Re: [patch,gomp4] make fortran loop variables implicitly private in openacc

[Tobias Burnus <burnus at net-b dot de>]

Cesar Philippidis wrote:
> According to section 2.6.1 in the openacc spec, fortran loop variables
> should be implicitly private like in openmp. This patch does just so.

Makes sense. Looking at the patch, I wonder whether the context is 
properly handled when mixing OpenMP and OpenACC. I have the feeling that 
one then might end up using the OpenACC context when one should use the 
OpenMP context. However, I have not fully followed the program flow. For 
instance, would something like

!$oacc parallel
!$omp simd private(i) reduction(+:c)
do i = 1, n
...
end do

be properly handled?

> Also, while working on this patch, I noticed that I made the check for
> variables appearing in multiple openacc clauses too strict. A private
> variable may also appear inside a reduction clause. I've also included a
> fix for this in this patch.

In OpenMP, one has (OMP 4.0, 2.14.3): "A list item that specifies a 
given variable may not appear in more than one clause on the same 
directive, except that a variable may be specified in both firstprivate 
and lastprivate clauses."
And in 2.14.3.3, OpenMP has: "List items that appear in a private, 
firstprivate, or reduction clause in a parallel construct may also 
appear in a private clause in an enclosed parallel,task, or worksharing, 
or simd construct.

I tried to find it in something similar in OpenACC - but I failed. I 
found in (OpenACC 2.0a, 2.7.11) a reference to reduction with private, 
which implies that a reduction variable my be private, but I didn't find 
much more. In particular, it is not clear to me whether it would permit 
only those which are private implicitly or in an oacc parallel region or 
also in an explicit private clause in the same directive. Can you point 
me to the spec?

Additionally, I wonder whether you shouldn't also add a test case for 
the reduction with private.

Tobias