LLVM  4.0.0
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 <cassert>
19 #include <cstddef>
20 #include <cstdint>
21 #include <iterator>
22 #include <set>
23 
24 namespace llvm {
25 
26 /// EquivalenceClasses - This represents a collection of equivalence classes and
27 /// supports three efficient operations: insert an element into a class of its
28 /// own, union two classes, and find the class for a given element. In
29 /// addition to these modification methods, it is possible to iterate over all
30 /// of the equivalence classes and all of the elements in a class.
31 ///
32 /// This implementation is an efficient implementation that only stores one copy
33 /// of the element being indexed per entry in the set, and allows any arbitrary
34 /// type to be indexed (as long as it can be ordered with operator<).
35 ///
36 /// Here is a simple example using integers:
37 ///
38 /// \code
39 /// EquivalenceClasses<int> EC;
40 /// EC.unionSets(1, 2); // insert 1, 2 into the same set
41 /// EC.insert(4); EC.insert(5); // insert 4, 5 into own sets
42 /// EC.unionSets(5, 1); // merge the set for 1 with 5's set.
43 ///
44 /// for (EquivalenceClasses<int>::iterator I = EC.begin(), E = EC.end();
45 /// I != E; ++I) { // Iterate over all of the equivalence sets.
46 /// if (!I->isLeader()) continue; // Ignore non-leader sets.
47 /// for (EquivalenceClasses<int>::member_iterator MI = EC.member_begin(I);
48 /// MI != EC.member_end(); ++MI) // Loop over members in this set.
49 /// cerr << *MI << " "; // Print member.
50 /// cerr << "\n"; // Finish set.
51 /// }
52 /// \endcode
53 ///
54 /// This example prints:
55 /// 4
56 /// 5 1 2
57 ///
58 template <class ElemTy>
60  /// ECValue - The EquivalenceClasses data structure is just a set of these.
61  /// Each of these represents a relation for a value. First it stores the
62  /// value itself, which provides the ordering that the set queries. Next, it
63  /// provides a "next pointer", which is used to enumerate all of the elements
64  /// in the unioned set. Finally, it defines either a "end of list pointer" or
65  /// "leader pointer" depending on whether the value itself is a leader. A
66  /// "leader pointer" points to the node that is the leader for this element,
67  /// if the node is not a leader. A "end of list pointer" points to the last
68  /// node in the list of members of this list. Whether or not a node is a
69  /// leader is determined by a bit stolen from one of the pointers.
70  class ECValue {
71  friend class EquivalenceClasses;
72  mutable const ECValue *Leader, *Next;
73  ElemTy Data;
74 
75  // ECValue ctor - Start out with EndOfList pointing to this node, Next is
76  // Null, isLeader = true.
77  ECValue(const ElemTy &Elt)
78  : Leader(this), Next((ECValue*)(intptr_t)1), Data(Elt) {}
79 
80  const ECValue *getLeader() const {
81  if (isLeader()) return this;
82  if (Leader->isLeader()) return Leader;
83  // Path compression.
84  return Leader = Leader->getLeader();
85  }
86 
87  const ECValue *getEndOfList() const {
88  assert(isLeader() && "Cannot get the end of a list for a non-leader!");
89  return Leader;
90  }
91 
92  void setNext(const ECValue *NewNext) const {
93  assert(getNext() == nullptr && "Already has a next pointer!");
94  Next = (const ECValue*)((intptr_t)NewNext | (intptr_t)isLeader());
95  }
96 
97  public:
98  ECValue(const ECValue &RHS) : Leader(this), Next((ECValue*)(intptr_t)1),
99  Data(RHS.Data) {
100  // Only support copying of singleton nodes.
101  assert(RHS.isLeader() && RHS.getNext() == nullptr && "Not a singleton!");
102  }
103 
104  bool operator<(const ECValue &UFN) const { return Data < UFN.Data; }
105 
106  bool isLeader() const { return (intptr_t)Next & 1; }
107  const ElemTy &getData() const { return Data; }
108 
109  const ECValue *getNext() const {
110  return (ECValue*)((intptr_t)Next & ~(intptr_t)1);
111  }
112 
113  template<typename T>
114  bool operator<(const T &Val) const { return Data < Val; }
115  };
116 
117  /// TheMapping - This implicitly provides a mapping from ElemTy values to the
118  /// ECValues, it just keeps the key as part of the value.
119  std::set<ECValue> TheMapping;
120 
121 public:
122  EquivalenceClasses() = default;
124  operator=(RHS);
125  }
126 
128  TheMapping.clear();
129  for (iterator I = RHS.begin(), E = RHS.end(); I != E; ++I)
130  if (I->isLeader()) {
131  member_iterator MI = RHS.member_begin(I);
132  member_iterator LeaderIt = member_begin(insert(*MI));
133  for (++MI; MI != member_end(); ++MI)
134  unionSets(LeaderIt, member_begin(insert(*MI)));
135  }
136  return *this;
137  }
138 
139  //===--------------------------------------------------------------------===//
140  // Inspection methods
141  //
142 
143  /// iterator* - Provides a way to iterate over all values in the set.
144  typedef typename std::set<ECValue>::const_iterator iterator;
145  iterator begin() const { return TheMapping.begin(); }
146  iterator end() const { return TheMapping.end(); }
147 
148  bool empty() const { return TheMapping.empty(); }
149 
150  /// member_* Iterate over the members of an equivalence class.
