[clang] [llvm] [openmp] [Clang][OpenMP] Implement Loop splitting `#pragma omp split` directive (PR #183261)

[Amit Tiwari via llvm-commits]

amitamd7 wrote:

For me, with the version change, all the tests passed except `nonconstant_count.c` which happens to have an incorrect expectation and should be deleted. I'm marking its changes in `split_messages.cpp`.

https://github.com/llvm/llvm-project/pull/183261