[LV] Bundle sub reductions into VPExpressionRecipe

SamTebbs33 · SamTebbs33 · commit 1a5f4e42e4f9 · 2025-07-06T22:21:12.000+01:00
This PR bundles sub reductions into the VPExpressionRecipe class and
adjusts the cost functions to take the negation into account.
diff --git a/llvm/include/llvm/Analysis/TargetTransformInfo.h b/llvm/include/llvm/Analysis/TargetTransformInfo.h
@@ -1645,8 +1645,10 @@ class TargetTransformInfo {
   /// extensions. This is the cost of as:
   /// ResTy vecreduce.add(mul (A, B)).
   /// ResTy vecreduce.add(mul(ext(Ty A), ext(Ty B)).
+  /// The multiply can optionally be negated, which signifies that it is a sub
+  /// reduction.
   LLVM_ABI InstructionCost getMulAccReductionCost(
-      bool IsUnsigned, Type *ResTy, VectorType *Ty,
+      bool IsUnsigned, Type *ResTy, VectorType *Ty, bool Negated,
       TTI::TargetCostKind CostKind = TTI::TCK_RecipThroughput) const;
 
   /// Calculate the cost of an extended reduction pattern, similar to
diff --git a/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h b/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
@@ -960,7 +960,7 @@ class TargetTransformInfoImplBase {
 
   virtual InstructionCost
   getMulAccReductionCost(bool IsUnsigned, Type *ResTy, VectorType *Ty,
-                         TTI::TargetCostKind CostKind) const {
+                         bool Negated, TTI::TargetCostKind CostKind) const {
     return 1;
   }
 
diff --git a/llvm/include/llvm/CodeGen/BasicTTIImpl.h b/llvm/include/llvm/CodeGen/BasicTTIImpl.h
@@ -3116,7 +3116,10 @@ class BasicTTIImplBase : public TargetTransformInfoImplCRTPBase<T> {
 
   InstructionCost
   getMulAccReductionCost(bool IsUnsigned, Type *ResTy, VectorType *Ty,
+                         bool Negated,
                          TTI::TargetCostKind CostKind) const override {
+    if (Negated)
+      return InstructionCost::getInvalid(CostKind);
     // Without any native support, this is equivalent to the cost of
     // vecreduce.add(mul(ext(Ty A), ext(Ty B))) or
     // vecreduce.add(mul(A, B)).
diff --git a/llvm/lib/Analysis/TargetTransformInfo.cpp b/llvm/lib/Analysis/TargetTransformInfo.cpp
@@ -1274,9 +1274,10 @@ InstructionCost TargetTransformInfo::getExtendedReductionCost(
 }
 
 InstructionCost TargetTransformInfo::getMulAccReductionCost(
-    bool IsUnsigned, Type *ResTy, VectorType *Ty,
+    bool IsUnsigned, Type *ResTy, VectorType *Ty, bool Negated,
     TTI::TargetCostKind CostKind) const {
-  return TTIImpl->getMulAccReductionCost(IsUnsigned, ResTy, Ty, CostKind);
+  return TTIImpl->getMulAccReductionCost(IsUnsigned, ResTy, Ty, Negated,
+                                         CostKind);
 }
 
 InstructionCost
diff --git a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -5316,8 +5316,10 @@ InstructionCost AArch64TTIImpl::getExtendedReductionCost(
 
 InstructionCost
 AArch64TTIImpl::getMulAccReductionCost(bool IsUnsigned, Type *ResTy,
-                                       VectorType *VecTy,
+                                       VectorType *VecTy, bool Negated,
                                        TTI::TargetCostKind CostKind) const {
+  if (Negated)
+    return InstructionCost::getInvalid(CostKind);
   EVT VecVT = TLI->getValueType(DL, VecTy);
   EVT ResVT = TLI->getValueType(DL, ResTy);
 
@@ -5332,7 +5334,8 @@ AArch64TTIImpl::getMulAccReductionCost(bool IsUnsigned, Type *ResTy,
       return LT.first + 2;
   }
 
