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//===- GenericDomTree.h - Generic dominator trees for graphs ----*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
/// \file
/// This file defines a set of templates that efficiently compute a dominator
/// tree over a generic graph. This is used typically in LLVM for fast
/// dominance queries on the CFG, but is fully generic w.r.t. the underlying
/// graph types.
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/GraphTraits.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
namespace llvm {
/// DominatorBase - Base class that other, more interesting dominator analyses
/// inherit from.
template <class NodeT>
class DominatorBase {
std::vector<NodeT*> Roots;
const bool IsPostDominators;
inline explicit DominatorBase(bool isPostDom) :
Roots(), IsPostDominators(isPostDom) {}
/// getRoots - Return the root blocks of the current CFG. This may include
/// multiple blocks if we are computing post dominators. For forward
/// dominators, this will always be a single block (the entry node).
inline const std::vector<NodeT*> &getRoots() const { return Roots; }
/// isPostDominator - Returns true if analysis based of postdoms
bool isPostDominator() const { return IsPostDominators; }
// DomTreeNodeBase - Dominator Tree Node
template<class NodeT> class DominatorTreeBase;
struct PostDominatorTree;
template <class NodeT>
class DomTreeNodeBase {
NodeT *TheBB;
DomTreeNodeBase<NodeT> *IDom;
std::vector<DomTreeNodeBase<NodeT> *> Children;
mutable int DFSNumIn, DFSNumOut;
template<class N> friend class DominatorTreeBase;
friend struct PostDominatorTree;
typedef typename std::vector<DomTreeNodeBase<NodeT> *>::iterator iterator;
typedef typename std::vector<DomTreeNodeBase<NodeT> *>::const_iterator
iterator begin() { return Children.begin(); }
iterator end() { return Children.end(); }
const_iterator begin() const { return Children.begin(); }
const_iterator end() const { return Children.end(); }
NodeT *getBlock() const { return TheBB; }
DomTreeNodeBase<NodeT> *getIDom() const { return IDom; }
const std::vector<DomTreeNodeBase<NodeT>*> &getChildren() const {
return Children;
DomTreeNodeBase(NodeT *BB, DomTreeNodeBase<NodeT> *iDom)
: TheBB(BB), IDom(iDom), DFSNumIn(-1), DFSNumOut(-1) { }
DomTreeNodeBase<NodeT> *addChild(DomTreeNodeBase<NodeT> *C) {
return C;
size_t getNumChildren() const {
return Children.size();
void clearAllChildren() {
bool compare(const DomTreeNodeBase<NodeT> *Other) const {
if (getNumChildren() != Other->getNumChildren())
return true;
SmallPtrSet<const NodeT *, 4> OtherChildren;
for (const_iterator I = Other->begin(), E = Other->end(); I != E; ++I) {
const NodeT *Nd = (*I)->getBlock();
for (const_iterator I = begin(), E = end(); I != E; ++I) {
const NodeT *N = (*I)->getBlock();
if (OtherChildren.count(N) == 0)
return true;
return false;
void setIDom(DomTreeNodeBase<NodeT> *NewIDom) {
assert(IDom && "No immediate dominator?");
if (IDom != NewIDom) {
typename std::vector<DomTreeNodeBase<NodeT>*>::iterator I =
std::find(IDom->Children.begin(), IDom->Children.end(), this);
assert(I != IDom->Children.end() &&
"Not in immediate dominator children set!");
// I am no longer your child...
