qiskit-toqm performs layout changes always.

...when configured using one of its optimization strategies. This is because
non-optimal configurations (i.e. anything using GreedyMapper under the
hood) aren't compatible with the layout search parameter, and in fact
break when it is provided. These configurations happen to always perform
layout (without the explicit search) through a different means. To make
everything consistent, it should be assumed that no matter which optimization
strategy is used, layout changes will be made via routing.

qiskit-toqm users can still create a custom strategy if they wish to use
an optimal configuration that does not make layout changes, and then
use their own pass manager.

qiskit/compiler/transpiler.py

@@ -137,8 +137,7 @@ def transpile(
 
                     [qr[0], None, None, qr[1], None, qr[2]]
 
-        layout_method: Name of layout selection pass
-            ('trivial', 'dense', 'noise_adaptive', 'sabre', 'toqm')
+        layout_method: Name of layout selection pass ('trivial', 'dense', 'noise_adaptive', 'sabre')
         routing_method: Name of routing pass
             ('basic', 'lookahead', 'stochastic', 'sabre', 'toqm', 'none')
         translation_method: Name of translation pass ('unroller', 'translator', 'synthesis')

qiskit/transpiler/preset_passmanagers/level0.py

@@ -126,11 +126,6 @@ def _choose_layout_condition(property_set):
         _choose_layout = NoiseAdaptiveLayout(backend_properties)
     elif layout_method == "sabre":
         _choose_layout = SabreLayout(coupling_map, max_iterations=1, seed=seed_transpiler)
-    elif layout_method == "toqm":
-        HAS_TOQM.require_now("TOQM-based layout")
-        if routing_method != "toqm":
-            raise TranspilerError("Layout method 'toqm' requires routing method 'toqm'.")
-        _choose_layout = TrivialLayout(coupling_map)
     else:
         raise TranspilerError("Invalid layout method %s." % layout_method)
 
@@ -157,16 +152,18 @@ def _swap_needs_basis(property_set):
         _swap += [SabreSwap(coupling_map, heuristic="basic", seed=seed_transpiler)]
     elif routing_method == "toqm":
         HAS_TOQM.require_now("TOQM-based routing")
-        from qiskit_toqm import ToqmSwap, ToqmStrategyO1
+        from qiskit_toqm import ToqmSwap, ToqmStrategyO0
+
+        if initial_layout:
+            raise TranspilerError("Initial layouts are not supported with TOQM-based routing.")
 
         # Note: BarrierBeforeFinalMeasurements is skipped intentionally since ToqmSwap
         #       does not yet support barriers.
         _swap = [
             ToqmSwap(
                 coupling_map,
                 instruction_durations,
-                perform_layout=(layout_method == "toqm"),
-                strategy=ToqmStrategyO1(),
+                strategy=ToqmStrategyO0(),
                 basis_gates=basis_gates,
                 backend_properties=backend_properties,
             )

qiskit/transpiler/preset_passmanagers/level1.py

@@ -183,11 +183,6 @@ def _vf2_match_not_found(property_set):
         _improve_layout = NoiseAdaptiveLayout(backend_properties)
     elif layout_method == "sabre":
         _improve_layout = SabreLayout(coupling_map, max_iterations=2, seed=seed_transpiler)
-    elif layout_method == "toqm":
-        HAS_TOQM.require_now("TOQM-based layout")
-        if routing_method != "toqm":
-            raise TranspilerError("Layout method 'toqm' requires routing method 'toqm'.")
-        _improve_layout = TrivialLayout(coupling_map)
     else:
         raise TranspilerError("Invalid layout method %s." % layout_method)
 
@@ -216,13 +211,15 @@ def _swap_needs_basis(property_set):
         HAS_TOQM.require_now("TOQM-based routing")
         from qiskit_toqm import ToqmSwap, ToqmStrategyO1
 
+        if initial_layout:
+            raise TranspilerError("Initial layouts are not supported with TOQM-based routing.")
+
         # Note: BarrierBeforeFinalMeasurements is skipped intentionally since ToqmSwap
         #       does not yet support barriers.
         _swap = [
             ToqmSwap(
                 coupling_map,
                 instruction_durations,
-                perform_layout=(layout_method == "toqm"),
                 strategy=ToqmStrategyO1(),
                 basis_gates=basis_gates,
                 backend_properties=backend_properties,

qiskit/transpiler/preset_passmanagers/level2.py

@@ -167,11 +167,6 @@ def _vf2_match_not_found(property_set):
         _choose_layout_1 = NoiseAdaptiveLayout(backend_properties)
     elif layout_method == "sabre":
         _choose_layout_1 = SabreLayout(coupling_map, max_iterations=2, seed=seed_transpiler)
-    elif layout_method == "toqm":
-        HAS_TOQM.require_now("TOQM-based layout")
-        if routing_method != "toqm":
-            raise TranspilerError("Layout method 'toqm' requires routing method 'toqm'.")
-        _choose_layout_1 = TrivialLayout(coupling_map)
     else:
         raise TranspilerError("Invalid layout method %s." % layout_method)
 
@@ -200,13 +195,15 @@ def _swap_needs_basis(property_set):
         HAS_TOQM.require_now("TOQM-based routing")
         from qiskit_toqm import ToqmSwap, ToqmStrategyO2
 
+        if initial_layout:
+            raise TranspilerError("Initial layouts are not supported with TOQM-based routing.")
+
         # Note: BarrierBeforeFinalMeasurements is skipped intentionally since ToqmSwap
         #       does not yet support barriers.
         _swap = [
             ToqmSwap(
                 coupling_map,
                 instruction_durations,
-                perform_layout=(layout_method == "toqm"),
                 strategy=ToqmStrategyO2(),
                 basis_gates=basis_gates,
                 backend_properties=backend_properties,

qiskit/transpiler/preset_passmanagers/level3.py

@@ -169,11 +169,6 @@ def _vf2_match_not_found(property_set):
         _choose_layout_1 = NoiseAdaptiveLayout(backend_properties)
     elif layout_method == "sabre":
         _choose_layout_1 = SabreLayout(coupling_map, max_iterations=4, seed=seed_transpiler)
-    elif layout_method == "toqm":
-        HAS_TOQM.require_now("TOQM-based layout")
-        if routing_method != "toqm":
-            raise TranspilerError("Layout method 'toqm' requires routing method 'toqm'.")
-        _choose_layout_1 = TrivialLayout(coupling_map)
     else:
         raise TranspilerError("Invalid layout method %s." % layout_method)
 
@@ -202,13 +197,15 @@ def _swap_needs_basis(property_set):
         HAS_TOQM.require_now("TOQM-based routing")
         from qiskit_toqm import ToqmSwap, ToqmStrategyO3
 
+        if initial_layout:
+            raise TranspilerError("Initial layouts are not supported with TOQM-based routing.")
+
         # Note: BarrierBeforeFinalMeasurements is skipped intentionally since ToqmSwap
         #       does not yet support barriers.
         _swap = [
             ToqmSwap(
                 coupling_map,
                 instruction_durations,
-                perform_layout=(layout_method == "toqm"),
                 strategy=ToqmStrategyO3(),
                 basis_gates=basis_gates,
                 backend_properties=backend_properties,