🐛 Fix CtrlOp::getBodyUnitary() for operations with parameters

[taminob]

Description

While debugging test cases in #1426, I finally figured out why CtrlOp::getBodyUnitary() sometimes returned an invalid UnitaryOpInterface.
Whenever an operation has at least one parameter, the first operation in the modifier's body will be a arith.constant and not the unitary operation like it is currently assumed in the function.

This PR resolves this by iterating over all operations in the body and only returning when the first UnitaryOpInterface operation has been found or there is none.
It affects all crx, crzz, cu, ... operations.

Required for #1426

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.

[coderabbitai]

📝 Walkthrough

Walkthrough

Updated CHANGELOG.md with PR #1464 reference. Modified getBodyUnitary() in both QC and QCO CtrlOp implementations to iterate through body operations instead of assuming the first operation is a UnitaryOpInterface, returning nullptr if none found. Added corresponding test case.

Changes

Cohort / File(s)	Summary
Changelog CHANGELOG.md	Added PR #1464 entry to Unreleased section under MLIR dialect infrastructure items
CtrlOp Implementation mlir/lib/Dialect/QC/IR/Modifiers/CtrlOp.cpp, mlir/lib/Dialect/QCO/IR/Modifiers/CtrlOp.cpp	Modified getBodyUnitary() to safely iterate over all operations in body region to find first UnitaryOpInterface match, returning nullptr if none exists, instead of directly accessing front operation
QCO CtrlOp Test mlir/unittests/Dialect/QCO/IR/Modifiers/test_qco_ctrl.cpp	Added new test case bodyUnitaryWithParameter validating getBodyUnitary() retrieval from 2-qubit CRX operation

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• 🐛 Fix one-time-use of variables for the ctrl modifier #1436: Also modifies QCO CtrlOp implementation and body handling logic
• 🐛 Rename CtrlOp region to region to avoid hiding trait method getBody() #1430: Changes CtrlOp body-access logic including region accessors and getBody() usage

Suggested reviewers

• burgholzer

Poem

🐰 A rabbit's ode to safer bounds:
No more assuming fronts of ops so bright,
We iterate with care through body's height,
Each unitary found gets gentle sight,
Safe nullptr returns make all things right! ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description check	✅ Passed	The PR description covers the problem, solution, and scope; includes required checklist items with most checked as complete. However, the checklist shows documentation, changelog, and upgrade guide items are not fully marked as done, though a changelog entry appears in the raw summary.
Title check	✅ Passed	The title clearly identifies the main fix: CtrlOp::getBodyUnitary() handling for operations with parameters, which directly matches the primary change in the changeset.

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✨ Finishing touches

• 📝 Generate docstrings

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[codecov]

Codecov Report

❌ Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
mlir/lib/Dialect/QC/IR/Modifiers/CtrlOp.cpp	66.6%	1 Missing ⚠️
mlir/lib/Dialect/QCO/IR/Modifiers/CtrlOp.cpp	75.0%	1 Missing ⚠️

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