invoke.texi

gcc库的原代码,对编程有很大帮助.

only if you have been very careful about using @code{const} in
declarations and prototypes.  Otherwise, it will just be a nuisance;
this is why we did not make @samp{-Wall} request these warnings.

@item -Wconversion
Warn if a prototype causes a type conversion that is different from what
would happen to the same argument in the absence of a prototype.  This
includes conversions of fixed point to floating and vice versa, and
conversions changing the width or signedness of a fixed point argument
except when the same as the default promotion.

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

@item -Waggregate-return
Warn if any functions that return structures or unions are defined or
called.  (In languages where you can return an array, this also elicits
a warning.)

@item -Wstrict-prototypes
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.)

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

@item -Wmissing-declarations
Warn if a global function is defined without a previous declaration.
Do so even if the definition itself provides a prototype.
Use this option to detect global functions that are not declared in
header files.

@item -Wredundant-decls
Warn if anything is declared more than once in the same scope, even in
cases where multiple declaration is valid and changes nothing.

@item -Wnested-externs
Warn if an @code{extern} declaration is encountered within an function.

@item -Winline
Warn if a function can not be inlined, and either it was declared as inline,
or else the @samp{-finline-functions} option was given.

@item -Woverloaded-virtual
@cindex overloaded virtual fn, warning
@cindex warning for overloaded virtual fn
Warn when a derived class function declaration may be an error in
defining a virtual function (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.  With this option, the
compiler warns when you define a function with the same name as a
virtual function, but with a type signature that does not match any
declarations from the base class.

@item -Wsynth (C++ only)
@cindex warning for synthesized methods
@cindex synthesized methods, warning
Warn when g++'s synthesis behavior does not match that of cfront.  For
instance:

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

main ()
@{
  A a,b;
  a = b;
@}
@end smallexample

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

@item -Werror
Make all warnings into errors.
@end table

@node Debugging Options
@section Options for Debugging Your Program or GNU CC
@cindex options, debugging
@cindex debugging information options

GNU CC has various special options that are used for debugging
either your program or GCC:

@table @code
@item -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, @samp{-g} enables use of extra
debugging information that only GDB can use; this extra information
makes debugging work better in GDB but will probably make other debuggers
crash or
refuse to read the program.  If you want to control for certain whether
to generate the extra information, use @samp{-gstabs+}, @samp{-gstabs},
@samp{-gxcoff+}, @samp{-gxcoff}, @samp{-gdwarf+}, or @samp{-gdwarf}
(see below).

Unlike most other C compilers, GNU CC allows you to use @samp{-g} with
@samp{-O}.  The shortcuts taken by optimized code may occasionally
produce surprising results: some variables you declared may not exist
at all; flow of control may briefly move where you did not expect it;
some statements may not be executed because they compute constant
results or their values were already at hand; some statements may
execute in different places because they were moved out of loops.

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

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

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

@item -gstabs
Produce debugging information in stabs format (if that is supported),
without GDB extensions.  This is the format used by DBX on most BSD
systems.  On MIPS, Alpha and System V Release 4 systems this option
produces stabs debugging output which is not understood by DBX or SDB.
On System V Release 4 systems this option requires the GNU assembler.

@item -gstabs+
Produce debugging information in stabs format (if that is supported),
using GNU extensions understood only by the GNU debugger (GDB).  The
use of these extensions is likely to make other debuggers crash or
refuse to read the program.

@item -gcoff
Produce debugging information in COFF format (if that is supported).
This is the format used by SDB on most System V systems prior to
System V Release 4.

@item -gxcoff
Produce debugging information in XCOFF format (if that is supported).
This is the format used by the DBX debugger on IBM RS/6000 systems.

@item -gxcoff+
Produce debugging information in XCOFF format (if that is supported),
using GNU extensions understood only by the GNU debugger (GDB).  The
use of these extensions is likely to make other debuggers crash or
refuse to read the program, and may cause assemblers other than the GNU
assembler (GAS) to fail with an error.

@item -gdwarf
Produce debugging information in DWARF format (if that is supported).
This is the format used by SDB on most System V Release 4 systems.

@item -gdwarf+
Produce debugging information in DWARF format (if that is supported),
using GNU extensions understood only by the GNU debugger (GDB).  The
use of these extensions is likely to make other debuggers crash or
refuse to read the program.

@item -g@var{level}
@itemx -ggdb@var{level}
@itemx -gstabs@var{level}
@itemx -gcoff@var{level}
@itemx -gxcoff@var{level}
@itemx -gdwarf@var{level}
Request debugging information and also use @var{level} to specify how
much information.  The default level is 2.

