Qiskit / qiskit / 27204478280

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Commit Message

Parallelize unitary synthesis (#16275)

* Parallelize unitary synthesis

This commit parallelizes the UnitarySynthesis transpiler pass to perform
the synthesis in parallel. The DAG recreation still needs to be done
serially. When in parallel mode it will collect all the synthesis
results into a HashMap mapping the node indices of the unitary gates
to the synthesis output. The the dag is iterated over serially in
topological order to rebuild the dag and if the node is in the hashmap
it will insert the synthesis output instead of copying the original
node. The serial path runs the synthesis as it iterates over the dag
for recreation as before performing synthesis whenever it encounters a
unitary gate node. This speeds up the runtime of the pass as the
synthesis step is typically the bottleneck of the pass and not the dag
manipulation.

* Remove drain method and use into_data_iter

* Correctly handle failure to synthesize a 1q unitary

* Add release note

* Document the pass is multithreaded

* Add test with ParameterVector phase

* Add docstring for enum result variants

* Use a const for the parallel threshold value

* Add docstrings for private helper functions

* Document arguments to internal run_unitary_synthesis function

* Ensure we use parallel mode for tests

The parallel mode of the pass only runs if there are >50 nodes to
execute. This commit updates a couple of tests to test the pass
in parallel mode. One was specifically intended to test it in this mode
but was not using enough gates to trigger the parallelism.

* Update test/python/transpiler/test_unitary_synthesis.py

Co-authored-by: Shelly Garion <46566946+ShellyGarion@users.noreply.github.com>

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Co-authored-by: Shelly Garion <46566946+ShellyGarion@users.noreply.github.com>

Coverage Stats

339 of 424 new or added lines in 5 files covered. (79.95%)

11 existing lines in 4 files now uncovered.

110660 of 126453 relevant lines covered (87.51%)

954265.66 hits per line