.TH GCC 1 "28 November 1990" "Version 1.40"
.de BP
.sp
.ti -.2i
\(**
..
.SH NAME
gcc \- GNU project C Compiler
.SH SYNOPSIS
.B gcc
[ options ] files
.SH WARNING
This man page is an extract of the documentation of the
.I GNU C compiler
and is limited to the meaning of the options.
.B It is not kept up to date.
If you want to be certain of the information
below, check it in the manual "Using and Porting GCC".  Refer to the Info file
.B gcc.info
or the DVI file
.B gcc.dvi
which are made from the Texinfo source file
.BR gcc.texinfo .
.SH DESCRIPTION
The
.I GNU C compiler
uses a command syntax much like the Unix C compiler.
The
.I gcc
program accepts options and file names as operands.
Multiple single-letter options may
.I not
be grouped:
.B \-dr
is very different from
.BR "\-d \-r" .
 
When you invoke GNU CC, it normally does preprocessing, compilation,
assembly and linking.
File names which end in
.B .c
are taken as C source to be preprocessed and compiled;
file names ending in
.B .i
are taken as preprocessor output to be compiled;
compiler output files plus any input files with names ending in
.B .s
are assembled;
then the resulting object files, plus any other input files,
are linked together to produce an executable.
 
Command options allow you to stop this process at an intermediate stage.
For example, the 
.B \-c
option says not to run the linker.
Then the output consists of object files output by the assembler.
 
Other command options are passed on to one stage of processing.
Some options control the preprocessor and others the compiler itself.
Yet other options control the assembler and linker;
these are not documented here, but you rarely need to use any of them.
.SH OPTIONS
Here are the options to control the overall compilation process,
including those that say whether to link, whether to assemble, and so on.
.TP
.BI \-o " file"
Place output in file
.IR file .
This applies regardless to whatever sort of output is being produced,
whether it be an executable file, an object file,
an assembler file or preprocessed C code.
.sp
If 
.B \-o
is not specified, the default is to put an executable file in
.BR a.out ,
the object file
.IB source .c
in
.IB source .o\fR,
an assembler file in
.IB source .s\fR,
and preprocessed C on standard output.
.TP
.B \-c
Compile or assemble the source files, but do not link.
Produce object files with names made by replacing
.B .c
or
.B .s
with
.B .o
at the end of the input file names.
Do nothing at all for object files specified as input.
.TP
.B \-S
Compile into assembler code but do not assemble.
The assembler output file name is made by replacing
.B .c
with
.B .s
at the end of the input file name.
Do nothing at all for assembler source files or
object files specified as input.
.TP
.B \-E
Run only the C preprocessor.
Preprocess all the C source files specified and output
the results to standard output.
.TP
.B \-v
Compiler driver program prints the commands it executes as it runs
the preprocessor, compiler proper, assembler and linker.
Some of these are directed to print their own version numbers.
.TP
.B \-pipe
Use pipes rather than temporary files for communication between the
various stages of compilation.
This fails to work on some systems where the assembler is unable
to read from a pipe; but the GNU assembler has no trouble.
.TP
.BI \-B prefix
Compiler driver program tries
.I prefix
as a prefix for each program it tries to run.
These programs are
.IR cpp ,
.IR cc1 ,
.I as
and
.IR ld .
.sp
For each subprogram to be run, the compiler driver first tries the
.B \-B
prefix, if any.
If that name is not found, or if
.B \-B
was not specified, the driver tries two standard prefixes, which are
.B /usr/lib/gcc-
and
.BR /usr/local/lib/gcc- .
If neither of those results in a file name that is found, the
unmodified program name is searched for using the directories
specified in your
.B PATH
environment variable.
.sp
The run-time support file
.B gnulib
is also searched for using the
.B \-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, you can do without it.
.sp
You can get a similar result from the environment variable
.BR GCC_EXEC_PREFIX ;
if it is defined, its value is used as a prefix in the same way.
If both the
.B \-B
option and the
.B GCC_EXEC_PREFIX
variable are present, the
.B \-B
option is used first and the environment variable value second.
.TP
.BI -b prefix
The argument
.I prefix
is used as a second prefix for the compiler executables and libraries.
This prefix is optional: the compiler tries each file first with it,
then without it.
This prefix follows the prefix specified with
.B \-B
or the default prefixes.
