[ET-VK] Tag tensors in list args that mix None entries

[Sanjays2402]

Fixes #22510

Summary

TagMemoryMetaPass skipped any list argument that was not composed entirely of tensor nodes. aten.index.Tensor reaches the edge dialect as index.Tensor(x, [None, idx]), so the index tensor never received a storage/memory-layout representation, and any op implementation asserting on the layout of that tensor would fail.

Changes

• backends/vulkan/utils.py: added tensor_nodes_in_arg(), which returns the tensor nodes of an argument while skipping None entries.

• backends/vulkan/_passes/tag_memory_meta_pass.py: use the helper everywhere the pass walks a list argument —

  • set_arg_node_repr_or_transition skips None entries when tagging list args,
  • is_non_constant_tensor_node accepts lists whose non-None entries are all non-constant tensor nodes,
  • get_arg_tensor_source_repset / constrain_op_arg_repset use the first tensor node of a list as the representative instead of arg[0] (which could be None),
  • constrain_op_repsets now constrains args that contain at least one tensor node.

  Lists composed entirely of tensors behave exactly as before.

• backends/vulkan/test/test_vulkan_passes.py: regression test exporting x[:, idx] (with idx a graph input) and asserting the pass tags the index tensor node.

Test evidence

• Reproduced the bug on main (897fc8e): after TagMemoryMetaPass, the idx node in index.Tensor(x, [None, idx]) had no node_repr. With this fix it is tagged (BUFFER / TENSOR_WIDTH_PACKED, matching the index op's storage requirement for higher-rank self).
• python -m unittest executorch.backends.vulkan.test.test_vulkan_passes: 12 tests, all pass, including the new test_tag_memory_meta_pass_tags_tensor_in_mixed_none_list (verified it fails on unmodified code).
• black --check and flake8 --select=E9,F clean on all touched files.

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This PR was authored with AI assistance (Muse).

[pytorch-bot]

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• ✅ login: Sanjays2402 / name: Sanjay Santhanam (f5ec7b0)

[Sanjays2402]

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