On the Complexity of Register Coalescing

Memory transfers are becoming more important to optimize, for both performance and power consumption. With this goal in mind, new register allocation schemes are developed, which revisit not only the spilling problem but also the coalescing problem. Indeed, a more aggressive strategy to avoid load/store instructions may increase the constraints to suppress (coalesce) move instructions. This paper is devoted to the complexity of the coalescing phase, in particular in the light of recent developments on the SSA form. We distinguish several optimizations that occur in coalescing heuristics: a) aggressive coalescing removes as many moves as possible, regardless of the colorability of the resulting interference graph; b) conservative coalescing removes as many moves as possible while keeping the colorability of the graph; c) incremental conservative coalescing removes one particular move while keeping the colorability of the graph; d) optimistic coalescing coalesces moves aggressively, the...

• Type: Conference
• Year: 2007
• Where: CGO
• Authors: Florent Bouchez, Alain Darte, Fabrice Rastello
• Keywords: CGO 2007, Coalescing Problem, Conservative Coalescing, Incremental Conservative Coalescing, Software Engineering