--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/graal/com.oracle.graal.options.test/src/com/oracle/graal/options/test/TestOptionValue.java	Tue Nov 05 12:48:21 2013 +0100
@@ -0,0 +1,102 @@
+/*
+ * 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 com.oracle.graal.options.test;
+
+import static com.oracle.graal.options.test.TestOptionValue.Options.*;
+import static org.junit.Assert.*;
+
+import org.junit.*;
+
+import com.oracle.graal.options.*;
+import com.oracle.graal.options.OptionValue.OverrideScope;
+
+public class TestOptionValue {
+
+    public static class Options {
+        public static final OptionValue<Boolean> Stable = new StableOptionValue<>(true);
+        public static final OptionValue<String> Mutable = new OptionValue<>("original");
+        public static final OptionValue<String> SecondMutable = new OptionValue<>("second");
+    }
+
+    static final OptionDescriptor stable = new OptionDescriptor("Stable", Boolean.class, "", Options.class, "Stable", Stable);
+    static final OptionDescriptor mutable = new OptionDescriptor("Mutable", String.class, "", Options.class, "Mutable", Mutable);
+    static final OptionDescriptor secondMutable = new OptionDescriptor("SecondMutable", String.class, "", Options.class, "SecondMutable", SecondMutable);
+
+    @Test
+    public void testMutable() {
+        assertEquals("original", Mutable.getValue());
+        try (OverrideScope s1 = OptionValue.override(Mutable, "override1")) {
+            assertEquals("override1", Mutable.getValue());
+            try (OverrideScope s2 = OptionValue.override(Mutable, "override2")) {
+                assertEquals("override2", Mutable.getValue());
+            }
+            assertEquals("override1", Mutable.getValue());
+            try (OverrideScope s3 = OptionValue.override(Mutable, "override3")) {
+                assertEquals("override3", Mutable.getValue());
+            }
+            assertEquals("override1", Mutable.getValue());
+        }
+        assertEquals("original", Mutable.getValue());
+        try (OverrideScope s1 = OptionValue.override(Mutable, "original")) {
+            assertEquals("original", Mutable.getValue());
+        }
+    }
+
+    @Test
+    public void testMultiple() {
+        assertEquals("original", Mutable.getValue());
+        assertEquals("second", SecondMutable.getValue());
+        try (OverrideScope s1 = OptionValue.override(Mutable, "override1", SecondMutable, "secondOverride1")) {
+            assertEquals("override1", Mutable.getValue());
+            assertEquals("secondOverride1", SecondMutable.getValue());
+            try (OverrideScope s2 = OptionValue.override(Mutable, "override2", SecondMutable, "secondOverride2")) {
+                assertEquals("override2", Mutable.getValue());
+                assertEquals("secondOverride2", SecondMutable.getValue());
+            }
+            assertEquals("override1", Mutable.getValue());
+            assertEquals("secondOverride1", SecondMutable.getValue());
+            try (OverrideScope s3 = OptionValue.override(Mutable, "override3", SecondMutable, "secondOverride3")) {
+                assertEquals("override3", Mutable.getValue());
+                assertEquals("secondOverride3", SecondMutable.getValue());
+            }
+            assertEquals("override1", Mutable.getValue());
+            assertEquals("secondOverride1", SecondMutable.getValue());
+        }
+        assertEquals("original", Mutable.getValue());
+        assertEquals("second", SecondMutable.getValue());
+        try (OverrideScope s1 = OptionValue.override(Mutable, "original", SecondMutable, "second")) {
+            assertEquals("original", Mutable.getValue());
+            assertEquals("second", SecondMutable.getValue());
+        }
+    }
+
+    @Test
+    public void testStable() {
+        assertTrue(Stable.getValue());
+        try (OverrideScope s = OptionValue.override(Stable, false)) {
+            fail("cannot override stable option");
+        } catch (IllegalArgumentException e) {
+            // expected
+        }
+    }
+}

--- a/graal/com.oracle.graal.options/src/com/oracle/graal/options/OptionValue.java	Tue Nov 05 11:14:42 2013 +0100
+++ b/graal/com.oracle.graal.options/src/com/oracle/graal/options/OptionValue.java	Tue Nov 05 12:48:21 2013 +0100
@@ -22,12 +22,114 @@
  */
 package com.oracle.graal.options;
 
+import java.util.*;
+import java.util.Map.Entry;
+
 /**
  * An option value.
  */
 public class OptionValue<T> {
 
