From e264f62ca09a8f65c87a46d562a4d0f9ec5d457e Mon Sep 17 00:00:00 2001 From: Shih-wei Liao Date: Wed, 10 Feb 2010 11:10:31 -0800 Subject: Check in LLVM r95781. --- lib/Analysis/ValueTracking.cpp | 1438 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 1438 insertions(+) create mode 100644 lib/Analysis/ValueTracking.cpp (limited to 'lib/Analysis/ValueTracking.cpp') diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp new file mode 100644 index 0000000000..f9331e76d0 --- /dev/null +++ b/lib/Analysis/ValueTracking.cpp @@ -0,0 +1,1438 @@ +//===- 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/GlobalAlias.h" +#include "llvm/IntrinsicInst.h" +#include "llvm/LLVMContext.h" +#include "llvm/Operator.h" +#include "llvm/Target/TargetData.h" +#include "llvm/Support/GetElementPtrTypeIterator.h" +#include "llvm/Support/MathExtras.h" +#include +using namespace llvm; + +/// ComputeMaskedBits - Determine which of the bits specified in Mask are +/// known to be either zero or one and return them in the KnownZero/KnownOne +/// bit sets. This code only analyzes bits in Mask, in order to short-circuit +/// processing. +/// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that +/// we cannot optimize based on the assumption that it is zero without changing +/// it to be an explicit zero. If we don't change it to zero, other code could +/// optimized based on the contradictory assumption that it is non-zero. +/// Because instcombine aggressively folds operations with undef args anyway, +/// this won't lose us code quality. +/// +/// This function is defined on values with integer type, values with pointer +/// type (but only if TD is non-null), and vectors of integers. In the case +/// where V is a vector, the mask, known zero, and known one values are the +/// same width as the vector element, and the bit is set only if it is true +/// for all of the elements in the vector. +void llvm::ComputeMaskedBits(Value *V, const APInt &Mask, + APInt &KnownZero, APInt &KnownOne, + const TargetData *TD, unsigned Depth) { + const unsigned MaxDepth = 6; + assert(V && "No Value?"); + assert(Depth <= MaxDepth && "Limit Search Depth"); + unsigned BitWidth = Mask.getBitWidth(); + assert((V->getType()->isIntOrIntVector() || isa(V->getType())) && + "Not integer or pointer type!"); + assert((!TD || + TD->getTypeSizeInBits(V->getType()->getScalarType()) == BitWidth) && + (!V->getType()->isIntOrIntVector() || + V->getType()->getScalarSizeInBits() == BitWidth) && + KnownZero.getBitWidth() == BitWidth && + KnownOne.getBitWidth() == BitWidth && + "V, Mask, KnownOne and KnownZero should have same BitWidth"); + + if (ConstantInt *CI = dyn_cast(V)) { + // We know all of the bits for a constant! + KnownOne = CI->getValue() & Mask; + KnownZero = ~KnownOne & Mask; + return; + } + // Null and aggregate-zero are all-zeros. + if (isa(V) || + isa(V)) { + KnownOne.clear(); + KnownZero = Mask; + return; + } + // Handle a constant vector by taking the intersection of the known bits of + // each element. + if (ConstantVector *CV = dyn_cast(V)) { + KnownZero.set(); KnownOne.set(); + for (unsigned i = 0, e = CV->getNumOperands(); i != e; ++i) { + APInt KnownZero2(BitWidth, 0), KnownOne2(BitWidth, 0); + ComputeMaskedBits(CV->getOperand(i), Mask, KnownZero2, KnownOne2, + TD, Depth); + KnownZero &= KnownZero2; + KnownOne &= KnownOne2; + } + return; + } + // The address of an aligned GlobalValue has trailing zeros. + if (GlobalValue *GV = dyn_cast(V)) { + unsigned Align = GV->getAlignment(); + if (Align == 0 && TD && GV->getType()->getElementType()->isSized()) { + const Type *ObjectType = GV->getType()->getElementType(); + // If the object is defined in the current Module, we'll be giving + // it the preferred alignment. Otherwise, we have to assume that it + // may only have the minimum ABI alignment. + if (!GV->isDeclaration() && !GV->mayBeOverridden()) + Align = TD->getPrefTypeAlignment(ObjectType); + else + Align = TD->getABITypeAlignment(ObjectType); + } + if (Align > 0) + KnownZero = Mask & APInt::getLowBitsSet(BitWidth, + CountTrailingZeros_32(Align)); + else + KnownZero.clear(); + KnownOne.clear(); + return; + } + // A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has + // the bits of its aliasee. + if (GlobalAlias *GA = dyn_cast(V)) { + if (GA->mayBeOverridden()) { + KnownZero.clear(); KnownOne.clear(); + } else { + ComputeMaskedBits(GA->getAliasee(), Mask, KnownZero, KnownOne, + TD, Depth+1); + } + return; + } + + KnownZero.clear(); KnownOne.clear(); // Start out not knowing anything. + + if (Depth == MaxDepth || Mask == 0) + return; // Limit search depth. + + Operator *I = dyn_cast(V); + if (!I) return; + + APInt KnownZero2(KnownZero), KnownOne2(KnownOne); + switch (I->getOpcode()) { + default: break; + case Instruction::And: { + // If either the LHS or the RHS are Zero, the result is zero. + ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1); + APInt Mask2(Mask & ~KnownZero); + ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, + Depth+1); + assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); + assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); + + // Output known-1 bits are only known if set in both the LHS & RHS. + KnownOne &= KnownOne2; + // Output known-0 are known to be clear if zero in either the LHS | RHS. + KnownZero |= KnownZero2; + return; + } + case Instruction::Or: { + ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1); + APInt Mask2(Mask & ~KnownOne); + ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, + Depth+1); + assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); + assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); + + // Output known-0 bits are only known if clear in both the LHS & RHS. + KnownZero &= KnownZero2; + // Output known-1 are known to be set if set in either the LHS | RHS. + KnownOne |= KnownOne2; + return; + } + case Instruction::Xor: { + ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1); + ComputeMaskedBits(I->getOperand(0), Mask, KnownZero2, KnownOne2, TD, + Depth+1); + assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); + assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); + + // Output known-0 bits are known if clear or set in both the LHS & RHS. + APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2); + // Output known-1 are known to be set if set in only one of the LHS, RHS. + KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2); + KnownZero = KnownZeroOut; + return; + } + case Instruction::Mul: { + APInt Mask2 = APInt::getAllOnesValue(BitWidth); + ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero, KnownOne, TD,Depth+1); + ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, + Depth+1); + assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); + assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); + + // If low bits are zero in either operand, output low known-0 bits. + // Also compute a conserative estimate for high known-0 bits. + // More trickiness is possible, but this is sufficient for the + // interesting case of alignment computation. + KnownOne.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: { + const Type *SrcTy = I->getOperand(0)->getType(); + + unsigned SrcBitWidth; + // Note that we handle pointer operands here because of inttoptr/ptrtoint + // which fall through here. + if (isa(SrcTy)) + SrcBitWidth = TD->getTypeSizeInBits(SrcTy); + else + SrcBitWidth = SrcTy->getScalarSizeInBits(); + + 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(SrcTy)) && + // TODO: For now, not handling conversions like: + // (bitcast i64 %x to <2 x i32>) + !isa(I->getType())) { + ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, TD, + Depth+1); + return; + } + break; + } + case Instruction::SExt: { + // Compute the bits in the result that are not present in the input. + unsigned SrcBitWidth = I->getOperand(0)->getType()->getScalarSizeInBits(); + + APInt MaskIn(Mask); + 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(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(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(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(I->getOperand(0))) { + // We