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e78496e5f1
Probably the best way to know that all getOperand() calls have been handled is to replace that API instead of updating. llvm-svn: 101579
1569 lines
61 KiB
C++
1569 lines
61 KiB
C++
//===- ValueTracking.cpp - Walk computations to compute properties --------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file contains routines that help analyze properties that chains of
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// computations have.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/GlobalVariable.h"
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#include "llvm/GlobalAlias.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/LLVMContext.h"
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#include "llvm/Operator.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Support/GetElementPtrTypeIterator.h"
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#include "llvm/Support/MathExtras.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include <cstring>
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using namespace llvm;
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/// ComputeMaskedBits - Determine which of the bits specified in Mask are
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/// known to be either zero or one and return them in the KnownZero/KnownOne
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/// bit sets. This code only analyzes bits in Mask, in order to short-circuit
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/// processing.
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/// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that
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/// we cannot optimize based on the assumption that it is zero without changing
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/// it to be an explicit zero. If we don't change it to zero, other code could
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/// optimized based on the contradictory assumption that it is non-zero.
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/// Because instcombine aggressively folds operations with undef args anyway,
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/// this won't lose us code quality.
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///
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/// This function is defined on values with integer type, values with pointer
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/// type (but only if TD is non-null), and vectors of integers. In the case
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/// where V is a vector, the mask, known zero, and known one values are the
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/// same width as the vector element, and the bit is set only if it is true
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/// for all of the elements in the vector.
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void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
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APInt &KnownZero, APInt &KnownOne,
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const TargetData *TD, unsigned Depth) {
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const unsigned MaxDepth = 6;
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assert(V && "No Value?");
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assert(Depth <= MaxDepth && "Limit Search Depth");
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unsigned BitWidth = Mask.getBitWidth();
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assert((V->getType()->isIntOrIntVectorTy() || V->getType()->isPointerTy())
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&& "Not integer or pointer type!");
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assert((!TD ||
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TD->getTypeSizeInBits(V->getType()->getScalarType()) == BitWidth) &&
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(!V->getType()->isIntOrIntVectorTy() ||
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V->getType()->getScalarSizeInBits() == BitWidth) &&
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KnownZero.getBitWidth() == BitWidth &&
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KnownOne.getBitWidth() == BitWidth &&
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"V, Mask, KnownOne and KnownZero should have same BitWidth");
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if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
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// We know all of the bits for a constant!
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KnownOne = CI->getValue() & Mask;
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KnownZero = ~KnownOne & Mask;
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return;
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}
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// Null and aggregate-zero are all-zeros.
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if (isa<ConstantPointerNull>(V) ||
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isa<ConstantAggregateZero>(V)) {
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KnownOne.clear();
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KnownZero = Mask;
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return;
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}
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// Handle a constant vector by taking the intersection of the known bits of
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// each element.
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if (ConstantVector *CV = dyn_cast<ConstantVector>(V)) {
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KnownZero.set(); KnownOne.set();
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for (unsigned i = 0, e = CV->getNumOperands(); i != e; ++i) {
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APInt KnownZero2(BitWidth, 0), KnownOne2(BitWidth, 0);
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ComputeMaskedBits(CV->getOperand(i), Mask, KnownZero2, KnownOne2,
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TD, Depth);
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KnownZero &= KnownZero2;
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KnownOne &= KnownOne2;
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}
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return;
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}
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// The address of an aligned GlobalValue has trailing zeros.
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if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
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unsigned Align = GV->getAlignment();
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if (Align == 0 && TD && GV->getType()->getElementType()->isSized()) {
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const Type *ObjectType = GV->getType()->getElementType();
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// If the object is defined in the current Module, we'll be giving
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// it the preferred alignment. Otherwise, we have to assume that it
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// may only have the minimum ABI alignment.
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if (!GV->isDeclaration() && !GV->mayBeOverridden())
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Align = TD->getPrefTypeAlignment(ObjectType);
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else
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Align = TD->getABITypeAlignment(ObjectType);
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}
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if (Align > 0)
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KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
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CountTrailingZeros_32(Align));
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else
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KnownZero.clear();
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KnownOne.clear();
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return;
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}
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// A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has
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// the bits of its aliasee.
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if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
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if (GA->mayBeOverridden()) {
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KnownZero.clear(); KnownOne.clear();
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} else {
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ComputeMaskedBits(GA->getAliasee(), Mask, KnownZero, KnownOne,
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TD, Depth+1);
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}
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return;
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}
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KnownZero.clear(); KnownOne.clear(); // Start out not knowing anything.
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if (Depth == MaxDepth || Mask == 0)
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return; // Limit search depth.
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Operator *I = dyn_cast<Operator>(V);
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if (!I) return;
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APInt KnownZero2(KnownZero), KnownOne2(KnownOne);
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switch (I->getOpcode()) {
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default: break;
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case Instruction::And: {
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// If either the LHS or the RHS are Zero, the result is zero.
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ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
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APInt Mask2(Mask & ~KnownZero);
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ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
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// Output known-1 bits are only known if set in both the LHS & RHS.
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KnownOne &= KnownOne2;
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// Output known-0 are known to be clear if zero in either the LHS | RHS.
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KnownZero |= KnownZero2;
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return;
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}
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case Instruction::Or: {
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ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
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APInt Mask2(Mask & ~KnownOne);
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ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
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// Output known-0 bits are only known if clear in both the LHS & RHS.
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KnownZero &= KnownZero2;
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// Output known-1 are known to be set if set in either the LHS | RHS.
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KnownOne |= KnownOne2;
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return;
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}
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case Instruction::Xor: {
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ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
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ComputeMaskedBits(I->getOperand(0), Mask, KnownZero2, KnownOne2, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
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// Output known-0 bits are known if clear or set in both the LHS & RHS.
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APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2);
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// Output known-1 are known to be set if set in only one of the LHS, RHS.
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KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2);
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KnownZero = KnownZeroOut;
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return;
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}
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case Instruction::Mul: {
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APInt Mask2 = APInt::getAllOnesValue(BitWidth);
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ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero, KnownOne, TD,Depth+1);
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ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
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// If low bits are zero in either operand, output low known-0 bits.
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// Also compute a conserative estimate for high known-0 bits.
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// More trickiness is possible, but this is sufficient for the
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// interesting case of alignment computation.
