[llvm] [LoopBoundSplit] Fix edge connections during transformation (PR #192106)

[Congzhe Cao via llvm-commits]

CongzheUalberta wrote:

I've updated the patch to address the comments. Specifically:

1) I moved the two DomTree updates to more appropriate locations and added `DT.verify()` accordingly, to improve robustness of the pass.

2) I updated the comments and other things as you suggested.

Would appreciate it if you could take another look, thanks! @efriedma-quic 

https://github.com/llvm/llvm-project/pull/192106