C++ SmallVectorImpl::assign方法代码示例

unsigned ConstraintGraph::computeConnectedComponents(
           SmallVectorImpl<TypeVariableType *> &typeVars,
           SmallVectorImpl<unsigned> &components) {
  // Track those type variables that the caller cares about.
  llvm::SmallPtrSet<TypeVariableType *, 4> typeVarSubset(typeVars.begin(),
                                                         typeVars.end());
  typeVars.clear();

  // Initialize the components with component == # of type variables,
  // a sentinel value indicating
  unsigned numTypeVariables = TypeVariables.size();
  components.assign(numTypeVariables, numTypeVariables);

  // Perform a depth-first search from each type variable to identify
  // what component it is in.
  unsigned numComponents = 0;
  for (unsigned i = 0; i != numTypeVariables; ++i) {
    auto typeVar = TypeVariables[i];

    // Look up the node for this type variable.
    auto nodeAndIndex = lookupNode(typeVar);

    // If we're already assigned a component for this node, skip it.
    unsigned &curComponent = components[nodeAndIndex.second];
    if (curComponent != numTypeVariables)
      continue;

    // Record this component.
    unsigned component = numComponents++;

    // Note that this node is part of this component, then visit it.
    curComponent = component;
    connectedComponentsDFS(*this, nodeAndIndex.first, component, components);
  }

  // Figure out which components have unbound type variables; these
  // are the only components and type variables we want to report.
  SmallVector<bool, 4> componentHasUnboundTypeVar(numComponents, false);
  for (unsigned i = 0; i != numTypeVariables; ++i) {
    // If this type variable has a fixed type, skip it.
    if (CS.getFixedType(TypeVariables[i]))
      continue;

    // If we only care about a subset, and this type variable isn't in that
    // subset, skip it.
    if (!typeVarSubset.empty() && typeVarSubset.count(TypeVariables[i]) == 0)
      continue;

    componentHasUnboundTypeVar[components[i]] = true;
  }

  // Renumber the old components to the new components.
  SmallVector<unsigned, 4> componentRenumbering(numComponents, 0);
  numComponents = 0;
  for (unsigned i = 0, n = componentHasUnboundTypeVar.size(); i != n; ++i) {
    // Skip components that have no unbound type variables.
    if (!componentHasUnboundTypeVar[i])
      continue;

    componentRenumbering[i] = numComponents++;
  }

  // Copy over the type variables in the live components and remap
  // component numbers.
  unsigned outIndex = 0;
  for (unsigned i = 0, n = TypeVariables.size(); i != n; ++i) {
    // Skip type variables in dead components.
    if (!componentHasUnboundTypeVar[components[i]])
      continue;

    typeVars.push_back(TypeVariables[i]);
    components[outIndex] = componentRenumbering[components[i]];
    ++outIndex;
  }
  components.erase(components.begin() + outIndex, components.end());

  return numComponents;
}

/// CollectSingleShuffleElements - If V is a shuffle of values that ONLY returns
/// elements from either LHS or RHS, return the shuffle mask and true.
/// Otherwise, return false.
static bool CollectSingleShuffleElements(Value *V, Value *LHS, Value *RHS,
                                         SmallVectorImpl<Constant*> &Mask) {
  assert(V->getType() == LHS->getType() && V->getType() == RHS->getType() &&
         "Invalid CollectSingleShuffleElements");
  unsigned NumElts = cast<VectorType>(V->getType())->getNumElements();

  if (isa<UndefValue>(V)) {
    Mask.assign(NumElts, UndefValue::get(Type::getInt32Ty(V->getContext())));
    return true;
  }

  if (V == LHS) {
    for (unsigned i = 0; i != NumElts; ++i)
      Mask.push_back(ConstantInt::get(Type::getInt32Ty(V->getContext()), i));
    return true;
  }

  if (V == RHS) {
    for (unsigned i = 0; i != NumElts; ++i)
      Mask.push_back(ConstantInt::get(Type::getInt32Ty(V->getContext()),
                                      i+NumElts));
    return true;
  }

  if (InsertElementInst *IEI = dyn_cast<InsertElementInst>(V)) {
    // If this is an insert of an extract from some other vector, include it.
    Value *VecOp    = IEI->getOperand(0);
    Value *ScalarOp = IEI->getOperand(1);
    Value *IdxOp    = IEI->getOperand(2);

    if (!isa<ConstantInt>(IdxOp))
      return false;
    unsigned InsertedIdx = cast<ConstantInt>(IdxOp)->getZExtValue();

    if (isa<UndefValue>(ScalarOp)) {  // inserting undef into vector.
      // Okay, we can handle this if the vector we are insertinting into is
      // transitively ok.
      if (CollectSingleShuffleElements(VecOp, LHS, RHS, Mask)) {
        // If so, update the mask to reflect the inserted undef.
        Mask[InsertedIdx] = UndefValue::get(Type::getInt32Ty(V->getContext()));
        return true;
      }
    } else if (ExtractElementInst *EI = dyn_cast<ExtractElementInst>(ScalarOp)){
      if (isa<ConstantInt>(EI->getOperand(1)) &&
          EI->getOperand(0)->getType() == V->getType()) {
        unsigned ExtractedIdx =
        cast<ConstantInt>(EI->getOperand(1))->getZExtValue();

