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Diffstat (limited to 'contrib/llvm/lib/Analysis/ValueTracking.cpp')
| -rw-r--r-- | contrib/llvm/lib/Analysis/ValueTracking.cpp | 2034 |
1 files changed, 2034 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Analysis/ValueTracking.cpp b/contrib/llvm/lib/Analysis/ValueTracking.cpp new file mode 100644 index 0000000..45dcc5e --- /dev/null +++ b/contrib/llvm/lib/Analysis/ValueTracking.cpp @@ -0,0 +1,2034 @@ +//===- 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/ADT/SmallPtrSet.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/GlobalAlias.h" +#include "llvm/IR/GlobalVariable.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/IR/Metadata.h" +#include "llvm/IR/Operator.h" +#include "llvm/Support/ConstantRange.h" +#include "llvm/Support/GetElementPtrTypeIterator.h" +#include "llvm/Support/MathExtras.h" +#include "llvm/Support/PatternMatch.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 DataLayout *TD) { + if (unsigned BitWidth = Ty->getScalarSizeInBits()) + return BitWidth; + assert(isa<PointerType>(Ty) && "Expected a pointer type!"); + return TD ? TD->getPointerSizeInBits() : 0; +} + +static void ComputeMaskedBitsAddSub(bool Add, Value *Op0, Value *Op1, bool NSW, + APInt &KnownZero, APInt &KnownOne, + APInt &KnownZero2, APInt &KnownOne2, + const DataLayout *TD, unsigned Depth) { + if (!Add) { + if (ConstantInt *CLHS = dyn_cast<ConstantInt>(Op0)) { + // We know that the top bits of C-X are clear if X contains less bits + // than C (i.e. no wrap-around can happen). For example, 20-X is + // positive if we can prove that X is >= 0 and < 16. + if (!CLHS->getValue().isNegative()) { + unsigned BitWidth = KnownZero.getBitWidth(); + unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros(); + // NLZ can't be BitWidth with no sign bit + APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1); + llvm::ComputeMaskedBits(Op1, 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); + } + } + } + } + + unsigned BitWidth = KnownZero.getBitWidth(); + + // If one of the operands has trailing zeros, then the bits that the + // other operand has in those bit positions will be preserved in the + // result. For an add, this works with either operand. For a subtract, + // this only works if the known zeros are in the right operand. + APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0); + llvm::ComputeMaskedBits(Op0, LHSKnownZero, LHSKnownOne, TD, Depth+1); + assert((LHSKnownZero & LHSKnownOne) == 0 && + "Bits known to be one AND zero?"); + unsigned LHSKnownZeroOut = LHSKnownZero.countTrailingOnes(); + + llvm::ComputeMaskedBits(Op1, KnownZero2, KnownOne2, TD, Depth+1); + assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); + unsigned RHSKnownZeroOut = KnownZero2.countTrailingOnes(); + + // Determine which operand has more trailing zeros, and use that + // many bits from the other operand. + if (LHSKnownZeroOut > RHSKnownZeroOut) { + if (Add) { + APInt Mask = APInt::getLowBitsSet(BitWidth, LHSKnownZeroOut); + KnownZero |= KnownZero2 & Mask; + KnownOne |= KnownOne2 & Mask; + } else { + // If the known zeros are in the left operand for a subtract, + // fall back to the minimum known zeros in both operands. + KnownZero |= APInt::getLowBitsSet(BitWidth, + std::min(LHSKnownZeroOut, + RHSKnownZeroOut)); + } + } else if (RHSKnownZeroOut >= LHSKnownZeroOut) { + APInt Mask = APInt::getLowBitsSet(BitWidth, RHSKnownZeroOut); + KnownZero |= LHSKnownZero & Mask; + KnownOne |= LHSKnownOne & Mask; + } + + // Are we still trying to solve for the sign bit? + if (!KnownZero.isNegative() && !KnownOne.isNegative()) { + if (NSW) { + if (Add) { + // Adding two positive numbers can't wrap into negative + if (LHSKnownZero.isNegative() && KnownZero2.isNegative()) + KnownZero |= APInt::getSignBit(BitWidth); + // and adding two negative numbers can't wrap into positive. + else if (LHSKnownOne.isNegative() && KnownOne2.isNegative()) + KnownOne |= APInt::getSignBit(BitWidth); + } else { + // Subtracting a negative number from a positive one can't wrap + if (LHSKnownZero.isNegative() && KnownOne2.isNegative()) + KnownZero |= APInt::getSignBit(BitWidth); + // neither can subtracting a positive number from a negative one. + else if (LHSKnownOne.isNegative() && KnownZero2.isNegative()) + KnownOne |= APInt::getSignBit(BitWidth); + } + } + } +} + +static void ComputeMaskedBitsMul(Value *Op0, Value *Op1, bool NSW, + APInt &KnownZero, APInt &KnownOne, + APInt &KnownZero2, APInt &KnownOne2, + const DataLayout *TD, unsigned Depth) { + unsigned BitWidth = KnownZero.getBitWidth(); + ComputeMaskedBits(Op1, KnownZero, KnownOne, TD, Depth+1); + ComputeMaskedBits(Op0, 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?"); + + bool isKnownNegative = false; + bool isKnownNonNegative = false; + // If the multiplication is known not to overflow, compute the sign bit. + if (NSW) { + if (Op0 == Op1) { + // The product of a number with itself is non-negative. + isKnownNonNegative = true; + } else { + bool isKnownNonNegativeOp1 = KnownZero.isNegative(); + bool isKnownNonNegativeOp0 = KnownZero2.isNegative(); + bool isKnownNegativeOp1 = KnownOne.isNegative(); + bool isKnownNegativeOp0 = KnownOne2.isNegative(); + // The product of two numbers with the same sign is non-negative. + isKnownNonNegative = (isKnownNegativeOp1 && isKnownNegativeOp0) || + (isKnownNonNegativeOp1 && isKnownNonNegativeOp0); + // The product of a negative number and a non-negative number is either + // negative or zero. + if (!isKnownNonNegative) + isKnownNegative = (isKnownNegativeOp1 && isKnownNonNegativeOp0 && + isKnownNonZero(Op0, TD, Depth)) || + (isKnownNegativeOp0 && isKnownNonNegativeOp1 && + isKnownNonZero(Op1, TD, Depth)); + } + } + + // 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); + + // Only make use of no-wrap flags if we failed to compute the sign bit + // directly. This matters if the multiplication always overflows, in + // which case we prefer to follow the result of the direct computation, + // though as the program is invoking undefined behaviour we can choose + // whatever we like here. + if (isKnownNonNegative && !KnownOne.isNegative()) + KnownZero.setBit(BitWidth - 1); + else if (isKnownNegative && !KnownZero.isNegative()) + KnownOne.setBit(BitWidth - 1); +} + +void llvm::computeMaskedBitsLoad(const MDNode &Ranges, APInt &KnownZero) { + unsigned BitWidth = KnownZero.getBitWidth(); + unsigned NumRanges = Ranges.getNumOperands() / 2; + assert(NumRanges >= 1); + + // Use the high end of the ranges to find leading zeros. + unsigned MinLeadingZeros = BitWidth; + for (unsigned i = 0; i < NumRanges; ++i) { + ConstantInt *Lower = cast<ConstantInt>(Ranges.getOperand(2*i + 0)); + ConstantInt *Upper = cast<ConstantInt>(Ranges.getOperand(2*i + 1)); + ConstantRange Range(Lower->getValue(), Upper->getValue()); + if (Range.isWrappedSet()) + MinLeadingZeros = 0; // -1 has no zeros + unsigned LeadingZeros = (Upper->getValue() - 1).countLeadingZeros(); + MinLeadingZeros = std::min(LeadingZeros, MinLeadingZeros); + } + + KnownZero = APInt::getHighBitsSet(BitWidth, MinLeadingZeros); +} +/// ComputeMaskedBits - Determine which of the bits are known to be either zero +/// or one and return them in the KnownZero/KnownOne bit sets. +/// +/// 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, 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, APInt &KnownZero, APInt &KnownOne, + const DataLayout *TD, unsigned Depth) { + assert(V && "No Value?"); + assert(Depth <= MaxDepth && "Limit Search Depth"); + unsigned BitWidth = KnownZero.getBitWidth(); + + assert((V->getType()->isIntOrIntVectorTy() || + V->getType()->getScalarType()->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(); + KnownZero = ~KnownOne; + return; + } + // Null and aggregate-zero are all-zeros. + if (isa<ConstantPointerNull>(V) || + isa<ConstantAggregateZero>(V)) { + KnownOne.clearAllBits(); + KnownZero = APInt::getAllOnesValue(BitWidth); + return; + } + // Handle a constant vector