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Subject: [Bug libstdc++/104719] Use of `std::move` in libstdc++ leads to
 worsened debug performance
Date: Wed, 04 May 2022 15:34:43 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104719

--- Comment #15 from CVS 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:ef8d5ac08b5e60f35c52087d88c0235c8ce6b65b

commit r13-113-gef8d5ac08b5e60f35c52087d88c0235c8ce6b65b
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Mar 25 10:28:28 2022 +0000

    libstdc++: Simplify std::array accessors [PR104719]

    This removes the __array_traits::_S_ref and __array_traits::_S_ptr
    accessors, which only exist to make the special case of std::array<T, 0>
    syntactically well-formed.

    By changing the empty type used as the std::array<T, 0>::_M_elems data
    member to support operator[] and conversion to a pointer, we can write
    code using the natural syntax. The indirection through _S_ref and
    _S_ptr is removed for the common case, and a function call is only used
    for the special case of zero-size arrays.

    The invalid member access for zero-sized arrays is changed to use
    __builtin_trap() instead of a null dereference. This guarantees a
    runtime error if it ever gets called, instead of undefined behaviour
    that is likely to get optimized out as unreachable.

    libstdc++-v3/ChangeLog:

            PR libstdc++/104719
            * include/std/array (__array_traits::_S_ref): Remove.
            (__array_traits::_S_ptr): Remove.
            (__array_traits<T, 0>::_Type): Define operator[] and operator T*
            to provide an array-like API.
            (array::_AT_Type): Remove public typeef.
            (array::operator[], array::at, array::front, array::back): Use
            index operator to access _M_elems instead of _S_ref.
            (array::data): Use implicit conversion from _M_elems to pointer.
            (swap(array&, array&)): Use __enable_if_t helper.
            (get<I>): Use index operator to access _M_elems.
            * testsuite/23_containers/array/tuple_interface/get_neg.cc:
            Adjust dg-error line numbers.=