Re: [Qemu-devel] [PATCH] RFC: TCG constant propagation.

[Filip Navara]

On Thu, Jul 23, 2009 at 11:25 AM, Laurent
Desnogues<address@hidden> wrote:
> On Thu, Jul 23, 2009 at 11:08 AM, Filip Navara<address@hidden> wrote:
>> Also it looks that the actual code size is worse for TCG ARM target
>> with this optimization. To mitigate it I propose the other attached
>> patch which uses the barrel shifter for more optimal generation of the
>> "movi" operation. I can't test it, so any help is welcome.
>
> This is wrong for two reasons:
>   - this is a rotation, you only check for shifts

I deliberately didn't do it, but it's surely an opportunity for
further optimization.

>   - the rotation amount is multiplied by 2 before being applied to the
>     8-bit immediate field.

As Paul already pointed out, that's compensated by the shift (<< 7
instead of << 8) and the "& ~1" after ctz32 call.

Attached is fixed version of the patch, I forgot one "return" there.

Best regards,
Filip Navara

0002-Use-ARM-barrel-shifter-for-more-optimal-generation-o.patch
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