gcc.1

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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.
.TP
.B \-fkeep\-inline\-functions
Even if all calls to a given function are integrated, and the function
is declared \c
.B static\c
\&, nevertheless output a separate run-time
callable version of the function.
.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.

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.
.PP

The following options control specific optimizations.  The `\|\c
.B \-O2\c
\&\|'
option turns on all of these optimizations except `\|\c
.B \-funroll\-loops\c
\&\|'
and `\|\c
.B \-funroll\-all\-loops\c
\&\|'.  

The `\|\c
.B \-O\c
\&\|' option usually turns on
the `\|\c
.B \-fthread\-jumps\c
\&\|' and `\|\c
.B \-fdelayed\-branch\c
\&\|' options, but
specific machines may change the default optimizations.

You can use the following flags in the rare cases when ``fine-tuning''
of optimizations to be performed is desired.
.TP
.B \-fstrength\-reduce
Perform the optimizations of loop strength reduction and
elimination of iteration variables.
.TP
.B \-fthread\-jumps
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 destination of the
second branch or a point immediately following it, depending on whether
the condition is known to be true or false.
.TP
.B \-funroll\-loops
Perform the optimization of loop unrolling.  This is only done for loops
whose number of iterations can be determined at compile time or run time.
.TP
.B \-funroll\-all\-loops
Perform the optimization of loop unrolling.  This is done for all loops.
This usually makes programs run more slowly.
.TP
.B \-fcse\-follow\-jumps
In common subexpression elimination, scan through jump instructions in
certain cases.  This is not as powerful as completely global CSE, but
not as slow either.
.TP
.B \-frerun\-cse\-after\-loop
Re-run common subexpression elimination after loop optimizations has been
performed.  
.TP
.B \-felide\-constructors
.I
(C++ only.)
Use this option to instruct the compiler to be smarter about when it can
elide constructors.  Without this flag, GNU C++ and cfront both
generate effectively the same code for:
.sp
.br
A\ foo\ ();
.br
A\ x\ (foo\ ());\ \ \ //\ x\ initialized\ by\ `foo\ ()',\ no\ ctor\ called
.br
A\ y\ =\ foo\ ();\ \ \ //\ call\ to\ `foo\ ()'\ heads\ to\ temporary,
.br
\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ //\ y\ is\ initialized\ from\ the\ temporary.
.br
.sp
Note the difference!  With this flag, GNU C++ initializes `\|\c
.B y\c
\&\|' directly
from the call to 
.B foo ()
without going through a temporary.
.TP
.B \-fexpensive\-optimizations
Perform a number of minor optimizations that are relatively expensive.
.TP
.B \-fdelayed\-branch
If supported for the target machine, attempt to reorder instructions
to exploit instruction slots available after delayed branch
instructions.
.TP
.B \-fschedule\-insns
If supported for the target machine, attempt to reorder instructions 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 instruction is required.
.TP
.B \-fschedule\-insns2
Similar to `\|\c
.B \-fschedule\-insns\c
\&\|', 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.
.PP

.SH TARGET OPTIONS
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
installed side by side.  Then you specify which one to use with the
`\|\c
.B \-b\c
\&\|' option.

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.
.TP
.BI "\-b " "machine"\c
\&
The argument \c
.I machine\c
\& specifies the target machine for compilation.
This is useful when you have installed GNU CC as a cross-compiler.

The value to use for \c
.I machine\c
\& 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 `\|\c
.B configure
i386v\c
\&\|', meaning to compile for an 80386 running System V, then you
would specify `\|\c
.B \-b i386v\c
\&\|' to run that cross compiler.

When you do not specify `\|\c
.B \-b\c
\&\|', it normally means to compile for
the same type of machine that you are using.
.TP
.BI "\-V " "version"\c
\&
The argument \c
.I version\c
\& specifies which version of GNU CC to run.
This is useful when multiple versions are installed.  For example,
\c
.I version\c
\& might be `\|\c
.B 2.0\c
\&\|', meaning to run GNU CC version 2.0.

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

.SH MACHINE DEPENDENT OPTIONS
Each of the target machine types can have its own special options,
starting with `\|\c
.B \-m\c
\&\|', to choose among various hardware models or
configurations\(em\&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.

