[Bug fortran/69128] New: [4.9/5/6 Regression] OpenMP workshare problem with SUM()

[anlauf at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69128

            Bug ID: 69128
           Summary: [4.9/5/6 Regression] OpenMP workshare problem with
                    SUM()
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: anlauf at gmx dot de
  Target Milestone: ---

Reported in

https://gcc.gnu.org/ml/fortran/2015-12/msg00112.html

% gfc-trunk workshare-sum.f90 -fopenmp
workshare-sum.f90:16:0:

 !$omp parallel workshare


Error: work-sharing region may not be closely nested inside of work-sharing,
'critical', 'ordered', 'master', explicit 'task' or 'taskloop' region


The error shows up with 4.7/4.8/4.9/5/6.  No error with 4.6.

The error appears for SUM(), but not e.g. for MAXVAL().

The code is accepted by ifort, sunf95, crayftn.

Testcase:

% cat workshare-sum.f90
program test
  implicit none
  real, allocatable :: a(:,:), b(:)
  integer :: dim1, dim2, i,j
  dim1=10000
  dim2=500
  allocate(a(dim1,dim2),b(dim1))
  call random_number(a)

!$omp parallel do
  do i=1,dim1
     b(i) = sum(a(i,:), dim=1)
  end do
!$omp end parallel do

!$omp parallel workshare
! b(:) = maxval(a(:,:), dim=2)  ! No problem with maxval()
  b(:) = sum(a(:,:), dim=2)     ! Failure with sum()
!$omp end parallel workshare
end program