1 //===-- llvm/ADT/EquivalenceClasses.h - Generic Equiv. Classes --*- 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 //===----------------------------------------------------------------------===//
10 // Generic implementation of equivalence classes through the use Tarjan's
11 // efficient union-find algorithm.
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_ADT_EQUIVALENCECLASSES_H
16 #define LLVM_ADT_EQUIVALENCECLASSES_H
18 #include "llvm/System/DataTypes.h"
23 /// EquivalenceClasses - This represents a collection of equivalence classes and
24 /// supports three efficient operations: insert an element into a class of its
25 /// own, union two classes, and find the class for a given element. In
26 /// addition to these modification methods, it is possible to iterate over all
27 /// of the equivalence classes and all of the elements in a class.
29 /// This implementation is an efficient implementation that only stores one copy
30 /// of the element being indexed per entry in the set, and allows any arbitrary
31 /// type to be indexed (as long as it can be ordered with operator<).
33 /// Here is a simple example using integers:
35 /// EquivalenceClasses<int> EC;
36 /// EC.unionSets(1, 2); // insert 1, 2 into the same set
37 /// EC.insert(4); EC.insert(5); // insert 4, 5 into own sets
38 /// EC.unionSets(5, 1); // merge the set for 1 with 5's set.
40 /// for (EquivalenceClasses<int>::iterator I = EC.begin(), E = EC.end();
41 /// I != E; ++I) { // Iterate over all of the equivalence sets.
42 /// if (!I->isLeader()) continue; // Ignore non-leader sets.
43 /// for (EquivalenceClasses<int>::member_iterator MI = EC.member_begin(I);
44 /// MI != EC.member_end(); ++MI) // Loop over members in this set.
45 /// cerr << *MI << " "; // Print member.
46 /// cerr << "\n"; // Finish set.
49 /// This example prints:
53 template <class ElemTy>
54 class EquivalenceClasses {
55 /// ECValue - The EquivalenceClasses data structure is just a set of these.
56 /// Each of these represents a relation for a value. First it stores the
57 /// value itself, which provides the ordering that the set queries. Next, it
58 /// provides a "next pointer", which is used to enumerate all of the elements
59 /// in the unioned set. Finally, it defines either a "end of list pointer" or
60 /// "leader pointer" depending on whether the value itself is a leader. A
61 /// "leader pointer" points to the node that is the leader for this element,
62 /// if the node is not a leader. A "end of list pointer" points to the last
63 /// node in the list of members of this list. Whether or not a node is a
64 /// leader is determined by a bit stolen from one of the pointers.
66 friend class EquivalenceClasses;
67 mutable const ECValue *Leader, *Next;
69 // ECValue ctor - Start out with EndOfList pointing to this node, Next is
70 // Null, isLeader = true.
71 ECValue(const ElemTy &Elt)
72 : Leader(this), Next((ECValue*)(intptr_t)1), Data(Elt) {}
74 const ECValue *getLeader() const {
75 if (isLeader()) return this;
76 if (Leader->isLeader()) return Leader;
78 return Leader = Leader->getLeader();
80 const ECValue *getEndOfList() const {
81 assert(isLeader() && "Cannot get the end of a list for a non-leader!");
85 void setNext(const ECValue *NewNext) const {
86 assert(getNext() == 0 && "Already has a next pointer!");
87 Next = (const ECValue*)((intptr_t)NewNext | (intptr_t)isLeader());
90 ECValue(const ECValue &RHS) : Leader(this), Next((ECValue*)(intptr_t)1),
92 // Only support copying of singleton nodes.
93 assert(RHS.isLeader() && RHS.getNext() == 0 && "Not a singleton!");
96 bool operator<(const ECValue &UFN) const { return Data < UFN.Data; }
98 bool isLeader() const { return (intptr_t)Next & 1; }
99 const ElemTy &getData() const { return Data; }
101 const ECValue *getNext() const {
102 return (ECValue*)((intptr_t)Next & ~(intptr_t)1);
106 bool operator<(const T &Val) const { return Data < Val; }
109 /// TheMapping - This implicitly provides a mapping from ElemTy values to the
110 /// ECValues, it just keeps the key as part of the value.
111 std::set<ECValue> TheMapping;
114 EquivalenceClasses() {}
115 EquivalenceClasses(const EquivalenceClasses &RHS) {
119 const EquivalenceClasses &operator=(const EquivalenceClasses &RHS) {
121 for (iterator I = RHS.begin(), E = RHS.end(); I != E; ++I)
123 member_iterator MI = RHS.member_begin(I);
124 member_iterator LeaderIt = member_begin(insert(*MI));
125 for (++MI; MI != member_end(); ++MI)
126 unionSets(LeaderIt, member_begin(insert(*MI)));
131 //===--------------------------------------------------------------------===//
132 // Inspection methods
135 /// iterator* - Provides a way to iterate over all values in the set.
