docs/remarks/OMP131.rst

Rewriting generic-mode kernel with a customized state machine. [OMP131]
=======================================================================

.. _omp131:

This optimization remark indicates that a generic-mode kernel on the device was
specialized for the given target region. When offloading in generic-mode, a
state machine is required to schedule the work between the parallel worker
threads. This optimization specializes the state machine in cases where there is
a known number of parallel regions inside the kernel. A much simpler state
machine can be used if it is known that there is no nested parallelism and the
number of regions to schedule is a static amount.

Examples
--------

This optimization should occur on any generic-mode kernel that has visibility on
all parallel regions, but cannot be moved to SPMD-mode and has no nested
parallelism.

.. code-block:: c++

   #pragma omp declare target
   int TID;
   #pragma omp end declare target

   void foo() {
   #pragma omp target
   {
    TID = omp_get_thread_num();
    #pragma omp parallel
    {
      work();
    }
   }
   }

.. code-block:: console

   $ clang++ -fopenmp -fopenmp-targets=nvptx64 -O2 -Rpass=openmp-opt omp131.cpp
   omp131.cpp:8:1: remark: Rewriting generic-mode kernel with a customized state machine. [OMP131]
   #pragma omp target
   ^

Diagnostic Scope
----------------

OpenMP target offloading optimization remark.