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KnownOne.clear();
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unsigned TrailZ = KnownZero.countTrailingOnes() +
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KnownZero2.countTrailingOnes();
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unsigned LeadZ = std::max(KnownZero.countLeadingOnes() +
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KnownZero2.countLeadingOnes(),
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BitWidth) - BitWidth;
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TrailZ = std::min(TrailZ, BitWidth);
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LeadZ = std::min(LeadZ, BitWidth);
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KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) |
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APInt::getHighBitsSet(BitWidth, LeadZ);
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KnownZero &= Mask;
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return;
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}
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case Instruction::UDiv: {
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// For the purposes of computing leading zeros we can conservatively
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// treat a udiv as a logical right shift by the power of 2 known to
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// be less than the denominator.
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APInt AllOnes = APInt::getAllOnesValue(BitWidth);
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ComputeMaskedBits(I->getOperand(0),
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AllOnes, KnownZero2, KnownOne2, TD, Depth+1);
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unsigned LeadZ = KnownZero2.countLeadingOnes();
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KnownOne2.clear();
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KnownZero2.clear();
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ComputeMaskedBits(I->getOperand(1),
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AllOnes, KnownZero2, KnownOne2, TD, Depth+1);
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unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros();
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if (RHSUnknownLeadingOnes != BitWidth)
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LeadZ = std::min(BitWidth,
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LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);
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KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ) & Mask;
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return;
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}
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case Instruction::Select:
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ComputeMaskedBits(I->getOperand(2), Mask, KnownZero, KnownOne, TD, Depth+1);
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ComputeMaskedBits(I->getOperand(1), Mask, KnownZero2, KnownOne2, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
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// Only known if known in both the LHS and RHS.
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KnownOne &= KnownOne2;
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KnownZero &= KnownZero2;
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return;
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case Instruction::FPTrunc:
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case Instruction::FPExt:
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case Instruction::FPToUI:
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case Instruction::FPToSI:
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case Instruction::SIToFP:
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case Instruction::UIToFP:
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return; // Can't work with floating point.
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case Instruction::PtrToInt:
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case Instruction::IntToPtr:
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// We can't handle these if we don't know the pointer size.
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if (!TD) return;
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// FALL THROUGH and handle them the same as zext/trunc.
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case Instruction::ZExt:
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case Instruction::Trunc: {
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const Type *SrcTy = I->getOperand(0)->getType();
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unsigned SrcBitWidth;
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// Note that we handle pointer operands here because of inttoptr/ptrtoint
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// which fall through here.
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if (SrcTy->isPointerTy())
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SrcBitWidth = TD->getTypeSizeInBits(SrcTy);
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else
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SrcBitWidth = SrcTy->getScalarSizeInBits();
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APInt MaskIn(Mask);
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MaskIn.zextOrTrunc(SrcBitWidth);
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KnownZero.zextOrTrunc(SrcBitWidth);
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KnownOne.zextOrTrunc(SrcBitWidth);
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ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD,
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Depth+1);
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KnownZero.zextOrTrunc(BitWidth);
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KnownOne.zextOrTrunc(BitWidth);
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// Any top bits are known to be zero.
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if (BitWidth > SrcBitWidth)
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KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
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return;
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}
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case Instruction::BitCast: {
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const Type *SrcTy = I->getOperand(0)->getType();
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if ((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) &&
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// TODO: For now, not handling conversions like:
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// (bitcast i64 %x to <2 x i32>)
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!I->getType()->isVectorTy()) {
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ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, TD,
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Depth+1);
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return;
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}
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break;
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}
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case Instruction::SExt: {
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// Compute the bits in the result that are not present in the input.
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unsigned SrcBitWidth = I->getOperand(0)->getType()->getScalarSizeInBits();
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APInt MaskIn(Mask);
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MaskIn.trunc(SrcBitWidth);
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KnownZero.trunc(SrcBitWidth);
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KnownOne.trunc(SrcBitWidth);
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ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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KnownZero.zext(BitWidth);
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KnownOne.zext(BitWidth);
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// If the sign bit of the input is known set or clear, then we know the
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// top bits of the result.
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if (KnownZero[SrcBitWidth-1]) // Input sign bit known zero
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KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
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else if (KnownOne[SrcBitWidth-1]) // Input sign bit known set
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KnownOne |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
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return;
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}
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case Instruction::Shl:
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// (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
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if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
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uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
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APInt Mask2(Mask.lshr(ShiftAmt));
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ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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KnownZero <<= ShiftAmt;
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KnownOne <<= ShiftAmt;
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KnownZero |= APInt::getLowBitsSet(BitWidth, ShiftAmt); // low bits known 0
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return;
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}
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break;
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case Instruction::LShr:
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// (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
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if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
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// Compute the new bits that are at the top now.
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uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
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// Unsigned shift right.
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APInt Mask2(Mask.shl(ShiftAmt));
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ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero,KnownOne, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
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KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
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// high bits known zero.
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KnownZero |= APInt::getHighBitsSet(BitWidth, ShiftAmt);
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return;
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}
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break;
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case Instruction::AShr:
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// (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
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if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
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// Compute the new bits that are at the top now.
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uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
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// Signed shift right.
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APInt Mask2(Mask.shl(ShiftAmt));
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ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD,
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Depth+1);
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assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
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KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
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KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
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APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt));
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if (KnownZero[BitWidth-ShiftAmt-1]) // New bits are known zero.
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KnownZero |= HighBits;
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else if (KnownOne[BitWidth-ShiftAmt-1]) // New bits are known one.
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KnownOne |= HighBits;
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return;
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}
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break;
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case Instruction::Sub: {
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if (ConstantInt *CLHS = dyn_cast<ConstantInt>(I->getOperand(0))) {
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// We know that the top bits of C-X are clear if X contains less bits
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// than C (i.e. no wrap-around can happen). For example, 20-X is
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// positive if we can prove that X is >= 0 and < 16.
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if (!CLHS->getValue().isNegative()) {
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unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros();
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// NLZ can't be BitWidth with no sign bit
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APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
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ComputeMaskedBits(I->getOperand(1), MaskV, KnownZero2, KnownOne2,
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TD, Depth+1);
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// If all of the MaskV bits are known to be zero, then we know the
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// output top bits are zero, because we now know that the output is
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// from [0-C].
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if ((KnownZero2 & MaskV) == MaskV) {
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unsigned NLZ2 = CLHS->getValue().countLeadingZeros();
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// Top bits known zero.
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KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2) & Mask;
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}
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}
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}
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}
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// fall through
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case Instruction::Add: {
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// If one of the operands has trailing zeros, then the bits that the
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// other operand has in those bit positions will be preserved in the
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// result. For an add, this works with either operand. For a subtract,
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// this only works if the known zeros are in the right operand.
