Begin implementing intra-basic block liveness analysis #1
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This code is exposing a bug in the live-in checking, which suggests that the core algorithm may be implemented incorrectly. This'll take some solid debugging and investigation to figure out.
This PR adds the logic for checking when registers stop being used within a single basic block so that registers can be used more efficiently (i.e. A = A + 1 doesn't need a new register each time).
When commenting out the
!live_inregister freeing on basic block entry, the code miscompiles and the loop only executes once instead of 4 times. This is surprising as the live-in register freeing is more of an optimization than a hard requirement (when we lack register pressure at least)... This is suggestive of another bug in the code added by this PR