Set InstrItinData for RegPair

Hi All,

Say we implement i64 as register pair, then a load i64 instruction might look like this:

A0_A1 = load64 A2

I am not sure how to set InstrItinData properly. Should I treat A0_A1 as one, or two operands? MI treats A0_A1 as one operand, maybe I should align InstrItinData with MI? Thanks.