| //===- 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/Constants.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/GlobalVariable.h" |
| #include "llvm/IntrinsicInst.h" |
| #include "llvm/Target/TargetData.h" |
| #include "llvm/Support/GetElementPtrTypeIterator.h" |
| #include "llvm/Support/MathExtras.h" |
| #include <cstring> |
| using namespace llvm; |
| |
| /// getOpcode - If this is an Instruction or a ConstantExpr, return the |
| /// opcode value. Otherwise return UserOp1. |
| static unsigned getOpcode(const Value *V) { |
| if (const Instruction *I = dyn_cast<Instruction>(V)) |
| return I->getOpcode(); |
| if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) |
| return CE->getOpcode(); |
| // Use UserOp1 to mean there's no opcode. |
| return Instruction::UserOp1; |
| } |
| |
| |
| /// 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. |
| void llvm::ComputeMaskedBits(Value *V, const APInt &Mask, |
| APInt &KnownZero, APInt &KnownOne, |
| TargetData *TD, unsigned Depth) { |
| assert(V && "No Value?"); |
| assert(Depth <= 6 && "Limit Search Depth"); |
| uint32_t BitWidth = Mask.getBitWidth(); |
| assert((V->getType()->isInteger() || isa<PointerType>(V->getType())) && |
| "Not integer or pointer type!"); |
| assert((!TD || TD->getTypeSizeInBits(V->getType()) == BitWidth) && |
| (!isa<IntegerType>(V->getType()) || |
| V->getType()->getPrimitiveSizeInBits() == 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 is all-zeros. |
| if (isa<ConstantPointerNull>(V)) { |
| KnownOne.clear(); |
| KnownZero = Mask; |
| 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()) |
| Align = TD->getPrefTypeAlignment(GV->getType()->getElementType()); |
| if (Align > 0) |
| KnownZero = Mask & APInt::getLowBitsSet(BitWidth, |
| CountTrailingZeros_32(Align)); |
| else |
| KnownZero.clear(); |
| KnownOne.clear(); |
| return; |
| } |
| |
| KnownZero.clear(); KnownOne.clear(); // Start out not knowing anything. |
| |
| if (Depth == 6 || Mask == 0) |
| return; // Limit search depth. |
| |
| User *I = dyn_cast<User>(V); |
| if (!I) return; |
| |
| APInt KnownZero2(KnownZero), KnownOne2(KnownOne); |
| switch (getOpcode(I)) { |
| 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.clear(); |
| 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.clear(); |
| KnownZero2.clear(); |
| 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: { |
| // Note that we handle pointer operands here because of inttoptr/ptrtoint |
| // which fall through here. |
| const Type *SrcTy = I->getOperand(0)->getType(); |
| uint32_t SrcBitWidth = TD ? |
| TD->getTypeSizeInBits(SrcTy) : |
| SrcTy->getPrimitiveSizeInBits(); |
| APInt MaskIn(Mask); |
| MaskIn.zextOrTrunc(SrcBitWidth); |
| KnownZero.zextOrTrunc(SrcBitWidth); |
| KnownOne.zextOrTrunc(SrcBitWidth); |
| ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD, |
| Depth+1); |
| KnownZero.zextOrTrunc(BitWidth); |
| KnownOne.zextOrTrunc(BitWidth); |
| // Any top bits are known to be zero. |
| if (BitWidth > SrcBitWidth) |
| KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth); |
| return; |
| } |
| case Instruction::BitCast: { |
| const Type *SrcTy = I->getOperand(0)->getType(); |
| if (SrcTy->isInteger() || isa<PointerType>(SrcTy)) { |
| 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. |
| const IntegerType *SrcTy = cast<IntegerType>(I->getOperand(0)->getType()); |
| uint32_t SrcBitWidth = SrcTy->getBitWidth(); |
| |
| APInt MaskIn(Mask); |
| MaskIn.trunc(SrcBitWidth); |
| KnownZero.trunc(SrcBitWidth); |
| 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.zext(BitWidth); |
| 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); |
| |
| // 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: { |
| // Output known-0 bits are known if clear or set in both the low clear bits |
| // common to both LHS & RHS. For example, 8+(X<<3) is known to have the |
| // low 3 bits clear. |
| APInt Mask2 = APInt::getLowBitsSet(BitWidth, Mask.countTrailingOnes()); |
| ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, |
| Depth+1); |
| assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); |
| unsigned KnownZeroOut = KnownZero2.countTrailingOnes(); |
| |
| ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero2, KnownOne2, TD, |
| Depth+1); |
| assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); |
| KnownZeroOut = std::min(KnownZeroOut, |
| KnownZero2.countTrailingOnes()); |
| |
| KnownZero |= APInt::getLowBitsSet(BitWidth, KnownZeroOut); |
| return; |
| } |
| case Instruction::SRem: |