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APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
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APInt Mask2 = APInt::getLowBitsSet(BitWidth,
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BitWidth - Mask.countLeadingZeros());
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ComputeMaskedBits(I->getOperand(0), Mask2, LHSKnownZero, LHSKnownOne, TD,
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Depth+1);
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assert((LHSKnownZero & LHSKnownOne) == 0 &&
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"Bits known to be one AND zero?");
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unsigned LHSKnownZeroOut = LHSKnownZero.countTrailingOnes();
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ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero2, KnownOne2, TD,
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Depth+1);
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assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
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unsigned RHSKnownZeroOut = KnownZero2.countTrailingOnes();
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// Determine which operand has more trailing zeros, and use that
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// many bits from the other operand.
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if (LHSKnownZeroOut > RHSKnownZeroOut) {
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if (I->getOpcode() == Instruction::Add) {
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APInt Mask = APInt::getLowBitsSet(BitWidth, LHSKnownZeroOut);
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KnownZero |= KnownZero2 & Mask;
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KnownOne |= KnownOne2 & Mask;
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} else {
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// If the known zeros are in the left operand for a subtract,
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// fall back to the minimum known zeros in both operands.
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KnownZero |= APInt::getLowBitsSet(BitWidth,
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std::min(LHSKnownZeroOut,
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RHSKnownZeroOut));
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}
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} else if (RHSKnownZeroOut >= LHSKnownZeroOut) {
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APInt Mask = APInt::getLowBitsSet(BitWidth, RHSKnownZeroOut);
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KnownZero |= LHSKnownZero & Mask;
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KnownOne |= LHSKnownOne & Mask;
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}
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return;
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}
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case Instruction::SRem:
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if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
|
|
APInt RA = Rem->getValue().abs();
|
|
if (RA.isPowerOf2()) {
|
|
APInt LowBits = RA - 1;
|
|
APInt Mask2 = LowBits | APInt::getSignBit(BitWidth);
|
|
ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
|
|
Depth+1);
|
|
|
|
// The low bits of the first operand are unchanged by the srem.
|
|
KnownZero = KnownZero2 & LowBits;
|
|
KnownOne = KnownOne2 & LowBits;
|
|
|
|
// If the first operand is non-negative or has all low bits zero, then
|
|
// the upper bits are all zero.
|
|
if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits))
|
|
KnownZero |= ~LowBits;
|
|
|
|
// If the first operand is negative and not all low bits are zero, then
|
|
// the upper bits are all one.
|
|
if (KnownOne2[BitWidth-1] && ((KnownOne2 & LowBits) != 0))
|
|
KnownOne |= ~LowBits;
|
|
|
|
KnownZero &= Mask;
|
|
KnownOne &= Mask;
|
|
|
|
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
|
|
}
|
|
}
|
|
break;
|
|
case Instruction::URem: {
|
|
if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
|
|
APInt RA = Rem->getValue();
|
|
if (RA.isPowerOf2()) {
|
|
APInt LowBits = (RA - 1);
|
|
APInt Mask2 = LowBits & Mask;
|
|
KnownZero |= ~LowBits & Mask;
|
|
ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD,
|
|
Depth+1);
|
|
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
|
|
break;
|
|
}
|
|
}
|
|
|
|
// Since the result is less than or equal to either operand, any leading
|
|
// zero bits in either operand must also exist in the result.
|
|
APInt AllOnes = APInt::getAllOnesValue(BitWidth);
|
|
ComputeMaskedBits(I->getOperand(0), AllOnes, KnownZero, KnownOne,
|
|
TD, Depth+1);
|
|
ComputeMaskedBits(I->getOperand(1), AllOnes, KnownZero2, KnownOne2,
|
|
TD, Depth+1);
|
|
|
|
unsigned Leaders = std::max(KnownZero.countLeadingOnes(),
|
|
KnownZero2.countLeadingOnes());
|
|
KnownOne.clear();
|
|
KnownZero = APInt::getHighBitsSet(BitWidth, Leaders) & Mask;
|
|
break;
|
|
}
|
|
|
|
case Instruction::Alloca: {
|
|
AllocaInst *AI = cast<AllocaInst>(V);
|
|
unsigned Align = AI->getAlignment();
|
|
if (Align == 0 && TD)
|
|
Align = TD->getABITypeAlignment(AI->getType()->getElementType());
|
|
|
|
if (Align > 0)
|
|
KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
|
|
CountTrailingZeros_32(Align));
|
|
break;
|
|
}
|
|
case Instruction::GetElementPtr: {
|
|
// Analyze all of the subscripts of this getelementptr instruction
|
|
// to determine if we can prove known low zero bits.
|
|
APInt LocalMask = APInt::getAllOnesValue(BitWidth);
|
|
APInt LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0);
|
|
ComputeMaskedBits(I->getOperand(0), LocalMask,
|
|
LocalKnownZero, LocalKnownOne, TD, Depth+1);
|
|
unsigned TrailZ = LocalKnownZero.countTrailingOnes();
|
|
|
|
gep_type_iterator GTI = gep_type_begin(I);
|
|
for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) {
|
|
Value *Index = I->getOperand(i);
|
|
if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
|
|
// Handle struct member offset arithmetic.
|
|
if (!TD) return;
|
|
const StructLayout *SL = TD->getStructLayout(STy);
|
|
unsigned Idx = cast<ConstantInt>(Index)->getZExtValue();
|
|
uint64_t Offset = SL->getElementOffset(Idx);
|
|
TrailZ = std::min(TrailZ,
|
|
CountTrailingZeros_64(Offset));
|
|
} else {
|
|
// Handle array index arithmetic.
|
|
const Type *IndexedTy = GTI.getIndexedType();
|
|
if (!IndexedTy->isSized()) return;
|
|
unsigned GEPOpiBits = Index->getType()->getScalarSizeInBits();
|
|
uint64_t TypeSize = TD ? TD->getTypeAllocSize(IndexedTy) : 1;
|
|
LocalMask = APInt::getAllOnesValue(GEPOpiBits);
|
|
LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0);
|
|
ComputeMaskedBits(Index, LocalMask,
|
|
LocalKnownZero, LocalKnownOne, TD, Depth+1);
|
|
TrailZ = std::min(TrailZ,
|
|
unsigned(CountTrailingZeros_64(TypeSize) +
|
|
LocalKnownZero.countTrailingOnes()));
|
|
}
|
|
}
|
|
|
|
KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) & Mask;
|
|
break;
|
|
}
|
|
case Instruction::PHI: {
|
|
PHINode *P = cast<PHINode>(I);
|
|
// Handle the case of a simple two-predecessor recurrence PHI.
|
|
// There's a lot more that could theoretically be done here, but
|
|
// this is sufficient to catch some interesting cases.
