Re: [PATCH 0/12] GCC _BitInt support [PR102989]

[Andrew Pinski <pinskia@gmail.com>]

On Thu, Aug 10, 2023 at 12:13 AM Jakub Jelinek via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Thu, Aug 10, 2023 at 06:55:05AM +0000, Richard Biener wrote:
> > On Wed, 9 Aug 2023, Joseph Myers wrote:
> >
> > > On Wed, 9 Aug 2023, Jakub Jelinek via Gcc-patches wrote:
> > >
> > > > - _Complex _BitInt(N) isn't supported; again mainly because none of the psABIs
> > > >   mention how those should be passed/returned; in a limited way they are
> > > >   supported internally because the internal functions into which
> > > >   __builtin_{add,sub,mul}_overflow{,_p} is lowered return COMPLEX_TYPE as a
> > > >   hack to return 2 values without using references/pointers
> > >
> > > What happens when the usual arithmetic conversions are applied to
> > > operands, one of which is a complex integer type and the other of which is
> > > a wider _BitInt type?  I don't see anything in the code to disallow this
> > > case (which would produce an expression with a _Complex _BitInt type), or
> > > any testcases for it.
> > >
> > > Other testcases I think should be present (along with any corresponding
> > > changes needed to the code itself):
> > >
> > > * Verifying that the new integer constant suffix is rejected for C++.
> > >
> > > * Verifying appropriate pedwarn-if-pedantic for the new constant suffix
> > > for versions of C before C2x (and probably for use of _BitInt type
> > > specifiers before C2x as well) - along with the expected -Wc11-c2x-compat
> > > handling (in C2x mode) / -pedantic -Wno-c11-c2x-compat in older modes.
> >
> > Can we go as far as deprecating our _Complex int extension for
> > C17 and make it unavailable for C2x, side-stepping the issue?
> > Or maybe at least considering that for C2x?
>
> I can just sorry at it for now.  And now that I search through the x86-64
> psABI again, it doesn't mention complex integers at all, so we are there on
> our own.  And it seems we don't have anything for complex integers on the
> library side and the complex lowering is before bitint lowering, so it might
> just work with < 10 lines of changes in code + testsuite, but if we do
> enable it, let's do it incrementally.

_Complex int division also has issues which is another reason to
deprecate/remove it; see PR 104937 for that and
https://gcc.gnu.org/legacy-ml/gcc/2001-11/msg00790.html (which was the
first time to deprecate _Complex int;
https://gcc.gnu.org/legacy-ml/gcc/2001-11/msg00863.html).

Thanks,
Andrew


>
>         Jakub
>