Re: [PATCH, OpenMP 5.1, Fortran] Strictly-structured block support for OpenMP directives

[Jakub Jelinek <jakub@redhat.com>]

On Thu, Oct 07, 2021 at 07:09:07PM +0200, Jakub Jelinek wrote:
> The workshare/parallel workshare case is unclear, I've filed
> https://github.com/OpenMP/spec/issues/3153
> for it.  Either don't allow block if workshare_stmts_only for now
> until that is clarified, or if we do, we need to make sure that it does the
> expected thing, does that gfc_trans_block_construct call ensure it?
> 
> Then we have the
> https://github.com/OpenMP/spec/issues/3154
> issue Tobias discovered, if that issue is resolved to end always applying to
> the directive before the block statement, I think your patch handles it that
> way but we want testsuite coverage for some of those cases.

Just want to follow-up on this, we now have resolutions of the
https://github.com/OpenMP/spec/issues/3153
https://github.com/OpenMP/spec/issues/3154
https://github.com/OpenMP/spec/issues/3155
issues and we can use that to guide this patch.
BLOCK is now explicitly allowed for workshare around the body of
workshare/parallel workshare or around the body of critical in it but not
arbitrarily nested.  My understanding of the patch is that it most likely
implements that, just we need a testsuite coverage that
!$omp workshare
block
  a = 1
  b = 2
  !$omp critical
  block
    c = 3
  end block
end block
is fine (also with !$omp end {criticial,workshare} after the block), but
that
!$omp workshare
a = 1
block
  b = 2
  c = 3
end block
!$omp end workshare
etc. is diagnosed.
For Tobias' issue that !$omp end whatever after end block for strictly
structured block binds to the directive above the strictly structured block
I think the patch also implements it but we want again testsuite coverage,
that
subroutine foo
!$omp parallel
!$omp parallel
block
end block
!$omp end parallel
!$omp end parallel
end subroutine foo
subroutine bar
!$omp teams
!$omp parallel
block
end block
!$omp end teams
end subroutine bar
is fine while e.g.
subroutine baz
!$omp parallel
!$omp parallel
block
end block
!$omp end parallel
end subroutine baz
is not (!$omp end parallel pairs with the inner parallel rather than outer,
and the outer parallel's body doesn't start with BLOCK, so needs to be
paired with its !$omp end parallel).
And lastly, the 3rd ticket clarifies that for the separating directives
for Fortran basically the 5.0 state remains except that the body can be now
also optionally wrapped in a single BLOCK.
(And for C/C++ allows no statements at all in between the separating
directives or after/before them but still requires the {}s around it like
5.1 and earlier.  Here we implement the 5.1 wording and let's stay with
that.)
Thinking more about the Fortran case for !$omp sections, there is an
ambiguity.
!$omp sections
block
  !$omp section
end block
is clear and !$omp end sections is optional, but
!$omp sections
block
end block
is ambiguous during parsing, it could be either followed by !$omp section
and then the BLOCK would be first section, or by !$omp end sections and then
it would be clearly the whole sections, with first section being empty
inside of the block, or if it is followed by something else, it is
ambiguous whether the block ... end block is part of the first section,
followed by something and then we should be looking later for either
!$omp section or !$omp end section to prove that, or if
!$omp sections
block
end block
was the whole sections construct and we shouldn't await anything further.
I'm afraid back to the drawing board.

	Jakub