[Bug libstdc++/90192] std::vector<T>::resize(n, v) requires more than it should (CopyInsertable)

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90192

--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tomasz Kaminski <tkaminsk@gcc.gnu.org>:

https://gcc.gnu.org/g:390f3a690cf5c6bc8f7290484cafa6617c1757d4

commit r16-3399-g390f3a690cf5c6bc8f7290484cafa6617c1757d4
Author: Tomasz KamiÅski <tkaminsk@redhat.com>
Date:   Mon Aug 25 13:15:35 2025 +0200

    libstdc++: Do not require assignment for vector::resize(n, v) [PR90192]

    This patch introduces a new function, _M_fill_append, which is invoked when
    copies of the same value are appended to the end of a vector. Unlike
    _M_fill_insert(end(), n, v), _M_fill_append never permute elements in
place,
    so it does not require:
    * vector element type to be assignable;
    * a copy of the inserted value, in the case where it points to an
      element of the vector.

    vector::resize(n, v) now uses _M_fill_append, fixing the non-conformance
where
    element types were required to be assignable.

    In addition, _M_fill_insert(end(), n, v) now delegates to _M_fill_append,
which
    eliminates an unnecessary copy of v when the existing capacity is used.

            PR libstdc++/90192

    libstdc++-v3/ChangeLog:

            * include/bits/stl_vector.h (vector<T>::_M_fill_append): Declare.
            (vector<T>::fill): Use _M_fill_append instead of _M_fill_insert.
            * include/bits/vector.tcc (vector<T>::_M_fill_append): Define
            (vector<T>::_M_fill_insert): Delegate to _M_fill_append when
            elements are appended.
            * testsuite/23_containers/vector/modifiers/moveable.cc: Updated
            copycount for inserting at the end (appending).
            * testsuite/23_containers/vector/modifiers/resize.cc: New test.
            * testsuite/backward/hash_set/check_construct_destroy.cc: Updated
            copycount, the hash_set constructor uses insert to fill buckets
            with nullptrs.

    Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
    Signed-off-by: Tomasz KamiÅski <tkaminsk@redhat.com>