These are the `\|\c
.B \-m\c
\&\|' options defined for the 68000 series:
.TP
.B \-m68020
.TP
.B \-mc68020
Generate output for a 68020 (rather than a 68000).  This is the
default if you use the unmodified sources.
.TP
.B \-m68000
.TP
.B \-mc68000
Generate output for a 68000 (rather than a 68020).
.TP
.B \-m68881
Generate output containing 68881 instructions for floating point.
This is the default if you use the unmodified sources.
.TP
.B \-mfpa
Generate output containing Sun FPA instructions for floating point.
.TP
.B \-msoft\-float
Generate output containing library calls for floating point.
.I
WARNING: 
the requisite libraries are not part of GNU CC.  Normally 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.
.TP
.B \-mshort
Consider type \c
.B int\c
\& to be 16 bits wide, like \c
.B short int\c
\&.
.TP
.B \-mnobitfield
Do not use the bit-field instructions.  `\|\c
.B \-m68000\c
\&\|' implies
`\|\c
.B \-mnobitfield\c
\&\|'.
.TP
.B \-mbitfield
Do use the bit-field instructions.  `\|\c
.B \-m68020\c
\&\|' implies
`\|\c
.B \-mbitfield\c
\&\|'.  This is the default if you use the unmodified
sources.
.TP
.B \-mrtd
Use a different function-calling convention, in which functions
that take a fixed number of arguments return with the \c
.B rtd\c
\&
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 \c
.B printf\c
\&);
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 \c
.B rtd\c
\& instruction is supported by the 68010 and 68020
processors, but not by the 68000.
.PP

These `\|\c
.B \-m\c
\&\|' options are defined for the Vax:
.TP
.B \-munix
Do not output certain jump instructions (\c
.B aobleq\c
\& and so on)
that the Unix assembler for the Vax cannot handle across long
ranges.
.TP
.B \-mgnu
Do output those jump instructions, on the assumption that you
will assemble with the GNU assembler.
.TP
.B \-mg
Output code for g-format floating point numbers instead of d-format.
.PP

These `\|\c
.B \-m\c
\&\|' switches are supported on the Sparc:
.TP
.B \-mfpu
Generate output containing floating point instructions.  This is the
default if you use the unmodified sources.
.TP
.B \-mno\-epilogue
Generate separate return instructions for \c
.B return\c
\& statements.
This has both advantages and disadvantages; I don't recall what they
are.
.PP

These `\|\c
.B \-m\c
\&\|' options are defined for the Convex:
.TP
.B \-mc1
Generate output for a C1.  This is the default when the compiler is
configured for a C1.
.TP
.B \-mc2
Generate output for a C2.  This is the default when the compiler is
configured for a C2.
.TP
.B \-margcount
Generate code which puts an argument count in the word preceding each
argument list.  Some non-portable Convex and Vax programs need this word.
(Debuggers don't, except for functions with variable-length argument
lists; this information is in the symbol table.)
.TP
.B \-mnoargcount
Omit the argument count word.  This is the default if you use the
unmodified sources.
.PP

These `\|\c
.B \-m\c
\&\|' options are defined for the AMD Am29000:
.TP
.B \-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.
.TP
.B \-mnodw
Generate code that assumes the DW bit is not set.
.TP
.B \-mbw
Generate code that assumes the system supports byte and halfword write
operations.  This is the default.
.TP
.B \-mnbw
Generate code that assumes the systems does not support byte and
halfword write operations.  This implies `\|\c
.B \-mnodw\c
\&\|'.
.TP
.B \-msmall
Use a small memory model that assumes that all function addresses are
either within a single 256 KB segment or at an absolute address of less
than 256K.  This allows the \c
.B call\c
\& instruction to be used instead
of a \c
.B const\c
\&, \c
.B consth\c
\&, \c
.B calli\c
\& sequence.
.TP
.B \-mlarge
Do not assume that the \c
.B call\c
\& instruction can be used; this is the
default.
.TP
.B \-m29050
Generate code for the Am29050.
.TP
.B \-m29000
Generate code for the Am29000.  This is the default.
.TP
.B \-mkernel\-registers
Generate references to registers \c
.B gr64-gr95\c
\& instead of
\c
.B gr96-gr127\c
\&.  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 `\|\c
.B \-f\c
\&\|' flags
must use the normal, user-mode, names.
.TP
.B \-muser\-registers
Use the normal set of global registers, \c
.B gr96-gr127\c
\&.  This is the
default.
.TP
.B \-mstack\-check
Insert a call to \c
.B __msp_check\c
\& after each stack adjustment.  This
is often used for kernel code.
.PP

