Fix handling of conditions in SabreDAG creation

qiskit/transpiler/passes/routing/sabre_swap.py

@@ -210,11 +210,18 @@ def run(self, dag):
 
         dag_list = []
         for node in dag.topological_op_nodes():
+            cargs = [self._clbit_indices[x] for x in node.cargs]
+            if node.op.condition is not None:
+                for clbit in dag._bits_in_condition(node.op.condition):
+                    clbit_index = self._clbit_indices[clbit]
+                    if clbit_index not in cargs:
+                        cargs.append(clbit_index)
+
             dag_list.append(
                 (
                     node._node_id,
                     [self._qubit_indices[x] for x in node.qargs],
-                    [self._clbit_indices[x] for x in node.cargs],
+                    cargs,
                 )
             )
         front_layer = np.asarray([x._node_id for x in dag.front_layer()], dtype=np.uintp)

test/python/transpiler/test_sabre_swap.py

@@ -262,6 +262,51 @@ def test_classical_condition(self):
             actual = PassManager([TrivialLayout(cm), SabreSwap(cm)]).run(qc)
             self.assertEqual(expected, actual)
 
+    def test_classical_condition_cargs(self):
+        """Test that classical conditions are preserved even if missing from cargs DAGNode field.
+
+        Created from reproduction in https://github.com/Qiskit/qiskit-terra/issues/8675
+        """
+        with self.subTest("missing measurement"):
+            qc = QuantumCircuit(3, 1)
+            qc.cx(0, 2).c_if(0, 0)
+            qc.measure(1, 0)
+            qc.h(2).c_if(0, 0)
+            expected = QuantumCircuit(3, 1)
+            expected.swap(1, 2)
+            expected.cx(0, 1).c_if(0, 0)
+            expected.measure(2, 0)
+            expected.h(1).c_if(0, 0)
+            result = SabreSwap(CouplingMap.from_line(3), seed=12345)(qc)
+            self.assertEqual(result, expected)
+        with self.subTest("reordered measurement"):
+            qc = QuantumCircuit(3, 1)
+            qc.cx(0, 1).c_if(0, 0)
+            qc.measure(1, 0)
+            qc.h(0).c_if(0, 0)
+            expected = QuantumCircuit(3, 1)
+            expected.cx(0, 1).c_if(0, 0)
+            expected.measure(1, 0)
+            expected.h(0).c_if(0, 0)
+            result = SabreSwap(CouplingMap.from_line(3), seed=12345)(qc)
+            self.assertEqual(result, expected)
+
+    def test_conditional_measurement(self):
+        """Test that instructions with cargs and conditions are handled correctly."""
+        qc = QuantumCircuit(3, 2)
+        qc.cx(0, 2).c_if(0, 0)
+        qc.measure(2, 0).c_if(1, 0)
+        qc.h(2).c_if(0, 0)
+        qc.measure(1, 1)
+        expected = QuantumCircuit(3, 2)
+        expected.swap(1, 2)
+        expected.cx(0, 1).c_if(0, 0)
+        expected.measure(1, 0).c_if(1, 0)
+        expected.h(1).c_if(0, 0)
+        expected.measure(2, 1)
+        result = SabreSwap(CouplingMap.from_line(3), seed=12345)(qc)
+        self.assertEqual(result, expected)
+
 
 if __name__ == "__main__":
     unittest.main()