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From: "pskocik at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/108194] GCC won't treat two compatible function types as
 compatible if any of them (or both of them) is declared _Noreturn
Date: Thu, 22 Dec 2022 17:10:33 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108194

--- Comment #6 from Petr Skocik <pskocik at gmail dot com> ---
(In reply to Petr Skocik from comment #5)
> (In reply to Andrew Pinski from comment #4)
> > Invalid as mentioned in r13-3135-gfa258f6894801a .
>=20
> I believe it's still a bug for pre-c2x __typeof.
> While it is GCC's prerogative to include _Noreturn/__attribute((noreturn))
> into the type for its own __typeof (which, BTW, I think is better design
> than the standardized semantics), I think two otherwise compatible functi=
on
> types should still remain compatible if they both either have or don't ha=
ve
> _Noreturn/__attribute((noreturn)). But treating `_Noreturn void
> NR_FN_A(void);`=20
> as INcompatible with `_Noreturn void NR_FN_B(void);` that's just wonky, I=
MO.

OK, the bug was MINE after all.

For bug report archeologists: I was doing what was meant to be a full
(qualifers-including) type comparison wrong. While something like
_Generic((__typeof(type0)*)0, __typeof(type1)*:1, default:0) suffices to get
around _Generic dropping qualifs (const/volatile/_Atomic) in its controlling
expression, for function pointer types at single pointer layer of indirecti=
on,
the _Noreturn attribute will still get dropped in the controlling expressio=
n of
_Generic (I guess that makes sense because they're much more closely relate=
d to
functions that how another pointer type would be related to its target type)
and another pointer layer of indirection if required as in
`_Generic((__typeof(type0)**)0, __typeof(type1)**:1, default:0)`.

Thanks you all very much, especially joseph@codesourcery.com, who pointed me
(pun intended) to the right solution over email. :)=