[llvm] [LV] Allow reductions with partial alias masking (PR #200813)

[Sander de Smalen via llvm-commits]

https://github.com/sdesmalen-arm approved this pull request.

The tests seem to cover most special case reductions and the resulting IR looks correct, and the code change is minimal and sensible, so overall it looks good to me. Please give @fhahn a chance to take a look as well to see if anything is missing.

https://github.com/llvm/llvm-project/pull/200813