https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68823
--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Sebastian Pop from comment #7)
> (In reply to Martin Liška from comment #5)
> > Created attachment 40662 [details]
> > Isolated graphite dump for miscompiled function
> >
> > As shown in the dump file, there are dependencies for the problematic stmts:
> >
> > Adding must write to depedence graph: pdr_121 (write
> > in gimple stmt: MEM[(Element_t[2] &)_7][0] = _9;
> > data accesses: { S_3[i2] -> [2, o1, 0] : 8*floor((o1)/8) = o1 and
> > 18446744073709551616*floor((8i2 - o1)/18446744073709551616) = 8i2 - o1 and 0
> > <= o1 <= 18446744073709551608 }
> >
> > Adding read to depedence graph: pdr_124 (read
> > in gimple stmt: _15 = MEM[(int *)_14];
> > data accesses: { S_6[i1] -> [2, o1] : 18446744073709551616*floor((-8i1 +
> > o1)/18446744073709551616) = -8i1 + o1 and 0 <= o1 <= 18446744073709551608 }
> >
> > If I understand the notation correctly, both have equal alias set (2). Do
> > you see Sebastian why the dependence is not caught?
> >
>
> S_3[i2] -> [2, o1, 0]
> S_6[i1] -> [2, o1]
>
> we do not detect the dependence because the two arrays do not have the same
> number of subscripts: also on the gimple representation we have
>
> MEM[(Element_t[2] &)_7][0] = _9;
> vs.
> _15 = MEM[(int *)_14];
But then with different number of subscripts (and also likely different
DR_BASE_OBJECT) you can't do anything with them and have to assume
dependence. See initialize_data_dependence_relation:
/* If the references do not access the same object, we do not know
whether they alias or not. We do not care about TBAA or alignment
info so we can use OEP_ADDRESS_OF to avoid false negatives.
But the accesses have to use compatible types as otherwise the
built indices would not match. */
if (!operand_equal_p (DR_BASE_OBJECT (a), DR_BASE_OBJECT (b), OEP_ADDRESS_OF)
|| !types_compatible_p (TREE_TYPE (DR_BASE_OBJECT (a)),
TREE_TYPE (DR_BASE_OBJECT (b))))
{
DDR_ARE_DEPENDENT (res) = chrec_dont_know;
return res;
not sure how you communicate that to ISL of course... is it what you
use "alias-sets" for? To create extra dependence egdes?
