[libc++] Extract a clean base support API for std::atomic

libcxx/include/CMakeLists.txt

@@ -212,11 +212,13 @@ set(files
   __atomic/atomic_sync.h
   __atomic/check_memory_order.h
   __atomic/contention_t.h
-  __atomic/cxx_atomic_impl.h
   __atomic/fence.h
   __atomic/is_always_lock_free.h
   __atomic/kill_dependency.h
   __atomic/memory_order.h
+  __atomic/support.h
+  __atomic/support/c11.h
+  __atomic/support/gcc.h
   __atomic/to_gcc_order.h
   __bit/bit_cast.h
   __bit/bit_ceil.h

libcxx/include/__atomic/atomic.h

@@ -11,9 +11,9 @@
 
 #include <__atomic/atomic_sync.h>
 #include <__atomic/check_memory_order.h>
-#include <__atomic/cxx_atomic_impl.h>
 #include <__atomic/is_always_lock_free.h>
 #include <__atomic/memory_order.h>
+#include <__atomic/support.h>
 #include <__config>
 #include <__cstddef/ptrdiff_t.h>
 #include <__functional/operations.h>

libcxx/include/__atomic/atomic_flag.h

@@ -11,8 +11,8 @@
 
 #include <__atomic/atomic_sync.h>
 #include <__atomic/contention_t.h>
-#include <__atomic/cxx_atomic_impl.h>
 #include <__atomic/memory_order.h>
+#include <__atomic/support.h>
 #include <__chrono/duration.h>
 #include <__config>
 #include <__memory/addressof.h>

libcxx/include/__atomic/atomic_sync.h

@@ -10,7 +10,6 @@
 #define _LIBCPP___ATOMIC_ATOMIC_SYNC_H
 
 #include <__atomic/contention_t.h>
-#include <__atomic/cxx_atomic_impl.h>
 #include <__atomic/memory_order.h>
 #include <__atomic/to_gcc_order.h>
 #include <__chrono/duration.h>

libcxx/include/__atomic/contention_t.h

@@ -9,7 +9,7 @@
 #ifndef _LIBCPP___ATOMIC_CONTENTION_T_H
 #define _LIBCPP___ATOMIC_CONTENTION_T_H
 
-#include <__atomic/cxx_atomic_impl.h>
+#include <__atomic/support.h>
 #include <__config>
 #include <cstdint>
 

libcxx/include/__atomic/fence.h

@@ -9,8 +9,8 @@
 #ifndef _LIBCPP___ATOMIC_FENCE_H
 #define _LIBCPP___ATOMIC_FENCE_H
 
-#include <__atomic/cxx_atomic_impl.h>
 #include <__atomic/memory_order.h>
+#include <__atomic/support.h>
 #include <__config>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)

