[Bug c++/67302] New: copy elision in return (expression)

[Bug c++/67302] New: copy elision in return (expression)

[osensei80 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67302

            Bug ID: 67302
           Summary: copy elision in return (expression)
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: osensei80 at gmail dot com
  Target Milestone: ---

Consider:

struct A
{
  A() { std::cout << "default ctor\n"; }
  A(const A&) { std::cout << "copy ctor\n"; }
  A(A&&) { std::cout << "move ctor\n"; }
};

A bar()
{
  A a;
  return( a );
}

int main()
{
  bar();
}

Compiling with option -std=c++11 the output is "default ctor". But compiling
with -std=c++14 or -std=c++1z the output is

default ctor
move ctor

Why get's the move not elided?

[Bug c++/67302] copy elision in return (expression)

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67302

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-08-21
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The useless parentheses on the return expression disable elision, but that's a
bug.

[Bug c++/67302] [C++14] copy elision in return (expression)

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67302

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org
            Summary|copy elision in return      |[C++14] copy elision in
                   |(expression)                |return (expression)

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Possibly started with the introduction of force_paren_expr in r197248

The fix for Bug 63437 allows it to compile, but didn't re-enable elision.

[Bug c++/67302] [C++14] copy elision in return (expression)

[antoshkka at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67302

Antony Polukhin <antoshkka at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |antoshkka at gmail dot com

--- Comment #3 from Antony Polukhin <antoshkka at gmail dot com> ---
Can reproduce with GCC 10.1 https://godbolt.org/z/tYvccG

[Bug c++/67302] [C++14] copy elision in return (expression)

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67302

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

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

[Bug c++/67302] [C++14] copy elision in return (expression)

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67302

--- Comment #4 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:21761d2b2b01f6cef4287c646845f6b3006546aa

commit r12-1698-g21761d2b2b01f6cef4287c646845f6b3006546aa
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon Jun 21 07:54:29 2021 -0400

    c++: REF_PARENTHESIZED_P wrapper inhibiting NRVO [PR67302]

    Here, in C++14 or later, we remember the parentheses around 'a' in the
    return statement by using a REF_PARENTHESIZED_P wrapper, which ends up
    inhibiting NRVO because we don't look through this wrapper before
    checking the conditions for NRVO.  This patch fixes this by calling
    maybe_undo_parenthesized_ref sooner in check_return_expr.

            PR c++/67302

    gcc/cp/ChangeLog:

            * typeck.c (check_return_expr): Call maybe_undo_parenthesized_ref
            sooner, before the NRVO handling.

    gcc/testsuite/ChangeLog:

            * g++.dg/opt/nrv21.C: New test.

[Bug c++/67302] [C++14] copy elision in return (expression)

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67302

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
   Target Milestone|---                         |12.0
             Status|ASSIGNED                    |RESOLVED

--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 12, thanks for the bug report.