https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110617
--- Comment #7 from Alejandro Colomar <alx at kernel dot org> --- Hi Xi, Richard! On 2023-07-11 10:34, xry111 at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110617 > > --- Comment #6 from Xi Ruoyao <xry111 at gcc dot gnu.org> --- > Anyway I'm already too frustrated about this so I'll not continue > working on nonnull within Glibc headers. If you don't like this just close it > as WONTFIX. > I understand your frustration. I'll continue your work, if you don't mind. On 2023-07-11 09:46, rguenth at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110617 > > --- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> --- > I think a -f... option to disable the code generation effects would make more > sense than adding another attribute kind. > The idea of a -f... option makes sense. However, I'm skeptical about being able to reach null correctness via an attribute. I think a qualifier, similar to restrict or const, would be better qualified (pun not intended 😄 for this task. Clang's _Nonnull (and _Nullable, and friends) are such qualifiers, similar to restrict. I think they are better designed for the goal of having diagnostics if null correctness is breached. However, they have issues as qualifiers, since the standard says they should be dropped in lvalue to rvalue conversions (restrict shares this same issue). There's been a suggestion in an LLVM forum to add an _Optional qualifier to the pointee, which would workaround the issue that qualifiers are dropped. I'll put both alternatives next to each other for comparison: #pragma clang assume_nonnull begin int i; int *p; int *_Nullable q; _Optional int *r; p = NULL; // warn q = NULL; // Ok r = NULL; // Ok p = &i; // Ok q = &i; // Ok r = &i; // Ok p = r; // warn: '_Optional' qualifier is discarded in assignment q = p; // Ok r = p; // Ok #pragma clang assume_nonnull end Cheers, Alex -- <http://www.alejandro-colomar.es/> GPG key fingerprint: A9348594CE31283A826FBDD8D57633D441E25BB5
