Inhibit all warning messages.

	      Inhibit warning messages about the use of #import.

	      Issue  all  the warnings demanded by strict ANSI standard C; re‐
	      ject all programs that use forbidden extensions.

	      Valid ANSI standard C programs should compile properly  with  or
	      without  this  option  (though a rare few will require `-ansi').
	      However, without this option, certain GNU extensions and	tradi‐
	      tional C features are supported as well.	With this option, they
	      are rejected.  There is no reason to use this option; it	exists
	      only to satisfy pedants.

	      `-pedantic'  does	 not cause warning messages for use of the al‐
	      ternate keywords whose names begin and end with `__'.   Pedantic
	      warnings	are also disabled in the expression that follows __ex‐
	      tension__.  However, only system header files should  use	 these
	      escape routes; application programs should avoid them.

	      Like  `-pedantic',  except  that errors are produced rather than

       -W     Print extra warning messages for these events:

	  ·   A nonvolatile automatic variable might be changed by a  call  to
	      longjmp.	 These warnings are possible only in optimizing compi‐

	      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	 prob‐

	  ·   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 warn‐

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

	      Spurious warnings can occur because GNU CC does not realize that
	      certain  functions  (including abort and longjmp) will never re‐

	  ·   An expression-statement or the left-hand side of a comma expres‐
	      sion  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.

	  ·   An unsigned value is compared against zero with `>' or `<='.

	      Warn whenever a function or parameter is implicitly declared.

	      Warn  whenever a function is defined with a return-type that de‐
	      faults to int.  Also warn about any return statement with no re‐
	      turn-value in a function whose return-type is not void.

	      Warn whenever a local variable is unused aside from its declara‐
	      tion, whenever a function is declared static but never  defined,
	      and  whenever  a	statement computes a result that is explicitly
	      not used.

	      Warn whenever a switch statement has an index of	enumeral  type
	      and lacks a case for one or more of the named codes of that enu‐
	      meration.	 (The presence of a default label prevents this	 warn‐
	      ing.)   case  labels  outside the enumeration range also provoke
	      warnings when this option is used.

	      Warn whenever a comment-start sequence `/∗' appears  in  a  com‐

	      Warn  if	any  trigraphs	are encountered (assuming they are en‐

	      Check calls to printf and scanf, etc., to make sure that the ar‐
	      guments  supplied	 have  types  appropriate to the format string

	      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.

	      An automatic variable is used without first being initialized.

	      These warnings are possible only in optimizing compilation,  be‐
	      cause  they  require data flow information that is computed only
	      when optimizing.	If you don't specify `-O',  you	 simply	 won't
	      get these warnings.

	      These  warnings occur only for variables that are candidates for
	      register allocation.  Therefore, they do not occur for  a	 vari‐
	      able  that  is  declared volatile, or whose address is taken, or
	      whose size is other than 1, 2, 4 or 8 bytes.  Also, they do  not
	      occur  for  structures,  unions or arrays, even when they are in

	      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 GNU CC is not smart
	      enough to see all the reasons why the code might be correct  de‐
	      spite  appearing	to  have an error.  Here is one example of how
	      this can happen:

		int x;
		switch (y)
		  case 1: x = 1;
		  case 2: x = 4;
		  case 3: x = 5;
		foo (x);

	      If the value of y is always 1, 2 or 3, then x is always initial‐
	      ized,  but  GNU  CC  doesn't  know this.	Here is another common

		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.

	      Some spurious warnings can be avoided if you declare as volatile
	      all the functions you use that never return.

	      Warn if parentheses are omitted in certain contexts.

	      When  using templates in a C++ program, warn if debugging is not
	      yet fully available (C++ only).

       -Wall  All of the above `-W' options combined.  These are all  the  op‐
	      tions which pertain to usage that we recommend avoiding and that
	      we believe is easy to avoid, even in conjunction with macros.

       The remaining `-W...' options are not implied by `-Wall'	 because  they
       warn  about  constructions that we consider reasonable to use, on occa‐
       sion, in clean programs.

	      Warn about certain constructs that behave differently in	tradi‐
	      tional and ANSI C.

	  ·   Macro  arguments	occurring within string constants in the macro
	      body.  These would substitute the argument in traditional C, but
	      are part of the constant in ANSI C.

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

	  ·   A switch statement has an operand of type long.

	      Warn whenever a local variable shadows another local variable.

	      Warn whenever two distinct identifiers match in  the  first  len
	      characters.   This may help you prepare a program that will com‐
	      pile with certain obsolete, brain-damaged compilers.

	      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

	      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 ∗.

	      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.

	      Give string constants the type const char[length] so that	 copy‐
	      ing  the address of one into a non-const char ∗ pointer will get
	      a warning.  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.

	      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

	      Warn  if	any functions that return structures or unions are de‐
	      fined or called.	(In languages where you can return  an	array,
	      this also elicits a warning.)

	      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.)

	      Warn if a global function is defined without a  previous	proto‐
	      type declaration.	 This warning is issued even if the definition
	      itself provides a prototype.  The aim is to detect global	 func‐
	      tions that fail to be declared in header files.

	      Warn if a global function is defined without a previous declara‐
	      tion.  Do so even if the definition itself provides a prototype.
	      Use this option to detect global functions that are not declared
	      in header files.

	      Warn if anything is declared more than once in the  same	scope,
	      even  in	cases  where multiple declaration is valid and changes

	      Warn if an extern declaration is encountered within an function.

	      Warn about conversion between different enumeration  types  (C++

	      (C++  only.)   In	 a  derived  class, the definitions of virtual
	      functions must match the type signature of  a  virtual  function
	      declared in the base class.  Use this option to request warnings
	      when a derived class declares a function that may	 be  an	 erro‐
	      neous attempt to define a virtual function: that is, warn when a
	      function with the same name as a virtual function	 in  the  base
	      class,  but with a type signature that doesn't match any virtual
	      functions from the base class.

	      Warn if a function can not be inlined, and  either  it  was  de‐
	      clared as inline, or else the -finline-functions option was giv‐

	      Treat warnings as errors; abort compilation after any warning.

       GNU CC 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).  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 informa‐
	      tion  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 infor‐
	      mation,  use  `-gstabs+',	 `-gstabs',   `-gxcoff+',   `-gxcoff',
	      `-gdwarf+', or `-gdwarf' (see below).