136 typedef typename std::set<ECValue>::const_iterator iterator;
137 iterator begin() const { return TheMapping.begin(); }
138 iterator end() const { return TheMapping.end(); }
140 bool empty() const { return TheMapping.empty(); }
142 /// member_* Iterate over the members of an equivalence class.
144 class member_iterator;
145 member_iterator member_begin(iterator I) const {
146 // Only leaders provide anything to iterate over.
147 return member_iterator(I->isLeader() ? &*I : 0);
149 member_iterator member_end() const {
150 return member_iterator(0);
153 /// findValue - Return an iterator to the specified value. If it does not
154 /// exist, end() is returned.
155 iterator findValue(const ElemTy &V) const {
156 return TheMapping.find(V);
159 /// getLeaderValue - Return the leader for the specified value that is in the
160 /// set. It is an error to call this method for a value that is not yet in
161 /// the set. For that, call getOrInsertLeaderValue(V).
162 const ElemTy &getLeaderValue(const ElemTy &V) const {
163 member_iterator MI = findLeader(V);
164 assert(MI != member_end() && "Value is not in the set!");
168 /// getOrInsertLeaderValue - Return the leader for the specified value that is
169 /// in the set. If the member is not in the set, it is inserted, then
171 const ElemTy &getOrInsertLeaderValue(const ElemTy &V) const {
172 member_iterator MI = findLeader(insert(V));
173 assert(MI != member_end() && "Value is not in the set!");
177 /// getNumClasses - Return the number of equivalence classes in this set.
178 /// Note that this is a linear time operation.
179 unsigned getNumClasses() const {
181 for (iterator I = begin(), E = end(); I != E; ++I)
182 if (I->isLeader()) ++NC;
187 //===--------------------------------------------------------------------===//
190 /// insert - Insert a new value into the union/find set, ignoring the request
191 /// if the value already exists.
192 iterator insert(const ElemTy &Data) {
193 return TheMapping.insert(Data).first;
196 /// findLeader - Given a value in the set, return a member iterator for the
197 /// equivalence class it is in. This does the path-compression part that
198 /// makes union-find "union findy". This returns an end iterator if the value
199 /// is not in the equivalence class.
201 member_iterator findLeader(iterator I) const {
202 if (I == TheMapping.end()) return member_end();
203 return member_iterator(I->getLeader());
205 member_iterator findLeader(const ElemTy &V) const {
206 return findLeader(TheMapping.find(V));
210 /// union - Merge the two equivalence sets for the specified values, inserting
211 /// them if they do not already exist in the equivalence set.
212 member_iterator unionSets(const ElemTy &V1, const ElemTy &V2) {
213 iterator V1I = insert(V1), V2I = insert(V2);
214 return unionSets(findLeader(V1I), findLeader(V2I));
216 member_iterator unionSets(member_iterator L1, member_iterator L2) {
217 assert(L1 != member_end() && L2 != member_end() && "Illegal inputs!");
218 if (L1 == L2) return L1; // Unifying the same two sets, noop.
220 // Otherwise, this is a real union operation. Set the end of the L1 list to
221 // point to the L2 leader node.
222 const ECValue &L1LV = *L1.Node, &L2LV = *L2.Node;
223 L1LV.getEndOfList()->setNext(&L2LV);
225 // Update L1LV's end of list pointer.
226 L1LV.Leader = L2LV.getEndOfList();
228 // Clear L2's leader flag:
229 L2LV.Next = L2LV.getNext();
231 // L2's leader is now L1.
236 class member_iterator : public std::iterator<std::forward_iterator_tag,
237 const ElemTy, ptrdiff_t> {
238 typedef std::iterator<std::forward_iterator_tag,
239 const ElemTy, ptrdiff_t> super;
241 friend class EquivalenceClasses;
243 typedef size_t size_type;
244 typedef typename super::pointer pointer;
245 typedef typename super::reference reference;
247 explicit member_iterator() {}
248 explicit member_iterator(const ECValue *N) : Node(N) {}
249 member_iterator(const member_iterator &I) : Node(I.Node) {}
251 reference operator*() const {
252 assert(Node != 0 && "Dereferencing end()!");
253 return Node->getData();
255 reference operator->() const { return operator*(); }
257 member_iterator &operator++() {
258 assert(Node != 0 && "++'d off the end of the list!");
259 Node = Node->getNext();
263 member_iterator operator++(int) { // postincrement operators.
264 member_iterator tmp = *this;
269 bool operator==(const member_iterator &RHS) const {
270 return Node == RHS.Node;
272 bool operator!=(const member_iterator &RHS) const {
273 return Node != RHS.Node;
278 } // End llvm namespace