Re: [wwwdocs] Vectorizer's updates to 4.3.0 changes

[Andi Kleen <andi at firstfloor dot org>]

On Tue, Mar 11, 2008 at 06:50:51AM -0400, Jakub Jelinek wrote:
> On Tue, Mar 11, 2008 at 11:41:32AM +0100, Andi Kleen wrote:
> > > +     <li>The <code>-ftree-vectorize</code> option is now on by default
> > > under
> > > +     <code>-O3</code>.
> > 
> > That seems awfully brief. I would recommend you mention at least
> > e.g. that it needs sse2 or altivec enabled and roughly what the 
> > vectorizer does (in very high level terms for users) and that it may 
> > increase code size.
> 
> You don't need sse2 nor altivec enabled (though of course vectorization is
> better if you do).  Consider say:

I was actually aware of the integer vectorizations, but I expect you'll
only get significant benefits from the vectorizer with SSE2 (on x86 at least).
Ira mentioned this for PPC/Altivec too. So while you're technically correct
I expect for high level documentation purposes recommending SSE2/Altivec
would be still the right thing and most helpful to the users.

-Andi