Landing: a97f2ef0d90d

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Project / Subsystem

gcc / tree-optimization

Date

2026-07-28

Author

Richard Biener

Commit

a97f2ef0d90d46144b39a8c9ea670b52dd13233a

Source

github

Perf win

Breaking

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All attributes

project: gcc
subsystem: tree-optimization
patch_id: —
commit_hash: a97f2ef0d90d46144b39a8c9ea670b52dd13233a
source_type: github
headline: tree-optimization/126404 - Fix CTZ pattern to not break reductions
tldr: Prevents the CTZ pattern recognizer from breaking vector reduction chains by avoiding recursion on reduction patterns.
author: Richard Biener
outcome: committed
performance_win: false
breaking_change: false
series_id: —
series_parts: []
tags: • optimization
• vectorizer
• bugfix
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/a97f2ef0d90d46144b39a8c9ea670b52dd13233a
date: 2026-07-28T00:00:00.000Z

A bug in the Count Trailing Zeros (CTZ) pattern recognition logic could cause it to incorrectly recurse into a temporary pattern statement. This led to the vectorizer breaking reduction chains because the setup was incomplete, resulting in multiple uses of the intermediate pattern. The fix ensures that the recognizer avoids recursing when the original pattern is part of a reduction, thus preserving the integrity of vector reductions.