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Re: [Qemu-devel] [PATCH] tci: Add implementation of rotl_i64, rotr_i64


From: Aurelien Jarno
Subject: Re: [Qemu-devel] [PATCH] tci: Add implementation of rotl_i64, rotr_i64
Date: Mon, 9 Sep 2013 18:47:51 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

On Mon, Sep 09, 2013 at 06:14:34PM +0200, Stefan Weil wrote:
> Am 09.09.2013 16:53, schrieb Aurelien Jarno:
> > On Wed, Sep 04, 2013 at 10:51:54PM +0200, Stefan Weil wrote:
> >> Am 04.09.2013 22:49, schrieb Stefan Weil:
> >>> It is used by qemu-ppc64 when running Debian's busybox-static.
> >>>
> >>> Signed-off-by: Stefan Weil <address@hidden>
> >>> ---
> >>>
> >>> This patch is also useful for QEMU 1.6.
> >> ... so I should have added qemu-stable. Done now.
> >>
> > Why is it needed for qemu-stable? It should only improve performance, as
> > these two ops are not mandatory ops. In general I don't think we should
> > have performance improvements in a stable minor release (unless of course
> > it's a big regression from previous).
> 
> Hi Aurelien,
> 
> tci has always set TCG_TARGET_HAS_rot_i64, and target-ppc64 uses the
> rotl_i64 and rotr_i64 TCG opcodes.
> 
> The old implementation just triggered a TODO assertion. That's how I
> implemented TCI: I started with TODO assertions for all opcodes and
> replaced them by real code as soon as I got a test case which used them.
> Now I have a test case :-)

Ok, so it might be a good idea to review the remaining non-implemented
optional ops and to disable them to avoid that in the future.

> => It's not a performance issue, but fixes a fatal assertion.
> => It should be used in 1.6.
> 

It should probably also be used in older versions, as rotl and rotr have
been used by various targets for a few years (at least since version
0.10.0, probably even before).

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
address@hidden                 http://www.aurel32.net



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