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We present a new algorithm for eliminating null pointer checks from programs written in JavaTM. However, the same approach should work for any languages requiring null checking. Our new algorithm moves null checks backwards and eliminates redundant null checks. This increases the opportunities for other optimizations to be applied by eliminating many null checks that impede code motion. In a separate pass, it moves null checks forwards and converts many null checks to hardware traps in order to minimize the execution costs for the remaining null checks. This algorithm has been implemented in the IBM Java Just-in-Time (JIT) compiler. Our experimental results show that our approach improves performance by up to 71% for jBYTEmark and up to 10% for SPECjvm98 over previously known algorithms.
By: Motohiro Kawahito, Hideaki Komatsu, and Toshio Nakatani
Published in: ACM SIGPLAN Notices, volume 35, (no 11), pages 139-149 in 2000
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