Fix handling of conditions in SabreDAG creation

qiskit/transpiler/passes/routing/sabre_swap.py

@@ -210,11 +210,16 @@ 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):
+                    cargs.add(self._clbit_indices[clbit])
+
             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)

src/sabre_swap/sabre_dag.rs

@@ -10,7 +10,7 @@
 // copyright notice, and modified files need to carry a notice indicating
 // that they have been altered from the originals.
 
-use hashbrown::HashMap;
+use hashbrown::{HashMap, HashSet};
 use numpy::PyReadonlyArray1;
 use pyo3::prelude::*;
 use retworkx_core::petgraph::prelude::*;
@@ -23,7 +23,7 @@ use retworkx_core::petgraph::prelude::*;
 #[pyo3(text_signature = "(num_qubits, num_clbits, nodes, front_layer, /)")]
 #[derive(Clone, Debug)]
 pub struct SabreDAG {
-    pub dag: DiGraph<(usize, Vec<usize>, Vec<usize>), ()>,
+    pub dag: DiGraph<(usize, Vec<usize>), ()>,
     pub first_layer: Vec<NodeIndex>,
 }
 
@@ -33,18 +33,18 @@ impl SabreDAG {
     pub fn new(
         num_qubits: usize,
         num_clbits: usize,
-        nodes: Vec<(usize, Vec<usize>, Vec<usize>)>,
+        nodes: Vec<(usize, Vec<usize>, HashSet<usize>)>,
         front_layer: PyReadonlyArray1<usize>,
     ) -> PyResult<Self> {
         let mut qubit_pos: Vec<usize> = vec![usize::MAX; num_qubits];
         let mut clbit_pos: Vec<usize> = vec![usize::MAX; num_clbits];
         let mut reverse_index_map: HashMap<usize, NodeIndex> = HashMap::with_capacity(nodes.len());
-        let mut dag: DiGraph<(usize, Vec<usize>, Vec<usize>), ()> =
+        let mut dag: DiGraph<(usize, Vec<usize>), ()> =
             Graph::with_capacity(nodes.len(), 2 * nodes.len());
         for node in &nodes {
             let qargs = &node.1;
             let cargs = &node.2;
-            let gate_index = dag.add_node(node.clone());
+            let gate_index = dag.add_node((node.0, qargs.clone()));
             reverse_index_map.insert(node.0, gate_index);
             for x in qargs {
                 if qubit_pos[*x] != usize::MAX {

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()