aboutsummaryrefslogtreecommitdiffstats
path: root/contrib/libs/llvm14/include/llvm/ADT/EquivalenceClasses.h
blob: 0d0514871354120f1ba3bba92bd976c2205469b7 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
#pragma once

#ifdef __GNUC__
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-parameter"
#endif

//===- llvm/ADT/EquivalenceClasses.h - Generic Equiv. Classes ---*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// Generic implementation of equivalence classes through the use Tarjan's
/// efficient union-find algorithm.
///
//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_EQUIVALENCECLASSES_H
#define LLVM_ADT_EQUIVALENCECLASSES_H

#include <cassert>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <set>

namespace llvm {

/// EquivalenceClasses - This represents a collection of equivalence classes and
/// supports three efficient operations: insert an element into a class of its
/// own, union two classes, and find the class for a given element.  In
/// addition to these modification methods, it is possible to iterate over all
/// of the equivalence classes and all of the elements in a class.
///
/// This implementation is an efficient implementation that only stores one copy
/// of the element being indexed per entry in the set, and allows any arbitrary
/// type to be indexed (as long as it can be ordered with operator< or a
/// comparator is provided).
///
/// Here is a simple example using integers:
///
/// \code
///  EquivalenceClasses<int> EC;
///  EC.unionSets(1, 2);                // insert 1, 2 into the same set
///  EC.insert(4); EC.insert(5);        // insert 4, 5 into own sets
///  EC.unionSets(5, 1);                // merge the set for 1 with 5's set.
///
///  for (EquivalenceClasses<int>::iterator I = EC.begin(), E = EC.end();
///       I != E; ++I) {           // Iterate over all of the equivalence sets.
///    if (!I->isLeader()) continue;   // Ignore non-leader sets.
///    for (EquivalenceClasses<int>::member_iterator MI = EC.member_begin(I);
///         MI != EC.member_end(); ++MI)   // Loop over members in this set.
///      cerr << *MI << " ";  // Print member.
///    cerr << "\n";   // Finish set.
///  }
/// \endcode
///
/// This example prints:
///   4
///   5 1 2
///
template <class ElemTy, class Compare = std::less<ElemTy>>
class EquivalenceClasses {
  /// ECValue - The EquivalenceClasses data structure is just a set of these.
  /// Each of these represents a relation for a value.  First it stores the
  /// value itself, which provides the ordering that the set queries.  Next, it
  /// provides a "next pointer", which is used to enumerate all of the elements
  /// in the unioned set.  Finally, it defines either a "end of list pointer" or
  /// "leader pointer" depending on whether the value itself is a leader.  A
  /// "leader pointer" points to the node that is the leader for this element,
  /// if the node is not a leader.  A "end of list pointer" points to the last
  /// node in the list of members of this list.  Whether or not a node is a
  /// leader is determined by a bit stolen from one of the pointers.
  class ECValue {
    friend class EquivalenceClasses;

    mutable const ECValue *Leader, *Next;
    ElemTy Data;

    // ECValue ctor - Start out with EndOfList pointing to this node, Next is
    // Null, isLeader = true.
    ECValue(const ElemTy &Elt)
      : Leader(this), Next((ECValue*)(intptr_t)1), Data(Elt) {}

    const ECValue *getLeader() const {
      if (isLeader()) return this;
      if (Leader->isLeader()) return Leader;
      // Path compression.
      return Leader = Leader->getLeader();
    }

    const ECValue *getEndOfList() const {
      assert(isLeader() && "Cannot get the end of a list for a non-leader!");
      return Leader;
    }

    void setNext(const ECValue *NewNext) const {
      assert(getNext() == nullptr && "Already has a next pointer!");
      Next = (const ECValue*)((intptr_t)NewNext | (intptr_t)isLeader());
    }

  public:
    ECValue(const ECValue &RHS) : Leader(this), Next((ECValue*)(intptr_t)1),
                                  Data(RHS.Data) {
      // Only support copying of singleton nodes.
      assert(RHS.isLeader() && RHS.getNext() == nullptr && "Not a singleton!");
    }

    bool isLeader() const { return (intptr_t)Next & 1; }
    const ElemTy &getData() const { return Data; }

    const ECValue *getNext() const {
      return (ECValue*)((intptr_t)Next & ~(intptr_t)1);
    }
  };

  /// A wrapper of the comparator, to be passed to the set.
  struct ECValueComparator {
    using is_transparent = void;

    ECValueComparator() : compare(Compare()) {}

    bool operator()(const ECValue &lhs, const ECValue &rhs) const {
      return compare(lhs.Data, rhs.Data);
    }

    template <typename T>
    bool operator()(const T &lhs, const ECValue &rhs) const {
      return compare(lhs, rhs.Data);
    }

    template <typename T>
    bool operator()(const ECValue &lhs, const T &rhs) const {
      return compare(lhs.Data, rhs);
    }

    const Compare compare;
  };

  /// TheMapping - This implicitly provides a mapping from ElemTy values to the
  /// ECValues, it just keeps the key as part of the value.
  std::set<ECValue, ECValueComparator> TheMapping;

public:
  EquivalenceClasses() = default;
  EquivalenceClasses(const EquivalenceClasses &RHS) {
    operator=(RHS);
  }

  const EquivalenceClasses &operator=(const EquivalenceClasses &RHS) {
    TheMapping.clear();
    for (iterator I = RHS.begin(), E = RHS.end(); I != E; ++I)
      if (I->isLeader()) {
        member_iterator MI = RHS.member_begin(I);
        member_iterator LeaderIt = member_begin(insert(*MI));
        for (++MI; MI != member_end(); ++MI)
          unionSets(LeaderIt, member_begin(insert(*MI)));
      }
    return *this;
  }

