[PATCH] D159322: LoopVectorize: Set branch_weight for conditional branches

[Mircea Trofin via Phabricator via llvm-commits]

mtrofin added a comment.

In D159322#4633005 <https://reviews.llvm.org/D159322#4633005>, @MatzeB wrote:

> For the discussion about the 127:1 ratio see also D158668 <https://reviews.llvm.org/D158668> (and discussion in D158642 <https://reviews.llvm.org/D158642> and D157462 <https://reviews.llvm.org/D157462>)

added a comment in D158642 <https://reviews.llvm.org/D158642> (api stuff, not actual weight values. xur@ might have an opinion about those)



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Comment at: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:1922
   bool CostTooHigh = false;
+  bool AddBranchWeights;
 
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This could be `const`, looks like, correct?


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Comment at: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:2870
+    // It is unlikely that we enter "Bypass".
+    MDBuilder MDB(Builder.getContext());
+    MDNode *BranchWeights = MDB.createBranchWeights(1, 127);
----------------
worth factoring the 3 lines in a little utility?


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Comment at: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:3110
+      unsigned TripCount = UF;
+      TripCount *= VF.isScalable() ? VF.getKnownMinValue() : VF.getFixedValue();
+      MDNode *BranchWeights = MDB.createBranchWeights(1, TripCount - 1);
----------------
can either of the VF methods return 0?


Repository:
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  https://reviews.llvm.org/D159322/new/

https://reviews.llvm.org/D159322