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Teach ComputeMaskedBits about sub nsw.
llvm-svn: 127548
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@ -431,16 +431,24 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
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}
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// Are we still trying to solve for the sign bit?
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if (I->getOpcode() == Instruction::Add &&
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Mask.isNegative() && !KnownZero.isNegative() && !KnownOne.isNegative()){
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if (Mask.isNegative() && !KnownZero.isNegative() && !KnownOne.isNegative()){
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OverflowingBinaryOperator *OBO = cast<OverflowingBinaryOperator>(I);
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if (OBO->hasNoSignedWrap()) {
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// Adding two positive numbers can't wrap into negative ...
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if (LHSKnownZero.isNegative() && KnownZero2.isNegative())
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KnownZero |= APInt::getSignBit(BitWidth);
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// and adding two negative numbers can't wrap into positive.
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else if (LHSKnownOne.isNegative() && KnownOne2.isNegative())
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KnownOne |= APInt::getSignBit(BitWidth);
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if (I->getOpcode() == Instruction::Add) {
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// Adding two positive numbers can't wrap into negative
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if (LHSKnownZero.isNegative() && KnownZero2.isNegative())
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KnownZero |= APInt::getSignBit(BitWidth);
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// and adding two negative numbers can't wrap into positive.
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else if (LHSKnownOne.isNegative() && KnownOne2.isNegative())
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KnownOne |= APInt::getSignBit(BitWidth);
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} else {
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// Subtracting a negative number from a positive one can't wrap
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if (LHSKnownZero.isNegative() && KnownOne2.isNegative())
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KnownZero |= APInt::getSignBit(BitWidth);
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// neither can subtracting a positive number from a negative one.
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else if (LHSKnownOne.isNegative() && KnownZero2.isNegative())
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KnownOne |= APInt::getSignBit(BitWidth);
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}
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}
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}
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@ -271,6 +271,29 @@ define i1 @srem2(i16 %X, i32 %Y) {
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%D = icmp slt i32 %C, 0
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ret i1 %D
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}
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; CHECK: @srem3
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; CHECK-NEXT: ret i1 false
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define i1 @srem3(i16 %X, i32 %Y) {
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%A = zext i16 %X to i32
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%B = or i32 2147483648, %A
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%C = sub nsw i32 1, %B
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%D = srem i32 %C, %Y
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%E = icmp slt i32 %D, 0
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ret i1 %E
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}
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; CHECK: @srem4
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; CHECK-NEXT: ret i1 false
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define i1 @srem4(i16 %X, i32 %Y) {
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%A = zext i16 %X to i32
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%B = or i32 2147483648, %A
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%C = sub nsw i32 %A, %B
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%D = srem i32 %C, %Y
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%E = icmp slt i32 %D, 0
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ret i1 %E
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}
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define i1 @udiv1(i32 %X) {
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; CHECK: @udiv1
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%A = udiv i32 %X, 1000000
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