https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85825
Bug ID: 85825 Summary: Incorrect selection of method in template<auto> class specialization. Product: gcc Version: 7.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: christosstratopoulos1 at gmail dot com Target Milestone: --- Created attachment 44144 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44144&action=edit The output of compilation with -save-temps Here is the full sample code that causes the issue: #include <cassert> enum class Frac : unsigned { half = 2, quarter = 4 }; enum class Whole : unsigned { two = 2, five = 5 }; template<unsigned, auto enumVal> class A; template<unsigned m, Frac f> class A<m, f> { public: constexpr double val() const noexcept { return 2.0; } }; template<unsigned m, Whole w> class A<m, w> { public: constexpr double val() const noexcept { return 1.0; } }; int main() { auto frac4 = A<100, Frac::quarter>{}.val(); auto whole5 = A<100, Whole::five>{}.val(); assert(frac4 != whole5); // passes auto frac2 = A<100, Frac::half>{}.val(); auto whole2 = A<100, Whole::two>{}.val(); assert(frac2 != whole2); // fails on g++ 7.x, fine on 8.1, 9 HEAD } This is a heavily reduced version of something I encountered at work today, originally when compiling some code for g++-7.3.0 on a Bash subsystem of a windows 10 install. I've attached a .ii for that file, and marked this as a g++-7.3 bug, but testing on wandbox.org has shown this holds for other g++ 7.x, but seems fine on 8 and 9. I first ran into this as a compile-time error when trying to compile with the windows version of clang 6, which reports "definition with same mangled name as other definition". I have not been able to repro this with online (Linux) versions of clang. Here is the output of g++-7 -v: Using built-in specs. COLLECT_GCC=g++-7 COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper OFFLOAD_TARGET_NAMES=nvptx-none OFFLOAD_TARGET_DEFAULT=1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 7.3.0-16ubuntu3~16.04.1' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --with-as=/usr/bin/x86_64-linux-gnu-as --with-ld=/usr/bin/x86_64-linux-gnu-ld --program-suffix=-7 --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 --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --with-system-zlib --with-target-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 7.3.0 (Ubuntu 7.3.0-16ubuntu3~16.04.1) and the command line invocation is g++-7 -std=c++17 gcc_bug_simple.cpp && ./a.out