Add synchronize_terminal_measurements transformer to replace `Synch…

…ronizeTerminalMeasurements` (quantumlib#4911)

- Part of quantumlib#4722
- Follows the new Transformer API quantumlib#4483
- Supports no compile tags NoCompile Tag for optimizers quantumlib#4253
- Fixes quantumlib#4907

cirq/__init__.py

@@ -371,6 +371,7 @@
     single_qubit_matrix_to_phased_x_z,
     single_qubit_matrix_to_phxz,
     single_qubit_op_to_framed_phase_form,
+    synchronize_terminal_measurements,
     TRANSFORMER,
     TransformerContext,
     TransformerLogger,

cirq/optimizers/synchronize_terminal_measurements.py

@@ -15,8 +15,10 @@
 
 from typing import List, Set, Tuple, cast
 from cirq import circuits, ops, protocols
+from cirq._compat import deprecated_class
 
 
+@deprecated_class(deadline='v1.0', fix='Use cirq.synchronize_terminal_measurements instead.')
 class SynchronizeTerminalMeasurements:
     """Move measurements to the end of the circuit.
 

cirq/optimizers/synchronize_terminal_measurements_test.py

@@ -16,9 +16,12 @@
 
 
 def assert_optimizes(before, after, measure_only_moment=True):
-    opt = cirq.SynchronizeTerminalMeasurements(measure_only_moment)
-    opt(before)
-    assert before == after
+    with cirq.testing.assert_deprecated(
+        "Use cirq.synchronize_terminal_measurements", deadline='v1.0'
+    ):
+        opt = cirq.SynchronizeTerminalMeasurements(measure_only_moment)
+        opt(before)
+        assert before == after
 
 
 def test_no_move():

cirq/transformers/__init__.py

@@ -43,6 +43,8 @@
 
 from cirq.transformers.align import align_left, align_right
 
+from cirq.transformers.synchronize_terminal_measurements import synchronize_terminal_measurements
+
 from cirq.transformers.transformer_api import (
     LogLevel,
     TRANSFORMER,

cirq/transformers/synchronize_terminal_measurements.py

@@ -0,0 +1,99 @@
+# Copyright 2022 The Cirq Developers
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Transformer pass to move terminal measurements to the end of circuit."""
+
+from typing import List, Optional, Set, Tuple, TYPE_CHECKING
+from cirq import protocols, ops
+from cirq.transformers import transformer_api
+
+if TYPE_CHECKING:
+    import cirq
+
+
+def find_terminal_measurements(
+    circuit: 'cirq.AbstractCircuit',
+) -> List[Tuple[int, 'cirq.Operation']]:
+    """Finds all terminal measurements in the given circuit.
+
+    A measurement is terminal if there are no other operations acting on the measured qubits
+    after the measurement operation occurs in the circuit.
+
+    Args:
+        circuit: The circuit to find terminal measurements in.
+
+    Returns:
+        List of terminal measurements, each specified as (moment_index, measurement_operation).
+    """
+
+    open_qubits: Set['cirq.Qid'] = set(circuit.all_qubits())
+    seen_control_keys: Set['cirq.MeasurementKey'] = set()
+    terminal_measurements: List[Tuple[int, 'cirq.Operation']] = []
+    for i in range(len(circuit) - 1, -1, -1):
+        moment = circuit[i]
+        for q in open_qubits:
+            op = moment.operation_at(q)
+            seen_control_keys |= protocols.control_keys(op)
+            if (
+                op is not None
+                and open_qubits.issuperset(op.qubits)
+                and protocols.is_measurement(op)
+                and not (seen_control_keys & protocols.measurement_key_objs(op))
+            ):
+                terminal_measurements.append((i, op))
+        open_qubits -= moment.qubits
+        if not open_qubits:
+            break
+    return terminal_measurements
+
+
+@transformer_api.transformer
+def synchronize_terminal_measurements(
+    circuit: 'cirq.AbstractCircuit',
+    *,
+    context: Optional['cirq.TransformerContext'] = None,
+    after_other_operations: bool = True,
+) -> 'cirq.Circuit':
+    """Move measurements to the end of the circuit.
+
+    Move all measurements in a circuit to the final moment, if it can accommodate them (without
+    overlapping with other operations). If `after_other_operations` is true, then a new moment will
+    be added to the end of the circuit containing all the measurements that should be brought
+    forward.
+
+    Args:
+          circuit: Input circuit to transform.
+          context: `cirq.TransformerContext` storing common configurable options for transformers.
+          after_other_operations: Set by default. If the circuit's final moment contains
+                non-measurement operations and this is set then a new empty moment is appended to
+                the circuit before pushing measurements to the end.
+    Returns:
+          Copy of the transformed input circuit.
+    """
+    if context is None:
+        context = transformer_api.TransformerContext()
+    terminal_measurements = [
+        (i, op)
+        for i, op in find_terminal_measurements(circuit)
+        if set(op.tags).isdisjoint(context.ignore_tags)
+    ]
+    ret = circuit.unfreeze(copy=True)
+    if not terminal_measurements:
+        return ret
+
+    ret.batch_remove(terminal_measurements)
+    if ret[-1] and after_other_operations:
+        ret.append(ops.Moment())
+    ret[-1] = ret[-1].with_operations(op for _, op in terminal_measurements)
+    return ret

