[Bug libgomp/106643] [gfortran + OpenACC] Allocate in module causes refcount error

["tschwinge at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106643

Thomas Schwinge <tschwinge at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |tschwinge at gcc dot gnu.org
         Resolution|---                         |FIXED
                 CC|                            |tschwinge at gcc dot gnu.org
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #4 from Thomas Schwinge <tschwinge at gcc dot gnu.org> ---
(In reply to Henry Le Berre from comment #0)
> ```
> /nethome/hberre3/USERSCRATCH/build-gcc-amdgpu//gcc/libgomp/oacc-mem.c:1153:
> goacc_enter_data_internal: Assertion `n->refcount != REFCOUNT_INFINITY &&
> n->refcount != REFCOUNT_LINK' failed.
> ```

ACK, and thanks for your detailed report.

> In order to generate this error, I had to create and dynamically allocate
> the array in another module. I initially wrote this in a single F90 file but
> the executable ran as expected.

Maybe the difference was that the '!$acc declare create(valls)' was in a
different scope?  Global scope (Fortran 'module' scope) is important here; then
"the associated region is the implicit region for the whole program" (as you
also had noted), which triggers this code path.

There are cases where it's relevant, but here, the separate module/main program
files are not necessary for demonstrating the issue.

On the other hand, it's helpful to include an OpenACC compute construct where
for 'valls' there is no explicit or implicit data clause due to "exposed
variable access" (OpenACC 3.2 term).  That means, in a separate 'subroutine'
accessing 'valls' in '!$acc declare create(valls)' instead of dummy argument. 
(... as I've implemented in the test case.)

So this is now fixed for GCC 13; not planning on backporting to current GCC
release branches.


> Our main code currently doesn't call `!$acc enter data create` for
> dynamically allocated arrays since it relies on NVIDIA (/PGI) hooking into
> the `allocate` call on the CPU. I ran into the above error when converting
> our allocation/deallocation routines.

ACK, GCC release branches and master branch are still missing support for
OpenACC "Changes from Version 2.0 to 2.5": "The 'declare create' directive with
a Fortran 'allocatable' has new behavior".  Preliminary support exists on the
devel/omp/gcc-12 branch (and earlier development branches), but needs to be
revised for upstream submission.