Inherent within complex instruction set architectures such as x86 are inefficiencies that do not exist in a simpler ISAs. Modern x86 implementations decode instructions into one or more micro-operations in order to deal with the complexity of the ISA. Since these micro-operations are not visible to the compiler, the stream of micro-operations can contain redundancies even in statically optimized x86 code. Within a processor implementation, however, barriers at the ISA level do not apply, and

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... se redundancies can be removed by optimizing the micro-operation stream. In this paper, we explore the opportunities to optimize code at the micro-operation granularity. We execute these microoperation optimizations using the rePLay Framework as a microarchitectural substrate. Using a simple set of seven optimizations, including two that aggressively and speculatively attempt to remove redundant load instructions, we examine the effects of dynamic optimization of micro-operations using a trace-driven simulation environment. Simulation reveals that across a sampling of SPECint 2000 and real x86 applications, rePLay is able to reduce micro-operation count by 21% and, in particular, load micro-operation count by 22%. These reductions correspond to a boost in observed instruction-level parallelism on an 8-wide optimizing rePLay processor by 17% over a non-optimizing configuration.