Effective Exploitation of a Zero Overhead Loop Buffer

A Zero Overhead Loop Buffer (ZOLB) is an architectural feature that is commonly found in DSP processors. This buffer can be viewed as a compiler managed cache that contains a sequence of instructions that will be executed a specified number of times. Unlike techniques such as loop unrolling, a loop buffer is a hardware technique that can be used to minimize loop overhead without the penalty of increasing code size. In addition, a ZOLB also requires relatively little space and power, which are both important considerations for most DSP applications. This paper describes strategies for generating code to effectively use a ZOLB. The authors have found that many common improving transformations used by optimizing compilers to improve code on conventional architectures are shown (1) to allow more loops to be placed in a ZOLB and (2) to further reduce loop overhead of the loops placed in a ZOLB. The results given in this paper demonstrate that this architectural feature can often be exploited with substantial improvements in execution time and slight reductions in code size. 1