nir: Make opt_algebraic handle undef
We really should make nir_opt_algebraic
handle undef instructions, similar to how it currently handles constants. That is, we should add ways to match and produce undef instructions. It would let us delete most of nir_opt_undef
, while making it easier to add patterns that make undef handling better, like making a better choice as to which side of a bcsel
with an undef condition to choose.
@jekstrand @idr