[llvm] [CodeGen] For ad hoc aliasing, additional regUnits are needed to fix lanemask representation (PR #139206)

[Jay Foad via llvm-commits]

jayfoad wrote:

> my patch is causing some LIT test fail, so I think we should go with your fix (as it makes more sense also), but still wants to add my changes pertaining to added TableGen test. So what would be ideal way to proceed on this?

I can merge my patch first (once it is approved) and then you can open a new PR to add extra tests?

https://github.com/llvm/llvm-project/pull/139206