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Elimination of parallel copies using code motion on data dependence graphs

Florian Brandner 1 Quentin Colombet 2 
2 COMPSYS - Compilation and embedded computing systems
Inria Grenoble - Rhône-Alpes, LIP - Laboratoire de l'Informatique du Parallélisme
Abstract : Register allocation regained much interest in recent years due to the development of decoupled strategies that split the problem into separate phases: spilling, register assignment, and copy elimination. Traditional approaches to copy elimination during register allocation are based on interference graphs and register coalescing. Variables are represented as nodes in a graph, which are coalesced, if they can be assigned the same register. However, decoupled approaches strive to avoid interference graphs and thus often resort to local recoloring. A common assumption of existing coalescing and recoloring approaches is that the original ordering of the instructions in the program is not changed. This work presents an extension of a local recoloring technique called Parallel Copy Motion. We perform code motion on data dependence graphs in order to eliminate useless copies and reorder instructions, while at the same time a valid register assignment is preserved. Our results show that even after traditional register allocation with coalescing our technique is able to eliminate an additional 3% (up to 9%) of the remaining copies and reduce the weighted costs of register copies by up to 25% for the SPECINT 2000 benchmarks. In comparison to Parallel Copy Motion, our technique removes 11% (up to 20%) more copies and up to 39% more of the copy costs.
keyword : Copy elimination
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Submitted on : Sunday, December 23, 2012 - 10:51:30 PM
Last modification on : Tuesday, October 25, 2022 - 4:18:11 PM




Florian Brandner, Quentin Colombet. Elimination of parallel copies using code motion on data dependence graphs. Computer Languages, Systems and Structures, 2013, 39 (1), pp.25 - 47. ⟨10.1016/⟩. ⟨hal-00768781⟩



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