Re: Making code auto vectorizable

[Tim Janik <timj gtk org>]

On Tue, 2 May 2006, Stefan Westerfeld wrote:

>   Hi!
>
> On Tue, Apr 18, 2006 at 05:51:52PM +0200, Tim Janik wrote:

> > > which is not (currently) recognized by the tree vectorizer. Rewriting
> > > the loop without this construct, like this:
> > >
> > > int i;
> > > for (i = 0; i < n_values; i++)
> > >   output[i] = input[i];
> > >
> > > leads to a vectorizable loop. Note that this only works if i is signed,
> > > so using a guint for iterating does not enable vectorization (it took me
> > > quite some trial and error to figure that out).
> >
> > what compiler version is this?
> > does the guint/gint problem persist in gcc-4.2snapshot?
>
> Yes, it does. And there is another change in gcc-snapshot: it doesn't
> vectorize the loop any more, unless __restrict__ is used to declare that
> the input and output buffer don't have a data dependency. I've updated
> my patch accordingly.

> > the rest looks good. provided it has been properly tested,
> > this can go into CVS. do we have a feature test for BseAdder
> > already?
>
> We do have a feature test and it still passes with the vectorized loop.
> Should I commit the updated patch with the __restrict__ keyword added?
> It might be necessary to look whether the compiler has support for it.

no, first, we should define "restrict" to __restrict__ if it is supported
and to nothing otherwise. and second, the bseadder code could be rewritten
in terms of bse_block_copy_float() and bse_block_add_floats(), right?
then, we should use that instead.

>   Cu... Stefan

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ciaoTJ