https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110867
--- Comment #2 from prathamesh3492 at gcc dot gnu.org --- (In reply to Stefan Schulze Frielinghaus from comment #1) > The optimization introduced by r14-2879-g7cdd0860949c6c hits during > combination of insn > > (insn 31 3 32 2 (set (reg:SI 118 [ _1 ]) > (mem:SI (reg/v/f:SI 115 [ a ]) [1 *a_4(D)+0 S4 A64])) "t.c":15:7 758 > {*arm_movsi_vfp} > (nil)) > > and > > (insn 9 32 10 2 (set (reg:CC 100 cc) > (compare:CC (reg:SI 118 [ _1 ]) > (const_int -2147483648 [0xffffffff80000000]))) "t.c":15:6 272 > {*arm_cmpsi_insn} > (nil)) > > The idea of r14-2879-g7cdd0860949c6c is to get rid of large constants while > performing an unsigned comparison. In this case it looks like a 32-bit > constant is sign-extended into a 64-bit constant and then a 32-bit > comparison is done. While writing the optimization I always assumed that > the constant does fit into int_mode which is apparently not the case here. > Thus one possible solution would be to simply bail out in those cases: > > diff --git a/gcc/combine.cc b/gcc/combine.cc > index 0d99fa541c5..e46d202d0a7 100644 > --- a/gcc/combine.cc > +++ b/gcc/combine.cc > @@ -11998,11 +11998,15 @@ simplify_compare_const (enum rtx_code code, > machine_mode mode, > x0 >= 0x40. */ > if ((code == LEU || code == LTU || code == GEU || code == GTU) > && is_a <scalar_int_mode> (GET_MODE (op0), &int_mode) > + && HWI_COMPUTABLE_MODE_P (int_mode) > && MEM_P (op0) > && !MEM_VOLATILE_P (op0) > /* The optimization makes only sense for constants which are big > enough > so that we have a chance to chop off something at all. */ > && (unsigned HOST_WIDE_INT) const_op > 0xff > + /* Bail out, if the constant does not fit into INT_MODE. */ > + && (unsigned HOST_WIDE_INT) const_op > + < ((HOST_WIDE_INT_1U << (GET_MODE_PRECISION (int_mode) - 1) << 1) - > 1) > /* Ensure that we do not overflow during normalization. */ > && (code != GTU || (unsigned HOST_WIDE_INT) const_op < > HOST_WIDE_INT_M1U)) > { > > Does this resolve the problem for you? Yes, it worked thanks! I will do a full bootstrap+test with your fix and let you know the results. Thanks, Prathamesh