[Bug c++/98675] New: Accessing member of temporary outside its lifetime allowed in constexpr function

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98675

            Bug ID: 98675
           Summary: Accessing member of temporary outside its lifetime
                    allowed in constexpr function
           Product: gcc
           Version: 10.2.1
            Status: UNCONFIRMED
          Keywords: accepts-invalid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

struct X {
    int i = 0;

    constexpr int& get() { return i; }
};

constexpr int g()
{
    const auto& i = X{}.get();
    return i;  // undefined
}

constexpr auto i = g();


G++ fails to diagnose the error here.

Clang says:

<source>:13:16: error: constexpr variable 'i' must be initialized by a constant
expression
constexpr auto i = g();
               ^   ~~~
<source>:10:12: note: read of object outside its lifetime is not allowed in a
constant expression
    return i;  // undefined
           ^
<source>:13:20: note: in call to 'g()'
constexpr auto i = g();
                   ^


Intel says:

<source>(13): error: expression must have a constant value
  constexpr auto i = g();
                     ^
<source>(10): note: attempt to access expired storage
      return i;  // undefined
             ^