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 12038891561

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 18 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.02%) to 88.934%

---

Files with Coverage Reduction	New Missed Lines	%
crates/accelerate/src/unitary_synthesis.rs	1	92.2%
crates/qasm2/src/lex.rs	5	91.73%
crates/qasm2/src/parse.rs	12	97.15%

Totals
Change from base Build 12038603859:	-0.02%
Covered Lines:	79405
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.

[mtreinish]

The code and test LGTM, thanks for doing this! Before we merge it though do you mind adding a release note to document this fix was included in the next release? The process to do this is documented here: https://github.com/Qiskit/qiskit/blob/main/CONTRIBUTING.md#release-notes

[mtreinish]

LGTM, thanks for adding the release note so quickly.

[mtreinish]

I'd probably word this as "recurse into control flow blocks in the circuit". But we can also do this as part of the release prep PR #13447

[haimeng-zhang]

Thank you for the suggestion! Is there a way that I can still fix this, either in this PR or the release prep PR #13447?

[mtreinish]

If you have a suggested alternative wording you can let @raynelfss know, I asked him to just update the text as part of the other release note editing he's working on in #13447.

In general we're not too picky about the exact release note content in PR reviews and as there are always a fair amount of edits needed before we can publish them. So it's simple for whoever is driving a given release to just copy-edit the text of a release note all at once in that final PR for a release.

[1ucian0]

@Mergifyio backport stable/1.4

[mergify]

backport stable/1.4

❌ No backport have been created

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