A Representation for Bit Section Based Analysis and Optimization

Programs manipulating data at subword level are growing in number and importance. Examples are programs running on network processors, media processors, or general purpose processors with media extensions. In addition data compression techniques which are vital for embedded system applications result in code operating on subword level as well. Performing analysis on word level, however, is too coarse grain missing opportunities for optimizations. In this paper we introduce a novel program representation which allows reasoning at subword level. This is achieved by making accesses to subwords explicit. First in a local phase statements are analyzed and accesses at subword level identified. Then in a global phase the control-flow is taken into account and the accesses are related to one another. As a result various traditional analyses can be performed on our representation at subword level very easily. We discuss the algorithms for constructing the program representation in detail and illustrate their application with examples.