[LV] Move check if any vector insts will be generated to VPlan.

llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h

@@ -226,7 +226,7 @@ class VPBuilder {
 
 /// TODO: The following VectorizationFactor was pulled out of
 /// LoopVectorizationCostModel class. LV also deals with
-/// VectorizerParams::VectorizationFactor and VectorizationCostTy.
+/// VectorizerParams::VectorizationFactor.
 /// We need to streamline them.
 
 /// Information about vectorization costs.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -1090,7 +1090,7 @@ class LoopVectorizationCostModel {
   bool selectUserVectorizationFactor(ElementCount UserVF) {
     collectUniformsAndScalars(UserVF);
     collectInstsToScalarize(UserVF);
-    return expectedCost(UserVF).first.isValid();
+    return expectedCost(UserVF).isValid();
   }
 
   /// \return The size (in bits) of the smallest and widest types in the code
@@ -1591,20 +1591,13 @@ class LoopVectorizationCostModel {
     Scalars.clear();
   }
 
-  /// The vectorization cost is a combination of the cost itself and a boolean
-  /// indicating whether any of the contributing operations will actually
-  /// operate on vector values after type legalization in the backend. If this
-  /// latter value is false, then all operations will be scalarized (i.e. no
-  /// vectorization has actually taken place).
-  using VectorizationCostTy = std::pair<InstructionCost, bool>;
-
   /// Returns the expected execution cost. The unit of the cost does
   /// not matter because we use the 'cost' units to compare different
   /// vector widths. The cost that is returned is *not* normalized by
   /// the factor width. If \p Invalid is not nullptr, this function
   /// will add a pair(Instruction*, ElementCount) to \p Invalid for
   /// each instruction that has an Invalid cost for the given VF.
-  VectorizationCostTy
+  InstructionCost
   expectedCost(ElementCount VF,
                SmallVectorImpl<InstructionVFPair> *Invalid = nullptr);
 
@@ -1642,12 +1635,7 @@ class LoopVectorizationCostModel {
 
   /// Returns the execution time cost of an instruction for a given vector
   /// width. Vector width of one means scalar.
-  VectorizationCostTy getInstructionCost(Instruction *I, ElementCount VF);
-
-  /// The cost-computation logic from getInstructionCost which provides
-  /// the vector type as an output parameter.
-  InstructionCost getInstructionCost(Instruction *I, ElementCount VF,
-                                     Type *&VectorTy);
+  InstructionCost getInstructionCost(Instruction *I, ElementCount VF);
 
   /// Return the cost of instructions in an inloop reduction pattern, if I is
   /// part of that pattern.
@@ -4795,9 +4783,101 @@ static void emitInvalidCostRemarks(SmallVector<InstructionVFPair> InvalidCosts,
   } while (!Tail.empty());
 }
 
