Instead of re-building the interference graph every time we spill, we
modify it in place so we can avoid recalculating liveness and the whole
O(n^2) interference graph building process. We make a simplifying
assumption in order to do so which is that all spill/fill temporary
registers live for the entire duration of the instruction around which
we're spilling. This isn't quite true because a spill into the source
of an instruction doesn't need to interfere with its destination, for
instance. Not re-calculating liveness also means that we aren't
adjusting spill costs based on the new liveness. The combination of
these things results in a bit of churn in spilling. It takes a large
cut out of the run-time of shader-db on my laptop.
Shader-db results on Kaby Lake:
total instructions in shared programs: 15311224 -> 15311360 (<.01%)
instructions in affected programs: 77027 -> 77163 (0.18%)
helped: 11
HURT: 18
total cycles in shared programs: 355544739 -> 355830749 (0.08%)
cycles in affected programs: 203273745 -> 203559755 (0.14%)
helped: 234
HURT: 190
total spills in shared programs: 12049 -> 12042 (-0.06%)
spills in affected programs: 2465 -> 2458 (-0.28%)
helped: 9
HURT: 16
total fills in shared programs: 25112 -> 25165 (0.21%)
fills in affected programs: 6819 -> 6872 (0.78%)
helped: 11
HURT: 16
Total CPU time (seconds): 2469.68 -> 2360.22 (-4.43%)
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
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