diff options
| -rw-r--r-- | lib/Analysis/ValueTracking.cpp | 206 |
1 files changed, 123 insertions, 83 deletions
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp index ed4f243fb6..904c27e89d 100644 --- a/lib/Analysis/ValueTracking.cpp +++ b/lib/Analysis/ValueTracking.cpp @@ -41,6 +41,95 @@ static unsigned getBitWidth(Type *Ty, const TargetData *TD) { return TD ? TD->getPointerSizeInBits() : 0; } +static void ComputeMaskedBitsAddSub(bool Add, Value *Op0, Value *Op1, bool NSW, + const APInt &Mask, + APInt &KnownZero, APInt &KnownOne, + APInt &KnownZero2, APInt &KnownOne2, + const TargetData *TD, unsigned Depth) { + if (!Add) { + if (ConstantInt *CLHS = dyn_cast<ConstantInt>(Op0)) { + // We know that the top bits of C-X are clear if X contains less bits + // than C (i.e. no wrap-around can happen). For example, 20-X is + // positive if we can prove that X is >= 0 and < 16. + if (!CLHS->getValue().isNegative()) { + unsigned BitWidth = Mask.getBitWidth(); + unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros(); + // NLZ can't be BitWidth with no sign bit + APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1); + llvm::ComputeMaskedBits(Op1, MaskV, KnownZero2, KnownOne2, TD, Depth+1); + + // If all of the MaskV bits are known to be zero, then we know the + // output top bits are zero, because we now know that the output is + // from [0-C]. + if ((KnownZero2 & MaskV) == MaskV) { + unsigned NLZ2 = CLHS->getValue().countLeadingZeros(); + // Top bits known zero. + KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2) & Mask; + } + } + } + } + + unsigned BitWidth = Mask.getBitWidth(); + + // If one of the operands has trailing zeros, then the bits that the + // other operand has in those bit positions will be preserved in the + // result. For an add, this works with either operand. For a subtract, + // this only works if the known zeros are in the right operand. + APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0); + APInt Mask2 = APInt::getLowBitsSet(BitWidth, + BitWidth - Mask.countLeadingZeros()); + llvm::ComputeMaskedBits(Op0, Mask2, LHSKnownZero, LHSKnownOne, TD, Depth+1); + assert((LHSKnownZero & LHSKnownOne) == 0 && + "Bits known to be one AND zero?"); + unsigned LHSKnownZeroOut = LHSKnownZero.countTrailingOnes(); + + llvm::ComputeMaskedBits(Op1, Mask2, KnownZero2, KnownOne2, TD, Depth+1); + assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); + unsigned RHSKnownZeroOut = KnownZero2.countTrailingOnes(); + + // Determine which operand has more trailing zeros, and use that + // many bits from the other operand. + if (LHSKnownZeroOut > RHSKnownZeroOut) { + if (Add) { + APInt Mask = APInt::getLowBitsSet(BitWidth, LHSKnownZeroOut); + KnownZero |= KnownZero2 & Mask; + KnownOne |= KnownOne2 & Mask; + } else { + // If the known zeros are in the left operand for a subtract, + // fall back to the minimum known zeros in both operands. + KnownZero |= APInt::getLowBitsSet(BitWidth, + std::min(LHSKnownZeroOut, + RHSKnownZeroOut)); + } + } else if (RHSKnownZeroOut >= LHSKnownZeroOut) { + APInt Mask = APInt::getLowBitsSet(BitWidth, RHSKnownZeroOut); + KnownZero |= LHSKnownZero & Mask; + KnownOne |= LHSKnownOne & Mask; + } + + // Are we still trying to solve for the sign bit? + if (Mask.isNegative() && !KnownZero.isNegative() && !KnownOne.isNegative()) { + if (NSW) { + if (Add) { + // Adding two positive numbers can't wrap into negative + if (LHSKnownZero.isNegative() && KnownZero2.isNegative()) + KnownZero |= APInt::getSignBit(BitWidth); + // and adding two negative numbers can't wrap into positive. + else if (LHSKnownOne.isNegative() && KnownOne2.isNegative()) + KnownOne |= APInt::getSignBit(BitWidth); + } else { + // Subtracting a negative number from a positive one can't wrap + if (LHSKnownZero.isNegative() && KnownOne2.isNegative()) + KnownZero |= APInt::getSignBit(BitWidth); + // neither can subtracting a positive number from a negative one. + else if (LHSKnownOne.isNegative() && KnownZero2.isNegative()) + KnownOne |= APInt::getSignBit(BitWidth); + } + } + } +} + /// ComputeMaskedBits - Determine which of the bits specified in Mask are /// known to be either zero or one and return them in the KnownZero/KnownOne /// bit sets. This code only analyzes bits in Mask, in order to short-circuit @@ -424,91 +513,18 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask, } break; case Instruction::Sub: { - if (ConstantInt *CLHS = dyn_cast<ConstantInt>(I->getOperand(0))) { - // We know that the top bits of C-X are clear if X contains less bits - // than C (i.e. no wrap-around can happen). For example, 20-X is - // positive if we can prove that X is >= 0 and < 16. - if (!CLHS->getValue().isNegative()) { - unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros(); - // NLZ can't be BitWidth with no sign bit - APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1); - ComputeMaskedBits(I->getOperand(1), MaskV, KnownZero2, KnownOne2, - TD, Depth+1); - - // If all of the MaskV bits are known to be zero, then we know the - // output top bits are zero, because we now know that the output is - // from [0-C]. - if ((KnownZero2 & MaskV) == MaskV) { - unsigned NLZ2 = CLHS->getValue().countLeadingZeros(); - // Top bits known zero. - KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2) & Mask; - } - } - } + bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap(); + ComputeMaskedBitsAddSub(false, I->getOperand(0), I->getOperand(1), NSW, + Mask, KnownZero, KnownOne, KnownZero2, KnownOne2, + TD, Depth); + break; } - // fall through case Instruction::Add: { - // If one of the operands has trailing zeros, then the bits that the - // other operand has in those bit positions will be preserved in the - // result. For an add, this works with either operand. For a subtract, - // this only works if the known zeros are in the right operand. - APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0); - APInt Mask2 = APInt::getLowBitsSet(BitWidth, - BitWidth - Mask.countLeadingZeros()); - ComputeMaskedBits(I->getOperand(0), Mask2, LHSKnownZero, LHSKnownOne, TD, - Depth+1); - assert((LHSKnownZero & LHSKnownOne) == 0 && - "Bits known to be one AND zero?"); - unsigned LHSKnownZeroOut = LHSKnownZero.countTrailingOnes(); - - ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero2, KnownOne2, TD, - Depth+1); - assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); - unsigned RHSKnownZeroOut = KnownZero2.countTrailingOnes(); - - // Determine which operand has more trailing zeros, and use that - // many bits from the other operand. - if (LHSKnownZeroOut > RHSKnownZeroOut) { - if (I->getOpcode() == Instruction::Add) { - APInt Mask = APInt::getLowBitsSet(BitWidth, LHSKnownZeroOut); - KnownZero |= KnownZero2 & Mask; - KnownOne |= KnownOne2 & Mask; - } else { - // If the known zeros are in the left operand for a subtract, - // fall back to the minimum known zeros in both operands. - KnownZero |= APInt::getLowBitsSet(BitWidth, - std::min(LHSKnownZeroOut, - RHSKnownZeroOut)); - } - } else if (RHSKnownZeroOut >= LHSKnownZeroOut) { - APInt Mask = APInt::getLowBitsSet(BitWidth, RHSKnownZeroOut); - KnownZero |= LHSKnownZero & Mask; - KnownOne |= LHSKnownOne & Mask; - } - - // Are we still trying to solve for the sign bit? - if (Mask.isNegative() && !KnownZero.isNegative() && !KnownOne.isNegative()){ - OverflowingBinaryOperator *OBO = cast<OverflowingBinaryOperator>(I); - if (OBO->hasNoSignedWrap()) { - if (I->getOpcode() == Instruction::Add) { - // Adding two positive numbers can't wrap into negative - if (LHSKnownZero.isNegative() && KnownZero2.isNegative()) - KnownZero |= APInt::getSignBit(BitWidth); - // and adding two negative numbers can't wrap into positive. - else if (LHSKnownOne.isNegative() && KnownOne2.isNegative()) - KnownOne |= APInt::getSignBit(BitWidth); - } else { - // Subtracting a negative number from a positive one can't wrap - if (LHSKnownZero.isNegative() && KnownOne2.isNegative()) - KnownZero |= APInt::getSignBit(BitWidth); - // neither can subtracting a positive number from a negative one. - else if (LHSKnownOne.isNegative() && KnownZero2.isNegative()) - KnownOne |= APInt::getSignBit(BitWidth); - } - } - } - - return; + bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap(); + ComputeMaskedBitsAddSub(true, I->getOperand(0), I->getOperand(1), NSW, + Mask, KnownZero, KnownOne, KnownZero2, KnownOne2, + TD, Depth); + break; } case Instruction::SRem: if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) { @@ -740,6 +756,30 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask, } } break; + case Instruction::ExtractValue: + if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I->getOperand(0))) { + ExtractValueInst *EVI = cast<ExtractValueInst>(I); + if (EVI->getNumIndices() != 1) break; + if (EVI->getIndices()[0] == 0) { + switch (II->getIntrinsicID()) { + default: break; + case Intrinsic::uadd_with_overflow: + case Intrinsic::sadd_with_overflow: + ComputeMaskedBitsAddSub(true, II->getArgOperand(0), + II->getArgOperand(1), false, Mask, + KnownZero, KnownOne, KnownZero2, KnownOne2, + TD, Depth); + break; + case Intrinsic::usub_with_overflow: + case Intrinsic::ssub_with_overflow: + ComputeMaskedBitsAddSub(false, II->getArgOperand(0), + II->getArgOperand(1), false, Mask, + KnownZero, KnownOne, KnownZero2, KnownOne2, + TD, Depth); + break; + } + } + } } } |