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Copies the not-yet-implemented items planned for removal from the LLVM-20 to the LLVM-21 release notes. This allows to better keep track of the status of the next release.
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4.9 KiB
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118 lines
4.9 KiB
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===========================================
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Libc++ 21.0.0 (In-Progress) Release Notes
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===========================================
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.. contents::
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:local:
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:depth: 2
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Written by the `Libc++ Team <https://libcxx.llvm.org>`_
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.. warning::
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These are in-progress notes for the upcoming libc++ 20.0.0 release.
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Release notes for previous releases can be found on
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`the Download Page <https://releases.llvm.org/download.html>`_.
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Introduction
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============
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This document contains the release notes for the libc++ C++ Standard Library,
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part of the LLVM Compiler Infrastructure, release 20.0.0. Here we describe the
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status of libc++ in some detail, including major improvements from the previous
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release and new feature work. For the general LLVM release notes, see `the LLVM
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documentation <https://llvm.org/docs/ReleaseNotes.html>`_. All LLVM releases may
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be downloaded from the `LLVM releases web site <https://llvm.org/releases/>`_.
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For more information about libc++, please see the `Libc++ Web Site
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<https://libcxx.llvm.org>`_ or the `LLVM Web Site <https://llvm.org>`_.
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Note that if you are reading this file from a Git checkout or the
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main Libc++ web page, this document applies to the *next* release, not
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the current one. To see the release notes for a specific release, please
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see the `releases page <https://llvm.org/releases/>`_.
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What's New in Libc++ 21.0.0?
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==============================
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Implemented Papers
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------------------
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- N4258: Cleaning-up noexcept in the Library (`Github <https://github.com/llvm/llvm-project/issues/99937>`__)
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- P0767R1: Deprecate POD (`Github <https://github.com/llvm/llvm-project/issues/104013>`__)
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- P1361R2: Integration of chrono with text formatting (`Github <https://github.com/llvm/llvm-project/issues/100014>`__)
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- P2255R2: A type trait to detect reference binding to temporary (implemented the type traits only) (`Github <https://github.com/llvm/llvm-project/issues/105180>`__)
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- P2562R1: ``constexpr`` Stable Sorting (`Github <https://github.com/llvm/llvm-project/issues/105360>`__)
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- P0472R3: Put std::monostate in <utility> (`Github <https://github.com/llvm/llvm-project/issues/127874>`__)
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- P1222R4: A Standard ``flat_set`` (`Github <https://github.com/llvm/llvm-project/issues/105193>`__)
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- P3247R2: Deprecate the notion of trivial types (`Github <https://github.com/llvm/llvm-project/issues/118387>`__)
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Improvements and New Features
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-----------------------------
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- The ``std::ranges::{copy, copy_n, copy_backward, move, move_backward, rotate}`` algorithms have been optimized for
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``std::vector<bool>::iterator``, resulting in a performance improvement of up to 2000x.
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- The ``std::ranges::equal`` algorithm has been optimized for ``std::vector<bool>::iterator``, resulting in a performance
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improvement of up to 188x.
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- The ``std::ranges::swap_ranges`` algorithm has been optimized for ``std::vector<bool>::iterator``, resulting in a
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performance improvement of up to 611x.
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- Updated formatting library to Unicode 16.0.0.
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- The ``num_put::do_put`` integral overloads have been optimized, resulting in a performance improvement of up to 2.4x.
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Deprecations and Removals
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-------------------------
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- ``std::is_pod`` and ``std::is_pod_v`` are deprecated in C++20 and later.
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- ``std::is_trivial`` and ``std::is_trivial_v`` are deprecated in C++26 and later.
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Potentially breaking changes
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----------------------------
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- The implementation of ``num_put::do_put`` has been replaced to improve the performance, which can lead to different
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output when printing pointers.
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Upcoming Deprecations and Removals
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----------------------------------
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LLVM 21
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~~~~~~~
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- The status of the C++03 implementation will be frozen after the LLVM 21 release. This means that starting in LLVM 22,
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non-critical bug fixes may not be back-ported to C++03, including LWG issues. C++03 is a legacy platform, where most
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projects are no longer actively maintained. To reduce the amount of fixes required to keep such legacy projects
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compiling with up-to-date toolchains, libc++ will aim to freeze the status of the headers in C++03 mode to avoid
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unintended breaking changes. See https://discourse.llvm.org/t/rfc-freezing-c-03-headers-in-libc for more details.
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If you are using C++03 in your project, you should consider moving to a newer version of the Standard to get the most
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out of libc++.
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- The ``_LIBCPP_VERBOSE_ABORT_NOT_NOEXCEPT`` macro will be removed in LLVM 21, making ``std::__libcpp_verbose_abort``
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unconditionally ``noexcept``.
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- Non-conforming extension ``packaged_task::result_type`` will be removed in LLVM 21.
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LLVM 22
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~~~~~~~
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- TODO
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ABI Affecting Changes
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---------------------
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- When using GCC, the ``std`` namespace is now annotated with ``[[gnu::visibility("default")]]``. This may cause more
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symbols to be exported from shared libraries when building with ``-fvisibility=hidden``. This also fixes RTTI
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comparison between shared libraries, since all RTTI has the correct visibility now. There is no behaviour change on
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Clang.
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Build System Changes
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--------------------
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- TODO
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