Cortex-M: run op tests against a selectable target

[rascani]

Summary

Add an explicit --cortex-m-target pytest option (conftest, defaulting to cortex-m55) for the op tests. Implementation tests take the target as a parametrized fixture, so it appears in the test id and drives both the AoT config and the matching per-target FVP runner; dialect tests stay target-agnostic since their graph output does not depend on the target.

A new reusable workflow (_test_cortex_m_ops.yml) builds the runner for each target and runs only the implementation tests against it; trunk.yml invokes it for cortex-m7 and cortex-m0plus. cortex-m55 coverage continues to run on pull via the existing job.

Test plan

CI

Authored with Claude Code.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/20081

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❌ 2 New Failures, 2 Unclassified Failures

As of commit e1f8392 with merge base 26b4be8 ():

NEW FAILURES - The following jobs have failed:

• pull / unittest-editable / linux / linux-job (gh)
  examples/models/test/test_export.py::ExportTest::test_efficient_sam_export_to_executorch
• trunk / test-qnn-optimum-model (fp32, mobilevit_v2) / linux-job (gh)
  RuntimeError: Command docker exec -t 19363a4de90d27e516d2643dd893b07e1d0a5beb9b06ab7e442d0e16172577fa /exec failed with exit code 92

UNCLASSIFIED FAILURES - DrCI could not classify the following jobs because the workflow did not run on the merge base. The failures may be pre-existing on trunk or introduced by this PR:

• trunk / test-cortex-m-ops / run (cortex-m0plus) / cortex-m-ops-cortex-m0plus (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  RuntimeError: Command docker exec -t be3604166fb4da739021eb465d81d388100972af75f681eff6a68316375c73e5 /exec failed with exit code 1
• trunk / test-cortex-m-ops / run (cortex-m7) / cortex-m-ops-cortex-m7 (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  RuntimeError: Command docker exec -t a178f351757f4068dc7c709314390234d02cc2a6315658101f4bfd91c1d6aa01 /exec failed with exit code 1

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

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