Landing: 811cc466193d

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Project / Subsystem

gcc / c++

Date

2026-05-19

Author

Marek Polacek

Commit

811cc466193d7efcfcc07d2081b1284d97fc91a1

Source

github

Perf win

Yes

Breaking

No

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All attributes

project: gcc
subsystem: c++
patch_id: —
commit_hash: 811cc466193d7efcfcc07d2081b1284d97fc91a1
source_type: github
headline: C++ frontend improves alias recognition with lambda template arguments
tldr: GCC's C++ frontend now more efficiently recognizes aliases involving lambda template arguments, leading to minor compilation speed improvements.
author: Marek Polacek
outcome: committed
performance_win: true
breaking_change: false
series_id: —
series_parts: []
tags: • c++
• frontend
• performance
• templates
• lambdas
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/811cc466193d7efcfcc07d2081b1284d97fc91a1
date: 2026-05-19T00:00:00.000Z

This commit enhances the GCC C++ frontend’s ability to recognize dependencies when lambda expressions are used as template arguments. A new flag, TYPE_DECL_OPAQUE_ALIAS_P, is introduced to mark declarations, avoiding expensive tree traversals in dependent_opaque_alias_p. This optimization specifically targets deeply nested lambdas, which previously fooled the alias detection logic. The change yields a marginal but measurable improvement in compilation time, particularly for complex C++ codebases like range-v3.