Why compiler can't optimize this c++ code?

My code is like this:

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

const std::string makeKv(const std::map<std::string, std::string> &tagkv) {
    std::ostringstream oss;
    bool first = true;
    for (const auto &kv : tagkv) {
        if (first) {
            first = false;
            } else {
            oss << '|';
            }
        oss << kv.first << '=' << kv.second;
        }
    return oss.str();
}

void compileOptimizer(const std::string &s) {
    std::cout << s <<std::endl;
}

void compileOptimizer(const std::map<std::string, std::string> &m) {
    std::string s = makeKv (m);
    compileOptimizer(s);
}

void test() {
    for (int i = 0; i < 100; i++) {
        compileOptimizer (k);
    }
}

int main(int argc, char **argv) {
    test ();
}

I'm using g++ (Debian 4.9.2-10) 4.9.2 With the command:

g++ -std=c++11 -O3 -S -fverbose-asm

In my understanding, the compiler should optimize the function test as

void test() {
    for (int i = 0; i < 100; i++) {
        compileOptimizer ("k=v");
    }
}

So the makeKv not be called so many times. But when I see the asm code, I'm not found the const string "k=v" in decompile code(in advanced decompile tools that can show all const string).

So I doubt it may not optimize this code like I understanding?

How can I make sure that, and how can I let compiler optimize as I expect.