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[InstCombine] Check for undef first before freeze #96769

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Jul 13, 2024
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[InstCombine] Check for undef first before freeze #96769

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28 changes: 21 additions & 7 deletions llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -166,7 +166,9 @@ static Value *foldMulShl1(BinaryOperator &Mul, bool CommuteOperands,
if (match(Y, m_OneUse(m_Add(m_BinOp(Shift), m_One()))) &&
match(Shift, m_OneUse(m_Shl(m_One(), m_Value(Z))))) {
bool PropagateNSW = HasNSW && Shift->hasNoSignedWrap();
Value *FrX = Builder.CreateFreeze(X, X->getName() + ".fr");
Value *FrX = X;
if (!isGuaranteedNotToBeUndef(X))
FrX = Builder.CreateFreeze(X, X->getName() + ".fr");
Value *Shl = Builder.CreateShl(FrX, Z, "mulshl", HasNUW, PropagateNSW);
return Builder.CreateAdd(Shl, FrX, Mul.getName(), HasNUW, PropagateNSW);
}
Expand All @@ -177,7 +179,9 @@ static Value *foldMulShl1(BinaryOperator &Mul, bool CommuteOperands,
// This increases uses of X, so it may require a freeze, but that is still
// expected to be an improvement because it removes the multiply.
if (match(Y, m_OneUse(m_Not(m_OneUse(m_Shl(m_AllOnes(), m_Value(Z))))))) {
Value *FrX = Builder.CreateFreeze(X, X->getName() + ".fr");
Value *FrX = X;
if (!isGuaranteedNotToBeUndef(X))
FrX = Builder.CreateFreeze(X, X->getName() + ".fr");
Value *Shl = Builder.CreateShl(FrX, Z, "mulshl");
return Builder.CreateSub(Shl, FrX, Mul.getName());
}
Expand Down Expand Up @@ -392,7 +396,9 @@ Instruction *InstCombinerImpl::visitMul(BinaryOperator &I) {
auto RemOpc = Div->getOpcode() == Instruction::UDiv ? Instruction::URem
: Instruction::SRem;
// X must be frozen because we are increasing its number of uses.
Value *XFreeze = Builder.CreateFreeze(X, X->getName() + ".fr");
Value *XFreeze = X;
if (!isGuaranteedNotToBeUndef(X))
XFreeze = Builder.CreateFreeze(X, X->getName() + ".fr");
Value *Rem = Builder.CreateBinOp(RemOpc, XFreeze, DivOp1);
if (DivOp1 == Y)
return BinaryOperator::CreateSub(XFreeze, Rem);
Expand Down Expand Up @@ -1252,7 +1258,9 @@ Instruction *InstCombinerImpl::commonIDivTransforms(BinaryOperator &I) {
// 1 / 0 --> undef ; 1 / 1 --> 1 ; 1 / -1 --> -1 ; 1 / anything else --> 0
// (Op1 + 1) u< 3 ? Op1 : 0
// Op1 must be frozen because we are increasing its number of uses.
Value *F1 = Builder.CreateFreeze(Op1, Op1->getName() + ".fr");
Value *F1 = Op1;
if (!isGuaranteedNotToBeUndef(Op1))
F1 = Builder.CreateFreeze(Op1, Op1->getName() + ".fr");
Value *Inc = Builder.CreateAdd(F1, Op0);
Value *Cmp = Builder.CreateICmpULT(Inc, ConstantInt::get(Ty, 3));
return SelectInst::Create(Cmp, F1, ConstantInt::get(Ty, 0));
Expand Down Expand Up @@ -2165,7 +2173,9 @@ Instruction *InstCombinerImpl::visitURem(BinaryOperator &I) {
// Op0 urem C -> Op0 < C ? Op0 : Op0 - C, where C >= signbit.
// Op0 must be frozen because we are increasing its number of uses.
if (match(Op1, m_Negative())) {
Value *F0 = Builder.CreateFreeze(Op0, Op0->getName() + ".fr");
Value *F0 = Op0;
if (!isGuaranteedNotToBeUndef(Op0))
F0 = Builder.CreateFreeze(Op0, Op0->getName() + ".fr");
Value *Cmp = Builder.CreateICmpULT(F0, Op1);
Value *Sub = Builder.CreateSub(F0, Op1);
return SelectInst::Create(Cmp, F0, Sub);
Expand All @@ -2177,7 +2187,9 @@ Instruction *InstCombinerImpl::visitURem(BinaryOperator &I) {
// urem Op0, (sext i1 X) --> (Op0 == -1) ? 0 : Op0
Value *X;
if (match(Op1, m_SExt(m_Value(X))) && X->getType()->isIntOrIntVectorTy(1)) {
Value *FrozenOp0 = Builder.CreateFreeze(Op0, Op0->getName() + ".frozen");
Value *FrozenOp0 = Op0;
if (!isGuaranteedNotToBeUndef(Op0))
FrozenOp0 = Builder.CreateFreeze(Op0, Op0->getName() + ".frozen");
Value *Cmp =
Builder.CreateICmpEQ(FrozenOp0, ConstantInt::getAllOnesValue(Ty));
return SelectInst::Create(Cmp, ConstantInt::getNullValue(Ty), FrozenOp0);
Expand All @@ -2188,7 +2200,9 @@ Instruction *InstCombinerImpl::visitURem(BinaryOperator &I) {
Value *Val =
simplifyICmpInst(ICmpInst::ICMP_ULT, X, Op1, SQ.getWithInstruction(&I));
if (Val && match(Val, m_One())) {
Value *FrozenOp0 = Builder.CreateFreeze(Op0, Op0->getName() + ".frozen");
Value *FrozenOp0 = Op0;
if (!isGuaranteedNotToBeUndef(Op0))
FrozenOp0 = Builder.CreateFreeze(Op0, Op0->getName() + ".frozen");
Value *Cmp = Builder.CreateICmpEQ(FrozenOp0, Op1);
return SelectInst::Create(Cmp, ConstantInt::getNullValue(Ty), FrozenOp0);
}
Expand Down
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