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From: "f.b.brokken at rug dot nl" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/104202] New: when defining a std::string in a module
 implementation file using -O2 g++ segfaults
Date: Mon, 24 Jan 2022 10:57:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104202

            Bug ID: 104202
           Summary: when defining a std::string in a module implementation
                    file using -O2 g++ segfaults
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: f.b.brokken at rug dot nl
  Target Milestone: ---

Created attachment 52274
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D52274&action=3Dedit
Output of the compiler (segfaults) when compiling 'mod.cc'

Using the following main file (main.cc):

---------------------------------
#include <iostream>
import mod;
int main()
{
    std::cout << modstr << '\n';
}
---------------------------------

defining the module mod interface in a separate file (zfirst.cc):

---------------------------------
module;
#include <string>
export module mod;
export extern std::string modstr;
---------------------------------

and initializing modstr in a separate module implementation file (mod.cc):

-------------------------------
module;
#include <string>
module mod;
std::string modstr{ "hello" };
-------------------------------

compiles OK when using the following compiler options:

--std=3Dc++20 -Wall -Wextra -fno-strict-aliasing -fwrapv -fmodules-ts

but when adding the option -O2 the compiler segfaults (compiler output is
attached). Omitting the -Wextra -fno-strict-aliasing -fwrapv  options makes=
 no
difference.

The compilation was performed on a (yesterday) updated Debian testing
distribution using=20

g++ (Debian 12-20211217-1) 12.0.0 20211217 (experimental) [master
r12-6027-g774269aa4b9]
Copyright (C) 2021 Free Software Foundation, Inc.

If you need any additional information, please let me know.
Kind regards,

Frank.=