No, it occupies one three-input slot in the same encoding block with writers (writerBlock). It is able to do so because pick is not actually moving any data, the way that copying bits to the input register of an adder does. Pick only controls the routing of the data going someplace else. There’s no real pick FU, in the sense of an adder FU.
The two-input block (exuBlock, adds and muls and such) does have real data movement and the wires to carry it. Real writers (not the pick that is encoded in the same block, put the pure sink operations that move data to the scratchpad or specRegs) have only one input. ReaderBloc operations (popular constants, specReg and scratchpad reads) have no inputs. And the whole flow side (control flow, memory) has an extremely ad hoc data movement pattern in which different slots can have different operand counts depending on what FUs are connected where.
It’s as regular as we can make it, but no more than that 🙂