1 //===- GenericDomTree.h - Generic dominator trees for graphs ----*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
11 /// This file defines a set of templates that efficiently compute a dominator
12 /// tree over a generic graph. This is used typically in LLVM for fast
13 /// dominance queries on the CFG, but is fully generic w.r.t. the underlying
16 //===----------------------------------------------------------------------===//
18 #ifndef LLVM_SUPPORT_GENERIC_DOM_TREE_H
19 #define LLVM_SUPPORT_GENERIC_DOM_TREE_H
21 #include "llvm/ADT/DenseMap.h"
22 #include "llvm/ADT/DepthFirstIterator.h"
23 #include "llvm/ADT/GraphTraits.h"
24 #include "llvm/ADT/SmallPtrSet.h"
25 #include "llvm/ADT/SmallVector.h"
26 #include "llvm/Support/Compiler.h"
27 #include "llvm/Support/raw_ostream.h"
32 //===----------------------------------------------------------------------===//
33 /// DominatorBase - Base class that other, more interesting dominator analyses
36 template <class NodeT>
39 std::vector<NodeT*> Roots;
40 const bool IsPostDominators;
41 inline explicit DominatorBase(bool isPostDom) :
42 Roots(), IsPostDominators(isPostDom) {}
45 /// getRoots - Return the root blocks of the current CFG. This may include
46 /// multiple blocks if we are computing post dominators. For forward
47 /// dominators, this will always be a single block (the entry node).
49 inline const std::vector<NodeT*> &getRoots() const { return Roots; }
51 /// isPostDominator - Returns true if analysis based of postdoms
53 bool isPostDominator() const { return IsPostDominators; }
57 //===----------------------------------------------------------------------===//
58 // DomTreeNodeBase - Dominator Tree Node
59 template<class NodeT> class DominatorTreeBase;
60 struct PostDominatorTree;
62 template <class NodeT>
63 class DomTreeNodeBase {
65 DomTreeNodeBase<NodeT> *IDom;
66 std::vector<DomTreeNodeBase<NodeT> *> Children;
67 mutable int DFSNumIn, DFSNumOut;
69 template<class N> friend class DominatorTreeBase;
70 friend struct PostDominatorTree;
72 typedef typename std::vector<DomTreeNodeBase<NodeT> *>::iterator iterator;
73 typedef typename std::vector<DomTreeNodeBase<NodeT> *>::const_iterator
76 iterator begin() { return Children.begin(); }
77 iterator end() { return Children.end(); }
78 const_iterator begin() const { return Children.begin(); }
79 const_iterator end() const { return Children.end(); }
81 NodeT *getBlock() const { return TheBB; }
82 DomTreeNodeBase<NodeT> *getIDom() const { return IDom; }
83 const std::vector<DomTreeNodeBase<NodeT>*> &getChildren() const {
87 DomTreeNodeBase(NodeT *BB, DomTreeNodeBase<NodeT> *iDom)
88 : TheBB(BB), IDom(iDom), DFSNumIn(-1), DFSNumOut(-1) { }
90 DomTreeNodeBase<NodeT> *addChild(DomTreeNodeBase<NodeT> *C) {
91 Children.push_back(C);
95 size_t getNumChildren() const {
96 return Children.size();
99 void clearAllChildren() {
103 bool compare(const DomTreeNodeBase<NodeT> *Other) const {
104 if (getNumChildren() != Other->getNumChildren())
107 SmallPtrSet<const NodeT *, 4> OtherChildren;
108 for (const_iterator I = Other->begin(), E = Other->end(); I != E; ++I) {
109 const NodeT *Nd = (*I)->getBlock();
110 OtherChildren.insert(Nd);
113 for (const_iterator I = begin(), E = end(); I != E; ++I) {
114 const NodeT *N = (*I)->getBlock();
115 if (OtherChildren.count(N) == 0)
121 void setIDom(DomTreeNodeBase<NodeT> *NewIDom) {
122 assert(IDom && "No immediate dominator?");
123 if (IDom != NewIDom) {
124 typename std::vector<DomTreeNodeBase<NodeT>*>::iterator I =
125 std::find(IDom->Children.begin(), IDom->Children.end(), this);
126 assert(I != IDom->Children.end() &&
127 "Not in immediate dominator children set!");
128 // I am no longer your child...
