[llvm] [DemandedBits] Support non-constant shift amounts (PR #148880)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon commented:

Looks very good overall, with extensive testing, although I'll leave the final sign-off to @dtcxzyw.

https://github.com/llvm/llvm-project/pull/148880