Revert https://codereview.chromium.org/1291903002 (protobuf roll).

third_party/protobuf/src/google/protobuf/stubs/atomicops_internals_pnacl.h

Index: third_party/protobuf/src/google/protobuf/stubs/atomicops_internals_pnacl.h
diff --git a/third_party/protobuf/src/google/protobuf/stubs/atomicops_internals_pnacl.h b/third_party/protobuf/src/google/protobuf/stubs/atomicops_internals_pnacl.h
index 3b314fd0c9af5c6c4b582d304cd098a2f380a3fe..04a91a83f87c62cd0ed31ce9280a9cb42020b562 100644
--- a/third_party/protobuf/src/google/protobuf/stubs/atomicops_internals_pnacl.h
+++ b/third_party/protobuf/src/google/protobuf/stubs/atomicops_internals_pnacl.h
@@ -1,6 +1,6 @@
 // Protocol Buffers - Google's data interchange format
 // Copyright 2012 Google Inc.  All rights reserved.
-// https://developers.google.com/protocol-buffers/
+// http://code.google.com/p/protobuf/
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
@@ -33,197 +33,39 @@
 #ifndef GOOGLE_PROTOBUF_ATOMICOPS_INTERNALS_PNACL_H_
 #define GOOGLE_PROTOBUF_ATOMICOPS_INTERNALS_PNACL_H_
 
-#include <atomic>
-
 namespace google {
 namespace protobuf {
 namespace internal {
 
-// This implementation is transitional and maintains the original API for
-// atomicops.h. This requires casting memory locations to the atomic types, and
-// assumes that the API and the C++11 implementation are layout-compatible,
-// which isn't true for all implementations or hardware platforms. The static
-// assertion should detect this issue, were it to fire then this header
-// shouldn't be used.
-//
-// TODO(jfb) If this header manages to stay committed then the API should be
-//           modified, and all call sites updated.
-typedef volatile std::atomic<Atomic32>* AtomicLocation32;
-static_assert(sizeof(*(AtomicLocation32) nullptr) == sizeof(Atomic32),
-              "incompatible 32-bit atomic layout");
-
-inline void MemoryBarrier() {
-#if defined(__GLIBCXX__)
-  // Work around libstdc++ bug 51038 where atomic_thread_fence was declared but
-  // not defined, leading to the linker complaining about undefined references.
-  __atomic_thread_fence(std::memory_order_seq_cst);
-#else
-  std::atomic_thread_fence(std::memory_order_seq_cst);
-#endif
-}
-
 inline Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr,
                                          Atomic32 old_value,
                                          Atomic32 new_value) {
-  ((AtomicLocation32)ptr)
-      ->compare_exchange_strong(old_value,
-                                new_value,
-                                std::memory_order_relaxed,
-                                std::memory_order_relaxed);
-  return old_value;
-}
-
-inline Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr,
-                                         Atomic32 new_value) {
-  return ((AtomicLocation32)ptr)
-      ->exchange(new_value, std::memory_order_relaxed);
-}
-
-inline Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr,
-                                          Atomic32 increment) {
-  return increment +
-         ((AtomicLocation32)ptr)
-             ->fetch_add(increment, std::memory_order_relaxed);
+  return __sync_val_compare_and_swap(ptr, old_value, new_value);
 }
 
-inline Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
-                                        Atomic32 increment) {
-  return increment + ((AtomicLocation32)ptr)->fetch_add(increment);
+inline void MemoryBarrier() {
+  __sync_synchronize();
 }
 
 inline Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
                                        Atomic32 old_value,
                                        Atomic32 new_value) {
-  ((AtomicLocation32)ptr)
-      ->compare_exchange_strong(old_value,
-                                new_value,
-                                std::memory_order_acquire,
-                                std::memory_order_acquire);
-  return old_value;
-}
-
-inline Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
-                                       Atomic32 old_value,
-                                       Atomic32 new_value) {
-  ((AtomicLocation32)ptr)
-      ->compare_exchange_strong(old_value,
-                                new_value,
-                                std::memory_order_release,
-                                std::memory_order_relaxed);
-  return old_value;
-}
-
-inline void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value) {
-  ((AtomicLocation32)ptr)->store(value, std::memory_order_relaxed);
-}
-
-inline void Acquire_Store(volatile Atomic32* ptr, Atomic32 value) {
-  ((AtomicLocation32)ptr)->store(value, std::memory_order_relaxed);
+  Atomic32 ret = NoBarrier_CompareAndSwap(ptr, old_value, new_value);
   MemoryBarrier();
+  return ret;
 }
 