        // This must be extracting from either LHS or RHS.
        if (EI->getOperand(0) == LHS || EI->getOperand(0) == RHS) {
          // Okay, we can handle this if the vector we are insertinting into is
          // transitively ok.
          if (CollectSingleShuffleElements(VecOp, LHS, RHS, Mask)) {
            // If so, update the mask to reflect the inserted value.
            if (EI->getOperand(0) == LHS) {
              Mask[InsertedIdx % NumElts] =
              ConstantInt::get(Type::getInt32Ty(V->getContext()),
                               ExtractedIdx);
            } else {
              assert(EI->getOperand(0) == RHS);
              Mask[InsertedIdx % NumElts] =
              ConstantInt::get(Type::getInt32Ty(V->getContext()),
                               ExtractedIdx+NumElts);
            }
            return true;
          }
        }
      }
    }
  }
  // TODO: Handle shufflevector here!

  return false;
}

static ShuffleOps CollectShuffleElements(Value *V,
                                         SmallVectorImpl<Constant *> &Mask,
                                         Value *PermittedRHS) {
  assert(V->getType()->isVectorTy() && "Invalid shuffle!");
  unsigned NumElts = cast<VectorType>(V->getType())->getNumElements();

  if (isa<UndefValue>(V)) {
    Mask.assign(NumElts, UndefValue::get(Type::getInt32Ty(V->getContext())));
    return std::make_pair(
        PermittedRHS ? UndefValue::get(PermittedRHS->getType()) : V, nullptr);
  }

  if (isa<ConstantAggregateZero>(V)) {
    Mask.assign(NumElts, ConstantInt::get(Type::getInt32Ty(V->getContext()),0));
    return std::make_pair(V, nullptr);
  }

  if (InsertElementInst *IEI = dyn_cast<InsertElementInst>(V)) {
    // If this is an insert of an extract from some other vector, include it.
    Value *VecOp    = IEI->getOperand(0);
    Value *ScalarOp = IEI->getOperand(1);
    Value *IdxOp    = IEI->getOperand(2);

    if (ExtractElementInst *EI = dyn_cast<ExtractElementInst>(ScalarOp)) {
      if (isa<ConstantInt>(EI->getOperand(1)) && isa<ConstantInt>(IdxOp)) {
        unsigned ExtractedIdx =
          cast<ConstantInt>(EI->getOperand(1))->getZExtValue();
        unsigned InsertedIdx = cast<ConstantInt>(IdxOp)->getZExtValue();

        // Either the extracted from or inserted into vector must be RHSVec,
        // otherwise we'd end up with a shuffle of three inputs.
        if (EI->getOperand(0) == PermittedRHS || PermittedRHS == nullptr) {
          Value *RHS = EI->getOperand(0);
          ShuffleOps LR = CollectShuffleElements(VecOp, Mask, RHS);
          assert(LR.second == nullptr || LR.second == RHS);

          if (LR.first->getType() != RHS->getType()) {
            // We tried our best, but we can't find anything compatible with RHS
            // further up the chain. Return a trivial shuffle.
            for (unsigned i = 0; i < NumElts; ++i)
              Mask[i] = ConstantInt::get(Type::getInt32Ty(V->getContext()), i);
            return std::make_pair(V, nullptr);
          }

          unsigned NumLHSElts = RHS->getType()->getVectorNumElements();
          Mask[InsertedIdx % NumElts] =
            ConstantInt::get(Type::getInt32Ty(V->getContext()),
                             NumLHSElts+ExtractedIdx);
          return std::make_pair(LR.first, RHS);
        }

        if (VecOp == PermittedRHS) {
          // We've gone as far as we can: anything on the other side of the
          // extractelement will already have been converted into a shuffle.
          unsigned NumLHSElts =
              EI->getOperand(0)->getType()->getVectorNumElements();
          for (unsigned i = 0; i != NumElts; ++i)
            Mask.push_back(ConstantInt::get(
                Type::getInt32Ty(V->getContext()),
                i == InsertedIdx ? ExtractedIdx : NumLHSElts + i));
          return std::make_pair(EI->getOperand(0), PermittedRHS);
        }

        // If this insertelement is a chain that comes from exactly these two
        // vectors, return the vector and the effective shuffle.
        if (EI->getOperand(0)->getType() == PermittedRHS->getType() &&
            CollectSingleShuffleElements(IEI, EI->getOperand(0), PermittedRHS,
                                         Mask))
          return std::make_pair(EI->getOperand(0), PermittedRHS);
      }
    }
  }

  // Otherwise, can't do anything fancy.  Return an identity vector.
  for (unsigned i = 0; i != NumElts; ++i)
    Mask.push_back(ConstantInt::get(Type::getInt32Ty(V->getContext()), i));
  return std::make_pair(V, nullptr);
}