C++ Constant::getAggregateElement方法代码示例

void InstrProfiling::lowerCoverageData(GlobalVariable *CoverageData) {
  CoverageData->setSection(getCoverageSection());
  CoverageData->setAlignment(8);

  Constant *Init = CoverageData->getInitializer();
  // We're expecting { i32, i32, i32, i32, [n x { i8*, i32, i32 }], [m x i8] }
  // for some C. If not, the frontend's given us something broken.
  assert(Init->getNumOperands() == 6 && "bad number of fields in coverage map");
  assert(isa<ConstantArray>(Init->getAggregateElement(4)) &&
         "invalid function list in coverage map");
  ConstantArray *Records = cast<ConstantArray>(Init->getAggregateElement(4));
  for (unsigned I = 0, E = Records->getNumOperands(); I < E; ++I) {
    Constant *Record = Records->getOperand(I);
    Value *V = const_cast<Value *>(Record->getOperand(0))->stripPointerCasts();

    assert(isa<GlobalVariable>(V) && "Missing reference to function name");
    GlobalVariable *Name = cast<GlobalVariable>(V);

    // If we have region counters for this name, we've already handled it.
    auto It = RegionCounters.find(Name);
    if (It != RegionCounters.end())
      continue;

    // Move the name variable to the right section.
    Name->setSection(getNameSection());
    Name->setAlignment(1);
  }
}

static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
                   AssumptionCache *AC) {
  // Assume undef could be zero.
  if (isa<UndefValue>(V))
    return true;

  VectorType *VecTy = dyn_cast<VectorType>(V->getType());
  if (!VecTy) {
    KnownBits Known = computeKnownBits(V, DL, 0, AC, dyn_cast<Instruction>(V), DT);
    return Known.isZero();
  }

  // Per-component check doesn't work with zeroinitializer
  Constant *C = dyn_cast<Constant>(V);
  if (!C)
    return false;

  if (C->isZeroValue())
    return true;

  // For a vector, KnownZero will only be true if all values are zero, so check
  // this per component
  for (unsigned I = 0, N = VecTy->getNumElements(); I != N; ++I) {
    Constant *Elem = C->getAggregateElement(I);
    if (isa<UndefValue>(Elem))
      return true;

    KnownBits Known = computeKnownBits(Elem, DL);
    if (Known.isZero())
      return true;
  }

  return false;
}

static bool isConstantIntVector(Value *Mask) {
  Constant *C = dyn_cast<Constant>(Mask);
  if (!C)
    return false;

  unsigned NumElts = Mask->getType()->getVectorNumElements();
  for (unsigned i = 0; i != NumElts; ++i) {
    Constant *CElt = C->getAggregateElement(i);
    if (!CElt || !isa<ConstantInt>(CElt))
      return false;
  }

  return true;
}

/// \brief Given a vector and an element number, see if the scalar value is
/// already around as a register, for example if it were inserted then extracted
/// from the vector.
llvm::Value *llvm::findScalarElement(llvm::Value *V, unsigned EltNo) {
  assert(V->getType()->isVectorTy() && "Not looking at a vector?");
  VectorType *VTy = cast<VectorType>(V->getType());
  unsigned Width = VTy->getNumElements();
  if (EltNo >= Width)  // Out of range access.
    return UndefValue::get(VTy->getElementType());

  if (Constant *C = dyn_cast<Constant>(V))
    return C->getAggregateElement(EltNo);

  if (InsertElementInst *III = dyn_cast<InsertElementInst>(V)) {
    // If this is an insert to a variable element, we don't know what it is.
    if (!isa<ConstantInt>(III->getOperand(2)))
      return nullptr;
    unsigned IIElt = cast<ConstantInt>(III->getOperand(2))->getZExtValue();

    // If this is an insert to the element we are looking for, return the
    // inserted value.
    if (EltNo == IIElt)
      return III->getOperand(1);

    // Otherwise, the insertelement doesn't modify the value, recurse on its
    // vector input.
    return findScalarElement(III->getOperand(0), EltNo);
  }

  if (ShuffleVectorInst *SVI = dyn_cast<ShuffleVectorInst>(V)) {
    unsigned LHSWidth = SVI->getOperand(0)->getType()->getVectorNumElements();
    int InEl = SVI->getMaskValue(EltNo);
    if (InEl < 0)
      return UndefValue::get(VTy->getElementType());
    if (InEl < (int)LHSWidth)
      return findScalarElement(SVI->getOperand(0), InEl);
    return findScalarElement(SVI->getOperand(1), InEl - LHSWidth);
  }

