1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
|
===========================================
Libc++ 21.0.0 (In-Progress) Release Notes
===========================================
.. contents::
:local:
:depth: 2
Written by the `Libc++ Team <https://libcxx.llvm.org>`_
.. warning::
These are in-progress notes for the upcoming libc++ 21.0.0 release.
Release notes for previous releases can be found on
`the Download Page <https://releases.llvm.org/download.html>`_.
Introduction
============
This document contains the release notes for the libc++ C++ Standard Library,
part of the LLVM Compiler Infrastructure, release 21.0.0. Here we describe the
status of libc++ in some detail, including major improvements from the previous
release and new feature work. For the general LLVM release notes, see `the LLVM
documentation <https://llvm.org/docs/ReleaseNotes.html>`_. All LLVM releases may
be downloaded from the `LLVM releases web site <https://llvm.org/releases/>`_.
For more information about libc++, please see the `Libc++ Web Site
<https://libcxx.llvm.org>`_ or the `LLVM Web Site <https://llvm.org>`_.
Note that if you are reading this file from a Git checkout or the
main Libc++ web page, this document applies to the *next* release, not
the current one. To see the release notes for a specific release, please
see the `releases page <https://llvm.org/releases/>`_.
What's New in Libc++ 21.0.0?
==============================
Implemented Papers
------------------
- N4258: Cleaning-up noexcept in the Library (`Github <https://github.com/llvm/llvm-project/issues/99937>`__)
- P0767R1: Deprecate POD (`Github <https://github.com/llvm/llvm-project/issues/104013>`__)
- P1361R2: Integration of chrono with text formatting (`Github <https://github.com/llvm/llvm-project/issues/100014>`__)
- P2255R2: A type trait to detect reference binding to temporary (implemented the type traits only) (`Github <https://github.com/llvm/llvm-project/issues/105180>`__)
- P2372R3: Fixing locale handling in chrono formatters (`Github <https://github.com/llvm/llvm-project/issues/100043>`__)
- P2562R1: ``constexpr`` Stable Sorting (`Github <https://github.com/llvm/llvm-project/issues/105360>`__)
- P0472R3: Put std::monostate in <utility> (`Github <https://github.com/llvm/llvm-project/issues/127874>`__)
- P1222R4: A Standard ``flat_set`` (`Github <https://github.com/llvm/llvm-project/issues/105193>`__)
- P2897R7: ``aligned_accessor``: An mdspan accessor expressing pointer over-alignment (`Github <https://github.com/llvm/llvm-project/issues/118372>`__)
- P3247R2: Deprecate the notion of trivial types (`Github <https://github.com/llvm/llvm-project/issues/118387>`__)
- P3372R3: ``constexpr`` containers and adaptors (`Github <https://github.com/llvm/llvm-project/issues/127876>`__) (``forward_list``, ``list``, ``priority_queue``, ``flat_map``, and ``flat_set`` are implemented)
- P2441R2: ``views::join_with`` (`Github <https://github.com/llvm/llvm-project/issues/105185>`__)
- P2711R1: Making multi-param constructors of ``views`` ``explicit`` (`Github <https://github.com/llvm/llvm-project/issues/105252>`__)
- P2770R0: Stashing stashing ``iterators`` for proper flattening (`Github <https://github.com/llvm/llvm-project/issues/105250>`__)
- P2655R3: ``common_reference_t`` of ``reference_wrapper`` Should Be a Reference Type (`Github <https://github.com/llvm/llvm-project/issues/105260>`__)
Improvements and New Features
-----------------------------
- The ``std::ranges::{copy, copy_n, copy_backward, move, move_backward, rotate}`` algorithms have been optimized for
``std::vector<bool>::iterator``, resulting in a performance improvement of up to 2000x.
- The ``std::ranges::equal`` algorithm has been optimized for ``std::vector<bool>::iterator``, resulting in a performance
improvement of up to 188x.
