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We've built up quite a few links directly to github within the code base. We should instead use `llvm.org/PR<issue-number>` to link to bugs, since that is resilient to the bug tracker changing in the future. This is especially relevant for tests linking to bugs, since they will probably be there for decades to come. A nice side effect is that these links are significantly shorter than the GH links, making them much less of an eyesore. This patch also replaces a few links that linked to the old bugzilla instance on llvm.org.
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===========================================
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Libc++ 22.0.0 (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++ 22.0.0 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 22.0.0. 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++ 22.0.0?
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==============================
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Implemented Papers
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------------------
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- P2321R2: ``zip`` (`Github <https://llvm.org/PR105169>`__) (The paper is partially implemented. ``zip_transform_view``
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is implemented in this release)
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- P3168R2: Give ``std::optional`` Range Support (`Github <https://llvm.org/PR105430>`__)
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Improvements and New Features
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-----------------------------
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- The performance of ``map::map(const map&)`` has been improved up to 2.3x
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- The performance of ``map::operator=(const map&)`` has been improved by up to 11x
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- The performance of ``unordered_set::unordered_set(const unordered_set&)`` has been improved by up to 3.3x.
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- The performance of ``unordered_set::operator=(const unordered_set&)`` has been improved by up to 5x.
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- The performance of ``map::erase`` and ``set::erase`` has been improved by up to 2x
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- The performance of ``find(key)`` in ``map``, ``set``, ``multimap`` and ``multiset`` has been improved by up to 2.3x
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- Some reallocations are now avoided in `std::filesystem::path::lexically_relative`, resulting in a performance
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improvement of up to 1.7x.
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- The performance of the ``(iterator, iterator)`` constructors of ``map``, ``set``, ``multimap`` and ``multiset``
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has been improved by up to 3x
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- The performance of ``insert(iterator, iterator)`` of ``map``, ``set``, ``multimap`` and ``multiset`` has been improved
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by up to 2.5x
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- The performance of ``erase(iterator, iterator)`` in the unordered containers has been improved by up to 1.9x
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- The performance of ``map::insert_or_assign`` has been improved by up to 2x
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- ``ofstream::write`` has been optimized to pass through large strings to system calls directly instead of copying them
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in chunks into a buffer.
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Deprecations and Removals
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-------------------------
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Potentially breaking changes
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----------------------------
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- The algorithm for ``multi{map,set}::find`` has been modified such that it doesn't necessarily return an iterator to
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the first equal element in the container. This was never guaranteed by the Standard, but libc++ previously happened to
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always return the first equal element, like other implementations do. Starting with this release, code relying on the
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first element being returned from ``find`` will be broken, and ``lower_bound`` or ``equal_range`` should be used
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instead.
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- The ABI flag ``_LIBCPP_ABI_NO_REVERSE_ITERATOR_SECOND_MEMBER`` has been split off from
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``_LIBCPP_ABI_NO_ITERATOR_BASES``. If you are using this flag and care about ABI stability, you should set
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``_LIBCPP_ABI_NO_REVERSE_ITERATOR_SECOND_MEMBER`` as well.
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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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- The ABI flag ``_LIBCPP_ABI_NO_REVERSE_ITERATOR_SECOND_MEMBER`` has been split off from
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``_LIBCPP_ABI_NO_ITERATOR_BASES``. If you are using this flag and care about ABI stability, you should set
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``_LIBCPP_ABI_NO_REVERSE_ITERATOR_SECOND_MEMBER`` as well.
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Build System Changes
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--------------------
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