Only run translation stage in optimization loop if necessary

qiskit/transpiler/passes/utils/gates_basis.py

@@ -25,6 +25,8 @@ def __init__(self, basis_gates):
             basis_gates (list): The list of strings representing the set of basis gates.
         """
         super().__init__()
+        if basis_gates is None:
+            basis_gates = []
         self._basis_gates = set(basis_gates)
 
     def run(self, dag):

qiskit/transpiler/preset_passmanagers/level3.py

@@ -61,6 +61,8 @@
 from qiskit.transpiler.passes import PulseGates
 from qiskit.transpiler.passes import Error
 from qiskit.transpiler.passes import ContainsInstruction
+from qiskit.transpiler.passes import GatesInBasis
+from qiskit.transpiler.runningpassmanager import ConditionalController
 
 from qiskit.transpiler import TranspilerError
 
@@ -322,6 +324,16 @@ def _contains_delay(property_set):
     else:
         _alignments = []
 
+    # Build nested Flow controllers
+
+    # Check if the gates are in the basis to determine whether to run _unroll passes
+    _unroll_check = [GatesInBasis(basis_gates)]
+
+    def _unroll_condition(property_set):
+        return not property_set["all_gates_in_basis"]
+
+    _flow_unroll = [ConditionalController(_unroll, condition=_unroll_condition)]
+
     # Build pass manager
     pm3 = PassManager()
     pm3.append(_unroll3q)
@@ -346,12 +358,15 @@ def _contains_delay(property_set):
         # inserted by UnitarySynthesis which is direction aware but only via
         # the coupling map which with a target doesn't give a full picture
         if target is not None:
-            pm3.append(_depth_check + _opt + _unroll + _direction, do_while=_opt_control)
+            pm3.append(
+                _depth_check + _opt + _unroll_check + _flow_unroll + _direction,
+                do_while=_opt_control,
+            )
         else:
-            pm3.append(_depth_check + _opt + _unroll, do_while=_opt_control)
+            pm3.append(_depth_check + _opt + _unroll_check + _flow_unroll, do_while=_opt_control)
     else:
         pm3.append(_reset)
-        pm3.append(_depth_check + _opt + _unroll, do_while=_opt_control)
+        pm3.append(_depth_check + _opt + _unroll_check + _flow_unroll, do_while=_opt_control)
     if inst_map and inst_map.has_custom_gate():
         pm3.append(PulseGates(inst_map=inst_map))
     if scheduling_method:

test/python/transpiler/test_preset_passmanagers.py

@@ -23,9 +23,11 @@
 from qiskit.circuit import Qubit
 from qiskit.compiler import transpile, assemble
 from qiskit.transpiler import CouplingMap, Layout
-from qiskit.circuit.library import U2Gate, U3Gate
+from qiskit.transpiler.passes import GatesInBasis, Collect2qBlocks
+from qiskit.circuit.library import U2Gate, U3Gate, QuantumVolume
 from qiskit.test import QiskitTestCase
 from qiskit.test.mock import (
+    FakeBelem,
     FakeTenerife,
     FakeMelbourne,
     FakeJohannesburg,
@@ -202,6 +204,31 @@ def test_alignment_constraints_called_with_delay_in_circuit(self, level):
             transpile(circuit, backend=FakeJohannesburg(), optimization_level=level)
         mock.assert_called_once()
 
+    def test_unroll_only_if_not_gates_in_basis(self):
+        """Test that the list of passes _unroll only runs if a gate is not in the basis."""
+        qcomp = FakeBelem()
+        qv_circuit = QuantumVolume(3)
+        gates_in_basis_true_count = 0
+        collect_2q_blocks_count = 0
+
+        # pylint: disable=unused-argument
+        def counting_callback_func(pass_, dag, time, property_set, count):
+            nonlocal gates_in_basis_true_count
+            nonlocal collect_2q_blocks_count
+            if isinstance(pass_, GatesInBasis) and property_set["all_gates_in_basis"]:
+                gates_in_basis_true_count += 1
+            if isinstance(pass_, Collect2qBlocks):
+                collect_2q_blocks_count += 1
+
+        transpile(
+            qv_circuit,
+            backend=qcomp,
+            optimization_level=3,
+            callback=counting_callback_func,
+            translation_method="synthesis",
+        )
+        self.assertEqual(gates_in_basis_true_count + 1, collect_2q_blocks_count)
+
 
 @ddt
 class TestTranspileLevels(QiskitTestCase):