[libcxx] Allow use of <atomic> in C++03. Try 3.

Summary:
After putting this question up on cfe-dev I have decided that it would be best to allow the use of `<atomic>` in C++03. Although static initialization is a concern the syntax required to get it is C++11 only. Meaning that C++11 constant static initialization cannot silently break in C++03, it will always cause a syntax error. Furthermore `ATOMIC_VAR_INIT` and `ATOMIC_FLAG_INIT` remain defined in C++03 even though they cannot be used because C++03 usages will cause better error messages.

The main change in this patch is to replace `__has_feature(cxx_atomic)`, which only returns true when C++ >= 11, to `__has_extension(c_atomic)` which returns true whenever clang supports the required atomic builtins.


This patch adds the following macros:
* `_LIBCPP_HAS_C_ATOMIC_IMP`      - Defined on clang versions which provide the C `_Atomic` keyword.
* `_LIBCPP_HAS_GCC_ATOMIC_IMP` - Defined on GCC > 4.7. We must use the fallback atomic implementation.
* `_LIBCPP_HAS_NO_ATOMIC_HEADER` - Defined when it is not safe to include `<atomic>`.

`_LIBCPP_HAS_C_ATOMIC_IMP` and `_LIBCPP_HAS_GCC_ATOMIC_IMP` are mutually exclusive, only one should be defined. If neither is defined then `<atomic>` is not implemented and including `<atomic>` will issue an error.

Reviewers: chandlerc, jroelofs, mclow.lists

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D11555

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@245463 91177308-0d34-0410-b5e6-96231b3b80d8

include/__config

@@ -37,6 +37,9 @@
 #ifndef __has_builtin
 #define __has_builtin(__x) 0
 #endif
+#ifndef __has_extension
+#define __has_extension(__x) 0
+#endif
 #ifndef __has_feature
 #define __has_feature(__x) 0
 #endif
@@ -773,4 +776,15 @@ extern "C" void __sanitizer_annotate_contiguous_container(
 #define _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
 #endif
 
-#endif  // _LIBCPP_CONFIG
+#if __has_extension(c_atomic)
+#define _LIBCPP_HAS_C_ATOMIC_IMP
+#elif _GNUC_VER > 407
+#define _LIBCPP_HAS_GCC_ATOMIC_IMP
+#endif
+
+#if (!defined(_LIBCPP_HAS_C_ATOMIC_IMP) && !defined(_LIBCPP_HAS_GCC_ATOMIC_IMP)) \
+     || defined(_LIBCPP_HAS_NO_THREADS)
+#define _LIBCPP_HAS_NO_ATOMIC_HEADER
+#endif
+
+#endif // _LIBCPP_CONFIG

include/atomic

@@ -535,21 +535,20 @@ void atomic_signal_fence(memory_order m) noexcept;
 
 #ifdef _LIBCPP_HAS_NO_THREADS
 #error <atomic> is not supported on this single threaded system
-#else // !_LIBCPP_HAS_NO_THREADS
+#endif
+#if !defined(_LIBCPP_HAS_C_ATOMIC_IMP) && !defined(_LIBCPP_HAS_GCC_ATOMIC_IMP)
+#error <atomic> is not implemented
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if !__has_feature(cxx_atomic) && _GNUC_VER < 407
-#error <atomic> is not implemented
-#else
-
 typedef enum memory_order
 {
     memory_order_relaxed, memory_order_consume, memory_order_acquire,
     memory_order_release, memory_order_acq_rel, memory_order_seq_cst
 } memory_order;
 
