| //===- ValueTracking.cpp - Walk computations to compute properties --------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file contains routines that help analyze properties that chains of |
| // computations have. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Analysis/ValueTracking.h" |
| #include "llvm/Analysis/InstructionSimplify.h" |
| #include "llvm/Constants.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/GlobalVariable.h" |
| #include "llvm/GlobalAlias.h" |
| #include "llvm/IntrinsicInst.h" |
| #include "llvm/LLVMContext.h" |
| #include "llvm/Operator.h" |
| #include "llvm/Target/TargetData.h" |
| #include "llvm/Support/GetElementPtrTypeIterator.h" |
| #include "llvm/Support/MathExtras.h" |
| #include "llvm/Support/PatternMatch.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include <cstring> |
| using namespace llvm; |
| using namespace llvm::PatternMatch; |
| |
| const unsigned MaxDepth = 6; |
| |
| /// getBitWidth - Returns the bitwidth of the given scalar or pointer type (if |
| /// unknown returns 0). For vector types, returns the element type's bitwidth. |
| static unsigned getBitWidth(Type *Ty, const TargetData *TD) { |
| if (unsigned BitWidth = Ty->getScalarSizeInBits()) |
| return BitWidth; |
| assert(isa<PointerType>(Ty) && "Expected a pointer type!"); |
| return TD ? TD->getPointerSizeInBits() : 0; |
| } |
| |
| /// 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 |
| /// processing. |
| /// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that |
| /// we cannot optimize based on the assumption that it is zero without changing |
| /// it to be an explicit zero. If we don't change it to zero, other code could |
| /// optimized based on the contradictory assumption that it is non-zero. |
| /// Because instcombine aggressively folds operations with undef args anyway, |
| /// this won't lose us code quality. |
| /// |
| /// This function is defined on values with integer type, values with pointer |
| /// type (but only if TD is non-null), and vectors of integers. In the case |
| /// where V is a vector, the mask, known zero, and known one values are the |
| /// same width as the vector element, and the bit is set only if it is true |
| /// for all of the elements in the vector. |
| void llvm::ComputeMaskedBits(Value *V, const APInt &Mask, |
| APInt &KnownZero, APInt &KnownOne, |
| const TargetData *TD, unsigned Depth) { |
| assert(V && "No Value?"); |
| assert(Depth <= MaxDepth && "Limit Search Depth"); |
| unsigned BitWidth = Mask.getBitWidth(); |
| assert((V->getType()->isIntOrIntVectorTy() || V->getType()->isPointerTy()) |
| && "Not integer or pointer type!"); |
| assert((!TD || |
| TD->getTypeSizeInBits(V->getType()->getScalarType()) == BitWidth) && |
| (!V->getType()->isIntOrIntVectorTy() || |
| V->getType()->getScalarSizeInBits() == BitWidth) && |
| KnownZero.getBitWidth() == BitWidth && |
| KnownOne.getBitWidth() == BitWidth && |
| "V, Mask, KnownOne and KnownZero should have same BitWidth"); |
| |
| if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) { |
| // We know all of the bits for a constant! |
| KnownOne = CI->getValue() & Mask; |
| KnownZero = ~KnownOne & Mask; |
| return; |
| } |
| // Null and aggregate-zero are all-zeros. |
| if (isa<ConstantPointerNull>(V) || |
| isa<ConstantAggregateZero>(V)) { |
| KnownOne.clearAllBits(); |
| KnownZero = Mask; |
| return; |
| } |
| // Handle a constant vector by taking the intersection of the known bits of |
| // each element. |
| if (ConstantVector *CV = dyn_cast<ConstantVector>(V)) { |
| KnownZero.setAllBits(); KnownOne.setAllBits(); |
| for (unsigned i = 0, e = CV->getNumOperands(); i != e; ++i) { |
| APInt KnownZero2(BitWidth, 0), KnownOne2(BitWidth, 0); |
| ComputeMaskedBits(CV->getOperand(i), Mask, KnownZero2, KnownOne2, |
| TD, Depth); |
| KnownZero &= KnownZero2; |
| KnownOne &= KnownOne2; |
| } |
| return; |
| } |
| // The address of an aligned GlobalValue has trailing zeros. |
| if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) { |
| unsigned Align = GV->getAlignment(); |
| if (Align == 0 && TD && GV->getType()->getElementType()->isSized()) { |
| Type *ObjectType = GV->getType()->getElementType(); |
| // If the object is defined in the current Module, we'll be giving |
| // it the preferred alignment. Otherwise, we have to assume that it |
| // may only have the minimum ABI alignment. |
| if (!GV->isDeclaration() && !GV->mayBeOverridden()) |
| Align = TD->getPrefTypeAlignment(ObjectType); |
| else |
| Align = TD->getABITypeAlignment(ObjectType); |
| } |
| if (Align > 0) |
| KnownZero = Mask & APInt::getLowBitsSet(BitWidth, |
| CountTrailingZeros_32(Align)); |
| else |
| KnownZero.clearAllBits(); |
| KnownOne.clearAllBits(); |
| return; |
| } |
| // A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has |
| // the bits of its aliasee. |
| if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) { |
| if (GA->mayBeOverridden()) { |
| KnownZero.clearAllBits(); KnownOne.clearAllBits(); |
| } else { |
| ComputeMaskedBits(GA->getAliasee(), Mask, KnownZero, KnownOne, |
| TD, Depth+1); |
| } |
| return; |
| } |
| |
| if (Argument *A = dyn_cast<Argument>(V)) { |
| // Get alignment information off byval arguments if specified in the IR. |
| if (A->hasByValAttr()) |
| if (unsigned Align = A->getParamAlignment()) |
| KnownZero = Mask & APInt::getLowBitsSet(BitWidth, |
| CountTrailingZeros_32(Align)); |
| return; |
| } |
| |
| // Start out not knowing anything. |
| KnownZero.clearAllBits(); KnownOne.clearAllBits(); |
| |
| if (Depth == MaxDepth || Mask == 0) |
| return; // Limit search depth. |
| |
| Operator *I = dyn_cast<Operator>(V); |
| if (!I) return; |
| |
| APInt KnownZero2(KnownZero), KnownOne2(KnownOne); |
| switch (I->getOpcode()) { |
| default: break; |
| case Instruction::And: { |
| // If either the LHS or the RHS are Zero, the result is zero. |
| ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1); |
| APInt Mask2(Mask & ~KnownZero); |
| ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, |
| Depth+1); |
| assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); |
| assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); |
| |
| // Output known-1 bits are only known if set in both the LHS & RHS. |
| KnownOne &= KnownOne2; |
| // Output known-0 are known to be clear if zero in either the LHS | RHS. |
| KnownZero |= KnownZero2; |
| return; |
| } |
| case Instruction::Or: { |
| ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1); |
| APInt Mask2(Mask & ~KnownOne); |
| ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, |
| Depth+1); |
| assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); |
| assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); |
| |
| // Output known-0 bits are only known if clear in both the LHS & RHS. |
| KnownZero &= KnownZero2; |
| // Output known-1 are known to be set if set in either the LHS | RHS. |
| KnownOne |= KnownOne2; |
| return; |
| } |
| case Instruction::Xor: { |
| ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1); |
| ComputeMaskedBits(I->getOperand(0), Mask, KnownZero2, KnownOne2, TD, |
| Depth+1); |
| assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); |
| assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); |
| |
| // Output known-0 bits are known if clear or set in both the LHS & RHS. |
| APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2); |
| // Output known-1 are known to be set if set in only one of the LHS, RHS. |
| KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2); |
| KnownZero = KnownZeroOut; |
| return; |
| } |
| case Instruction::Mul: { |
| APInt Mask2 = APInt::getAllOnesValue(BitWidth); |
| ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero, KnownOne, TD,Depth+1); |
| ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, |
| Depth+1); |
| assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); |
| assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); |
| |
| // If low bits are zero in either operand, output low known-0 bits. |
| // Also compute a conserative estimate for high known-0 bits. |
| // More trickiness is possible, but this is sufficient for the |
