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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/99928] New: [OpenMP] reduction variable in combined
 target construct wrongly mapped as firstprivate
Date: Tue, 06 Apr 2021 08:39:50 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99928

            Bug ID: 99928
           Summary: [OpenMP] reduction variable in combined target
                    construct wrongly mapped as firstprivate
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Keywords: openmp, wrong-code
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org
                CC: anlauf at gcc dot gnu.org, jakub at gcc dot gnu.org
  Target Milestone: ---

Reported by Harald at
https://gcc.gnu.org/pipermail/fortran/2021-March/055896.html
with a Fortran program. But it also occurs for C as shown below.

OpenMP 5.1 has:
"If a list item appears in a reduction, lastprivate or linear clause
 on a combined target construct then it is treated as if it also appears
 in a map clause with a map-type of tofrom." (2.21.7)

Likewise OpenMP 5.0 in 2.19.7.

The FE chops the target-teams into target + teams and for target;
's' is implicitly mapped as 'firstprivate' instead of as 'map(tofrom:'.

It seems as if this is best done on the C/C++/Fortran FE which still sees t=
hat
it is a combined target construct.

int a[10];

int s2()
{
  int s =3D 0;
  #pragma omp target data map(a,s)
  {
    #pragma omp target teams reduction(+:s)
    {
      for (int i=3D0; i < 10; i++)
        s +=3D a[i];
    }
  }
  return s;
}

Original dump:

 #pragma omp target data map(tofrom:s) map(tofrom:a)
  #pragma omp target
        #pragma omp teams reduction(+:s)

omplower dump:

        #pragma omp target data map(tofrom:s [len: 4]) map(tofrom:a [len: 4=
0])
#pragma omp target num_teams(0) thread_limit(0) firstprivate(s) map(tofrom:a
[len: 40])
#pragma omp teams reduction(+:s) shared(a)=