Loop Nest Optimizer

• LNO performs loop restructuring to optimize data access:

  • loop interchange
  • loop unrolling
  • loop blocking for cache
  • loop fusion
  • loop fission
  • pre-fetching

• LNO is controlled with compiler options and/or compiler directives or pragmas; same options for both

  • LNO is the default at -O3, but can be turned on/off individually by -LNO:opt=[1|0]
  • directives/pragma syntax:
    • Fortran: C*$* keyword [=value(s)]
    • C/C++ : #pragma keyword [=value(s)]
  • directives/pragmas can be disabled with the compiler switch -LNO:ignore_pragmas

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