This patch optimizes the compilation performance of std::is_function by dispatching to the new __is_function built-in trait.
libstdc++-v3/ChangeLog: * include/std/type_traits (is_function): Use __is_function built-in trait. (is_function_v): Likewise. Optimize its implementation. Move this under is_const_v as this depends on is_const_v. Signed-off-by: Ken Matsui <kmat...@gcc.gnu.org> --- libstdc++-v3/include/std/type_traits | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits index db880d87f60..b6d0441129b 100644 --- a/libstdc++-v3/include/std/type_traits +++ b/libstdc++-v3/include/std/type_traits @@ -637,6 +637,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { }; /// is_function +#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_function) + template<typename _Tp> + struct is_function + : public __bool_constant<__is_function(_Tp)> + { }; +#else template<typename _Tp> struct is_function : public __bool_constant<!is_const<const _Tp>::value> { }; @@ -648,6 +654,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION template<typename _Tp> struct is_function<_Tp&&> : public false_type { }; +#endif #ifdef __cpp_lib_is_null_pointer // C++ >= 11 /// is_null_pointer (LWG 2247). @@ -3255,8 +3262,7 @@ template <typename _Tp> inline constexpr bool is_union_v = __is_union(_Tp); template <typename _Tp> inline constexpr bool is_class_v = __is_class(_Tp); -template <typename _Tp> - inline constexpr bool is_function_v = is_function<_Tp>::value; +// is_function_v is defined below, after is_const_v. #if _GLIBCXX_USE_BUILTIN_TRAIT(__is_reference) template <typename _Tp> @@ -3293,6 +3299,19 @@ template <typename _Tp> inline constexpr bool is_const_v = false; template <typename _Tp> inline constexpr bool is_const_v<const _Tp> = true; + +#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_function) +template <typename _Tp> + inline constexpr bool is_function_v = __is_function(_Tp); +#else +template <typename _Tp> + inline constexpr bool is_function_v = !is_const_v<const _Tp>; +template <typename _Tp> + inline constexpr bool is_function_v<_Tp&> = false; +template <typename _Tp> + inline constexpr bool is_function_v<_Tp&&> = false; +#endif + template <typename _Tp> inline constexpr bool is_volatile_v = false; template <typename _Tp> -- 2.43.0