Two block constructs in a PARALLEL region

1

I’d be grateful for some advice. Consider the following code:

program test
implicit none

!$OMP PARALLEL
block

end block
block

end block
!$OMP END PARALLEL

end program

Intel fortran (ifort and ifx) and GFortran versions 8 - 11 compile the code fine.

However, GFortran versions 14 and 15 yield:

> gfortran -fopenmp test.f90

test.f90:12:18:

12 | !$OMP END PARALLEL
   |                  1
Error: Unexpected !$OMP END PARALLEL statement at (1)

This only happens when there are two blocks in the same PARALLEL region.

Is this somehow non-complaint OpenMP or a compiler bug?

1 Like
2

OpenMP 6.0 adds blocks as parallel scopes (screenshot taken from this presentation)

image
image1274×717 94.2 KB

But I’m not sure if this is the issue here.

GCC 12 added support for OpenMP strictly structured blocks, from OpenMP 5.2 spec, page 3:

image
image998×361 38.6 KB

and page 52:

image
image968×224 28.5 KB

Perhaps this can be used as a workaround?

!$OMP PARALLEL
block
  block

  end block 
  block

  end block
end block

Edit: link to compiler explorer: Compiler Explorer

1 Like
3

Thanks @ivanpribec your workaround works.

However, I’ve since found that inserting a line of anything before the first block also fixes the problem:

program test
implicit none
integer i

!$OMP PARALLEL
i=1
block

end block
block

end block
!$OMP END PARALLEL

end program

I think this may be a compiler bug.

4

@ivanpribec
GCC 12 added support for OpenMP strictly structured blocks, from OpenMP 5.2 spec, page 3:

I think you’re correct. I submitted a bug report here and the first comment indicated that the two block code is valid in OpenMP 5.0 but not in 5.1. Your workaround was also suggested.

A somewhat confusing change.

Anyway, thanks again.