[Mesa-dev] [PATCH 0/3] [RFC] mesa/st: glsl_to_tgsi: improved temp-reg lifetime estimation

[Nicolai Hähnle]

On 14.06.2017 08:30, Gert Wollny wrote:
> Am Dienstag, den 13.06.2017, 11:07 +0200 schrieb Nicolai Hähnle:
>>
>>
>> I'm curious what you'd suggest for getting rid of allocations anyway.
> 
> As the refactoring goes I think I will end up with a hybrid approach:
> In the temporaries  I will not keep the full time line, but the
> important read/write information - just like you suggested. However, I
> will not resolve the scopes at the end of each loop, but only after the
> program is fully scanned. For that I need to keep the information of
> all scopes available and links to the key scopes fro each temporary.

Okay. Hmm, I think in a sense what you might end up doing is resolving 
scopes lazily. That does sound good, and I'm starting to see how it 
might be possible. Try to keep the data structures clean so that you can 
easily explain all the variables in comments. That should help a lot.

> 
> Equal to what you pointed out above, I'll need three allocations for
> this:
> 
> - the vector for the scopes,
> - the vector for the temporaries
> - a stack to handle the scope changes.
> 
> To not limit the number of scopes and the scope nesting level the scope
> vector and the stack might do re-allocations though.
> 
> I think right now I will not go for tracking whether a temporary is
> written in both if/else branches or all switch cases. What I want to
> achieve is that the drivers don't get into trouble because too many
> temporaries need to be allocated when the TGSI is translated into byte
> code (test case R600 with 124 free usable registers), and so far this
> seems to work without tackling this detail.

Sounds good. If I'm understanding the "lazy scope resolution" correctly, 
it might even be not too difficult to add if/else and switch case 
resolution after the fact. Anyway, it's not needed for a first version.

Cheers,
Nicolai


> 
> Thank you again for your insights,
> Gert
> 


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