https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115092
--- Comment #9 from Segher Boessenkool <segher at gcc dot gnu.org> --- (In reply to Jakub Jelinek from comment #8) > > Yeah, that look like it is missing some test. > > I'd go with > --- gcc/combine.cc.jj 2024-05-07 18:10:10.415874636 +0200 > +++ gcc/combine.cc 2024-05-15 13:33:26.555081215 +0200 > @@ -11852,8 +11852,10 @@ simplify_compare_const (enum rtx_code co > `and'ed with that bit), we can replace this with a comparison > with zero. */ > if (const_op > - && (code == EQ || code == NE || code == GE || code == GEU > - || code == LT || code == LTU) > + && (code == EQ || code == NE || code == GEU || code == LTU > + /* This optimization is incorrect for signed >= INT_MIN or > + < INT_MIN, those are always true or always false. */ > + || ((code == GE || code == LT) && const_op > 0)) > && is_a <scalar_int_mode> (mode, &int_mode) > && GET_MODE_PRECISION (int_mode) - 1 < HOST_BITS_PER_WIDE_INT > && pow2p_hwi (const_op & GET_MODE_MASK (int_mode)) Pre-approved. Thanks! > Seems there is no canonical way to return this is always true or this is > always false, > sure, we could make up something like NE 1 0 or EQ 1 0 or similar, but it > wouldn't likely match and the question is if it would simplify. Later code will likely pick this up. More likely than with the GE anyway :-) > The const_op == -1 handling below this looks correct to me. Yup. > > That needs to be fixed of course, but independent of that, this should > > really > > have been completely folded away earlier already? > > It would if one wouldn't carefully disable tons of optimizations (say -O1, > so no (significant) VRP, dom* disabled, fre disabled). Ha :-)
