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https://github.com/c64scene-ar/llvm-6502.git
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3889a2cb05
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@6842 91177308-0d34-0410-b5e6-96231b3b80d8
227 lines
8.2 KiB
C++
227 lines
8.2 KiB
C++
//===-- Support/TarjanSCCIterator.h - Tarjan SCC iterator -------*- C++ -*-===//
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//
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// This builds on the Support/GraphTraits.h file to find the strongly
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// connected components (SCCs) of a graph in O(N+E) time using
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// Tarjan's DFS algorithm.
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//
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// The SCC iterator has the important property that if a node in SCC S1
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// has an edge to a node in SCC S2, then it visits S1 *after* S2.
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//
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// To visit S1 *before* S2, use the TarjanSCCIterator on the Inverse graph.
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// (NOTE: This requires some simple wrappers and is not supported yet.)
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//
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//===----------------------------------------------------------------------===//
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#ifndef SUPPORT_TARJANSCCITERATOR_H
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#define SUPPORT_TARJANSCCITERATOR_H
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#include "Support/GraphTraits.h"
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#include "Support/Statistic.h"
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#include "Support/iterator"
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#include <vector>
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#include <stack>
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#include <map>
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#include <assert.h>
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//--------------------------------------------------------------------------
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// class SCC : A simple representation of an SCC in a generic Graph.
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//--------------------------------------------------------------------------
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template<class GraphT, class GT = GraphTraits<GraphT> >
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struct SCC: public std::vector<typename GT::NodeType*> {
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typedef typename GT::NodeType NodeType;
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typedef typename GT::ChildIteratorType ChildItTy;
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typedef std::vector<typename GT::NodeType*> super;
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typedef typename super::iterator iterator;
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typedef typename super::const_iterator const_iterator;
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typedef typename super::reverse_iterator reverse_iterator;
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typedef typename super::const_reverse_iterator const_reverse_iterator;
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// HasLoop() -- Test if this SCC has a loop. If it has more than one
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// node, this is trivially true. If not, it may still contain a loop
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// if the node has an edge back to itself.
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bool HasLoop() const {
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if (size() > 1) return true;
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NodeType* N = front();
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for (ChildItTy CI=GT::child_begin(N), CE=GT::child_end(N); CI != CE; ++CI)
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if (*CI == N)
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return true;
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return false;
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}
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};
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//--------------------------------------------------------------------------
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// class TarjanSCC_iterator: Enumerate the SCCs of a directed graph, in
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// reverse topological order of the SCC DAG.
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//--------------------------------------------------------------------------
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namespace {
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Statistic<> NumSCCs("NumSCCs", "Number of Strongly Connected Components");
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Statistic<> MaxSCCSize("MaxSCCSize", "Size of largest Strongly Connected Component");
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}
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template<class GraphT, class GT = GraphTraits<GraphT> >
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class TarjanSCC_iterator : public forward_iterator<SCC<GraphT, GT>, ptrdiff_t>
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{
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typedef SCC<GraphT, GT> SccTy;
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typedef forward_iterator<SccTy, ptrdiff_t> super;
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typedef typename super::reference reference;
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typedef typename super::pointer pointer;
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typedef typename GT::NodeType NodeType;
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typedef typename GT::ChildIteratorType ChildItTy;
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// The visit counters used to detect when a complete SCC is on the stack.
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// visitNum is the global counter.
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// nodeVisitNumbers are per-node visit numbers, also used as DFS flags.
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unsigned long visitNum;
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std::map<NodeType *, unsigned long> nodeVisitNumbers;
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// SCCNodeStack - Stack holding nodes of the SCC.
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std::stack<NodeType *> SCCNodeStack;
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// CurrentSCC - The current SCC, retrieved using operator*().
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SccTy CurrentSCC;
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// VisitStack - Used to maintain the ordering. Top = current block
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// First element is basic block pointer, second is the 'next child' to visit
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std::stack<std::pair<NodeType *, ChildItTy> > VisitStack;
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// MinVistNumStack - Stack holding the "min" values for each node in the DFS.
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// This is used to track the minimum uplink values for all children of
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// the corresponding node on the VisitStack.
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std::stack<unsigned long> MinVisitNumStack;
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// A single "visit" within the non-recursive DFS traversal.
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void DFSVisitOne(NodeType* N) {
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++visitNum; // Global counter for the visit order
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nodeVisitNumbers[N] = visitNum;
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SCCNodeStack.push(N);
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MinVisitNumStack.push(visitNum);
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VisitStack.push(make_pair(N, GT::child_begin(N)));
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DEBUG(std::cerr << "TarjanSCC: Node " << N <<
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" : visitNum = " << visitNum << "\n");
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}
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// The stack-based DFS traversal; defined below.
