aco/spill: refactor live-in registerDemand calculation

This also fixes some hypothetical issue for loops without phis
and for loops with higher register pressure at the end of the
loop preheader.

No fossil-db changes.

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9196>
1 file changed