SPEC CPU2006 Flag Description for the Intel(R) C++ Compiler 9.1 for 32-bit applications and Intel(R) Fortran Compiler 9.1 for 64-bit 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 IA-32 Windows platforms, -O1 sets the following:

    /Qunroll0, /Oi-, /Op-, /Oy, /Gy, /Os, /GF (/Qvc7 and above), /Gf (/Qvc6 and below), /Ob2, and /Og

  • Includes:
    • -Qunroll_n
    • -Oi-
    • -Op-
    • -Oy
    • -Gy
    • -Os
    • -GF
    • -Gf
    • -Ob_n
    • -Og
• • -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
    On IA-32 Windows platforms, -O2 sets the following:
    

    /Og, /Oi-, /Os, /Oy, /Ob2, /GF (/Qvc7 and above), /Gf (/Qvc6 and below), /Gs, and /Gy.

  • Includes:
    • -Oi-
    • -Gs
    • -Oy
    • -Gy
    • -Os
    • -GF
    • -Gf
    • -Ob_n
    • -Og
    • -O1
      • -Qunroll_n
      • -Oi-
      • -Op-
      • -Oy
      • -Gy
      • -Os
      • -GF
      • -Gf
      • -Ob_n
      • -Og
• • -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 IA-32 and Intel EM64T processors, 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 IA-32 Windows platforms, -O3 sets the following:

    /GF (/Qvc7 and above), /Gf (/Qvc6 and below), and /Ob2

  • Includes:
    • -GF
    • -Gf
    • -Ob_n
    • -O2
      • -Oi-
      • -Gs
      • -Oy
      • -Gy
      • -Os
      • -GF
      • -Gf
      • -Ob_n
      • -Og
      • -O1
        • -Qunroll_n
        • -Oi-
        • -Op-
        • -Oy
        • -Gy
        • -Os
        • -GF
        • -Gf
        • -Ob_n
        • -Og
• • -Qip
  • -Qip\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.

• • -Qipo
  • -Qipo\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

• • -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)

    -Qipo (enables interprocedural optimizations across files)

    -QxP  (generate code specialized for Intel Pentium 4 processor and compatible Intel processors with Streaming SIMD Extensions 3)

    -Qprec-div- (disable -Qprec-div) where -Qprec-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 xP or QxP option which can't be overridden. The options set by /fast may change from release to release.

  • Includes:
    • -O3
      • -GF
      • -Gf
      • -Ob_n
      • -O2
        • -Oi-
        • -Gs
        • -Oy
        • -Gy
        • -Os
        • -GF
        • -Gf
        • -Ob_n
        • -Og
        • -O1
          • -Qunroll_n
          • -Oi-
          • -Op-
          • -Oy
          • -Gy
          • -Os
          • -GF
          • -Gf
          • -Ob_n
          • -Og
    • -Qipo
    • -QxP
    • -Qprec-div-
• • -QxP
  • -QxP\b

  • Code is optimized for Intel Core Duo processors, Intel Core Solo processors, Intel Pentium 4 processors with Streaming SIMD Extensions 3, and compatible Intel processors with Streaming SIMD Extensions 3. 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.

• • -Qauto_ilp32
  • -Qauto_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 2**32 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.

• • -Qprec-div-
  • -Qprec-div
  • (disable/enable[default] -Qprec-div[-])

    This option improves precision of floating-point divides. It has a slight impact on speed.

    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, use this option to disable the floating-point division-to-multiplication optimization. The result is more accurate, with some loss of performance.

    If you specify -no-prec-div (Linux and Mac OS) or /Qprec-div- (Windows), it enables optimizations that give slightly less precise results than full IEEE division.

• • -prof_gen
  • -Qprof_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
  • -Qprof_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, -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

• • -Qcxx_features
  • -Qcxx_features\b

  • Enable C++ Exception Handling and RTTI This option has the same effect as specifying /GX /GR.

  • Includes:
    • -GX
    • -GR
• • -GX
  • -GX\b

  • This option enables C++ exception handling.

• • -GR
  • -GR\b

  • Enables C++ Run Time Type Information (RTTI).

• • -link_force_multiple1
  • \b\-Fe\$\@\-link\b

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

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

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

• • -SmartHeap32
  • shlW32M.lib\b

  • 32-bit MicroQuill SmartHeap Library 8.0 for Windows available from http://www.microquill.com/

• • -SmartHeapx64
  • shlW64M.lib\b

  • 64-bit MicroQuill SmartHeap Library 8.0 for Windows available from http://www.microquill.com/

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

  • set the stack reserve amount specified to the linker

• • -Qunroll_n
  • -Qunroll\d+\b

  • Tells the compiler the maximum number of times to unroll loops.

• • -Oi-
  • -Oi-\b

  • Disables inline expansion of all intrinsic functions.

• • -Op-
  • -Oi-\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.