Landing: 3c5cc8819fe0

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Project / Subsystem

gcc / match

Date

2026-08-19

Author

Kyrylo Tkachov

Commit

3c5cc8819fe03b63cba9ff82569623d092fdf0f5

Source

github

Perf win

Breaking

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All attributes

project: gcc
subsystem: match
patch_id: —
commit_hash: 3c5cc8819fe03b63cba9ff82569623d092fdf0f5
source_type: github
headline: Match: Rejects NARROW_CLIP saturating truncation at minimum value for correctness.
tldr: Pattern matching for unsigned integer narrow clip saturating truncation now rejects cases involving the minimum value to avoid incorrect results.
author: Kyrylo Tkachov
outcome: committed
performance_win: false
breaking_change: false
series_id: —
series_parts: []
tags: • match
• optimization
• bugfix
• integer arithmetic
• saturating arithmetic
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/3c5cc8819fe03b63cba9ff82569623d092fdf0f5
date: 2026-08-19T00:00:00.000Z

This commit adjusts the unsigned_integer_narrow_clip pattern in GCC’s matcher to reject cases where the operand is known to be the minimum value of its type. The original pattern could incorrectly rewrite a program when the minimum value was present, leading to a stored value of NT_MAX instead of the expected 0 on certain targets. The updated pattern now requires the minimum value not to occur, preserving correctness and resolving PR126981.