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

[Abhay Kanhere via llvm-commits]

AbhayKanhere wrote:

> > While testing, found a hang introduced by the PR: https://llvm.godbolt.org/z/1oxezWe7G
> 
It is pre-existing bug -- not introduced by my change.  calling findLoopHeaders unconditionally does not cause a hang singe Loopheaders are no longer empyty.
cause: 
   323 -  if (!ThreadAcrossLoopHeaders)           <--- we skip adding LoopHeaders with thread-across-loop-headers flag.
      324 -    findLoopHeaders(*F); 


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