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We present a novel approach which combines compiler, instruction set, and microarchitecture support to turn off functional units that are idle for long periods of time for reducing static power dissipation by idle functional units using power gating [2,9]. The compiler identifies program regions in which functional units are expected to be idle and communicates this information to the hardware by issuing directives for turning units off at entry points of idle regions and directives for turning them back on at exits from such regions. The microarchitecture is designed to treat the compiler directives as hints ignoring a pair of off and on directives if they are too close together. The results of experiments show that some of the functional units can be kept off for over 90% of the time at the cost of minimal performance degradation of under 1%.

Embedded systems are constrained by limited on-chip memory and by real time performance requirements. The traditional approach to solve these problems has been to write the embedded code in assembly language, which can no longer be followed due to the increasing complexity of the embedded systems. Programming in high-level language simplifies the software development cycle, incurring a code size and a performance penalty. Traditional compiler optimizations have focussed on improving code speed rather than code density or code size. We present optimizations that improve code density and performance.