[Bug middle-end/103988] New: [OpenACC][2.7] Support array vars in reductions

[Bug middle-end/103988] New: [OpenACC][2.7] Support array vars in reductions

[burnus at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103988

            Bug ID: 103988
           Summary: [OpenACC][2.7] Support array vars in reductions
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: openacc
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org
                CC: tschwinge at gcc dot gnu.org
  Target Milestone: ---

Created attachment 52168
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52168&action=edit
Fortran testcase from Mikel Mendizabal's email report

Reported at https://gcc.gnu.org/pipermail/gcc/2022-January/238094.html

GCC currently only supports scalars in OpenACC reduction clauses.
(That matches OpenACC 2.6, which is supported since GCC 10.)

Expected: Support arrays as reduction variables as specified since OpenACC 2.7.


OpenACC 2.7 has the following (at a glance, OpenACC 3.2's wording is the same):

"If the reduction var is an array or subarray, the array reduction operation is
logically equivalent to applying that reduction operation to each element of
the array or subarray individually.
If the reduction var is a composite variable, the reduction operation is
logically equivalent to applying that reduction operation to each member of the
composite variable individually."

(+ some restrictions and some notes about the supported data types)


I note that GCC's OpenMP implementation supports arrays and array sections
(array sections not yet for the Fortran FE). Thus, the array part should be
relatively simple. (The composite-variable feature is OpenACC only.)