Any reason to use stl::vector instead if ccl::vector from util_vector.h? API-wise they should be exactly the same, but this gives extra memory profiling for Blender.

Code style, no space after keyword. I would also suggest always use braces, even for single line bodies. Makes code more explicit and avoids noise in the future.

Same applies to the cases below.

Wondering whether it's better to do

const texture_id = kernel_tex_type(id);
if(texture_id == ...)

Same as above. And cases below.

Would suggest making it a constant similar to primitive type so if we add more types we don't have to scroll over all code and replace bits.

We don't use c++ casts in Cycles, we use C-like casts.

Same as above.

Should these magic numbers be constants somewhere?

Not sure why the comment is changed, we still convert single channel and half slots which are not available on fermi to other slot types. It's easier to read a one sentence comment, rather than read 4 if/else lines.

Code style (no gap between if and brace), also wrong in other places.

Initially I thought I could get half precision textures on Fermi too by assigning the texture slots as needed, but that ended up not being the case. This commend was a relict of that.