These `\|\c
.B \-m\c
\&\|' options are defined for Motorola 88K architectures:
.TP
.B \-mbig\-pic
Emit position-independent code, suitable for dynamic linking, even if
branches need large displacements.  Equivalent to the general-use option `\|\c
.B \-fPIC\c
\&\|'.
The general-use option `\|\c
.B \-fpic\c
\&\|',
by contrast, only emits valid 88k code if all branches involve small
displacements. 
GCC does not emit position-independent code by default.
.TP
.B \-midentify\-revision
Include an \c
.B ident\c
\& directive in the assembler output recording the
source file name, compiler name and version, timestamp, and compilation
flags used.
.TP
.B \-mno\-underscores
In assembler output, emit symbol names without adding an underscore
character at the beginning of each name.  The default is to use an
underscore as prefix on each name.
.TP
.B \-mno\-check\-zero\-division
.TP
.B \-mcheck\-zero\-division
Early models of the 88K architecture had problems with division by zero;
in particular, many of them didn't trap.  Use these options 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
`\|\c
.B \-mcheck\-zero\-division\c
\&\|' by default.
.TP
.B \-mocs\-debug\-info
.TP
.B \-mno\-ocs\-debug\-info
Include (or omit) additional debugging information (about
registers 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.
.TP
.B \-mocs\-frame\-position
.TP
.B \-mno\-ocs\-frame\-position
Force (or do not require) register values to be stored in a particular
place in stack frames, as specified in OCS.  The DG/UX, Delta88 SVr3.2,
and BCS configurations use `\|\c
.B \-mocs\-frame\-position\c
\&\|'; other 88k
configurations have the default `\|\c
.B \-mno\-ocs\-frame\-position\c
\&\|'.
.TP
.B \-moptimize\-arg\-area
.TP
.B \-mno\-optimize\-arg\-area
Control how to store function arguments in stack frames.
`\|\c
.B \-moptimize\-arg\-area\c
\&\|' saves space, but may break some
debuggers (not GDB).  `\|\c
.B \-mno\-optimize\-arg\-area\c
\&\|' conforms better to
standards.   By default GCC does not optimize the argument area.
.TP
.BI "\-mshort\-data\-" "num"\c
\&
.I num\c
\&
Generate smaller data references by making them relative to \c
.B r0\c
\&,
which allows loading a value using a single instruction (rather than the
usual two).  You control which data references are affected by
specifying \c
.I num\c
\& with this option.  For example, if you specify
`\|\c
.B \-mshort\-data\-512\c
\&\|', then the data references affected are those
involving displacements of less than 512 bytes.
`\|\c
.B \-mshort\-data\-\c
.I num\c
\&\c
\&\|' is not effective for \c
.I num\c
\& greater
than 64K.
.TP
.B \-msvr4
.TP
.B \-msvr3
Turn on (`\|\c
.B \-msvr4\c
\&\|') or off (`\|\c
.B \-msvr3\c
\&\|') compiler extensions
related to System V release 4 (SVr4).  This controls the following:
.TP
\ \ \ \(bu 
Which variant of the assembler syntax to emit (which you can select
independently using `\|\c
.B \-mversion03.00\c
\&\|').  
.TP
\ \ \ \(bu
`\|\c
.B \-msvr4\c
\&\|' makes the C preprocessor recognize `\|\c
.B #pragma weak\c
\&\|'
.TP
\ \ \ \(bu
`\|\c
.B \-msvr4\c
\&\|' makes GCC issue additional declaration directives used in
SVr4.  
.PP
`\|\c
.B \-msvr3\c
\&\|' is the default for all m88K configurations except
the SVr4 configuration.
.TP
.B \-mtrap\-large\-shift
.TP
.B \-mhandle\-large\-shift
Include code to detect bit-shifts of more than 31 bits; respectively,
trap such shifts or emit code to handle them properly.  By default GCC
makes no special provision for large bit shifts.
.TP
.B \-muse\-div\-instruction
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 d