dag.two_qubit_ops bites again

Qiskit · Nov 2, 2021 · b7eb52c · b7eb52c
1 parent f8b0041
commit b7eb52c
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Showing 2 changed files with 28 additions and 7 deletions.
diff --git a/qiskit/transpiler/passes/layout/vf2_layout.py b/qiskit/transpiler/passes/layout/vf2_layout.py
@@ -20,6 +20,7 @@
 from retworkx import PyGraph, PyDiGraph, vf2_mapping
 from qiskit.transpiler.layout import Layout
 from qiskit.transpiler.basepasses import AnalysisPass
+from qiskit.transpiler.exceptions import TranspilerError
 
 
 class VF2Layout(AnalysisPass):
@@ -50,10 +51,15 @@ def run(self, dag):
         """run the layout method"""
         qubits = dag.qubits
         qubit_indices = {qubit: index for index, qubit in enumerate(qubits)}
-        interactions = [
-            (qubit_indices[gate.qargs[0]], qubit_indices[gate.qargs[1]])
-            for gate in dag.two_qubit_ops()
-        ]
+
+        interactions = []
+        for node in dag.op_nodes(include_directives=False):
+            len_args = len(node.qargs)
+            if len_args == 2:
+                interactions.append((qubit_indices[node.qargs[0]], qubit_indices[node.qargs[1]]))
+            if len_args >= 3:
+                raise TranspilerError("VF2Layout only can handle 2-qubit gates or less. Node "
+                                      f"{node.name} ({node}) is {len_args}-qubit")
 
         if self.strict_direction:
             cm_graph = self.coupling_map.graph

diff --git a/test/python/transpiler/test_vf2_layout.py b/test/python/transpiler/test_vf2_layout.py
@@ -17,7 +17,7 @@
 import retworkx
 
 from qiskit import QuantumRegister, QuantumCircuit
-from qiskit.transpiler import CouplingMap
+from qiskit.transpiler import CouplingMap, TranspilerError
 from qiskit.transpiler.passes import VF2Layout
 from qiskit.converters import circuit_to_dag
 from qiskit.test import QiskitTestCase
@@ -112,7 +112,7 @@ class TestVF2LayoutLattice(LayoutTestCase):
     def graph_state_from_pygraph(self, graph):
         """Creates a GraphState circuit from a PyGraph"""
         adjacency_matrix = retworkx.adjacency_matrix(graph)
-        return GraphState(adjacency_matrix)
+        return GraphState(adjacency_matrix).decompose()
 
     def test_hexagonal_lattice_graph_20_in_25(self):
         """A 20x20 interaction map in 25x25 coupling map"""
@@ -282,7 +282,7 @@ def test_perfect_fit_Manhattan(self):
         adj_matrix = numpy.zeros((65, 65))
         adj_matrix[rows, cols] = 1
 
-        circuit = GraphState(adj_matrix)
+        circuit = GraphState(adj_matrix).decompose()
         circuit.measure_all()
 
         dag = circuit_to_dag(circuit)
@@ -320,6 +320,21 @@ def test_seed(self):
 
         self.assertNotEqual(layout_1, layout_2)
 
+    def test_3_q_gate(self):
+        """The pass does not handle gates with more than 2 qubits"""
+        seed_1 = 42
+
+        cmap5 = FakeTenerife().configuration().coupling_map
+
+        qr = QuantumRegister(3, "qr")
+        circuit = QuantumCircuit(qr)
+        circuit.ccx(qr[1], qr[0], qr[2])
+        dag = circuit_to_dag(circuit)
+
+        pass_1 = VF2Layout(CouplingMap(cmap5), seed=seed_1)
+        with self.assertRaises(TranspilerError):
+            pass_1.run(dag)
+
 
 if __name__ == "__main__":
     unittest.main()