[Bug c++/82560] New: Temporary object created as a default argument not destructed

[gdutor at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82560

            Bug ID: 82560
           Summary: Temporary object created as a default argument not
                    destructed
           Product: gcc
           Version: 7.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gdutor at gmail dot com
  Target Milestone: ---

Created attachment 42374
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42374&action=edit
Source code that reproduce the bug

This is the code trigger the leaking bug.
=====================================================
#include <iostream>
#include <vector>
#include <memory>

class Foo {
public:
    Foo(const char *str) : str_(str) {
        std::cout << "Foo(const char*)" << std::endl;
    }
    Foo(const Foo&) {
        std::cout << "Foo(const Foo&)" << std::endl;
    }
    ~Foo() {
        std::cout << "~Foo()" << std::endl;
    }
    std::string str_;
};

class Bar {
public:
    Bar(Foo foo = "implicitly casted to Foo") : foo_(foo) {
        std::cout << "Bar(Foo)" << std::endl;
    }
    ~Bar() {
        std::cout << "~Bar()" << std::endl;
    }

    Foo foo_;
};

int main()
{
    auto ptr = std::make_unique<Bar>();
    return 0;
}
=====================================================

Compile and run it:
=================
$ g++ -std=c++14 leak.cpp
$ ./a.out
Foo(const char*)
Foo(const Foo&)
Bar(Foo)
~Bar()
~Foo()
=================

As the outputs indicate, two Foo objects are created, while the destructor of
Foo invoked only once.

Here is what g++ -v prints:
=================
Using built-in specs.
COLLECT_GCC=third-party/gcc-7.1.0/glibc-2.17/bin/g++
COLLECT_LTO_WRAPPER=/data/admin/Workspace/third-party/gcc-7.1.0/glibc-2.17/bin/../libexec/gcc/x86_64-pc-linux-gnu/7.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: third-party/gcc-7.1.0/source/gcc-7.1.0/configure
--prefix=third-party/gcc-7.1.0/glibc-2.17
--with-gmp=third-party/gcc-7.1.0/../gmp-6.1.2/glibc-2.17
--with-mpfr=third-party/gcc-7.1.0/../mpfr-3.1.6/glibc-2.17
--with-mpc=third-party/gcc-7.1.0/../mpc-1.0.3/glibc-2.17 --without-isl
--enable-static-libjava --disable-multiarch --disable-multilib
--enable-languages=c,c++,go --disable-libada --disable-libvtv
--enable-default-pie --disable-nls --disable-lto
Thread model: posix
gcc version 7.1.0 (GCC)
=================