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In addition to changes in the tables the extended grapheme clustering algorithm has been overhauled. Before I considered a separate state machine to implement the rules. With the new rule GB9c this became more attractive and the design has changed. This change initially had quite an impact on the performance. By making the state machine persistent the performance was improved greatly. Note it is still slower than before due to the larger Unicode tables. Before -------------------------------------------------------------------- Benchmark Time CPU Iterations -------------------------------------------------------------------- BM_ascii_text<char> 1891 ns 1889 ns 369504 BM_unicode_text<char> 106642 ns 106397 ns 6576 BM_cyrillic_text<char> 73420 ns 73277 ns 9445 BM_japanese_text<char> 62485 ns 62387 ns 11153 BM_emoji_text<char> 1895 ns 1893 ns 369525 BM_ascii_text<wchar_t> 2015 ns 2013 ns 346887 BM_unicode_text<wchar_t> 92119 ns 92017 ns 7598 BM_cyrillic_text<wchar_t> 62637 ns 62568 ns 11117 BM_japanese_text<wchar_t> 53850 ns 53785 ns 12803 BM_emoji_text<wchar_t> 2016 ns 2014 ns 347325 After -------------------------------------------------------------------- Benchmark Time CPU Iterations -------------------------------------------------------------------- BM_ascii_text<char> 1906 ns 1904 ns 369409 BM_unicode_text<char> 265462 ns 265175 ns 2628 BM_cyrillic_text<char> 181063 ns 180865 ns 3871 BM_japanese_text<char> 130927 ns 130789 ns 5324 BM_emoji_text<char> 1892 ns 1890 ns 370537 BM_ascii_text<wchar_t> 2038 ns 2035 ns 343689 BM_unicode_text<wchar_t> 277603 ns 277282 ns 2526 BM_cyrillic_text<wchar_t> 188558 ns 188339 ns 3727 BM_japanese_text<wchar_t> 133084 ns 132943 ns 5262 BM_emoji_text<wchar_t> 2012 ns 2010 ns 348015 Persistent -------------------------------------------------------------------- Benchmark Time CPU Iterations -------------------------------------------------------------------- BM_ascii_text<char> 1904 ns 1899 ns 367472 BM_unicode_text<char> 133609 ns 133287 ns 5246 BM_cyrillic_text<char> 90185 ns 89941 ns 7796 BM_japanese_text<char> 75137 ns 74946 ns 9316 BM_emoji_text<char> 1906 ns 1901 ns 368081 BM_ascii_text<wchar_t> 2703 ns 2696 ns 259153 BM_unicode_text<wchar_t> 131497 ns 131168 ns 5341 BM_cyrillic_text<wchar_t> 87071 ns 86840 ns 8076 BM_japanese_text<wchar_t> 72279 ns 72099 ns 9682 BM_emoji_text<wchar_t> 2021 ns 2016 ns 346767
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===========================================
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Libc++ 19.0.0 (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++ 19.0.0 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 19.0.0. 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++ 19.0.0?
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==============================
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Implemented Papers
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------------------
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- P2637R3 - Member ``visit``
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- P2652R2 - Disallow User Specialization of ``allocator_traits``
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- P2819R2 - Add ``tuple`` protocol to ``complex``
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- P2495R3 - Interfacing ``stringstream``\s with ``string_view``
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- P2867R2 - Remove Deprecated ``strstream``\s From C++26
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- P2872R3 - Remove ``wstring_convert`` From C++26
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- P3142R0 - Printing Blank Lines with ``println`` (as DR against C++23)
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- P2302R4 - ``std::ranges::contains``
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- P1659R3 - ``std::ranges::starts_with`` and ``std::ranges::ends_with``
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Improvements and New Features
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-----------------------------
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- The performance of growing ``std::vector`` has been improved for trivially relocatable types.
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- The performance of ``ranges::fill`` and ``ranges::fill_n`` has been improved for ``vector<bool>::iterator``\s,
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resulting in a performance increase of up to 1400x.
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- The ``std::mismatch`` algorithm has been optimized for integral types, which can lead up to 40x performance
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improvements.
