Stop shuffling coupling map node indices in VF2 passes (Qiskit#13492)

* Stop shuffling coupling map node indices in VF2 passes

This commit updates the preset pass manager construction usage of the
VF2Layout and VF2PostLayout to stop shuffling the coupling map nodes by
default. The theory behind the node shuffling is that since we limit the
search space in the interest of runtime shuffling the node indices would
change the search order to hopefully find a match that would be
otherwise missed because we hit the internal state visit limit. However,
this is showing in practice not to having a huge impact, especially
since we're using the ordering heuristic from vf2++ that orders nodes by
degree for the vf2 search. However, in the case of a circuit that was
hardware efficient this can have the negative effect of making it harder
for vf2 to find potential matches, especially on regular lattices. For
example, in cases of a square grid lattice coupling map, and a path
interaction graph (e.g. 0->1->2->3) the shuffling makes it much harder
to find the mapping. This is because the lattice graphs the node degree
is the same (or fall into the same few types of nodes) so the influence
of the vf2++ heuristic isn't as significant and the index order has a
larger impact because it is the search order for vf2. For smaller graphs
this wasn't as noticeable but as devices scale up this effect has more of
an impact.

Since we rely solely on VF2 to find a perfect layout at higher
optimization levels this shuffling is not desireable because we always
want to find the perfect layout if it exists, especially for hardware
efficient circuits that are constructed to not require swaps. So
prioritizing the results for hardware efficient circuits is desireable
by default.

From an API impact perspective this doesn't change any of the interfaces
or defaults for the VF2 passes in the interest of backwards
compatibility. The only change is that this updates how we instantiate
the VF2 passes to always use a deterministic node ordering independent
of any user specified seed. This will be fully deterministic even in
cases the user specifies a seed value for the transpilation, the output
just might not be the same as before with the fixed seed; which is not
guaranteed between releases.

* Fix expected value in primitives test

* Restore removed argument functionality and change default instead

* Fix lint

Author: mtreinish

qiskit/transpiler/preset_passmanagers/builtin_plugins.py

@@ -238,7 +238,6 @@ class BasicSwapPassManager(PassManagerStagePlugin):
 
     def pass_manager(self, pass_manager_config, optimization_level=None) -> PassManager:
         """Build routing stage PassManager."""
-        seed_transpiler = pass_manager_config.seed_transpiler
         target = pass_manager_config.target
         coupling_map = pass_manager_config.coupling_map
         backend_properties = pass_manager_config.backend_properties
@@ -257,7 +256,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
                 routing_pass,
                 target,
                 coupling_map=coupling_map,
-                seed_transpiler=seed_transpiler,
+                seed_transpiler=-1,
                 use_barrier_before_measurement=True,
             )
         if optimization_level == 1:
@@ -268,7 +267,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
                 vf2_call_limit=vf2_call_limit,
                 vf2_max_trials=vf2_max_trials,
                 backend_properties=backend_properties,
-                seed_transpiler=seed_transpiler,
+                seed_transpiler=-1,
                 check_trivial=True,
                 use_barrier_before_measurement=True,
             )
@@ -280,7 +279,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
                 vf2_call_limit=vf2_call_limit,
                 vf2_max_trials=vf2_max_trials,
                 backend_properties=backend_properties,
-                seed_transpiler=seed_transpiler,
+                seed_transpiler=-1,
                 use_barrier_before_measurement=True,
             )
         if optimization_level == 3:
@@ -291,7 +290,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
                 vf2_call_limit=vf2_call_limit,
                 vf2_max_trials=vf2_max_trials,
                 backend_properties=backend_properties,
-                seed_transpiler=seed_transpiler,
+                seed_transpiler=-1,
                 use_barrier_before_measurement=True,
             )
         raise TranspilerError(f"Invalid optimization level specified: {optimization_level}")
@@ -324,7 +323,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
                 routing_pass,
                 target,
                 coupling_map=coupling_map,
-                seed_transpiler=seed_transpiler,
+                seed_transpiler=-1,
                 use_barrier_before_measurement=True,
             )
         if optimization_level == 1:
@@ -335,7 +334,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
                 vf2_call_limit=vf2_call_limit,
                 vf2_max_trials=vf2_max_trials,
                 backend_properties=backend_properties,
-                seed_transpiler=seed_transpiler,
+                seed_transpiler=-1,
                 check_trivial=True,
                 use_barrier_before_measurement=True,
             )
@@ -347,7 +346,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
                 vf2_call_limit=vf2_call_limit,
                 vf2_max_trials=vf2_max_trials,
                 backend_properties=backend_properties,
-                seed_transpiler=seed_transpiler,
+                seed_transpiler=-1,
                 use_barrier_before_measurement=True,
             )
         raise TranspilerError(f"Invalid optimization level specified: {optimization_level}")
@@ -358,7 +357,6 @@ class LookaheadSwapPassManager(PassManagerStagePlugin):
 