     /**
+     * Temporarily changes the value for an option. The {@linkplain OptionValue#getValue() value} of
+     * {@code option} is set to {@code value} until {@link OverrideScope#close()} is called on the
+     * object returned by this method.
+     * <p>
+     * Since the returned object is {@link AutoCloseable} the try-with-resource construct can be
+     * used:
+     * 
+     * <pre>
+     * try (OverrideScope s = OptionValue.override(myOption, myValue) {
+     *     // code that depends on myOption == myValue
+     * }
+     * </pre>
+     */
+    public static OverrideScope override(OptionValue<?> option, Object value) {
+        OverrideScope current = overrideScopes.get();
+        if (current == null) {
+            if (!value.equals(option.getValue())) {
+                return new SingleOverrideScope(option, value);
+            }
+            Map<OptionValue<?>, Object> overrides = Collections.emptyMap();
+            return new MultipleOverridesScope(current, overrides);
+        }
+        return new MultipleOverridesScope(current, option, value);
+    }
+
+    /**
+     * Temporarily changes the values for a set of options. The {@linkplain OptionValue#getValue()
+     * value} of each {@code option} in {@code overrides} is set to the corresponding {@code value}
+     * in {@code overrides} until {@link OverrideScope#close()} is called on the object returned by
+     * this method.
+     * <p>
+     * Since the returned object is {@link AutoCloseable} the try-with-resource construct can be
+     * used:
+     * 
+     * <pre>
+     * Map<OptionValue, Object> overrides = new HashMap<>();
+     * overrides.put(myOption1, myValue1);
+     * overrides.put(myOption2, myValue2);
+     * try (OverrideScope s = OptionValue.override(overrides) {
+     *     // code that depends on myOption == myValue
+     * }
+     * </pre>
+     */
+    public static OverrideScope override(Map<OptionValue<?>, Object> overrides) {
+        OverrideScope current = overrideScopes.get();
+        if (current == null && overrides.size() == 1) {
+            Entry<OptionValue<?>, Object> single = overrides.entrySet().iterator().next();
+            OptionValue<?> option = single.getKey();
+            Object overrideValue = single.getValue();
+            if (!overrideValue.equals(option.getValue())) {
+                return new SingleOverrideScope(option, overrideValue);
+            }
+        }
+        return new MultipleOverridesScope(current, overrides);
+    }
+
+    /**
+     * Temporarily changes the values for a set of options. The {@linkplain OptionValue#getValue()
+     * value} of each {@code option} in {@code overrides} is set to the corresponding {@code value}
+     * in {@code overrides} until {@link OverrideScope#close()} is called on the object returned by
+     * this method.
+     * <p>
+     * Since the returned object is {@link AutoCloseable} the try-with-resource construct can be
+     * used:
+     * 
+     * <pre>
+     * try (OverrideScope s = OptionValue.override(myOption1, myValue1, myOption2, myValue2) {
+     *     // code that depends on myOption == myValue
+     * }
+     * </pre>
+     * 
+     * @param overrides overrides in the form {@code [option1, override1, option2, override2, ...]}
+     */
+    public static OverrideScope override(Object... overrides) {
+        OverrideScope current = overrideScopes.get();
+        if (current == null && overrides.length == 2) {
+            OptionValue<?> option = (OptionValue<?>) overrides[0];
+            Object overrideValue = overrides[1];
+            if (!overrideValue.equals(option.getValue())) {
+                return new SingleOverrideScope(option, overrideValue);
+            }
+        }
+        Map<OptionValue<?>, Object> map = Collections.emptyMap();
+        for (int i = 0; i < overrides.length; i += 2) {
+            OptionValue<?> option = (OptionValue<?>) overrides[i];
+            Object overrideValue = overrides[i + 1];
+            if (!overrideValue.equals(option.getValue())) {
+                if (map.isEmpty()) {
+                    map = new HashMap<>();
+                }
+                map.put(option, overrideValue);
+            }
+        }
+        return new MultipleOverridesScope(current, map);
+    }
+
+    private static ThreadLocal<OverrideScope> overrideScopes = new ThreadLocal<>();
+
+    /**
      * The raw option value.
      */
     protected T value;
@@ -80,6 +182,13 @@
      * Gets the value of this option.
      */
     public T getValue() {
+        OverrideScope overrideScope = overrideScopes.get();
+        if (overrideScope != null) {
+            T override = overrideScope.getOverride(this);
+            if (override != null) {
+                return override;
+            }
+        }
         if (value == UNINITIALIZED) {
