/*

 * Copyright (c) 2009, 2015, 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 org.graalvm.compiler.nodes.calc;

import org.graalvm.compiler.core.common.type.AbstractPointerStamp;

import org.graalvm.compiler.core.common.type.ObjectStamp;

import org.graalvm.compiler.core.common.type.Stamp;

import org.graalvm.compiler.graph.NodeClass;

import org.graalvm.compiler.graph.spi.CanonicalizerTool;

import org.graalvm.compiler.nodeinfo.NodeCycles;

import org.graalvm.compiler.nodeinfo.NodeInfo;

import org.graalvm.compiler.nodes.LogicConstantNode;

import org.graalvm.compiler.nodes.LogicNode;

import org.graalvm.compiler.nodes.PiNode;

import org.graalvm.compiler.nodes.UnaryOpLogicNode;

import org.graalvm.compiler.nodes.ValueNode;

import org.graalvm.compiler.nodes.spi.LIRLowerable;

import org.graalvm.compiler.nodes.spi.NodeLIRBuilderTool;

import org.graalvm.compiler.nodes.spi.Virtualizable;

import org.graalvm.compiler.nodes.spi.VirtualizerTool;

import org.graalvm.compiler.nodes.type.StampTool;

import org.graalvm.compiler.nodes.util.GraphUtil;

import jdk.vm.ci.meta.TriState;

/**

 * An IsNullNode will be true if the supplied value is null, and false if it is non-null.

 */

@NodeInfo(cycles = NodeCycles.CYCLES_2)

public final class IsNullNode extends UnaryOpLogicNode implements LIRLowerable, Virtualizable {

    public static final NodeClass<IsNullNode> TYPE = NodeClass.create(IsNullNode.class);

    public IsNullNode(ValueNode object) {

        super(TYPE, object);

        assert object != null;

    }

    public static LogicNode create(ValueNode forValue) {

        return canonicalized(null, forValue);

    }

    public static LogicNode tryCanonicalize(ValueNode forValue) {

        if (StampTool.isPointerAlwaysNull(forValue)) {

            return LogicConstantNode.tautology();

        } else if (StampTool.isPointerNonNull(forValue)) {

            return LogicConstantNode.contradiction();

        }

        return null;

    }

    @Override

    public void generate(NodeLIRBuilderTool gen) {

        // Nothing to do.

    }

    @Override

    public boolean verify() {

        assertTrue(getValue() != null, "is null input must not be null");

        return super.verify();

    }

    @Override

    public ValueNode canonical(CanonicalizerTool tool, ValueNode forValue) {

        return canonicalized(this, forValue);

    }

    private static LogicNode canonicalized(IsNullNode isNullNode, ValueNode forValue) {

        IsNullNode self = isNullNode;

        LogicNode result = tryCanonicalize(forValue);

        if (result != null) {

            return result;

        }

        if (forValue instanceof PiNode) {

            return IsNullNode.create(GraphUtil.skipPi(forValue));

        }

        if (forValue instanceof ConvertNode) {

            ConvertNode convertNode = (ConvertNode) forValue;

            if (convertNode.mayNullCheckSkipConversion()) {

                return IsNullNode.create(convertNode.getValue());

            }

        }

        if (self == null) {

            self = new IsNullNode(GraphUtil.skipPi(forValue));

        }

        return self;

    }

    @Override

    public void virtualize(VirtualizerTool tool) {

        ValueNode alias = tool.getAlias(getValue());

        if (fold != TriState.UNKNOWN) {

            tool.replaceWithValue(LogicConstantNode.forBoolean(fold.isTrue(), graph()));

        }

    }

    @Override

    public Stamp getSucceedingStampForValue(boolean negated) {

        // Ignore any more precise input stamp since canonicalization will skip through PiNodes

        return negated ? pointerStamp.asNonNull() : pointerStamp.asAlwaysNull();

    }

    @Override

    public TriState tryFold(Stamp valueStamp) {

        if (valueStamp instanceof ObjectStamp) {

            ObjectStamp objectStamp = (ObjectStamp) valueStamp;

            if (objectStamp.alwaysNull()) {

                return TriState.TRUE;

            } else if (objectStamp.nonNull()) {

                return TriState.FALSE;

            }

        }

        return TriState.UNKNOWN;

    }

}