In order to curb microprocessor power consumption, we propose an L1 data cache which can be reconfigured dynamically at runtime according to the cache requirements of a given application. A two phase approach is used involving both compile time information, and the runtime monitoring of program performance. The compiler predicts L1 data cache requirements of loop nests in the input program, and instructs the hardware on how much L1 data cache to enable during a loop nest's execution. For regions of the program not analyzable at compile time, the hardware itself monitors program performance and reconfigures the L1 data cache so as to maintain cache performance while minimizing cache power consumption. In addition to this, we provide a study of data reuses inside loop nests of the SPEC CPU2000 and Mediabench benchmarks. The sensitivity of data reuses to L1 data cache associativity is analyzed to illustrated the potential power savings a reconfigurable L1 data cache can achieve.