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

[Vikash Gupta via llvm-commits]

vg0204 wrote:

@jayfoad before closing this PR ( as its alternative fix of yours has been merged), could you comment on additional tests (in this PR) that may be needed as, your fix also have the similar tests. Then only it makes sense to add it extra tests as new PR as suggested by you!

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