✨ Compose multi-op modifier bodies on N targets in getUnitaryMatrix

[simon1hofmann]

Description

Extend InvOp and CtrlOp::getUnitaryMatrix() to compose multi-operation modifier bodies on N ≥ 1 target wires, not only single-qubit sequences on one target.

Replace composeSingleQubitBodyMatrix with composeNTargetBodyMatrix(Block&, numTargets), which:

• Maps block arguments to wire indices 0..N-1 (MSB-first, matching Matrix2x2::embedInNqubit)
• Walks the body in program order, tracking SSA wires through barriers and unitary ops
• Embeds each 1Q/2Q compile-time unitary into a 2^N DynamicMatrix and accumulates via premultiplyBy
• Handles GPhaseOp as a global phase factor
• Rejects bodies with >2-qubit ops, unknown qubit-touching ops, or numTargets > 10

InvOp returns the adjoint of the composed matrix; CtrlOp wraps it with the existing I_{2^c} ⊗ U controlled embed.

Also adds DynamicMatrix::premultiplyBy (const-ref and rvalue overloads) to support efficient in-place accumulation.

Prerequisite for #1812

AI Assistance

Used Composer 2.5 via Cursor for parts of this change. I reviewed the full
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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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✅ All modified and coverable lines are covered by tests.

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[simon1hofmann]

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📝 Walkthrough

Walkthrough

This PR generalizes modifier body matrix composition to N targets, updates Ctrl/Inv modifier unitary computation to use it, adds supporting DynamicMatrix premultiplication helpers, and expands tests plus changelog entries.

Changes

N-target composition feature

Layer / File(s)	Summary
Header contracts mlir/include/mlir/Dialect/QCO/QCOUtils.h, mlir/include/mlir/Dialect/QCO/Utils/Matrix.h	Declares kMaxModifierTargetQubits, composeNTargetBodyMatrix, and the new DynamicMatrix::premultiplyBy(const DynamicMatrix&) plus embedded premultiply declarations.
Composition and matrix helpers mlir/lib/Dialect/QCO/IR/QCOUtils.cpp, mlir/lib/Dialect/QCO/Utils/Matrix.cpp	Implements N-target body composition with wire mapping, barrier/global-phase handling, and unitary embedding, and defines the DynamicMatrix premultiplication helpers.
CtrlOp and InvOp wiring mlir/lib/Dialect/QCO/IR/Modifiers/CtrlOp.cpp, mlir/lib/Dialect/QCO/IR/Modifiers/InvOp.cpp	Switches composed-body unitary computation to composeNTargetBodyMatrix for both controlled and inverse modifiers.
Tests and changelog mlir/unittests/Dialect/QCO/IR/test_qco_ir_matrix.cpp, mlir/unittests/Dialect/QCO/IR/CMakeLists.txt, mlir/unittests/Dialect/QCO/Utils/test_unitary_matrix.cpp, CHANGELOG.md	Adds inverse/composition test coverage, DynamicMatrix premultiply tests, test target formatting changes, and the changelog update.

Estimated code review effort: 4 (Complex) | ~60 minutes

Possibly related issues

• ✨ Implement getUnitaryMatrix() for multi-operation modifiers #1760: Matches the added multi-operation modifier-body support in CtrlOp and InvOp.

Possibly related PRs

• munich-quantum-toolkit/core#1436: Updates target aliasing and block-argument mapping used by controlled modifier composition.
• munich-quantum-toolkit/core#1672: Changes InvOp::getUnitaryMatrix and related QCO matrix utilities at the same computation boundary.
• munich-quantum-toolkit/core#1809: Also updates modifier unitary computation through shared QCO utility paths.

Suggested reviewers: burgholzer

Poem

I’m a rabbit with matrices bright,
Hopping through qubits left and right.
Barriers shift, inverses sing,
Premultiply makes the whole board swing.
N targets now dance in one line—
🐇✨ a tidy quantum alignment.

🚥 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 clearly summarizes the core change: composing multi-operation modifier bodies on N targets in getUnitaryMatrix.
Description check	✅ Passed	The description includes summary, context, dependency note, AI disclosure, and checklist, matching the template well.

