Re: how to detect that the vector extension is available

[Vincent Torri <vtorri at univ-evry dot fr>]

On Wed, 28 Sep 2011, Ian Lance Taylor wrote:

> Vincent Torri <vtorri@univ-evry.fr> writes:
>
> > I want to write an autoconf test to see if the vector extension is
> > available or not.
> >
> > if I have
> >
> > typedef int v4si __attribute__ ((vector_size (16)));
> >
> > I can check the size of v4si.
> >
> > I'm wondering if it's sufficient. Indeed, with my gcc 4.4.5, the size
> > of v4si is 16 bytes, but the code in the doc [1]:
> >
> > v4si a, b;
> > a=b+1;
> >
> > fails with error "can't convert between vector values of different
> > size". With gcc 4.7, it  works.
> >
> > So :
>
> > 3) is there better code for such check ?
>
> I guess it depends on exactly what you want to check.  With current gcc
> vector_size will work even if the target does not actually support
> vectors in hardware.  So if you want to check whether you can use
> vectors in your code this test will suffice.  If you want to check
> whether you will actually get any hardware speedup, you will need a
> different check.

That would indeed interest us to know if the vectors are hardware 
accelerated. Do you have an idea of such check ?

thanks

Vincent Torri