[gcc r15-1247] libstdc++: Optimize std::is_unbounded_array compilation performance

[Ken Matsui]

https://gcc.gnu.org/g:b38aefbbc90a3334c6c5ba6569816d348a1a0c91

commit r15-1247-gb38aefbbc90a3334c6c5ba6569816d348a1a0c91
Author: Ken Matsui <kmatsui@gcc.gnu.org>
Date:   Mon Sep 11 13:58:35 2023 -0700

    libstdc++: Optimize std::is_unbounded_array compilation performance
    
    This patch optimizes the compilation performance of
    std::is_unbounded_array by dispatching to the new
    __is_unbounded_array built-in trait.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/type_traits (is_unbounded_array_v): Use
            __is_unbounded_array built-in trait.
    
    Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
    Reviewed-by: Patrick Palka <ppalka@redhat.com>
    Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

Diff:
---
 libstdc++-v3/include/std/type_traits | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 748fa186881d..efbe273d38a9 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -3682,11 +3682,16 @@ template<typename _Ret, typename _Fn, typename... _Args>
   /// True for a type that is an array of unknown bound.
   /// @ingroup variable_templates
   /// @since C++20
+# if _GLIBCXX_USE_BUILTIN_TRAIT(__is_unbounded_array)
+  template<typename _Tp>
+    inline constexpr bool is_unbounded_array_v = __is_unbounded_array(_Tp);
+# else
   template<typename _Tp>
     inline constexpr bool is_unbounded_array_v = false;
 
   template<typename _Tp>
     inline constexpr bool is_unbounded_array_v<_Tp[]> = true;
+# endif
 
   /// True for a type that is an array of known bound.
   /// @since C++20