[Bug c++/104202] New: when defining a std::string in a module implementation file using -O2 g++ segfaults

["f.b.brokken at rug dot nl" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104202

            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=52274&action=edit
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=c++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 

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.