[llvm] [InstCombine] Fold `((A ^ B) & C) | A` -> `A | (B & C)` (PR #76572)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

I think this list of transforms has reached the point where we need to generalize it if we want to keep adding increasingly exotic variants to it.

The general transform here is that in `x | y` we can simplify x by replacing occurrences of y with 0 -- as long as we only look through bitwise operations. Similar for & and -1.

If we don't care about multi-use, this could be done with https://github.com/llvm/llvm-project/blob/9b7cf5bfb08b6e506216ef354dfd61adb15acbff/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp#L1225 + a bitwise op limit.

https://github.com/llvm/llvm-project/pull/76572