[Nouveau] TLD instruction usage in non-linked sampler mode

[Ilia Mirkin]

Hello,

This question is in the context of Tesla / Fermi generations, which
have explicit bindings for textures / samplers. It might also apply to
Kepler+, not quite as sure due to the bindless nature.

I've been trying to understand how the TLD operation works (which is
used to implement texelFetch in GLSL). It does not appear to the op
takes an explicit sampler id at all (unlike all the other texturing
operations). In unlinked TSC mode (i.e. method 0x1234 == 0), my
observation is that it desperately wants for a valid sampler to be
bound to sampler slot 0. Of course I don't think TLD actually needs
anything from the sampler, which makes this all the more odd.

Is that a correct assessment of the operation of the TLD instruction?
Is there any way to make it just not care about the sampler binding?
Does the DirectX driver just always keep something bound to sampler
slot 0? (And what happens on Kepler+? Does it always look at TSC ID ==
0?)

(I kind of assume that all these problems go away in linked TSC mode,
since it'd naturally just look up the TSC entry associated with the
bound TIC.)

Thanks,

  -ilia