2020-02-14 05:46:33 +08:00
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========================================
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2020-07-15 17:40:53 +08:00
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Clang 12.0.0 (In-Progress) Release Notes
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2020-02-14 05:46:33 +08:00
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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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2020-07-15 17:40:53 +08:00
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These are in-progress notes for the upcoming Clang 12 release.
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2020-02-14 05:46:33 +08:00
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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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2020-07-15 17:40:53 +08:00
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frontend, part of the LLVM Compiler Infrastructure, release 12.0.0. Here we
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2020-02-14 05:46:33 +08:00
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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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2020-07-15 17:40:53 +08:00
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What's New in Clang 12.0.0?
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2020-02-14 05:46:33 +08:00
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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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2020-07-15 17:40:53 +08:00
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- ...
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2020-06-05 00:45:04 +08:00
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2020-02-14 05:46:33 +08:00
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Non-comprehensive list of changes in this release
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-------------------------------------------------
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2020-08-22 21:41:40 +08:00
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- The builtin intrinsics ``__builtin_bitreverse8``, ``__builtin_bitreverse16``,
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``__builtin_bitreverse32`` and ``__builtin_bitreverse64`` may now be used
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within constant expressions.
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2020-08-22 21:34:08 +08:00
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- The builtin intrinsics ``__builtin_rotateleft8``, ``__builtin_rotateleft16``,
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``__builtin_rotateleft32`` and ``__builtin_rotateleft64`` may now be used
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within constant expressions.
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- The builtin intrinsics ``__builtin_rotateright8``, ``__builtin_rotateright16``,
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``__builtin_rotateright32`` and ``__builtin_rotateright64`` may now be used
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within constant expressions.
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2020-05-26 02:44:35 +08:00
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2020-02-14 05:46:33 +08:00
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New Compiler Flags
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------------------
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2020-07-15 17:40:53 +08:00
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- ...
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2020-07-11 21:07:27 +08:00
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2020-07-11 20:53:50 +08:00
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- -fpch-codegen and -fpch-debuginfo generate shared code and/or debuginfo
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for contents of a precompiled header in a separate object file. This object
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file needs to be linked in, but its contents do not need to be generated
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for other objects using the precompiled header. This should usually save
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compile time. If not using clang-cl, the separate object file needs to
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be created explicitly from the precompiled header.
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Example of use:
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.. code-block:: console
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$ clang++ -x c++-header header.h -o header.pch -fpch-codegen -fpch-debuginfo
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$ clang++ -c header.pch -o shared.o
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$ clang++ -c source.cpp -o source.o -include-pch header.pch
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$ clang++ -o binary source.o shared.o
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- Using -fpch-instantiate-templates when generating the precompiled header
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usually increases the amount of code/debuginfo that can be shared.
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- In some cases, especially when building with optimizations enabled, using
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-fpch-codegen may generate so much code in the shared object that compiling
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it may be a net loss in build time.
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- Since headers may bring in private symbols of other libraries, it may be
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sometimes necessary to discard unused symbols (such as by adding
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-Wl,--gc-sections on ELF platforms to the linking command, and possibly
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adding -fdata-sections -ffunction-sections to the command generating
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the shared object).
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2020-02-14 05:46:33 +08:00
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Deprecated Compiler Flags
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-------------------------
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The following options are deprecated and ignored. They will be removed in
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future versions of Clang.
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- ...
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Modified Compiler Flags
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-----------------------
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2020-08-04 06:11:28 +08:00
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- On ELF, ``-gz`` now defaults to ``-gz=zlib`` with the integrated assembler.
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It produces ``SHF_COMPRESSED`` style compression of debug information. GNU
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binutils 2.26 or newer, or lld is required to link produced object files. Use
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``-gz=zlib-gnu`` to get the old behavior.
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2020-11-17 07:04:55 +08:00
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- Now that `this` pointers are tagged with `nonnull` and `dereferenceable(N)`,
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`-fno-delete-null-pointer-checks` has gained the power to remove the
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`nonnull` attribute on `this` for configurations that need it to be nullable.
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2020-02-14 05:46:33 +08:00
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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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2020-10-18 19:34:41 +08:00
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- Added support for the C++20 likelihood attributes ``[[likely]]`` and
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``[[unlikely]]``. As an extension they can be used in C++11 and newer.
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This extension is enabled by default.
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2020-02-14 05:46:33 +08:00
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Windows Support
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---------------
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C Language Changes in Clang
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---------------------------
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2020-03-03 01:33:14 +08:00
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- ...
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2020-02-14 05:46:33 +08:00
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C++ Language Changes in Clang
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-----------------------------
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2020-07-15 17:40:53 +08:00
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- ...
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2020-02-14 05:46:33 +08:00
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C++1z Feature Support
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^^^^^^^^^^^^^^^^^^^^^
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...
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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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OpenMP Support in Clang
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-----------------------
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- ...
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CUDA Support in Clang
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---------------------
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- ...
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2020-08-21 04:37:51 +08:00
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X86 Support in Clang
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--------------------
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2020-08-21 17:19:41 +08:00
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- The x86 intrinsics ``_mm_popcnt_u32``, ``_mm_popcnt_u64``, ``_popcnt32``,
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``_popcnt64``, ``__popcntd`` and ``__popcntq`` may now be used within
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2020-08-22 21:12:05 +08:00
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constant expressions.
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2020-08-21 04:37:51 +08:00
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2020-08-21 18:37:40 +08:00
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- The x86 intrinsics ``_bit_scan_forward``, ``__bsfd`` and ``__bsfq`` may now
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2020-08-22 21:12:05 +08:00
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be used within constant expressions.
