1. An apparatus executing a set of instructions, the instructions including one or more fields, wherein a field of a given instruction specifies a source of an operand of the given instruction or a destination of a result of the given instruction, and wherein the apparatus comprises: processing means for executing the instructions; and a register file, coupled to the processing means, for storing operands and results of the instructions, wherein, the register file includes a plurality of register sets, and the register file is responsive to one or more of the fields in a given instruction to retrieve an operand of the given instruction from, or store a result of the given instruction into, a given register in a given one of the register sets as identified by the one or more fields in the given instruction.