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LoopVectorize: We don't need an identity element for min/max reductions
We can just use the initial element that feeds the reduction. max(max(x, y), z) == max(max(x,y), max(x,z)) radar://13723044 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181141 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -498,8 +498,7 @@ public:
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/// This function returns the identity element (or neutral element) for
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/// the operation K.
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static Constant *getReductionIdentity(ReductionKind K, Type *Tp,
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MinMaxReductionKind MinMaxK);
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static Constant *getReductionIdentity(ReductionKind K, Type *Tp);
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private:
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/// Check if a single basic block loop is vectorizable.
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/// At this point we know that this is a loop with a constant trip count
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@ -1501,8 +1500,7 @@ InnerLoopVectorizer::createEmptyLoop(LoopVectorizationLegality *Legal) {
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/// This function returns the identity element (or neutral element) for
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/// the operation K.
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Constant*
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LoopVectorizationLegality::getReductionIdentity(ReductionKind K, Type *Tp,
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MinMaxReductionKind MinMaxK) {
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LoopVectorizationLegality::getReductionIdentity(ReductionKind K, Type *Tp) {
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switch (K) {
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case RK_IntegerXor:
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case RK_IntegerAdd:
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@ -1521,24 +1519,6 @@ LoopVectorizationLegality::getReductionIdentity(ReductionKind K, Type *Tp,
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case RK_FloatAdd:
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// Adding zero to a number does not change it.
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return ConstantFP::get(Tp, 0.0L);
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case RK_IntegerMinMax:
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switch(MinMaxK) {
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default: llvm_unreachable("Unknown min/max predicate");
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case MRK_UIntMin:
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return ConstantInt::getAllOnesValue(Tp);
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case MRK_UIntMax:
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return ConstantInt::get(Tp, 0);
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case MRK_SIntMin: {
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unsigned BitWidth = Tp->getPrimitiveSizeInBits();
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return ConstantInt::get(Tp->getContext(),
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APInt::getSignedMaxValue(BitWidth));
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}
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case LoopVectorizationLegality::MRK_SIntMax: {
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unsigned BitWidth = Tp->getPrimitiveSizeInBits();
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return ConstantInt::get(Tp->getContext(),
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APInt::getSignedMinValue(BitWidth));
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}
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}
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default:
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llvm_unreachable("Unknown reduction kind");
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}
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@ -1761,16 +1741,23 @@ InnerLoopVectorizer::vectorizeLoop(LoopVectorizationLegality *Legal) {
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// Find the reduction identity variable. Zero for addition, or, xor,
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// one for multiplication, -1 for And.
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Constant *Iden =
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LoopVectorizationLegality::getReductionIdentity(RdxDesc.Kind,
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VecTy->getScalarType(),
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RdxDesc.MinMaxKind);
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Constant *Identity = ConstantVector::getSplat(VF, Iden);
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Value *Identity;
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Value *VectorStart;
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if (RdxDesc.Kind == LoopVectorizationLegality::RK_IntegerMinMax)
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// MinMax reduction have the start value as their identify.
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VectorStart = Identity = Builder.CreateVectorSplat(VF, RdxDesc.StartValue,
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"minmax.ident");
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else {
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Constant *Iden =
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LoopVectorizationLegality::getReductionIdentity(RdxDesc.Kind,
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VecTy->getScalarType());
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Identity = ConstantVector::getSplat(VF, Iden);
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// This vector is the Identity vector where the first element is the
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// incoming scalar reduction.
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Value *VectorStart = Builder.CreateInsertElement(Identity,
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RdxDesc.StartValue, Zero);
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// This vector is the Identity vector where the first element is the
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// incoming scalar reduction.
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VectorStart = Builder.CreateInsertElement(Identity,
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RdxDesc.StartValue, Zero);
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}
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// Fix the vector-loop phi.
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// We created the induction variable so we know that the
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@ -6,8 +6,11 @@ target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f3
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; Signed tests.
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; Turn this into a max reduction.
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; Turn this into a max reduction. Make sure we use a splat to initialize the
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; vector for the reduction.
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; CHECK: @max_red
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; CHECK: %[[VAR:.*]] = insertelement <2 x i32> undef, i32 %max, i32 0
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; CHECK: {{.*}} = shufflevector <2 x i32> %[[VAR]], <2 x i32> undef, <2 x i32> zeroinitializer
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; CHECK: icmp sgt <2 x i32>
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; CHECK: select <2 x i1>
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; CHECK: middle.block
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