[OpenACC] reduction(+:norm) leads to Error: !$OMP DECLARE REDUCTION plus not found at (1)

[jeffhammond]

OpenACC seems to be translated to OpenMP but fails to comprehend the build-in + operator in reductions, even though OpenMP does.

jhammond@nuclear:~/PRK/FORTRAN$ /usr/local/bin/flang -g -O3 -fopenacc acc-red.F90
flang_unparsed_file_ca2f7203507f_0.f90:21:42:

   21 | !$ACC PARALLEL LOOP COLLAPSE(2) REDUCTION(PLUS:norm)
      |                                          1
Error: !$OMP DECLARE REDUCTION plus not found at (1)
flang: in /home/jhammond/PRK/FORTRAN, gfortran failed with exit status 1: gfortran -g -O3 -fopenacc -g -O3 -fopenacc acc-red.F90

acc-red.F90

program main
  use iso_fortran_env
  use prk
  implicit none
  integer :: err
  integer(kind=INT32) ::  n,i,j
  real(kind=REAL64), allocatable :: B(:,:)
  real(kind=REAL64) :: norm

  allocate( B(n,n), stat=err)
  if (err .ne. 0) then
    write(*,'(a,i3)') 'allocation of A returned ',err
    stop 1
  endif

  !$acc data pcopy(B)

  !$acc parallel loop collapse(2)
  do j=1,n
    do i=1,n
      B(i,j) = i+j
    enddo
  enddo

  !$acc parallel loop collapse(2) reduction(+:norm)
  do j=1,n
    do i=1,n
      norm = norm + abs(B(i,j))
    enddo
  enddo

  !$acc end data

  deallocate( B )
  print*,norm

end program main

It's fine when OpenMP is used directly:

jhammond@nuclear:~/PRK/FORTRAN$ /usr/local/bin/flang -g -O3 -fopenmp omp-red.F90 && echo OK
OK
jhammond@nuclear:~/PRK/FORTRAN$ cat omp-red.F90
program main
  use iso_fortran_env
  use prk
  implicit none
  integer :: err
  integer(kind=INT32) ::  n,i,j
  real(kind=REAL64), allocatable :: B(:,:)
  real(kind=REAL64) :: norm

  allocate( B(n,n), stat=err)
  if (err .ne. 0) then
    write(*,'(a,i3)') 'allocation of A returned ',err
    stop 1
  endif

  !$omp parallel do collapse(2)
  do j=1,n
    do i=1,n
      B(i,j) = i+j
    enddo
  enddo
  !$omp end parallel do

  !$omp parallel do collapse(2) reduction(+:norm)
  do j=1,n
    do i=1,n
      norm = norm + abs(B(i,j))
    enddo
  enddo
  !$omp end parallel do

  deallocate( B )
  print*,norm

end program main