	      Unlike  most  other  C  compilers, GNU CC allows you to use `-g'
	      with `-O'.  The shortcuts taken by optimized code may  occasion‐
	      ally 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 GNU CC is generated with the  ca‐
       pability for more than one debugging format.

       -ggdb  Produce  debugging  information in the native format (if that is
	      supported), including GDB extensions if at all possible.

	      Produce debugging information in stabs format (if that  is  sup‐
	      ported), without GDB extensions.	This is the format used by DBX
	      on most BSD systems.

	      Produce debugging information in stabs format (if that  is  sup‐
	      ported),	using GNU extensions understood only by the GNU debug‐
	      ger (GDB).  The use of these extensions is likely to make	 other
	      debuggers crash or refuse to read the program.

       -gcoff Produce  debugging  information  in COFF format (if that is sup‐
	      ported).	This is the format used by SDB on most System  V  sys‐
	      tems prior to System V Release 4.

	      Produce  debugging  information in XCOFF format (if that is sup‐
	      ported).	This is the format used by the	DBX  debugger  on  IBM
	      RS/6000 systems.

	      Produce  debugging  information in XCOFF format (if that is sup‐
	      ported), using GNU extensions understood only by the GNU	debug‐
	      ger  (GDB).  The use of these extensions is likely to make other
	      debuggers crash or refuse to read the program.

	      Produce debugging information in DWARF format (if that  is  sup‐
	      ported).	 This  is  the format used by SDB on most System V Re‐
	      lease 4 systems.

	      Produce debugging information in DWARF format (if that  is  sup‐
	      ported),	using GNU extensions understood only by the GNU debug‐
	      ger (GDB).  The use of these extensions is likely to make	 other
	      debuggers crash or refuse to read the program.

       -gcofflevel -gxcofflevel

	      Request  debugging information and also use level to specify how
	      much information.	 The default level is 2.

	      Level 1 produces minimal information, enough  for	 making	 back‐
	      traces  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 defi‐
	      nitions present in the program.  Some  debuggers	support	 macro
	      expansion when you use `-g3'.

       -p     Generate	extra  code  to write profile information suitable for
	      the analysis program prof.

       -pg    Generate extra code to write profile  information	 suitable  for
	      the analysis program gprof.

       -a     Generate	extra  code  to	 write	profile	 information for basic
	      blocks, which will record the number of times each  basic	 block
	      is  executed.   This  data  could	 be analyzed by a program like
	      tcov.  Note, however, that the format of the data	 is  not  what
	      tcov  expects.   Eventually  GNU	gprof  should  be  extended to
	      process this data.

	      Says to make debugging dumps during compilation at times	speci‐
	      fied  by letters.	 This is used for debugging the compiler.  The
	      file names for most of the dumps are made by appending a word to
	      the source file name (e.g.  `foo.c.rtl' or `foo.c.jump').

       -dM    Dump  all	 macro	definitions,  at the end of preprocessing, and
	      write no output.

       -dN    Dump all macro names, at the end of preprocessing.

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

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

       -dr    Dump after RTL generation, to `file.rtl'.

       -dx    Just  generate RTL for a function instead of compiling it.  Usu‐
	      ally used with `r'.

       -dj    Dump after first jump optimization, to `file.jump'.

       -ds    Dump after CSE (including the jump optimization  that  sometimes
	      follows CSE), to `file.cse'.

       -dL    Dump after loop optimization, to `file.loop'.

       -dt    Dump  after the second CSE pass (including the jump optimization
	      that sometimes follows CSE), to `file.cse2'.

       -df    Dump after flow analysis, to `file.flow'.

       -dc    Dump after instruction combination, to `file.combine'.

       -dS    Dump  after  the	 first	 instruction   scheduling   pass,   to

       -dl    Dump after local register allocation, to `file.lreg'.

       -dg    Dump after global register allocation, to `file.greg'.

       -dR    Dump   after   the   second   instruction	 scheduling  pass,  to

       -dJ    Dump after last jump optimization, to `file.jump2'.

       -dd    Dump after delayed branch scheduling, to `file.dbr'.

       -dk    Dump after conversion from registers to stack, to `file.stack'.

       -da    Produce all the dumps listed above.

       -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.

	      When running a cross-compiler, pretend that the  target  machine
	      uses  the	 same floating point format as the host machine.  This
	      causes incorrect output of the actual  floating  constants,  but
	      the actual instruction sequence will probably be the same as GNU
	      CC would make when running on the target machine.

	      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.cpp' and `foo.s', as well as `foo.o'.

	      Print  the  full absolute name of the library file library  that
	      would be used when linking—and do not do	anything  else.	  With
	      this  option,  GNU CC does not compile or link anything; it just
	      prints the file name.

	      Same as `-print-file-name=libgcc.a'.

	      Like `-print-file-name', but searches  for  a  program  such  as

       These options control various sorts of optimizations:


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

	      Without `-O', the compiler's goal is to reduce the cost of  com‐
	      pilation	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.

	      Without `-O', only variables declared register are allocated  in
	      registers.   The	resulting compiled code is a little worse than
	      produced by PCC without `-O'.

	      With `-O', the compiler tries to reduce code size and  execution

	      When  you	 specify  `-O',	 the  two options `-fthread-jumps' and
	      `-fdefer-pop' are turned on.  On machines that have delay slots,
	      the  `-fdelayed-branch' option is turned on.  For those machines
	      that can support debugging even without  a  frame	 pointer,  the
	      `-fomit-frame-pointer'  option  is  turned on.  On some machines
	      other flags may also be turned on.

       -O2    Optimize even more.  Nearly all supported optimizations that  do
	      not  involve  a  space-speed  tradeoff  are performed.  Loop un‐
	      rolling and function inlining are not  done,  for	 example.   As
	      compared	to -O, this option increases both compilation time and
	      the performance of the generated code.

       -O3    Optimize yet more. This turns on everything -O2 does, along with
	      also turning on -finline-functions.

       -O0    Do not optimize.

	      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'.  The following list shows only  one	 form—
       the one which is not the default.  You can figure out the other form by
       either removing `no-' or adding it.

	      Do not store floating point variables in registers.   This  pre‐
	      vents 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.

	      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.