✨ Finishing Touches

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch compose-n-target-body-matrix

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Actionable comments posted: 3

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

mlir/unittests/Dialect/QCO/IR/test_qco_ir_matrix.cpp (1)

244-257: 🩺 Stability & Availability | 🟡 Minor | ⚡ Quick win

Missing ASSERT_TRUE(matrix) before dereference.

Unlike every other test in this file using the same getUnitaryMatrix() → std::optional<DynamicMatrix> pattern (e.g. ControlledHOpMatrix, ControlledXHOpMatrix, ControlledInverseHTOpMatrix), CXOpMatrix dereferences matrix->isApprox(...) without first asserting matrix is engaged. std::optional::operator-> does not check engagement, so an unexpected nullopt here would be UB rather than a clear test failure.

🛡️ Proposed fix

   const auto matrix = firstCtrlOp(*moduleOp).getUnitaryMatrix();
+  ASSERT_TRUE(matrix);
 
   const Matrix4x4 expected =

🤖 Prompt for 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.

In `@mlir/unittests/Dialect/QCO/IR/test_qco_ir_matrix.cpp` around lines 244 - 257,
The CXOpMatrix test is missing an explicit engagement check before dereferencing
the optional returned by getUnitaryMatrix(). In QCOMatrixTest::CXOpMatrix, add
an ASSERT_TRUE on the matrix result before calling matrix->isApprox(...),
matching the pattern used by the other unit tests in this file such as
ControlledHOpMatrix and ControlledXHOpMatrix. This keeps the test from
dereferencing a disengaged std::optional and makes failures clear.

🤖 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/QCOUtils.cpp`:
- Around line 33-80: Add brief Doxygen-style `///` comments for the new internal
helpers `lookupWireId`, `propagateWireIds`, and `embedUnitaryInBody` in
`QCOUtils.cpp`, matching the style used by sibling static helpers like
`entryIsApprox` and `checkedDim`. Keep the comments short but descriptive enough
to explain each helper’s role so the file complies with the C++ Doxygen
guideline.
- Around line 82-154: The current composeNTargetBodyMatrix path in QCOUtils.cpp
scales poorly because each UnitaryOpInterface is embedded into a full
DynamicMatrix and then premultiplyBy does a dense multiply, which becomes cubic
near the kMaxModifierTargetQubits cap. Update composeNTargetBodyMatrix and its
unitary handling so 1Q/2Q gates apply directly to the accumulator using
index-based stride updates instead of building a full embedded matrix, while
keeping the existing BarrierOp, GPhaseOp, and wireIds propagation behavior
intact.

---

Outside diff comments:
In `@mlir/unittests/Dialect/QCO/IR/test_qco_ir_matrix.cpp`:
- Around line 244-257: The CXOpMatrix test is missing an explicit engagement
check before dereferencing the optional returned by getUnitaryMatrix(). In
QCOMatrixTest::CXOpMatrix, add an ASSERT_TRUE on the matrix result before
calling matrix->isApprox(...), matching the pattern used by the other unit tests
in this file such as ControlledHOpMatrix and ControlledXHOpMatrix. This keeps
the test from dereferencing a disengaged std::optional and makes failures clear.

🪄 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: e420ba71-f155-4491-92ce-20bacefe05ec

📥 Commits

Reviewing files that changed from the base of the PR and between 26a0d98 and 0c4463e.

📒 Files selected for processing (10)

• CHANGELOG.md
• mlir/include/mlir/Dialect/QCO/QCOUtils.h
• mlir/include/mlir/Dialect/QCO/Utils/Matrix.h
• mlir/lib/Dialect/QCO/IR/Modifiers/CtrlOp.cpp
• mlir/lib/Dialect/QCO/IR/Modifiers/InvOp.cpp
• mlir/lib/Dialect/QCO/IR/QCOUtils.cpp
• mlir/lib/Dialect/QCO/Utils/Matrix.cpp
• mlir/unittests/Dialect/QCO/IR/CMakeLists.txt
• mlir/unittests/Dialect/QCO/IR/test_qco_ir_matrix.cpp
• mlir/unittests/Dialect/QCO/Utils/test_unitary_matrix.cpp

[simon1hofmann]

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