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Date: Fri, 28 May 2010 11:24:26 +0530
From: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
To: Michael Neuling <mikey@neuling.org>
Subject: Re: [RFC PATCH] powerpc: Emulate nop too
Message-ID: <20100528055426.GD25946@in.ibm.com>
References: <20100520124955.GA29903@brick.ozlabs.ibm.com>
	<20100527141203.GA20770@in.ibm.com> <23979.1275013723@neuling.org>
	<20100528041645.GB25946@in.ibm.com> <7278.1275020610@neuling.org>
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Cc: linuxppc-dev@ozlabs.org, Paul Mackerras <paulus@samba.org>,
	Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
	"K.Prasad" <prasad@linux.vnet.ibm.com>
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On Fri, May 28, 2010 at 02:23:30PM +1000, Michael Neuling wrote:
> 
> 
> In message <20100528041645.GB25946@in.ibm.com> you wrote:
> > On Fri, May 28, 2010 at 12:28:43PM +1000, Michael Neuling wrote:
> > > 
> > > 
> > > In message <20100527141203.GA20770@in.ibm.com> you wrote:
> > > > Hi Paul,
> > > > 
> > > > While we are at it, can we also add nop to the list of emulated
> > > > instructions?
> > > > 
> > > > Ananth
> > > > ---
> > > > From: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
> > > > 
> > > > Emulate ori 0,0,0 (nop).
> > > > 
> > > > The long winded way is to do:
> > > > 
> > > >         case 24:
> > > >                 rd = (instr >> 21) & 0x1f;
> > > >                 if (rd != 0)
> > > >                         break;
> > > >                 rb = (instr >> 11) & 0x1f;
> > > >                 if (rb != 0)
> > > >                         break;
> > > 
> > > Don't we just need rb == rd?
> > 
> > Sure. But for this case, just checking against the opcode seems simple
> > enough.
> 
> Simple, sure.  You could not emulate anything and remove the code
> altogether.  That would be truly simple. :-P

Ah.. I misunderstood your initial point about rb == rd with imm = 0.

> Why not eliminate as much as possible?
> 
> Anyway, sounds like paulus as a better solution.

Right.

Ananth