[Bug c++/105637] New: [11 Regression] Wrong overload selected in base class

[Bug c++/105637] New: [11 Regression] Wrong overload selected in base class

[ted at lyncon dot se]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105637

            Bug ID: 105637
           Summary: [11 Regression] Wrong overload selected in base class
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ted at lyncon dot se
  Target Milestone: ---

This compiles fine in 11.3 but selects the non-const `BaseClass` overload in
12.1:
```
struct BaseClass {
    // Commenting out this non-const function out will fix the compilation:
    int baseDevice() { return 1; }
    int baseDevice() const { return 2; }
};

template <class ObjectClass>
struct DerivedClass : BaseClass {};

template <class ObjectClass>
struct TopClass : DerivedClass<ObjectClass> {
public:
    virtual int failsToCompile() const {
        // This should choose to call the const function, but it tries to call
        // the non-const version.
        return BaseClass::baseDevice();                   // error!
        //return this->baseDevice();                      // works
        //return DerivedClass<ObjectClass>::baseDevice(); // works
    }
};

int main() {
    TopClass<int> x; 
}
```

[Bug c++/105637] [12/13 Regression] Wrong overload selected in base class

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105637

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-05-17
            Summary|[12 Regression] Wrong       |[12/13 Regression] Wrong
                   |overload selected in base   |overload selected in base
                   |class                       |class
   Target Milestone|---                         |12.2
      Known to work|                            |11.3.0
     Ever confirmed|0                           |1
                 CC|                            |ppalka at gcc dot gnu.org
      Known to fail|                            |12.1.0, 13.0
           Keywords|                            |rejects-valid
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
             Status|UNCONFIRMED                 |ASSIGNED

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Started with r12-6075-g2decd2cabe5a4f.

[Bug c++/105637] [12/13 Regression] Wrong overload selected in base class

[john.robert.lefebvre at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105637

Rob Lefebvre <john.robert.lefebvre at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |john.robert.lefebvre@gmail.
                   |                            |com

--- Comment #2 from Rob Lefebvre <john.robert.lefebvre at gmail dot com> ---
This came from my project via a stack overflow post.  Thanks to Ted for
submitting it.  FYI, this is from an older version of the Teigha DXF libraries,
now called Drawings I think, https://www.opendesign.com/products/drawings.

[Bug c++/105637] [12/13 Regression] Wrong overload selected in base class

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105637

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug c++/105637] [12/13 Regression] Wrong overload selected in base class

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105637

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:44a5bd6d933d86ed988fc4695aa00f122cf83eb4

commit r13-984-g44a5bd6d933d86ed988fc4695aa00f122cf83eb4
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Jun 3 12:06:59 2022 -0400

    c++: cv-quals of dummy obj for non-dep memfn call [PR105637]

    In non-dependent23.C below we expect the Base::foo calls to
    resolve to the second, third and fourth overloads respectively in light
    of the cv-qualifiers of 'this' in each case.  But ever since
    r12-6075-g2decd2cabe5a4f, the calls incorrectly resolve to the first
    overload at instantiation time.

    This happens because the calls to Base::foo are all deemed
    non-dependent (ever since r7-755-g23cb72663051cd made us ignore 'this'
    dependence when considering the dependence of a non-static memfn call),
    hence we end up checking the call ahead of time, using as the object
    argument a dummy object of type Base.  Since this object argument is
    cv-unqualified, the calls in turn resolve to the unqualified overload
    of baseDevice.  Before r12-6075 this incorrect result would just get
    silently discarded and we'd end up redoing OR at instantiation time
    using 'this' as the object argument.  But after r12-6075 we now reuse
    this incorrect result at instantiation time.

    This patch fixes this by making maybe_dummy_object respect the cv-quals
    of (the non-lambda) 'this' when returning a dummy object.  Thus, ahead
    of time OR using a dummy object will give us the right answer that's
    consistent with the instantiation time answer.

    An earlier version of this patch didn't handle 'this'-capturing lambdas
    correctly, which broke lambda-this22.C below.

            PR c++/105637

    gcc/cp/ChangeLog:

            * tree.cc (maybe_dummy_object): When returning a dummy
            object, respect the cv-quals of 'this' if available.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/lambda/lambda-this22.C: New test.
            * g++.dg/template/non-dependent23.C: New test.

[Bug c++/105637] [12 Regression] Wrong overload selected in base class

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105637

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[12/13 Regression] Wrong    |[12 Regression] Wrong
                   |overload selected in base   |overload selected in base
                   |class                       |class

--- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed on trunk so far.

[Bug c++/105637] [12 Regression] Wrong overload selected in base class

[ted at lyncon dot se]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105637

--- Comment #5 from Ted Lyngmo <ted at lyncon dot se> ---
Excellent and thanks!

[Bug c++/105637] [12 Regression] Wrong overload selected in base class

[john.robert.lefebvre at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105637

--- Comment #6 from Rob Lefebvre <john.robert.lefebvre at gmail dot com> ---
Thank you!

[Bug c++/105637] [12 Regression] Wrong overload selected in base class

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105637

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:41487bff13fa98607ab5548bc1a0dca71147a5ac

commit r12-8603-g41487bff13fa98607ab5548bc1a0dca71147a5ac
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Jun 3 12:06:59 2022 -0400

    c++: cv-quals of dummy obj for non-dep memfn call [PR105637]

    In non-dependent23.C below we expect the Base::foo calls to
    resolve to the second, third and fourth overloads respectively in light
    of the cv-qualifiers of 'this' in each case.  But ever since
    r12-6075-g2decd2cabe5a4f, the calls incorrectly resolve to the first
    overload at instantiation time.

    This happens because the calls to Base::foo are all deemed
    non-dependent (ever since r7-755-g23cb72663051cd made us ignore 'this'
    dependence when considering the dependence of a non-static memfn call),
    hence we end up checking the call ahead of time, using as the object
    argument a dummy object of type Base.  Since this object argument is
    cv-unqualified, the calls in turn resolve to the unqualified overload
    of baseDevice.  Before r12-6075 this incorrect result would just get
    silently discarded and we'd end up redoing OR at instantiation time
    using 'this' as the object argument.  But after r12-6075 we now reuse
    this incorrect result at instantiation time.

    This patch fixes this by making maybe_dummy_object respect the cv-quals
    of (the non-lambda) 'this' when returning a dummy object.  Thus, ahead
    of time OR using a dummy object will give us the right answer that's
    consistent with the instantiation time answer.

    An earlier version of this patch didn't handle 'this'-capturing lambdas
    correctly, which broke lambda-this22.C below.

            PR c++/105637

    gcc/cp/ChangeLog:

            * tree.cc (maybe_dummy_object): When returning a dummy
            object, respect the cv-quals of 'this' if available.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/lambda/lambda-this22.C: New test.
            * g++.dg/template/non-dependent23.C: New test.

    (cherry picked from commit 44a5bd6d933d86ed988fc4695aa00f122cf83eb4)

[Bug c++/105637] [12 Regression] Wrong overload selected in base class

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105637

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #8 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 12.2/13