[LV] Account for predicated stores in instruction costs

This patch ensures that we scale the estimated cost of predicated stores by
block probability. This is a follow-on patch for r284123.

llvm-svn: 284126

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index e41f414ef3c..ab5dc930a32 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -6700,6 +6700,12 @@ unsigned LoopVectorizationCostModel::getInstructionCost(Instruction *I,
       // we might create due to scalarization.
       Cost += getScalarizationOverhead(I, VF, TTI);
 
+      // If we have a predicated store, it may not be executed for each vector
+      // lane. Scale the cost by the probability of executing the predicated
+      // block.
+      if (Legal->isScalarWithPredication(I))
+        Cost /= getReciprocalPredBlockProb();
+
       return Cost;
     }