[llvm] [LoopPeel] Implement initial peeling off the last loop iteration. (PR #139551)

[Florian Hahn via llvm-commits]

fhahn wrote:

> It looks like we're seeing miscompilations after [3fcfce4](https://github.com/llvm/llvm-project/commit/3fcfce4c5e5fd1c3072e8db1d692c93459e8cd74). Do any of the follow up commits here address issues that are likely to manifest as miscompilations?

there were a few follow-ups that might help resolve potential mis-compiles. Can you still reproduce the failure with current `main`? If so it would be great if you could share a reproducer.

https://github.com/llvm/llvm-project/pull/139551