Otherwise, we get an effectively random spill reg because we no longer
have the information from RA to guide us. Also, a completely clean
graph has undefined data in in_stack which is used for choosing the
spill reg so it really is non-deterministic.
Fixes: e99081e76d "intel/fs/ra: Spill without destroying the..."
Tested-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>