SIMD benchmark

[Manu]

On 17 January 2012 05:55, bearophile <bearophileHUGS at lycos.com> wrote:

> Walter:
>
> > But don't worry, I'm not planning on working on that at the moment :-)
>
> Until better optimizations are implemented, I see a "simple" optimization
> for vector ops. When the compiler knows an arrays are very small it unrolls
> the operation in-place:
>
> int n = 5;
> auto a = new int[n];
> auto b = new int[n];
> a[] += b[];
>
> ==>
>
> int n = 5;
> auto a = new int[n]; // a and b are dynamic arrays,
> auto b = new int[n]; // but their length is easy to find at compile-time
> a[0] += b[0];
> a[1] += b[1];
> a[2] += b[2];
> a[3] += b[4];
> a[5] += b[5];
>

If this doesn't already exist, I think it's quite important. I was thinking
about needing to repeatedly specialise a template last night for a bunch of
short lengths of arrays, for this exact reason.
Unrolling short loops must be one of the most trivial and worthwhile
optimisations...
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