Parallel region merged with parallel region at <location>. [OMP150]

This optimization remark indicates that a parallel region was merged with others into a single parallel region. Parallel region merging fuses consecutive parallel regions to reduce the team activation overhead of forking and increases the scope of possible OpenMP-specific optimizations within merged parallel regions. This optimization can also guard sequential code between two parallel regions if applicable.

Example

This optimization should apply to any compatible and consecutive parallel regions. In this case the sequential region between the parallel regions will be guarded so it is only executed by a single thread in the new merged region.

void foo() {
#pragma omp parallel
  parallel_work();

  sequential_work();

#pragma omp parallel
  parallel_work();
}

$ clang++ -fopenmp -O2 -Rpass=openmp-opt -mllvm -openmp-opt-enable-merging omp150.cpp
omp150.cpp:2:1: remark: Parallel region merged with parallel region at merge.cpp:7:1. [OMP150]
#pragma omp parallel
^

Diagnostic Scope

OpenMP optimization remark.