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2020-08-21 18:37:40 +08:00
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- The x86 intrinsics ``_bit_scan_reverse``, ``__bsrd`` and ``__bsrq`` may now
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2020-08-22 21:12:05 +08:00
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be used within constant expressions.
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2020-08-21 18:37:40 +08:00
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2020-08-21 17:53:17 +08:00
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- The x86 intrinsics ``__bswap``, ``__bswapd``, ``__bswap64`` and ``__bswapq``
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2020-08-22 21:12:05 +08:00
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may now be used within constant expressions.
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2020-08-21 17:53:17 +08:00
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2020-08-23 17:27:46 +08:00
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- The x86 intrinsics ``_castf32_u32``, ``_castf64_u64``, ``_castu32_f32`` and
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``_castu64_f64`` may now be used within constant expressions.
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2020-08-23 23:11:39 +08:00
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- The x86 intrinsics ``__rolb``, ``__rolw``, ``__rold``, ``__rolq`, ``_rotl``,
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``_rotwl`` and ``_lrotl`` may now be used within constant expressions.
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- The x86 intrinsics ``__rorb``, ``__rorw``, ``__rord``, ``__rorq`, ``_rotr``,
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``_rotwr`` and ``_lrotr`` may now be used within constant expressions.
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2020-10-25 00:00:33 +08:00
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- Support for ``-march=alderlake``, ``-march=sapphirerapids`` and
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``-march=znver3`` was added.
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2020-10-13 00:35:22 +08:00
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- Support for ``-march=x86-64-v[234]`` has been added.
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See :doc:`UsersManual` for details about these micro-architecture levels.
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2020-08-26 02:56:43 +08:00
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2020-08-27 06:58:38 +08:00
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- The -mtune command line option is no longer ignored for X86. This can be used
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to request microarchitectural optimizations independent on -march. -march=<cpu>
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implies -mtune=<cpu>. -mtune=generic is the default with no -march or -mtune
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specified.
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2020-10-22 16:46:07 +08:00
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- Support for ``HRESET`` instructions has been added.
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- Support for ``UINTR`` instructions has been added.
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2020-10-21 15:57:43 +08:00
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2020-10-30 12:58:05 +08:00
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- Support for ``AVXVNNI`` instructions has been added.
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2020-02-14 05:46:33 +08:00
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Internal API Changes
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--------------------
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2020-07-15 17:40:53 +08:00
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These are major API changes that have happened since the 11.0.0 release of
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2020-02-14 05:46:33 +08:00
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Clang. If upgrading an external codebase that uses Clang as a library,
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this section should help get you past the largest hurdles of upgrading.
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2020-07-15 17:40:53 +08:00
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- ...
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Removed a RecursiveASTVisitor feature to visit operator kinds with different methods
Summary:
This feature was only used in two places, but contributed a non-trivial
amount to the complexity of RecursiveASTVisitor, and was buggy (see my
recent patches where I was fixing the bugs that I noticed). I don't
think the convenience benefit of this feature is worth the complexity.
Besides complexity, another issue with the current state of
RecursiveASTVisitor is the non-uniformity in how it handles different
AST nodes. All AST nodes follow a regular pattern, but operators are
special -- and this special behavior not documented. Correct usage of
RecursiveASTVisitor relies on shadowing member functions with specific
names and signatures. Near misses don't cause any compile-time errors,
incorrectly named or typed methods are just silently ignored. Therefore,
predictability of RecursiveASTVisitor API is quite important.
This change reduces the size of the `clang` binary by 38 KB (0.2%) in
release mode, and by 7 MB (0.3%) in debug mode. The `clang-tidy` binary
is reduced by 205 KB (0.3%) in release mode, and by 5 MB (0.4%) in debug
mode. I don't think these code size improvements are significant enough
to justify this change on its own (for me, the primary motivation is
reducing code complexity), but they I think are a nice side-effect.
Reviewers: rsmith, sammccall, ymandel, aaron.ballman
Reviewed By: rsmith, sammccall, ymandel, aaron.ballman
Subscribers: cfe-commits
Tags: #clang
Differential Revision: https://reviews.llvm.org/D82921
2020-07-03 23:01:01 +08:00
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2020-02-14 05:46:33 +08:00
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Build System Changes
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--------------------
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2020-07-15 17:40:53 +08:00
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These are major changes to the build system that have happened since the 11.0.0
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2020-02-14 05:46:33 +08:00
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release of Clang. Users of the build system should adjust accordingly.
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2020-07-15 17:40:53 +08:00
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- ...
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2020-02-14 05:46:33 +08:00
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AST Matchers
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------------
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2020-11-05 06:57:42 +08:00
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- The behavior of TK_IgnoreUnlessSpelledInSource with the traverse() matcher
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has been changed to no longer match on template instantiations or on
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implicit nodes which are not spelled in the source.
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2020-05-27 20:20:05 +08:00
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2020-02-14 05:46:33 +08:00
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clang-format
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------------
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2020-07-18 18:35:01 +08:00
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- Option ``BitFieldColonSpacing`` has been added that decides how
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space should be added around identifier, colon and bit-width in
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bitfield definitions.
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.. code-block:: c++
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// Both (default)
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struct F {
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unsigned dscp : 6;
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unsigned ecn : 2; // AlignConsecutiveBitFields=true
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};
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// None
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struct F {
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unsigned dscp:6;
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unsigned ecn :2;
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};
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// Before
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struct F {
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unsigned dscp :6;
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unsigned ecn :2;
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};
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// After
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struct F {
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unsigned dscp: 6;
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unsigned ecn : 2;
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};
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2020-05-20 14:48:45 +08:00
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2020-02-14 05:46:33 +08:00
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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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2020-03-23 05:18:40 +08:00
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API documentation which are up-to-date with the Git version of
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2020-02-14 05:46:33 +08:00
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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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