On Mon, Jan 14, 2019 at 9:42 AM Jakub Jelinek <ja...@redhat.com> wrote:
>
> On Mon, Jan 14, 2019 at 09:29:03AM +0100, Richard Biener wrote:
> > So why is this not just
> >
> > return (__UINTPTR_TYPE__)__x > (__UINTPTR_TYPE__)__y;
> >
> > or with the casts elided? Does the C++ standard say pointers are
> > to be compared unsigned here? Or do all targets GCC support
> > lay out the address space in a way that this is correct for pointers
> > into distinct objects?
>
> See PR78420 for details on why it is done that way.
I see. So the __builtin_is_constant_evaluated thing makes it
"correct" (but then eventually exposing the non-total order issue again).
And if I read the PR correctly we'd really like to be able to write
if (__builtin_constant_p (<expr>, &result))
return result;
to make sure whatever undesired-in-the-IL things of <expr>
do not leak there.
Btw, wouldn't sth like
if (__builtin_is_constant_evaluated())
{
union U { __UINTPTR_TYPE__ u; _Tp *p } __ux, __uy;
__ux.p = __x;
__uy.p = __y;
return __ux.u < __uy.u;
}
be more correct and consistent? Well, or any other way of
evading that reinterpret-cast "issue"?
Richard.
>
> Jakub
