[llvm] [InstCombine] isKnownNonNegative should recognize `b - a` after `a <= b` (PR #145105)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

This should probably be directly in computeKnownBits() rather than isKnownNonNegative()?

https://github.com/llvm/llvm-project/pull/145105