llvm/llvm-project

[C++20] [Modules] Not proper module initializer

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#174,065 opened on Dec 31, 2025

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ABIclang:moduleshelp wantedplatform:windows

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Description

In my local linux machine, for

export module a;

When I generate the code, I can see:

define void @_ZGIW1a() #0 section ".text.startup" {
entry:
  ret void
}

this is used for initializing entities for the module unit. Itanium C++ ABI asks us to generate this even if we don't need to initialize any thing.

But if I turned MSVC ABI, I can say nothing for the initializer. We need input from MSVC, either formal docs or developers, how should we do here. And if we missed anything, we need to implement the module initializer for Windows ABI.

Estimated difficulty: medium

Contributor guide

Research direction
Study the MSVC ABI documentation for module initializers and implement the missing function for Windows target.
Tech stack
cpp
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
C++compiler development
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40