Subject: Re: [PATCH v1 1/3] powerpc: Align bytes before fall back to .Lshort in powerpc memcmp

From: Simon Guo <[email-masked]>
Date: Wed, 20 Sep 2017 17:56:35 +0800

On Tue, Sep 19, 2017 at 10:12:50AM +0000, David Laight wrote:
> From: [email-masked]
> > Sent: 19 September 2017 11:04
> > Currently memcmp() in powerpc will fall back to .Lshort (compare per byte
> > mode) if either src or dst address is not 8 bytes aligned. It can be
> > opmitized if both addresses are with the same offset with 8 bytes boundary.
> > 
> > memcmp() can align the src/dst address with 8 bytes firstly and then
> > compare with .Llong mode.
> 
> Why not mask both addresses with ~7 and mask/shift the read value to ignore
> the unwanted high (BE) or low (LE) bits.
> 
> The same can be done at the end of the compare with any final, partial word.
> 
> 	David
>  

Yes. That will be better. A prototyping shows ~5% improvement on 32 bytes 
size comparison with v1. I will rework on v2.

Thanks for the suggestion.

BR,
- Simon