[Bug c++/58173] New: [C++11] Bad interaction between sizeof... and remainder (%) operators

[lucdanton at free dot fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58173

            Bug ID: 58173
           Summary: [C++11] Bad interaction between sizeof... and
                    remainder (%) operators
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lucdanton at free dot fr

$ g++-snapshot --version
g++-snapshot (GCC) 4.9.0 20130806 (experimental)

$ cat main.cpp 
template<typename... T>
struct foo {
    static constexpr auto N = sizeof...(T);

    struct bar {
        static_assert( N == 5, "" );
        static_assert( (-1) % 5 == -1, "" );
        static_assert( (-1) % N != -1, "" );
    };
};

int main()
{
    foo<int, int, int, int, int>::bar();
}

$ g++-snapshot -std=c++11 main.cpp

-------------------

That is, the compiler does not reject the program even though the three
assertions cannot all hold simultaneously. As far as I can tell factoring the
sizeof...(T) expression into N isn't necessary for the bug, and the use of the
remainder operator is.

This seems to happen with 4.8.1 as well.