Landing: ac91bb5b441c

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Project / Subsystem

gcc / aarch64

Date

2026-06-29

Author

Pengfei Li

Commit

ac91bb5b441cd7330c1644937830fe83201c69c3

Source

github

Perf win

Yes

Breaking

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All attributes

project: gcc
subsystem: aarch64
patch_id: —
commit_hash: ac91bb5b441cd7330c1644937830fe83201c69c3
source_type: github
headline: AArch64: Cap suggested unroll factor for small known-niters loops
tldr: AArch64 vectorizer caps suggested unroll factor for small loops to avoid unnecessary overhead.
author: Pengfei Li
outcome: committed
performance_win: true
breaking_change: false
series_id: —
series_parts: []
tags: • aarch64
• vectorization
• optimization
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/ac91bb5b441cd7330c1644937830fe83201c69c3
date: 2026-06-29T00:00:00.000Z

The AArch64 backend now caps the suggested unroll factor for small, known-iteration loops during vectorization. This prevents the backend from suggesting an excessively high unroll factor (e.g., 4 when only 1 or 2 are needed), which could lead to suboptimal code generation due to extra epilogue loops. The cap is calculated using CEIL(niters, VF) to ensure all scalar iterations are covered by the vectorized loop.