+/// Check if any recipe of \p Plan will generate a vector value, which will be
+/// assigned a vector register.
+static bool willGenerateVectors(VPlan &Plan, ElementCount VF,
+                                const TargetTransformInfo &TTI) {
+  assert(VF.isVector() && "Checking a scalar VF?");
+  VPTypeAnalysis TypeInfo(Plan.getCanonicalIV()->getScalarType(),
+                          Plan.getCanonicalIV()->getScalarType()->getContext());
+  // Set of types known to not generate vector values.
+  DenseSet<Type *> WillNotWiden;
+  for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
+           vp_depth_first_shallow(Plan.getVectorLoopRegion()->getEntry()))) {
+    for (VPRecipeBase &R : *VPBB) {
+      // Continue early if the recipe is considered to not produce a vector
+      //  result. Note that this includes VPInstruction where some opcodes may
+      // produce a vector, to preserve existing behavior as VPInstructions model
+      // aspects not directly mapped to existing IR instructions.
+      switch (R.getVPDefID()) {
+      case VPDef::VPDerivedIVSC:
+      case VPDef::VPScalarIVStepsSC:
+      case VPDef::VPScalarCastSC:
+      case VPDef::VPReplicateSC:
+      case VPDef::VPInstructionSC:
+      case VPDef::VPCanonicalIVPHISC:
+      case VPDef::VPVectorPointerSC:
+      case VPDef::VPExpandSCEVSC:
+      case VPDef::VPEVLBasedIVPHISC:
+      case VPDef::VPPredInstPHISC:
+      case VPDef::VPBranchOnMaskSC:
+        continue;
+      case VPDef::VPReductionSC:
+      case VPDef::VPActiveLaneMaskPHISC:
+      case VPDef::VPWidenCallSC:
+      case VPDef::VPWidenCanonicalIVSC:
+      case VPDef::VPWidenCastSC:
+      case VPDef::VPWidenGEPSC:
+      case VPDef::VPWidenSC:
+      case VPDef::VPWidenSelectSC:
+      case VPDef::VPBlendSC:
+      case VPDef::VPFirstOrderRecurrencePHISC:
+      case VPDef::VPWidenPHISC:
+      case VPDef::VPWidenIntOrFpInductionSC:
+      case VPDef::VPWidenPointerInductionSC:
+      case VPDef::VPReductionPHISC:
+      case VPDef::VPInterleaveSC:
+      case VPDef::VPWidenLoadEVLSC:
+      case VPDef::VPWidenLoadSC:
+      case VPDef::VPWidenStoreEVLSC:
+      case VPDef::VPWidenStoreSC:
+        break;
+      default:
+        llvm_unreachable("unhandled recipe");
+      }
+
+      auto WillWiden = [&TTI, VF](Type *ScalarTy) {
+        Type *VectorTy = ToVectorTy(ScalarTy, VF);
+        unsigned NumLegalParts = TTI.getNumberOfParts(VectorTy);
+        if (!NumLegalParts)
+          return false;
+        if (VF.isScalable()) {
+          // <vscale x 1 x iN> is assumed to be profitable over iN because
+          // scalable registers are a distinct register class from scalar
+          // ones. If we ever find a target which wants to lower scalable
+          // vectors back to scalars, we'll need to update this code to
+          // explicitly ask TTI about the register class uses for each part.
+          return NumLegalParts <= VF.getKnownMinValue();
+        }
+        // Two or more parts that share a register - are vectorized.
+        return NumLegalParts < VF.getKnownMinValue();
+      };
+
+      // If no def nor is a store, e.g., branches, continue - no value to check.
+      if (R.getNumDefinedValues() == 0 &&
+          !isa<VPWidenStoreRecipe, VPWidenStoreEVLRecipe, VPInterleaveRecipe>(
+              &R))
+        continue;
+      // For multi-def recipes, currently only interleaved loads, suffice to
+      // check first def only.
+      // For stores check their stored value; for interleaved stores suffice
+      // the check first stored value only. In all cases this is the second
+      // operand.
+      VPValue *ToCheck =
+          R.getNumDefinedValues() >= 1 ? R.getVPValue(0) : R.getOperand(1);
+      Type *ScalarTy = TypeInfo.inferScalarType(ToCheck);
+      if (!WillNotWiden.insert({ScalarTy}).second)
+        continue;
+      if (WillWiden(ScalarTy))
+        return true;
+    }
+  }
+
+  return false;
+}
+
 VectorizationFactor LoopVectorizationPlanner::selectVectorizationFactor() {
-  InstructionCost ExpectedCost =
-      CM.expectedCost(ElementCount::getFixed(1)).first;
+  InstructionCost ExpectedCost = CM.expectedCost(ElementCount::getFixed(1));
   LLVM_DEBUG(dbgs() << "LV: Scalar loop costs: " << ExpectedCost << ".\n");
   assert(ExpectedCost.isValid() && "Unexpected invalid cost for scalar loop");
   assert(any_of(VPlans,
@@ -4826,9 +4906,8 @@ VectorizationFactor LoopVectorizationPlanner::selectVectorizationFactor() {
       if (VF.isScalar())
         continue;
 
-      LoopVectorizationCostModel::VectorizationCostTy C =
-          CM.expectedCost(VF, &InvalidCosts);
-      VectorizationFactor Candidate(VF, C.first, ScalarCost.ScalarCost);
+      InstructionCost C = CM.expectedCost(VF, &InvalidCosts);
+      VectorizationFactor Candidate(VF, C, ScalarCost.ScalarCost);
 
 #ifndef NDEBUG
       unsigned AssumedMinimumVscale =
@@ -4845,7 +4924,7 @@ VectorizationFactor LoopVectorizationPlanner::selectVectorizationFactor() {
       LLVM_DEBUG(dbgs() << ".\n");
 #endif
 
