OPT(5) Last changed: 3-10-98
OPT - Miscellaneous compiler optimizations option group
-OPT: ...
IRIX systems
This man page describes the general optimization options accepted by
the f90(1), f77(1), CC(1), cc(1), and c89(1) commands.
The -OPT: option group controls miscellaneous optimizations. This
option overrides default optimizations.
You can specify more than one suboption to the -OPT: option either by
using colons to separate each suboption or by specifying multiple
options on the command line. For example, the following command lines
are equivalent:
f90 -OPT:cis=ON:cray_ivdep=OFF b.f
f90 -OPT:cis=ON -OPT:cray_ivdep=OFF b.f
Some -OPT: suboptions are specified with a setting that either enables
or disables the feature. To enable a feature, specify the suboption
either alone or with =1, =ON, or =TRUE. To disable a feature, specify
the suboption with either =0, =OFF, or =FALSE. For example, the
following command lines are equivalent:
f90 -OPT:cis:cray_ivdep=OFF:div_split=FALSE a.f
f90 -OPT:cis=1:cray_ivdep=0:div_split=OFF a.f
For brevity, this man page shows only the ON or OFF settings to
suboptions, but 0, 1, TRUE, and FALSE are also allowed as settings.
There are other options to the compiler commands that control
optimization. For information on the general optimization levels, see
the -O option on the command man page for your compiler. For
information about inlining and interprocedural optimization, see the
-INLINE: ... option or the ipa(5) man page. For information on loop
nest optimization, see the lno(5) man page.
The -OPT: option accepts the following suboptions:
Suboptions Action
alias=name Specifies the pointer aliasing model to be used. By
specifiying one of the following for name, the compiler is
able to make assumptions throughout the compilation:
name Assumption
ANY or COMMON_SCALAR ANY specifies that any two memory
references can be aliased unless
the compiler can determine
otherwise. Default pointer
aliasing model.
COMMON_SCALAR specifies that scalar
variables that are defined in a
common block along with array
variables are not referenced or
modified by any accesses of the
array variables.
(C and C++ only)
cray_pointer or no_cray_pointer
cray_pointer asserts that a
pointee's storage is never overlaid
on another variable's storage. The
pointee is stored in memory before
a call to an external procedure and
is read out of memory as its next
reference. It is also stored
before a RETURN or END statement of
a subprogram
no_cray_pointer asserts that a
pointee's storage can overlay on
another variable's storage.
Default.
(Fortran 90 or FORTRAN 77)
TYPED or NO_TYPED TYPED specifies that pointers of
distinct base types are assumed to
point to distinct, non-overlapping
objects.
NO_TYPED specifies that pointers to
different base types may point to
the same object.
(C and C++ only)
UNNAMED or NO_UNNAMED UNNAMED specifies that pointers are
assumed never to point to named
objects.
NO_UNNAMED specifies that the
pointer may point to named object.
(C and C++ only)
RESTRICT or NO_RESTRICT RESTRICT specifies that distinct
pointers are assumed to point to
distinct, non-overlapping objects.
NO_RESTRICT specifies that distinct
pointers may point to overlapping
storage.
(C and C++ only)
parm or no_parm parm asserts that Fortran
parameters do not alias to any
other variable. Default.
no_parm asserts that Fortran
parameters can alias to any other
variable.
(Fortran 90 or FORTRAN 77)
cis[ = ( ON|OFF )]
Converts SIN/COS pairs with the same argument to a single
call that calculates both values at once. The default is
ON.
const_copy_limit=n
(cc, c89, and f77 only) Do not do const/copy propagation if
there are more than n expressions in a subprogram. Default
is n=10000.
cray_ivdep[ = ( ON|OFF )]
Specifies that the compiler should use UNICOS semantics when
a !DIR$ IVDEP directive (Fortran) or a #pragma ivdep
statement (C) is encountered. With UNICOS semantics, the
compiler ignores all loop iteration dependencies. The
default is OFF. Also see the -OPT:liberal_ivdep[ = ( ON|OFF
)] option.
div_split[ = ( ON|OFF )]
Enables or disables the calculation of x/y as x*(1.0/y).
