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/**
 * Copyright (C) 2010-2018 Gordon Fraser, Andrea Arcuri and EvoSuite
 * contributors
 *
 * This file is part of EvoSuite.
 *
 * EvoSuite 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 3.0 of the License, or
 * (at your option) any later version.
 *
 * EvoSuite 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 Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with EvoSuite. If not, see .
 */
package org.evosuite.graphs.cdg;

import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.evosuite.graphs.EvoSuiteGraph;
import org.evosuite.graphs.cfg.ControlFlowGraph;
import org.jgrapht.graph.DefaultEdge;


/**
 *
 * Given a CFG this class computes the immediateDominators and the
 * dominatingFrontiers for each CFG vertex
 *
 * The current algorithm to determine the immediateDominators runs in time
 * O(e*log n) where e is the number of control flow edges and n the number of
 * CFG vertices and is taken from:
 *
 * "A Fast Algorithm for Finding Dominators in a Flowgraph" THOMAS LENGAUER and
 * ROBERT ENDRE TARJAN 1979, Stanford University
 *
 * DOI: 10.1145/357062.357071
 * http://portal.acm.org/citation.cfm?doid=357062.357071
 *
 *
 * The algorithm for computing the dominatingFrontiers when given the
 * immediateDominators is taken from
 *
 * "Efficiently Computing Static Single Assignment Form and the Control
 * Dependence Graph" RON CYTRON, JEANNE FERRANTE, BARRY K. ROSEN, and MARK N.
 * WEGMAN IBM Research Division and F. KENNETH ZADECK Brown University 1991
 *
 * @author Andre Mis
 */
public class DominatorTree extends EvoSuiteGraph, DefaultEdge> {

	private static Logger logger = LoggerFactory.getLogger(DominatorTree.class);

	private int nodeCount = 0;
	private final ControlFlowGraph cfg;

	private final Map> dominatorNodesMap = new LinkedHashMap>();
	private final Map> dominatorIDMap = new LinkedHashMap>();
	private final Map> dominatingFrontiers = new LinkedHashMap>();

	/**
	 * Will start the computation of all immediateDominators for the given CFG
	 * which can later be retrieved via getImmediateDominator()
	 *
	 * @param cfg a {@link org.evosuite.graphs.cfg.ControlFlowGraph} object.
	 */
	public DominatorTree(ControlFlowGraph cfg) {
		super(DefaultEdge.class);

		logger.debug("Computing DominatorTree for " + cfg.getName());

		this.cfg = cfg;

		createDominatorNodes();

		V root = cfg.determineEntryPoint(); // TODO change to getEntryPoint()
		logger.debug("determined root: " + root);
		DominatorNode rootNode = getDominatorNodeFor(root);

		depthFirstAnalyze(rootNode);

		computeSemiDominators();
		computeImmediateDominators(rootNode);

		createDominatorTree();

		computeDominatorFrontiers(rootNode);

		//		toDot();
	}

	private void createDominatorTree() {

		// add dominator nodes
		addVertices(dominatorIDMap.values());

		logger.debug("DTNodes: " + vertexCount());

		// build up tree by adding for each node v an edge from v.iDom to v
		for (DominatorNode v : vertexSet()) {
			if (v.isRootNode())
				continue;
			if (addEdge(v.immediateDominator, v) == null)
				throw new IllegalStateException(
				        "internal error while building dominator tree edges");

			logger.debug("added DTEdge from " + v.immediateDominator.n + " to " + v.n);
		}

		logger.debug("DTEdges: " + edgeCount());

		// sanity check
		if (isEmpty())
			throw new IllegalStateException("expect dominator trees to not be empty");
		// check tree is connected
		if (!isConnected())
			throw new IllegalStateException("dominator tree expected to be connected");
		// TODO more sanity checks - no one likes to be insane ;)
	}

	private void computeDominatorFrontiers(DominatorNode currentNode) {

		// TODO check assumption: exitPoints in original CFG are exitPoints in resulting DominatorTree

		for (DominatorNode child : getChildren(currentNode))
			computeDominatorFrontiers(child);

		logger.debug("computing dominatingFrontier for: " + currentNode.toString());

		Set dominatingFrontier = dominatingFrontiers.get(currentNode);
		if (dominatingFrontier == null)
			dominatingFrontier = new HashSet();

		// "local"
		for (V child : cfg.getChildren(currentNode.node)) {
			DominatorNode y = getDominatorNodeFor(child);
			if (y.immediateDominator.n != currentNode.n) {
				logger.debug("  LOCAL adding to DFs: " + y.node);
				dominatingFrontier.add(y.node);
			}
		}