| if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) { |
| APInt RA = Rem->getValue(); |
| if (RA.isPowerOf2() || (-RA).isPowerOf2()) { |
| APInt LowBits = RA.isStrictlyPositive() ? (RA - 1) : ~RA; |
| APInt Mask2 = LowBits | APInt::getSignBit(BitWidth); |
| ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, |
| Depth+1); |
| |
| // If the sign bit of the first operand is zero, the sign bit of |
| // the result is zero. If the first operand has no one bits below |
| // the second operand's single 1 bit, its sign will be zero. |
| if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits)) |
| KnownZero2 |= ~LowBits; |
| |
| KnownZero |= KnownZero2 & Mask; |
| |
| assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?"); |
| } |
| } |
| 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); |
| |
| uint32_t Leaders = std::max(KnownZero.countLeadingOnes(), |
| KnownZero2.countLeadingOnes()); |
| KnownOne.clear(); |
| KnownZero = APInt::getHighBitsSet(BitWidth, Leaders) & Mask; |
| break; |
| } |
| |
| case Instruction::Alloca: |
| case Instruction::Malloc: { |
| AllocationInst *AI = cast<AllocationInst>(V); |
| unsigned Align = AI->getAlignment(); |
| if (Align == 0 && TD) { |
| if (isa<AllocaInst>(AI)) |
| Align = TD->getPrefTypeAlignment(AI->getType()->getElementType()); |
| else if (isa<MallocInst>(AI)) { |
| // Malloc returns maximally aligned memory. |
| Align = TD->getABITypeAlignment(AI->getType()->getElementType()); |
| Align = |
| std::max(Align, |
| (unsigned)TD->getABITypeAlignment(Type::DoubleTy)); |
| Align = |
| std::max(Align, |
| (unsigned)TD->getABITypeAlignment(Type::Int64Ty)); |
| } |
| } |
| |
| 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 (const 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. |
| const Type *IndexedTy = GTI.getIndexedType(); |
| if (!IndexedTy->isSized()) return; |
| unsigned GEPOpiBits = Index->getType()->getPrimitiveSizeInBits(); |
| uint64_t TypeSize = TD ? TD->getABITypeSize(IndexedTy) : 1; |
| LocalMask = APInt::getAllOnesValue(GEPOpiBits); |
| LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0); |
| ComputeMaskedBits(Index, LocalMask, |
| LocalKnownZero, LocalKnownOne, TD, Depth+1); |
| TrailZ = std::min(TrailZ, |
| 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); |
| User *LU = dyn_cast<User>(L); |
| if (!LU) |
| continue; |
| unsigned Opcode = getOpcode(LU); |
| // 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()); |
| KnownOne2.clear(); |
| KnownZero2.clear(); |
| ComputeMaskedBits(L, Mask2, KnownZero2, KnownOne2, TD, Depth+1); |
| KnownZero = Mask & |
| APInt::getLowBitsSet(BitWidth, |
| KnownZero2.countTrailingOnes()); |
| 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; |
| } |
| } |
| } |
| break; |
| } |
| } |
| |
| /// 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. |
| bool llvm::MaskedValueIsZero(Value *V, const APInt &Mask, |
| 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, TargetData *TD, unsigned Depth) { |
| const IntegerType *Ty = cast<IntegerType>(V->getType()); |
| unsigned TyBits = Ty->getBitWidth(); |
| 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. |
| |
| User *U = dyn_cast<User>(V); |
| switch (getOpcode(V)) { |
| default: break; |
| case Instruction::SExt: |
| Tmp = TyBits-cast<IntegerType>(U->getOperand(0)->getType())->getBitWidth(); |
| 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; |
| } |
| 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(0))) |
| 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; |
| break; |
| |
| 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; |
| break; |
| 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())); |
| } |
| |
| /// 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 Instruction *I = dyn_cast<Instruction>(V); |
| if (I == 0) return false; |
| |
| // (add x, 0.0) is guaranteed to return +0.0, not -0.0. |
| if (I->getOpcode() == Instruction::Add && |
| 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->getOperand(1), Depth+1); |
| |
| if (const CallInst *CI = dyn_cast<CallInst>(I)) |
| if (const Function *F = CI->getCalledFunction()) { |
| if (F->isDeclaration()) { |
| switch (F->getNameLen()) { |
| case 3: // abs(x) != -0.0 |
| if (!strcmp(F->getNameStart(), "abs")) return true; |
| break; |
| case 4: // abs[lf](x) != -0.0 |
| if (!strcmp(F->getNameStart(), "absf")) return true; |
| if (!strcmp(F->getNameStart(), "absl")) return true; |
| break; |
| } |
| } |
| } |
| |
| return false; |
| } |
| |
