Making the base e functions IR operations is not a clear win. i965
doesn't support it, it doesn't look like r600 supports it, but r500
does. It should be easily supportable as a lowering pass, though.
Following a discussion in #dri-devel, I think this makes more sense
than implementing it as RSQ RCP CMP as Mesa did. The i965 has a
hardware sqrt that should work, and AMD is suppposed to be able to
implement it as RSQ RCP with an alternate floating point mode so that
the 0.0 case is handled like we want.