-#if _GNUC_VER >= 407
+#if defined(_LIBCPP_HAS_GCC_ATOMIC_IMP)
 namespace __gcc_atomic {
 template <typename _Tp>
 struct __gcc_atomic_t {
@@ -805,7 +804,7 @@ static inline _Tp __c11_atomic_fetch_xor(_Atomic(_Tp)* __a, _Tp __pattern,
   return __atomic_fetch_xor(&__a->__a_value, __pattern,
                             __gcc_atomic::__to_gcc_order(__order));
 }
-#endif // _GNUC_VER >= 407
+#endif // _LIBCPP_HAS_GCC_ATOMIC_IMP
 
 template <class _Tp>
 inline _LIBCPP_INLINE_VISIBILITY
@@ -825,7 +824,7 @@ struct __atomic_base  // false
     _LIBCPP_INLINE_VISIBILITY
     bool is_lock_free() const volatile _NOEXCEPT
     {
-#if __has_feature(cxx_atomic)
+#if defined(_LIBCPP_HAS_C_ATOMIC_IMP)
     return __c11_atomic_is_lock_free(sizeof(_Tp));
 #else
     return __atomic_is_lock_free(sizeof(_Tp), 0);
@@ -1779,8 +1778,6 @@ typedef atomic<uintmax_t> atomic_uintmax_t;
 #define ATOMIC_FLAG_INIT {false}
 #define ATOMIC_VAR_INIT(__v) {__v}
 
-// lock-free property
-
 #define ATOMIC_BOOL_LOCK_FREE      __GCC_ATOMIC_BOOL_LOCK_FREE
 #define ATOMIC_CHAR_LOCK_FREE      __GCC_ATOMIC_CHAR_LOCK_FREE
 #define ATOMIC_CHAR16_T_LOCK_FREE  __GCC_ATOMIC_CHAR16_T_LOCK_FREE
@@ -1792,10 +1789,6 @@ typedef atomic<uintmax_t> atomic_uintmax_t;
 #define ATOMIC_LLONG_LOCK_FREE     __GCC_ATOMIC_LLONG_LOCK_FREE
 #define ATOMIC_POINTER_LOCK_FREE   __GCC_ATOMIC_POINTER_LOCK_FREE
 
-#endif  //  !__has_feature(cxx_atomic)
-
 _LIBCPP_END_NAMESPACE_STD
 
-#endif  // !_LIBCPP_HAS_NO_THREADS
-
 #endif  // _LIBCPP_ATOMIC

include/ios

@@ -216,7 +216,7 @@ storage-class-specifier const error_category& iostream_category() noexcept;
 #include <__locale>
 #include <system_error>
 
-#if __has_feature(cxx_atomic) && !defined(_LIBCPP_HAS_NO_THREADS)
+#if !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER)
 #include <atomic>     // for __xindex_
 #endif
 
@@ -367,7 +367,9 @@ private:
     int*            __index_;
     size_t          __event_size_;
     size_t          __event_cap_;
-#if __has_feature(cxx_atomic) && !defined(_LIBCPP_HAS_NO_THREADS)
+// TODO(EricWF): Enable this for both Clang and GCC. Currently it is only
+// enabled with clang.
+#if defined(_LIBCPP_HAS_C_ATOMIC_IMP) && !defined(_LIBCPP_HAS_NO_THREADS)
     static atomic<int> __xindex_;
 #else
     static int      __xindex_;

include/memory

@@ -612,7 +612,7 @@ void* align(size_t alignment, size_t size, void*& ptr, size_t& space);
     #include <cassert>
 #endif
 
-#if __has_feature(cxx_atomic) && !defined(_LIBCPP_HAS_NO_THREADS)
+#if !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER)
 #  include <atomic>
 #endif
 
@@ -5381,7 +5381,9 @@ inline _LIBCPP_INLINE_VISIBILITY
 basic_ostream<_CharT, _Traits>&
 operator<<(basic_ostream<_CharT, _Traits>& __os, shared_ptr<_Yp> const& __p);
 
-#if __has_feature(cxx_atomic) && !defined(_LIBCPP_HAS_NO_THREADS)
+// TODO(EricWF): Enable this for both Clang and GCC. Currently it is only
+// enabled with clang.
+#if defined(_LIBCPP_HAS_C_ATOMIC_IMP) && !defined(_LIBCPP_HAS_NO_THREADS)
 
 class _LIBCPP_TYPE_VIS __sp_mut
 {
@@ -5507,7 +5509,7 @@ atomic_compare_exchange_weak_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v
     return atomic_compare_exchange_weak(__p, __v, __w);
 }
 
