[ET-VK] Fix missing memory barrier for first-use writes on aliased tensors #17346
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…nsors Pull Request resolved: #17309 Tensors sharing physical memory via SharedObject each track their own `last_access_` independently. When a tensor's first access is a write, `prev_stage` is `NO_STAGE`, causing `transition()` to use `TOP_OF_PIPE_BIT` as `srcStageMask` with no `srcAccessMask` — effectively a no-op barrier. If the same physical memory was previously written through a different aliased tensor handle, this creates a WAW hazard where the new write may execute before or concurrently with the prior write, producing non-deterministic results. This was observed as non-deterministic q8ta_conv2d output in ResNet50: running the model twice with the same input produced slightly different quantized int8 values. Adding a debug print shader after each conv2d dispatch masked the issue because the print node's read-after-write barrier serialized GPU work. The fix: when `prev_stage` is `NO_STAGE` and the current access is a write, use `COMPUTE_SHADER_BIT` with `SHADER_WRITE_BIT` instead of `TOP_OF_PIPE_BIT` with no access flags. This ensures all prior compute shader work completes and its writes are made visible before the new write begins. Authored with Claude. ghstack-source-id: 339884030 @exported-using-ghexport Differential Revision: [D92715369](https://our.internmc.facebook.com/intern/diff/D92715369/)
🔗 Helpful Links🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/17346
Note: Links to docs will display an error until the docs builds have been completed. ❌ 3 New Failures, 52 Pending, 2 Unrelated FailuresAs of commit b2de9f0 with merge base ba89c69 ( NEW FAILURES - The following jobs have failed:
BROKEN TRUNK - The following jobs failed but were present on the merge base:👉 Rebase onto the `viable/strict` branch to avoid these failures
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This PR was created by the merge bot to help merge the original PR into the main branch.
ghstack PR number: #17309 by @SS-JIA
^ Please use this as the source of truth for the PR details, comments, and reviews
ghstack PR base: https://github.com/pytorch/executorch/tree/gh/SS-JIA/412/base
ghstack PR head: https://github.com/pytorch/executorch/tree/gh/SS-JIA/412/head
Merge bot PR base: https://github.com/pytorch/executorch/tree/main
Merge bot PR head: https://github.com/pytorch/executorch/tree/gh/SS-JIA/412/orig
Differential Revision: D92715369
@diff-train-skip-merge