Question

I get some warning with template and g++ -Os.
Why ?
How to remove these warning with -Os -Winline ?

Edit 1: g++ v4.6.1 And if I replace uint32_t by unsigned int my main error is corrected: ( This bug has been reported: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52888 )

Event.h:109:12: attention : inlining failed in call to ‘uint32_t Event<ParamT>::attach(ListenerT*, bool (ListenerT::*)(ParamT)) [with ListenerT = Listener, ParamT = unsigned int, uint32_t = unsigned int]’: mismatched arguments [-Winline]

Edit 2: The following warning seem to be a g++ error (http://gcc.gnu.org/ml/gcc-help/2012-07/msg00029.html) ( I havn’t any ~Player() ) inlining failed in call to ‘Player::~Player()’: call is unlikely and code size would grow [-Winline]

Edit 3: For removing the previous warning, add Player::~Player() __attribute__ ((noinline)) {}

.

Code for testing: Event.h

#ifndef EVENT_H
#define EVENT_H

#include <map>
#include <stdint.h>

/***************************************************************************//*!
* @brief Collect Listener
* @tparam ParamT        Param type of the function
*/
template<typename ParamT>
class EventHandlerBase
{
    public:
        virtual bool notify( ParamT param ) = 0;
};


/***************************************************************************//*!
* @brief Conteneur d'un receveur d'event.
* @tparam ListenerT     Object type
* @tparam ParamT        Param type of the function
*/
template<typename ListenerT, typename ParamT>
class EventHandler : public EventHandlerBase<ParamT>
{
    private:
        typedef bool (ListenerT::*PtrMember)(ParamT);

    private:
        ListenerT*      m_object;//!< Object listener
        PtrMember       m_member;//!< Function listener

    public:
        /********************************************************************//*!
        * @brief Constructor
        * @param[in] object     Instance listener
        * @param[in] member     Function listener ( Function need to be a public member of {object} )
        * @return[NONE]
        */
        EventHandler( ListenerT* object, PtrMember member )
        {
            m_object = object;
            m_member = member;
        }


        /*******************************************************************//*!
        * @brief Emit a signal to listeners
        * @param[in] param      Data
        * @return FALSE for breaking event loop
        */
        bool notify( ParamT param )
        {
            return (m_object->*m_member)(param);
        }
};


/***************************************************************************//*!
* @brief Event system
* @tparam ParamT        Param type of the function
*/
template<typename ParamT>
class Event
{
    private:
        typedef typename std::map< uint32_t, EventHandlerBase<ParamT>* > HandlersMap;

    private:
        HandlersMap     m_handlers;//!< Contient la liste des instances::fonctions en écoute sur cet event
        uint32_t        m_counter;//!< Permet de gérer les id

    public:
        /********************************************************************//*!
        * @brief Constructor
        * @return[NONE]
        */
        Event()
        {
            m_counter = 0;
        }


        /********************************************************************//*!
        * @brief Destructor
        * @return[NONE]
        */
        ~Event()
        {
            typename HandlersMap::iterator it = m_handlers.begin();
            for(; it != m_handlers.end(); it++)
            {
                if( it->second )
                    delete it->second;
            }
        }


        /*******************************************************************//*!
        * @brief Link a function and instance to this event
        * @param[in] object     Instance listener
        * @param[in] PtrMember  Function listener ( Function need to be a public member of {object} )
        * @return Connection ID
        *
        * @warning DO NOT FORGET TO CALL Event::detach(uint32_t) if you delete {object}
        */
        template<typename ListenerT>
        uint32_t attach( ListenerT* object, bool (ListenerT::*PtrMember)(ParamT) )
        {
            m_handlers[m_counter] = new EventHandler<ListenerT,ParamT>(object, PtrMember);
            m_counter++;
            return m_counter-1;
        }


        /*******************************************************************//*!
        * @brief Emit a signal to listeners
        * @param[in] param      Data
        * @return[NONE]
        */
        void notify( ParamT param )
        {
            typename HandlersMap::iterator it = m_handlers.begin();
            for(; it != m_handlers.end(); it++)
            {
                if( !it->second->notify(param) )
                    return ;
            }
        }


