--- a/graal/com.oracle.max.graal.compiler/src/com/oracle/max/graal/compiler/GraalOptions.java	Tue Jun 28 15:28:30 2011 +0200
+++ b/graal/com.oracle.max.graal.compiler/src/com/oracle/max/graal/compiler/GraalOptions.java	Tue Jun 28 15:48:05 2011 +0200
@@ -103,6 +103,7 @@
     public static boolean TraceDeadCodeElimination           = ____;
     public static boolean TraceMemoryMaps                    = ____;
     public static boolean TraceReadElimination               = ____;
+    public static boolean TraceGVN                           = ____;
     public static int     TraceBytecodeParserLevel           = 0;
     public static boolean QuietBailout                       = ____;
 
@@ -142,6 +143,7 @@
     public static boolean CommentedAssembly                  = ____;
     public static boolean PrintLIRWithAssembly               = ____;
 
+    public static boolean OptGVN                             = true;
     public static boolean OptCanonicalizer                   = true;
     public static boolean OptLoops                           = true;
 }

--- a/graal/com.oracle.max.graal.compiler/src/com/oracle/max/graal/compiler/graph/IR.java	Tue Jun 28 15:28:30 2011 +0200
+++ b/graal/com.oracle.max.graal.compiler/src/com/oracle/max/graal/compiler/graph/IR.java	Tue Jun 28 15:48:05 2011 +0200
@@ -99,6 +99,10 @@
             new CanonicalizerPhase().apply(graph);
             new DeadCodeEliminationPhase().apply(graph);
         }
+
+        if (GraalOptions.OptGVN) {
+            new GlobalValueNumberingPhase().apply(graph);
+        }
 //
 //        new EscapeAnalysisPhase().apply(graph);
 
@@ -109,6 +113,9 @@
         if (GraalOptions.Lower) {
             new LoweringPhase(compilation.runtime).apply(graph);
             new MemoryPhase().apply(graph);
+            if (GraalOptions.OptGVN) {
+                new GlobalValueNumberingPhase().apply(graph);
+            }
             new ReadEliminationPhase().apply(graph);
         }
 

--- a/graal/com.oracle.max.graal.compiler/src/com/oracle/max/graal/compiler/ir/ReadNode.java	Tue Jun 28 15:28:30 2011 +0200
+++ b/graal/com.oracle.max.graal.compiler/src/com/oracle/max/graal/compiler/ir/ReadNode.java	Tue Jun 28 15:48:05 2011 +0200
@@ -47,6 +47,11 @@
     }
 
     @Override
+    public boolean valueEqual(Node i) {
+        return i instanceof ReadNode;
+    }
+
+    @Override
     public Node copy(Graph into) {
         return new ReadNode(super.kind, null, null, into);
     }

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/graal/com.oracle.max.graal.compiler/src/com/oracle/max/graal/compiler/phases/GlobalValueNumberingPhase.java	Tue Jun 28 15:48:05 2011 +0200
@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2011, 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.max.graal.compiler.phases;
+
+import com.oracle.max.graal.compiler.*;
+import com.oracle.max.graal.compiler.debug.*;
+import com.oracle.max.graal.compiler.ir.*;
+import com.oracle.max.graal.graph.*;
+
+/**
+ * Duplicates every node in the graph to test the implementation of the {@link com.oracle.max.graal.graph.Node#copy()} method in node subclasses.
+ */
+public class GlobalValueNumberingPhase extends Phase {
+
+    @Override
+    protected void run(Graph graph) {
+        NodeBitMap visited = graph.createNodeBitMap();
+        for (Node n : graph.getNodes()) {
+            apply(n, visited);
+        }
+    }
+
+    private void apply(Node n, NodeBitMap visited) {
+        if (n != null && !visited.isMarked(n)) {
+            visited.mark(n);
+            for (Node input : n.inputs()) {
+                apply(input, visited);
+            }
+            Node newNode = n.graph().ideal(n);
+            if (GraalOptions.TraceGVN && newNode != n) {
+                TTY.println("GVN applied and new node is " + newNode);
+            }
+        }
+    }
+}