[Bug fortran/93554] [8/9/10 Regression] ICE in expand_oacc_for, at omp-expand.c:6035 since r6-4364-ge4834818d22f5c66

[burnus at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93554

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |burnus at gcc dot gnu.org

--- Comment #2 from Tobias Burnus <burnus at gcc dot gnu.org> ---
The analogous OpenMP variant [omp target / omp do private(x)] works.

The problem seems to be that "private(x)" implies that the data is device
private and, hence, it is finalized after the loop and before returning to the
host. – But the OpenACC code expects that directly after the loop the "omp
return" (internal) pragma comes.

* * *

The code flow is:
  expand_omp_for
    -> t  (for OpenACC)
    -> expand_omp_for_static_nochunk (for OpenMP)
i.e. the input in those functions is the same.

 * * *

One has:
debug_bb(region->entry):
  <bb 6> :
  #pragma omp for private(i) private(x)
  for (i = 0; i <= 31; i = i + 1)

debug_bb(region->cont):
  <bb 7> :
  x.a = 1;
  #pragma omp continue (i, i)

debug_bb(region->exit):
  <bb 10> :
  #pragma omp return

HOWEVER:
  BRANCH_EDGE (entry_bb)->dest
is the code after the region->exit (autodeallocation of the allocatable
component x%b); namely "debug_bb((*region->entry->succs)[1]->dest)" 
[with …[0]->flag == 1 == EDGE_FALLTHRU]:
  D.3967 = x.b.data;
  if (D.3967 != 0B)
    goto <bb 9>; [INV]
  else
    goto <bb 10>; [INV]

Hence, the second condition of the assert fails for OpenACC:
  gcc_assert (EDGE_COUNT (entry_bb->succs) == 2
              && BRANCH_EDGE (entry_bb)->dest == exit_bb);
and likewise the later
      gcc_assert (FALLTHRU_EDGE (cont_bb)->dest == exit_bb);

In OpenMP, the result is the same but there one operates checks:
  BRANCH_EDGE (entry_bb)->dest == FALLTHRU_EDGE (cont_bb)->dest
[OpenMP: "bool broken_loop = region->cont == NULL", which is similar to the
handling of cont == NULL in the OpenACC code.]