/*
 * Copyright (c) 2011, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code 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 Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package com.oracle.graal.nodes.calc;

import com.oracle.graal.api.meta.*;
import com.oracle.graal.graph.*;
import com.oracle.graal.nodes.*;
import com.oracle.graal.nodes.spi.*;

@NodeInfo(shortName = "==")
public final class ObjectEqualsNode extends CompareNode implements Virtualizable {

    /**
     * Constructs a new object equality comparison node.
     * 
     * @param x the instruction producing the first input to the instruction
     * @param y the instruction that produces the second input to this instruction
     */
    public ObjectEqualsNode(ValueNode x, ValueNode y) {
        super(x, y);
        assert x.kind() == Kind.Object;
        assert y.kind() == Kind.Object;
    }

    @Override
    public Condition condition() {
        return Condition.EQ;
    }

    @Override
    public boolean unorderedIsTrue() {
        return false;
    }

    @Override
    public ValueNode canonical(CanonicalizerTool tool) {
        if (x() == y()) {
            return ConstantNode.forBoolean(true, graph());
        }

        if (x().objectStamp().alwaysNull()) {
            return graph().unique(new IsNullNode(y()));
        } else if (y().objectStamp().alwaysNull()) {
            return graph().unique(new IsNullNode(x()));
        }
        if (x().stamp().alwaysDistinct(y().stamp())) {
            return ConstantNode.forBoolean(false, graph());
        }

        return super.canonical(tool);
    }

    @Override
    public void virtualize(VirtualizerTool tool) {
        State stateX = tool.getObjectState(x());
        State stateY = tool.getObjectState(y());
        boolean xVirtual = stateX != null && stateX.getState() == EscapeState.Virtual;
        boolean yVirtual = stateY != null && stateY.getState() == EscapeState.Virtual;

        if (xVirtual ^ yVirtual) {
            // one of them is virtual: they can never be the same objects
            tool.replaceWithValue(ConstantNode.forBoolean(false, graph()));
        } else if (xVirtual && yVirtual) {
            // both are virtual: check if they refer to the same object
            tool.replaceWithValue(ConstantNode.forBoolean(stateX == stateY, graph()));
        }
    }
}