Re: [Qemu-devel] [PULL 5/8] tcg: Put opcodes in a linked list

[Artyom Tarasenko]

On Mon, Aug 17, 2015 at 5:44 PM, Richard Henderson <address@hidden> wrote:
> On 08/17/2015 04:35 AM, Artyom Tarasenko wrote:
>> Hi Richard,
>>
>> this patch seems to break a build when USE_LIVENESS_ANALYSIS is undefined.
>
> I suppose that's possible.  If so, it must be a trivial error somewhere.
> Why in the world would you want !USE_LIVENESS_ANALYSIS?
>
> Are you simply trying to see what sort of performance impact it has?  I can
> tell you it's fairly important for generating x86 code.  The two operand 
> nature
> of the ISA means that if we don't know that the source operand is dead, we
> often have to introduce an extra move to preserve it.

~ a year ago there was a report that !USE_LIVENESS_ANALYSIS brings 5%
speed improvement when running qemu-system-sparc64 . I'd like to see
how does it look today. I see tcg_liveness_analysis taking 3%-5% in a
perf top output,  on the other hand the produced code must be more
efficient, so it's interesting to see how does it sum up.

Artyom

-- 
Regards,
Artyom Tarasenko

SPARC and PPC PReP under qemu blog: http://tyom.blogspot.com/search/label/qemu