1 /*
   2  * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  */
  23 package org.graalvm.compiler.graph;
  24 
  25 /**
  26  * An entity that depends upon {@linkplain Graph#maybeCompress() stable} node identifiers.
  27  */
  28 class NodeIdAccessor {
  29     final Graph graph;
  30     final int epoch;
  31 
  32     NodeIdAccessor(Graph graph) {
  33         this.graph = graph;
  34         this.epoch = graph.compressions;
  35     }
  36 
  37     Graph getGraph() {
  38         return graph;
  39     }
  40 
  41     /**
  42      * Verifies that node identifiers have not changed since this object was created.
  43      *
  44      * @return true if the check succeeds
  45      * @throws VerificationError if the check fails
  46      */
  47     boolean verifyIdsAreStable() {
  48         int compressions = graph.compressions - epoch;
  49         if (compressions != 0) {
  50             throw new VerificationError("accessing node id in %s across %d graph compression%s", graph, compressions, compressions == 1 ? "" : "s");
  51         }
  52         return true;
  53     }
  54 
  55     /**
  56      * Gets the identifier for a node. If assertions are enabled, this method asserts that the
  57      * identifier is stable.
  58      */
  59     int getNodeId(Node node) {
  60         assert verifyIdsAreStable();
  61         return node.id();
  62     }
  63 }