know that the top bits of C-X are clear if X contains less bits + // than C (i.e. no wrap-around can happen). For example, 20-X is + // positive if we can prove that X is >= 0 and < 16. + if (!CLHS->getValue().isNegative()) { + unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros(); + // NLZ can't be BitWidth with no sign bit + APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1); + ComputeMaskedBits(I->getOperand(1), MaskV, KnownZero2, KnownOne2, + TD, Depth+1); + + // If all of the MaskV bits are known to be zero, then we know the + // output top bits are zero, because we now know that the output is + // from [0-C]. + if ((KnownZero2 & MaskV) == MaskV) { + unsigned NLZ2 = CLHS->getValue().countLeadingZeros(); + // Top bits known zero. + KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2) & Mask; + } + } + } + } + // fall through + case Instruction::Add: { + // If one of the operands has trailing zeros, then the bits that the + // other operand has in those bit positions will be preserved in the + // result. For an add, this works with either operand. For a subtract, + // this only works if the known zeros are in the right operand. + APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0); + APInt Mask2 = APInt::getLowBitsSet(BitWidth, + BitWidth - Mask.countLeadingZeros()); + ComputeMaskedBits(I->getOperand(0), Mask2, LHSKnownZero, LHSKnownOne, TD, + Depth+1); + assert((LHSKnownZero & LHSKnownOne) == 0 && + "Bits known to be one AND zero?"); + unsigned LHSKnownZeroOut = LHSKnownZero.countTrailingOnes(); + + ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero2, KnownOne2, TD, + Depth+1); + assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); + unsigned RHSKnownZeroOut = KnownZero2.countTrailingOnes(); + + // Determine which operand has more trailing zeros, and use that + // many bits from the other operand. + if (LHSKnownZeroOut > RHSKnownZeroOut) { + if (I->getOpcode() == Instruction::Add) { + APInt Mask = APInt::getLowBitsSet(BitWidth, LHSKnownZeroOut); + KnownZero |= KnownZero2 & Mask; + KnownOne |= KnownOne2 & Mask; + } else { + // If the known zeros are in the left operand for a subtract, + // fall back to the minimum known zeros in both operands. + KnownZero |= APInt::getLowBitsSet(BitWidth, + std::min(LHSKnownZeroOut, + RHSKnownZeroOut)); + } + } else if (RHSKnownZeroOut >= LHSKnownZeroOut) { + APInt Mask = APInt::getLowBitsSet(BitWidth, RHSKnownZeroOut); + KnownZero |= LHSKnownZero & Mask; + KnownOne |= LHSKnownOne & Mask; + } + return; + } + case Instruction::SRem: + if (ConstantInt *Rem = dyn_cast(I->getOperand(1))) { + APInt RA = Rem->getValue().abs(); + if (RA.isPowerOf2()) { + APInt LowBits = RA - 1; + APInt Mask2 = LowBits | APInt::getSignBit(BitWidth); + ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, + Depth+1); + + // The low bits of the first operand are unchanged by the srem. + KnownZero = KnownZero2 & LowBits; + KnownOne = KnownOne2 & LowBits; + + // If the first operand is non-negative or has all low bits zero, then + // the upper bits are all zero. + if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits)) + KnownZero |= ~LowBits; + + // If the first operand is negative and not all low bits are zero, then + // the upper bits are all one. + if (KnownOne2[BitWidth-1] && ((KnownOne2 & LowBits) != 0)) + KnownOne |= ~LowBits; + + KnownZero &= Mask; + KnownOne &= Mask; + + assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); + } + } + break; + case Instruction::URem: { + if (ConstantInt *Rem = dyn_cast(I->getOperand(1))) { + APInt RA = Rem->getValue(); + if (RA.isPowerOf2()) { + APInt LowBits = (RA - 1); + APInt Mask2 = LowBits & Mask; + KnownZero |= ~LowBits & Mask; + ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD, + Depth+1); + assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); + break; + } + } + + // Since the result is less than or equal to either operand, any leading + // zero bits in either