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Stop shuffling coupling map node indices in VF2 passes (#13685)
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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 desirable 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 desirable
by default. Especially since most connectivity graphs are lattices and
will exhibit the negative impacts for hardware efficient circuits.

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.

This is a partial backport of #13492 without the API implications on the
generate function from the original PR because that is only valid for 2.0.
The change in what the preset pass managers do when running VF2 is valid
though because it doesn't change our API guarantees around the
transpilation, it just increases the likelihood of a match being found.
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@mtreinish
mtreinish authored Jan 20, 2025
1 parent 6151f16 commit a623960
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Showing 2 changed files with 20 additions and 23 deletions.
41 changes: 19 additions & 22 deletions qiskit/transpiler/preset_passmanagers/builtin_plugins.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand All @@ -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:
Expand All @@ -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,
)
Expand All @@ -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:
Expand All @@ -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}")
Expand Down Expand Up @@ -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:
Expand All @@ -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,
)
Expand All @@ -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}")
Expand All @@ -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
Expand All @@ -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:
Expand All @@ -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,
)
Expand All @@ -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:
Expand All @@ -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}")
Expand Down Expand Up @@ -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:
Expand All @@ -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,
)
Expand All @@ -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:
Expand All @@ -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}")
Expand All @@ -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(
Expand All @@ -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,
)

Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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,
Expand Down
2 changes: 1 addition & 1 deletion test/python/primitives/test_backend_estimator.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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)
Expand Down

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