Fix InverseCancellation to run in classical blocks

[haimeng-zhang]

Fix issue #13437.

Summary

The InverseCancellation pass cancels pairs of gates that are inverses of each other; it now behaves as expected when running inside classical blocks of a control flow.

Details and comments

This PR fixed the bug reported in #13437 by adding the decorator @control_flow.trivial_recurse so that the pass can be iterated over all control-flow nodes.

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[coveralls]

Pull Request Test Coverage Report for Build 11965151140

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.009%) to 88.944%

---

Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/lex.rs	3	92.23%

Totals
Change from base Build 11957091507:	0.009%
Covered Lines:	79414
Relevant Lines:	89285

---

💛 - Coveralls

[kevinhartman]

Thanks for doing this!

Can you also add some tests? You can probably just more or less copy the tests we had for CXCancellation's control flow handling into test_inverse_cancellation.py.

qiskit/test/python/transpiler/test_cx_cancellation.py

Lines 146 to 199 in 94cea41

	def test_if_else(self):
	"""Test that the pass recurses in a simple if-else."""
	with self.assertWarns(DeprecationWarning):
	pass_ = CXCancellation()
	inner_test = QuantumCircuit(4, 1)
	inner_test.cx(0, 1)
	inner_test.cx(0, 1)
	inner_test.cx(2, 3)
	inner_expected = QuantumCircuit(4, 1)
	inner_expected.cx(2, 3)
	test = QuantumCircuit(4, 1)
	test.h(0)
	test.measure(0, 0)
	test.if_else((0, True), inner_test.copy(), inner_test.copy(), range(4), [0])
	expected = QuantumCircuit(4, 1)
	expected.h(0)
	expected.measure(0, 0)
	expected.if_else((0, True), inner_expected, inner_expected, range(4), [0])
	self.assertEqual(pass_(test), expected)
	def test_nested_control_flow(self):
	"""Test that collection recurses into nested control flow."""
	with self.assertWarns(DeprecationWarning):
	pass_ = CXCancellation()
	qubits = [Qubit() for _ in [None] * 4]
	clbit = Clbit()
	inner_test = QuantumCircuit(qubits, [clbit])
	inner_test.cx(0, 1)
	inner_test.cx(0, 1)
	inner_test.cx(2, 3)
	inner_expected = QuantumCircuit(qubits, [clbit])
	inner_expected.cx(2, 3)
	true_body = QuantumCircuit(qubits, [clbit])
	true_body.while_loop((clbit, True), inner_test.copy(), [0, 1, 2, 3], [0])
	test = QuantumCircuit(qubits, [clbit])
	test.for_loop(range(2), None, inner_test.copy(), [0, 1, 2, 3], [0])
	test.if_else((clbit, True), true_body, None, [0, 1, 2, 3], [0])
	expected_if_body = QuantumCircuit(qubits, [clbit])
	expected_if_body.while_loop((clbit, True), inner_expected, [0, 1, 2, 3], [0])
	expected = QuantumCircuit(qubits, [clbit])
	expected.for_loop(range(2), None, inner_expected, [0, 1, 2, 3], [0])
	expected.if_else((clbit, True), expected_if_body, None, [0, 1, 2, 3], [0])
	self.assertEqual(pass_(test), expected)

[haimengz]

Thanks for doing this!

Can you also add some tests? You can probably just more or less copy the tests we had for CXCancellation's control flow handling into test_inverse_cancellation.py.

qiskit/test/python/transpiler/test_cx_cancellation.py

Lines 146 to 199 in 94cea41

	def test_if_else(self):
	"""Test that the pass recurses in a simple if-else."""
	with self.assertWarns(DeprecationWarning):
	pass_ = CXCancellation()
	inner_test = QuantumCircuit(4, 1)
	inner_test.cx(0, 1)
	inner_test.cx(0, 1)
	inner_test.cx(2, 3)
	inner_expected = QuantumCircuit(4, 1)
	inner_expected.cx(2, 3)
	test = QuantumCircuit(4, 1)
	test.h(0)
	test.measure(0, 0)
	test.if_else((0, True), inner_test.copy(), inner_test.copy(), range(4), [0])
	expected = QuantumCircuit(4, 1)
	expected.h(0)
	expected.measure(0, 0)
	expected.if_else((0, True), inner_expected, inner_expected, range(4), [0])
	self.assertEqual(pass_(test), expected)
	def test_nested_control_flow(self):
	"""Test that collection recurses into nested control flow."""
	with self.assertWarns(DeprecationWarning):
	pass_ = CXCancellation()
	qubits = [Qubit() for _ in [None] * 4]
	clbit = Clbit()
	inner_test = QuantumCircuit(qubits, [clbit])
	inner_test.cx(0, 1)
	inner_test.cx(0, 1)
	inner_test.cx(2, 3)
	inner_expected = QuantumCircuit(qubits, [clbit])
	inner_expected.cx(2, 3)
	true_body = QuantumCircuit(qubits, [clbit])
	true_body.while_loop((clbit, True), inner_test.copy(), [0, 1, 2, 3], [0])
	test = QuantumCircuit(qubits, [clbit])
	test.for_loop(range(2), None, inner_test.copy(), [0, 1, 2, 3], [0])
	test.if_else((clbit, True), true_body, None, [0, 1, 2, 3], [0])
	expected_if_body = QuantumCircuit(qubits, [clbit])
	expected_if_body.while_loop((clbit, True), inner_expected, [0, 1, 2, 3], [0])
	expected = QuantumCircuit(qubits, [clbit])
	expected.for_loop(range(2), None, inner_expected, [0, 1, 2, 3], [0])
	expected.if_else((clbit, True), expected_if_body, None, [0, 1, 2, 3], [0])
	self.assertEqual(pass_(test), expected)

Done! Please kindly review.