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An easy-to-learn/use static analysis framework for Java
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/*
 * Tai-e: A Static Analysis Framework for Java
 *
 * Copyright (C) 2022 Tian Tan 
 * Copyright (C) 2022 Yue Li 
 *
 * This file is part of Tai-e.
 *
 * Tai-e is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation, either version 3
 * of the License, or (at your option) any later version.
 *
 * Tai-e is distributed in the hope that it will be useful,but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General
 * Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with Tai-e. If not, see .
 */

package pascal.taie.util.graph;

import pascal.taie.util.Indexer;
import pascal.taie.util.SimpleIndexer;
import pascal.taie.util.collection.IndexMap;
import pascal.taie.util.collection.IndexerBitSet;
import pascal.taie.util.collection.SetEx;
import pascal.taie.util.collection.Sets;

import java.util.ArrayDeque;
import java.util.Collections;
import java.util.Deque;
import java.util.Map;
import java.util.Set;

/**
 * Finds dominators for the nodes in given {@link Graph}.
 */
public class DominatorFinder {

    /**
     * The graph associated with this finder.
     */
    private final Graph graph;

    /**
     * Indexer for nodes in the graph. This is used to store nodes in bit set.
     */
    private final Indexer indexer;

    /**
     * Head nodes of the graph.
     */
    private final Set heads;

    /**
     * Maps a node N to all its dominators.
     */
    private final Map> node2Doms;

    /**
     * Maps a node N to all nodes dominated by N.
     * This map is computed on-demand by {@link #findDominatedNodes()}.
     */
    private Map> dom2Nodes;

    private final boolean isSparse;

    public DominatorFinder(Graph graph) {
        this(graph, true);
    }

    public DominatorFinder(Graph graph, boolean isSparse) {
        this(graph, new SimpleIndexer<>(), isSparse);
    }

    /**
     * Constructs a dominator finder with a graph and given indexer.
     * Note that {@code indexer} must assign continuous indexes for nodes in
     * {@code graph}, starting from 0, otherwise the finder may throw exception.
     */
    public DominatorFinder(Graph graph, Indexer indexer, boolean isSparse) {
        this.graph = graph;
        this.indexer = indexer;
        this.isSparse = isSparse;
        this.heads = Sets.newSet();
        this.node2Doms = new IndexMap<>(indexer, graph.getNumberOfNodes());
        findDominators();
    }

    private void findDominators() {
        // build full set
        SetEx fullSet = new IndexerBitSet<>(indexer, isSparse);
        fullSet.addAll(graph.getNodes());
        // initialize dominators
        Deque workList = new ArrayDeque<>();
        for (N node : graph) {
            SetEx doms;
            if (graph.getInDegreeOf(node) == 0) {
                // node is head
                heads.add(node);
                // head nodes are only dominated by themselves
                doms = new IndexerBitSet<>(indexer, isSparse);
                doms.add(node);
            } else {
                // other nodes are initially dominated by all nodes
                // make it a reference of fullSet to save time and memory
                // notes that it should not be updated in place
                doms = fullSet;
                // add to work-list for further processing
                workList.add(node);
            }
            node2Doms.put(node, doms);
        }
        // process work-list
        while (!workList.isEmpty()) {
            N node = workList.pop();
            SetEx oldDoms = node2Doms.get(node);
            SetEx newDoms = fullSet;
            // intersect dominators of all predecessors
            for (N pred : graph.getPredsOf(node)) {
                SetEx doms = node2Doms.get(pred);
                if (newDoms != fullSet) {
                    newDoms.retainAll(doms);
                } else if (doms != fullSet) {
                    newDoms = doms.copy();
                }
            }
            // each node dominates itself
            newDoms.add(node);
            if (!oldDoms.equals(newDoms)) {
                node2Doms.put(node, newDoms);
                workList.addAll(graph.getSuccsOf(node));
            }
        }
    }

    /**
     * @return the dominators of {@code node}.
     */
    public Set getDominatorsOf(N node) {
        return Collections.unmodifiableSet(node2Doms.get(node));
    }

    /**
     * @return the nodes dominated by the {@code dominator}.
     */
    public Set getNodesDominatedBy(N dominator) {
        if (dom2Nodes == null) {
            findDominatedNodes();
        }
        return Collections.unmodifiableSet(dom2Nodes.get(dominator));
    }

    private void findDominatedNodes() {
        dom2Nodes = new IndexMap<>(indexer, graph.getNumberOfNodes());
        for (N node : graph) {
            for (N dom : node2Doms.get(node)) {
                dom2Nodes.computeIfAbsent(dom,
                                __ -> new IndexerBitSet<>(indexer, isSparse))
                        .add(node);
            }
        }
    }

    /**
     * @return {@code true} if {@code dominator} is a dominator of {@code node}.
     */
    public boolean isDominatedBy(N node, N dominator) {
        return node2Doms.get(node).contains(dominator);
    }
}