Previously, we used a string name. It was nice for translating out of GLSL
IR (which also does that) but cumbersome the rest of the time.
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
We also make the return types match GLSL. The GLSL spec specifies that
findMSB and findLSB return a signed integer. Previously, nir had them
return unsigned. This updates nir's behavior to match what GLSL expects.
We also update the nir-to-fs generator to take the new instructions. While
we're at it, we fix the case where the input to findMSB is zero.
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
