[OpenMP] Race on the IsSPMD global during runtime initialization

[jdoerfert]

We have a race as we read the IsSPMD global inside mapping::getBlockSize() before kernel initialization is done and the value is available to all threads.

Similar errors existed before, this one was introduced as we started to adjust getBlockSize for the extra warp/wave in generic mode.

[llvmbot]

@llvm/issue-subscribers-openmp

[jdoerfert]

/cherry-pick 57b4c52

[llvmbot]

Failed to cherry-pick: 57b4c52

https://github.com/llvm/llvm-project/actions/runs/1855574016

Please manually backport the fix and push it to your github fork. Once this is done, please add a comment like this:

/branch <user>/<repo>/<branch>

[jdoerfert]

/cherry-pick 57b4c52

[llvmbot]

/branch llvmbot/llvm-project/issue53857

[llvmbot]

/pull-request llvmbot#78