Re: [PATCH] c++/60760 - arithmetic on null pointers should not be allowed in constant expressions

[Martin Sebor <msebor at gmail dot com>]

On 07/18/2016 11:51 AM, Jason Merrill wrote:
> On 07/06/2016 06:20 PM, Martin Sebor wrote:
> > @@ -2911,6 +2923,14 @@ cxx_eval_indirect_ref (const constexpr_ctx
> > *ctx, tree t,
>
> >        if (*non_constant_p)
>
> >      return t;
>
> >
>
> > +      if (integer_zerop (op0))
>
> > +    {
>
> > +      if (!ctx->quiet)
>
> > +        error ("dereferencing a null pointer");
>
> > +      *non_constant_p = true;
>
> > +      return t;
>
> > +    }
>
> I'm skeptical of checking this here, since *p is valid for null p; &*p
> is even a constant expression.  And removing this hunk doesn't seem to
> break any of your tests.
>
> OK with that hunk removed.

With it removed the constexpr-nullptr-2.C test fails on line 64:

  constexpr const int *pi0 = &pa2->pa1->pa0->i;   // { dg-error "null 
pointer|not a constant" }

Here, pa2 and pa1 are non-null but pa0 is null.

Martin