[Mesa-dev] RFC: mesa/st dynamic sampler support in tgsi

[Ilia Mirkin]

Hello,

I'm in the process of working out the details of adding dynamic
sampler support to mesa/st as part of ARB_gpu_shader5. Unfortunately
I've run into a bit of a roadblock.

One approach I've tried is to load the indirect sampler index into an
address register and then use that as the offset. However in order to
realistically support that I need a 3rd address register, while right
now tgsi_ureg limits it to 2 address registers. Would it be OK to
relax the restriction to 3? (The reason I need a third is that if e.g.
the dst has a reladdr, I'd have to change a bunch of stuff to make
that function properly without a 3rd addr reg, since I can't just MOV
the sampler to a temp like it does for all the other src's.)

Another apporach I've tried is to just use a TEMP register as the
indirect offset here. Unfortunately this gets destroyed by
st_glsl_to_tgsi's various optimizations which assume that temp
registers can't be reladdr's and so messes up the values. I started
adding support for that, but then quickly realized that was probably
not the right thing to do.

So... should I increase the number of address registers to 1? Or is
there some other simple approach that I'm missing?

Thanks,

  -ilia