Integrate FinalizeLayouts into the PassManager harness

This commit integrates the function that finalize layouts was performing
into the passmanager harnesss. We'll always need to run the equivalent
of finalize layout if any passes are setting a virtual permutation so
using a standalone pass that can be forgotten is potentially error
prone. This inlines the logic as part of the passmanager's output
preparation stage so we always finalize the layout.

qiskit/transpiler/passes/__init__.py

@@ -90,7 +90,6 @@
    ElidePermutations
    NormalizeRXAngle
    OptimizeAnnotated
-   FinalizeLayouts
 
 Calibration
 =============
@@ -241,7 +240,6 @@
 from .optimization import ElidePermutations
 from .optimization import NormalizeRXAngle
 from .optimization import OptimizeAnnotated
-from .optimization import FinalizeLayouts
 
 # circuit analysis
 from .analysis import ResourceEstimation

qiskit/transpiler/passes/optimization/__init__.py

@@ -38,4 +38,3 @@
 from .elide_permutations import ElidePermutations
 from .normalize_rx_angle import NormalizeRXAngle
 from .optimize_annotated import OptimizeAnnotated
-from .finalize_layouts import FinalizeLayouts

qiskit/transpiler/passmanager.py

@@ -29,7 +29,7 @@
 from qiskit.passmanager.exceptions import PassManagerError
 from .basepasses import BasePass
 from .exceptions import TranspilerError
-from .layout import TranspileLayout
+from .layout import TranspileLayout, Layout
 
 _CircuitsT = Union[List[QuantumCircuit], QuantumCircuit]
 
@@ -69,6 +69,7 @@ def _passmanager_backend(
     ) -> QuantumCircuit:
         out_program = dag_to_circuit(passmanager_ir, copy_operations=False)
 
+        self._finalize_layouts(passmanager_ir)
         out_name = kwargs.get("output_name", None)
         if out_name is not None:
             out_program.name = out_name
@@ -96,6 +97,48 @@ def _passmanager_backend(
 
         return out_program
 
+    def _finalize_layouts(self, dag):
+        if (virtual_permutation_layout := self.property_set["virtual_permutation_layout"]) is None:
+            return
+
+        self.property_set.pop("virtual_permutation_layout")
+
+        # virtual_permutation_layout is usually created before extending the layout with ancillas,
+        # so we extend the permutation to be identity on ancilla qubits
+        original_qubit_indices = self.property_set.get("original_qubit_indices", None)
+        for oq in original_qubit_indices:
+            if oq not in virtual_permutation_layout:
+                virtual_permutation_layout[oq] = original_qubit_indices[oq]
+
+        t_qubits = dag.qubits
+
+        if (t_initial_layout := self.property_set.get("layout", None)) is None:
+            t_initial_layout = Layout(dict(enumerate(t_qubits)))
+
+        if (t_final_layout := self.property_set.get("final_layout", None)) is None:
+            t_final_layout = Layout(dict(enumerate(t_qubits)))
+
+        # Ordered list of original qubits
+        original_qubits_reverse = {v: k for k, v in original_qubit_indices.items()}
+        original_qubits = []
+        for i in range(len(original_qubits_reverse)):
+            original_qubits.append(original_qubits_reverse[i])
+
+        virtual_permutation_layout_inv = virtual_permutation_layout.inverse(
+            original_qubits, original_qubits
+        )
+
+        t_initial_layout_inv = t_initial_layout.inverse(original_qubits, t_qubits)
+
+        # ToDo: this can possibly be made simpler
+        new_final_layout = t_initial_layout_inv
+        new_final_layout = new_final_layout.compose(virtual_permutation_layout_inv, original_qubits)
+        new_final_layout = new_final_layout.compose(t_initial_layout, original_qubits)
+        new_final_layout = new_final_layout.compose(t_final_layout, t_qubits)
+
+        self.property_set["layout"] = t_initial_layout
+        self.property_set["final_layout"] = new_final_layout
+
     def append(
         self,
         passes: Task | list[Task],

releasenotes/notes/add-elide-swaps-b0a4c373c9af1efd.yaml

@@ -39,9 +39,3 @@ features:
 
     The pass also sets the ``virtual_permutation_layout`` property set, storing
     the permutation of the virtual qubits that was optimized away.
-
-  - |
-    Added a new transpiler pass, :class:`~.FinalizeLayouts`,
-    which is designed to run after the :ref:`routing_stage` and update the
-    ``final_layout`` property set based on ``layout`` and
-    ``virtual_permutation_layout``.

