CUDA: Host-side virtual destructor of template class leaks into PTX as weak function

[mkuron]

Consider the following bit of code:

void _Adjust_manually_vector_aligned()
{}

template <size_t>
constexpr void _Deallocate() {
    _Adjust_manually_vector_aligned();
}

struct basic_string {
    constexpr ~basic_string() {
        _Deallocate<8>();
    }
};

template <class Var_t>
class E {
  virtual ~E() = default;
  basic_string _name;
};

template class E<float>;

Including this into a CUDA file (you don't even have to use the class in a device-side function or variable) leads to errors like ptxas fatal : Unresolved extern function '_Z31_Adjust_manually_vector_alignedv' or, when compiling with -fgpu-rdc, corresponding errors from nvlink. The resulting PTX contains unreferenced .weak .funcs of the defaulted virtual destructor. This bears some similarity to #98151, but the circumstances under which the extraneous symbol is emitted differ.

The code for basic_string and the functions it calls was reduced from https://github.com/microsoft/STL/blob/vs-2022-17.0/stl/inc/xstring and https://github.com/microsoft/STL/blob/vs-2022-17.0/stl/inc/xmemory. The current issue makes it impossible to use std::string in template classes with defaulted virtual destructors when using CUDA on Windows in C++20 mode.

Godbolt: https://godbolt.org/z/7MTda4Kq4

NVCC does not show this issue, it never generates .weak .func symbols for host-side destructors. Clang appears to only be generating these extraneous .weak .func symbols for code that exactly follows the above pattern; eliminating the templates, the virtual, the default, or the constexprs makes the problem go away.