Thoughts on llvm/clang in base

[B. Estrade]

On Mon, Oct 15, 2012 at 10:27:16PM +0200, Carsten Mattner wrote:
> On Mon, Oct 15, 2012 at 4:55 PM, B. Estrade <estrabd at gmail.com> wrote:
> > On Mon, Oct 15, 2012 at 03:45:48PM +0100, peeter (must) wrote:
> >> On Mon, Oct 15, 2012 at 3:33 PM, B. Estrade <estrabd at gmail.com> wrote:
> >> > On Mon, Oct 15, 2012 at 03:17:08PM +0100, peeter (must) wrote:
> >> >> Just to chime in with this, we're using OpenMPI on DF and it'd be
> >> >> very, very bad news for us if support for OpenMPI would be
> >> >> discontinued for the mentioned reason. We'd need to change the
> >> >> platform then. . .
> >> >>
> >> >> Cheers, Peeter
> >> >
> >> > Do you mean OpenMP (shared memory) or OpenMPI (message passing?).
> >> >
> >> > OpenMPI is a separate library and not tied into a compiler or its
> >> > runtime like OpenMP is (e.g., "GOMP" is the GCC project to handle the
> >> > frontend/transformations/runtime).
> >
> > No problem, it happens all the time in this alphabet soup world in
> > which we live.
> >
> > OpenMPI does have some things that allow you to combine OpenMP
> > and OpenMPI for hybrid message passing/shared memory programs.
> >
> > OpenMPI (as you know) is a library, and pretty agnostic to the
> > platform and compiler suite.  OpenMP must be facilitated by the
> > compiler because their are frontend changes that must be made to
> > recognize and transform the source code directives as well as a
> > runtime that supports the OpenMP standard API during execution.  It's
> > a common mistake, though.
> >
> >     http://www.openmp.org
> >
> >     http://www.openmpi.org
> >
> > GCC supports OpenMP directly, though OpenMPI can certainly be built
> > with GCC (and infact, most often is in commidity beowulf clusters).
> >
> >     http://gcc.gnu.org/projects/gomp/
> >
> > Cheers,
> > Brett
> 
> Some comments:
> - There are active OpenMP efforts for inclusion in clang

Nothing on par with GCC or a commercial compiler; nothing that would
be considered for base. Maybe one day such support for LLVM will
exist, but it will be a long time.

> - Nothing prevents you from using gcc for your project while building base
> or world with clang. John, anything wrong with that?
> 
> Therefore I don't see any issue for your OpenMP requirement.

The issue is that OpenMP support in the base compiler (i.e., out of
the box) is a huge plus - in my book anyway.

My goal with the original posting of mine is simply to raise awareness
of the issue. I am very well versed in my options.

Thank you,
Brett

> 
> >> >
> >> > Thank you,
> >> > Brett
> >> >
> >> >>
> >> >> --
> >> >
> >>
> >> Oops! Sorry, I meant OpenMPI, the message passing interface. If this
> >> has no relevance to the topic, then apologies for the confusion.
> >>
> >> Peeter

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