--- a/truffle/com.oracle.truffle.api/src/com/oracle/truffle/api/nodes/NodeClass.java	Wed Nov 04 20:31:27 2015 -0800
+++ b/truffle/com.oracle.truffle.api/src/com/oracle/truffle/api/nodes/NodeClass.java	Wed Nov 04 20:33:11 2015 -0800
@@ -53,6 +53,8 @@
         }
     };
 
+    private static final NodeFieldAccessor[] EMPTY_NODE_FIELD_ARRAY = new NodeFieldAccessor[0];
+
     // The comprehensive list of all fields.
     private final NodeFieldAccessor[] fields;
     // Separate arrays for the frequently accessed fields.
@@ -68,11 +70,11 @@
         return nodeClasses.get(clazz);
     }
 
-    public static NodeClass get(Node clazz) {
-        return clazz.getNodeClass();
+    public static NodeClass get(Node node) {
+        return node.getNodeClass();
     }
 
-    public NodeClass(Class<? extends Node> clazz) {
+    NodeClass(Class<? extends Node> clazz) {
         List<NodeFieldAccessor> fieldsList = new ArrayList<>();
         NodeFieldAccessor parentFieldTmp = null;
         NodeFieldAccessor nodeClassFieldTmp = null;
@@ -115,12 +117,12 @@
             throw new AssertionError("parent field not found");
         }
 
-        this.fields = fieldsList.toArray(new NodeFieldAccessor[fieldsList.size()]);
+        this.fields = fieldsList.toArray(EMPTY_NODE_FIELD_ARRAY);
         this.nodeClassField = nodeClassFieldTmp;
         this.parentField = parentFieldTmp;
-        this.childFields = childFieldList.toArray(new NodeFieldAccessor[childFieldList.size()]);
-        this.childrenFields = childrenFieldList.toArray(new NodeFieldAccessor[childrenFieldList.size()]);
-        this.cloneableFields = cloneableFieldList.toArray(new NodeFieldAccessor[cloneableFieldList.size()]);
+        this.childFields = childFieldList.toArray(EMPTY_NODE_FIELD_ARRAY);
+        this.childrenFields = childrenFieldList.toArray(EMPTY_NODE_FIELD_ARRAY);
+        this.cloneableFields = cloneableFieldList.toArray(EMPTY_NODE_FIELD_ARRAY);
         this.clazz = clazz;
     }
 

--- a/truffle/com.oracle.truffle.api/src/com/oracle/truffle/api/utilities/CyclicAssumption.java	Wed Nov 04 20:31:27 2015 -0800
+++ b/truffle/com.oracle.truffle.api/src/com/oracle/truffle/api/utilities/CyclicAssumption.java	Wed Nov 04 20:33:11 2015 -0800
@@ -24,10 +24,11 @@
  */
 package com.oracle.truffle.api.utilities;
 
+import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
+
 import com.oracle.truffle.api.Assumption;
 import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.api.Truffle;
-import java.util.concurrent.atomic.AtomicReference;
 
 /**
  * Holds an {@link Assumption}, and knows how to recreate it with the same properties on
@@ -39,22 +40,24 @@
 public class CyclicAssumption {
 
     private final String name;
-    private final AtomicReference<Assumption> assumption;
+    private volatile Assumption assumption;
+
+    private static final AtomicReferenceFieldUpdater<CyclicAssumption, Assumption> ASSUMPTION_UPDATER = AtomicReferenceFieldUpdater.newUpdater(CyclicAssumption.class, Assumption.class, "assumption");
 
     public CyclicAssumption(String name) {
         this.name = name;
-        this.assumption = new AtomicReference<>(Truffle.getRuntime().createAssumption(name));
+        this.assumption = Truffle.getRuntime().createAssumption(name);
     }
 
     @TruffleBoundary
     public void invalidate() {
         Assumption newAssumption = Truffle.getRuntime().createAssumption(name);
-        Assumption oldAssumption = assumption.getAndSet(newAssumption);
+        Assumption oldAssumption = ASSUMPTION_UPDATER.getAndSet(this, newAssumption);
         oldAssumption.invalidate();
     }
 
     public Assumption getAssumption() {
-        return assumption.get();
+        return assumption;
     }
 
 }