Add support for QuantumCircuit.layout to qpy

qiskit/qpy/__init__.py

@@ -126,6 +126,62 @@
 by ``num_circuits`` in the file header). There is no padding between the
 circuits in the data.
 
+.. _qpy_version_8:
+
+Version 8
+=========
+
+Version 8 adds support for handling a :class:`~.TranspileLayout` stored in the
+:attr:`.QuantumCircuit.layout` attribute. In version 8 immediately following the
+calibrations block at the end of the circuit payload there is now the
+``LAYOUT`` struct. This struct outlines the size of the three attributes of a
+:class:`~.TranspileLayout` class.
+
+LAYOUT
+------
+
+.. code-block:: c
+
+    struct {
+        int32_t initial_layout_size;
+        int32_t input_mapping_size;
+        int32_t final_layout_size;
+        uint32_t extra_registers;
+    }
+
+If any of the signed values are ``-1`` this indicates the corresponding
+attribute is ``None``
+
+Immediately following the ``LAYOUT`` struct there is a :ref:`qpy_registers` struct
+for ``extra_registers`` (specifically the format introduced in :ref:`qpy_version_4`
+standalone register definitions that aren't present in the circuit. Then there
+are ``initial_layout_size`` ``INITIAL_LAYOUT_BIT`` structs to define the
+:attr:`.TranspileLayout.initial_layout` attribute.
+
+INITIAL_LAYOUT_BIT
+------------------
+
+.. code-block:: c
+
+    struct {
+        int32_t index;
+        int32_t register_size;
+    }
+
+Where a value of ``-1`` indicates ``None`` (as in no register is associated
+with the bit). Following each ``INITIAL_LAYOUT_BIT`` struct is ``register_size``
+bytes for a ``utf8`` encoded string for the register name.
+
+Following the initial layout there is ``input_mapping_size`` array of
+``uint32_t`` integers representing the positions of the phyiscal bit from the
+initial layout. This enbables constructing a list of virtual bits where the
+array index is it's input mapping position.
+
+Finally, there is an array of ``final_layout_size`` ``uint32_t`` integers. Each
+element is an index in the circuit's ``qubits`` attribute which enables building
+a mapping from qubit starting position to the output position at the end of the
+circuit.
+
 .. _qpy_version_7:
 
 Version 7

qiskit/qpy/binary_io/circuits.py

@@ -14,6 +14,7 @@
 
 """Binary IO for circuit objects."""
 
+from collections import defaultdict
 import io
 import json
 import struct
@@ -36,6 +37,7 @@
 from qiskit.qpy.binary_io import value, schedules
 from qiskit.quantum_info.operators import SparsePauliOp
 from qiskit.synthesis import evolution as evo_synth
+from qiskit.transpiler.layout import Layout, TranspileLayout
 
 
 def _read_header_v2(file_obj, version, vectors, metadata_deserializer=None):
@@ -761,6 +763,143 @@ def _write_registers(file_obj, in_circ_regs, full_bits):
     return len(in_circ_regs) + len(out_circ_regs)
 
