SPEC CPU2006 Flag Description for the Intel(R) C++ Compiler 10.1 for IA32 and Intel 64 applications and Intel(R) Fortran Compiler 10.1 for IA32 and Intel 64 applications

Optimization Flags

• • -O1
  • -O1\b

  • 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

  • Includes:
    • -funroll-loops0
    • -fno-builtin
    • -mieee-fp
    • -fomit-frame-pointer
    • -ffunction-sections
    • -ftz
• • -O2
  • -O2\b

  • 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
    

• • -O3
  • -O3\b

  • 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.

  • Includes:
    • -O2
    • -fomit-frame-pointer
• • -unroll_n
  • -unroll\d+\b

  • Tells the compiler the maximum number of times to unroll loops. For example -unroll2 would unroll a maximum of 2 times.

• • -ip
  • -ip\b

  • 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.

• • -ipo
  • -ipo\b

  • 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

• • -auto-ilp32
  • -auto-ilp32\b

  • 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.

• • -noformain
  • -nofor_main\b

  • 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.

• • -disablescalarrep
  • -scalar-rep-

  • -scalar-rep enables scalar replacement performed during loop transformation. To use this option, you must also specify O3. -scalar-rep- disables this optimization.

• • -no-alias
  • -fno-alias\b

  • This options tells the compiler to assume no aliasing in the program.

• • -fast
  • -fast\b

  • 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.

  • Includes:
    • -O3
      • -O2
      • -fomit-frame-pointer
    • -ipo
    • -xT
    • -static
    • -no-prec-div
• • -xT
  • -xT\b

  • 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.

• • -QxB
  • -QxB\b

  • 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.

• • -QxW
  • -QxW\b

  • 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.

• • -parallel
  • -parallel\b

  • 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

• • -libguide.lib
  • libguide.lib\b

  • 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.

• • -libguide40.lib
  • libguide40.lib\b

  • 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.

• • -archSSE2
  • -arch\:SSE2\b

  • Optimizes for Intel Pentium 4 and compatible processors with Streaming SIMD Extensions 2 (SSE2).

• • -no-prec-div
  • -no-prec.div
  • (disable/enable[default] -prec-div)

    -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.

• • -prof_gen
  • -prof-gen\b

  • 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.

• • -prof_use
  • -prof-use\b

  • 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

• • -fomit-frame-pointer
  • -fomit-frame-pointer\b
  • This option determines whether EBP is used as a general-purpose register in optimizations.
    Option -fomit-frame-pointer allows this use.
    Option -fno-omit-frame-pointer disallows it.
• • -funroll-loops0
  • -funroll-loops0

  • Disable loop unrolling.

• • -fno-builtin
  • -fno-builtin

  • -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
  • (-mieee-fp|-mno-ieee-fp)

  • -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.

• • -ffunction-sections
  • -ffunction-sections

  • Places each function in its own COMDAT section.

• • -ftz
  • -ftz

  • 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.

• • -link_force_multiple1
  • -Wl.*muldefs\b

  • Enable SmartHeap and/or other library usage by forcing the linker to ignore multiple definitions if present

• • -link_force_multiple2
  • .*FORCE.*MULTIPLE\b

  • Enable SmartHeap library usage by forcing the linker to ignore multiple definitions

• • -SmartHeap
  • -L/opt/SmartHeap_8.1/lib -lsmartheap\b

  • MicroQuill SmartHeap Library V8.1 available from http://www.microquill.com/

• • -Enable-64bit-compiler
  • -L/opt/intel/cce/10.0.023/lib -I/opt/intel/cce/10.0.023/include\b

  • Enable the use of the 64-bit compiler by passing the directory names for the library and include files

• • -set_stack_space
  • (?:/\S+/)?/F\d*

  • set the stack reserve amount specified to the linker

• • -ansi-alias
  • -ansi-alias\b

  • Enable/disable(DEFAULT) use of ANSI aliasing rules in optimizations; user asserts that the program adheres to these rules.

