C++ DominatorTree::getNode方法代码示例

/// Return true if the specified block dominates at least
/// one of the blocks in the specified list.
static bool
blockDominatesAnExit(BasicBlock *BB,
                     DominatorTree &DT,
                     const SmallVectorImpl<BasicBlock *> &ExitBlocks) {
    DomTreeNode *DomNode = DT.getNode(BB);
    return any_of(ExitBlocks, [&](BasicBlock *EB) {
        return DT.dominates(DomNode, DT.getNode(EB));
    });
}

/// SinkInstruction - Determine whether it is safe to sink the specified machine
/// instruction out of its current block into a successor.
static bool SinkInstruction(Instruction *Inst,
                            SmallPtrSetImpl<Instruction *> &Stores,
                            DominatorTree &DT, LoopInfo &LI, AAResults &AA) {

  // Don't sink static alloca instructions.  CodeGen assumes allocas outside the
  // entry block are dynamically sized stack objects.
  if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
    if (AI->isStaticAlloca())
      return false;

  // Check if it's safe to move the instruction.
  if (!isSafeToMove(Inst, AA, Stores))
    return false;

  // FIXME: This should include support for sinking instructions within the
  // block they are currently in to shorten the live ranges.  We often get
  // instructions sunk into the top of a large block, but it would be better to
  // also sink them down before their first use in the block.  This xform has to
  // be careful not to *increase* register pressure though, e.g. sinking
  // "x = y + z" down if it kills y and z would increase the live ranges of y
  // and z and only shrink the live range of x.

  // SuccToSinkTo - This is the successor to sink this instruction to, once we
  // decide.
  BasicBlock *SuccToSinkTo = nullptr;

  // Instructions can only be sunk if all their uses are in blocks
  // dominated by one of the successors.
  // Look at all the dominated blocks and see if we can sink it in one.
  DomTreeNode *DTN = DT.getNode(Inst->getParent());
  for (DomTreeNode::iterator I = DTN->begin(), E = DTN->end();
      I != E && SuccToSinkTo == nullptr; ++I) {
    BasicBlock *Candidate = (*I)->getBlock();
    // A node always immediate-dominates its children on the dominator
    // tree.
    if (IsAcceptableTarget(Inst, Candidate, DT, LI))
      SuccToSinkTo = Candidate;
  }

  // If no suitable postdominator was found, look at all the successors and
  // decide which one we should sink to, if any.
  for (succ_iterator I = succ_begin(Inst->getParent()),
      E = succ_end(Inst->getParent()); I != E && !SuccToSinkTo; ++I) {
    if (IsAcceptableTarget(Inst, *I, DT, LI))
      SuccToSinkTo = *I;
  }

  // If we couldn't find a block to sink to, ignore this instruction.
  if (!SuccToSinkTo)
    return false;

  LLVM_DEBUG(dbgs() << "Sink" << *Inst << " (";
             Inst->getParent()->printAsOperand(dbgs(), false); dbgs() << " -> ";
             SuccToSinkTo->printAsOperand(dbgs(), false); dbgs() << ")\n");

  // Move the instruction.
  Inst->moveBefore(&*SuccToSinkTo->getFirstInsertionPt());
  return true;
}

static void clearDomtree(Function *F, DominatorTree &DT) {
  DomTreeNode *N = DT.getNode(&F->getEntryBlock());
  std::vector<BasicBlock *> Nodes;
  for (po_iterator<DomTreeNode *> I = po_begin(N), E = po_end(N); I != E; ++I)
    Nodes.push_back(I->getBlock());

  for (std::vector<BasicBlock *>::iterator I = Nodes.begin(), E = Nodes.end();
       I != E; ++I)
    DT.eraseNode(*I);
}

