Re: Can offsetting a non-null pointer result in a null one?

[Marc Glisse <marc dot glisse at inria dot fr>]

On Mon, 20 Aug 2018, Richard Biener wrote:

> > P p+ N is nonnull if P or N is known to be nonnull
> > (and something similar for &p->field and others)
>
> But we already do that.

Oups... I never noticed, I should have checked.

>      else if (code == POINTER_PLUS_EXPR)
>        {
>          /* For pointer types, we are really only interested in asserting
>             whether the expression evaluates to non-NULL.  */
>          if (range_is_nonnull (&vr0) || range_is_nonnull (&vr1))
>            set_value_range_to_nonnull (vr, expr_type);
>          else if (range_is_null (&vr0) && range_is_null (&vr1))
>            set_value_range_to_null (vr, expr_type);
>          else
>            set_value_range_to_varying (vr);
>        }
>
> Ah, range_is_nonnull (&vr1) is only matching ~[0,0].  We'd
> probably want VR_RANGE && !range_includes_zero_p here.  That
> range_is_nonnull is probably never true due to canonicalization.

That explains it. Yes please. I am surprised there isn't a helper like 
range_includes_zero_p or value_inside_range that takes a value_range* as 
argument so we don't have to worry about the type of range (the closest 
seems to be value_ranges_intersect_p with a singleton range, but that 
function seems dead and broken). When POINTER_PLUS_EXPR is changed to take 
a signed argument, your suggested test will need updating :-(

--
Marc Glisse