[llvm] [InstCombine] Fold `ctpop(X) eq/ne 1` if X is non-zero (PR #67268)

[Nikita Popov via llvm-commits]

nikic wrote:

In theory yes, but in practice CGP drops assumes at the very start, and I don't want to have a special ctpop fold run before that. I'd only take that if we stop dropping assumes in CGP (which is on the long-term roadmap, but tricky).

https://github.com/llvm/llvm-project/pull/67268