Re: [PATCH v3 51/81] target/arm: Pass separate addend to {U, S}DOT helpers

[LIU Zhiwei]

On 2020/9/23 22:46, Richard Henderson wrote:

> On 9/23/20 3:01 AM, LIU Zhiwei wrote:
> > On 2020/9/19 2:37, Richard Henderson wrote:
> > > For SVE, we potentially have a 4th argument coming from the
> > > movprfx instruction.  Currently we do not optimize movprfx,
> > > so the problem is not visible.
> > >         
> > Hi Richard,
> >
> > I am a little confused.  If it is not immediately preceded by a MOVPRFX
> > instruction, the addend will
> > still be used.
> >
> > Is it right?
> >       
> If movprfx is not used, then the addend register will be the same as the
> destination register.
>     
    Get it.
    
    Could you see again the definition of HELPER(gvec_udot_idx_h) or the
    HELPER(gvec_sdot_idx_h)?
    
    I think it is wrong there, it code sequence is like this:
d0 = a[i+0]
//dot calculation
d[i+0] += d0
    Because when addend is the destination register, it has no reason to
    add destination register twice.
    
    Best Regards,
    Zhiwei
> r~
>