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``` Benchmark old new Difference % Difference ---------------------------------------------- -------------- -------------- ------------ -------------- std::copy(CharT*,_CharT*,_ostreambuf_iterator) 8115.45 329.54 -7785.91 -95.94% ```
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===========================================
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Libc++ 23.0.0 (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++ 23.0.0 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 23.0.0. 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++ 23.0.0?
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==============================
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Implemented Papers
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------------------
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- P2440R1: ``ranges::iota``, ``ranges::shift_left`` and ``ranges::shift_right`` (`Github <https://llvm.org/PR105184>`__)
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Improvements and New Features
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-----------------------------
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- The ``std::ranges::fold_left_with_iter`` algorithm has been optimized for
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segmented iterators, resulting in a performance improvement of up to 1.38x
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for ``std::deque<int>`` iterators.
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- ``std::copy(CharT*, CharT*, ostreambuf_iterator<CharT>)`` has been optimized, resulting in performance improvements
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of up to 25x.
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Deprecations and Removals
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-------------------------
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- The ``std::launch::any`` enumerator that was accidentally provided as an extension is now deprecated.
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It will be removed in LLVM 25.
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Potentially breaking changes
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----------------------------
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Announcements About Future Releases
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-----------------------------------
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ABI Affecting Changes
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---------------------
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- ``std::allocator`` is trivially default constructible since LLVM 22. The behaviour can be reverted by defining
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``_LIBCPP_DEPRECATED_ABI_NON_TRIVIAL_ALLOCATOR``. Please inform the libc++ team if you need this flag, since it will
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be removed in LLVM 24 if there is no evidence that it's required.
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- ``bitset::operator[]`` returns ``bool`` since LLVM 22, making libc++ conforming. The behaviour can be reverted by
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defining ``_LIBCPP_DEPRECATED_ABI_BITSET_CONST_SUBSCRIPT_RETURN_REF``. Please inform the libc++ team if you need this
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flag, since it will be removed in LLVM 24 if there is no evidence that it's required.
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Build System Changes
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--------------------
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