        /*******************************************************************//*!
        * @brief Unlink a listener.
        * @param[in] id     Connection ID from Event::attach
        * @return TRUE if removed
        */
        bool detach( uint32_t id )
        {
            typename HandlersMap::iterator it = m_handlers.find(id);

            if( it == m_handlers.end() )
                return false;

            delete it->second;
            m_handlers.erase(it);
            return true;
        }
};

#endif // EVENT_H

Main.cpp

#include <stdio.h>
#include "Event.h"

class Player
{
    public:
        Event<uint32_t> e_speed;

    private:
        uint32_t        m_speed;

    public:
        Player()
        {
            m_speed = 15;
        }
        void setSpeed( uint32_t speed )
        {
            m_speed = speed;
            e_speed.notify(speed);
        }
};

class Listener
{
    private:
        Player      m_player;

    public:
        Listener()
        {
            m_player.e_speed.attach(this, &Listener::SLOT_speed);
        }
        bool SLOT_speed( uint32_t speed )
        {
            printf("Speed changed to %u\n", speed);
            return true;
        }
        Player* player()
        {
            return &m_player;
        }
};

int main()
{
    Listener l;
    l.player()->setSpeed(42);

    return 0;
}

Compile this code with: g++ -Os -W -Wall -Winline *.cpp
You will get these warning:

Event.h:109:12: attention : inlining failed in call to ‘uint32_t Event<ParamT>::attach(ListenerT*, bool (ListenerT::*)(ParamT)) [with ListenerT = Listener, ParamT = unsigned int, uint32_t = unsigned int]’: mismatched arguments [-Winline]
main.cpp:32:56: attention : appelé d'ici [-Winline]
main.cpp:4:7: attention : inlining failed in call to ‘Player::~Player()’: call is unlikely and code size would grow [-Winline]
main.cpp:31:3: attention : appelé d'ici [-Winline]
main.cpp:4:7: attention : inlining failed in call to ‘Player::~Player()’: call is unlikely and code size would grow [-Winline]
main.cpp:24:7: attention : appelé d'ici [-Winline]
main.cpp:4:7: attention : inlining failed in call to ‘Player::~Player()’: call is unlikely and code size would grow [-Winline]
main.cpp:24:7: attention : appelé d'ici [-Winline]

Answer 1

It seems that g++ expands typedefs before using them as template arguments, but fails to expand typedefs not used as template arguments when comparing them with the former.

A simpler version of your code illustrates this :

#include <iostream>

typedef unsigned int uint32_t;

template <typename T>
class Foo {
    public :
        template <typename C>
        void fun(C* c, void (C::*f)(T)) {
            (c->*f)(42);
        }
};

class BarBad {
    private :
        Foo<uint32_t> foo;

    public :
        BarBad() {
            foo.fun(this, &BarBad::fun);
        }
        void fun(uint32_t t) {
            std::cout << t << std::endl;
        }
};

template <typename T>
class BarGood {
    private :
        Foo<T> foo;

    public :
        BarGood() {
            foo.fun(this, &BarGood<T>::fun);
        }
        void fun(T t) {
            std::cout << t << std::endl;
        }
};

int main(void) {
    BarBad bb;
    BarGood<uint32_t> bg;
    return 0;
}

This code only gets a warning for the BarBad code :

test.cpp: In function ‘int main()’:
test.cpp:9: warning: inlining failed in call to ‘void Foo<T>::fun(C*, void (C::*)(T)) [with C = BarBad, T = unsigned int]’: function not considered for inlining
test.cpp:20: warning: called from here

In BarBad, when calling Foo<uint32_t>::fun, the type of the second parameter is void (BarBad::*)(uint32_t), but the called function expects void (BarBad::*)(unsigned int), and fails to see that uint32_t and unsigned int are the same types.

In BarGood<uint32_t>, when calling Foo<uint32_t>::fun, the type of the second parameter is void (BarGood<uint32_t>::*)(unsigned int), which matches what the called function expects.

This feels like a compiler bug to me. And a bit of searching turned up this bug report :

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52888

I haven’t tested whether the solution there fixes this issue too, but it sounds like it would.