1. In a microprocessor, a conditional execution apparatus, comprising: translation logic, for translating an extended instruction into corresponding micro instructions, wherein said extended instruction comprises: an extended prefix, for specifying a condition, wherein execution of an operation prescribed by said extended instruction depends upon realization of said condition; and an extended prefix tag, for indicating said extended prefix, wherein said extended prefix tag is an otherwise architecturally specified opcode within an instruction set for the microprocessor; and extended execution logic, coupled to said translation logic, for receiving said corresponding micro instructions, and for evaluating said condition, wherein, if said condition is not realized, then said extended execution logic precludes execution of said operation.