129 IDom->Children.erase(I);
131 // Switch to new dominator
133 IDom->Children.push_back(this);
137 /// getDFSNumIn/getDFSNumOut - These are an internal implementation detail, do
139 unsigned getDFSNumIn() const { return DFSNumIn; }
140 unsigned getDFSNumOut() const { return DFSNumOut; }
142 // Return true if this node is dominated by other. Use this only if DFS info
144 bool DominatedBy(const DomTreeNodeBase<NodeT> *other) const {
145 return this->DFSNumIn >= other->DFSNumIn &&
146 this->DFSNumOut <= other->DFSNumOut;
150 template<class NodeT>
151 inline raw_ostream &operator<<(raw_ostream &o,
152 const DomTreeNodeBase<NodeT> *Node) {
153 if (Node->getBlock())
154 Node->getBlock()->printAsOperand(o, false);
156 o << " <<exit node>>";
158 o << " {" << Node->getDFSNumIn() << "," << Node->getDFSNumOut() << "}";
163 template<class NodeT>
164 inline void PrintDomTree(const DomTreeNodeBase<NodeT> *N, raw_ostream &o,
166 o.indent(2*Lev) << "[" << Lev << "] " << N;
167 for (typename DomTreeNodeBase<NodeT>::const_iterator I = N->begin(),
168 E = N->end(); I != E; ++I)
169 PrintDomTree<NodeT>(*I, o, Lev+1);
172 //===----------------------------------------------------------------------===//
173 /// DominatorTree - Calculate the immediate dominator tree for a function.
176 template<class FuncT, class N>
177 void Calculate(DominatorTreeBase<typename GraphTraits<N>::NodeType>& DT,
180 template<class NodeT>
181 class DominatorTreeBase : public DominatorBase<NodeT> {
182 bool dominatedBySlowTreeWalk(const DomTreeNodeBase<NodeT> *A,
183 const DomTreeNodeBase<NodeT> *B) const {
185 assert(isReachableFromEntry(B));
186 assert(isReachableFromEntry(A));
188 const DomTreeNodeBase<NodeT> *IDom;
189 while ((IDom = B->getIDom()) != nullptr && IDom != A && IDom != B)
190 B = IDom; // Walk up the tree
191 return IDom != nullptr;
195 typedef DenseMap<NodeT*, DomTreeNodeBase<NodeT>*> DomTreeNodeMapType;
196 DomTreeNodeMapType DomTreeNodes;
197 DomTreeNodeBase<NodeT> *RootNode;
199 mutable bool DFSInfoValid;
200 mutable unsigned int SlowQueries;
201 // Information record used during immediate dominators computation.
208 InfoRec() : DFSNum(0), Parent(0), Semi(0), Label(nullptr) {}
211 DenseMap<NodeT*, NodeT*> IDoms;
213 // Vertex - Map the DFS number to the NodeT*
214 std::vector<NodeT*> Vertex;
216 // Info - Collection of information used during the computation of idoms.
217 DenseMap<NodeT*, InfoRec> Info;
220 for (typename DomTreeNodeMapType::iterator I = this->DomTreeNodes.begin(),
221 E = DomTreeNodes.end(); I != E; ++I)
223 DomTreeNodes.clear();
230 // NewBB is split and now it has one successor. Update dominator tree to
231 // reflect this change.
