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We present a physical-synthesis based power optimization technique that simultaneously explores the four transforms, multiple Vdd, multiple Vth , cell sizing, and placement, to find a minimum power solution under timing and other constraints. The optimal selection of the design options of all transforms for all cells in the circuit is solved using a new optimization technique called discretized network flow that we have recently developed. Among the constraints we consider, timing and the voltage-island constraints are the two most important and complex ones. The voltage-island constraint specifies the maximum allowed number of voltage islands in the layout, and the requirement that each island be rectangular. We develop an approach that along with the option selection process can simultaneously determine the voltage islands needed, as well as satisfy all given constraints. Experimental results on ISCAS'89 and Faraday benchmarks show that compared to an initial wire length (WL)-optimized placement with high supply and low threshold voltage levels, we obtain a power reduction by up to 42% and an average of 30% for the same delay as that of the initial design. These improvements are also 44-50% relatively better than the improvements yielded by sequentially applying the four power reduction transforms, which is the currently standard method for applying multiple transforms. Finally, compared to an industry tool Synopsys IC Compiler (ICC) that also applies all four transforms, our method reduces power by an additional amount of up to 19%, and an average of 16%.