by taking the intersection of the known bits of + // each element. There is no real need to handle ConstantVector here, because + // we don't handle undef in any particularly useful way. + if (ConstantDataSequential *CDS = dyn_cast<ConstantDataSequential>(V)) { + // We know that CDS must be a vector of integers. Take the intersection of + // each element. + KnownZero.setAllBits(); KnownOne.setAllBits(); + APInt Elt(KnownZero.getBitWidth(), 0); + for (unsigned i = 0, e = CDS->getNumElements(); i != e; ++i) { + Elt = CDS->getElementAsInteger(i); + KnownZero &= ~Elt; + KnownOne &= Elt; + } + 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) { + if (GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV)) { + Type *ObjectType = GVar->getType()->getElementType(); + if (ObjectType->isSized()) { + // 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 (!GVar->isDeclaration() && !GVar->isWeakForLinker()) + Align = TD->getPreferredAlignment(GVar); + else + Align = TD->getABITypeAlignment(ObjectType); + } + } + } + if (Align > 0) + KnownZero = 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(), KnownZero, KnownOne, TD, Depth+1); + } + return; + } + + if (Argument *A = dyn_cast<Argument>(V)) { + unsigned Align = 0; + + if (A->hasByValAttr()) { + // Get alignment information off byval arguments if specified in the IR. + Align = A->getParamAlignment(); + } else if (TD && A->hasStructRetAttr()) { + // An sret parameter has at least the ABI alignment of the return type. + Type *EltTy = cast<PointerType>(A->getType())->getElementType(); + if (EltTy->isSized()) + Align = TD->getABITypeAlignment(EltTy); + } + + if (Align) + KnownZero = APInt::getLowBitsSet(BitWidth, CountTrailingZeros_32(Align)); + return; + } + + // Start out not knowing anything. + KnownZero.clearAllBits(); KnownOne.clearAllBits(); + + if (Depth == MaxDepth) + 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::Load: + if (MDNode *MD = cast<LoadInst>(I)->getMetadata(LLVMContext::MD_range)) + computeMaskedBitsLoad(*MD, KnownZero); + return; + case Instruction::And: { + // If either the LHS or the RHS are Zero, the result is zero. + ComputeMaskedBits(I->getOperand(1), KnownZero, KnownOne, TD, Depth+1); + ComputeMaskedBits(I->getOperand(0), 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), KnownZero, KnownOne, TD, Depth+1); + ComputeMaskedBits(I->getOperand(0), 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), KnownZero, KnownOne, TD, Depth+1); + ComputeMaskedBits(I->getOperand(0), 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: { + bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap(); + ComputeMaskedBitsMul(I->getOperand(0), I->getOperand(1), NSW, + KnownZero, KnownOne, KnownZero2, KnownOne2, TD, Depth); + break; + } + 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. + ComputeMaskedBits(I->getOperand(0), KnownZero2, KnownOne2, TD, Depth+1); + unsigned LeadZ = KnownZero2.countLeadingOnes(); + + KnownOne2.clearAllBits(); + KnownZero2.clearAllBits(); + ComputeMaskedBits(I->getOperand(1), 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); + return; + } + case Instruction::Select: + ComputeMaskedBits(I->getOperand(2), KnownZero, KnownOne, TD, Depth+1); + ComputeMaskedBits(I->getOperand(1), 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(TD) { + SrcBitWidth = TD->getTypeSizeInBits(SrcTy->getScalarType()); + } else { + SrcBitWidth = SrcTy->getScalarSizeInBits(); + if (!SrcBitWidth) return; + } + + assert(SrcBitWidth && "SrcBitWidth can't be zero"); + KnownZero = KnownZero.zextOrTrunc(SrcBitWidth); + KnownOne = KnownOne.zextOrTrunc(SrcBitWidth); + ComputeMaskedBits(I->getOperand(0), 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), 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(); + + KnownZero = KnownZero.trunc(SrcBitWidth); + KnownOne = KnownOne.trunc(SrcBitWidth); + ComputeMaskedBits(I->getOperand(0), 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); + ComputeMaskedBits(I->getOperand(0), 