-      if (!C.second && !ForceVectorization) {
+      if (!ForceVectorization && !willGenerateVectors(*P, VF, TTI)) {
         LLVM_DEBUG(
             dbgs()
             << "LV: Not considering vector loop of width " << VF
@@ -5146,7 +5225,7 @@ LoopVectorizationCostModel::selectInterleaveCount(ElementCount VF,
   // If we did not calculate the cost for VF (because the user selected the VF)
   // then we calculate the cost of VF here.
   if (LoopCost == 0) {
-    LoopCost = expectedCost(VF).first;
+    LoopCost = expectedCost(VF);
     assert(LoopCost.isValid() && "Expected to have chosen a VF with valid cost");
 
     // Loop body is free and there is no need for interleaving.
@@ -5717,15 +5796,14 @@ InstructionCost LoopVectorizationCostModel::computePredInstDiscount(
 
     // Compute the cost of the vector instruction. Note that this cost already
     // includes the scalarization overhead of the predicated instruction.
-    InstructionCost VectorCost = getInstructionCost(I, VF).first;
+    InstructionCost VectorCost = getInstructionCost(I, VF);
 
     // Compute the cost of the scalarized instruction. This cost is the cost of
     // the instruction as if it wasn't if-converted and instead remained in the
     // predicated block. We will scale this cost by block probability after
     // computing the scalarization overhead.
     InstructionCost ScalarCost =
-        VF.getFixedValue() *
-        getInstructionCost(I, ElementCount::getFixed(1)).first;
+        VF.getFixedValue() * getInstructionCost(I, ElementCount::getFixed(1));
 
     // Compute the scalarization overhead of needed insertelement instructions
     // and phi nodes.
@@ -5769,14 +5847,13 @@ InstructionCost LoopVectorizationCostModel::computePredInstDiscount(
   return Discount;
 }
 
-LoopVectorizationCostModel::VectorizationCostTy
-LoopVectorizationCostModel::expectedCost(
+InstructionCost LoopVectorizationCostModel::expectedCost(
     ElementCount VF, SmallVectorImpl<InstructionVFPair> *Invalid) {
-  VectorizationCostTy Cost;
+  InstructionCost Cost;
 
   // For each block.
   for (BasicBlock *BB : TheLoop->blocks()) {
-    VectorizationCostTy BlockCost;
+    InstructionCost BlockCost;
 
     // For each instruction in the old loop.
     for (Instruction &I : BB->instructionsWithoutDebug()) {
@@ -5785,22 +5862,19 @@ LoopVectorizationCostModel::expectedCost(
           (VF.isVector() && VecValuesToIgnore.count(&I)))
         continue;
 
-      VectorizationCostTy C = getInstructionCost(&I, VF);
+      InstructionCost C = getInstructionCost(&I, VF);
 
       // Check if we should override the cost.
-      if (C.first.isValid() &&
-          ForceTargetInstructionCost.getNumOccurrences() > 0)
-        C.first = InstructionCost(ForceTargetInstructionCost);
+      if (C.isValid() && ForceTargetInstructionCost.getNumOccurrences() > 0)
+        C = InstructionCost(ForceTargetInstructionCost);
 
       // Keep a list of instructions with invalid costs.
-      if (Invalid && !C.first.isValid())
+      if (Invalid && !C.isValid())
         Invalid->emplace_back(&I, VF);
 
-      BlockCost.first += C.first;
-      BlockCost.second |= C.second;
-      LLVM_DEBUG(dbgs() << "LV: Found an estimated cost of " << C.first
-                        << " for VF " << VF << " For instruction: " << I
-                        << '\n');
+      BlockCost += C;
+      LLVM_DEBUG(dbgs() << "LV: Found an estimated cost of " << C << " for VF "
+                        << VF << " For instruction: " << I << '\n');
     }
 
     // If we are vectorizing a predicated block, it will have been
@@ -5811,10 +5885,9 @@ LoopVectorizationCostModel::expectedCost(
     // cost by the probability of executing it. blockNeedsPredication from
     // Legal is used so as to not include all blocks in tail folded loops.
     if (VF.isScalar() && Legal->blockNeedsPredication(BB))
-      BlockCost.first /= getReciprocalPredBlockProb();
+      BlockCost /= getReciprocalPredBlockProb();
 
-    Cost.first += BlockCost.first;
-    Cost.second |= BlockCost.second;
+    Cost += BlockCost;
   }
 
   return Cost;
@@ -6213,49 +6286,6 @@ LoopVectorizationCostModel::getMemoryInstructionCost(Instruction *I,
   return getWideningCost(I, VF);
 }
 
