Compiler-directed power gating is an approach in which sleep instructions are inserted appropriately at compile time into the application code to selectively deactivate the functional units in microprocessors during their idle periods to reduce power dissipation due to leakage. Although the effect of code transformations on dynamic and system power has been investigated and reported in the literature, such a study is lacking in the context of power gating. In this paper, we investigate and report how the leakage savings in both integer and floating point units can be improved using machine-dependent and independent optimizations in a compiler-directed power gating framework. In our study, it is ensured that power gating is applied only when the leakage savings are considerably more than the various overheads incurred in its implementation. The target embedded processor is modeled on the ARMv4 architecture, which is modified to support the power gating of its arithmetic functional units. For experimentation, GCC is used as the compiler infrastructure and Simplescalar-ARM is used as the detailed architectural simulator for reporting power and performance metrics for embedded applications belonging to the MiBench and MediaBench benchmark suites. Experimental results suggest that the additional savings in leakage energy due to one or more of the optimizations may vary largely depending on the benchmark. Moreover, the overhead of sleep instructions can be reduced by up to 50 times by performing procedure inlining.
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