Re: SSE5 patches part 2

[Uros Bizjak <ubizjak at gmail dot com>]

Michael Meissner wrote:

> > > > Please do not use unspecs, unless you really can't describe
> > > > instruction with existing RTL codes. The problem with uspecs is, that
> > > > they hide all of the insn details, so various optimization passes
> > > > (combine!) can't do nothing with it.
> > > >    
> > > >         
> > > I plan to do so in the future.  Note however, that the pperm, permps, 
> > > permpd
> > > instructions can't really be defined by RTL.  The special case of using 
> > > pperm
> > > to sign/zero extend or pack can be expressable, but you need to load the 
> > > funny
> > > constant that does the proper permutation.
> > >  
> > >       
> > I didn't investigate this in detail, but you could use pshuf insns as an 
> > example how to use funny constants.
> >     
>
> Just to expound on the pperm and perm{s,d} instructions.

Thanks for your kind explanation! The control byte (loaded to xmm reg 
and not an immediate value!) is really "funny", in the sense that it 
changes the operation of the insn. I fully agree with you, that this 
insn is one of the candidates for unspec.

Thanks again,
Uros.