Arguments are the N top-most elements of the stack. Top-most argument is first. Thus elements have to be pushed on stack in reverse order.
Operation will pop N elements from the stack.
| NaryInstr (Oper* op) | NaryInstr | 
Caller must not delete / modify operation.
Parameters:
| op | operation of this instruction | 
| ~NaryInstr () | ~NaryInstr | 
| INSTR_VISITABLE () | INSTR_VISITABLE | 
| const Oper&  op () | op | 
[const]
Returns: operation associated with this instruction.