/// Returns true if this loop is known to contain a call safepoint which
/// must unconditionally execute on any iteration of the loop which returns
/// to the loop header via an edge from Pred.  Returns a conservative correct
/// answer; i.e. false is always valid.
static bool containsUnconditionalCallSafepoint(Loop *L, BasicBlock *Header,
                                               BasicBlock *Pred,
                                               DominatorTree &DT,
                                               const TargetLibraryInfo &TLI) {
  // In general, we're looking for any cut of the graph which ensures
  // there's a call safepoint along every edge between Header and Pred.
  // For the moment, we look only for the 'cuts' that consist of a single call
  // instruction in a block which is dominated by the Header and dominates the
  // loop latch (Pred) block.  Somewhat surprisingly, walking the entire chain
  // of such dominating blocks gets substantially more occurrences than just
  // checking the Pred and Header blocks themselves.  This may be due to the
  // density of loop exit conditions caused by range and null checks.
  // TODO: structure this as an analysis pass, cache the result for subloops,
  // avoid dom tree recalculations
  assert(DT.dominates(Header, Pred) && "loop latch not dominated by header?");

  BasicBlock *Current = Pred;
  while (true) {
    for (Instruction &I : *Current) {
      if (auto CS = CallSite(&I))
        // Note: Technically, needing a safepoint isn't quite the right
        // condition here.  We should instead be checking if the target method
        // has an
        // unconditional poll. In practice, this is only a theoretical concern
        // since we don't have any methods with conditional-only safepoint
        // polls.
        if (needsStatepoint(CS, TLI))
          return true;
    }

    if (Current == Header)
      break;
    Current = DT.getNode(Current)->getIDom()->getBlock();
  }

  return false;
}

//.........这里部分代码省略.........
  DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>();
  DominanceFrontier *DF = P->getAnalysisIfAvailable<DominanceFrontier>();
  LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>();
  ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>();
  
  // If we have nothing to update, just return.
  if (DT == 0 && DF == 0 && LI == 0 && PI == 0)
    return NewBB;

  // Now update analysis information.  Since the only predecessor of NewBB is
  // the TIBB, TIBB clearly dominates NewBB.  TIBB usually doesn't dominate
  // anything, as there are other successors of DestBB.  However, if all other
  // predecessors of DestBB are already dominated by DestBB (e.g. DestBB is a
  // loop header) then NewBB dominates DestBB.
  SmallVector<BasicBlock*, 8> OtherPreds;

  // If there is a PHI in the block, loop over predecessors with it, which is
  // faster than iterating pred_begin/end.
  if (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
      if (PN->getIncomingBlock(i) != NewBB)
        OtherPreds.push_back(PN->getIncomingBlock(i));
  } else {
    for (pred_iterator I = pred_begin(DestBB), E = pred_end(DestBB);
         I != E; ++I)
      if (*I != NewBB)
        OtherPreds.push_back(*I);
  }
  
  bool NewBBDominatesDestBB = true;
  
  // Should we update DominatorTree information?
  if (DT) {
    DomTreeNode *TINode = DT->getNode(TIBB);

    // The new block is not the immediate dominator for any other nodes, but
    // TINode is the immediate dominator for the new node.
    //
    if (TINode) {       // Don't break unreachable code!
      DomTreeNode *NewBBNode = DT->addNewBlock(NewBB, TIBB);
      DomTreeNode *DestBBNode = 0;
     
      // If NewBBDominatesDestBB hasn't been computed yet, do so with DT.
      if (!OtherPreds.empty()) {
        DestBBNode = DT->getNode(DestBB);
        while (!OtherPreds.empty() && NewBBDominatesDestBB) {
          if (DomTreeNode *OPNode = DT->getNode(OtherPreds.back()))
            NewBBDominatesDestBB = DT->dominates(DestBBNode, OPNode);
          OtherPreds.pop_back();
        }
        OtherPreds.clear();
      }
      
      // If NewBBDominatesDestBB, then NewBB dominates DestBB, otherwise it
      // doesn't dominate anything.
      if (NewBBDominatesDestBB) {
        if (!DestBBNode) DestBBNode = DT->getNode(DestBB);
        DT->changeImmediateDominator(DestBBNode, NewBBNode);
      }
    }
  }

  // Should we update DominanceFrontier information?
  if (DF) {
    // If NewBBDominatesDestBB hasn't been computed yet, do so with DF.
    if (!OtherPreds.empty()) {

