Fix VGF runtime aborts on 0-dim tensor inputs and Python scalar coercion (#19446)

[psiddh]

Summary:

The ARM-backend VGF tests (e.g. test_sum_dim_intlist_vgf_quant and
test_sum_dim_intlist_vgf_no_quant for all 19 parametrizations) were
hard-aborting the pytest process with two latent bugs that compounded:

1. C++ aten_bridge nullptr assert on 0-dim tensors (T270603238).
   executorch/extension/aten_util/aten_bridge.cpp::check_tensor_meta had two
   unconditional ET_CHECK_MSG(b.{sizes,strides}().data() != nullptr, ...)
   asserts. For 0-dim (scalar) tensors, sizes()/strides() are empty
   IntArrayRefs whose .data() may legitimately return nullptr. The
   process aborted on every valid scalar tensor input. Fix: gate the nullptr
   checks on b.dim() > 0. The subsequent loops are no-ops when dim() == 0 and dim_order_to_stride_nocheck already early-returns for dims == 0 (dim_order_util.h:132-134), so the relaxed asserts are safe.

2. VGF Python runner over-wrapping non-tensor inputs (Error::InvalidArgument
   0x12). runner_fb.run_vgf previously called torch.tensor(x) on
   every non-tensor input (including None/bool/int), producing
   0-dim tensors. The lowered method's signature, however, expects EValue
   tags Int/Bool/None for those slots — receiving a Tensor
   caused Method::set_inputs to reject the inputs. The pybindings layer
   (pybindings.cpp:804-809) already natively handles
   None/bool/int Python objects; the runner just had to stop
   interfering. Fix: only wrap Python float (and other unknown types) as
   0-dim tensors — the original addmm alpha/beta motivation. Pass
   None/bool/int through unchanged.

3. Regression tests for the C++ fix in
   executorch/extension/aten_util/test/aten_bridge_test.cpp:
   AliasETensorToATenTensorZeroDim and AliasATTensorToETensorZeroDim
   construct true 0-dim tensors via at::scalar_tensor and verify the
   bridge does not abort. The existing AliasETensorToATenTensorFail death
   test still fires for ranked tensors with empty strides because that case
   has dim() == 3 > 0.

Fixes T270603238.

Differential Revision: D104603739

[pytorch-bot]

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⏳ 1 Pending, 2 Unrelated Failures

As of commit 358b4e2 with merge base a49171d ():

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

• pull / test-moshi-linux / linux-job (gh) (matched linux rule in flaky-rules.json)
  E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/o/openjpeg2/libopenjp2-7_2.4.0-6ubuntu0.4_amd64.deb 404 Not Found [IP: 172.66.152.176 80]
• pull / test-qnn-testsuite-linux / test-backend-linux (qnn, models) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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[meta-codesync]

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[Copilot]

Pull request overview

Fixes hard aborts when bridging between ATen tensors and ExecuTorch tensors for valid 0-dim (scalar) tensors by avoiding invalid nullptr assertions on empty metadata arrays.

Changes:

• Relax check_tensor_meta to only assert non-null sizes/strides storage for ranked tensors (dim() > 0).
• Add regression tests covering zero-dimensional aliasing in both bridge directions.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
extension/aten_util/aten_bridge.cpp	Gates sizes/strides nullptr checks on dim() > 0 to allow valid scalar tensor metadata.
extension/aten_util/test/aten_bridge_test.cpp	Adds regression tests for 0-dim tensor aliasing to ensure the bridge doesn’t abort.

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