| // interesting case of alignment computation. |
| KnownOne.clearAllBits(); |
| unsigned TrailZ = KnownZero.countTrailingOnes() + |
| KnownZero2.countTrailingOnes(); |
| unsigned LeadZ = std::max(KnownZero.countLeadingOnes() + |
| KnownZero2.countLeadingOnes(), |
| BitWidth) - BitWidth; |
| |
| TrailZ = std::min(TrailZ, BitWidth); |
| LeadZ = std::min(LeadZ, BitWidth); |
| KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) | |
| APInt::getHighBitsSet(BitWidth, LeadZ); |
| KnownZero &= Mask; |
| return; |
| } |
| case Instruction::UDiv: { |
| // For the purposes of computing leading zeros we can conservatively |
| // treat a udiv as a logical right shift by the power of 2 known to |
| // be less than the denominator. |
| APInt AllOnes = APInt::getAllOnesValue(BitWidth); |
| ComputeMaskedBits(I->getOperand(0), |
| AllOnes, KnownZero2, KnownOne2, TD, Depth+1); |
| unsigned LeadZ = KnownZero2.countLeadingOnes(); |
| |
| KnownOne2.clearAllBits(); |
| KnownZero2.clearAllBits(); |
| ComputeMaskedBits(I->getOperand(1), |
| AllOnes, KnownZero2, KnownOne2, TD, Depth+1); |
| unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros(); |
| if (RHSUnknownLeadingOnes != BitWidth) |
| LeadZ = std::min(BitWidth, |
| LeadZ + BitWidth - RHSUnknownLeadingOnes - 1); |
| |
| KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ) & Mask; |
| return; |
| } |
| case Instruction::Select: |
| ComputeMaskedBits(I->getOperand(2), Mask, KnownZero, KnownOne, TD, Depth+1); |
| ComputeMaskedBits(I->getOperand(1), Mask, KnownZero2, KnownOne2, TD, |
| Depth+1); |
| assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); |
| assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); |
| |
| // Only known if known in both the LHS and RHS. |
| KnownOne &= KnownOne2; |
| KnownZero &= KnownZero2; |
| return; |
| case Instruction::FPTrunc: |
| case Instruction::FPExt: |
| case Instruction::FPToUI: |
| case Instruction::FPToSI: |
| case Instruction::SIToFP: |
| case Instruction::UIToFP: |
| return; // Can't work with floating point. |
| case Instruction::PtrToInt: |
| case Instruction::IntToPtr: |
| // We can't handle these if we don't know the pointer size. |
| if (!TD) return; |
| // FALL THROUGH and handle them the same as zext/trunc. |
| case Instruction::ZExt: |
| case Instruction::Trunc: { |
| Type *SrcTy = I->getOperand(0)->getType(); |
| |
| unsigned SrcBitWidth; |
| // Note that we handle pointer operands here because of inttoptr/ptrtoint |
| // which fall through here. |
| if (SrcTy->isPointerTy()) |
| SrcBitWidth = TD->getTypeSizeInBits(SrcTy); |
| else |
| SrcBitWidth = SrcTy->getScalarSizeInBits(); |
| |
| APInt MaskIn = Mask.zextOrTrunc(SrcBitWidth); |
| KnownZero = KnownZero.zextOrTrunc(SrcBitWidth); |
| KnownOne = KnownOne.zextOrTrunc(SrcBitWidth); |
| ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD, |
| Depth+1); |
| KnownZero = KnownZero.zextOrTrunc(BitWidth); |
| KnownOne = KnownOne.zextOrTrunc(BitWidth); |
| // Any top bits are known to be zero. |
| if (BitWidth > SrcBitWidth) |
| KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth); |
| return; |
| } |
| case Instruction::BitCast: { |
| Type *SrcTy = I->getOperand(0)->getType(); |
| if ((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) && |
| // TODO: For now, not handling conversions like: |
| // (bitcast i64 %x to <2 x i32>) |
| !I->getType()->isVectorTy()) { |
| ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, TD, |
| Depth+1); |
| return; |
| } |
| break; |
| } |
| case Instruction::SExt: { |
| // Compute the bits in the result that are not present in the input. |
| unsigned SrcBitWidth = I->getOperand(0)->getType()->getScalarSizeInBits(); |
| |
| APInt MaskIn = Mask.trunc(SrcBitWidth); |
| KnownZero = KnownZero.trunc(SrcBitWidth); |
| KnownOne = KnownOne.trunc(SrcBitWidth); |
| ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD, |
| Depth+1); |
| assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); |
| KnownZero = KnownZero.zext(BitWidth); |
| KnownOne = KnownOne.zext(BitWidth); |
| |
| // If the sign bit of the input is known set or clear, then we know the |
| // top bits of the result. |
| if (KnownZero[SrcBitWidth-1]) // Input sign bit known zero |
| KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth); |
| else if (KnownOne[SrcBitWidth-1]) // Input sign bit known set |
| KnownOne |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth); |
| return; |
| } |
| case Instruction::Shl: |
| // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0 |
| if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) { |
| uint64_t ShiftAmt = SA->getLimitedValue(BitWidth); |
| APInt Mask2(Mask.lshr(ShiftAmt)); |
| ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD, |
| Depth+1); |
| assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); |
| KnownZero <<= ShiftAmt; |
| KnownOne <<= ShiftAmt; |
| KnownZero |= APInt::getLowBitsSet(BitWidth, ShiftAmt); // low bits known 0 |
| return; |
| } |
| break; |
| case Instruction::LShr: |
| // (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0 |
| if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) { |
| // Compute the new bits that are at the top now. |
| uint64_t ShiftAmt = SA->getLimitedValue(BitWidth); |
| |
| // Unsigned shift right. |
| APInt Mask2(Mask.shl(ShiftAmt)); |
| ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero,KnownOne, TD, |
| Depth+1); |
| assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); |
| KnownZero = APIntOps::lshr(KnownZero, ShiftAmt); |
| KnownOne = APIntOps::lshr(KnownOne, ShiftAmt); |
| // high bits known zero. |
| KnownZero |= APInt::getHighBitsSet(BitWidth, ShiftAmt); |
| return; |
| } |
| break; |
| case Instruction::AShr: |
| // (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0 |
| if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) { |
| // Compute the new bits that are at the top now. |
| uint64_t ShiftAmt = SA->getLimitedValue(BitWidth-1); |
| |
| // Signed shift right. |
| APInt Mask2(Mask.shl(ShiftAmt)); |
| ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD, |
| Depth+1); |
| assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); |
| KnownZero = APIntOps::lshr(KnownZero, ShiftAmt); |
| KnownOne = APIntOps::lshr(KnownOne, ShiftAmt); |
| |
| APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt)); |
| if (KnownZero[BitWidth-ShiftAmt-1]) // New bits are known zero. |
| KnownZero |= HighBits; |
| else if (KnownOne[BitWidth-ShiftAmt-1]) // New bits are known one. |
| KnownOne |= HighBits; |
| return; |
| } |
| 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; |
| } |
| } |
| } |
| } |
| // 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; |
| } |
| case Instruction::SRem: |
| if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) { |
| APInt RA = Rem->getValue().abs(); |
| if (RA.isPowerOf2()) { |
| APInt LowBits = RA - 1; |
| APInt Mask2 = LowBits | APInt::getSignBit(BitWidth); |
| ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, |
| Depth+1); |
| |
| // The low bits of the first operand are unchanged by the srem. |
| KnownZero = KnownZero2 & LowBits; |
| KnownOne = KnownOne2 & LowBits; |
| |
| // If the first operand is non-negative or has all low bits zero, then |
| // the upper bits are all zero. |
| if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits)) |
| KnownZero |= ~LowBits; |
| |
| // If the first operand is negative and not all low bits are zero, then |
| // the upper bits are all one. |
| if (KnownOne2[BitWidth-1] && ((KnownOne2 & LowBits) != 0)) |
| KnownOne |= ~LowBits; |
| |
| KnownZero &= Mask; |
| KnownOne &= Mask; |
| |
| assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); |
| } |
| } |
| |
| // The sign bit is the LHS's sign bit, except when the result of the |
| // remainder is zero. |
| if (Mask.isNegative() && KnownZero.isNonNegative()) { |
| APInt Mask2 = APInt::getSignBit(BitWidth); |
| APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0); |
| ComputeMaskedBits(I->getOperand(0), Mask2, LHSKnownZero, LHSKnownOne, TD, |
| Depth+1); |
| // If it's known zero, our sign bit is also zero. |
