Spill metric

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A spill metric is a heuristic metric used by register allocators to decide which registers to spill. Popular spill metrics are:

  • cost / degree - introduced in Chaitin's algorithm
  • cost / degree2 - emphasizes the spill's effect on neighbours
  • cost - emphasizes run time
  • minimising number of spill operations

Where cost is the estimated cost of spilling a value from registers into memory.