-//===-- Support/SCCIterator.h - Strongly Connected Comp. Iter. --*- C++ -*-===//
+//===---- ADT/SCCIterator.h - Strongly Connected Comp. Iter. ----*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
-//
-// This builds on the llvm/ADT/GraphTraits.h file to find the strongly connected
-// components (SCCs) of a graph in O(N+E) time using Tarjan's DFS algorithm.
-//
-// The SCC iterator has the important property that if a node in SCC S1 has an
-// edge to a node in SCC S2, then it visits S1 *after* S2.
-//
-// To visit S1 *before* S2, use the scc_iterator on the Inverse graph.
-// (NOTE: This requires some simple wrappers and is not supported yet.)
-//
+/// \file
+///
+/// This builds on the llvm/ADT/GraphTraits.h file to find the strongly
+/// connected components (SCCs) of a graph in O(N+E) time using Tarjan's DFS
+/// algorithm.
+///
+/// The SCC iterator has the important property that if a node in SCC S1 has an
+/// edge to a node in SCC S2, then it visits S1 *after* S2.
+///
+/// To visit S1 *before* S2, use the scc_iterator on the Inverse graph. (NOTE:
+/// This requires some simple wrappers and is not supported yet.)
+///
//===----------------------------------------------------------------------===//
#ifndef LLVM_ADT_SCCITERATOR_H
#define LLVM_ADT_SCCITERATOR_H
+#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/GraphTraits.h"
#include "llvm/ADT/iterator.h"
-#include <map>
#include <vector>
namespace llvm {
-//===----------------------------------------------------------------------===//
+/// \brief Enumerate the SCCs of a directed graph in reverse topological order
+/// of the SCC DAG.
///
-/// scc_iterator - Enumerate the SCCs of a directed graph, in
-/// reverse topological order of the SCC DAG.
-///
-template<class GraphT, class GT = GraphTraits<GraphT> >
+/// This is implemented using Tarjan's DFS algorithm using an internal stack to
+/// build up a vector of nodes in a particular SCC. Note that it is a forward
+/// iterator and thus you cannot backtrack or re-visit nodes.
+template <class GraphT, class GT = GraphTraits<GraphT>>
class scc_iterator
- : public forward_iterator<std::vector<typename GT::NodeType>, ptrdiff_t> {
- typedef typename GT::NodeType NodeType;
+ : public iterator_facade_base<
+ scc_iterator<GraphT, GT>, std::forward_iterator_tag,
+ const std::vector<typename GT::NodeType *>, ptrdiff_t> {
+ typedef typename GT::NodeType NodeType;
typedef typename GT::ChildIteratorType ChildItTy;
- typedef std::vector<NodeType*> SccTy;
- typedef forward_iterator<SccTy, ptrdiff_t> super;
- typedef typename super::reference reference;
- typedef typename super::pointer pointer;
-
- // The visit counters used to detect when a complete SCC is on the stack.
- // visitNum is the global counter.
- // nodeVisitNumbers are per-node visit numbers, also used as DFS flags.
+ typedef std::vector<NodeType *> SccTy;
+ typedef typename scc_iterator::reference reference;
+
+ /// Element of VisitStack during DFS.
+ struct StackElement {
+ NodeType *Node; ///< The current node pointer.
+ ChildItTy NextChild; ///< The next child, modified inplace during DFS.
+ unsigned MinVisited; ///< Minimum uplink value of all children of Node.
+
+ StackElement(NodeType *Node, const ChildItTy &Child, unsigned Min)
+ : Node(Node), NextChild(Child), MinVisited(Min) {}
+
+ bool operator==(const StackElement &Other) const {
+ return Node == Other.Node &&
+ NextChild == Other.NextChild &&
+ MinVisited == Other.MinVisited;
+ }
+ };
+
+ /// The visit counters used to detect when a complete SCC is on the stack.
+ /// visitNum is the global counter.
