[llvm] PHIElimination: add target hook to control reuse. (PR #163604)

[Junjie Gu via llvm-commits]

jgu222 wrote:

> Is this the problem solved by SIOptimizeVGPRLiveRange?
> 
> You generally want to work in terms of common subclasses than exact class checks

Updated the PR with checking on common subclasses. It works for my case.

https://github.com/llvm/llvm-project/pull/163604