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Selecting one of the following will take you directly to that section:
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 Linux systems using IA-32 architecture and Intel 64 architecture,
-O1 sets the following options:
-funroll-loops0, -fno-builtin, -mno-ieee-fp,
-fomit-frame-pointer, -ffunction-sections, -ftz
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 systems using IA-32 architecture and Intel 64 architecture,
when O3 is used with options
-ax or -x (Linux) or with options /Qax or /Qx (Windows), the compiler
performs more aggressive data dependency analysis than for O2, which
may result in longer compilation times.
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.
On Linux systems, the O3 option sets option
-fomit-frame-pointer.
Tells the compiler the maximum number of times to unroll loops. For example -unroll2 would unroll a maximum of 2 times.
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
This option 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/-Qipo option and must be able to analyze all library/external calls the program makes.
This option requires that the size of the program executable never exceeds 232 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.
-scalar-rep enables scalar replacement performed during loop transformation. To use this option, you must also specify O3. -scalar-rep- disables this optimization.
This options tells the compiler to assume no aliasing in the program.
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)
-xT (generate code specialized for Intel(R) Core(TM)2 Duo processors, Intel(R) Core(TM)2 Quad processors and Intel(R) Xeon(R) processors with SSSE3)
-static Statically link in libraries at link time
-no-prec-div (disable -prec-div) where -prec-div improves precision of FP divides (some speed impact)
To override one of the options set by -fast, specify that option after the -fast option on the command line. The exception is the xT option which can't be overridden. The options set by -fast may change from release to release.
Code is optimized for Intel(R) Core(TM)2 Duo processors, Intel(R) Core(TM)2 Quad processors and Intel(R) Xeon(R) processors with SSSE3. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.
Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.
Code is optimized for Intel Pentium M and compatible Intel processors. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.
Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.
Code is optimized for Intel Pentium 4 and compatible Intel processors; this is the default for Intel?EM64T systems. The resulting code may contain unconditional use of features that are not supported on other processors.
Tells the auto-parallelizer to generate multithreaded code for loops that can be safely executed in parallel. To use this option, you must also specify option O2 or O3. The default numbers of threads spawned is equal to the number of processors detected in the system where the binary is compiled. Can be changed by setting the environment variable OMP_NUM_THREADS
The use of -Qparallel to generate auto-parallelized code requires spport libraries that are dynamically linked by default. Specifying libguide.lib on the link line, statically links in libguide.lib to allow auto-parallelized binaries to work on systems which do not have the dynamic version of this library installed.
The use of -Qparallel to generate auto-parallelized code requires spport libraries that are dynamically linked by default. Specifying libguide40.lib on the link line, statically links in libguide40.lib to allow auto-parallelized binaries to work on systems which do not have the dynamic version of this library installed.
Optimizes for Intel Pentium 4 and compatible processors with Streaming SIMD Extensions 2 (SSE2).
-no-prec-div enables optimizations that give slightly less precise results than full IEEE division.
When you specify -no-prec-div along with some optimizations, such as -xN and -xB (Linux) or /QxN and /QxB (Windows), the compiler may change floating-point division computations into multiplication by the reciprocal of the denominator. For example, A/B is computed as A * (1/B) to improve the speed of the computation.
However, sometimes the value produced by this transformation is not as accurate as full IEEE division. When it is important to have fully precise IEEE division, do not use -no-prec-div which will enable the default -prec-div and the result is more accurate, with some loss of performance.
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, -prof-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
Disable loop unrolling.
-f[no-]builtin[-func]
func A comma-separated list of intrinsic functions.
This option enables [disables] inline expansion of one or more intrinsic functions. If -func is not specified, -fno-builtin disables inline expansion for all intrinsic functions.
-mieee-fp : This option maintains floating-point precision
while disabling some optimizations. It restricts optimization
to maintain declared precision and to ensure that
floating-point arithmetic conforms more closely
to the ANSI* language and IEEE* arithmetic standards.
For most programs, specifying this option adversely affects
performance. If you are not sure whether your application
needs this option, try compiling and running your program
both with and without it to evaluate the effects
on both performance and precision.
-mno-ieee-fp : The compiler provides good accuracy and run-time performance at the expense of less consistent floating-point results.
Places each function in its own COMDAT section.
This option flushes denormal results to zero when the application is in the gradual underflow mode. It may improve performance if the denormal values are not critical to your application's behavior.
Enable SmartHeap and/or other library usage by forcing the linker to ignore multiple definitions if present
Enable SmartHeap library usage by forcing the linker to ignore multiple definitions
MicroQuill SmartHeap Library V8.1 available from http://www.microquill.com/
Enable the use of the 64-bit compiler by passing the directory names for the library and include files
set the stack reserve amount specified to the linker
Enable/disable(DEFAULT) use of ANSI aliasing rules in optimizations; user asserts that the program adheres to these rules.
Enable/disable(DEFAULT) the compiler to generate prefetch instructions to prefetch data.
Directs the compiler to inline calloc() calls as malloc()/memset()
The compiler adds setup code in the C/C++/Fortran main function to enable optimal malloc algorithms:
Function: int mallopt (int param, int value) When calling mallopt, the param argument specifies the parameter to be set, and value the new value to be set. Possible choices for param, as defined in malloc.h, are:
Enables cache/bandwidth optimization for stores under conditionals (within vector loops) This option tells the compiler to perform a conditional check in a vectorized loop. This checking avoids unnecessary stores and may improve performance by conserving bandwidth.
Enable compiler to generate runtime control code for effective automatic parallelization. This option generates code to perform run-time checks for loops that have symbolic loop bounds. If the granularity of a loop is greater than the parallelization threshold, the loop will be executed in parallel. If you do not specify this option, the compiler may not parallelize loops with symbolic loop bounds if the compile-time granularity estimation of a loop can not ensure it is beneficial to parallelize the loop.
