Re: [PATCH] Use __is_same_as for std::is_same and std::is_same_v

[Jonathan Wakely <jwakely@redhat.com>]

On 16/10/19 10:42 +0100, Jonathan Wakely wrote:
>On 12/10/19 18:15 +0200, Romain Geissler wrote:
>>Le sam. 12 oct. 2019 à 17:44, Romain Geissler
>><romain.geissler@gmail.com> a écrit :
>>>
>>>It looks like this creates the following error when I try to bootstrap
>>>clang 9.0.0 using the latest gcc and libstdc++ from trunk. Note that
>>>with g++, there is no problem, however it looks like clang++ has some
>>>problem with the new header. I don't know if this is an issue on
>>>libstdc++ side or clang++ side.
>>
>>__is_same_as is not implemented as a compiler builtin in clang++
>
>Sigh, I guess that explains why we weren't using it already.
>
>>unlike g++, thus the error on clang 9.0.0 side. It looks like current
>>clang trunk doesn't define __is_same_as either. Until clang implements
>>this support (if it ever will), usage of __is_same_as in libstdc++
>>shall be conditional, only when __has_builtin(__is_same_as) is true
>>(however that would require that gcc implements __has_builtin, as
>>implemented here:
>>https://gcc.gnu.org/ml/gcc-patches/2019-10/msg00062.html )
>
>No, we don't need GCC to support __has_builtin, because we know GCC
>supports __is_same_as so there's no need to check for it.
>
>So something like this would work fine:
>
>#if __GNUC__ >= 10
># define _GLIBCXX_HAVE__IS_SAME_AS
>#elif defined(__has_builtin)
># if __has_builtin(__is_same_as)
>#  define _GLIBCXX_HAVE__IS_SAME_AS
># endif
>#endif

It looks like Clang provides __is_same instead.

I'll commit a fix today.