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========================================
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Clang 14.0.0 (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 `LLVM Team <https://llvm.org/>`_
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.. warning::
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These are in-progress notes for the upcoming Clang 14 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 Clang C/C++/Objective-C
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frontend, part of the LLVM Compiler Infrastructure, release 14.0.0. Here we
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describe the status of Clang in some detail, including major
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improvements from the previous release and new feature work. For the
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general LLVM release notes, see `the LLVM
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documentation <https://llvm.org/docs/ReleaseNotes.html>`_. All LLVM
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releases may be downloaded from the `LLVM releases web
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site <https://llvm.org/releases/>`_.
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For more information about Clang or LLVM, including information about the
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latest release, please see the `Clang Web Site <https://clang.llvm.org>`_ or the
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`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 Clang 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 Clang 14.0.0?
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===========================
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Some of the major new features and improvements to Clang are listed
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here. Generic improvements to Clang as a whole or to its underlying
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infrastructure are described first, followed by language-specific
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sections with improvements to Clang's support for those languages.
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Major New Features
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------------------
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- ...
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Improvements to Clang's diagnostics
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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- -Wbitwise-instead-of-logical (part of -Wbool-operation) warns about use of bitwise operators with boolean operands which have side effects.
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- Added diagnostic groups to control diagnostics for attribute extensions by
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adding groups ``-Wc++N-attribute-extensions`` (where ``N`` is the standard
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release being diagnosed against). These new groups are automatically implied
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when passing ``-Wc++N-extensions``. Resolves PR33518.
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Non-comprehensive list of changes in this release
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-------------------------------------------------
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- Maximum _ExtInt size was decreased from 16,777,215 bits to 8,388,608 bits.
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Motivation for this was discussed in PR51829.
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- Configuration file syntax extended with ``<CFGDIR>`` token. This expands to
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the base path of the current config file. See :ref:`configuration-files` for
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details.
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New Compiler Flags
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------------------
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- Clang plugin arguments can now be passed through the compiler driver via
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``-fplugin-arg-pluginname-arg``, similar to GCC's ``-fplugin-arg``.
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Deprecated Compiler Flags
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-------------------------
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- -Wweak-template-vtables has been deprecated and no longer has any effect. The
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flag will be removed in the next release.
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Modified Compiler Flags
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-----------------------
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- Support has been added for the following processors (``-mcpu`` identifiers in parentheses):
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- RISC-V SiFive E20 (``sifive-e20``).
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- RISC-V SiFive E21 (``sifive-e21``).
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- RISC-V SiFive E24 (``sifive-e24``).
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- RISC-V SiFive E34 (``sifive-e34``).
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- RISC-V SiFive S21 (``sifive-s21``).
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- RISC-V SiFive S51 (``sifive-s51``).
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- RISC-V SiFive S54 (``sifive-s54``).
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- RISC-V SiFive S76 (``sifive-s76``).
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- Support has been added for the following architectures (``-march`` identifiers in parentheses):
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- Armv9-A (``armv9-a``).
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- Armv9.1-A (``armv9.1-a``).
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- Armv9.2-A (``armv9.2-a``).
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Removed Compiler Flags
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-------------------------
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- ...
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New Pragmas in Clang
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--------------------
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- ...
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Attribute Changes in Clang
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--------------------------
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- Attributes loaded as clang plugins which are sensitive to LangOpts must
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now override ``acceptsLangOpts`` instead of ``diagLangOpts``.
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Returning false will produce a generic "attribute ignored" diagnostic, as
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with clang's built-in attributes.
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If plugins want to provide richer diagnostics, they can do so when the
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attribute is handled instead, e.g. in ``handleDeclAttribute``.
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(This was changed in order to better support attributes in code completion).
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- __has_cpp_attribute, __has_c_attribute, __has_attribute, and __has_declspec
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will now macro expand their argument. This causes a change in behavior for
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code using ``__has_cpp_attribute(__clang__::attr)`` (and same for
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``__has_c_attribute``) where it would previously expand to ``0`` for all
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attributes, but will now issue an error due to the expansion of the
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predefined ``__clang__`` macro.
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Windows Support
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---------------
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- An MSVC compatibility workaround for C++ operator names was removed. As a
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result, the ``<query.h>`` Windows SDK header may not compile out of the box.
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Users should use a recent SDK and pass ``-DQUERY_H_RESTRICTION_PERMISSIVE``
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or pass ``/permissive`` to disable C++ operator names altogether. See
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`PR42427 <https://llvm.org/pr42427>` for more info.
