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Part of https://github.com/llvm/llvm-project/issues/102817. This patch attempts to optimize the performance of `ranges::fold_left_with_iter` for segmented iterators. - before ``` # | rng::fold_left(vector<int>)/8 2.78 ns 2.78 ns 241953718 # | rng::fold_left(vector<int>)/32 12.2 ns 12.2 ns 57579851 # | rng::fold_left(vector<int>)/50 19.2 ns 19.2 ns 36487764 # | rng::fold_left(vector<int>)/8192 3226 ns 3226 ns 216811 # | rng::fold_left(vector<int>)/1048576 441842 ns 441839 ns 1592 # | rng::fold_left(deque<int>)/8 2.83 ns 2.83 ns 243888678 # | rng::fold_left(deque<int>)/32 16.6 ns 16.6 ns 42297458 # | rng::fold_left(deque<int>)/50 22.3 ns 22.3 ns 31387998 # | rng::fold_left(deque<int>)/8192 2492 ns 2492 ns 281637 # | rng::fold_left(deque<int>)/1048576 324936 ns 324936 ns 2154 # | rng::fold_left(list<int>)/8 2.54 ns 2.54 ns 275946635 # | rng::fold_left(list<int>)/32 16.2 ns 16.2 ns 42901634 # | rng::fold_left(list<int>)/50 54.7 ns 54.7 ns 12767450 # | rng::fold_left(list<int>)/8192 15154 ns 15154 ns 56744 # | rng::fold_left(list<int>)/1048576 4976906 ns 4976867 ns 158 ``` - after ``` # | rng::fold_left(vector<int>)/8 2.74 ns 2.74 ns 255954900 # | rng::fold_left(vector<int>)/32 12.1 ns 12.1 ns 57843462 # | rng::fold_left(vector<int>)/50 19.2 ns 19.2 ns 36422594 # | rng::fold_left(vector<int>)/8192 3202 ns 3202 ns 218265 # | rng::fold_left(vector<int>)/1048576 435718 ns 435709 ns 1609 # | rng::fold_left(deque<int>)/8 2.52 ns 2.52 ns 277288254 # | rng::fold_left(deque<int>)/32 14.1 ns 14.1 ns 52244463 # | rng::fold_left(deque<int>)/50 16.2 ns 16.2 ns 43131857 # | rng::fold_left(deque<int>)/8192 1695 ns 1695 ns 415620 # | rng::fold_left(deque<int>)/1048576 277729 ns 277731 ns 2532 # | rng::fold_left(list<int>)/8 2.55 ns 2.55 ns 277025050 # | rng::fold_left(list<int>)/32 16.2 ns 16.2 ns 43058857 # | rng::fold_left(list<int>)/50 54.7 ns 54.7 ns 12705516 # | rng::fold_left(list<int>)/8192 15236 ns 15235 ns 56840 # | rng::fold_left(list<int>)/1048576 4827263 ns 4827147 ns 152 ```
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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 (partial): ``ranges::iota`` and ``ranges::shift_left`` are supported (`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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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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