232 template<class N, class GraphT>
233 void Split(DominatorTreeBase<typename GraphT::NodeType>& DT,
234 typename GraphT::NodeType* NewBB) {
235 assert(std::distance(GraphT::child_begin(NewBB),
236 GraphT::child_end(NewBB)) == 1 &&
237 "NewBB should have a single successor!");
238 typename GraphT::NodeType* NewBBSucc = *GraphT::child_begin(NewBB);
240 std::vector<typename GraphT::NodeType*> PredBlocks;
241 typedef GraphTraits<Inverse<N> > InvTraits;
242 for (typename InvTraits::ChildIteratorType PI =
243 InvTraits::child_begin(NewBB),
244 PE = InvTraits::child_end(NewBB); PI != PE; ++PI)
245 PredBlocks.push_back(*PI);
247 assert(!PredBlocks.empty() && "No predblocks?");
249 bool NewBBDominatesNewBBSucc = true;
250 for (typename InvTraits::ChildIteratorType PI =
251 InvTraits::child_begin(NewBBSucc),
252 E = InvTraits::child_end(NewBBSucc); PI != E; ++PI) {
253 typename InvTraits::NodeType *ND = *PI;
254 if (ND != NewBB && !DT.dominates(NewBBSucc, ND) &&
255 DT.isReachableFromEntry(ND)) {
256 NewBBDominatesNewBBSucc = false;
261 // Find NewBB's immediate dominator and create new dominator tree node for
263 NodeT *NewBBIDom = nullptr;
265 for (i = 0; i < PredBlocks.size(); ++i)
266 if (DT.isReachableFromEntry(PredBlocks[i])) {
267 NewBBIDom = PredBlocks[i];
271 // It's possible that none of the predecessors of NewBB are reachable;
272 // in that case, NewBB itself is unreachable, so nothing needs to be
277 for (i = i + 1; i < PredBlocks.size(); ++i) {
278 if (DT.isReachableFromEntry(PredBlocks[i]))
279 NewBBIDom = DT.findNearestCommonDominator(NewBBIDom, PredBlocks[i]);
282 // Create the new dominator tree node... and set the idom of NewBB.
283 DomTreeNodeBase<NodeT> *NewBBNode = DT.addNewBlock(NewBB, NewBBIDom);
285 // If NewBB strictly dominates other blocks, then it is now the immediate
286 // dominator of NewBBSucc. Update the dominator tree as appropriate.
287 if (NewBBDominatesNewBBSucc) {
288 DomTreeNodeBase<NodeT> *NewBBSuccNode = DT.getNode(NewBBSucc);
289 DT.changeImmediateDominator(NewBBSuccNode, NewBBNode);
294 explicit DominatorTreeBase(bool isPostDom)
295 : DominatorBase<NodeT>(isPostDom), DFSInfoValid(false), SlowQueries(0) {}
296 virtual ~DominatorTreeBase() { reset(); }
298 /// compare - Return false if the other dominator tree base matches this
299 /// dominator tree base. Otherwise return true.
300 bool compare(const DominatorTreeBase &Other) const {
302 const DomTreeNodeMapType &OtherDomTreeNodes = Other.DomTreeNodes;
303 if (DomTreeNodes.size() != OtherDomTreeNodes.size())
306 for (typename DomTreeNodeMapType::const_iterator
307 I = this->DomTreeNodes.begin(),
308 E = this->DomTreeNodes.end(); I != E; ++I) {
309 NodeT *BB = I->first;
310 typename DomTreeNodeMapType::const_iterator OI = OtherDomTreeNodes.find(BB);
311 if (OI == OtherDomTreeNodes.end())
314 DomTreeNodeBase<NodeT>* MyNd = I->second;
315 DomTreeNodeBase<NodeT>* OtherNd = OI->second;
317 if (MyNd->compare(OtherNd))
324 virtual void releaseMemory() { reset(); }
326 /// getNode - return the (Post)DominatorTree node for the specified basic
327 /// block. This is the same as using operator[] on this class.
329 inline DomTreeNodeBase<NodeT> *getNode(NodeT *BB) const {
330 return DomTreeNodes.lookup(BB);
333 /// getRootNode - This returns the entry node for the CFG of the function. If
334 /// this tree represents the post-dominance relations for a function, however,
335 /// this root may be a node with the block == NULL. This is the case when
336 /// there are multiple exit nodes from a particular function. Consumers of
337 /// post-dominance information must be capable of dealing with this
340 DomTreeNodeBase<NodeT> *getRootNode() { return RootNode; }
341 const DomTreeNodeBase<NodeT> *getRootNode() const { return RootNode; }
343 /// Get all nodes dominated by R, including R itself.
344 void getDescendants(NodeT *R, SmallVectorImpl<NodeT *> &Result) const {
346 const DomTreeNodeBase<NodeT> *RN = getNode(R);
348 return; // If R is unreachable, it will not be present in the DOM tree.
349 SmallVector<const DomTreeNodeBase<NodeT> *, 8> WL;
352 while (!WL.empty()) {
353 const DomTreeNodeBase<NodeT> *N = WL.pop_back_val();
354 Result.push_back(N->getBlock());
355 WL.append(N->begin(), N->end());
359 /// properlyDominates - Returns true iff A dominates B and A != B.