| // 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. |
| Value *BuildSubAggregate(Value *From, Value* To, const Type *IndexedType, |
| SmallVector<unsigned, 10> &Idxs, |
| unsigned IdxSkip, |
| Instruction *InsertBefore) { |
| const 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 succesfully 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.begin(), Idxs.end()); |
| |
| if (!V) |
| return NULL; |
| |
| // Insert the value in the new (sub) aggregrate |
| return llvm::InsertValueInst::Create(To, V, Idxs.begin() + IdxSkip, |
| Idxs.end(), "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 |
| Value *BuildSubAggregate(Value *From, const unsigned *idx_begin, |
| const unsigned *idx_end, Instruction *InsertBefore) { |
| assert(InsertBefore && "Must have someplace to insert!"); |
| const Type *IndexedType = ExtractValueInst::getIndexedType(From->getType(), |
| idx_begin, |
| idx_end); |
| Value *To = UndefValue::get(IndexedType); |
| SmallVector<unsigned, 10> Idxs(idx_begin, idx_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, const unsigned *idx_begin, |
| const unsigned *idx_end, Instruction *InsertBefore) { |
| // Nothing to index? Just return V then (this is useful at the end of our |
| // recursion) |
| if (idx_begin == idx_end) |
| return V; |
| // We have indices, so V should have an indexable type |
| assert((isa<StructType>(V->getType()) || isa<ArrayType>(V->getType())) |
| && "Not looking at a struct or array?"); |
| assert(ExtractValueInst::getIndexedType(V->getType(), idx_begin, idx_end) |
| && "Invalid indices for type?"); |
| const CompositeType *PTy = cast<CompositeType>(V->getType()); |
| |
| if (isa<UndefValue>(V)) |
| return UndefValue::get(ExtractValueInst::getIndexedType(PTy, |
| idx_begin, |
| idx_end)); |
| else if (isa<ConstantAggregateZero>(V)) |
| return Constant::getNullValue(ExtractValueInst::getIndexedType(PTy, |
| idx_begin, |
| idx_end)); |
| else if (Constant *C = dyn_cast<Constant>(V)) { |
| if (isa<ConstantArray>(C) || isa<ConstantStruct>(C)) |
| // Recursively process this constant |
| return FindInsertedValue(C->getOperand(*idx_begin), idx_begin + 1, idx_end, |
| 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_begin; |
| for (const unsigned *i = I->idx_begin(), *e = I->idx_end(); |
| i != e; ++i, ++req_idx) { |
| if (req_idx == idx_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, idx_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_begin, idx_end, |
| 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(), req_idx, idx_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_end - idx_begin); |
| // Allocate some space to put the new indices in |
| SmallVector<unsigned, 5> Idxs; |
| Idxs.reserve(size); |
| // Add indices from the extract value instruction |
| for (const unsigned *i = I->idx_begin(), *e = I->idx_end(); |
| i != e; ++i) |
| Idxs.push_back(*i); |
| |
| // Add requested indices |
| for (const unsigned *i = idx_begin, *e = idx_end; i != e; ++i) |
| Idxs.push_back(*i); |
| |
| assert(Idxs.size() == size |
| && "Number of indices added not correct?"); |
| |
| return FindInsertedValue(I->getAggregateOperand(), Idxs.begin(), Idxs.end(), |
| InsertBefore); |
| } |
| // Otherwise, we don't know (such as, extracting from a function return value |
| // or load instruction) |
| return 0; |
| } |
| |
| /// 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(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 (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 |
| User *GEP = 0; |
| if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(V)) { |
| GEP = GEPI; |
| } else if (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. |
| const PointerType *PT = cast<PointerType>(GEP->getOperand(0)->getType()); |
| const ArrayType *AT = dyn_cast<ArrayType>(PT->getElementType()); |
| if (AT == 0 || AT->getElementType() != Type::Int8Ty) |
| 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. |
| 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 (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. |
| GlobalVariable* GV = dyn_cast<GlobalVariable>(V); |
| if (!GV || !GV->isConstant() || !GV->hasInitializer()) |
| return false; |
| 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 |
| ConstantArray *Array = dyn_cast<ConstantArray>(GlobalInit); |
| if (Array == 0 || Array->getType()->getElementType() != Type::Int8Ty) |
| 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) { |
| Constant *Elt = Array->getOperand(i); |
| 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; |
| } |
