Improve performance of #pragma omp single
Improve performance of #pragma omp single

EPCC Performance of single is considerably worse than plain barrier.
Adding a read-only check to the code before the atomic compare-and-store
helps considerably.

Patch by Terry Wilmarth.

Differential Revision: http://reviews.llvm.org/D21893


git-svn-id: f99161ee8ccfe2101cbe1bdda2220bce2ed25485@274369 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/openmp,llvm-mirror/openmp,llvm-mirror/openmp,llvm-mirror/openmp,llvm-mirror/openmp