Re: [PATCH] Fix bogus -Wstringop-overflow warning in Ada

[Richard Biener <richard.guenther@gmail.com>]

On Thu, Aug 18, 2022 at 4:46 PM Eric Botcazou <botcazou@adacore.com> wrote:
>
> > Hmm :/  But that means we _should_ force a sign extension but only
> > from ptrofftype_p ()?  That is, your test above should maybe read
> >
> >    signop sgn = TYPE_SIGN (type);
> >    if (ptrofftype_p (type))
> >      sgn = SIGNED;
> >
> > assuming 'type' is the type of lowbnd
>
> Yes, that's essentially equivalent to what get_offset_range does, but I'm not
> sure why having two slightly different ways of doing it would be better than a
> single one here,   Maybe replace the call to get_precision in both places with
> TYPE_PRECSION (type) then?

I wasn't aware of the copy in get_offset_range.  To cite:

  wide_int wr[2];
  if (!get_range (x, stmt, wr, rvals))
    return false;

  signop sgn = SIGNED;
  /* Only convert signed integers or unsigned sizetype to a signed
     offset and avoid converting large positive values in narrower
     types to negative offsets.  */
  if (TYPE_UNSIGNED (type)
      && wr[0].get_precision () < TYPE_PRECISION (sizetype))
    sgn = UNSIGNED;

  r[0] = offset_int::from (wr[0], sgn);
  r[1] = offset_int::from (wr[1], sgn);

I guess the main issue here is that the machinery converts to offset_int
prematurely and thus needs to do it even when it's not clear in what context
(POINTER_PLUS_EXPR offset or not) it is used.  The code unfortunately
is a bit of a mess and I'm not too familiar with it.  I'm OK with your
original patch, given the above it's consistent (even if maybe broken).

Thanks,
Richard.

>
> --
> Eric Botcazou
>
>
>