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[CQT-484] Two qubit gates merge filters identities #723

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Merged
davidbakker123 merged 3 commits into from
Oct 22, 2026
Merged

[CQT-484] Two qubit gates merge filters identities #723

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90a4332
added fix
Oct 22, 2026
8d068c5
Don't filter out non-gates
Oct 22, 2026
cbc0b40
Process review comments; remove old checks
Oct 22, 2026
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13 changes: 6 additions & 7 deletions opensquirrel/passes/merger/two_qubit_gates_merger.py
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Original file line number Diff line number Diff line change
Expand Up @@ -167,18 +167,17 @@ def merge(self, ir: IR, qubit_register_size: int) -> None:

"""
graph = build_graph(ir)
if len(graph.nodes) == 1:
return

groups = group_gates(graph)
statements = []

for group in groups:
statement_indices, qubit_indices = group
if len(qubit_indices) == 2 and len(statement_indices) > 1:
merged_gate = _merge_gate_group(ir, group)
statements.append(merged_gate)
if len(qubit_indices) == 2:
statement = _merge_gate_group(ir, group)
else:
statements.append(ir.statements[statement_indices.pop()])
statement = ir.statements[statement_indices.pop()]

if not (isinstance(statement, Gate) and statement.is_identity()):
statements.append(statement)

ir.statements = statements
8 changes: 7 additions & 1 deletion tests/passes/merger/test_two_qubit_gates_merger.py
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Original file line number Diff line number Diff line change
Expand Up @@ -179,7 +179,6 @@ def merger() -> TwoQubitGatesMerger:
(CircuitBuilder(1).H(0).to_circuit(), CircuitBuilder(1).H(0).to_circuit()),
(CircuitBuilder(2).CNOT(0, 1).to_circuit(), CircuitBuilder(2).CNOT(0, 1).to_circuit()),
(CircuitBuilder(2).CNOT(0, 1).CNOT(1, 0).CNOT(0, 1).to_circuit(), CircuitBuilder(2).SWAP(0, 1).to_circuit()),
(CircuitBuilder(2).SWAP(0, 1).SWAP(0, 1).to_circuit(), CircuitBuilder(2).I(0).to_circuit()),
(CircuitBuilder(2).SWAP(0, 1).CZ(0, 1).S(0).S(1).to_circuit(), CircuitBuilder(2).ISWAP(0, 1).to_circuit()),
(CircuitBuilder(2).H(1).CNOT(0, 1).H(1).to_circuit(), CircuitBuilder(2).CZ(0, 1).to_circuit()),
(CircuitBuilder(2).CV(0, 1).CV(0, 1).to_circuit(), CircuitBuilder(2).CNOT(0, 1).to_circuit()),
Expand Down Expand Up @@ -296,3 +295,10 @@ def test_two_qubit_gates_merger_with_non_instructions(
"Both should be either TwoQubitGate or SingleQubitGate."
)
raise TypeError(msg)


def test_two_qubit_gates_merger_filters_out_identity_gates(merger: TwoQubitGatesMerger) -> None:
circuit = CircuitBuilder(2).SWAP(0, 1).SWAP(0, 1).to_circuit()
merger.merge(circuit.ir, circuit.qubit_register_size)

assert len(circuit.ir.statements) == 0
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