The default is div_split=OFF.
This is typically enabled by the -OPT:IEEE_arithmetic=3
option. Also see the -OPT:recip option. This option should
be used with caution because it produces less accurate
results.
fast_bit_intrinsics[ = ( ON|OFF )]
ON turns off the check for the bit count being within range
for Fortran bit intrinsics (for example, BTEST and ISHFT).
The default is OFF.
fast_complex[ = ( ON|OFF )]
fast_complex=ON enables fast calculations for values
declared as type complex. When set to ON, complex absolute
value (norm) and complex division use fast algorithms that
overflow for an operand (divisor, in the case of division)
that has an absolute value that is larger than the square
root of the largest representable floating-point number (or
underflow for a value that is smaller than the square root
of the smallest representable floating point number).
The default is OFF. fast_complex=ON is enabled if
-OPT:roundoff=3 is in effect.
fast_exp[ = ( ON|OFF )]
fast_exp=ON enables optimization of exponentiation by
replacing the run-time call for exponentiation by
multiplication and/or square root operations for certain
compile-time constant exponents (integers and halves). This
can produce differently rounded results than the run-time
function. fast_exp=ON is in effect unless -OPT:roundoff=1
is in effect. The default is ON.
fast_io[ = ( ON|OFF )]
(C/C++ only) Enables inlining of printf(), fprintf(),
sprintf(), scanf(), fscanf(), sscanf(), and printw(). This
option is in effect only when the candidates for inlining
are marked as intrinsic in the stdio.h and curses.h files.
The default is OFF.
fast_nint[ = ( ON|OFF )]
fast_nint=ON uses hardware features to implement NINT and
ANINT (both single- and double-precision versions). The
default is OFF, but fast_nint=ON is enabled by default if
-OPT:roundoff=3 is in effect. fast_nint=ON is also enabled
when fast_trunc=ON is in effect.
FORTRAN 77 and Fortran 90 only: This violates the FORTRAN
77 and Fortran 90 standards for certain argument values
because it rounds as specified by the IEEE standard, rather
than as specified by the Fortran standards (for example,
FORTRAN 77 specifies that NINT(1.5) is 2, and NINT(2.5) is
3, while IEEE rounds both of these to 2). If fast_trunc is
also enabled, NINT and ANINT are implemented with round
instructions (i.e., fast_nint takes precedence for these
intrinsics).
fast_sqrt[ = ( ON|OFF )]
fast_sqrt=ON calculates square roots using the identity
sqrt(x) = x*rsqrt(x), where rsqrt is the reciprocal square
root operation. The default is OFF. This option is ignored
unless -mips4 and -r8000 are also in effect.
WARNING: This option results in sqrt(0.0) producing a NaN
result. Use it only when zero sqrt operands are not valid.
fast_trunc[ = ( ON|OFF )]
fast_trunc=ON inlines the NINT, ANINT, AINT, and AMOD
Fortran intrinsics, both single- and double-precision
versions. The default is OFF. fast_trunc=ON is enabled
automatically if -OPT:roundoff=1 (or greater) is in effect.
FORTRAN 77 and Fortran 90 only: Although this is compliant
with the FORTRAN 77 and Fortran 90 standards, it reduces the
valid argument range. If fast_nint is also enabled, NINT
and ANINT are implemented with round instructions (that is,
fast_nint takes precedence for these intrinsics).
fold_reassociate[ = ( ON|OFF )]
fold_reassociate=ON allows optimizations involving
reassociation of floating-point quantities. The default is
OFF. fold_reassociate=ON is enabled automatically when -O3
is in effect or when -OPT:roundoff=2 or greater is in
effect.
fold_unsafe_relops[ = ( ON|OFF )]
fold_unsafe_relops=ON folds relational operators in the
presence of possible integer overflow. The default is ON.
fold_unsigned_relops[ = ( ON|OFF )]
fold_unsigned_relops=ON folds unsigned relational operators
in the presence of possible integer overflow. The default
is OFF.
got_call_conversion[ = ( ON|OFF )]
got_call_conversion=ON loads function addresses to be moved
out of loops. The load is set up with the proper relocation
so that the address is resolved at program start-up time.