 
+def _write_layout(file_obj, circuit):
+    if circuit.layout is None:
+        # Write a null header if there is no layout present
+        file_obj.write(struct.pack(formats.LAYOUT_PACK, False, -1, -1, -1, 0))
+        return
+    initial_size = -1
+    input_qubit_mapping = {}
+    initial_layout_array = []
+    extra_registers = defaultdict(list)
+    if circuit.layout.initial_layout is not None:
+        initial_size = len(circuit.layout.initial_layout)
+        layout_mapping = circuit.layout.initial_layout.get_physical_bits()
+        for i in range(circuit.num_qubits):
+            qubit = layout_mapping[i]
+            input_qubit_mapping[qubit] = i
+            if qubit._register is not None or qubit._index is not None:
+                if qubit._register not in circuit.qregs:
+                    extra_registers[qubit._register].append(qubit)
+                initial_layout_array.append((qubit._index, qubit._register))
+            else:
+                initial_layout_array.append((None, None))
+    input_qubit_size = -1
+    input_qubit_mapping_array = []
+    if circuit.layout.input_qubit_mapping is not None:
+        input_qubit_size = len(circuit.layout.input_qubit_mapping)
+        input_qubit_mapping_array = [None] * input_qubit_size
+        layout_mapping = circuit.layout.initial_layout.get_virtual_bits()
+        for qubit, index in circuit.layout.input_qubit_mapping.items():
+            if (
+                getattr(qubit, "_register", None) is not None
+                and getattr(qubit, "_index", None) is not None
+            ):
+                if qubit._register not in circuit.qregs:
+                    extra_registers[qubit._register].append(qubit)
+                input_qubit_mapping_array[index] = layout_mapping[qubit]
+            else:
+                input_qubit_mapping_array[index] = layout_mapping[qubit]
+    final_layout_size = -1
+    final_layout_array = []
+    if circuit.layout.final_layout is not None:
+        final_layout_size = len(circuit.layout.final_layout)
+        final_layout_physical = circuit.layout.final_layout.get_physical_bits()
+        for i in range(circuit.num_qubits):
+            virtual_bit = final_layout_physical[i]
+            final_layout_array.append(circuit.find_bit(virtual_bit).index)
+
+    file_obj.write(
+        struct.pack(
+            formats.LAYOUT_PACK,
+            True,
+            initial_size,
+            input_qubit_size,
+            final_layout_size,
+            len(extra_registers),
+        )
+    )
+    _write_registers(
+        file_obj, list(extra_registers), [x for bits in extra_registers.values() for x in bits]
+    )
+    for virt in initial_layout_array:
+        index = -1
+        if virt[0] is not None:
+            index = virt[0]
+        reg_size = -1
+        reg_name_bytes = None
+        if virt[1] is not None:
+            reg_name_bytes = virt[1].name.encode(common.ENCODE)
+            reg_size = len(reg_name_bytes)
+        file_obj.write(
+            struct.pack(
+                formats.INITIAL_LAYOUT_BIT_PACK,
+                index,
+                reg_size,
+            )
+        )
+        if reg_name_bytes is not None:
+            file_obj.write(reg_name_bytes)
+    for i in input_qubit_mapping_array:
+        file_obj.write(struct.pack("!I", i))
+    for i in final_layout_array:
+        file_obj.write(struct.pack("!I", i))
+
+
+def _read_layout(file_obj, circuit):
+    header = formats.LAYOUT._make(
+        struct.unpack(formats.LAYOUT_PACK, file_obj.read(formats.LAYOUT_SIZE))
+    )
+    if not header.exists:
+        return
+    registers = {
+        name: QuantumRegister(len(v[1]), name)
+        for name, v in _read_registers_v4(file_obj, header.extra_registers)["q"].items()
+    }
+    initial_layout = None
+    initial_layout_virtual_bits = []
+    for _ in range(header.initial_layout_size):
+        virtual_bit = formats.INITIAL_LAYOUT_BIT._make(
+            struct.unpack(
+                formats.INITIAL_LAYOUT_BIT_PACK,
+                file_obj.read(formats.INITIAL_LAYOUT_BIT_SIZE),
+            )
+        )
+        if virtual_bit.index == -1 and virtual_bit.register_size == -1:
+            qubit = Qubit()
+        else:
+            register_name = file_obj.read(virtual_bit.register_size).decode(common.ENCODE)
+            if register_name in registers:
+                qubit = registers[register_name][virtual_bit.index]
+            else:
+                register = next(filter(lambda x, name=register_name: x.name == name, circuit.qregs))
+                qubit = register[virtual_bit.index]
+        initial_layout_virtual_bits.append(qubit)
+    if initial_layout_virtual_bits:
+        initial_layout = Layout.from_qubit_list(initial_layout_virtual_bits)
+    input_qubit_mapping = None
+    input_qubit_mapping_array = []
+    for _ in range(header.input_mapping_size):
+        input_qubit_mapping_array.append(
+            struct.unpack("!I", file_obj.read(struct.calcsize("!I")))[0]
+        )
+    if input_qubit_mapping_array:
+        input_qubit_mapping = {}
+        physical_bits = initial_layout.get_physical_bits()
+        for index, bit in enumerate(input_qubit_mapping_array):
+            input_qubit_mapping[physical_bits[bit]] = index
+    final_layout = None
+    final_layout_array = []
+    for _ in range(header.final_layout_size):
+        final_layout_array.append(struct.unpack("!I", file_obj.read(struct.calcsize("!I")))[0])
+
+    if final_layout_array:
+        layout_dict = {circuit.qubits[bit]: index for index, bit in enumerate(final_layout_array)}
+        final_layout = Layout(layout_dict)
+
+    circuit._layout = TranspileLayout(initial_layout, input_qubit_mapping, final_layout)
+
+
 def write_circuit(file_obj, circuit, metadata_serializer=None):
     """Write a single QuantumCircuit object in the file like object.
 
