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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/97435] Lifetime of temporaries not correctly extending when
 optiimzation are enabled
Date: Thu, 15 Oct 2020 08:51:38 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97435

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Yes, this is undefined behaviour.

It's equivalent to:

const int& f(const int& i) { return i; }
const int& i =3D f(5);
int j =3D i;  // undefined

Lifetime is only extended if the reference is bound directly to the tempora=
ry
object, not to another reference that happens to be bound to it inside some
function.

Consider the case where the body of A::operator+=3D is not visible to the
compiler. How is it supposed to know whether the returned value refers to *=
this
or not, and therefore how is it supposed to know whether to destroy the
temporary A(5) immediately or not?=