[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
diff --git a/include/memory b/include/memory index 750034b..38ce433 100644 --- a/include/memory +++ b/include/memory
@@ -612,7 +612,7 @@ #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 @@ 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 @@ 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 