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OptimizeSwapBeforeMeasure only when last measurements #5906

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OptimizeSwapBeforeMeasure only when last measurements #5906

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OptimizeSwapBeforeMeasure only when last measurements
1ucian0 Feb 25, 2021
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test
1ucian0 Feb 25, 2021
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small optimization
1ucian0 Feb 25, 2021
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docstring
1ucian0 Feb 25, 2021
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unused import
1ucian0 Feb 25, 2021
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1ucian0 Feb 25, 2021
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58 changes: 31 additions & 27 deletions qiskit/transpiler/passes/optimization/optimize_swap_before_measure.py
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Original file line number Diff line number Diff line change
Expand Up @@ -13,9 +13,9 @@

"""Remove the swaps followed by measurement (and adapt the measurement)."""

from qiskit.circuit import Measure
from qiskit.circuit.library.standard_gates import SwapGate
from qiskit.transpiler.basepasses import TransformationPass
from qiskit.transpiler import Layout
from qiskit.dagcircuit import DAGCircuit


Expand All @@ -35,29 +35,33 @@ def run(self, dag):
Returns:
DAGCircuit: the optimized DAG.
"""
swaps = dag.op_nodes(SwapGate)
for swap in swaps[::-1]:
final_successor = []
for successor in dag.successors(swap):
final_successor.append(successor.type == 'out' or (successor.type == 'op' and
successor.op.name == 'measure'))
if all(final_successor):
# the node swap needs to be removed and, if a measure follows, needs to be adapted
swap_qargs = swap.qargs
measure_layer = DAGCircuit()
for qreg in dag.qregs.values():
measure_layer.add_qreg(qreg)
for creg in dag.cregs.values():
measure_layer.add_creg(creg)
for successor in list(dag.successors(swap)):
if successor.type == 'op' and successor.op.name == 'measure':
# replace measure node with a new one, where qargs is set with the "other"
# swap qarg.
dag.remove_op_node(successor)
old_measure_qarg = successor.qargs[0]
new_measure_qarg = swap_qargs[swap_qargs.index(old_measure_qarg) - 1]
measure_layer.apply_operation_back(Measure(), [new_measure_qarg],
[successor.cargs[0]])
dag.compose(measure_layer)
dag.remove_op_node(swap)
return dag

new_dag = DAGCircuit()
new_dag.metadata = dag.metadata
new_dag._global_phase = dag._global_phase
for creg in dag.cregs.values():
new_dag.add_creg(creg)
for qreg in dag.qregs.values():
new_dag.add_qreg(qreg)
Comment on lines +39 to +45
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Suggested change
new_dag = DAGCircuit()
new_dag.metadata = dag.metadata
new_dag._global_phase = dag._global_phase
for creg in dag.cregs.values():
new_dag.add_creg(creg)
for qreg in dag.qregs.values():
new_dag.add_qreg(qreg)
new_dag = dag._copy_circuit_metadata()

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nice one. Why is _copy_circuit_metadata a private method?

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Initially because it was used internally, but then was useful to passes that needed to rebuild the dag (but preserve metadata) like the layout routing passes. Making it public seems like a good idea.


_layout = Layout.generate_trivial_layout(*dag.qregs.values())
_trivial_layout = Layout.generate_trivial_layout(*dag.qregs.values())

for node in dag.topological_op_nodes():
if node.type == 'op':
qargs = [_trivial_layout[_layout[qarg]] for qarg in node.qargs]
if isinstance(node.op, SwapGate):
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Does this apply for all swaps or only those added by routing?

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does not distinguish from where is the SWAP coming from.

swap = node
final_successor = []
for successor in dag.successors(swap):
if successor.type == 'op' and successor.op.name == 'measure':
is_final_measure = all([s.type == 'out'
for s in dag.successors(successor)])
else:
is_final_measure = False
final_successor.append(successor.type == 'out' or is_final_measure)
if all(final_successor):
_layout.swap(*qargs)
continue
new_dag.apply_operation_back(node.op, qargs, node.cargs)
return new_dag
172 changes: 106 additions & 66 deletions test/python/transpiler/test_optimize_swap_before_measure.py
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Original file line number Diff line number Diff line change
Expand Up @@ -73,72 +73,6 @@ def test_optimize_1swap_2measure(self):

self.assertEqual(circuit_to_dag(expected), after)

