MPI2007 Flag Description
Linux Networx LS-1, Scali MPI Connect 5.6.1, PathScale 3.0 compilers

Base Optimization Flags

C benchmarks

• • -march=core
  • 
  • OPTIMIZE

  • Compiler will optimize code for selected platform. The default value, auto, means to optimize for the platform on which the compiler is running, as determined by reading /proc/cpuinfo. anyx86 means a generic 32-bit x86 processor without SSE2 support.

• • -O3
  • 
  • COPTIMIZE

  • Specify the basic level of optimization desired.
    The options can be one of the following:

    0    Turn off all optimizations.

    1    Turn on local optimizations that can be done quickly. Do peephole optimizations and instruction scheduling.

    2    Turn on extensive optimization. This is the default.
    The optimizations at this level are generally conservative, in the sense that they are virtually always beneficial and avoid changes which affect such things as floating point accuracy. In addition to the level 1 optimizations, do inner loop unrolling, if-conversion, two passes of instruction scheduling, global register allocation, dead store elimination, instruction scheduling across basic blocks, and partial redundancy elimination.

    3    Turn on aggressive optimization.
    The optimizations at this level are distinguished from -O2 by their aggressiveness, generally seeking highest-quality generated code even if it requires extensive compile time. They may include optimizations that are generally beneficial but may hurt performance.
    This includes but is not limited to turning on the Loop Nest Optimizer, -LNO:opt=1, and setting -OPT:roundoff=1:IEEE_arithmetic=2:Olimit=9000:reorg_common=ON.

    s    Specify that code size is to be given priority in tradeoffs with execution time.

    If no value is specified, 2 is assumed.

• • -OPT:Ofast
  • 
  • COPTIMIZE

  • -OPT:Ofast
    Use optimizations selected to maximize performance. Although the optimizations are generally safe, they may affect floating point accuracy due to rearrangement of computations. This effectively turns on the following optimizations: -OPT:ro=2:Olimit=0:div_split=ON:alias=typed.

  • Includes:
    • -OPT:ro
    • -OPT:Olimit
    • -OPT:div_split
    • -OPT:alias

C++ benchmarks

126.lammps

• • -march=core
  • 
  • OPTIMIZE

  • Compiler will optimize code for selected platform. The default value, auto, means to optimize for the platform on which the compiler is running, as determined by reading /proc/cpuinfo. anyx86 means a generic 32-bit x86 processor without SSE2 support.

• • -O3
  • 
  • CXXOPTIMIZE

  • Specify the basic level of optimization desired.
    The options can be one of the following:

    0    Turn off all optimizations.

    1    Turn on local optimizations that can be done quickly. Do peephole optimizations and instruction scheduling.

    2    Turn on extensive optimization. This is the default.
    The optimizations at this level are generally conservative, in the sense that they are virtually always beneficial and avoid changes which affect such things as floating point accuracy. In addition to the level 1 optimizations, do inner loop unrolling, if-conversion, two passes of instruction scheduling, global register allocation, dead store elimination, instruction scheduling across basic blocks, and partial redundancy elimination.

    3    Turn on aggressive optimization.
    The optimizations at this level are distinguished from -O2 by their aggressiveness, generally seeking highest-quality generated code even if it requires extensive compile time. They may include optimizations that are generally beneficial but may hurt performance.
    This includes but is not limited to turning on the Loop Nest Optimizer, -LNO:opt=1, and setting -OPT:roundoff=1:IEEE_arithmetic=2:Olimit=9000:reorg_common=ON.

    s    Specify that code size is to be given priority in tradeoffs with execution time.

    If no value is specified, 2 is assumed.

• • -OPT:Ofast
  • 
  • CXXOPTIMIZE

  • -OPT:Ofast
    Use optimizations selected to maximize performance. Although the optimizations are generally safe, they may affect floating point accuracy due to rearrangement of computations. This effectively turns on the following optimizations: -OPT:ro=2:Olimit=0:div_split=ON:alias=typed.

  • Includes:
    • -OPT:ro
    • -OPT:Olimit
    • -OPT:div_split
    • -OPT:alias
• • -CG:local_fwd_sched=on
  • 
  • CXXOPTIMIZE

  • -CG:local_fwd_sched : Change the instruction scheduling algorithm to work forward instead of backward for the instructions in each basic block. The default is OFF for 64-bit ABI, and ON for 32-bit ABI.

Fortran benchmarks

• • -march=core
  • 
  • OPTIMIZE

  • Compiler will optimize code for selected platform. The default value, auto, means to optimize for the platform on which the compiler is running, as determined by reading /proc/cpuinfo. anyx86 means a generic 32-bit x86 processor without SSE2 support.

