[PATCH] D92177: [NFC][InstructionCost] Refactor LoopVectorizationCostModel::selectVectorizationFactor

[David Sherwood via Phabricator via llvm-commits]

david-arm updated this revision to Diff 308297.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D92177/new/

https://reviews.llvm.org/D92177

Files:
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp


Index: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -5408,54 +5408,56 @@
 LoopVectorizationCostModel::selectVectorizationFactor(ElementCount MaxVF) {
   assert(!MaxVF.isScalable() && "scalable vectors not yet supported");
 
-  float Cost = expectedCost(ElementCount::getFixed(1)).first;
-  const float ScalarCost = Cost;
-  unsigned Width = 1;
-  LLVM_DEBUG(dbgs() << "LV: Scalar loop costs: " << (int)ScalarCost << ".\n");
+  unsigned ExpectedCost = expectedCost(ElementCount::getFixed(1)).first;
+  LLVM_DEBUG(dbgs() << "LV: Scalar loop costs: " << ExpectedCost << ".\n");
+
+  std::pair<unsigned, unsigned> MinCost = {ExpectedCost, 1};
+  const std::pair<unsigned, unsigned> ScalarCost = MinCost;
 
   bool ForceVectorization = Hints->getForce() == LoopVectorizeHints::FK_Enabled;
   if (ForceVectorization && MaxVF.isVector()) {
     // Ignore scalar width, because the user explicitly wants vectorization.
     // Initialize cost to max so that VF = 2 is, at least, chosen during cost
     // evaluation.
-    Cost = std::numeric_limits<float>::max();
+    MinCost.first = std::numeric_limits<unsigned>::max();
   }
 
+  auto isLowerVectorCost = [](const std::pair<unsigned, unsigned> LHS,
+                              const std::pair<unsigned, unsigned> RHS) {
+    return (float(LHS.first) / LHS.second) < (float(RHS.first) / RHS.second);
+  };
+
   for (unsigned i = 2; i <= MaxVF.getFixedValue(); i *= 2) {
     // Notice that the vector loop needs to be executed less times, so
     // we need to divide the cost of the vector loops by the width of
     // the vector elements.
     VectorizationCostTy C = expectedCost(ElementCount::getFixed(i));
-    float VectorCost = C.first / (float)i;
+    std::pair<unsigned, unsigned> VectorCost = {C.first, i};
     LLVM_DEBUG(dbgs() << "LV: Vector loop of width " << i
-                      << " costs: " << (int)VectorCost << ".\n");
+                      << " costs: " << (C.first / i) << ".\n");
     if (!C.second && !ForceVectorization) {
       LLVM_DEBUG(
           dbgs() << "LV: Not considering vector loop of width " << i
                  << " because it will not generate any vector instructions.\n");
       continue;
     }
-    if (VectorCost < Cost) {
-      Cost = VectorCost;
-      Width = i;
-    }
+    if (isLowerVectorCost(VectorCost, MinCost))
+      MinCost = VectorCost;
   }
 
   if (!EnableCondStoresVectorization && NumPredStores) {
     reportVectorizationFailure("There are conditional stores.",
         "store that is conditionally executed prevents vectorization",
         "ConditionalStore", ORE, TheLoop);
-    Width = 1;
-    Cost = ScalarCost;
+    MinCost = ScalarCost;
   }
 
-  LLVM_DEBUG(if (ForceVectorization && Width > 1 && Cost >= ScalarCost) dbgs()
+  LLVM_DEBUG(if (ForceVectorization && MinCost.second > 1 &&
+                 isLowerVectorCost(ScalarCost, MinCost)) dbgs()
              << "LV: Vectorization seems to be not beneficial, "
              << "but was forced by a user.\n");
-  LLVM_DEBUG(dbgs() << "LV: Selecting VF: " << Width << ".\n");
-  VectorizationFactor Factor = {ElementCount::getFixed(Width),
-                                (unsigned)(Width * Cost)};
-  return Factor;
+  LLVM_DEBUG(dbgs() << "LV: Selecting VF: " << MinCost.second << ".\n");
+  return {ElementCount::getFixed(MinCost.second), MinCost.first};
 }
 
 std::pair<unsigned, unsigned>


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