|
|
if (P->getNumIncomingValues() == 2) {
|
|
for (unsigned i = 0; i != 2; ++i) {
|
|
Value *L = P->getIncomingValue(i);
|
|
Value *R = P->getIncomingValue(!i);
|
|
Operator *LU = dyn_cast<Operator>(L);
|
|
if (!LU)
|
|
continue;
|
|
unsigned Opcode = LU->getOpcode();
|
|
// Check for operations that have the property that if
|
|
// both their operands have low zero bits, the result
|
|
// will have low zero bits.
|
|
if (Opcode == Instruction::Add ||
|
|
Opcode == Instruction::Sub ||
|
|
Opcode == Instruction::And ||
|
|
Opcode == Instruction::Or ||
|
|
Opcode == Instruction::Mul) {
|
|
Value *LL = LU->getOperand(0);
|
|
Value *LR = LU->getOperand(1);
|
|
// Find a recurrence.
|
|
if (LL == I)
|
|
L = LR;
|
|
else if (LR == I)
|
|
L = LL;
|
|
else
|
|
break;
|
|
// Ok, we have a PHI of the form L op= R. Check for low
|
|
// zero bits.
|
|
APInt Mask2 = APInt::getAllOnesValue(BitWidth);
|
|
ComputeMaskedBits(R, Mask2, KnownZero2, KnownOne2, TD, Depth+1);
|
|
Mask2 = APInt::getLowBitsSet(BitWidth,
|
|
KnownZero2.countTrailingOnes());
|
|
|
|
// We need to take the minimum number of known bits
|
|
APInt KnownZero3(KnownZero), KnownOne3(KnownOne);
|
|
ComputeMaskedBits(L, Mask2, KnownZero3, KnownOne3, TD, Depth+1);
|
|
|
|
KnownZero = Mask &
|
|
APInt::getLowBitsSet(BitWidth,
|
|
std::min(KnownZero2.countTrailingOnes(),
|
|
KnownZero3.countTrailingOnes()));
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
// 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<IntrinsicInst>(I)) {
|
|
switch (II->getIntrinsicID()) {
|
|
default: break;
|
|
case Intrinsic::ctpop:
|
|
case Intrinsic::ctlz:
|
|
case Intrinsic::cttz: {
|
|
unsigned LowBits = Log2_32(BitWidth)+1;
|
|
KnownZero = APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
|
|
/// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
|
|
/// this predicate to simplify operations downstream. Mask is known to be zero
|
|
/// for bits that V cannot have.
|
|
///
|
|
/// This function is defined on values with integer type, values with pointer
|
|
/// type (but only if TD is non-null), and vectors of integers. In the case
|
|
/// where V is a vector, the mask, known zero, and known one values are the
|
|
/// same width as the vector element, and the bit is set only if it is true
|
|
/// for all of the elements in the vector.
|
|
bool llvm::MaskedValueIsZero(Value *V, const APInt &Mask,
|
|
const TargetData *TD, unsigned Depth) {
|
|
APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0);
|
|
ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth);
|
|
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
|
|
return (KnownZero & Mask) == Mask;
|
|
}
|
|
|
|
|
|
|
|
/// ComputeNumSignBits - Return the number of times the sign bit of the
|
|
/// register is replicated into the other bits. We know that at least 1 bit
|
|
/// is always equal to the sign bit (itself), but other cases can give us
|
|
/// information. For example, immediately after an "ashr X, 2", we know that
|
|
/// the top 3 bits are all equal to each other, so we return 3.
|
|
///
|
|
/// 'Op' must have a scalar integer type.
|
|
///
|
|
unsigned llvm::ComputeNumSignBits(Value *V, const TargetData *TD,
|
|
unsigned Depth) {
|
|
assert((TD || V->getType()->isIntOrIntVectorTy()) &&
|
|
"ComputeNumSignBits requires a TargetData object to operate "
|
|
"on non-integer values!");
|
|
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<Operator>(V);
|
|
switch (Operator::getOpcode(V)) {
|
|
default: break;
|
|
case Instruction::SExt:
|
|
Tmp = TyBits - U->getOperand(0)->getType()->getScalarSizeInBits();
|
|
return ComputeNumSignBits(U->getOperand(0), TD, Depth+1) + Tmp;
|
|
|
|
case Instruction::AShr:
|
|
Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
|
|
// ashr X, C -> adds C sign bits.
|
|
if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) {
|
|
Tmp += C->getZExtValue();
|
|
if (Tmp > TyBits) Tmp = TyBits;
|
|
}
|
|
return Tmp;
|
|
case Instruction::Shl:
|
|
if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) {
|
|
// shl destroys sign bits.
|
|
Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
|
|
if (C->getZExtValue() >= TyBits || // Bad shift.
|
|
C->getZExtValue() >= Tmp) break; // Shifted all sign bits out.
|
|
return Tmp - C->getZExtValue();
|
|
}
|
|
break;
|
|
case Instruction::And:
|
|
case Instruction::Or:
|
|
case Instruction::Xor: // NOT is handled here.
|
|
// Logical binary ops preserve the number of sign bits at the worst.
|
|
Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
|
|
if (Tmp != 1) {
|
|
Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
|
|
FirstAnswer = std::min(Tmp, Tmp2);
|
|
// We computed what we know about the sign bits as our first
|
|
// answer. Now proceed to the generic code that uses
|
|
// ComputeMaskedBits, and pick whichever answer is better.
|
|
}
|
|
break;
|
|
|
|
case Instruction::Select:
|
|
Tmp = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
|
|
if (Tmp == 1) return 1; // Early out.
|
|
Tmp2 = ComputeNumSignBits(U->getOperand(2), TD, Depth+1);
|
|
return std::min(Tmp, Tmp2);
|
|
|
|
case Instruction::Add:
|
|
// Add can have at most one carry bit. Thus we know that the output
|
|
// is, at worst, one more bit than the inputs.
|
|
Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
|
|
if (Tmp == 1) return 1; // Early out.
|
|
|
|
// Special case decrementing a value (ADD X, -1):
|
|
if (ConstantInt *CRHS = dyn_cast<ConstantInt>(U->getOperand(1)))
|
|
if (CRHS->isAllOnesValue()) {
|
|
APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
|
|
APInt Mask = APInt::getAllOnesValue(TyBits);
|
|
ComputeMaskedBits(U->getOperand(0), Mask, KnownZero, KnownOne, TD,
|
|
Depth+1);
|
|
|
|
// If the input is known to be 0 or 1, the output is 0/-1, which is all
|
|
// sign bits set.
|
|
if ((KnownZero | APInt(TyBits, 1)) == Mask)
|
|
return TyBits;
|
|
|
|
// If we are subtracting one from a positive number, there is no carry
|
|
// out of the result.
