[gcc r15-1248] libstdc++: Optimize std::add_pointer compilation performance

[Ken Matsui]

https://gcc.gnu.org/g:24da955ab442107909a06f3ef722f4dbf6751236

commit r15-1248-g24da955ab442107909a06f3ef722f4dbf6751236
Author: Ken Matsui <kmatsui@gcc.gnu.org>
Date:   Wed Feb 14 03:42:33 2024 -0800

    libstdc++: Optimize std::add_pointer compilation performance
    
    This patch optimizes the compilation performance of std::add_pointer
    by dispatching to the new __add_pointer built-in trait.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/type_traits (add_pointer): Use __add_pointer
            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 | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index efbe273d38a9..e179015be934 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -2135,6 +2135,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { };
 #endif
 
+  /// add_pointer
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__add_pointer)
+  template<typename _Tp>
+    struct add_pointer
+    { using type = __add_pointer(_Tp); };
+#else
   template<typename _Tp, typename = void>
     struct __add_pointer_helper
     { using type = _Tp; };
@@ -2143,7 +2149,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     struct __add_pointer_helper<_Tp, __void_t<_Tp*>>
     { using type = _Tp*; };
 
-  /// add_pointer
   template<typename _Tp>
     struct add_pointer
     : public __add_pointer_helper<_Tp>
@@ -2156,6 +2161,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp>
     struct add_pointer<_Tp&&>
     { using type = _Tp*; };
+#endif
 
 #if __cplusplus > 201103L
   /// Alias template for remove_pointer