SPEC MPI2007 Flag Descriptions for HP-MPI
HEADER for PORTABILITY
]]>
HEADER for OPTIMIZATION
]]>
Enables optimizations for speed and disables some optimizations that
increase code size and affect speed.
To limit code size, this option:
- Enables global optimization; this includes data-flow analysis,
code motion, strength reduction and test replacement, split-lifetime
analysis, and instruction scheduling.
- Disables intrinsic recognition and intrinsics inlining.
The O1 option may improve performance for applications with very large
code size, many branches, and execution time not dominated by code within loops.
On Linux64 platforms, -O1 disable software pipelining and global code scheduling.
On Intel Itanium processors, this option also enables optimizations for server applications
(straight-line and branch-like code with a flat profile).
-unroll0, -fbuiltin, -mno-ieee-fp, -fomit-frame-pointer (same as -fp), -ffunction-sections
]]>
Enables optimizations for speed. This is the generally recommended
optimization level. This option also enables:
- Inlining of intrinsics
- Intra-file interprocedural optimizations, which include:
- inlining
- constant propagation
- forward substitution
- routine attribute propagation
- variable address-taken analysis
- dead static function elimination
- removal of unreferenced variables
- The following capabilities for performance gain:
- constant propagation
- copy propagation
- dead-code elimination
- global register allocation
- global instruction scheduling and control speculation
- loop unrolling
- optimized code selection
- partial redundancy elimination
- strength reduction/induction variable simplification
- variable renaming
- exception handling optimizations
- tail recursions
- peephole optimizations
- structure assignment lowering and optimizations
- dead store elimination
]]>
Enables O2 optimizations plus more aggressive optimizations,
such as prefetching, scalar replacement, and loop and memory
access transformations. Enables optimizations for maximum speed,
such as:
- Loop unrolling, including instruction scheduling
- Code replication to eliminate branches
- Padding the size of certain power-of-two arrays to allow
more efficient cache use.
On Intel Itanium processors, the O3 option enables optimizations
for technical computing applications (loop-intensive code):
loop optimizations and data prefetch.
The O3 optimizations may not cause higher performance unless loop and
memory access transformations take place. The optimizations may slow
down code in some cases compared to O2 optimizations.
The O3 option is recommended for applications that have loops that heavily
use floating-point calculations and process large data sets.
]]>
-i-static prevents linking intel libraries as shared libraries.
]]>
This option enables additional interprocedural optimizations for single
file compilation. These optimizations are a subset of full intra-file
interprocedural optimizations. One of these optimizations enables the
compiler to perform inline function expansion for calls to functions
defined within the current source file.
Multi-file ip optimizations that includes:
- inline function expansion
- interprocedural constant propogation
- dead code elimination
- propagation of function characteristics
- passing arguments in registers
- loop-invariant code motion
]]>
The -fast option enhances execution speed across the entire program
by including the following options that can improve run-time performance:
-O3 (maximum speed and high-level optimizations)
-ipo (enables interprocedural optimizations across files)
-static (link libraries statically)
To override one of the options set by /fast, specify that option after the
-fast option on the command line. The options set by /fast may change from
release to release.
]]>
Instrument program for profiling for the first phase of
two-phase profile guided otimization. This instrumentation gathers information
about a program's execution paths and data values but does not gather
information from hardware performance counters. The profile instrumentation
also gathers data for optimizations which are unique to profile-feedback
optimization.
]]>
Instructs the compiler to produce a profile-optimized
executable and merges available dynamic information (.dyn)
files into a pgopti.dpi file. If you perform multiple
executions of the instrumented program, -Qprof_use merges
the dynamic information files again and overwrites the
previous pgopti.dpi file.
Without any other options, the current directory is
searched for .dyn files
]]>
Tells the compiler the maximum number of times (n) to unroll loops.
Enables inline expansion of all intrinsic functions.
Disables conformance to the ANSI C and IEEE 754 standards for
floating-point arithmetic.
]]>
Allows use of EBP as a general-purpose register in optimizations.
