Liveness-Based pointer analysis

  • Authors:

  • Uday P. Khedker;Alan Mycroft;Prashant Singh Rawat

  • Affiliations:

  • Indian Institute of Technology Bombay, India;University of Cambridge, UK;Indian Institute of Technology Bombay, India

  • Venue:
  • SAS'12 Proceedings of the 19th international conference on Static Analysis
  • Year:
  • 2012

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Abstract

Precise flow- and context-sensitive pointer analysis (FCPA) is generally considered prohibitively expensive for large programs; most tools relax one or both of the requirements for scalability. We argue that precise FCPA has been over-harshly judged--the vast majority of points-to pairs calculated by existing algorithms are never used by any client analysis or transformation because they involve dead variables. We therefore formulate a FCPA in terms of a joint points-to and liveness analysis which we call L-FCPA. We implemented a naive L-FCPA in GCC-4.6.0 using linked lists. Evaluation on SPEC2006 showed significant increase in the precision of points-to pairs compared to GCC's analysis. Interestingly, our naive implementation turned out to be faster than GCC's analysis for all programs under 30kLoC. Further, L-FCPA showed that fewer than 4% of basic blocks had more than 8 points-to pairs. We conclude that the usable points-to information and the required context information is small and sparse and argue that approximations (e.g. weakening flow or context sensitivity) are not only undesirable but also unnecessary for performance.