[llvm] [SCEV] Use context sensative reasoning in howFarToZero (PR #94525)

[Nikita Popov via llvm-commits]

https://github.com/nikic approved this pull request.

Unfortunately the overhead stays about the same: http://llvm-compile-time-tracker.com/compare.php?from=21711f89b9d85028160611f725bd33d7832d1d46&to=234423fe3d82181c2cc1a7a614f60b46dea70297&stat=instructions%3Au

But it's small enough that I'm okay with landing this if it's useful.

https://github.com/llvm/llvm-project/pull/94525