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C Language Changes in Clang
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---------------------------
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- The value of ``__STDC_VERSION__`` has been bumped to ``202000L`` when passing
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``-std=c2x`` so that it can be distinguished from C17 mode. This value is
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expected to change again when C23 is published.
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- Wide multi-characters literals such as ``L'ab'`` that would previously be interpreted as ``L'b'``
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are now ill-formed in all language modes. The motivation for this change is outlined in
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`P2362 <wg21.link/P2362>`_.
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- Support for ``__attribute__((error("")))`` and
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``__attribute__((warning("")))`` function attributes have been added.
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- The maximum allowed alignment has been increased from 2^29 to 2^32.
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- Clang now supports the ``_BitInt(N)`` family of bit-precise integer types
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from C23. This type was previously exposed as ``_ExtInt(N)``, which is now a
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deprecated alias for ``_BitInt(N)`` (so diagnostics will mention ``_BitInt``
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even if source uses ``_ExtInt``). ``_BitInt(N)`` and ``_ExtInt(N)`` are the
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same types in all respects beyond spelling and the deprecation warning.
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``_BitInt(N)`` is supported as an extension in older C modes and in all C++
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modes. Note: the ABI for ``_BitInt(N)`` is still in the process of being
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stabilized, so this type should not yet be used in interfaces that require
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ABI stability.
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- When using ``asm goto`` with outputs whose constraint modifier is ``"+"``, we
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now change the numbering of the labels to occur after hidden tied inputs for
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better compatibility with GCC. For better portability between different
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compilers and versions, symbolic references rather than numbered references
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should be preferred. See
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`this thread <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103640>` for more
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info.
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C++ Language Changes in Clang
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-----------------------------
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- ...
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C++20 Feature Support
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^^^^^^^^^^^^^^^^^^^^^
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...
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C++2b Feature Support
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^^^^^^^^^^^^^^^^^^^^^
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- Implemented `P1938R3: if consteval <https://wg21.link/P1938R3>`_.
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- Implemented `P2360R0: Extend init-statement to allow alias-declaration <https://wg21.link/P2360R0>`_.
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CUDA Language Changes in Clang
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------------------------------
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- Clang now supports CUDA versions up to 11.5.
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- Default GPU architecture has been changed from sm_20 to sm_35.
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Objective-C Language Changes in Clang
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-------------------------------------
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OpenCL C Language Changes in Clang
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----------------------------------
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...
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ABI Changes in Clang
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--------------------
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- The ``_ExtInt(N)`` extension has been standardized in C23 as ``_BitInt(N)``.
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The mangling of this type in C++ has accordingly changed: under the Microsoft
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ABI it is now mangled using the ``_BitInt`` spelling, and under the Itanium ABI
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it is now mangled using a dedicated production. Note: the ABI for ``_BitInt(N)``
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is still in the process of being stabilized, so this type should not yet be
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used in interfaces that require ABI stability.
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OpenMP Support in Clang
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-----------------------
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- ``clang-nvlink-wrapper`` tool introduced to support linking of cubin files archived in an archive. See :doc:`ClangNvlinkWrapper`.
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CUDA Support in Clang
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---------------------
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- ...
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X86 Support in Clang
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--------------------
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- Support for ``AVX512-FP16`` instructions has been added.
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Arm and AArch64 Support in Clang
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--------------------------------
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- Support has been added for the following processors (command-line identifiers in parentheses):
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- Arm Cortex-A510 (``cortex-a510``)
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- Arm Cortex-X2 (``cortex-x2``)
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- Arm Cortex-A710 (``cortex-A710``)
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- The -mtune flag is no longer ignored for AArch64. It is now possible to
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tune code generation for a particular CPU with -mtune without setting any
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architectural features. For example, compiling with
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"-mcpu=generic -mtune=cortex-a57" will not enable any Cortex-A57 specific
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architecture features, but will enable certain optimizations specific to
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Cortex-A57 CPUs and enable the use of a more accurate scheduling model.
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Floating Point Support in Clang
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-------------------------------
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- The default setting of FP contraction (FMA) is now -ffp-contract=on (for
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languages other than CUDA/HIP) even when optimization is off. Previously,
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the default behavior was equivalent to -ffp-contract=off (-ffp-contract
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was not set).
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Related to this, the switch -ffp-model=precise now implies -ffp-contract=on
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rather than -ffp-contract=fast, and the documentation of these features has
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been clarified. Previously, the documentation claimed that -ffp-model=precise
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was the default, but this was incorrect because the precise model implied
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-ffp-contract=fast, whereas the (now corrected) default behavior is
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-ffp-contract=on.
