[InstCombine] Fold binary op of reductions.

Mikhail Gudim · Mikhail Gudim · commit d4de22ea090f · 2025-01-10T10:09:38.000-08:00
Replace binary of of two reductions with one reduction of the binary op
applied to vectors. For example:

```
%v0_red = tail call i32 @llvm.vector.reduce.add.v16i32(&lt;16 x i32&gt; %v0)
%v1_red = tail call i32 @llvm.vector.reduce.add.v16i32(&lt;16 x i32&gt; %v1)
%res = add i32 %v0_red, %v1_red
```
gets transformed to:

```
%1 = add &lt;16 x i32&gt; %v0, %v1
%res = call i32 @llvm.vector.reduce.add.v16i32(&lt;16 x i32&gt; %1)
```
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1528,6 +1528,9 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
   if (Instruction *X = foldVectorBinop(I))
     return X;
 
+  if (Instruction *X = foldBinopOfReductions(I))
+    return replaceInstUsesWith(I, X);
+
   if (Instruction *Phi = foldBinopWithPhiOperands(I))
     return Phi;
 
@@ -2378,19 +2381,8 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) {
     }
   }
 
-  auto m_AddRdx = [](Value *&Vec) {
-    return m_OneUse(m_Intrinsic<Intrinsic::vector_reduce_add>(m_Value(Vec)));
-  };
-  Value *V0, *V1;
-  if (match(Op0, m_AddRdx(V0)) && match(Op1, m_AddRdx(V1)) &&
-      V0->getType() == V1->getType()) {
-    // Difference of sums is sum of differences:
-    // add_rdx(V0) - add_rdx(V1) --> add_rdx(V0 - V1)
-    Value *Sub = Builder.CreateSub(V0, V1);
-    Value *Rdx = Builder.CreateIntrinsic(Intrinsic::vector_reduce_add,
-                                         {Sub->getType()}, {Sub});
-    return replaceInstUsesWith(I, Rdx);
-  }
+  if (Instruction *X = foldBinopOfReductions(I))
+    return replaceInstUsesWith(I, X);
 
   if (Constant *C = dyn_cast<Constant>(Op0)) {
     Value *X;
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2372,6 +2372,9 @@ Instruction *InstCombinerImpl::visitAnd(BinaryOperator &I) {
   if (Instruction *X = foldVectorBinop(I))
     return X;
 
+  if (Instruction *X = foldBinopOfReductions(I))
+    return replaceInstUsesWith(I, X);
+
   if (Instruction *Phi = foldBinopWithPhiOperands(I))
     return Phi;
 
@@ -3552,6 +3555,9 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
   if (Instruction *X = foldVectorBinop(I))
     return X;
 
+  if (Instruction *X = foldBinopOfReductions(I))
+    return replaceInstUsesWith(I, X);
+
   if (Instruction *Phi = foldBinopWithPhiOperands(I))
     return Phi;
 
@@ -4663,6 +4669,9 @@ Instruction *InstCombinerImpl::visitXor(BinaryOperator &I) {
   if (Instruction *X = foldVectorBinop(I))
     return X;
 
+  if (Instruction *X = foldBinopOfReductions(I))
+    return replaceInstUsesWith(I, X);
+
   if (Instruction *Phi = foldBinopWithPhiOperands(I))
     return Phi;
 
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -594,6 +594,7 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
 
   /// Canonicalize the position of binops relative to shufflevector.
   Instruction *foldVectorBinop(BinaryOperator &Inst);
+  Instruction *foldBinopOfReductions(BinaryOperator &Inst);
   Instruction *foldVectorSelect(SelectInst &Sel);
   Instruction *foldSelectShuffle(ShuffleVectorInst &Shuf);
 
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -201,6 +201,9 @@ Instruction *InstCombinerImpl::visitMul(BinaryOperator &I) {
   if (Instruction *X = foldVectorBinop(I))
     return X;
 
+  if (Instruction *X = foldBinopOfReductions(I))
+    return replaceInstUsesWith(I, X);
+
   if (Instruction *Phi = foldBinopWithPhiOperands(I))
     return Phi;
 
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2312,6 +2312,63 @@ Instruction *InstCombinerImpl::foldVectorBinop(BinaryOperator &Inst) {
   return nullptr;
 }
 
