[llvm] [LoopRotate] Rotate loop if this makes exit count computable (PR #162654)

[Nikita Popov via llvm-commits]

nikic wrote:

It looks like this has a large impact on compile-time: https://llvm-compile-time-tracker.com/compare.php?from=4f80c064eb2933c00c0ba9b7826aa3631cf3b5c2&to=08496a966850e06788de4bbf75e521ee5ed1363c&stat=instructions%3Au The clang thin link is up +0.5%.

Don't know whether that's due to the transform itself or whether it's because this enables expensive followup transforms.

https://github.com/llvm/llvm-project/pull/162654