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/ADT/iterator"
19 #include "llvm/Support/DataTypes.h"
24 /// EquivalenceClasses - This represents a collection of equivalence classes and
25 /// supports three efficient operations: insert an element into a class of its
26 /// own, union two classes, and find the class for a given element. In
27 /// addition to these modification methods, it is possible to iterate over all
28 /// of the equivalence classes and all of the elements in a class.
30 /// This implementation is an efficient implementation that only stores one copy
31 /// of the element being indexed per entry in the set, and allows any arbitrary
32 /// type to be indexed (as long as it can be ordered with operator<).
34 /// Here is a simple example using integers:
36 /// EquivalenceClasses<int> EC;
37 /// EC.unionSets(1, 2); // insert 1, 2 into the same set
38 /// EC.insert(4); EC.insert(5); // insert 4, 5 into own sets
39 /// EC.unionSets(5, 1); // merge the set for 1 with 5's set.
41 /// for (EquivalenceClasses<int>::iterator I = EC.begin(), E = EC.end();
42 /// I != E; ++I) { // Iterate over all of the equivalence sets.
43 /// if (!I->isLeader()) continue; // Ignore non-leader sets.
44 /// for (EquivalenceClasses<int>::member_iterator MI = EC.member_begin(I);
45 /// MI != EC.member_end(); ++MI) // Loop over members in this set.
46 /// cerr << *MI << " "; // Print member.
47 /// cerr << "\n"; // Finish set.
50 /// This example prints:
54 template <class ElemTy>
55 class EquivalenceClasses {
56 /// ECValue - The EquivalenceClasses data structure is just a set of these.
57 /// Each of these represents a relation for a value. First it stores the
58 /// value itself, which provides the ordering that the set queries. Next, it
59 /// provides a "next pointer", which is used to enumerate all of the elements
60 /// in the unioned set. Finally, it defines either a "end of list pointer" or
61 /// "leader pointer" depending on whether the value itself is a leader. A
62 /// "leader pointer" points to the node that is the leader for this element,
63 /// if the node is not a leader. A "end of list pointer" points to the last
64 /// node in the list of members of this list. Whether or not a node is a
65 /// leader is determined by a bit stolen from one of the pointers.
67 friend class EquivalenceClasses;
68 mutable const ECValue *Leader, *Next;
70 // ECValue ctor - Start out with EndOfList pointing to this node, Next is
71 // Null, isLeader = true.
72 ECValue(const ElemTy &Elt)
73 : Leader(this), Next((ECValue*)(intptr_t)1), Data(Elt) {}
75 const ECValue *getLeader() const {
76 if (isLeader()) return this;
77 if (Leader->isLeader()) return Leader;
79 return Leader = Leader->getLeader();
81 const ECValue *getEndOfList() const {
82 assert(isLeader() && "Cannot get the end of a list for a non-leader!");
86 void setNext(const ECValue *NewNext) const {
87 assert(getNext() == 0 && "Already has a next pointer!");
88 Next = (const ECValue*)((intptr_t)NewNext | (intptr_t)isLeader());
91 ECValue(const ECValue &RHS) : Leader(this), Next((ECValue*)(intptr_t)1),
93 // Only support copying of singleton nodes.
94 assert(RHS.isLeader() && RHS.getNext() == 0 && "Not a singleton!");
97 bool operator<(const ECValue &UFN) const { return Data < UFN.Data; }
99 bool isLeader() const { return (intptr_t)Next & 1; }
100 const ElemTy &getData() const { return Data; }
102 const ECValue *getNext() const {
103 return (ECValue*)((intptr_t)Next & ~(intptr_t)1);
107 bool operator<(const T &Val) const { return Data < Val; }
110 /// TheMapping - This implicitly provides a mapping from ElemTy values to the
111 /// ECValues, it just keeps the key as part of the value.
112 std::set<ECValue> TheMapping;
115 EquivalenceClasses() {}
116 EquivalenceClasses(const EquivalenceClasses &RHS) {
120 const EquivalenceClasses &operator=(const EquivalenceClasses &RHS) {
122 for (iterator I = RHS.begin(), E = RHS.end(); I != E; ++I)
124 member_iterator MI = RHS.member_begin(I);
125 member_iterator LeaderIt = member_begin(insert(*MI));
126 for (++MI; MI != member_end(); ++MI)
127 unionSets(LeaderIt, member_begin(insert(*MI)));
132 //===--------------------------------------------------------------------===//
133 // Inspection methods
136 /// iterator* - Provides a way to iterate over all values in the set.
