[llvm] [InstCombine] Extend `foldICmpAddConstant` to disjoint `or`. (PR #75899)

[Nikita Popov via llvm-commits]

nikic wrote:

I see, thanks. A possible way to fix this would be to try to take into account already known bits when adding known bits from conditions, i.e. `x sgt -15` implies `x sgt 0` if the low 4 bits of x are known zero. But I don't think this is worth bothering with.

(It looks like the patch needs a rebase.)

https://github.com/llvm/llvm-project/pull/75899