             value = initialValue();
         }
@@ -93,4 +202,117 @@
     public void setValue(Object v) {
         this.value = (T) v;
     }
+
+    /**
+     * An object whose {@link #close()} method reverts the option value overriding initiated by
+     * {@link OptionValue#override(OptionValue, Object)} or {@link OptionValue#override(Map)}.
+     */
+    public abstract static class OverrideScope implements AutoCloseable {
+        abstract void addToInherited(Map<OptionValue, Object> inherited);
+
+        abstract <T> T getOverride(OptionValue<T> option);
+
+        public abstract void close();
+    }
+
+    static class SingleOverrideScope extends OverrideScope {
+
+        private final OptionValue<?> option;
+        private final Object value;
+
+        public SingleOverrideScope(OptionValue<?> option, Object value) {
+            if (option instanceof StableOptionValue) {
+                throw new IllegalArgumentException("Cannot override stable option " + option);
+            }
+            this.option = option;
+            this.value = value;
+            overrideScopes.set(this);
+        }
+
+        @Override
+        void addToInherited(Map<OptionValue, Object> inherited) {
+            inherited.put(option, value);
+        }
+
+        @SuppressWarnings("unchecked")
+        @Override
+        <T> T getOverride(OptionValue<T> key) {
+            if (key == this.option) {
+                return (T) value;
+            }
+            return null;
+        }
+
+        @Override
+        public void close() {
+            overrideScopes.set(null);
+        }
+    }
+
+    static class MultipleOverridesScope extends OverrideScope {
+        final OverrideScope parent;
+        final Map<OptionValue, Object> overrides;
+
+        public MultipleOverridesScope(OverrideScope parent, OptionValue<?> option, Object value) {
+            this.parent = parent;
+            this.overrides = new HashMap<>();
+            if (parent != null) {
+                parent.addToInherited(overrides);
+            }
+            if (option instanceof StableOptionValue) {
+                throw new IllegalArgumentException("Cannot override stable option " + option);
+            }
+            if (!value.equals(option.getValue())) {
+                this.overrides.put(option, value);
+            }
+            if (!overrides.isEmpty()) {
+                overrideScopes.set(this);
+            }
+        }
+
+        MultipleOverridesScope(OverrideScope parent, Map<OptionValue<?>, Object> overrides) {
+            this.parent = parent;
+            if (overrides.isEmpty() && parent == null) {
+                this.overrides = Collections.emptyMap();
+                return;
+            }
+            this.overrides = new HashMap<>();
+            if (parent != null) {
+                parent.addToInherited(this.overrides);
+            }
+            for (Map.Entry<OptionValue<?>, Object> e : overrides.entrySet()) {
+                OptionValue<?> option = e.getKey();
+                if (option instanceof StableOptionValue) {
+                    throw new IllegalArgumentException("Cannot override stable option " + option);
+                }
+                if (!e.getValue().equals(option.getValue())) {
+                    this.overrides.put(option, e.getValue());
+                }
+            }
+            if (!this.overrides.isEmpty()) {
+                overrideScopes.set(this);
+            }
+        }
+
+        @Override
+        void addToInherited(Map<OptionValue, Object> inherited) {
+            if (parent != null) {
+                parent.addToInherited(inherited);
+            }
+            inherited.putAll(overrides);
+        }
+
+        @SuppressWarnings("unchecked")
+        @Override
+        <T> T getOverride(OptionValue<T> option) {
+            return (T) overrides.get(option);
+        }
+
+        @Override
+        public void close() {
+            if (!overrides.isEmpty()) {
+                overrideScopes.set(parent);
+            }
+        }
+    }
 }

--- a/mx/projects	Tue Nov 05 11:14:42 2013 +0100
+++ b/mx/projects	Tue Nov 05 12:48:21 2013 +0100
@@ -200,6 +200,14 @@
 project@com.oracle.graal.options@annotationProcessorForDependents=true
 project@com.oracle.graal.options@workingSets=Graal,Codegen
 
+# graal.options.test
+project@com.oracle.graal.options.test@subDir=graal
+project@com.oracle.graal.options.test@sourceDirs=src
+project@com.oracle.graal.options.test@dependencies=com.oracle.graal.options,JUNIT
+project@com.oracle.graal.options.test@checkstyle=com.oracle.graal.graph
+project@com.oracle.graal.options.test@javaCompliance=1.7
+project@com.oracle.graal.options.test@workingSets=Graal
+
 # graal.graph
 project@com.oracle.graal.graph@subDir=graal
 project@com.oracle.graal.graph@sourceDirs=src