[Mesa-stable] [Mesa-dev] [PATCH v2 07/52] intel/fs: Use a pair of 1-wide MOVs instead of SEL for any/all

[Matt Turner]

On Tue, Oct 17, 2017 at 2:53 PM, Jason Ekstrand <jason at jlekstrand.net> wrote:
> On Tue, Oct 17, 2017 at 2:18 PM, Matt Turner <mattst88 at gmail.com> wrote:
>>
>> On 10/12, Jason Ekstrand wrote:
>>>
>>> For some reason, the any/all predicates don't work properly with SIMD32.
>>> In particular, it appears that a SEL with a QtrCtrl of 2H doesn't read
>>> the correct subset of the flag register and you end up getting garbage
>>> in the second half.  Work around this by using a pair of 1-wide MOVs and
>>> scattering the result.  This fixes the any/all instructions for SIMD32.
>>
>>
>> Huh. I can see a lot of potential for hardware misbehavior here...
>>
>> Making things 1-wide makes a lot of sense, regardless of the bug you're
>> seeing. I'm in favor of that change.
>>
>> I picked a SEL instead of a predicated MOV instruction since the latter
>> is considered by our optimizer to be a partial write, and as such isn't
>> subject to CSE, etc. The difference is probably trivial, but I'd rather
>> just commit a patch to change things to be 1-wide, not s/SEL/MOV/, and
>> drop the added comments from the code.
>
>
> I'm pretty sure a 1-wide SEL is also going to be considered a partial write.

Oh, true. No preference then.