Landing: 17c7aeffec9e

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Project / Subsystem

gcc / tree-optimization

Date

2026-09-30

Author

Dominic P

Commit

17c7aeffec9e1f7576957fdcb21e380d4e209c6f

Source

github

Perf win

Breaking

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All attributes

project: gcc
subsystem: tree-optimization
patch_id: —
commit_hash: 17c7aeffec9e1f7576957fdcb21e380d4e209c6f
source_type: github
headline: forwprop: Reset MOD result range when X is negative
tldr: Fixes incorrect constant folding of the MOD operator when the dividend can be negative.
author: Dominic P
outcome: committed
performance_win: false
breaking_change: false
series_id: —
series_parts: []
tags: • optimization
• compiler
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/17c7aeffec9e1f7576957fdcb21e380d4e209c6f
date: 2026-09-30T00:00:00.000Z

The forward propagation pass in GCC incorrectly preserved the range of a MOD result even when the dividend was negative. This led to incorrect folding of the result to zero in specific cases. This change resets the flow-sensitive information of the MOD result when its value is rewritten under these conditions, ensuring accurate constant propagation.