| if (LHSKnownZero.isNegative()) |
| KnownZero |= LHSKnownZero; |
| } |
| |
| break; |
| case Instruction::URem: { |
| if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) { |
| APInt RA = Rem->getValue(); |
| if (RA.isPowerOf2()) { |
| APInt LowBits = (RA - 1); |
| APInt Mask2 = LowBits & Mask; |
| KnownZero |= ~LowBits & Mask; |
| ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD, |
| Depth+1); |
| assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); |
| break; |
| } |
| } |
| |
| // Since the result is less than or equal to either operand, any leading |
| // zero bits in either operand must also exist in the result. |
| APInt AllOnes = APInt::getAllOnesValue(BitWidth); |
| ComputeMaskedBits(I->getOperand(0), AllOnes, KnownZero, KnownOne, |
| TD, Depth+1); |
| ComputeMaskedBits(I->getOperand(1), AllOnes, KnownZero2, KnownOne2, |
| TD, Depth+1); |
| |
| unsigned Leaders = std::max(KnownZero.countLeadingOnes(), |
| KnownZero2.countLeadingOnes()); |
| KnownOne.clearAllBits(); |
| KnownZero = APInt::getHighBitsSet(BitWidth, Leaders) & Mask; |
| break; |
| } |
| |
| case Instruction::Alloca: { |
| AllocaInst *AI = cast<AllocaInst>(V); |
| unsigned Align = AI->getAlignment(); |
| if (Align == 0 && TD) |
| Align = TD->getABITypeAlignment(AI->getType()->getElementType()); |
| |
| if (Align > 0) |
| KnownZero = Mask & APInt::getLowBitsSet(BitWidth, |
| CountTrailingZeros_32(Align)); |
| break; |
| } |
| case Instruction::GetElementPtr: { |
| // Analyze all of the subscripts of this getelementptr instruction |
| // to determine if we can prove known low zero bits. |
| APInt LocalMask = APInt::getAllOnesValue(BitWidth); |
| APInt LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0); |
| ComputeMaskedBits(I->getOperand(0), LocalMask, |
| LocalKnownZero, LocalKnownOne, TD, Depth+1); |
| unsigned TrailZ = LocalKnownZero.countTrailingOnes(); |
| |
| gep_type_iterator GTI = gep_type_begin(I); |
| for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) { |
| Value *Index = I->getOperand(i); |
| if (StructType *STy = dyn_cast<StructType>(*GTI)) { |
| // Handle struct member offset arithmetic. |
| if (!TD) return; |
| const StructLayout *SL = TD->getStructLayout(STy); |
| unsigned Idx = cast<ConstantInt>(Index)->getZExtValue(); |
| uint64_t Offset = SL->getElementOffset(Idx); |
| TrailZ = std::min(TrailZ, |
| CountTrailingZeros_64(Offset)); |
| } else { |
| // Handle array index arithmetic. |
| Type *IndexedTy = GTI.getIndexedType(); |
| if (!IndexedTy->isSized()) return; |
| unsigned GEPOpiBits = Index->getType()->getScalarSizeInBits(); |
| uint64_t TypeSize = TD ? TD->getTypeAllocSize(IndexedTy) : 1; |
| LocalMask = APInt::getAllOnesValue(GEPOpiBits); |
| LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0); |
| ComputeMaskedBits(Index, LocalMask, |
| LocalKnownZero, LocalKnownOne, TD, Depth+1); |
| TrailZ = std::min(TrailZ, |
| unsigned(CountTrailingZeros_64(TypeSize) + |
| LocalKnownZero.countTrailingOnes())); |
| } |
| } |
| |
| KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) & Mask; |
| break; |
| } |
| case Instruction::PHI: { |
| PHINode *P = cast<PHINode>(I); |
| // Handle the case of a simple two-predecessor recurrence PHI. |
| // There's a lot more that could theoretically be done here, but |
| // this is sufficient to catch some interesting cases. |
| if (P->getNumIncomingValues() == 2) { |
| for (unsigned i = 0; i != 2; ++i) { |
| Value *L = P->getIncomingValue(i); |
| Value *R = P->getIncomingValue(!i); |
| Operator *LU = dyn_cast<Operator>(L); |
| if (!LU) |
| continue; |
| unsigned Opcode = LU->getOpcode(); |
| // Check for operations that have the property that if |
| // both their operands have low zero bits, the result |
| // will have low zero bits. |
| if (Opcode == Instruction::Add || |
| Opcode == Instruction::Sub || |
| Opcode == Instruction::And || |
| Opcode == Instruction::Or || |
| Opcode == Instruction::Mul) { |
| Value *LL = LU->getOperand(0); |
| Value *LR = LU->getOperand(1); |
| // Find a recurrence. |
| if (LL == I) |
| L = LR; |
| else if (LR == I) |
| L = LL; |
| else |
| break; |
| // Ok, we have a PHI of the form L op= R. Check for low |
| // zero bits. |
| APInt Mask2 = APInt::getAllOnesValue(BitWidth); |
| ComputeMaskedBits(R, Mask2, KnownZero2, KnownOne2, TD, Depth+1); |
| Mask2 = APInt::getLowBitsSet(BitWidth, |
| KnownZero2.countTrailingOnes()); |
| |
| // We need to take the minimum number of known bits |
| APInt KnownZero3(KnownZero), KnownOne3(KnownOne); |
| ComputeMaskedBits(L, Mask2, KnownZero3, KnownOne3, TD, Depth+1); |
| |
| KnownZero = Mask & |
| APInt::getLowBitsSet(BitWidth, |
| std::min(KnownZero2.countTrailingOnes(), |
| KnownZero3.countTrailingOnes())); |
| break; |
| } |
| } |
| } |
| |
| // Unreachable blocks may have zero-operand PHI nodes. |
| if (P->getNumIncomingValues() == 0) |
| return; |
| |
| // Otherwise take the unions of the known bit sets of the operands, |
| // taking conservative care to avoid excessive recursion. |
| if (Depth < MaxDepth - 1 && !KnownZero && !KnownOne) { |
| // Skip if every incoming value references to ourself. |
| if (P->hasConstantValue() == P) |
| break; |
| |
| KnownZero = APInt::getAllOnesValue(BitWidth); |
| KnownOne = APInt::getAllOnesValue(BitWidth); |
| for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) { |
| // Skip direct self references. |
| if (P->getIncomingValue(i) == P) continue; |
| |
| KnownZero2 = APInt(BitWidth, 0); |
| KnownOne2 = APInt(BitWidth, 0); |
| // Recurse, but cap the recursion to one level, because we don't |
| // want to waste time spinning around in loops. |
| ComputeMaskedBits(P->getIncomingValue(i), KnownZero | KnownOne, |
| KnownZero2, KnownOne2, TD, MaxDepth-1); |
| KnownZero &= KnownZero2; |
| KnownOne &= KnownOne2; |
| // If all bits have been ruled out, there's no need to check |
| // more operands. |
| if (!KnownZero && !KnownOne) |
| break; |
| } |
| } |
| break; |
| } |
| case Instruction::Call: |
| if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { |
| switch (II->getIntrinsicID()) { |
| default: break; |
| case Intrinsic::ctpop: |
| case Intrinsic::ctlz: |
| case Intrinsic::cttz: { |
| unsigned LowBits = Log2_32(BitWidth)+1; |
| KnownZero = APInt::getHighBitsSet(BitWidth, BitWidth - LowBits); |
| break; |
| } |
| case Intrinsic::x86_sse42_crc32_64_8: |
| case Intrinsic::x86_sse42_crc32_64_64: |
| KnownZero = APInt::getHighBitsSet(64, 32); |
| break; |
| } |
| } |
| break; |
| } |
| } |
| |
| /// ComputeSignBit - Determine whether the sign bit is known to be zero or |
| /// one. Convenience wrapper around ComputeMaskedBits. |
| void llvm::ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne, |
| const TargetData *TD, unsigned Depth) { |
| unsigned BitWidth = getBitWidth(V->getType(), TD); |
| if (!BitWidth) { |
| KnownZero = false; |
| KnownOne = false; |
| return; |
| } |
| APInt ZeroBits(BitWidth, 0); |
| APInt OneBits(BitWidth, 0); |
| ComputeMaskedBits(V, APInt::getSignBit(BitWidth), ZeroBits, OneBits, TD, |
| Depth); |
| KnownOne = OneBits[BitWidth - 1]; |
| KnownZero = ZeroBits[BitWidth - 1]; |
| } |
| |
| /// isPowerOfTwo - Return true if the given value is known to have exactly one |
| /// bit set when defined. For vectors return true if every element is known to |
| /// be a power of two when defined. Supports values with integer or pointer |
| /// types and vectors of integers. |
| bool llvm::isPowerOfTwo(Value *V, const TargetData *TD, unsigned Depth) { |
| if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) |
| return CI->getValue().isPowerOf2(); |
| // TODO: Handle vector constants. |
| |
| // 1 << X is clearly a power of two if the one is not shifted off the end. If |
| // it is shifted off the end then the result is undefined. |
| if (match(V, m_Shl(m_One(), m_Value()))) |
| return true; |
| |
| // (signbit) >>l X is clearly a power of two if the one is not shifted off the |
| // bottom. If it is shifted off the bottom then the result is undefined. |
| if (match(V, m_LShr(m_SignBit(), m_Value()))) |
| return true; |
| |
| // The remaining tests are all recursive, so bail out if we hit the limit. |
