https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90030
Bug ID: 90030
Summary: Fortran OpenACC subarray data alignment
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Keywords: openacc
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: tschwinge at gcc dot gnu.org
CC: jakub at gcc dot gnu.org
Target Milestone: ---
As reported by Cesar in
<https://gcc.gnu.org/ml/gcc-patches/2015-09/msg01664.html>, and later
re-submitted in <https://gcc.gnu.org/ml/gcc-patches/2018-08/msg01911.html>.
> In both OpenACC and OpenMP, each subarray has at least two data mappings
> associated with them, one for the pointer and another for the data in
> the array section (fortan also has a pset mapping). One problem I
> observed in fortran is that array section data is casted to char *.
> Consequently, when lower_omp_target assigns alignment for the subarray
> data, it does so incorrectly. This is a problem on nvptx if you have a
> data clause such as
>
> integer foo
> real*8 bar (100)
>
> !$acc data copy (foo, bar(1:100))
>
> Here, the data associated with bar could get aligned on a 4 byte
> boundary instead of 8 byte. That causes problems on nvptx targets.
>
> My fix for this is to prevent the fortran front end from casting the
> data pointers to char *. I only prevented casting on the code which
> handles OMP_CLAUSE_MAP. The subarrays associated with OMP_CLAUSE_SHARED
> also get casted to char *, but I left those as-is because I'm not that
> familiar with how non-OpenMP target regions get lowered.
