exir: add flatbuffer Program serialization for performance

[chizkiyahu]

Title

Introduce flatbuffer serializer as default for program serialization

Summary

Add a FlatBuffers-based serializer at exir/_serialize/_flatbuffer_program.py and make it the default serializer for program artifacts. The new serializer achieves large efficiency gains across our model suite while retaining robustness via a JSON fallback and detailed error logging.

Before

python -> json -> binary

After

python -> binary

Performance

Measured across ~600 models:

• ~36.3× average speedup (serialize latency).
• ~61.6% average reduction in memory usage during serialization.

Tests

Unit tests added at:

• exir/_serialize/test/test_flatbuffer_program.py

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

[pytorch-bot]

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[Copilot]

Pull request overview

This PR introduces a FlatBuffers-based serializer to achieve significant performance improvements in program serialization (36.3× speedup, 61.6% memory reduction). The new serializer converts Python Program objects directly to binary format, bypassing the previous JSON intermediate step while maintaining robustness through a fallback mechanism.

Changes:

• New FlatBuffers serializer module at exir/_serialize/_flatbuffer_program.py with direct Python-to-binary conversion
• Updated default serialization path in _program.py to use the new FlatBuffer serializer with JSON fallback for robustness
• Comprehensive unit tests covering roundtrip serialization, path equivalence validation, and error handling

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
exir/_serialize/_flatbuffer_program.py	Implements direct Python-to-FlatBuffer serialization logic, avoiding JSON intermediate representation
exir/_serialize/_program.py	Integrates the new FlatBuffer serializer as the default path with JSON fallback for error cases
exir/_serialize/test/test_flatbuffer_program.py	Tests for the new serializer including roundtrip validation and alignment verification
exir/_serialize/test/TARGETS	Adds test target for the new FlatBuffer program tests
exir/_serialize/TARGETS	Registers the new _flatbuffer_program.py module in the build system

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[chizkiyahu]

@pytorchbot label ciflow/trunk

[pytorch-bot]

To add these label(s) (ciflow/trunk) to the PR, please first approve the workflows that are awaiting approval (scroll to the bottom of this page).

This helps ensure we don't trigger CI on this PR until it is actually authorized to do so. Please ping one of the reviewers if you do not have access to approve and run workflows.

[chizkiyahu]

@pytorchbot label "partner: arm"

[chizkiyahu]

@pytorchbot label ciflow/trunk

[pytorch-bot]

To add these label(s) (ciflow/trunk) to the PR, please first approve the workflows that are awaiting approval (scroll to the bottom of this page).

This helps ensure we don't trigger CI on this PR until it is actually authorized to do so. Please ping one of the reviewers if you do not have access to approve and run workflows.

[chizkiyahu]

@pytorchbot label "release notes: exir"

[zingo]

Hi @SS-JIA / @swolchok here is one nore thet is outside or Arm folders that we don't want to review ourself :)