https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104931
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Richard Biener from comment #3) > The bug was made latent by g:51d464b608b38b9e2007948d10b1e0f1dcec142c which > ensured that > > /* If the loop exits immediately, there is nothing to do. */ > tree tem = fold_binary (code, boolean_type_node, iv0->base, iv1->base); > if (tem && integer_zerop (tem)) > { > if (!every_iteration) > return false; > niter->niter = build_int_cst (unsigned_type_for (type), 0); > niter->max = 0; > return true; > } > > triggered, folding (_2 + 4294967272) + 12 < _2 + 4294967272 to false. That's > the following part of the revision, and it probably triggers when doing > expand_simple_operations. > > diff --git a/gcc/match.pd b/gcc/match.pd > index 84c9b918041..f5dcbf32bc7 100644 > --- a/gcc/match.pd > +++ b/gcc/match.pd > @@ -2143,6 +2143,11 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) > (simplify > (pointer_plus (pointer_plus:s @0 @1) @3) > (pointer_plus @0 (plus @1 @3))) > +#if GENERIC > +(simplify > + (pointer_plus (convert:s (pointer_plus:s @0 @1)) @3) > + (convert:type (pointer_plus @0 (plus @1 @3)))) > +#endif > > /* Pattern match > > It does seem to me that niter analysis relies on statically detecting > not rolling loops, at least for the cases we assume no overflow happens > and we use number_of_iterations_lt_to_ne. I can't convince myself that > only INTEGER_CST appearant negative delta are problematic for > pointer types (which we always assume to have no overflow), but that would > be the most simplistic solution here. Still "negative" delta values should > be problematic for all cases, and since we only restrict us to constant > modulo, delta can also be non-constant. I verified backporting the above fixes the issue. That's really the patch I'm most comfortable with at this point ... :/