test/python/transpiler/test_elide_permutations.py

@@ -17,7 +17,6 @@
 from qiskit.circuit.quantumcircuit import QuantumCircuit
 from qiskit.circuit.library.generalized_gates import PermutationGate
 from qiskit.transpiler import PassManager
-from qiskit.transpiler.passes.optimization.finalize_layouts import FinalizeLayouts
 from qiskit.transpiler.passes.optimization.elide_permutations import ElidePermutations
 from qiskit.circuit.controlflow import IfElseOp
 from qiskit.quantum_info import Operator
@@ -317,7 +316,6 @@ def test_not_run_after_layout(self):
             optimization_level=3, initial_layout=list(range(2, -1, -1)), seed_transpiler=42
         )
         spm.layout += ElidePermutations()
-        spm.post_optimization = PassManager([FinalizeLayouts()])
         res = spm.run(qc)
         self.assertTrue(Operator.from_circuit(res).equiv(Operator(qc)))
         self.assertIn("swap", res.count_ops())
@@ -335,7 +333,6 @@ def test_unitary_equivalence(self):
         with self.subTest("no coupling map"):
             spm = generate_preset_pass_manager(optimization_level=3, seed_transpiler=42)
             spm.init += ElidePermutations()
-            spm.post_optimization = PassManager([FinalizeLayouts()])
             res = spm.run(qc)
             self.assertTrue(Operator.from_circuit(res).equiv(Operator(qc)))
 
@@ -344,7 +341,6 @@ def test_unitary_equivalence(self):
                 optimization_level=3, seed_transpiler=42, coupling_map=CouplingMap.from_line(3)
             )
             spm.init += ElidePermutations()
-            spm.post_optimization = PassManager([FinalizeLayouts()])
             res = spm.run(qc)
             self.assertTrue(Operator.from_circuit(res).equiv(Operator(qc)))
 
@@ -366,7 +362,6 @@ def test_unitary_equivalence_routing_and_basis_translation(self):
         with self.subTest("no coupling map"):
             spm = generate_preset_pass_manager(optimization_level=3, seed_transpiler=42)
             spm.init += ElidePermutations()
-            spm.post_optimization = PassManager([FinalizeLayouts()])
             res = spm.run(qc)
             self.assertTrue(Operator.from_circuit(res).equiv(Operator(qc)))
 
@@ -378,7 +373,6 @@ def test_unitary_equivalence_routing_and_basis_translation(self):
                 basis_gates=["u", "cz"],
             )
             spm.init += ElidePermutations()
-            spm.post_optimization = PassManager([FinalizeLayouts()])
             res = spm.run(qc)
             self.assertTrue(Operator.from_circuit(res).equiv(Operator(qc)))
 
@@ -390,7 +384,6 @@ def test_unitary_equivalence_routing_and_basis_translation(self):
                 basis_gates=["u", "cz"],
             )
             spm.init += ElidePermutations()
-            spm.post_optimization = PassManager([FinalizeLayouts()])
             res = spm.run(qc)
             self.assertTrue(Operator.from_circuit(res).equiv(Operator(qc)))
 
@@ -403,7 +396,6 @@ def test_unitary_equivalence_routing_and_basis_translation(self):
                 coupling_map=CouplingMap.from_line(5),
             )
             spm.init += ElidePermutations()
-            spm.post_optimization = PassManager([FinalizeLayouts()])
             res = spm.run(qc)
             self.assertTrue(Operator.from_circuit(res).equiv(Operator(qc)))
 
@@ -414,7 +406,6 @@ def test_unitary_equivalence_routing_and_basis_translation(self):
                 coupling_map=CouplingMap.from_line(8),
             )
             spm.init += ElidePermutations()
-            spm.post_optimization = PassManager([FinalizeLayouts()])
             res = spm.run(qc)
 
             qc_with_ancillas = QuantumCircuit(8)
@@ -429,7 +420,6 @@ def test_unitary_equivalence_routing_and_basis_translation(self):
                 coupling_map=CouplingMap.from_line(8),
             )
             spm.init += ElidePermutations()
-            spm.post_optimization = PassManager([FinalizeLayouts()])
             res = spm.run(qc)
 
             qc_with_ancillas = QuantumCircuit(8)