|
|
if (KnownZero.isNegative())
|
|
return Tmp;
|
|
}
|
|
|
|
Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
|
|
if (Tmp2 == 1) return 1;
|
|
return std::min(Tmp, Tmp2)-1;
|
|
|
|
case Instruction::Sub:
|
|
Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
|
|
if (Tmp2 == 1) return 1;
|
|
|
|
// Handle NEG.
|
|
if (ConstantInt *CLHS = dyn_cast<ConstantInt>(U->getOperand(0)))
|
|
if (CLHS->isNullValue()) {
|
|
APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
|
|
APInt Mask = APInt::getAllOnesValue(TyBits);
|
|
ComputeMaskedBits(U->getOperand(1), Mask, KnownZero, KnownOne,
|
|
TD, Depth+1);
|
|
// If the input is known to be 0 or 1, the output is 0/-1, which is all
|
|
// sign bits set.
|
|
if ((KnownZero | APInt(TyBits, 1)) == Mask)
|
|
return TyBits;
|
|
|
|
// If the input is known to be positive (the sign bit is known clear),
|
|
// the output of the NEG has the same number of sign bits as the input.
|
|
if (KnownZero.isNegative())
|
|
return Tmp2;
|
|
|
|
// Otherwise, we treat this like a SUB.
|
|
}
|
|
|
|
// Sub can have at most one carry bit. Thus we know that the output
|
|
// is, at worst, one more bit than the inputs.
|
|
Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
|
|
if (Tmp == 1) return 1; // Early out.
|
|
return std::min(Tmp, Tmp2)-1;
|
|
|
|
case Instruction::PHI: {
|
|
PHINode *PN = cast<PHINode>(U);
|
|
// Don't analyze large in-degree PHIs.
|
|
if (PN->getNumIncomingValues() > 4) break;
|
|
|
|
// Take the minimum of all incoming values. This can't infinitely loop
|
|
// because of our depth threshold.
|
|
Tmp = ComputeNumSignBits(PN->getIncomingValue(0), TD, Depth+1);
|
|
for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
if (Tmp == 1) return Tmp;
|
|
Tmp = std::min(Tmp,
|
|
ComputeNumSignBits(PN->getIncomingValue(i), TD, Depth+1));
|
|
}
|
|
return Tmp;
|
|
}
|
|
|
|
case Instruction::Trunc:
|
|
// FIXME: it's tricky to do anything useful for this, but it is an important
|
|
// case for targets like X86.
|
|
break;
|
|
}
|
|
|
|
// Finally, if we can prove that the top bits of the result are 0's or 1's,
|
|
// use this information.
|
|
APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
|
|
APInt Mask = APInt::getAllOnesValue(TyBits);
|
|
ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth);
|
|
|
|
if (KnownZero.isNegative()) { // sign bit is 0
|
|
Mask = KnownZero;
|
|
} else if (KnownOne.isNegative()) { // sign bit is 1;
|
|
Mask = KnownOne;
|
|
} else {
|
|
// Nothing known.
|
|
return FirstAnswer;
|
|
}
|
|
|
|
// Okay, we know that the sign bit in Mask is set. Use CLZ to determine
|
|
// the number of identical bits in the top of the input value.
|
|
Mask = ~Mask;
|
|
Mask <<= Mask.getBitWidth()-TyBits;
|
|
// Return # leading zeros. We use 'min' here in case Val was zero before
|
|
// shifting. We don't want to return '64' as for an i32 "0".
|
|
return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros()));
|
|
}
|
|
|
|
/// ComputeMultiple - This function computes the integer multiple of Base that
|
|
/// equals V. If successful, it returns true and returns the multiple in
|
|
/// Multiple. If unsuccessful, it returns false. It looks
|
|
/// through SExt instructions only if LookThroughSExt is true.
|
|
bool llvm::ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
|
|
bool LookThroughSExt, unsigned Depth) {
|
|
const unsigned MaxDepth = 6;
|
|
|
|
assert(V && "No Value?");
|
|
assert(Depth <= MaxDepth && "Limit Search Depth");
|
|
assert(V->getType()->isIntegerTy() && "Not integer or pointer type!");
|
|
|
|
const 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);
|
|
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<Constant>(Op1) && isa<Constant>(Mul0)) {
|
|
// V == Base * (Mul0 * Op1), so return (Mul0 * Op1)
|
|
Multiple = ConstantExpr::getMul(cast<Constant>(Mul0),
|
|
cast<Constant>(Op1));
|
|
return true;
|
|
}
|
|
|
|
if (ConstantInt *Mul0CI = dyn_cast<ConstantInt>(Mul0))
|
|
if (Mul0CI->getValue() == 1) {
|
|
// V == Base * Op1, so return Op1
|
|
Multiple = Op1;
|
|
return true;
|
|
}
|
|
}
|
|
|
|
if (M1) {
|
|
if (isa<Constant>(Op0) && isa<Constant>(Mul1)) {
|
|
// V == Base * (Mul1 * Op0), so return (Mul1 * Op0)
|
|
Multiple = ConstantExpr::getMul(cast<Constant>(Mul1),
|
|
cast<Constant>(Op0));
|
|
return true;
|
|
}
|
|
|
|
if (ConstantInt *Mul1CI = dyn_cast<ConstantInt>(Mul1))
|
|
if (Mul1CI->getValue() == 1) {
|
|
// V == Base * Op0, so return Op0
|
|
Multiple = Op0;
|
|
return true;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// We could not determine if V is a multiple of Base.
|
|
return false;
|
|
}
|
|
|
|
/// CannotBeNegativeZero - Return true if we can prove that the specified FP
|
|
/// value is never equal to -0.0.
|
|
///
|
|
/// NOTE: this function will need to be revisited when we support non-default
|
|
/// rounding modes!
|
|
///
|
|
bool llvm::CannotBeNegativeZero(const Value *V, unsigned Depth) {
|
|
if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
|
|
return !CFP->getValueAPF().isNegZero();
|
|
|
|
if (Depth == 6)
|
|
return 1; // Limit search depth.
|
|
|
|
const Operator *I = dyn_cast<Operator>(V);
|
|
if (I == 0) return false;
|
|
|
|
// (add x, 0.0) is guaranteed to return +0.0, not -0.0.
|
|
if (I->getOpcode() == Instruction::FAdd &&
|
|
isa<ConstantFP>(I->getOperand(1)) &&
|
|
cast<ConstantFP>(I->getOperand(1))->isNullValue())
|
|
return true;
|
|
|
|
// sitofp and uitofp turn into +0.0 for zero.
