[llvm] [JumpThreading] Thread a common icmp across PHI nodes (PR #221125)

[Abhay Kanhere via llvm-commits]

AbhayKanhere wrote:

> I tried to reduce some of the cases I think are regressions. Each of the function in https://llvm.godbolt.org/z/EWxjWTGr5 regresses with the patch AFAICT

I provided a patch to ensure we don't duplicate calls. I tried to fix the patch so that we can recover selects missed with this patch -- this is the increase in code you see 1. select vs. branch + code. 

https://github.com/llvm/llvm-project/pull/221125