On Sun, Mar 28, 2010 at 10:37:07PM +0100, Артем Шинкаров wrote:
> Hi,
>
> I have a project in mind which I'm going to propose to the GCC in terms of
> Google Summer of Code. My project is not on the list of project ideas
> (http://gcc.gnu.org/wiki/SummerOfCode) that is why it would be very
> interesting
> for me to hear any opinions and maybe even to find a mentor.
>
>
> 1. Project idea
>
> A brief project idea is to create an abstract layer for vectorized
> computations. This would allow to write a portable vectorized code.
>
>
> 2. State of the art
>
> Nowadays most of processors have a support for SIMD computations. However, the
> problem is that each hardware has a different set of SIMD instructions: Intel
> MMX+SSE+AVX, PowerPC Altivec, ARM iWMMXt, and so on. GCC supports most of
> architecture-specific instructions providing built-in functions. It is
> considerably convenient to use these functions when you want to optimize some
> piece of code. The problem starts when you want to make this code portable.
> It is not a very common task, and of course GCC has a vectorizer.
> Unfortunately, there are many examples which show that it is relatively simple
> for a human to find a right place in the code and vectorize it, but it is
> extremely hard for the compiler to do the same. As a result we end up with the
> code which is not using the capabilities of the architecture.
> It would be much easier for the programmer to use an abstract layer to
> implement a vectorized code. A compiler should deal with the portability
> issues
> dispatching the code from the abstract layer to the particular architecture.
> My
> experience shows that there are no such a library for C/C++ that could solve
> the problem. There are some attempts like: http://libsimd.sourceforge.net/ but
> it is only a small part of the idea, and unfortunately the development is
> suspended. Or maybe I am wrong and everything is already written?
Note, the powerpc and cell compilers have the notion of a vector keyword that
is followed by a type (powerpc needs -maltivec and/or -mvsx to enable it). So
you can write:
vector float sum (vector float a, vector float b) { return a+b; }
Now, ideally, it would be useful to have sytax so you could change the vector
size, and the compiler would do the conversion to/from hw types to abstract
types.
--
Michael Meissner, IBM
4 Technology Place Drive, MS 2203A, Westford, MA, 01886, USA
meiss...@linux.vnet.ibm.com