-  return BaseT::getMulAccReductionCost(IsUnsigned, ResTy, VecTy, CostKind);
+  return BaseT::getMulAccReductionCost(IsUnsigned, ResTy, VecTy, Negated,
+                                       CostKind);
 }
 
 InstructionCost
diff --git a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.h b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.h
@@ -447,7 +447,7 @@ class AArch64TTIImpl final : public BasicTTIImplBase<AArch64TTIImpl> {
                            TTI::TargetCostKind CostKind) const override;
 
   InstructionCost getMulAccReductionCost(
-      bool IsUnsigned, Type *ResTy, VectorType *Ty,
+      bool IsUnsigned, Type *ResTy, VectorType *Ty, bool Negated,
       TTI::TargetCostKind CostKind = TTI::TCK_RecipThroughput) const override;
 
   InstructionCost
diff --git a/llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp b/llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
@@ -1884,8 +1884,10 @@ InstructionCost ARMTTIImpl::getExtendedReductionCost(
 
 InstructionCost
 ARMTTIImpl::getMulAccReductionCost(bool IsUnsigned, Type *ResTy,
-                                   VectorType *ValTy,
+                                   VectorType *ValTy, bool Negated,
                                    TTI::TargetCostKind CostKind) const {
+  if (Negated)
+    return InstructionCost::getInvalid(CostKind);
   EVT ValVT = TLI->getValueType(DL, ValTy);
   EVT ResVT = TLI->getValueType(DL, ResTy);
 
@@ -1906,7 +1908,8 @@ ARMTTIImpl::getMulAccReductionCost(bool IsUnsigned, Type *ResTy,
       return ST->getMVEVectorCostFactor(CostKind) * LT.first;
   }
 
-  return BaseT::getMulAccReductionCost(IsUnsigned, ResTy, ValTy, CostKind);
+  return BaseT::getMulAccReductionCost(IsUnsigned, ResTy, ValTy, Negated,
+                                       CostKind);
 }
 
 InstructionCost
diff --git a/llvm/lib/Target/ARM/ARMTargetTransformInfo.h b/llvm/lib/Target/ARM/ARMTargetTransformInfo.h
@@ -299,6 +299,7 @@ class ARMTTIImpl final : public BasicTTIImplBase<ARMTTIImpl> {
                            TTI::TargetCostKind CostKind) const override;
   InstructionCost
   getMulAccReductionCost(bool IsUnsigned, Type *ResTy, VectorType *ValTy,
+                         bool Negated,
                          TTI::TargetCostKind CostKind) const override;
 
   InstructionCost
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -5538,7 +5538,7 @@ LoopVectorizationCostModel::getReductionPatternCost(Instruction *I,
                              TTI::CastContextHint::None, CostKind, RedOp);
 
     InstructionCost RedCost = TTI.getMulAccReductionCost(
-        IsUnsigned, RdxDesc.getRecurrenceType(), ExtType, CostKind);
+        IsUnsigned, RdxDesc.getRecurrenceType(), ExtType, false, CostKind);
 
     if (RedCost.isValid() &&
         RedCost < ExtCost * 2 + MulCost + Ext2Cost + BaseCost)
@@ -5583,7 +5583,7 @@ LoopVectorizationCostModel::getReductionPatternCost(Instruction *I,
           TTI.getArithmeticInstrCost(Instruction::Mul, VectorTy, CostKind);
 
       InstructionCost RedCost = TTI.getMulAccReductionCost(
-          IsUnsigned, RdxDesc.getRecurrenceType(), ExtType, CostKind);
+          IsUnsigned, RdxDesc.getRecurrenceType(), ExtType, false, CostKind);
       InstructionCost ExtraExtCost = 0;
       if (Op0Ty != LargestOpTy || Op1Ty != LargestOpTy) {
         Instruction *ExtraExtOp = (Op0Ty != LargestOpTy) ? Op0 : Op1;
@@ -5602,7 +5602,7 @@ LoopVectorizationCostModel::getReductionPatternCost(Instruction *I,
           TTI.getArithmeticInstrCost(Instruction::Mul, VectorTy, CostKind);
 
