Add fast path for contiguous innermost-dim reduction in sum.IntList_out#18789
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meta-codesync[bot] merged 1 commit intopytorch:mainfrom Apr 9, 2026
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Add fast path for contiguous innermost-dim reduction in sum.IntList_out#18789meta-codesync[bot] merged 1 commit intopytorch:mainfrom
meta-codesync[bot] merged 1 commit intopytorch:mainfrom
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Summary: Add a fast path to the portable sum.IntList_out kernel for the common case of reducing a contiguous tensor over its innermost (last) dimension with matching input/output dtypes. The fast path uses a tight loop over contiguous memory (`acc += row[j]`) that the compiler can auto-vectorize, bypassing the generic MapReduceOverDimListPlan infrastructure which has 5 layers of lambda indirection, per-output-element get_init_index() calls, and strided access patterns. Differential Revision: D99293418
🔗 Helpful Links🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/18789
Note: Links to docs will display an error until the docs builds have been completed. ❗ 1 Active SEVsThere are 1 currently active SEVs. If your PR is affected, please view them below: ❌ 1 New Failure, 2 Unrelated FailuresAs of commit 561b4d4 with merge base 463f07b ( NEW FAILURE - The following job has failed:
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…ut (pytorch#18789) Summary: Add a fast path to the portable sum.IntList_out kernel for the common case of reducing a contiguous tensor over its innermost (last) dimension with matching input/output dtypes. The fast path uses a tight loop over contiguous memory (`acc += row[j]`) that the compiler can auto-vectorize, bypassing the generic MapReduceOverDimListPlan infrastructure which has 5 layers of lambda indirection, per-output-element get_init_index() calls, and strided access patterns. Differential Revision: D99293418
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…ut (pytorch#18789) Summary: Add a fast path to the portable sum.IntList_out kernel for the common case of reducing a contiguous tensor over its innermost (last) dimension with matching input/output dtypes. The fast path uses a tight loop over contiguous memory (`acc += row[j]`) that the compiler can auto-vectorize, bypassing the generic MapReduceOverDimListPlan infrastructure which has 5 layers of lambda indirection, per-output-element get_init_index() calls, and strided access patterns. Differential Revision: D99293418
manuelcandales
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Summary:
Add a fast path to the portable sum.IntList_out kernel for the common case of reducing a contiguous tensor over its innermost (last) dimension with matching input/output dtypes. The fast path uses a tight loop over contiguous memory (
acc += row[j]) that the compiler can auto-vectorize, bypassing the generic MapReduceOverDimListPlan infrastructure which has5 layers of lambda indirection, per-output-element get_init_index() calls, and strided access patterns.
Differential Revision: D99293418