//.........这里部分代码省略.........
  DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>();
  LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>();

  // If we have nothing to update, just return.
  if (DT == 0 && LI == 0)
    return NewBB;

  // Now update analysis information.  Since the only predecessor of NewBB is
  // the TIBB, TIBB clearly dominates NewBB.  TIBB usually doesn't dominate
  // anything, as there are other successors of DestBB.  However, if all other
  // predecessors of DestBB are already dominated by DestBB (e.g. DestBB is a
  // loop header) then NewBB dominates DestBB.
  SmallVector<BasicBlock*, 8> OtherPreds;

  // If there is a PHI in the block, loop over predecessors with it, which is
  // faster than iterating pred_begin/end.
  if (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
      if (PN->getIncomingBlock(i) != NewBB)
        OtherPreds.push_back(PN->getIncomingBlock(i));
  } else {
    for (pred_iterator I = pred_begin(DestBB), E = pred_end(DestBB);
         I != E; ++I) {
      BasicBlock *P = *I;
      if (P != NewBB)
        OtherPreds.push_back(P);
    }
  }

  bool NewBBDominatesDestBB = true;

  // Should we update DominatorTree information?
  if (DT) {
    DomTreeNode *TINode = DT->getNode(TIBB);

    // The new block is not the immediate dominator for any other nodes, but
    // TINode is the immediate dominator for the new node.
    //
    if (TINode) {       // Don't break unreachable code!
      DomTreeNode *NewBBNode = DT->addNewBlock(NewBB, TIBB);
      DomTreeNode *DestBBNode = 0;

      // If NewBBDominatesDestBB hasn't been computed yet, do so with DT.
      if (!OtherPreds.empty()) {
        DestBBNode = DT->getNode(DestBB);
        while (!OtherPreds.empty() && NewBBDominatesDestBB) {
          if (DomTreeNode *OPNode = DT->getNode(OtherPreds.back()))
            NewBBDominatesDestBB = DT->dominates(DestBBNode, OPNode);
          OtherPreds.pop_back();
        }
        OtherPreds.clear();
      }

      // If NewBBDominatesDestBB, then NewBB dominates DestBB, otherwise it
      // doesn't dominate anything.
      if (NewBBDominatesDestBB) {
        if (!DestBBNode) DestBBNode = DT->getNode(DestBB);
        DT->changeImmediateDominator(DestBBNode, NewBBNode);
      }
    }
  }

  // Update LoopInfo if it is around.
  if (LI) {
    if (Loop *TIL = LI->getLoopFor(TIBB)) {
      // If one or the other blocks were not in a loop, the new block is not

/// For every instruction from the worklist, check to see if it has any uses
/// that are outside the current loop.  If so, insert LCSSA PHI nodes and
/// rewrite the uses.
bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
                                    DominatorTree &DT, LoopInfo &LI) {
    SmallVector<Use *, 16> UsesToRewrite;
    SmallSetVector<PHINode *, 16> PHIsToRemove;
    PredIteratorCache PredCache;
    bool Changed = false;

    // Cache the Loop ExitBlocks across this loop.  We expect to get a lot of
    // instructions within the same loops, computing the exit blocks is
    // expensive, and we're not mutating the loop structure.
    SmallDenseMap<Loop*, SmallVector<BasicBlock *,1>> LoopExitBlocks;

    while (!Worklist.empty()) {
        UsesToRewrite.clear();

        Instruction *I = Worklist.pop_back_val();
        BasicBlock *InstBB = I->getParent();
        Loop *L = LI.getLoopFor(InstBB);
        if (!LoopExitBlocks.count(L))
            L->getExitBlocks(LoopExitBlocks[L]);
        assert(LoopExitBlocks.count(L));
        const SmallVectorImpl<BasicBlock *> &ExitBlocks = LoopExitBlocks[L];

        if (ExitBlocks.empty())
            continue;

