[EylonKrause]

Summary

PyTorch drops a last ceil_mode pooling window that would start in the right padding, so e.g. max_pool2d(kernel=2, stride=4, padding=0, ceil_mode=True) on a width of 7 gives 2 output columns, the same as floor mode. The input then has a remainder that no window uses.

SizeAdjustInputPass skipped every ceil_mode pool, so that remainder was never sliced off and adjust_pooling_pad_if_needed returned a negative post padding (-1 above). MAX_POOL2D and AVG_POOL2D were then emitted with a negative pad, which the TOSA reference model rejects ("At least one pad is smaller than zero"). For avg_pool2d with count_include_pad=True, DecomposeAvgPool2dPass fell back to padding with the full symmetric pad instead, which kept the dropped window and produced one output element too many.

This change:

• slices the unused input for ceil_mode pools with static spatial shapes in every dimension where ceil_mode does not add an output element (when the last window is dropped, the ceil and floor output sizes are equal, so the floor-mode slice is exact);
• does not add post padding in DecomposeAvgPool2dPass when the needed post padding is negative.

Dynamic (SymInt) spatial shapes keep the previous behaviour.

Release notes: arm

Test plan

• New cases ceil_mode_last_window_dropped / ceil_mode_last_window_dropped_padding in test_max_pool.py and ceil_mode_last_window_dropped / ceil_mode_last_window_dropped_count_include_pad in test_avg_pool2d.py. The TOSA FP/INT/INT a16w8 variants fail on main and pass with this change.
• Random sweep of ceil_mode max_pool2d/avg_pool2d configurations through TosaPipelineFP and the TOSA reference model: 146/300 fail on main; the remaining 17 failures with this change are all divisor_override + ceil_mode value mismatches, a separate issue (separate PR). Floor mode: 200/200 pass before and after.
• pytest -c backends/arm/test/pytest.ini backends/arm/test/ops/test_max_pool.py backends/arm/test/ops/test_avg_pool2d.py backends/arm/test/passes (excluding u55/u85/vgf): no new failures.
• Not run locally: the u55/u85/vgf variants (no Corstone FVP / Vela installed here), so those rely on CI.
• ufmt check and flake8 clean on the changed files.

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

[pytorch-bot]

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As of commit 4f22175 with merge base 81acbc1 ():

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[linux-foundation-easycla]

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• ✅ login: EylonKrause / name: Eylon Eliyahu Krause (b9e74bd)

[pytorch-bot]

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[zingo]

Thanks a lot for this PRs :) I kicked of some extended testing. As this is the first contribution to the project you will need to sign a EasyCLA, I hope that is OK, instructions are in a comment in this issue see #24893 (comment) :)

[EylonKrause]

@pytorchbot label "release notes: arm"

[EylonKrause]

Thanks @zingo! I pushed a follow-up commit for the lintrunner findings: _ceil_mode_adds_output now returns a plain bool (mypy saw bool | SymBool), and its docstring is rewrapped for docformatter. The WebGPU jobs failed with curl: (22) download errors, and the unittest failures are also on the merge base, so those look unrelated.