"Guaranteeing Instruction Fetch Behavior with a Lookahead Instruction Fetch Engine (LIFE)" by Dr. David Whalley

Date: October 9, 2009
Time: 1:00 pm – 2:00 pm

Where: BSB 3.02.02 (Loeffler Room)

Granteeing Instruction Fetch Behavior with a Lookahead Instruction Fetch Engine (LIFE)"
by Dr. David Whalley (Florida State University)


Very small instruction caches have been shown to greatly reduce fetch energy. However, for many applications the use of a small filter cache can lead to an unacceptable increase in execution time. We propose the Lookahead Instruction Fetch Engine (LIFE), which is designed to exploit the regularity present ininstruction fetch. At the nucleus of LIFE is the Tagless Hit Instruction Cache (TH-IC). Using a few metadata bits per line, we are able to more efficiently track the cache contents and "guarantee" when hits will occur in our small TH-IC. When a hit is not guaranteed, we can instead fetch directlyfrom the L1 instruction cache. The energy savings is greater than using a filter cache due to the faster execution time, the reduction in ITLB accesses,and the elimination of tag comparisons on cache hits. We extend TH-IC by eliminating accesses to the branch predictor (BP), the branch target buffer (BTB), and the return address stack (RAS) when we can guarantee that the next instruction is not a branch. LIFE enables designers to boost instruction fetch efficiency by reducing energy cost without negatively affecting performance.


David Whalley received his PhD in CS from the University of Virginia in 1990. He is currently the E.P. Miles professor and chair of the Computer Science Department at Florida State University. His research interests include low-level compiler optimizations, tools for supporting the development and maintenance of compilers, program performance evaluation tools, predicting execution time, computer architecture, and embedded systems. Some of the techniques that he developed for new compiler optimizations and diagnostic tools are currently being applied in industrial and academic compilers. His research is currently supported by the National Science Foundation. More information about his background and research can be found on his home page: http://www.cs.fsu.edu/~whalley.