        // Tokens cannot be used in PHI nodes, so we skip over them.
        // We can run into tokens which are live out of a loop with catchswitch
        // instructions in Windows EH if the catchswitch has one catchpad which
        // is inside the loop and another which is not.
        if (I->getType()->isTokenTy())
            continue;

        for (Use &U : I->uses()) {
            Instruction *User = cast<Instruction>(U.getUser());
            BasicBlock *UserBB = User->getParent();
            if (PHINode *PN = dyn_cast<PHINode>(User))
                UserBB = PN->getIncomingBlock(U);

            if (InstBB != UserBB && !L->contains(UserBB))
                UsesToRewrite.push_back(&U);
        }

        // If there are no uses outside the loop, exit with no change.
        if (UsesToRewrite.empty())
            continue;

        ++NumLCSSA; // We are applying the transformation

        // Invoke instructions are special in that their result value is not
        // available along their unwind edge. The code below tests to see whether
        // DomBB dominates the value, so adjust DomBB to the normal destination
        // block, which is effectively where the value is first usable.
        BasicBlock *DomBB = InstBB;
        if (InvokeInst *Inv = dyn_cast<InvokeInst>(I))
            DomBB = Inv->getNormalDest();

        DomTreeNode *DomNode = DT.getNode(DomBB);

        SmallVector<PHINode *, 16> AddedPHIs;
        SmallVector<PHINode *, 8> PostProcessPHIs;

        SmallVector<PHINode *, 4> InsertedPHIs;
        SSAUpdater SSAUpdate(&InsertedPHIs);
        SSAUpdate.Initialize(I->getType(), I->getName());

        // Insert the LCSSA phi's into all of the exit blocks dominated by the
        // value, and add them to the Phi's map.
        for (BasicBlock *ExitBB : ExitBlocks) {
            if (!DT.dominates(DomNode, DT.getNode(ExitBB)))
                continue;

            // If we already inserted something for this BB, don't reprocess it.
            if (SSAUpdate.HasValueForBlock(ExitBB))
                continue;

            PHINode *PN = PHINode::Create(I->getType(), PredCache.size(ExitBB),
                                          I->getName() + ".lcssa", &ExitBB->front());

            // Add inputs from inside the loop for this PHI.
            for (BasicBlock *Pred : PredCache.get(ExitBB)) {
                PN->addIncoming(I, Pred);

                // If the exit block has a predecessor not within the loop, arrange for
                // the incoming value use corresponding to that predecessor to be
                // rewritten in terms of a different LCSSA PHI.
                if (!L->contains(Pred))
                    UsesToRewrite.push_back(
                        &PN->getOperandUse(PN->getOperandNumForIncomingValue(
                                               PN->getNumIncomingValues() - 1)));
            }

            AddedPHIs.push_back(PN);

            // Remember that this phi makes the value alive in this block.
            SSAUpdate.AddAvailableValue(ExitBB, PN);

//.........这里部分代码省略.........

/// Given \p BBs as input, find another set of BBs which collectively
/// dominates \p BBs and have the minimal sum of frequencies. Return the BB
/// set found in \p BBs.
static void findBestInsertionSet(DominatorTree &DT, BlockFrequencyInfo &BFI,
                                 BasicBlock *Entry,
                                 SmallPtrSet<BasicBlock *, 8> &BBs) {
  assert(!BBs.count(Entry) && "Assume Entry is not in BBs");
  // Nodes on the current path to the root.
  SmallPtrSet<BasicBlock *, 8> Path;
  // Candidates includes any block 'BB' in set 'BBs' that is not strictly
  // dominated by any other blocks in set 'BBs', and all nodes in the path
  // in the dominator tree from Entry to 'BB'.
  SmallPtrSet<BasicBlock *, 16> Candidates;
  for (auto BB : BBs) {
    // Ignore unreachable basic blocks.
    if (!DT.isReachableFromEntry(BB))
      continue;
    Path.clear();
    // Walk up the dominator tree until Entry or another BB in BBs
    // is reached. Insert the nodes on the way to the Path.
    BasicBlock *Node = BB;
    // The "Path" is a candidate path to be added into Candidates set.
    bool isCandidate = false;
    do {
      Path.insert(Node);
      if (Node == Entry || Candidates.count(Node)) {
        isCandidate = true;
        break;
      }
      assert(DT.getNode(Node)->getIDom() &&
             "Entry doens't dominate current Node");
      Node = DT.getNode(Node)->getIDom()->getBlock();
    } while (!BBs.count(Node));

