/* 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);
    }
    
}