Cortex-M backend: Refactor ConvertToCortexMPass

[AdrianLundell]

Change to use the general AtenToDialectPass structure, quantized_op_fusion_pass
to be changed similarly in an upcoming PR.

Removes the 1-1 ensure check as it was to restrictive, cortex-m backend needs to both insert scratch nodes and for BMM an additional transpose at the time of dialect replacement.

Bonus small fix: Moves yolo import into test to avoid download at test collection time

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils @Sebastian-Larsson @robell @rascani

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/20070

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 1 Cancelled Job

As of commit c338d86 with merge base e56be3e ():

CANCELLED JOB - The following job was cancelled. Please retry:

• pull / unittest-nxp-neutron / linux-job (gh)
  ##[error]The operation was canceled.

This comment was automatically generated by Dr. CI and updates every 15 minutes.

[Copilot]

Pull request overview

Refactors the Cortex-M backend’s ATen→dialect lowering to use the shared AtenToDialectPass substitution/decorator structure (replacing ConvertToCortexMPass), and relaxes the prior 1:1 “call_function count preserved” postcondition to allow scratch/aux node insertion (needed for CMSIS-NN scratch buffers and BMM transpose handling). Also adjusts the YOLO test to avoid triggering weights download during test collection.

Changes:

• Remove the requires()/ensures() “call_function count preserved” check from AtenToDialectPass and delete the corresponding test.
• Introduce AtenToCortexMPass and wire it into the Cortex-M pass manager in place of ConvertToCortexMPass.
• Move YOLO model instantiation/weights loading into the test body to avoid collection-time side effects.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
backends/transforms/test/test_aten_to_dialect_pass.py	Removes the test that asserted the old 1:1 call_function count invariant.
backends/transforms/aten_to_dialect_pass.py	Removes the 1:1 substitution invariant enforcement (requires/ensures).
backends/cortex_m/test/models/test_yolo11.py	Defers YOLO weights/model creation to test runtime to avoid collection-time downloads.
backends/cortex_m/passes/cortex_m_pass_manager.py	Switches the pass pipeline to use AtenToCortexMPass.
backends/cortex_m/passes/aten_to_cortex_m_pass.py	New pass implementing Cortex-M dialect substitutions + scratch alloc sizing logic.
backends/cortex_m/passes/init.py	Updates public pass imports to expose AtenToCortexMPass.

Comments suppressed due to low confidence (1)

backends/cortex_m/test/models/test_yolo11.py:28

• McuTestCase.model is typed as torch.nn.Module, but this test passes None with a type-ignore. This can hide real issues and could break if future test helpers start using test_case.model. Use a lightweight placeholder module instead so the dataclass contract stays valid.

    "yolo11n": McuTestCase(
        model=None,  # type: ignore[arg-type]
        example_inputs=lambda: (
            torch.randn(1, 3, 640, 640).to(memory_format=torch.channels_last),
        ),
    ),

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[rascani]

Can you also update backends/cortex_m/passes/BUCK?

[rascani]

Shall we delete convert_to_cortex_m_pass.py?

[rascani]

Can you update the docstring here since its no longer 1:1?