Add ContractIdleWiresInControlFlow optimisation pass

[jakelishman]

Summary

This transpiler pass removes data dependencies on idle qubits from control-flow operations. For example, given a circuit such as::

from qiskit.circuit import QuantumCircuit

qc = QuantumCircuit(1, 1)
qc.x(0)
with qc.if_test((qc.clbits[0], True)):
    qc.x(0)
    qc.x(0)
qc.x(0)

the current optimisation passes will collapse the inner control-flow block to the identity, but the qubit dependency will remain, preventing the outer two X gates from being cancelled. This pass removes the now-spurious dependency, making it possible to detect and remove the two X gates in a follow-up loop iteration.

As an accidental side-effect of their algorithms, the control-flow-aware routing passes currently do this when they run. This aims to move the logic into a suitable place to run before routing (so the spurious dependency never arises in routing in the first place) and in the low-level optimisation stage.

The aim of this pass is also to centralise the logic, so when the addition of the new box scope with different semantics around whether a wire is truly idle in the box or not, the routers aren't accidentally breaking them, and it's clearer when the modifications happen.

Details and comments

Built on top of #13774, since it's very convenient to have that method for writing the tests. This is one part of #13768.

I haven't hooked this up to the preset pass-managers in this commit; I wanted to do that after #13768 is fixed properly and potentially once box itself has landed.

[qiskit-bot]

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

• @Qiskit/terra-core

[coveralls]

Pull Request Test Coverage Report for Build 13156083905

Details

• 51 of 51 (100.0%) changed or added relevant lines in 3 files are covered.
• 11 unchanged lines in 4 files lost coverage.
• Overall coverage remained the same at 88.667%

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Files with Coverage Reduction	New Missed Lines	%
crates/accelerate/src/two_qubit_decompose.rs	1	92.08%
crates/accelerate/src/unitary_synthesis.rs	1	92.97%
crates/qasm2/src/lex.rs	3	92.23%
crates/qasm2/src/parse.rs	6	97.61%

Totals
Change from base Build 13154732632:	0.0%
Covered Lines:	79006
Relevant Lines:	89104

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💛 - Coveralls

[jakelishman]

Rebased over main and no longer on hold.