@@ -830,6 +969,7 @@ def write_circuit(file_obj, circuit, metadata_serializer=None):
 
     # Write calibrations
     _write_calibrations(file_obj, circuit.calibrations, metadata_serializer)
+    _write_layout(file_obj, circuit)
 
 
 def read_circuit(file_obj, version, metadata_deserializer=None):
@@ -947,5 +1087,6 @@ def read_circuit(file_obj, version, metadata_deserializer=None):
                 f"as they weren't used in the circuit: {circ.name}",
                 UserWarning,
             )
-
+    if version >= 8:
+        _read_layout(file_obj, circ)
     return circ

qiskit/qpy/common.py

@@ -20,7 +20,7 @@
 
 from qiskit.qpy import formats
 
-QPY_VERSION = 7
+QPY_VERSION = 8
 ENCODE = "utf8"
 
 

qiskit/qpy/formats.py

@@ -261,3 +261,14 @@
 MAP_ITEM = namedtuple("MAP_ITEM", ["key_size", "type", "size"])
 MAP_ITEM_PACK = "!H1cH"
 MAP_ITEM_SIZE = struct.calcsize(MAP_ITEM_PACK)
+
+LAYOUT = namedtuple(
+    "LAYOUT",
+    ["exists", "initial_layout_size", "input_mapping_size", "final_layout_size", "extra_registers"],
+)
+LAYOUT_PACK = "!?iiiI"
+LAYOUT_SIZE = struct.calcsize(LAYOUT_PACK)
+
+INITIAL_LAYOUT_BIT = namedtuple("INITIAL_LAYOUT_BIT", ["index", "register_size"])
+INITIAL_LAYOUT_BIT_PACK = "!ii"
+INITIAL_LAYOUT_BIT_SIZE = struct.calcsize(INITIAL_LAYOUT_BIT_PACK)

releasenotes/notes/qpy-layout-927ab34f2b47f4aa.yaml

@@ -0,0 +1,12 @@
+---
+upgrade:
+  - |
+    The QPY format version emitted by :class:`~.qpy.dump` has increased to 8.
+    This new format version adds support for serializing the
+    :attr:`.QuantumCircuit.layout` attribute.
+fixes:
+  - |
+    Fixed the :mod:`~qiskit.qpy` serialization of :attr:`.QuantumCircuit.layout`
+    attribue. Previously, the :attr:`~.QuantumCircuit.layout` attribute would
+    have been dropped when serializing a circuit to QPY.
+    Fixed `#10112 <https://github.com/Qiskit/qiskit-terra/issues/10112>`__