.sp
Thus,
.B \-bvax- \-Bcc/
in the presence of environment variable
.B GCC_EXEC_PREFIX
with definition
.B /u/foo/
causes GNU CC to try the following file names for the preprocessor executable:
.sp
        \fBcc/vax-cpp
.br
        cc/cpp
.br
        /u/foo/vax-cpp
.br
        /u/foo/cpp
.br
        /usr/local/lib/gcc-vax-cpp
.br
        /usr/local/lib/gcc-cpp
.br
        /usr/lib/gcc-vax-cpp
.br
        /usr/lib/gcc-cpp\fR
 
These options control the details of C compilation itself.
.TP
.B \-ansi
Support all ANSI standard C programs.
.sp
This turns off certain features of GNU C that are incompatible with
ANSI C, such as the
.BR asm ,
.B inline
and
.B typeof
keywords, and predefined macros such as
.B unix
and
.B vax
that identify the type of system you are using.
It also enables the undesirable and rarely used ANSI trigraph feature.
.sp
The alternate keywords
.BR __asm__ ,
.B __inline__
and
.B __typeof__
continue to work despite
.BR \-ansi .
You would not want to use them in an ANSI C program, of course,
but it useful to put them in header files that might be included
in compilations done with
.BR \-ansi .
Alternate predefined macros such as
.B __unix__
and
.B __vax__
are also available, with or without
.BR \-ansi .
.sp
The
.B \-ansi
option does not cause non-ANSI programs to be rejected gratuitously.
For that,
.B \-pedantic
is required in addition to
.BR \-ansi .
.sp
The macro 
.B __STRICT_ANSI__
is predefined when the
.B \-ansi
option is used.
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.
.TP
.B \-traditional
Attempt to support some aspects of traditional C compilers.
Specifically:
.BP
All
.B extern
declarations take effect globally even if they are
written inside of a function definition.
This includes implicit declarations of functions.
.BP
The keywords
.BR typeof ,
.BR inline ,
.BR signed ,
.B const
and
.B volatile
are not recognized.
.BP
Comparisons between pointers and integers are always allowed.
.BP
Integer types
.B "unsigned short"
and
.B "unsigned char"
promote to
.BR "unsigned int" .
.BP
Out-of-range floating point literals are not an error.
.BP
All automatic variables not declared
.B register
are preserved by
.IR longjmp (3C).
Ordinarily, GNU C follows ANSI C: automatic variables not declared
.B volatile
may be clobbered.
.BP
In the preprocessor, comments convert to nothing at all,
rather than to a space.
This allows traditional token concatenation.
.BP
In the preprocessor, macro arguments are recognized within string
constants in a macro definition (and their values are stringified, though
without additional quote marks, when they appear in such a context).
The preprocessor always considers a string constant to end at a newline.
.BP
The predefined macro
.B __STDC__
is not defined when you use
.BR \-traditional ,
but
.B __GNUC__
is (since the GNU extensions which
.B __GNUC__
indicates are not affected by
.BR \-traditional ).
If you need to write header files that work differently depending on whether
.B \-traditional
is in use, by testing both of these predefined macros you can distinguish
four situations: GNU C, traditional GNU C, other ANSI C compilers, and
other old C compilers.
.TP
.B \-O
Optimize.
Optimizing compilation takes somewhat more time,
and a lot more memory for a large function.
.sp
Without
.BR \-O ,
the compiler's goal is to reduce the cost of compilation and
to make debugging produce the expected results.
Statements are independent: if you stop the program with a breakpoint
between statements, you can then assign a new value to any variable or
change the program counter to any other statement in the function and
get exactly the results you would expect from the source code.
.sp
Without
.BR \-O ,
only variables declared
.B register
are allocated in registers.
The resulting compiled code is a little worse than produced by PCC without
.BR \-O .
.sp
With
.BR \-O ,
the compiler tries to reduce code size and execution time.
.sp
Some of the
.B \-f
options described below turn specific kinds of optimization on or off.
.TP
.B \-g
Produce debugging information in the operating system's
native format (for DBX or SDB).
GDB also can work with this debugging information.
.sp
Unlike most other C compilers, GNU CC allows you to use
.B \-g
with
.BR \-O .
The shortcuts taken by optimized code may occasionally
produce surprising results: some variables you declared may not exist
at all; flow of control may briefly move where you did not expect it;
some statements may not be executed because they compute constant
results or their values were already at hand; some statements may
execute in different places because they were moved out of loops.
