[Bug tree-optimization/68823] [6/7 Regression][graphite] tramp3d-v4 compiled with -floop-nest-optimize crashes

[spop at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68823

--- Comment #11 from Sebastian Pop <spop at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #10)
> 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?

alias-sets differ for two arrays with bases that have been proven to be
different.
If they may point to the same thing, they will have the same number.