[Mesa-dev] r600g: status of my work on the shader optimization
Mathias.Froehlich at gmx.net
Fri Feb 15 23:10:49 PST 2013
On Friday, February 15, 2013 15:00:24 Vadim Girlin wrote:
> "LLVM backend is the future" is a pretty abstract argument. I prefer to
> operate with real facts. After a year of LLVM backend development what
> are the real benefits for the users? What are the real use cases where
> the users might prefer LLVM backend? To me this situation looks like the
> use of LLVM requires a lot more time and development efforts than the
> custom solution, despite the initial expectations. Maybe you are right
> and the LLVM backend will become the best alternative for users sometime
> in the future, but I only have some today's results:
I am curious how this compares for shaders like used in
which is one of the bigger programs I know of. That one is taken from a Paper
from INRIA regarding atmospheric scattering. The git archive is just some
striped down variants of that to make it at least display with our radeon type
drivers. You need float textures enabled in the configure step. The only
variants that have a chance to run on the oss drivers is Main.noprecompute and
Main.nogeometry once you compiled this dirty proof of concept files.
That saied, the shaders there are far from programmed optimal IMO. But they
render fast on the binary blobs. And I think they are a good example what you
will find in the wild. People out there expect to find a decent compiler even in
an OpenGL driver. I mean a compiler that does not just translate a tight pre
optimized shader into the apropriate backend language, but a compiler that
knows about all the tricks that are required to optimize more complex and less
good written programs. Doing good optimizers - not only the backend ones - is
a hard and longish busines which is easily underestimated.
In the long term I would vote for your knowledge about these machines
available in llvm to get the best of both worlds.
my 2 cents...
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