[gcc r13-2350] libstdc++: Use built-ins for some variable templates

[Jonathan Wakely]

https://gcc.gnu.org/g:cd20d9482a1f10ddf1c398c1a1d8421f97dfdefa

commit r13-2350-gcd20d9482a1f10ddf1c398c1a1d8421f97dfdefa
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Aug 31 15:00:24 2022 +0100

    libstdc++: Use built-ins for some variable templates
    
    This avoids having to instantiate a class template that just uses the
    same built-in anyway.
    
    None of the corresponding class templates have any type-completeness
    static assertions, so we're not losing any diagnostics by using the
    built-ins directly.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/type_traits (is_enum_v, is_class_v, is_union_v)
            (is_empty_v, is_polymoprhic_v, is_abstract_v, is_final_v)
            (is_base_of_v, is_aggregate_v): Use built-in directly instead of
            instantiating class template.

Diff:
---
 libstdc++-v3/include/std/type_traits | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 5b8314f24fd..52cca8bf3af 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -3165,11 +3165,11 @@ template <typename _Tp>
   inline constexpr bool is_member_function_pointer_v =
     is_member_function_pointer<_Tp>::value;
 template <typename _Tp>
-  inline constexpr bool is_enum_v = is_enum<_Tp>::value;
+  inline constexpr bool is_enum_v = __is_enum(_Tp);
 template <typename _Tp>
-  inline constexpr bool is_union_v = is_union<_Tp>::value;
+  inline constexpr bool is_union_v = __is_union(_Tp);
 template <typename _Tp>
-  inline constexpr bool is_class_v = is_class<_Tp>::value;
+  inline constexpr bool is_class_v = __is_class(_Tp);
 template <typename _Tp>
   inline constexpr bool is_function_v = is_function<_Tp>::value;
 template <typename _Tp>
@@ -3206,14 +3206,14 @@ template <typename _Tp>
   _GLIBCXX17_DEPRECATED
   inline constexpr bool is_literal_type_v = is_literal_type<_Tp>::value;
 #pragma GCC diagnostic pop
- template <typename _Tp>
-  inline constexpr bool is_empty_v = is_empty<_Tp>::value;
 template <typename _Tp>
-  inline constexpr bool is_polymorphic_v = is_polymorphic<_Tp>::value;
+  inline constexpr bool is_empty_v = __is_empty(_Tp);
 template <typename _Tp>
-  inline constexpr bool is_abstract_v = is_abstract<_Tp>::value;
+  inline constexpr bool is_polymorphic_v = __is_polymorphic(_Tp);
 template <typename _Tp>
-  inline constexpr bool is_final_v = is_final<_Tp>::value;
+  inline constexpr bool is_abstract_v = __is_abstract(_Tp);
+template <typename _Tp>
+  inline constexpr bool is_final_v = __is_final(_Tp);
 template <typename _Tp>
   inline constexpr bool is_signed_v = is_signed<_Tp>::value;
 template <typename _Tp>
@@ -3318,7 +3318,7 @@ template <typename _Tp, typename _Up>
   inline constexpr bool is_same_v = std::is_same<_Tp, _Up>::value;
 #endif
 template <typename _Base, typename _Derived>
-  inline constexpr bool is_base_of_v = is_base_of<_Base, _Derived>::value;
+  inline constexpr bool is_base_of_v = __is_base_of(_Base, _Derived);
 template <typename _From, typename _To>
   inline constexpr bool is_convertible_v = is_convertible<_From, _To>::value;
 template<typename _Fn, typename... _Args>
@@ -3356,16 +3356,19 @@ template<typename _Ret, typename _Fn, typename... _Args>
 
 #ifdef _GLIBCXX_HAVE_BUILTIN_IS_AGGREGATE
 # define __cpp_lib_is_aggregate 201703L
-  /// is_aggregate
+  /// is_aggregate - true if the type is an aggregate.
   /// @since C++17
   template<typename _Tp>
     struct is_aggregate
     : bool_constant<__is_aggregate(remove_cv_t<_Tp>)>
     { };
 
-  /// @ingroup variable_templates
+  /** is_aggregate_v - true if the type is an aggregate.
+   *  @ingroup variable_templates
+   *  @since C++17
+   */
   template<typename _Tp>
-    inline constexpr bool is_aggregate_v = is_aggregate<_Tp>::value;
+    inline constexpr bool is_aggregate_v = __is_aggregate(remove_cv_t<_Tp>);
 #endif
 #endif // C++17