Re: [Mesa3d-dev] GLSL compiler back-end (was Re: Mesa release plans)

[Brian P. <bri...@tu...>]

Ian Romanick wrote:
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> Brian Paul wrote:
>> Ian Romanick wrote:
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>>> Brian Paul wrote:
>>>> I'd like to release Mesa 6.5.3 pretty soon (to be considered a 
>>>> development release) then follow up fairly quickly with a Mesa 7.0 
>>>> release.  The jump to 7.0 would indicate the jump to OpenGL 2.x API support.
>>> Woohoo!
>>>
>>>> I might cut a pre-release candidate today...
>>> Will either of these releases include the glsl-compiler-1 work?
>> Yes, that branch was merged to master a while ago.
> 
> D'oh!  How did I miss that?  Must have been asleep at the keys...
> 
> Anyway, I started looking at the code a bit this morning.  Do you have
> any advice for where a person might insert a processor-specific compiler
> back-end?  It looks like I could just hook in at _mesa_execute_program,
> but I'm wondering if there's a better place.

Well, in device drivers that generate a specific GPU program from Mesa's 
generic GPU rograms, this usually happens during state validation.

Alternately, the driver can use the ctx->Driver.ProgramStringNotify() 
hook which is called after the text program string has been compiled 
into instructions (though, I see I'm not calling that from the GLSL 
compiler - oops).

The decision there is whether you want to translate the program when 
it's compiled, or when it's first used.

But if you want to do something driver-independent, you probably can't 
use ProgramStringNotify() because you might collide with the driver's 
use of it.

I'm thinking we might need to implement a callback manager so that any 
number of modules could register a callback to get informed of newly 
compiled programs.

The other thing is program/shader linking.  Linking often involves 
changing register indexes.  The simplest thing to do there is to 
regenerate the derived programs (from scratch) after linking.  A more 
sophisticated approach would be to pass the linking information to the 
driver/translator so it could do the relocations, etc.

I'll have to think about this a bit more.

-Brian