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From: "mbtrash at yandex dot ru" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/101961] New: Missing returned object destructor call after
 exception throw
Date: Wed, 18 Aug 2021 14:34:00 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101961

            Bug ID: 101961
           Summary: Missing returned object destructor call after
                    exception throw
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mbtrash at yandex dot ru
  Target Milestone: ---

14.3.2 Exception handling:Constructors and destructors:2
(https://eel.is/c++draft/except.ctor#2)
says
"If an exception is thrown during the destruction of temporaries or local
variables for a return statement ([stmt.return]), the destructor for the
returned object (if any) is also invoked"

And it contains example (https://eel.is/c++draft/except.ctor#example-1) with
description
"...the local variable y is destroyed, causing stack unwinding, resulting in
the destruction of the returned object, ..."

Trying to recreate this example with following code

#include <iostream>
using namespace std;

struct S{
  int i =3D 123;
  S(int i) :i(i) {cout<<"S("<<i<<")"<<endl;}
  ~S() {cout<<"~S("<<i<<")"<<endl;}
};

struct T {
  T() {cout<<"T()"<<endl;}
  ~T() noexcept(false) {
    cout<<"~T()"<<endl;
    throw 0;
  }
};

S foo() {
  try {
    T t;
    return {3};
  } catch (...){}
  return {4};
}

int main() {
  foo();
}

Output doesn't have S{3}'s (returned object) destruction line:
T()
S(3)
~T()
S(4)
~S(4)

while should be
T()
S(3)
~T()
~S(3) <-----!
S(4)
~S(4)

Link to godbolt:
https://godbolt.org/z/hP9z5rYKG=