https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68131
--- Comment #3 from Marc Glisse <glisse at gcc dot gnu.org> --- (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. But the much simpler transformation: a+b<a => b<0 does not require any VRP info and would let the next VRP pass finish the work.
