[Mesa-dev] [PATCH 4/4] nir: link time opt duplicate varyings

[Timothy Arceri]

On 15/12/18 1:16 pm, Timothy Arceri wrote:
> On 15/12/18 7:32 am, Marek Olšák wrote:
>> For patches 1-3:
>>
>> Reviewed-by: Marek Olšák <marek.olsak at amd.com 
>> <mailto:marek.olsak at amd.com>>
>>
> 
> Thanks!
> 
>> I'm not so knowledgeable to be able to comment on patch 4.
>>
>> Does it also merge varyings such as (x,y,undef,undef) and 
>> (x,undef,undef,w)? There is a game which outputs (x,y,z,undef) and 
>> (x,y,undef,undef) where the vertex shader is a SSO.
> 
> No. All of the link-time optimisations in NIR are currently only applied 
> at actual link-time. I've often thought about adding a way to apply 
> these to SSO shaders but this is unlikely something I will end up 
> working on since our main focus these days is on Vulkan and there we 
> always link the entire pipeline so its not an issue.
> 

Just to be clear. The exiting NIR link-time optimisations we have will 
already convert (x,y,undef,undef) and (x,undef,undef,w) to (x,y,x,w).

This pass just takes things further, eliminating components holding the 
same value if we can detect it.