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Add argument for repeating transformations to optimize_for_target_gateset #6426

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Add argument for repeating transformations to optimize_for_target_gateset #6426

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5aae8a3
Add argument for repeating transformations to optimize_for_target_gat…
NoureldinYosri Jan 26, 2024
91d5bd1
add argument to preserve moment strucutre
NoureldinYosri Jan 29, 2024
1e744bf
remove circuit compression
NoureldinYosri Jan 30, 2024
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54 changes: 39 additions & 15 deletions cirq-core/cirq/transformers/optimize_for_target_gateset.py
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@

"""Transformers to rewrite a circuit using gates from a given target gateset."""

from typing import Optional, Callable, Hashable, Sequence, TYPE_CHECKING
from typing import Optional, Callable, Hashable, Sequence, TYPE_CHECKING, Union

from cirq import circuits
from cirq.protocols import decompose_protocol as dp
Expand Down Expand Up @@ -102,20 +102,26 @@ def optimize_for_target_gateset(
context: Optional['cirq.TransformerContext'] = None,
gateset: Optional['cirq.CompilationTargetGateset'] = None,
ignore_failures: bool = True,
max_num_passes: Union[int, None] = 1,
) -> 'cirq.Circuit':
"""Transforms the given circuit into an equivalent circuit using gates accepted by `gateset`.

Repeat max_num_passes times or when `max_num_passes=None` until no further changes can be done
1. Run all `gateset.preprocess_transformers`
2. Convert operations using built-in cirq decompose + `gateset.decompose_to_target_gateset`.
3. Run all `gateset.postprocess_transformers`

Note:
The optimizer is heuristic and may not produce optimal results even with max_num_passes=None.

Args:
circuit: Input circuit to transform. It will not be modified.
context: `cirq.TransformerContext` storing common configurable options for transformers.
gateset: Target gateset, which should be an instance of `cirq.CompilationTargetGateset`.
ignore_failures: If set, operations that fail to convert are left unchanged. If not set,
conversion failures raise a ValueError.

max_num_passes: The maximum number of passes to do. A value of `None` means keep iterating
until no further improvements can be done.
Returns:
An equivalent circuit containing gates accepted by `gateset`.

Expand All @@ -126,20 +132,38 @@ def optimize_for_target_gateset(
return _decompose_operations_to_target_gateset(
circuit, context=context, ignore_failures=ignore_failures
)
if isinstance(max_num_passes, int):
_outerloop = lambda: range(max_num_passes)
else:

def _outerloop():
while True:
yield 0

initial_num_moments, initial_num_ops = len(circuit), len(tuple(circuit.all_operations()))
for _ in _outerloop():
for transformer in gateset.preprocess_transformers:
circuit = transformer(circuit, context=context)

circuit = _decompose_operations_to_target_gateset(
circuit,
context=context,
gateset=gateset,
decomposer=gateset.decompose_to_target_gateset,
ignore_failures=ignore_failures,
tags_to_decompose=(gateset._intermediate_result_tag,),
)

for transformer in gateset.preprocess_transformers:
circuit = transformer(circuit, context=context)

circuit = _decompose_operations_to_target_gateset(
circuit,
context=context,
gateset=gateset,
decomposer=gateset.decompose_to_target_gateset,
ignore_failures=ignore_failures,
tags_to_decompose=(gateset._intermediate_result_tag,),
)
for transformer in gateset.postprocess_transformers:
circuit = transformer(circuit, context=context)

for transformer in gateset.postprocess_transformers:
circuit = transformer(circuit, context=context)
circuit = circuits.Circuit(
op for op in circuit.all_operations()
) # Ensure the circuit is contracted.
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This leads to a loss of moment structure. When we wrote this function originally, preserving moment structure was an important requirement. Are you sure we want to do this?

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what was the original requirement exactly? the circuit in the issue is supposed to endup with 3 moments as per @eliottrosenberg which can't happen without some sort of contraction. probably there is a way to do the contraction without destroying the moment structure. but we need to clarify what it's exactly that we want to preserve or if we simply need another preserve_moment_structure parameter

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Yeah, I think reducing the number of moments is generally a good thing. In general, this can't preserve the number of moments (i.e. if I ask it to transform a cirq.ISWAP gate into CZ).

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@tanujkhattar apart from this line. the current implementation doesn't preserve the moment structure, for example look at the output in the issue. CZ(4, 5) is earlier than it should and PhXZ(a=0,x=1,z=0)(6)───PhXZ(a=0.5,x=-0.5,z=1)(6)-CZ(5, 6) are a lot later than they should.

