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 23 using namespace llvm; 24 25 void 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 32 unsigned 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 53 unsigned 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 60 void 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 67 void 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