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 * Copyright (c) 2013, 2018, 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
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 * questions.
 */


package org.graalvm.compiler.replacements;

import static org.graalvm.compiler.nodeinfo.NodeCycles.CYCLES_IGNORED;
import static org.graalvm.compiler.nodeinfo.NodeSize.SIZE_IGNORED;
import static org.graalvm.compiler.replacements.SnippetTemplate.DEFAULT_REPLACER;

import java.util.Arrays;

import org.graalvm.compiler.api.replacements.Fold;
import org.graalvm.compiler.api.replacements.Snippet;
import org.graalvm.compiler.api.replacements.Snippet.ConstantParameter;
import org.graalvm.compiler.api.replacements.SnippetReflectionProvider;
import org.graalvm.compiler.core.common.type.StampFactory;
import org.graalvm.compiler.debug.DebugHandlersFactory;
import org.graalvm.compiler.debug.GraalError;
import org.graalvm.compiler.graph.NodeClass;
import org.graalvm.compiler.nodeinfo.NodeInfo;
import org.graalvm.compiler.nodes.FixedWithNextNode;
import org.graalvm.compiler.nodes.NamedLocationIdentity;
import org.graalvm.compiler.nodes.StructuredGraph;
import org.graalvm.compiler.nodes.ValueNode;
import org.graalvm.compiler.nodes.spi.Lowerable;
import org.graalvm.compiler.nodes.spi.LoweringTool;
import org.graalvm.compiler.options.OptionValues;
import org.graalvm.compiler.phases.util.Providers;
import org.graalvm.compiler.replacements.SnippetTemplate.AbstractTemplates;
import org.graalvm.compiler.replacements.SnippetTemplate.Arguments;
import org.graalvm.compiler.replacements.SnippetTemplate.SnippetInfo;
import org.graalvm.compiler.serviceprovider.GraalUnsafeAccess;
import org.graalvm.compiler.word.ObjectAccess;
import jdk.internal.vm.compiler.word.LocationIdentity;

import jdk.vm.ci.code.TargetDescription;
import sun.misc.Unsafe;

This node can be used to add a counter to the code that will estimate the dynamic number of calls
by adding an increment to the compiled code. This should of course only be used for
debugging/testing purposes.
A unique counter will be created for each unique name passed to the constructor. Depending on the
value of withContext, the name of the root method is added to the counter's name.
/**
 * This node can be used to add a counter to the code that will estimate the dynamic number of calls
 * by adding an increment to the compiled code. This should of course only be used for
 * debugging/testing purposes.
 *
 * A unique counter will be created for each unique name passed to the constructor. Depending on the
 * value of withContext, the name of the root method is added to the counter's name.
 */
@NodeInfo(cycles = CYCLES_IGNORED, size = SIZE_IGNORED)
public class SnippetCounterNode extends FixedWithNextNode implements Lowerable {

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

    @Input protected ValueNode increment;

    protected final SnippetCounter counter;

    public SnippetCounterNode(SnippetCounter counter, ValueNode increment) {
        super(TYPE, StampFactory.forVoid());
        this.counter = counter;
        this.increment = increment;
    }

    public SnippetCounter getCounter() {
        return counter;
    }

    public ValueNode getIncrement() {
        return increment;
    }

    @NodeIntrinsic
    public static native void add(@ConstantNodeParameter SnippetCounter counter, int increment);

    public static void increment(@ConstantNodeParameter SnippetCounter counter) {
        add(counter, 1);
    }

    @Override
    public void lower(LoweringTool tool) {
        if (graph().getGuardsStage().areFrameStatesAtDeopts()) {
            SnippetCounterSnippets.Templates templates = tool.getReplacements().getSnippetTemplateCache(SnippetCounterSnippets.Templates.class);
            templates.lower(this, tool);
        }
    }

    
Add SNIPPET_COUNTER_LOCATION to privateLocations if it isn't already there. 
Params:
privateLocations – 
Returns:
a copy of privateLocations with any needed locations added/**
     * Add {@link #SNIPPET_COUNTER_LOCATION} to {@code privateLocations} if it isn't already there.
     *
     * @param privateLocations
     * @return a copy of privateLocations with any needed locations added
     */
    public static LocationIdentity[] addSnippetCounters(LocationIdentity[] privateLocations) {
        for (LocationIdentity location : privateLocations) {
            if (location.equals(SNIPPET_COUNTER_LOCATION)) {
                return privateLocations;
            }
        }
        LocationIdentity[] result = Arrays.copyOf(privateLocations, privateLocations.length + 1);
        result[result.length - 1] = SnippetCounterNode.SNIPPET_COUNTER_LOCATION;
        return result;
    }

    
We do not want to use the LocationIdentity of the SnippetCounter.value() field, so that the usage in snippets is always possible. If a method accesses the counter via the field and the snippet, the result might not be correct though. /**
     * We do not want to use the {@link LocationIdentity} of the {@link SnippetCounter#value()}
     * field, so that the usage in snippets is always possible. If a method accesses the counter via
     * the field and the snippet, the result might not be correct though.
     */
    public static final LocationIdentity SNIPPET_COUNTER_LOCATION = NamedLocationIdentity.mutable("SnippetCounter");

    static class SnippetCounterSnippets implements Snippets {

        private static final Unsafe UNSAFE = GraalUnsafeAccess.getUnsafe();

        @Fold
        static int countOffset() {
            try {
                return (int) UNSAFE.objectFieldOffset(SnippetCounter.class.getDeclaredField("value"));
            } catch (Exception e) {
                throw new GraalError(e);
            }
        }

        @Snippet
        public static void add(@ConstantParameter SnippetCounter counter, int increment) {
            long loadedValue = ObjectAccess.readLong(counter, countOffset(), SNIPPET_COUNTER_LOCATION);
            ObjectAccess.writeLong(counter, countOffset(), loadedValue + increment, SNIPPET_COUNTER_LOCATION);
        }

        public static class Templates extends AbstractTemplates {

            private final SnippetInfo add = snippet(SnippetCounterSnippets.class, "add", SNIPPET_COUNTER_LOCATION);

            Templates(OptionValues options, Iterable<DebugHandlersFactory> factories, Providers providers, SnippetReflectionProvider snippetReflection, TargetDescription target) {
                super(options, factories, providers, snippetReflection, target);
            }

            public void lower(SnippetCounterNode counter, LoweringTool tool) {
                StructuredGraph graph = counter.graph();
                Arguments args = new Arguments(add, graph.getGuardsStage(), tool.getLoweringStage());
                args.addConst("counter", counter.getCounter());
                args.add("increment", counter.getIncrement());

                template(counter, args).instantiate(providers.getMetaAccess(), counter, DEFAULT_REPLACER, args);
            }
        }
    }
}