https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110867
--- Comment #3 from prathamesh3492 at gcc dot gnu.org ---
(In reply to prathamesh3492 from comment #2)
> (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.
Bootstrap+testing works fine with your fix. Thanks!
>
> Thanks,
> Prathamesh
