Arm backend: Eliminate dead shape ops

[oscarandersson8218]

Shape ops get their dim_order from their users. If a shape-op does not have any users, it will therefore not get a dim_order and crash during serialization. To avoid this, we can simply delete any unused shape op from the graph before serialization.

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

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/18902

• 📄 Preview Python docs built from this PR

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

❌ 4 New Failures, 3 Unrelated Failures

As of commit 9430708 with merge base 87e65ac ():

NEW FAILURES - The following jobs have failed:

• Test CoreML Backend / test-coreml / test-backend-macos (coreml, models) / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• trunk / test-torchao-huggingface-checkpoints (lfm2_5_1_2b, linux.arm64.2xlarge, executorch-ubuntu-22.04-g... / linux-job (gh)
  RuntimeError: Command docker exec -t 9a3523546591262fce81f53a3a4ac49b84220cb43032ae2d1ec570c916bf428f /exec failed with exit code 1
• trunk / test-torchao-huggingface-checkpoints (phi_4_mini, linux.arm64.2xlarge, executorch-ubuntu-22.04-gc... / linux-job (gh)
  RuntimeError: Command docker exec -t 43f6e00c7b32d22ecdbf87dbb9c2319ca1d489e64798cbfdd1e128d312d3e927 /exec failed with exit code 1
• trunk / test-torchao-huggingface-checkpoints (qwen3_4b, linux.arm64.2xlarge, executorch-ubuntu-22.04-gcc1... / linux-job (gh)
  RuntimeError: Command docker exec -t 554364329cff5650326395a68f52a30155134d334ea44f31f1c823169ee232b7 /exec failed with exit code 1

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• trunk / unittest-release / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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

[oscarandersson8218]

Unrelated failures.