	      Use  heuristics  to compile faster (C++ only).  These heuristics
	      are not enabled by default, since they are  only	effective  for
	      certain input files.  Other input files compile more slowly.

	      The  first time the compiler must build a call to a member func‐
	      tion (or reference to a data  member),  it  must	(1)  determine
	      whether  the class implements member functions of that name; (2)
	      resolve which member function to call (which  involves  figuring
	      out  what	 sorts	of  type conversions need to be made); and (3)
	      check the visibility of the member function to the caller.   All
	      of  this	adds  up  to slower compilation.  Normally, the second
	      time a call is made to that member  function  (or	 reference  to
	      that  data  member), it must go through the same lengthy process
	      again.  This means that code like this

		cout << "This " << p << " has " << n << " legs.\n";

	      makes six passes through all three steps.	 By using  a  software
	      cache,  a “hit” significantly reduces this cost.	Unfortunately,
	      using the cache introduces another  layer	 of  mechanisms	 which
	      must  be	implemented, and so incurs its own overhead.  `-fmemo‐
	      ize-lookups' enables the software cache.

	      Because access privileges (visibility)  to  members  and	member
	      functions	 may differ from one function context to the next, g++
	      may need to flush the cache.  With the `-fmemoize-lookups' flag,
	      the cache is flushed after every function that is compiled.  The
	      `-fsave-memoized' flag enables the same software cache, but when
	      the  compiler  determines	 that the context of the last function
	      compiled would yield the same  access  privileges	 of  the  next
	      function to compile, it preserves the cache.  This is most help‐
	      ful when defining many member functions for the same class: with
	      the  exception  of  member  functions which are friends of other
	      classes, each member function has exactly the same access privi‐
	      leges as every other, and the cache need not be flushed.

	      Don't  make  member  functions  inline by default merely because
	      they are defined inside the class scope (C++ only).

	      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

	      Force memory operands to be copied into registers	 before	 doing
	      arithmetic  on them.  This may produce better code by making all
	      memory references potential common  subexpressions.   When  they
	      are  not	common	subexpressions, instruction combination should
	      eliminate the separate register-load.  I am interested in	 hear‐
	      ing about the difference this makes.

	      Force  memory  address constants to be copied into registers be‐
	      fore doing arithmetic on them.  This  may	 produce  better  code
	      just as `-fforce-mem' may.  I am interested in hearing about the
	      difference this makes.

	      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 most machines.

	      On some machines, such as the Vax, this flag has no effect,  be‐
	      cause  the  standard  calling sequence automatically handles the
	      frame pointer and nothing is saved by pretending it doesn't  ex‐
	      ist.   The machine-description macro FRAME_POINTER_REQUIRED con‐
	      trols whether a target machine supports this flag.

	      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	 func‐
	      tion  is	declared static, then GCC normally does not output the
	      function as assembler code in its own right.

	      Enable values to be allocated in registers that  will  be	 clob‐
	      bered  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 oth‐
	      erwise be produced.

	      This option is enabled by default on certain  machines,  usually
	      those which have no call-preserved registers to use instead.

	      Even  if	all  calls to a given function are integrated, and the
	      function is declared static, nevertheless output a separate run-
	      time callable version of the function.

	      Do  not  put function addresses in registers; make each instruc‐
	      tion that calls a constant function contain the  function's  ad‐
	      dress explicitly.

	      This  option  results  in	 less efficient code, but some strange
	      hacks that alter the assembler output may be confused by the op‐
	      timizations performed when this option is not used.

	      Disable any machine-specific peephole optimizations.

	      This option allows GCC to violate some ANSI or IEEE rules/speci‐
	      fications in the interest of optimizing code for speed.  For ex‐
	      ample,  it  allows  the compiler to assume arguments to the sqrt
	      function are non-negative numbers.

	      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 ANSI rules/specifications for
	      math functions.

       The following options control specific optimizations.  The `-O2' option
       turns on all of these optimizations except `-funroll-loops' and	`-fun‐

       The  `-O'  option  usually  turns  on  the  `-fthread-jumps' and `-fde‐
       layed-branch' options, but specific machines may change the default op‐

       You can use the following flags in the rare cases when “fine-tuning” of
       optimizations to be performed is desired.

	      Perform the optimizations of loop strength reduction and	elimi‐
	      nation of iteration variables.

	      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 des‐
	      tination of the second branch or a point	immediately  following
	      it,  depending  on  whether the condition is known to be true or

	      Perform the optimization of loop unrolling.  This is  only  done
	      for  loops  whose number of iterations can be determined at com‐
	      pile time or run time.

	      Perform the optimization of loop unrolling.  This	 is  done  for
	      all loops.  This usually makes programs run more slowly.

	      In  common subexpression elimination, scan through jump instruc‐
	      tions 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.

	      This  is similar to `-fcse-follow-jumps', but causes CSE to fol‐
	      low jumps which conditionally skip over blocks.	When  CSE  en‐
	      counters	 a   simple   if   statement   with  no	 else  clause,
	      `-fcse-skip-blocks' causes CSE to follow	the  jump  around  the
	      body of the if.

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

	      Elide constructors when this seems plausible (C++	 only).	  With
	      this  flag,  GNU C++ initializes y directly from the call to foo
	      without going through a temporary in the following code:

	      A foo (); A y = foo ();

	      Without this option, GNU C++ first initializes y by calling  the
	      appropriate  constructor	for type A; then assigns the result of
	      foo to a temporary; and, finally, replaces the initial value  of
	      `y' with the temporary.

	      The default behavior (`-fno-elide-constructors') is specified by
	      the draft ANSI C++ standard.   If	 your  program's  constructors
	      have  side  effects,  using `-felide-constructors' can make your
	      program act differently, since some  constructor	calls  may  be

	      Perform  a number of minor optimizations that are relatively ex‐

	      If supported for the target machine, attempt to reorder instruc‐
	      tions  to	 exploit  instruction  slots  available	 after delayed
	      branch instructions.

	      If supported for the target machine, attempt to reorder instruc‐
	      tions  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  instruc‐
	      tion is required.

	      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.

       By  default, GNU CC compiles code for the same type of machine that you
       are using.  However, it can also be installed as a  cross-compiler,  to
       compile	for  some  other  type of machine.  In fact, several different
       configurations of GNU CC, for different target  machines,  can  be  in‐
       stalled	side by side.  Then you specify which one to use with the `-b'

       In addition, older and newer versions of GNU CC can be  installed  side
       by  side.   One	of them (probably the newest) will be the default, but
       you may sometimes wish to use another.

