Revert of Update implementation of atomics with latest Chromium version but use compiler builtin atomics

src/base/atomicops_internals_portable.h

-// Copyright 2016 the V8 project 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).
-//
-// 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 "src/base/build_config.h"
-
-namespace v8 {
-namespace base {
-
-// This implementation is transitional and maintains the original API for
-// atomicops.h.
-
-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) {
-  __atomic_compare_exchange_n(ptr, &old_value, new_value, false,
-                              __ATOMIC_RELAXED, __ATOMIC_RELAXED);
-  return old_value;
-}
-
-inline Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr,
-                                         Atomic32 new_value) {
-  return __atomic_exchange_n(ptr, new_value, __ATOMIC_RELAXED);
-}
-
-inline Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr,
-                                          Atomic32 increment) {
-  return increment + __atomic_fetch_add(ptr, increment, __ATOMIC_RELAXED);
-}
-
-inline Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
-                                        Atomic32 increment) {
-  return increment + __atomic_fetch_add(ptr, increment, __ATOMIC_SEQ_CST);
-}
-
-inline Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
-                                       Atomic32 old_value, Atomic32 new_value) {
-  __atomic_compare_exchange_n(ptr, &old_value, new_value, false,
-                              __ATOMIC_ACQUIRE, __ATOMIC_ACQUIRE);
-  return old_value;
-}
-
-inline Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
-                                       Atomic32 old_value, Atomic32 new_value) {
-  __atomic_compare_exchange_n(ptr, &old_value, new_value, false,
-                              __ATOMIC_RELEASE, __ATOMIC_RELAXED);
-  return old_value;
-}
-
-inline void NoBarrier_Store(volatile Atomic8* ptr, Atomic8 value) {
-  __atomic_store_n(ptr, value, __ATOMIC_RELAXED);
-}
-
-inline void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value) {
-  __atomic_store_n(ptr, value, __ATOMIC_RELAXED);
-}
-
-inline void Release_Store(volatile Atomic32* ptr, Atomic32 value) {
-  __atomic_store_n(ptr, value, __ATOMIC_RELEASE);
-}
-
-inline Atomic8 NoBarrier_Load(volatile const Atomic8* ptr) {
-  return __atomic_load_n(ptr, __ATOMIC_RELAXED);
-}
-
-inline Atomic32 NoBarrier_Load(volatile const Atomic32* ptr) {
-  return __atomic_load_n(ptr, __ATOMIC_RELAXED);
-}
-
-inline Atomic32 Acquire_Load(volatile const Atomic32* ptr) {
-  return __atomic_load_n(ptr, __ATOMIC_ACQUIRE);
-}
-
-#if defined(V8_HOST_ARCH_64_BIT)
-
-inline Atomic64 NoBarrier_CompareAndSwap(volatile Atomic64* ptr,
-                                         Atomic64 old_value,
-                                         Atomic64 new_value) {
-  __atomic_compare_exchange_n(ptr, &old_value, new_value, false,
-                              __ATOMIC_RELAXED, __ATOMIC_RELAXED);
-  return old_value;
-}
-
-inline Atomic64 NoBarrier_AtomicExchange(volatile Atomic64* ptr,
-                                         Atomic64 new_value) {
-  return __atomic_exchange_n(ptr, new_value, __ATOMIC_RELAXED);
-}
-
-inline Atomic64 NoBarrier_AtomicIncrement(volatile Atomic64* ptr,
-                                          Atomic64 increment) {
-  return increment + __atomic_fetch_add(ptr, increment, __ATOMIC_RELAXED);
-}
-
-inline Atomic64 Barrier_AtomicIncrement(volatile Atomic64* ptr,
-                                        Atomic64 increment) {
-  return increment + __atomic_fetch_add(ptr, increment, __ATOMIC_SEQ_CST);
-}
-
-inline Atomic64 Acquire_CompareAndSwap(volatile Atomic64* ptr,
-                                       Atomic64 old_value, Atomic64 new_value) {
-  __atomic_compare_exchange_n(ptr, &old_value, new_value, false,
-                              __ATOMIC_ACQUIRE, __ATOMIC_ACQUIRE);
-  return old_value;
-}
-
-inline Atomic64 Release_CompareAndSwap(volatile Atomic64* ptr,
-                                       Atomic64 old_value, Atomic64 new_value) {
-  __atomic_compare_exchange_n(ptr, &old_value, new_value, false,
-                              __ATOMIC_RELEASE, __ATOMIC_RELEASE);
-  return old_value;
-}
-
-inline void NoBarrier_Store(volatile Atomic64* ptr, Atomic64 value) {
-  __atomic_store_n(ptr, value, __ATOMIC_RELAXED);
-}
-
-inline void Release_Store(volatile Atomic64* ptr, Atomic64 value) {
-  __atomic_store_n(ptr, value, __ATOMIC_RELEASE);
-}
-
-inline Atomic64 NoBarrier_Load(volatile const Atomic64* ptr) {
-  return __atomic_load_n(ptr, __ATOMIC_RELAXED);
-}
-
-inline Atomic64 Acquire_Load(volatile const Atomic64* ptr) {
-  return __atomic_load_n(ptr, __ATOMIC_ACQUIRE);
-}
-
-#endif  // defined(V8_HOST_ARCH_64_BIT)
-}  // namespace base
-}  // namespace v8
-
-#endif  // V8_BASE_ATOMICOPS_INTERNALS_PORTABLE_H_