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From: Blue Swirl <blauwirbel@gmail.com>
Date: Wed, 11 May 2011 22:15:32 +0300
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Subject: Re: [Qemu-devel] TCG: AREG0 removal planning
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On Wed, May 11, 2011 at 9:39 PM, Llu=C3=ADs <xscript@gmx.net> wrote:
> Blue Swirl writes:
>
>> On Wed, May 11, 2011 at 12:28 AM, Paul Brook <paul@codesourcery.com> wro=
te:
>>> In practice generated code probably accesses CPUState often enough that=
 a
>>> dedicated register isn't a bad idea. =C2=A0My guess is that eliminating=
 it from C
>>> code gets us almost all of the useful benefit. =C2=A0Removing it from t=
he code
>>> generator (i.e. TCG_AREG0) may be more pain that it's worth.
>
>> I don't think moving the helpers from op_helper.c to helper.c will be
>> a performance win if AREG0 is not eliminated. The code gets to use one
>> register more, but AREG0 needs to be moved to a function argument
>> register in most cases and AREG0 has to be restored. I think the
>> benefit should come from generated code getting one more available
>> register.
>
> So, it all boils down to the amount of register spilling that can be
> avoided in TCG-generated code when eliminating the reserved register for
> AREG0. Am I right?

For the generated code, yes.