[Bug libstdc++/124463] [15/16 Regression] Big (10x) performance regression for std::deque<unsigned char>

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124463

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

https://gcc.gnu.org/g:892451e7b6aa50a19d094045c28d4d53d26d2929

commit r16-8142-g892451e7b6aa50a19d094045c28d4d53d26d2929
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Mar 13 17:11:04 2026 +0000

    libstdc++: Optimize __uninitialized_copy_a for std::deque iterators
[PR124463]

    I reimplemented uninitialized_copy and uninitialized_move in
    r15-4473-g3abe751ea86e34 so that they no longer delegate to std::copy,
    but that meant that they were no longer optimized for std::deque
    iterators, leading to performance regressions for operations on a
    std::deque with trivial element types. This adds new overloads of
    __uninitialized_copy_a and __uninitialized_move_a to handle std::deque
    iterators, restoring the lost performance.

    There are also overloads of std::fill for deque iterators which are no
    longer used for std::uninitialized_fill. This does not add replacements
    for those, so there will still be lost performance for std::deque
    operations that depend on std::uninitialized_fill. Similarly, inserting
    or assigning from istreambuf_iterator into a std::deque no longer uses
    the std::copy overloads for those types, and that isn't fixed by this
    patch either.

    libstdc++-v3/ChangeLog:

            PR libstdc++/124463
            * include/bits/deque.tcc (__uninitialized_copy_a): Define
            overloads for input and output iterators being std::deque
            iterators, and for only the output iterator being a std::deque
            iterator.
            (__uninitialized_move_a): Overload for input and output
            iterators being std::deque iterators.
            * include/bits/stl_uninitialized.h (__uninitialized_copy_a)
            (__uninitialized_move_a): Declare overloads for std::deque
            iterators.

    Reviewed-by: Tomasz KamiÅski <tkaminsk@redhat.com>