    // If isCandidate is false, Node is another Block in BBs dominating
    // current 'BB'. Drop the nodes on the Path.
    if (!isCandidate)
      continue;

    // Add nodes on the Path into Candidates.
    Candidates.insert(Path.begin(), Path.end());
  }

  // Sort the nodes in Candidates in top-down order and save the nodes
  // in Orders.
  unsigned Idx = 0;
  SmallVector<BasicBlock *, 16> Orders;
  Orders.push_back(Entry);
  while (Idx != Orders.size()) {
    BasicBlock *Node = Orders[Idx++];
    for (auto ChildDomNode : DT.getNode(Node)->getChildren()) {
      if (Candidates.count(ChildDomNode->getBlock()))
        Orders.push_back(ChildDomNode->getBlock());
    }
  }

  // Visit Orders in bottom-up order.
  using InsertPtsCostPair =
      std::pair<SmallPtrSet<BasicBlock *, 16>, BlockFrequency>;

  // InsertPtsMap is a map from a BB to the best insertion points for the
  // subtree of BB (subtree not including the BB itself).
  DenseMap<BasicBlock *, InsertPtsCostPair> InsertPtsMap;
  InsertPtsMap.reserve(Orders.size() + 1);
  for (auto RIt = Orders.rbegin(); RIt != Orders.rend(); RIt++) {
    BasicBlock *Node = *RIt;
    bool NodeInBBs = BBs.count(Node);
    SmallPtrSet<BasicBlock *, 16> &InsertPts = InsertPtsMap[Node].first;
    BlockFrequency &InsertPtsFreq = InsertPtsMap[Node].second;

    // Return the optimal insert points in BBs.
    if (Node == Entry) {
      BBs.clear();
      if (InsertPtsFreq > BFI.getBlockFreq(Node) ||
          (InsertPtsFreq == BFI.getBlockFreq(Node) && InsertPts.size() > 1))
        BBs.insert(Entry);
      else
        BBs.insert(InsertPts.begin(), InsertPts.end());
      break;
    }

    BasicBlock *Parent = DT.getNode(Node)->getIDom()->getBlock();
    // Initially, ParentInsertPts is empty and ParentPtsFreq is 0. Every child
    // will update its parent's ParentInsertPts and ParentPtsFreq.
    SmallPtrSet<BasicBlock *, 16> &ParentInsertPts = InsertPtsMap[Parent].first;
    BlockFrequency &ParentPtsFreq = InsertPtsMap[Parent].second;
    // Choose to insert in Node or in subtree of Node.
    // Don't hoist to EHPad because we may not find a proper place to insert
    // in EHPad.
    // If the total frequency of InsertPts is the same as the frequency of the
    // target Node, and InsertPts contains more than one nodes, choose hoisting
    // to reduce code size.
    if (NodeInBBs ||
        (!Node->isEHPad() &&
         (InsertPtsFreq > BFI.getBlockFreq(Node) ||
          (InsertPtsFreq == BFI.getBlockFreq(Node) && InsertPts.size() > 1)))) {
      ParentInsertPts.insert(Node);
      ParentPtsFreq += BFI.getBlockFreq(Node);
    } else {
      ParentInsertPts.insert(InsertPts.begin(), InsertPts.end());
//.........这里部分代码省略.........

