gcc.1

这是完整的gcc源代码

.br
	\ \ ...
.br
	\ \ if (change_y) y = save_y;
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	}
.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;
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	}
.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
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 .