Architectural simulators are essential tools for computer architecture and systems research and development. Simulators, however, are becoming frustratingly slow, because they must now model increasingly complex micro-architectures running realistic workloads. Previously, we developed a technique called fast-forwarding, which applied partial evaluation and mermoization to improve the performance of detailed architectural simulations by as much as an order of magnitude [14].

Our new out-of-order processor simulatol; FastSim, uses two innovations to speed up simulation 8--15 times (vs. Wisconsin SimpleScalar) with no loss in simulation accuracy. First, FastSim uses speculative direct-execution to accelerate the functional emulation of speculatively executed program code. Second, it uses a variation on memoization---a well-known technique in programming language implementation---to cache microarchitecture states and the resulting simulator actions, and then "fast forwards" the simulation the next time a cached state is reached. Fast-forwarding accelerates simulation by an order of magnitude, while producing exactly the same, cycle-accurate result as conventional simulation.

Modern microprocessors offer more instruction-level parallelism than most programs and compilers can currently exploit. The resulting disparity between a machine's peak and actual performance, while frustrating for computer architects and chip manufacturers, opens the exciting possibility of low-cost instrumentation for measurement, simulation, or emulation. Instrumentation code that executes in previously unused processor cycles is effectively hidden. On two superscalar SPARC processors, a simple, local scheduler hid an average of 13% of the overhead cost of profiling instrumentation in the SPECINT benchmarks and an average of 33% of the profiling cost in the SPECFP benchmarks.

EEL (Executable Editing Library) is a library for building tools to analyze and modify an executable (compiled) program. The systems and languages communities have built many tools for error detection, fault isolation, architecture translation, performance measurement, simulation, and optimization using this approach of modifying executables. Currently, however, tools of this sort are difficult and time-consuming to write and are usually closely tied to a particular machine and operating system. EEL supports a machine- and system-independent editing model that enables tool builders to modify an executable without being aware of the details of the underlying architecture or operating system or being concerned with the consequences of deleting instructions or adding foreign code.