Chaitin and his colleagues at IBM in Yorktown Heights built the first global register allocator based on graph coloring. This thesis describes a series of improvements and extensions to the Yorktown allocator. There are four primary results: Optimistic coloring Chaitin's coloring heuristic pessimistically assumes any node of high degree will not be colored and must therefore be spilled. By optimistically assuming that nodes of high degree will receive colors, I often achieve lower spill costs and faster code; my results are never worse. Coloring pairs The pessimism of Chaitin's coloring heuristic is emphasized when trying to color register pairs. My heuristic handles pairs as a natural consequence of its optimism. Rematerialization Chaitin et al. introduced the idea of rematerialization to avoid the expense of spilling and reloading certain simple values. By propagating rematerialization information around the SSA graph using a simple variation of Wegman and Zadeck's constant propag...

This paper presents a fast new algorithm for modeling and reasoning about interferences for variables in a program without constructing an interference graph. It then describes how to use this information to minimize copy insertion for φ-node instantiation during the conversion of the static single assignment (SSA) form into the control-flow graph (CFG), effectively yielding a new, very fast copy coalescing and live-range identification algorithm. This paper proves some properties of the SSA form that enable construction of data structures to compute interference information for variables that are considered for folding. The asymptotic complexity of our SSA-to-CFG conversion algorithm is O(nα(n)), where n is the number of instructions in the program. Performing copy folding during the SSA-to-CFG conversion eliminates the need for a separate coalescing phase while simplifying the intermediate code. This may make graph-coloring register allocation more practical in just in time (JIT) and other time-critical compilers For example, Sun’s Hotspot Server Compiler already employs a graph-coloring register allocator[10]. This paper also presents an improvement to the classical interference-graph based coalescing optimization that shows a decrease in memory usage of up to three orders of magnitude and a decrease of a factor of two in compilation time, while providing the exact same results. We present experimental results that demonstrate that our algorithm is almost as precise (within one percent on average) as the improved interference-graph-based coalescing algorithm, while requiring three times less compilation time.

This paper presents a new al gS ithm for operator strengM reduction, called OSR. OSR improves upon an earlier alg orithm due to Allen, Cocke, and Kennedy [Allen et al. 1981]. OSR operates on the static sing e assig4 ent (SSA) form of a procedure [Cytron et al. 1991]. By taking advantag of the properties of SSA form, we have derived an alg--- ithm that is simple to understand, quick to implement, and, in practice, fast to run. Its asymptotic complexity is, in the worst case, the same as the Allen, Cocke, and Kennedy al gS ithm (ACK). OSR achieves optimization results that are equivalent to those obtained with the ACK alg orithm. OSR has been implemented in several research and production compilers