https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117986
Bug ID: 117986
Summary: templated auto parameter with lambda as default value
can result in duplicate symbols
Product: gcc
Version: 11.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: emilia144 at proton dot me
Target Milestone: ---
Hello, I am compiling the following code with g++ 11.4.0, -std=c++20, on WSL
(Windows Subsystem for Linux) Ubuntu:
```cpp
template<auto f = []() {}>
struct Templated {
void g() {
f();
}
};
int main() {
auto fake = []() {};
Templated<> templated;
templated.g();
auto help = []() {};
help();
}
```
with error:
```
/tmp/ccE3iRCY.s: Assembler messages:
/tmp/ccE3iRCY.s:29: Error: symbol `_ZZ4mainENKUlvE0_clEv' is already defined
```
I think this has something to do with the automatically generated types behind
the lambdas, and their generated names? When I remove some of the lambdas, or
give them different parameter names, this seems to compile fine.
## Used versions
$ g++ --version
gives:
```
g++ (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
```
Unfortunately I am not really able to test this code with a g++ version above
11 because of the operating system I am on. This code does compile correctly
with clang++ and with g++ on other platforms, so it is a platform-specific
issue.
$ wsl --version
gives:
```
WSL version: 2.3.26.0
Kernel version: 5.15.167.4-1
WSLg version: 1.0.65
MSRDC version: 1.2.5620
Direct3D version: 1.611.1-81528511
DXCore version: 10.0.26100.1-240331-1435.ge-release
Windows version: 10.0.19045.5131
```
## Verbose output
$ g++ -std=c++20 bugreport.cpp --verbose
gives:
```
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/11/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
11.4.0-1ubuntu1~22.04' --with-bugurl=file:///usr/share/doc/gcc-11/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-11
--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-bootstrap --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-11-XeT9lY/gcc-11-11.4.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-11-XeT9lY/gcc-11-11.4.0/debian/tmp-gcn/usr
--without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
--with-build-config=bootstrap-lto-lean --enable-link-serialization=2
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.4.0 (Ubuntu 11.4.0-1ubuntu1~22.04)
COLLECT_GCC_OPTIONS='-std=c++20' '-v' '-shared-libgcc' '-mtune=generic'
'-march=x86-64' '-dumpdir' 'a-'
/usr/lib/gcc/x86_64-linux-gnu/11/cc1plus -quiet -v -imultiarch
x86_64-linux-gnu -D_GNU_SOURCE bugreport.cpp -quiet -dumpdir a- -dumpbase
bugreport.cpp -dumpbase-ext .cpp -mtune=generic -march=x86-64 -std=c++20
-version -fasynchronous-unwind-tables -fstack-protector-strong -Wformat
-Wformat-security -fstack-clash-protection -fcf-protection -o /tmp/ccE3iRCY.s
GNU C++20 (Ubuntu 11.4.0-1ubuntu1~22.04) version 11.4.0 (x86_64-linux-gnu)
compiled by GNU C version 11.4.0, GMP version 6.2.1, MPFR version
4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring duplicate directory "/usr/include/x86_64-linux-gnu/c++/11"
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/11/include-fixed"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-linux-gnu/11/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/include/c++/11
/usr/include/x86_64-linux-gnu/c++/11
/usr/include/c++/11/backward
/usr/lib/gcc/x86_64-linux-gnu/11/include
/usr/local/include
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
GNU C++20 (Ubuntu 11.4.0-1ubuntu1~22.04) version 11.4.0 (x86_64-linux-gnu)
compiled by GNU C version 11.4.0, GMP version 6.2.1, MPFR version
4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: d591828bb4d392ae8b7b160e5bb0b95f
COLLECT_GCC_OPTIONS='-std=c++20' '-v' '-shared-libgcc' '-mtune=generic'
'-march=x86-64' '-dumpdir' 'a-'
as -v --64 -o /tmp/ccq1Sj9i.o /tmp/ccE3iRCY.s
GNU assembler version 2.38 (x86_64-linux-gnu) using BFD version (GNU Binutils
for Ubuntu) 2.38
/tmp/ccE3iRCY.s: Assembler messages:
/tmp/ccE3iRCY.s:29: Error: symbol `_ZZ4mainENKUlvE0_clEv' is already defined
```
