Do not overwrite already optimized code.

src/runtime.cc

 // Copyright 2012 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 8745 matching lines @@
     }
   }
 
   // Failed.
   if (FLAG_trace_osr) {
     PrintF("[OSR - Failed: ");
     function->PrintName();
     PrintF(" at AST id %d]\n", ast_id.ToInt());
   }
 
-  function->ReplaceCode(function->shared()->code());
+  if (!function->IsOptimized()) {
+    function->ReplaceCode(function->shared()->code());
+  }
   return NULL;
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_SetAllocationTimeout) {
   SealHandleScope shs(isolate);
   ASSERT(args.length() == 2 || args.length() == 3);
 #ifdef DEBUG
   CONVERT_SMI_ARG_CHECKED(interval, 0);
   CONVERT_SMI_ARG_CHECKED(timeout, 1);
@@ skipping 6218 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal