On Thu, 27 Jul 2023, Ken Matsui via Gcc-patches wrote:
> This patch uses _GLIBCXX_HAS_BUILTIN_TRAIT macro instead of
> __has_builtin in the type_traits header. This macro supports to toggle
> the use of built-in traits in the type_traits header through
> _GLIBCXX_NO_BUILTIN_TRAITS macro, without needing to modify the
> source code.
>
> libstdc++-v3/ChangeLog:
>
> * include/std/type_traits (__has_builtin): Replace with ...
> (_GLIBCXX_HAS_BUILTIN): ... this.
>
> Signed-off-by: Ken Matsui <kmat...@gcc.gnu.org>
> ---
> libstdc++-v3/include/std/type_traits | 26 +++++++++++++-------------
> 1 file changed, 13 insertions(+), 13 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/type_traits
> b/libstdc++-v3/include/std/type_traits
> index 9f086992ebc..12423361b6e 100644
> --- a/libstdc++-v3/include/std/type_traits
> +++ b/libstdc++-v3/include/std/type_traits
> @@ -1411,7 +1411,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> : public __bool_constant<__is_base_of(_Base, _Derived)>
> { };
>
> -#if __has_builtin(__is_convertible)
> +#if _GLIBCXX_HAS_BUILTIN_TRAIT(__is_convertible)
> template<typename _From, typename _To>
> struct is_convertible
> : public __bool_constant<__is_convertible(_From, _To)>
> @@ -1462,7 +1462,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> #if __cplusplus >= 202002L
> #define __cpp_lib_is_nothrow_convertible 201806L
>
> -#if __has_builtin(__is_nothrow_convertible)
> +#if _GLIBCXX_HAS_BUILTIN_TRAIT(__is_nothrow_convertible)
> /// is_nothrow_convertible_v
> template<typename _From, typename _To>
> inline constexpr bool is_nothrow_convertible_v
> @@ -1537,7 +1537,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> { using type = _Tp; };
>
> /// remove_cv
> -#if __has_builtin(__remove_cv)
> +#if _GLIBCXX_HAS_BUILTIN_TRAIT(__remove_cv)
> template<typename _Tp>
> struct remove_cv
> { using type = __remove_cv(_Tp); };
> @@ -1606,7 +1606,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> // Reference transformations.
>
> /// remove_reference
> -#if __has_builtin(__remove_reference)
> +#if _GLIBCXX_HAS_BUILTIN_TRAIT(__remove_reference)
> template<typename _Tp>
> struct remove_reference
> { using type = __remove_reference(_Tp); };
> @@ -2963,7 +2963,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> template<typename _Tp,
> bool _Nothrow = noexcept(_S_conv<_Tp>(_S_get())),
> typename = decltype(_S_conv<_Tp>(_S_get())),
> -#if __has_builtin(__reference_converts_from_temporary)
> +#if _GLIBCXX_HAS_BUILTIN_TRAIT(__reference_converts_from_temporary)
> bool _Dangle = __reference_converts_from_temporary(_Tp, _Res_t)
> #else
> bool _Dangle = false
> @@ -3420,7 +3420,7 @@ template<typename _Ret, typename _Fn, typename... _Args>
> */
> #define __cpp_lib_remove_cvref 201711L
>
> -#if __has_builtin(__remove_cvref)
> +#if _GLIBCXX_HAS_BUILTIN_TRAIT(__remove_cvref)
> template<typename _Tp>
> struct remove_cvref
> { using type = __remove_cvref(_Tp); };
> @@ -3515,7 +3515,7 @@ template<typename _Ret, typename _Fn, typename... _Args>
> : public bool_constant<is_unbounded_array_v<_Tp>>
> { };
>
> -#if __has_builtin(__is_layout_compatible)
> +#if _GLIBCXX_HAS_BUILTIN_TRAIT(__is_layout_compatible)
Hmm, I was thinking we'd use this macro only for traits that have a
fallback non-built-in implementation so that we could easily use/test
their fallback implementation. For traits that don't have such a
fallback, using this macro would mean that trait would no longer get
defined at all, which doesn't seem as useful. Perhaps let's initially
adjust only the traits that have a fallback implementation?
We could then verify that using the fallback implementation for all such
traits works as expected by running the testsuite with:
make check RUNTESTFLAGS="conformance.exp
--target_board=unix/-D_GLIBCXX_NO_BUILTIN_TRAITS"
>
> /// @since C++20
> template<typename _Tp, typename _Up>
> @@ -3529,7 +3529,7 @@ template<typename _Ret, typename _Fn, typename... _Args>
> constexpr bool is_layout_compatible_v
> = __is_layout_compatible(_Tp, _Up);
>
> -#if __has_builtin(__builtin_is_corresponding_member)
> +#if _GLIBCXX_HAS_BUILTIN_TRAIT(__builtin_is_corresponding_member)
> #define __cpp_lib_is_layout_compatible 201907L
>
> /// @since C++20
> @@ -3540,7 +3540,7 @@ template<typename _Ret, typename _Fn, typename... _Args>
> #endif
> #endif
>
> -#if __has_builtin(__is_pointer_interconvertible_base_of)
> +#if _GLIBCXX_HAS_BUILTIN_TRAIT(__is_pointer_interconvertible_base_of)
> /// True if `_Derived` is standard-layout and has a base class of type
> `_Base`
> /// @since C++20
> template<typename _Base, typename _Derived>
> @@ -3554,7 +3554,7 @@ template<typename _Ret, typename _Fn, typename... _Args>
> constexpr bool is_pointer_interconvertible_base_of_v
> = __is_pointer_interconvertible_base_of(_Base, _Derived);
>
> -#if __has_builtin(__builtin_is_pointer_interconvertible_with_class)
> +#if
> _GLIBCXX_HAS_BUILTIN_TRAIT(__builtin_is_pointer_interconvertible_with_class)
> #define __cpp_lib_is_pointer_interconvertible 201907L
>
> /// True if `__mp` points to the first member of a standard-layout type
> @@ -3590,8 +3590,8 @@ template<typename _Ret, typename _Fn, typename... _Args>
> template<typename _Tp>
> inline constexpr bool is_scoped_enum_v = is_scoped_enum<_Tp>::value;
>
> -#if __has_builtin(__reference_constructs_from_temporary) \
> - && __has_builtin(__reference_converts_from_temporary)
> +#if _GLIBCXX_HAS_BUILTIN_TRAIT(__reference_constructs_from_temporary) \
> + && _GLIBCXX_HAS_BUILTIN_TRAIT(__reference_converts_from_temporary)
>
> #define __cpp_lib_reference_from_temporary 202202L
>
> @@ -3632,7 +3632,7 @@ template<typename _Ret, typename _Fn, typename... _Args>
> template<typename _Tp, typename _Up>
> inline constexpr bool reference_converts_from_temporary_v
> = reference_converts_from_temporary<_Tp, _Up>::value;
> -#endif // __has_builtin for reference_from_temporary
> +#endif // _GLIBCXX_HAS_BUILTIN_TRAIT for reference_from_temporary
> #endif // C++23
>
> #if _GLIBCXX_HAVE_IS_CONSTANT_EVALUATED
> --
> 2.41.0
>
>
