Basic libav profiling

[Ira Rosen]

On 18 August 2011 12:45, Andrew Stubbs <andrew.stubbs at linaro.org> wrote:
> On 18/08/11 06:56, Ira Rosen wrote:
>>>
>>> How can I tell the vectoriser that a input is a multiple of something?
>>
>> Unfortunately, I don't think you can.
>
> I think you can do something like this:
>
> void multiple(struct image * __restrict dst, struct image * __restrict
> src, int h)
> {
>   if (h & 0xf)
>     __gcc_unreachable ();
>
>   for (int i = 0; i < h; i++) {
>       dst->d[i] = A*src->d[i] + B*src->d[i+1];
>   }
> }
>
> [Just off the top of my head - you'd have to check the syntax for
> gcc_unreachable.]
>
> That should allow the value range propagation to do the right thing whilst
> inserting no real code, but whether that's properly hooked into
> vectorization I have no idea?

Yes, the problem is that the vectorizer (or more precisely loop
iteration analysis in tree-ssa-loop-niter.c) doesn't use this
information.

Ira

>
> Andrew
>