/*

 * 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

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 */

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.CompressionNode;

import org.graalvm.compiler.nodes.LogicConstantNode;

import org.graalvm.compiler.nodes.LogicNode;

import org.graalvm.compiler.nodes.NodeView;

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.NarrowOopStamp;

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

import jdk.vm.ci.meta.JavaConstant;

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);

    /*

     * When linear pointer compression is enabled, compressed and uncompressed nulls differ.

     */

    private final JavaConstant nullConstant;

    private IsNullNode(ValueNode object, JavaConstant nullConstant) {

        super(TYPE, object);

        this.nullConstant = nullConstant;

        assert object != null;

    }

    public IsNullNode(ValueNode object) {

        this(object, JavaConstant.NULL_POINTER);

        assertNonNarrow(object);

    }

    public JavaConstant nullConstant() {

        return nullConstant;

    }

    public static LogicNode create(ValueNode forValue) {

        assertNonNarrow(forValue);

        return canonicalized(null, forValue, JavaConstant.NULL_POINTER);

    }

    public static LogicNode create(ValueNode forValue, JavaConstant nullConstant) {

        assert nullConstant.isNull() : "Null constant is not null: " + nullConstant;

        return canonicalized(null, forValue, nullConstant);

    }

    private static void assertNonNarrow(ValueNode object) {

        assert !(object.stamp(NodeView.DEFAULT) instanceof NarrowOopStamp) : "Value to compare against null is a NarrowOop" + object;

    }

    @Override

    public void generate(NodeLIRBuilderTool gen) {

        // Nothing to do.

    }

    @Override

    public boolean verify() {

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

        assertTrue(getValue().stamp(NodeView.DEFAULT) instanceof AbstractPointerStamp, "input must be a pointer not %s", getValue().stamp(NodeView.DEFAULT));

        return super.verify();

    }

    @Override

    public ValueNode canonical(CanonicalizerTool tool, ValueNode forValue) {

        return canonicalized(this, forValue, nullConstant);

    }

    private static LogicNode canonicalized(IsNullNode node, ValueNode forValue, JavaConstant forNullConstant) {

        JavaConstant nullConstant = forNullConstant;

        ValueNode value = forValue;

        while (true) {

            if (StampTool.isPointerAlwaysNull(value)) {

                return LogicConstantNode.tautology();

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

                return LogicConstantNode.contradiction();

            }

            if (value instanceof ConvertNode) {

                ConvertNode convertNode = (ConvertNode) value;

                if (convertNode.mayNullCheckSkipConversion()) {

                    value = convertNode.getValue();

                    continue;

                }

                /*

                 * CompressionNode.mayNullCheckSkipConversion returns false when linear pointer

                 * compression is enabled.

                 */

                if (value instanceof CompressionNode) {

                    CompressionNode compressionNode = (CompressionNode) value;

                    nullConstant = compressionNode.nullConstant();

                    value = compressionNode.getValue();

                    continue;

                }

            }

            /*

             * If we are at original node, just return it. Otherwise create a new node.

             */

            return (node != null && value == forValue) ? node : new IsNullNode(value, nullConstant);

        }

    }

    @Override

    public void virtualize(VirtualizerTool tool) {

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

        TriState fold = tryFold(alias.stamp(NodeView.DEFAULT));

        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

        AbstractPointerStamp pointerStamp = (AbstractPointerStamp) getValue().stamp(NodeView.DEFAULT).unrestricted();

        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;

    }

}