|
|
if (isa<SIToFPInst>(I) || isa<UIToFPInst>(I))
|
|
return true;
|
|
|
|
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
|
|
// sqrt(-0.0) = -0.0, no other negative results are possible.
|
|
if (II->getIntrinsicID() == Intrinsic::sqrt)
|
|
return CannotBeNegativeZero(II->getOperand(1), 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->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(V->getType()->isIntegerTy() && "Not an integer value");
|
|
|
|
// Limit our recursion depth.
|
|
if (Depth == 6) {
|
|
Scale = 1;
|
|
Offset = 0;
|
|
return V;
|
|
}
|
|
|
|
if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
|
|
if (ConstantInt *RHSC = dyn_cast<ConstantInt>(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<SExtInst>(V) || isa<ZExtInst>(V)) {
|
|
Value *CastOp = cast<CastInst>(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<std::pair<const Value*, int64_t> > &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<Operator>(V);
|
|
if (Op == 0) {
|
|
// The only non-operator case we can handle are GlobalAliases.
|
|
if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(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<GEPOperator>(Op);
|
|
if (GEPOp == 0)
|
|
return V;
|
|
|
|
// Don't attempt to analyze GEPs over unsized objects.
|
|
if (!cast<PointerType>(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<StructType>(*GTI++)) {
|
|
// For a struct, add the member offset.
|
|
unsigned FieldNo = cast<ConstantInt>(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<ConstantInt>(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<IntegerType>(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<unsigned, 10> &Idxs,
|
|
unsigned IdxSkip,
|
|
Instruction *InsertBefore) {
|
|
const llvm::StructType *STy = llvm::dyn_cast<llvm::StructType>(IndexedType);
|
|
if (STy) {
|
|
// Save the original To argument so we can modify it
|
|
Value *OrigTo = To;
|
|
// General case, the type indexed by Idxs is a struct
|
|
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
|
|
// Process each struct element recursively
|
|
Idxs.push_back(i);
|
|
Value *PrevTo = To;
|
|
To = BuildSubAggregate(From, To, STy->getElementType(i), Idxs, IdxSkip,
|
|
InsertBefore);
|
|
Idxs.pop_back();
|
|
if (!To) {
|
|
// Couldn't find any inserted value for this index? Cleanup
|
|
while (PrevTo != OrigTo) {
|
|
InsertValueInst* Del = cast<InsertValueInst>(PrevTo);
|
|
PrevTo = Del->getAggregateOperand();
|
|
Del->eraseFromParent();
|
|
}
|
|
// Stop processing elements
|
|
break;
|
|
}
|
|
}
|
|
// If we succesfully found a value for each of our subaggregates
|
|
if (To)
|
|
return To;
|
|
}
|
|
// Base case, the type indexed by SourceIdxs is not a struct, or not all of
|
|
// the struct's elements had a value that was inserted directly. In the latter
|
|
// case, perhaps we can't determine each of the subelements individually, but
|
|
// we might be able to find the complete struct somewhere.
|
|
|
|
// Find the value that is at that particular spot
|
|
Value *V = FindInsertedValue(From, Idxs.begin(), Idxs.end());
|
|
|
|
if (!V)
|
|
return NULL;
|
|
|
|
// Insert the value in the new (sub) aggregrate
|
|
return llvm::InsertValueInst::Create(To, V, Idxs.begin() + IdxSkip,
|
|
Idxs.end(), "tmp", InsertBefore);
|
|
}
|
|
|
|
// This helper takes a nested struct and extracts a part of it (which is again a
|
|
// struct) into a new value. For example, given the struct:
|
|
// { a, { b, { c, d }, e } }
|
|
// and the indices "1, 1" this returns
|
|
// { c, d }.
|
|
//
|
|
// It does this by inserting an insertvalue for each element in the resulting
|
|
// struct, as opposed to just inserting a single struct. This will only work if
|
|
// each of the elements of the substruct are known (ie, inserted into From by an
|
|
// insertvalue instruction somewhere).
|
|
//
|
|
// All inserted insertvalue instructions are inserted before InsertBefore
|
|
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<unsigned, 10> Idxs(idx_begin, idx_end);
|
|
unsigned IdxSkip = Idxs.size();
|
|
|
|
return BuildSubAggregate(From, To, IndexedType, Idxs, IdxSkip, InsertBefore);
|
|
}
|
|
|
|
/// FindInsertedValue - Given an aggregrate and an sequence of indices, see if
|
|
/// the scalar value indexed is already around as a register, for example if it
|
|
/// were inserted directly into the aggregrate.
|
|
///
|
|
/// If InsertBefore is not null, this function will duplicate (modified)
|
|
/// insertvalues when a part of a nested struct is extracted.
|
|
Value *llvm::FindInsertedValue(Value *V, const unsigned *idx_begin,
|
|
const unsigned *idx_end, Instruction *InsertBefore) {
|
|
// Nothing to index? Just return V then (this is useful at the end of our
|
|
// recursion)
|
|
if (idx_begin == idx_end)
|
|
return V;
|
|
// We have indices, so V should have an indexable type
|
|
assert((V->getType()->isStructTy() || V->getType()->isArrayTy())
|
|
&& "Not looking at a struct or array?");
|
|
assert(ExtractValueInst::getIndexedType(V->getType(), idx_begin, idx_end)
|
|
&& "Invalid indices for type?");
|
|
const CompositeType *PTy = cast<CompositeType>(V->getType());
|
|
|
|
if (isa<UndefValue>(V))
|
|
return UndefValue::get(ExtractValueInst::getIndexedType(PTy,
|
|
idx_begin,
|
|
idx_end));
|
|
else if (isa<ConstantAggregateZero>(V))
|
|
return Constant::getNullValue(ExtractValueInst::getIndexedType(PTy,
|
|
idx_begin,
|
|
idx_end));
|
|
else if (Constant *C = dyn_cast<Constant>(V)) {
|
|
if (isa<ConstantArray>(C) || isa<ConstantStruct>(C))
|
|
// Recursively process this constant
|
|
return FindInsertedValue(C->getOperand(*idx_begin), idx_begin + 1,
|
|
idx_end, InsertBefore);
|
|
} else if (InsertValueInst *I = dyn_cast<InsertValueInst>(V)) {
|
|
// Loop the indices for the insertvalue instruction in parallel with the
|
|
// requested indices
|
|
const unsigned *req_idx = idx_begin;
|
|
for (const unsigned *i = I->idx_begin(), *e = I->idx_end();
|
|
i != e; ++i, ++req_idx) {
|
|
if (req_idx == idx_end) {
|
|
if (InsertBefore)
|
|
// The requested index identifies a part of a nested aggregate. Handle
|
|
// this specially. For example,
|
|
// %A = insertvalue { i32, {i32, i32 } } undef, i32 10, 1, 0
|
|
// %B = insertvalue { i32, {i32, i32 } } %A, i32 11, 1, 1
|
|
// %C = extractvalue {i32, { i32, i32 } } %B, 1
|
|
// This can be changed into
|
|
// %A = insertvalue {i32, i32 } undef, i32 10, 0
|
|
// %C = insertvalue {i32, i32 } %A, i32 11, 1
|
|
// which allows the unused 0,0 element from the nested struct to be
|
|
// removed.
