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Open Access Publications from the University of California

Optimal register assignment to loops for embedded code generation

  • Author(s): Kolson, David J.
  • Nicolau, Alexandru
  • Dutt, Nikil
  • et al.

One of the challenging tasks in code generation for embedded systems is register assignment. When more live variables than registers exist, some variables will necessarily be accessed from data memory. Because loops are typically executed many times and are often time-critical, good register assignment in loops is exceedingly important as accessing data memory can degrade performance. The issue of finding an optimal register assignment to loops has been open for some time. In this paper, we present a technique for optimal (i.e., spill minimizing) register assignment to loops. First, we present a technique for register assignment to processor cores which are characterized by a consolidated register file. Then, we extend the technique to include architecture styles which are characterized by the partitioning of registers into multiple register files and/or a combination of general - and special - purpose registers. Experimental results demonstrate that, while the optimal algorithm may be computationally prohibitive, heuristic versions obtain results with performance better than that of an existing graph coloring approach.

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