/*
 * Copyright (c) 2009, 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.nodes.*;
import com.oracle.graal.nodes.spi.*;
import com.oracle.graal.nodes.type.*;

/**
 * An IsNullNode will be true if the supplied value is null, and false if it is non-null.
 */
public final class IsNullNode extends BooleanNode implements Canonicalizable, LIRLowerable, Virtualizable {

    @Input private ValueNode object;

    public ValueNode object() {
        return object;
    }

    /**
     * Constructs a new IsNullNode instruction.
     * 
     * @param object the instruction producing the object to check against null
     */
    public IsNullNode(ValueNode object) {
        super(StampFactory.condition());
        assert object.kind() == Kind.Object : object;
        this.object = object;
    }

    @Override
    public void generate(LIRGeneratorTool gen) {
        // Nothing to do.
    }

    @Override
    public boolean verify() {
        assertTrue(object() != null, "is null input must not be null");
        assertTrue(object().kind() == Kind.Object, "is null input must be an object");
        return super.verify();
    }

    @Override
    public ValueNode canonical(CanonicalizerTool tool) {
        Constant constant = object().asConstant();
        if (constant != null) {
            assert constant.getKind() == Kind.Object;
            return ConstantNode.forBoolean(constant.isNull(), graph());
        }
        if (object.objectStamp().nonNull()) {
            return ConstantNode.forBoolean(false, graph());
        }
        return this;
    }

    @Override
    public void virtualize(VirtualizerTool tool) {
        if (tool.getObjectState(object) != null) {
            tool.replaceWithValue(ConstantNode.forBoolean(false, graph()));
        }
    }
}