[llvm] [KnownBits] Add fast path for udiv by pow2 and overloads for shift ops by constant (PR #189779)

[Max Graey via llvm-commits]

MaxGraey wrote:

At least they've added a TODO for future improvements and made it easier to work with RHS constants. Now there's no need to manually construct KnownBits for constants.

https://github.com/llvm/llvm-project/pull/189779