C ++ compiler optimization discards specialized patterns

I noticed that the template specialization in .cpp files is discarded if compiler optimization is enabled. I found this in a large application, and I welded the problem with a simple example.

First I define a new class in obj.h

#ifndef _OBJ_H_
#define _OBJ_H_

class Obj { };

#endif //_OBJ_H_

Then I define a new template function in templates.h

#ifndef _TEMPLATES_H_
#define _TEMPLATES_H_

template<typename T>
int get()
{
    return 0;
}

#endif //_TEMPLATES_H_

... and specialization for the Obj class in templates.cpp

#include "templates.h"
#include "obj.h"

template<>
int get<Obj>()
{
    return 1;
}

Then I call the main function:

#include <stdio.h>
#include "templates.h"
#include "obj.h"

int main()
{
    printf("Get: %d\n", get<Obj>());
    return 0;
}

Compiling this example with different levels -Ogives different outputs.

$ g++ -o a main.cpp templates.cpp -O0
$ ./a
Get: 1

$ g++ -o a main.cpp templates.cpp -O2 #same with -O3, -O4, Os
$ ./a
Get: 0

g++ clang. g++ 4.7.2 clang 3.4.
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