Re: Combined constructs' clause splitting

[Tom de Vries <Tom_deVries at mentor dot com>]

On 19/11/15 01:03, Cesar Philippidis wrote:
> On 11/08/2015 07:45 AM, Tom de Vries wrote:
> > On 07/11/15 12:45, Thomas Schwinge wrote:
> > > Hi!
> > >
> > > On Fri, 6 Nov 2015 15:31:23 -0800, Cesar Philippidis
> > > <cesar@codesourcery.com> wrote:
> > > > I've applied this patch to gomp-4_0-branch which backports most of my
> > > > front end changes from trunk. Note that I found a regression while
> > > > testing, which is also present in trunk. It looks like
> > > > kernels-acc-loop-reduction.c is failing because I'm incorrectly
> > > > propagating the reduction variable to both to the kernels and loop
> > > > constructs for combined 'acc kernels loop'. The problem here is that
> > > > kernels don't support the reduction clause. I'll fix that next week.
> > >
> > > Always need to consider both what the specification allows -- and thus
> > > what the front ends accept/refuse -- as well as what we might do
> > > differently, internally in later processing stages.  I have not analyzed
> > > whether it makes sense to have the OMP_CLAUSE_REDUCTION of a combined
> > > "kernels loop reduction([...])" construct be attached to the outer
> > > OACC_KERNELS or inner OACC_LOOP, or duplicated for both.
> > >
> > > Tom, if you need a solution for that right now/want to restore the
> > > previous behavior (attached to innter OACC_LOOP only), here's what you
> > > should try: in gcc/c-family/c-omp.c:c_oacc_split_loop_clauses remove the
> > > special handling for OMP_CLAUSE_REDUCTION, and move it to "Loop clauses"
> > > section,
> >
> > Committed to gomp-4_0-branch, as attached.
>
> Can you port this patch to trunk? Originally we were attaching the
> reduction clause to both the acc loop and parallel construct so that the
> reduction variable would get a copy clause implicitly. However, Nathan
> later interpreted
>
>    #pragma acc parallel reduction(+:var)
>
> as
>
>    #pragma acc parallel reduction(+:var) private(var)
>
> Therefore, the burden is on the user to ensure that 'var' is transferred
> to the parallel region in an appropriate data clause. As a result, we
> only need to associate reductions with loops now. So your patch is good
> for trunk.

Hi Cesar,

that patch was submitted for trunk as part of the kernels support:

https://gcc.gnu.org/ml/gcc-patches/2015-11/msg00994.html

Thanks,
- Tom