// and efficient method that combines multiple factors.
			idx := -1
			for i, p := range b.Preds {
				// If the predecessor has not been visited yet, skip it because its end state
				// (redRegs and spillLive) has not been computed yet.
				pb := p.b
				if s.blockOrder[pb.ID] >= s.blockOrder[b.ID] {
					continue
				}
				if idx == -1 {
					idx = i
					continue
				}