JIT: consider boosting priority of GC type temps when sorting to determine tracked set

[AndyAyersMS]

Idea that was prompted by dotnet/aspnetcore#7724.

If we fail to track a GC temp, we incur an extra prolog cost to zero the temp. Seems like we should include this zeroing as an explicit extra weighted cost factor in the sort functionWtdRefCntCmp. Currently GCness is only used as a tiebreaker if weighted costs match.

category:cq
theme:basic-cq
skill-level:beginner
cost:medium

[mikedn]

Maybe we should make the tracked variable count limit configurable and experiment with raising it a bit, perhaps using 1024 instead of 512 would not make much difference on today's hardware.

[AndyAyersMS]

Could very well be the case. It seems likely very few methods reach this limit.