[Bug c++/107079] [10/11/12 Regression] ICE initializing lifetime-extended constexpr variable that stores its this pointer

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107079

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Marek Polacek
<mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:fb82334341e21ad0254f63e942be276f62d111cf

commit r12-9233-gfb82334341e21ad0254f63e942be276f62d111cf
Author: Marek Polacek <polacek@redhat.com>
Date:   Wed Feb 8 14:02:48 2023 -0500

    c++: ICE initing lifetime-extended constexpr var [PR107079]

    We ICE on the simple:

      struct X { const X* x = this; };
      constexpr const X& x = X{};

    where store_init_value initializes 'x' with

      &TARGET_EXPR <D.2768, {.x=(const struct X *) &<PLACEHOLDER_EXPR struct
X>}>

    but we must lifetime-extend via extend_ref_init_temps and we get

      _ZGR1x_.x = (const struct X *) &<PLACEHOLDER_EXPR struct X> >>>;, (const
struct X &) &_ZGR1x_;

    Since 'x' was declared constexpr, we do cxx_constant_init and we hit
    the preeval code added in r269003 while evaluating the INIT_EXPR:

      _ZGR1x_.x = (const struct X *) &<PLACEHOLDER_EXPR struct X> >>>

    but we have no ctx.ctor or ctx.object here so lookup_placeholder won't
    find anything that could replace X and we ICE on
     7861       /* A placeholder without a referent.  We can get here when
     7862          checking whether NSDMIs are noexcept, or in
massage_init_elt;
     7863          just say it's non-constant for now.  */
     7864       gcc_assert (ctx->quiet);
    because cxx_constant_init means !ctx->quiet.  It's not correct that
    there isn't a referent.  I think the following patch is a pretty
    straightforward fix: pass the _ZGR var down to maybe_constant_init so
    that it can replace the PLACEHOLDER_EXPR with _ZGR1x_.

    The commented assert in the test doesn't pass: we complain that _ZGR1x_
    isn't a constexpr variable because we don't implement DR2126 (PR101588).

            PR c++/107079

    gcc/cp/ChangeLog:

            * call.cc (set_up_extended_ref_temp): Pass var to
maybe_constant_init.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/constexpr-nsdmi2.C: New test.

    (cherry picked from commit 67b82bc1b29b82e4577df9491793624f3a8eb12f)