HP Labs Technical Reports

Control CPR: A Branch Height Reduction Optimization for EPIC Architectures

Schlansker, Michael; Mahlke, Scott; Johnson, Richard

HPL-1999-34

Keyword(s): ILP; critical path reduction; compilers

Abstract: The challenge of exploiting high degrees of instruction-level parallelism is often hampered by frequent branching. Both exposed branch latency and low branch throughput can restrict parallelism. Control critical path reduction (control CPR) is a compilation technique to address these problems. Control CPR can reduce the dependence height of critical paths through branch operations as well as decrease the number of executed branches. In this paper, we present an approach to control CPR that recognizes sequences of branches using profiling statistics. The control CPR transformation is applied to the predominant path through this sequence. Our approach, its implementation, and experimental results are present. This work demonstrates that control CPR enhances instruction-level parallelism for a variety of application programs and improves their performance across a range of processors.

14 Pages

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