/// Given an instruction in the loop, check to see if it has any uses that are
/// outside the current loop.  If so, insert LCSSA PHI nodes and rewrite the
/// uses.
static bool processInstruction(Loop &L, Instruction &Inst, DominatorTree &DT,
                               const SmallVectorImpl<BasicBlock *> &ExitBlocks,
                               PredIteratorCache &PredCache, LoopInfo *LI) {
  SmallVector<Use *, 16> UsesToRewrite;

  // Tokens cannot be used in PHI nodes, so we skip over them.
  // We can run into tokens which are live out of a loop with catchswitch
  // instructions in Windows EH if the catchswitch has one catchpad which
  // is inside the loop and another which is not.
  if (Inst.getType()->isTokenTy())
    return false;

  BasicBlock *InstBB = Inst.getParent();

  for (Use &U : Inst.uses()) {
    Instruction *User = cast<Instruction>(U.getUser());
    BasicBlock *UserBB = User->getParent();
    if (PHINode *PN = dyn_cast<PHINode>(User))
      UserBB = PN->getIncomingBlock(U);

    if (InstBB != UserBB && !L.contains(UserBB))
      UsesToRewrite.push_back(&U);
  }

  // If there are no uses outside the loop, exit with no change.
  if (UsesToRewrite.empty())
    return false;

  ++NumLCSSA; // We are applying the transformation

  // Invoke instructions are special in that their result value is not available
  // along their unwind edge. The code below tests to see whether DomBB
  // dominates the value, so adjust DomBB to the normal destination block,
  // which is effectively where the value is first usable.
  BasicBlock *DomBB = Inst.getParent();
  if (InvokeInst *Inv = dyn_cast<InvokeInst>(&Inst))
    DomBB = Inv->getNormalDest();

  DomTreeNode *DomNode = DT.getNode(DomBB);

  SmallVector<PHINode *, 16> AddedPHIs;
  SmallVector<PHINode *, 8> PostProcessPHIs;

  SSAUpdater SSAUpdate;
  SSAUpdate.Initialize(Inst.getType(), Inst.getName());

  // Insert the LCSSA phi's into all of the exit blocks dominated by the
  // value, and add them to the Phi's map.
  for (BasicBlock *ExitBB : ExitBlocks) {
    if (!DT.dominates(DomNode, DT.getNode(ExitBB)))
      continue;

    // If we already inserted something for this BB, don't reprocess it.
    if (SSAUpdate.HasValueForBlock(ExitBB))
      continue;

    PHINode *PN = PHINode::Create(Inst.getType(), PredCache.size(ExitBB),
                                  Inst.getName() + ".lcssa", &ExitBB->front());

    // Add inputs from inside the loop for this PHI.
    for (BasicBlock *Pred : PredCache.get(ExitBB)) {
      PN->addIncoming(&Inst, Pred);

      // If the exit block has a predecessor not within the loop, arrange for
      // the incoming value use corresponding to that predecessor to be
      // rewritten in terms of a different LCSSA PHI.
      if (!L.contains(Pred))
        UsesToRewrite.push_back(
            &PN->getOperandUse(PN->getOperandNumForIncomingValue(
                 PN->getNumIncomingValues() - 1)));
    }

    AddedPHIs.push_back(PN);

    // Remember that this phi makes the value alive in this block.
    SSAUpdate.AddAvailableValue(ExitBB, PN);

    // LoopSimplify might fail to simplify some loops (e.g. when indirect
    // branches are involved). In such situations, it might happen that an exit
    // for Loop L1 is the header of a disjoint Loop L2. Thus, when we create
    // PHIs in such an exit block, we are also inserting PHIs into L2's header.
    // This could break LCSSA form for L2 because these inserted PHIs can also
    // have uses outside of L2. Remember all PHIs in such situation as to
    // revisit than later on. FIXME: Remove this if indirectbr support into
    // LoopSimplify gets improved.
    if (auto *OtherLoop = LI->getLoopFor(ExitBB))
      if (!L.contains(OtherLoop))
        PostProcessPHIs.push_back(PN);
  }

  // Rewrite all uses outside the loop in terms of the new PHIs we just
  // inserted.
  for (Use *UseToRewrite : UsesToRewrite) {
    // If this use is in an exit block, rewrite to use the newly inserted PHI.
    // This is required for correctness because SSAUpdate doesn't handle uses in
    // the same block.  It assumes the PHI we inserted is at the end of the
    // block.
//.........这里部分代码省略.........