Departmental Papers (CIS)
Date of this Version
Vlad Petric, Tingting Sha, and Amir Roth, "RENO: A Rename-Based Instruction Optimizer", . June 2005.
RENO is a modified MIPS R10000 register renamer that uses map-table "short-circuiting" to implement dynamic versions of several well-known static optimizations: move elimination, common subexpression elimination, register allocation, and constant folding. Because it implements these optimizations dynamically, RENO can apply optimizations in certain situations where static compilers cannot.
Several of RENO’s component optimizations have been previously proposed as independent mechanisms. Unified renaming  implements dynamic move elimination and speculative memory bypassing  (the dynamic counterpart of register allocation). Register integration  implements commonsubexpression elimination and speculative memory bypassing. RENO unifies these mechanisms and adds a dynamic version of constant folding, RENOCF. RENOCF uses an extended map table format and a limited form of dynamic operation fusion.
Cycle-level simulation shows that RENO dynamically eliminates (i.e., optimizes away) 22% of the dynamic instructions in both SPECint2000 and MediaBench. RENOCF is responsible for 12% and 17% of the eliminations, respectively. Because dataflow dependences are collapsed around eliminated instructions, performance improves by 8% and 13%, respectively. Alternatively, because eliminated instructions do not consume issue queue entries, physical registers, or issue, bypass, register file, and execution bandwidth, RENO can be used to absorb the performance impact of a significantly scaled-down execution core.
Date Posted: 25 February 2006
Copyright 2005 IEEE. Reprinted from Proceedings of the 32nd International Symposium on Computer Architecture 2005 (ISCA 2005), pages 98-109.
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