       -b machine
	      The argument machine specifies the target machine	 for  compila‐
	      tion.  This is useful when you have installed GNU CC as a cross-

	      The value to use for machine is the same as was specified as the
	      machine  type  when configuring GNU CC as a cross-compiler.  For
	      example, if a  cross-compiler  was  configured  with  `configure
	      i386v',  meaning	to compile for an 80386 running System V, then
	      you would specify `-b i386v' to run that cross compiler.

	      When you do not specify `-b', it normally means to  compile  for
	      the same type of machine that you are using.

       -V version
	      The  argument  version specifies which version of GNU CC to run.
	      This is useful when multiple versions are installed.  For	 exam‐
	      ple, version might be `2.0', meaning to run GNU CC version 2.0.

	      The default version, when you do not specify `-V', is controlled
	      by the way GNU CC is installed.  Normally, it will be a  version
	      that is recommended for general use.

       Each  of	 the  target  machine  types can have its own special options,
       starting with `-m', to choose among various hardware models or configu‐
       rations—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 op‐
       tions, usually for command-line compatibility with other	 compilers  on
       the same platform.

       These are the `-m' options defined for the 68000 series:


	      Generate	output for a 68000.  This is the default when the com‐
	      piler is configured for 68000-based systems.


	      Generate output for a 68020 (rather than a 68000).  This is  the
	      default when the compiler is configured for 68020-based systems.

	      Generate	output	containing  68881  instructions	 for  floating
	      point.  This is the default for most 68020-based systems	unless
	      -nfp was specified when the compiler was configured.

	      Generate	output for a 68030.  This is the default when the com‐
	      piler is configured for 68030-based systems.

	      Generate output for a 68040.  This is the default when the  com‐
	      piler is configured for 68040-based systems.

	      Generate	output	for  a 68040, without using any of the new in‐
	      structions.  This results in code which can run relatively effi‐
	      ciently on either a 68020/68881 or a 68030 or a 68040.

       -mfpa  Generate	output	containing  Sun	 FPA instructions for floating

	      Generate output containing library  calls	 for  floating	point.
	      WARNING:	the  requisite libraries are not part of GNU CC.  Nor‐
	      mally 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.

	      Consider type int to be 16 bits wide, like short int.

	      Do not use the bit-field instructions.  `-m68000' implies `-mno‐

	      Do use the bit-field instructions.   `-m68020'  implies  `-mbit‐
	      field'.  This is the default if you use the unmodified sources.

       -mrtd  Use  a different function-calling convention, in which functions
	      that take a fixed number of arguments return with	 the  rtd  in‐
	      struction,  which	 pops  their  arguments while returning.  This
	      saves one instruction in the caller since there is  no  need  to
	      pop the arguments there.

	      This  calling  convention	 is incompatible with the one normally
	      used on Unix, so you cannot use it if you need to call libraries
	      compiled with the Unix compiler.

	      Also,  you  must	provide	 function prototypes for all functions
	      that take variable numbers of arguments (including printf); oth‐
	      erwise incorrect code will be generated for calls to those func‐

	      In addition, seriously incorrect code will result if you call  a
	      function	with  too  many arguments.  (Normally, extra arguments
	      are harmlessly ignored.)

	      The rtd instruction is supported by the 68010 and 68020  proces‐
	      sors, but not by the 68000.

       These `-m' options are defined for the Vax:

       -munix Do  not output certain jump instructions (aobleq and so on) that
	      the Unix assembler for the Vax cannot handle across long ranges.

       -mgnu  Do output those jump instructions, on the	 assumption  that  you
	      will assemble with the GNU assembler.

       -mg    Output  code  for	 g-format floating point numbers instead of d-

       These `-m' switches are supported on the SPARC:


	      Generate output containing floating point instructions.  This is
	      the default.


	      Generate	output	containing  library  calls for floating point.
	      Warning: there is no GNU floating-point library for SPARC.  Nor‐
	      mally 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.


	      With -mepilogue (the default), the compiler  always  emits  code
	      for function exit at the end of each function.  Any function ex‐
	      it in the middle of the function (such as a return statement  in
	      C) will generate a jump to the exit code at the end of the func‐

	      With -mno-epilogue, the compiler tries to emit exit code	inline
	      at every function exit.



	      These three options select variations on the SPARC architecture.

	      By default (unless specifically configured for the Fujitsu SPAR‐
	      Clite), GCC generates code for the v7 variant of the  SPARC  ar‐

	      -mv8  will  give you SPARC v8 code.  The only difference from v7
	      code is that the compiler emits the integer multiply and integer
	      divide instructions which exist in SPARC v8 but not in SPARC v7.

	      -msparclite will give you SPARClite code.	 This adds the integer
	      multiply, integer divide step and scan (ffs) instructions	 which
	      exist in SPARClite but not in SPARC v7.


	      These two options select the processor for which the code is op‐

	      With -mcypress (the default), the compiler  optimises  code  for
	      the Cypress CY7C602 chip, as used in the SparcStation/SparcServ‐
	      er 3xx series. This is also appropriate for the older  SparcSta‐
	      tion 1, 2, IPX etc.

	      With -msupersparc the compiler optimises code for the SuperSparc
	      cpu, as used in the SparcStation 10, 1000 and 2000 series.  This
	      flag also enables use of the full SPARC v8 instruction set.

       These `-m' options are defined for the Convex:

       -mc1   Generate output for a C1.	 This is the default when the compiler
	      is configured for a C1.

       -mc2   Generate output for a C2.	 This is the default when the compiler
	      is configured for a C2.

	      Generate code which puts an argument count in the word preceding
	      each argument list.  Some nonportable Convex  and	 Vax  programs
	      need  this  word.	  (Debuggers  don't, except for functions with
	      variable-length argument lists; this info is in the  symbol  ta‐

	      Omit  the	 argument  count word.	This is the default if you use
	      the unmodified sources.

       These `-m' options are defined for the AMD Am29000:

       -mdw   Generate code that assumes the DW bit is set,  i.e.,  that  byte
	      and  halfword operations are directly supported by the hardware.
	      This is the default.

