ludovic.cour...@inria.fr (Ludovic Courtès) writes:
> I understand. However, I’m concerned about keeping the information at
> compile-time. For example:
>
> extern void foo (int a, int x[a]);
> static void bar (void) {
> int x[123];
> foo (456, x);
> }
>
> Here the compiler could emit a diagnostic in ‘bar’.
>
> IOW, ABI restrictions ABI imply that nothing can be done in the body of
> ‘foo’; however, the information could still used at call sites.
I see. That seems to have some potential. It would be a gcc extension,
of course. Perhaps something like
extern void foo (int a, int x[__attribute__ ((dim (a)))])
could be implemented. This would issue an error if foo were called such
that the length of the x were not at least a. A serious problem with
this approach would be that it is not reliable, since the caller of foo
might not know the length of the array being passed as a pointer. I
suppose it would be possible to issue runtime checks when static checks
don't work, and issue a compilation error in cases were no runtime check
is possible. Without those checks I think the extension would be ill
advised. With those checks I don't know how often it would usable in
practice.
Ian
