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From: David Gibson <david@gibson.dropbear.id.au>
To: Richard Henderson <richard.henderson@linaro.org>
Cc: qemu-devel@nongnu.org, lagarcia@br.ibm.com,
	lucas.araujo@eldorado.org.br, fernando.valle@eldorado.org.br,
	qemu-ppc@nongnu.org, andre.silva@eldorado.org.br,
	"Bruno Larsen \(billionai\)" <bruno.larsen@eldorado.org.br>,
	matheus.ferst@eldorado.org.br, luis.pires@eldorado.org.br
Subject: Re: [PATCH 2/4] target/ppc: added solutions for building with disable-tcg
Date: Tue, 13 Apr 2021 16:42:13 +1000	[thread overview]
Message-ID: <YHU9Rez8KNZ1FKZi@yekko.fritz.box> (raw)
In-Reply-To: <26d5b8e4-693d-f747-3b7f-d984a43f0209@linaro.org>

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On Mon, Apr 12, 2021 at 08:40:47AM -0700, Richard Henderson wrote:
> On 4/11/21 10:08 PM, David Gibson wrote:
> > Not directly related to what you're trying to accomplish here, but the
> > whole vscr_sat thing looks really weird.  I have no idea why we're
> > splitting out the storage of VSCR[SAT] for the TCG case at all.  If
> > you wanted to clean that up as a preliminary, I'd be grateful.
> 
> That's about efficiently implementing the vector saturation instructions in
> TCG.  See GEN_VXFORM_SAT in translate/vmx-impl.c.inc.
> 
> The SAT bit is represented as a vector that e.g. compares the result of
> addition with the result of saturating addition.  We don't need to resolve
> that to a single bit until the VSCR register is read.

Aha, thanks for the input.

Long term, that might benefit from KVM specific code paths that don't
bother with this then.  However, for the first cut, it's simpler to
just keep the current representation, even though it's pretty odd for
KVM.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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  reply	other threads:[~2021-04-13  7:45 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-09 15:19 [RFC PATCH 0/4] target/ppc: add disable-tcg option Bruno Larsen (billionai)
2021-04-09 15:19 ` [PATCH 1/4] target/ppc: Code motion required to build disabling tcg Bruno Larsen (billionai)
2021-04-09 19:48   ` Fabiano Rosas
2021-04-12  4:34     ` David Gibson
2021-04-09 15:19 ` [PATCH 2/4] target/ppc: added solutions for building with disable-tcg Bruno Larsen (billionai)
2021-04-09 20:40   ` Fabiano Rosas
2021-04-12  5:08   ` David Gibson
2021-04-12 15:40     ` Richard Henderson
2021-04-13  6:42       ` David Gibson [this message]
2021-04-09 15:19 ` [PATCH 3/4] target/ppc: Add stubs for tcg functions, so it builds Bruno Larsen (billionai)
2021-04-19  5:28   ` David Gibson
2021-04-09 15:19 ` [PATCH 4/4] target/ppc: updated build rules for disable-tcg option Bruno Larsen (billionai)
2021-04-09 15:57 ` [RFC PATCH 0/4] target/ppc: add " no-reply
2021-04-12  5:13   ` David Gibson
2021-04-12  4:32 ` David Gibson

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