Question

I’ve had a really bizarre problem that I’ve reduced to the following test case:

#include <iostream>
#include <map>
#include <string>

struct Test
{
    std::map<std::string, void (Test::*)()> m;
    Test()
    {
        this->m["test1"] = &Test::test1;
        this->m["test2"] = &Test::test2;
    }
    void test1() { }
    void test2() { }
    void dispatch(std::string s)
    {
        if (this->m.at(s) == &Test::test1)
        { std::cout << "test1 will be called..." << std::endl; }
        else if (this->m.at(s) == &Test::test2)
        { std::cout << "test2 will be called..." << std::endl; }
        (this->*this->m.at(s))();
    }
};

int main()
{
    Test t;
    t.dispatch("test1");
    t.dispatch("test2");
}

It outputs

test1 will be called…
test1 will be called…

when optimizations are enabled, which is really bizarre. What’s going on?

Answer 1

It turns out Visual C++’s linker can merge functions with identical definitions into one.
Whether that’s legal or not according to C++, I have no idea; it affects observable behavior, so it looks like a bug to me. Someone else with more information may want to chime in on that though.