Re: [Mesa3d-dev] RFC: GSOC Proposal: R300/Gallium GLSL Compiler

[Marek O. <ma...@gm...>]

On Sun, Apr 4, 2010 at 6:14 AM, Tom Stellard <tst...@gm...> wrote:

> On Sun, Apr 04, 2010 at 01:09:51AM +0200, Marek Olšák wrote:
> >
> > Since Nicolai has already implemented the branch emulation and some other
> > optimizations, it would be nice to take over his work. I tried to use the
> > branch emulation on vertex shaders and it did not work correctly, I guess
> it
> > needs little fixing. See this branch in his repo:
> > http://cgit.freedesktop.org/~nh/mesa/log/?h=r300g-glsl<http://cgit.freedesktop.org/%7Enh/mesa/log/?h=r300g-glsl>
> <http://cgit.freedesktop.org/%7Enh/mesa/log/?h=r300g-glsl>
> > Especially this commit implements exactly what you propose (see comments
> in
> > the code):
> >
> http://cgit.freedesktop.org/~nh/mesa/commit/?h=r300g-glsl&id=71c8d4c745da23b0d4f3974353b19fad89818d7f<http://cgit.freedesktop.org/%7Enh/mesa/commit/?h=r300g-glsl&id=71c8d4c745da23b0d4f3974353b19fad89818d7f>
> <
> http://cgit.freedesktop.org/%7Enh/mesa/commit/?h=r300g-glsl&id=71c8d4c745da23b0d4f3974353b19fad89818d7f
> >
> >
> > Reusing this code for Gallium seems more reasonable to me than
> reinventing
> > the wheel and doing basically the same thing elsewhere. I recommend
> > implementing a TGSI backend in the r300 compiler, which will make
> possible
> > using it with TGSI shaders. So basically a TGSI shader would be converted
> to
> > the RC representation the way it's done in r300g right now, and code for
> > converting RC -> hw code would get replaced by conversion RC -> TGSI.
> Both
> > RC and TGSI are very similar so it'll be pretty straightforward. With a
> TGSI
> > backend, another step would be to make a nice hw-independent and
> > configurable interface on top of it which should go to util. So far it's
> > simple, now comes some real work: fixing the branch emulation and
> continuing
> > from (2) in your list.
>
> I am not sure if I follow you here, so let me know if I am understanding
> this correctly.  What you are suggesting is to take Nicolai's branch,
> which right now does TGSI -> RC -> Branch Emulation in RC -> hw code and
> instead of converting from RC to hw code convert from RC back into TGSI.
>

That's right.


> Then, pull the TGSI -> RC -> Branch Emulation in RC -> TGSI path out of
> the r300 compiler and place it in gallium/auxillary/util so it can be used
> by other Gallium drivers that want to emulate branches.  Is this correct?
>

Sorry I should have been more clear. The whole RC may stay in
src/mesa/drivers/dri/r300/compiler as it is now.

I think these are parts that should go to util:
- TGSI -> RC conversion
- RC -> TGSI conversion
- Hw-independent interface to the compiler, i.e. one function (or more)
which takes a TGSI shader and returns a TGSI shader. It should do both
conversions above and use r300/compiler directly.

In the long-term, the compiler should probably be moved to src/compiler or
something like that (since both classic and gallium drivers may use it), but
you don't need to care about that if you don't want to.

-Marek