Nevertheless it proves possible to debug optimized output.
This makes it reasonable to use the optimizer for programs
that might have bugs.
.TP
.B \-w
Inhibit all warning messages.
.TP
.B \-W
Print extra warning messages for these events:
.BP
An automatic variable is used without first being initialized.
.sp
These warnings are possible only in optimizing compilation,
because they require data flow information that is computed only
when optimizing.
If you don't specify
.BR \-O ,
you simply won't get these warnings.
.sp
These warnings occur only for variables that are candidates for
register allocation.
Therefore, they do not occur for a variable that is declared
.BR 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 registers.
.sp
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.
.sp
These warnings are made optional because GNU CC is not smart
enough to see all the reasons why the code might be correct
despite appearing to have an error.
Here is one example of how this can happen:
.sp
        {
.br
        \ \ int x;
.br
        \ \ switch (y)
.br
        \ \ \ \ {
.br
        \ \ \ \ case 1: x = 1;
.br
        \ \ \ \ \ \ break;
.br
        \ \ \ \ case 2: x = 4;
.br
        \ \ \ \ \ \ break;
.br
        \ \ \ \ case 3: x = 5;
.br
        \ \ \ \ }
.br
        \ \ foo (x);
.br
        }
.sp
If the value of 
.I y
is always 1, 2 or 3, then
.I x
is always initialized, but GNU CC doesn't know this.
Here is another common case:
.sp
        {
.br
        \ \ int save_y;
.br
        \ \ if (change_y) save_y = y, y = new_y;
.br
        \ \ ...
.br
        \ \ if (change_y) y = save_y;
.br
        }
.sp
This has no bug because
.I save_y
is used only if it is set.
.sp
Some spurious warnings can be avoided if you declare as
.B volatile
all the functions you use that never return.
.BP
A nonvolatile automatic variable might be changed by a call to
.IR longjmp (3C).
These warnings as well are possible only in optimizing compilation.
.sp
The compiler sees only the calls to
.IR setjmp (3C).
It cannot know where
.IR longjmp (3C)
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
.IR longjmp (3C)
cannot in fact be called at the place which would cause a problem.
.BP
A function can return either with or without a value.
(Falling off the end of the function body is considered returning without
a value.)
For example, this function would evoke such a warning:
.sp
        foo (a)
.br
        {
.br
        \ \ if (a > 0)
.br
        \ \ \ \ return a;
.br
        }
.sp
Spurious warnings can occur because GNU CC does not realize that
certain functions (including
.IR abort (3C)
and 
.IR longjmp (3C))
will never return.
.BP
An expression-statement contains no side effects.
.sp
In the future, other useful warnings may also be enabled by this option.
.TP
.B \-Wimplicit
Warn whenever a function is implicitly declared.
.TP
.B \-Wreturn-type
Warn whenever a function is defined with a return-type that defaults to
.BR int .
Also warn about any
.B return
statement with no return-value in a function whose return-type is not
.BR void .
.TP
.B \-Wunused
Warn whenever a local variable is unused aside from its declaration,
and whenever a function is declared static but never defined.
.TP
.B \-Wswitch
Warn whenever a
.B switch
statement has an index of enumeral type and lacks a
.B case
for one or more of the named codes of that enumeration.
(The presence of a
.B default
label prevents this warning.)
.B case
labels outside the enumeration range also provoke
warnings when this option is used.
.TP
.B \-Wcomment
Warn whenever a comment-start sequence
.B /\(**
appears in a comment.
.TP
.B \-Wtrigraphs
Warn if any trigraphs are encountered (assuming they are enabled).
.TP
.B \-Wall
All of the above 
.B \-W
options combined.
These are all the options which pertain to usage that we do not recommend and
that we believe is always easy to avoid, even in conjunction with macros.
.sp 
The other
.BR \-W ...
options below are not implied by
.B \-Wall
because certain kinds of useful macros are almost impossible to write
without causing those warnings.
.TP
.B \-Wshadow
Warn whenever a local variable shadows another local variable.
.TP
.BI \-Wid-clash- len
Warn whenever two distinct identifiers match in the first
.I len
characters.
This may help you prepare a program that will compile with certain obsolete,
brain-damaged compilers.
.TP
.B \-Wpointer-arith
Warn about anything that depends on the size of a function type or of
.BR void .