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. + ComputeMaskedBits(I->getOperand(0), 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. + ComputeMaskedBits(I->getOperand(0), 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: { + bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap(); + ComputeMaskedBitsAddSub(false, I->getOperand(0), I->getOperand(1), NSW, + KnownZero, KnownOne, KnownZero2, KnownOne2, TD, + Depth); + break; + } + case Instruction::Add: { + bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap(); + ComputeMaskedBitsAddSub(true, I->getOperand(0), I->getOperand(1), NSW, + KnownZero, KnownOne, KnownZero2, KnownOne2, TD, + Depth); + break; + } + case Instruction::SRem: + if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) { + APInt RA = Rem->getValue().abs(); + if (RA.isPowerOf2()) { + APInt LowBits = RA - 1; + ComputeMaskedBits(I->getOperand(0), 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; + + 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 (KnownZero.isNonNegative()) { + APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0); + ComputeMaskedBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, TD, + Depth+1); + // If it's known zero, our sign bit is also zero. + if (LHSKnownZero.isNegative()) + KnownZero.setBit(BitWidth - 1); + } + + break; + case Instruction::URem: { + if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) { + APInt RA = Rem->getValue(); + if (RA.isPowerOf2()) { + APInt LowBits = (RA - 1); + ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD, + Depth+1); + assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); + KnownZero |= ~LowBits; + KnownOne &= LowBits; + 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. + ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1); + ComputeMaskedBits(I->getOperand(1), KnownZero2, KnownOne2, TD, Depth+1); + + unsigned Leaders = std::max(KnownZero.countLeadingOnes(), + KnownZero2.countLeadingOnes()); + KnownOne.clearAllBits(); + KnownZero = APInt::getHighBitsSet(BitWidth, Leaders); + 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 = 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 LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0); + ComputeMaskedBits(I->getOperand(0), 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; + LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0); + ComputeMaskedBits(Index, LocalKnownZero, LocalKnownOne, TD, Depth+1); + TrailZ = std::min(TrailZ, + unsigned(CountTrailingZeros_64(TypeSize) + + LocalKnownZero.countTrailingOnes())); + } + } + + KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ); + 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. + ComputeMaskedBits(R, KnownZero2, KnownOne2, TD, Depth+1); + + // We need to take the minimum number of known bits + APInt KnownZero3(KnownZero), KnownOne3(KnownOne); + ComputeMaskedBits(L, KnownZero3, KnownOne3, TD, Depth+1); + + KnownZero = 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 (dyn_cast_or_null<UndefValue>(P->hasConstantValue())) + 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), 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::ctlz: + case Intrinsic::cttz: { + unsigned LowBits = Log2_32(BitWidth)+1; + // If this call is undefined for 0, the result will be less than 2^n. + if (II->getArgOperand(1) == ConstantInt::getTrue(II->getContext())) + LowBits -= 1; + KnownZero = APInt::getHighBitsSet(BitWidth, BitWidth - LowBits); + break; + } + case Intrinsic::ctpop: { + 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; + case Instruction::ExtractValue: + if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I->getOperand(0))) { + ExtractValueInst *EVI = cast<ExtractValueInst>(I); + if (EVI->getNumIndices() != 1) break; + if (EVI->getIndices()[0] == 0) { + switch (II->getIntrinsicID()) { + default: break; + case Intrinsic::uadd_with_overflow: + case Intrinsic::sadd_with_overflow: + ComputeMaskedBitsAddSub(true, II->getArgOperand(0), + II->getArgOperand(1), false, KnownZero, + KnownOne, KnownZero2, KnownOne2, TD, Depth); + break; + case