soot.toolkits.graph.DominatorAnalysis Maven / Gradle / Ivy

package soot.toolkits.graph;

/*-
 * #%L
 * Soot - a J*va Optimization Framework
 * %%
 * Copyright (C) 2003 Jennifer Lhotak
 * %%
 * This program 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 2.1 of the
 * License, or (at your option) any later version.
 * 
 * This program 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 General Lesser Public License for more details.
 * 
 * You should have received a copy of the GNU General Lesser Public
 * License along with this program.  If not, see
 * .
 * #L%
 */

import java.util.List;

import soot.Unit;
import soot.jimple.Stmt;
import soot.toolkits.scalar.ArraySparseSet;
import soot.toolkits.scalar.FlowSet;
import soot.toolkits.scalar.ForwardFlowAnalysis;

// STEP 1: What are we computing?
// SETS OF Units that are dominators => Use ArraySparseSet.
//
// STEP 2: Precisely define what we are computing.
// For each statement compute the set of stmts that dominate it 
// 
// STEP 3: Decide whether it is a backwards or forwards analysis.
// FORWARDS
//
//
/**
 * @deprecated use {@link MHGDominatorsFinder} instead
 */
@Deprecated
public class DominatorAnalysis extends ForwardFlowAnalysis> {

  private UnitGraph g;
  private FlowSet allNodes;

  public DominatorAnalysis(UnitGraph g) {
    super(g);
    this.g = g;

    initAllNodes();

    doAnalysis();

  }

  private void initAllNodes() {
    allNodes = new ArraySparseSet();
    for (Unit u : g) {
      allNodes.add(u);
    }
  }

  // STEP 4: Is the merge operator union or intersection?
  // INTERSECTION

  @Override
  protected void merge(FlowSet in1, FlowSet in2, FlowSet out) {
    in1.intersection(in2, out);
  }

  @Override
  protected void copy(FlowSet source, FlowSet dest) {
    source.copy(dest);
  }

  // STEP 5: Define flow equations.
  // dom(s) = s U ( ForAll Y in pred(s): Intersection (dom(y)))
  // ie: dom(s) = s and whoever dominates all the predeccessors of s
  //
  @Override
  protected void flowThrough(FlowSet in, Unit s, FlowSet out) {

    if (isUnitStartNode(s)) {
      // System.out.println("s: "+s+" is start node");
      out.clear();
      out.add(s);
      // System.out.println("in: "+in+" out: "+out);
    } else {

      // System.out.println("s: "+s+" is not start node");
      // FlowSet domsOfPreds = allNodes.clone();

      // for each pred of s
      for (Unit pred : g.getPredsOf(s)) {
        // get the unitToBeforeFlow and find the intersection
        // System.out.println("pred: "+pred);
        FlowSet next = getFlowAfter(pred);
        // System.out.println("next: "+next);
        // System.out.println("in before intersect: "+in);
        in.intersection(next, in);
        // System.out.println("in after intersect: "+in);
      }

      // intersected with in

      // System.out.println("out init: "+out);
      out.intersection(in, out);
      out.add(s);
      // System.out.println("out after: "+out);
    }
  }

  private boolean isUnitStartNode(Unit s) {
    // System.out.println("head: "+g.getHeads().get(0));
    if (s.equals(g.getHeads().get(0))) {
      return true;
    }
    return false;
  }

  // STEP 6: Determine value for start/end node, and
  // initial approximation.
  // dom(startNode) = startNode
  // dom(node) = allNodes
  //
  @Override
  protected FlowSet entryInitialFlow() {

    FlowSet fs = new ArraySparseSet();
    List heads = g.getHeads();
    if (heads.size() != 1) {
      throw new RuntimeException("Expect one start node only.");
    }
    fs.add(heads.get(0));
    return fs;
  }

  @Override
  protected FlowSet newInitialFlow() {
    return allNodes.clone();
  }

  /**
   * Returns true if s post-dominates t.
   */
  public boolean dominates(Stmt s, Stmt t) {
    return getFlowBefore(t).contains(s);
  }

}