--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/truffle/com.oracle.truffle.api/src/com/oracle/truffle/api/utilities/AssumedValue.java	Wed Jun 17 10:58:08 2015 +0200
@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2013, 2014, 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.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * 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 com.oracle.truffle.api.utilities;
+
+import com.oracle.truffle.api.*;
+import com.oracle.truffle.api.CompilerDirectives.CompilationFinal;
+import com.oracle.truffle.api.nodes.*;
+
+/**
+ * A value that the compiler can assume is constant, but can be changed by invalidation.
+ * <p>
+ * Compiled code that uses the value will be invalidated each time the value changes, so you should
+ * take care to only change values infrequently, or to monitor the number of times the value has
+ * changed and at some point to replace the value with something more generic so that it does not
+ * have to be changed and code does not have to keep being recompiled.
+ */
+public class AssumedValue<T> {
+
+    private final String name;
+
+    @CompilationFinal private T value;
+    @CompilationFinal private Assumption assumption;
+
+    public AssumedValue(T initialValue) {
+        this(null, initialValue);
+    }
+
+    public AssumedValue(String name, T initialValue) {
+        this.name = name;
+        value = initialValue;
+        assumption = Truffle.getRuntime().createAssumption(name);
+    }
+
+    /**
+     * Get the current value, updating it if it has been {@link #set}. The compiler may be able to
+     * make this method return a constant value, but still accommodate mutation.
+     */
+    public T get() {
+        try {
+            assumption.check();
+        } catch (InvalidAssumptionException e) {
+            // No need to rewrite anything - just pick up the new values
+        }
+
+        return value;
+    }
+
+    /**
+     * Set a new value, which will be picked up the next time {@link #get} is called.
+     */
+    public void set(T newValue) {
+        CompilerDirectives.transferToInterpreter();
+
+        value = newValue;
+        final Assumption oldAssumption = assumption;
+        assumption = Truffle.getRuntime().createAssumption(name);
+        oldAssumption.invalidate();
+    }
+
+}