Re: Combined constructs' clause splitting

[Cesar Philippidis <cesar@codesourcery.com>]

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.

Cesar