1. A method of executing instructions in a processing unit of the type including a core with at least one fixed point execution unit and at least one auxiliary execution unit external to the core, wherein the auxiliary execution unit has a higher priority than the fixed point execution unit, the method comprising: concurrently forwarding an instruction to fixed point and auxiliary decode logic respectively associated with fixed point and auxiliary types of execution units; concurrently decoding the instruction with the fixed point decode logic and the auxiliary decode logic; in response to the fixed point decode logic decoding the instruction as a valid instruction for the fixed point type of execution unit and the auxiliary decode logic decoding the instruction as an invalid instruction for the auxiliary type of execution unit, forwarding the instruction to the fixed point execution unit for execution thereby; in response to the fixed point decode logic decoding the instruction as an invalid instruction for the fixed point type of execution unit and the auxiliary decode logic decoding the instruction as a valid instruction for the auxiliary type of execution unit, forwarding the instruction to the auxiliary execution unit for execution thereby; in response to the fixed point decode logic decoding the instruction as a valid instruction for the fixed point type of execution unit and the auxiliary decode logic decoding the instruction as a valid instruction for the auxiliary type of execution unit, asserting an invalidate signal to the fixed point decode logic to disable forwarding of the instruction to the fixed point execution unit and forwarding the instruction to the auxiliary execution unit for execution thereby; and in response to the fixed point decode logic decoding the instruction as an invalid instruction for the fixed point type of execution unit and the auxiliary decode logic decoding the instruction as an invalid instruction for the auxiliary type of execution unit, signaling an illegal instruction program interrupt.