cirq/transformers/synchronize_terminal_measurements_test.py

@@ -0,0 +1,214 @@
+# Copyright 2022 The Cirq Developers
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import cirq
+
+NO_COMPILE_TAG = "no_compile_tag"
+
+
+def assert_optimizes(before, after, measure_only_moment=True, with_context=False):
+    transformed_circuit = (
+        cirq.synchronize_terminal_measurements(before, after_other_operations=measure_only_moment)
+        if not with_context
+        else cirq.synchronize_terminal_measurements(
+            before,
+            context=cirq.TransformerContext(ignore_tags=(NO_COMPILE_TAG,)),
+            after_other_operations=measure_only_moment,
+        )
+    )
+    cirq.testing.assert_same_circuits(transformed_circuit, after)
+
+
+def test_no_move():
+    q1 = cirq.NamedQubit('q1')
+    before = cirq.Circuit([cirq.Moment([cirq.H(q1)])])
+    after = before
+    assert_optimizes(before=before, after=after)
+
+
+def test_simple_align():
+    q1 = cirq.NamedQubit('q1')
+    q2 = cirq.NamedQubit('q2')
+    before = cirq.Circuit(
+        [
+            cirq.Moment([cirq.H(q1), cirq.H(q2)]),
+            cirq.Moment([cirq.measure(q1).with_tags(NO_COMPILE_TAG), cirq.Z(q2)]),
+            cirq.Moment([cirq.measure(q2)]),
+        ]
+    )
+    after = cirq.Circuit(
+        [
+            cirq.Moment([cirq.H(q1), cirq.H(q2)]),
+            cirq.Moment([cirq.Z(q2)]),
+            cirq.Moment([cirq.measure(q1).with_tags(NO_COMPILE_TAG), cirq.measure(q2)]),
+        ]
+    )
+    assert_optimizes(before=before, after=after)
+    assert_optimizes(before=before, after=before, with_context=True)
+
+
+def test_simple_partial_align():
+    q1 = cirq.NamedQubit('q1')
+    q2 = cirq.NamedQubit('q2')
+    before = cirq.Circuit(
+        [
+            cirq.Moment([cirq.measure(q1), cirq.Z(q2)]),
+            cirq.Moment([cirq.Z(q1), cirq.measure(q2).with_tags(NO_COMPILE_TAG)]),
+        ]
+    )
+    after = cirq.Circuit(
+        [
+            cirq.Moment([cirq.measure(q1), cirq.Z(q2)]),
+            cirq.Moment([cirq.Z(q1)]),
+            cirq.Moment([cirq.measure(q2).with_tags(NO_COMPILE_TAG)]),
+        ]
+    )
+    assert_optimizes(before=before, after=after)
+    assert_optimizes(before=before, after=before, with_context=True)
+
+
+def test_slide_forward_one():
+    q1 = cirq.NamedQubit('q1')
+    q2 = cirq.NamedQubit('q2')
+    q3 = cirq.NamedQubit('q3')
+    before = cirq.Circuit(
+        [
+            cirq.Moment([cirq.H(q1), cirq.measure(q2).with_tags(NO_COMPILE_TAG), cirq.measure(q3)]),
+        ]
+    )
+    after = cirq.Circuit(
+        [
+            cirq.Moment([cirq.H(q1)]),
+            cirq.Moment([cirq.measure(q2).with_tags(NO_COMPILE_TAG), cirq.measure(q3)]),
+        ]
+    )
+    after_no_compile = cirq.Circuit(
+        [
+            cirq.Moment([cirq.H(q1), cirq.measure(q2).with_tags(NO_COMPILE_TAG)]),
+            cirq.Moment([cirq.measure(q3)]),
+        ]
+    )
+    assert_optimizes(before=before, after=after)
+    assert_optimizes(before=before, after=after_no_compile, with_context=True)
+
+
+def test_no_slide_forward_one():
+    q1 = cirq.NamedQubit('q1')
+    q2 = cirq.NamedQubit('q2')
+    q3 = cirq.NamedQubit('q3')
+    before = cirq.Circuit(
+        [
+            cirq.Moment([cirq.H(q1), cirq.measure(q2), cirq.measure(q3)]),
+        ]
+    )
+    after = cirq.Circuit(
+        [
+            cirq.Moment([cirq.H(q1), cirq.measure(q2), cirq.measure(q3)]),