libcxx/include/__atomic/support.h

@@ -0,0 +1,124 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___ATOMIC_SUPPORT_H
+#define _LIBCPP___ATOMIC_SUPPORT_H
+
+#include <__config>
+#include <__type_traits/is_trivially_copyable.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+//
+// This file implements base support for atomics on the platform.
+//
+// The following operations and types must be implemented (where _Atmc
+// is __cxx_atomic_base_impl for readability):
+//
+// clang-format off
+//
+// template <class _Tp>
+// struct __cxx_atomic_base_impl;
+//
+// #define __cxx_atomic_is_lock_free(__size)
+//
+// void __cxx_atomic_thread_fence(memory_order __order) noexcept;
+// void __cxx_atomic_signal_fence(memory_order __order) noexcept;
+//
+// template <class _Tp>
+// void __cxx_atomic_init(_Atmc<_Tp> volatile* __a, _Tp __val) noexcept;
+// template <class _Tp>
+// void __cxx_atomic_init(_Atmc<_Tp>* __a, _Tp __val) noexcept;
+//
+// template <class _Tp>
+// void __cxx_atomic_store(_Atmc<_Tp> volatile* __a, _Tp __val, memory_order __order) noexcept;
+// template <class _Tp>
+// void __cxx_atomic_store(_Atmc<_Tp>* __a, _Tp __val, memory_order __order) noexcept;
+//
+// template <class _Tp>
+// _Tp __cxx_atomic_load(_Atmc<_Tp> const volatile* __a, memory_order __order) noexcept;
+// template <class _Tp>
+// _Tp __cxx_atomic_load(_Atmc<_Tp> const* __a, memory_order __order) noexcept;
+//
+// template <class _Tp>
+// void __cxx_atomic_load_inplace(_Atmc<_Tp> const volatile* __a, _Tp* __dst, memory_order __order) noexcept;
+// template <class _Tp>
+// void __cxx_atomic_load_inplace(_Atmc<_Tp> const* __a, _Tp* __dst, memory_order __order) noexcept;
+//
+// template <class _Tp>
+// _Tp __cxx_atomic_exchange(_Atmc<_Tp> volatile* __a, _Tp __value, memory_order __order) noexcept;
+// template <class _Tp>
+// _Tp __cxx_atomic_exchange(_Atmc<_Tp>* __a, _Tp __value, memory_order __order) noexcept;
+//
+// template <class _Tp>
+// bool __cxx_atomic_compare_exchange_strong(_Atmc<_Tp> volatile* __a, _Tp* __expected, _Tp __value, memory_order __success, memory_order __failure) noexcept;
+// template <class _Tp>
+// bool __cxx_atomic_compare_exchange_strong(_Atmc<_Tp>* __a, _Tp* __expected, _Tp __value, memory_order __success, memory_order __failure) noexcept;
+//
+// template <class _Tp>
+// bool __cxx_atomic_compare_exchange_weak(_Atmc<_Tp> volatile* __a, _Tp* __expected, _Tp __value, memory_order __success, memory_order __failure) noexcept;
+// template <class _Tp>
+// bool __cxx_atomic_compare_exchange_weak(_Atmc<_Tp>* __a, _Tp* __expected, _Tp __value, memory_order __success, memory_order __failure) noexcept;
+//
+// template <class _Tp>
+// _Tp __cxx_atomic_fetch_add(_Atmc<_Tp> volatile* __a, _Tp __delta, memory_order __order) noexcept;
+// template <class _Tp>
+// _Tp __cxx_atomic_fetch_add(_Atmc<_Tp>* __a, _Tp __delta, memory_order __order) noexcept;
+//
+// template <class _Tp>
+// _Tp* __cxx_atomic_fetch_add(_Atmc<_Tp*> volatile* __a, ptrdiff_t __delta, memory_order __order) noexcept;
+// template <class _Tp>
+// _Tp* __cxx_atomic_fetch_add(_Atmc<_Tp*>* __a, ptrdiff_t __delta, memory_order __order) noexcept;
+//
+// template <class _Tp>
+// _Tp __cxx_atomic_fetch_sub(_Atmc<_Tp> volatile* __a, _Tp __delta, memory_order __order) noexcept;
+// template <class _Tp>
+// _Tp __cxx_atomic_fetch_sub(_Atmc<_Tp>* __a, _Tp __delta, memory_order __order) noexcept;
+// template <class _Tp>
+// _Tp* __cxx_atomic_fetch_sub(_Atmc<_Tp*> volatile* __a, ptrdiff_t __delta, memory_order __order) noexcept;
+// template <class _Tp>
+// _Tp* __cxx_atomic_fetch_sub(_Atmc<_Tp*>* __a, ptrdiff_t __delta, memory_order __order) noexcept;
+//
+// template <class _Tp>
+// _Tp __cxx_atomic_fetch_and(_Atmc<_Tp> volatile* __a, _Tp __pattern, memory_order __order) noexcept;
+// template <class _Tp>
+// _Tp __cxx_atomic_fetch_and(_Atmc<_Tp>* __a, _Tp __pattern, memory_order __order) noexcept;
+//
+// template <class _Tp>
+// _Tp __cxx_atomic_fetch_or(_Atmc<_Tp> volatile* __a, _Tp __pattern, memory_order __order) noexcept;
+// template <class _Tp>
+// _Tp __cxx_atomic_fetch_or(_Atmc<_Tp>* __a, _Tp __pattern, memory_order __order) noexcept;
+// template <class _Tp>
+// _Tp __cxx_atomic_fetch_xor(_Atmc<_Tp> volatile* __a, _Tp __pattern, memory_order __order) noexcept;
+// template <class _Tp>
+// _Tp __cxx_atomic_fetch_xor(_Atmc<_Tp>* __a, _Tp __pattern, memory_order __order) noexcept;
+//
+// clang-format on
+//
+
+#if _LIBCPP_HAS_GCC_ATOMIC_IMP
+#  include <__atomic/support/gcc.h>
+#elif _LIBCPP_HAS_C_ATOMIC_IMP
+#  include <__atomic/support/c11.h>
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <typename _Tp, typename _Base = __cxx_atomic_base_impl<_Tp> >
+struct __cxx_atomic_impl : public _Base {
+  static_assert(is_trivially_copyable<_Tp>::value, "std::atomic<T> requires that 'T' be a trivially copyable type");
+
+  _LIBCPP_HIDE_FROM_ABI __cxx_atomic_impl() _NOEXCEPT = default;
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __cxx_atomic_impl(_Tp __value) _NOEXCEPT : _Base(__value) {}
+};
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___ATOMIC_SUPPORT_H