Retain all deprecated Bit properties in QPY roundtrip (backport #9525)
#9603
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
![mergify[bot]](https://avatars.githubusercontent.com/in/10562?s=60&v=4){kind=small}
* Retain more deprecated Bit properties in QPY roundtrip A major bugfix for QPY's handling of loose circuit bits in c0ac5fb (gh-9095) caused the deprecated bit properties `index` and `register` to be lost after the QPY roundtrip. As far as Terra's data model is concerned, the two circuits would still compare equal after this loss; the output registers would still be equal to the inputs, and bit equality is not considered directly since it general bit instances are not expected to be equal between circuits. Losing this information caused some downstream issues for the IBM runtime, which was still relying on `Bit.index` working in some cases, despite it issuing a deprecating warning since Terra 0.17 (April 2021). While this can be corrected downstream, QPY can still do a better job of roundtripping the deprecated information while it is still present. The QPY format does not currently store enough information to _completely_ roundtrip this information in cases that some but not all owned bits from a register are present in the circuit. (This partial data is a decent part of the cause of the bugs that gh-9095 fixed.) Since this is just in the support of deprecated functionality that Terra's data model does not even require for circuit equality (QPY's goal), it seems not worth it to produce a new QPY binary format version to store this, when the deprecated properties being removed would obsolete the format again immediately. * Fix lint * Correct deprecated bit information in QPY This allows complete round-tripping of all the deprecated register+index information in the `Bit` instances through QPY, restoring us to the _intended_ behaviour before gh-9095. The behaviour in the dumper before that did not allow full reconstruction, because some of the information was lost for bits that were encountered in more than one register. This fixes the dumper to always output all the indexing information for all bits, not to use `-1` whenever a bit _is_ in the circuit but has previously been encountered. The `standalone` field on a register is sufficient to tell whether the bits contained in it should have their "owner" information set; it's not possible (in valid Qiskit code) to have a register that owns only _some_ of its bits. To accomodate this, the register reader now needs to be two-pass. * Add deprecated-bit checks to backwards compatibility tests * Rewrite release note * Improve internal documentation --------- Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com> (cherry picked from commit b6aba59)
|
Thank you for opening a new pull request. Before your PR can be merged it will first need to pass continuous integration tests and be reviewed. Sometimes the review process can be slow, so please be patient. While you're waiting, please feel free to review other open PRs. While only a subset of people are authorized to approve pull requests for merging, everyone is encouraged to review open pull requests. Doing reviews helps reduce the burden on the core team and helps make the project's code better for everyone. One or more of the the following people are requested to review this:
|
jakelishman
approved these changes
Feb 16, 2023
jakelishman
added
Changelog: Bugfix
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
This is an automatic backport of pull request #9525 done by Mergify.
Mergify commands and options
More conditions and actions can be found in the documentation.
You can also trigger Mergify actions by commenting on this pull request:
@Mergifyio refreshwill re-evaluate the rules@Mergifyio rebasewill rebase this PR on its base branch@Mergifyio updatewill merge the base branch into this PR@Mergifyio backport <destination>will backport this PR on<destination>branchAdditionally, on Mergify dashboard you can:
Finally, you can contact us on https://mergify.com