Loop unrolling is a well known loop transformation that has been used in optimizing compilers for over three decades. In this paper, we address the problems of automatically selecting unroll factors for perfectly nested loops, and generating compact code for the selected unroll factors. Compared to past work, the contributions of our work include (i) a more detailed cost model that inclu- des register locality, instruction-level parallelism and instruction-cache consid- erations; (ii) a new code generation algorithm that generates more compact code than the unroll-and-jam transformation; and (iii) a new algorithm for efficiently enumerating feasible unroll vectors.
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