       InstructionCost RedCost = TTI.getMulAccReductionCost(
-          true, RdxDesc.getRecurrenceType(), VectorTy, CostKind);
+          true, RdxDesc.getRecurrenceType(), VectorTy, false, CostKind);
 
       if (RedCost.isValid() && RedCost < MulCost + BaseCost)
         return I == RetI ? RedCost : 0;
diff --git a/llvm/lib/Transforms/Vectorize/VPlan.h b/llvm/lib/Transforms/Vectorize/VPlan.h
@@ -2757,6 +2757,12 @@ class VPExpressionRecipe : public VPSingleDefRecipe {
     /// vector operands, performing a reduction.add on the result, and adding
     /// the scalar result to a chain.
     MulAccReduction,
+    /// Represent an inloop multiply-accumulate reduction, multiplying the
+    /// extended vector operands, negating the multiplication, performing a
+    /// reduction.add
+    /// on the result, and adding
+    /// the scalar result to a chain.
+    ExtNegatedMulAccReduction,
   };
 
   /// Type of the expression.
@@ -2780,6 +2786,11 @@ class VPExpressionRecipe : public VPSingleDefRecipe {
                      VPWidenRecipe *Mul, VPReductionRecipe *Red)
       : VPExpressionRecipe(ExpressionTypes::ExtMulAccReduction,
                            {Ext0, Ext1, Mul, Red}) {}
+  VPExpressionRecipe(VPWidenCastRecipe *Ext0, VPWidenCastRecipe *Ext1,
+                     VPWidenRecipe *Mul, VPWidenRecipe *Sub,
+                     VPReductionRecipe *Red)
+      : VPExpressionRecipe(ExpressionTypes::ExtNegatedMulAccReduction,
+                           {Ext0, Ext1, Mul, Sub, Red}) {}
 
   ~VPExpressionRecipe() override {
     for (auto *R : reverse(ExpressionRecipes))
diff --git a/llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp b/llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp
@@ -2672,13 +2672,17 @@ InstructionCost VPExpressionRecipe::computeCost(ElementCount VF,
         RedTy, SrcVecTy, std::nullopt, Ctx.CostKind);
   }
   case ExpressionTypes::MulAccReduction:
-    return Ctx.TTI.getMulAccReductionCost(false, RedTy, SrcVecTy, Ctx.CostKind);
+    return Ctx.TTI.getMulAccReductionCost(false, RedTy, SrcVecTy, false,
+                                          Ctx.CostKind);
 
-  case ExpressionTypes::ExtMulAccReduction:
+  case ExpressionTypes::ExtNegatedMulAccReduction:
+  case ExpressionTypes::ExtMulAccReduction: {
+    bool Negated = ExpressionType == ExpressionTypes::ExtNegatedMulAccReduction;
     return Ctx.TTI.getMulAccReductionCost(
         cast<VPWidenCastRecipe>(ExpressionRecipes.front())->getOpcode() ==
             Instruction::ZExt,
-        RedTy, SrcVecTy, Ctx.CostKind);
+        RedTy, SrcVecTy, Negated, Ctx.CostKind);
+  }
   }
   llvm_unreachable("Unknown VPExpressionRecipe::ExpressionTypes enum");
 }
@@ -2725,6 +2729,31 @@ void VPExpressionRecipe::print(raw_ostream &O, const Twine &Indent,
     O << ")";
     break;
   }
+  case ExpressionTypes::ExtNegatedMulAccReduction: {
+    getOperand(getNumOperands() - 1)->printAsOperand(O, SlotTracker);
+    O << " + ";
+    O << "reduce."
+      << Instruction::getOpcodeName(
+             RecurrenceDescriptor::getOpcode(Red->getRecurrenceKind()))
+      << " (sub (0, mul";
+    auto *Mul = cast<VPWidenRecipe>(ExpressionRecipes[2]);
+    Mul->printFlags(O);
+    O << "(";
+    getOperand(0)->printAsOperand(O, SlotTracker);
+    auto *Ext0 = cast<VPWidenCastRecipe>(ExpressionRecipes[0]);
+    O << " " << Instruction::getOpcodeName(Ext0->getOpcode()) << " to "
+      << *Ext0->getResultType() << "), (";
+    getOperand(1)->printAsOperand(O, SlotTracker);
+    auto *Ext1 = cast<VPWidenCastRecipe>(ExpressionRecipes[1]);
+    O << " " << Instruction::getOpcodeName(Ext1->getOpcode()) << " to "
+      << *Ext1->getResultType() << ")";
+    if (Red->isConditional()) {
+      O << ", ";
+      Red->getCondOp()->printAsOperand(O, SlotTracker);
+    }
+    O << "))";
+    break;
+  }
   case ExpressionTypes::MulAccReduction:
   case ExpressionTypes::ExtMulAccReduction: {
     getOperand(getNumOperands() - 1)->printAsOperand(O, SlotTracker);
diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -2908,16 +2908,17 @@ tryToMatchAndCreateMulAccumulateReduction(VPReductionRecipe *Red,
 
