a method and apparatus for storing and using “ register use ” information to determine when a register is being used for the last time so that power savings may be achieved is disclosed . the register use information may take the form of “ last read ” information for a particular register . the last read information may be used to force the value of the register , after being read , to zero or to clock only that register while masking off the other registers . several methods and hardware variations are disclosed for using the register use information to achieve power savings .