seed-sabre-with-layout-17d46e1a6f516b0e.yaml

---
features:
  - |
    Added support to the :class:`.SabreLayout` pass to add trials with specified
    starting layouts. The :class:`.SabreLayout` transpiler pass typically
    runs multiple layout trials that all start with fully random layouts which
    then use a routing pass to permute that layout instead of inserting swaps
    to find a layout which will result in fewer swap gates. This new feature
    enables running an :class:`.AnalysisPass` prior to :class:`.SabreLayout`
    which sets the ``"sabre_starting_layout"`` field in the property set
    to provide the :class:`.SabreLayout` with additional starting layouts
    to use in its internal trials. For example, if you wanted to run
    :class:`.DenseLayout` as the starting point for one trial in
    :class:`.SabreLayout` you would do something like::

        from qiskit.providers.fake_provider import FakeSherbrooke
        from qiskit.transpiler import AnalysisPass, PassManager
        from qiskit.transpiler.preset_passmanagers import generate_preset_pass_manager
        from qiskit.transpiler.passes import DenseLayout

        class SabreDenseLayoutTrial(AnalysisPass):

          def __init__(self, target):
              self.dense_pass = DenseLayout(target=target)
              super().__init__()

          def run(self, dag):
              self.dense_pass.run(dag)
              self.property_set["sabre_starting_layouts"] = [self.dense_pass.property_set["layout"]]

        backend = FakeSherbrooke()
        opt_level_1 = generate_preset_pass_manager(1, backend)
        pre_layout = PassManager([SabreDenseLayoutTrial(backend.target)])
        opt_level_1.pre_layout = pre_layout

    Then when the ``opt_level_1`` :class:`.StagedPassManager` is run with a circuit the output
    of the :class:`.DenseLayout` pass will be used for one of the :class:`.SabreLayout` trials
    in addition to the 5 fully random trials that run by default in optimization level 1.