[Bug c++/11750] class scope using-declaration lookup not implemented

[Bug c++/11750] class scope using-declaration lookup not implemented

[balakrishnan.erode at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11750

Balakrishnan B <balakrishnan.erode at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |balakrishnan.erode at gmail
                   |                            |dot com

--- Comment #6 from Balakrishnan B <balakrishnan.erode at gmail dot com> 2011-01-12 16:57:07 UTC ---
(In reply to comment #0)
> Paragraph 10.3/2 in the C++ standard [ISO/IEC 14882:1998] provides the
> following
> code example:
> 
> <quote>
> 
> struct A {
>     virtual void f();
> };
> struct B : virtual A {
>     virtual void f();
> };
> 
> struct C : B , virtual A {
>     using A::f; 
> };
> void foo() {
>     C c; 
>     c.f();      // calls B::f, the final overrider
>     c.C::f();   // calls A::f because of the using-declaration
> }
> 
> </quote>
> 
> When a similar program is compiled using G++ 3.3, the method call 'c.f()' in
> function foo() incorrectly invokes A::f and not B::f as specified in the
> standard.
> 
> <example>
> <code main.cpp>
> #include <iostream>
> 
> struct A {
>     virtual void f() { std::cout << "A::f()\n"; }
> };
> struct B : virtual A {
>     virtual void f() { std::cout << "B::f()\n"; }
> };
> struct C : B, virtual A {
>     using A::f;
> };
> 
> int main()
> {
>     C c;
>     c.f();      // ERROR - Incorrectly invokes A::f
>     c.C::f();   // OK - Invokes A::f
> }
> </code>
> 
> <build>
> $ g++ main.cpp
> 
> $ ldd a.out
>         libstdc++.so.5 =>
> /usr/local/gcc/3.3/lib/gcc-lib/i686-pc-linux-gnu/3.3/libstdc++.so.5
> (0x40017000)
>         libm.so.6 => /lib/tls/libm.so.6 (0x400e4000)
>         libgcc_s.so.1 =>
> /usr/local/gcc/3.3/lib/gcc-lib/i686-pc-linux-gnu/3.3/libgcc_s.so.1 (0x40106000)
>         libc.so.6 => /lib/tls/libc.so.6 (0x42000000)
>         /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)
> </build>
> 
> <output>
> $ ./a.out
> A::f()
> A::f()
> </output>
> 
> </example>

Im using g++ 4.4.5
With the same example with my main function as below,
int main()
{
      C c;
      c.f() // Calls A::f
      C* pc = &c;
      pc->f() // Calls B::f
}

With the same object when accessed directly produces different results and when
accessed using a pointer of same type produces a different result. Even if gcc
violates standard, there has to be some proper explanation.

[Bug c++/11750] class scope using-declaration lookup not implemented

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11750

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-01-12 17:10:17 UTC ---
(In reply to comment #6)
> 
> With the same object when accessed directly produces different results and when
> accessed using a pointer of same type produces a different result. Even if gcc
> violates standard, there has to be some proper explanation.

The explanation is "it's a bug"

[Bug c++/11750] class scope using-declaration lookup not implemented

[aschepler at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11750

--- Comment #8 from Andrew Schepler <aschepler at gmail dot com> 2011-01-12 17:16:29 UTC ---
(In reply to comment #6)
> > struct A {
> >     virtual void f();
> > };
> > struct B : virtual A {
> >     virtual void f();
> > };
> > 
> > struct C : B , virtual A {
> >     using A::f; 
> > };

> Im using g++ 4.4.5
> With the same example with my main function as below,
> int main()
> {
>       C c;
>       c.f() // Calls A::f
>       C* pc = &c;
>       pc->f() // Calls B::f
> }
> 
> With the same object when accessed directly produces different results and when
> accessed using a pointer of same type produces a different result. Even if gcc
> violates standard, there has to be some proper explanation.

The reason is that when f is invoked via a pointer or reference, g++ uses the
vtable lookup to call the correct final override.  But when the object in the
member access is not a pointer or reference (it is a non-reference identifier
as here, or qualified id, or class member), g++ can usually optimize away the
virtual call and just call the correct member function.  In this case the logic
for calling the correct member function for that optimization is incorrect, but
virtual calls still work correctly.

[Bug c++/11750] class scope using-declaration lookup not implemented

[fabien at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11750

fabien at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2005-12-18 20:22:49         |2011-11-21 20:22:49

[Bug c++/11750] class scope using-declaration lookup not implemented

[fabien at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11750

--- Comment #9 from fabien at gcc dot gnu.org 2012-11-14 20:12:56 UTC ---
Author: fabien
Date: Wed Nov 14 20:12:47 2012
New Revision: 193504

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=193504
Log:
gcc/testsuite/ChangeLog

2012-11-14  Fabien Chêne  <fabien@gcc.gnu.org>

    PR c++/11750
    * g++.dg/inherit/vitual9.C: New.

gcc/cp/ChangeLog

2012-11-14  Fabien Chêne  <fabien@gcc.gnu.org>

    PR c++/11750
    * call.c (build_new_method_call_1): Check that the instance type
    and the function context are the same before setting the flag
    LOOKUP_NONVIRTUAL.

Added:
    trunk/gcc/testsuite/g++.dg/inherit/virtual9.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/call.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/11750] class scope using-declaration lookup not implemented

[fabien at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11750

fabien at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.8.0

--- Comment #10 from fabien at gcc dot gnu.org 2012-11-14 20:20:21 UTC ---
Fixed in 4.8.

[Bug c++/11750] class scope using-declaration lookup not implemented

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=11750

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |meng at g dot clemson.edu

--- Comment #11 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 55385 has been marked as a duplicate of this bug. ***