[llvm] [LoopPeel] LCSSA form is destroyed by LoopPeel, preserve it (PR #78696)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

Can you please explain in what way LCSSA form gets broken? How does the IR look like after peeling but before simplification?

Just calling formLCSSARecursively() is of course correct, but it's better to understand why LCSSA gets broken and whether we can fix it incrementally instead.

https://github.com/llvm/llvm-project/pull/78696