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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/98675] New: Accessing member of temporary outside its
 lifetime allowed in constexpr function
Date: Thu, 14 Jan 2021 11:53:09 +0000
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X-Bugzilla-Component: c++
X-Bugzilla-Version: 10.2.1
X-Bugzilla-Keywords: accepts-invalid
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98675

            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 =3D 0;

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

constexpr int g()
{
    const auto& i =3D X{}.get();
    return i;  // undefined
}

constexpr auto i =3D g();


G++ fails to diagnose the error here.

Clang says:

<source>:13:16: error: constexpr variable 'i' must be initialized by a cons=
tant
expression
constexpr auto i =3D 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 =3D g();
                   ^


Intel says:

<source>(13): error: expression must have a constant value
  constexpr auto i =3D g();
                     ^
<source>(10): note: attempt to access expired storage
      return i;  // undefined
             ^=