   // Clamp the range if using multiply-accumulate-reduction is profitable.
   auto IsMulAccValidAndClampRange =
-      [&](bool isZExt, VPWidenRecipe *Mul, VPWidenCastRecipe *Ext0,
-          VPWidenCastRecipe *Ext1, VPWidenCastRecipe *OuterExt) -> bool {
+      [&](bool IsZExt, VPWidenRecipe *Mul, VPWidenCastRecipe *Ext0,
+          VPWidenCastRecipe *Ext1, VPWidenCastRecipe *OuterExt,
+          bool Negated = false) -> bool {
     return LoopVectorizationPlanner::getDecisionAndClampRange(
         [&](ElementCount VF) {
           TTI::TargetCostKind CostKind = TTI::TCK_RecipThroughput;
           Type *SrcTy =
               Ext0 ? Ctx.Types.inferScalarType(Ext0->getOperand(0)) : RedTy;
           auto *SrcVecTy = cast<VectorType>(toVectorTy(SrcTy, VF));
-          InstructionCost MulAccCost =
-              Ctx.TTI.getMulAccReductionCost(isZExt, RedTy, SrcVecTy, CostKind);
+          InstructionCost MulAccCost = Ctx.TTI.getMulAccReductionCost(
+              IsZExt, RedTy, SrcVecTy, Negated, CostKind);
           InstructionCost MulCost = Mul->computeCost(VF, Ctx);
           InstructionCost RedCost = Red->computeCost(VF, Ctx);
           InstructionCost ExtCost = 0;
@@ -2935,14 +2936,22 @@ tryToMatchAndCreateMulAccumulateReduction(VPReductionRecipe *Red,
   };
 
   VPValue *VecOp = Red->getVecOp();
+  VPValue *Mul = nullptr;
+  VPValue *Sub = nullptr;
   VPValue *A, *B;
+  // Sub reductions will have a sub between the add reduction and vec op.
+  if (match(VecOp,
+            m_Binary<Instruction::Sub>(m_SpecificInt(0), m_VPValue(Mul))))
+    Sub = VecOp;
+  else
+    Mul = VecOp;
   // Try to match reduce.add(mul(...)).
-  if (match(VecOp, m_Mul(m_VPValue(A), m_VPValue(B)))) {
+  if (match(Mul, m_Mul(m_VPValue(A), m_VPValue(B)))) {
     auto *RecipeA =
         dyn_cast_if_present<VPWidenCastRecipe>(A->getDefiningRecipe());
     auto *RecipeB =
         dyn_cast_if_present<VPWidenCastRecipe>(B->getDefiningRecipe());
-    auto *Mul = cast<VPWidenRecipe>(VecOp->getDefiningRecipe());
+    auto *MulR = cast<VPWidenRecipe>(Mul->getDefiningRecipe());
 
