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Date: Tue, 23 Jun 2009 12:48:10 -0700
From: Nathan Froyd <froydnj@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH] target-ppc: fix evmergelo and evmergelohi
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To: qemu-devel@nongnu.org

On Thu, Jun 04, 2009 at 01:46:41PM -0700, Nathan Froyd wrote:
> For 32-bit PPC targets, we translated:
> 
> evmergelo rX, rX, rY
> 
> as:
> 
> rX-lo = rY-lo
> rX-hi = rX-lo
> 
> which is wrong, because we should be transferring rX-lo first.  This
> problem is fixed by swapping the order in which we write the parts of
> rX.
> 
> Similarly, we translated:
> 
> evmergelohi rX, rX, rY
> 
> as:
> 
> rX-lo = rY-hi
> rX-hi = rX-lo
> 
> In this case, we can't swap the assignment statements, because that
> would just cause problems for:
> 
> evmergelohi rX, rY, rX
> 
> Instead, we detect the first case and save rX-lo in a temporary
> variable:
> 
> tmp = rX-lo
> rX-lo = rY-hi
> rX-hi = tmp
> 
> These problems don't occur on PPC64 targets because we don't split the
> SPE registers into hi/lo parts for such targets.

Ping.

-Nathan