LLVM  3.7.0
EquivalenceClasses.h
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1 //===-- llvm/ADT/EquivalenceClasses.h - Generic Equiv. Classes --*- C++ -*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // Generic implementation of equivalence classes through the use Tarjan's
11 // efficient union-find algorithm.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #ifndef LLVM_ADT_EQUIVALENCECLASSES_H
16 #define LLVM_ADT_EQUIVALENCECLASSES_H
17 
18 #include "llvm/Support/DataTypes.h"
19 #include <cassert>
20 #include <cstddef>
21 #include <set>
22 
23 namespace llvm {
24 
25 /// EquivalenceClasses - This represents a collection of equivalence classes and
26 /// supports three efficient operations: insert an element into a class of its
27 /// own, union two classes, and find the class for a given element. In
28 /// addition to these modification methods, it is possible to iterate over all
29 /// of the equivalence classes and all of the elements in a class.
30 ///
31 /// This implementation is an efficient implementation that only stores one copy
32 /// of the element being indexed per entry in the set, and allows any arbitrary
33 /// type to be indexed (as long as it can be ordered with operator<).
34 ///
35 /// Here is a simple example using integers:
36 ///
37 /// \code
38 /// EquivalenceClasses<int> EC;
39 /// EC.unionSets(1, 2); // insert 1, 2 into the same set
40 /// EC.insert(4); EC.insert(5); // insert 4, 5 into own sets
41 /// EC.unionSets(5, 1); // merge the set for 1 with 5's set.
42 ///
43 /// for (EquivalenceClasses<int>::iterator I = EC.begin(), E = EC.end();
44 /// I != E; ++I) { // Iterate over all of the equivalence sets.
45 /// if (!I->isLeader()) continue; // Ignore non-leader sets.
46 /// for (EquivalenceClasses<int>::member_iterator MI = EC.member_begin(I);
47 /// MI != EC.member_end(); ++MI) // Loop over members in this set.
48 /// cerr << *MI << " "; // Print member.
49 /// cerr << "\n"; // Finish set.
50 /// }
51 /// \endcode
52 ///
53 /// This example prints:
54 /// 4
55 /// 5 1 2
56 ///
57 template <class ElemTy>
59  /// ECValue - The EquivalenceClasses data structure is just a set of these.
60  /// Each of these represents a relation for a value. First it stores the
61  /// value itself, which provides the ordering that the set queries. Next, it
62  /// provides a "next pointer", which is used to enumerate all of the elements
63  /// in the unioned set. Finally, it defines either a "end of list pointer" or
64  /// "leader pointer" depending on whether the value itself is a leader. A
65  /// "leader pointer" points to the node that is the leader for this element,
66  /// if the node is not a leader. A "end of list pointer" points to the last
67  /// node in the list of members of this list. Whether or not a node is a
68  /// leader is determined by a bit stolen from one of the pointers.
69  class ECValue {
70  friend class EquivalenceClasses;
71  mutable const ECValue *Leader, *Next;
72  ElemTy Data;
73  // ECValue ctor - Start out with EndOfList pointing to this node, Next is
74  // Null, isLeader = true.
75  ECValue(const ElemTy &Elt)
76  : Leader(this), Next((ECValue*)(intptr_t)1), Data(Elt) {}
77 
78  const ECValue *getLeader() const {
79  if (isLeader()) return this;
80  if (Leader->isLeader()) return Leader;
81  // Path compression.
82  return Leader = Leader->getLeader();
83  }
84  const ECValue *getEndOfList() const {
85  assert(isLeader() && "Cannot get the end of a list for a non-leader!");
86  return Leader;
87  }
88 
89  void setNext(const ECValue *NewNext) const {
90  assert(getNext() == nullptr && "Already has a next pointer!");
91  Next = (const ECValue*)((intptr_t)NewNext | (intptr_t)isLeader());
92  }
93  public:
94  ECValue(const ECValue &RHS) : Leader(this), Next((ECValue*)(intptr_t)1),
95  Data(RHS.Data) {
96  // Only support copying of singleton nodes.