     // Match reduce.add(mul(ext, ext)).
     if (RecipeA && RecipeB &&
@@ -2951,12 +2960,16 @@ tryToMatchAndCreateMulAccumulateReduction(VPReductionRecipe *Red,
         match(RecipeB, m_ZExtOrSExt(m_VPValue())) &&
         IsMulAccValidAndClampRange(RecipeA->getOpcode() ==
                                        Instruction::CastOps::ZExt,
-                                   Mul, RecipeA, RecipeB, nullptr)) {
-      return new VPExpressionRecipe(RecipeA, RecipeB, Mul, Red);
+                                   MulR, RecipeA, RecipeB, nullptr, Sub)) {
+      if (Sub)
+        return new VPExpressionRecipe(
+            RecipeA, RecipeB, MulR,
+            cast<VPWidenRecipe>(Sub->getDefiningRecipe()), Red);
+      return new VPExpressionRecipe(RecipeA, RecipeB, MulR, Red);
     }
     // Match reduce.add(mul).
-    if (IsMulAccValidAndClampRange(true, Mul, nullptr, nullptr, nullptr))
-      return new VPExpressionRecipe(Mul, Red);
+    if (IsMulAccValidAndClampRange(true, MulR, nullptr, nullptr, nullptr, Sub))
+      return new VPExpressionRecipe(MulR, Red);
   }
   // Match reduce.add(ext(mul(ext(A), ext(B)))).
   // All extend recipes must have same opcode or A == B
diff --git a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
@@ -1401,8 +1401,8 @@ static void analyzeCostOfVecReduction(const IntrinsicInst &II,
                              TTI::CastContextHint::None, CostKind, RedOp);
 
     CostBeforeReduction = ExtCost * 2 + MulCost + Ext2Cost;
-    CostAfterReduction =
-        TTI.getMulAccReductionCost(IsUnsigned, II.getType(), ExtType, CostKind);
+    CostAfterReduction = TTI.getMulAccReductionCost(IsUnsigned, II.getType(),
+                                                    ExtType, false, CostKind);
     return;
   }
   CostAfterReduction = TTI.getArithmeticReductionCost(ReductionOpc, VecRedTy,
diff --git a/llvm/test/Transforms/LoopVectorize/vplan-printing-reductions.ll b/llvm/test/Transforms/LoopVectorize/vplan-printing-reductions.ll

Original file line number	Diff line number	Diff line change
`@@ -960,7 +960,7 @@ class TargetTransformInfoImplBase {`
`960`	`960`
`961`	`961`	`virtual InstructionCost`
`962`	`962`	`getMulAccReductionCost(bool IsUnsigned, Type ResTy, VectorType Ty,`
`963`		`- TTI::TargetCostKind CostKind) const {`
	`963`	`+ bool Negated, TTI::TargetCostKind CostKind) const {`
`964`	`964`	`return 1;`
`965`	`965`	`}`
`966`	`966`
Original file line number	Diff line number	Diff line change
`@@ -1274,9 +1274,10 @@ InstructionCost TargetTransformInfo::getExtendedReductionCost(`
`1274`	`1274`	`}`
`1275`	`1275`
`1276`	`1276`	`InstructionCost TargetTransformInfo::getMulAccReductionCost(`
`1277`		`- bool IsUnsigned, Type ResTy, VectorType Ty,`
	`1277`	`+ bool IsUnsigned, Type ResTy, VectorType Ty, bool Negated,`
`1278`	`1278`	`TTI::TargetCostKind CostKind) const {`
`1279`		`- return TTIImpl->getMulAccReductionCost(IsUnsigned, ResTy, Ty, CostKind);`
	`1279`	`+ return TTIImpl->getMulAccReductionCost(IsUnsigned, ResTy, Ty, Negated,`
	`1280`	`+ CostKind);`
`1280`	`1281`	`}`
`1281`	`1282`
`1282`	`1283`	`InstructionCost`