An empirical evaluation of chains of recurrences for array dependence testing

Code restructuring compilers rely heavily on program analysis techniques to automatically detect data dependences between program statements. Dependences between statement instances in the iteration space of a loop nest impose ordering constraints that must be preserved in order to produce valid optimized, vectorized, and parallelized loop nests. This paper evaluates a new approach for fast and accurate nonlinear array dependence testing using Chains of Recurrences (CRs). A flow-sensitive loop analysis algorithm is presented for constructing the CR forms of array index expressions. Unlike other approaches, the CR forms are directly integrated into a standard dependence test to solve nonlinear CR-based dependence equations. To study the coverage and performance of the proposed CR-based enhancements of a standard test, we chose the inexact Banerjee test. We implemented a new CR-based Banerjee test in the Polaris compiler and compared the results to the Omega test and Range test on a set of SPEC and LAPACK Benchmark programs. The experimental results suggest that a CR enhancement can dramatically increase the effectiveness of a dependence test without a significant cost increase. More surprisingly, the findings indicate that the enhanced test exceeds the capabilities of the Omega and Range tests for many nonlinear dependence relations detected in the PERFECT Club and LAPACK Benchmark programs.