GNU C assigns these types a size of 1, for convenience in calculations with
.B void \(**
pointers and pointers to functions.
.TP
.B \-Wcast-qual
Warn whenever a pointer is cast so as to remove a type qualifier from
the target type.
For example, warn if a 
.B const char \(**
is cast to an ordinary
.BR "char \(**" .
.TP
.B \-Wwrite-strings
Give string constants the type
.B const char[\fIlength\fB]
so that copying the address of one into a
.RB 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
.B const
in declarations and prototypes.
Otherwise, it will just be a nuisance; this is why we did not make
.B \-Wall
request these warnings.
.TP
.B \-p
Generate extra code to write profile information suitable
for the analysis program
.IR prof (1).
.TP
.B \-pg
Generate extra code to write profile information suitable for the
analysis program
.IR gprof (1).
.TP
.B \-a
Generate extra code to write profile information for basic blocks,
suitable for the analysis program
.IR tcov (1).
Eventually GNU
.IR gprof (1)
should be extended to process this data.
.TP
.BI \-l library
Search a standard list of directories for a library named
.IR library ,
which is actually a file named
.BR lib\fIlibrary\fB.a .
The linker uses this file as if it had been specified precisely by name.
.sp
The directories searched include several standard system directories
plus any that you specify with
.BR \-L .
.sp
Normally the files found this way are library files--archive files
whose members are object files.
The linker handles an archive file by scanning through it for members
which define symbols that have so far been referenced but not defined.
But if the file that is found is an ordinary object file, it is linked
in the usual fashion.
The only difference between using an
.B \-l
option and specifying a file name is that
.B \-l
searches several directories.
.TP
.BI \-L dir
Add directory
.I dir
to the list of directories to be searched for
.BR \-l .
.TP
.B \-nostdlib
Don't use the standard system libraries and startup files when linking.
Only the files you specify (plus 
.BR gnulib )
will be passed to the linker.
.TP
.BI \-m machinespec
Machine-dependent option specifying something about the type of target machine.
These options are defined by the macro
.B TARGET_SWITCHES
in the machine description.
The default for the options is also defined by that macro,
which enables you to change the defaults.
.sp

.B \-mfp-printf
.in +.5i
.B COHERENT
floating-point option.  This is equivalent to the
.B -f
option.  Gcc will instruct the linker to use the version of printf
which supports floating point specifiers.  The default links an
integer-only version of printf to save memory.
.in -.5i

These are the
.B \-m
options defined in the 68000 machine description:
.sp
.B \-m68020
.br
.B \-mc68020
.in +.5i
Generate output for a 68020 (rather than a 68000).
This is the default if you use the unmodified sources.
.in -.5i
.sp
.B \-m68000
.br
.B \-mc68000
.in +.5i
Generate output for a 68000 (rather than a 68020).
.in -.5i
.sp
.B \-m68881
.in +.5i
Generate output containing 68881 instructions for floating point.
This is the default if you use the unmodified sources.
.in -.5i
.sp
.B \-mfpa
.in +.5i
Generate output containing Sun FPA instructions for floating point.
.in -.5i
.sp
.B \-msoft-float
.in +.5i
Generate output containing library calls for floating point.
.in -.5i
.sp
.B \-mshort
.in +.5i
Consider type
.B int
to be 16 bits wide, like
.BR "short int" .
.in -.5i
.sp
.B \-mnobitfield
.in +.5i
Do not use the bit-field instructions.
.B \-m68000
implies
.BR \-mnobitfield .
.in -.5i
.sp
.B \-mbitfield
.in +.5i
Do use the bit-field instructions.
.B \-m68020
implies
.BR \-mbitfield .
This is the default if you use the unmodified sources.
.in -.5i
.sp
.B \-mrtd
.in +.5i
Use a different function-calling convention, in which functions
that take a fixed number of arguments return with the
.B rtd
instruction, which pops their arguments while returning.
This saves one instruction in the caller since there is no need to pop
the arguments there.
.sp
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.
.sp
Also, you must provide function prototypes for all functions that
take variable numbers of arguments (including 
.BR printf (3S));
otherwise incorrect code will be generated for calls to those functions.
.sp
In addition, seriously incorrect code will result if you call a
function with too many arguments.
(Normally, extra arguments are harmlessly ignored.)
.sp
The
.B rtd
instruction is supported by the 68010 and 68020 processors,
but not by the 68000.
.in -.5i
.sp
These
.B \-m
options are defined in the Vax machine description:
.sp
.B \-munix
.in +.5i
Do not output certain jump instructions 
.RB ( aobleq
and so on) that the Unix assembler for the Vax
cannot handle across long ranges.
.in -.5i
.sp
.B \-mgnu
.in +.5i
Do output those jump instructions, on the assumption that you
will assemble with the GNU assembler.
.in -.5i
.sp
.B \-mg
.in +.5i
Output code for g-format floating point numbers instead of d-format.
.in -.5i
.sp
These
.B \-m
switches are supported on the Sparc:
.sp
.B \-mfpu
.in +.5i
Generate output containing floating point instructions.
This is the default if you use the unmodified sources.
.in -.5i
.sp
.B \-msoft-float
.in +.5i
Generate output containing library calls for floating point.
.in -.5i
.sp
.B \-mno-epilogue
.in +.5i
Generate separate return instructions for
.B return
statements.
This has both advantages and disadvantages; I don't recall what they are.
.in -.5i
.sp
These
.B \-m
options are defined in the Convex machine description:
.sp
.B \-mc1
.in +.5i
Generate output for a C1.
This is the default when the compiler is configured for a C1.
.in -.5i
.sp
.B \-mc2
.in +.5i
Generate output for a C2.
This is the default when the compiler is configured for a C2.
.in -.5i
.sp
.B \-margcount
.in +.5i
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; this info is in the symbol table.)
.in -.5i
.sp
.B \-mnoargcount
.in +.5i
Omit the argument count word.
This is the default if you use the unmodified sources.
.in -.5i
.TP
.BI \-f flag
Specify machine-independent flags.
Most flags have both positive and negative forms; the negative form of
.B \-ffoo
would be
.BR \-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
.B no-
or adding it.
.TP
.B \-fpcc-struct-return
Use the same convention for returning
.B struct
and
.B union
values that is used by the usual C compiler on your system.
This convention is less efficient for small structures, and on many
machines it fails to be reentrant; but it has the advantage of allowing
intercallability between GCC-compiled code and PCC-compiled code.
.TP
.B \-ffloat-store
Do not store floating-point variables in registers.
This prevents undesirable excess precision on machines such as the
68000 where the floating registers (of the 68881) keep more
precision than a 
.B double
is supposed to have.
.sp
For most programs, the excess precision does only good, but a few
programs rely on the precise definition of IEEE floating point.
Use
.B \-ffloat-store
for such programs.
.TP
.B \-fno-asm
Do not recognize
.BR asm ,
.B inline
or
.B typeof
as a keyword.
These words may then be used as identifiers.
You can use
.BR __asm__ ,
.B __inline__
and
.B __typeof__
instead.
.TP
.B \-fno-defer-pop
Always pop the arguments to each function call as soon as that
function returns.
Normally the compiler (when optimizing) lets arguments accumulate
on the stack for several function calls and pops them all at once.
.TP
.B \-fstrength-reduce
Perform the optimizations of loop strength reduction and
elimination of iteration variables.
.TP
.B \-fcombine-regs
Allow the combine pass to combine an instruction that copies one
register into another.
This might or might not produce better code when used in addition to
.BR \-O .
I am interested in hearing about the difference this makes.
.TP
.B \-fforce-mem
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 hearing about the difference this makes.
.TP
.B \-fforce-addr
Force memory address constants to be copied into registers before
doing arithmetic on them.
This may produce better code just as
.B \-fforce-mem
may.
I am interested in hearing about the difference this makes.
.TP
.B \-fomit-frame-pointer
Don't keep the frame pointer in a register for functions that
don't need one.
This avoids the instructions to save, set up and restore frame pointers;
it also makes an extra register available in many functions.
.B "It also makes debugging impossible."
.sp
On some machines, such as the Vax, this flag has no effect, because
the standard calling sequence automatically handles the frame pointer
and nothing is saved by pretending it doesn't exist.
The machine-description macro
.B FRAME_POINTER_REQUIRED
controls whether a target machine supports this flag.
.TP
.B \-finline-functions
Integrate all simple functions into their callers.
The compiler heuristically decides which functions are simple
enough to be worth integrating in this way.
.sp
If all calls to a given function are integrated, and the function is declared
.BR static ,
then the function is normally not output as assembler code in its own right.
.TP
.B \-fcaller-saves
Enable values to be allocated in registers that will be clobbered by
function calls, by emitting extra instructions to save and restore the
registers around such calls.
