Live-range unsplitting for faster optimal coalescing

Register allocation is often a two-phase approach: spilling of registers to memory, followed by coalescing of registers. Extreme liverange splitting (i.e. live-range splitting after each statement) enables optimal solutions based on ILP, for both spilling and coalescing. However, while the solutions are easily found for spilling, for coalescing they are more elusive. This difficulty stems from the huge size of interference graphs resulting from live-range splitting. This paper focuses on coalescing in the context of extreme liverange splitting. It presents some theoretical properties that give rise to an algorithm for reducing interference graphs. This reduction consists mainly in finding and removing useless splitting points. It is followed by a graph decomposition based on clique separators. The reduction and decomposition are general enough, so that any coalescing algorithm can be applied afterwards. Our strategy for reducing and decomposing interference graphs preserves the opti...

• Type: Conference
• Year: 2009
• Where: LCTRTS
• Authors: Sandrine Blazy, Benoît Robillard
• Keywords: Coalescing Algorithm, LCTRTS 2009, Optimal Coalescing, Optimal Coalescing Challenge, Software Engineering