operand must also exist in the result. + APInt AllOnes = APInt::getAllOnesValue(BitWidth); + ComputeMaskedBits(I->getOperand(0), AllOnes, KnownZero, KnownOne, + TD, Depth+1); + ComputeMaskedBits(I->getOperand(1), AllOnes, KnownZero2, KnownOne2, + TD, Depth+1); + + unsigned Leaders = std::max(KnownZero.countLeadingOnes(), + KnownZero2.countLeadingOnes()); + KnownOne.clear(); + KnownZero = APInt::getHighBitsSet(BitWidth, Leaders) & Mask; + break; + } + + case Instruction::Alloca: { + AllocaInst *AI = cast(V); + unsigned Align = AI->getAlignment(); + if (Align == 0 && TD) + Align = TD->getABITypeAlignment(AI->getType()->getElementType()); + + if (Align > 0) + KnownZero = Mask & APInt::getLowBitsSet(BitWidth, + CountTrailingZeros_32(Align)); + break; + } + case Instruction::GetElementPtr: { + // Analyze all of the subscripts of this getelementptr instruction + // to determine if we can prove known low zero bits. + APInt LocalMask = APInt::getAllOnesValue(BitWidth); + APInt LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0); + ComputeMaskedBits(I->getOperand(0), LocalMask, + LocalKnownZero, LocalKnownOne, TD, Depth+1); + unsigned TrailZ = LocalKnownZero.countTrailingOnes(); + + gep_type_iterator GTI = gep_type_begin(I); + for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) { + Value *Index = I->getOperand(i); + if (const StructType *STy = dyn_cast(*GTI)) { + // Handle struct member offset arithmetic. + if (!TD) return; + const StructLayout *SL = TD->getStructLayout(STy); + unsigned Idx = cast(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()->getScalarSizeInBits(); + uint64_t TypeSize = TD ? TD->getTypeAllocSize(IndexedTy) : 1; + LocalMask = APInt::getAllOnesValue(GEPOpiBits); + LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0); + ComputeMaskedBits(Index, LocalMask, + LocalKnownZero, LocalKnownOne, TD, Depth+1); + TrailZ = std::min(TrailZ, + unsigned(CountTrailingZeros_64(TypeSize) + + LocalKnownZero.countTrailingOnes())); + } + } + + KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) & Mask; + break; + } + case Instruction::PHI: { + PHINode *P = cast(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(L); + if (!LU) + continue; + unsigned Opcode = LU->getOpcode(); + // Check for operations that have the property that if + // both their operands have low zero bits, the result + // will have low zero bits. + if (Opcode == Instruction::Add || + Opcode == Instruction::Sub || + Opcode == Instruction::And || + Opcode == Instruction::Or || + Opcode == Instruction::Mul) { + Value *LL = LU->getOperand(0); + Value *LR = LU->getOperand(1); + // Find a recurrence. + if (LL == I) + L = LR; + else if (LR == I) + L = LL; + else + break; + // Ok, we have a PHI of the form L op= R. Check for low + // zero bits. + APInt Mask2 = APInt::getAllOnesValue(BitWidth); + ComputeMaskedBits(R, Mask2, KnownZero2, KnownOne2, TD, Depth+1); + Mask2 = APInt::getLowBitsSet(BitWidth, + KnownZero2.countTrailingOnes()); + + // We need to take the minimum number of known bits + APInt KnownZero3(KnownZero), KnownOne3(KnownOne); + ComputeMaskedBits(L, Mask2, KnownZero3, KnownOne3, TD, Depth+1); + + KnownZero = Mask & + APInt::getLowBitsSet(BitWidth, + std::min(KnownZero2.countTrailingOnes(), + KnownZero3.countTrailingOnes())); + break; + } + } + } + + // 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) { + KnownZero = APInt::getAllOnesValue(BitWidth); + KnownOne = APInt::getAllOnesValue(BitWidth); + for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) { + // Skip direct self references. + if (P->getIncomingValue(i) == P) continue; + + KnownZero2 = APInt(BitWidth, 0); + KnownOne2 = APInt(BitWidth, 0); + // Recurse, but cap the recursion to one level, because we don't + // want to waste time spinning around in loops. + ComputeMaskedBits(P->getIncomingValue(i), KnownZero | KnownOne, + KnownZero2, KnownOne2, TD, MaxDepth-1); + KnownZero &= KnownZero2; + KnownOne &= KnownOne2; + // If all bits have been ruled out, there's no need to check + // more operands. + if (!KnownZero && !KnownOne) + break; + } + } + break; + } + case Instruction::Call: + if (IntrinsicInst *II = dyn_cast(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. +/// +/// This function is defined on values with integer type, values with pointer +/// type (but only if TD is non-null), and vectors of integers. In the case +/// where V is a vector, the mask, known zero, and known one values are the +/// same width as the vector element, and the bit is set only if it is true +/// for all of the elements in the vector. +bool llvm::MaskedValueIsZero(Value *V, const APInt &Mask, + const TargetData *TD, unsigned Depth) { + APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0); + ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth); + assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); + return (KnownZero & Mask) == Mask; +} + + + +/// ComputeNumSignBits - Return the number of times the sign bit of the +/// register is replicated into the other bits. We know that at least 1 bit +/// is always equal to the sign bit (itself), but other cases can give us +/// information. For example, immediately after an "ashr X, 2", we know that +/// the top 3 bits are all equal to each other, so we return 3. +/// +/// 'Op' must have a scalar integer type. +/// +unsigned llvm::ComputeNumSignBits(Value *V, const TargetData *TD, + unsigned Depth) { + assert((TD || V->getType()->isIntOrIntVector()) && + "ComputeNumSignBits requires a TargetData object to operate " + "on non-integer values!"); + const 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(V); + switch (Operator::getOpcode(V)) { + default: break; + case Instruction::SExt: + Tmp = TyBits - U->getOperand(0)->getType()->getScalarSizeInBits(); + return ComputeNumSignBits(U->getOperand(0), TD, Depth+1) + Tmp; + + case Instruction::AShr: + Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1); + // ashr X, C -> adds C sign bits. + if (ConstantInt *C = dyn_cast(U->getOperand(1))) { + Tmp += C->getZExtValue(); + if (Tmp > TyBits) Tmp = TyBits; + } + return Tmp; + case Instruction::Shl: + if (ConstantInt *C = dyn_cast(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(U->getOperand(1))) + if (CRHS->isAllOnesValue()) { + APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); + APInt Mask = APInt::getAllOnesValue(TyBits); + ComputeMaskedBits(U->getOperand(0), Mask, KnownZero, KnownOne, TD, + Depth+1); + + // If the input is known to be 0 or 1, the output is 0/-1, which is all + // sign bits set. + if ((KnownZero | APInt(TyBits, 1)) == Mask) + return TyBits; + + // If we are subtracting one from a positive number, there is no carry + // out of the result. + if (KnownZero.isNegative()) + return Tmp; + } + + Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1); + if (Tmp2 == 1) return 1; + return std::min(Tmp, Tmp2)-1; + + case Instruction::Sub: + Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1); + if (Tmp2 == 1) return 1; + + // Handle NEG. + if (ConstantInt *CLHS = dyn_cast(U->getOperand(0))) + if (CLHS->isNullValue()) { + APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); + APInt Mask = APInt::getAllOnesValue(TyBits); + ComputeMaskedBits(U->getOperand(1), Mask, KnownZero, KnownOne, + TD, Depth+1); + // If the input is known to be 0 or 1, the output is 0/-1, which is all + // sign bits set. + if ((KnownZero | APInt(TyBits, 1)) == Mask) + return TyBits; + + // If the input is known to be positive (the sign bit is known clear), + // the output of the NEG has the same number of sign bits as the input. + if (KnownZero.isNegative()) + return Tmp2; + + // Otherwise, we treat this like a SUB. + } + + // Sub can have at most one carry bit. Thus we know that the output + // is, at worst, one more bit than the inputs. + Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1); + if (Tmp == 1) return 1; // Early out. + return std::min(Tmp, Tmp2)-1; + + case Instruction::PHI: { + PHINode *PN = cast(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(1), TD, Depth+1)); + } + return Tmp; + } + + case Instruction::Trunc: + // FIXME: it's tricky to do anything useful for this, but it is an important + // case for targets like X86. + break; + } + + // Finally, if we can prove that the top bits of the result are 0's or 1's, + // use this information. + APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); + APInt Mask = APInt::getAllOnesValue(TyBits); + ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth); + + if (KnownZero.isNegative()) { // sign bit is 0 + Mask = KnownZero; + } else if (KnownOne.isNegative()) { // sign bit is 1; + Mask = KnownOne; + } else { + // Nothing known. + return FirstAnswer; + } + + // Okay, we know that the sign bit in Mask is set. Use CLZ to determine + // the number of identical bits in the top of the input value. + Mask = ~Mask; + Mask <<= Mask.getBitWidth()-TyBits; + // Return # leading zeros. We use 'min' here in case Val was zero before + // shifting. We don't want to return '64' as for an i32 "0". + return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros())); +} + +/// ComputeMultiple - This function computes the integer multiple of Base that +/// equals V. If successful, it returns true and returns the multiple in +/// Multiple. If unsuccessful, it returns false. It looks +/// through SExt instructions only if LookThroughSExt is true. +bool llvm::ComputeMultiple(Value *V, unsigned Base, Value *&Multiple, + bool LookThroughSExt, unsigned Depth) { + const unsigned MaxDepth = 6; + + assert(V && "No Value?"); + assert(Depth <= MaxDepth && "Limit Search Depth"); + assert(V->getType()->isInteger() && "Not integer or pointer type!"); + + const Type *T = V->getType(); + + ConstantInt *CI = dyn_cast(V); + + if (Base == 0) + return false; + + if (Base == 1) { + Multiple = V; + return true; + } + + ConstantExpr *CO = dyn_cast(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(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(Op1); + if (!Op1CI) return false; + // Turn Op0 << Op1 into Op0 * 2^Op1 + APInt Op1Int = Op1CI->getValue(); + uint64_t BitToSet = Op1Int.getLimitedValue(Op1Int.getBitWidth() - 1); + Op1 = ConstantInt::get(V->getContext(), + APInt(Op1Int.getBitWidth(), 0).set(BitToSet)); + } + + Value *Mul0 = NULL; + Value *Mul1 = NULL; + bool M0 = ComputeMultiple(Op0, Base, Mul0, + LookThroughSExt, Depth+1); + bool M1 = ComputeMultiple(Op1, Base, Mul1, + LookThroughSExt, Depth+1); + + if (M0) { + if (isa(Op1) && isa(Mul0)) { + // V == Base * (Mul0 * Op1), so return (Mul0 * Op1) + Multiple = ConstantExpr::getMul(cast(Mul0), + cast(Op1)); + return true; + } + + if (ConstantInt *Mul0CI = dyn_cast(Mul0)) + if (Mul0CI->getValue() == 1) { + // V == Base * Op1, so return Op1 + Multiple = Op1; + return true; + } + } + + if (M1) { + if (isa(Op0) && isa(Mul1)) { + // V == Base * (Mul1 * Op0), so return (Mul1 * Op0) + Multiple = ConstantExpr::getMul(cast(Mul1), + cast(Op0)); + return true; + } + + if (ConstantInt *Mul1CI = dyn_cast(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(V)) + return !CFP->getValueAPF().isNegZero(); + + if (Depth == 6) + return 1; // Limit search depth. + + const Operator *I = dyn_cast(V); + if (I == 0) return false; + + // (add x, 0.0) is guaranteed to return +0.0, not -0.0. + if (I->getOpcode() == Instruction::FAdd && + isa(I->getOperand(1)) && + cast(I->getOperand(1))->isNullValue()) + return true; + + // sitofp and uitofp turn into +0.0 for zero. + if (isa(I) || isa(I)) + return true; + + if (const IntrinsicInst *II = dyn_cast(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(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->getOperand(1), Depth+1); + } + } + + return false; +} + + +/// GetLinearExpression - Analyze the specified value as a linear expression: +/// "A*V + B", where A and B are constant integers. Return the scale and offset +/// values as APInts and return V as a Value*. The incoming Value is known to +/// have IntegerType. Note that this looks through extends, so the high bits +/// may not be represented in the result. +static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset, + const