[gcc r15-1246] libstdc++: Optimize std::is_volatile compilation performance

[Ken Matsui]

https://gcc.gnu.org/g:bb99672e0c49d8b8822664eaabc10cd51a42aab4

commit r15-1246-gbb99672e0c49d8b8822664eaabc10cd51a42aab4
Author: Ken Matsui <kmatsui@gcc.gnu.org>
Date:   Wed Mar 22 16:28:06 2023 -0700

    libstdc++: Optimize std::is_volatile compilation performance
    
    This patch optimizes the compilation performance of std::is_volatile
    by dispatching to the new __is_volatile built-in trait.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/type_traits (is_volatile): Use __is_volatile
            built-in trait.
            (is_volatile_v): Likewise.
    
    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 | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 8df0cf3ac3b8..748fa186881d 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -851,6 +851,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
   /// is_volatile
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_volatile)
+  template<typename _Tp>
+    struct is_volatile
+    : public __bool_constant<__is_volatile(_Tp)>
+    { };
+#else
   template<typename>
     struct is_volatile
     : public false_type { };
@@ -858,6 +864,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp>
     struct is_volatile<_Tp volatile>
     : public true_type { };
+#endif
 
   /// is_trivial
   template<typename _Tp>
@@ -3360,10 +3367,15 @@ template <typename _Tp>
   inline constexpr bool is_function_v<_Tp&&> = false;
 #endif
 
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_volatile)
+template <typename _Tp>
+  inline constexpr bool is_volatile_v = __is_volatile(_Tp);
+#else
 template <typename _Tp>
   inline constexpr bool is_volatile_v = false;
 template <typename _Tp>
   inline constexpr bool is_volatile_v<volatile _Tp> = true;
+#endif
 
 template <typename _Tp>
   inline constexpr bool is_trivial_v = __is_trivial(_Tp);