Automatic tuning of whole applications using direct search and a performance-based transformation system

Abstract. In many cases, simple analytical models used by traditional compilers are no longer able to yield effectively optimized code for com-plex programs because of the enormous complexity of processor archi-tectures. A promising alternative approach for optimizing applications effectively has been the use of search-based empirical methods. The suc-cess of empirically tuned library generators such as ATLAS has shown that this strategy can be effective for domain-specific programs. How-ever, to date there has been no general-purpose tool for effective empiri-cal optimization of whole programs. The main obstacle to this approach has been the need for evaluating a prohibitively large number of alter-native program variants. To address this problem, we have developed a prototype tool for automatic application tuning that uses loop-level performance feedback and a direct search strategy to guide search for the best set of optimization parameters. Experiments on four different architectures show that direct search can be an effective technique for finding good values for transformation parameters in a reasonable time.