C++ PHINode::setDebugLoc方法代码示例

Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
  // If there is no definition of the renamed variable in this block, just use
  // GetValueAtEndOfBlock to do our work.
  if (!HasValueForBlock(BB))
    return GetValueAtEndOfBlock(BB);

  // Otherwise, we have the hard case.  Get the live-in values for each
  // predecessor.
  SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues;
  Value *SingularValue = nullptr;

  // We can get our predecessor info by walking the pred_iterator list, but it
  // is relatively slow.  If we already have PHI nodes in this block, walk one
  // of them to get the predecessor list instead.
  if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
    for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
      BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
      Value *PredVal = GetValueAtEndOfBlock(PredBB);
      PredValues.push_back(std::make_pair(PredBB, PredVal));

      // Compute SingularValue.
      if (i == 0)
        SingularValue = PredVal;
      else if (PredVal != SingularValue)
        SingularValue = nullptr;
    }
  } else {
    bool isFirstPred = true;
    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
      BasicBlock *PredBB = *PI;
      Value *PredVal = GetValueAtEndOfBlock(PredBB);
      PredValues.push_back(std::make_pair(PredBB, PredVal));

      // Compute SingularValue.
      if (isFirstPred) {
        SingularValue = PredVal;
        isFirstPred = false;
      } else if (PredVal != SingularValue)
        SingularValue = nullptr;
    }
  }

  // If there are no predecessors, just return undef.
  if (PredValues.empty())
    return UndefValue::get(ProtoType);

  // Otherwise, if all the merged values are the same, just use it.
  if (SingularValue)
    return SingularValue;

  // Otherwise, we do need a PHI: check to see if we already have one available
  // in this block that produces the right value.
  if (isa<PHINode>(BB->begin())) {
    SmallDenseMap<BasicBlock*, Value*, 8> ValueMapping(PredValues.begin(),
                                                       PredValues.end());
    PHINode *SomePHI;
    for (BasicBlock::iterator It = BB->begin();
         (SomePHI = dyn_cast<PHINode>(It)); ++It) {
      if (IsEquivalentPHI(SomePHI, ValueMapping))
        return SomePHI;
    }
  }

  // Ok, we have no way out, insert a new one now.
  PHINode *InsertedPHI = PHINode::Create(ProtoType, PredValues.size(),
                                         ProtoName, &BB->front());

  // Fill in all the predecessors of the PHI.
  for (const auto &PredValue : PredValues)
    InsertedPHI->addIncoming(PredValue.second, PredValue.first);

  // See if the PHI node can be merged to a single value.  This can happen in
  // loop cases when we get a PHI of itself and one other value.
  if (Value *V =
          SimplifyInstruction(InsertedPHI, BB->getModule()->getDataLayout())) {
    InsertedPHI->eraseFromParent();
    return V;
  }

  // Set the DebugLoc of the inserted PHI, if available.
  DebugLoc DL;
  if (const Instruction *I = BB->getFirstNonPHI())
      DL = I->getDebugLoc();
  InsertedPHI->setDebugLoc(DL);

  // If the client wants to know about all new instructions, tell it.
  if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);

  DEBUG(dbgs() << "  Inserted PHI: " << *InsertedPHI << "\n");
  return InsertedPHI;
}