137 typedef typename std::set<ECValue>::const_iterator iterator;
138 iterator begin() const { return TheMapping.begin(); }
139 iterator end() const { return TheMapping.end(); }
141 bool empty() const { return TheMapping.empty(); }
143 /// member_* Iterate over the members of an equivalence class.
145 class member_iterator;
146 member_iterator member_begin(iterator I) const {
147 // Only leaders provide anything to iterate over.
148 return member_iterator(I->isLeader() ? &*I : 0);
150 member_iterator member_end() const {
151 return member_iterator(0);
154 /// findValue - Return an iterator to the specified value. If it does not
155 /// exist, end() is returned.
156 iterator findValue(const ElemTy &V) const {
157 return TheMapping.find(V);
160 /// getLeaderValue - Return the leader for the specified value that is in the
161 /// set. It is an error to call this method for a value that is not yet in
162 /// the set. For that, call getOrInsertLeaderValue(V).
163 const ElemTy &getLeaderValue(const ElemTy &V) const {
164 member_iterator MI = findLeader(V);
165 assert(MI != member_end() && "Value is not in the set!");
169 /// getOrInsertLeaderValue - Return the leader for the specified value that is
170 /// in the set. If the member is not in the set, it is inserted, then
172 const ElemTy &getOrInsertLeaderValue(const ElemTy &V) const {
173 member_iterator MI = findLeader(insert(V));
174 assert(MI != member_end() && "Value is not in the set!");
178 /// getNumClasses - Return the number of equivalence classes in this set.
179 /// Note that this is a linear time operation.
180 unsigned getNumClasses() const {
182 for (iterator I = begin(), E = end(); I != E; ++I)
183 if (I->isLeader()) ++NC;
188 //===--------------------------------------------------------------------===//
191 /// insert - Insert a new value into the union/find set, ignoring the request
192 /// if the value already exists.
193 iterator insert(const ElemTy &Data) {
194 return TheMapping.insert(Data).first;
197 /// findLeader - Given a value in the set, return a member iterator for the
198 /// equivalence class it is in. This does the path-compression part that
199 /// makes union-find "union findy". This returns an end iterator if the value
200 /// is not in the equivalence class.
202 member_iterator findLeader(iterator I) const {
203 if (I == TheMapping.end()) return member_end();
204 return member_iterator(I->getLeader());
206 member_iterator findLeader(const ElemTy &V) const {
207 return findLeader(TheMapping.find(V));
211 /// union - Merge the two equivalence sets for the specified values, inserting
212 /// them if they do not already exist in the equivalence set.
213 member_iterator unionSets(const ElemTy &V1, const ElemTy &V2) {
214 iterator V1I = insert(V1), V2I = insert(V2);
215 return unionSets(findLeader(V1I), findLeader(V2I));
217 member_iterator unionSets(member_iterator L1, member_iterator L2) {
218 assert(L1 != member_end() && L2 != member_end() && "Illegal inputs!");
219 if (L1 == L2) return L1; // Unifying the same two sets, noop.
221 // Otherwise, this is a real union operation. Set the end of the L1 list to
222 // point to the L2 leader node.
223 const ECValue &L1LV = *L1.Node, &L2LV = *L2.Node;
224 L1LV.getEndOfList()->setNext(&L2LV);
226 // Update L1LV's end of list pointer.
227 L1LV.Leader = L2LV.getEndOfList();
229 // Clear L2's leader flag:
230 L2LV.Next = L2LV.getNext();
232 // L2's leader is now L1.
237 class member_iterator : public forward_iterator<ElemTy, ptrdiff_t> {
238 typedef forward_iterator<const ElemTy, ptrdiff_t> super;
240 friend class EquivalenceClasses;
242 typedef size_t size_type;
243 typedef typename super::pointer pointer;
244 typedef typename super::reference reference;
246 explicit member_iterator() {}
247 explicit member_iterator(const ECValue *N) : Node(N) {}
248 member_iterator(const member_iterator &I) : Node(I.Node) {}
250 reference operator*() const {
251 assert(Node != 0 && "Dereferencing end()!");
252 return Node->getData();
254 reference operator->() const { return operator*(); }
256 member_iterator &operator++() {
257 assert(Node != 0 && "++'d off the end of the list!");
258 Node = Node->getNext();
262 member_iterator operator++(int) { // postincrement operators.
263 member_iterator tmp = *this;
268 bool operator==(const member_iterator &RHS) const {
269 return Node == RHS.Node;
271 bool operator!=(const member_iterator &RHS) const {
272 return Node != RHS.Node;
277 } // End llvm namespace