Re: OpenMP 4.0

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

José Luis García Pallero wrote:
> I don't know if this is the correct place for this question, but I
> haven't found any mailing list on the GOMP webpage.
> The OpenMP 4.0 specifications were launched ten days ago. This new
> standard includes several interesting characteristics as SIMD and
> accelerators directives and error handling facilities. Is planned to
> add this new version of OpenMP to libgomp and, then, to GCC 4.9?

Well, it takes a while until features are implemented - and the 
implementation work can only start after a specification/standard is 
sufficiently finished to not change in a major way.

Having said that, there is a GCC branch called gomp-4_0-branch (see
http://gcc.gnu.org/svn.html), which is used for the on-going 
implementation. I think SIMD already partially works (with C/C++, not 
yet with Fortran).

I believe that it is planed to support OpenMP 4 in GCC 4.9.


Tim Prince wrote
> OpenMP 4.0 simd facilities are related to Cilk(tm) Plus pragmas, for which there is a gcc branch on git (although I haven't figured out that stuff).

As far as I gathered, Cilk+'s pragmas and OpenMP'pragmas are supposed to 
be handled identically. (I think there were some differences but they 
got resolved by changing Cilk+.) There are some Cilk+ branches, which 
aim at consolidating the effort with OpenMP. Actually, some Cilk+ 
patches has been submitted for inclusion - thus, expect more for this. 
(The submitted patches do not include SIMD as far as I know. The 
branches do support it.)


> For example, I know of no one planning to implement user defined reduction. Some talk about proposing a specific standard on indexed min/max before deciding about user defined reductions.

I think the gomp-4_0-branch already supports min/max since quite some 
time. (For C/C++; Fortran supports it already since older OpenMP specs.) 
Additionally, I believe that Jakub intents to implement user-defined 
reductions (UDR) and that he has already done some prep work on the 
branch. Ignoring "omp target", UDR seems to be the biggest new feature.

(Regarding "omp target" and other accelerator/GPU/hybrid-system support: 
I think there is quite some interest to get it working with GCC, 
however, it probably will take until 4.10 or longer.)


> Among my ulterior motives for asking is my attempt to write a book centered on HPC development topics.

That sounds interesting!


Tobias

PS: Regarding SIMD, in GCC 4.9 itself, some basic support has already 
been merged a few days ago. However, it is not yet accessible from user 
code (no front-end support) and I have the impression the information is 
not yet used for optimization. But expect soon some support (possibly 
something like #pragma simd, #pragma vector for C/C++ and usage for DO 
CONCURRENT in Fortran) - but I don't know which pragma and when the 
support will be added.