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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/107085] __reference_constructs_from_temporary does not
 detect static up-cast
Date: Fri, 07 Oct 2022 22:06:20 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107085

--- Comment #11 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:895dd027d5dda51a95d242aec8a49a6dfa5db58d

commit r13-3173-g895dd027d5dda51a95d242aec8a49a6dfa5db58d
Author: Marek Polacek <polacek@redhat.com>
Date:   Wed Oct 5 15:51:30 2022 -0400

    c++: fixes for derived-to-base reference binding [PR107085]

    This PR reports that

      struct Base {};
      struct Derived : Base {};
      static_assert(__reference_constructs_from_temporary(Base const&,
Derived));

    doesn't pass, which it should: it's just like

      const Base& b(Derived{});

    where we bind 'b' to the Base subobject of a temporary object of type
    Derived.  The ck_base conversion didn't have ->need_temporary_p set bec=
ause
    we didn't need to create a temporary object just for the base, but the
whole
    object is a temporary so we're still binding to a temporary.  Since the
    Base subobject is an xvalue, a new function is introduced.

            PR c++/107085

    gcc/cp/ChangeLog:

            * call.cc (conv_binds_ref_to_temporary): New.
            (ref_conv_binds_directly): Rename to...
            (ref_conv_binds_to_temporary): ...this.  Use
            conv_binds_ref_to_temporary.
            * cp-tree.h (ref_conv_binds_directly): Rename to...
            (ref_conv_binds_to_temporary): ...this.
            * method.cc (ref_xes_from_temporary): Use
ref_conv_binds_to_temporary.
            * parser.cc (warn_for_range_copy): Likewise.

    gcc/testsuite/ChangeLog:

            * g++.dg/ext/reference_constructs_from_temporary1.C: Adjust
expected
            result.
            * g++.dg/ext/reference_converts_from_temporary1.C: Likewise.
            * g++.dg/cpp0x/elision4.C: New test.=