[Bug c++/100963] New: GCC 11 regression: templated constructor with std::initializer_list<T> is not selected

[Bug c++/100963] New: GCC 11 regression: templated constructor with std::initializer_list<T> is not selected

[j.l.k at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100963

            Bug ID: 100963
           Summary: GCC 11 regression: templated constructor with
                    std::initializer_list<T> is not selected
           Product: gcc
           Version: 11.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: j.l.k at gmx dot com
  Target Milestone: ---

Consider the following program (preprocessed source is attached):

```
#include <iostream>

struct A
{
    explicit A(int)
    {
        std::cout << "A(int) constructor called" << std::endl;
    }

    A(std::initializer_list<int>)
    {
        std::cout << "A's constructor with initializer_list called" <<
std::endl;
    }
};

struct B
{
    explicit B(int)
    {
        std::cout << "B(int) constructor called" << std::endl;
    }

    template<typename T>
    B(std::initializer_list<T>)
    {
        std::cout << "B's constructor with initializer_list called" <<
std::endl;
    }
};

int main()
{
    A({0});
    B({0});
}
```

When compiled with GCC 11 (`g++ -std=c++14
gcc11_initializer_list_constructor.cpp -o gcc11_initializer_list_constructor`),
the program gives the following output:

A's constructor with initializer_list called
B(int) constructor called

Whereas with GCC 10 it produced this as expected:

A's constructor with initializer_list called
B's constructor with initializer_list called

Tested with GCC 11.1.0 from Arch Linux, the PKGBUILD is located here: 
https://github.com/archlinux/svntogit-packages/blob/92c91ef891e9e2ed48f7f75921eb6321a2c7947d/trunk/PKGBUILD

[Bug c++/100963] [11/12 Regression] GCC 11 regression: templated constructor with std::initializer_list<T> is not selected

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100963

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
   Target Milestone|---                         |11.2
            Summary|GCC 11 regression:          |[11/12 Regression] GCC 11
                   |templated constructor with  |regression: templated
                   |std::initializer_list<T> is |constructor with
                   |not selected                |std::initializer_list<T> is
                   |                            |not selected

[Bug c++/100963] [11/12 Regression] GCC 11 regression: templated constructor with std::initializer_list<T> is not selected

[j.l.k at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100963

Jakub Klinkovský <j.l.k at gmx dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |j.l.k at gmx dot com

--- Comment #1 from Jakub Klinkovský <j.l.k at gmx dot com> ---
Created attachment 50962
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50962&action=edit
preprocessed file for the test case

[Bug c++/100963] [11/12 Regression] GCC 11 regression: templated constructor with std::initializer_list<T> is not selected

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100963

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
      Known to work|                            |10.3.0, 9.4.0
      Known to fail|                            |11.1.0
                 CC|                            |jason at gcc dot gnu.org,
                   |                            |ppalka at gcc dot gnu.org
   Last reconfirmed|                            |2021-06-08

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Confirmed, started with r11-7289.

Reduced:

#include <initializer_list>

struct B {
  B(int) = delete;
  template<class T> B(std::initializer_list<T>);
};

int main() {
  B({0});
}

[Bug c++/100963] [11/12 Regression] GCC 11 regression: templated constructor with std::initializer_list<T> is not selected

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100963

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

[Bug c++/100963] [11/12 Regression] GCC 11 regression: templated constructor with std::initializer_list<T> is not selected

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100963

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

https://gcc.gnu.org/g:91349e57bbfd010156b9128b2ad751c8843e7245

commit r12-1299-g91349e57bbfd010156b9128b2ad751c8843e7245
Author: Jason Merrill <jason@redhat.com>
Date:   Tue Jun 8 09:19:58 2021 -0400

    c++: braced-list overload resolution [PR100963]

    My PR969626 patch made us ignore template candidates when there's a perfect
    non-template candidate.  In this case, we were considering B(int) a perfect
    match for B({0}), but the brace elision makes it imperfect.

            PR c++/100963

    gcc/cp/ChangeLog:

            * call.c (perfect_conversion_p): Check check_narrowing.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/initlist124.C: New test.

[Bug c++/100963] [11/12 Regression] GCC 11 regression: templated constructor with std::initializer_list<T> is not selected

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100963

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:5af06ce836d4d8d1654db3855db8b86a994faf49

commit r11-8526-g5af06ce836d4d8d1654db3855db8b86a994faf49
Author: Jason Merrill <jason@redhat.com>
Date:   Tue Jun 8 09:19:58 2021 -0400

    c++: braced-list overload resolution [PR100963]

    My PR969626 patch made us ignore template candidates when there's a perfect
    non-template candidate.  In this case, we were considering B(int) a perfect
    match for B({0}), but the brace elision makes it imperfect.

            PR c++/100963

    gcc/cp/ChangeLog:

            * call.c (perfect_conversion_p): Check check_narrowing.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/initlist124.C: New test.

[Bug c++/100963] [11/12 Regression] GCC 11 regression: templated constructor with std::initializer_list<T> is not selected

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100963

Jason Merrill <jason at gcc dot gnu.org> changed:

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

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for 11.2/12.