[PATCH v26 09/13] libstdc++: Optimize std::add_rvalue_reference compilation performance

[Jonathan Wakely]

On 11/05/24 02:01 -0700, Ken Matsui wrote:
>This patch optimizes the compilation performance of
>std::add_rvalue_reference by dispatching to the new
>__add_rvalue_reference built-in trait.
>
>libstdc++-v3/ChangeLog:
>
>	* include/std/type_traits (add_rvalue_reference): Use
>	__add_rvalue_reference built-in trait.
>	(__add_rvalue_reference_helper): Likewise.
>
>Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
>---
> 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 effa3fbcb75..824cad90a25 100644
>--- a/libstdc++-v3/include/std/type_traits
>+++ b/libstdc++-v3/include/std/type_traits
>@@ -1185,6 +1185,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>     };
>
>   /// @cond undocumented
>+#if _GLIBCXX_USE_BUILTIN_TRAIT(__add_rvalue_reference)
>+  template<typename _Tp>
>+    struct __add_rvalue_reference_helper
>+    { using type = __add_rvalue_reference(_Tp); };
>+#else
>   template<typename _Tp, typename = void>
>     struct __add_rvalue_reference_helper
>     { using type = _Tp; };
>@@ -1192,6 +1197,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>   template<typename _Tp>
>     struct __add_rvalue_reference_helper<_Tp, __void_t<_Tp&&>>
>     { using type = _Tp&&; };
>+#endif
>
>   template<typename _Tp>
>     using __add_rval_ref_t = typename __add_rvalue_reference_helper<_Tp>::type;

Same comment as for add_lvalue_reference.

>@@ -1748,9 +1754,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> #endif
>
>   /// add_rvalue_reference
>+#if _GLIBCXX_USE_BUILTIN_TRAIT(__add_rvalue_reference)
>+  template<typename _Tp>
>+    struct add_rvalue_reference
>+    { using type = __add_rvalue_reference(_Tp); };
>+#else
>   template<typename _Tp>
>     struct add_rvalue_reference
>     { using type = __add_rval_ref_t<_Tp>; };
>+#endif
>
> #if __cplusplus > 201103L
>   /// Alias template for remove_reference
>-- 
>2.44.0
>