Ejemplo n.º 1
0
// NewBB is split and now it has one successor. Update dominace frontier to
// reflect this change.
void DominanceFrontier::splitBlock(BasicBlock *NewBB) {
  assert(NewBB->getTerminator()->getNumSuccessors() == 1
         && "NewBB should have a single successor!");
  BasicBlock *NewBBSucc = NewBB->getTerminator()->getSuccessor(0);

  SmallVector<BasicBlock*, 8> PredBlocks;
  for (pred_iterator PI = pred_begin(NewBB), PE = pred_end(NewBB);
       PI != PE; ++PI)
      PredBlocks.push_back(*PI);  

  if (PredBlocks.empty())
    // If NewBB does not have any predecessors then it is a entry block.
    // In this case, NewBB and its successor NewBBSucc dominates all
    // other blocks.
    return;

  // NewBBSucc inherits original NewBB frontier.
  DominanceFrontier::iterator NewBBI = find(NewBB);
  if (NewBBI != end()) {
    DominanceFrontier::DomSetType NewBBSet = NewBBI->second;
    DominanceFrontier::DomSetType NewBBSuccSet;
    NewBBSuccSet.insert(NewBBSet.begin(), NewBBSet.end());
    addBasicBlock(NewBBSucc, NewBBSuccSet);
  }

  // If NewBB dominates NewBBSucc, then DF(NewBB) is now going to be the
  // DF(PredBlocks[0]) without the stuff that the new block does not dominate
  // a predecessor of.
  DominatorTree &DT = getAnalysis<DominatorTree>();
  if (DT.dominates(NewBB, NewBBSucc)) {
    DominanceFrontier::iterator DFI = find(PredBlocks[0]);
    if (DFI != end()) {
      DominanceFrontier::DomSetType Set = DFI->second;
      // Filter out stuff in Set that we do not dominate a predecessor of.
      for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
             E = Set.end(); SetI != E;) {
        bool DominatesPred = false;
        for (pred_iterator PI = pred_begin(*SetI), E = pred_end(*SetI);
             PI != E; ++PI)
          if (DT.dominates(NewBB, *PI))
            DominatesPred = true;
        if (!DominatesPred)
          Set.erase(SetI++);
        else
          ++SetI;
      }

      if (NewBBI != end()) {
        for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
               E = Set.end(); SetI != E; ++SetI) {
          BasicBlock *SB = *SetI;
          addToFrontier(NewBBI, SB);
        }
      } else 
        addBasicBlock(NewBB, Set);
    }
    
  } else {
    // DF(NewBB) is {NewBBSucc} because NewBB does not strictly dominate
    // NewBBSucc, but it does dominate itself (and there is an edge (NewBB ->
    // NewBBSucc)).  NewBBSucc is the single successor of NewBB.
    DominanceFrontier::DomSetType NewDFSet;
    NewDFSet.insert(NewBBSucc);
    addBasicBlock(NewBB, NewDFSet);
  }
  
  // Now we must loop over all of the dominance frontiers in the function,
  // replacing occurrences of NewBBSucc with NewBB in some cases.  All
  // blocks that dominate a block in PredBlocks and contained NewBBSucc in
  // their dominance frontier must be updated to contain NewBB instead.
  //
  for (Function::iterator FI = NewBB->getParent()->begin(),
         FE = NewBB->getParent()->end(); FI != FE; ++FI) {
    DominanceFrontier::iterator DFI = find(FI);
    if (DFI == end()) continue;  // unreachable block.
    
    // Only consider nodes that have NewBBSucc in their dominator frontier.
    if (!DFI->second.count(NewBBSucc)) continue;

    // Verify whether this block dominates a block in predblocks.  If not, do
    // not update it.
    bool BlockDominatesAny = false;
    for (SmallVectorImpl<BasicBlock*>::const_iterator BI = PredBlocks.begin(), 
           BE = PredBlocks.end(); BI != BE; ++BI) {
      if (DT.dominates(FI, *BI)) {
        BlockDominatesAny = true;
        break;
      }
    }

    // If NewBBSucc should not stay in our dominator frontier, remove it.
    // We remove it unless there is a predecessor of NewBBSucc that we
    // dominate, but we don't strictly dominate NewBBSucc.
    bool ShouldRemove = true;
    if ((BasicBlock*)FI == NewBBSucc || !DT.dominates(FI, NewBBSucc)) {
      // Okay, we know that PredDom does not strictly dominate NewBBSucc.
      // Check to see if it dominates any predecessors of NewBBSucc.
      for (pred_iterator PI = pred_begin(NewBBSucc),
           E = pred_end(NewBBSucc); PI != E; ++PI)
        if (DT.dominates(FI, *PI)) {
          ShouldRemove = false;
          break;
        }
    }
    
    if (ShouldRemove)
      removeFromFrontier(DFI, NewBBSucc);
    if (BlockDominatesAny && (&*FI == NewBB || !DT.dominates(FI, NewBB)))
      addToFrontier(DFI, NewBB);
  }
}
Ejemplo n.º 2
0
// NewBB is split and now it has one successor. Update dominance frontier to
// reflect this change.
void DominanceFrontier::splitBlock(BasicBlock *NewBB) {
  assert(NewBB->getTerminator()->getNumSuccessors() == 1 &&
         "NewBB should have a single successor!");
  BasicBlock *NewBBSucc = NewBB->getTerminator()->getSuccessor(0);

