Recent research demonstrates that voltage islands provide the flexibility to reduce power by selectively shutting down the different regions of the chip and/or running the select parts of the chip at different voltage/frequency levels. As against most of the prior work on voltage islands that mainly focused on the architecture design and IP placement issues, this paper studies the necessary software compiler support for voltage islands. Specifically, we focus on an embedded multiprocessor architecture that supports both voltage islands and control domains within these islands, and determine how an optimizing compiler can automatically map an embedded application onto this architecture. Our experiments with the proposed compiler support show that our approach is very effective in reducing energy consumption.