Index: rvm/src/org/jikesrvm/compilers/opt/runtimesupport/VM_OptCompiledMethod.java
===================================================================
--- rvm/src/org/jikesrvm/compilers/opt/runtimesupport/VM_OptCompiledMethod.java	(revision 13976)
+++ rvm/src/org/jikesrvm/compilers/opt/runtimesupport/VM_OptCompiledMethod.java	(working copy)
@@ -253,7 +253,7 @@
 
   @Interruptible
   public void createFinalOSRMap(IR ir) {
-    this._osrMap = new OSR_EncodedOSRMap(ir.MIRInfo.osrVarMap);
+    this._osrMap = OSR_EncodedOSRMap.makeMap(ir.MIRInfo.osrVarMap);
   }
 
   public OSR_EncodedOSRMap getOSRMap() {
Index: rvm/src/org/jikesrvm/osr/OSR_EncodedOSRMap.java
===================================================================
--- rvm/src/org/jikesrvm/osr/OSR_EncodedOSRMap.java	(revision 13976)
+++ rvm/src/org/jikesrvm/osr/OSR_EncodedOSRMap.java	(working copy)
@@ -17,6 +17,7 @@
 import org.jikesrvm.VM;
 import org.jikesrvm.compilers.opt.inlining.CallSiteTree;
 import org.jikesrvm.compilers.opt.ir.Instruction;
+import org.jikesrvm.util.VM_HashMap;
 import org.vmmagic.pragma.Inline;
 import org.vmmagic.unboxed.Offset;
 
@@ -28,15 +29,15 @@
  * all OSR map info for that method.
  */
 
-public class OSR_EncodedOSRMap implements VM_OptGCMapIteratorConstants, OSR_Constants {
+public final class OSR_EncodedOSRMap implements VM_OptGCMapIteratorConstants, OSR_Constants {
 
-  /* osr info entries */
-  private long[] mapEntries;
+  /** osr info entries */
+  private final long[] mapEntries;
 
-  /* the last entry index. */
-  private int lastEntry;
+  /** the last entry index. */
+  private final int lastEntry;
 
-  /* the OSR map */
+  /** the OSR map */
   private int[] osrMaps;
   private int mapSize = 16;
   private int lastIndex = 0;
@@ -68,9 +69,8 @@
     return regnum - FIRST_GCMAP_REG + 1;
   }
 
-  /*
- */
-  public OSR_EncodedOSRMap(OSR_VariableMap varMap) {
+  /** Constructor  */
+  private OSR_EncodedOSRMap(OSR_VariableMap varMap) {
     int entries = varMap.getNumberOfElements();
 
     this.lastEntry = entries - 1;
@@ -80,15 +80,65 @@
       this.osrMaps = new int[mapSize];
       translateMap(varMap.list);
       resizeOsrMaps();
+    } else {
+      this.mapEntries = null;
     }
 
-    /*
-if (VM.TraceOnStackReplacement) {
-  printMap();
-}
-    */
+    //if (VM.TraceOnStackReplacement) {
+    //  printMap();
+    //}
   }
 
+  public int hashCode() {
+    if (osrMaps == null) return -1;
+    int val=0;
+    for (int i=0; i < osrMaps.length; i++) {
+      val ^= osrMaps[i];
+    }
+    return val;
+  }
+
+  public boolean equals(Object obj) {
+    if (!(obj instanceof OSR_EncodedOSRMap)) {
+      return false;
+    }
+    OSR_EncodedOSRMap that = (OSR_EncodedOSRMap)obj;
+    if (lastEntry == that.lastEntry) {
+      if (mapEntries != null && that.mapEntries != null) {
+        if (mapEntries.length != that.mapEntries.length) return false;
+        for (int i=0; i < mapEntries.length; i++) {
+          if (mapEntries[i] != that.mapEntries[i]) return false;
+        }
+      } else {
+        if (mapEntries != null || that.mapEntries != null) return false;
+		}
+		if (osrMaps != null && that.osrMaps != null) {
+        if (osrMaps.length != that.osrMaps.length) return false;
+        for (int i=0; i < osrMaps.length; i++) {
+          if (osrMaps[i] != that.osrMaps[i]) return false;
+        }
+      } else {
+        if (osrMaps != null || that.osrMaps != null) return false;
+      }
+      return true;
+    }
+	 return false;        
+  }
+
+  private static final VM_HashMap<OSR_EncodedOSRMap, OSR_EncodedOSRMap>
+    uniqueMap = new VM_HashMap<OSR_EncodedOSRMap, OSR_EncodedOSRMap>();
+
+  public static OSR_EncodedOSRMap makeMap(OSR_VariableMap varMap) {
+    OSR_EncodedOSRMap encodedMap = new OSR_EncodedOSRMap(varMap);
+    OSR_EncodedOSRMap result = uniqueMap.get(encodedMap);
+    if (result != null) {
+      return result;
+    } else {
+      uniqueMap.put(encodedMap, encodedMap);
+      return encodedMap;
+    }
+  }
+
   /*
    * translates a list of OSR_MapElement to encoding,
    * we can not trust the osrlist is in the increasing order of