Possible bug in g++ - template specialization

Possible bug in g++ - template specialization

[Maciej Cencora]

Hi,

I think I've found a bug in g++. Let's say we have following files:

// a.hpp

template<typename T>
void func1()
{
	// general code
}

// a.cpp

#include "a.hpp"

template<>
void func1<int>()
{
	// specialized code
}

// main.cpp

#include "a.hpp"

int main(void)
{
	func1<int>();
	
	return 0;
}


Now when we run the program compiled with: g++ main.cpp a.cpp -o main
specialized version of func1 will be called, but when compiled with
-Os flag the general version will be called.
I'm not an expert but I believe the -Os behaviour is the correct one.

Please CC me when replying, as I'm not subscribed to the mailing list.

Regards,
Maciej Cencora

Re: Possible bug in g++ - template specialization

[Richard Guenther]

On Fri, Jul 10, 2009 at 1:48 PM, Maciej Cencora<m.cencora@gmail.com> wrote:
> Hi,
>
> I think I've found a bug in g++. Let's say we have following files:
>
> // a.hpp
>
> template<typename T>
> void func1()
> {
>        // general code
> }
>
> // a.cpp
>
> #include "a.hpp"
>
> template<>
> void func1<int>()
> {
>        // specialized code
> }
>
> // main.cpp
>
> #include "a.hpp"
>
> int main(void)
> {
>        func1<int>();
>
>        return 0;
> }
>
>
> Now when we run the program compiled with: g++ main.cpp a.cpp -o main
> specialized version of func1 will be called, but when compiled with
> -Os flag the general version will be called.
> I'm not an expert but I believe the -Os behaviour is the correct one.

By not making the specialized version available at the point of
instantiation you are violating the one-definition rule (ODR, no need
to diagnose it) and the behavior is undefined.

Richard.