[Bug tree-optimization/68131] missed optimization and warning for broken overflow check

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68131

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Marc Glisse from comment #3)
> (In reply to Richard Biener from comment #2)
> > We indeed do not have this optimization, only A + CST CMP CST to A CMP CST'
> > and related.  Note that _9 might be negative so we also need range info
> > for this.  VRPs symbolic range stuff isn't good enough to simplify this.
> 
> If we want to simplify directly to false, I would expect a match.pd pattern
> using tree_expr_nonnegative_p to work in this case (conversion from a
> smaller unsigned). By the way, maybe tree_single_nonnegative_warnv_p could
> try looking at get_range_info before forwarding to
> gimple_stmt_nonnegative_warnv_p.

Oh I filed PR 111959 (and will be submitting a patch later today) for that.