-LoopVectorizationCostModel::VectorizationCostTy
-LoopVectorizationCostModel::getInstructionCost(Instruction *I,
-                                               ElementCount VF) {
-  // If we know that this instruction will remain uniform, check the cost of
-  // the scalar version.
-  if (isUniformAfterVectorization(I, VF))
-    VF = ElementCount::getFixed(1);
-
-  if (VF.isVector() && isProfitableToScalarize(I, VF))
-    return VectorizationCostTy(InstsToScalarize[VF][I], false);
-
-  // Forced scalars do not have any scalarization overhead.
-  auto ForcedScalar = ForcedScalars.find(VF);
-  if (VF.isVector() && ForcedScalar != ForcedScalars.end()) {
-    auto InstSet = ForcedScalar->second;
-    if (InstSet.count(I))
-      return VectorizationCostTy(
-          (getInstructionCost(I, ElementCount::getFixed(1)).first *
-           VF.getKnownMinValue()),
-          false);
-  }
-
-  Type *VectorTy;
-  InstructionCost C = getInstructionCost(I, VF, VectorTy);
-
-  bool TypeNotScalarized = false;
-  if (VF.isVector() && VectorTy->isVectorTy()) {
-    if (unsigned NumParts = TTI.getNumberOfParts(VectorTy)) {
-      if (VF.isScalable())
-        // <vscale x 1 x iN> is assumed to be profitable over iN because
-        // scalable registers are a distinct register class from scalar ones.
-        // If we ever find a target which wants to lower scalable vectors
-        // back to scalars, we'll need to update this code to explicitly
-        // ask TTI about the register class uses for each part.
-        TypeNotScalarized = NumParts <= VF.getKnownMinValue();
-      else
-        TypeNotScalarized = NumParts < VF.getKnownMinValue();
-    } else
-      C = InstructionCost::getInvalid();
-  }
-  return VectorizationCostTy(C, TypeNotScalarized);
-}
-
 InstructionCost LoopVectorizationCostModel::getScalarizationOverhead(
     Instruction *I, ElementCount VF, TTI::TargetCostKind CostKind) const {
 
@@ -6646,8 +6676,25 @@ void LoopVectorizationCostModel::setVectorizedCallDecision(ElementCount VF) {
 }
 
 InstructionCost
-LoopVectorizationCostModel::getInstructionCost(Instruction *I, ElementCount VF,
-                                               Type *&VectorTy) {
+LoopVectorizationCostModel::getInstructionCost(Instruction *I,
+                                               ElementCount VF) {
+  // If we know that this instruction will remain uniform, check the cost of
+  // the scalar version.
+  if (isUniformAfterVectorization(I, VF))
+    VF = ElementCount::getFixed(1);
+
+  if (VF.isVector() && isProfitableToScalarize(I, VF))
+    return InstsToScalarize[VF][I];
+
+  // Forced scalars do not have any scalarization overhead.
+  auto ForcedScalar = ForcedScalars.find(VF);
+  if (VF.isVector() && ForcedScalar != ForcedScalars.end()) {
+    auto InstSet = ForcedScalar->second;
+    if (InstSet.count(I))
+      return getInstructionCost(I, ElementCount::getFixed(1)) *
+             VF.getKnownMinValue();
+  }
+
   Type *RetTy = I->getType();
   if (canTruncateToMinimalBitwidth(I, VF))
     RetTy = IntegerType::get(RetTy->getContext(), MinBWs[I]);
@@ -6670,6 +6717,7 @@ LoopVectorizationCostModel::getInstructionCost(Instruction *I, ElementCount VF,
   };
   (void) hasSingleCopyAfterVectorization;
 
+  Type *VectorTy;
   if (isScalarAfterVectorization(I, VF)) {
     // With the exception of GEPs and PHIs, after scalarization there should
     // only be one copy of the instruction generated in the loop. This is
@@ -6685,6 +6733,10 @@ LoopVectorizationCostModel::getInstructionCost(Instruction *I, ElementCount VF,
   } else
     VectorTy = ToVectorTy(RetTy, VF);
 
+  if (VF.isVector() && VectorTy->isVectorTy() &&
+      !TTI.getNumberOfParts(VectorTy))
+    return InstructionCost::getInvalid();
+
   // TODO: We need to estimate the cost of intrinsic calls.
   switch (I->getOpcode()) {
   case Instruction::GetElementPtr: