gcc.texinfo

这是完整的gcc源代码

plus any that you specify with @samp{-L}.

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

@item -L@var{dir}
Add directory @var{dir} to the list of directories to be searched
for @samp{-l}.

@item -nostdlib
Don't use the standard system libraries and startup files when linking.
Only the files you specify will be passed to the linker.

@item -m@var{machinespec}
Machine-dependent option specifying something about the type of target
machine.  These options are defined by the macro
@code{TARGET_SWITCHES} in the machine description.  The default for
the options is also defined by that macro, which enables you to change
the defaults.@refill

These are the @samp{-m} options defined in the 68000 machine
description:

@table @samp
@item -m68020
@itemx -mc68020
Generate output for a 68020 (rather than a 68000).  This is the
default if you use the unmodified sources.

@item -m68000
@item -mc68000
Generate output for a 68000 (rather than a 68020).

@item -m68881
Generate output containing 68881 instructions for floating point.
This is the default if you use the unmodified sources.

@item -mfpa
Generate output containing Sun FPA instructions for floating point.

@item -msoft-float
Generate output containing library calls for floating point.

@item -mshort
Consider type @code{int} to be 16 bits wide, like @code{short int}.

@item -mnobitfield
Do not use the bit-field instructions.  @samp{-m68000} implies
@samp{-mnobitfield}.

@item -mbitfield
Do use the bit-field instructions.  @samp{-m68020} implies
@samp{-mbitfield}.  This is the default if you use the unmodified
sources.

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

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

Also, you must provide function prototypes for all functions that
take variable numbers of arguments (including @code{printf});
otherwise incorrect code will be generated for calls to those
functions.

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

The @code{rtd} instruction is supported by the 68010 and 68020
processors, but not by the 68000.
@end table

These @samp{-m} options are defined in the Vax machine description:

@table @samp
@item -munix
Do not output certain jump instructions (@code{aobleq} and so on)
that the Unix assembler for the Vax cannot handle across long
ranges.

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

@item -mg
Output code for g-format floating point numbers instead of d-format.
@end table

These @samp{-m} switches are supported on the Sparc:

@table @samp
@item -mfpu
Generate output containing floating point instructions.  This is the
default if you use the unmodified sources.

@ignore
@item -msoft-float
Generate output containing library calls for floating point.

@end ignore
@item -mno-epilogue
Generate separate return instructions for @code{return} statements.
This has both advantages and disadvantages; I don't recall what they
are.
@end table

These @samp{-m} options are defined in the Convex machine description:

@table @samp
@item -mc1
Generate output for a C1.  This is the default when the compiler is
configured for a C1.

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

@item -margcount
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.)

@item -mnoargcount
Omit the argument count word.  This is the default if you use the
unmodified sources.
@end table

@item -f@var{flag}
Specify machine-independent flags.  Most flags have both positive and
negative forms; the negative form of @samp{-ffoo} would be
@samp{-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 @samp{no-} or adding it.

@table @samp
@item -fpcc-struct-return
Use the same convention for returning @code{struct} and @code{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.

@item -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 @code{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 @samp{-ffloat-store} for such programs.

@item -fno-asm
Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
keyword.  These words may then be used as identifiers.  You can
use @code{__asm__}, @code{__inline__} and @code{__typeof__} instead.

@item -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.

@item -fstrength-reduce
Perform the optimizations of loop strength reduction and
elimination of iteration variables.

@item -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 @samp{-O}.  I am interested in
hearing about the difference this makes.

@item -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.

@item -fforce-addr
Force memory address constants to be copied into registers before
doing arithmetic on them.  This may produce better code just as
@samp{-fforce-mem} may.  I am interested in hearing about the
difference this makes.

@item -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.  @strong{It also makes debugging impossible.}

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
@code{FRAME_POINTER_REQUIRED} controls whether a target machine
supports this flag.  @xref{Registers}.@refill

@item -finline-functions
Integrate all simple functions into their callers.  The compiler
heuristically decides which functions are simple enough to be
worth integrating in this way.

If all calls to a given function are integrated, and the function
is declared @code{static}, then the function is normally not
output as assembler code in its own right.

@item -fcaller-saves
Enable values to be allocated in registers that will be clobbered by
function calls, by emitting extra instructions to save and restore the
registers around such calls.  Such allocation is done only when it
seems to result in better code than would otherwise be produced.

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

Don't use @samp{-fcaller-saves} together with
@samp{-fomit-frame-pointer}.  This combination does not work.

@item -fkeep-inline-functions
Even if all calls to a given function are integrated, and the
function is declared @code{static}, nevertheless output a
separate run-time callable version of the function.

@item -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.  @samp{-traditional} also has this effect.

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

@item -fcond-mismatch
Allow conditional expressions with mismatched types in the second and
third arguments.  The value of such an expression is void.

@item -fno-function-cse
Do not put function addresses in registers; make each instruction
that calls a constant function contain the function's address
explicitly.

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

@item -fvolatile
Consider all memory references through pointers to be volatile.

@item -fshared-data
Requests that the data and non-@code{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.

@item -funsigned-char
Let the type @code{char} be the unsigned, like @code{unsigned char}.

Each kind of machine has a default for what @code{char} should
be.  It is either like @code{unsigned char} by default or like
@code{signed char} by default.  (Actually, at present, the
default is always signed.)

The type @code{char} is always a distinct type from either
@code{signed char} or @code{unsigned char}, even though its
behavior is always just like one of those two.

Note that this is equivalent to @samp{-fno-signed-char}, which is the
negative form of @samp{-fsigned-char}.

@item -fsigned-char
Let the type @code{char} be signed, like @code{signed char}.

Note that this is equivalent to @samp{-fno-unsigned-char}, which is
the negative form of @samp{-funsigned-char}.

@item -fdelayed-branch
If supported for the target machine, attempt to reorder instructions
to exploit instruction slots available after delayed branch
instructions.

@item -ffixed-@var{reg}
Treat the register named @var{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).

@var{reg} must be the name of a register.  The register names
accepted are machine-specific and are defined in the
@code{REGISTER_NAMES} macro in the machine description macro
file.

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

@item -fcall-used-@var{reg}
Treat the register named @var{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 @var{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.

@item -fcall-saved-@var{reg}
Treat the register named @var{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 @var{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.
@end table

@item -d@var{letters}
Says to make debugging dumps at times specified by @var{letters}.
Here are the possible letters:

@table @samp
@item r
Dump after RTL generation.
@item j