Landing: e88f8d7bfc81

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Project / Subsystem

gcc / tree-optimization

Date

2026-05-11

Author

Richard Biener

Commit

e88f8d7bfc811f6d152c42ba009255506f5beba1

Source

github

Perf win

Breaking

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All attributes

project: gcc
subsystem: tree-optimization
patch_id: —
commit_hash: e88f8d7bfc811f6d152c42ba009255506f5beba1
source_type: github
headline: Loop idiom recognition avoids speculating no-op load/store.
tldr: GCC's loop idiom recognition avoids speculating load/store pairs for modes that cannot transfer bits, preventing undefined behavior.
author: Richard Biener
outcome: committed
performance_win: false
breaking_change: false
series_id: —
series_parts: []
tags: • optimization
• bugfix
• loop optimization
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/e88f8d7bfc811f6d152c42ba009255506f5beba1
date: 2026-05-11T00:00:00.000Z

The loop idiom recognition pass in GCC was speculating load/store pairs for modes where bit transfer is impossible. This commit prevents the speculation for such modes, including boolean types and bitfield accesses. It also avoids undefined behavior when bitfield loads are out-of-bounds.