Oracle-Based Partial Evaluation

We present Oracle-Based Partial Evaluation (OBPE), a novel approach to on-line Partial Evaluation (PE) which decides the control strategy to use for each call pattern by using an oracle function which compares the results of specializing such call pattern w.r.t. a set of strategies. Our proposal is motivated by Poly-Controlled Partial Evaluation (PCPE), which allows using different control strategies for different call patterns. Given a set CS of control strategies, the best PCPE specialized programs outperform the specialized programs obtained by traditional PE for any of the control strategies in CS, especially when resource-aware specialization is performed. Unfortunately, computing all PCPE specialized programs and then choosing a posteriori the best one is too costly in practice. In contrast, in OBPE a single specialized program is computed. We have developed an empirical oracle whose parameters are approximated from a set of training data, by using constraint logic programming. Our experimental results show that the additional cost of OBPE when compared with traditional PE is a constant factor and that, at least in our experiments, OBPE obtains significantly better specializations. We argue that our proposal is relevant in practice and introduces clear improvements over standard PE. Our work is developed in the context of logic programs, though the ideas are in principle of interest to the PE of any programming language.