[Mesa-dev] Add an ASSERTED macro to use in place of MAYBE_UNUSED?

[Kristian Høgsberg]

On Mon, Apr 22, 2019 at 3:11 PM Matt Turner <mattst88 at gmail.com> wrote:
>
> On Mon, Apr 22, 2019 at 1:09 PM Kristian Høgsberg <hoegsberg at gmail.com> wrote:
> >
> > On Mon, Apr 22, 2019 at 12:11 PM Jason Ekstrand <jason at jlekstrand.net> wrote:
> > >
> > > All,
> > >
> > > I've seen discussions come up several times lately about whether you should use MAYBE_UNUSED or UNUSED in what scenario and why do we have two of them anyway.  That got me thinking a bit.  Maybe what we actually want instead of MAYBE_UNUSED is something like this:
> > >
> > > #ifdef NDEBUG
> > > #define ASSERTED UNUSED
> > > #else
> > > #define ASSERTED
> > > #endif
> > >
> > > That way, if you only need a parameter for asserts, you can declare it ASSERTED and it won't warn in release builds will still throw a warning if you do a debug build which doesn't use it.  Of course, there are other times when something is validly MAYBE_UNUSED such as auto-generated code or the genX code we use on Intel.  However, this provides additional meaning and means the compiler warnings are still useful even after you've relegated a value to assert-only.
> > >
> > > Thoughts?  I'm also open to a better name; that's the best I could do in 5 minutes.
> >
> > I think that's going in the wrong direction - if anything I think that
> > having both UNUSED and MAYBE_UNUSED is redundant and feel that just
> > UNUSED would be fine. __attribute__((unused)) doesn't mean "strictly
> > not used", it means "don't warn if this isn't used".
>
> I agree that having both UNUSED and MAYBE_UNUSED is silly and I would
> be happy to see MAYBE_UNUSED go away.
>
> I think the advantage of Jason's proposal is that we are alerted if
> there is actually dead code. E.g., if we remove the assert that used a
> variable, we currently won't get a warning from the compiler that the
> variable is unused. At least in release builds we would, if we did
> what Jason suggests.
>
> Maybe we do what Jason suggests and then remove MAYBE_UNUSED?

Right... I see now, that's sounds reasonable.

Kristian