Use 'local-exec' for threadlocal_heap_ in tcmalloc.

third_party/tcmalloc/chromium/src/thread_cache.h

 // Copyright (c) 2008, Google Inc.
 // 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
@@ skipping 251 matching lines @@
   // This code links against pyautolib.so, which causes dlopen() on that shared
   // object to fail when -fprofile-generate is used with it. Ideally
   // pyautolib.so should not link against this code. There is a bug filed for
   // that:
   // http://code.google.com/p/chromium/issues/detail?id=124489
   // For now the workaround is to pass in -DPGO_GENERATE when building Chrome
   // for instrumentation (-fprofile-generate).
   // For all non-instrumentation builds, this define will not be set and the
   // performance benefit of "intial-exec" will be achieved.
 #if defined(HAVE___ATTRIBUTE__) && !defined(PGO_GENERATE)
+  // If we are not using component build, we can further optimize it.
+#if !defined(COMPONENT_BUILD)
+   __attribute__ ((tls_model ("local-exec")))
+#else
    __attribute__ ((tls_model ("initial-exec")))
+#endif
 # endif
    ;
 #endif
 
   // Thread-specific key.  Initialization here is somewhat tricky
   // because some Linux startup code invokes malloc() before it
   // is in a good enough state to handle pthread_keycreate().
   // Therefore, we use TSD keys only after tsd_inited is set to true.
   // Until then, we use a slow path to get the heap object.
   static bool tsd_inited_;
@@ skipping 138 matching lines @@
 // because we may be in the thread destruction code and may have
 // already cleaned up the cache for this thread.
 inline ThreadCache* ThreadCache::GetCacheIfPresent() {
   if (!tsd_inited_) return NULL;
   return GetThreadHeap();
 }
 
 }  // namespace tcmalloc
 
 #endif  // TCMALLOC_THREAD_CACHE_H_