// Switch to new dominator
IDom = NewIDom;
/// getDFSNumIn/getDFSNumOut - These are an internal implementation detail, do
/// not call them.
unsigned getDFSNumIn() const { return DFSNumIn; }
unsigned getDFSNumOut() const { return DFSNumOut; }
// Return true if this node is dominated by other. Use this only if DFS info
// is valid.
bool DominatedBy(const DomTreeNodeBase<NodeT> *other) const {
return this->DFSNumIn >= other->DFSNumIn &&
this->DFSNumOut <= other->DFSNumOut;
template<class NodeT>
inline raw_ostream &operator<<(raw_ostream &o,
const DomTreeNodeBase<NodeT> *Node) {
if (Node->getBlock())
Node->getBlock()->printAsOperand(o, false);
o << " <<exit node>>";
o << " {" << Node->getDFSNumIn() << "," << Node->getDFSNumOut() << "}";
return o << "\n";
template<class NodeT>
inline void PrintDomTree(const DomTreeNodeBase<NodeT> *N, raw_ostream &o,
unsigned Lev) {
o.indent(2*Lev) << "[" << Lev << "] " << N;
for (typename DomTreeNodeBase<NodeT>::const_iterator I = N->begin(),
E = N->end(); I != E; ++I)
PrintDomTree<NodeT>(*I, o, Lev+1);
/// DominatorTree - Calculate the immediate dominator tree for a function.
template<class FuncT, class N>
void Calculate(DominatorTreeBase<typename GraphTraits<N>::NodeType>& DT,
FuncT& F);
template<class NodeT>
class DominatorTreeBase : public DominatorBase<NodeT> {
bool dominatedBySlowTreeWalk(const DomTreeNodeBase<NodeT> *A,
const DomTreeNodeBase<NodeT> *B) const {
assert(A != B);
const DomTreeNodeBase<NodeT> *IDom;
while ((IDom = B->getIDom()) != nullptr && IDom != A && IDom != B)
B = IDom; // Walk up the tree
return IDom != nullptr;
typedef DenseMap<NodeT*, DomTreeNodeBase<NodeT>*> DomTreeNodeMapType;
DomTreeNodeMapType DomTreeNodes;
DomTreeNodeBase<NodeT> *RootNode;
mutable bool DFSInfoValid;
mutable unsigned int SlowQueries;
// Information record used during immediate dominators computation.
struct InfoRec {
unsigned DFSNum;
unsigned Parent;
unsigned Semi;
NodeT *Label;
InfoRec() : DFSNum(0), Parent(0), Semi(0), Label(nullptr) {}
DenseMap<NodeT*, NodeT*> IDoms;
// Vertex - Map the DFS number to the NodeT*
std::vector<NodeT*> Vertex;
// Info - Collection of information used during the computation of idoms.
DenseMap<NodeT*, InfoRec> Info;
void reset() {
for (typename DomTreeNodeMapType::iterator I = this->DomTreeNodes.begin(),
E = DomTreeNodes.end(); I != E; ++I)
delete I->second;
RootNode = nullptr;
// NewBB is split and now it has one successor. Update dominator tree to
// reflect this change.
template<class N, class GraphT>
void Split(DominatorTreeBase<typename GraphT::NodeType>& DT,
typename GraphT::NodeType* NewBB) {
GraphT::child_end(NewBB)) == 1 &&
"NewBB should have a single successor!");
typename GraphT::NodeType* NewBBSucc = *GraphT::child_begin(NewBB);
std::vector<typename GraphT::NodeType*> PredBlocks;
typedef GraphTraits<Inverse<N> > InvTraits;
for (typename InvTraits::ChildIteratorType PI =
PE = InvTraits::child_end(NewBB); PI != PE; ++PI)
assert(!PredBlocks.empty() && "No predblocks?");
bool NewBBDominatesNewBBSucc = true;
for (typename InvTraits::ChildIteratorType PI =
E = InvTraits::child_end(NewBBSucc); PI != E; ++PI) {
typename InvTraits::NodeType *ND = *PI;
if (ND != NewBB && !DT.dominates(NewBBSucc, ND) &&
DT.isReachableFromEntry(ND)) {
NewBBDominatesNewBBSucc = false;
// Find NewBB's immediate dominator and create new dominator tree node for
// NewBB.