Level 1 produces minimal information, enough for making backtraces in
parts of the program that you don't plan to debug.  This includes
descriptions of functions and external variables, but no information
about local variables and no line numbers.

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

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

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

@cindex @code{tcov}
@item -a
Generate extra code to write profile information for basic blocks, which will
record the number of times each basic block is executed, the basic block start
address, and the function name containing the basic block.  If @samp{-g} is
used, the line number and filename of the start of the basic block will also be
recorded.  If not overridden by the machine description, the default action is
to append to the text file @file{bb.out}.

This data could be analyzed by a program like @code{tcov}.  Note,
however, that the format of the data is not what @code{tcov} expects.
Eventually GNU @code{gprof} should be extended to process this data.

@item -d@var{letters}
Says to make debugging dumps during compilation at times specified by
@var{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.  @file{foo.c.rtl} or @file{foo.c.jump}).  Here are the
possible letters for use in @var{letters}, and their meanings:

@table @samp
@item M
Dump all macro definitions, at the end of preprocessing, and write no
output.
@item N
Dump all macro names, at the end of preprocessing.
@item D
Dump all macro definitions, at the end of preprocessing, in addition to
normal output.
@item y
Dump debugging information during parsing, to standard error.
@item r
Dump after RTL generation, to @file{@var{file}.rtl}.
@item x
Just generate RTL for a function instead of compiling it.  Usually used
with @samp{r}.
@item j
Dump after first jump optimization, to @file{@var{file}.jump}.
@item s
Dump after CSE (including the jump optimization that sometimes
follows CSE), to @file{@var{file}.cse}.
@item L
Dump after loop optimization, to @file{@var{file}.loop}.
@item t
Dump after the second CSE pass (including the jump optimization that
sometimes follows CSE), to @file{@var{file}.cse2}.
@item f
Dump after flow analysis, to @file{@var{file}.flow}.
@item c
Dump after instruction combination, to the file
@file{@var{file}.combine}.
@item S
Dump after the first instruction scheduling pass, to
@file{@var{file}.sched}.
@item l
Dump after local register allocation, to
@file{@var{file}.lreg}.
@item g
Dump after global register allocation, to
@file{@var{file}.greg}.
@item R
Dump after the second instruction scheduling pass, to
@file{@var{file}.sched2}.
@item J
Dump after last jump optimization, to @file{@var{file}.jump2}.
@item d
Dump after delayed branch scheduling, to @file{@var{file}.dbr}.
@item k
Dump after conversion from registers to stack, to @file{@var{file}.stack}.
@item a
Produce all the dumps listed above.
@item m
Print statistics on memory usage, at the end of the run, to
standard error.
@item p
Annotate the assembler output with a comment indicating which
pattern and alternative was used.
@end table

@item -fpretend-float
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.

@item -save-temps
Store the usual ``temporary'' intermediate files permanently; place them
in the current directory and name them based on the source file.  Thus,
compiling @file{foo.c} with @samp{-c -save-temps} would produce files
@file{foo.i} and @file{foo.s}, as well as @file{foo.o}.

@item -print-file-name=@var{library}
Print the full absolute name of the library file @var{library} that
would be used when linking---and don't do anything else.  With this
option, GNU CC does not compile or link anything; it just prints the
file name.

@item -print-prog-name=@var{program}
Like @samp{-print-file-name}, but searches for a program such as @samp{cpp}.

@item -print-libgcc-file-name
Same as @samp{-print-file-name=libgcc.a}.

This is useful when you use @samp{-nostdlib} or @samp{-nodefaultlibs}
but you do want to link with @file{libgcc.a}.  You can do

@example
gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
@end example

@item -print-search-dirs
Print the name of the configured installation directory and a list of
program and library directories gcc will search---and don't do anything else.

This is useful when gcc prints the error message
@samp{installation problem, cannot exec cpp: No such file or directory}.
To resolve this you either need to put @file{cpp} and the other compiler
components where gcc expects to find them, or you can set the environment
variable @code{GCC_EXEC_PREFIX} to the directory where you installed them.
Don't forget the trailing '/'.
@xref{Environment Variables}.
@end table

@node Optimize Options
@section Options That Control Optimization
@cindex optimize options
@cindex options, optimization

These options control various sorts of optimizations:

@table @code
@item -O
@itemx -O1
Optimize.  Optimizing compilation takes somewhat more time, and a lot
more memory for a large function.

Without @samp{-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 othe