[llvm] [InstCombine] Use KnownBits predicate helpers (PR #115874)

[via llvm-commits]

goldsteinn wrote:

> The reason this only makes a different for pointers is that simplifyICmpInst calls isKnownNonEqual, which does a KnownBits based check for integers, but not pointers.
> 
> So an alternative fix would be to adjust isKnownNonEqual() to handle this for pointers as well.

The two don't seem mutually exclusive. This patch has value IMO even if it's just dropping some bespoke logic for better tested/implemented apis

https://github.com/llvm/llvm-project/pull/115874