[llvm] [InstCombine] Convert fshl(x, 0, y) to shl(x, and(y, BitWidth - 1)) when BitWidth is pow2 (PR #122362)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

Can you please add an alive2 proof to the PR description?

https://github.com/llvm/llvm-project/pull/122362