test/python/qpy/test_circuit_load_from_qpy.py

@@ -16,12 +16,13 @@
 
 from ddt import ddt, data
 
-from qiskit.circuit import QuantumCircuit
-from qiskit.providers.fake_provider import FakeHanoi
+from qiskit.circuit import QuantumCircuit, QuantumRegister, Qubit
+from qiskit.providers.fake_provider import FakeHanoi, FakeSherbrooke
 from qiskit.qpy import dump, load
 from qiskit.test import QiskitTestCase
 from qiskit.transpiler import PassManager
 from qiskit.transpiler import passes
+from qiskit.compiler import transpile
 
 
 class QpyCircuitTestCase(QiskitTestCase):
@@ -35,6 +36,8 @@ def assert_roundtrip_equal(self, circuit):
         new_circuit = load(qpy_file)[0]
 
         self.assertEqual(circuit, new_circuit)
+        if getattr(circuit, "layout", None):
+            self.assertEqual(circuit.layout, new_circuit.layout)
 
 
 @ddt
@@ -67,3 +70,67 @@ def test_rzx_calibration_echo(self, angle):
         rzx_qc = pass_manager.run(test_qc)
 
         self.assert_roundtrip_equal(rzx_qc)
+
+
+@ddt
+class TestLayout(QpyCircuitTestCase):
+    """Test circuit serialization for layout preservation."""
+
+    @data(0, 1, 2, 3)
+    def test_transpile_layout(self, opt_level):
+        """Test layout preserved after transpile."""
+        qc = QuantumCircuit(2)
+        qc.h(0)
+        qc.cx(0, 1)
+        qc.measure_all()
+        backend = FakeSherbrooke()
+        tqc = transpile(qc, backend, optimization_level=opt_level)
+        self.assert_roundtrip_equal(tqc)
+
+    @data(0, 1, 2, 3)
+    def test_custom_register_name(self, opt_level):
+        """Test layout preserved with custom register names."""
+        qr = QuantumRegister(5, name="abc123")
+        qc = QuantumCircuit(qr)
+        qc.h(0)
+        qc.cx(0, 1)
+        qc.cx(0, 2)
+        qc.cx(0, 3)
+        qc.cx(0, 4)
+        qc.measure_all()
+        backend = FakeSherbrooke()
+        tqc = transpile(qc, backend, optimization_level=opt_level)
+        self.assert_roundtrip_equal(tqc)
+
+    @data(0, 1, 2, 3)
+    def test_no_register(self, opt_level):
+        """Test layout preserved with no register."""
+        qubits = [Qubit(), Qubit()]
+        qc = QuantumCircuit(qubits)
+        qc.h(0)
+        qc.cx(0, 1)
+        qc.measure_all()
+        backend = FakeSherbrooke()
+        tqc = transpile(qc, backend, optimization_level=opt_level)
+        # Manually validate to deal with qubit equality needing exact objects
+        qpy_file = io.BytesIO()
+        dump(tqc, qpy_file)
+        qpy_file.seek(0)
+        new_circuit = load(qpy_file)[0]
+        self.assertEqual(tqc, new_circuit)
+        initial_layout_old = tqc.layout.initial_layout.get_physical_bits()
+        initial_layout_new = new_circuit.layout.initial_layout.get_physical_bits()
+        for i in initial_layout_old:
+            self.assertIsInstance(initial_layout_old[i], Qubit)
+            self.assertIsInstance(initial_layout_new[i], Qubit)
+            if initial_layout_old[i]._register is not None:
+                self.assertEqual(initial_layout_new[i], initial_layout_old[i])
+            else:
+                self.assertIsNone(initial_layout_new[i]._register)
+                self.assertIsNone(initial_layout_old[i]._index)
+                self.assertIsNone(initial_layout_new[i]._index)
+        self.assertEqual(
+            list(tqc.layout.input_qubit_mapping.values()),
+            list(new_circuit.layout.input_qubit_mapping.values()),
+        )
+        self.assertEqual(tqc.layout.final_layout, new_circuit.layout.final_layout)