1. A method of performing in a computer processor conversion of a mask register into a list of index values in response to a single vector packed convert a mask register into a list of index values instruction that includes a destination vector register operand, a source writemask register operand, and an opcode, the method comprising steps of: executing the single vector packed convert a mask register into a list of index values to identify which active bit positions of the source writemask register are to be stored as index values in the destination vector register; and storing the index values, only one per packed data element position, in the destination vector register.