Call may contain unknown parallel regions. Use [[omp::assume(“omp_no_parallelism”)]] to override. [OMP133]

This analysis remark identifies calls that prevented OMP131 from providing the generic-mode kernel with a fully specialized state machine. This remark will identify each call that may contain unknown parallel regions that caused the kernel to require a fallback.

Examples

This will occur for any generic-mode kernel that may contain unknown parallel regions. This is typically coupled with the OMP132 remark.

extern void setup();

void foo() {
#pragma omp target
{
  setup();
  #pragma omp parallel
  {
    work();
  }
}
}

$ clang++ -fopenmp -fopenmp-targets=nvptx64 -O2 -Rpass-analysis=openmp-opt omp133.cpp
omp133.cpp:6:5: remark: Call may contain unknown parallel regions. Use
`[[omp::assume("omp_no_parallelism")]]` to override. [OMP133]
setup();
^

The remark suggests marking the function with the assumption that it contains no parallel regions. If this is done then the kernel will be rewritten with a fully specialized state machine.

[[omp::assume("omp_no_parallelism")]] extern void setup();


void foo() {
#pragma omp target
{
  setup();
  #pragma omp parallel
  {
    work();
  }
}
}

$ clang++ -fopenmp -fopenmp-targets=nvptx64 -O2 -Rpass=openmp-opt omp133.cpp
omp133.cpp:4:1: remark: Rewriting generic-mode kernel with a customized state machine. [OMP131]
#pragma omp target
^

Diagnostic Scope

OpenMP target offloading analysis remark.