[Mesa-dev] [PATCH 1/2] nir: add an isinf opcode, and an option to use it.

[Roland Scheidegger]

Am 17.03.2017 um 02:29 schrieb Dave Airlie:
> On 17 March 2017 at 11:09, Jason Ekstrand <jason at jlekstrand.net> wrote:
>> On March 16, 2017 5:04:37 PM Dave Airlie <airlied at gmail.com> wrote:
>>
>>> From: Dave Airlie <airlied at redhat.com>
>>>
>>> In order to get isinf(NaN) correct, at least radv can't
>>> use an unordered equals which feq has to be for us, this
>>> passes isinf to the backend and let's it sort it out as it
>>> pleases.
>>
>>
>> I think comparisons are something that were going to need to sort out better
>> in general.  SPIR-V's rules are stricter than GL (at least the way we
>> interpret it).  Could you please be more specific about the issue?
> 
> IsInf(NaN) unordered appears to end up at true, when the spec for isinf
> says it should be false.
> 
> well SPIR-V has the unorder and ordered stuff for OpenCL kernels, just
> not sure what want in NIR in this area. If I default to using ordered compares
> for NIR I get isnan and funord fails last I tried.

FWIW tgsi uses ordered for all comparisons except not equal.
Ok well maybe not all drivers do, but that's what I'd consider what it
should be (radeonsi does that too at a quick glance). Because, well, you
guessed it, d3d10... GL of course won't mandate anything with its super
relaxed nan rules. But this pretty much matches what you get with
ordinary comparison operators in c, so may uneducated guess is it would
be a good match for nir too...


Roland