| if (Depth++ == MaxDepth) |
| return false; |
| |
| if (ZExtInst *ZI = dyn_cast<ZExtInst>(V)) |
| return isPowerOfTwo(ZI->getOperand(0), TD, Depth); |
| |
| if (SelectInst *SI = dyn_cast<SelectInst>(V)) |
| return isPowerOfTwo(SI->getTrueValue(), TD, Depth) && |
| isPowerOfTwo(SI->getFalseValue(), TD, Depth); |
| |
| // An exact divide or right shift can only shift off zero bits, so the result |
| // is a power of two only if the first operand is a power of two and not |
| // copying a sign bit (sdiv int_min, 2). |
| if (match(V, m_LShr(m_Value(), m_Value())) || |
| match(V, m_UDiv(m_Value(), m_Value()))) { |
| PossiblyExactOperator *PEO = cast<PossiblyExactOperator>(V); |
| if (PEO->isExact()) |
| return isPowerOfTwo(PEO->getOperand(0), TD, Depth); |
| } |
| |
| return false; |
| } |
| |
| /// isKnownNonZero - Return true if the given value is known to be non-zero |
| /// when defined. For vectors return true if every element is known to be |
| /// non-zero when defined. Supports values with integer or pointer type and |
| /// vectors of integers. |
| bool llvm::isKnownNonZero(Value *V, const TargetData *TD, unsigned Depth) { |
| if (Constant *C = dyn_cast<Constant>(V)) { |
| if (C->isNullValue()) |
| return false; |
| if (isa<ConstantInt>(C)) |
| // Must be non-zero due to null test above. |
| return true; |
| // TODO: Handle vectors |
| return false; |
| } |
| |
| // The remaining tests are all recursive, so bail out if we hit the limit. |
| if (Depth++ == MaxDepth) |
| return false; |
| |
| unsigned BitWidth = getBitWidth(V->getType(), TD); |
| |
| // X | Y != 0 if X != 0 or Y != 0. |
| Value *X = 0, *Y = 0; |
| if (match(V, m_Or(m_Value(X), m_Value(Y)))) |
| return isKnownNonZero(X, TD, Depth) || isKnownNonZero(Y, TD, Depth); |
| |
| // ext X != 0 if X != 0. |
| if (isa<SExtInst>(V) || isa<ZExtInst>(V)) |
| return isKnownNonZero(cast<Instruction>(V)->getOperand(0), TD, Depth); |
| |
| // shl X, Y != 0 if X is odd. Note that the value of the shift is undefined |
| // if the lowest bit is shifted off the end. |
| if (BitWidth && match(V, m_Shl(m_Value(X), m_Value(Y)))) { |
| // shl nuw can't remove any non-zero bits. |
| BinaryOperator *BO = cast<BinaryOperator>(V); |
| if (BO->hasNoUnsignedWrap()) |
| return isKnownNonZero(X, TD, Depth); |
| |
| APInt KnownZero(BitWidth, 0); |
| APInt KnownOne(BitWidth, 0); |
| ComputeMaskedBits(X, APInt(BitWidth, 1), KnownZero, KnownOne, TD, Depth); |
| if (KnownOne[0]) |
| return true; |
| } |
| // shr X, Y != 0 if X is negative. Note that the value of the shift is not |
| // defined if the sign bit is shifted off the end. |
| else if (match(V, m_Shr(m_Value(X), m_Value(Y)))) { |
| // shr exact can only shift out zero bits. |
| BinaryOperator *BO = cast<BinaryOperator>(V); |
| if (BO->isExact()) |
| return isKnownNonZero(X, TD, Depth); |
| |
| bool XKnownNonNegative, XKnownNegative; |
| ComputeSignBit(X, XKnownNonNegative, XKnownNegative, TD, Depth); |
| if (XKnownNegative) |
| return true; |
| } |
| // div exact can only produce a zero if the dividend is zero. |
| else if (match(V, m_IDiv(m_Value(X), m_Value()))) { |
| BinaryOperator *BO = cast<BinaryOperator>(V); |
| if (BO->isExact()) |
| return isKnownNonZero(X, TD, Depth); |
| } |
| // X + Y. |
| else if (match(V, m_Add(m_Value(X), m_Value(Y)))) { |
| bool XKnownNonNegative, XKnownNegative; |
| bool YKnownNonNegative, YKnownNegative; |
| ComputeSignBit(X, XKnownNonNegative, XKnownNegative, TD, Depth); |
| ComputeSignBit(Y, YKnownNonNegative, YKnownNegative, TD, Depth); |
| |
| // If X and Y are both non-negative (as signed values) then their sum is not |
| // zero unless both X and Y are zero. |
| if (XKnownNonNegative && YKnownNonNegative) |
| if (isKnownNonZero(X, TD, Depth) || isKnownNonZero(Y, TD, Depth)) |
| return true; |
| |
| // If X and Y are both negative (as signed values) then their sum is not |
| // zero unless both X and Y equal INT_MIN. |
| if (BitWidth && XKnownNegative && YKnownNegative) { |
| APInt KnownZero(BitWidth, 0); |
| APInt KnownOne(BitWidth, 0); |
| APInt Mask = APInt::getSignedMaxValue(BitWidth); |
| // The sign bit of X is set. If some other bit is set then X is not equal |
| // to INT_MIN. |
| ComputeMaskedBits(X, Mask, KnownZero, KnownOne, TD, Depth); |
| if ((KnownOne & Mask) != 0) |
| return true; |
| // The sign bit of Y is set. If some other bit is set then Y is not equal |
| // to INT_MIN. |
| ComputeMaskedBits(Y, Mask, KnownZero, KnownOne, TD, Depth); |
| if ((KnownOne & Mask) != 0) |
| return true; |
| } |
| |
| // The sum of a non-negative number and a power of two is not zero. |
| if (XKnownNonNegative && isPowerOfTwo(Y, TD, Depth)) |
| return true; |
| if (YKnownNonNegative && isPowerOfTwo(X, TD, Depth)) |
| return true; |
| } |
| // (C ? X : Y) != 0 if X != 0 and Y != 0. |
| else if (SelectInst *SI = dyn_cast<SelectInst>(V)) { |
| if (isKnownNonZero(SI->getTrueValue(), TD, Depth) && |
| isKnownNonZero(SI->getFalseValue(), TD, Depth)) |
| return true; |
| } |
| |
| if (!BitWidth) return false; |
| APInt KnownZero(BitWidth, 0); |
| APInt KnownOne(BitWidth, 0); |
| ComputeMaskedBits(V, APInt::getAllOnesValue(BitWidth), KnownZero, KnownOne, |
| TD, Depth); |
| return KnownOne != 0; |
| } |
| |
| /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use |
| /// this predicate to simplify operations downstream. Mask is known to be zero |
| /// for bits that V cannot have. |
| /// |
| /// This function is defined on values with integer type, values with pointer |
| /// type (but only if TD is non-null), and vectors of integers. In the case |
| /// where V is a vector, the mask, known zero, and known one values are the |
| /// same width as the vector element, and the bit is set only if it is true |
| /// for all of the elements in the vector. |
| bool llvm::MaskedValueIsZero(Value *V, const APInt &Mask, |
| const TargetData *TD, unsigned Depth) { |
| APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0); |
| ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth); |
| assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); |
| return (KnownZero & Mask) == Mask; |
| } |
| |
| |
| |
| /// ComputeNumSignBits - Return the number of times the sign bit of the |
| /// register is replicated into the other bits. We know that at least 1 bit |
| /// is always equal to the sign bit (itself), but other cases can give us |
| /// information. For example, immediately after an "ashr X, 2", we know that |
| /// the top 3 bits are all equal to each other, so we return 3. |
| /// |
| /// 'Op' must have a scalar integer type. |
| /// |
| unsigned llvm::ComputeNumSignBits(Value *V, const TargetData *TD, |
| unsigned Depth) { |
| assert((TD || V->getType()->isIntOrIntVectorTy()) && |
| "ComputeNumSignBits requires a TargetData object to operate " |
| "on non-integer values!"); |
| Type *Ty = V->getType(); |
| unsigned TyBits = TD ? TD->getTypeSizeInBits(V->getType()->getScalarType()) : |
| Ty->getScalarSizeInBits(); |
| unsigned Tmp, Tmp2; |
| unsigned FirstAnswer = 1; |
| |
| // Note that ConstantInt is handled by the general ComputeMaskedBits case |
| // below. |
| |
| if (Depth == 6) |
| return 1; // Limit search depth. |
| |
| Operator *U = dyn_cast<Operator>(V); |
| switch (Operator::getOpcode(V)) { |
| default: break; |
| case Instruction::SExt: |
| Tmp = TyBits - U->getOperand(0)->getType()->getScalarSizeInBits(); |
| return ComputeNumSignBits(U->getOperand(0), TD, Depth+1) + Tmp; |
| |
| case Instruction::AShr: |
| Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1); |
| // ashr X, C -> adds C sign bits. |
| if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) { |
| Tmp += C->getZExtValue(); |
| if (Tmp > TyBits) Tmp = TyBits; |
| } |
| // vector ashr X, <C, C, C, C> -> adds C sign bits |
| if (ConstantVector *C = dyn_cast<ConstantVector>(U->getOperand(1))) { |
| if (ConstantInt *CI = dyn_cast_or_null<ConstantInt>(C->getSplatValue())) { |
| Tmp += CI->getZExtValue(); |
| if (Tmp > TyBits) Tmp = TyBits; |
| } |
| } |
| return Tmp; |
| case Instruction::Shl: |
| if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) { |
| // shl destroys sign bits. |
| Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1); |
| if (C->getZExtValue() >= TyBits || // Bad shift. |
| C->getZExtValue() >= Tmp) break; // Shifted all sign bits out. |
| return Tmp - C->getZExtValue(); |
| } |
| break; |
| case Instruction::And: |
| case Instruction::Or: |
| case Instruction::Xor: // NOT is handled here. |
| // Logical binary ops preserve the number of sign bits at the worst. |
| Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1); |
| if (Tmp != 1) { |
| Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1); |
| FirstAnswer = std::min(Tmp, Tmp2); |
| // We computed what we know about the sign bits as our first |
| // answer. Now proceed to the generic code that uses |
| // ComputeMaskedBits, and pick whichever answer is better. |
| } |
| break; |
| |
| case Instruction::Select: |
| Tmp = ComputeNumSignBits(U->getOperand(1), TD, Depth+1); |
| if (Tmp == 1) return 1; // Early out. |
| Tmp2 = ComputeNumSignBits(U->getOperand(2), TD, Depth+1); |
| return std::min(Tmp, Tmp2); |
| |
| case Instruction::Add: |
| // Add can have at most one carry bit. Thus we know that the output |
| // is, at worst, one more bit than the inputs. |
| Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1); |
| if (Tmp == 1) return 1; // Early out. |
| |
| // Special case decrementing a value (ADD X, -1): |
| if (ConstantInt *CRHS = dyn_cast<ConstantInt>(U->getOperand(1))) |
| if (CRHS->isAllOnesValue()) { |
| APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); |
| APInt Mask = APInt::getAllOnesValue(TyBits); |
| ComputeMaskedBits(U->getOperand(0), Mask, KnownZero, KnownOne, TD, |
| Depth+1); |
| |
| // If the input is known to be 0 or 1, the output is 0/-1, which is all |
| // sign bits set. |
| if ((KnownZero | APInt(TyBits, 1)) == Mask) |
| return TyBits; |
| |
| // If we are subtracting one from a positive number, there is no carry |
| // out of the result. |
| if (KnownZero.isNegative()) |
| return Tmp; |
| } |
| |
| Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1); |
| if (Tmp2 == 1) return 1; |
| return std::min(Tmp, Tmp2)-1; |
| |
| case Instruction::Sub: |
| Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1); |
| if (Tmp2 == 1) return 1; |
| |
| // Handle NEG. |
| if (ConstantInt *CLHS = dyn_cast<ConstantInt>(U->getOperand(0))) |
| if (CLHS->isNullValue()) { |
| APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); |
| APInt Mask = APInt::getAllOnesValue(TyBits); |
| ComputeMaskedBits(U->getOperand(1), Mask, KnownZero, KnownOne, |
| TD, Depth+1); |
| // If the input is known to be 0 or 1, the output is 0/-1, which is all |
| // sign bits set. |
| if ((KnownZero | APInt(TyBits, 1)) == Mask) |
| return TyBits; |
| |
| // If the input is known to be positive (the sign bit is known clear), |
| // the output of the NEG has the same number of sign bits as the input. |
| if (KnownZero.isNegative()) |
| return Tmp2; |
| |
| // Otherwise, we treat this like a SUB. |
| } |
| |
| // Sub can have at most one carry bit. Thus we know that the output |
| // is, at worst, one more bit than the inputs. |
| Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1); |
| if (Tmp == 1) return 1; // Early out. |
| return std::min(Tmp, Tmp2)-1; |
| |
| case Instruction::PHI: { |
| PHINode *PN = cast<PHINode>(U); |
| // Don't analyze large in-degree PHIs. |
| if (PN->getNumIncomingValues() > 4) break; |
| |
| // Take the minimum of all incoming values. This can't infinitely loop |
| // because of our depth threshold. |
| Tmp = ComputeNumSignBits(PN->getIncomingValue(0), TD, Depth+1); |
| for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) { |
| if (Tmp == 1) return Tmp; |
| Tmp = std::min(Tmp, |
| ComputeNumSignBits(PN->getIncomingValue(i), TD, Depth+1)); |
| } |
| return Tmp; |
| } |
| |
| case Instruction::Trunc: |
| // FIXME: it's tricky to do anything useful for this, but it is an important |
| // case for targets like X86. |
| break; |
| } |
| |
| // Finally, if we can prove that the top bits of the result are 0's or 1's, |
| // use this information. |
| APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); |
| APInt Mask = APInt::getAllOnesValue(TyBits); |
| ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth); |
| |
| if (KnownZero.isNegative()) { // sign bit is 0 |
| Mask = KnownZero; |
| } else if (KnownOne.isNegative()) { // sign bit is 1; |
| Mask = KnownOne; |
| } else { |
| // Nothing known. |
| return FirstAnswer; |
| } |
| |
| // Okay, we know that the sign bit in Mask is set. Use CLZ to determine |
| // the number of identical bits in the top of the input value. |
| Mask = ~Mask; |
| Mask <<= Mask.getBitWidth()-TyBits; |
| // Return # leading zeros. We use 'min' here in case Val was zero before |
| // shifting. We don't want to return '64' as for an i32 "0". |
| return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros())); |
| } |
| |
| /// ComputeMultiple - This function computes the integer multiple of Base that |
| /// equals V. If successful, it returns true and returns the multiple in |
| /// Multiple. If unsuccessful, it returns false. It looks |
| /// through SExt instructions only if LookThroughSExt is true. |
| bool llvm::ComputeMultiple(Value *V, unsigned Base, Value *&Multiple, |
| bool LookThroughSExt, unsigned Depth) { |
| const unsigned MaxDepth = 6; |
| |
| assert(V && "No Value?"); |
| assert(Depth <= MaxDepth && "Limit Search Depth"); |
| assert(V->getType()->isIntegerTy() && "Not integer or pointer type!"); |
| |
| Type *T = V->getType(); |
| |
| ConstantInt *CI = dyn_cast<ConstantInt>(V); |
| |
| if (Base == 0) |
| return false; |
| |
| if (Base == 1) { |
| Multiple = V; |
| return true; |
| } |
| |
| ConstantExpr *CO = dyn_cast<ConstantExpr>(V); |
| Constant *BaseVal = ConstantInt::get(T, Base); |
| if (CO && CO == BaseVal) { |
| // Multiple is 1. |
| Multiple = ConstantInt::get(T, 1); |
| return true; |
| } |
| |
| if (CI && CI->getZExtValue() % Base == 0) { |
| Multiple = ConstantInt::get(T, CI->getZExtValue() / Base); |
| return true; |
| } |
| |
| if (Depth == MaxDepth) return false; // Limit search depth. |
| |
| Operator *I = dyn_cast<Operator>(V); |
| if (!I) return false; |
| |
| switch (I->getOpcode()) { |
| default: break; |
| case Instruction::SExt: |
| if (!LookThroughSExt) return false; |
| // otherwise fall through to ZExt |
| case Instruction::ZExt: |
| return ComputeMultiple(I->getOperand(0), Base, Multiple, |
| LookThroughSExt, Depth+1); |
| case Instruction::Shl: |
| case Instruction::Mul: { |
| Value *Op0 = I->getOperand(0); |
| Value *Op1 = I->getOperand(1); |
| |
| if (I->getOpcode() == Instruction::Shl) { |
| ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1); |
| if (!Op1CI) return false; |
| // Turn Op0 << Op1 into Op0 * 2^Op1 |
| APInt Op1Int = Op1CI->getValue(); |
| uint64_t BitToSet = Op1Int.getLimitedValue(Op1Int.getBitWidth() - 1); |
| APInt API(Op1Int.getBitWidth(), 0); |
| API.setBit(BitToSet); |
| Op1 = ConstantInt::get(V->getContext(), API); |
| } |
| |
| Value *Mul0 = NULL; |
| if (ComputeMultiple(Op0, Base, Mul0, LookThroughSExt, Depth+1)) { |
| if (Constant *Op1C = dyn_cast<Constant>(Op1)) |
| if (Constant *MulC = dyn_cast<Constant>(Mul0)) { |
| if (Op1C->getType()->getPrimitiveSizeInBits() < |
| MulC->getType()->getPrimitiveSizeInBits()) |
| Op1C = ConstantExpr::getZExt(Op1C, MulC->getType()); |
| if (Op1C->getType()->getPrimitiveSizeInBits() > |
| MulC->getType()->getPrimitiveSizeInBits()) |
| MulC = ConstantExpr::getZExt(MulC, Op1C->getType()); |
| |
| // V == Base * (Mul0 * Op1), so return (Mul0 * Op1) |
| Multiple = ConstantExpr::getMul(MulC, Op1C); |
| return true; |
| } |
| |
| if (ConstantInt *Mul0CI = dyn_cast<ConstantInt>(Mul0)) |
| if (Mul0CI->getValue() == 1) { |
| // V == Base * Op1, so return Op1 |
| Multiple = Op1; |
| return true; |
| } |
| } |
| |
| Value *Mul1 = NULL; |
| if (ComputeMultiple(Op1, Base, Mul1, LookThroughSExt, Depth+1)) { |
| if (Constant *Op0C = dyn_cast<Constant>(Op0)) |
| if (Constant *MulC = dyn_cast<Constant>(Mul1)) { |
| if (Op0C->getType()->getPrimitiveSizeInBits() < |
| MulC->getType()->getPrimitiveSizeInBits()) |