     def pass_manager(self, pass_manager_config, optimization_level=None) -> PassManager:
         """Build routing stage PassManager."""
-        seed_transpiler = pass_manager_config.seed_transpiler
         target = pass_manager_config.target
         coupling_map = pass_manager_config.coupling_map
         coupling_map_routing = target
@@ -376,7 +374,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
                 routing_pass,
                 target,
                 coupling_map=coupling_map,
-                seed_transpiler=seed_transpiler,
+                seed_transpiler=-1,
                 use_barrier_before_measurement=True,
             )
         if optimization_level == 1:
@@ -388,7 +386,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
                 vf2_call_limit=vf2_call_limit,
                 vf2_max_trials=vf2_max_trials,
                 backend_properties=backend_properties,
-                seed_transpiler=seed_transpiler,
+                seed_transpiler=-1,
                 check_trivial=True,
                 use_barrier_before_measurement=True,
             )
@@ -401,7 +399,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
                 vf2_call_limit=vf2_call_limit,
                 vf2_max_trials=vf2_max_trials,
                 backend_properties=backend_properties,
-                seed_transpiler=seed_transpiler,
+                seed_transpiler=-1,
                 use_barrier_before_measurement=True,
             )
         if optimization_level == 3:
@@ -413,7 +411,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
                 vf2_call_limit=vf2_call_limit,
                 vf2_max_trials=vf2_max_trials,
                 backend_properties=backend_properties,
-                seed_transpiler=seed_transpiler,
+                seed_transpiler=-1,
                 use_barrier_before_measurement=True,
             )
         raise TranspilerError(f"Invalid optimization level specified: {optimization_level}")
@@ -448,7 +446,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
                 routing_pass,
                 target,
                 coupling_map=coupling_map,
-                seed_transpiler=seed_transpiler,
+                seed_transpiler=-1,
                 use_barrier_before_measurement=True,
             )
         if optimization_level == 1:
@@ -466,7 +464,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
                 vf2_call_limit=vf2_call_limit,
                 vf2_max_trials=vf2_max_trials,
                 backend_properties=backend_properties,
-                seed_transpiler=seed_transpiler,
+                seed_transpiler=-1,
                 check_trivial=True,
                 use_barrier_before_measurement=True,
             )
@@ -486,7 +484,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
                 vf2_call_limit=vf2_call_limit,
                 vf2_max_trials=vf2_max_trials,
                 backend_properties=backend_properties,
-                seed_transpiler=seed_transpiler,
+                seed_transpiler=-1,
                 use_barrier_before_measurement=True,
             )
         if optimization_level == 3:
@@ -504,7 +502,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
                 vf2_call_limit=vf2_call_limit,
                 vf2_max_trials=vf2_max_trials,
                 backend_properties=backend_properties,
-                seed_transpiler=seed_transpiler,
+                seed_transpiler=-1,
                 use_barrier_before_measurement=True,
             )
         raise TranspilerError(f"Invalid optimization level specified: {optimization_level}")
@@ -515,7 +513,6 @@ class NoneRoutingPassManager(PassManagerStagePlugin):
 
     def pass_manager(self, pass_manager_config, optimization_level=None) -> PassManager:
         """Build routing stage PassManager."""
-        seed_transpiler = pass_manager_config.seed_transpiler
         target = pass_manager_config.target
         coupling_map = pass_manager_config.coupling_map
         routing_pass = Error(
@@ -527,7 +524,7 @@ def pass_manager(self, pass_manager_config, optimization_level=None) -> PassMana
             routing_pass,
             target,
             coupling_map=coupling_map,
-            seed_transpiler=seed_transpiler,
+            seed_transpiler=-1,
             use_barrier_before_measurement=True,
         )
 
