We can't move the shuffle to a new block so this only works if the
shuffle and the bcsel are in the same block. Fortunately, in the
motivating case, this is true.
Also, we have to be careful around discard. We could try really hard to
just avoid moving them past discard but we choose to simply bail if we
see a discard instead.
Fixes: 4ff4d4e569 "nir/opt_intrinsic: Optimize bcsel(b, shuffle..."
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9068>
(cherry picked from commit ceb6986d34)
1d23aa2618