https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71031
--- Comment #10 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to Eric Botcazou from comment #9)
> > The situation (+ UINT_MAX) is equal to [1, od_5] - 1 which would mean
> > a result range of ideally [0, od_5 - 1].
>
> Right.
>
> > I think Eric added this code so he may want to have a look here to see
> > what general solution is appropriate.
> >
> > But yes, instead of asserting we can always drop to VR_VARYING ...
>
> That's what the block of code just above was added for:
>
> /* If we have overflow for the constant part and the resulting
> range will be symbolic, drop to VR_VARYING. */
> if ((min_ovf && sym_min_op0 != sym_min_op1)
> || (max_ovf && sym_max_op0 != sym_max_op1))
> {
> set_value_range_to_varying (vr);
> return;
> }
>
> so a safe fix is to extend it to catch this case:
>
> /* If we have overflow for the constant part and the resulting
> range will be symbolic, drop to VR_VARYING. */
> if ((min_ovf || max_ovf)
> && (sym_min_op0 != sym_min_op1 || sym_max_op0 != sym_max_op1))
> {
> set_value_range_to_varying (vr);
> return;
> }
That makes sense. I'll do that.
> If we want to compute the above expected range, we need to enter the
> business of symbolic ranges with TYPE_OVERFLOW_WRAPS, which is rather
> delicate. And we also need to short circuit the final call to
> compare_values, which will drop to VR_VARYING if I'm not mistaken.
Yea, it is (at least for me ;).
Thanks Eric & Richi!
