[llvm] [CVP] Implement type narrowing for LShr (PR #119577)

[via llvm-commits]

adam-bzowski wrote:

> I don't think CVP should be doing this transform. This looks like the job of TruncInstCombine in AggressiveInstCombine?

I don't think it would work. TruncInstCombine doesn't use LazyValueInfo, which is essential here. That's why it fits CVP more, which already deals with similar narrowings.

https://github.com/llvm/llvm-project/pull/119577