Extended Description

Hi,

We have observed a problem with vectorization and the newest LLVM/Clang trunk (older versions seem to be affected as well). We have a loop with a potential race condition for which we force vectorization using "#pragma clang loop vectorize(assume_safety)." Despite that, Clang fails to vectorize our loop reporting that it "cannot identify array bounds." After investigating the IR after each pass, we found a potential cause of this issue. It seems like the "MD_mem_parallel_loop_access" metadata did not get transferred over when converting an invoke to a call. We could fix the problem by adding the following line to the changeToCall() method in Local.cpp:

NewCall->copyMetadata(*II, LLVMContext::MD_mem_parallel_loop_access);

This is similar to to what is done in SROA, but we are not sure whether this is a valid fix for the observed issue.

Please note that we are aware of the WIP under D52116 and D52117, but our fix (with additional copying of "LLVMContext::MD_access_group" in the same call) was also required to get the loop vectorized after applying those two patches.

Thanks,
Moritz