@@ -793,7 +790,7 @@ def _swap_mapped(property_set):
             )
             choose_layout_1 = VF2Layout(
                 coupling_map=pass_manager_config.coupling_map,
-                seed=pass_manager_config.seed_transpiler,
+                seed=-1,
                 call_limit=int(5e4),  # Set call limit to ~100ms with rustworkx 0.10.2
                 properties=pass_manager_config.backend_properties,
                 target=pass_manager_config.target,
@@ -826,7 +823,7 @@ def _swap_mapped(property_set):
         elif optimization_level == 2:
             choose_layout_0 = VF2Layout(
                 coupling_map=pass_manager_config.coupling_map,
-                seed=pass_manager_config.seed_transpiler,
+                seed=-1,
                 call_limit=int(5e6),  # Set call limit to ~10s with rustworkx 0.10.2
                 properties=pass_manager_config.backend_properties,
                 target=pass_manager_config.target,
@@ -861,7 +858,7 @@ def _swap_mapped(property_set):
         elif optimization_level == 3:
             choose_layout_0 = VF2Layout(
                 coupling_map=pass_manager_config.coupling_map,
-                seed=pass_manager_config.seed_transpiler,
+                seed=-1,
                 call_limit=int(3e7),  # Set call limit to ~60s with rustworkx 0.10.2
                 properties=pass_manager_config.backend_properties,
                 target=pass_manager_config.target,

qiskit/transpiler/preset_passmanagers/common.py

@@ -281,7 +281,7 @@ def generate_routing_passmanager(
     coupling_map=None,
     vf2_call_limit=None,
     backend_properties=None,
-    seed_transpiler=None,
+    seed_transpiler=-1,
     check_trivial=False,
     use_barrier_before_measurement=True,
     vf2_max_trials=None,
@@ -300,7 +300,10 @@ def generate_routing_passmanager(
         backend_properties (BackendProperties): Properties of a backend to
             synthesize for (e.g. gate fidelities).
         seed_transpiler (int): Sets random seed for the stochastic parts of
-            the transpiler.
+            the transpiler. This is currently only used for :class:`.VF2PostLayout` and the
+            default value of ``-1`` is strongly recommended (which is no randomization).
+            If a value of ``None`` is provided this will seed from system
+            entropy.
         check_trivial (bool): If set to true this will condition running the
             :class:`~.VF2PostLayout` pass after routing on whether a trivial
             layout was tried and was found to not be perfect. This is only
@@ -358,7 +361,7 @@ def _swap_condition(property_set):
                     target,
                     coupling_map,
                     backend_properties,
-                    seed_transpiler,
+                    seed=seed_transpiler,
                     call_limit=vf2_call_limit,
                     max_trials=vf2_max_trials,
                     strict_direction=False,

releasenotes/notes/vf2-order-3ef2b4ca5ebd0588.yaml

@@ -0,0 +1,12 @@
+---
+upgrade_transpiler:
+  - |
+    The default value for the :func:`.generate_routing_passmanager` argument
+    ``seed_transpiler`` has changed from ``None`` to ``-1``. This was done
+    because this flag was only used to configure the :class:`.VF2PostLayout`
+    transpiler pass in the output, and for that pass in particular the
+    randomization typically only hurts performance and is not desirable.
+    If you were relying on the previous default value you can restore this
+    behavior by explicitly setting the argument ``seed_transpiler=None``. If
+    you were explicitly setting a seed value for this parameter there is no
+    change in behavior.

test/python/primitives/test_backend_estimator.py

@@ -440,7 +440,7 @@ def test_layout(self, backend):
                 estimator.set_transpile_options(seed_transpiler=15, optimization_level=1)
                 value = estimator.run(qc, op, shots=10000).result().values[0]
             if optionals.HAS_AER:
-                ref_value = -0.9954 if isinstance(backend, GenericBackendV2) else -0.916
+                ref_value = -0.9954 if isinstance(backend, GenericBackendV2) else -0.934
             else:
                 ref_value = -1
             self.assertEqual(value, ref_value)