1. A method of executing instructions in a processor, the method comprising: receiving a plurality of instructions, wherein the plurality of instructions includes first instructions in a first thread and second instructions in a second thread; forming a common issue group including an instruction of a first instruction type and an instruction of a second instruction type, wherein forming the common issue group comprises: adding the instruction of the first instruction type from the first thread to the common issue group if the first thread includes at least one instruction of the first instruction type; and adding the instruction of the first instruction type from the second thread to the common issue group if the first thread does not include at least one instruction of the first instruction type; and issuing the common issue group to a first execution unit and a second execution unit, wherein the instruction of the first instruction type is issued to the first execution unit and wherein the instruction of the second instruction type is issued to the second execution unit, wherein the first execution unit is not configured to execute any instruction of the second instruction type.