Fast enumeration of maximal valid subgraphs for custom-instruction identification

Abstract

Extensible processors are increasingly becoming popular as they allow for incorporating custom instructions to meet design constraints. However, identifying custom instructions under architectural input/output ports constraint is a time consuming process particularly when large applications are considered. To rapidly identify the most profitable custom instructions with large inputs and outputs, this paper proposes a novel identification algorithm for enumerating maximal convex subgraphs containing no invalid node (i.e., maximal valid subgraphs). The proposed enumerating strategy is based on divide-and-conquer with a top-down manner, rather than the bottom-up manner utilized in the state-of-the-art. The division operation only considers invalid inner nodes of the given DFG, rather than taking all the invalid nodes into account, and thus accelerates enumeration of the maximal valid subgraphs. Experimental results show that, the improvement over the latest work is more than 90% for 60% DFG instances of the acknowledged benchmarks.