Landing: 1c8ca0108746

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Project / Subsystem

gcc / match

Date

2026-06-17

Author

Eikansh Gupta

Commit

1c8ca0108746d3a7452134f9d1c2e5d89857fed7

Source

github

Perf win

No

Breaking

No

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All attributes

project: gcc
subsystem: match
patch_id: —
commit_hash: 1c8ca0108746d3a7452134f9d1c2e5d89857fed7
source_type: github
headline: MATCH: fold signbit comparison and conditional negate to copysign [PR109843]
tldr: MATCH rule simplifies signbit comparisons and conditional negations into copysign operations.
author: Eikansh Gupta
outcome: committed
performance_win: false
breaking_change: false
series_id: —
series_parts: []
tags: • optimization
• MATCH
• copysign
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/1c8ca0108746d3a7452134f9d1c2e5d89857fed7
date: 2026-06-17T00:00:00.000Z

A new rule has been added to the GCC MATCH optimization patterns to recognize and simplify a common code sequence involving sign bit comparisons and conditional negations. The pattern (signbit (x) cmp1 0) cmp (signbit (y) cmp2 0) ? y : -y is now folded into a copysign(y, +-x) operation. This transformation preserves the magnitude of y while taking its sign from x (or -x), and can be emitted as IFN_COPYSIGN on supporting targets, leading to more efficient code for operations like copysign and potentially improving performance.