A linear-scan algorithm directs the global allocation of register candidates to registers based on a simple linear sweep over the program being compiled. This approach to register allocation makes sense for systems, such as those for dynamic compilation, where compilation speed is important. In contrast, most commercial and research optimizing compilers rely on a graph-coloring approach to global register allocation. In this paper, we compare the performance of a linear-scan method against a modern graph-coloring method. We implement both register allocators within the Machine SUIF extension of the Stanford SUIF compiler system. Experimental results show that linear scan is much faster than coloring on benchmarks with large numbers of register candidates. We also describe improvements to the linear-scan approach that do not change its linear character, but allow it to produce code of a quality near to that produced by graph coloring.
In linear scan register allocation REF [4], a prepass computes lifetimes and lifetime holes and then directs global allocation of registers with a simple linear sweep over the program being compiled.
Quality and speed in linear-scan register allocation
PLDI '98
Computer Science