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@Qiskit/terra-core@kevinhartman@mtreinish
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Summary
Fixes #13081.
Details and comments
If a Sabre trial does not find a set of Swaps to route nodes, the "release valve" adds Swaps to route the two-qubit gate in between the the closest two qubits. In rare cases, this leads to more than one gate being routable, which was not handled correctly previously.
As I understand it this should only ever occur if the release-valve adds a single swap and we have a scenario like
If more than one swap gate is applied it should not be possible that two gates are routable, so the code now only checks for a second routable gate if we insert a single swap. If someone can find a counterexample we can change the code to check for any routable gate after the release valve 🙂
This is an automatic backport of pull request #13114 done by Mergify.