✨ Add OpenQASM-to-QC translation

[denialhaag]

Description

This is a rebased version of #1671 after #1671 was automatically closed when #1751 was merged.

Original description by @J4MMlE:

Description

This PR adds a direct OpenQASM-to-QC translation that bypasses the qc::QuantumComputation.

The new flow reuses the existing parser and walks the AST directly to emit QC dialect ops. Skipping QuantumComputation removes an intermediate step and enables previously unsupported QASM3 features, such as gate modifiers, classical computations, and control flow structures.

What works

• All standard gates plus Qiskit-style MCX variants
• Gate modifiers: ctrl @, negctrl @, inv @, nested combinations
• Register declarations, qubit/bit allocation
• Measure, reset, barrier
• if/else over quantum statements
• Hardware qubits convert to qc.static
• Broadcasting (register-width gate calls)

Current limitations

• Gate parameters must be compile-time constants
• pow modifier is unsupported (but will/should be once #1603 is merged)
• Layout pragmas are unsupported (they have no equivalent in QC)

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.

[codecov]

Codecov Report

❌ Patch coverage is 81.62839% with 88 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../lib/Dialect/QC/Translation/TranslateQASM3ToQC.cpp	81.6%	88 Missing ⚠️

📢 Thoughts on this report? Let us know!

[burgholzer]

This generally looks very good to me as a direct port of the QuantumComputation QASM Importer 🙌
I only have a couple of inline comments or requests for changes.
We should be able to merge this quickly.

A thought that came up while reviewing this: how much is the current architecture of the parser and the visitor implementation limiting us in terms of expanding the capabilities?
There are quite a few things from the OQ3 spec that we would want to support (loops being one of the most prominent ones).
Would it be interesting to define our own OpenQASM3 dialect (inspired by the qe-compiler one) that can directly parse in QASM files. And then we would write a conversion to MLIR standard dialects plus QC. Does that make sense? Is that overkill? To me it feels like this could generally make sense. What do you think?

[denialhaag]

A thought that came up while reviewing this: how much is the current architecture of the parser and the visitor implementation limiting us in terms of expanding the capabilities?
There are quite a few things from the OQ3 spec that we would want to support (loops being one of the most prominent ones).
Would it be interesting to define our own OpenQASM3 dialect (inspired by the qe-compiler one) that can directly parse in QASM files. And then we would write a conversion to MLIR standard dialects plus QC. Does that make sense? Is that overkill? To me it feels like this could generally make sense. What do you think?

I will think about this a bit and respond tomorrow!

[denialhaag]

@coderabbitai review

[coderabbitai]

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Review finished.

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[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/include/mlir/Dialect/QC/Translation/TranslateQASM3ToQC.h`:
- Around line 13-26: The function translateQASM3ToQC uses OwningOpRef<ModuleOp>
as its return type but the header does not directly include the definition of
OwningOpRef, relying instead on transitive includes from BuiltinOps.h. Add
`#include` <mlir/IR/OwningOpRef.h> to the include section at the top of the file
along with the other mlir includes to make this header self-contained and
explicit about its dependencies.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

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

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 4b5a8e6b-daab-46b3-96dc-c6efd737f14b

📥 Commits

Reviewing files that changed from the base of the PR and between 40e31f7 and 86bbf4b.

📒 Files selected for processing (7)

• mlir/include/mlir/Dialect/QC/Translation/TranslateQASM3ToQC.h
• mlir/lib/Dialect/QC/Translation/TranslateQASM3ToQC.cpp
• mlir/tools/mqt-cc/CMakeLists.txt
• mlir/tools/mqt-cc/mqt-cc.cpp
• mlir/unittests/Dialect/QC/Translation/test_qasm3_translation.cpp
• mlir/unittests/programs/qasm_programs.cpp
• mlir/unittests/programs/qasm_programs.h

💤 Files with no reviewable changes (1)

• mlir/tools/mqt-cc/CMakeLists.txt

[burgholzer]

This is very close to being mergable 🙂

[denialhaag]

Thanks a lot for getting this started, @J4MMlE! Your initial version was a great foundation! 🙂