Add LLM support for cuda backend

[larryliu0820]

Summary

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Test plan

[PLEASE REMOVE] How did you test this PR? Please write down any manual commands you used and note down tests that you have written if applicable.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/17316

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❗ 1 Merge Blocking SEVs

There is 1 active merge blocking SEVs. Please view them below:

• (merge blocking) CI is down due to a github accident

If you must merge, use @pytorchbot merge -f.

❌ 21 New Failures, 2 Unrelated Failures

As of commit 7e6928e with merge base 6bac07e ():

NEW FAILURES - The following jobs have failed:

• Lint / android-java-format / linux-job (gh)
  RuntimeError: Command docker exec -t 35a75dae95a6ed1350e5890183e04f65829d1f46dbbeef9268607194eda7129c /exec failed with exit code 1
• Lint / lintrunner / linux-job (gh)
  >>> Lint for examples/models/gemma3/e2e_runner.cpp:
• pull / android / build-llm-demo / linux-job (gh)
  RuntimeError: Command docker exec -t 61a8b4438bb4a21784d92305c100d38d68ada06b2198ad7f33370db4e81b1c41 /exec failed with exit code 1
• pull / test-moshi-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 21283f9fda6d0c77577ede772d589efd7509215509d83019f31b190444b309ab /exec failed with exit code 1
• pull / test-parakeet-xnnpack-linux / linux-job (gh)
  RuntimeError: Command docker exec -t fc3882e764314a60373b448ad60939c6b7d5c6d0ad9e860db084bc176d258cfc /exec failed with exit code 1
• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 70b5dca1ab55bd7dba32ea6d4558a027549db8700f44248380cd51488a92a977 /exec failed with exit code 1
• pull / test-samsung-quantmodels-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 91c7811775cb1946f78584fbadf55e89c162cff85f096661301f3b4f030eff62 /exec failed with exit code 1
• pull / test-vulkan-operators-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 61ec52dad237f83323f5ecb709b8396613aab645ad6374427f7ac0c2db683fef /exec failed with exit code 127
• pull / unittest-arm-backend-with-no-deps (test_pytest_models_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t ba1aff4c22ba475dd3a87c10cf918d9652a6ffe62d89a0e827bc53b2594ab631 /exec failed with exit code 1
• pull / unittest-editable / macos / macos-job (gh)
  backends/xnnpack/test/ops/test_conv2d.py::TestConv2d::test_fp16_conv2d
• Test CUDA Builds / check-all-cuda-builds (gh)
  Process completed with exit code 1.
• Test CUDA Builds / test-cuda-pybind (gemma3-4b, --quantize) / linux-job (gh)
  RuntimeError: Command docker exec -t 587d161fb222c01d93b7e469c6dc315fcf297ecc96ce3315ba5507c34cfb2ea7 /exec failed with exit code 1
• Test CUDA Builds / test-cuda-pybind (gemma3-4b) / linux-job (gh)
  RuntimeError: Command docker exec -t afa14e50beee597263cbbffe59e6cf639ec4cd4c7093887ca22ff6b16acfbe88 /exec failed with exit code 1
• Test CUDA Builds / test-model-cuda-e2e (openai, whisper-large-v3-turbo, non-quantized) / linux-job (gh)
  RuntimeError: Command docker exec -t f2d6b0940c791f24c1841883493cc298b85f15fbc8ac9363c3fc1d1c24d88b51 /exec failed with exit code 1
• Test CUDA Builds / test-model-cuda-e2e (openai, whisper-large-v3-turbo, quantized-int4-tile-packed) / linux-job (gh)
  RuntimeError: Command docker exec -t 33bb8c1ab3d847d8ffa9c06cc1cd94842d80e6df8a70717ab12b44f2ba8740c6 /exec failed with exit code 1
• Test CUDA Builds / test-model-cuda-e2e (openai, whisper-large-v3-turbo, quantized-int4-weight-only) / linux-job (gh)
  RuntimeError: Command docker exec -t 1b2b49f9e67fea0167956972cc291451fe54a68a81b0acbf748748d4dc4a1a83 /exec failed with exit code 1
• Test CUDA Builds / test-model-cuda-e2e (openai, whisper-small, non-quantized) / linux-job (gh)
  RuntimeError: Command docker exec -t 3dd48db089ca4125f745dfc31b6a28d3acffe369bb001039ba3de4c89f41080a /exec failed with exit code 1
• Test CUDA Builds / test-model-cuda-e2e (openai, whisper-small, quantized-int4-tile-packed) / linux-job (gh)
  RuntimeError: Command docker exec -t d71fc76a85eb918b1aae0e44ec005d3452e92f0721e887105d5e045342012f1b /exec failed with exit code 1
• Test CUDA Builds / test-model-cuda-e2e (openai, whisper-small, quantized-int4-weight-only) / linux-job (gh)
  RuntimeError: Command docker exec -t bf536072600ab1705f6527a40fa24822fd3a7b61dab71899912e97ff2e25a47b /exec failed with exit code 1
• Test Metal Backend / export-model-metal-artifact (nvidia, parakeet-tdt, quantized-int4-metal) / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• Test Metal Backend / test-metal-backend-modules / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 127

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• Test CUDA Builds / test-executorch-cuda-build-13.0 / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test CUDA Builds / test-models-cuda (mv2) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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