[usamahz]

Summary

Pointwise quantized chains currently leave separate operations for backends to lower, limiting LUT fusion and duplicating graph search. Add a shared pass that finds single-input, single-output pointwise regions and evaluates each region as one lookup table. Arm uses the pass for int8 and int16 tables, while Cortex-M configures its backend-specific lowering through a subclass. The pass fuses unary operators and add, subtract, multiply, and divide with scalar constants.

Table evaluation keeps FP32 intermediates and quantizes only the final entries using backend rounding. Region boundaries preserve standalone requantization, avoid fusing pure Q/DQ, and retain valid suffixes after multi-input operations.

For review, start with backends/transforms/fuse_elementwise_to_lut.py, then the Arm and Cortex-M pass integrations and their tests.

Jira: MLETORCH-2880

Authored with AI assistance using OpenAI Codex.

Test plan

• 116 local tests passed using these focused commands (29 Arm and 87 shared/Cortex-M). CMSIS-NN was used for quantization and SDPA coverage; five FVP-only cases were deselected.

pytest -q backends/arm/test/passes/test_arm_fuse_elementwise_to_lut.py backends/arm/test/passes/test_insert_table_ops_lowering.py backends/arm/test/passes/test_insert_table_ops_pass.py
pytest -q backends/transforms/test/test_fuse_elementwise_to_lut.py backends/cortex_m/test/test_cortex_m_fuse_elementwise_to_lut.py backends/cortex_m/test/test_activation_lut.py
pytest -q backends/cortex_m/test/misc/test_quantization.py
pytest -q backends/cortex_m/test/ops/test_sdpa.py -k 'not test_implementation_sdpa'

• Four representative Arm models passed lowering checks.
• Local pre-commit and pre-push checks passed.
• Arm extended CI passed for patch set 6.

Full TOSA reference and FVP validation were unavailable locally.

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils @Sebastian-Larsson @robell @rascani

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/24985

• 📄 Preview Python docs built from this PR

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❌ 3 New Failures

As of commit 9792a0e with merge base f8373ec ():

NEW FAILURES - The following jobs have failed:

• Apple / build-demo-ios / macos-job (gh)
  RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 65
• Lint / lintrunner-mypy (gh)
  >>> Lint for backends/arm/_passes/insert_table_ops.py:
• pull / android / run-emulator (gh)
  adb: device offline

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[zingo]

Hi @rascani and @digantdesai this adds a file outside Arm :)