| Op0C = ConstantExpr::getZExt(Op0C, MulC->getType()); |
| if (Op0C->getType()->getPrimitiveSizeInBits() > |
| MulC->getType()->getPrimitiveSizeInBits()) |
| MulC = ConstantExpr::getZExt(MulC, Op0C->getType()); |
| |
| // V == Base * (Mul1 * Op0), so return (Mul1 * Op0) |
| Multiple = ConstantExpr::getMul(MulC, Op0C); |
| return true; |
| } |
| |
| if (ConstantInt *Mul1CI = dyn_cast<ConstantInt>(Mul1)) |
| if (Mul1CI->getValue() == 1) { |
| // V == Base * Op0, so return Op0 |
| Multiple = Op0; |
| return true; |
| } |
| } |
| } |
| } |
| |
| // We could not determine if V is a multiple of Base. |
| return false; |
| } |
| |
| /// CannotBeNegativeZero - Return true if we can prove that the specified FP |
| /// value is never equal to -0.0. |
| /// |
| /// NOTE: this function will need to be revisited when we support non-default |
| /// rounding modes! |
| /// |
| bool llvm::CannotBeNegativeZero(const Value *V, unsigned Depth) { |
| if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V)) |
| return !CFP->getValueAPF().isNegZero(); |
| |
| if (Depth == 6) |
| return 1; // Limit search depth. |
| |
| const Operator *I = dyn_cast<Operator>(V); |
| if (I == 0) return false; |
| |
| // (add x, 0.0) is guaranteed to return +0.0, not -0.0. |
| if (I->getOpcode() == Instruction::FAdd && |
| isa<ConstantFP>(I->getOperand(1)) && |
| cast<ConstantFP>(I->getOperand(1))->isNullValue()) |
| return true; |
| |
| // sitofp and uitofp turn into +0.0 for zero. |
| if (isa<SIToFPInst>(I) || isa<UIToFPInst>(I)) |
| return true; |
| |
| if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) |
| // sqrt(-0.0) = -0.0, no other negative results are possible. |
| if (II->getIntrinsicID() == Intrinsic::sqrt) |
| return CannotBeNegativeZero(II->getArgOperand(0), Depth+1); |
| |
| if (const CallInst *CI = dyn_cast<CallInst>(I)) |
| if (const Function *F = CI->getCalledFunction()) { |
| if (F->isDeclaration()) { |
| // abs(x) != -0.0 |
| if (F->getName() == "abs") return true; |
| // fabs[lf](x) != -0.0 |
| if (F->getName() == "fabs") return true; |
| if (F->getName() == "fabsf") return true; |
| if (F->getName() == "fabsl") return true; |
| if (F->getName() == "sqrt" || F->getName() == "sqrtf" || |
| F->getName() == "sqrtl") |
| return CannotBeNegativeZero(CI->getArgOperand(0), Depth+1); |
| } |
| } |
| |
| return false; |
| } |
| |
| /// isBytewiseValue - If the specified value can be set by repeating the same |
| /// byte in memory, return the i8 value that it is represented with. This is |
| /// true for all i8 values obviously, but is also true for i32 0, i32 -1, |
| /// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated |
| /// byte store (e.g. i16 0x1234), return null. |
| Value *llvm::isBytewiseValue(Value *V) { |
| // All byte-wide stores are splatable, even of arbitrary variables. |
| if (V->getType()->isIntegerTy(8)) return V; |
| |
| // Handle 'null' ConstantArrayZero etc. |
| if (Constant *C = dyn_cast<Constant>(V)) |
| if (C->isNullValue()) |
| return Constant::getNullValue(Type::getInt8Ty(V->getContext())); |
| |
| // Constant float and double values can be handled as integer values if the |
| // corresponding integer value is "byteable". An important case is 0.0. |
| if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) { |
| if (CFP->getType()->isFloatTy()) |
| V = ConstantExpr::getBitCast(CFP, Type::getInt32Ty(V->getContext())); |
| if (CFP->getType()->isDoubleTy()) |
| V = ConstantExpr::getBitCast(CFP, Type::getInt64Ty(V->getContext())); |
| // Don't handle long double formats, which have strange constraints. |
| } |
| |
| // We can handle constant integers that are power of two in size and a |
| // multiple of 8 bits. |
| if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) { |
| unsigned Width = CI->getBitWidth(); |
| if (isPowerOf2_32(Width) && Width > 8) { |
| // We can handle this value if the recursive binary decomposition is the |
| // same at all levels. |
| APInt Val = CI->getValue(); |
| APInt Val2; |
| while (Val.getBitWidth() != 8) { |
| unsigned NextWidth = Val.getBitWidth()/2; |
| Val2 = Val.lshr(NextWidth); |
| Val2 = Val2.trunc(Val.getBitWidth()/2); |
| Val = Val.trunc(Val.getBitWidth()/2); |
| |
| // If the top/bottom halves aren't the same, reject it. |
| if (Val != Val2) |
| return 0; |
| } |
| return ConstantInt::get(V->getContext(), Val); |
| } |
| } |
| |
| // A ConstantArray is splatable if all its members are equal and also |
| // splatable. |
| if (ConstantArray *CA = dyn_cast<ConstantArray>(V)) { |
| if (CA->getNumOperands() == 0) |
| return 0; |
| |
| Value *Val = isBytewiseValue(CA->getOperand(0)); |
| if (!Val) |
| return 0; |
| |
| for (unsigned I = 1, E = CA->getNumOperands(); I != E; ++I) |
| if (CA->getOperand(I-1) != CA->getOperand(I)) |
| return 0; |
| |
| return Val; |
| } |
| |
| // Conceptually, we could handle things like: |
| // %a = zext i8 %X to i16 |
| // %b = shl i16 %a, 8 |
| // %c = or i16 %a, %b |
| // but until there is an example that actually needs this, it doesn't seem |
| // worth worrying about. |
| return 0; |
| } |
| |
| |
| // This is the recursive version of BuildSubAggregate. It takes a few different |
| // arguments. Idxs is the index within the nested struct From that we are |
| // looking at now (which is of type IndexedType). IdxSkip is the number of |
| // indices from Idxs that should be left out when inserting into the resulting |
| // struct. To is the result struct built so far, new insertvalue instructions |
| // build on that. |
| static Value *BuildSubAggregate(Value *From, Value* To, Type *IndexedType, |
| SmallVector<unsigned, 10> &Idxs, |
| unsigned IdxSkip, |
| Instruction *InsertBefore) { |
| llvm::StructType *STy = llvm::dyn_cast<llvm::StructType>(IndexedType); |
| if (STy) { |
| // Save the original To argument so we can modify it |
| Value *OrigTo = To; |
| // General case, the type indexed by Idxs is a struct |
| for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { |
| // Process each struct element recursively |
| Idxs.push_back(i); |
| Value *PrevTo = To; |
| To = BuildSubAggregate(From, To, STy->getElementType(i), Idxs, IdxSkip, |
| InsertBefore); |
| Idxs.pop_back(); |
| if (!To) { |
| // Couldn't find any inserted value for this index? Cleanup |
| while (PrevTo != OrigTo) { |
| InsertValueInst* Del = cast<InsertValueInst>(PrevTo); |
| PrevTo = Del->getAggregateOperand(); |
| Del->eraseFromParent(); |
| } |
| // Stop processing elements |
| break; |
| } |
| } |
| // If we successfully found a value for each of our subaggregates |
| if (To) |
| return To; |
| } |
| // Base case, the type indexed by SourceIdxs is not a struct, or not all of |
| // the struct's elements had a value that was inserted directly. In the latter |
| // case, perhaps we can't determine each of the subelements individually, but |
| // we might be able to find the complete struct somewhere. |
| |
| // Find the value that is at that particular spot |
| Value *V = FindInsertedValue(From, Idxs); |
| |
| if (!V) |
| return NULL; |
| |
| // Insert the value in the new (sub) aggregrate |
| return llvm::InsertValueInst::Create(To, V, makeArrayRef(Idxs).slice(IdxSkip), |
| "tmp", InsertBefore); |
| } |
| |
| // This helper takes a nested struct and extracts a part of it (which is again a |
| // struct) into a new value. For example, given the struct: |
| // { a, { b, { c, d }, e } } |
| // and the indices "1, 1" this returns |
| // { c, d }. |
| // |
| // It does this by inserting an insertvalue for each element in the resulting |
| // struct, as opposed to just inserting a single struct. This will only work if |
| // each of the elements of the substruct are known (ie, inserted into From by an |
| // insertvalue instruction somewhere). |
| // |
| // All inserted insertvalue instructions are inserted before InsertBefore |
| static Value *BuildSubAggregate(Value *From, ArrayRef<unsigned> idx_range, |
| Instruction *InsertBefore) { |
| assert(InsertBefore && "Must have someplace to insert!"); |
| Type *IndexedType = ExtractValueInst::getIndexedType(From->getType(), |
| idx_range); |
| Value *To = UndefValue::get(IndexedType); |
