/* Soot - a J*va Optimization Framework
 * Copyright (C) 2000 Patrick Lam
 *
 * 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.
 */

/*
 * Modified by the Sable Research Group and others 1997-1999.  
 * See the 'credits' file distributed with Soot for the complete list of
 * contributors.  (Soot is distributed at http://www.sable.mcgill.ca/soot)
 */


package soot.jimple;

import soot.*;
import java.util.*;

/** Provides naive side effect information. 
 * Relies on no context information; instead, does the least 
 * conservative thing possible even in the possible presence of badness. 
 *
 * Possible weakness of SideEffectTester: consider a Box.  We don't 
 * have a name for "what-is-inside-the-box" and so we can't 
 * ask questions about it.  But perhaps we need only ask questions
 * about the box itself; the sideeffect tester can deal with
 * that internally. */

//  ArrayRef, 
//  CaughtExceptionRef, 
//  FieldRef, 
//  IdentityRef, 
//  InstanceFieldRef, 
//  InstanceInvokeExpr, 
//  Local,  
//  StaticFieldRef

public class NaiveSideEffectTester implements SideEffectTester
{
    public void newMethod( SootMethod m ) {
    }

    /** Returns true if the unit can read from v.
     * Does not deal with expressions; deals with Refs. */
    public boolean unitCanReadFrom(Unit u, Value v)
    {
        Stmt s = (Stmt)u;

        // This doesn't really make any sense, but we need to return something.
        if (v instanceof Constant)
            return false;

        if (v instanceof Expr)
            throw new RuntimeException("can't deal with expr");

        // If it's an invoke, then only locals are safe.
        if (s.containsInvokeExpr())
        {
	    if (!(v instanceof Local))
		return true;
        }

        // otherwise, use boxes tell all.
        Iterator useIt = u.getUseBoxes().iterator();
        while (useIt.hasNext())
        {
            Value use = (Value)useIt.next();

            if (use.equivTo(v))
                return true;

            Iterator vUseIt = v.getUseBoxes().iterator();
            while (vUseIt.hasNext())
            {
                if (use.equivTo(vUseIt.next()))
                    return true;
            }
        }
        return false;
    }

    public boolean unitCanWriteTo(Unit u, Value v)
    {
        Stmt s = (Stmt)u;

        if (v instanceof Constant)
            return false;

        if (v instanceof Expr)
            throw new RuntimeException("can't deal with expr");

        // If it's an invoke, then only locals are safe.
        if (s.containsInvokeExpr())
        {
            if (!(v instanceof Local))
                return true;
        }

        // otherwise, def boxes tell all.
        Iterator defIt = u.getDefBoxes().iterator();
        while (defIt.hasNext())
        {
            Value def = ((ValueBox)(defIt.next())).getValue();
            Iterator useIt = v.getUseBoxes().iterator();
            while (useIt.hasNext())
            {
                Value use = ((ValueBox)useIt.next()).getValue();
                if (def.equivTo(use))
                  return true;
            }
            // also handle the container of all these useboxes!
            if (def.equivTo(v))
                return true;

            // deal with aliasing - handle case where they
            // are a read to the same field, regardless of
            // base object.
            if (v instanceof InstanceFieldRef && 
                def instanceof InstanceFieldRef)
            {
                if (((InstanceFieldRef)v).getField() ==
                    ((InstanceFieldRef)def).getField())
                    return true;
            }
        }
        return false;
    }
}