GuaranteedDefs.java example

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/* Soot - a J*va Optimization Framework
 * Copyright (C) 2003 Navindra Umanee <navindra@cs.mcgill.ca>
 *
 * 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.toolkits.scalar;

import java.util.*;

import soot.*;
import soot.options.*;
import soot.toolkits.graph.*;

/**
 * Find all locals guaranteed to be defined at (just before) a given
 * program point.
 *
 * @author Navindra Umanee
 **/
public class GuaranteedDefs
{
    protected Map<Unit, List> unitToGuaranteedDefs;

    public GuaranteedDefs(UnitGraph graph)
    {
        if(Options.v().verbose())
            G.v().out.println("[" + graph.getBody().getMethod().getName() +
                               "]     Constructing GuaranteedDefs...");

        GuaranteedDefsAnalysis analysis = new GuaranteedDefsAnalysis(graph);

        // build map
        {
            unitToGuaranteedDefs = new HashMap<Unit, List>(graph.size() * 2 + 1, 0.7f);
            Iterator unitIt = graph.iterator();

            while(unitIt.hasNext()){
                Unit s = (Unit) unitIt.next();
                FlowSet set = (FlowSet) analysis.getFlowBefore(s);
                unitToGuaranteedDefs.put
                    (s, Collections.unmodifiableList(set.toList()));
            }
        }
    }

    /**
     * Returns a list of locals guaranteed to be defined at (just
     * before) program point <tt>s</tt>.
     **/
    public List getGuaranteedDefs(Unit s)
    {
        return unitToGuaranteedDefs.get(s);
    }
}

/**
 * Flow analysis to determine all locals guaranteed to be defined at a
 * given program point.
 **/
class GuaranteedDefsAnalysis extends ForwardFlowAnalysis
{
    FlowSet emptySet = new ArraySparseSet();
    Map<Unit, FlowSet> unitToGenerateSet;

    GuaranteedDefsAnalysis(UnitGraph graph)
    {
        super(graph);
        DominatorsFinder df = new MHGDominatorsFinder(graph);
        unitToGenerateSet = new HashMap<Unit, FlowSet>(graph.size() * 2 + 1, 0.7f);

        // pre-compute generate sets
        for(Iterator unitIt = graph.iterator(); unitIt.hasNext();){
            Unit s = (Unit) unitIt.next();
            FlowSet genSet = emptySet.clone();
            
            for(Iterator domsIt = df.getDominators(s).iterator(); domsIt.hasNext();){
                Unit dom = (Unit) domsIt.next();
                for(Iterator boxIt = dom.getDefBoxes().iterator(); boxIt.hasNext();){
                    ValueBox box = (ValueBox) boxIt.next();
                    if(box.getValue() instanceof Local)
                        genSet.add(box.getValue(), genSet);
                }
            }
            
            unitToGenerateSet.put(s, genSet);
        }

        doAnalysis();
    }

    /**
     * All INs are initialized to the empty set.
     **/
    protected Object newInitialFlow()
    {
        return emptySet.clone();
    }

    /**
     * IN(Start) is the empty set
     **/
    protected Object entryInitialFlow()
    {
        return emptySet.clone();
    }

    /**
     * OUT is the same as IN plus the genSet.
     **/
    protected void flowThrough(Object inValue, Object unit, Object outValue)
    {
        FlowSet
            in = (FlowSet) inValue,
            out = (FlowSet) outValue;

        // perform generation (kill set is empty)
        in.union(unitToGenerateSet.get(unit), out);
    }

    /**
     * All paths == Intersection.
     **/
    protected void merge(Object in1, Object in2, Object out)
    {
        FlowSet
            inSet1 = (FlowSet) in1,
            inSet2 = (FlowSet) in2,
            outSet = (FlowSet) out;

        inSet1.intersection(inSet2, outSet);
    }

    protected void copy(Object source, Object dest)
    {
        FlowSet
            sourceSet = (FlowSet) source,
            destSet = (FlowSet) dest;

        sourceSet.copy(destSet);
    }
}