360 /// Note that this is not a constant time operation!
362 bool properlyDominates(const DomTreeNodeBase<NodeT> *A,
363 const DomTreeNodeBase<NodeT> *B) const {
368 return dominates(A, B);
371 bool properlyDominates(const NodeT *A, const NodeT *B) const;
373 /// isReachableFromEntry - Return true if A is dominated by the entry
374 /// block of the function containing it.
375 bool isReachableFromEntry(const NodeT* A) const {
376 assert(!this->isPostDominator() &&
377 "This is not implemented for post dominators");
378 return isReachableFromEntry(getNode(const_cast<NodeT *>(A)));
381 inline bool isReachableFromEntry(const DomTreeNodeBase<NodeT> *A) const {
385 /// dominates - Returns true iff A dominates B. Note that this is not a
386 /// constant time operation!
388 inline bool dominates(const DomTreeNodeBase<NodeT> *A,
389 const DomTreeNodeBase<NodeT> *B) const {
390 // A node trivially dominates itself.
394 // An unreachable node is dominated by anything.
395 if (!isReachableFromEntry(B))
398 // And dominates nothing.
399 if (!isReachableFromEntry(A))
402 // Compare the result of the tree walk and the dfs numbers, if expensive
403 // checks are enabled.
405 assert((!DFSInfoValid ||
406 (dominatedBySlowTreeWalk(A, B) == B->DominatedBy(A))) &&
407 "Tree walk disagrees with dfs numbers!");
411 return B->DominatedBy(A);
413 // If we end up with too many slow queries, just update the
414 // DFS numbers on the theory that we are going to keep querying.
416 if (SlowQueries > 32) {
418 return B->DominatedBy(A);
421 return dominatedBySlowTreeWalk(A, B);
424 bool dominates(const NodeT *A, const NodeT *B) const;
426 NodeT *getRoot() const {
427 assert(this->Roots.size() == 1 && "Should always have entry node!");
428 return this->Roots[0];
431 /// findNearestCommonDominator - Find nearest common dominator basic block
432 /// for basic block A and B. If there is no such block then return NULL.
433 NodeT *findNearestCommonDominator(NodeT *A, NodeT *B) {
434 assert(A->getParent() == B->getParent() &&
435 "Two blocks are not in same function");
437 // If either A or B is a entry block then it is nearest common dominator
438 // (for forward-dominators).
439 if (!this->isPostDominator()) {
440 NodeT &Entry = A->getParent()->front();
441 if (A == &Entry || B == &Entry)
445 // If B dominates A then B is nearest common dominator.
449 // If A dominates B then A is nearest common dominator.
453 DomTreeNodeBase<NodeT> *NodeA = getNode(A);
454 DomTreeNodeBase<NodeT> *NodeB = getNode(B);
456 // If we have DFS info, then we can avoid all allocations by just querying
457 // it from each IDom. Note that because we call 'dominates' twice above, we
458 // expect to call through this code at most 16 times in a row without
459 // building valid DFS information. This is important as below is a *very*
462 DomTreeNodeBase<NodeT> *IDomA = NodeA->getIDom();
464 if (NodeB->DominatedBy(IDomA))
465 return IDomA->getBlock();
466 IDomA = IDomA->getIDom();
471 // Collect NodeA dominators set.
472 SmallPtrSet<DomTreeNodeBase<NodeT>*, 16> NodeADoms;
473 NodeADoms.insert(NodeA);
474 DomTreeNodeBase<NodeT> *IDomA = NodeA->getIDom();
476 NodeADoms.insert(IDomA);
477 IDomA = IDomA->getIDom();
480 // Walk NodeB immediate dominators chain and find common dominator node.
481 DomTreeNodeBase<NodeT> *IDomB = NodeB->getIDom();
483 if (NodeADoms.count(IDomB) != 0)
484 return IDomB->getBlock();
486 IDomB = IDomB->getIDom();
492 const NodeT *findNearestCommonDominator(const NodeT *A, const NodeT *B) {
493 // Cast away the const qualifiers here. This is ok since
494 // const is re-introduced on the return type.