97  assert(RHS.isLeader() && RHS.getNext() == nullptr && "Not a singleton!");
98  }
99 
100  bool operator<(const ECValue &UFN) const { return Data < UFN.Data; }
101 
102  bool isLeader() const { return (intptr_t)Next & 1; }
103  const ElemTy &getData() const { return Data; }
104 
105  const ECValue *getNext() const {
106  return (ECValue*)((intptr_t)Next & ~(intptr_t)1);
107  }
108 
109  template<typename T>
110  bool operator<(const T &Val) const { return Data < Val; }
111  };
112 
113  /// TheMapping - This implicitly provides a mapping from ElemTy values to the
114  /// ECValues, it just keeps the key as part of the value.
115  std::set<ECValue> TheMapping;
116 
117 public:
120  operator=(RHS);
121  }
122 
124  TheMapping.clear();
125  for (iterator I = RHS.begin(), E = RHS.end(); I != E; ++I)
126  if (I->isLeader()) {
128  member_iterator LeaderIt = member_begin(insert(*MI));
129  for (++MI; MI != member_end(); ++MI)
130  unionSets(LeaderIt, member_begin(insert(*MI)));
131  }
132  return *this;
133  }
134 
135  //===--------------------------------------------------------------------===//
136  // Inspection methods
137  //
138 
139  /// iterator* - Provides a way to iterate over all values in the set.
140  typedef typename std::set<ECValue>::const_iterator iterator;
141  iterator begin() const { return TheMapping.begin(); }
142  iterator end() const { return TheMapping.end(); }
143 
144  bool empty() const { return TheMapping.empty(); }
145 
146  /// member_* Iterate over the members of an equivalence class.
147  ///
148  class member_iterator;
150  // Only leaders provide anything to iterate over.
151  return member_iterator(I->isLeader() ? &*I : nullptr);
152  }
154  return member_iterator(nullptr);
155  }
156 
157  /// findValue - Return an iterator to the specified value. If it does not
158  /// exist, end() is returned.
159  iterator findValue(const ElemTy &V) const {
160  return TheMapping.find(V);
161  }
162 
163  /// getLeaderValue - Return the leader for the specified value that is in the
164  /// set. It is an error to call this method for a value that is not yet in
165  /// the set. For that, call getOrInsertLeaderValue(V).
166  const ElemTy &getLeaderValue(const ElemTy &V) const {
168  assert(MI != member_end() && "Value is not in the set!");
169  return *MI;
170  }
171 
172  /// getOrInsertLeaderValue - Return the leader for the specified value that is
173  /// in the set. If the member is not in the set, it is inserted, then
174  /// returned.
175  const ElemTy &getOrInsertLeaderValue(const ElemTy &V) {
177  assert(MI != member_end() && "Value is not in the set!");
178  return *MI;
179  }
180 
181  /// getNumClasses - Return the number of equivalence classes in this set.
182  /// Note that this is a linear time operation.
183  unsigned getNumClasses() const {
184  unsigned NC = 0;
185  for (iterator I = begin(), E = end(); I != E; ++I)
186  if (I->isLeader()) ++NC;
187  return NC;
188  }
189 
190 
191  //===--------------------------------------------------------------------===//
192  // Mutation methods
193 
194  /// insert - Insert a new value into the union/find set, ignoring the request
195  /// if the value already exists.
196  iterator insert(const ElemTy &Data) {
197  return TheMapping.insert(ECValue(Data)).first;
198  }
199 
200  /// findLeader - Given a value in the set, return a member iterator for the
201  /// equivalence class it is in. This does the path-compression part that
202  /// makes union-find "union findy". This returns an end iterator if the value
203  /// is not in the equivalence class.
204  ///
206  if (I == TheMapping.end()) return member_end();
207  return member_iterator(I->getLeader());
208  }
209  member_iterator findLeader(const ElemTy &V) const {
210  return findLeader(TheMapping.find(V));
211  }
212 
213 
214  /// union - Merge the two equivalence sets for the specified values, inserting
215  /// them if they do not already exist in the equivalence set.
