[llvm] [SLP]Improve minbitwidth analysis. (PR #84536)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> Thanks, will investigate

Thanks! If fixing it takes long, I'd appreicate a revert, but otherwise I'm fine waiting a bit for a forward fix if that's possible.

https://github.com/llvm/llvm-project/pull/84536