+static Intrinsic::ID getReductionForBinop(Instruction::BinaryOps Opc) {
+  switch (Opc) {
+  default:
+    break;
+  case Instruction::Add:
+    return Intrinsic::vector_reduce_add;
+  case Instruction::Mul:
+    return Intrinsic::vector_reduce_mul;
+  case Instruction::And:
+    return Intrinsic::vector_reduce_and;
+  case Instruction::Or:
+    return Intrinsic::vector_reduce_or;
+  case Instruction::Xor:
+    return Intrinsic::vector_reduce_xor;
+  }
+  return Intrinsic::not_intrinsic;
+}
+
+Instruction *InstCombinerImpl::foldBinopOfReductions(BinaryOperator &Inst) {
+  Instruction::BinaryOps BinOpOpc = Inst.getOpcode();
+  Intrinsic::ID ReductionIID = getReductionForBinop(BinOpOpc);
+  if (BinOpOpc == Instruction::Sub)
+    ReductionIID = Intrinsic::vector_reduce_add;
+  if (ReductionIID == Intrinsic::not_intrinsic)
+    return nullptr;
+
+  auto checkIntrinsicAndGetItsArgument = [](Value *V,
+                                            Intrinsic::ID IID) -> Value * {
+    IntrinsicInst *II = dyn_cast<IntrinsicInst>(V);
+    if (!II)
+      return nullptr;
+    if (II->getIntrinsicID() == IID && II->hasOneUse())
+      return II->getArgOperand(0);
+    return nullptr;
+  };
+
+  Value *V0 = checkIntrinsicAndGetItsArgument(Inst.getOperand(0), ReductionIID);
+  if (!V0)
+    return nullptr;
+  Value *V1 = checkIntrinsicAndGetItsArgument(Inst.getOperand(1), ReductionIID);
+  if (!V1)
+    return nullptr;
+
+  Type *VTy = V0->getType();
+  if (V1->getType() != VTy)
+    return nullptr;
+
+  Value *VectorBO = Builder.CreateBinOp(BinOpOpc, V0, V1);
+
+  if (PossiblyDisjointInst *PDInst = dyn_cast<PossiblyDisjointInst>(&Inst))
+    if (auto *PDVectorBO = dyn_cast<PossiblyDisjointInst>(VectorBO))
+      PDVectorBO->setIsDisjoint(PDInst->isDisjoint());
+
+  Instruction *Rdx = Builder.CreateIntrinsic(ReductionIID, {VTy}, {VectorBO});
+  return Rdx;
+}
+
 /// Try to narrow the width of a binop if at least 1 operand is an extend of
 /// of a value. This requires a potentially expensive known bits check to make
 /// sure the narrow op does not overflow.
diff --git a/llvm/test/Transforms/InstCombine/fold-binop-of-reductions.ll b/llvm/test/Transforms/InstCombine/fold-binop-of-reductions.ll
@@ -4,9 +4,8 @@
 define i32 @add_of_reduce_add(<16 x i32> %v0, <16 x i32> %v1) {
 ; CHECK-LABEL: define i32 @add_of_reduce_add(
 ; CHECK-SAME: <16 x i32> [[V0:%.*]], <16 x i32> [[V1:%.*]]) {
-; CHECK-NEXT:    [[V0_RED:%.*]] = tail call i32 @llvm.vector.reduce.add.v16i32(<16 x i32> [[V0]])
-; CHECK-NEXT:    [[V1_RED:%.*]] = tail call i32 @llvm.vector.reduce.add.v16i32(<16 x i32> [[V1]])
-; CHECK-NEXT:    [[RES:%.*]] = add i32 [[V0_RED]], [[V1_RED]]
+; CHECK-NEXT:    [[TMP1:%.*]] = add <16 x i32> [[V0]], [[V1]]
+; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.vector.reduce.add.v16i32(<16 x i32> [[TMP1]])
 ; CHECK-NEXT:    ret i32 [[RES]]
 ;
