git: 0e426a4a3468 - stable/12 - [libcxx] Guard C++20 atomic type aliases

The branch stable/12 has been updated by dim:

URL: https://cgit.FreeBSD.org/src/commit/?id=0e426a4a346876e61adc0b3981a91fe1e039c1ee

commit 0e426a4a346876e61adc0b3981a91fe1e039c1ee
Author:     Dimitry Andric <dim@FreeBSD.org>
AuthorDate: 2021-12-17 22:10:49 +0000
Commit:     Dimitry Andric <dim@FreeBSD.org>
CommitDate: 2021-12-22 10:01:33 +0000

    [libcxx] Guard C++20 atomic type aliases
    
    Apply abandoned llvm review https://reviews.llvm.org/D75183 anyway:
    
    The std::atomic_signed_lock_free and std::atomic_unsigned_lock_free
    typedefs are a C++20 feature and should be guarded with an #if, so that
    they don't get defined in C++17 and prior versions.
    
    Also with the current implementation inclusion of the <atomic> header
    will fail the compilation for targets that don't have lock-free atomic
    integers (e.g. Armv6-M) because __libcpp_signed_lock_free and
    __libcpp_unsigned_lock_free will not get defined. We should not try to
    define std::atomic_signed_lock_free and std::atomic_unsigned_lock_free
    in this case as well (according to [atomics.alias]/2 these typedefs are
    optional in freestanding implementations).
---
 contrib/llvm-project/libcxx/include/atomic | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/contrib/llvm-project/libcxx/include/atomic b/contrib/llvm-project/libcxx/include/atomic
index 5ab48f55ddd3..264023405516 100644
--- a/contrib/llvm-project/libcxx/include/atomic
+++ b/contrib/llvm-project/libcxx/include/atomic
@@ -2761,6 +2761,8 @@ typedef atomic<uintmax_t> atomic_uintmax_t;
 # define _LIBCPP_CONTENTION_LOCK_FREE false
 #endif
 
+#if _LIBCPP_STD_VER > 17
+
 #if ATOMIC_LLONG_LOCK_FREE == 2
 typedef conditional<_LIBCPP_CONTENTION_LOCK_FREE, __cxx_contention_t, long long>::type          __libcpp_signed_lock_free;
 typedef conditional<_LIBCPP_CONTENTION_LOCK_FREE, __cxx_contention_t, unsigned long long>::type __libcpp_unsigned_lock_free;
@@ -2775,10 +2777,15 @@ typedef conditional<_LIBCPP_CONTENTION_LOCK_FREE, __cxx_contention_t, char>::typ
 typedef conditional<_LIBCPP_CONTENTION_LOCK_FREE, __cxx_contention_t, unsigned char>::type      __libcpp_unsigned_lock_free;
 #else
     // No signed/unsigned lock-free types
+# define _LIBCPP_CANNOT_DEFINE_ATOMIC_LOCK_FREE_TYPE_ALIASES
 #endif
 
+#ifndef _LIBCPP_CANNOT_DEFINE_ATOMIC_LOCK_FREE_TYPE_ALIASES
 typedef atomic<__libcpp_signed_lock_free> atomic_signed_lock_free;
 typedef atomic<__libcpp_unsigned_lock_free> atomic_unsigned_lock_free;
+#endif
+
+#endif // _LIBCPP_STD_VER > 17
 
 #define ATOMIC_FLAG_INIT {false}
 #define ATOMIC_VAR_INIT(__v) {__v}