       -mnodw Generate code that assumes the DW bit is not set.

       -mbw   Generate code that assumes the system supports byte and halfword
	      write operations.	 This is the default.

       -mnbw  Generate code that assumes the systems does not support byte and
	      halfword write operations.  This implies `-mnodw'.

	      Use a small memory model that assumes that all function address‐
	      es  are  either within a single 256 KB segment or at an absolute
	      address of less than 256K.  This allows the call instruction  to
	      be used instead of a const, consth, calli sequence.

	      Do not assume that the call instruction can be used; this is the

	      Generate code for the Am29050.

	      Generate code for the Am29000.  This is the default.

	      Generate	references   to	  registers   gr64-gr95	  instead   of
	      gr96-gr127.   This option can be used when compiling kernel code
	      that wants a set of global registers disjoint from that used  by
	      user-mode code.

	      Note that when this option is used, register names in `-f' flags
	      must use the normal, user-mode, names.

	      Use the normal set of global registers, gr96-gr127.  This is the

	      Insert  a call to __msp_check after each stack adjustment.  This
	      is often used for kernel code.

       These `-m' options are defined for Motorola 88K architectures:

	      Generate code that works well on both the m88100 and the m88110.

	      Generate code that works best for the m88100, but that also runs
	      on the m88110.

	      Generate code that works best for the m88110, and may not run on
	      the m88100.

	      Include an ident directive in the assembler output recording the
	      source file name, compiler name and version, timestamp, and com‐
	      pilation flags used.

	      In assembler output, emit symbol names without adding an	under‐
	      score  character	at the beginning of each name.	The default is
	      to use an underscore as prefix on each name.


	      Early models of the 88K architecture had problems with  division
	      by zero; in particular, many of them didn't trap.	 Use these op‐
	      tions to avoid including (or to include  explicitly)  additional
	      code  to	detect	division by zero and signal an exception.  All
	      GCC configurations for the 88K  use  `-mcheck-zero-division'  by


	      Include (or omit) additional debugging information (about regis‐
	      ters used in each stack frame) as specified in the 88Open Object
	      Compatibility  Standard,	“OCS”.	 This extra information is not
	      needed by GDB.  The default for DG/UX, SVr4, and Delta 88 SVr3.2
	      is  to  include  this information; other 88k configurations omit
	      this information by default.


	      Force (or do not require) register values to be stored in a par‐
	      ticular  place in stack frames, as specified in OCS.  The DG/UX,
	      Delta88 SVr3.2, and BCS  configurations  use  `-mocs-frame-posi‐
	      tion';	other	 88k	configurations	  have	 the   default


	      Control how to store function arguments in stack frames.	`-mop‐
	      timize-arg-area'	saves space, but may break some debuggers (not
	      GDB).  `-mno-optimize-arg-area' conforms	better	to  standards.
	      By default GCC does not optimize the argument area.

	      num  Generate smaller data references by making them relative to
	      r0, which allows loading a  value	 using	a  single  instruction
	      (rather  than the usual two).  You control which data references
	      are affected by specifying num with this option.	 For  example,
	      if  you specify `-mshort-data-512', then the data references af‐
	      fected are those involving displacements of less than 512 bytes.
	      `-mshort-data-num' is not effective for num greater than 64K.


	      Do, or do not, generate code to guarantee sequential consistency
	      of volatile memory references.

	      GNU CC always guarantees consistency by default,	for  the  pre‐
	      ferred processor submodel.  How this is done depends on the sub‐

	      The m88100 processor does not reorder memory references  and  so
	      always  provides	sequential consistency.	 If you use `-m88100',
	      GNU CC does not generate any special instructions for sequential

	      The order of memory references made by the m88110 processor does
	      not always match the order of the instructions requesting	 those
	      references.   In	particular, a load instruction may execute be‐
	      fore a preceding store instruction.   Such  reordering  violates
	      sequential consistency of volatile memory references, when there
	      are multiple processors.	When you use `-m88000'	or  `-m88110',
	      GNU CC generates special instructions when appropriate, to force
	      execution in the proper order.

	      The extra code generated to guarantee consistency may affect the
	      performance of your application.	If you know that you can safe‐
	      ly forgo this guarantee, you may use the option `-mno-serialize-

	      If  you  use the `-m88100' option but require sequential consis‐
	      tency when running on  the  m88110  processor,  you  should  use


       -msvr3 Turn on (`-msvr4') or off (`-msvr3') compiler extensions related
	      to System V release 4 (SVr4).  This controls the following:

	  ·   Which variant of the assembler syntax to emit (which you can se‐
	      lect independently using `-mversion-03.00').

	  ·   `-msvr4' makes the C preprocessor recognize `#pragma weak'

	  ·   `-msvr4'	makes GCC issue additional declaration directives used
	      in SVr4.

       `-msvr3' is the default for all m88K  configurations  except  the  SVr4


	      Include  code to detect bit-shifts of more than 31 bits; respec‐
	      tively, trap such shifts or emit code to handle  them  properly.
	      By default GCC makes no special provision for large bit shifts.

	      Very  early  models of the 88K architecture didn't have a divide
	      instruction, so GCC avoids that  instruction  by	default.   Use
	      this option to specify that it's safe to use the divide instruc‐

	      In the DG/UX configuration, there are two flavors of SVr4.  This
	      option  modifies -msvr4 to select whether the hybrid-COFF or re‐
	      al-ELF flavor is used.  All other configurations ignore this op‐

	      Warn  when  a function passes a struct as an argument or result.
	      Structure-passing conventions have changed during the  evolution
	      of the C language, and are often the source of portability prob‐
	      lems.  By default, GCC issues no such warning.

       These options are defined for the IBM RS6000:


	      Control whether or not floating-point constants go in the	 Table
	      of  Contents  (TOC), a table of all global variable and function
	      addresses.  By default GCC puts floating-point constants	there;
	      if  the  TOC overflows, `-mno-fp-in-toc' will reduce the size of
	      the TOC, which may avoid the overflow.

       These `-m' options are defined for the IBM RT PC:

	      Use an in-line code sequence for integer	multiplies.   This  is
	      the default.

	      Call lmul$$ for integer multiples.

