Re: WG14 paper for removing restrict from nptr in strtol(3)

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Jul 09, 2024 at 11:07:59AM +0200, Alejandro Colomar wrote:
> > > restrict, as of what -Wrestrict warns about, seems a reasonable
> > > thing.
> > > 
> > > How about a [[gnu::restrict()]] attribute, similar to
> > > [[gnu::access()]],
> > > which is simpler than the qualifier?  Since restrict is only
> > > meaningful
> > > in function boundaries, it would make sense to have a function
> > > attribute.  We don't want a qualifier that must follow discarding
> > > rules.
> > 
> > If it doesn't have the same meaning as "restrict" then perhaps call the
> > proposed attribute something other than "restrict"?
> 
> Yup, I was thinking that maybe noalias is a better name.

Name is one thing, but you'd also need to clearly define what it means.
When restrict is access based, it is clear what it means.

If you want something else which is not based on accesses and which should
allow warnings in the callers, I suppose you need to specify not just the
pointer but the extent as well (and maybe stride) or that it is an '\0'
terminated string, because if you want to say that for
void foo (char *, const char *, int);
the 2 pointers don't really alias, the size information is missing.  So,
shall the new warning warn on
struct S { char a[1024]; char b[1024]; } s;
foo (s.a, s.b, 512);
or not?  Or foo (s.a, s.a + 512, 512);

	Jakub