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

[Marek Olšák]

Could you please show us an example in TGSI where a 3rd address
register is needed?

Thanks,

Marek

On Tue, Aug 5, 2014 at 6:54 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> 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
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