001/*
002 * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
003 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004 *
005 * This code is free software; you can redistribute it and/or modify it
006 * under the terms of the GNU General Public License version 2 only, as
007 * published by the Free Software Foundation.
008 *
009 * This code is distributed in the hope that it will be useful, but WITHOUT
010 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
011 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
012 * version 2 for more details (a copy is included in the LICENSE file that
013 * accompanied this code).
014 *
015 * You should have received a copy of the GNU General Public License version
016 * 2 along with this work; if not, write to the Free Software Foundation,
017 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
018 *
019 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
020 * or visit www.oracle.com if you need additional information or have any
021 * questions.
022 */
023package com.oracle.graal.graph;
024
025/**
026 * An entity that depends upon {@linkplain Graph#maybeCompress() stable} node identifiers.
027 */
028class NodeIdAccessor {
029    final Graph graph;
030    final int epoch;
031
032    public NodeIdAccessor(Graph graph) {
033        this.graph = graph;
034        this.epoch = graph.compressions;
035    }
036
037    Graph getGraph() {
038        return graph;
039    }
040
041    /**
042     * Verifies that node identifiers have not changed since this object was created.
043     *
044     * @return true if the check succeeds
045     * @throws VerificationError if the check fails
046     */
047    public boolean verifyIdsAreStable() {
048        int compressions = graph.compressions - epoch;
049        if (compressions != 0) {
050            throw new VerificationError("accessing node id in %s across %d graph compression%s", graph, compressions, compressions == 1 ? "" : "s");
051        }
052        return true;
053    }
054
055    /**
056     * Gets the identifier for a node. If assertions are enabled, this method asserts that the
057     * identifier is stable.
058     */
059    public int getNodeId(Node node) {
060        assert verifyIdsAreStable();
061        return node.id();
062    }
063}