-#endif  // __has_feature(cxx_atomic) && !defined(_LIBCPP_HAS_NO_THREADS)
+#endif  // defined(_LIBCPP_HAS_C_ATOMIC_IMP) && !defined(_LIBCPP_HAS_NO_THREADS)
 
 //enum class
 struct _LIBCPP_TYPE_VIS pointer_safety

src/ios.cpp

@@ -152,7 +152,7 @@ ios_base::getloc() const
 }
 
 // xalloc
-#if __has_feature(cxx_atomic) && !defined(_LIBCPP_HAS_NO_THREADS)
+#if defined(_LIBCPP_HAS_C_ATOMIC_IMP) && !defined(_LIBCPP_HAS_NO_THREADS)
 atomic<int> ios_base::__xindex_ = ATOMIC_VAR_INIT(0);
 #else
 int ios_base::__xindex_ = 0;

src/memory.cpp

@@ -124,7 +124,7 @@ __shared_weak_count::__get_deleter(const type_info&) const _NOEXCEPT
 
 #endif  // _LIBCPP_NO_RTTI
 
-#if __has_feature(cxx_atomic) && !defined(_LIBCPP_HAS_NO_THREADS)
+#if defined(_LIBCPP_HAS_C_ATOMIC_IMP) && !defined(_LIBCPP_HAS_NO_THREADS)
 
 static const std::size_t __sp_mut_count = 16;
 static pthread_mutex_t mut_back_imp[__sp_mut_count] =
@@ -177,7 +177,7 @@ __get_sp_mut(const void* p)
     return muts[hash<const void*>()(p) & (__sp_mut_count-1)];
 }
 
-#endif // __has_feature(cxx_atomic) && !_LIBCPP_HAS_NO_THREADS
+#endif // defined(_LIBCPP_HAS_C_ATOMIC_IMP) && !defined(_LIBCPP_HAS_NO_THREADS)
 
 void
 declare_reachable(void*)

test/std/atomics/atomics.flag/atomic_flag_clear.pass.cpp

@@ -22,13 +22,13 @@
 int main()
 {
     {
-        std::atomic_flag f = ATOMIC_FLAG_INIT;
+        std::atomic_flag f(false);
         f.test_and_set();
         atomic_flag_clear(&f);
         assert(f.test_and_set() == 0);
     }
     {
-        volatile std::atomic_flag f = ATOMIC_FLAG_INIT;
+        volatile std::atomic_flag f(false);
         f.test_and_set();
         atomic_flag_clear(&f);
         assert(f.test_and_set() == 0);

test/std/atomics/atomics.flag/atomic_flag_clear_explicit.pass.cpp

@@ -22,37 +22,37 @@
 int main()
 {
     {
-        std::atomic_flag f = ATOMIC_FLAG_INIT;
+        std::atomic_flag f(false);
         f.test_and_set();
         atomic_flag_clear_explicit(&f, std::memory_order_relaxed);
         assert(f.test_and_set() == 0);
     }
     {
-        std::atomic_flag f = ATOMIC_FLAG_INIT;
+        std::atomic_flag f(false);
         f.test_and_set();
         atomic_flag_clear_explicit(&f, std::memory_order_release);
         assert(f.test_and_set() == 0);
     }
     {
-        std::atomic_flag f = ATOMIC_FLAG_INIT;
+        std::atomic_flag f(false);
         f.test_and_set();
         atomic_flag_clear_explicit(&f, std::memory_order_seq_cst);
         assert(f.test_and_set() == 0);
     }
     {
-        volatile std::atomic_flag f = ATOMIC_FLAG_INIT;
+        volatile std::atomic_flag f(false);
         f.test_and_set();
         atomic_flag_clear_explicit(&f, std::memory_order_relaxed);
         assert(f.test_and_set() == 0);
     }
     {
-        volatile std::atomic_flag f = ATOMIC_FLAG_INIT;
+        volatile std::atomic_flag f(false);
         f.test_and_set();
         atomic_flag_clear_explicit(&f, std::memory_order_release);
         assert(f.test_and_set() == 0);
     }
     {
-        volatile std::atomic_flag f = ATOMIC_FLAG_INIT;
+        volatile std::atomic_flag f(false);
         f.test_and_set();
         atomic_flag_clear_explicit(&f, std::memory_order_seq_cst);
         assert(f.test_and_set() == 0);

