Implement __eq__ for remaining standard-library gates except mcx

[jakelishman]

Summary

Most standard-library gates had a specialised __eq__ added in gh-11370, but a small number were left over. This adds specialisation to almost all the stragglers, which were mostly old soft-deperecated gates. Despite not appearing in most circuits, these gates have an outsized effect on equality comparisons if they ever do appear, because they involve construction of entire definition fields.

Details and comments

You can see the improvement here in the OQ3 exporter for circuits containing some of the affected gates; it uses gate equality at one part of the symbol lookup. For example, given this circuit:

from qiskit.circuit.random import random_circuit
from qiskit import qasm3

circ = random_circuit(200, 200, seed=42)

The time of qasm3.dumps(circ) on my machine went from about 1.15(2)s to 0.76(2)s with this PR, despite only about 9% of the gates in the circuit being affected by this PR.

[qiskit-bot]

One or more of the following people are relevant to this code:

• @Cryoris
• @Qiskit/terra-core
• @ajavadia

[coveralls]

Pull Request Test Coverage Report for Build 11351094849

Details

• 16 of 16 (100.0%) changed or added relevant lines in 5 files are covered.
• 14 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+0.01%) to 88.665%

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Files with Coverage Reduction	New Missed Lines	%
qiskit/transpiler/passes/synthesis/unitary_synthesis.py	2	88.19%
crates/qasm2/src/lex.rs	5	92.23%
qiskit/synthesis/two_qubit/xx_decompose/decomposer.py	7	90.77%

Totals
Change from base Build 11349069953:	0.01%
Covered Lines:	73185
Relevant Lines:	82541

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💛 - Coveralls

[Cryoris]

LGTM 👍🏻

Just two questions:

• Would it make sense to move __eq__ just to Gate and ControlledGate (with the two special cases of MCPhase/U1 that adds the num_ctrl_qubits check)?
• I assume you didn't add it to MCX due to all the different gate flavors, right? If yes then we should remember to add this once the flavors are gone and we just have the MCXGate block 🙂

[jakelishman]

The trouble is that these specialised __eq__ methods need to be opt-in, when the type is certain that there are no other modifications. The base Gate and ControlledGate can't know that it's safe to override this; they won't know how the _define method is implemented, so they need to fail safer (which is actually what they do). These checks don't need to assert tests on the definitions, because they can know equality without creating them.

For mcx: yeah, I didn't want to get into the can of worms of all the different variants, and what should be considered == between them.