	      Generate	full-size  floating  point  data blocks, including the
	      minimum amount of scratch space recommended by IBM.  This is the

	      Do  not  include	extra  scratch	space  in  floating point data
	      blocks.  This results in smaller	code,  but  slower  execution,
	      since scratch space must be allocated dynamically.

	      Use a calling sequence incompatible with the IBM calling conven‐
	      tion in which floating point arguments are  passed  in  floating
	      point  registers.	  Note	that  varargs.h and stdargs.h will not
	      work with floating point operands if this option is specified.

	      Use the normal calling convention for floating point  arguments.
	      This is the default.

	      Return  structures  of more than one word in memory, rather than
	      in a register.  This provides compatibility  with	 the  MetaWare
	      HighC (hc) compiler.  Use `-fpcc-struct-return' for compatibili‐
	      ty with the Portable C Compiler (pcc).

	      Return some structures of more than one word in registers,  when
	      convenient.   This  is  the default.  For compatibility with the
	      IBM-supplied  compilers,	use  either  `-fpcc-struct-return'  or

       These `-m' options are defined for the MIPS family of computers:

	      Assume  the defaults for the machine type cpu-type when schedul‐
	      ing instructions.	 The default cpu-type is default, which	 picks
	      the  longest cycles times for any of the machines, in order that
	      the code run at reasonable  rates	 on  all  MIPS	cpu's.	 Other
	      choices  for cpu-type are r2000, r3000, r4000, and r6000.	 While
	      picking a specific cpu-type will schedule	 things	 appropriately
	      for  that	 particular  chip,  the compiler will not generate any
	      code that does not meet level 1 of the MIPS ISA (instruction set
	      architecture) without the -mips2 or -mips3 switches being used.

       -mips2 Issue  instructions from level 2 of the MIPS ISA (branch likely,
	      square  root  instructions).   The  -mcpu=r4000  or  -mcpu=r6000
	      switch must be used in conjunction with -mips2.

       -mips3 Issue instructions from level 3 of the MIPS ISA (64 bit instruc‐
	      tions).  The -mcpu=r4000 switch must be used in conjunction with



	      These options don't work at present.

	      Generate	code  for the MIPS assembler, and invoke mips-tfile to
	      add normal debug information.  This is the default for all plat‐
	      forms  except  for  the  OSF/1  reference	 platform,  using  the
	      OSF/rose object format.	If  any	 of  the  -ggdb,  -gstabs,  or
	      -gstabs+ switches are used, the mips-tfile program will encapsu‐
	      late the stabs within MIPS ECOFF.

       -mgas  Generate code for the GNU assembler.  This is the default on the
	      OSF/1 reference platform, using the OSF/rose object format.


	      The  -mrnames switch says to output code using the MIPS software
	      names for the registers, instead of the hardware names  (ie,  a0
	      instead of $4).  The GNU assembler does not support the -mrnames
	      switch, and the MIPS assembler will be  instructed  to  run  the
	      MIPS  C  preprocessor  over  the	source	file.  The -mno-rnames
	      switch is default.


	      The -mgpopt switch says to write all of  the  data  declarations
	      before the instructions in the text section, to all the MIPS as‐
	      sembler to generate one word memory references instead of	 using
	      two  words for short global or static data items.	 This is on by
	      default if optimization is selected.


	      For each non-inline function processed, the -mstats switch caus‐
	      es  the  compiler to emit one line to the standard error file to
	      print statistics about the program (number of  registers	saved,
	      stack size, etc.).


	      The  -mmemcpy  switch makes all block moves call the appropriate
	      string function (memcpy or bcopy) instead of possibly generating
	      inline code.


	      The  -mno-mips-tfile  switch causes the compiler not postprocess
	      the object file with the mips-tfile program, after the MIPS  as‐
	      sembler has generated it to add debug support.  If mips-tfile is
	      not run, then no local variables will be available to the debug‐
	      ger.   In addition, stage2 and stage3 objects will have the tem‐
	      porary file names passed to the assembler embedded in the object
	      file, which means the objects will not compare the same.

	      Generate	output	containing  library  calls for floating point.
	      WARNING: the requisite libraries are not part of GNU  CC.	  Nor‐
	      mally 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.

	      Generate output containing floating point instructions.  This is
	      the default if you use the unmodified sources.

       -mfp64 Assume  that the FR bit in the status word is on, and that there
	      are 32 64-bit floating point registers,  instead	of  32	32-bit
	      floating point registers.	 You must also specify the -mcpu=r4000
	      and -mips3 switches.

       -mfp32 Assume that there are 32 32-bit floating point registers.	  This
	      is the default.


	      Emit  (or	 do  not  emit) the .abicalls, .cpload, and .cprestore
	      pseudo operations that some System V.4 ports  use	 for  position
	      independent code.


	      The  -mhalf-pic switch says to put pointers to extern references
	      into the data section and load them up, rather than put the ref‐
	      erences  in  the	text  section.	 This  option does not work at
	      present.	-Gnum 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.  This allows the assembler  to  emit
	      one  word	 memory	 reference  instructions  based	 on the global
	      pointer (gp or $28), instead of the normal two words  used.   By
	      default,	num  is	 8 when the MIPS assembler is used, and 0 when
	      the GNU assembler is used.  The -Gnum switch is also  passed  to
	      the  assembler  and linker.  All modules should be compiled with
	      the same -Gnum value.

       -nocpp Tell the MIPS assembler to not run it's preprocessor  over  user
	      assembler files (with a `.s' suffix) when assembling them.

       These `-m' options are defined for the Intel 80386 family of computers:

	      Control whether or not code is optimized for a 486 instead of an
	      386.  Code generated for a 486 will run on a 386 and vice versa.

	      Generate	output	containing  library  calls for floating point.
	      Warning: the requisite libraries are not part of GNU  CC.	  Nor‐
	      mally 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.

	      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

	      The  option  `-mno-fp-ret-in-387'	 causes	 such values to be re‐
	      turned in ordinary CPU registers instead.

       These `-m' options are defined for the HPPA family of computers:

	      Generate code for a PA 1.0 processor.

	      Generate code for a PA 1.1 processor.

	      Generate code which is suitable for use in kernels.  Specifical‐
	      ly,  avoid add instructions in which one of the arguments is the
	      DP register; generate addil instructions instead.	 This avoids a
	      rather serious bug in the HP-UX linker.

