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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.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package org.graalvm.compiler.phases.graph;

import java.util.ArrayDeque;
import java.util.Deque;

import org.graalvm.compiler.graph.Node;
import org.graalvm.compiler.graph.NodeBitMap;
import org.graalvm.compiler.nodes.AbstractBeginNode;
import org.graalvm.compiler.nodes.AbstractMergeNode;
import org.graalvm.compiler.nodes.ControlSinkNode;
import org.graalvm.compiler.nodes.ControlSplitNode;
import org.graalvm.compiler.nodes.EndNode;
import org.graalvm.compiler.nodes.FixedNode;
import org.graalvm.compiler.nodes.FixedWithNextNode;
import org.graalvm.compiler.nodes.LoopBeginNode;
import org.graalvm.compiler.nodes.LoopEndNode;

This iterator implements a reverse post order iteration over the fixed nodes in the graph,
starting at the given fixed node.
No changes to the fixed nodes are expected during the iteration, they cause undefined behavior.
/**
 * This iterator implements a reverse post order iteration over the fixed nodes in the graph,
 * starting at the given fixed node.
 *
 * No changes to the fixed nodes are expected during the iteration, they cause undefined behavior.
 */
public abstract class StatelessPostOrderNodeIterator {

    private final NodeBitMap visitedEnds;
    private final Deque<AbstractBeginNode> nodeQueue;
    private final FixedNode start;

    public StatelessPostOrderNodeIterator(FixedNode start) {
        visitedEnds = start.graph().createNodeBitMap();
        nodeQueue = new ArrayDeque<>();
        this.start = start;
    }

    public void apply() {
        FixedNode current = start;

        do {
            if (current instanceof LoopBeginNode) {
                loopBegin((LoopBeginNode) current);
                current = ((LoopBeginNode) current).next();
                assert current != null;
            } else if (current instanceof LoopEndNode) {
                loopEnd((LoopEndNode) current);
                assert !visitedEnds.isMarked(current);
                visitedEnds.mark(current);
                current = nodeQueue.pollFirst();
            } else if (current instanceof AbstractMergeNode) {
                merge((AbstractMergeNode) current);
                current = ((AbstractMergeNode) current).next();
                assert current != null;
            } else if (current instanceof FixedWithNextNode) {
                node(current);
                current = ((FixedWithNextNode) current).next();
            } else if (current instanceof EndNode) {
                end((EndNode) current);
                queueMerge((EndNode) current);
                current = nodeQueue.pollFirst();
            } else if (current instanceof ControlSinkNode) {
                node(current);
                current = nodeQueue.pollFirst();
            } else if (current instanceof ControlSplitNode) {
                controlSplit((ControlSplitNode) current);
                for (Node node : current.successors()) {
                    nodeQueue.addFirst((AbstractBeginNode) node);
                }
                current = nodeQueue.pollFirst();
            } else {
                assert false : current;
            }
        } while (current != null);
        finished();
    }

    private void queueMerge(EndNode end) {
        assert !visitedEnds.isMarked(end);
        visitedEnds.mark(end);
        AbstractMergeNode merge = end.merge();
        boolean endsVisited = true;
        for (int i = 0; i < merge.forwardEndCount(); i++) {
            if (!visitedEnds.isMarked(merge.forwardEndAt(i))) {
                endsVisited = false;
                break;
            }
        }
        if (endsVisited) {
            nodeQueue.add(merge);
        }
    }

    protected void node(@SuppressWarnings("unused") FixedNode node) {
        // empty default implementation
    }

    protected void end(EndNode endNode) {
        node(endNode);
    }

    protected void merge(AbstractMergeNode merge) {
        node(merge);
    }

    protected void loopBegin(LoopBeginNode loopBegin) {
        node(loopBegin);
    }

    protected void loopEnd(LoopEndNode loopEnd) {
        node(loopEnd);
    }

    protected void controlSplit(ControlSplitNode controlSplit) {
        node(controlSplit);
    }

    protected void finished() {
        // nothing to do
    }
}