Re: [Qemu-devel] [RFC][PATCH v2 4/4] configure: add CONFIG_QEMU_LDST_OPTIMIZATION for TCG qemu_ld/st optimization

[Yeongkyoon Lee <yeongkyoon.lee@samsung.com>]

On 2012년 07월 07일 16:51, Blue Swirl wrote:
> On Fri, Jul 6, 2012 at 11:43 AM, Yeongkyoon Lee
> <yeongkyoon.lee@samsung.com> wrote:
>> On 2012년 07월 05일 23:06, Peter Maydell wrote:
>>> On 5 July 2012 14:23, Yeongkyoon Lee <yeongkyoon.lee@samsung.com> wrote:
>>>> Add an option "--enable-ldst-optimization" to enable
>>>> CONFIG_QEMU_LDST_OPTIMIZATION macro for TCG qemu_ld/st optimization. It only
>>>> works with CONFIG_SOFTMMU and doesn't work with CONFIG_TCG_PASS_AREG0.
>>> This shouldn't be a user settable config option -- we should
>>> just identify what the optimal setting is for the guest/target
>>> combination and use it.
>>
>> It looks better remove the option after it is confirmed that it works well
>> for all the guest target architectures.
>>
>>
>>>>    case "$target_arch2" in
>>>>      alpha | sparc* | xtensa* | ppc*)
>>>>        echo "CONFIG_TCG_PASS_AREG0=y" >> $config_target_mak
>>>> +    # qemu_ld/st optimization is not available with
>>>> CONFIG_TCG_PASS_AREG0
>>>> +    target_ldst_optimization="no"
>>> PASS_AREG0 is the way of the future -- you need to fix the ldst
>>> optimization to work with it.
>>
>> There are two reasons to prevent working with PASS_AREG0.
>> The first one is I'm not sure the history and future PASS_AREG0 and have not
>> tested PASS_AREG0 which is only enabled for some guest architectures..
>> The second is a problem of too many conditional paths in sources.
>> I think it is not late to combine the ldst optimization with PASS_AREG0
>> after the ldst optimization agreed as default.
> It looks like you already support PASS_AREG0, the slow path code just
> passes AREG0 as the first call argument.
>
>

The code in slow path is currently dead code just for future PASS_AREG0 
porting.
It needs some porting for actual working.