[Mesa-dev] [Mesa-stable] [PATCH] nv50/ir: skip optimizing ADD+SHL to SHLADD when src(1) is 0

[Ilia Mirkin]

On Tue, Sep 26, 2017 at 6:30 AM, Samuel Pitoiset
<samuel.pitoiset at gmail.com> wrote:
>
>
> On 09/26/2017 12:29 PM, Juan A. Suarez Romero wrote:
>>
>> On Mon, 2017-05-01 at 12:11 -0400, Ilia Mirkin wrote:
>>>
>>> On Mon, May 1, 2017 at 12:09 PM, Samuel Pitoiset
>>> <samuel.pitoiset at gmail.com> wrote:
>>>>
>>>> On 05/01/2017 05:59 PM, Ilia Mirkin wrote:
>>>>>
>>>>>
>>>>> I think this is off. It shouldn't matter what the code sequence is,
>>>>> it's all representable. You need to teach replaceZero to not mess
>>>>> things up for SHLADD's src(1).
>>>>
>>>>
>>>>
>>>> It's representable but stupid to do it. We should keep the ADD there and
>>>> this also avoids a workaround in the replaceZero logic just for that.
>>>>
>>>> IMHO, this is the better solution.
>>>
>>>
>>> Yes, that would be a better optimization. However at this stage, you
>>> have a y = SHL(x, 0) + ADD(y, z). I think it makes sense to combine
>>> them into one and let DCE take care of it.
>>>
>>> Ideally we wouldn't get into such a situation, but the real issue is
>>> that a perfectly representable (if dumb) instruction like SHLADD(x, 0,
>>> y) gets messed up by replaceZero. We should fix replaceZero. We should
>>> also try to avoid generating such stupid instructions.
>>>
>>
>> So what was the final conclusion for this patch? Was replaceZero fixed?
>
>
> I don't think it has been fixed, but I could be wrong.

https://cgit.freedesktop.org/mesa/mesa/commit/src/gallium/drivers/nouveau/codegen?id=82e77d4e4484b5d4f6a7b4751a17c882e6d2ad69