	      Generate code that can be linked against HP-UX shared libraries.
	      This option is not fully function yet, and is not on by  default
	      for  any	PA target.  Using this option can cause incorrect code
	      to be generated by the compiler.

	      Don't generate code that	will  be  linked  against  shared  li‐
	      braries.	This is the default for all PA targets.

	      Generate	code which allows calls to functions greater than 256K
	      away from the caller when the caller and callee are in the  same
	      source  file.  Do not turn this option on unless code refuses to
	      link with “branch out of range errors from the linker.

	      Prevent floating point registers from being used in any  manner.
	      This  is necessary for compiling kernels which perform lazy con‐
	      text switching of floating point registers.  If you use this op‐
	      tion  and attempt to perform floating point operations, the com‐
	      piler will abort.

	      Prevent the compiler from using indexing	address	 modes.	  This
	      avoids some rather obscure problems when compiling MIG generated
	      code under MACH.

	      Add a colon to the end of	 label	definitions  (for  ELF	assem‐

       These `-m' options are defined for the Intel 80960 family of computers:

	      Assume  the  defaults for the machine type cpu-type for instruc‐
	      tion and addressing-mode availability and	 alignment.   The  de‐
	      fault  cpu-type is kb; other choices are ka, mc, ca, cf, sa, and


	      The -mnumerics option indicates that the processor does  support
	      floating-point  instructions.  The -msoft-float option indicates
	      that floating-point support should not be assumed.


	      Do (or do not) attempt to alter leaf procedures to  be  callable
	      with  the	 bal instruction as well as call.  This will result in
	      more efficient code for explicit calls when the bal  instruction
	      can  be  substituted  by the assembler or linker, but less effi‐
	      cient code in other cases, such as calls via function  pointers,
	      or using a linker that doesn't support this optimization.


	      Do (or do not) make additional attempts (beyond those of the ma‐
	      chine-independent portions of the compiler) to optimize tail-re‐
	      cursive  calls  into  branches.  You may not want to do this be‐
	      cause the detection of cases where this is not valid is not  to‐
	      tally complete.  The default is -mno-tail-call.


	      Assume  (or  do not assume) that the use of a complex addressing
	      mode is a win on this implementation of the i960.	  Complex  ad‐
	      dressing	modes  may not be worthwhile on the K-series, but they
	      definitely are on the C-series.  The default is currently -mcom‐
	      plex-addr for all processors except the CB and CC.


	      Align  code  to  8-byte boundaries for faster fetching (or don't
	      bother).	Currently turned on by default for C-series  implemen‐
	      tations only.



	      Enable compatibility with iC960 v2.0 or v3.0.


	      Enable compatibility with the iC960 assembler.


	      Do not permit (do permit) unaligned accesses.

	      Enable  structure-alignment  compatibility  with Intel's gcc re‐
	      lease version 1.3 (based on gcc 1.37).  Currently this is	 buggy
	      in that #pragma align 1 is always assumed as well, and cannot be
	      turned off.

       These `-m' options are defined for the DEC Alpha implementations:


	      Use (do not use) the hardware  floating-point  instructions  for
	      floating-point  operations.   When  -msoft-float	is  specified,
	      functions in `libgcc1.c' will be used to perform	floating-point
	      operations.   Unless  they are replaced by routines that emulate
	      the floating-point operations, or compiled in such a way	as  to
	      call  such emulations routines, these routines will issue float‐
	      ing-point operations.   If you are compiling for an Alpha	 with‐
	      out  floating-point operations, you must ensure that the library
	      is built so as not to call them.

	      Note that Alpha implementations  without	floating-point	opera‐
	      tions are required to have floating-point registers.


	      Generate code that uses (does not use) the floating-point regis‐
	      ter set.	-mno-fp-regs implies -msoft-float.  If	the  floating-
	      point  register  set  is	not  used, floating point operands are
	      passed in integer registers as if they were integers and	float‐
	      ing-point	 results  are  passed in $0 instead of $f0.  This is a
	      non-standard calling sequence, so any function with a  floating-
	      point  argument  or  return  value  called by code compiled with
	      -mno-fp-regs must also be compiled with that option.

	      A typical use of this option is building a kernel that does  not
	      use,  and	 hence	need  not save and restore, any floating-point

       These additional options are available on System V Release 4  for  com‐
       patibility with other compilers on those systems:

       -G     On  SVr4	systems, gcc accepts the option `-G' (and passes it to
	      the system linker),  for	compatibility  with  other  compilers.
	      However,	we  suggest you use `-symbolic' or `-shared' as appro‐
	      priate, instead of supplying linker options on the  gcc  command

       -Qy    Identify	the  versions  of each tool used by the compiler, in a
	      .ident assembler directive in the output.

       -Qn    Refrain from adding .ident directives to the output  file	 (this
	      is the default).

	      Search the directories dirs, and no others, for libraries speci‐
	      fied with `-l'.  You can separate directory entries in dirs from
	      one another with colons.

	      Look  in the directory dir to find the M4 preprocessor.  The as‐
	      sembler uses this option.

       These machine-independent options  control  the	interface  conventions
       used in code generation.

       Most  of	 them  begin  with `-f'.  These options 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.

	      Assume that objects reached through references are not null (C++

	      Normally, GNU C++ makes conservative assumptions	about  objects
	      reached  through	references.   For  example,  the compiler must
	      check that a is not null in code like the following:

	      obj &a = g (); a.f (2);

	      Checking that references of this sort have non-null  values  re‐
	      quires  extra code, however, and it is unnecessary for many pro‐
	      grams.  You can use `-fnonnull-objects' to omit the  checks  for
	      null, if your program doesn't require checking.

	      Use  the	same  convention for returning struct and union values
	      that is used by the usual C compiler on your system.  This  con‐
	      vention  is less efficient for small structures, and on many ma‐
	      chines it fails to be reentrant; but it has the advantage of al‐
	      lowing  intercallability	between GCC-compiled code and PCC-com‐
	      piled code.

	      Use the convention that struct and union values are returned  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-re‐
	      turn,  GNU  CC  defaults to whichever convention is standard for
	      the target.  If there is no standard convention, GNU CC defaults
	      to -fpcc-struct-return.

	      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

	      Use the same size for double as for float .