NodeT *NewBBIDom = nullptr;
unsigned i = 0;
for (i = 0; i < PredBlocks.size(); ++i)
if (DT.isReachableFromEntry(PredBlocks[i])) {
NewBBIDom = PredBlocks[i];
// It's possible that none of the predecessors of NewBB are reachable;
// in that case, NewBB itself is unreachable, so nothing needs to be
// changed.
if (!NewBBIDom)
for (i = i + 1; i < PredBlocks.size(); ++i) {
if (DT.isReachableFromEntry(PredBlocks[i]))
NewBBIDom = DT.findNearestCommonDominator(NewBBIDom, PredBlocks[i]);
// Create the new dominator tree node... and set the idom of NewBB.
DomTreeNodeBase<NodeT> *NewBBNode = DT.addNewBlock(NewBB, NewBBIDom);
// If NewBB strictly dominates other blocks, then it is now the immediate
// dominator of NewBBSucc. Update the dominator tree as appropriate.
if (NewBBDominatesNewBBSucc) {
DomTreeNodeBase<NodeT> *NewBBSuccNode = DT.getNode(NewBBSucc);
DT.changeImmediateDominator(NewBBSuccNode, NewBBNode);
explicit DominatorTreeBase(bool isPostDom)
: DominatorBase<NodeT>(isPostDom), DFSInfoValid(false), SlowQueries(0) {}
virtual ~DominatorTreeBase() { reset(); }
/// compare - Return false if the other dominator tree base matches this
/// dominator tree base. Otherwise return true.
bool compare(const DominatorTreeBase &Other) const {
const DomTreeNodeMapType &OtherDomTreeNodes = Other.DomTreeNodes;
if (DomTreeNodes.size() != OtherDomTreeNodes.size())
return true;
for (typename DomTreeNodeMapType::const_iterator
I = this->DomTreeNodes.begin(),
E = this->DomTreeNodes.end(); I != E; ++I) {
NodeT *BB = I->first;
typename DomTreeNodeMapType::const_iterator OI = OtherDomTreeNodes.find(BB);
if (OI == OtherDomTreeNodes.end())
return true;
DomTreeNodeBase<NodeT>* MyNd = I->second;
DomTreeNodeBase<NodeT>* OtherNd = OI->second;
if (MyNd->compare(OtherNd))
return true;
return false;
virtual void releaseMemory() { reset(); }
/// getNode - return the (Post)DominatorTree node for the specified basic
/// block. This is the same as using operator[] on this class.
inline DomTreeNodeBase<NodeT> *getNode(NodeT *BB) const {
return DomTreeNodes.lookup(BB);
inline DomTreeNodeBase<NodeT> *operator[](NodeT *BB) const {
return getNode(BB);
/// getRootNode - This returns the entry node for the CFG of the function. If
/// this tree represents the post-dominance relations for a function, however,
/// this root may be a node with the block == NULL. This is the case when
/// there are multiple exit nodes from a particular function. Consumers of
/// post-dominance information must be capable of dealing with this
/// possibility.
DomTreeNodeBase<NodeT> *getRootNode() { return RootNode; }
const DomTreeNodeBase<NodeT> *getRootNode() const { return RootNode; }
/// Get all nodes dominated by R, including R itself.
void getDescendants(NodeT *R, SmallVectorImpl<NodeT *> &Result) const {
const DomTreeNodeBase<NodeT> *RN = getNode(R);
if (!RN)
return; // If R is unreachable, it will not be present in the DOM tree.
SmallVector<const DomTreeNodeBase<NodeT> *, 8> WL;
while (!WL.empty()) {
const DomTreeNodeBase<NodeT> *N = WL.pop_back_val();
WL.append(N->begin(), N->end());
/// properlyDominates - Returns true iff A dominates B and A != B.
