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llvm/lib/Analysis/ValueTracking.cpp
Kostya Serebryany 42a9da35b8 Don't speculate loads under ThreadSanitizer 
Summary:
Don't speculate loads under ThreadSanitizer.
This fixes https://code.google.com/p/thread-sanitizer/issues/detail?id=40
Also discussed here: http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-November/067929.html

Reviewers: chandlerc

Reviewed By: chandlerc

CC: llvm-commits, dvyukov

Differential Revision: http://llvm-reviews.chandlerc.com/D2227

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195324 91177308-0d34-0410-b5e6-96231b3b80d8
2013-11-21 07:29:28 +00:00

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//===- 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/Analysis/MemoryBuiltins.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;
return TD ? TD->getPointerTypeSizeInBits(Ty) : 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(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(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(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;
// Handle case when index is vector zeroinitializer
Constant *CIndex = cast<Constant>(Index);
if (CIndex->isZeroValue())
continue;
if (CIndex->getType()->isVectorTy())
Index = CIndex->getSplatValue();
unsigned Idx = cast<ConstantInt>(Index)->getZExtValue();
const StructLayout *SL = TD->getStructLayout(STy);
uint64_t Offset = SL->getElementOffset(Idx);
TrailZ = std::min<unsigned>(TrailZ,
countTrailingZeros(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(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_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;
}
// Adding a power-of-two or zero to the same power-of-two or zero yields
// either the original power-of-two, a larger power-of-two or zero.
if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
OverflowingBinaryOperator *VOBO = cast<OverflowingBinaryOperator>(V);
if (OrZero || VOBO->hasNoUnsignedWrap() || VOBO->hasNoSignedWrap()) {
if (match(X, m_And(m_Specific(Y), m_Value())) ||
match(X, m_And(m_Value(), m_Specific(Y))))
if (isKnownToBeAPowerOfTwo(Y, OrZero, Depth))
return true;
if (match(Y, m_And(m_Specific(X), m_Value())) ||
match(Y, m_And(m_Value(), m_Specific(X))))
if (isKnownToBeAPowerOfTwo(X, OrZero, Depth))
return true;
unsigned BitWidth = V->getType()->getScalarSizeInBits();
APInt LHSZeroBits(BitWidth, 0), LHSOneBits(BitWidth, 0);
ComputeMaskedBits(X, LHSZeroBits, LHSOneBits, 0, Depth);
APInt RHSZeroBits(BitWidth, 0), RHSOneBits(BitWidth, 0);
ComputeMaskedBits(Y, RHSZeroBits, RHSOneBits, 0, Depth);
// If i8 V is a power of two or zero:
// ZeroBits: 1 1 1 0 1 1 1 1
// ~ZeroBits: 0 0 0 1 0 0 0 0
if ((~(LHSZeroBits & RHSZeroBits)).isPowerOf2())
// If OrZero isn't set, we cannot give back a zero result.
// Make sure either the LHS or RHS has a bit set.
if (OrZero || RHSOneBits.getBoolValue() || LHSOneBits.getBoolValue())
return true;
}
}
// 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,
SmallVectorImpl<unsigned> &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 *DL) {
// Without DataLayout, conservatively assume 64-bit offsets, which is
// the widest we support.
unsigned BitWidth = DL ? DL->getPointerTypeSizeInBits(Ptr->getType()) : 64;
APInt ByteOffset(BitWidth, 0);
while (1) {
if (Ptr->getType()->isVectorTy())
break;
if (GEPOperator *GEP = dyn_cast<GEPOperator>(Ptr)) {
if (DL) {
APInt GEPOffset(BitWidth, 0);
if (!GEP->accumulateConstantOffset(*DL, 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() ||
// Speculative load may create a race that did not exist in the source.
LI->getParent()->getParent()->hasFnAttribute(Attribute::SanitizeThread))
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, const TargetLibraryInfo *TLI) {
// 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();
// operator new never returns null.
if (isOperatorNewLikeFn(V, TLI, /*LookThroughBitCast=*/true))
return true;
return false;
}
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