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The GraalVM compiler and the Graal-truffle optimizer.
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/*
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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.  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.
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package jdk.graal.compiler.virtual.phases.ea;

import static jdk.graal.compiler.core.common.GraalOptions.EscapeAnalysisIterations;
import static jdk.graal.compiler.core.common.GraalOptions.EscapeAnalyzeOnly;

import java.util.Optional;

import org.graalvm.collections.EconomicSet;
import jdk.graal.compiler.debug.DebugCloseable;
import jdk.graal.compiler.graph.Node;
import jdk.graal.compiler.nodes.GraphState;
import jdk.graal.compiler.nodes.GraphState.StageFlag;
import jdk.graal.compiler.nodes.StructuredGraph;
import jdk.graal.compiler.nodes.StructuredGraph.ScheduleResult;
import jdk.graal.compiler.nodes.cfg.ControlFlowGraph;
import jdk.graal.compiler.nodes.spi.CoreProviders;
import jdk.graal.compiler.nodes.spi.VirtualizableAllocation;
import jdk.graal.compiler.nodes.virtual.VirtualInstanceNode;
import jdk.graal.compiler.nodes.virtual.VirtualObjectNode;
import jdk.graal.compiler.options.Option;
import jdk.graal.compiler.options.OptionKey;
import jdk.graal.compiler.options.OptionType;
import jdk.graal.compiler.options.OptionValues;
import jdk.graal.compiler.phases.BasePhase;
import jdk.graal.compiler.phases.common.CanonicalizerPhase;
import jdk.graal.compiler.phases.graph.ReentrantBlockIterator;
import jdk.graal.compiler.phases.schedule.SchedulePhase;

/**
 * Performs Partial Escape analysis on a
 * {@link StructuredGraph}. Partial Escape Analysis on individual branches allows Graal to determine
 * whether an object is accessible (="escapes") outside the allocating method or thread. This
 * information is used to perform scalar replacement of an object allocation. This allows the
 * compiler to replace an allocation with its scalar field values which can then reside in
 * registers. Enabling the removal of memory allocation, field accesses etc.
 *
 * PEA traverses a {@link StructuredGraph} in reverse post order ({@link ReentrantBlockIterator}),
 * i.e., every basic block is visited as soon as all its predecessor blocks have been visited.
 *
 * PEA is built upon the machinery of {@link EffectsPhase} and {@link EffectsClosure}: during
 * traversal it collects a list of {@link EffectList.Effect} that is applied in reverse post order
 * on the graph after analysis. This is necessary, as virtualized allocations can be materialized at
 * a later point in time of the traversal algorithm, which may causes a materialization at an early
 * point in the IR.
 *
 * If PEA traversal encounters a {@link VirtualizableAllocation} it tries to virtualize it, i.e.,
 * enqueue an effect that replaces the allocation with a {@link VirtualInstanceNode}. If the
 * allocation stays virtual until the end of the traversal it can be completely scalar replaced, if
 * it materializes at a later point in the CFG, the phase materializes the allocation as late as
 * possible in the final program. This can often shift allocations inside less frequently executed
 * branches.
 *
 * Details for the algorithm can be found in
 * this thesis.
 */
public class PartialEscapePhase extends EffectsPhase {

    static class Options {
        //@formatter:off
        @Option(help = "", type = OptionType.Debug)
        public static final OptionKey OptEarlyReadElimination = new OptionKey<>(true);
        //@formatter:on
    }

    private final boolean readElimination;
    private final BasePhase cleanupPhase;

    public PartialEscapePhase(boolean iterative, CanonicalizerPhase canonicalizer, OptionValues options) {
        this(iterative, Options.OptEarlyReadElimination.getValue(options), canonicalizer, null, options);
    }

    public PartialEscapePhase(boolean iterative, CanonicalizerPhase canonicalizer, BasePhase cleanupPhase, OptionValues options) {
        this(iterative, Options.OptEarlyReadElimination.getValue(options), canonicalizer, cleanupPhase, options);
    }

    public PartialEscapePhase(boolean iterative, boolean readElimination, CanonicalizerPhase canonicalizer, BasePhase cleanupPhase, OptionValues options) {
        super(iterative ? EscapeAnalysisIterations.getValue(options) : 1, canonicalizer);
        this.readElimination = readElimination;
        this.cleanupPhase = cleanupPhase;
    }

    public PartialEscapePhase(int iterations, boolean readElimination, CanonicalizerPhase canonicalizer, BasePhase cleanupPhase) {
        super(iterations, canonicalizer);
        this.readElimination = readElimination;
        this.cleanupPhase = cleanupPhase;
    }

    public PartialEscapePhase(boolean iterative, boolean readElimination, CanonicalizerPhase canonicalizer, BasePhase cleanupPhase, OptionValues options,
                    SchedulePhase.SchedulingStrategy strategy) {
        super(iterative ? EscapeAnalysisIterations.getValue(options) : 1, canonicalizer, false, strategy);
        this.readElimination = readElimination;
        this.cleanupPhase = cleanupPhase;
    }

    @Override
    protected void postIteration(StructuredGraph graph, CoreProviders context, EconomicSet changedNodes) {
        super.postIteration(graph, context, changedNodes);
        if (cleanupPhase != null) {
            cleanupPhase.apply(graph, context);
        }
    }

    @Override
    public Optional notApplicableTo(GraphState graphState) {
        return NotApplicable.ifAny(
                        super.notApplicableTo(graphState),
                        NotApplicable.unlessRunBefore(this, StageFlag.HIGH_TIER_LOWERING, graphState),
                        cleanupPhase != null ? cleanupPhase.notApplicableTo(graphState) : ALWAYS_APPLICABLE);
    }

    @Override
    @SuppressWarnings("try")
    protected void run(StructuredGraph graph, CoreProviders context) {
        if (VirtualUtil.matches(graph, EscapeAnalyzeOnly.getValue(graph.getOptions()))) {
            if (readElimination || graph.hasVirtualizableAllocation()) {
                try (DebugCloseable ignored = graph.getOptimizationLog().enterPartialEscapeAnalysis()) {
                    runAnalysis(graph, context);
                }
            }
        }
    }

    @Override
    protected Closure createEffectsClosure(CoreProviders context, ScheduleResult schedule, ControlFlowGraph cfg, OptionValues options) {
        for (VirtualObjectNode virtual : cfg.graph.getNodes(VirtualObjectNode.TYPE)) {
            virtual.resetObjectId();
        }
        assert schedule != null;
        if (readElimination) {
            return new PEReadEliminationClosure(schedule, context);
        } else {
            return new PartialEscapeClosure.Final(schedule, context);
        }
    }

    @Override
    public boolean checkContract() {
        return false;
    }
}