https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126280
Bug ID: 126280
Summary: "used but never defined" SFINAE warning for function
template in specific circumstances
Product: gcc
Version: 14.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: a.777.kiselev at gmail dot com
Target Milestone: ---
Repro:
template<typename T>
using op_t = T(*)(T);
template<typename T>
static T inc(T a) {
return a + 1;
}
template<typename T>
static T wrapper(const op_t<T> f, const T v) {
return f(v);
}
template<typename T, op_t<T>... ops>
static T agg(T v) {
((v = wrapper(ops, v)), ...);
return v;
}
template<int N>
static int test() {
return agg<int, inc<int>>(0);
}
// [[maybe_unused]] static void _workaround() {
// (void) inc<int>;
// }
int job() {
return test<1>();
}
Actual result:
$ g++ -std=gnu++23 -fPIC -Wall -Wextra -g -O3 -c test.cpp -o test.o
test.cpp:7:10: warning: ‘T inc(T) [with T = int]’ used but never defined
7 | static T inc(T a) {
| ^~~
Uncommenting _workaround() removes the warning and produces a symbol for `int
inc(int)`.
Known affected builds:
Using built-in specs.
COLLECT_GCC=/home/alex/opt/gcc-14.4.0/bin/g++
COLLECT_LTO_WRAPPER=/home/alex/opt/gcc-14.4.0/libexec/gcc/x86_64-pc-linux-gnu/14.4.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ./configure --enable-languages=c,c++ --disable-multilib
--with-system-zlib --with-target-system-zlib=auto
--prefix=/home/alex/opt/gcc-14.4.0
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 14.4.0 (GCC)
===
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-linux-gnu/14/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='Debian 14.2.0-19'
--with-bugurl=file:///usr/share/doc/gcc-14/README.Bugs
--enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2,rust --prefix=/usr
--with-gcc-major-version-only --program-suffix=-14
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/libexec --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-libstdcxx-backtrace
--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/reproducible-path/gcc-14-14.2.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/reproducible-path/gcc-14-14.2.0/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
--with-build-config=bootstrap-lto-lean --enable-link-serialization=3
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 14.2.0 (Debian 14.2.0-19)
===
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='Debian 12.4.0-5'
--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/reproducible-path/gcc-12-12.4.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/reproducible-path/gcc-12-12.4.0/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 12.4.0 (Debian 12.4.0-5)