• • -prefetch
  • -prefetch\b

  • Enable/disable(DEFAULT) the compiler to generate prefetch instructions to prefetch data.

• • -inline-calloc
  • -inline-calloc\b

  • Directs the compiler to inline calloc() calls as malloc()/memset()

• • -opt-malloc-options
  • -opt-malloc-options=3\b

  • The compiler adds setup code in the C/C++/Fortran main function to enable optimal malloc algorithms:

    n=0: Default, no changes to the malloc options. No call to mallopt() is made.
    n=1: M_MMAP_MAX=2 and M_TRIM_THRESHOLD=0x10000000. Call mallopt with the two settings.
    n=2: M_MMAP_MAX=2 and M_TRIM_THRESHOLD=0x40000000. Call mallopt with these two settings.
    n=3: M_MMAP_MAX_=0 and M_TRIM_THRESHOLD=-1. Call mallopt with these two settings. This will cause use of sbrk() calls instead of mmap() calls to get memory from the system.
    

    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:

    M_TRIM_THRESHOLD This is the minimum size (in bytes) of the top-most, releasable chunk that will cause sbrk to be called with a negative argument in order to return memory to the system.
    M_TOP_PAD This parameter determines the amount of extra memory to obtain from the system when a call to sbrk is required. It also specifies the number of bytes to retain when shrinking the heap by calling sbrk with a negative argument. This provides the necessary hysteresis in heap size such that excessive amounts of system calls can be avoided.
    M_MMAP_THRESHOLD All chunks larger than this value are allocated outside the normal heap, using the mmap system call. This way it is guaranteed that the memory for these chunks can be returned to the system on free. Note that requests smaller than this threshold might still be allocated via mmap. M_MMAP_MAX The maximum number of chunks to allocate with mmap. Setting this to zero disables all use of mmap.
    

• • -vec-guard-write
  • -vec-guard-write\b

  • 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.

• • -par-runtime-control
  • -par-runtime-control\b

  • 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.

• • -opt-ra-region-strategy-block
  • -opt-ra-region-strategy.block\b

  • Select the method that the register allocator uses to partition each routine into regions

    • routine - one region per routine
    • block - one region per block
    • trace - one region per trace
    • loop - one region per loop
    • default - compiler selects best option

• • -opt-ra-region-strategy-routine
  • -opt-ra-region-strategy.routine\b

  • Select the method that the register allocator uses to partition each routine into regions

    • routine - one region per routine
    • block - one region per block
    • trace - one region per trace
    • loop - one region per loop
    • default - compiler selects best option

• • -opt-multi-version-aggressive
  • -opt-multi-version-aggressive\b

  • 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.

• • -auto
  • -auto\b

  • Make all local variables AUTOMATIC. Same as -automatic

• • -unroll-aggressive
  • -unroll-aggressive\b

  • Enables more aggressive unrolling heuristics

• • -opt-streaming-stores
  • -opt-streaming-stores.(always|never|auto)\b

  • -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

• • -Oi-
  • -Oi-

  • Disables inline expansion of all intrinsic functions.

• • -Op-
  • -Op-\b

  • Disables conformance to the ANSI C and IEEE 754 standards for floating-point arithmetic.

• • -Oy
  • -Oy\b

  • Allows use of EBP as a general-purpose register in optimizations.

• • -Os
  • -Os\b

  • This option enables most speed optimizations, but disables some that increase code size for a small speed benefit.

• • -Og
  • -Og\b

  • This option enables global optimizations.

• • -Ob_n
  • -Ob(0|1|2)\b

  • 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.

• • -Gy
  • -Gy\b

  • This option tells the compiler to separate functions into COMDATs for the linker.

• • -GF
  • -GF\b

  • This option enables read only string-pooling optimization.

• • -Gf
  • -Gf\b

  • This option enables read/write string-pooling optimization.

• • -Gs
  • -Gs\b

  • This option disables stack-checking for routines with 4096 bytes of local variables and compiler temporaries.