Only remove the code object that caused the monomorphic prototype...

src/objects.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2409 matching lines @@
     }
     if (name->Equals(String::cast(key))) {
       Code* code = Code::cast(cache->get(i + 1));
       if (code->flags() == flags) return code;
     }
   }
   return Heap::undefined_value();
 }
 
 
-bool Map::IncludedInCodeCache(Code* code) {
+int Map::IndexInCodeCache(Code* code) {
   FixedArray* array = code_cache();
   int len = array->length();
   for (int i = 0; i < len; i += 2) {
-    if (array->get(i+1) == code) return true;
+    if (array->get(i + 1) == code) return i + 1;
   }
-  return false;
+  return -1;
+}
+
+
+void Map::RemoveFromCodeCache(int index) {
+  FixedArray* array = code_cache();
+  ASSERT(array->length() >= index && array->get(index)->IsCode());
+  array->set_undefined(index - 1);  // key
+  array->set_undefined(index);  // code
 }
 
 
 void FixedArray::FixedArrayIterateBody(ObjectVisitor* v) {
   IteratePointers(v, kHeaderSize, kHeaderSize + length() * kPointerSize);
 }
 
 
 static bool HasKey(FixedArray* array, Object* key) {
   int len0 = array->length();
@@ skipping 3808 matching lines @@
   // No break point.
   if (break_point_objects()->IsUndefined()) return 0;
   // Single beak point.
   if (!break_point_objects()->IsFixedArray()) return 1;
   // Multiple break points.
   return FixedArray::cast(break_point_objects())->length();
 }
 
 
 } }  // namespace v8::internal