>>> import qiskit as qk
>>> qc = qk.QuantumCircuit(3,1)
>>> qc.ccx(2,1,0).c_if(qc.cregs[0], 0)
<qiskit.circuit.instructionset.InstructionSet object at 0x129ed7908>
>>> qc.measure(2,0)
<qiskit.circuit.instructionset.InstructionSet object at 0x12a1619e8>
>>> print(qc)
         ┌───┐
q_0: |0>─┤ X ├────
         └─┬─┘
q_1: |0>───■──────
           │   ┌─┐
q_2: |0>───■───┤M├
        ┌──┴──┐└╥┘
 c_0: 0 ╡ = 0 ╞═╩═
        └─────┘
>>> qk.transpile(qc, optimization_level=2,backend=FakeTenerife())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/kevin.krsulichibm.com/q/qiskit-terra/qiskit/compiler/transpile.py", line 159, in transpile
    circuits = parallel_map(_transpile_circuit, list(zip(circuits, transpile_configs)))
  File "/Users/kevin.krsulichibm.com/q/qiskit-terra/qiskit/tools/parallel.py", line 100, in parallel_map
    return [task(values[0], *task_args, **task_kwargs)]
  File "/Users/kevin.krsulichibm.com/q/qiskit-terra/qiskit/compiler/transpile.py", line 180, in _transpile_circuit
    return transpile_circuit(circuit, transpile_config)
  File "/Users/kevin.krsulichibm.com/q/qiskit-terra/qiskit/transpiler/transpile_circuit.py", line 62, in transpile_circuit
    return pass_manager.run(circuit)
  File "/Users/kevin.krsulichibm.com/q/qiskit-terra/qiskit/transpiler/passmanager.py", line 138, in run
    dag = self._do_pass(pass_, dag, passset.options)
  File "/Users/kevin.krsulichibm.com/q/qiskit-terra/qiskit/transpiler/passmanager.py", line 168, in _do_pass
    dag = self._run_this_pass(pass_, dag)
  File "/Users/kevin.krsulichibm.com/q/qiskit-terra/qiskit/transpiler/passmanager.py", line 179, in _run_this_pass
    new_dag = pass_.run(dag)
  File "/Users/kevin.krsulichibm.com/q/qiskit-terra/qiskit/transpiler/passes/commutative_cancellation.py", line 109, in run
    raise TranspilerError("internal error")
qiskit.transpiler.exceptions.TranspilerError: 'internal error'