Package soot.jimple.toolkits.pointer

Source Code of soot.jimple.toolkits.pointer.StrongLocalMustAliasAnalysis

/* Soot - a J*va Optimization Framework
* Copyright (C) 2003 Ondrej Lhotak
*
* This library 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 library 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 this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/

package soot.jimple.toolkits.pointer;

import java.util.HashSet;
import java.util.List;
import java.util.Set;

import soot.Local;
import soot.RefLikeType;
import soot.Unit;
import soot.Value;
import soot.ValueBox;
import soot.jimple.Stmt;
import soot.toolkits.graph.StronglyConnectedComponents;
import soot.toolkits.graph.StronglyConnectedComponentsFast;
import soot.toolkits.graph.UnitGraph;

/**
* A special version of the local must-alias analysis that takes redefinitions within loops into account.
* For variable that is redefined in a loop, the must-alias information is invalidated and set to
* {@link LocalMustAliasAnalysis#UNKNOWN}.
* E.g. assume the following example:
* <code>
* while(..) {
*   c = foo();        //(1)
*   c.doSomething();  //(2)
* }
* </code>
*
* While it is certainly true that c at (2) must-alias c at (1) (they have the same value number), it is also true that
* in a second iteration, c at (2) may not alias the previous c at (2).
* @author Eric Bodden
*/
public class StrongLocalMustAliasAnalysis extends LocalMustAliasAnalysis {

    protected Set<Integer> invalidInstanceKeys;
   
    public StrongLocalMustAliasAnalysis(UnitGraph g) {
        super(g);
        invalidInstanceKeys = new HashSet<Integer>();
        /*
         * Find all SCCs, then invalidate all instance keys for variable defined within an SCC.
         */
        StronglyConnectedComponentsFast<Unit> sccAnalysis = new StronglyConnectedComponentsFast<Unit>(g);
        for (List<Unit> scc : sccAnalysis.getTrueComponents()) {
      for (Unit unit : scc) {
        for (ValueBox vb : unit.getDefBoxes()) {
          Value defValue = vb.getValue();
          if(defValue instanceof Local) {
            Local defLocal = (Local) defValue;
            if(defLocal.getType() instanceof RefLikeType) {
              Object instanceKey = getFlowBefore(unit).get(defLocal);
              //if key is not already UNKNOWN
              if(instanceKey instanceof Integer) {
                Integer intKey = (Integer) instanceKey;
                invalidInstanceKeys.add(intKey);
              }
            }
          }
        }
      }
    }
    }
   
    /**
     * {@inheritDoc}
     */
    @Override
    public boolean mustAlias(Local l1, Stmt s1, Local l2, Stmt s2) {
        Object l1n = getFlowBefore(s1).get(l1);
        Object l2n = getFlowBefore(s2).get(l2);

        if (l1n == UNKNOWN || l2n == UNKNOWN ||
            invalidInstanceKeys.contains(l1n) || invalidInstanceKeys.contains(l2n))
            return false;

        return l1n == l2n;
    }
   
    /**
     * {@inheritDoc}
     */
    @Override
    public String instanceKeyString(Local l, Stmt s) {
        Object ln = getFlowBefore(s).get(l);
        if(invalidInstanceKeys.contains(ln)) {
            return UNKNOWN_LABEL;
        }
        return super.instanceKeyString(l, s);
    }
   
}
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