https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114731
--- Comment #15 from Alejandro Colomar <alx at kernel dot org> ---
(In reply to uecker from comment #13)
> A couple of comments:
>
> In principle, those warnings are not false positives. The design of _Generic
> requires that the non-taken branches are valid in C, so some warnings are
> required by the C standard. We can tweak warnings (which we already did for
> some), but I do not think it is possible to solve all issues in this wa.
I showed you an example program in comment #12 that is an evidence that either
there's no requirement by ISO C that this results in a diagnostic, or maybe
it's required by GCC is already violating the standard here. I'm repeating it
here:
$ cat constraint.c
void f(int *);
int
main(void)
{
unsigned u;
f(&u);
}
$ cc constraint.c -S
$
>
> There are different ways to work around this:
>
> One can work around using explicit casts and/or temporary values so that the
> code of all branches is always valid.
It's too error prone.
> It may be helpful to flatten multi-level _Generic to one level by matching
> an artificial function pointer type:
>
> #define foo(a, b) _Generic((void(*)(typeof(a), typeof(b)))0, void(*)(int,
> int): ...)
The thing is that the intermediate macros are also an intended API, so I need
to either call it using two levels of macros, or reimplement it in the caller.
This is also repetitive and error-prone, just like the casts.
