optimization_level=3 triggers error in unrolling

[1ucian0]

Originally posted by @itoko in #2339 (comment)

The follow input triggers and an issue in the unroller.

from qiskit import QuantumCircuit, QuantumRegister, QiskitError
from qiskit.compiler import transpile
from qiskit.transpiler import CouplingMap
q = QuantumRegister(2)
qc = QuantumCircuit(q)
qc.cx(q[0], q[1])
qc.cx(q[0], q[1])
coupling = CouplingMap([[0, 1]])
compiled = transpile(qc, coupling_map=CouplingMap([[0, 1]]), optimization_level=3)
print(compiled)

QiskitError: "Cannot unroll the circuit to the given basis, ['cx', 'cx']. No rule to expand instruction U."

[sassan72]

I encountered the same error. QiskitError: 'Cannot unroll the circuit to the given basis, method. No rule to expand instruction ry.'

QiskitError Traceback (most recent call last)
in
13 #g, g_bias = zip(*Parallel(n_jobs=-2)(delayed(gradients)(var_corrected, feats_train_batch[j], Y_train_batch[j], bias_corrected) for j in range(batch_size) ))
14 for j in range(batch_size):
---> 15 g, g_bias = gradients(var_corrected, feats_train_batch[j], Y_train_batch[j], bias_corrected)
16 grads += g / batch_size
17 grad_bias +=g_bias / batch_size

in gradients(params, feature, label, bias)
77 grads[i][j][2] = 0.5 * (imaginary(params, params_bis, feature) - imag)
78 params_bis[i][j][2]-=np.pi
---> 79 p = execute_circuit(params, feature, bias=bias)
80 grad_bias = (p - label) / (p * (1 - p))
81 grads *= grad_bias

in execute_circuit(params, feature, bias)
58 circuit = create_circuit(params, circuit, [0,1,2,3])
59 circuit.measure(0,c)
---> 60 result = execute(circuit,backend, backend_options).result()
61
62 counts = result.get_counts(circuit)

/opt/anaconda3/lib/python3.7/site-packages/qiskit/execute.py in execute(experiments, backend, basis_gates, coupling_map, backend_properties, initial_layout, seed_transpiler, optimization_level, pass_manager, qobj_id, qobj_header, shots, memory, max_credits, seed_simulator, default_qubit_los, default_meas_los, schedule_los, meas_level, meas_return, memory_slots, memory_slot_size, rep_time, parameter_binds, schedule_circuit, inst_map, meas_map, scheduling_method, **run_config)
249 seed_transpiler=seed_transpiler,
250 optimization_level=optimization_level,
--> 251 backend=backend)
252
253 if schedule_circuit:

/opt/anaconda3/lib/python3.7/site-packages/qiskit/compiler/transpile.py in transpile(circuits, backend, basis_gates, coupling_map, backend_properties, initial_layout, layout_method, routing_method, seed_transpiler, optimization_level, pass_manager, callback, output_name)
208
209 # Transpile circuits in parallel
--> 210 circuits = parallel_map(_transpile_circuit, list(zip(circuits, transpile_args)))
211
212 if len(circuits) == 1:

/opt/anaconda3/lib/python3.7/site-packages/qiskit/tools/parallel.py in parallel_map(task, values, task_args, task_kwargs, num_processes)
103 """
104 if len(values) == 1:
--> 105 return [task(values[0], *task_args, **task_kwargs)]
106
107 Publisher().publish("terra.parallel.start", len(values))

/opt/anaconda3/lib/python3.7/site-packages/qiskit/compiler/transpile.py in _transpile_circuit(circuit_config_tuple)
305
306 return pass_manager.run(circuit, callback=transpile_config['callback'],
--> 307 output_name=transpile_config['output_name'])
308
309

/opt/anaconda3/lib/python3.7/site-packages/qiskit/transpiler/passmanager.py in run(self, circuits, output_name, callback)
212 """
213 if isinstance(circuits, QuantumCircuit):
--> 214 return self._run_single_circuit(circuits, output_name, callback)
215 elif len(circuits) == 1:
216 return self._run_single_circuit(circuits[0], output_name, callback)

/opt/anaconda3/lib/python3.7/site-packages/qiskit/transpiler/passmanager.py in _run_single_circuit(self, circuit, output_name, callback)
275 if callback is None and self.callback: # TODO to remove with init(callback)
276 callback = self.callback
--> 277 result = running_passmanager.run(circuit, output_name=output_name, callback=callback)
278 self.property_set = running_passmanager.property_set
279 return result

/opt/anaconda3/lib/python3.7/site-packages/qiskit/transpiler/runningpassmanager.py in run(failed resolving arguments)
113 for passset in self.working_list:
114 for pass_ in passset:
--> 115 dag = self.do_pass(pass, dag, passset.options)
116
117 circuit = dag_to_circuit(dag)

/opt/anaconda3/lib/python3.7/site-packages/qiskit/transpiler/runningpassmanager.py in do_pass(self, pass, dag, options)
143 # Run the pass itself, if not already run
144 if pass_ not in self.valid_passes:
--> 145 dag = self.run_this_pass(pass, dag)
146
147 # update the valid_passes property

/opt/anaconda3/lib/python3.7/site-packages/qiskit/transpiler/runningpassmanager.py in run_this_pass(self, pass, dag)
155 # Measure time if we have a callback or logging set
156 start_time = time()
--> 157 new_dag = pass_.run(dag)
158 end_time = time()
159 run_time = end_time - start_time

/opt/anaconda3/lib/python3.7/site-packages/qiskit/transpiler/passes/basis/unroller.py in run(self, dag)
95 raise QiskitError("Cannot unroll the circuit to the given basis, %s. "
96 "No rule to expand instruction %s." %
---> 97 (str(self.basis), node.op.name))
98
99 # hacky way to build a dag on the same register as the rule is defined

QiskitError: 'Cannot unroll the circuit to the given basis, method. No rule to expand instruction ry.'

[kdk]

Hi @sassan72 , this sounds like a separate issue (that is triggering the same error). Can you open a new issue with your python version, qiskit version, and some example code that replicates the error you're seeing?