The default is OFF when -O2 or lower is in effect.
got_call_conversion=ON when -O3 is in effect.
NOTE: This option should be disabled when compiling shared
objects that contain function addresses that may be
preempted by rld(1). For more information, see the dso(5)
man page.
IEEE_arithmetic=n
Specifies the level of conformance to ANSI/IEEE 754-1985,
the IEEE Standard for Binary Floating-point Arithmetic,
which describes a standard for, among other things, NaN and
inf operands, arithmetic round off, and overflow. n can be
one of the following:
n Description
1 Inhibits optimizations that produce less accurate
results than required by ANSI/IEEE 754-1985. This is
the default.
2 Allows compiler optimizations that can produce less
accurate inexact results (but accurate exact results) on
the target hardware. That is, expressions that would
have produced a NaN or an inf may produce different
answers, but otherwise answers are the same as those
obtained when IEEE_arithmetic=1 is in effect. Examples:
0*X may be changed to 0, and X/X may be changed to 1
even though this is inaccurate when X is +inf, -inf, or
NaN.
3 Performs arbitrary, mathematically valid
transformations, even if they can produce inaccurate
results for operations specified in ANSI/IEEE 754-1985.
These transformations can cause overflow or underflow
for a valid operand range. An example is the conversion
of x/y to x*recip(y) for MIPS IV targets. Also see the
-OPT:roundoff=n option.
IEEE_comparisons[ = ( ON|OFF )]
Forces all comparisons to yield results that conform to
ANSI/IEEE 754-1985, the IEEE Standard for Binary Floatingpoint
Arithmetic, which describes a standard for NaN and inf
operands. The default is IEEE_comparisons=OFF.
IEEE_comparisons=OFF produces non-IEEE results for
comparisons. For example, x=x is treated as TRUE without
executing a test.
NOTE: This option has been deprecated and will be removed in
a future release. The preferred alternative is the
-OPT:IEEE_NaN_inf= option.
(Fortran 90 only)
IEEE_NaN_inf[ = ( ON|OFF )]
IEEE_NaN_inf=ON forces all operations that might have IEEE-754
NaN or infinity operands to yield results that conform to
ANSI/IEEE 754-1985, the IEEE Standard for Binary Floatingpoint
Arithmetic, which specifies the standard for NaN and inf
operands. The default is OFF.
IEEE_NaN_inf=OFF produces non-IEEE results for various
operations. For example, x=x is treated as TRUE without
executing a test and x/x is simplified to 1 without dividing.
Turning this option on may suppress many such common
optimizations and hurt performance.
inline_intrinsics[ = ( ON|OFF )]
inline_intrinsics=OFF turns all Fortran intrinsics that have a
library function into a call to that function. The default is
ON.
liberal_ivdep[ = ( ON|OFF )]
Instructs the compiler to ignore all vector dependencies when
encountering IVDEP directives. The default is OFF.
Olimit=n
Specifies that any routine bigger than n should not be
optimized. If -O2 or greater is in effect and a routine is so
big that the compile speed may be slow, the compiler generates
a message indicating the Olimit value that is needed to
optimize. You can recompile with that value of n, or you can
recompile with -OPT:Olimit=0 and avoid having any Olimit
cutoff.
pad_common[ = ( ON|OFF )]
pad_common=ON reorganizes common blocks to improve the cache
behavior of accesses to members of the common block. This may
involve adding padding between members and/or breaking a
common block into a collection of common blocks. The default
is OFF.
This option should not be used unless the common block
definitions (including EQUIVALENCE) are consistent among all
sources comprising a program. In addition, pad_common=ON
should not be specified if common blocks are initialized with
DATA statements. If specified, pad_common=ON must be used for
all of source files in the program.
pad_common=ON is supported for Fortran only. It should not be
used if a common block is referenced from C code.
recip[ = ( ON|OFF )]
recip=ON specifies that faster, but potentially less accurate,
reciprocal operations should be performed. The default is
OFF.
