[PATCH] D131287: Fix branch weight in FoldCondBranchOnValueKnownInPredecessor pass in SimplifyCFG

Tue Aug 23 17:13:21 PDT 2022

LukeZhuang added a comment.

Hi @paulkirth, sorry for the late reply. If I understand it correctly, BlockFrequencyInfo can only be used with profile information. I have found the original author of updateBlockFreqAndEdgeWeight(https://reviews.llvm.org/D10979 and https://reviews.llvm.org/D15519), that's why the author added `if (HasProfileData)` and only do the fix when have profile data.
However, this code is 7 years ago and we added __builtin_expect_with_probability in 2020. This probability issue(that example at the beginning of my description) can also happen even without profile data, the user will find the probability of executing `bar` is not expected. So it’s not sufficient for us to only do this with profile data. This is our concern about using BlockFrequencyInfo.
And again thank you very much for the kind and useful comments! I think all of them are reasonable and is working on it.

Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D131287/new/

https://reviews.llvm.org/D131287