Places each function in its own COMDAT section.
]]>
Specifies the level of inline function expansion.
Ob0 - Disables inlining of user-defined functions. Note that
statement functions are always inlined.
Ob1 - Enables inlining when an inline keyword or an inline
attribute is specified. Also enables inlining according
to the C++ language.
Ob2 - Enables inlining of any function at the compiler's
discretion.
]]>
-static prevents linking with shared libraries.
]]>
This option enables read only string-pooling optimization.
This option enables read/write string-pooling optimization.
This option disables stack-checking for routines with 4096 bytes
of local variables and compiler temporaries.
]]>
Enable SmartHeap library usage by forcing the linker to
ignore multiple definitions
Enable SmartHeap library usage by forcing the linker to
ignore multiple definitions
Generates specialized code to run exclusively on processors with the extensions T.
This option can generate SSSE3, SSE3, SSE2, and SSE instructions for Intel processors,
and it can optimize for the Intel (R) Core (TM) 2 Duo processor family.
Flushes denormal floating point results to zero when the application is in gradual
underflow mode.
Enables optimizations that give slightly less precise results
than full IEEE division. With some optimizations, such as -xN
and -xB, the compiler may change floating-point division compu-
tations into multiplication by the reciprocal of the denomina-
tor. For example, A/B is computed as A * (1/B) to improve the
speed of the computation.
The default is -prec-div, which provides fully precise IEEE
division. It improves precision of floating-point divides by
disabling floating-point division-to-multiplication optimiza-
tions, resulting in greater accuracy with some loss of perfor-
mance.
Disables the insertion of software prefetching by the compiler.
Default is -prefetch.
Specifies the percentage multiplier that should be applied to all inlining options
that define upper limits. The value is a positive integer specifying the
percentage value. The default value is 100 (a factor of 1).
Enables use of faster but slightly less accurate code sequences for math
functions, including sqrt, reciprocal sqrt, divide and reciprocal. When
compared to strict IEEE* precision, this option slightly reduces the
accuracy of floating-point calculations performed by these functions,
usually limited to the least significant digit.
This option also performs reassociation transformations, which can alter the
order of operations, over a larger scope. The increased reasssociation
enables generation of more optimal sequences of floating-point multiply-add
instructions than not using this option. Note that use of floating-point
multiply-add can cause programs to produce different numerical results due
to changes in rounding.
Tells the compiler to assume the program does adhere to
to the Fortran 95 Standard type
aliasability rules (default).
Tells the compiler to assume the program does adhere to
the rules defined in the ISO C Standard. The default is to not assume such
adherence. If your C/C++ program adheres to these
rules, then -ansi-alias will allow the compiler to optimize
more aggressively. If it doesn't adhere to these
rules, then assuming so can cause the compiler to generate
incorrect code.
Do not assume arguments may be aliased. (DEFAULT = -alias-args).
Tells the compiler not to assume aliasing in the program (DEFAULT = -falias).
Instructs the compiler to analyze and transform the program so that 64-bit pointers are shrunk to 32-bit
pointers, and 64-bit longs (on Linux) are shrunk into 32-bit longs wherever it is legal and safe to do so.
In order for this option to be effective the compiler must be able to optimize using the -ipo option and
must be able to analyze all library or external calls the program makes.
This option requires that the size of the program executable never exceeds 2 (to the 32nd power) bytes and
all data values can be represented within 32 bits. If the program can run correctly in a 32-bit system,
these requirements are implicitly satisfied. If the program violates these size restrictions, unpredictable
behavior might occur.
The -Wl option directs the compiler to pass a list of arguments
to the linker. In this case, "-z muldefs" is passed to the
linker. For the Gnu linker (ld), the "-z keyword" option accepts
several recognized keywords. Keyword "muldefs" allows multiple
definitions. The muldefs keyword will enable, for example,
linking with third party libraries like SmartHeap from
Microquill.
Rule to eat the paths from SmartHeap library inclusion.
MicroQuill SmartHeap Library available from http://www.microquill.com/