Revert of tcmalloc: Use C++11 atomics where appropriate.

third_party/tcmalloc/chromium/src/base/atomicops_internals_portable.h

-// Copyright (c) 2014 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// This file is an internal atomic implementation, use atomicops.h instead.
-//
-// This implementation uses C++11 atomics' member functions. The code base is
-// currently written assuming atomicity revolves around accesses instead of
-// C++11's memory locations. The burden is on the programmer to ensure that all
-// memory locations accessed atomically are never accessed non-atomically (tsan
-// should help with this).
-//
-// TODO(jfb) Modify the atomicops.h API and user code to declare atomic
-//           locations as truly atomic. See the static_assert below.
-//
-// Of note in this implementation:
-//  * All NoBarrier variants are implemented as relaxed.
-//  * All Barrier variants are implemented as sequentially-consistent.
-//  * Compare exchange's failure ordering is always the same as the success one
-//    (except for release, which fails as relaxed): using a weaker ordering is
-//    only valid under certain uses of compare exchange.
-//  * Acquire store doesn't exist in the C11 memory model, it is instead
-//    implemented as a relaxed store followed by a sequentially consistent
-//    fence.
-//  * Release load doesn't exist in the C11 memory model, it is instead
-//    implemented as sequentially consistent fence followed by a relaxed load.
-//  * Atomic increment is expected to return the post-incremented value, whereas
-//    C11 fetch add returns the previous value. The implementation therefore
-//    needs to increment twice (which the compiler should be able to detect and
-//    optimize).
-
-#ifndef BASE_ATOMICOPS_INTERNALS_PORTABLE_H_
-#define BASE_ATOMICOPS_INTERNALS_PORTABLE_H_
-
-#include <atomic>
-#include <stdint.h>
-
-typedef int32_t Atomic32;
-#define BASE_HAS_ATOMIC64 1  // Use only in tests and base/atomic*
-
-namespace base {
-namespace subtle {
-
-// 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);
-}
-
-inline Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
-                                        Atomic32 increment) {
-  return increment + ((AtomicLocation32)ptr)->fetch_add(increment);
-}
-
-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);
-  MemoryBarrier();
-}
-
-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);
-}
-
-#if defined(BASE_HAS_ATOMIC64)
-typedef int64_t Atomic64;
-
-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) {
-  MemoryBarrier();
-  return ((AtomicLocation64)ptr)->load(std::memory_order_relaxed);
-}
-#endif  // defined(BASE_HAS_ATOMIC64)
-}  // namespace subtle
-}  // namespace base
-
-#endif  // BASE_ATOMICOPS_INTERNALS_PORTABLE_H_