🐛 Harden MLIR constant folding

[simon1hofmann]

🤖 AI text below 🤖

Description

Extends the shared MQT constant-folding helper found during the #2255 MLIR contract audit.

• keep the existing memoized recursive evaluation of pure SSA expression DAGs;
• recognize dialect-defined constant-like operations through MLIR's existing m_Constant matcher instead of accepting only arith.constant;
• add a focused index.constant regression.

Following review, this drops the speculative iterative worklist and synthetic 10,000-operation depth contract. The PR is now limited to the demonstrated constant-like folding gap.

This is one focused replacement for draft PR #2287. It addresses part of #2255 without closing the umbrella audit issue.

Validation

• focused MQT utilities target build — passed
• mqt-core-mlir-unittests-mqt-utils --gtest_brief=1 — 21/21 passed
• commit hooks, including clang-format — passed
• git diff --check — passed

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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AI assistance disclosure: Codex narrowed this focused change in response to review feedback, validated it, and updated this description.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[burgholzer]

Just one small request, otherwise this one looks pretty clean to me.

[coderabbitai]

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[burgholzer]

Yeah, this makes more sense to me 👍🏼 let's get it in this way!