Landing: dad7275f7cc5

← All landings

Project / Subsystem

gcc / c++/templates

Date

2026-09-07

Author

Iain Sandoe

Commit

dad7275f7cc570fe222777285d8e8dbf274bb772

Source

github

Perf win

No

Breaking

No

View on GitHub →

All attributes

project: gcc
subsystem: c++/templates
patch_id: —
commit_hash: dad7275f7cc570fe222777285d8e8dbf274bb772
source_type: github
headline: C++: Fix folding of CONSTRUCTOR in templates to avoid invalid expressions.
tldr: C++ template instantiation now correctly avoids folding CONSTRUCTORs that have already been processed, fixing an issue with template expression substitution.
author: Iain Sandoe
outcome: committed
performance_win: false
breaking_change: false
series_id: —
series_parts: []
tags: • c++
• templates
• compiler bug
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/dad7275f7cc570fe222777285d8e8dbf274bb772
date: 2026-09-07T00:00:00.000Z

This commit addresses a bug in C++ template instantiation where the compiler attempted to re-fold a CONSTRUCTOR expression within a template. This occurred after the Non-Type Template Parameter Declaration (NSDMI) had already been folded, leading to invalid expressions that the template substitution machinery could not handle.

The fix, implemented in typeck2.cc, prevents the folding of CONSTRUCTORs in such scenarios, resolving the issue and ensuring correct template instantiation. A new test case is added to verify the fix.