Re: [PATCH v5 6/6] libstdc++: make std::is_object dispatch to new built-in traits

[François Dumont via Gcc-patches]

On 13/06/2023 00:22, Ken Matsui via Libstdc++ wrote:
This patch gets std::is_object to dispatch to new built-in traits,
__is_function, __is_reference, and __is_void.

libstdc++-v3/ChangeLog:
        * include/std/type_traits (is_object): Use new built-in traits,
        __is_function, __is_reference, and __is_void.
        (__is_object): Define this built-in-like macro.
        (is_object_v): Use built-in traits through the build-in-like macro.

Signed-off-by: Ken Matsui <kmat...@cs.washington.edu>
---
  libstdc++-v3/include/std/type_traits | 19 +++++++++++++++++++
  1 file changed, 19 insertions(+)

diff --git a/libstdc++-v3/include/std/type_traits 
b/libstdc++-v3/include/std/type_traits
index 780fcc00135..93335f94385 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -682,11 +682,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
      { };
  
    /// is_object
+#if __has_builtin(__is_function) && __has_builtin(__is_reference) \
+    && __has_builtin(__is_void)
+
+#define __is_object(_Tp) \
+  (!(__is_function(_Tp) || __is_reference(_Tp) || __is_void(_Tp)))

Is this evaluation order random ? Are all those builtin functions 
performances equivalent ?

I would have felt that __is_void is the simplest/fastest cause only for 
'void' so would have put it first.

+
+  template<typename _Tp>
+    struct is_object
+    : public __bool_constant<__is_object(_Tp)>
+    { };
+#else
    template<typename _Tp>
      struct is_object
      : public __not_<__or_<is_function<_Tp>, is_reference<_Tp>,
                            is_void<_Tp>>>::type
      { };
+#endif
  
    template<typename>
      struct is_member_pointer;
@@ -3235,8 +3247,15 @@ template <typename _Tp>
    inline constexpr bool is_arithmetic_v = is_arithmetic<_Tp>::value;
  template <typename _Tp>
    inline constexpr bool is_fundamental_v = is_fundamental<_Tp>::value;
+
+#ifdef __is_object
+template <typename _Tp>
+  inline constexpr bool is_object_v = __is_object(_Tp);
+#else
  template <typename _Tp>
    inline constexpr bool is_object_v = is_object<_Tp>::value;
+#endif
+
  template <typename _Tp>
    inline constexpr bool is_scalar_v = is_scalar<_Tp>::value;
  template <typename _Tp>