def test_optimize_nswap_nmeasure(self):
""" Remove severals swap affecting multiple measurements
┌─┐ ┌─┐
q_0: ─X──X─────X────┤M├───────────────────────────────── q_0: ──────┤M├───────────────
│ │ │ └╥┘ ┌─┐ ┌─┐└╥┘
q_1: ─X──X──X──X──X──╫─────X────┤M├───────────────────── q_1: ───┤M├─╫────────────────
│ │ ║ │ └╥┘ ┌─┐ ┌─┐└╥┘ ║
q_2: ───────X──X──X──╫──X──X─────╫──X────┤M├──────────── q_2: ┤M├─╫──╫────────────────
│ ║ │ ║ │ └╥┘┌─┐ └╥┘ ║ ║ ┌─┐
q_3: ─X─────X──X─────╫──X──X──X──╫──X─────╫─┤M├───────── q_3: ─╫──╫──╫────┤M├─────────
│ │ ║ │ │ ║ ║ └╥┘┌─┐ ║ ║ ║ └╥┘ ┌─┐
q_4: ─X──X──X──X─────╫──X──X──X──╫──X─────╫──╫─┤M├────── ==> q_4: ─╫──╫──╫─────╫───────┤M├
│ │ ║ │ ║ │ ║ ║ └╥┘┌─┐ ║ ║ ║ ┌─┐ ║ └╥┘
q_5: ────X──X──X──X──╫──X──X─────╫──X──X──╫──╫──╫─┤M├─── q_5: ─╫──╫──╫─┤M├─╫────────╫─
│ │ ║ │ ║ │ ║ ║ ║ └╥┘┌─┐ ║ ║ ║ └╥┘ ║ ┌─┐ ║
q_6: ─X──X──X──X──X──╫──X──X─────╫─────X──╫──╫──╫──╫─┤M├ q_6: ─╫──╫──╫──╫──╫─┤M├────╫─
│ │ │ ║ │ ┌─┐ ║ ║ ║ ║ ║ └╥┘ ║ ║ ║ ║ ║ └╥┘┌─┐ ║
q_7: ─X──X─────X─────╫──X─┤M├────╫────────╫──╫──╫──╫──╫─ q_7: ─╫──╫──╫──╫──╫──╫─┤M├─╫─
║ └╥┘ ║ ║ ║ ║ ║ ║ ║ ║ ║ ║ ║ ║ └╥┘ ║
c: 8/════════════════╩═════╩═════╩════════╩══╩══╩══╩══╩═ c: 8/═╩══╩══╩══╩══╩══╩══╩══╩═
0 7 1 2 3 4 5 6 0 1 2 3 4 5 6 7
"""
circuit = QuantumCircuit(8, 8)
circuit.swap(3, 4)
circuit.swap(6, 7)
circuit.swap(0, 1)
circuit.swap(6, 7)
circuit.swap(4, 5)
circuit.swap(0, 1)
circuit.swap(5, 6)
circuit.swap(3, 4)
circuit.swap(1, 2)
circuit.swap(6, 7)
circuit.swap(4, 5)
circuit.swap(2, 3)
circuit.swap(0, 1)
circuit.swap(5, 6)
circuit.swap(1, 2)
circuit.swap(6, 7)
circuit.swap(4, 5)
circuit.swap(2, 3)
circuit.swap(3, 4)
circuit.swap(3, 4)
circuit.swap(5, 6)
circuit.swap(1, 2)
circuit.swap(4, 5)
circuit.swap(2, 3)
circuit.swap(5, 6)
circuit.measure(range(8), range(8))
dag = circuit_to_dag(circuit)

expected = QuantumCircuit(8, 8)
expected.measure(0, 2)
expected.measure(1, 1)
expected.measure(2, 0)
expected.measure(3, 4)
expected.measure(4, 7)
expected.measure(5, 3)
expected.measure(6, 5)
expected.measure(7, 6)

pass_ = OptimizeSwapBeforeMeasure()
after = pass_.run(dag)

self.assertEqual(circuit_to_dag(expected), after)

def test_cannot_optimize(self):
""" Cannot optimize when swap is not at the end in all of the successors
qr0:--X-----m--
Expand Down Expand Up @@ -218,6 +152,112 @@ def test_optimize_overlap_swap(self):

self.assertEqual(expected, after)