 inline void Release_Store(volatile Atomic32* ptr, Atomic32 value) {
-  ((AtomicLocation32)ptr)->store(value, std::memory_order_release);
-}
-
-inline Atomic32 NoBarrier_Load(volatile const Atomic32* ptr) {
-  return ((AtomicLocation32)ptr)->load(std::memory_order_relaxed);
-}
-
-inline Atomic32 Acquire_Load(volatile const Atomic32* ptr) {
-  return ((AtomicLocation32)ptr)->load(std::memory_order_acquire);
-}
-
-inline Atomic32 Release_Load(volatile const Atomic32* ptr) {
   MemoryBarrier();
-  return ((AtomicLocation32)ptr)->load(std::memory_order_relaxed);
+  *ptr = value;
 }
 
-#if defined(GOOGLE_PROTOBUF_ARCH_64_BIT)
-
-typedef volatile std::atomic<Atomic64>* AtomicLocation64;
-static_assert(sizeof(*(AtomicLocation64) nullptr) == sizeof(Atomic64),
-              "incompatible 64-bit atomic layout");
-
-inline Atomic64 NoBarrier_CompareAndSwap(volatile Atomic64* ptr,
-                                         Atomic64 old_value,
-                                         Atomic64 new_value) {
-  ((AtomicLocation64)ptr)
-      ->compare_exchange_strong(old_value,
-                                new_value,
-                                std::memory_order_relaxed,
-                                std::memory_order_relaxed);
-  return old_value;
-}
-
-inline Atomic64 NoBarrier_AtomicExchange(volatile Atomic64* ptr,
-                                         Atomic64 new_value) {
-  return ((AtomicLocation64)ptr)
-      ->exchange(new_value, std::memory_order_relaxed);
-}
-
-inline Atomic64 NoBarrier_AtomicIncrement(volatile Atomic64* ptr,
-                                          Atomic64 increment) {
-  return increment +
-         ((AtomicLocation64)ptr)
-             ->fetch_add(increment, std::memory_order_relaxed);
-}
-
-inline Atomic64 Barrier_AtomicIncrement(volatile Atomic64* ptr,
-                                        Atomic64 increment) {
-  return increment + ((AtomicLocation64)ptr)->fetch_add(increment);
-}
-
-inline Atomic64 Acquire_CompareAndSwap(volatile Atomic64* ptr,
-                                       Atomic64 old_value,
-                                       Atomic64 new_value) {
-  ((AtomicLocation64)ptr)
-      ->compare_exchange_strong(old_value,
-                                new_value,
-                                std::memory_order_acquire,
-                                std::memory_order_acquire);
-  return old_value;
-}
-
-inline Atomic64 Release_CompareAndSwap(volatile Atomic64* ptr,
-                                       Atomic64 old_value,
-                                       Atomic64 new_value) {
-  ((AtomicLocation64)ptr)
-      ->compare_exchange_strong(old_value,
-                                new_value,
-                                std::memory_order_release,
-                                std::memory_order_relaxed);
-  return old_value;
-}
-
-inline void NoBarrier_Store(volatile Atomic64* ptr, Atomic64 value) {
-  ((AtomicLocation64)ptr)->store(value, std::memory_order_relaxed);
-}
-
-inline void Acquire_Store(volatile Atomic64* ptr, Atomic64 value) {
-  ((AtomicLocation64)ptr)->store(value, std::memory_order_relaxed);
-  MemoryBarrier();
-}
-
-inline void Release_Store(volatile Atomic64* ptr, Atomic64 value) {
-  ((AtomicLocation64)ptr)->store(value, std::memory_order_release);
-}
-
-inline Atomic64 NoBarrier_Load(volatile const Atomic64* ptr) {
-  return ((AtomicLocation64)ptr)->load(std::memory_order_relaxed);
-}
-
-inline Atomic64 Acquire_Load(volatile const Atomic64* ptr) {
-  return ((AtomicLocation64)ptr)->load(std::memory_order_acquire);
-}
-
-inline Atomic64 Release_Load(volatile const Atomic64* ptr) {
+inline Atomic32 Acquire_Load(volatile const Atomic32* ptr) {
+  Atomic32 value = *ptr;
   MemoryBarrier();
-  return ((AtomicLocation64)ptr)->load(std::memory_order_relaxed);
+  return value;
 }
 
-#endif  // defined(GOOGLE_PROTOBUF_ARCH_64_BIT)
-
 }  // namespace internal
 }  // namespace protobuf
 }  // namespace google