|
|
return BuildSubAggregate(V, idx_begin, req_idx, InsertBefore);
|
|
else
|
|
// We can't handle this without inserting insertvalues
|
|
return 0;
|
|
}
|
|
|
|
// This insert value inserts something else than what we are looking for.
|
|
// See if the (aggregrate) value inserted into has the value we are
|
|
// looking for, then.
|
|
if (*req_idx != *i)
|
|
return FindInsertedValue(I->getAggregateOperand(), idx_begin, idx_end,
|
|
InsertBefore);
|
|
}
|
|
// If we end up here, the indices of the insertvalue match with those
|
|
// requested (though possibly only partially). Now we recursively look at
|
|
// the inserted value, passing any remaining indices.
|
|
return FindInsertedValue(I->getInsertedValueOperand(), req_idx, idx_end,
|
|
InsertBefore);
|
|
} else if (ExtractValueInst *I = dyn_cast<ExtractValueInst>(V)) {
|
|
// If we're extracting a value from an aggregrate that was extracted from
|
|
// something else, we can extract from that something else directly instead.
|
|
// However, we will need to chain I's indices with the requested indices.
|
|
|
|
// Calculate the number of indices required
|
|
unsigned size = I->getNumIndices() + (idx_end - idx_begin);
|
|
// Allocate some space to put the new indices in
|
|
SmallVector<unsigned, 5> Idxs;
|
|
Idxs.reserve(size);
|
|
// Add indices from the extract value instruction
|
|
for (const unsigned *i = I->idx_begin(), *e = I->idx_end();
|
|
i != e; ++i)
|
|
Idxs.push_back(*i);
|
|
|
|
// Add requested indices
|
|
for (const unsigned *i = idx_begin, *e = idx_end; i != e; ++i)
|
|
Idxs.push_back(*i);
|
|
|
|
assert(Idxs.size() == size
|
|
&& "Number of indices added not correct?");
|
|
|
|
return FindInsertedValue(I->getAggregateOperand(), Idxs.begin(), Idxs.end(),
|
|
InsertBefore);
|
|
}
|
|
// Otherwise, we don't know (such as, extracting from a function return value
|
|
// or load instruction)
|
|
return 0;
|
|
}
|
|
|
|
/// GetConstantStringInfo - This function computes the length of a
|
|
/// null-terminated C string pointed to by V. If successful, it returns true
|
|
/// and returns the string in Str. If unsuccessful, it returns false.
|
|
bool llvm::GetConstantStringInfo(const Value *V, std::string &Str,
|
|
uint64_t Offset,
|
|
bool StopAtNul) {
|
|
// If V is NULL then return false;
|
|
if (V == NULL) return false;
|
|
|
|
// Look through bitcast instructions.
|
|
if (const BitCastInst *BCI = dyn_cast<BitCastInst>(V))
|
|
return GetConstantStringInfo(BCI->getOperand(0), Str, Offset, StopAtNul);
|
|
|
|
// If the value is not a GEP instruction nor a constant expression with a
|
|
// GEP instruction, then return false because ConstantArray can't occur
|
|
// any other way
|
|
const User *GEP = 0;
|
|
if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(V)) {
|
|
GEP = GEPI;
|
|
} else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
|
|
if (CE->getOpcode() == Instruction::BitCast)
|
|
return GetConstantStringInfo(CE->getOperand(0), Str, Offset, StopAtNul);
|
|
if (CE->getOpcode() != Instruction::GetElementPtr)
|
|
return false;
|
|
GEP = CE;
|
|
}
|
|
|
|
if (GEP) {
|
|
// Make sure the GEP has exactly three arguments.
|
|
if (GEP->getNumOperands() != 3)
|
|
return false;
|
|
|
|
// Make sure the index-ee is a pointer to array of i8.
|
|
const PointerType *PT = cast<PointerType>(GEP->getOperand(0)->getType());
|
|
const ArrayType *AT = dyn_cast<ArrayType>(PT->getElementType());
|
|
if (AT == 0 || !AT->getElementType()->isIntegerTy(8))
|
|
return false;
|
|
|
|
// Check to make sure that the first operand of the GEP is an integer and
|
|
// has value 0 so that we are sure we're indexing into the initializer.
|
|
const ConstantInt *FirstIdx = dyn_cast<ConstantInt>(GEP->getOperand(1));
|
|
if (FirstIdx == 0 || !FirstIdx->isZero())
|
|
return false;
|
|
|
|
// If the second index isn't a ConstantInt, then this is a variable index
|
|
// into the array. If this occurs, we can't say anything meaningful about
|
|
// the string.
|
|
uint64_t StartIdx = 0;
|
|
if (const ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
|
|
StartIdx = CI->getZExtValue();
|
|
else
|
|
return false;
|
|
return GetConstantStringInfo(GEP->getOperand(0), Str, StartIdx+Offset,
|
|
StopAtNul);
|
|
}
|
|
|
|
// The GEP instruction, constant or instruction, must reference a global
|
|
// variable that is a constant and is initialized. The referenced constant
|
|
// initializer is the array that we'll use for optimization.
|
|
const GlobalVariable* GV = dyn_cast<GlobalVariable>(V);
|
|
if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer())
|
|
return false;
|
|
const Constant *GlobalInit = GV->getInitializer();
|
|
|
|
// Handle the ConstantAggregateZero case
|
|
if (isa<ConstantAggregateZero>(GlobalInit)) {
|
|
// This is a degenerate case. The initializer is constant zero so the
|
|
// length of the string must be zero.
|
|
Str.clear();
|
|
return true;
|
|
}
|
|
|
|
// Must be a Constant Array
|
|
const ConstantArray *Array = dyn_cast<ConstantArray>(GlobalInit);
|
|
if (Array == 0 || !Array->getType()->getElementType()->isIntegerTy(8))
|
|
return false;
|
|
|
|
// Get the number of elements in the array
|
|
uint64_t NumElts = Array->getType()->getNumElements();
|
|
|
|
if (Offset > NumElts)
|
|
return false;
|
|
|
|
// Traverse the constant array from 'Offset' which is the place the GEP refers
|
|
// to in the array.
