[llvm] [LoopPeel] Add new option to peeling loops to make PHIs into IVs (PR #121104)

[Ryotaro Kasuga via llvm-commits]

kasuga-fj wrote:

Gentle ping @nikic . 
For now, I've added a flag and disabled this feature by default, so I don't think this patch will affect existing cases. I'd like to enable it by default in the future, after addressing the cases in `peel-loop-phi-analysis-iv.ll`, where undesired peeling happens.

https://github.com/llvm/llvm-project/pull/121104