495 return findNearestCommonDominator(const_cast<NodeT *>(A),
496 const_cast<NodeT *>(B));
499 //===--------------------------------------------------------------------===//
500 // API to update (Post)DominatorTree information based on modifications to
503 /// addNewBlock - Add a new node to the dominator tree information. This
504 /// creates a new node as a child of DomBB dominator node,linking it into
505 /// the children list of the immediate dominator.
506 DomTreeNodeBase<NodeT> *addNewBlock(NodeT *BB, NodeT *DomBB) {
507 assert(getNode(BB) == nullptr && "Block already in dominator tree!");
508 DomTreeNodeBase<NodeT> *IDomNode = getNode(DomBB);
509 assert(IDomNode && "Not immediate dominator specified for block!");
510 DFSInfoValid = false;
511 return DomTreeNodes[BB] =
512 IDomNode->addChild(new DomTreeNodeBase<NodeT>(BB, IDomNode));
515 /// changeImmediateDominator - This method is used to update the dominator
516 /// tree information when a node's immediate dominator changes.
518 void changeImmediateDominator(DomTreeNodeBase<NodeT> *N,
519 DomTreeNodeBase<NodeT> *NewIDom) {
520 assert(N && NewIDom && "Cannot change null node pointers!");
521 DFSInfoValid = false;
525 void changeImmediateDominator(NodeT *BB, NodeT *NewBB) {
526 changeImmediateDominator(getNode(BB), getNode(NewBB));
529 /// eraseNode - Removes a node from the dominator tree. Block must not
530 /// dominate any other blocks. Removes node from its immediate dominator's
531 /// children list. Deletes dominator node associated with basic block BB.
532 void eraseNode(NodeT *BB) {
533 DomTreeNodeBase<NodeT> *Node = getNode(BB);
534 assert(Node && "Removing node that isn't in dominator tree.");
535 assert(Node->getChildren().empty() && "Node is not a leaf node.");
537 // Remove node from immediate dominator's children list.
538 DomTreeNodeBase<NodeT> *IDom = Node->getIDom();
540 typename std::vector<DomTreeNodeBase<NodeT>*>::iterator I =
541 std::find(IDom->Children.begin(), IDom->Children.end(), Node);
542 assert(I != IDom->Children.end() &&
543 "Not in immediate dominator children set!");
544 // I am no longer your child...
545 IDom->Children.erase(I);
548 DomTreeNodes.erase(BB);
552 /// removeNode - Removes a node from the dominator tree. Block must not
553 /// dominate any other blocks. Invalidates any node pointing to removed
555 void removeNode(NodeT *BB) {
556 assert(getNode(BB) && "Removing node that isn't in dominator tree.");
557 DomTreeNodes.erase(BB);
560 /// splitBlock - BB is split and now it has one successor. Update dominator
561 /// tree to reflect this change.
562 void splitBlock(NodeT* NewBB) {
563 if (this->IsPostDominators)
564 this->Split<Inverse<NodeT*>, GraphTraits<Inverse<NodeT*> > >(*this, NewBB);
566 this->Split<NodeT*, GraphTraits<NodeT*> >(*this, NewBB);
569 /// print - Convert to human readable form
571 void print(raw_ostream &o) const {
572 o << "=============================--------------------------------\n";
573 if (this->isPostDominator())
574 o << "Inorder PostDominator Tree: ";
576 o << "Inorder Dominator Tree: ";
577 if (!this->DFSInfoValid)
578 o << "DFSNumbers invalid: " << SlowQueries << " slow queries.";
581 // The postdom tree can have a null root if there are no returns.
583 PrintDomTree<NodeT>(getRootNode(), o, 1);
587 template<class GraphT>
588 friend typename GraphT::NodeType* Eval(
589 DominatorTreeBase<typename GraphT::NodeType>& DT,
590 typename GraphT::NodeType* V,
591 unsigned LastLinked);
593 template<class GraphT>
594 friend unsigned DFSPass(DominatorTreeBase<typename GraphT::NodeType>& DT,
595 typename GraphT::NodeType* V,
598 template<class FuncT, class N>
599 friend void Calculate(DominatorTreeBase<typename GraphTraits<N>::NodeType>& DT,
602 /// updateDFSNumbers - Assign In and Out numbers to the nodes while walking
603 /// dominator tree in dfs order.
