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Re: [Qemu-devel] Re: [PATCH 08/11] QMP: Port balloon command

From: Jamie Lokier
Subject: Re: [Qemu-devel] Re: [PATCH 08/11] QMP: Port balloon command
Date: Sun, 28 Jun 2009 23:11:12 +0100
User-agent: Mutt/1.5.13 (2006-08-11)

Blue Swirl wrote:
> On 6/28/09, Filip Navara <address@hidden> wrote:
> > On Sun, Jun 28, 2009 at 5:52 PM, Avi Kivity<address@hidden> wrote:
> >  > It really isn't very complicated, and
> >  > the thread only got so long because the topic is relatively simple.  
> > Post an
> >  > RFC and a mile-long patchset about changing TCG to SSA form, and see how 
> > you
> >  > get no replies.
> >
> >
> > I wouldn't even dare to push the SSA patch... Mile-long doesn't
> >  describe it precisely enough. Imagine it was applied to all the
> >  targets.
> Is there a speed benefit from using the SSA form?

You can do some nice optimisations on SSA form, but you can do them
without SSA too.  It's just that SSA makes it easier to think about
some things.

SSA is only useful for interesting control flow graphs with many basic
blocks, though.  As far as I know, QEMU only translates code in linear
instruction traces - so most SSA optimisations don't apply, and those
which remain are easy to think about in any representation.

-- Jamie

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