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A Java Optimization Framework
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package soot.toolkits.graph;

/*-
 * #%L
 * Soot - a J*va Optimization Framework
 * %%
 * Copyright (C) 2007 Eric Bodden
 * %%
 * 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.Collection;
import java.util.Comparator;
import java.util.TreeSet;

import soot.Body;
import soot.jimple.Stmt;
import soot.jimple.toolkits.annotation.logic.Loop;
import soot.jimple.toolkits.annotation.logic.LoopFinder;

/**
 * A loop nesting tree, implemented as a tree-map. Loops are represented by pairs of head-statements and the respective loop.
 * The iterator over this collection returns the loop in such an order that a loop l will always returned before a loop m if
 * l is an inner loop of m.
 *
 * @author Eric Bodden
 */
public class LoopNestTree extends TreeSet {

  /**
   * Comparator, stating that a loop l1 is smaller than a loop l2 if l2 contains all statements of l1.
   *
   * @author Eric Bodden
   */
  private static class LoopNestTreeComparator implements Comparator {

    @Override
    public int compare(Loop loop1, Loop loop2) {
      Collection stmts1 = loop1.getLoopStatements();
      Collection stmts2 = loop2.getLoopStatements();
      if (stmts1.equals(stmts2)) {
        assert loop1.getHead().equals(loop2.getHead()); // should really have the same head then
        // equal (same) loops
        return 0;
      } else if (stmts1.containsAll(stmts2)) {
        // 1 superset of 2
        return 1;
      } else if (stmts2.containsAll(stmts1)) {
        // 1 subset of 2
        return -1;
      }
      // overlap (?) or disjoint: order does not matter;
      // however we must *not* return 0 as this would only keep one of the two loops;
      // hence, return 1
      return 1;
    }
  }

  /**
   * Builds a loop nest tree from a method body using {@link LoopFinder}.
   */
  public LoopNestTree(Body b) {
    this(computeLoops(b));
  }

  /**
   * Builds a loop nest tree from a mapping from loop headers to statements in the loop.
   */
  public LoopNestTree(Collection loops) {
    super(new LoopNestTreeComparator());
    addAll(loops);
  }

  private static Collection computeLoops(Body b) {
    return new LoopFinder().getLoops(b);
  }

  public boolean hasNestedLoops() {
    // TODO could be speeded up by just comparing two consecutive
    // loops returned by the iterator
    LoopNestTreeComparator comp = new LoopNestTreeComparator();
    for (Loop loop1 : this) {
      for (Loop loop2 : this) {
        if (comp.compare(loop1, loop2) != 0) {
          return true;
        }
      }
    }
    return false;
  }
}