- The ``std::ranges::swap_ranges`` algorithm has been optimized for ``std::vector<bool>::iterator``, resulting in a
performance improvement of up to 611x.
- Updated formatting library to Unicode 16.0.0.
- The ``num_put::do_put`` integral overloads have been optimized, resulting in a performance improvement of up to 2.4x.
- The ``std::stable_sort`` algorithm uses radix sort for floating-point types now, which can improve the performance
up to 10x, depending on type of sorted elements and the initial state of the sorted array.
- The segmented iterator optimization for ``std::for_each`` has been backported to C++11. Previously it was only available
in C++23 and later.
- The ``std::for_each_n``, ``std::ranges::for_each`` and ``std::ranges::for_each_n`` algorithms have been optimized for
segmented iterators, resulting in a performance improvement of up to 17.7x for ``std::deque<short>`` iterators, and up
to 13.9x for ``std::join_view<vector<vector<short>>>`` iterators.
- The ``bitset::to_string`` function has been optimized, resulting in a performance improvement of up to 8.3x for bitsets
with uniformly distributed zeros and ones, and up to 13.5x and 16.1x for sparse and dense bitsets, respectively.
- The ``flat_map::insert`` and ``flat_set::insert_range`` have been optimized, resulting in a performance improvement of up
to 10x for inserting elements into a ``flat_map`` when the input range is a ``flat_map`` or a ``zip_view``.
- ``ctype::tolower`` and ``ctype::toupper`` have been optimized, resulting in a 2x performance improvement.
Deprecations and Removals
-------------------------
- ``std::is_pod`` and ``std::is_pod_v`` are deprecated in C++20 and later.
- ``std::is_trivial`` and ``std::is_trivial_v`` are deprecated in C++26 and later.
- The ``_LIBCPP_VERBOSE_ABORT_NOT_NOEXCEPT`` has been removed, making ``std::__libcpp_verbose_abort``
unconditionally ``noexcept``.
- libc++ no longer adds ``constexpr`` to ``std::hash<std::vector<bool, A>>::operator()``, as the ``constexpr`` addition
since C++20 was an unintended extension.
- The non-conforming extension ``packaged_task::result_type`` has been removed in LLVM 21.
Potentially breaking changes
----------------------------
- The implementation of ``num_put::do_put`` has been replaced to improve the performance, which can lead to different
output when printing pointers.
- User-defined specializations of ``std::common_reference`` are diagnosed now. To customize the common reference type, ``std::basic_common_reference`` should be specialized instead.
- ``std::function`` used to have allocator support, which was removed from the Standard by `http://wg21.link/p0302r1`
due to issues with its design and inconsistent support from implementations. Previously, libc++ would provide
allocator-aware APIs in ``std::function`` in C++11 and C++14, but ignores the allocator argument in all places but
one. Starting in this release, the allocator argument is always ignored.
Announcements About Future Releases
-----------------------------------
LLVM 22
~~~~~~~
- The status of the C++03 implementation will be frozen after the LLVM 21 release. This means that starting in LLVM 22,
non-critical bug fixes may not be back-ported to C++03, including LWG issues. C++03 is a legacy platform, where most
projects are no longer actively maintained. To reduce the amount of fixes required to keep such legacy projects
compiling with up-to-date toolchains, libc++ will aim to freeze the status of the headers in C++03 mode to avoid
unintended breaking changes. See https://discourse.llvm.org/t/rfc-freezing-c-03-headers-in-libc for more details.
If you are using C++03 in your project, you should consider moving to a newer version of the Standard to get the most
out of libc++.
ABI Affecting Changes
---------------------
- When using GCC, the ``std`` namespace is now annotated with ``[[gnu::visibility("default")]]``. This may cause more
symbols to be exported from shared libraries when building with ``-fvisibility=hidden``. This also fixes RTTI
comparison between shared libraries, since all RTTI has the correct visibility now. There is no behaviour change on
Clang.
Build System Changes
--------------------
- TODO
|
