Qiskit / qiskit / 9024231968

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Commit Message

Fix runtime scaling of StarPreRouting pass (#12376) (#12382)

This commit fixes a runtime performance scaling issue with the new
StarPreRouting pass. If there are any stars identified by the pass when
the pass goes to pre-route those star connectivity blocks it specifies a
custom lexicographical topological sort key to ensure the stars are
kept together in the sort. However the mechanism by which this sort key
was generated scaled quadratically with the number of DAG nodes in the
identified stars. This ended up being a large runtime performance
bottleneck. This commit fixes this issue by pre-computing the sort key
for all nodes in the stars and putting that in a dictionary so that when
we call rustworkx to perform the topological sort the sort key callback
does not become the bottleneck for the entire pass.

(cherry picked from commit 4a6c57044)

Co-authored-by: Matthew Treinish <mtreinish@kortar.org>

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