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Let's continue the discussion on the original issue here - #6422 (comment)


num_moments, num_ops = len(circuit), len(tuple(circuit.all_operations()))
if (num_moments, num_ops) == (initial_num_moments, initial_num_ops):
# Stop early. No further optimizations can be done.
break
initial_num_moments, initial_num_ops = num_moments, num_ops
return circuit.unfreeze(copy=False)
72 changes: 72 additions & 0 deletions cirq-core/cirq/transformers/optimize_for_target_gateset_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,8 @@
# See the License for the specific language governing permissions and
# limitations under the License.

from typing import Union

import cirq
from cirq.protocols.decompose_protocol import DecomposeResult
from cirq.transformers.optimize_for_target_gateset import _decompose_operations_to_target_gateset
Expand Down Expand Up @@ -243,3 +245,73 @@ def test_optimize_for_target_gateset_deep():
1: ───#2───────────────────────────────────────────────────────────────────────────
''',
)


@pytest.mark.parametrize('max_num_passes', [2, None])
def test_optimize_for_target_gateset_multiple_passes(max_num_passes: Union[int, None]):
gateset = cirq.CZTargetGateset()

input_circuit = cirq.Circuit(
[
cirq.Moment(
cirq.X(cirq.LineQubit(1)),
cirq.X(cirq.LineQubit(2)),
cirq.X(cirq.LineQubit(3)),
cirq.X(cirq.LineQubit(6)),
),
cirq.Moment(
cirq.H(cirq.LineQubit(0)),
cirq.H(cirq.LineQubit(1)),
cirq.H(cirq.LineQubit(2)),
cirq.H(cirq.LineQubit(3)),
cirq.H(cirq.LineQubit(4)),
cirq.H(cirq.LineQubit(5)),
cirq.H(cirq.LineQubit(6)),
),
cirq.Moment(
cirq.H(cirq.LineQubit(1)), cirq.H(cirq.LineQubit(3)), cirq.H(cirq.LineQubit(5))
),
cirq.Moment(
cirq.CZ(cirq.LineQubit(0), cirq.LineQubit(1)),
cirq.CZ(cirq.LineQubit(2), cirq.LineQubit(3)),
cirq.CZ(cirq.LineQubit(4), cirq.LineQubit(5)),
),
cirq.Moment(
cirq.CZ(cirq.LineQubit(2), cirq.LineQubit(1)),
cirq.CZ(cirq.LineQubit(4), cirq.LineQubit(3)),
cirq.CZ(cirq.LineQubit(6), cirq.LineQubit(5)),
),
]
)

desired_circuit = cirq.Circuit(
cirq.PhasedXZGate(axis_phase_exponent=0.5, x_exponent=-0.5, z_exponent=1.0).on(
cirq.LineQubit(4)
),
cirq.PhasedXZGate(axis_phase_exponent=-1.0, x_exponent=1, z_exponent=0).on(
cirq.LineQubit(1)
),
cirq.PhasedXZGate(axis_phase_exponent=-0.5, x_exponent=0.5, z_exponent=0.0).on(
cirq.LineQubit(2)
),
cirq.PhasedXZGate(axis_phase_exponent=0.5, x_exponent=-0.5, z_exponent=1.0).on(
cirq.LineQubit(0)
),
cirq.PhasedXZGate(axis_phase_exponent=-1.0, x_exponent=1, z_exponent=0).on(
cirq.LineQubit(3)
),
cirq.PhasedXZGate(axis_phase_exponent=-0.5, x_exponent=0.5, z_exponent=0.0).on(
cirq.LineQubit(6)
),
cirq.CZ(cirq.LineQubit(4), cirq.LineQubit(5)),
cirq.CZ(cirq.LineQubit(0), cirq.LineQubit(1)),
cirq.CZ(cirq.LineQubit(2), cirq.LineQubit(3)),
cirq.CZ(cirq.LineQubit(2), cirq.LineQubit(1)),
cirq.CZ(cirq.LineQubit(4), cirq.LineQubit(3)),
cirq.CZ(cirq.LineQubit(6), cirq.LineQubit(5)),
)

got = cirq.optimize_for_target_gateset(
input_circuit, gateset=gateset, max_num_passes=max_num_passes
)
assert got == desired_circuit
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