1 /* 2 * Copyright (c) 2015, 2015, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 */ 23 package org.graalvm.compiler.graph; 24 25 /** 26 * Union-find data structure for {@link Node Nodes}. 27 * 28 * All operations have an accumulated worst-case complexity of O(a(n)), where a(n) is the inverse of 29 * the Ackermann function A(n,n). 30 */ 31 public class NodeUnionFind extends NodeIdAccessor { 32 33 private int[] rank; 34 private int[] parent; 35 36 /** 37 * Create a new union-find data structure for a {@link Graph}. Initially, all nodes are in their 38 * own equivalence set. 39 */ 40 public NodeUnionFind(Graph graph) { 41 super(graph); 42 rank = new int[graph.nodeIdCount()]; 43 parent = new int[graph.nodeIdCount()]; 44 for (int i = 0; i < parent.length; i++) { 45 parent[i] = i; 46 } 47 } 48 49 /** 50 * Merge the equivalence sets of two nodes. 51 * 52 * After calling this function, find(a) == find(b). 53 */ 54 public void union(Node a, Node b) { 55 union(getNodeId(a), getNodeId(b)); 56 } 57 58 /** 59 * Get a representative element of the equivalence set of a node. 60 * 61 * This function returns the same representative element for all members of the same equivalence 62 * set, i.e., find(a) == find(b) if and only if a and b are in the same set. 63 */ 64 public Node find(Node a) { 65 int id = find(getNodeId(a)); 66 return graph.getNode(id); 67 } 68 69 public boolean equiv(Node a, Node b) { 70 return find(getNodeId(a)) == find(getNodeId(b)); 71 } 72 73 private void union(int a, int b) { 74 int aRoot = find(a); 75 int bRoot = find(b); 76 if (aRoot != bRoot) { 77 if (rank[aRoot] < rank[bRoot]) { 78 parent[aRoot] = bRoot; 79 } else { 80 parent[bRoot] = aRoot; 81 if (rank[aRoot] == rank[bRoot]) { 82 rank[aRoot]++; 83 } 84 } 85 } 86 } 87 88 private int find(int a) { 89 int ret = a; 90 while (ret != parent[ret]) { 91 parent[ret] = parent[parent[ret]]; 92 ret = parent[ret]; 93 } 94 return ret; 95 } 96 }