[Bug c++/113791] New: Incorrect handling of lvalue to rvalue conversion in ternary operator

[Bug c++/113791] New: Incorrect handling of lvalue to rvalue conversion in ternary operator

[Mark_B53 at yahoo dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113791

            Bug ID: 113791
           Summary: Incorrect handling of lvalue to rvalue conversion in
                    ternary operator
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: Mark_B53 at yahoo dot com
  Target Milestone: ---

#include <unordered_map>
#include <iostream>

template<template<class, class, class...> class Map, typename Key, typename T,
typename KeyP, typename... Args>
T getMapEntry(const Map<Key, T, Args...>& map, const KeyP& key, T&& defval) {
    static_assert(std::is_convertible_v<KeyP, Key>);
    auto i = map.find(key);
    return i != map.end() ? i->second : std::move(defval);
}

class Foo {
public:
    Foo() { std::cout << __PRETTY_FUNCTION__ << '\n'; }
    ~Foo() { std::cout << __PRETTY_FUNCTION__ << '\n'; }
    Foo(const Foo&) { std::cout << __PRETTY_FUNCTION__ << '\n'; }
    Foo& operator=(const Foo&) { std::cout << __PRETTY_FUNCTION__ << '\n';
return *this; }
    Foo(Foo&&) { std::cout << __PRETTY_FUNCTION__ << '\n'; }
    Foo& operator=(Foo&&) { std::cout << __PRETTY_FUNCTION__ << '\n'; return
*this; }
};

int main() {
    std::unordered_map<int, Foo> map;
    auto&& ret = getMapEntry(map, 123U, Foo{});
    return 0;
}

GCC outputs:
Foo::Foo()
Foo::Foo(Foo&&)
Foo::~Foo()
Foo::~Foo()

Correct output:
Foo::Foo()
Foo::Foo(const Foo &)
Foo::~Foo()
Foo::~Foo()

Posted on https://stackoverflow.com/questions/77948860/

Maybe related to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87605

[Bug c++/113791] Incorrect handling of lvalue to rvalue conversion in ternary operator

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113791

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org
     Ever confirmed|0                           |1
           Keywords|                            |needs-reduction
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2024-02-06

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Confirmed.  Not a regression AFAICS.

[Bug c++/113791] Incorrect handling of lvalue to rvalue conversion in ternary operator

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113791

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|needs-reduction             |rejects-valid

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
template <typename> struct remove_reference;
template <typename _Tp> struct remove_reference<_Tp &> {
  typedef _Tp type;
};
template <typename _Tp> typename remove_reference<_Tp>::type &&move(_Tp &&);
template <typename _T2> struct pair {
  _T2 second;
};
struct Foo {
  Foo();
  Foo(const Foo &);
  Foo(Foo &&) = delete;
};
struct _Node_const_iterator {
  const pair<Foo> *operator->();
};
template <typename, typename, typename = int> struct unordered_map {
  _Node_const_iterator find(int);
};
bool b;
template <template <class, class, class> class Map, typename... Args>
void getMapEntry(Map<Args...> map, int key, Foo defval) {
  auto i = map.find(key);
  b ? i->second : move(defval);
}
int main() {
  unordered_map<int, int> map;
  getMapEntry(map, 3, {});
}

[Bug c++/113791] Incorrect handling of lvalue to rvalue conversion in ternary operator

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113791

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Little more reduced:
```
struct Foo {
  Foo();
  Foo(const Foo &);
  Foo(Foo &&) = delete;
};
Foo &&pp();
void f(const Foo b) {
  true ? b : pp();
}
```

[Bug c++/113791] Incorrect handling of lvalue to rvalue conversion in ternary operator

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113791

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=102251,
                   |                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=87605

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
related to PR 87605 and PR 102251

[Bug c++/113791] Incorrect handling of lvalue to rvalue conversion in ternary operator

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113791

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Looking.  It's https://cplusplus.github.io/CWG/issues/1895.html which we don't
implement yet.

[Bug c++/113791] Incorrect handling of lvalue to rvalue conversion in ternary operator

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113791

--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Stage 1 work.  Putting this aside for GCC 15.