/// Note that this is not a constant time operation!
bool properlyDominates(const DomTreeNodeBase<NodeT> *A,
const DomTreeNodeBase<NodeT> *B) const {
if (!A || !B)
return false;
if (A == B)
return false;
return dominates(A, B);
bool properlyDominates(const NodeT *A, const NodeT *B) const;
/// isReachableFromEntry - Return true if A is dominated by the entry
/// block of the function containing it.
bool isReachableFromEntry(const NodeT* A) const {
assert(!this->isPostDominator() &&
"This is not implemented for post dominators");
return isReachableFromEntry(getNode(const_cast<NodeT *>(A)));
inline bool isReachableFromEntry(const DomTreeNodeBase<NodeT> *A) const {
return A;
/// dominates - Returns true iff A dominates B. Note that this is not a
/// constant time operation!
inline bool dominates(const DomTreeNodeBase<NodeT> *A,
const DomTreeNodeBase<NodeT> *B) const {
// A node trivially dominates itself.
if (B == A)
return true;
// An unreachable node is dominated by anything.
if (!isReachableFromEntry(B))
return true;
// And dominates nothing.
if (!isReachableFromEntry(A))
return false;
// Compare the result of the tree walk and the dfs numbers, if expensive
// checks are enabled.
#ifdef XDEBUG
assert((!DFSInfoValid ||
(dominatedBySlowTreeWalk(A, B) == B->DominatedBy(A))) &&
"Tree walk disagrees with dfs numbers!");
if (DFSInfoValid)
return B->DominatedBy(A);
// If we end up with too many slow queries, just update the
// DFS numbers on the theory that we are going to keep querying.
if (SlowQueries > 32) {
return B->DominatedBy(A);
return dominatedBySlowTreeWalk(A, B);
bool dominates(const NodeT *A, const NodeT *B) const;
NodeT *getRoot() const {
assert(this->Roots.size() == 1 && "Should always have entry node!");
return this->Roots[0];
/// findNearestCommonDominator - Find nearest common dominator basic block
/// for basic block A and B. If there is no such block then return NULL.
NodeT *findNearestCommonDominator(NodeT *A, NodeT *B) {
assert(A->getParent() == B->getParent() &&
"Two blocks are not in same function");
// If either A or B is a entry block then it is nearest common dominator
// (for forward-dominators).
if (!this->isPostDominator()) {
NodeT &Entry = A->getParent()->front();
if (A == &Entry || B == &Entry)
return &Entry;
// If B dominates A then B is nearest common dominator.
if (dominates(B, A))
return B;
// If A dominates B then A is nearest common dominator.
if (dominates(A, B))
return A;
DomTreeNodeBase<NodeT> *NodeA = getNode(A);
DomTreeNodeBase<NodeT> *NodeB = getNode(B);
// If we have DFS info, then we can avoid all allocations by just querying
// it from each IDom. Note that because we call 'dominates' twice above, we
// expect to call through this code at most 16 times in a row without
// building valid DFS information. This is important as below is a *very*
// slow tree walk.
if (DFSInfoValid) {
DomTreeNodeBase<NodeT> *IDomA = NodeA->getIDom();
while (IDomA) {
if (NodeB->DominatedBy(IDomA))
return IDomA->getBlock();
IDomA = IDomA->getIDom();
return nullptr;
// Collect NodeA dominators set.
SmallPtrSet<DomTreeNodeBase<NodeT>*, 16> NodeADoms;
DomTreeNodeBase<NodeT> *IDomA = NodeA->getIDom();
while (IDomA) {
IDomA = IDomA->getIDom();
// Walk NodeB immediate dominators chain and find common dominator node.
DomTreeNodeBase<NodeT> *IDomB = NodeB->getIDom();
while (IDomB) {
if (NodeADoms.count(IDomB) != 0)
return IDomB->getBlock();
IDomB = IDomB->getIDom();
return nullptr;
const NodeT *findNearestCommonDominator(const NodeT *A, const NodeT *B) {
// Cast away the const qualifiers here. This is ok since
// const is re-introduced on the return type.
return findNearestCommonDominator(const_cast<NodeT *>(A),
const_cast<NodeT *>(B));
// API to update (Post)DominatorTree information based on modifications to
// the CFG...