test/std/atomics/atomics.flag/clear.pass.cpp

@@ -22,49 +22,49 @@
 int main()
 {
     {
-        std::atomic_flag f = ATOMIC_FLAG_INIT;
+        std::atomic_flag f(false);
         f.test_and_set();
         f.clear();
         assert(f.test_and_set() == 0);
     }
     {
-        std::atomic_flag f = ATOMIC_FLAG_INIT;
+        std::atomic_flag f(false);
         f.test_and_set();
         f.clear(std::memory_order_relaxed);
         assert(f.test_and_set() == 0);
     }
     {
-        std::atomic_flag f = ATOMIC_FLAG_INIT;
+        std::atomic_flag f(false);
         f.test_and_set();
         f.clear(std::memory_order_release);
         assert(f.test_and_set() == 0);
     }
     {
-        std::atomic_flag f = ATOMIC_FLAG_INIT;
+        std::atomic_flag f(false);
         f.test_and_set();
         f.clear(std::memory_order_seq_cst);
         assert(f.test_and_set() == 0);
     }
     {
-        volatile std::atomic_flag f = ATOMIC_FLAG_INIT;
+        volatile std::atomic_flag f(false);
         f.test_and_set();
         f.clear();
         assert(f.test_and_set() == 0);
     }
     {
-        volatile std::atomic_flag f = ATOMIC_FLAG_INIT;
+        volatile std::atomic_flag f(false);
         f.test_and_set();
         f.clear(std::memory_order_relaxed);
         assert(f.test_and_set() == 0);
     }
     {
-        volatile std::atomic_flag f = ATOMIC_FLAG_INIT;
+        volatile std::atomic_flag f(false);
         f.test_and_set();
         f.clear(std::memory_order_release);
         assert(f.test_and_set() == 0);
     }
     {
-        volatile std::atomic_flag f = ATOMIC_FLAG_INIT;
+        volatile std::atomic_flag f(false);
         f.test_and_set();
         f.clear(std::memory_order_seq_cst);
         assert(f.test_and_set() == 0);

test/std/atomics/atomics.flag/init.pass.cpp

@@ -8,6 +8,7 @@
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads
+// XFAIL: c++98, c++03
 
 // <atomic>
 

test/std/atomics/atomics.flag/init03.pass.cpp

@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// UNSUPPORTED: libcpp-has-no-threads
+
+// <atomic>
+
+// struct atomic_flag
+
+// TESTING EXTENSION atomic_flag(bool)
+
+#include <atomic>
+#include <cassert>
+
+int main()
+{
+    std::atomic_flag f(false);
+    assert(f.test_and_set() == 0);
+}

test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_compare_exchange_strong.pass.cpp

@@ -24,10 +24,11 @@
 #include <type_traits>
 #include <cassert>
 
+#include "atomic_helpers.h"
+
 template <class T>
-void
-test()
-{
+struct TestFn {
+  void operator()() const {
     {
         typedef std::atomic<T> A;
         A a;
@@ -52,37 +53,10 @@ test()
         assert(a == T(2));
         assert(t == T(2));
     }
-}
-
-struct A
-{
-    int i;
-
-    explicit A(int d = 0) noexcept {i=d;}
-
-    friend bool operator==(const A& x, const A& y)
-        {return x.i == y.i;}
+  }
 };
 
 int main()
 {
-    test<A>();
-    test<char>();
-    test<signed char>();
-    test<unsigned char>();
-    test<short>();
-    test<unsigned short>();
-    test<int>();
-    test<unsigned int>();
-    test<long>();
-    test<unsigned long>();
-    test<long long>();
-    test<unsigned long long>();
-    test<wchar_t>();
-#ifndef _LIBCPP_HAS_NO_UNICODE_CHARS
-    test<char16_t>();
-    test<char32_t>();
-#endif  // _LIBCPP_HAS_NO_UNICODE_CHARS
-    test<int*>();
-    test<const int*>();
+    TestEachAtomicType<TestFn>()();
 }