[Cplex] Short SIMD vector types

Mattson, Timothy G timothy.g.mattson at intel.com
Mon Jun 3 16:52:00 CEST 2013


I agree that short SIMD vector types would be useful.  I frequently find it easier to code with vector intrinsics then to figure out how to get a compiler to vectorize my code.    Less black magic and more engineering.

Having a portable notation for these short vector operations would be handy.  We have them in OpenCL, but given the way work is decomposed for execution on a GPU, I'm not sure how useful they are.  But we have gone to great effort to define an extension to C that handles short vector types.

It would be interesting to discuss these as a group and get a broader set of eyeballs to look over what we've done in the OpenCL world.   If we decide to add this functionality to C/C++ and if the OpenCL notation is a reasonable solution to the problem, it would be nice to adopt it.   The less fragmentation in the programming language space, the better.

--Tim

-----Original Message-----
From: cplex-bounces at open-std.org [mailto:cplex-bounces at open-std.org] On Behalf Of Jeff Hammond
Sent: Monday, June 03, 2013 7:37 AM
To: Al Grant
Cc: cplex at open-std.org
Subject: Re: [Cplex] Short SIMD vector types

This would be tremendously useful to have in C.  I'm really tired of having to spin a one-off implementation of vectorized code for every FPU ISA out there nor do I want to be dependent on the OpenMP SIMD extensions since I primarily use Pthreads.

IBM has defined vector types for Blue Gene systems in C++ (I can't remember if they work strictly as an extension to C or not since it really doesn't matter); I can share the details if people are interested in looking at that.  I suppose someone from IBM Toronto is on this list and can elaborate on the design details.

Best,

Jeff

On Mon, Jun 3, 2013 at 6:46 AM, Al Grant <Al.Grant at arm.com> wrote:
> Hi,
>
> Are short SIMD vector types something that CPLEX is interested in standardizing?
>
> Many C implementations already provide these as non-standard 
> predefined types (called e.g. "int16x4_t") and/or by means of 
> constructing short vectors out of existing types (like GCC's "vector" 
> attribute).  The intuition is they map on to registers of media instruction sets like SSE, AltiVec, NEON etc.
>
> They are standard in OpenCL, although they are not how OpenCL provides 
> large-scale parallelism.  But they might be relevant to large-scale 
> parallelism in that the vector type construction could be extended to 
> construct large vectors that could be handled in whatever size chunks fit the target architecture.
>
> If there's an existing proposal on this I'd be grateful for a pointer to it.
>
> Thanks
>
> Al Grant
>
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--
Jeff Hammond
Argonne Leadership Computing Facility
University of Chicago Computation Institute jhammond at alcf.anl.gov / (630) 252-5381 http://www.linkedin.com/in/jeffhammond
https://wiki.alcf.anl.gov/parts/index.php/User:Jhammond
ALCF docs: http://www.alcf.anl.gov/user-guides
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