/// addNewBlock - Add a new node to the dominator tree information. This
/// creates a new node as a child of DomBB dominator node,linking it into
/// the children list of the immediate dominator.
DomTreeNodeBase<NodeT> *addNewBlock(NodeT *BB, NodeT *DomBB) {
assert(getNode(BB) == nullptr && "Block already in dominator tree!");
DomTreeNodeBase<NodeT> *IDomNode = getNode(DomBB);
assert(IDomNode && "Not immediate dominator specified for block!");
DFSInfoValid = false;
return DomTreeNodes[BB] =
IDomNode->addChild(new DomTreeNodeBase<NodeT>(BB, IDomNode));
/// changeImmediateDominator - This method is used to update the dominator
/// tree information when a node's immediate dominator changes.
void changeImmediateDominator(DomTreeNodeBase<NodeT> *N,
DomTreeNodeBase<NodeT> *NewIDom) {
assert(N && NewIDom && "Cannot change null node pointers!");
DFSInfoValid = false;
void changeImmediateDominator(NodeT *BB, NodeT *NewBB) {
changeImmediateDominator(getNode(BB), getNode(NewBB));
/// eraseNode - Removes a node from the dominator tree. Block must not
/// dominate any other blocks. Removes node from its immediate dominator's
/// children list. Deletes dominator node associated with basic block BB.
void eraseNode(NodeT *BB) {
DomTreeNodeBase<NodeT> *Node = getNode(BB);
assert(Node && "Removing node that isn't in dominator tree.");
assert(Node->getChildren().empty() && "Node is not a leaf node.");
// Remove node from immediate dominator's children list.
DomTreeNodeBase<NodeT> *IDom = Node->getIDom();
if (IDom) {
typename std::vector<DomTreeNodeBase<NodeT>*>::iterator I =
std::find(IDom->Children.begin(), IDom->Children.end(), Node);
assert(I != IDom->Children.end() &&
"Not in immediate dominator children set!");
// I am no longer your child...
delete Node;
/// removeNode - Removes a node from the dominator tree. Block must not
/// dominate any other blocks. Invalidates any node pointing to removed
/// block.
void removeNode(NodeT *BB) {
assert(getNode(BB) && "Removing node that isn't in dominator tree.");
/// splitBlock - BB is split and now it has one successor. Update dominator
/// tree to reflect this change.
void splitBlock(NodeT* NewBB) {
if (this->IsPostDominators)
this->Split<Inverse<NodeT*>, GraphTraits<Inverse<NodeT*> > >(*this, NewBB);
this->Split<NodeT*, GraphTraits<NodeT*> >(*this, NewBB);
/// print - Convert to human readable form
void print(raw_ostream &o) const {
o << "=============================--------------------------------\n";
if (this->isPostDominator())
o << "Inorder PostDominator Tree: ";
o << "Inorder Dominator Tree: ";
if (!this->DFSInfoValid)
o << "DFSNumbers invalid: " << SlowQueries << " slow queries.";
o << "\n";
// The postdom tree can have a null root if there are no returns.
if (getRootNode())
PrintDomTree<NodeT>(getRootNode(), o, 1);
template<class GraphT>
friend typename GraphT::NodeType* Eval(
DominatorTreeBase<typename GraphT::NodeType>& DT,
typename GraphT::NodeType* V,
unsigned LastLinked);
template<class GraphT>
friend unsigned DFSPass(DominatorTreeBase<typename GraphT::NodeType>& DT,
typename GraphT::NodeType* V,
unsigned N);
template<class FuncT, class N>
friend void Calculate(DominatorTreeBase<typename GraphTraits<N>::NodeType>& DT,
FuncT& F);
/// updateDFSNumbers - Assign In and Out numbers to the nodes while walking
/// dominator tree in dfs order.
void updateDFSNumbers() const {
unsigned DFSNum = 0;
SmallVector<std::pair<const DomTreeNodeBase<NodeT>*,
typename DomTreeNodeBase<NodeT>::const_iterator>, 32> WorkStack;
const DomTreeNodeBase<NodeT> *ThisRoot = getRootNode();
if (!ThisRoot)
// Even in the case of multiple exits that form the post dominator root
// nodes, do not iterate over all exits, but start from the virtual root
// node. Otherwise bbs, that are not post dominated by any exit but by the
// virtual root node, will never be assigned a DFS number.