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void DFSVisitChildren() {
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assert(!VisitStack.empty());
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while (VisitStack.top().second != GT::child_end(VisitStack.top().first))
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{ // TOS has at least one more child so continue DFS
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NodeType *childN = *VisitStack.top().second++;
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if (nodeVisitNumbers.find(childN) == nodeVisitNumbers.end())
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{ // this node has never been seen
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DFSVisitOne(childN);
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}
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else
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{
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unsigned long childNum = nodeVisitNumbers[childN];
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if (MinVisitNumStack.top() > childNum)
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MinVisitNumStack.top() = childNum;
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}
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}
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}
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// Compute the next SCC using the DFS traversal.
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void GetNextSCC() {
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assert(VisitStack.size() == MinVisitNumStack.size());
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CurrentSCC.clear(); // Prepare to compute the next SCC
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while (! VisitStack.empty())
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{
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DFSVisitChildren();
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assert(VisitStack.top().second==GT::child_end(VisitStack.top().first));
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NodeType* visitingN = VisitStack.top().first;
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unsigned long minVisitNum = MinVisitNumStack.top();
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VisitStack.pop();
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MinVisitNumStack.pop();
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if (! MinVisitNumStack.empty() && MinVisitNumStack.top() > minVisitNum)
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MinVisitNumStack.top() = minVisitNum;
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DEBUG(std::cerr << "TarjanSCC: Popped node " << visitingN <<
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" : minVisitNum = " << minVisitNum << "; Node visit num = " <<
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nodeVisitNumbers[visitingN] << "\n");
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if (minVisitNum == nodeVisitNumbers[visitingN])
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{ // A full SCC is on the SCCNodeStack! It includes all nodes below
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// visitingN on the stack. Copy those nodes to CurrentSCC,
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// reset their minVisit values, and return (this suspends
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// the DFS traversal till the next ++).
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do {
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CurrentSCC.push_back(SCCNodeStack.top());
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SCCNodeStack.pop();
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nodeVisitNumbers[CurrentSCC.back()] = ~0UL;
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} while (CurrentSCC.back() != visitingN);
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++NumSCCs;
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if (CurrentSCC.size() > MaxSCCSize) MaxSCCSize = CurrentSCC.size();
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return;
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}
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}
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}
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inline TarjanSCC_iterator(NodeType *entryN) : visitNum(0) {
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DFSVisitOne(entryN);
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GetNextSCC();
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}
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inline TarjanSCC_iterator() { /* End is when DFS stack is empty */ }
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public:
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typedef TarjanSCC_iterator<GraphT, GT> _Self;
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// Provide static "constructors"...
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static inline _Self begin(GraphT& G) { return _Self(GT::getEntryNode(G)); }
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static inline _Self end (GraphT& G) { return _Self(); }
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// Direct loop termination test (I.fini() is more efficient than I == end())
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inline bool fini() const {
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assert(!CurrentSCC.empty() || VisitStack.empty());
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return CurrentSCC.empty();
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}
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inline bool operator==(const _Self& x) const {
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return VisitStack == x.VisitStack && CurrentSCC == x.CurrentSCC;
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}
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inline bool operator!=(const _Self& x) const { return !operator==(x); }
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// Iterator traversal: forward iteration only
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inline _Self& operator++() { // Preincrement
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GetNextSCC();
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return *this;
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}
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inline _Self operator++(int) { // Postincrement
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_Self tmp = *this; ++*this; return tmp;
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}
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// Retrieve a pointer to the current SCC. Returns NULL when done.
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inline const SccTy* operator*() const {
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assert(!CurrentSCC.empty() || VisitStack.empty());
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return CurrentSCC.empty()? NULL : &CurrentSCC;
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}
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inline SccTy* operator*() {
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assert(!CurrentSCC.empty() || VisitStack.empty());
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return CurrentSCC.empty()? NULL : &CurrentSCC;
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}
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};
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// Global constructor for the Tarjan SCC iterator. Use *I == NULL or I.fini()
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// to test termination efficiently, instead of I == the "end" iterator.
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template <class T>
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TarjanSCC_iterator<T> tarj_begin(T G)
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{
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return TarjanSCC_iterator<T>::begin(G);
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}
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template <class T>
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TarjanSCC_iterator<T> tarj_end(T G)
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{
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return TarjanSCC_iterator<T>::end(G);
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}
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//===----------------------------------------------------------------------===//
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#endif
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