1//===-- llvm/ADT/IntEqClasses.h - Equiv. Classes of Integers ----*- 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// Equivalence classes for small integers. This is a mapping of the integers
11// 0 .. N-1 into M equivalence classes numbered 0 .. M-1.
12//
13// Initially each integer has its own equivalence class. Classes are joined by
14// passing a representative member of each class to join().
15//
16// Once the classes are built, compress() will number them 0 .. M-1 and prevent
17// further changes.
18//
19//===----------------------------------------------------------------------===//
20
21#ifndef LLVM_ADT_INTEQCLASSES_H
22#define LLVM_ADT_INTEQCLASSES_H
23
24#include "llvm/ADT/SmallVector.h"
25
26namespace llvm {
27
28class IntEqClasses {
29  /// EC - When uncompressed, map each integer to a smaller member of its
30  /// equivalence class. The class leader is the smallest member and maps to
31  /// itself.
32  ///
33  /// When compressed, EC[i] is the equivalence class of i.
34  SmallVector<unsigned, 8> EC;
35
36  /// NumClasses - The number of equivalence classes when compressed, or 0 when
37  /// uncompressed.
38  unsigned NumClasses;
39
40public:
41  /// IntEqClasses - Create an equivalence class mapping for 0 .. N-1.
42  IntEqClasses(unsigned N = 0) : NumClasses(0) { grow(N); }
43
44  /// grow - Increase capacity to hold 0 .. N-1, putting new integers in unique
45  /// equivalence classes.
46  /// This requires an uncompressed map.
47  void grow(unsigned N);
48
49  /// clear - Clear all classes so that grow() will assign a unique class to
50  /// every integer.
51  void clear() {
52    EC.clear();
53    NumClasses = 0;
54  }
55
56  /// Join the equivalence classes of a and b. After joining classes,
57  /// findLeader(a) == findLeader(b). This requires an uncompressed map.
58  /// Returns the new leader.
59  unsigned join(unsigned a, unsigned b);
60
61  /// findLeader - Compute the leader of a's equivalence class. This is the
62  /// smallest member of the class.
63  /// This requires an uncompressed map.
64  unsigned findLeader(unsigned a) const;
65
66  /// compress - Compress equivalence classes by numbering them 0 .. M.
67  /// This makes the equivalence class map immutable.
68  void compress();
69
70  /// getNumClasses - Return the number of equivalence classes after compress()
71  /// was called.
72  unsigned getNumClasses() const { return NumClasses; }
73
74  /// operator[] - Return a's equivalence class number, 0 .. getNumClasses()-1.
75  /// This requires a compressed map.
76  unsigned operator[](unsigned a) const {
77    assert(NumClasses && "operator[] called before compress()");
78    return EC[a];
79  }
80
81  /// uncompress - Change back to the uncompressed representation that allows
82  /// editing.
83  void uncompress();
84};
85
86} // End llvm namespace
87
88#endif
89