✨ Add replaceWithAdditionalQubits utility function to qco.if

[MatthiasReumann]

Description

Adds the analog of MLIR's replaceWithreplaceWithAdditionalIterOperands to the qco::IfOp.

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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• I have disclosed the use of AI tools in the PR description as per our AI Usage Guidelines.
• AI-assisted commits include an Assisted-by: [Model Name] via [Tool Name] footer.
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[MatthiasReumann]

@coderabbitai full review

[coderabbitai]

✅ Action performed

Full review finished.

[coderabbitai]

📝 Walkthrough

Walkthrough

Adds a new IfOp::replaceWithAdditionalQubits helper in QCOOps.td and IfOp.cpp that creates a replacement qco.if with extra qubit operands and updated branch yields. Updates CHANGELOG.md with the PR citation and link.

Changes

IfOp qubit expansion

Layer / File(s)	Summary
IfOp interface declaration mlir/include/mlir/Dialect/QCO/IR/QCOOps.td	Declares IfOp::replaceWithAdditionalQubits(RewriterBase&, ValueRange) as a C++ extra class method with documentation.
IfOp replacement implementation mlir/lib/Dialect/QCO/IR/SCF/IfOp.cpp	Implements the method: builds a new IfOp with combined qubit operands, merges then/else blocks with expanded arguments, and rewrites YieldOp terminators to yield additional qubit values.
Changelog entry CHANGELOG.md	Adds #1872 to the Unreleased → Added citation line and the PR links section.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• munich-quantum-toolkit/core#1506: Both PRs modify the QCO IfOp implementation in QCOOps.td/SCF/IfOp.cpp, with #1506 introducing the base semantics extended here.

Suggested labels: feature

Suggested reviewers: burgholzer

Poem

A rabbit hops through branches two,
Then and else, both bend anew,
Extra qubits join the yield,
New IfOp born upon the field,
Hop, hop, hooray — the code compiles true! 🐇✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title is concise and accurately names the new replaceWithAdditionalQubits utility for qco.if.
Description check	✅ Passed	The description includes a clear summary and the required checklist, and the omitted issue/dependency details appear acceptable here.

✨ Finishing Touches

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch enh/qco-if-extend-qubits-func

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[coderabbitai]

Actionable comments posted: 2

🤖 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/lib/Dialect/QCO/IR/SCF/IfOp.cpp`:
- Around line 360-361: The insertion point set on the YieldOp is redundant
because replaceOpWithNewOp<YieldOp>(yield, newResults) already inserts the new
op at the erased op’s location. Remove the unnecessary
rewriter.setInsertionPoint(yield) call in the IfOp lowering path and leave the
replacement call as the only insertion-site logic.
- Around line 340-343: The new region block in IfOp::create/rewriting currently
hardcodes every block argument to QubitType, which breaks qtensor operands and
causes a type mismatch with qco.if’s Variadic<LinearType> signature. Update the
block creation to preserve the original operand types by using inits.getTypes()
when building the argument type list, so the region arguments match the
operand/result types for both qubits and qtensors.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 47b3d03e-7dd0-4086-926c-8e136383c065

📥 Commits

Reviewing files that changed from the base of the PR and between 0cb7894 and a31907f.

📒 Files selected for processing (3)

• CHANGELOG.md
• mlir/include/mlir/Dialect/QCO/IR/QCOOps.td
• mlir/lib/Dialect/QCO/IR/SCF/IfOp.cpp

[MatthiasReumann]

@coderabbitai full review

[coderabbitai]

✅ Action performed

Full review finished.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 27 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
mlir/lib/Dialect/QCO/IR/SCF/IfOp.cpp	0.0%	27 Missing ⚠️

📢 Thoughts on this report? Let us know!

[MatthiasReumann]

@burgholzer

Should we add an additional test-suite for this function or rely on the usage of the function in #1870 for coverage?

[burgholzer]

@burgholzer

Should we add an additional test-suite for this function or rely on the usage of the function in #1870 for coverage?

Let's rely on #1870. 👍🏼

[burgholzer]

Just a couple of smaller comments. Generally LGTM

[MatthiasReumann]

@coderabbitai full review

[coderabbitai]

✅ Action performed

Full review finished.

[coderabbitai]

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/lib/Dialect/QCO/IR/SCF/IfOp.cpp`:
- Around line 345-373: Replace the original IfOp before returning the new one in
the IfOp::replace/clone flow: processRegion correctly migrates the then/else
bodies into newIfOp, but the old op is never rewritten, so existing uses still
reference its results. Update the logic around processRegion and the final
return to call rewriter.replaceOp on the current IfOp with the corresponding
results from newIfOp, or otherwise ensure the caller performs that replacement
consistently.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: b1a67669-b1e7-4162-8028-772f9bf73d1a

📥 Commits

Reviewing files that changed from the base of the PR and between ca33c41 and ebb4254.

📒 Files selected for processing (3)

• CHANGELOG.md
• mlir/include/mlir/Dialect/QCO/IR/QCOOps.td
• mlir/lib/Dialect/QCO/IR/SCF/IfOp.cpp

[burgholzer]

Pushed one commit that simplifies part of the implementation a bit.
Feel free to merge if you agree with the implementation and the CI is green.

[MatthiasReumann]

@burgholzer Thanks for the cleanup! Looks good 🚀