[llvm] [InstCombine] Fold `(x < y) ? -1 : zext(x != y)` into `u/scmp(x,y)` (PR #101049)

[David Green via llvm-commits]

davemgreen wrote:

> Do you currently see vectorization for three-way comparison patterns? I wouldn't really expect these to occur in vectorizable contexts.

You might be right, but all kinds of weird and wonderful things can come up at times. It would be like this, right? https://godbolt.org/z/denMv3fjf

I'm not against the patch and don't have any motivating case that needs vectorization. It might be worth adding some basic vector costmodel/isTriviallyVectorizable support at some point though.

https://github.com/llvm/llvm-project/pull/101049