| SmallVector<unsigned, 10> Idxs(idx_range.begin(), idx_range.end()); |
| unsigned IdxSkip = Idxs.size(); |
| |
| return BuildSubAggregate(From, To, IndexedType, Idxs, IdxSkip, InsertBefore); |
| } |
| |
| /// FindInsertedValue - Given an aggregrate and an sequence of indices, see if |
| /// the scalar value indexed is already around as a register, for example if it |
| /// were inserted directly into the aggregrate. |
| /// |
| /// If InsertBefore is not null, this function will duplicate (modified) |
| /// insertvalues when a part of a nested struct is extracted. |
| Value *llvm::FindInsertedValue(Value *V, ArrayRef<unsigned> idx_range, |
| Instruction *InsertBefore) { |
| // Nothing to index? Just return V then (this is useful at the end of our |
| // recursion) |
| if (idx_range.empty()) |
| return V; |
| // We have indices, so V should have an indexable type |
| assert((V->getType()->isStructTy() || V->getType()->isArrayTy()) |
| && "Not looking at a struct or array?"); |
| assert(ExtractValueInst::getIndexedType(V->getType(), idx_range) |
| && "Invalid indices for type?"); |
| CompositeType *PTy = cast<CompositeType>(V->getType()); |
| |
| if (isa<UndefValue>(V)) |
| return UndefValue::get(ExtractValueInst::getIndexedType(PTy, |
| idx_range)); |
| else if (isa<ConstantAggregateZero>(V)) |
| return Constant::getNullValue(ExtractValueInst::getIndexedType(PTy, |
| idx_range)); |
| else if (Constant *C = dyn_cast<Constant>(V)) { |
| if (isa<ConstantArray>(C) || isa<ConstantStruct>(C)) |
| // Recursively process this constant |
| return FindInsertedValue(C->getOperand(idx_range[0]), idx_range.slice(1), |
| InsertBefore); |
| } else if (InsertValueInst *I = dyn_cast<InsertValueInst>(V)) { |
| // Loop the indices for the insertvalue instruction in parallel with the |
| // requested indices |
| const unsigned *req_idx = idx_range.begin(); |
| for (const unsigned *i = I->idx_begin(), *e = I->idx_end(); |
| i != e; ++i, ++req_idx) { |
| if (req_idx == idx_range.end()) { |
| if (InsertBefore) |
| // The requested index identifies a part of a nested aggregate. Handle |
| // this specially. For example, |
| // %A = insertvalue { i32, {i32, i32 } } undef, i32 10, 1, 0 |
| // %B = insertvalue { i32, {i32, i32 } } %A, i32 11, 1, 1 |
| // %C = extractvalue {i32, { i32, i32 } } %B, 1 |
| // This can be changed into |
| // %A = insertvalue {i32, i32 } undef, i32 10, 0 |
| // %C = insertvalue {i32, i32 } %A, i32 11, 1 |
| // which allows the unused 0,0 element from the nested struct to be |
| // removed. |
| return BuildSubAggregate(V, makeArrayRef(idx_range.begin(), req_idx), |
| InsertBefore); |
| else |
| // We can't handle this without inserting insertvalues |
| return 0; |
| } |
| |
| // This insert value inserts something else than what we are looking for. |
| // See if the (aggregrate) value inserted into has the value we are |
| // looking for, then. |
| if (*req_idx != *i) |
| return FindInsertedValue(I->getAggregateOperand(), idx_range, |
| InsertBefore); |
| } |
| // If we end up here, the indices of the insertvalue match with those |
| // requested (though possibly only partially). Now we recursively look at |
| // the inserted value, passing any remaining indices. |
| return FindInsertedValue(I->getInsertedValueOperand(), |
| makeArrayRef(req_idx, idx_range.end()), |
| InsertBefore); |
| } else if (ExtractValueInst *I = dyn_cast<ExtractValueInst>(V)) { |
| // If we're extracting a value from an aggregrate that was extracted from |
| // something else, we can extract from that something else directly instead. |
| // However, we will need to chain I's indices with the requested indices. |
| |
| // Calculate the number of indices required |
| unsigned size = I->getNumIndices() + idx_range.size(); |
| // Allocate some space to put the new indices in |
| SmallVector<unsigned, 5> Idxs; |
| Idxs.reserve(size); |
| // Add indices from the extract value instruction |
| Idxs.append(I->idx_begin(), I->idx_end()); |
| |
| // Add requested indices |
| Idxs.append(idx_range.begin(), idx_range.end()); |
| |
| assert(Idxs.size() == size |
| && "Number of indices added not correct?"); |
| |
| return FindInsertedValue(I->getAggregateOperand(), Idxs, InsertBefore); |
| } |
| // Otherwise, we don't know (such as, extracting from a function return value |
| // or load instruction) |
| return 0; |
| } |
| |
| /// GetPointerBaseWithConstantOffset - Analyze the specified pointer to see if |
| /// it can be expressed as a base pointer plus a constant offset. Return the |
| /// base and offset to the caller. |
| Value *llvm::GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset, |
| const TargetData &TD) { |
| Operator *PtrOp = dyn_cast<Operator>(Ptr); |
| if (PtrOp == 0) return Ptr; |
| |
| // Just look through bitcasts. |
| if (PtrOp->getOpcode() == Instruction::BitCast) |
| return GetPointerBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD); |
| |
| // If this is a GEP with constant indices, we can look through it. |
| GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp); |
| if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr; |
| |
| gep_type_iterator GTI = gep_type_begin(GEP); |
| for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E; |
| ++I, ++GTI) { |
| ConstantInt *OpC = cast<ConstantInt>(*I); |
| if (OpC->isZero()) continue; |
| |
| // Handle a struct and array indices which add their offset to the pointer. |
| if (StructType *STy = dyn_cast<StructType>(*GTI)) { |
| Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue()); |
| } else { |
| uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()); |
| Offset += OpC->getSExtValue()*Size; |
| } |
| } |
| |
| // Re-sign extend from the pointer size if needed to get overflow edge cases |
| // right. |
| unsigned PtrSize = TD.getPointerSizeInBits(); |
| if (PtrSize < 64) |
| Offset = (Offset << (64-PtrSize)) >> (64-PtrSize); |
| |
| return GetPointerBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD); |
| } |
| |
| |
| /// GetConstantStringInfo - This function computes the length of a |
| /// null-terminated C string pointed to by V. If successful, it returns true |
| /// and returns the string in Str. If unsuccessful, it returns false. |
| bool llvm::GetConstantStringInfo(const Value *V, std::string &Str, |
| uint64_t Offset, |
| bool StopAtNul) { |
| // If V is NULL then return false; |
| if (V == NULL) return false; |
| |
| // Look through bitcast instructions. |
| if (const BitCastInst *BCI = dyn_cast<BitCastInst>(V)) |
| return GetConstantStringInfo(BCI->getOperand(0), Str, Offset, StopAtNul); |
| |
| // If the value is not a GEP instruction nor a constant expression with a |
| // GEP instruction, then return false because ConstantArray can't occur |
| // any other way |
| const User *GEP = 0; |
| if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(V)) { |
| GEP = GEPI; |
| } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) { |
| if (CE->getOpcode() == Instruction::BitCast) |
| return GetConstantStringInfo(CE->getOperand(0), Str, Offset, StopAtNul); |
| if (CE->getOpcode() != Instruction::GetElementPtr) |
| return false; |
| GEP = CE; |
| } |
| |
| if (GEP) { |
| // Make sure the GEP has exactly three arguments. |
| if (GEP->getNumOperands() != 3) |
| return false; |
| |
| // Make sure the index-ee is a pointer to array of i8. |
| PointerType *PT = cast<PointerType>(GEP->getOperand(0)->getType()); |
| ArrayType *AT = dyn_cast<ArrayType>(PT->getElementType()); |
| if (AT == 0 || !AT->getElementType()->isIntegerTy(8)) |
| return false; |
| |
| // Check to make sure that the first operand of the GEP is an integer and |
| // has value 0 so that we are sure we're indexing into the initializer. |
| const ConstantInt *FirstIdx = dyn_cast<ConstantInt>(GEP->getOperand(1)); |
| if (FirstIdx == 0 || !FirstIdx->isZero()) |
| return false; |
| |
| // If the second index isn't a ConstantInt, then this is a variable index |
| // into the array. If this occurs, we can't say anything meaningful about |
| // the string. |
| uint64_t StartIdx = 0; |
| if (const ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(2))) |
| StartIdx = CI->getZExtValue(); |
