--- a/graal/com.oracle.graal.graph/src/com/oracle/graal/graph/Graph.java	Wed Sep 04 10:40:56 2013 +0200
+++ b/graal/com.oracle.graal.graph/src/com/oracle/graal/graph/Graph.java	Wed Sep 04 13:21:30 2013 +0200
@@ -40,6 +40,11 @@
 
     private final ArrayList<Node> nodes;
 
+    /**
+     * Records the modification count for nodes. This is only used in assertions.
+     */
+    private int[] nodeModCounts;
+
     // these two arrays contain one entry for each NodeClass, indexed by NodeClass.iterableId.
     // they contain the first and last pointer to a linked list of all nodes with this type.
     private final ArrayList<Node> nodeCacheFirst;
@@ -87,6 +92,18 @@
         this(null);
     }
 
+    static final boolean MODIFICATION_COUNTS_ENABLED = assertionsEnabled();
+
+    /**
+     * Determines if assertions are enabled for the {@link Graph} class.
+     */
+    @SuppressWarnings("all")
+    private static boolean assertionsEnabled() {
+        boolean enabled = false;
+        assert enabled = true;
+        return enabled;
+    }
+
     /**
      * Creates an empty Graph with a given name.
      * 
@@ -97,6 +114,27 @@
         nodeCacheFirst = new ArrayList<>(NodeClass.cacheSize());
         nodeCacheLast = new ArrayList<>(NodeClass.cacheSize());
         this.name = name;
+        if (MODIFICATION_COUNTS_ENABLED) {
+            nodeModCounts = new int[nodes.size()];
+        }
+    }
+
+    int modCount(Node node) {
+        if (node.id >= 0 && node.id < nodeModCounts.length) {
+            return nodeModCounts[node.id];
+        }
+        return 0;
+    }
+
+    void incModCount(Node node) {
+        if (node.id >= 0) {
+            if (node.id >= nodeModCounts.length) {
+                nodeModCounts = Arrays.copyOf(nodeModCounts, node.id + 30);
+            }
+            nodeModCounts[node.id]++;
+        } else {
+            assert false;
+        }
     }
 
     /**

--- a/graal/com.oracle.graal.graph/src/com/oracle/graal/graph/Node.java	Wed Sep 04 10:40:56 2013 +0200
+++ b/graal/com.oracle.graal.graph/src/com/oracle/graal/graph/Node.java	Wed Sep 04 13:21:30 2013 +0200
@@ -22,6 +22,8 @@
  */
 package com.oracle.graal.graph;
 
+import static com.oracle.graal.graph.Graph.*;
+
 import java.lang.annotation.*;
 import java.util.*;
 
@@ -121,7 +123,6 @@
 
     private NodeUsagesList usages;
     private Node predecessor;
-    private int modCount;
 
     public Node() {
         this.graph = null;
@@ -165,11 +166,16 @@
     }
 
     final int modCount() {
-        return modCount;
+        if (MODIFICATION_COUNTS_ENABLED && graph != null) {
+            return graph.modCount(this);
+        }
+        return 0;
     }
 
     final void incModCount() {
-        modCount++;
+        if (MODIFICATION_COUNTS_ENABLED && graph != null) {
+            graph.incModCount(this);
+        }
     }
 
     public boolean isDeleted() {
@@ -375,7 +381,6 @@
         into.register(newNode);
         newNode.usages = new NodeUsagesList();
         newNode.predecessor = null;
-        newNode.modCount = 0;
         return newNode;
     }
 

--- a/graal/com.oracle.graal.graph/src/com/oracle/graal/graph/NodeClass.java	Wed Sep 04 10:40:56 2013 +0200
+++ b/graal/com.oracle.graal.graph/src/com/oracle/graal/graph/NodeClass.java	Wed Sep 04 13:21:30 2013 +0200
@@ -22,6 +22,8 @@
  */
 package com.oracle.graal.graph;
 
+import static com.oracle.graal.graph.Graph.*;
+
 import java.lang.reflect.*;
 import java.util.*;
 import java.util.Map.Entry;
@@ -432,7 +434,7 @@
          */
         private NodeClassIterator(Node node, long[] offsets, int directCount) {
             this.node = node;
-            this.modCount = node.modCount();
+            this.modCount = MODIFICATION_COUNTS_ENABLED ? node.modCount() : 0;
             this.offsets = offsets;
             this.directCount = directCount;
             index = NOT_ITERABLE;