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

[Alexander Kornienko via llvm-commits]

alexfh wrote:

It looks like we're seeing miscompilations after 3fcfce4c5e5fd1c3072e8db1d692c93459e8cd74. Do any of the follow up commits here address issues that are likely to manifest as miscompilations?

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