Register allocation: try aggressive coalescing first - #594
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Run a first round of coloring with aggressive coalescing of moves. If this causes spilling, retry with iterated coalescing, like before. This should result in fewer moves for functions that can run entirely in registers.
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The IRC graph coloring algorithm is often too prudent with the coalescing of moves, leaving moves unchanged by fear that coalescing them could cause more spilling.
As an experiment, this PR runs a first round of coloring with aggressive coalescing of moves. If this causes spilling, it retries coloring with iterated coalescing, like before.
This should result in fewer moves for functions that can run entirely in registers. For other functions, there should be no difference with the current coloring strategy. The only possible downside is increased compilation time because of the extra round of coloring.
I haven't tried to evaluate the impact on code size and execution times yet.