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InstCombine: Fix a potential bug in 0 - (X sdiv C) -> (X sdiv -C)
While *most* (X sdiv 1) operations will get caught by InstSimplify, it is still possible for a sdiv to appear in the worklist which hasn't been simplified yet. This means that it is possible for 0 - (X sdiv 1) to get transformed into (X sdiv -1); dividing by -1 can make the transform produce undef values instead of the proper result. Sorry for the lack of testcase, it's a bit problematic because it relies on the exact order of operations in the worklist. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215818 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -53,6 +53,9 @@ public:
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/// getNullValue.
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bool isNullValue() const;
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/// \brief Returns true if the value is one.
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bool isOneValue() const;
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/// isAllOnesValue - Return true if this is the value that would be returned by
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/// getAllOnesValue.
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bool isAllOnesValue() const;
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@ -107,6 +107,28 @@ bool Constant::isAllOnesValue() const {
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return false;
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}
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bool Constant::isOneValue() const {
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// Check for 1 integers
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if (const ConstantInt *CI = dyn_cast<ConstantInt>(this))
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return CI->isOne();
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// Check for FP which are bitcasted from 1 integers
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if (const ConstantFP *CFP = dyn_cast<ConstantFP>(this))
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return CFP->getValueAPF().bitcastToAPInt() == 1;
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// Check for constant vectors which are splats of 1 values.
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if (const ConstantVector *CV = dyn_cast<ConstantVector>(this))
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if (Constant *Splat = CV->getSplatValue())
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return Splat->isOneValue();
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// Check for constant vectors which are splats of 1 values.
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if (const ConstantDataVector *CV = dyn_cast<ConstantDataVector>(this))
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if (Constant *Splat = CV->getSplatValue())
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return Splat->isOneValue();
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return false;
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}
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bool Constant::isMinSignedValue() const {
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// Check for INT_MIN integers
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if (const ConstantInt *CI = dyn_cast<ConstantInt>(this))
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@ -1583,7 +1583,7 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
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// 0 - (X sdiv C) -> (X sdiv -C) provided the negation doesn't overflow.
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if (match(Op1, m_SDiv(m_Value(X), m_Constant(C))) && match(Op0, m_Zero()) &&
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!C->isMinSignedValue())
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!C->isMinSignedValue() && !C->isOneValue())
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return BinaryOperator::CreateSDiv(X, ConstantExpr::getNeg(C));
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// 0 - (X << Y) -> (-X << Y) when X is freely negatable.
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