Qiskit / qiskit / 15079260336

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Committed by web-flow

Commit Message

Revert "Port star_preroute to rust" (#14381)

* Revert "Port star_preroute to rust"

This commit reverts the move of star prerouting to run in Rust. At the
time of this commit it was before the majority of the transpiler
infrastructure was ported to rust. At that time the pass was ported we
had a few one off passes that were ported to rust and we had to manage
the Python rust boundary carefully. The pattern was typically to define
custom rust data types that provided an alternate view of the
DAGCircuit and the target for compilation that was built out of the
Python space dag and target. The star prerouting pass was ported to
Rust and leveraged the existing infrastructure used by SabreSwap and
SabreLayout as the function of the pass on a DAG was very similar to
Sabre (finding where to insert swaps and rebuilding the dag where
swaps are needed). At the time this was a pragmatic choice to
accelerate the pass and not need to wait for the needed infrastructure
to be written in Rust. However in practice the performance gains the
Rust porting of the algorithm provided were not as large as was
originally hoped and now the code of the pass is tied directly to
the current implementation of sabre. As the sabre interface layer is
being re-written in #14317 this is proving to be a blocker for that
effort. This commit reverts the current rust implementation to unblock
the sabre refactoring effort.

It's still definitely worth porting this pass to Rust but we now have
sufficient infrastructure in Rust to write full transpiler passes
without Python. We should follow up this PR and rewrite the star
prerouting pass so that full pass operates completely in rust and
directly leverages the native data structures that exist in Rust now
instead of the hybrid approach that ties the is tightly coupled to the
internals of the sabre pass.

This reverts commit b23c54523.

* Add back reverted alt text for plot in docs

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