def test_optimize_nswap_nmeasure(self):
""" Remove several swap affecting multiple measurements
┌─┐ ┌─┐
q_0: ─X──X─────X────┤M├───────────────────────────────── q_0: ──────┤M├───────────────
│ │ │ └╥┘ ┌─┐ ┌─┐└╥┘
q_1: ─X──X──X──X──X──╫─────X────┤M├───────────────────── q_1: ───┤M├─╫────────────────
│ │ ║ │ └╥┘ ┌─┐ ┌─┐└╥┘ ║
q_2: ───────X──X──X──╫──X──X─────╫──X────┤M├──────────── q_2: ┤M├─╫──╫────────────────
│ ║ │ ║ │ └╥┘┌─┐ └╥┘ ║ ║ ┌─┐
q_3: ─X─────X──X─────╫──X──X──X──╫──X─────╫─┤M├───────── q_3: ─╫──╫──╫────┤M├─────────
│ │ ║ │ │ ║ ║ └╥┘┌─┐ ║ ║ ║ └╥┘ ┌─┐
q_4: ─X──X──X──X─────╫──X──X──X──╫──X─────╫──╫─┤M├────── ==> q_4: ─╫──╫──╫─────╫───────┤M├
│ │ ║ │ ║ │ ║ ║ └╥┘┌─┐ ║ ║ ║ ┌─┐ ║ └╥┘
q_5: ────X──X──X──X──╫──X──X─────╫──X──X──╫──╫──╫─┤M├─── q_5: ─╫──╫──╫─┤M├─╫────────╫─
│ │ ║ │ ║ │ ║ ║ ║ └╥┘┌─┐ ║ ║ ║ └╥┘ ║ ┌─┐ ║
q_6: ─X──X──X──X──X──╫──X──X─────╫─────X──╫──╫──╫──╫─┤M├ q_6: ─╫──╫──╫──╫──╫─┤M├────╫─
│ │ │ ║ │ ┌─┐ ║ ║ ║ ║ ║ └╥┘ ║ ║ ║ ║ ║ └╥┘┌─┐ ║
q_7: ─X──X─────X─────╫──X─┤M├────╫────────╫──╫──╫──╫──╫─ q_7: ─╫──╫──╫──╫──╫──╫─┤M├─╫─
║ └╥┘ ║ ║ ║ ║ ║ ║ ║ ║ ║ ║ ║ ║ └╥┘ ║
c: 8/════════════════╩═════╩═════╩════════╩══╩══╩══╩══╩═ c: 8/═╩══╩══╩══╩══╩══╩══╩══╩═
0 7 1 2 3 4 5 6 0 1 2 3 4 5 6 7
"""
circuit = QuantumCircuit(8, 8)
circuit.swap(3, 4)
circuit.swap(6, 7)
circuit.swap(0, 1)
circuit.swap(6, 7)
circuit.swap(4, 5)
circuit.swap(0, 1)
circuit.swap(5, 6)
circuit.swap(3, 4)
circuit.swap(1, 2)
circuit.swap(6, 7)
circuit.swap(4, 5)
circuit.swap(2, 3)
circuit.swap(0, 1)
circuit.swap(5, 6)
circuit.swap(1, 2)
circuit.swap(6, 7)
circuit.swap(4, 5)
circuit.swap(2, 3)
circuit.swap(3, 4)
circuit.swap(3, 4)
circuit.swap(5, 6)
circuit.swap(1, 2)
circuit.swap(4, 5)
circuit.swap(2, 3)
circuit.swap(5, 6)
circuit.measure(range(8), range(8))

expected = QuantumCircuit(8, 8)
expected.measure(0, 2)
expected.measure(1, 1)
expected.measure(2, 0)
expected.measure(3, 4)
expected.measure(4, 7)
expected.measure(5, 3)
expected.measure(6, 5)
expected.measure(7, 6)

pass_manager = PassManager()
pass_manager.append(
[OptimizeSwapBeforeMeasure(), DAGFixedPoint()],
do_while=lambda property_set: not property_set['dag_fixed_point'])
after = pass_manager.run(circuit)

self.assertEqual(expected, after)


class TestOptimizeSwapBeforeMeasureMidMeasure(QiskitTestCase):
""" Test swap-followed-by-measure optimizations, with mid-circuit measurement."""

def test_mid_circuit(self):
"""Test mid-circuit measurement"""
qr1 = QuantumRegister(1, 'qr1')
qr2 = QuantumRegister(2, 'qr2')
cr = ClassicalRegister(3, 'cr')
circuit = QuantumCircuit(qr1, qr2, cr)
circuit.h(qr1[0])
circuit.h(qr2[1])
circuit.swap(qr1[0], qr2[0])
circuit.measure(qr1[0], cr[0])
circuit.measure(qr2[0], cr[1])
circuit.cx(qr1[0], qr2[1])
circuit.swap(qr1[0], qr2[0])
circuit.measure(qr1[0], cr[0])
circuit.measure(qr2[0], cr[1])

expected = QuantumCircuit(qr1, qr2, cr)
expected.h(qr1[0])
expected.h(qr2[1])
expected.swap(qr1[0], qr2[0])
expected.measure(qr1[0], cr[0])
expected.measure(qr2[0], cr[1])
expected.cx(qr1[0], qr2[1])
expected.measure(qr2[0], cr[0])
expected.measure(qr1[0], cr[1])

pass_manager = PassManager()
pass_manager.append(
[OptimizeSwapBeforeMeasure(), DAGFixedPoint()],
do_while=lambda property_set: not property_set['dag_fixed_point'])
after = pass_manager.run(circuit)

self.assertEqual(expected, after)


if __name__ == '__main__':
unittest.main()