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- The ``std::ranges::minmax`` algorithm has been optimized for integral types, resulting in a performance increase of
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up to 100x.
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- The ``_LIBCPP_ENABLE_CXX26_REMOVED_STRSTREAM`` macro has been added to make the declarations in ``<strstream>`` available.
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- The ``_LIBCPP_ENABLE_CXX26_REMOVED_WSTRING_CONVERT`` macro has been added to make the declarations in ``<locale>``
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available.
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- The formatting library is updated to Unicode 15.1.0.
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Deprecations and Removals
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-------------------------
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- TODO: The ``LIBCXX_ENABLE_ASSERTIONS`` CMake variable that was used to enable the safe mode has been deprecated and setting
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it triggers an error; use the ``LIBCXX_HARDENING_MODE`` CMake variable with the value ``extensive`` instead. Similarly,
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the ``_LIBCPP_ENABLE_ASSERTIONS`` macro has been deprecated (setting it to ``1`` still enables the extensive mode in
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the LLVM 19 release while also issuing a deprecation warning). See :ref:`the hardening documentation
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<using-hardening-modes>` for more details.
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- The base template for ``std::char_traits`` has been removed in LLVM 19. If you are using ``std::char_traits`` with
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types other than ``char``, ``wchar_t``, ``char8_t``, ``char16_t``, ``char32_t`` or a custom character type for which you
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specialized ``std::char_traits``, your code will stop working. The Standard does not mandate that a base template is
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provided, and such a base template is bound to be incorrect for some types, which could currently cause unexpected behavior
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while going undetected.
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- The ``_LIBCPP_ENABLE_NARROWING_CONVERSIONS_IN_VARIANT`` macro that changed the behavior for narrowing conversions
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in ``std::variant`` has been removed in LLVM 19.
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- The ``_LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_MEMBERS`` and ``_LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_VOID_SPECIALIZATION``
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macros have been removed in LLVM 19.
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- TODO: The ``_LIBCPP_ENABLE_CXX17_REMOVED_FEATURES`` and ``_LIBCPP_ENABLE_CXX20_REMOVED_FEATURES`` macros have
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been removed in LLVM 19. C++17 and C++20 removed features can still be re-enabled individually.
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- The ``_LIBCPP_INLINE_VISIBILITY`` and ``_VSTD`` macros have been removed in LLVM 19.
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- The ``_LIBCPP_ATOMIC_ONLY_USE_BUILTINS`` configuration option has been removed in LLVM 19. This should not affect
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many users, except perhaps users using the library with ``-ffreestanding`` with a toolchain where compiler-rt or
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libatomic is not available. If you are one such user, please reach out to the libc++ developers so we can collaborate
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on a path for supporting atomics properly on freestanding platforms.
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- LWG3430 disallow implicit conversion of the source arguments to ``std::filesystem::path`` when
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constructing ``std::basic_*fstream``. This effectively removes the possibility to directly construct
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a ``std::basic_*fstream`` from a ``std::basic_string_view``, a input-iterator or a C-string, instead
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you can construct a temporary ``std::basic_string``. This change has been applied to C++17 and later.
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Upcoming Deprecations and Removals
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----------------------------------
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LLVM 20
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~~~~~~~
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- The ``LIBCXX_ENABLE_ASSERTIONS`` CMake variable and the ``_LIBCPP_ENABLE_ASSERTIONS`` macro that were used to enable
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the safe mode will be removed in LLVM 20.
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LLVM 21
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~~~~~~~
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TODO
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ABI Affecting Changes
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---------------------
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- The optional POSIX macro ``ENODATA`` has been deprecated in C++ and POSIX 2017. The
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``random_device`` could throw a ``system_error`` with this value. It now
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throws ``ENOMSG``.
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Build System Changes
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--------------------
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- The ``LIBCXX_EXECUTOR`` and ``LIBCXXABI_EXECUTOR`` CMake variables have been removed. Please
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set ``LIBCXX_TEST_PARAMS`` to ``executor=<...>`` instead.
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