If -O3 or -OPT:IEEE_arithmetic=2 or above are in effect,
recip=ON is enabled. The recip=ON setting is effective only
if -r8000 is in effect.
reorg_common[ = ( ON|OFF )]
reorg_common=ON reorganizes common blocks to improve the cache
behavior of accesses to members of the common block. The
reorganization is done only if the compiler detects that it is
safe to do so.
reorg_common=ON is enabled when -O3 is in effect and when all
files that reference the common block are compiled at -O3.
reorg_common=OFF is set when the file that contains the common
block is compiled at -O2 (or below).
roundoff=n
Specifies the level of acceptable departure from source
language floating-point, round-off, and overflow semantics. n
can be one of the following:
n Description
0 Inhibits optimizations that might affect the
floating-point behavior. This is the default when
optimization levels -O0, -O1, and -O2 are in effect.
1 Allows simple transformations that might cause limited
round-off or overflow differences. Compounding such
transformations could have more extensive effects.
2 Allows more extensive transformations, such as the
reordering of reduction loops. This is the default level
when -O3 is in effect.
3 Enables any mathematically valid transformation.
To obtain best performance in conjunction with software
pipelining, specify roundoff=2 or roundoff=3. This is because
reassociation is required for many transformations to break
recurrences in loops. Also see the descriptions for the
-OPT:IEEE_arithmetic, -OPT:fast_complex, -OPT:fast_trunc, and
-OPT:fast_nint options.
rsqrt[ = ( ON|OFF )]
rsqrt=ON specifies that faster, but potentially less accurate,
square root operations should be performed. The default is
OFF.
If -OPT:IEEE_arithmetic=2 (or above) or -O3 are in effect,
rsqrt=ON is enabled.
space[ = ( ON|OFF )]
space=ON specifies that code space is to be given priority in
tradeoffs with execution time in optimization choices. For
instance, this forces all exits from a function to go through
a single exit block. The default is OFF.
swp[ = ( ON|OFF )]
swp=ON enables software pipelining. swp=ON is enabled when
-O3 is in effect. The default is OFF.
unroll_analysis[ = ( ON|OFF )]
unroll_analysis=ON analyzes resource usage and recurrences in
bodies of innermost loops that do not qualify for being fully
unrolled. Such loops are unrolled only to the extent to which
there is a potential benefit in doing so. A loop could be
unrolled, for example, to decrease the shortest possible
schedule length per iteration. The default is ON.
unroll_analysis=OFF can have the negative effect of unrolling
loops less than the upper limit dictated by the
OPT:unroll_times_max and OPT:unroll_size specifications.
unroll_size=n
Specifies the maximum size (in instructions) of an unrolled
loop. Specify an integer for n. The default is 320.
This option indirectly determines which loops can be fully
unrolled. Also see the -OPT:unroll_times_max option.
unroll_times_max=n
Specifies the maximum number of times a loop will be unrolled
if it is not going to be fully unrolled. Specify an integer
for n. The default is 8 when -mips4 is in effect. The
default is 4 when -mips3 is in effect. Also see the
-OPT:unroll_size option.
wrap_around_unsafe_opt[ = ( ON|OFF )]
wrap_around_unsafe_opt=OFF disables both the induction
variable replacement and linear function test replacement
optimizations. By default, these optimizations are enabled at
-O2 and -O3. This option is disabled by default at -O0.
Setting this option to OFF can degrade performance. It is
provided, however, as a diagnostic tool to identify the
situation described previously.
cc(1), CC(1), cord(1), dso(1), f77(1), f90(1), fpmode(1), hinv(1),
ld(1), make(1), pixie(1), pmake(1), prof(1), rld(1), smake(1).
math(3M).
auto_p(5), gp_overflow(5), ipa(5), lno(5), pe_environ(5).
C Language Reference Manual, publication 007-0701-120
MIPSpro C and C++ Pragmas, publication 007-3587-001
Compiler Information File (CIF) Reference Manual, publication SR-2401
MIPSPro 7 Fortran 90 Commands and Directives Reference Manual,
publication SR-3907
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