Do not overwrite already optimized code.

BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/189603006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19791 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/optimizing-compiler-thread.cc

@@ -258,9 +258,13 @@ void OptimizingCompilerThread::InstallOptimizedFunctions() {
       uint32_t offset = code->TranslateAstIdToPcOffset(info->osr_ast_id());
       BackEdgeTable::RemoveStackCheck(code, offset);
     } else {
-      Handle<Code> code = Compiler::GetConcurrentlyOptimizedCode(job);
-      function->ReplaceCode(
-          code.is_null() ? function->shared()->code() : *code);
+      if (function->IsOptimized()) {
+        DisposeOptimizedCompileJob(job, false);
+      } else {
+        Handle<Code> code = Compiler::GetConcurrentlyOptimizedCode(job);
+        function->ReplaceCode(
+            code.is_null() ? function->shared()->code() : *code);
+      }
     }
   }
 }

src/runtime.cc

@@ -8735,7 +8735,9 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_CompileForOnStackReplacement) {
     PrintF(" at AST id %d]\n", ast_id.ToInt());
   }
 
-  function->ReplaceCode(function->shared()->code());
+  if (!function->IsOptimized()) {
+    function->ReplaceCode(function->shared()->code());
+  }
   return NULL;
 }