Subscript out of range error generated spuriously with OpenMP, pgf90 19.10-0

The following self-contained reproducer code generates a Subscript out of range error that I believe is spurious, but that is also the likely cause of a segmentation violation in the full code from which this reproducer was reduced.

I am providing this in the form of a session log captured on a Linux (Sandybridge) workstation running Centos 7. The session first shows a listing of the code, then the output of two compiles and executions. First time is a success. Second time, compiled with -DBREAK, shows the out of range error. Note that the out of range error actually occurs prior to the loop that’s affected by #defining BREAK in the compile.

I have tested with another compiler and this reproducer code (and the code from which it’s reduced) both work correctly whether or not the second loop is $!omp parallel.

Thank you,


Script started on Tue 25 Feb 2020 01:41:07 PM MST
$ pgf90 -V

pgf90 19.10-0 LLVM 64-bit target on x86-64 Linux -tp sandybridge
PGI Compilers and Tools
Copyright (c) 2019, NVIDIA CORPORATION.  All rights reserved.
$ cat visckernel.F90
program visckernel
  implicit none

  ! from mod_types
  integer, parameter :: r8 = SELECTED_REAL_KIND(12)

  integer  ib,  neblk
  real(kind=r8), dimension(6,423440)  :: rhs_visc_cgc
  integer                             :: ngl, nglx, ngly, nglz, npts,  nvar

! for epx
  real(kind=r8),allocatable,dimension(:,:,:,:)      :: erhs_visc_new    ! (leblk, npts,nvar, neblk)

  ngl = 4
  nglx = 4
  ngly = 4
  nglz = 4
  npts = 64
  nvar = 6
  neblk = 15288

  allocate(erhs_visc_new (1,npts,nvar,neblk) )


!$omp parallel do private(ib)
  do ib = 1,1
    call create_laplacian_ep3( erhs_visc_new(:,:,:,ib) )
#ifdef BREAK
!$omp parallel do
  do ib = 1,1
    call create_global_epx(erhs_visc_new)


subroutine create_laplacian_ep3(rhs_visc  )
  implicit none
  real(kind=r8) :: rhs_visc (:,:,:)
end subroutine create_laplacian_ep3

subroutine create_global_epx(rhs)
  implicit none
  real(kind=r8) :: rhs(:,:,:,:)   ! (1,npts,nvar,neblk)
end subroutine create_global_epx

end program visckernel

$ pgf90 -mp -c -C -O0 -g -traceback visckernel.F90 -o visckernel.o
$ pgf90 -mp  -traceback -C -O0 -g visckernel.o -o ./visckernel
$  ./visckernel
 visckernel.F90           24     46964736
 visckernel.F90           25            1           64            6
$ pgf90 -mp -c -C -O0 -g -traceback -DBREAK visckernel.F90 -o visckernel.o
$ pgf90 -mp  -traceback -C -O0 -g visckernel.o -o ./visckernel
$  ./visckernel
 visckernel.F90           24     46964736
 visckernel.F90           25            1           64            6
0: Subscript out of range for array erhs_visc_new (visckernel.F90: 29)
    subscript=1, lower bound=15288, upper bound=30575, dimension=1
$ exit

Script done on Tue 25 Feb 2020 01:42:14 PM MST

Thanks John. I’ve added a problem report (TPR #28156) and sent it to our compiler engineers for further investigation.

Note that the error does not occur with our older non-LLVM compilers so you might try adding “-Mnollvm” to your flags to see if it helps the full application as well.