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