Re: [RFC v1 2/2] Makeconfig: Compile glibc with -fno-delete-null-pointer-checks

[Florian Weimer <fweimer@redhat.com>]

* Richard Biener:

> On Tue, 11 Jul 2023, Alejandro Colomar wrote:
>
>> Don't undefine __nonnull to prevent compiler optimizations.  Instead,
>> tell the compiler to not optimize based on the attribute, via the
>> appropriate flag.
>
> I'll note that using -fno-delete-null-pointer-checks doesn't work
> (anymore?) to preserve the nullptr check in
>
> int __attribute__((nonnull)) foo (int *p) 
> {
>   if (p)
>     return *p;
>   return 0;
> }
>
> so the documentation of 'nonnull' which says
>
> @item The compiler may also perform optimizations based on the
> knowledge that certain function arguments cannot be null.  These
> optimizations can be disabled by the
> @option{-fno-delete-null-pointer-checks} option. @xref{Optimize Options}.
>
> isn't accurate.

That's the paragraph about function calls, not function definitions.
The above is a function definition.  So it's not a counterexample.  The
second paragraph says that the optimization behavior you see is
currently not controllable by an option.

Thanks,
Florian