		// "up"
		for (DominatorNode z : getChildren(currentNode))
			for (V y : dominatingFrontiers.get(z.node))
				if (getDominatorNodeFor(y).immediateDominator.n != currentNode.n) {
					logger.debug("  UP adding to DFs: " + y);
					dominatingFrontier.add(y);
				}

		dominatingFrontiers.put(currentNode.node, dominatingFrontier);
	}

	/**
	 * Given a node of this objects CFG this method returns it's previously
	 * computed immediateDominator
	 *
	 * The immediateDominator iDom of a node v has the following properties:
	 *
	 * 1) iDom dominates v
	 *
	 * 2) every other dominator of v dominates iDom
	 *
	 * A node w dominates v or is a dominator of v if and only if every path
	 * from the CFG's entryPoint to v contains w
	 *
	 * @param v
	 *            A node within this objects CFG for wich the immediateDominator
	 *            is to be returned
	 * @return a V object.
	 */
	public V getImmediateDominator(V v) {
		if (v == null)
			throw new IllegalArgumentException("null given");
		DominatorNode domNode = dominatorNodesMap.get(v);
		if (domNode == null)
			throw new IllegalStateException("unknown vertice given");

		if (domNode.immediateDominator == null) {
			// sanity check: this is only allowed to happen if v is root of CFG
			if (domNode.n != 1)
				throw new IllegalStateException(
				        "expect known node without iDom to be root of CFG");

			return null;
		}

		return domNode.immediateDominator.node;
	}

	/**
	 * Getter for the field dominatingFrontiers.
	 *
	 * @param v a V object.
	 * @return a {@link java.util.Set} object.
	 */
	public Set getDominatingFrontiers(V v) {
		if (v == null)
			throw new IllegalStateException("null given");

		return dominatingFrontiers.get(v);
	}

	// computation

	private void createDominatorNodes() {

		for (V v : cfg.vertexSet())
			dominatorNodesMap.put(v, new DominatorNode(v));
	}

	private void depthFirstAnalyze(DominatorNode currentNode) {
		// step 1

		initialize(currentNode);

		for (V w : cfg.getChildren(currentNode.node)) {
			DominatorNode wNode = getDominatorNodeFor(w);
			if (wNode.semiDominator == null) {
				wNode.parent = currentNode;
				depthFirstAnalyze(wNode);
			}
		}
	}

	private void initialize(DominatorNode currentNode) {

		nodeCount++;
		currentNode.n = nodeCount;
		currentNode.semiDominator = currentNode;

		logger.debug("created " + currentNode.toString() + " for "
		        + currentNode.node.toString());

		dominatorIDMap.put(nodeCount, currentNode);
	}

	private void computeSemiDominators() {

		for (int i = nodeCount; i >= 2; i--) {
			DominatorNode w = getDominatorNodeById(i);

			// step 2
			for (V current : cfg.getParents(w.node)) {
				DominatorNode v = getDominatorNodeFor(current);
				DominatorNode u = v.eval();

				if (u.semiDominator.n < w.semiDominator.n)
					w.semiDominator = u.semiDominator;
			}

			w.semiDominator.bucket.add(w);
			w.link(w.parent);

			// step 3
			while (!w.parent.bucket.isEmpty()) {

				DominatorNode v = w.parent.getFromBucket();
				if (!w.parent.bucket.remove(v))
					throw new IllegalStateException("internal error");

				DominatorNode u = v.eval();
				v.immediateDominator = (u.semiDominator.n < v.semiDominator.n ? u
				        : w.parent);
			}
		}
	}

	private void computeImmediateDominators(DominatorNode rootNode) {
		// step 4
		for (int i = 2; i <= nodeCount; i++) {
			DominatorNode w = getDominatorNodeById(i);

			if (w.immediateDominator != w.semiDominator)
				w.immediateDominator = w.immediateDominator.immediateDominator;

			//			logger.debug("iDom for node "+i+" was: "+w.immediateDominator.n);
		}

		rootNode.immediateDominator = null;
	}

	private DominatorNode getDominatorNodeById(int id) {
		DominatorNode r = dominatorIDMap.get(id);
		if (r == null)
			throw new IllegalArgumentException("id unknown to this tree");

		return r;
	}

	private DominatorNode getDominatorNodeFor(V v) {
		DominatorNode r = dominatorNodesMap.get(v);
		if (r == null)
			throw new IllegalStateException(
			        "expect dominatorNodesMap to contain domNodes for all Vs");

		return r;
	}

	/** {@inheritDoc} */
	@Override
	public String getName() {
		return "DominatorTree" + graphId;
	}
}