Select the method that the register allocator uses to partition each routine into regions
Select the method that the register allocator uses to partition each routine into regions
Multi-versioning is used for generating different versions of the loop based on run time dependence testing, alignment and checking for short/long trip counts. If this option is turned on, it will trigger more versioning at the expense of creating more overhead to check for pointer aliasing and scalar replacement.
Make all local variables AUTOMATIC. Same as -automatic
Enables more aggressive unrolling heuristics
-opt-streaming-stores keyword
This option enables generation of streaming stores for optimization. This method stores data with instructions that use a non-temporal buffer, which minimizes memory hierarchy pollution.
For this option to be effective, the compiler must be able to generate SSE2 (or higher) instructions.
Possible keywords are:
always - enables generation of streaming stores under
the assumption that the application is memory bound
auto - compiler decides when streaming stores are used (DEFAULT)
never - disables generation of streaming stores
Disables 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.
This option enables most speed optimizations, but disables some that increase code size for a small speed benefit.
This option enables global optimizations.
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.
This option tells the compiler to separate functions into COMDATs for the linker.
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.
For mixed-language benchmarks, tell the compiler to convert routine names to lowercase for compatibility
For mixed-language benchmarks, tell the compiler to assume that routine names end with an underscore
Tell the compiler to treat source files as C++ regardless of the file extension
This option specifies that the main program is not written in Fortran. It is a link-time option that prevents the compiler from linking for_main.o into applications.
For example, if the main program is written in C and calls a Fortran subprogram, specify -nofor-main when compiling the program with the ifort command. If you omit this option, the main program must be a Fortran program.
Invoke the Intel C compiler 10.1 for IA-32 applications.
Invoke the Intel C++ compiler 10.1 for IA-32 applications.
Invoke the Intel Fortran compiler 10.1 for IA-32 applications.
Compiler option to set the path for include files. Used in some peak benchmarks which were built using the Intel 32-bit C/C++ compiler.
Compiler option to set the path for library files. Used in some peak benchmarks which were built using the Intel 32-bit C/C++ compiler.
Compiler option to set the path for include files. Used in some peak benchmarks which were built using the Intel 32-bit Fortran compiler.
Compiler option to set the path for library files. Used in some peak benchmarks which were built using the Intel 32-bit Fortran compiler.
Invoke the Intel C compiler 10.1 for Intel 64 applications.
You need binutils 2.16.91.0.7 or later with this compiler to support new instructions on Intel Core 2 processors
Invoke the Intel C++ compiler 10.1 for Intel 64 applications.
You need binutils 2.16.91.0.7 or later with this compiler to support new instructions on Intel Core 2 processors
Invoke the Intel Fortran compiler 10.1 for Intel 64 applications.
You need binutils 2.16.91.0.7 or later with this compiler to support new instructions on Intel Core 2 processors
Compiler option to statically link in libraries at link time
One or more of the following settings may have been set. If so, the corresponding notes sections of the report will say so; and you can read below to find out more about what these settings mean.
OMP_NUM_THREADS
This Environment Variable
sets the maximum number of threads to use for OpenMP* parallel regions
if no other value is specified in the application.
This environment variable applies to both -openmp and -parallel
(Linux and Mac OS X) or /Qopenmp and /Qparallel (Windows).
Example syntax on a Linux system with 8 cores:
export OMP_NUM_THREADS=8
Default is the number of cores visible to the OS.
KMP_STACKSIZE=integer[B|K|M|G|T] (Linux)
Sets the number of bytes to allocate for each parallel thread to use as its private stack. Use the optional suffix B, K, M, G, or T, to specify bytes, kilobytes, megabytes, gigabytes, or terabytes. The default setting is 2M on IA32 and 4M on IA64.
KMP_AFFINITY
KMP_AFFINITY = < physical | logical >, starting-core-id
This Environment Variable
specifies the static mapping of user threads to physical cores,
for example, if you have a system
configured with 8 cores, OMP_NUM_THREADS=8 and KMP_AFFINITY=physical,2.
Thread 0 will mapped to core 2, thread 1 will be mapped to core 3, and
so on in a round-robin fashion.
Hardware Prefetch:
This BIOS option allows the enabling/disabling of a processor mechanism to prefetch data into the cache according to a pattern-recognition algorithm.
In some cases, setting this option to Disabled may improve performance. Users should only disable this option after performing application benchmarking to verify improved performance in their environment.
Adjacent Cache-Line Prefetch:
This BIOS option allows the enabling/disabling of a processor mechanism to fetch the adjacent cache line within an 128-byte sector that contains the data needed due to a cache line miss.
In some cases, setting this option to Disabled may improve performance. Users should only disable this option after performing application benchmarking to verify improved performance in their environment.
Snoop Filter Enabled/Disabled:
This BIOS option enables/disables the Snoop Filter.
The Snoop Filter is designed to reduce system bus utilization
coming from cache misses. On the Intel 5000X and 5400 chipset,
it is built as a cache structure able to minimize unnecessary
snoop traffic.
When enabled, it can lead to significant memory performance
improvements for several workstation applications
on suitable memory configurations.
ulimit -s < n | unlimited >
This Linux command (a bash builtin command) sets the stack size to n kbytes, or unlimited to allow the stack size to grow without limit.
submit= MYMASK=`printf '0x%x' \$((1<<\$SPECCOPYNUM))`; /usr/bin/taskset \$MYMASK $command
When running multiple copies of benchmarks, the SPEC config file feature submit is sometimes used to cause individual jobs to be bound to specific processors. This specific submit command is used for Linux. The description of the elements of the command are: