🎨 Retain register name by simon1hofmann · Pull Request #2014 · munich-quantum-toolkit/core

simon1hofmann · 2026-08-06T11:18:59Z

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Description

This PR retains source-level qubit-register names across the QC and QCO MLIR dialects. The builders attach non-empty names to the backing memref.alloc or qtensor.alloc using the mqt.qubit_register_name string attribute and reject duplicate non-empty names.

The attribute is populated by the QuantumComputation and typed OpenQASM translations, preserved by the QC-to-QCO and QCO-to-QC conversions, and reused for OpenQASM emission when it is a valid, unique OpenQASM identifier. Invalid or conflicting names fall back to generated identifiers. QIR emission remains unchanged because quantum-register names have no corresponding QIR runtime recording semantics.

Codex materially assisted with implementation, tests, review preparation, conflict resolution, and validation. The human author remains responsible for the contribution.

Fixes #1616.

Checklist

The pull request only contains commits that are focused and relevant to this change.
I have added appropriate tests that cover the new/changed functionality.
I have updated the documentation to reflect these changes.
I have added entries to the changelog for any noteworthy additions, changes, fixes, or removals.
I have added migration instructions to the upgrade guide (if needed).
The changes follow the project's style guidelines and introduce no new warnings.
The changes are fully tested and pass the CI checks.
I have reviewed my own code changes.

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codecov · 2026-08-06T11:45:23Z

Codecov Report

✅ All modified and coverable lines are covered by tests.

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simon1hofmann · 2026-08-06T11:50:36Z

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coderabbitai · 2026-08-06T11:50:41Z

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coderabbitai · 2026-08-06T11:54:02Z

📝 Walkthrough

Summary by CodeRabbit

New Features
- Quantum register allocations can retain source-level names.
- Register names are preserved across QC/QCO conversions and generated program metadata.
- OpenQASM output reuses declared register names.
- Duplicate non-empty register names are rejected.
Bug Fixes
- Improved translation fidelity for named quantum registers.
Tests
- Added coverage for name preservation, output generation, and duplicate-name validation.
Documentation
- Updated the unreleased changelog with the latest infrastructure contribution and reference.

Walkthrough

The change preserves quantum-register names across QC and QCO allocation, conversion, and translation paths. Named allocations store mqt.quantum_register_name. Duplicate names are rejected, and OpenQASM3 reuses valid stored names.

Changes

Quantum register name propagation

Layer / File(s)	Summary
Named allocation contract and storage `mlir/include/mlir/Dialect/Utils/Utils.h`, `mlir/include/mlir/Dialect/QC/Builder/QCProgramBuilder.h`, `mlir/include/mlir/Dialect/QCO/Builder/QCOProgramBuilder.h`, `mlir/lib/Dialect/QC/Builder/QCProgramBuilder.cpp`, `mlir/lib/Dialect/QCO/Builder/QCOProgramBuilder.cpp`	QC and QCO allocation APIs accept optional names. Named allocations store `mqt.quantum_register_name`. Duplicate non-empty names are rejected.
Translation and conversion propagation `mlir/lib/Conversion/`, `mlir/lib/Dialect/QC/Translation/`	Translation passes source names to allocation APIs. QC/QCO conversions copy the name attribute. OpenQASM3 uses valid stored names and generates unique fallback names.
Regression validation and changelog `mlir/unittests/Conversion/`, `mlir/unittests/Dialect/QC/`, `mlir/unittests/Dialect/QCO/*`, `CHANGELOG.md`	Tests verify name retention, OpenQASM emission, and duplicate-name diagnostics. The changelog records PR `#2014`.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Sequence Diagram(s)

sequenceDiagram
  participant SourceRegister
  participant Translation
  participant AllocationBuilder
  participant Conversion
  participant OpenQASM3
  SourceRegister->>Translation: provide register name
  Translation->>AllocationBuilder: allocate register with name
  AllocationBuilder->>AllocationBuilder: validate uniqueness
  AllocationBuilder-->>Translation: return allocation with name attribute
  Conversion->>Conversion: copy name attribute
  OpenQASM3->>Conversion: read stored register name
  Conversion-->>OpenQASM3: emit named register

Possibly related PRs

munich-quantum-toolkit/core#1580: Both changes modify QC/QCO register allocation APIs and register representation.
munich-quantum-toolkit/core#1623: Both changes modify quantum allocation metadata in QC/QCO conversion paths.
munich-quantum-toolkit/core#1627: Both changes modify qubit-register allocation APIs and translation call sites.

Suggested reviewers: burgholzer, denialhaag

Poem

A rabbit gives each register a name,
QC and QCO carry the same.
Through conversion, labels stay bright,
OpenQASM prints them right.
Duplicate names? Not in sight!

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 6.06% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The implementation preserves quantum-register names with the requested memref attribute and adds regression tests for the linked issue [`#1616`].
Out of Scope Changes check	✅ Passed	The changes consistently support quantum-register name preservation across builders, conversions, translations, emission, and tests.
Title check	✅ Passed	The title clearly and concisely describes the main change: retaining quantum register names.
Description check	✅ Passed	The description covers the change, motivation, issue, testing, changelog, AI disclosure, and checklist status.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

Create stacked PR
Commit on current branch

✨ Simplify code

Create PR with simplified code
Commit simplified code in branch codex/1616-retain-quantum-register-name

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burgholzer

This looks like a great start.

Just a few quick side comments:

does the OpenQASM importer already do this? Feels like it should also preserve the name.
is this attribute retained across dialect conversions? Ideally, it would propagate through the QCO conversion and lead to a nice OpenQASM roundtrip. (Maybe this is already handled though)
is there anything to do for QIR emission? (Both on classical and quantum registers)
is there anything to do for the OpenQASM emission?

denialhaag

Thanks a lot for getting this started, @simon1hofmann! 🙂

Below, you can find two things that jumped out to me. In addition to that, I agree with @burgholzer's comment above. I would expect some changes in the OpenQASM translations and the QIR conversions to be necessary. 🤔

simon1hofmann · 2026-08-06T14:37:19Z

This looks like a great start.

Just a few quick side comments:

does the OpenQASM importer already do this? Feels like it should also preserve the name.

is this attribute retained across dialect conversions? Ideally, it would propagate through the QCO conversion and lead to a nice OpenQASM roundtrip. (Maybe this is already handled though)

is there anything to do for QIR emission? (Both on classical and quantum registers)

is there anything to do for the OpenQASM emission?

You're right, these should be added as well.

Concerning QIR emission, __quantum__rt__qubit_allocate_array only expects a size parameter (https://www.qir-alliance.org/qir-runner/qir_backend/fn.__quantum__rt__qubit_allocate_array.html). Should we add custom metadata or just ~~emit~~ omit the name?

denialhaag · 2026-08-06T14:46:14Z

Concerning QIR emission, __quantum__rt__qubit_allocate_array only expects a size parameter (https://www.qir-alliance.org/qir-runner/qir_backend/fn.__quantum__rt__qubit_allocate_array.html). Should we add custom metadata or just emit the name?

I think you are right; register names only make sense for classical registers in the context of output recording. 🤔

burgholzer · 2026-08-06T15:21:33Z

Concerning QIR emission, __quantum__rt__qubit_allocate_array only expects a size parameter (https://www.qir-alliance.org/qir-runner/qir_backend/fn.__quantum__rt__qubit_allocate_array.html). Should we add custom metadata or just emit the name?

I think you are right; register names only make sense for classical registers in the context of output recording. 🤔

yeah. for QIR emission, quantum registers do not really matter 👍🏼

simon1hofmann · 2026-08-06T15:41:39Z

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coderabbitai · 2026-08-06T15:41:45Z

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simon1hofmann · 2026-08-06T16:01:40Z

@coderabbitai full review

coderabbitai · 2026-08-06T16:01:47Z

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@mlir/unittests/Dialect/QC/Translation/test_openqasm3_emission.cpp`:
- Around line 530-545: Extend ReusesQuantumRegisterNames with an invalid stored
register name, then require strict OpenQASM parsing of the emitted result.
Assert the output does not declare the invalid name while preserving the
existing valid-name assertion.

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ℹ️ Review info

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Run ID: ce584dc3-5254-4e6c-aed3-fda634cf5aca

📥 Commits

Reviewing files that changed from the base of the PR and between 52cf1e7 and cb20786.

📒 Files selected for processing (18)

CHANGELOG.md
mlir/include/mlir/Dialect/QC/Builder/QCProgramBuilder.h
mlir/include/mlir/Dialect/QCO/Builder/QCOProgramBuilder.h
mlir/include/mlir/Dialect/Utils/Utils.h
mlir/lib/Conversion/QCOToQC/QCOToQC.cpp
mlir/lib/Conversion/QCToQCO/QCToQCO.cpp
mlir/lib/Dialect/QC/Builder/QCProgramBuilder.cpp
mlir/lib/Dialect/QC/Translation/OpenQASMToQCEmitter.cpp
mlir/lib/Dialect/QC/Translation/TranslateQCToOpenQASM3.cpp
mlir/lib/Dialect/QC/Translation/TranslateQuantumComputationToQC.cpp
mlir/lib/Dialect/QCO/Builder/QCOProgramBuilder.cpp
mlir/unittests/Conversion/QCOToQC/test_qco_to_qc.cpp
mlir/unittests/Conversion/QCToQCO/test_qc_to_qco.cpp
mlir/unittests/Dialect/QC/IR/test_qc_ir.cpp
mlir/unittests/Dialect/QC/Translation/test_openqasm3_emission.cpp
mlir/unittests/Dialect/QC/Translation/test_qasm3_translation.cpp
mlir/unittests/Dialect/QC/Translation/test_quantum_computation_translation.cpp
mlir/unittests/Dialect/QCO/IR/test_qco_ir.cpp

