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 presented. 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. 1 Introduction Increases in microprocessor performance are driven by both increased clock speed and...

This report describes parallelization techniques for accelerating a broad class of recurrences on processors with instruction level parallelism. We introduce a new technique, called blocked back-substitution, which has lower operation count and higher performance than previous methods. The blocked back-substitution technique requires unrolling and non-symmetric optimization of innermost loop iterations. We present metrics to characterize the performance of software-pipelined loops and compare these metrics for a range of height reduction techniques and processor architectures.

ILP, critical path reduction, compilers The challenge of exploiting high degrees of instructionlevel 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 presented. 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.