Intrinsic::usub_with_overflow: + case Intrinsic::ssub_with_overflow: + ComputeMaskedBitsAddSub(false, II->getArgOperand(0), + II->getArgOperand(1), false, KnownZero, + KnownOne, KnownZero2, KnownOne2, TD, Depth); + break; + case Intrinsic::umul_with_overflow: + case Intrinsic::smul_with_overflow: + ComputeMaskedBitsMul(II->getArgOperand(0), II->getArgOperand(1), + false, KnownZero, KnownOne, + KnownZero2, KnownOne2, TD, Depth); + 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 DataLayout *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, ZeroBits, OneBits, TD, Depth); + KnownOne = OneBits[BitWidth - 1]; + KnownZero = ZeroBits[BitWidth - 1]; +} + +/// isKnownToBeAPowerOfTwo - 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::isKnownToBeAPowerOfTwo(Value *V, bool OrZero, unsigned Depth) { + if (Constant *C = dyn_cast<Constant>(V)) { + if (C->isNullValue()) + return OrZero; + if (ConstantInt *CI = dyn_cast<ConstantInt>(C)) + 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; + + Value *X = 0, *Y = 0; + // A shift of a power of two is a power of two or zero. + if (OrZero && (match(V, m_Shl(m_Value(X), m_Value())) || + match(V, m_Shr(m_Value(X), m_Value())))) + return isKnownToBeAPowerOfTwo(X, /*OrZero*/true, Depth); + + if (ZExtInst *ZI = dyn_cast<ZExtInst>(V)) + return isKnownToBeAPowerOfTwo(ZI->getOperand(0), OrZero, Depth); + + if (SelectInst *SI = dyn_cast<SelectInst>(V)) + return isKnownToBeAPowerOfTwo(SI->getTrueValue(), OrZero, Depth) && + isKnownToBeAPowerOfTwo(SI->getFalseValue(), OrZero, Depth); + + if (OrZero && match(V, m_And(m_Value(X), m_Value(Y)))) { + // A power of two and'd with anything is a power of two or zero. + if (isKnownToBeAPowerOfTwo(X, /*OrZero*/true, Depth) || + isKnownToBeAPowerOfTwo(Y, /*OrZero*/true, Depth)) + return true; + // X & (-X) is always a power of two or zero. + if (match(X, m_Neg(m_Specific(Y))) || match(Y, m_Neg(m_Specific(X)))) + return true; + return false; + } + + // 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_Exact(m_LShr(m_Value(), m_Value()))) || + match(V, m_Exact(m_UDiv(m_Value(), m_Value())))) { + return isKnownToBeAPowerOfTwo(cast<Operator>(V)->getOperand(0), OrZero, Depth); + } + + return false; +} + +/// \brief Test whether a GEP's result is known to be non-null. +/// +/// Uses properties inherent in a GEP to try to determine whether it is known +/// to be non-null. +/// +/// Currently this routine does not support vector GEPs. +static bool isGEPKnownNonNull(GEPOperator *GEP, const DataLayout *DL, + unsigned Depth) { + if (!GEP->isInBounds() || GEP->getPointerAddressSpace() != 0) + return false; + + // FIXME: Support vector-GEPs. + assert(GEP->getType()->isPointerTy() && "We only support plain pointer GEP"); + + // If the base pointer is non-null, we cannot walk to a null address with an + // inbounds GEP in address space zero. + if (isKnownNonZero(GEP->getPointerOperand(), DL, Depth)) + return true; + + // Past this, if we don't have DataLayout, we can't do much. + if (!DL) + return false; + + // Walk the GEP operands and see if any operand introduces a non-zero offset. + // If so, then the GEP cannot produce a null pointer, as doing so would + // inherently violate the inbounds contract within address space zero. + for (gep_type_iterator GTI = gep_type_begin(GEP), GTE = gep_type_end(GEP); + GTI != GTE; ++GTI) { + // Struct types are easy -- they must always be indexed by a constant. + if (StructType *STy = dyn_cast<StructType>(*GTI)) { + ConstantInt *OpC = cast<ConstantInt>(GTI.getOperand()); + unsigned ElementIdx = OpC->getZExtValue(); + const StructLayout *SL = DL->getStructLayout(STy); + uint64_t ElementOffset = SL->getElementOffset(ElementIdx); + if (ElementOffset > 0) + return true; + continue; + } + + // If we have a zero-sized type, the index doesn't matter. Keep looping. + if (DL->getTypeAllocSize(GTI.getIndexedType()) == 0) + continue; + + // Fast path the constant operand case both