[Mesa-dev] r600g: status of the r600-sb branch

[Vadim Girlin]

On 04/19/2013 08:35 PM, Christian König wrote:
> Hey Vadim,
>
> Am 19.04.2013 18:18, schrieb Vadim Girlin:
>> [SNIP]
>>
>> In theory, yes, some optimizations in this branch are typically used
>> on the earlier compilation stages, not on the target machine code. On
>> the other hand, there are some differences that might make it harder,
>> e.g. many algorithms require SSA form, and though it's possible to do
>> similar optimizations without SSA, it would be hard to implement. Also
>> I wanted to support both default backend and llvm backend for
>> increased testing coverage and to be able to compare the efficiency of
>> the algorithms in my experiments etc.
>
> Yeah I know, missing an SSA implementation is also something that always
> bothered me a bit with both TGSI and GLSL (while I haven't done much
> with GLSL, so maybe I misjudge here).
>
> Can you name the different algorithms used?

There is a short description of the algorithms and passes in the 
notes.markdown file [1] in that branch, there are also links in the end 
to the full description of some algorithms, though some of them were 
modified/adapted for this branch.

> It's not a strict prerequisite, but I think we both agree that doing
> things like LICM on R600 bytecode isn't the best idea over all (when
> doing it on GLSL would be beneficial for all drivers not only r600).

In fact there is no special LICM pass, it's done by the GCM (Global Code 
Motion, [2]), which probably could be also called global scheduler. In 
fact in my branch this pass is combined with some hw-specific scheduling 
logic, e.g. grouping fetch/alu instructions to reduce clause type 
switching in the code and the number of required CF instructions, 
potentially it can also schedule clauses to expose more parallelism with 
the BARRIER bit usage.

Vadim

  [1] 
http://cgit.freedesktop.org/~vadimg/mesa/tree/src/gallium/drivers/r600/sb/notes.markdown?h=r600-sb
  [2] 
http://www.cs.washington.edu/education/courses/cse501/06wi/reading/click-pldi95.pdf

> Regards,
> Christian.