WorkStack.push_back(std::make_pair(ThisRoot, ThisRoot->begin()));
ThisRoot->DFSNumIn = DFSNum++;
while (!WorkStack.empty()) {
const DomTreeNodeBase<NodeT> *Node = WorkStack.back().first;
typename DomTreeNodeBase<NodeT>::const_iterator ChildIt =
// If we visited all of the children of this node, "recurse" back up the
// stack setting the DFOutNum.
if (ChildIt == Node->end()) {
Node->DFSNumOut = DFSNum++;
} else {
// Otherwise, recursively visit this child.
const DomTreeNodeBase<NodeT> *Child = *ChildIt;
WorkStack.push_back(std::make_pair(Child, Child->begin()));
Child->DFSNumIn = DFSNum++;
SlowQueries = 0;
DFSInfoValid = true;
DomTreeNodeBase<NodeT> *getNodeForBlock(NodeT *BB) {
if (DomTreeNodeBase<NodeT> *Node = getNode(BB))
return Node;
// Haven't calculated this node yet? Get or calculate the node for the
// immediate dominator.
NodeT *IDom = getIDom(BB);
assert(IDom || this->DomTreeNodes[nullptr]);
DomTreeNodeBase<NodeT> *IDomNode = getNodeForBlock(IDom);
// Add a new tree node for this NodeT, and link it as a child of
// IDomNode
DomTreeNodeBase<NodeT> *C = new DomTreeNodeBase<NodeT>(BB, IDomNode);
return this->DomTreeNodes[BB] = IDomNode->addChild(C);
inline NodeT *getIDom(NodeT *BB) const {
return IDoms.lookup(BB);
inline void addRoot(NodeT* BB) {
/// recalculate - compute a dominator tree for the given function
template<class FT>
void recalculate(FT& F) {
typedef GraphTraits<FT*> TraitsTy;
if (!this->IsPostDominators) {
// Initialize root
NodeT *entry = TraitsTy::getEntryNode(&F);
this->IDoms[entry] = nullptr;
this->DomTreeNodes[entry] = nullptr;
Calculate<FT, NodeT*>(*this, F);
} else {
// Initialize the roots list
for (typename TraitsTy::nodes_iterator I = TraitsTy::nodes_begin(&F),
E = TraitsTy::nodes_end(&F); I != E; ++I) {
if (TraitsTy::child_begin(I) == TraitsTy::child_end(I))
// Prepopulate maps so that we don't get iterator invalidation issues later.
this->IDoms[I] = nullptr;
this->DomTreeNodes[I] = nullptr;
Calculate<FT, Inverse<NodeT*> >(*this, F);
// These two functions are declared out of line as a workaround for building
// with old (< r147295) versions of clang because of pr11642.
template<class NodeT>
bool DominatorTreeBase<NodeT>::dominates(const NodeT *A, const NodeT *B) const {
if (A == B)
return true;
// Cast away the const qualifiers here. This is ok since
// this function doesn't actually return the values returned
// from getNode.
return dominates(getNode(const_cast<NodeT *>(A)),
getNode(const_cast<NodeT *>(B)));
template<class NodeT>
DominatorTreeBase<NodeT>::properlyDominates(const NodeT *A, const NodeT *B) const {
if (A == B)
return false;
// Cast away the const qualifiers here. This is ok since
// this function doesn't actually return the values returned
// from getNode.
return dominates(getNode(const_cast<NodeT *>(A)),
getNode(const_cast<NodeT *>(B)));