Landing: 2ae9740dde82

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Project / Subsystem

gcc / tree-optimization

Date

2026-10-02

Author

Richard Biener

Commit

2ae9740dde8225371d3791a71b99d52ef686e2cc

Source

github

Perf win

Yes

Breaking

View on GitHub →

All attributes

project: gcc
subsystem: tree-optimization
patch_id: —
commit_hash: 2ae9740dde8225371d3791a71b99d52ef686e2cc
source_type: github
headline: tree-optimization: Fix missed FRE in loop
tldr: Improves loop optimizations by ensuring FRE does not abort prematurely on PHI nodes in CFG cycles.
author: Richard Biener
outcome: committed
performance_win: true
breaking_change: false
series_id: —
series_parts: []
tags: • optimization
• loop
• bugfix
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/2ae9740dde8225371d3791a71b99d52ef686e2cc
date: 2026-10-02T00:00:00.000Z

This commit fixes a missed optimization in the Free Register Elimination (FRE) pass for loops. A previous correctness fix caused FRE to incorrectly abort when encountering a loop PHI node within a control flow graph (CFG) cycle. The change modifies the maybe_skip_until function to stop the traversal when it revisits the original PHI node, allowing constant propagation and avoiding the bug.