[clang] [llvm] [InstCombine] Support folding intrinsics into phis (PR #151115)

[Antonio Frighetto via llvm-commits]

https://github.com/antoniofrighetto approved this pull request.

LG. From https://github.com/dtcxzyw/llvm-opt-benchmark/pull/2617, it seems like this might not fully subsume https://github.com/llvm/llvm-project/pull/149858; though, this looks an independent improvement regardless (if fine with regressions).

https://github.com/llvm/llvm-project/pull/151115