Re: [ARM] Implement __builtin_bswap32() via ARMv6 "rev" instruction

[Andrew Thomas Pinski <pinskia at gmail dot com>]

Sent from my iPhone

On Dec 8, 2008, at 9:37 AM, "Alexandre Pereira Nunes" <alexandre.nunes@gmail.com 
> wrote:

> > 2008/12/8 Paul Brook <paul@codesourcery.com>:
> > On Monday 08 December 2008, Alexandre Pereira Nunes wrote:
> > > A patch follows. I didn't take care of the scheduling case the  
> > > correct
> > > way, tought (aliased to clz class).
> >
> > Please read http://gcc.gnu.org/contribute.html
> >
> > In particular you need a copyright assignment, ChangeLog entry, and  
> > testing.
>
> I can provide these, tough as for the copyright assignment, the
> document mentions I can declare the changes in public domain, and
> since I already published something (which may or may not be used by
> someone in the future), I hereby do so.
>
> > You should also be able to implement bswap16, and while we're here  
> > it probably
> > makes sense to implement an optimized bswap sequence for pre-v6  
> > cores.
> Arm has rev constructs for 16 bit packed integers, however AFAIK gcc
> has no builtin for these yet, and without this, it won't internally
> have any use for this instruction pattern, correct? I only saw
> mentions to bswap32 and bswap64 on the documentation.

That is because bswap16 is the same as a rotate in 16bit mode by 8.

Thanks,
Andrew Pinski

> I'll take a look on the optimized bswap32 sequences for previous cores
> and get these expanded when not optimizing for size, IIRC I saw
> similar patterns on some other architecture machine description.
>
>
> > Once all that is fixed, patches should be sent to gcc-patches@gcc.gnu.org 
> > , not
> > this list.
>
> Roger that; Thanks.
>
> -- Alexandre