GCC 9 OpenMP issues

[Orion Poplawski]

Looks like GCC 9 is finally enforcing an OpenMP change:

 From https://gcc.gnu.org/ml/gcc-patches/2018-11/msg00628.html

- change data sharing for readonly variables without mutable members, 
they are
   no longer predetermined shared (this actually changed in earlier 
OpenMP standard
   releases, but was considered a mistake; for 5.0 it was decided it 
isn't going to
   be reverted; this makes a difference mainly when using default(none))


Which is now leading to some (expected) compilation failures:

BUILDSTDERR: nco_omp.c: In function 'nco_openmp_ini':
BUILDSTDERR: nco_omp.c:210:38: error: 'fp_stderr' not specified in 
enclosing 'parallel'
BUILDSTDERR:   210 |  if(nco_dbg_lvl_get() >= nco_dbg_fl) 
(void)fprintf(fp_stderr,"%s: INFO Small parallel test region spawned 
team of %d thread(s)\n",nco_prg_nm_get(),thr_nbr_act);
BUILDSTDERR:       | 
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
BUILDSTDERR: nco_omp.c:205:10: error: enclosing 'parallel'
BUILDSTDERR:   205 | # pragma omp parallel default(none) shared(thr_nbr_act)
BUILDSTDERR:       |          ^~~


The problem is that it's proving difficult to come up with a solution 
that compiles under both GCC 9 and GCC 8.

GCC 8 complains about just adding fp_stderr to shared():

nco_omp.c: In function 'nco_openmp_ini':
nco_omp.c:205:43: error: 'fp_stderr' is predetermined 'shared' for
'shared'
  # pragma omp parallel default(none) shared(fp_stderr,thr_nbr_act)

And apparently complains if you drop default(none) as well (from another 
project with the same problem):

[  9%] Building CXX object CMakeFiles/_CuraEngine.dir/src/layerPart.cpp.o
/home/ruben/Projects/CuraEngine/src/layerPart.cpp: In function ‘void 
cura::createLayerParts(cura::SliceMeshStorage&, cura::Slicer*)’:
/home/ruben/Projects/CuraEngine/src/layerPart.cpp:52:78: error: 
‘total_layers’ is predetermined ‘shared’ for ‘shared’
  #pragma omp parallel for shared(mesh, slicer, total_layers) 
schedule(dynamic)

https://github.com/nco/nco/issues/114
https://github.com/Ultimaker/CuraEngine/issues/984

Is there any hope of a common solution?

Thanks!

- Orion

-- 
Orion Poplawski
Manager of NWRA Technical Systems          720-772-5637
NWRA, Boulder/CoRA Office             FAX: [phone]
3380 Mitchell Lane                       orion(a)nwra.com
Boulder, CO 80301                 https://www.nwra.com/