https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102989
Lénárd Szolnoki <leni536 at gmail dot com> changed:
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CC| |leni536 at gmail dot com
--- Comment #33 from Lénárd Szolnoki <leni536 at gmail dot com> ---
(In reply to jos...@codesourcery.com from comment #32)
> On Fri, 28 Oct 2022, jakub at gcc dot gnu.org via Gcc-bugs wrote:
>
> > > That said, if C allows us to limit to 128bits then let's do that for now.
> > > 32bit targets will still see all the complication when we give that a
> > > stab.
> >
> > I'm afraid once we define BITINT_MAXWIDTH, it will become part of the ABI,
> > so
> > we can't increase it afterwards.
>
> I don't think it's part of the ABI; I think it's always OK to increase
> BITINT_MAXWIDTH, as long as the wider types don't need more alignment than
> the previous choice of max_align_t.
It's not part of the ABI until people put _BitInt(BITINT_MAXWIDTH) on ABI
boundaries of their libraries. If a ridiculously large BITINT_MAXWIDTH does
nothing more than discourages usages of _BitInt(BITINT_MAXWIDTH) in general,
than that's already great. We don't need an other intmax.
Also I don't want to think about the max N for _BitInt(N), similarly how I
don't want to think about the max N for int[N]. There might be implementation
limits, but it should be high enough so I don't have to think about those for
everyday coding.
> Thus, starting with a 128-bit limit (or indeed a 64-bit limit on 32-bit
> platforms, so that all the types fix within existing modes supported for
> arithmetic), and adding support for wider _BitInt later, would be a
> reasonable thing to do.
I disagree.
> (You still have ABI considerations even with such a limit: apart from the
> padding question, on x86_64 the ABI says _BitInt(128) is 64-bit aligned
> but __int128 is 128-bit aligned.)
>
> > Anyway, I'm afraid we probably don't have enough time to implement this
> > properly in stage1, so might need to target GCC 14 with it. Unless somebody
> > spends on it
> > the remaining 2 weeks full time.
>
> I think https://gcc.gnu.org/pipermail/gcc/2022-October/239704.html is
> still current as a list of C2x language features likely not to make it
> into GCC 13. (I hope to get auto and constexpr done in the next two
> weeks, and the other C2x language features not on that list are done.)
