Improve performance of barrier() (Qiskit#11345)

* Improve performance of barrier() * black * fix barrier statement in context * add test * black * fix label argument * Use `unittest` test method --------- Co-authored-by: Jake Lishman <[email protected]>
ShellyGarion · Jan 18, 2024 · 8a1fc09 · 8a1fc09
1 parent b97fb3a
commit 8a1fc09
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Showing 2 changed files with 19 additions and 6 deletions.
diff --git a/qiskit/circuit/quantumcircuit.py b/qiskit/circuit/quantumcircuit.py
@@ -3317,13 +3317,15 @@ def barrier(self, *qargs: QubitSpecifier, label=None) -> InstructionSet:
         """
         from .barrier import Barrier
 
-        qubits = (
+        if qargs:
             # This uses a `dict` not a `set` to guarantee a deterministic order to the arguments.
-            list({q: None for qarg in qargs for q in self.qbit_argument_conversion(qarg)})
-            if qargs
-            else self.qubits.copy()
-        )
-        return self.append(Barrier(len(qubits), label=label), qubits, [])
+            qubits = tuple({q: None for qarg in qargs for q in self.qbit_argument_conversion(qarg)})
+            return self.append(CircuitInstruction(Barrier(len(qubits), label=label), qubits, ()))
+        else:
+            qubits = self.qubits.copy()
+            return self._current_scope().append(
+                CircuitInstruction(Barrier(len(qubits), label=label), qubits, ())
+            )
 
     def delay(
         self,

diff --git a/test/python/circuit/test_circuit_operations.py b/test/python/circuit/test_circuit_operations.py
@@ -550,6 +550,17 @@ def test_barrier(self):
 
         self.assertEqual(qc, expected)
 
+    def test_barrier_in_context(self):
+        """Test barrier statement in context, see gh-11345"""
+        qc = QuantumCircuit(2, 2)
+        qc.h(0)
+        with qc.if_test((qc.clbits[0], False)):
+            qc.h(0)
+            qc.barrier()
+
+        operation_names = [c.operation.name for c in qc]
+        self.assertNotIn("barrier", operation_names)
+
     def test_measure_active(self):
         """Test measure_active
         Applies measurements only to non-idle qubits. Creates a ClassicalRegister of size equal to