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

[Hongtao Yu via Phabricator via llvm-commits]

hoy added inline comments.


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Comment at: llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp:783
+    MDBuilder MDB(B.getContext());
+    BranchWeights = MDB.createBranchWeights(1, 127);
+  }
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mtrofin wrote:
> one thought about the 1:127 ratio: how about we had a `MDBuilder::createUnrolledLoopSkipWeights()` doing the setting - more readable, API captures the intent, etc?
Can this be computed based on the loop preheader count and the main loop trip count? IIUC, the block execution count of the preheader indicates how many times the loop is entered from outside the loop. Thus that the loop trip count divided by the preheader count indicates an average trip count per loop execution. If that is greater than the unrolling factor, then the unrolled loop should be always executed?





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https://reviews.llvm.org/D158642