[llvm] [ValueTracking] Use select condition to help infer bits of arms (PR #84699)

[Nikita Popov via llvm-commits]

https://github.com/nikic requested changes to this pull request.

The implementation looks correct to me now, but unfortunately this has also made it too expensive: http://llvm-compile-time-tracker.com/compare.php?from=1bee754fc62ed053e347891e8967b645e95ddbae&to=a4b5288b2bdd57cc31551977d5413abbb95413a9&stat=instructions:u

https://github.com/llvm/llvm-project/pull/84699