TargetData *TD, unsigned Depth) { + assert(isa(V->getType()) && "Not an integer value"); + + // Limit our recursion depth. + if (Depth == 6) { + Scale = 1; + Offset = 0; + return V; + } + + if (BinaryOperator *BOp = dyn_cast(V)) { + if (ConstantInt *RHSC = dyn_cast(BOp->getOperand(1))) { + switch (BOp->getOpcode()) { + default: break; + case Instruction::Or: + // X|C == X+C if all the bits in C are unset in X. Otherwise we can't + // analyze it. + if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), TD)) + break; + // FALL THROUGH. + case Instruction::Add: + V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, TD, Depth+1); + Offset += RHSC->getValue(); + return V; + case Instruction::Mul: + V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, TD, Depth+1); + Offset *= RHSC->getValue(); + Scale *= RHSC->getValue(); + return V; + case Instruction::Shl: + V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, TD, Depth+1); + Offset <<= RHSC->getValue().getLimitedValue(); + Scale <<= RHSC->getValue().getLimitedValue(); + return V; + } + } + } + + // Since clients don't care about the high bits of the value, just scales and + // offsets, we can look through extensions. + if (isa(V) || isa(V)) { + Value *CastOp = cast(V)->getOperand(0); + unsigned OldWidth = Scale.getBitWidth(); + unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits(); + Scale.trunc(SmallWidth); + Offset.trunc(SmallWidth); + Value *Result = GetLinearExpression(CastOp, Scale, Offset, TD, Depth+1); + Scale.zext(OldWidth); + Offset.zext(OldWidth); + return Result; + } + + Scale = 1; + Offset = 0; + return V; +} + +/// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose it +/// into a base pointer with a constant offset and a number of scaled symbolic +/// offsets. +/// +/// The scaled symbolic offsets (represented by pairs of a Value* and a scale in +/// the VarIndices vector) are Value*'s that are known to be scaled by the +/// specified amount, but which may have other unrepresented high bits. As such, +/// the gep cannot necessarily be reconstructed from its decomposed form. +/// +/// When TargetData is around, this function is capable of analyzing everything +/// that Value::getUnderlyingObject() can look through. When not, it just looks +/// through pointer casts. +/// +const Value *llvm::DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, + SmallVectorImpl > &VarIndices, + const TargetData *TD) { + // Limit recursion depth to limit compile time in crazy cases. + unsigned MaxLookup = 6; + + BaseOffs = 0; + do { + // See if this is a bitcast or GEP. + const Operator *Op = dyn_cast(V); + if (Op == 0) { + // The only non-operator case we can handle are GlobalAliases. + if (const GlobalAlias *GA = dyn_cast(V)) { + if (!GA->mayBeOverridden()) { + V = GA->getAliasee(); + continue; + } + } + return V; + } + + if (Op->getOpcode() == Instruction::BitCast) { + V = Op->getOperand(0); + continue; + } + + const GEPOperator *GEPOp = dyn_cast(Op); + if (GEPOp == 0) + return V; + + // Don't attempt to analyze GEPs over unsized objects. + if (!cast(GEPOp->getOperand(0)->getType()) + ->getElementType()->isSized()) + return V; + + // If we are lacking TargetData information, we can't compute the offets of + // elements computed by GEPs. However, we can handle bitcast equivalent + // GEPs. + if (!TD) { + if (!GEPOp->hasAllZeroIndices()) + return V; + V = GEPOp->getOperand(0); + continue; + } + + // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices. + gep_type_iterator GTI = gep_type_begin(GEPOp); + for (User::const_op_iterator I = GEPOp->op_begin()+1, + E = GEPOp->op_end(); I != E; ++I) { + Value *Index = *I; + // Compute the (potentially symbolic) offset in bytes for this index. + if (const StructType *STy = dyn_cast(*GTI++)) { + // For a struct, add the member offset. + unsigned FieldNo = cast(Index)->getZExtValue(); + if (FieldNo == 0) continue; + + BaseOffs += TD->getStructLayout(STy)->getElementOffset(FieldNo); + continue; + } + + // For an array/pointer, add the