[libc++] Simplify __memory/shared_count.h a bit (#160048)

This removes a few checks that aren't required anymore and moves some
code around to the places where it's actually used.

libcxx/include/__memory/shared_count.h

@@ -22,37 +22,10 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 // NOTE: Relaxed and acq/rel atomics (for increment and decrement respectively)
 // should be sufficient for thread safety.
 // See https://llvm.org/PR22803
-#if (defined(__clang__) && __has_builtin(__atomic_add_fetch) && defined(__ATOMIC_RELAXED) &&                           \
-     defined(__ATOMIC_ACQ_REL)) ||                                                                                     \
-    defined(_LIBCPP_COMPILER_GCC)
-#  define _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT 1
-#else
-#  define _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT 0
-#endif
-
-template <class _ValueType>
-inline _LIBCPP_HIDE_FROM_ABI _ValueType __libcpp_relaxed_load(_ValueType const* __value) {
-#if _LIBCPP_HAS_THREADS && defined(__ATOMIC_RELAXED) &&                                                                \
-    (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
-  return __atomic_load_n(__value, __ATOMIC_RELAXED);
-#else
-  return *__value;
-#endif
-}
-
-template <class _ValueType>
-inline _LIBCPP_HIDE_FROM_ABI _ValueType __libcpp_acquire_load(_ValueType const* __value) {
-#if _LIBCPP_HAS_THREADS && defined(__ATOMIC_ACQUIRE) &&                                                                \
-    (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
-  return __atomic_load_n(__value, __ATOMIC_ACQUIRE);
-#else
-  return *__value;
-#endif
-}
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI _Tp __libcpp_atomic_refcount_increment(_Tp& __t) _NOEXCEPT {
-#if _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT && _LIBCPP_HAS_THREADS
+#if _LIBCPP_HAS_THREADS
   return __atomic_add_fetch(std::addressof(__t), 1, __ATOMIC_RELAXED);
 #else
   return __t += 1;
@@ -61,7 +34,7 @@ inline _LIBCPP_HIDE_FROM_ABI _Tp __libcpp_atomic_refcount_increment(_Tp& __t) _N
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI _Tp __libcpp_atomic_refcount_decrement(_Tp& __t) _NOEXCEPT {
-#if _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT && _LIBCPP_HAS_THREADS
+#if _LIBCPP_HAS_THREADS
   return __atomic_add_fetch(std::addressof(__t), -1, __ATOMIC_ACQ_REL);
 #else
   return __t -= 1;
@@ -95,7 +68,13 @@ public:
     return false;
   }
 #endif
-  _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __libcpp_relaxed_load(&__shared_owners_) + 1; }
+  _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT {
+#if _LIBCPP_HAS_THREADS
+    return __atomic_load_n(&__shared_owners_, __ATOMIC_RELAXED) + 1;
+#else
+    return __shared_owners_ + 1;
+#endif
+  }
 };
 
 class _LIBCPP_EXPORTED_FROM_ABI __shared_weak_count : private __shared_count {

libcxx/include/__mutex/once_flag.h

@@ -10,10 +10,9 @@
 #define _LIBCPP___MUTEX_ONCE_FLAG_H
 
 #include <__config>
-#include <__functional/invoke.h>
 #include <__memory/addressof.h>
-#include <__memory/shared_count.h> // __libcpp_acquire_load
 #include <__tuple/tuple_size.h>
+#include <__type_traits/invoke.h>
 #include <__utility/forward.h>
 #include <__utility/integer_sequence.h>
 #include <__utility/move.h>
@@ -118,6 +117,15 @@ void _LIBCPP_HIDE_FROM_ABI __call_once_proxy(void* __vp) {
 
 _LIBCPP_EXPORTED_FROM_ABI void __call_once(volatile once_flag::_State_type&, void*, void (*)(void*));
 
+template <class _ValueType>
+inline _LIBCPP_HIDE_FROM_ABI _ValueType __libcpp_acquire_load(_ValueType const* __value) {
+#if _LIBCPP_HAS_THREADS
+  return __atomic_load_n(__value, __ATOMIC_ACQUIRE);
+#else
+  return *__value;
+#endif
+}
+
 #ifndef _LIBCPP_CXX03_LANG
 
 template <class _Callable, class... _Args>

libcxx/include/mutex

@@ -500,6 +500,10 @@ _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
+#  if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 23
+#    include <typeinfo>
+#  endif
+
 #  if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
 #    include <atomic>
 #    include <concepts>
@@ -513,7 +517,6 @@ _LIBCPP_POP_MACROS
 #    include <stdexcept>
 #    include <system_error>
 #    include <type_traits>
-#    include <typeinfo>
 #  endif
 #endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
 

libcxx/test/libcxx/transitive_includes/cxx26.csv

@@ -669,7 +669,6 @@ mutex ctime
 mutex limits
 mutex ratio
 mutex tuple
-mutex typeinfo
 mutex version
 new version
 numbers version