216  member_iterator unionSets(const ElemTy &V1, const ElemTy &V2) {
217  iterator V1I = insert(V1), V2I = insert(V2);
218  return unionSets(findLeader(V1I), findLeader(V2I));
219  }
221  assert(L1 != member_end() && L2 != member_end() && "Illegal inputs!");
222  if (L1 == L2) return L1; // Unifying the same two sets, noop.
223 
224  // Otherwise, this is a real union operation. Set the end of the L1 list to
225  // point to the L2 leader node.
226  const ECValue &L1LV = *L1.Node, &L2LV = *L2.Node;
227  L1LV.getEndOfList()->setNext(&L2LV);
228 
229  // Update L1LV's end of list pointer.
230  L1LV.Leader = L2LV.getEndOfList();
231 
232  // Clear L2's leader flag:
233  L2LV.Next = L2LV.getNext();
234 
235  // L2's leader is now L1.
236  L2LV.Leader = &L1LV;
237  return L1;
238  }
239 
240  class member_iterator : public std::iterator<std::forward_iterator_tag,
241  const ElemTy, ptrdiff_t> {
242  typedef std::iterator<std::forward_iterator_tag,
243  const ElemTy, ptrdiff_t> super;
244  const ECValue *Node;
245  friend class EquivalenceClasses;
246  public:
247  typedef size_t size_type;
248  typedef typename super::pointer pointer;
249  typedef typename super::reference reference;
250 
251  explicit member_iterator() {}
252  explicit member_iterator(const ECValue *N) : Node(N) {}
253 
255  assert(Node != nullptr && "Dereferencing end()!");
256  return Node->getData();
257  }
258  pointer operator->() const { return &operator*(); }
259 
261  assert(Node != nullptr && "++'d off the end of the list!");
262  Node = Node->getNext();
263  return *this;
264  }
265 
266  member_iterator operator++(int) { // postincrement operators.
267  member_iterator tmp = *this;
268  ++*this;
269  return tmp;
270  }
271 
272  bool operator==(const member_iterator &RHS) const {
273  return Node == RHS.Node;
274  }
275  bool operator!=(const member_iterator &RHS) const {
276  return Node != RHS.Node;
277  }
278  };
279 };
280 
281 } // End llvm namespace
282 
283 #endif
member_iterator findLeader(const ElemTy &V) const
bool operator!=(const member_iterator &RHS) const
member_iterator unionSets(const ElemTy &V1, const ElemTy &V2)
union - Merge the two equivalence sets for the specified values, inserting them if they do not alread...
member_iterator member_begin(iterator I) const
bool operator==(const member_iterator &RHS) const
member_iterator member_end() const
EquivalenceClasses(const EquivalenceClasses &RHS)
iterator findValue(const ElemTy &V) const
findValue - Return an iterator to the specified value.
iterator insert(const ElemTy &Data)
insert - Insert a new value into the union/find set, ignoring the request if the value already exists...
std::set< ECValue >::const_iterator iterator
iterator* - Provides a way to iterate over all values in the set.
unsigned getNumClasses() const
getNumClasses - Return the number of equivalence classes in this set.
EquivalenceClasses - This represents a collection of equivalence classes and supports three efficient...
const EquivalenceClasses & operator=(const EquivalenceClasses &RHS)
const ElemTy & getOrInsertLeaderValue(const ElemTy &V)
getOrInsertLeaderValue - Return the leader for the specified value that is in the set...
#define NC
Definition: regutils.h:42
member_iterator findLeader(iterator I) const
findLeader - Given a value in the set, return a member iterator for the equivalence class it is in...
member_iterator unionSets(member_iterator L1, member_iterator L2)
#define I(x, y, z)
Definition: MD5.cpp:54
#define N
bool operator<(int64_t V1, const APSInt &V2)
Definition: APSInt.h:332
const ElemTy & getLeaderValue(const ElemTy &V) const
getLeaderValue - Return the leader for the specified value that is in the set.