forked from OSchip/llvm-project
45 lines
1.3 KiB
ReStructuredText
45 lines
1.3 KiB
ReStructuredText
.. _omp160:
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Removing parallel region with no side-effects. [OMP160]
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=======================================================
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This optimization remark indicates that a parallel region was deleted because it
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was not found to have any side-effects. This can occur if the region does not
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write any of its results to memory visible outside the region. This optimization
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is necessary because the barrier between sequential and parallel code typically
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prevents dead code elimination from completely removing the region. Otherwise
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there will still be overhead to fork and merge the threads with no work done.
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Example
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-------
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This optimization occurs whenever a parallel region was not found to have any
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side-effects. This can occur if the parallel region only reads memory or is
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simply empty.
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.. code-block:: c++
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void foo() {
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#pragma omp parallel
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{ }
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#pragma omp parallel
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{ int x = 1; }
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}
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}
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.. code-block:: console
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$ clang++ -fopenmp -O2 -Rpass=openmp-opt omp160.cpp
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omp160.cpp:4:1: remark: Removing parallel region with no side-effects. [OMP160] [-Rpass=openmp-opt]
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#pragma omp parallel
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^
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delete.cpp:2:1: remark: Removing parallel region with no side-effects. [OMP160] [-Rpass=openmp-opt]
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#pragma omp parallel
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^
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^
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Diagnostic Scope
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----------------
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OpenMP optimization remark.
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