  // Extract a value from a vector add operation with a constant zero.
  Value *Val = nullptr; Constant *Con = nullptr;
  if (match(V,
            llvm::PatternMatch::m_Add(llvm::PatternMatch::m_Value(Val),
                                      llvm::PatternMatch::m_Constant(Con)))) {
    if (Con->getAggregateElement(EltNo)->isNullValue())
      return findScalarElement(Val, EltNo);
  }

  // Otherwise, we don't know.
  return nullptr;
}

static bool isZero(Value *V, const DataLayout *DL) {
    // Assume undef could be zero.
    if (isa<UndefValue>(V))
        return true;

    VectorType *VecTy = dyn_cast<VectorType>(V->getType());
    if (!VecTy) {
        unsigned BitWidth = V->getType()->getIntegerBitWidth();
        APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
        computeKnownBits(V, KnownZero, KnownOne, DL);
        return KnownZero.isAllOnesValue();
    }

    // Per-component check doesn't work with zeroinitializer
    Constant *C = dyn_cast<Constant>(V);
    if (!C)
        return false;

    if (C->isZeroValue())
        return true;

    // For a vector, KnownZero will only be true if all values are zero, so check
    // this per component
    unsigned BitWidth = VecTy->getElementType()->getIntegerBitWidth();
    for (unsigned I = 0, N = VecTy->getNumElements(); I != N; ++I) {
        Constant *Elem = C->getAggregateElement(I);
        if (isa<UndefValue>(Elem))
            return true;

        APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
        computeKnownBits(Elem, KnownZero, KnownOne, DL);
        if (KnownZero.isAllOnesValue())
            return true;
    }

    return false;
}

Instruction *InstCombiner::visitSRem(BinaryOperator &I) {
  Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);

  if (Value *V = SimplifySRemInst(Op0, Op1, TD))
    return ReplaceInstUsesWith(I, V);

  // Handle the integer rem common cases
  if (Instruction *Common = commonIRemTransforms(I))
    return Common;
  
  if (Value *RHSNeg = dyn_castNegVal(Op1))
    if (!isa<Constant>(RHSNeg) ||
        (isa<ConstantInt>(RHSNeg) &&
         cast<ConstantInt>(RHSNeg)->getValue().isStrictlyPositive())) {
      // X % -Y -> X % Y
      Worklist.AddValue(I.getOperand(1));
      I.setOperand(1, RHSNeg);
      return &I;
    }

  // If the sign bits of both operands are zero (i.e. we can prove they are
  // unsigned inputs), turn this into a urem.
  if (I.getType()->isIntegerTy()) {
    APInt Mask(APInt::getSignBit(I.getType()->getPrimitiveSizeInBits()));
    if (MaskedValueIsZero(Op1, Mask) && MaskedValueIsZero(Op0, Mask)) {
      // X srem Y -> X urem Y, iff X and Y don't have sign bit set
      return BinaryOperator::CreateURem(Op0, Op1, I.getName());
    }
  }

  // If it's a constant vector, flip any negative values positive.
  if (isa<ConstantVector>(Op1) || isa<ConstantDataVector>(Op1)) {
    Constant *C = cast<Constant>(Op1);
    unsigned VWidth = C->getType()->getVectorNumElements();

    bool hasNegative = false;
    bool hasMissing = false;
    for (unsigned i = 0; i != VWidth; ++i) {
      Constant *Elt = C->getAggregateElement(i);
      if (Elt == 0) {
        hasMissing = true;
        break;
      }

      if (ConstantInt *RHS = dyn_cast<ConstantInt>(Elt))
        if (RHS->isNegative())
          hasNegative = true;
    }

    if (hasNegative && !hasMissing) {
      SmallVector<Constant *, 16> Elts(VWidth);
      for (unsigned i = 0; i != VWidth; ++i) {
        Elts[i] = C->getAggregateElement(i);  // Handle undef, etc.
        if (ConstantInt *RHS = dyn_cast<ConstantInt>(Elts[i])) {
          if (RHS->isNegative())
            Elts[i] = cast<ConstantInt>(ConstantExpr::getNeg(RHS));
        }
      }

      Constant *NewRHSV = ConstantVector::get(Elts);
      if (NewRHSV != C) {  // Don't loop on -MININT
        Worklist.AddValue(I.getOperand(1));
        I.setOperand(1, NewRHSV);
        return &I;
      }
    }
  }

  return 0;
}