Fix bug in sub op to ignore alpha != 1 (fixes: #11684)

[abhinaykukkadapu]

Summary

Sub node of XNNPack backend doesn't consider alpha value, this fixes the bug by falling back to portable ops and avoid partitioning the node.

(fixes: #11684)

Test plan

$ python -m unittest backends/xnnpack/test/ops/test_sub.py

Ran 3 tests in 7.262s

OK

Model run

import torch
from executorch.backends.xnnpack.partition.xnnpack_partitioner import XnnpackPartitioner
from executorch.exir import to_edge_transform_and_lower
from executorch.extension.pybindings.portable_lib import _load_for_executorch_from_buffer

class Model(torch.nn.Module):
    def forward(self, x, y):
        return torch.sub(x, y, alpha=10)

inputs = (
    torch.randn(10),
    torch.randn(10),
)
model = Model()

ep = torch.export.export(model, inputs)
lowered = to_edge_transform_and_lower(
    ep,
    partitioner=[XnnpackPartitioner()],
).to_executorch()

et_model = _load_for_executorch_from_buffer(lowered.buffer)

eager_output = model(*inputs)
et_output = et_model([*inputs])[0]

tolerance=1e-5
if torch.allclose(eager_output, et_output, atol=tolerance):
    print("Outputs are within the tolerance level.")
else:
    print("Outputs differ beyond the tolerance level.")

output

Outputs are within the tolerance level.

[pytorch-bot]

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❌ 2 New Failures, 2 Cancelled Jobs, 2 Unrelated Failures

As of commit f020907 with merge base daebcde ():

NEW FAILURES - The following jobs have failed:

• Build Presets / linux (pybind, linux.2xlarge, executorch-ubuntu-22.04-clang12) / build (gh)
• pull / test-phi-3-mini-runner-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 5d8fb7ebc8f1a5180928d14313990e56ea55b42b2e36024dfe575787a1457d71 /exec failed with exit code 139

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• Lint / lintrunner / linux-job (gh)
  The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.
• pull / test-models-linux-basic (mv3, portable, cmake, linux.2xlarge, executorch-ubuntu-22.04-clang12) / linux-job (gh)

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• pull / test-models-linux-basic (mv3, portable, buck2, linux.2xlarge, executorch-ubuntu-22.04-clang12) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.

BROKEN TRUNK - The following job failed but was present on the merge base:

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

• pull / test-moshi-linux / linux-job (gh) (trunk failure)
  test_exported_decoder_xnnpack

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