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-ffp-model=precise is now exactly the default mode of the compiler.
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- -fstrict-float-cast-overflow no longer has target specific behavior. Clang
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will saturate towards the smallest and largest representable integer values.
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NaNs will be converted to zero.
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Internal API Changes
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--------------------
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- A new sugar ``Type`` AST node represents types accessed via a C++ using
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declaration. Given code ``using std::error_code; error_code x;``, ``x`` has
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a ``UsingType`` which desugars to the previous ``RecordType``.
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Build System Changes
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--------------------
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- Linux distros can specify ``-DCLANG_DEFAULT_PIE_ON_LINUX=On`` to use ``-fPIE`` and
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``-pie`` by default. This matches GCC installations on many Linux distros
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(configured with ``--enable-default-pie``).
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(`D113372 <https://reviews.llvm.org/D113372>`_)
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AST Matchers
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------------
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- ``TypeLoc`` AST Matchers are now available. These matchers provide helpful
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utilities for matching ``TypeLoc`` nodes, such as the ``pointerTypeLoc``
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matcher or the ``hasReturnTypeLoc`` matcher. The addition of these matchers
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was made possible by changes to the handling of ``TypeLoc`` nodes that
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allows them to enjoy the same static type checking as other AST node kinds.
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- ``LambdaCapture`` AST Matchers are now available. These matchers allow for
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the binding of ``LambdaCapture`` nodes. The ``LambdaCapture`` matchers added
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include the ``lambdaCapture`` node matcher, the ``capturesVar`` traversal
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matcher, and ``capturesThis`` narrowing matcher.
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- The ``hasAnyCapture`` matcher now only accepts an inner matcher of type
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``Matcher<LambdaCapture>``. The matcher originally accepted an inner matcher
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of type ``Matcher<CXXThisExpr>`` or ``Matcher<VarDecl>``.
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- The ``usingType`` matcher is now available and needed to refer to types that
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are referred to via using C++ using declarations.
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The associated ``UsingShadowDecl`` can be matched using ``throughUsingDecl``
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and the underlying ``Type`` with ``hasUnderlyingType``.
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``hasDeclaration`` continues to see through the alias and apply to the
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underlying type.
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clang-format
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------------
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- Option ``AllowShortEnumsOnASingleLine: false`` has been improved, it now
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correctly places the opening brace according to ``BraceWrapping.AfterEnum``.
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- Option ``QualifierAlignment`` has been added in order to auto-arrange the
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positioning of specifiers/qualifiers
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`const` `volatile` `static` `inline` `constexpr` `restrict`
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in variable and parameter declarations to be either ``Right`` aligned
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or ``Left`` aligned or ``Custom`` using ``QualifierOrder``.
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- Option ``QualifierOrder`` has been added to allow the order
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`const` `volatile` `static` `inline` `constexpr` `restrict`
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to be controlled relative to the `type`.
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- Option ``SeparateDefinitionBlocks`` has been added to insert or remove empty
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lines between definition blocks including functions, classes, structs, enums,
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and namespaces.
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- Add a ``Custom`` style to ``SpaceBeforeParens``, to better configure the
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space before parentheses. The custom options can be set using
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``SpaceBeforeParensOptions``.
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- The command line argument `-style=<string>` has been extended so that a specific
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format file at location <format_file_path> can be selected. This is supported
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via the syntax: `-style=file:<format_file_path>`.
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- Improved C++20 Modules and Coroutines support.
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- Option ``AfterOverloadedOperator`` has been added in ``SpaceBeforeParensOptions``
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to allow space between overloaded operator and opening parentheses.
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libclang
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--------
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- ...
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Static Analyzer
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---------------
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- ...
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.. _release-notes-ubsan:
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Undefined Behavior Sanitizer (UBSan)
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------------------------------------
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Core Analysis Improvements
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==========================
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- ...
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New Issues Found
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================
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- ...
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Python Binding Changes
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----------------------
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The following methods have been added:
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- ...
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Significant Known Problems
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==========================
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Additional Information
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======================
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A wide variety of additional information is available on the `Clang web
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page <https://clang.llvm.org/>`_. The web page contains versions of the
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API documentation which are up-to-date with the Git version of
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the source code. You can access versions of these documents specific to
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this release by going into the "``clang/docs/``" directory in the Clang
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tree.
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If you have any questions or comments about Clang, please feel free to
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contact us via the `mailing
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list <https://lists.llvm.org/mailman/listinfo/cfe-dev>`_.
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