1 //===-- llvm/ADT/EquivalenceClasses.h - Generic Equiv. Classes --*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source 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"
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 /// std::cerr << *MI << " "; // Print member.
46 /// std::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() == 0) 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 bool isL = isLeader();
88 Next = (const ECValue*)((intptr_t)NewNext | 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;
116 //===--------------------------------------------------------------------===//
117 // Inspection methods
120 /// iterator* - Provides a way to iterate over all values in the set.
121 typedef typename std::set<ECValue>::const_iterator iterator;
122 iterator begin() const { return TheMapping.begin(); }
123 iterator end() const { return TheMapping.end(); }
125 /// member_* Iterate over the members of an equivalence class.
127 class member_iterator;
128 member_iterator member_begin(iterator I) const {
129 // Only leaders provide anything to iterate over.
130 return member_iterator(I->isLeader() ? &*I : 0);
132 member_iterator member_end() const {
133 return member_iterator(0);
136 //===--------------------------------------------------------------------===//
139 /// insert - Insert a new value into the union/find set, ignoring the request
140 /// if the value already exists.
141 iterator insert(const ElemTy &Data) {
142 return TheMapping.insert(Data).first;
145 /// findLeader - Given a value in the set, return a member iterator for the
146 /// equivalence class it is in. This does the path-compression part that
147 /// makes union-find "union findy". This returns an end iterator if the value
148 /// is not in the equivalence class.
150 member_iterator findLeader(iterator I) const {
151 if (I == TheMapping.end()) return member_end();
152 return member_iterator(I->getLeader());
154 member_iterator findLeader(const ElemTy &V) const {
155 return findLeader(TheMapping.find(V));
159 /// union - Merge the two equivalence sets for the specified values, inserting
160 /// them if they do not already exist in the equivalence set.
161 member_iterator unionSets(const ElemTy &V1, const ElemTy &V2) {
162 return unionSets(findLeader(insert(V1)), findLeader(insert(V2)));
164 member_iterator unionSets(member_iterator L1, member_iterator L2) {
165 assert(L1 != member_end() && L2 != member_end() && "Illegal inputs!");
166 if (L1 == L2) return L1; // Unifying the same two sets, noop.
168 // Otherwise, this is a real union operation. Set the end of the L1 list to
169 // point to the L2 leader node.
170 const ECValue &L1LV = *L1.Node, &L2LV = *L2.Node;
171 L1LV.getEndOfList()->setNext(&L2LV);
173 // Update L1LV's end of list pointer.
174 L1LV.Leader = L2LV.getEndOfList();
176 // Clear L2's leader flag:
177 L2LV.Next = L2LV.getNext();
179 // L2's leader is now L1.
184 class member_iterator : public forward_iterator<ElemTy, ptrdiff_t> {
185 typedef forward_iterator<const ElemTy, ptrdiff_t> super;
187 friend class EquivalenceClasses;
189 typedef size_t size_type;
190 typedef typename super::pointer pointer;
191 typedef typename super::reference reference;
193 explicit member_iterator() {}
194 explicit member_iterator(const ECValue *N) : Node(N) {}
195 member_iterator(const member_iterator &I) : Node(I.Node) {}
197 reference operator*() const {
198 assert(Node != 0 && "Dereferencing end()!");
199 return Node->getData();
201 reference operator->() const { return operator*(); }
203 member_iterator &operator++() {
204 assert(Node != 0 && "++'d off the end of the list!");
205 Node = Node->getNext();
209 member_iterator operator++(int) { // postincrement operators.
210 member_iterator tmp = *this;
215 bool operator==(const member_iterator &RHS) const {
216 return Node == RHS.Node;
218 bool operator!=(const member_iterator &RHS) const {
219 return Node != RHS.Node;
224 } // End llvm namespace