+ ///
+ /// nodeVisitNumbers are per-node visit numbers, also used as DFS flags.
unsigned visitNum;
- std::map<NodeType *, unsigned> nodeVisitNumbers;
+ DenseMap<NodeType *, unsigned> nodeVisitNumbers;
- // SCCNodeStack - Stack holding nodes of the SCC.
+ /// Stack holding nodes of the SCC.
std::vector<NodeType *> SCCNodeStack;
- // CurrentSCC - The current SCC, retrieved using operator*().
+ /// The current SCC, retrieved using operator*().
SccTy CurrentSCC;
- // VisitStack - Used to maintain the ordering. Top = current block
- // First element is basic block pointer, second is the 'next child' to visit
- std::vector<std::pair<NodeType *, ChildItTy> > VisitStack;
-
- // MinVistNumStack - Stack holding the "min" values for each node in the DFS.
- // This is used to track the minimum uplink values for all children of
- // the corresponding node on the VisitStack.
- std::vector<unsigned> MinVisitNumStack;
-
- // A single "visit" within the non-recursive DFS traversal.
- void DFSVisitOne(NodeType* N) {
- ++visitNum; // Global counter for the visit order
- nodeVisitNumbers[N] = visitNum;
- SCCNodeStack.push_back(N);
- MinVisitNumStack.push_back(visitNum);
- VisitStack.push_back(std::make_pair(N, GT::child_begin(N)));
- //DOUT << "TarjanSCC: Node " << N <<
- // " : visitNum = " << visitNum << "\n";
- }
+ /// DFS stack, Used to maintain the ordering. The top contains the current
+ /// node, the next child to visit, and the minimum uplink value of all child
+ std::vector<StackElement> VisitStack;
- // The stack-based DFS traversal; defined below.
- void DFSVisitChildren() {
- assert(!VisitStack.empty());
- while (VisitStack.back().second != GT::child_end(VisitStack.back().first)) {
- // TOS has at least one more child so continue DFS
- NodeType *childN = *VisitStack.back().second++;
- if (!nodeVisitNumbers.count(childN)) {
- // this node has never been seen
- DFSVisitOne(childN);
- } else {
- unsigned childNum = nodeVisitNumbers[childN];
- if (MinVisitNumStack.back() > childNum)
- MinVisitNumStack.back() = childNum;
- }
- }
- }
+ /// A single "visit" within the non-recursive DFS traversal.
+ void DFSVisitOne(NodeType *N);
- // Compute the next SCC using the DFS traversal.
- void GetNextSCC() {
- assert(VisitStack.size() == MinVisitNumStack.size());
- CurrentSCC.clear(); // Prepare to compute the next SCC
- while (!VisitStack.empty()) {
- DFSVisitChildren();
- assert(VisitStack.back().second ==GT::child_end(VisitStack.back().first));
- NodeType* visitingN = VisitStack.back().first;
- unsigned minVisitNum = MinVisitNumStack.back();
- VisitStack.pop_back();
- MinVisitNumStack.pop_back();
- if (!MinVisitNumStack.empty() && MinVisitNumStack.back() > minVisitNum)
- MinVisitNumStack.back() = minVisitNum;
-
- //DOUT << "TarjanSCC: Popped node " << visitingN <<
- // " : minVisitNum = " << minVisitNum << "; Node visit num = " <<
- // nodeVisitNumbers[visitingN] << "\n";
-
- if (minVisitNum == nodeVisitNumbers[visitingN]) {
- // A full SCC is on the SCCNodeStack! It includes all nodes below
- // visitingN on the stack. Copy those nodes to CurrentSCC,
- // reset their minVisit values, and return (this suspends
- // the DFS traversal till the next ++).
- do {
- CurrentSCC.push_back(SCCNodeStack.back());
- SCCNodeStack.pop_back();
- nodeVisitNumbers[CurrentSCC.back()] = ~0U;
- } while (CurrentSCC.back() != visitingN);
- return;
- }
- }
- }
+ /// The stack-based DFS traversal; defined below.