• • -O3
  • 
  • FOPTIMIZE

  • Specify the basic level of optimization desired.
    The options can be one of the following:

    0    Turn off all optimizations.

    1    Turn on local optimizations that can be done quickly. Do peephole optimizations and instruction scheduling.

    2    Turn on extensive optimization. This is the default.
    The optimizations at this level are generally conservative, in the sense that they are virtually always beneficial and avoid changes which affect such things as floating point accuracy. In addition to the level 1 optimizations, do inner loop unrolling, if-conversion, two passes of instruction scheduling, global register allocation, dead store elimination, instruction scheduling across basic blocks, and partial redundancy elimination.

    3    Turn on aggressive optimization.
    The optimizations at this level are distinguished from -O2 by their aggressiveness, generally seeking highest-quality generated code even if it requires extensive compile time. They may include optimizations that are generally beneficial but may hurt performance.
    This includes but is not limited to turning on the Loop Nest Optimizer, -LNO:opt=1, and setting -OPT:roundoff=1:IEEE_arithmetic=2:Olimit=9000:reorg_common=ON.

    s    Specify that code size is to be given priority in tradeoffs with execution time.

    If no value is specified, 2 is assumed.

• • -OPT:Ofast
  • 
  • FOPTIMIZE

  • -OPT:Ofast
    Use optimizations selected to maximize performance. Although the optimizations are generally safe, they may affect floating point accuracy due to rearrangement of computations. This effectively turns on the following optimizations: -OPT:ro=2:Olimit=0:div_split=ON:alias=typed.

  • Includes:
    • -OPT:ro
    • -OPT:Olimit
    • -OPT:div_split
    • -OPT:alias
• • -LANG:copyinout=off
  • 
  • FOPTIMIZE

  • -LANG:copyinout : When an array section is passed as the actual argument in a call, the compiler sometimes copies the array section to a temporary array and passes the temporary array, thus promoting locality in the accesses to the array argu- ment. This optimization is relevant only to Fortran, and this flag controls the aggressiveness of this optimization. The default is ON for -O2 or higher and OFF otherwise.

Benchmarks using both Fortran and C

• • -march=core
  • 
  • OPTIMIZE

  • Compiler will optimize code for selected platform. The default value, auto, means to optimize for the platform on which the compiler is running, as determined by reading /proc/cpuinfo. anyx86 means a generic 32-bit x86 processor without SSE2 support.

• • -O3
  • 
  • COPTIMIZE, FOPTIMIZE

  • Specify the basic level of optimization desired.
    The options can be one of the following:

    0    Turn off all optimizations.

    1    Turn on local optimizations that can be done quickly. Do peephole optimizations and instruction scheduling.

    2    Turn on extensive optimization. This is the default.
    The optimizations at this level are generally conservative, in the sense that they are virtually always beneficial and avoid changes which affect such things as floating point accuracy. In addition to the level 1 optimizations, do inner loop unrolling, if-conversion, two passes of instruction scheduling, global register allocation, dead store elimination, instruction scheduling across basic blocks, and partial redundancy elimination.

    3    Turn on aggressive optimization.
    The optimizations at this level are distinguished from -O2 by their aggressiveness, generally seeking highest-quality generated code even if it requires extensive compile time. They may include optimizations that are generally beneficial but may hurt performance.
    This includes but is not limited to turning on the Loop Nest Optimizer, -LNO:opt=1, and setting -OPT:roundoff=1:IEEE_arithmetic=2:Olimit=9000:reorg_common=ON.

    s    Specify that code size is to be given priority in tradeoffs with execution time.

    If no value is specified, 2 is assumed.

• • -OPT:Ofast
  • 
  • COPTIMIZE, FOPTIMIZE

  • -OPT:Ofast
    Use optimizations selected to maximize performance. Although the optimizations are generally safe, they may affect floating point accuracy due to rearrangement of computations. This effectively turns on the following optimizations: -OPT:ro=2:Olimit=0:div_split=ON:alias=typed.

  • Includes:
    • -OPT:ro
    • -OPT:Olimit
    • -OPT:div_split
    • -OPT:alias
• • -LANG:copyinout=off
  • 
  • FOPTIMIZE

  • -LANG:copyinout : When an array section is passed as the actual argument in a call, the compiler sometimes copies the array section to a temporary array and passes the temporary array, thus promoting locality in the accesses to the array argu- ment. This optimization is relevant only to Fortran, and this flag controls the aggressiveness of this optimization. The default is ON for -O2 or higher and OFF otherwise.