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 * 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.
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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.
/** * 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).isPointerStamp(), "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; } }