+ void DFSVisitChildren();
+
+ /// Compute the next SCC using the DFS traversal.
+ void GetNextSCC();
- inline scc_iterator(NodeType *entryN) : visitNum(0) {
+ scc_iterator(NodeType *entryN) : visitNum(0) {
DFSVisitOne(entryN);
GetNextSCC();
}
- inline scc_iterator() { /* End is when DFS stack is empty */ }
-public:
- typedef scc_iterator<GraphT, GT> _Self;
+ /// End is when the DFS stack is empty.
+ scc_iterator() {}
- // Provide static "constructors"...
- static inline _Self begin(GraphT& G) { return _Self(GT::getEntryNode(G)); }
- static inline _Self end (GraphT& G) { return _Self(); }
+public:
+ static scc_iterator begin(const GraphT &G) {
+ return scc_iterator(GT::getEntryNode(G));
+ }
+ static scc_iterator end(const GraphT &) { return scc_iterator(); }
- // Direct loop termination test (I.fini() is more efficient than I == end())
- inline bool fini() const {
+ /// \brief Direct loop termination test which is more efficient than
+ /// comparison with \c end().
+ bool isAtEnd() const {
assert(!CurrentSCC.empty() || VisitStack.empty());
return CurrentSCC.empty();
}
- inline bool operator==(const _Self& x) const {
+ bool operator==(const scc_iterator &x) const {
return VisitStack == x.VisitStack && CurrentSCC == x.CurrentSCC;
}
- inline bool operator!=(const _Self& x) const { return !operator==(x); }
- // Iterator traversal: forward iteration only
- inline _Self& operator++() { // Preincrement
+ scc_iterator &operator++() {
GetNextSCC();
return *this;
}
- inline _Self operator++(int) { // Postincrement
- _Self tmp = *this; ++*this; return tmp;
- }
- // Retrieve a reference to the current SCC
- inline const SccTy &operator*() const {
+ reference operator*() const {
assert(!CurrentSCC.empty() && "Dereferencing END SCC iterator!");
return CurrentSCC;
}
- inline SccTy &operator*() {
- assert(!CurrentSCC.empty() && "Dereferencing END SCC iterator!");
- return CurrentSCC;
+
+ /// \brief Test if the current SCC has a loop.
+ ///
+ /// If the SCC has more than one node, this is trivially true. If not, it may
+ /// still contain a loop if the node has an edge back to itself.
+ bool hasLoop() const;
+
+ /// This informs the \c scc_iterator that the specified \c Old node
+ /// has been deleted, and \c New is to be used in its place.
+ void ReplaceNode(NodeType *Old, NodeType *New) {
+ assert(nodeVisitNumbers.count(Old) && "Old not in scc_iterator?");
+ nodeVisitNumbers[New] = nodeVisitNumbers[Old];
+ nodeVisitNumbers.erase(Old);
+ }
+};
+
+template <class GraphT, class GT>
+void scc_iterator<GraphT, GT>::DFSVisitOne(NodeType *N) {
+ ++visitNum;
+ nodeVisitNumbers[N] = visitNum;
+ SCCNodeStack.push_back(N);
+ VisitStack.push_back(StackElement(N, GT::child_begin(N), visitNum));
+#if 0 // Enable if needed when debugging.
+ dbgs() << "TarjanSCC: Node " << N <<
+ " : visitNum = " << visitNum << "\n";
+#endif
+}
+
+template <class GraphT, class GT>
+void scc_iterator<GraphT, GT>::DFSVisitChildren() {
+ assert(!VisitStack.empty());
+ while (VisitStack.back().NextChild != GT::child_end(VisitStack.back().Node)) {
+ // TOS has at least one more child so continue DFS
+ NodeType *childN = *VisitStack.back().NextChild++;
+ typename DenseMap<NodeType *, unsigned>::iterator Visited =
+ nodeVisitNumbers.find(childN);
+ if (Visited == nodeVisitNumbers.end()) {
+ // this node has never been seen.