	      Requests that the data and non-const variables of this  compila‐
	      tion  be	shared data rather than private data.  The distinction
	      makes sense only on certain operating systems, where shared data
	      is shared between processes running the same program, while pri‐
	      vate data exists in one copy per process.

	      Allocate even uninitialized global variables in the bss  section
	      of  the  object  file,  rather  than  generating	them as common
	      blocks.  This has the effect that if the same  variable  is  de‐
	      clared  (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.

	      Ignore the `#ident' directive.

	      Do not output global initializations (such as  C++  constructors
	      and  destructors) in the form used by the GNU linker (on systems
	      where the GNU linker is the standard method of  handling	them).
	      Use this option when you want to use a non-GNU linker, which al‐
	      so requires using the collect2 program to make sure  the	system
	      linker  includes constructors and destructors.  (collect2 is in‐
	      cluded in the GNU CC distribution.)  For systems which must  use
	      collect2, the compiler driver gcc is configured to do this auto‐

	      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.

	      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).

	      Consider all memory references through pointers to be volatile.

	      Consider	all  memory references to extern and global data items
	      to be volatile.

       -fpic  If supported for the target machines, generate position-indepen‐
	      dent code, suitable for use in a shared library.

       -fPIC  If  supported  for the target machine, emit position-independent
	      code, suitable for dynamic linking, even if branches need	 large

	      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.

	      Treat the register named reg as an allocatable register that  is
	      clobbered	 by  function  calls.	It may be allocated for tempo‐
	      raries or variables that do not live across a  call.   Functions
	      compiled this way will not save and restore the register reg.

	      Use  of this flag for a register that has a fixed pervasive role
	      in the machine's execution model, such as the stack  pointer  or
	      frame pointer, will produce disastrous results.

	      This  flag does not have a negative form, because it specifies a
	      three-way choice.

	      Treat the register named reg as an allocatable register saved by
	      functions.   It  may  be allocated even for temporaries or vari‐
	      ables that live across a call.  Functions compiled this way will
	      save and restore the register reg if they use it.

	      Use  of this flag for a register that has a fixed pervasive role
	      in the machine's execution model, such as the stack  pointer  or
	      frame pointer, 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.

       Two `#pragma' directives are supported for GNU C++, to permit using the
       same header file for two purposes: as a definition of interfaces	 to  a
       given  object class, and as the full definition of the contents of that
       object class.

       #pragma interface
	      (C++ only.)  Use this directive in header files that define  ob‐
	      ject classes, to save space in most of the object files that use
	      those classes.  Normally, local copies  of  certain  information
	      (backup  copies  of  inline member functions, debugging informa‐
	      tion, and the internal tables that implement virtual  functions)
	      must  be	kept  in  each object file that includes class defini‐
	      tions.  You can use this pragma to avoid such duplication.  When
	      a	 header	 file  containing `#pragma interface' is included in a
	      compilation, this auxiliary information will  not	 be  generated
	      (unless  the  main input source file itself uses `#pragma imple‐
	      mentation').  Instead, the object files will contain  references
	      to be resolved at link time.

       #pragma implementation

       #pragma implementation "objects.h"
	      (C++ only.)  Use this pragma in a main input file, when you want
	      full output from included header files to be generated (and made
	      globally	visible).   The	 included header file, in turn, should
	      use `#pragma interface'.	Backup copies of inline	 member	 func‐
	      tions,  debugging	 information,  and the internal tables used to
	      implement virtual functions are all generated in	implementation

	      If you use `#pragma implementation' with no argument, it applies
	      to an include file with the same basename as your	 source	 file;
	      for  example,  in `allclass.cc', `#pragma implementation' by it‐
	      self is equivalent  to  `#pragma	implementation	"allclass.h"'.
	      Use the string argument if you want a single implementation file
	      to include code from multiple header files.

	      There is no way to split up the contents of a single header file
	      into multiple implementation files.

       file.c		  C source file
       file.h		  C header (preprocessor) file
       file.i		  preprocessed C source file
       file.C		  C++ source file
       file.cc		  C++ source file
       file.cxx		  C++ source file
       file.m		  Objective-C source file
       file.s		  assembly language file
       file.o		  object file
       a.out		  link edited output
       TMPDIR/cc∗	  temporary files
       LIBDIR/cpp	  preprocessor
       LIBDIR/cc1	  compiler for C
       LIBDIR/cc1plus	  compiler for C++
       LIBDIR/collect	  linker front end needed on some machines
       LIBDIR/libgcc.a	  GCC subroutine library
       /lib/crt[01n].o	  start-up routine
       LIBDIR/ccrt0	  additional start-up routine for C++
       /lib/libc.a	  standard C library, see
       /usr/include	  standard directory for #include files
       LIBDIR/include	  standard gcc directory for #include files
       LIBDIR/g++-include additional g++ directory for #include

       LIBDIR is usually /usr/local/lib/machine/version.
       TMPDIR  comes from the environment variable TMPDIR (default /usr/tmp if
       available, else /tmp).

       cpp(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1).
       `gcc', `cpp', `as', `ld', and `gdb' entries in info.
       Using and Porting GNU CC (for version 2.0), Richard M. Stallman; The  C
       Preprocessor,  Richard M. Stallman; Debugging with GDB: the GNU Source-
       Level Debugger, Richard M. Stallman and Roland H. Pesch; Using as:  the
       GNU Assembler, Dean Elsner, Jay Fenlason & friends; ld: the GNU linker,
       Steve Chamberlain and Roland Pesch.

       For instructions on reporting bugs, see the GCC manual.

       Copyright 1991, 1992, 1993 Free Software Foundation, Inc.

       Permission is granted to make and distribute verbatim  copies  of  this
       manual  provided	 the  copyright	 notice and this permission notice are
       preserved on all copies.

       Permission is granted to copy and distribute modified versions of  this
       manual under the conditions for verbatim copying, provided that the en‐
       tire resulting derived work is distributed under the terms of a permis‐
       sion notice identical to this one.

       Permission is granted to copy and distribute translations of this manu‐
       al into another language, under the above conditions for modified  ver‐
       sions,  except  that this permission notice may be included in transla‐
       tions approved by the Free Software Foundation instead of in the origi‐
       nal English.

       See the GNU CC Manual for the contributors to GNU CC.

GNU Tools			  1993/10/13				GCC(1)

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