RE: [gomp4] Some progress on #pragma omp simd

["Iyer, Balaji V" <balaji dot v dot iyer at intel dot com>]

Hello Aldy and Jakub,
 	Please see my response below.

Thanks,

Balaji V. Iyer.

> -----Original Message-----
> From: Aldy Hernandez [mailto:aldyh@redhat.com]
> Sent: Wednesday, April 24, 2013 7:22 PM
> To: Jakub Jelinek
> Cc: Iyer, Balaji V; Richard Henderson; gcc-patches@gcc.gnu.org
> Subject: Re: [gomp4] Some progress on #pragma omp simd
> 
> [Balaji, see below].
> 
> Ok, this is confusing.  While the document in the link you posted (the ICC
> manual?) says so, the document I'm following says otherwise.
> 
> I'm following this (which, until a few days was a link accessible from the cilk plus
> web page, though I no longer see it):

Yes, I am aware of the missing link. We are currently looking into it.

> 
> http://software.intel.com/sites/default/files/m/4/e/7/3/1/40297-
> Intel_Cilk_plus_lang_spec_2.htm
> 
> The document above is for version 1.1 of the Cilk Plus language extension
> specification, which I was told was the latest.  There it explicitly says that the
> clauses behave exactly like in OpenMP:
> 
> "The syntax and semantics of the various simd-openmp-data-clauses are
> detailed in the OpenMP specification.
> (http://www.openmp.org/mp-documents/spec30.pdf, Section 2.9.3)."
> 
> Balaji, can you verify which is correct?  For that matter, which are the official
> specs from which we should be basing this work?

Privatization clause makes a variable private for the simd lane. In general,  I would follow the spec. If you have further questions, please feel free to ask.

Thanks,

Balaji V. Iyer.

> 
> Aldy
> 
> 
> On 04/24/13 01:40, Jakub Jelinek wrote:
> > On Wed, Apr 24, 2013 at 08:25:36AM +0200, Jakub Jelinek wrote:
> >> BTW, the semantics of private/firstprivate/lastprivate desribed in
> >> http://software.intel.com/sites/products/documentation/studio/compose
> >> r/en-
> us/2011Update/compiler_c/cref_cls/common/cppref_pragma_simd.htm
> >> doesn't seem to match the semantics of those in #pragma omp simd.
> >> private in OpenMP I understand is private to the whole loop (or SIMD
> >> lane?;
> >
> > SIMD lane apparently.  Guess that is going to be quite difficult,
> > because at the point of omp lowering or expansion we are nowhere close
> > to knowing what vectorization factor we are going to choose, all we
> > have is an upper bound on that based on the target ISA and safelen clause.
> > If say private clause is used with C++ classes with non-trivial
> > ctors/dtors that would make a difference.  Plus how to represent this in the IL.
> >
> > struct A { A (); ~A (); A (const A &); int i; };
> >
> > void
> > foo ()
> > {
> >    A a, b;
> >    #pragma omp simd private (a) lastprivate (b)
> >    for (int i = 0; i < 10; i++)
> >      {
> >        a.i++;
> >        b.i++;
> >      }
> > }
> >
> > Right now what gomp4 branch does is that it will just construct
> > private vars around the whole loop, as in:
> > void
> > foo ()
> > {
> >    A a, b;
> >    {
> >      A a', b';
> >      int i;
> >      for (i = 0; i < 10; i++)
> >        {
> > 	a'.i++;
> > 	b'.i++;
> > 	if (i == 9)
> > 	  b = b';
> >        }
> >    }
> > }
> >
> > 	Jakub
> >