+ DFSVisitOne(childN);
+ continue;
+ }
+
+ unsigned childNum = Visited->second;
+ if (VisitStack.back().MinVisited > childNum)
+ VisitStack.back().MinVisited = childNum;
+ }
+}
+
+template <class GraphT, class GT> void scc_iterator<GraphT, GT>::GetNextSCC() {
+ CurrentSCC.clear(); // Prepare to compute the next SCC
+ while (!VisitStack.empty()) {
+ DFSVisitChildren();
+
+ // Pop the leaf on top of the VisitStack.
+ NodeType *visitingN = VisitStack.back().Node;
+ unsigned minVisitNum = VisitStack.back().MinVisited;
+ assert(VisitStack.back().NextChild == GT::child_end(visitingN));
+ VisitStack.pop_back();
+
+ // Propagate MinVisitNum to parent so we can detect the SCC starting node.
+ if (!VisitStack.empty() && VisitStack.back().MinVisited > minVisitNum)
+ VisitStack.back().MinVisited = minVisitNum;
+
+#if 0 // Enable if needed when debugging.
+ dbgs() << "TarjanSCC: Popped node " << visitingN <<
+ " : minVisitNum = " << minVisitNum << "; Node visit num = " <<
+ nodeVisitNumbers[visitingN] << "\n";
+#endif
+
+ if (minVisitNum != nodeVisitNumbers[visitingN])
+ continue;
+
+ // A full SCC is on the SCCNodeStack! It includes all nodes below
+ // visitingN on the stack. Copy those nodes to CurrentSCC,
+ // reset their minVisit values, and return (this suspends
+ // the DFS traversal till the next ++).
+ do {
+ CurrentSCC.push_back(SCCNodeStack.back());
+ SCCNodeStack.pop_back();
+ nodeVisitNumbers[CurrentSCC.back()] = ~0U;
+ } while (CurrentSCC.back() != visitingN);
+ return;
}
+}
- // hasLoop() -- Test if the current SCC has a loop. If it has more than one
- // node, this is trivially true. If not, it may still contain a loop if the
- // node has an edge back to itself.
- bool hasLoop() const {
+template <class GraphT, class GT>
+bool scc_iterator<GraphT, GT>::hasLoop() const {
assert(!CurrentSCC.empty() && "Dereferencing END SCC iterator!");
- if (CurrentSCC.size() > 1) return true;
+ if (CurrentSCC.size() > 1)
+ return true;
NodeType *N = CurrentSCC.front();
- for (ChildItTy CI = GT::child_begin(N), CE=GT::child_end(N); CI != CE; ++CI)
+ for (ChildItTy CI = GT::child_begin(N), CE = GT::child_end(N); CI != CE;
+ ++CI)
if (*CI == N)
return true;
return false;
}
-};
-
-// Global constructor for the SCC iterator.
-template <class T>
-scc_iterator<T> scc_begin(T G) {
+/// \brief Construct the begin iterator for a deduced graph type T.
+template <class T> scc_iterator<T> scc_begin(const T &G) {
return scc_iterator<T>::begin(G);
}
-template <class T>
-scc_iterator<T> scc_end(T G) {
+/// \brief Construct the end iterator for a deduced graph type T.
+template <class T> scc_iterator<T> scc_end(const T &G) {
return scc_iterator<T>::end(G);
}
+/// \brief Construct the begin iterator for a deduced graph type T's Inverse<T>.
+template <class T> scc_iterator<Inverse<T> > scc_begin(const Inverse<T> &G) {
+ return scc_iterator<Inverse<T> >::begin(G);
+}
+
+/// \brief Construct the end iterator for a deduced graph type T's Inverse<T>.
+template <class T> scc_iterator<Inverse<T> > scc_end(const Inverse<T> &G) {
+ return scc_iterator<Inverse<T> >::end(G);
+}
+
} // End llvm namespace
#endif
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