151  ///
152  class member_iterator;
153  member_iterator member_begin(iterator I) const {
154  // Only leaders provide anything to iterate over.
155  return member_iterator(I->isLeader() ? &*I : nullptr);
156  }
157  member_iterator member_end() const {
158  return member_iterator(nullptr);
159  }
160 
161  /// findValue - Return an iterator to the specified value. If it does not
162  /// exist, end() is returned.
163  iterator findValue(const ElemTy &V) const {
164  return TheMapping.find(V);
165  }
166 
167  /// getLeaderValue - Return the leader for the specified value that is in the
168  /// set. It is an error to call this method for a value that is not yet in
169  /// the set. For that, call getOrInsertLeaderValue(V).
170  const ElemTy &getLeaderValue(const ElemTy &V) const {
171  member_iterator MI = findLeader(V);
172  assert(MI != member_end() && "Value is not in the set!");
173  return *MI;
174  }
175 
176  /// getOrInsertLeaderValue - Return the leader for the specified value that is
177  /// in the set. If the member is not in the set, it is inserted, then
178  /// returned.
179  const ElemTy &getOrInsertLeaderValue(const ElemTy &V) {
180  member_iterator MI = findLeader(insert(V));
181  assert(MI != member_end() && "Value is not in the set!");
182  return *MI;
183  }
184 
185  /// getNumClasses - Return the number of equivalence classes in this set.
186  /// Note that this is a linear time operation.
187  unsigned getNumClasses() const {
188  unsigned NC = 0;
189  for (iterator I = begin(), E = end(); I != E; ++I)
190  if (I->isLeader()) ++NC;
191  return NC;
192  }
193 
194  //===--------------------------------------------------------------------===//
195  // Mutation methods
196 
197  /// insert - Insert a new value into the union/find set, ignoring the request
198  /// if the value already exists.
199  iterator insert(const ElemTy &Data) {
200  return TheMapping.insert(ECValue(Data)).first;
201  }
202 
203  /// findLeader - Given a value in the set, return a member iterator for the
204  /// equivalence class it is in. This does the path-compression part that
205  /// makes union-find "union findy". This returns an end iterator if the value
206  /// is not in the equivalence class.
207  ///
208  member_iterator findLeader(iterator I) const {
209  if (I == TheMapping.end()) return member_end();
210  return member_iterator(I->getLeader());
211  }
212  member_iterator findLeader(const ElemTy &V) const {
213  return findLeader(TheMapping.find(V));
214  }
215 
216  /// union - Merge the two equivalence sets for the specified values, inserting
217  /// them if they do not already exist in the equivalence set.
218  member_iterator unionSets(const ElemTy &V1, const ElemTy &V2) {
219  iterator V1I = insert(V1), V2I = insert(V2);
220  return unionSets(findLeader(V1I), findLeader(V2I));
221  }
222  member_iterator unionSets(member_iterator L1, member_iterator L2) {
223  assert(L1 != member_end() && L2 != member_end() && "Illegal inputs!");
224  if (L1 == L2) return L1; // Unifying the same two sets, noop.
225 
226  // Otherwise, this is a real union operation. Set the end of the L1 list to
227  // point to the L2 leader node.
228  const ECValue &L1LV = *L1.Node, &L2LV = *L2.Node;
229  L1LV.getEndOfList()->setNext(&L2LV);
230 
231  // Update L1LV's end of list pointer.
232  L1LV.Leader = L2LV.getEndOfList();
233 
234  // Clear L2's leader flag:
235  L2LV.Next = L2LV.getNext();
236 
237  // L2's leader is now L1.
238  L2LV.Leader = &L1LV;
239  return L1;
240  }
241 
242  class member_iterator : public std::iterator<std::forward_iterator_tag,
243  const ElemTy, ptrdiff_t> {
244  typedef std::iterator<std::forward_iterator_tag,
245  const ElemTy, ptrdiff_t> super;
246  const ECValue *Node;
247  friend class EquivalenceClasses;
248 
249  public:
250  typedef size_t size_type;
251  typedef typename super::pointer pointer;
252  typedef typename super::reference reference;
253 
254  explicit member_iterator() = default;
255  explicit member_iterator(const ECValue *N) : Node(N) {}
256 
258  assert(Node != nullptr && "Dereferencing end()!");
259  return Node->getData();
260  }
261  pointer operator->() const { return &operator*(); }
262 
264  assert(Node != nullptr && "++'d off the end of the list!");
265  Node = Node->getNext();
266  return *this;
267  }
268 
269  member_iterator operator++(int) { // postincrement operators.
270  member_iterator tmp = *this;
271  ++*this;
272  return tmp;
273  }
274 
275  bool operator==(const member_iterator &RHS) const {
276  return Node == RHS.Node;
277  }
278  bool operator!=(const member_iterator &RHS) const {
279  return Node != RHS.Node;
280  }
281  };
282 };
283 
284 } // end namespace llvm
285 
286 #endif // LLVM_ADT_EQUIVALENCECLASSES_H
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.
static GCRegistry::Add< CoreCLRGC > E("coreclr","CoreCLR-compatible GC")
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
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
bool operator<(int64_t V1, const APSInt &V2)
Definition: APSInt.h:326
const ElemTy & getLeaderValue(const ElemTy &V) const
getLeaderValue - Return the leader for the specified value that is in the set.
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