nir/lower_bit_size: optimize upcast of b2i8/b2i16

This also seems to be done by nir_opt_algebraic, but RADV will be moving
nir_lower_bit_size() to after that (so it doesn't create unsupported
8/16-bit instructions) and it doesn't seem worth creating a new pass just
for this simple optimization.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4791>
1 file changed