https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111089
Bug ID: 111089
Summary: ODR violation warning in std::variant implementation
when linking(LTO) C++20 and C++17 TUs
Product: gcc
Version: 12.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: damian.jarek93 at gmail dot com
Target Milestone: ---
Created attachment 55770
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55770&action=edit
ii files of a minimal example that reproduces the issue
When 2 TUs are LTO-linked, g++ complains about an ODR violation in
std::variant's implementation:
/usr/bin/g++-12 -flto -Wall -Wextra -g -flto=auto -fno-fat-lto-objects
CMakeFiles/main.dir/main.cpp.o -o main libcxx17-lib.a
/usr/include/c++/12/variant:244:12: note: type 'struct _Uninitialized' itself
violates the C++ One Definition Rule
244 | struct _Uninitialized<_Type, false>
| ^
/usr/include/c++/12/variant:378:11: note: type 'union _Variadic_union' itself
violates the C++ One Definition Rule
378 | union _Variadic_union<_First, _Rest...>
| ^
/workspaces/odr-bug-repro/cxx17.hpp:8:6: warning: 'test' violates the C++ One
Definition Rule [-Wodr]
8 | void test(std::variant<std::string, std::uint32_t> id);
| ^
/workspaces/odr-bug-repro/cxx17.cpp:5:6: note: type mismatch in parameter 1
5 | void test(std::variant<std::string, std::uint32_t> id)
| ^
/usr/include/c++/12/variant:1336:11: note: type 'struct variant' itself
violates the C++ One Definition Rule
1336 | class variant
| ^
/workspaces/odr-bug-repro/cxx17.cpp:5:6: note: 'test' was previously declared
here
5 | void test(std::variant<std::string, std::uint32_t> id)
|
The function 'void test(std::variant<std::string, std::uint32_t> id)' must be
defined in a TU compiled with -std=gnu++17 and called in a TU compiled with
-std=gnu++20.
Complete command line that reproduces the issue:
/usr/bin/g++-12 -std=gnu++20 -flto -Wall -Wextra -g -o main.cpp.o -c main.cpp
/usr/bin/g++-12 -std=gnu++17 -flto -Wall -Wextra -g -o cxx17.cpp.o -c
cxx17.cpp
/usr/bin/g++-12 -flto -Wall -Wextra -g -flto=auto -fno-fat-lto-objects
main.cpp.o cxx17.cpp.o -o main
g++ version:
Using built-in specs.
COLLECT_GCC=g++-12
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/12/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
12.3.0-1ubuntu1~22.04' --with-bugurl=file:///usr/share/doc/gcc-12/README.Bugs
--enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-12
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
--enable-gnu-unique-object --disable-vtable-verify --enable-plugin
--enable-default-pie --with-system-zlib --enable-libphobos-checking=release
--with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch
--disable-werror --enable-cet --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-12-ALHxjy/gcc-12-12.3.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-12-ALHxjy/gcc-12-12.3.0/debian/tmp-gcn/usr
--enable-offload-defaulted --without-cuda-driver --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.3.0 (Ubuntu 12.3.0-1ubuntu1~22.04)
I also tested this bug with g++ 13.1.0 and is still present there, although
the warning is slightly less verbose.
