[OpenMP] Improve default block count selection fow low block counts
If a combined loop has insufficient parallelism (= low trip count), we
might end up with too few teams/blocks. To counter that we can reduce
the number of threads per team we use. This patch implements a heuristic
and exposes a new environment variable to control the minimum of threads
to be employed in this case.
Issue reported by:
Felipe Cabarcas Jaramillo <cabarcas@udel.edu> (@fel-cab).
Reviewed By: tianshilei1992
Differential Revision: https://reviews.llvm.org/D152014
GitOrigin-RevId: 6629a96a8ce5f07c72bd4931180a3ca9fc535cbb
4 files changed
