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1.. _omp160:2 3Removing parallel region with no side-effects. [OMP160]4=======================================================5 6This optimization remark indicates that a parallel region was deleted because it7was not found to have any side-effects. This can occur if the region does not8write any of its results to memory visible outside the region. This optimization9is necessary because the barrier between sequential and parallel code typically10prevents dead code elimination from completely removing the region. Otherwise11there will still be overhead to fork and merge the threads with no work done.12 13Example14-------15 16This optimization occurs whenever a parallel region was not found to have any17side-effects. This can occur if the parallel region only reads memory or is18simply empty.19 20.. code-block:: c++21 22 void foo() {23 #pragma omp parallel24 { }25 #pragma omp parallel26 { int x = 1; }27 }28 }29 30.. code-block:: console31 32 $ clang++ -fopenmp -O2 -Rpass=openmp-opt omp160.cpp33 omp160.cpp:4:1: remark: Removing parallel region with no side-effects. [OMP160] [-Rpass=openmp-opt]34 #pragma omp parallel35 ^36 delete.cpp:2:1: remark: Removing parallel region with no side-effects. [OMP160] [-Rpass=openmp-opt]37 #pragma omp parallel38 ^39 ^40 41Diagnostic Scope42----------------43 44OpenMP optimization remark.45