/*
 * 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");
        assertTrue(getValue().stamp() instanceof AbstractPointerStamp, "input must be a pointer not %s", getValue().stamp());
        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());
        TriState fold = tryFold(alias.stamp());
        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().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;
    }
}