[llvm] [TableGen] Fix computeRegUnitLaneMasks for ad hoc aliasing (PR #79835)

[Kazushi Marukawa via llvm-commits]

kaz7 wrote:

Hi @jayfoad ,

Is it possible to ask review others about this PR in order to merge this?  As I said at https://github.com/llvm/llvm-project/pull/79831#issuecomment-1935900061, I think #79831 is not enough to cover the problem.

Recently the modification on live range (#88892) broke VE backend.  I don't inspect the patch deeply, but the patch itself seems reasonable.  And, if I apply this patch, it solves the problem.  I think that it just comes naturally to treat a lanemask == None as empty.  So, I'd like to fix the problem from the source.

https://github.com/llvm/llvm-project/pull/79835