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 * Copyright (c) 2013, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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
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package com.oracle.svm.hosted.nodes;

import org.graalvm.compiler.graph.IterableNodeType;
import org.graalvm.compiler.graph.Node;
import org.graalvm.compiler.graph.Node.ValueNumberable;
import org.graalvm.compiler.graph.NodeClass;
import org.graalvm.compiler.graph.spi.Canonicalizable;
import org.graalvm.compiler.graph.spi.CanonicalizerTool;
import org.graalvm.compiler.nodeinfo.InputType;
import org.graalvm.compiler.nodeinfo.NodeCycles;
import org.graalvm.compiler.nodeinfo.NodeInfo;
import org.graalvm.compiler.nodeinfo.NodeSize;
import org.graalvm.compiler.nodes.NodeView;
import org.graalvm.compiler.nodes.ParameterNode;
import org.graalvm.compiler.nodes.ValueNode;
import org.graalvm.compiler.nodes.calc.FloatingNode;
import org.graalvm.compiler.nodes.spi.ArrayLengthProvider;
import org.graalvm.compiler.nodes.spi.LIRLowerable;
import org.graalvm.compiler.nodes.spi.LimitedValueProxy;
import org.graalvm.compiler.nodes.spi.NodeLIRBuilderTool;
import org.graalvm.compiler.nodes.util.GraphUtil;

import com.oracle.svm.core.deopt.Deoptimizer;

import jdk.vm.ci.meta.ConstantReflectionProvider;

Wraps locals and bytecode stack elements at deoptimization points. DeoptProxyNodes are inserted
in deoptimization target methods to avoid global value numbering and rescheduling of local
variable (and stack) accesses across deoptimization points.
 This is needed to ensure that the values, which are set by the Deoptimizer at the deoptimization point, are really read from their locations (and not hold in a temporary register, etc.) /**
 * Wraps locals and bytecode stack elements at deoptimization points. DeoptProxyNodes are inserted
 * in deoptimization target methods to avoid global value numbering and rescheduling of local
 * variable (and stack) accesses across deoptimization points.
 * <p>
 * This is needed to ensure that the values, which are set by the {@link Deoptimizer} at the
 * deoptimization point, are really read from their locations (and not hold in a temporary register,
 * etc.)
 */
@NodeInfo(cycles = NodeCycles.CYCLES_0, size = NodeSize.SIZE_0)
public final class DeoptProxyNode extends FloatingNode implements LimitedValueProxy, ValueNumberable, LIRLowerable, Canonicalizable, IterableNodeType, ArrayLengthProvider {
    public static final NodeClass<DeoptProxyNode> TYPE = NodeClass.create(DeoptProxyNode.class);

    
The link to the deoptimization point to prevent rescheduling of this node.
/**
     * The link to the deoptimization point to prevent rescheduling of this node.
     */
    @Input(InputType.Anchor) protected ValueNode proxyPoint;

    
The original value, e.g. a ParameterNode /**
     * The original value, e.g. a {@link ParameterNode}
     */
    @Input protected ValueNode value;

    
A unique index for the deoptimization point. It prevents global value numbering across
deoptimization points, but enabled global value numbering between two deoptimization points.
/**
     * A unique index for the deoptimization point. It prevents global value numbering across
     * deoptimization points, but enabled global value numbering between two deoptimization points.
     */
    protected final int deoptIndex;

    protected DeoptProxyNode(ValueNode value, ValueNode proxyPoint, int deoptIndex) {
        super(TYPE, value.stamp(NodeView.DEFAULT));
        this.value = value;
        this.proxyPoint = proxyPoint;
        this.deoptIndex = deoptIndex;
    }

    public static ValueNode create(ValueNode value, ValueNode proxyPoint, int deoptIndex) {
        ValueNode synonym = findSynonym(value);
        if (synonym != null) {
            return synonym;
        }
        return new DeoptProxyNode(value, proxyPoint, deoptIndex);
    }

    @Override
    public boolean inferStamp() {
        return updateStamp(value.stamp(NodeView.DEFAULT));
    }

    @Override
    public ValueNode getOriginalNode() {
        return value;
    }

    @Override
    public void generate(NodeLIRBuilderTool gen) {
        gen.setResult(this, gen.operand(value));
    }

    @Override
    public Node canonical(CanonicalizerTool tool) {
        ValueNode synonym = findSynonym(value);
        return synonym != null ? synonym : this;
    }

    
No need to proxy constants.
/**
     * No need to proxy constants.
     */
    private static ValueNode findSynonym(ValueNode value) {
        return value.isConstant() ? value : null;
    }

    public boolean hasProxyPoint() {
        return proxyPoint != null;
    }

    @Override
    public ValueNode findLength(FindLengthMode mode, ConstantReflectionProvider constantReflection) {
        ValueNode length = GraphUtil.arrayLength(value, mode, constantReflection);
        return length != null && length.isConstant() ? length : null;
    }
}