Yep, I start to read it and it is clearly what I was looking for. But I am still wondering if this is so useful to make it here since some back ends (like Intel GPU fragment programs and maybe g80s (???) ) use struct of array layouts which do not need swizzle.
BTW, the simpler solution for these machines should be to transform the Mesa GPU code into a scalar code. So: ** mul a b c becomes mul a.x b.xxxx c.xxxx mul a.y b.yyyy c.yyyy mul a.z b.zzzz c.zzzz mul a.w b.wwww c.wwww and then, we re-analyze the program as a scalar one. Anyway, it may be still nice to have better programs higher in the sw stack. Thanks for your help. I am studying the r300 code Ben ________________________________________ From: Tom Stellard [tstel...@gmail.com] Sent: Wednesday, July 14, 2010 10:33 PM To: Segovia, Benjamin Cc: mesa-dev@lists.freedesktop.org Subject: Re: [Mesa-dev] Optimizations in mesa shader compiler On Wed, Jul 14, 2010 at 09:16:15PM -0700, Segovia, Benjamin wrote: > Thanks for that. It may be clearly useful. > > FYW, I output big shaders from nexuiz (> 100 inst) and clearly swizzling > kills opportunities of optimizations. A serie of instructions may be totally > useless but swizzles make the flow analysis more complicated. > For big nexuiz fragment shaders, almost all the moves may be removed. This > may lead to remove almost 40% of the instructions in these cases. > > I am not sure of the final speed up at the end. Intel GPUs use SoA > computations for the fragment programs. So, it should be easy to completely > remove the swizzle and to consider everything scalar. In that case, flow > analysis becomes easier. > However, despite that, the Intel Gen output still includes uncessary moves in > particular from GPR to message registers. Not sure it is still related. > > Hmmm. Cool. We may be able anyway to make it faster :) > > Ben > Hi, As Alex suggested, take a look at the r300 compiler. If you are looking to eliminate MOV instructions, the peephole() function in src/mesa/drivers/dri/r300/compiler/radeon_optimize.c might interest you. It does copy propagation and is a good example of dataflow analysis with swizzles. -Tom _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
