New Insights on Scalar Promotion with the Polyhedral Model

Memory accesses are a well known bottleneck whose impact might be mitigated by using properly the memory hierarchy until registers. In this paper, we address scalar promotion, a technique to turn temporary arrays into a collection of scalar variables to be allocated to registers. We revisit array scalarization in the light of the recent advances of the polyhedral model. We propose a general algorithm for array scalarization and we show a scalarization of stencil computations thanks to a preliminary preprocessing. Our scalarization algorithm operates on the polyhedral intermediate representation and could be plugged in a polyhedral compiler among other passes. In particular, our scalarization algorithm is parametrized by the program schedule, possibly computed by a previous compilation pass. We present a preliminary experimental validation with promising results.