  // NewBBSucc inherits original NewBB frontier.
  DominanceFrontier::iterator NewBBI = find(NewBB);
  if (NewBBI != end())
    addBasicBlock(NewBBSucc, NewBBI->second);

  // If NewBB dominates NewBBSucc, then DF(NewBB) is now going to be the
  // DF(NewBBSucc) without the stuff that the new block does not dominate
  // a predecessor of.
  DominatorTree &DT = getAnalysis<DominatorTree>();
  DomTreeNode *NewBBNode = DT.getNode(NewBB);
  DomTreeNode *NewBBSuccNode = DT.getNode(NewBBSucc);
  if (DT.dominates(NewBBNode, NewBBSuccNode)) {
    DominanceFrontier::iterator DFI = find(NewBBSucc);
    if (DFI != end()) {
      DominanceFrontier::DomSetType Set = DFI->second;
      // Filter out stuff in Set that we do not dominate a predecessor of.
      for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
             E = Set.end(); SetI != E;) {
        bool DominatesPred = false;
        for (pred_iterator PI = pred_begin(*SetI), E = pred_end(*SetI);
             PI != E; ++PI)
          if (DT.dominates(NewBBNode, DT.getNode(*PI))) {
            DominatesPred = true;
            break;
          }
        if (!DominatesPred)
          Set.erase(SetI++);
        else
          ++SetI;
      }

      if (NewBBI != end()) {
        for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
               E = Set.end(); SetI != E; ++SetI) {
          BasicBlock *SB = *SetI;
          addToFrontier(NewBBI, SB);
        }
      } else 
        addBasicBlock(NewBB, Set);
    }
    
  } else {
    // DF(NewBB) is {NewBBSucc} because NewBB does not strictly dominate
    // NewBBSucc, but it does dominate itself (and there is an edge (NewBB ->
    // NewBBSucc)).  NewBBSucc is the single successor of NewBB.
    DominanceFrontier::DomSetType NewDFSet;
    NewDFSet.insert(NewBBSucc);
    addBasicBlock(NewBB, NewDFSet);
  }

  // Now update dominance frontiers which either used to contain NewBBSucc
  // or which now need to include NewBB.

  // Collect the set of blocks which dominate a predecessor of NewBB or
  // NewSuccBB and which don't dominate both. This is an initial
  // approximation of the blocks whose dominance frontiers will need updates.
  SmallVector<DomTreeNode *, 16> AllPredDoms;

  // Compute the block which dominates both NewBBSucc and NewBB. This is
  // the immediate dominator of NewBBSucc unless NewBB dominates NewBBSucc.
  // The code below which climbs dominator trees will stop at this point,
  // because from this point up, dominance frontiers are unaffected.
  DomTreeNode *DominatesBoth = 0;
  if (NewBBSuccNode) {
    DominatesBoth = NewBBSuccNode->getIDom();
    if (DominatesBoth == NewBBNode)
      DominatesBoth = NewBBNode->getIDom();
  }

  // Collect the set of all blocks which dominate a predecessor of NewBB.
  SmallPtrSet<DomTreeNode *, 8> NewBBPredDoms;
  for (pred_iterator PI = pred_begin(NewBB), E = pred_end(NewBB); PI != E; ++PI)
    for (DomTreeNode *DTN = DT.getNode(*PI); DTN; DTN = DTN->getIDom()) {
      if (DTN == DominatesBoth)
        break;
      if (!NewBBPredDoms.insert(DTN))
        break;
      AllPredDoms.push_back(DTN);
    }

  // Collect the set of all blocks which dominate a predecessor of NewSuccBB.
  SmallPtrSet<DomTreeNode *, 8> NewBBSuccPredDoms;
  for (pred_iterator PI = pred_begin(NewBBSucc),
       E = pred_end(NewBBSucc); PI != E; ++PI)
    for (DomTreeNode *DTN = DT.getNode(*PI); DTN; DTN = DTN->getIDom()) {
      if (DTN == DominatesBoth)
        break;
      if (!NewBBSuccPredDoms.insert(DTN))
        break;
      if (!NewBBPredDoms.count(DTN))
        AllPredDoms.push_back(DTN);
    }

  // Visit all relevant dominance frontiers and make any needed updates.
  for (SmallVectorImpl<DomTreeNode *>::const_iterator I = AllPredDoms.begin(),
       E = AllPredDoms.end(); I != E; ++I) {
    DomTreeNode *DTN = *I;
    iterator DFI = find((*I)->getBlock());

    // Only consider nodes that have NewBBSucc in their dominator frontier.
    if (DFI == end() || !DFI->second.count(NewBBSucc)) continue;

    // If the block dominates a predecessor of NewBB but does not properly
    // dominate NewBB itself, add NewBB to its dominance frontier.
    if (NewBBPredDoms.count(DTN) &&
        !DT.properlyDominates(DTN, NewBBNode))
      addToFrontier(DFI, NewBB);

    // If the block does not dominate a predecessor of NewBBSucc or
    // properly dominates NewBBSucc itself, remove NewBBSucc from its
    // dominance frontier.
    if (!NewBBSuccPredDoms.count(DTN) ||
        DT.properlyDominates(DTN, NewBBSuccNode))
      removeFromFrontier(DFI, NewBBSucc);
  }
}