On Fri, 16 Jul 2021 at 09:40, Jonathan Wakely <jwakely....@gmail.com> wrote:
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>
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> On Fri, 16 Jul 2021, 09:38 Jonathan Wakely, <jwakely....@gmail.com> wrote:
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>> On Fri, 16 Jul 2021, 09:30 Jakub Jelinek via Libstdc++,
>> <libstd...@gcc.gnu.org> wrote:
>>>
>>> On Fri, Jul 16, 2021 at 10:27:09AM +0200, Jakub Jelinek via Gcc-patches
>>> wrote:
>>> > On Fri, Jul 16, 2021 at 08:41:06AM +0100, Jonathan Wakely via Gcc-patches
>>> > wrote:
>>> > > --- a/libstdc++-v3/include/bits/max_size_type.h
>>> > > +++ b/libstdc++-v3/include/bits/max_size_type.h
>>> > > @@ -417,7 +417,10 @@ namespace ranges
>>> > > #endif
>>> > >
>>> > > #if __SIZEOF_INT128__
>>> > > +#pragma GCC diagnostic push
>>> > > +#pragma GCC diagnostic ignored "-Wpedantic"
>>> > > using __rep = unsigned __int128;
>>> > > +#pragma GCC diagnostic pop
>>> >
>>> > At least in simple cases like this, wouldn't
>>> > using __rep = __extension__ unsigned __int128;
>>>
>>> __extension__ using __rep = unsigned __int128;
>>> actually (now tested).
>>
>>
>> Ah, thanks. I didn't find the right syntax, and I know __extension__ doesn't
>> work in other cases, like quad float literals, so I assumed it doesn't work
>> here. I suppose the literals don't work because the warning comes from the
>> processor, which doesn't understand __extension__ (and also ignores the
>> diagnostic pragma).
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> That grammar for a using-declaration makes no sense at all btw ;-)
Hmm, in fact it seems that we can just use the __uint128_t typedef
instead, which doesn't give a pedwarn:
using __rep = __uint128_t;
Is that typedef always available if __int128 is? There's a comment in
gcc/c-family/c-common.c that I don't understand:
#if HOST_BITS_PER_WIDE_INT >= 64
/* Note that this is different than the __int128 type that's part of
the generic __intN support. */
if (targetm.scalar_mode_supported_p (TImode))
lang_hooks.decls.pushdecl (build_decl (UNKNOWN_LOCATION,
TYPE_DECL,
get_identifier ("__int128_t"),
intTI_type_node));
#endif
They are the same type in C++, so what is "different"? Is it possible
for __int128 to be different from a TImode integer?
We can still use __extension__ elsewhere, for defining explicit
specializations using the non-standard integers, e.g.
#define __INT_N(TYPE) \
+ __extension__ \
template<> \
struct __is_integer<TYPE> \
{ \
enum { __value = 1 }; \
typedef __true_type __type; \
};
