--- /dev/null	2016-05-31 09:42:47.975716356 -0700
+++ new/src/jdk.vm.compiler/share/classes/org.graalvm.compiler.graph/src/org/graalvm/compiler/graph/NodeIdAccessor.java	2016-12-09 00:48:26.716553586 -0800
@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
+ * 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
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package org.graalvm.compiler.graph;
+
+/**
+ * An entity that depends upon {@linkplain Graph#maybeCompress() stable} node identifiers.
+ */
+class NodeIdAccessor {
+    final Graph graph;
+    final int epoch;
+
+    NodeIdAccessor(Graph graph) {
+        this.graph = graph;
+        this.epoch = graph.compressions;
+    }
+
+    Graph getGraph() {
+        return graph;
+    }
+
+    /**
+     * Verifies that node identifiers have not changed since this object was created.
+     *
+     * @return true if the check succeeds
+     * @throws VerificationError if the check fails
+     */
+    boolean verifyIdsAreStable() {
+        int compressions = graph.compressions - epoch;
+        if (compressions != 0) {
+            throw new VerificationError("accessing node id in %s across %d graph compression%s", graph, compressions, compressions == 1 ? "" : "s");
+        }
+        return true;
+    }
+
+    /**
+     * Gets the identifier for a node. If assertions are enabled, this method asserts that the
+     * identifier is stable.
+     */
+    int getNodeId(Node node) {
+        assert verifyIdsAreStable();
+        return node.id();
+    }
+}