--- a/graal/com.oracle.truffle.sl/src/com/oracle/truffle/sl/nodes/WriteLocalNode.java	Sun Dec 15 23:32:41 2013 +0100
+++ b/graal/com.oracle.truffle.sl/src/com/oracle/truffle/sl/nodes/WriteLocalNode.java	Tue Dec 17 15:44:02 2013 +0100
@@ -22,6 +22,7 @@
  */
 package com.oracle.truffle.sl.nodes;
 
+import com.oracle.truffle.api.*;
 import com.oracle.truffle.api.dsl.*;
 import com.oracle.truffle.api.frame.*;
 
@@ -36,22 +37,51 @@
         this(node.slot);
     }
 
-    @Specialization
+    @Specialization(guards = "isIntKind")
     public int write(VirtualFrame frame, int right) {
         frame.setInt(slot, right);
         return right;
     }
 
-    @Specialization
+    @Specialization(guards = "isBooleanKind")
     public boolean write(VirtualFrame frame, boolean right) {
         frame.setBoolean(slot, right);
         return right;
     }
 
-    @Specialization
+    @Specialization(guards = "isObjectKind")
     public Object writeGeneric(VirtualFrame frame, Object right) {
         frame.setObject(slot, right);
         return right;
     }
 
+    protected final boolean isIntKind() {
+        return isKind(FrameSlotKind.Int);
+    }
+
+    protected final boolean isBooleanKind() {
+        return isKind(FrameSlotKind.Boolean);
+    }
+
+    protected final boolean isObjectKind() {
+        if (slot.getKind() != FrameSlotKind.Object) {
+            CompilerDirectives.transferToInterpreter();
+            slot.setKind(FrameSlotKind.Object);
+        }
+        return true;
+    }
+
+    private boolean isKind(FrameSlotKind kind) {
+        return slot.getKind() == kind || initialSetKind(kind);
+    }
+
+    private boolean initialSetKind(FrameSlotKind kind) {
+        if (slot.getKind() == FrameSlotKind.Illegal) {
+            CompilerDirectives.transferToInterpreter();
+            slot.setKind(kind);
+            return true;
+        }
+        return false;
+    }
+
 }