Addressing instruction fetch bottlenecks by using an instruction register file

Stephen Roderick Hines, Gary Tyson, David Whalley
<span title="">2007</span> <i title="ACM Press"> <a target="_blank" rel="noopener" href="" style="color: black;">Proceedings of the 2007 ACM SIGPLAN/SIGBED conference on Languages, compilers, and tools - LCTES &#39;07</a> </i> &nbsp;
The Instruction Register File (IRF) is an architectural extension for providing improved access to frequently occurring instructions. An optimizing compiler can exploit an IRF by packing an application's instructions, resulting in decreased code size, reduced energy consumption and improved execution time primarily due to a smaller footprint in the instruction cache. The nature of the IRF also allows the execution of packed instructions to overlap with instruction fetch, thus providing a means
more &raquo; ... or tolerating increased fetch latencies, like those experienced by encrypted ICs as well as the presence of low-power L0 caches. Although previous research has focused on the direct benefits of instruction packing, this paper explores the use of increased fetch bandwidth provided by packed instructions. Small L0 caches improve energy efficiency but can increase execution time due to frequent cache misses. We show that this penalty can be significantly reduced by overlapping the execution of packed instructions with miss stalls. The IRF can also be used to supply additional instructions to a more aggressive execution engine, effectively reducing dependence on instruction cache bandwidth. This can improve energy efficiency, in addition to providing additional flexibility for evaluating various design tradeoffs in a pipeline with asymmetric instruction bandwidth. Thus, we show that the IRF is a complementary technique, operating as a buffer tolerating fetch bottlenecks, as well as providing additional fetch bandwidth for an aggressive pipeline backend.
<span class="external-identifiers"> <a target="_blank" rel="external noopener noreferrer" href="">doi:10.1145/1254766.1254800</a> <a target="_blank" rel="external noopener" href="">dblp:conf/lctrts/HinesTW07</a> <a target="_blank" rel="external noopener" href="">fatcat:fh4qhy3yfza25dunua3l5mrehu</a> </span>
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