Allows hardware to pack the move and following destructive operation
together into one constructive operation if possible.
e.g.
movprfx VTMP1.D, VectorLower.D
addp VTMP1.B, Pred, VTMP1.B, VectorUpper.B
is allowed to be merged as if it executed constructively like:
addp VTMP1.B, Pred, VectorLower.B, VectorUpper.B
if the hardware supports it. If it doesn't, then the instructions will
behave like a regular move and destructive addp operation separately.