element offset, explicitly scaled. + if (ConstantInt *CIdx = dyn_cast(Index)) { + if (CIdx->isZero()) continue; + BaseOffs += TD->getTypeAllocSize(*GTI)*CIdx->getSExtValue(); + continue; + } + + uint64_t Scale = TD->getTypeAllocSize(*GTI); + + // Use GetLinearExpression to decompose the index into a C1*V+C2 form. + unsigned Width = cast(Index->getType())->getBitWidth(); + APInt IndexScale(Width, 0), IndexOffset(Width, 0); + Index = GetLinearExpression(Index, IndexScale, IndexOffset, TD, 0); + + // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale. + // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale. + BaseOffs += IndexOffset.getZExtValue()*Scale; + Scale *= IndexScale.getZExtValue(); + + + // If we already had an occurrance of this index variable, merge this + // scale into it. For example, we want to handle: + // A[x][x] -> x*16 + x*4 -> x*20 + // This also ensures that 'x' only appears in the index list once. + for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) { + if (VarIndices[i].first == Index) { + Scale += VarIndices[i].second; + VarIndices.erase(VarIndices.begin()+i); + break; + } + } + + // Make sure that we have a scale that makes sense for this target's + // pointer size. + if (unsigned ShiftBits = 64-TD->getPointerSizeInBits()) { + Scale <<= ShiftBits; + Scale >>= ShiftBits; + } + + if (Scale) + VarIndices.push_back(std::make_pair(Index, Scale)); + } + + // Analyze the base pointer next. + V = GEPOp->getOperand(0); + } while (--MaxLookup); + + // If the chain of expressions is too deep, just return early. + return V; +} + + +// 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, const Type *IndexedType, + SmallVector &Idxs, + unsigned IdxSkip, + Instruction *InsertBefore) { + const llvm::StructType *STy = llvm::dyn_cast(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(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 +static 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 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(V->getType()) || isa(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(V->getType()); + + if (isa(V)) + return UndefValue::get(ExtractValueInst::getIndexedType(PTy, + idx_begin, + idx_end)); + else if (isa(V)) + return Constant::getNullValue(ExtractValueInst::getIndexedType(PTy, + idx_begin, + idx_end)); + else if (Constant *C = dyn_cast(V)) { + if (isa(C) || isa(C)) + // Recursively process this constant + return FindInsertedValue(C->getOperand(*idx_begin), idx_begin + 1, + idx_end, InsertBefore); + } else if (InsertValueInst *I = dyn_cast(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(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 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(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(V)) { + GEP = GEPI; + } else if (ConstantExpr *CE = dyn_cast(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(GEP->getOperand(0)->getType()); + const ArrayType *AT = dyn_cast(PT->getElementType()); + if (AT == 0 || !AT->getElementType()->isInteger(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. + ConstantInt *FirstIdx = dyn_cast(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(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(V); + if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer()) + return false; + Constant *GlobalInit = GV->getInitializer(); + + // Handle the ConstantAggregateZero case + if (isa(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(GlobalInit); + if (Array == 0 || !Array->getType()->getElementType()->isInteger(8)) + return false; + + // Get the number of elements in the array + uint64_t NumElts = Array->getType()->getNumElements(); + + if (Offset > NumElts) + return false; + + // Traverse the constant array from 'Offset' which is the place the GEP refers + // to in the array. + Str.reserve(NumElts-Offset); + for (unsigned i = Offset; i != NumElts; ++i) { + Constant *Elt = Array->getOperand(i); + ConstantInt *CI = dyn_cast(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; +} -- cgit v1.2.3