Instruction Precomputation: Dynamically Removing Redundant Computations Using Profiling

As a program executes, some computations are performed over and over again. These redundant computations increase the program’s execution time since they require multiple cycles to execute and because they consume limited processor resources. To minimize the performance degradation that redundant computations have on the processor, we propose using Instruction Precomputation hardware to dynamically remove these redundant computations. Instruction Precomputation profiles the program to determine the highest frequency redundant computations, which are loaded into the Precomputation Table before the program executes. During program execution, the processor accesses the Precomputation Table to determine whether or not an instruction is a redundant computation; instructions that are redundant computations receive their output value from the Precomputation Table and are removed from the pipeline. The key difference between Instruction Precomputation and Value Reuse another microarchitectural technique that dynamically removes redundant computations is that Instruction Precomputation does not dynamically update the Precomputation Table with the most recent redundant computations since it already contains the highest frequency ones. Consequently, Instruction Precomputation requires less chip area and has less impact on the clock period, as compared to Value Reuse. For a 2048entry Precomputation Table, dynamically removing redundant computations yields an average speedup of 10.53%, while, by comparison, a 2048-entry Value Reuse Table produces an average speedup of 7.43%. 0-8493-0052-5/00/$0.00+$.50 c © 2001 by CRC Press LLC 1