Re: [PATCHv5 4/4] KVM: emulator: optimize "rep ins" handling.

[Gleb Natapov <gleb@redhat.com>]

On Sun, Aug 05, 2012 at 06:03:12PM +0300, Avi Kivity wrote:
> On 07/30/2012 05:38 PM, Gleb Natapov wrote:
> > Optimize "rep ins" by allowing emulator to write back more than one
> > datum at a time. Introduce new operand type OP_MEM_STR which tells
> > writeback() that dst contains pointer to an array that should be written
> > back as opposite to just one data element.
> > 
> >  
> >  	if (ctxt->rep_prefix && (ctxt->d & String)) {
> > +		unsigned int count;
> >  		struct read_cache *r = &ctxt->io_read;
> > -		register_address_increment(ctxt, &ctxt->regs[VCPU_REGS_RCX], -1);
> > +		if ((ctxt->d & SrcMask) == SrcSI)
> > +			count = ctxt->src.count;
> > +		else
> > +			count = ctxt->dst.count;
> > +		register_address_increment(ctxt, &ctxt->regs[VCPU_REGS_RCX],
> > +				-count);
> >  
> 
> count is unsigned.  Does it sign extend correctly in
> register_address_increment()?
> 
I think it sign extent before register_address_increment() when compiler
sees -count. count is in the range 1-1024 here, so there shouldn't be a
problem. By I welcome better suggestions.

--
			Gleb.