Fast path for ThreadSpecific for main thread on TLS-slow platforms

third_party/WebKit/Source/platform/heap/ThreadState.h

 /*
  * Copyright (C) 2013 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 163 matching lines @@
   // Associate ThreadState object with the current thread. After this
   // call thread can start using the garbage collected heap infrastructure.
   // It also has to periodically check for safepoints.
   static void attachCurrentThread();
 
   // Disassociate attached ThreadState from the current thread. The thread
   // can no longer use the garbage collected heap after this call.
   static void detachCurrentThread();
 
   static ThreadState* current() {
-#if defined(__GLIBC__) || OS(ANDROID) || OS(FREEBSD)
-    // TLS lookup is fast in these platforms.
     return **s_threadSpecific;
-#else
-    uintptr_t dummy;
-    uintptr_t addressDiff =
-        s_mainThreadStackStart - reinterpret_cast<uintptr_t>(&dummy);
-    // This is a fast way to judge if we are in the main thread.
-    // If |&dummy| is within |s_mainThreadUnderestimatedStackSize| byte from
-    // the stack start of the main thread, we judge that we are in
-    // the main thread.
-    if (LIKELY(addressDiff < s_mainThreadUnderestimatedStackSize)) {
-      ASSERT(**s_threadSpecific == mainThreadState());
-      return mainThreadState();
-    }
-    // TLS lookup is slow.
-    return **s_threadSpecific;
-#endif
   }
 
   static ThreadState* mainThreadState() {
     return reinterpret_cast<ThreadState*>(s_mainThreadStateStorage);
   }
 
   static ThreadState* fromObject(const void*);
 
   bool isMainThread() const { return this == mainThreadState(); }
 #if ENABLE(ASSERT)
@@ skipping 292 matching lines @@
     return BlinkGC::Vector1ArenaIndex <= arenaIndex &&
            arenaIndex <= BlinkGC::Vector4ArenaIndex;
   }
   void allocationPointAdjusted(int arenaIndex);
   void promptlyFreed(size_t gcInfoIndex);
 
   void accumulateSweepingTime(double time) {
     m_accumulatedSweepingTime += time;
   }
 
-#if OS(WIN) && COMPILER(MSVC)
-  size_t threadStackSize();
-#endif
-
   void freePersistentNode(PersistentNode*);
 
   using PersistentClearCallback = void (*)(void*);
 
   void registerStaticPersistentNode(PersistentNode*, PersistentClearCallback);
   void releaseStaticPersistentNodes();
 
 #if defined(LEAK_SANITIZER)
   void enterStaticReferenceRegistrationDisabledScope();
   void leaveStaticReferenceRegistrationDisabledScope();
@@ skipping 120 matching lines @@
   // Should only be called under protection of threadAttachMutex().
   const Vector<std::unique_ptr<BlinkGCInterruptor>>& interruptors() const {
     return m_interruptors;
   }
 
   friend class SafePointAwareMutexLocker;
   friend class SafePointBarrier;
   friend class SafePointScope;
 
   static WTF::ThreadSpecific<ThreadState*>* s_threadSpecific;
-  static uintptr_t s_mainThreadStackStart;
-  static uintptr_t s_mainThreadUnderestimatedStackSize;
 
   // We can't create a static member of type ThreadState here
   // because it will introduce global constructor and destructor.
   // We would like to manage lifetime of the ThreadState attached
   // to the main thread explicitly instead and still use normal
   // constructor and destructor for the ThreadState class.
   // For this we reserve static storage for the main ThreadState
   // and lazily construct ThreadState in it using placement new.
   static uint8_t s_mainThreadStateStorage[];
 
   ThreadHeap* m_heap;
   ThreadIdentifier m_thread;
   std::unique_ptr<PersistentRegion> m_persistentRegion;
   BlinkGC::StackState m_stackState;
-#if OS(WIN) && COMPILER(MSVC)
-  size_t m_threadStackSize;
-#endif
   intptr_t* m_startOfStack;
   intptr_t* m_endOfStack;
 
   void* m_safePointScopeMarker;
   Vector<Address> m_safePointStackCopy;
   bool m_atSafePoint;
   Vector<std::unique_ptr<BlinkGCInterruptor>> m_interruptors;
   bool m_sweepForbidden;
   size_t m_noAllocationCount;
   size_t m_gcForbiddenCount;
@@ skipping 75 matching lines @@
 class ThreadStateFor<AnyThread> {
   STATIC_ONLY(ThreadStateFor);
 
  public:
   static ThreadState* state() { return ThreadState::current(); }
 };
 
 }  // namespace blink
 
 #endif  // ThreadState_h