+        ]
+    )
+    assert_optimizes(before=before, after=after, measure_only_moment=False)
+
+
+def test_blocked_shift_one():
+    q1 = cirq.NamedQubit('q1')
+    q2 = cirq.NamedQubit('q2')
+    before = cirq.Circuit(
+        [
+            cirq.Moment([cirq.H(q1), cirq.H(q2)]),
+            cirq.Moment([cirq.measure(q1), cirq.Z(q2)]),
+            cirq.Moment([cirq.H(q1), cirq.measure(q2).with_tags(NO_COMPILE_TAG)]),
+        ]
+    )
+    after = cirq.Circuit(
+        [
+            cirq.Moment([cirq.H(q1), cirq.H(q2)]),
+            cirq.Moment([cirq.measure(q1), cirq.Z(q2)]),
+            cirq.Moment([cirq.H(q1)]),
+            cirq.Moment([cirq.measure(q2).with_tags(NO_COMPILE_TAG)]),
+        ]
+    )
+    assert_optimizes(before=before, after=after)
+    assert_optimizes(before=before, after=before, with_context=True)
+
+
+def test_complex_move():
+    q1 = cirq.NamedQubit('q1')
+    q2 = cirq.NamedQubit('q2')
+    q3 = cirq.NamedQubit('q3')
+    before = cirq.Circuit(
+        [
+            cirq.Moment([cirq.H(q1), cirq.H(q2)]),
+            cirq.Moment([cirq.measure(q1), cirq.Z(q2)]),
+            cirq.Moment([cirq.H(q1), cirq.measure(q2).with_tags(NO_COMPILE_TAG)]),
+            cirq.Moment([cirq.H(q3)]),
+            cirq.Moment([cirq.X(q1), cirq.measure(q3).with_tags(NO_COMPILE_TAG)]),
+        ]
+    )
+    after = cirq.Circuit(
+        [
+            cirq.Moment([cirq.H(q1), cirq.H(q2)]),
+            cirq.Moment([cirq.measure(q1), cirq.Z(q2)]),
+            cirq.Moment([cirq.H(q1)]),
+            cirq.Moment([cirq.H(q3)]),
+            cirq.Moment([cirq.X(q1)]),
+            cirq.Moment(
+                [
+                    cirq.measure(q2).with_tags(NO_COMPILE_TAG),
+                    cirq.measure(q3).with_tags(NO_COMPILE_TAG),
+                ]
+            ),
+        ]
+    )
+    assert_optimizes(before=before, after=after)
+    assert_optimizes(before=before, after=before, with_context=True)
+
+
+def test_complex_move_no_slide():
+    q1 = cirq.NamedQubit('q1')
+    q2 = cirq.NamedQubit('q2')
+    q3 = cirq.NamedQubit('q3')
+    before = cirq.Circuit(
+        [
+            cirq.Moment([cirq.H(q1), cirq.H(q2)]),
+            cirq.Moment([cirq.measure(q1), cirq.Z(q2)]),
+            cirq.Moment([cirq.H(q1), cirq.measure(q2).with_tags(NO_COMPILE_TAG)]),
+            cirq.Moment([cirq.H(q3)]),
+            cirq.Moment([cirq.X(q1), cirq.measure(q3)]),
+        ]
+    )
+    after = cirq.Circuit(
+        [
+            cirq.Moment(cirq.H(q1), cirq.H(q2)),
+            cirq.Moment(cirq.measure(q1), cirq.Z(q2)),
+            cirq.Moment(cirq.H(q1)),
+            cirq.Moment(cirq.H(q3)),
+            cirq.Moment(cirq.X(q1), cirq.measure(q2).with_tags(NO_COMPILE_TAG), cirq.measure(q3)),
+        ]
+    )
+    assert_optimizes(before=before, after=after, measure_only_moment=False)
+    assert_optimizes(before=before, after=before, measure_only_moment=False, with_context=True)
+
+
+def test_multi_qubit():
+    q0, q1 = cirq.LineQubit.range(2)
+    circuit = cirq.Circuit(cirq.measure(q0, q1, key='m'), cirq.H(q1))
+    assert_optimizes(before=circuit, after=circuit)
+
+
+def test_classically_controlled_op():
+    q0, q1 = cirq.LineQubit.range(2)
+    circuit = cirq.Circuit(
+        cirq.H(q0), cirq.measure(q0, key='m'), cirq.X(q1).with_classical_controls('m')
+    )
+    assert_optimizes(before=circuit, after=circuit)