The hot path SSA form: Extending the static single assignment form for speculative optimizations

Abstract

The Static Single Assignment (SSA) form has been an eminent contribution towards analyzing programs for compiler optimizations. It has been affable to the design of simpler algorithms for existing optimizations, and has facilitated the development of new ones. However, speculative optimizations - optimizations targeted towards speeding-up the "common cases" of a program - have not been fortunate enough to savor an SSA-like intermediate form. We extend the SSA form for speculative analyses and optimizations by allowing only hot reaching definitions - definitions along frequent acyclic paths in the program profile - to reach its respective uses; we call this representation the Hot Path SSA form. We propose an algorithm for constructing such a form, and demonstrate its effectiveness by designing the analysis phase of a novel optimization - Speculative Sparse Conditional Constant Propagation: an almost obvious extension of Wegman and Zadeck's Sparse Conditional Constant Propagation algorithm. Our experiments on some SPEC2000 programs proves the potency of such an optimization. © 2010 Springer-Verlag.