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Subject: [Bug c++/65816] Constructor delegation does not perform
 zero-initialization
Date: Tue, 01 Jun 2021 20:21:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D65816

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:ac0bc21bd634a334ba8f323c39a11f01dfdc2aae

commit r12-1153-gac0bc21bd634a334ba8f323c39a11f01dfdc2aae
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Jun 1 12:23:49 2021 -0400

    c++: value-init vs zero-init in expand_aggr_init_1 [PR65816]

    In the case of value-initializing an object of class type T,
    [dcl.init.general]/8 says:

      - if T has either no default constructor ([class.default.ctor]) or
        a default constructor that is user-provided or deleted, then the
        object is default-initialized;
      - otherwise, the object is zero-initialized and ...  if T has a
        non-trivial default constructor, the object is default-initialized;

    But when determining whether to first zero-initialize the object,
    expand_aggr_init_1 incorrectly considers the user-providedness of _all_
    constructors rather than only that of the _default_ constructors.  This
    causes us to skip the zero-initialization step when the class type has a
    defaulted default constructor alongside a user-defined constructor.

    It seems the predicate type_has_non_user_provided_default_constructor
    accurately captures the above rule for when to first perform a
    zero-initialization during value-initialization, so this patch adjusts
    expand_aggr_init_1 to use this predicate instead.

            PR c++/65816

    gcc/cp/ChangeLog:

            * init.c (expand_aggr_init_1): Check
            type_has_non_user_provided_default_constructor instead of
            type_has_user_provided_constructor.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/constexpr-delegating3.C: New test.
            * g++.dg/cpp0x/dc10.C: New test.
            * g++.dg/cpp0x/initlist-base4.C: New test.
            * g++.dg/cpp2a/constexpr-init22.C: New test.

    libstdc++-v3/ChangeLog:

            * testsuite/23_containers/deque/allocator/default_init.cc,
            testsuite/23_containers/forward_list/allocator/default_init.cc,
            testsuite/23_containers/list/allocator/default_init.cc,
            testsuite/23_containers/map/allocator/default_init.cc,
            testsuite/23_containers/set/allocator/default_init.cc,
            testsuite/23_containers/vector/allocator/default_init.cc,
            testsuite/23_containers/vector/bool/allocator/default_init.cc:
            Remove xfail.=