Re: [PATCH] libstdc++: use new built-in trait __is_reference

[Xi Ruoyao <xry111@xry111.site>]

You need to CC libstdc++@gcc.gnu.org for any patches touching libstdc++.

On Sat, 2023-03-18 at 21:21 -0700, Ken Matsui via Gcc-patches wrote:
> libstdc++-v3/ChangeLog:
> 
> * include/std/type_traits (is_reference): Use __is_reference built-in
> trait.

Bad ChangeLog format.  You should have a tab (not 4 or 8 spaces, nor
nothing) to indent the ChangeLog content.

Is there any benefit to use a builtin, instead of the existing
implementation?  I can see no but maybe I'm stupid.

> ---
> diff --git a/libstdc++-v3/include/std/type_traits
> b/libstdc++-v3/include/std/type_traits

The patch fails to apply.  It seems because your mail client inserted an
additional newline before "b/".  Try to use git-send-email or configure
the mail client properly.

> index 2bd607a8b8f..18408d8ceb6 100644
> --- a/libstdc++-v3/include/std/type_traits
> +++ b/libstdc++-v3/include/std/type_traits
> @@ -639,6 +639,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>    // Composite type categories.
> 
>    /// is_reference
> +#if __has_builtin(__is_reference)
> +  template<typename _Tp>
> +    struct is_reference
> +    : public integral_constant<bool, __is_reference(_Tp)>

If a patch depends on another patch not applied yet, sent them in a
series.  Or people are puzzled because when this patch is applied alone,
the code fails to build.

> +    { };
> +#else
>    template<typename _Tp>
>      struct is_reference
>      : public false_type
> @@ -653,6 +659,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>      struct is_reference<_Tp&&>
>      : public true_type
>      { };
> +#endif
> 
>    /// is_arithmetic
>    template<typename _Tp>

-- 
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University