   %v0_red = tail call i32 @llvm.vector.reduce.add.v16i32(<16 x i32> %v0)
@@ -31,9 +30,8 @@ define i32 @sub_of_reduce_add(<16 x i32> %v0, <16 x i32> %v1) {
 define i32 @mul_of_reduce_mul(<16 x i32> %v0, <16 x i32> %v1) {
 ; CHECK-LABEL: define i32 @mul_of_reduce_mul(
 ; CHECK-SAME: <16 x i32> [[V0:%.*]], <16 x i32> [[V1:%.*]]) {
-; CHECK-NEXT:    [[V0_RED:%.*]] = tail call i32 @llvm.vector.reduce.mul.v16i32(<16 x i32> [[V0]])
-; CHECK-NEXT:    [[V1_RED:%.*]] = tail call i32 @llvm.vector.reduce.mul.v16i32(<16 x i32> [[V1]])
-; CHECK-NEXT:    [[RES:%.*]] = mul i32 [[V0_RED]], [[V1_RED]]
+; CHECK-NEXT:    [[TMP1:%.*]] = mul <16 x i32> [[V0]], [[V1]]
+; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.vector.reduce.mul.v16i32(<16 x i32> [[TMP1]])
 ; CHECK-NEXT:    ret i32 [[RES]]
 ;
   %v0_red = tail call i32 @llvm.vector.reduce.mul.v16i32(<16 x i32> %v0)
@@ -45,9 +43,8 @@ define i32 @mul_of_reduce_mul(<16 x i32> %v0, <16 x i32> %v1) {
 define i32 @and_of_reduce_and(<16 x i32> %v0, <16 x i32> %v1) {
 ; CHECK-LABEL: define i32 @and_of_reduce_and(
 ; CHECK-SAME: <16 x i32> [[V0:%.*]], <16 x i32> [[V1:%.*]]) {
-; CHECK-NEXT:    [[V0_RED:%.*]] = tail call i32 @llvm.vector.reduce.and.v16i32(<16 x i32> [[V0]])
-; CHECK-NEXT:    [[V1_RED:%.*]] = tail call i32 @llvm.vector.reduce.and.v16i32(<16 x i32> [[V1]])
-; CHECK-NEXT:    [[RES:%.*]] = and i32 [[V0_RED]], [[V1_RED]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and <16 x i32> [[V0]], [[V1]]
+; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.vector.reduce.and.v16i32(<16 x i32> [[TMP1]])
 ; CHECK-NEXT:    ret i32 [[RES]]
 ;
   %v0_red = tail call i32 @llvm.vector.reduce.and.v16i32(<16 x i32> %v0)
@@ -59,9 +56,8 @@ define i32 @and_of_reduce_and(<16 x i32> %v0, <16 x i32> %v1) {
 define i32 @or_of_reduce_or(<16 x i32> %v0, <16 x i32> %v1) {
 ; CHECK-LABEL: define i32 @or_of_reduce_or(
 ; CHECK-SAME: <16 x i32> [[V0:%.*]], <16 x i32> [[V1:%.*]]) {
-; CHECK-NEXT:    [[V0_RED:%.*]] = tail call i32 @llvm.vector.reduce.or.v16i32(<16 x i32> [[V0]])
-; CHECK-NEXT:    [[V1_RED:%.*]] = tail call i32 @llvm.vector.reduce.or.v16i32(<16 x i32> [[V1]])
-; CHECK-NEXT:    [[RES:%.*]] = or i32 [[V0_RED]], [[V1_RED]]
+; CHECK-NEXT:    [[TMP1:%.*]] = or <16 x i32> [[V0]], [[V1]]
+; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.vector.reduce.or.v16i32(<16 x i32> [[TMP1]])
 ; CHECK-NEXT:    ret i32 [[RES]]
 ;
   %v0_red = tail call i32 @llvm.vector.reduce.or.v16i32(<16 x i32> %v0)
@@ -73,9 +69,8 @@ define i32 @or_of_reduce_or(<16 x i32> %v0, <16 x i32> %v1) {
 define i32 @xor_of_reduce_xor(<16 x i32> %v0, <16 x i32> %v1) {
 ; CHECK-LABEL: define i32 @xor_of_reduce_xor(
 ; CHECK-SAME: <16 x i32> [[V0:%.*]], <16 x i32> [[V1:%.*]]) {
-; CHECK-NEXT:    [[V0_RED:%.*]] = tail call i32 @llvm.vector.reduce.xor.v16i32(<16 x i32> [[V0]])
-; CHECK-NEXT:    [[V1_RED:%.*]] = tail call i32 @llvm.vector.reduce.xor.v16i32(<16 x i32> [[V1]])
