Extended Linear Scan: An Alternate Foundation for Global Register Allocation
In this paper, we extend past work on Linear Scan register allocation, and propose two Extended Linear Scan (ELS) algorithms that retain the compile-time efficiency of past Linear Scan algorithms while delivering performance that can match or surpass that of Graph Coloring. Specifically, this paper makes the following contributions:
– We highlight three fundamental theoretical limitations in using Graph Coloring as a foundation for global register allocation, and introduce a basic Extended Linear Scan algorithm, ELS 0, which addresses all three limitations for the problem of Spill-Free Register Allocation.
– We introduce the ELS 1 algorithm which extends ELS 0 to obtain a greedy algorithm for the problem of Register Allocation with Total Spills.
– Finally, we present experimental results to compare the Graph Coloring and Extended Linear Scan algorithms. Our results show that the compile-time speedups for ELS 1 relative to GC were significant, and varied from 15× to 68×. In addition, the resulting execution time improved by up to 5.8%, with an average improvement of 2.3%.
Together, these results show that Extended Linear Scan is promising as an alternate foundation for global register allocation, compared to Graph Coloring, due to its compile-time scalability without loss of execution time performance.
KeywordsExtend Linear Graph Coloring Program Point Register Allocation Instruction Schedule
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