[RFC] Support for nonzero attribute

[Jonathan Wakely]

On Tue, 7 Jun 2022 at 20:40, Miika via Gcc <gcc@gcc.gnu.org> wrote:
>
> On Monday, June 6th, 2022 at 9:42 PM, Ben Boeckel <ben.boeckel@kitware.com> wrote:
> > > Based on Jakub's and Yair's comments I created a new attribute "inrange".
> > > Inrage takes three arguments, pos min and max.
> > > Pos being the argument position in the function, and min and max defines the
> > > range of valid integer. Both min and max are inclusive and work with enums.
> > > Warnings are enabled with the new flag: "-Winrange".
> >
> >
> > Is this something that could be applied to variables or types (I've not
> > much experience with GCC attribute internal mechanisms, so maybe not)?
>
> I took a closer look at it and looks like it can be applied.
>
> So trying to compile this:
> ```
> typedef int __attribute__((inrange(0, 100))) percentage_t;
> int main() {
>         int percentage __attribute__((inrange(0, 100))) = -1;
>         percentage_t per __attribute__((inrange(0, 100))) = -1;
> }
> ```
>
> Would print out something like this:
>
> foo.c: In function 'main':
> foo.c:3:59: warning: inrange variable 'percentage' requires integer in rage of 0..100 [-Winrange]

N.B. "rage" should be "range".

>From the diagnostic it's not clear to me whether this is an inclusive
range. Is 0 allowed? Is 100 allowed?

Using [0,100] interval notation would imply both endpoints are valid,
which I think matches the semantics of your attribute. Is interval
notation sufficiently widely understood to use here?