[PATCH] D158642: LoopUnrollRuntime: Add weights to all branches

[Matthias Braun via Phabricator via llvm-commits]

MatzeB added subscribers: spatel, lebedev.ri.
MatzeB added a comment.

I guess we may need a discussion about how to express these "nearly always taken" / "nearly never taken" branch weights as a hardcoded 1:127 ratio is pretty arbitrary.

Looking around I see `LikelyBranchWeight` in `llvm/Transforms/Scalar/LowerExpectIntrinsic.cpp` but it's private to the pass and a warning advises to use `TargetTransformInfo::getPredictableBranchThreshold()`. Intuitively it feels wrong to me to have branch_weights change based on the selected target, and I am not sure I follow why `LowerExpectIntrinsic` isn't using that function either despite recommending it...

CC @lebedev.ri @spatel


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https://reviews.llvm.org/D158642