| else |
| return false; |
| return GetConstantStringInfo(GEP->getOperand(0), Str, StartIdx+Offset, |
| StopAtNul); |
| } |
| |
| // The GEP instruction, constant or instruction, must reference a global |
| // variable that is a constant and is initialized. The referenced constant |
| // initializer is the array that we'll use for optimization. |
| const GlobalVariable* GV = dyn_cast<GlobalVariable>(V); |
| if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer()) |
| return false; |
| const Constant *GlobalInit = GV->getInitializer(); |
| |
| // Handle the ConstantAggregateZero case |
| if (isa<ConstantAggregateZero>(GlobalInit)) { |
| // This is a degenerate case. The initializer is constant zero so the |
| // length of the string must be zero. |
| Str.clear(); |
| return true; |
| } |
| |
| // Must be a Constant Array |
| const ConstantArray *Array = dyn_cast<ConstantArray>(GlobalInit); |
| if (Array == 0 || !Array->getType()->getElementType()->isIntegerTy(8)) |
| return false; |
| |
| // Get the number of elements in the array |
| uint64_t NumElts = Array->getType()->getNumElements(); |
| |
| if (Offset > NumElts) |
| return false; |
| |
| // Traverse the constant array from 'Offset' which is the place the GEP refers |
| // to in the array. |
| Str.reserve(NumElts-Offset); |
| for (unsigned i = Offset; i != NumElts; ++i) { |
| const Constant *Elt = Array->getOperand(i); |
| const ConstantInt *CI = dyn_cast<ConstantInt>(Elt); |
| if (!CI) // This array isn't suitable, non-int initializer. |
| return false; |
| if (StopAtNul && CI->isZero()) |
| return true; // we found end of string, success! |
| Str += (char)CI->getZExtValue(); |
| } |
| |
| // The array isn't null terminated, but maybe this is a memcpy, not a strcpy. |
| return true; |
| } |
| |
| // These next two are very similar to the above, but also look through PHI |
| // nodes. |
| // TODO: See if we can integrate these two together. |
| |
| /// GetStringLengthH - If we can compute the length of the string pointed to by |
| /// the specified pointer, return 'len+1'. If we can't, return 0. |
| static uint64_t GetStringLengthH(Value *V, SmallPtrSet<PHINode*, 32> &PHIs) { |
| // Look through noop bitcast instructions. |
| if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) |
| return GetStringLengthH(BCI->getOperand(0), PHIs); |
| |
| // If this is a PHI node, there are two cases: either we have already seen it |
| // or we haven't. |
| if (PHINode *PN = dyn_cast<PHINode>(V)) { |
| if (!PHIs.insert(PN)) |
| return ~0ULL; // already in the set. |
| |
| // If it was new, see if all the input strings are the same length. |
| uint64_t LenSoFar = ~0ULL; |
| for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { |
| uint64_t Len = GetStringLengthH(PN->getIncomingValue(i), PHIs); |
| if (Len == 0) return 0; // Unknown length -> unknown. |
| |
| if (Len == ~0ULL) continue; |
| |
| if (Len != LenSoFar && LenSoFar != ~0ULL) |
| return 0; // Disagree -> unknown. |
| LenSoFar = Len; |
| } |
| |
| // Success, all agree. |
| return LenSoFar; |
| } |
| |
| // strlen(select(c,x,y)) -> strlen(x) ^ strlen(y) |
| if (SelectInst *SI = dyn_cast<SelectInst>(V)) { |
| uint64_t Len1 = GetStringLengthH(SI->getTrueValue(), PHIs); |
| if (Len1 == 0) return 0; |
| uint64_t Len2 = GetStringLengthH(SI->getFalseValue(), PHIs); |
| if (Len2 == 0) return 0; |
| if (Len1 == ~0ULL) return Len2; |
| if (Len2 == ~0ULL) return Len1; |
| if (Len1 != Len2) return 0; |
| return Len1; |
| } |
| |
| // If the value is not a GEP instruction nor a constant expression with a |
| // GEP instruction, then return unknown. |
| User *GEP = 0; |
| if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(V)) { |
| GEP = GEPI; |
| } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) { |
| if (CE->getOpcode() != Instruction::GetElementPtr) |
| return 0; |
| GEP = CE; |
| } else { |
| return 0; |
| } |
| |
| // Make sure the GEP has exactly three arguments. |
| if (GEP->getNumOperands() != 3) |
| return 0; |
| |
| // Check to make sure that the first operand of the GEP is an integer and |
| // has value 0 so that we are sure we're indexing into the initializer. |
| if (ConstantInt *Idx = dyn_cast<ConstantInt>(GEP->getOperand(1))) { |
| if (!Idx->isZero()) |
| return 0; |
| } else |
| return 0; |
| |
| // If the second index isn't a ConstantInt, then this is a variable index |
| // into the array. If this occurs, we can't say anything meaningful about |
| // the string. |
| uint64_t StartIdx = 0; |
| if (ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(2))) |
| StartIdx = CI->getZExtValue(); |
| else |
| return 0; |
| |
| // The GEP instruction, constant or instruction, must reference a global |
| // variable that is a constant and is initialized. The referenced constant |
| // initializer is the array that we'll use for optimization. |
| GlobalVariable* GV = dyn_cast<GlobalVariable>(GEP->getOperand(0)); |
| if (!GV || !GV->isConstant() || !GV->hasInitializer() || |
| GV->mayBeOverridden()) |
| return 0; |
| Constant *GlobalInit = GV->getInitializer(); |
| |
| // Handle the ConstantAggregateZero case, which is a degenerate case. The |
| // initializer is constant zero so the length of the string must be zero. |
| if (isa<ConstantAggregateZero>(GlobalInit)) |
| return 1; // Len = 0 offset by 1. |
| |
| // Must be a Constant Array |
| ConstantArray *Array = dyn_cast<ConstantArray>(GlobalInit); |
| if (!Array || !Array->getType()->getElementType()->isIntegerTy(8)) |
| return false; |
| |
| // Get the number of elements in the array |
| uint64_t NumElts = Array->getType()->getNumElements(); |
| |
| // Traverse the constant array from StartIdx (derived above) which is |
| // the place the GEP refers to in the array. |
| for (unsigned i = StartIdx; i != NumElts; ++i) { |
| Constant *Elt = Array->getOperand(i); |
| ConstantInt *CI = dyn_cast<ConstantInt>(Elt); |
| if (!CI) // This array isn't suitable, non-int initializer. |
| return 0; |
| if (CI->isZero()) |
| return i-StartIdx+1; // We found end of string, success! |
| } |
| |
| return 0; // The array isn't null terminated, conservatively return 'unknown'. |
| } |
| |
| /// GetStringLength - If we can compute the length of the string pointed to by |
| /// the specified pointer, return 'len+1'. If we can't, return 0. |
| uint64_t llvm::GetStringLength(Value *V) { |
| if (!V->getType()->isPointerTy()) return 0; |
| |
| SmallPtrSet<PHINode*, 32> PHIs; |
| uint64_t Len = GetStringLengthH(V, PHIs); |
| // If Len is ~0ULL, we had an infinite phi cycle: this is dead code, so return |
| // an empty string as a length. |
| return Len == ~0ULL ? 1 : Len; |
| } |
| |
| Value * |
| llvm::GetUnderlyingObject(Value *V, const TargetData *TD, unsigned MaxLookup) { |
| if (!V->getType()->isPointerTy()) |
| return V; |
| for (unsigned Count = 0; MaxLookup == 0 || Count < MaxLookup; ++Count) { |
| if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) { |
| V = GEP->getPointerOperand(); |
| } else if (Operator::getOpcode(V) == Instruction::BitCast) { |
| V = cast<Operator>(V)->getOperand(0); |
| } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) { |
| if (GA->mayBeOverridden()) |
| return V; |
| V = GA->getAliasee(); |
| } else { |
| // See if InstructionSimplify knows any relevant tricks. |
| if (Instruction *I = dyn_cast<Instruction>(V)) |
| // TODO: Acquire a DominatorTree and use it. |
| if (Value *Simplified = SimplifyInstruction(I, TD, 0)) { |
| V = Simplified; |
| continue; |
| } |
| |
| return V; |
| } |
| assert(V->getType()->isPointerTy() && "Unexpected operand type!"); |
| } |
| return V; |
| } |
| |
| /// onlyUsedByLifetimeMarkers - Return true if the only users of this pointer |
| /// are lifetime markers. |
| /// |
| bool llvm::onlyUsedByLifetimeMarkers(const Value *V) { |
| for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end(); |
| UI != UE; ++UI) { |
| const IntrinsicInst *II = dyn_cast<IntrinsicInst>(*UI); |
| if (!II) return false; |
| |
| if (II->getIntrinsicID() != Intrinsic::lifetime_start && |
| II->getIntrinsicID() != Intrinsic::lifetime_end) |
| return false; |
| } |
| return true; |
| } |