604 void updateDFSNumbers() const {
607 SmallVector<std::pair<const DomTreeNodeBase<NodeT>*,
608 typename DomTreeNodeBase<NodeT>::const_iterator>, 32> WorkStack;
610 const DomTreeNodeBase<NodeT> *ThisRoot = getRootNode();
615 // Even in the case of multiple exits that form the post dominator root
616 // nodes, do not iterate over all exits, but start from the virtual root
617 // node. Otherwise bbs, that are not post dominated by any exit but by the
618 // virtual root node, will never be assigned a DFS number.
619 WorkStack.push_back(std::make_pair(ThisRoot, ThisRoot->begin()));
620 ThisRoot->DFSNumIn = DFSNum++;
622 while (!WorkStack.empty()) {
623 const DomTreeNodeBase<NodeT> *Node = WorkStack.back().first;
624 typename DomTreeNodeBase<NodeT>::const_iterator ChildIt =
625 WorkStack.back().second;
627 // If we visited all of the children of this node, "recurse" back up the
628 // stack setting the DFOutNum.
629 if (ChildIt == Node->end()) {
630 Node->DFSNumOut = DFSNum++;
631 WorkStack.pop_back();
633 // Otherwise, recursively visit this child.
634 const DomTreeNodeBase<NodeT> *Child = *ChildIt;
635 ++WorkStack.back().second;
637 WorkStack.push_back(std::make_pair(Child, Child->begin()));
638 Child->DFSNumIn = DFSNum++;
646 DomTreeNodeBase<NodeT> *getNodeForBlock(NodeT *BB) {
647 if (DomTreeNodeBase<NodeT> *Node = getNode(BB))
650 // Haven't calculated this node yet? Get or calculate the node for the
651 // immediate dominator.
652 NodeT *IDom = getIDom(BB);
654 assert(IDom || this->DomTreeNodes[nullptr]);
655 DomTreeNodeBase<NodeT> *IDomNode = getNodeForBlock(IDom);
657 // Add a new tree node for this NodeT, and link it as a child of
659 DomTreeNodeBase<NodeT> *C = new DomTreeNodeBase<NodeT>(BB, IDomNode);
660 return this->DomTreeNodes[BB] = IDomNode->addChild(C);
663 inline NodeT *getIDom(NodeT *BB) const {
664 return IDoms.lookup(BB);
667 inline void addRoot(NodeT* BB) {
668 this->Roots.push_back(BB);
672 /// recalculate - compute a dominator tree for the given function
674 void recalculate(FT& F) {
675 typedef GraphTraits<FT*> TraitsTy;
677 this->Vertex.push_back(nullptr);
679 if (!this->IsPostDominators) {
681 NodeT *entry = TraitsTy::getEntryNode(&F);
682 this->Roots.push_back(entry);
683 this->IDoms[entry] = nullptr;
684 this->DomTreeNodes[entry] = nullptr;
686 Calculate<FT, NodeT*>(*this, F);
688 // Initialize the roots list
689 for (typename TraitsTy::nodes_iterator I = TraitsTy::nodes_begin(&F),
690 E = TraitsTy::nodes_end(&F); I != E; ++I) {
691 if (TraitsTy::child_begin(I) == TraitsTy::child_end(I))
694 // Prepopulate maps so that we don't get iterator invalidation issues later.
695 this->IDoms[I] = nullptr;
696 this->DomTreeNodes[I] = nullptr;
699 Calculate<FT, Inverse<NodeT*> >(*this, F);
704 // These two functions are declared out of line as a workaround for building
705 // with old (< r147295) versions of clang because of pr11642.
706 template<class NodeT>
707 bool DominatorTreeBase<NodeT>::dominates(const NodeT *A, const NodeT *B) const {
711 // Cast away the const qualifiers here. This is ok since
712 // this function doesn't actually return the values returned
714 return dominates(getNode(const_cast<NodeT *>(A)),
715 getNode(const_cast<NodeT *>(B)));
717 template<class NodeT>
719 DominatorTreeBase<NodeT>::properlyDominates(const NodeT *A, const NodeT *B) const {
723 // Cast away the const qualifiers here. This is ok since
724 // this function doesn't actually return the values returned
726 return dominates(getNode(const_cast<NodeT *>(A)),
727 getNode(const_cast<NodeT *>(B)));