[PATCH] D32451: Improve profile-guided heuristics to use estimated trip count.

[Taewook Oh via Phabricator via llvm-commits]

twoh added a comment.

I don't have a strong opinion about treating static trip count and profile-based trip count or not. I treated them separately because existing implementation sets OptForSize to true instead of returning false when it makes a profile-based decision. It would be great if someone can explain the reason behind that.

@Ayal Yes, 'LoopEntryFreq < ColdEntryFreq' criteria kicks in if the loop latch has no associated frequencies but the function entry and loop preheader do. I actually observed such case in one of our internal code because loop transformations mess up the branch profile info. However, although I kept the criteria, I'm not sure about the effectiveness of that criteria as I wrote in the summary. Maybe we keep the criteria but modify it to 'LoopEntryFreq == 0' to disable vectorization for obviously cold loops.

I'll wait for other opinions, and if there's no input, will update the code per Ayal's suggestions. Thanks!


https://reviews.llvm.org/D32451