Subject: Re: [PATCH v6 2/4] powerpc/64: enhance memcmp() with VMX instruction for long bytes comparision

From: Segher Boessenkool <[email-masked]>
Date: Wed, 30 May 2018 03:35:40 -0500

On Wed, May 30, 2018 at 04:14:02PM +0800, Simon Guo wrote:
> Hi Segher,
> On Mon, May 28, 2018 at 06:05:59AM -0500, Segher Boessenkool wrote:
> > On Fri, May 25, 2018 at 12:07:34PM +0800, [email-masked] wrote:
> > > +	/* save and restore cr0 */
> > > +	mfocrf  r5,64
> > > +	EXIT_VMX_OPS
> > > +	mtocrf	64,r5
> > > +	b	.LcmpAB_lightweight
> > 
> > That's cr1, not cr0.  You can use mcrf instead, it is cheaper (esp. if
> > you have it in a non-volatile CR field before so you need only one, if any).
> > 
> You are right :) How about using mtcr/mfcr instead, I think they are
> fast as well and more readable.

Those are much worse than m[ft]ocrf.

You probably should just shuffle things around so that EXIT_VMX_OPS
does not clobber the CR field you need to keep.

Segher