[flat_tensor] Persist FreeableBuffers of external constants in method #8599
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Pull Request resolved: #8437 ## Problem Currently, the FlatTensorDataMap persists tensors, and returns a FreeableBuffer with an empty free function. The NamedDataMap should not persist data, as most cases (eg. delegate) will want it to be freed. Ownership should be on the caller; `get_data` returns a FreeableBuffer that 'owns' the data. The FreeableBuffer in turn is owned by the caller. NOTE: this doesn't support the case where we want to share plain tensors between methods/pte files at runtime. A custom NDM could support that use-case. ## This diff: 1. Introduces a 'NamedData' struct to method.h. This holds a key and a FreeeableBuffer. 2. Iterate over all the flatbuffer tensors to count the constants tagged with EXTERNAL. NOTE: this will increase load time for all users. Potentially allocate chunks of 16 and use a linked list to store external constants, or store this number in PTE file (see D69618283). 3. Allocate space for num_external_constants using the method allocator. 4. Iterate over all flatbuffer tensors and use the named_data_map to resolve EXTERNAL tensors into the array of NamedData. 5. Pass the resolved external constants to tensor_parser, along with NDM (used for mutable external tensors). 6. Resolved external tensors are stored inside method. They are freed when the method is destructed. Some notes: https://docs.google.com/document/d/1_PBi4JgODuClUPD4PCUWrKNjyUH54zOUHGUJ3QHDNes/edit?tab=t.0#heading=h.blsvwraxss7g ghstack-source-id: 267364187 TODO: add test case when two fqns point to the same data buffer. Differential Revision: [D69477027](https://our.internmc.facebook.com/intern/diff/D69477027/)
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🔗 Helpful Links🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/8599
Note: Links to docs will display an error until the docs builds have been completed. ❌ 1 New Failure, 32 PendingAs of commit d6b540e with merge base 75d4abc ( NEW FAILURE - The following job has failed:
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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: #8437 by @lucylq
^ 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/lucylq/40/base
ghstack PR head: https://github.com/pytorch/executorch/tree/gh/lucylq/40/head
Merge bot PR base: https://github.com/pytorch/executorch/tree/main
Merge bot PR head: https://github.com/pytorch/executorch/tree/gh/lucylq/40/orig
@diff-train-skip-merge