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

[Congzhe Cao via llvm-commits]

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CongzheUalberta wrote:

IIUC the PHI nodes being updated or created, i.e., `LCSSAPhi` and `PostLoopPN`, are not in the same loop as `PN` that we query SCEV on. `LCSSAPhi` and `PostLoopPN` exist in the preheader and header of the post-loop and `PN` is in the pre-loop. But anyhow, I'm wondering if you have suggestions to improve this code?

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