Such allocation is done only when it seems to result in better code than
would otherwise be produced.
.sp
This option is enabled by default on certain machines, usually those
which have no call-preserved registers to use instead.
.TP
.B \-fkeep-inline-functions
Even if all calls to a given function are integrated, and the function is
declared
.BR static ,
nevertheless output a separate run-time callable version of the function.
.TP
.B \-fwritable-strings
Store string constants in the writable data segment and don't uniquize them.
This is for compatibility with old programs which assume they can write
into string constants.
Writing into string constants is a very bad idea;
constants should be constant.
.TP
.B \-fcond-mismatch
Allow conditional expressions with mismatched types in the second and
third arguments.
The value of such an expression is void.
.TP
.B \-fno-function-cse
Do not put function addresses in registers; make each instruction that
calls a constant function contain the function's address explicitly.
.sp
This option results in less efficient code, but some strange hacks that
alter the assembler output may be confused by the optimizations performed
when this option is not used.
.TP
.B \-fvolatile
Consider all memory references through pointers to be volatile.
.TP
.B \-fshared-data
Requests that the data and
.RB non- const
variables of this compilation 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
private data exists in one copy per process.
.TP
.B \-funsigned-char
Let the type
.B char
be the unsigned, like
.BR "unsigned char" .
.sp
Each kind of machine has a default for what
.B char
should be.
It is either like
.B "unsigned char"
by default or like
.B "signed char"
by default.
(Actually, at present, the default is always signed.)
.sp
The type
.B char
is always a distinct type from either
.B "signed char"
or
.BR "unsigned char" ,
even though its behavior is always just like one of those two.
.sp
Note that this is equivalent to
.BR \-fno-signed-char ,
which is the negative form of
.BR \-fsigned-char .
.TP
.B \-fsigned-char
Let the type
.B char
be signed, like
.BR "signed char" .
.sp
Note that this is equivalent to
.BR \-fno-unsigned-char ,
which is the negative form of
.BR \-funsigned-char .
.TP
.B \-fdelayed-branch
If supported for the target machine, attempt to reorder instructions to
exploit instruction slots available after delayed branch instructions.
.TP
.BI \-ffixed- reg
Treat the register named
.I 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).
.sp
.I reg
must be the name of a register.
The register names accepted are machine-specific and are defined in the
.B REGISTER_NAMES
macro in the machine description macro file.
.sp
This flag does not have a negative form, because it specifies a
three-way choice.
.TP
.BI \-fcall-used- reg
Treat the register named
.I reg
as an allocatable register that is clobbered by function calls.
It may be allocated for temporaries or variables that do not live
across a call.
Functions compiled this way will not save and restore the register REG.
.sp
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.
.sp
This flag does not have a negative form, because it specifies a
three-way choice.
.TP
.BI \-fcall-saved- reg
Treat the register named
.I reg
as an allocatable register saved by functions.
It may be allocated even for temporaries or variables that live across a call.
Functions compiled this way will save and restore the register
.I reg
if they use it.
.sp
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.
.sp
A different sort of disaster will result from the use of this
flag for a register in which function values may be returned.
.sp
This flag does not have a negative form, because it specifies a
three-way choice.
.TP
.BI \-d letters
Says to make debugging dumps at times specified by
.IR letters .
Here are the possible letters:
.sp
.B r
.in +.5i
Dump after RTL generation.
.in -.5i
.B j
.in +.5i
Dump after first jump optimization.
.in -.5i
.B J
.in +.5i
Dump after last jump optimization.
.in -.5i
.B s
.in +.5i
Dump after CSE (including the jump optimization that sometimes follows CSE).
.in -.5i
.B L
.in +.5i
Dump after loop optimization.
.in -.5i
.B f
.in +.5i
Dump after flow analysis.
.in -.5i
.B c
.in +.5i
Dump after instruction combination.
.in -.5i
.B l
.in +.5i
Dump after local register allocation.
.in -.5i
.B g
.in +.5i
Dump after global register allocation.
.in -.5i
.B d
.in +.5i
Dump after delayed branch scheduling.
.in -.5i
.B m
.in +.5i
Print statistics on memory usage, at the end of the run.
.in -.5i
.TP
.B \-pedantic
Issue all the warnings demanded by strict ANSI standard C; reject
all programs that use forbidden extensions.
