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=======================================
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Clang 8.0.0 (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 8 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 8.0.0. 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 Subversion 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 8.0.0?
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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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- Clang supports use of a profile remapping file, which permits
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profile data captured for one version of a program to be applied
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when building another version where symbols have changed (for
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example, due to renaming a class or namespace).
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See the :doc:`UsersManual` for details.
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Improvements to Clang's diagnostics
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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- ``-Wextra-semi-stmt`` is a new diagnostic that diagnoses extra semicolons,
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much like ``-Wextra-semi``. This new diagnostic diagnoses all *unnecessary*
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null statements (expression statements without an expression), unless: the
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semicolon directly follows a macro that was expanded to nothing or if the
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semicolon is within the macro itself. This applies to macros defined in system
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headers as well as user-defined macros.
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.. code-block:: c++
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#define MACRO(x) int x;
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#define NULLMACRO(varname)
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void test() {
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; // <- warning: ';' with no preceding expression is a null statement
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while (true)
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; // OK, it is needed.
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switch (my_enum) {
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case E1:
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// stuff
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break;
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case E2:
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; // OK, it is needed.
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}
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MACRO(v0;) // Extra semicolon, but within macro, so ignored.
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MACRO(v1); // <- warning: ';' with no preceding expression is a null statement
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NULLMACRO(v2); // ignored, NULLMACRO expanded to nothing.
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}
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- ``-Wempty-init-stmt`` is a new diagnostic that diagnoses empty init-statements
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of ``if``, ``switch``, ``range-based for``, unless: the semicolon directly
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follows a macro that was expanded to nothing or if the semicolon is within the
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macro itself (both macros from system headers, and normal macros). This
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diagnostic is in the ``-Wextra-semi-stmt`` group and is enabled in
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``-Wextra``.
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.. code-block:: c++
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void test() {
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if(; // <- warning: init-statement of 'if' is a null statement
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true)
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;
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switch (; // <- warning: init-statement of 'switch' is a null statement
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x) {
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...
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}
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for (; // <- warning: init-statement of 'range-based for' is a null statement
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int y : S())
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;
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}
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Non-comprehensive list of changes in this release
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-------------------------------------------------
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- The experimental feature Pretokenized Headers (PTH) was removed in its
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entirely from Clang. The feature did not properly work with about 1/3 of the
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possible tokens available and was unmaintained.
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- The internals of libc++ include directory detection on MacOS have changed.
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Instead of running a search based on the ``-resource-dir`` flag, the search
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is now based on the path of the compiler in the filesystem. The default
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behaviour should not change. However, if you override ``-resource-dir``
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manually and rely on the old behaviour you will need to add appropriate
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compiler flags for finding the corresponding libc++ include directory.
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New Compiler Flags
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------------------
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- ``-fprofile-filter-files=[regexes]`` and ``-fprofile-exclude-files=[regexes]``.
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Clang has now options to filter or exclude some files when
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instrumenting for gcov-based profiling.
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See the :doc:`UsersManual` for details.
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- ...
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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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- As of clang 8, `alignof` and `_Alignof` return the ABI alignment of a type,
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as opposed to the preferred alignment. `__alignof` still returns the
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preferred alignment. `-fclang-abi-compat=7` (and previous) will make
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`alignof` and `_Alignof` return preferred alignment again.
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New Pragmas in Clang
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--------------------
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- Clang now supports adding multiple `#pragma clang attribute` attributes into
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a scope of pushed attributes.
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Attribute Changes in Clang
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--------------------------
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- ...
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Windows Support
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---------------
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- clang-cl now supports the use of the precompiled header options /Yc and /Yu
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without the filename argument. When these options are used without the
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filename, a `#pragma hdrstop` inside the source marks the end of the
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precompiled code.
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- clang-cl has a new command-line option, ``/Zc:dllexportInlines-``, similar to
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``-fvisibility-inlines-hidden`` on non-Windows, that makes class-level
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`dllexport` and `dllimport` attributes not apply to inline member functions.
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This can significantly reduce compile and link times. See the `User's Manual
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<UsersManual.html#the-zc-dllexportinlines-option>`_ for more info.
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- ...
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C Language Changes in Clang
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---------------------------
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- ...
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...
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C11 Feature Support
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^^^^^^^^^^^^^^^^^^^
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...
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C++ Language Changes in Clang
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-----------------------------
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- ...
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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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...
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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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- `_Alignof` and `alignof` now return the ABI alignment of a type, as opposed
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to the preferred alignment.
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- This is more in keeping with the language of the standards, as well as
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being compatible with gcc
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- `__alignof` and `__alignof__` still return the preferred alignment of
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a type
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- This shouldn't break any ABI except for things that explicitly ask for
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`alignas(alignof(T))`.
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- If you have interfaces that break with this change, you may wish to switch
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to `alignas(__alignof(T))`, instead of using the `-fclang-abi-compat`
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switch.
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OpenMP Support in Clang
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----------------------------------
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CUDA Support in Clang
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---------------------
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Internal API Changes
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--------------------
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These are major API changes that have happened since the 7.0.0 release of
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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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- ...
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AST Matchers
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------------
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- ...
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clang-format
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------------
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- ...
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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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...
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.. _release-notes-ubsan:
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Undefined Behavior Sanitizer (UBSan)
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------------------------------------
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* The Implicit Conversion Sanitizer (``-fsanitize=implicit-conversion``) group
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was extended. One more type of issues is caught - implicit integer sign change.
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(``-fsanitize=implicit-integer-sign-change``).
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This makes the Implicit Conversion Sanitizer feature-complete,
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with only missing piece being bitfield handling.
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While there is a ``-Wsign-conversion`` diagnostic group that catches this kind
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of issues, it is both noisy, and does not catch **all** the cases.
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.. code-block:: c++
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bool consume(unsigned int val);
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void test(int val) {
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(void)consume(val); // If the value was negative, it is now large positive.
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(void)consume((unsigned int)val); // OK, the conversion is explicit.
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}
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Like some other ``-fsanitize=integer`` checks, these issues are **not**
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undefined behaviour. But they are not *always* intentional, and are somewhat
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hard to track down. This group is **not** enabled by ``-fsanitize=undefined``,
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but the ``-fsanitize=implicit-integer-sign-change`` check
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is enabled by ``-fsanitize=integer``.
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(as is ``-fsanitize=implicit-integer-truncation`` check)
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* The Implicit Conversion Sanitizer (``-fsanitize=implicit-conversion``) has
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learned to sanitize compound assignment operators.
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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 Subversion 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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