1//===-- llvm/ADT/IntEqClasses.h - Equiv. Classes of Integers ----*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// Equivalence classes for small integers. This is a mapping of the integers
10// 0 .. N-1 into M equivalence classes numbered 0 .. M-1.
11//
12// Initially each integer has its own equivalence class. Classes are joined by
13// passing a representative member of each class to join().
14//
15// Once the classes are built, compress() will number them 0 .. M-1 and prevent
16// further changes.
17//
18//===----------------------------------------------------------------------===//
19
20#ifndef LLVM_ADT_INTEQCLASSES_H
21#define LLVM_ADT_INTEQCLASSES_H
22
23#include "llvm/ADT/SmallVector.h"
24
25namespace llvm {
26
27class IntEqClasses {
28  /// EC - When uncompressed, map each integer to a smaller member of its
29  /// equivalence class. The class leader is the smallest member and maps to
30  /// itself.
31  ///
32  /// When compressed, EC[i] is the equivalence class of i.
33  SmallVector<unsigned, 8> EC;
34
35  /// NumClasses - The number of equivalence classes when compressed, or 0 when
36  /// uncompressed.
37  unsigned NumClasses;
38
39public:
40  /// IntEqClasses - Create an equivalence class mapping for 0 .. N-1.
41  IntEqClasses(unsigned N = 0) : NumClasses(0) { grow(N); }
42
43  /// grow - Increase capacity to hold 0 .. N-1, putting new integers in unique
44  /// equivalence classes.
45  /// This requires an uncompressed map.
46  void grow(unsigned N);
47
48  /// clear - Clear all classes so that grow() will assign a unique class to
49  /// every integer.
50  void clear() {
51    EC.clear();
52    NumClasses = 0;
53  }
54
55  /// Join the equivalence classes of a and b. After joining classes,
56  /// findLeader(a) == findLeader(b). This requires an uncompressed map.
57  /// Returns the new leader.
58  unsigned join(unsigned a, unsigned b);
59
60  /// findLeader - Compute the leader of a's equivalence class. This is the
61  /// smallest member of the class.
62  /// This requires an uncompressed map.
63  unsigned findLeader(unsigned a) const;
64
65  /// compress - Compress equivalence classes by numbering them 0 .. M.
66  /// This makes the equivalence class map immutable.
67  void compress();
68
69  /// getNumClasses - Return the number of equivalence classes after compress()
70  /// was called.
71  unsigned getNumClasses() const { return NumClasses; }
72
73  /// operator[] - Return a's equivalence class number, 0 .. getNumClasses()-1.
74  /// This requires a compressed map.
75  unsigned operator[](unsigned a) const {
76    assert(NumClasses && "operator[] called before compress()");
77    return EC[a];
78  }
79
80  /// uncompress - Change back to the uncompressed representation that allows
81  /// editing.
82  void uncompress();
83};
84
85} // End llvm namespace
86
87#endif
88