  //===--------------------------------------------------------------------===//
  // Inspection methods
  //

  /// iterator* - Provides a way to iterate over all values in the set.
  using iterator = typename std::set<ECValue>::const_iterator;

  iterator begin() const { return TheMapping.begin(); }
  iterator end() const { return TheMapping.end(); }

  bool empty() const { return TheMapping.empty(); }

  /// member_* Iterate over the members of an equivalence class.
  class member_iterator;
  member_iterator member_begin(iterator I) const {
    // Only leaders provide anything to iterate over.
    return member_iterator(I->isLeader() ? &*I : nullptr);
  }
  member_iterator member_end() const {
    return member_iterator(nullptr);
  }

  /// findValue - Return an iterator to the specified value.  If it does not
  /// exist, end() is returned.
  iterator findValue(const ElemTy &V) const {
    return TheMapping.find(V);
  }

  /// getLeaderValue - Return the leader for the specified value that is in the
  /// set.  It is an error to call this method for a value that is not yet in
  /// the set.  For that, call getOrInsertLeaderValue(V).
  const ElemTy &getLeaderValue(const ElemTy &V) const {
    member_iterator MI = findLeader(V);
    assert(MI != member_end() && "Value is not in the set!");
    return *MI;
  }

  /// getOrInsertLeaderValue - Return the leader for the specified value that is
  /// in the set.  If the member is not in the set, it is inserted, then
  /// returned.
  const ElemTy &getOrInsertLeaderValue(const ElemTy &V) {
    member_iterator MI = findLeader(insert(V));
    assert(MI != member_end() && "Value is not in the set!");
    return *MI;
  }

  /// getNumClasses - Return the number of equivalence classes in this set.
  /// Note that this is a linear time operation.
  unsigned getNumClasses() const {
    unsigned NC = 0;
    for (iterator I = begin(), E = end(); I != E; ++I)
      if (I->isLeader()) ++NC;
    return NC;
  }

  //===--------------------------------------------------------------------===//
  // Mutation methods

  /// insert - Insert a new value into the union/find set, ignoring the request
  /// if the value already exists.
  iterator insert(const ElemTy &Data) {
    return TheMapping.insert(ECValue(Data)).first;
  }

  /// findLeader - Given a value in the set, return a member iterator for the
  /// equivalence class it is in.  This does the path-compression part that
  /// makes union-find "union findy".  This returns an end iterator if the value
  /// is not in the equivalence class.
  member_iterator findLeader(iterator I) const {
    if (I == TheMapping.end()) return member_end();
    return member_iterator(I->getLeader());
  }
  member_iterator findLeader(const ElemTy &V) const {
    return findLeader(TheMapping.find(V));
  }

  /// union - Merge the two equivalence sets for the specified values, inserting
  /// them if they do not already exist in the equivalence set.
  member_iterator unionSets(const ElemTy &V1, const ElemTy &V2) {
    iterator V1I = insert(V1), V2I = insert(V2);
    return unionSets(findLeader(V1I), findLeader(V2I));
  }
  member_iterator unionSets(member_iterator L1, member_iterator L2) {
    assert(L1 != member_end() && L2 != member_end() && "Illegal inputs!");
    if (L1 == L2) return L1;   // Unifying the same two sets, noop.

    // Otherwise, this is a real union operation.  Set the end of the L1 list to
    // point to the L2 leader node.
    const ECValue &L1LV = *L1.Node, &L2LV = *L2.Node;
    L1LV.getEndOfList()->setNext(&L2LV);

    // Update L1LV's end of list pointer.
    L1LV.Leader = L2LV.getEndOfList();

    // Clear L2's leader flag:
    L2LV.Next = L2LV.getNext();

    // L2's leader is now L1.
    L2LV.Leader = &L1LV;
    return L1;
  }

  // isEquivalent - Return true if V1 is equivalent to V2. This can happen if
  // V1 is equal to V2 or if they belong to one equivalence class.
  bool isEquivalent(const ElemTy &V1, const ElemTy &V2) const {
    // Fast path: any element is equivalent to itself.
    if (V1 == V2)
      return true;
    auto It = findLeader(V1);
    return It != member_end() && It == findLeader(V2);
  }

  class member_iterator {
    friend class EquivalenceClasses;

    const ECValue *Node;

  public:
    using iterator_category = std::forward_iterator_tag;
    using value_type = const ElemTy;
    using size_type = std::size_t;
    using difference_type = std::ptrdiff_t;
    using pointer = value_type *;
    using reference = value_type &;

    explicit member_iterator() = default;
    explicit member_iterator(const ECValue *N) : Node(N) {}

    reference operator*() const {
      assert(Node != nullptr && "Dereferencing end()!");
      return Node->getData();
    }
    pointer operator->() const { return &operator*(); }

    member_iterator &operator++() {
      assert(Node != nullptr && "++'d off the end of the list!");
      Node = Node->getNext();
      return *this;
    }

    member_iterator operator++(int) {    // postincrement operators.
      member_iterator tmp = *this;
      ++*this;
      return tmp;
    }

    bool operator==(const member_iterator &RHS) const {
      return Node == RHS.Node;
    }
    bool operator!=(const member_iterator &RHS) const {
      return Node != RHS.Node;
    }
  };
};

} // end namespace llvm

#endif // LLVM_ADT_EQUIVALENCECLASSES_H

#ifdef __GNUC__
#pragma GCC diagnostic pop
#endif