for efficiency and so we don't + // increment Depth when just zipping down an all-constant GEP. + if (ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand())) { + if (!OpC->isZero()) + return true; + continue; + } + + // We post-increment Depth here because while isKnownNonZero increments it + // as well, when we pop back up that increment won't persist. We don't want + // to recurse 10k times just because we have 10k GEP operands. We don't + // bail completely out because we want to handle constant GEPs regardless + // of depth. + if (Depth++ >= MaxDepth) + continue; + + if (isKnownNonZero(GTI.getOperand(), DL, Depth)) + return true; + } + + 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 DataLayout *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; + + // Check for pointer simplifications. + if (V->getType()->isPointerTy()) { + if (isKnownNonNull(V)) + return true; + if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) + if (isGEPKnownNonNull(GEP, TD, Depth)) + return true; + } + + unsigned BitWidth = getBitWidth(V->getType()->getScalarType(), 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. + OverflowingBinaryOperator *BO = cast<OverflowingBinaryOperator>(V); + if (BO->hasNoUnsignedWrap()) + return isKnownNonZero(X, TD, Depth); + + APInt KnownZero(BitWidth, 0); + APInt KnownOne(BitWidth, 0); + ComputeMaskedBits(X, 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. + PossiblyExactOperator *BO = cast<PossiblyExactOperator>(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_Exact(m_IDiv(m_Value(X), m_Value())))) { + 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, 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, 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 && isKnownToBeAPowerOfTwo(Y, /*OrZero*/false, Depth)) + return true; + if (YKnownNonNegative && isKnownToBeAPowerOfTwo(X, /*OrZero*/false, Depth)) + return true; + } + // X * Y. + else if (match(V, m_Mul(m_Value(X), m_Value(Y)))) { + OverflowingBinaryOperator *BO = cast<OverflowingBinaryOperator>(V); + // If X and Y are non-zero then so is X * Y as long as the multiplication + // does not overflow. + if ((BO->hasNoSignedWrap() || BO->hasNoUnsignedWrap()) && + isKnownNonZero(X, TD, Depth) && isKnownNonZero(Y, 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, 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 DataLayout *TD, unsigned Depth) { + APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0); + ComputeMaskedBits(V, 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 DataLayout *TD, + unsigned Depth) { + assert((TD || V->getType()->isIntOrIntVectorTy()) && + "ComputeNumSignBits requires a DataLayout 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. Vectors too. + const APInt *ShAmt; + if (match(U->getOperand(1), m_APInt(ShAmt))) { + Tmp += ShAmt->getZExtValue(); + if (Tmp > TyBits) Tmp = TyBits; + } + return Tmp; + } + case Instruction::Shl: { + const APInt *ShAmt; + if (match(U->getOperand(1), m_APInt(ShAmt))) { + // shl destroys sign bits. + Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1); + Tmp2 = ShAmt->getZExtValue(); + if (Tmp2 >= TyBits || // Bad shift. + Tmp2 >= Tmp) break; // Shifted all sign bits out. + return Tmp - Tmp2; + } + 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); + ComputeMaskedBits(U->getOperand(0), 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)).isAllOnesValue()) + 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); + ComputeMaskedBits(U->getOperand(1), 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)).isAllOnesValue()) + 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; + ComputeMaskedBits(V, 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; + + // Check if the nsz fast-math flag is set + if (const FPMathOperator *FPO = dyn_cast<FPMathOperator>(I)) + if (FPO->hasNoSignedZeros()) + return true; + + // (add x, 0.0) is guaranteed to return +0.0, not -0.0. + if (I->getOpcode() == Instruction::FAdd) + if (ConstantFP *CFP = dyn_cast<ConstantFP>(I->getOperand(1))) + if (CFP->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 ConstantDataArray/Vector is splatable if all its members are equal and + // also splatable. + if (ConstantDataSequential *CA = dyn_cast<ConstantDataSequential>(V)) { + Value *Elt = CA->getElementAsConstant(0); + Value *Val = isBytewiseValue(Elt); + if (!Val) + return 0; + + for (unsigned I = 1, E = CA->getNumElements(); I != E; ++I) + if (CA->getElementAsConstant(I) != Elt) + 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 = 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?"); + + if (Constant *C = dyn_cast<Constant>(V)) { + C = C->getAggregateElement(idx_range[0]); + if (C == 0) return 0; + return FindInsertedValue(C, idx_range.slice(1), InsertBefore); + } + + 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()) { + // We can't handle this without inserting insertvalues + if (!InsertBefore) + return 0; + + // 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); + } + + // 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); + } + + 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 DataLayout *TD) { + // Without DataLayout, conservatively assume 64-bit offsets, which is + // the widest we support. + unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64; + APInt ByteOffset(BitWidth, 0); + while (1) { + if (Ptr->getType()->isVectorTy()) + break; + + if (GEPOperator *GEP = dyn_cast<GEPOperator>(Ptr)) { + APInt GEPOffset(BitWidth, 0); + if (TD && !GEP->accumulateConstantOffset(*TD, GEPOffset)) + break; + ByteOffset += GEPOffset; + Ptr = GEP->getPointerOperand(); + } else if (Operator::getOpcode(Ptr) == Instruction::BitCast) { + Ptr = cast<Operator>(Ptr)->getOperand(0); + } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(Ptr)) { + if (GA->mayBeOverridden()) + break; + Ptr = GA->getAliasee(); + } else { + break; + } + } + Offset = ByteOffset.getSExtValue(); + return Ptr; +} + + +/// 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, StringRef &Str, + uint64_t Offset, bool TrimAtNul) { + assert(V); + + // Look through bitcast instructions and geps. + V = V->stripPointerCasts(); + + // If the value is a GEP instructionor constant expression, treat it as an + // offset. + if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) { + // 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); + } + + // 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; + + // Handle the all-zeros case + if (GV->getInitializer()->isNullValue()) { + // This is a degenerate case. The initializer is constant zero so the + // length of the string must be zero. + Str = ""; + return true; + } + + // Must be a Constant Array + const ConstantDataArray *Array = + dyn_cast<ConstantDataArray>(GV->getInitializer()); + if (Array == 0 || !Array->isString()) + return false; + + // Get the number of elements in the array + uint64_t NumElts = Array->getType()->getArrayNumElements(); + + // Start out with the entire array in the StringRef. + Str = Array->getAsString(); + + if (Offset > NumElts) + return false; + + // Skip over 'offset' bytes. + Str = Str.substr(Offset); + + if (TrimAtNul) { + // Trim off the \0 and anything after it. If the array is not nul + // terminated, we just return the whole end of string. The client may know + // some other way that the string is length-bound. + Str = Str.substr(0, Str.find('\0')); + } + 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. + V = V->stripPointerCasts(); + + // 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; + } + + // Otherwise, see if we can read the string. + StringRef StrData; + if (!getConstantStringInfo(V, StrData)) + return 0; + + return StrData.size()+1; +} + +/// 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 DataLayout *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; +} + +void +llvm::GetUnderlyingObjects(Value *V, + SmallVectorImpl<Value *> &Objects, + const DataLayout *TD, + unsigned MaxLookup) { + SmallPtrSet<Value *, 4> Visited; + SmallVector<Value *, 4> Worklist; + Worklist.push_back(V); + do { + Value *P = Worklist.pop_back_val(); + P = GetUnderlyingObject(P, TD, MaxLookup); + + if (!Visited.insert(P)) + continue; + + if (SelectInst *SI = dyn_cast<SelectInst>(P)) { + Worklist.push_back(SI->getTrueValue()); + Worklist.push_back(SI->getFalseValue()); + continue; + } + + if (PHINode *PN = dyn_cast<PHINode>(P)) { + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) + Worklist.push_back(PN->getIncomingValue(i)); + continue; + } + + Objects.push_back(P); + } while (!Worklist.empty()); +} + +/// 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; +} + +bool llvm::isSafeToSpeculativelyExecute(const Value *V, + const DataLayout *TD) { + const Operator *Inst = dyn_cast<Operator>(V); + if (!Inst) + return false; + + for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i) + if (Constant *C = dyn_cast<Constant>(Inst->getOperand(i))) + if (C->canTrap()) + return false; + + switch (Inst->getOpcode()) { + default: + return true; + case Instruction::UDiv: + case Instruction::URem: + // x / y is undefined if y == 0, but calcuations like x / 3 are safe. + return isKnownNonZero(Inst->getOperand(1), TD); + case Instruction::SDiv: + case Instruction::SRem: { + Value *Op = Inst->getOperand(1); + // x / y is undefined if y == 0 + if (!isKnownNonZero(Op, TD)) + return false; + // x / y might be undefined if y == -1 + unsigned BitWidth = getBitWidth(Op->getType(), TD); + if (BitWidth == 0) + return false; + APInt KnownZero(BitWidth, 0); + APInt KnownOne(BitWidth, 0); + ComputeMaskedBits(Op, KnownZero, KnownOne, TD); + return !!KnownZero; + } + case Instruction::Load: { + const LoadInst *LI = cast<LoadInst>(Inst); + if (!LI->isUnordered()) + return false; + return LI->getPointerOperand()->isDereferenceablePointer(); + } + case Instruction::Call: { + if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) { + switch (II->getIntrinsicID()) { + // These synthetic intrinsics have no side-effects, and just mark + // information about their operands. + // FIXME: There are other no-op synthetic instructions that potentially + // should be considered at least *safe* to speculate... + case Intrinsic::dbg_declare: + case Intrinsic::dbg_value: + return true; + + case Intrinsic::bswap: + case Intrinsic::ctlz: + case Intrinsic::ctpop: + case Intrinsic::cttz: + case Intrinsic::objectsize: + case Intrinsic::sadd_with_overflow: + case Intrinsic::smul_with_overflow: + case Intrinsic::ssub_with_overflow: + case Intrinsic::uadd_with_overflow: + case Intrinsic::umul_with_overflow: + case Intrinsic::usub_with_overflow: + return true; + // TODO: some fp intrinsics are marked as having the same error handling + // as libm. They're safe to speculate when they won't error. + // TODO: are convert_{from,to}_fp16 safe? + // TODO: can we list target-specific intrinsics here? + default: break; + } + } + return false; // The called function could have undefined behavior or + // side-effects, even if marked readnone nounwind. + } + case Instruction::VAArg: + case Instruction::Alloca: + case Instruction::Invoke: + case Instruction::PHI: + case Instruction::Store: + case Instruction::Ret: + case Instruction::Br: + case Instruction::IndirectBr: + case Instruction::Switch: + case Instruction::Unreachable: + case Instruction::Fence: + case Instruction::LandingPad: + case Instruction::AtomicRMW: + case Instruction::AtomicCmpXchg: + case Instruction::Resume: + return false; // Misc instructions which have effects + } +} + +/// isKnownNonNull - Return true if we know that the specified value is never +/// null. +bool llvm::isKnownNonNull(const Value *V) { + // Alloca never returns null, malloc might. + if (isa<AllocaInst>(V)) return true; + + // A byval argument is never null. + if (const Argument *A = dyn_cast<Argument>(V)) + return A->hasByValAttr(); + + // Global values are not null unless extern weak. + if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) + return !GV->hasExternalWeakLinkage(); + return false; +} |