|
|
Str.reserve(NumElts-Offset);
|
|
for (unsigned i = Offset; i != NumElts; ++i) {
|
|
const Constant *Elt = Array->getOperand(i);
|
|
const ConstantInt *CI = dyn_cast<ConstantInt>(Elt);
|
|
if (!CI) // This array isn't suitable, non-int initializer.
|
|
return false;
|
|
if (StopAtNul && CI->isZero())
|
|
return true; // we found end of string, success!
|
|
Str += (char)CI->getZExtValue();
|
|
}
|
|
|
|
// The array isn't null terminated, but maybe this is a memcpy, not a strcpy.
|
|
return true;
|
|
}
|
|
|
|
// These next two are very similar to the above, but also look through PHI
|
|
// nodes.
|
|
// TODO: See if we can integrate these two together.
|
|
|
|
/// GetStringLengthH - If we can compute the length of the string pointed to by
|
|
/// the specified pointer, return 'len+1'. If we can't, return 0.
|
|
static uint64_t GetStringLengthH(Value *V, SmallPtrSet<PHINode*, 32> &PHIs) {
|
|
// Look through noop bitcast instructions.
|
|
if (BitCastInst *BCI = dyn_cast<BitCastInst>(V))
|
|
return GetStringLengthH(BCI->getOperand(0), PHIs);
|
|
|
|
// If this is a PHI node, there are two cases: either we have already seen it
|
|
// or we haven't.
|
|
if (PHINode *PN = dyn_cast<PHINode>(V)) {
|
|
if (!PHIs.insert(PN))
|
|
return ~0ULL; // already in the set.
|
|
|
|
// If it was new, see if all the input strings are the same length.
|
|
uint64_t LenSoFar = ~0ULL;
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
uint64_t Len = GetStringLengthH(PN->getIncomingValue(i), PHIs);
|
|
if (Len == 0) return 0; // Unknown length -> unknown.
|
|
|
|
if (Len == ~0ULL) continue;
|
|
|
|
if (Len != LenSoFar && LenSoFar != ~0ULL)
|
|
return 0; // Disagree -> unknown.
|
|
LenSoFar = Len;
|
|
}
|
|
|
|
// Success, all agree.
|
|
return LenSoFar;
|
|
}
|
|
|
|
// strlen(select(c,x,y)) -> strlen(x) ^ strlen(y)
|
|
if (SelectInst *SI = dyn_cast<SelectInst>(V)) {
|
|
uint64_t Len1 = GetStringLengthH(SI->getTrueValue(), PHIs);
|
|
if (Len1 == 0) return 0;
|
|
uint64_t Len2 = GetStringLengthH(SI->getFalseValue(), PHIs);
|
|
if (Len2 == 0) return 0;
|
|
if (Len1 == ~0ULL) return Len2;
|
|
if (Len2 == ~0ULL) return Len1;
|
|
if (Len1 != Len2) return 0;
|
|
return Len1;
|
|
}
|
|
|
|
// If the value is not a GEP instruction nor a constant expression with a
|
|
// GEP instruction, then return unknown.
|
|
User *GEP = 0;
|
|
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(V)) {
|
|
GEP = GEPI;
|
|
} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
|
|
if (CE->getOpcode() != Instruction::GetElementPtr)
|
|
return 0;
|
|
GEP = CE;
|
|
} else {
|
|
return 0;
|
|
}
|
|
|
|
// Make sure the GEP has exactly three arguments.
|
|
if (GEP->getNumOperands() != 3)
|
|
return 0;
|
|
|
|
// Check to make sure that the first operand of the GEP is an integer and
|
|
// has value 0 so that we are sure we're indexing into the initializer.
|
|
if (ConstantInt *Idx = dyn_cast<ConstantInt>(GEP->getOperand(1))) {
|
|
if (!Idx->isZero())
|
|
return 0;
|
|
} else
|
|
return 0;
|
|
|
|
// If the second index isn't a ConstantInt, then this is a variable index
|
|
// into the array. If this occurs, we can't say anything meaningful about
|
|
// the string.
|
|
uint64_t StartIdx = 0;
|
|
if (ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
|
|
StartIdx = CI->getZExtValue();
|
|
else
|
|
return 0;
|
|
|
|
// The GEP instruction, constant or instruction, must reference a global
|
|
// variable that is a constant and is initialized. The referenced constant
|
|
// initializer is the array that we'll use for optimization.
|
|
GlobalVariable* GV = dyn_cast<GlobalVariable>(GEP->getOperand(0));
|
|
if (!GV || !GV->isConstant() || !GV->hasInitializer() ||
|
|
GV->mayBeOverridden())
|
|
return 0;
|
|
Constant *GlobalInit = GV->getInitializer();
|
|
|
|
// Handle the ConstantAggregateZero case, which is a degenerate case. The
|
|
// initializer is constant zero so the length of the string must be zero.
|
|
if (isa<ConstantAggregateZero>(GlobalInit))
|
|
return 1; // Len = 0 offset by 1.
|
|
|
|
// Must be a Constant Array
|
|
ConstantArray *Array = dyn_cast<ConstantArray>(GlobalInit);
|
|
if (!Array || !Array->getType()->getElementType()->isIntegerTy(8))
|
|
return false;
|
|
|
|
// Get the number of elements in the array
|
|
uint64_t NumElts = Array->getType()->getNumElements();
|
|
|
|
// Traverse the constant array from StartIdx (derived above) which is
|
|
// the place the GEP refers to in the array.
|
|
for (unsigned i = StartIdx; i != NumElts; ++i) {
|
|
Constant *Elt = Array->getOperand(i);
|
|
ConstantInt *CI = dyn_cast<ConstantInt>(Elt);
|
|
if (!CI) // This array isn't suitable, non-int initializer.
|
|
return 0;
|
|
if (CI->isZero())
|
|
return i-StartIdx+1; // We found end of string, success!
|
|
}
|
|
|
|
return 0; // The array isn't null terminated, conservatively return 'unknown'.
|
|
}
|
|
|
|
/// GetStringLength - If we can compute the length of the string pointed to by
|
|
/// the specified pointer, return 'len+1'. If we can't, return 0.
|
|
uint64_t llvm::GetStringLength(Value *V) {
|
|
if (!V->getType()->isPointerTy()) return 0;
|
|
|
|
SmallPtrSet<PHINode*, 32> PHIs;
|
|
uint64_t Len = GetStringLengthH(V, PHIs);
|
|
// If Len is ~0ULL, we had an infinite phi cycle: this is dead code, so return
|
|
// an empty string as a length.
|
|
return Len == ~0ULL ? 1 : Len;
|
|
}
|