.sp
Valid ANSI standard C programs should compile properly with or without
this option (though a rare few will require
.BR \-ansi ).
However, without this option, certain GNU extensions and traditional 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.
.sp
.B \-pedantic
does not cause warning messages for use of the alternate keywords whose
names begin and end with
.BR __ .
.TP
.B \-static
On Suns running version 4, this prevents linking with the shared
libraries.
.RB ( \-g
has the same effect.)
 
These options control the C preprocessor, which is run on each C source
file before actual compilation.  If you use the `-E' option, nothing
is done except C preprocessing.  Some of these options make sense only
together with `-E' because they request preprocessor output that is
not suitable for actual compilation.
.TP
.B \-C
Tell the preprocessor not to discard comments.
Used with the
.B \-E
option.
.TP
.BI \-I dir
Search directory
.I dir
for include files.
.TP
.B \-I-
Any directories specified with
.B \-I
options before the
.B \-I-
option are searched only for the case of
.B #include
\fB"\fIfile\fB"\fR; they are not searched for
.BR "#include <\fIfile\fB>" .
.sp
If additional directories are specified with
.B \-I
options after the
.BR \-I- ,
these directories are searched for all
.B #include
directives.
(Ordinarily
.I all
.B \-I
directories are used this way.)
.sp
In addition, the
.B \-I-
option inhibits the use of the current directory as the first
search directory for
.B #include
\fB"\fIfile\fB"\fR.
Therefore, the current directory is searched only if it is requested
explicitly with
.BR \-I. .
Specifying both
.B \-I-
and
.B -I.
allows you to control precisely which directories are searched before
the current one and which are searched after.
.TP
.B \-nostdinc
Do not search the standard system directories for header files.
Only the directories you have specified with
.B \-I
options (and the current directory, if appropriate) are searched.
.sp
Between
.B \-nostdinc
and
.BR \-I- ,
you can eliminate all directories from the search path
except those you specify.
.TP
.B \-M
Tell the preprocessor to output a rule suitable for
.BI make (1)
describing the dependencies of each source file.
For each source file, the preprocessor outputs one
.BR make -rule
whose target is the object file name for that source file and whose
dependencies are all the files
.BR #include d
in it.
This rule may be a single line or may be continued with
.B \\\\-newline
if it is long.
.sp
.B \-M
implies
.BR \-E .
.TP
.B \-MM
Like
.B \-M
but the output mentions only the user-header files included with
.B #include
\fB"\fIfile\fB"\fR.
System header files included with
.B "#include <\fIfile\fB>"
are omitted.
.sp
.B \-MM
implies
.BR \-E .
.TP
.BI \-D macro
Define macro
.I macro
with the empty string as its definition.
.TP
.BI \-D macro\fR=\fIdefn
Define macro
.I macro
as
.IR defn .
.TP
.BI \-U macro
Undefine macro
.IR macro .
.TP
.B \-trigraphs
Support ANSI C trigraphs.
You don't want to know about this brain-damage.
The
.B \-ansi
option also has this effect.
.SH FILES
.ta \w'LIBDIR/gcc-include 'u
file.c  C source file
.br
file.s  assembly language file
.br
file.o  object file
.br
a.out   link edited output
.br
/tmp/cc\(**     temporary files
.br
\fILIBDIR\fR/gcc-cpp    preprocessor
.br
\fILIBDIR\fR/gcc-cc1    compiler
.br
\fILIBDIR\fR/gcc-gnulib library needed by GCC on some machines
.br
/lib/crt[01n].o start-up routine
.br
/lib/libc.a     standard C library, see
.IR intro (3)
.br
/usr/include    standard directory for 
.B #include
files
.br
\fILIBDIR\fR/gcc-include        standard gcc directory for
.B #include
files
.sp
.I LIBDIR
is usually
.BR /usr/local/lib .
.SH "SEE ALSO"
as(1), ld(1), adb(1), dbx(1), sdb(1).
.SH BUGS
Bugs should be reported to
.BR bug-gcc@prep.ai.mit.edu .
Bugs tend actually to be fixed if they can be isolated, so it is in your
interest to report them in such a way that they can be easily reproduced.
.SH COPYING
Copyright (c) 1988 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
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.
 
Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be included in
translations approved by the Free Software Foundation instead of in
the original English.
.SH AUTHORS
See the GNU CC Manual for the contributors to GNU CC.
..
.