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From: "m-matti-a.lehtonen at iki dot fi" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/110328] New: Module related optimization is too aggressive
Date: Tue, 20 Jun 2023 18:26:33 +0000
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X-Bugzilla-Version: 12.3.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110328

            Bug ID: 110328
           Summary: Module related optimization is too aggressive
           Product: gcc
           Version: 12.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: m-matti-a.lehtonen at iki dot fi
  Target Milestone: ---

Created attachment 55375
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D55375&action=3Dedit
Example sources

When the module example (files test.cc and test2.cc) is compiles as
> g++-12 --std=3Dc++20 -Wall -Wextra -Werror -pedantic  -fmodules-ts -O1  -=
DNDEBUG test2.cc test.cc
it generates the following error:
> In file included from test.cc:4,
> of module test, imported at test2.cc:5:
> In destructor =E2=80=98virtual std::bad_optional_access::~bad_optional_ac=
cess()=E2=80=99,
>     inlined from =E2=80=98virtual std::bad_optional_access::~bad_optional=
_access()=E2=80=99 at > test2.cc:8:15:
> /usr/include/c++/12/optional:102:13: error: =E2=80=98this=E2=80=99 is use=
d uninitialized [-Werror=3Duninitialized]
>   102 |     virtual ~bad_optional_access() =3D default;
>       |             ^
> In file included from test2.cc:2:
> /usr/include/c++/12/optional: In destructor =E2=80=98virtual std::bad_opt=
ional_access::~bad_optional_access()=E2=80=99:
> /usr/include/c++/12/optional:102:13: note: =E2=80=98this=E2=80=99 was dec=
lared here
>   102 |     virtual ~bad_optional_access() =3D default;
>       |             ^

If the if statement at test2.cc is uncommented, no error is generated.

If basically the same code (file test3.cc) is compiled without using module=
s,
no problem
> g++-12 --std=3Dc++20 -Wall -Wextra -Werror -pedantic -O1  -DNDEBUG test3.=
cc

Exact version and system (Ubuntu 22.04.2 LTS)
> $ g++-12  --version
> g++-12 (Ubuntu 12.3.0-1ubuntu1~22.04) 12.3.0=