1//===-- llvm/ADT/IntEqClasses.cpp - Equivalence Classes of Integers -------===//
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#include "llvm/ADT/IntEqClasses.h"
21#include <cassert>
22
23using namespace llvm;
24
25void IntEqClasses::grow(unsigned N) {
26  assert(NumClasses == 0 && "grow() called after compress().");
27  EC.reserve(N);
28  while (EC.size() < N)
29    EC.push_back(EC.size());
30}
31
32unsigned IntEqClasses::join(unsigned a, unsigned b) {
33  assert(NumClasses == 0 && "join() called after compress().");
34  unsigned eca = EC[a];
35  unsigned ecb = EC[b];
36  // Update pointers while searching for the leaders, compressing the paths
37  // incrementally. The larger leader will eventually be updated, joining the
38  // classes.
39  while (eca != ecb)
40    if (eca < ecb) {
41      EC[b] = eca;
42      b = ecb;
43      ecb = EC[b];
44    } else {
45      EC[a] = ecb;
46      a = eca;
47      eca = EC[a];
48    }
49
50  return eca;
51}
52
53unsigned IntEqClasses::findLeader(unsigned a) const {
54  assert(NumClasses == 0 && "findLeader() called after compress().");
55  while (a != EC[a])
56    a = EC[a];
57  return a;
58}
59
60void IntEqClasses::compress() {
61  if (NumClasses)
62    return;
63  for (unsigned i = 0, e = EC.size(); i != e; ++i)
64    EC[i] = (EC[i] == i) ? NumClasses++ : EC[EC[i]];
65}
66
67void IntEqClasses::uncompress() {
68  if (!NumClasses)
69    return;
70  SmallVector<unsigned, 8> Leader;
71  for (unsigned i = 0, e = EC.size(); i != e; ++i)
72    if (EC[i] < Leader.size())
73      EC[i] = Leader[EC[i]];
74    else
75      Leader.push_back(EC[i] = i);
76  NumClasses = 0;
77}
78