The E ect of Code Expanding Optimizations on Instruction Cache Design

This paper shows that code expanding optimizations have strong and non-intuitive implications on instruction cache design. Three types of code expanding optimizations are studied in this paper: instruction placement, function inline expansion, and superscalar optimizations. Overall, instruction placement reduces the miss ratio of small caches. Function inline expansion improves the performance for small cache sizes, but degrades the performance of medium caches. Superscalar optimizations increases the cache size required for a given miss ratio. On the other hand, they also increase the sequentiality of instruction access so that a simple load-forward scheme e ectively cancels the negative e ects. Overall, we show that with load forwarding, the three types of code expanding optimizations jointly improve the performance of small caches and have little e ect on large caches. Index terms C compiler, code optimization, cache memory, code expansion, load forwarding, instruction placement, function inline expansion, superscalar optimizations. The authors are with the Center for Reliable and High-Performance Computing, University of Illinois, UrbanaChampaign, Illinois, 61801.