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
|
===========================================
Libc++ 19.0.0 (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++ 19.0.0 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 19.0.0. 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++ 19.0.0?
==============================
Implemented Papers
------------------
- P2637R3 - Member ``visit``
- P2652R2 - Disallow User Specialization of ``allocator_traits``
- P2819R2 - Add ``tuple`` protocol to ``complex``
- P2495R3 - Interfacing ``stringstream``\s with ``string_view``
- P2302R4 - ``std::ranges::contains``
- P1659R3 - ``std::ranges::starts_with`` and ``std::ranges::ends_with``
Improvements and New Features
-----------------------------
- The performance of growing ``std::vector`` has been improved for trivially relocatable types.
- The performance of ``ranges::fill`` and ``ranges::fill_n`` has been improved for ``vector<bool>::iterator``\s,
resulting in a performance increase of up to 1400x.
- The ``std::mismatch`` algorithm has been optimized for integral types, which can lead up to 40x performance
improvements.
Deprecations and Removals
-------------------------
- TODO: The ``LIBCXX_ENABLE_ASSERTIONS`` CMake variable that was used to enable the safe mode has been deprecated and setting
it triggers an error; use the ``LIBCXX_HARDENING_MODE`` CMake variable with the value ``extensive`` instead. Similarly,
the ``_LIBCPP_ENABLE_ASSERTIONS`` macro has been deprecated (setting it to ``1`` still enables the extensive mode in
the LLVM 19 release while also issuing a deprecation warning). See :ref:`the hardening documentation
<using-hardening-modes>` for more details.
- The base template for ``std::char_traits`` has been removed in LLVM 19. If you are using ``std::char_traits`` with
types other than ``char``, ``wchar_t``, ``char8_t``, ``char16_t``, ``char32_t`` or a custom character type for which you
specialized ``std::char_traits``, your code will stop working. The Standard does not mandate that a base template is
provided, and such a base template is bound to be incorrect for some types, which could currently cause unexpected behavior
while going undetected.
- The ``_LIBCPP_ENABLE_NARROWING_CONVERSIONS_IN_VARIANT`` macro that changed the behavior for narrowing conversions
in ``std::variant`` has been removed in LLVM 19.
- The ``_LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_MEMBERS`` and ``_LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_VOID_SPECIALIZATION``
macros have been removed in LLVM 19.
- TODO: The ``_LIBCPP_ENABLE_CXX17_REMOVED_FEATURES`` and ``_LIBCPP_ENABLE_CXX20_REMOVED_FEATURES`` macros have
been removed in LLVM 19. C++17 and C++20 removed features can still be re-enabled individually.
- The ``_LIBCPP_INLINE_VISIBILITY`` and ``_VSTD`` macros have been removed in LLVM 19.
- The ``_LIBCPP_ATOMIC_ONLY_USE_BUILTINS`` configuration option has been removed in LLVM 19. This should not affect
many users, except perhaps users using the library with ``-ffreestanding`` with a toolchain where compiler-rt or
libatomic is not available. If you are one such user, please reach out to the libc++ developers so we can collaborate
on a path for supporting atomics properly on freestanding platforms.
Upcoming Deprecations and Removals
----------------------------------
LLVM 20
~~~~~~~
- The ``LIBCXX_ENABLE_ASSERTIONS`` CMake variable and the ``_LIBCPP_ENABLE_ASSERTIONS`` macro that were used to enable
the safe mode will be removed in LLVM 20.
LLVM 21
~~~~~~~
TODO
ABI Affecting Changes
---------------------
TODO
Build System Changes
--------------------
- The ``LIBCXX_EXECUTOR`` and ``LIBCXXABI_EXECUTOR`` CMake variables have been removed. Please
set ``LIBCXX_TEST_PARAMS`` to ``executor=<...>`` instead.
|
