Reno: A rename-based instruction optimizer

The effectiveness of static code optimizations--including static optimizations performed "just-in-time"--is limited by some basic constraints: (i) a limited number of logical registers, (ii) a function- or region-bounded optimization scope, and (iii) the requirement that transformations be valid along all possible paths. RENO is a modified MIPS-R10000 style register renaming mechanism augmented with physical register reference counting 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 overcome some of the limitations faced by static compilers and apply optimizations where static compilers cannot. RENO has many more registers at its disposal--the entire physical register file. Its optimizations naturally cross function or any other compilation region boundary. And RENO performs optimizations along the dynamic path without being impacted by other, non-taken paths. If the dynamic path proves incorrect due to mispeculations, RENO optimizations are naturally rolled back along with the code they optimize. RENO unifies several previously proposed optimizations: dynamic move elimination [14] (RENOME), register integration [24] (RENOCSE), and speculative memory bypassing (the dynamic counterpart o