-; CHECK-NEXT:    [[RES:%.*]] = xor i32 [[V0_RED]], [[V1_RED]]
+; CHECK-NEXT:    [[TMP1:%.*]] = xor <16 x i32> [[V0]], [[V1]]
+; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.vector.reduce.xor.v16i32(<16 x i32> [[TMP1]])
 ; CHECK-NEXT:    ret i32 [[RES]]
 ;
   %v0_red = tail call i32 @llvm.vector.reduce.xor.v16i32(<16 x i32> %v0)
@@ -161,9 +156,8 @@ define i32 @multiple_use_of_reduction_1(<16 x i32> %v0, <16 x i32> %v1, ptr %p)
 define i32 @do_not_preserve_overflow_flags(<16 x i32> %v0, <16 x i32> %v1) {
 ; CHECK-LABEL: define i32 @do_not_preserve_overflow_flags(
 ; CHECK-SAME: <16 x i32> [[V0:%.*]], <16 x i32> [[V1:%.*]]) {
-; CHECK-NEXT:    [[V0_RED:%.*]] = tail call i32 @llvm.vector.reduce.add.v16i32(<16 x i32> [[V0]])
-; CHECK-NEXT:    [[V1_RED:%.*]] = tail call i32 @llvm.vector.reduce.add.v16i32(<16 x i32> [[V1]])
-; CHECK-NEXT:    [[RES:%.*]] = add nuw nsw i32 [[V0_RED]], [[V1_RED]]
+; CHECK-NEXT:    [[TMP1:%.*]] = add <16 x i32> [[V0]], [[V1]]
+; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.vector.reduce.add.v16i32(<16 x i32> [[TMP1]])
 ; CHECK-NEXT:    ret i32 [[RES]]
 ;
   %v0_red = tail call i32 @llvm.vector.reduce.add.v16i32(<16 x i32> %v0)
@@ -175,9 +169,8 @@ define i32 @do_not_preserve_overflow_flags(<16 x i32> %v0, <16 x i32> %v1) {
 define i32 @preserve_disjoint_flags(<16 x i32> %v0, <16 x i32> %v1) {
 ; CHECK-LABEL: define i32 @preserve_disjoint_flags(
 ; CHECK-SAME: <16 x i32> [[V0:%.*]], <16 x i32> [[V1:%.*]]) {
-; CHECK-NEXT:    [[V0_RED:%.*]] = tail call i32 @llvm.vector.reduce.or.v16i32(<16 x i32> [[V0]])
-; CHECK-NEXT:    [[V1_RED:%.*]] = tail call i32 @llvm.vector.reduce.or.v16i32(<16 x i32> [[V1]])
-; CHECK-NEXT:    [[RES:%.*]] = or disjoint i32 [[V0_RED]], [[V1_RED]]
+; CHECK-NEXT:    [[TMP1:%.*]] = or disjoint <16 x i32> [[V0]], [[V1]]
+; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.vector.reduce.or.v16i32(<16 x i32> [[TMP1]])
 ; CHECK-NEXT:    ret i32 [[RES]]
 ;
   %v0_red = tail call i32 @llvm.vector.reduce.or.v16i32(<16 x i32> %v0)
@@ -189,9 +182,8 @@ define i32 @preserve_disjoint_flags(<16 x i32> %v0, <16 x i32> %v1) {
 define i32 @add_of_reduce_add_vscale(<vscale x 16 x i32> %v0, <vscale x 16 x i32> %v1) {
 ; CHECK-LABEL: define i32 @add_of_reduce_add_vscale(
 ; CHECK-SAME: <vscale x 16 x i32> [[V0:%.*]], <vscale x 16 x i32> [[V1:%.*]]) {
-; CHECK-NEXT:    [[V0_RED:%.*]] = tail call i32 @llvm.vector.reduce.add.nxv16i32(<vscale x 16 x i32> [[V0]])
-; CHECK-NEXT:    [[V1_RED:%.*]] = tail call i32 @llvm.vector.reduce.add.nxv16i32(<vscale x 16 x i32> [[V1]])
-; CHECK-NEXT:    [[RES:%.*]] = add i32 [[V0_RED]], [[V1_RED]]
+; CHECK-NEXT:    [[TMP1:%.*]] = add <vscale x 16 x i32> [[V0]], [[V1]]
+; CHECK-NEXT:    [[RES:%.*]] = call i32 @llvm.vector.reduce.add.nxv16i32(<vscale x 16 x i32> [[TMP1]])
 ; CHECK-NEXT:    ret i32 [[RES]]
 ;
   %v0_red = tail call i32 @llvm.vector.reduce.add.nxv16i32(<vscale x 16 x i32> %v0)
