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package org.graalvm.compiler.phases.common;

import org.graalvm.compiler.debug.CounterKey;
import org.graalvm.compiler.debug.DebugContext;
import org.graalvm.compiler.graph.Node;
import org.graalvm.compiler.graph.NodeFlood;
import org.graalvm.compiler.nodes.AbstractEndNode;
import org.graalvm.compiler.nodes.GuardNode;
import org.graalvm.compiler.nodes.StructuredGraph;
import org.graalvm.compiler.options.Option;
import org.graalvm.compiler.options.OptionKey;
import org.graalvm.compiler.options.OptionType;
import org.graalvm.compiler.phases.Phase;

public class DeadCodeEliminationPhase extends Phase {

    public static class Options {

        // @formatter:off
        @Option(help = "Disable optional dead code eliminations", type = OptionType.Debug)
        public static final OptionKey<Boolean> ReduceDCE = new OptionKey<>(true);
        // @formatter:on
    }

    private static final CounterKey counterNodesRemoved = DebugContext.counter("NodesRemoved");

    public enum Optionality {
        Optional,
        Required;
    }

    
Creates a dead code elimination phase that will be run irrespective of Options.ReduceDCE.
/** * Creates a dead code elimination phase that will be run irrespective of * {@link Options#ReduceDCE}. */
public DeadCodeEliminationPhase() { this(Optionality.Required); }
Creates a dead code elimination phase that will be run only if it is non-optional or Options.ReduceDCE is false.
/** * Creates a dead code elimination phase that will be run only if it is * {@linkplain Optionality#Required non-optional} or {@link Options#ReduceDCE} is false. */
public DeadCodeEliminationPhase(Optionality optionality) { this.optional = optionality == Optionality.Optional; } private final boolean optional; @Override public void run(StructuredGraph graph) { if (optional && Options.ReduceDCE.getValue(graph.getOptions())) { return; } NodeFlood flood = graph.createNodeFlood(); int totalNodeCount = graph.getNodeCount(); flood.add(graph.start()); iterateSuccessorsAndInputs(flood); boolean changed = false; for (GuardNode guard : graph.getNodes(GuardNode.TYPE)) { if (flood.isMarked(guard.getAnchor().asNode())) { flood.add(guard); changed = true; } } if (changed) { iterateSuccessorsAndInputs(flood); } int totalMarkedCount = flood.getTotalMarkedCount(); if (totalNodeCount == totalMarkedCount) { // All nodes are live => nothing more to do. return; } else { // Some nodes are not marked alive and therefore dead => proceed. assert totalNodeCount > totalMarkedCount; } deleteNodes(flood, graph); } private static void iterateSuccessorsAndInputs(NodeFlood flood) { Node.EdgeVisitor consumer = new Node.EdgeVisitor() { @Override public Node apply(Node n, Node succOrInput) { assert succOrInput.isAlive() : "dead successor or input " + succOrInput + " in " + n; flood.add(succOrInput); return succOrInput; } }; for (Node current : flood) { if (current instanceof AbstractEndNode) { AbstractEndNode end = (AbstractEndNode) current; flood.add(end.merge()); } else { current.applySuccessors(consumer); current.applyInputs(consumer); } } } private static void deleteNodes(NodeFlood flood, StructuredGraph graph) { Node.EdgeVisitor consumer = new Node.EdgeVisitor() { @Override public Node apply(Node n, Node input) { if (input.isAlive() && flood.isMarked(input)) { input.removeUsage(n); } return input; } }; DebugContext debug = graph.getDebug(); for (Node node : graph.getNodes()) { if (!flood.isMarked(node)) { node.markDeleted(); node.applyInputs(consumer); counterNodesRemoved.increment(debug); } } } }