[Bug c++/113640] New: 'deducing this' lambda invoked multiple times unexpectedly

[Bug c++/113640] New: 'deducing this' lambda invoked multiple times unexpectedly

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113640

            Bug ID: 113640
           Summary: 'deducing this' lambda invoked multiple times
                    unexpectedly
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hewillk at gmail dot com
  Target Milestone: ---

#include <iostream>

int main() {
  auto l = [](this auto self, int n) {
    std::cout << n << " ";
    return self;
  };
  l(1)(42)(100);
}

https://godbolt.org/z/3rEoGsPWe

Clang prints "1 42 100" as expected, however, GCC prints "1 1 42 1 42 100",
which is weird.

[Bug c++/113640] 'deducing this' lambda invoked multiple times unexpectedly

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113640

--- Comment #1 from 康桓瑋 <hewillk at gmail dot com> ---
Noted that changing `this auto self` to `this auto&& self` will get the
expected results

[Bug c++/113640] 'deducing this' lambda invoked multiple times unexpectedly

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113640

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
   Last reconfirmed|                            |2024-01-30
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED
                 CC|                            |ppalka at gcc dot gnu.org

[Bug c++/113640] 'deducing this' lambda invoked multiple times unexpectedly

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113640

--- Comment #2 from GCC 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:0857a00fe3226db8801384743b6d44353dcac9da

commit r14-8631-g0857a00fe3226db8801384743b6d44353dcac9da
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Jan 30 10:44:56 2024 -0500

    c++: duplicated side effects of xobj arg [PR113640]

    We miscompile the below testcase because keep_unused_object_arg thinks
    the object argument of an xobj member function is unused, and so it ends
    up duplicating the argument's side effects.

            PR c++/113640

    gcc/cp/ChangeLog:

            * call.cc (keep_unused_object_arg): Punt for an xobj member
            function.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp23/explicit-obj-lambda14.C: New test.

    Reviewed-by: Jason Merrill <jason@redhat.com>

[Bug c++/113640] 'deducing this' lambda invoked multiple times unexpectedly

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113640

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |14.0
           Keywords|                            |wrong-code
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed, thanks for the report.