simon1hofmann · 2026-08-06T16:32:22Z

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coderabbitai · 2026-08-06T16:32:28Z

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denialhaag

This looks really clean to me now! I have three more comments, but I'll already now to not blcok the PR further. I'll leave the final say to @burgholzer. 😌

Co-authored-by: Daniel Haag <121057143+denialhaag@users.noreply.github.com> Signed-off-by: simon1hofmann <119581649+simon1hofmann@users.noreply.github.com>

…ntracked tensor initialization

…st for untracked tensor initialization" This reverts commit 4627ded.

denialhaag · 2026-08-07T14:48:22Z

Just as a reminder for ourselves: Depending on which of #2014 and #2017 gets merged second, we can mark it as fixing #1614. 🎉

# Conflicts: # CHANGELOG.md # mlir/unittests/Dialect/QC/Translation/test_quantum_computation_translation.cpp

burgholzer

This looks very clean now. I'll quickly push a PR resolving the conflicts, then tag this for auto-merge! 🥳

Signed-off-by: Daniel Haag <121057143+denialhaag@users.noreply.github.com>

🎨 Retain register name

3b49e00

simon1hofmann self-assigned this Aug 6, 2026

simon1hofmann added enhancement Improvement of existing feature c++ Anything related to C++ code MLIR Anything related to MLIR labels Aug 6, 2026

simon1hofmann added this to the MLIR Support milestone Aug 6, 2026

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simon1hofmann marked this pull request as ready for review August 6, 2026 12:01

simon1hofmann requested a review from denialhaag August 6, 2026 12:01

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Comment thread mlir/include/mlir/Dialect/QC/Builder/QCProgramBuilder.h

Comment thread mlir/lib/Dialect/QC/Builder/QCProgramBuilder.cpp

✨ Add register name to QCO and conversions

6d41e93

simon1hofmann added 2 commits August 6, 2026 16:47

🎨 Remove added empty line

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🚨 Fix linter warnings

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Comment thread mlir/unittests/Dialect/QC/Translation/test_openqasm3_emission.cpp Outdated

🐇 Address rabbits comments

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simon1hofmann requested a review from denialhaag August 6, 2026 16:33

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Comment thread mlir/include/mlir/Dialect/Utils/Utils.h Outdated

Comment thread mlir/include/mlir/Dialect/QC/Builder/QCProgramBuilder.h Outdated

Comment thread mlir/unittests/Conversion/QCToQCO/test_qc_to_qco.cpp

denialhaag requested a review from burgholzer August 6, 2026 18:21

Simon and others added 6 commits August 6, 2026 23:03

🎨 Rename quantum to qubit register

2c77c86

Update mlir/unittests/Conversion/QCToQCO/test_qc_to_qco.cpp

6184b74

Co-authored-by: Daniel Haag <121057143+denialhaag@users.noreply.github.com> Signed-off-by: simon1hofmann <119581649+simon1hofmann@users.noreply.github.com>

Trigger CI

c1916a5

☂️ Increase coverage

6a30686

✨ Validate tensor values in QCOProgramBuilder and add unit test for u…

4627ded

…ntracked tensor initialization

Revert "✨ Validate tensor values in QCOProgramBuilder and add unit te…

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…st for untracked tensor initialization" This reverts commit 4627ded.

denialhaag mentioned this pull request Aug 7, 2026

✨ Enhance QCOProgramBuilder with tracked qubit and tensor structures #2017

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Merge remote-tracking branch 'origin/main' into agent/review-pr-2014

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# Conflicts: # CHANGELOG.md # mlir/unittests/Dialect/QC/Translation/test_quantum_computation_translation.cpp

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Merge branch 'main' into codex/1616-retain-quantum-register-name

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Signed-off-by: Daniel Haag <121057143+denialhaag@users.noreply.github.com>

🎨 pre-commit fixes

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burgholzer deleted the codex/1616-retain-quantum-register-name branch August 10, 2026 14:15

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Summary by CodeRabbit

Walkthrough

Changes

Sequence Diagram(s)

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