Merge b1ca039 into 7bc2bfd

qiskit/transpiler/preset_passmanagers/level1.py

@@ -228,10 +228,10 @@ def _swap_mapped(property_set):
         target is not None and target.get_non_global_operation_names(strict_direction=True)
     ):
         pre_optimization = common.generate_pre_op_passmanager(
-            target, coupling_map, remove_reset_in_zero=True
+            target, coupling_map, remove_reset_in_zero=False
         )
     else:
-        pre_optimization = common.generate_pre_op_passmanager(remove_reset_in_zero=True)
+        pre_optimization = common.generate_pre_op_passmanager(remove_reset_in_zero=False)
     if optimization_method is None:
         optimization = PassManager()
         unroll = [pass_ for x in translation.passes() for pass_ in x["passes"]]

qiskit/transpiler/preset_passmanagers/level2.py

@@ -216,9 +216,9 @@ def _swap_mapped(property_set):
     if (coupling_map and not coupling_map.is_symmetric) or (
         target is not None and target.get_non_global_operation_names(strict_direction=True)
     ):
-        pre_optimization = common.generate_pre_op_passmanager(target, coupling_map, True)
+        pre_optimization = common.generate_pre_op_passmanager(target, coupling_map, False)
     else:
-        pre_optimization = common.generate_pre_op_passmanager(remove_reset_in_zero=True)
+        pre_optimization = common.generate_pre_op_passmanager(remove_reset_in_zero=False)
     if optimization_method is None:
         optimization = PassManager()
         unroll = [pass_ for x in translation.passes() for pass_ in x["passes"]]

qiskit/transpiler/preset_passmanagers/level3.py

@@ -30,7 +30,6 @@
 from qiskit.transpiler.passes import MinimumPoint
 from qiskit.transpiler.passes import Depth
 from qiskit.transpiler.passes import Size
-from qiskit.transpiler.passes import RemoveResetInZeroState
 from qiskit.transpiler.passes import Optimize1qGatesDecomposition
 from qiskit.transpiler.passes import CommutativeCancellation
 from qiskit.transpiler.passes import OptimizeSwapBeforeMeasure
@@ -207,7 +206,6 @@ def _opt_control(property_set):
             unitary_synthesis_plugin_config,
             hls_config,
         )
-    init.append(RemoveResetInZeroState())
     init.append(OptimizeSwapBeforeMeasure())
     init.append(RemoveDiagonalGatesBeforeMeasure())
     if coupling_map or initial_layout:
@@ -268,7 +266,7 @@ def _unroll_condition(property_set):
         if (coupling_map and not coupling_map.is_symmetric) or (
             target is not None and target.get_non_global_operation_names(strict_direction=True)
         ):
-            pre_optimization = common.generate_pre_op_passmanager(target, coupling_map, True)
+            pre_optimization = common.generate_pre_op_passmanager(target, coupling_map, False)
             _direction = [
                 pass_
                 for x in common.generate_pre_op_passmanager(target, coupling_map).passes()
@@ -280,7 +278,7 @@ def _unroll_condition(property_set):
                     do_while=_opt_control,
                 )
         else:
-            pre_optimization = common.generate_pre_op_passmanager(remove_reset_in_zero=True)
+            pre_optimization = common.generate_pre_op_passmanager(remove_reset_in_zero=False)
             optimization.append(
                 _opt + _unroll_if_out_of_basis + _minimum_point_check, do_while=_opt_control
             )

releasenotes/notes/keep-initial-resets-a5f75cb16c8edb57.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Disables the use of :class:`.RemoveResetInZeroState` in the preset passmanagers.
+    This better aligns circuits to the notion of arbitrary initial states
+    unless explicitly set to zeros with resets.

test/python/compiler/test_transpiler.py

@@ -802,14 +802,15 @@ def test_move_measurements(self):
             )
             self.assertTrue(is_last_measure)
 
-    def test_initialize_reset_should_be_removed(self):
-        """The reset in front of initializer should be removed when zero state"""
+    def test_initialize_reset_is_not_removed(self):
+        """The reset in front of initializer should NOT be removed at beginning"""
         qr = QuantumRegister(1, "qr")
         qc = QuantumCircuit(qr)
         qc.initialize([1.0 / math.sqrt(2), 1.0 / math.sqrt(2)], [qr[0]])
         qc.initialize([1.0 / math.sqrt(2), -1.0 / math.sqrt(2)], [qr[0]])
 
         expected = QuantumCircuit(qr)
+        expected.reset(qr[0])
         expected.append(U3Gate(np.pi / 2, 0, 0), [qr[0]])
         expected.reset(qr[0])
         expected.append(U3Gate(np.pi / 2, -np.pi, 0), [qr[0]])
@@ -828,7 +829,7 @@ def test_initialize_FakeMelbourne(self):
         out_dag = circuit_to_dag(out)
         reset_nodes = out_dag.named_nodes("reset")
 
-        self.assertEqual(reset_nodes, [])
+        self.assertEqual(len(reset_nodes), 3)
 
     def test_non_standard_basis(self):
         """Test a transpilation with a non-standard basis"""

test/python/compiler/test_transpiler_resets.py

@@ -0,0 +1,29 @@
+# This code is part of Qiskit.
+#
+# (C) Copyright IBM 2023.
+#
+# This code is licensed under the Apache License, Version 2.0. You may
+# obtain a copy of this license in the LICENSE.txt file in the root directory
+# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals.
+
+"""Tests for resets in the transpiler"""
+from qiskit import QuantumCircuit, transpile
+from qiskit.test import QiskitTestCase
+
+
+class TestResetsTranspiler(QiskitTestCase):
+    """Tests resets and transpilation"""
+
+    def test_init_resets_kept_preset_passmanagers(self):
+        """Test initial resets kept at all preset transpilation levels"""
+        num_qubits = 5
+        qc = QuantumCircuit(num_qubits)
+        qc.reset(range(num_qubits))
+
+        for level in range(4):
+            num_resets = transpile(qc, optimization_level=level).count_ops()["reset"]
+            self.assertEqual(num_resets, num_qubits)