Sorts gate array to have deterministic gate selection

[amruthpremjith]

AI/LLM disclosure

• I didn't use LLM tooling, or only used it privately.
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Fix #16138

Sort the gate array before selecting from it to return the same gates for the same set of inputs.

Tested with and without changes.

from qiskit.circuit.random.utils import random_clifford_circuit

cliff_circuit = random_clifford_circuit(num_qubits=10, num_gates=100, gates="all", seed=0)
print(cliff_circuit.count_ops())

Without change

(venv) amruthpremjith@MacBookPro qiskit % python3 test-6.py 
OrderedDict({'x': 10, 'h': 10, 'iswap': 9, 'cz': 9, 'z': 9, 's': 8, 'cy': 8, 'sx': 6, 'ecr': 6, 'cx': 6, 'dcx': 4, 'swap': 4, 'sdg': 4, 'y': 3, 'id': 3, 'sxdg': 1})
(venv) amruthpremjith@MacBookPro qiskit % python3 test-6.py
OrderedDict({'h': 10, 'sxdg': 10, 'iswap': 9, 'cz': 9, 'sdg': 9, 'z': 8, 'cy': 8, 'x': 6, 'ecr': 6, 'cx': 6, 'dcx': 4, 'swap': 4, 'sx': 4, 'id': 3, 'y': 3, 's': 1})

With change

(venv) amruthpremjith@MacBookPro qiskit % python3 test-6.py
OrderedDict({'z': 10, 'x': 10, 'ecr': 9, 'cy': 9, 'h': 9, 'sx': 8, 'cz': 8, 'id': 6, 'iswap': 6, 'cx': 6, 'swap': 4, 'dcx': 4, 'sxdg': 4, 's': 3, 'y': 3, 'sdg': 1})
(venv) amruthpremjith@MacBookPro qiskit % python3 test-6.py
OrderedDict({'z': 10, 'x': 10, 'ecr': 9, 'cy': 9, 'h': 9, 'sx': 8, 'cz': 8, 'id': 6, 'iswap': 6, 'cx': 6, 'swap': 4, 'dcx': 4, 'sxdg': 4, 's': 3, 'y': 3, 'sdg': 1})

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[alexanderivrii]

Thanks! That was fast. Do you think there is any meaningful test we could add? Could you also add a (short) bugfix release note?

[amruthpremjith]

Sure, maybe we can add a test case that runs it twice and compares the gate count?

[jakelishman]

The randomisation of set with string keys is fixed by PYTHONHASHSEED, which is only read/set once during initialisation of the Python interpreter, so just doing the same thing twice in the same process would pass without this change. We can test either by comparing a decent-sized circuit to a "blessed" value, or by spawning separate interpreters with different PYTHONHASHSEEDs and ensuring they come back the same.

[jakelishman]

sorted is perhaps a bit unnecessarily heavy as a normalisation step; dict is already consistently ordered (including the dict_keys iterator), so the sort of gates_2q isn't needed, and the top line can be something along the lines of

ignore_1q = {"v", "w", "id", "iden", "sinv"}
gates_1q = [gate for gate in _BASIS_1Q if gate not in ignore_1q]

and avoid the extra $\lg n$. (Not that this would be performance critical, but still.)

[amruthpremjith]

I updated it to the snippet you mentioned, I was thinking it was straightforward to just sort it it to be consistent across any changes in the source dictionary as well.

[alexanderivrii]

Lol, Jake beat me at replying :)

[coveralls]

Coverage Report for CI Build 25374288175

Coverage decreased (-0.01%) to 87.587%

Details

• Coverage decreased (-0.01%) from the base build.
• Patch coverage: 2 of 2 lines across 1 file are fully covered (100%).
• 20 coverage regressions across 4 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

20 previously-covered lines in 4 files lost coverage.

File	Lines Losing Coverage	Coverage
crates/circuit/src/parameter/symbol_expr.rs	8	73.93%
crates/qasm2/src/parse.rs	6	97.63%
crates/qasm2/src/lex.rs	5	91.77%
crates/circuit/src/parameter/parameter_expression.rs	1	90.53%

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Coverage Stats

Relevant Lines:	121826
Covered Lines:	106704
Line Coverage:	87.59%
Coverage Strength:	963202.31 hits per line

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💛 - Coveralls

[amruthpremjith]

I added a test case that passes in different seeds to a subprocess, without the change the test case failed and it was passing with it.