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=======================================
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Clang 7.0.0 (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 <http://llvm.org/>`_
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.. warning::
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These are in-progress notes for the upcoming Clang 7 release.
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Release notes for previous releases can be found on
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`the Download Page <http://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 7.0.0. 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 <http://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 <http://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 <http://clang.llvm.org>`_ or the
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`LLVM Web Site <http://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 <http://llvm.org/releases/>`_.
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What's New in Clang 7.0.0?
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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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- ``-Wc++98-compat-extra-semi`` is a new flag, which was previously inseparable
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from ``-Wc++98-compat-pedantic``. The latter still controls the new flag.
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- ``-Wextra-semi`` now also controls ``-Wc++98-compat-extra-semi``.
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Please do note that if you pass ``-Wno-c++98-compat-pedantic``, it implies
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``-Wno-c++98-compat-extra-semi``, so if you want that diagnostic, you need
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to explicitly re-enable it (e.g. by appending ``-Wextra-semi``).
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- ``-Wself-assign`` and ``-Wself-assign-field`` were extended to diagnose
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self-assignment operations using overloaded operators (i.e. classes).
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If you are doing such an assignment intentionally, e.g. in a unit test for
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a data structure, the first warning can be disabled by passing
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``-Wno-self-assign-overloaded``, also the warning can be suppressed by adding
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``*&`` to the right-hand side or casting it to the appropriate reference type.
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Non-comprehensive list of changes in this release
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-------------------------------------------------
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- Clang binary and libraries have been renamed from 7.0 to 7.
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For example, the ``clang`` binary will be called ``clang-7``
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instead of ``clang-7.0``.
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- Clang implements a collection of recent fixes to the C++ standard's definition
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of "standard-layout". In particular, a class is only considered to be
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standard-layout if all base classes and the first data member (or bit-field)
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can be laid out at offset zero.
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- Clang's handling of the GCC ``packed`` class attribute in C++ has been fixed
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to apply only to non-static data members and not to base classes. This fixes
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an ABI difference between Clang and GCC, but creates an ABI difference between
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Clang 7 and earlier versions. The old behavior can be restored by setting
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``-fclang-abi-compat`` to ``6`` or earlier.
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- Clang implements the proposed resolution of LWG issue 2358, along with the
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`corresponding change to the Itanium C++ ABI
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<https://github.com/itanium-cxx-abi/cxx-abi/pull/51>`_, which make classes
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containing only unnamed non-zero-length bit-fields be considered non-empty.
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This is an ABI break compared to prior Clang releases, but makes Clang
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generate code that is ABI-compatible with other compilers. The old
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behavior can be restored by setting ``-fclang-abi-compat`` to ``6`` or
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lower.
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- An existing tool named ``diagtool`` has been added to the release. As the
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name suggests, it helps with dealing with diagnostics in ``clang``, such as
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finding out the warning hierarchy, and which of them are enabled by default
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or for a particular compiler invocation.
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- ...
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New Compiler Flags
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------------------
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- :option:`-fstrict-float-cast-overflow` and
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:option:`-fno-strict-float-cast-overflow`.
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When a floating-point value is not representable in a destination integer
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type, the code has undefined behavior according to the language standard. By
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default, Clang will not guarantee any particular result in that case. With the
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'no-strict' option, Clang attempts to match the overflowing behavior of the
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target's native float-to-int conversion instructions.
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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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- Before Clang 7, we prepended the `#` character to the `--autocomplete`
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argument to enable cc1 flags. For example, when the `-cc1` or `-Xclang` flag
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is in the :program:`clang` invocation, the shell executed
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`clang --autocomplete=#-<flag to be completed>`. Clang 7 now requires the
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whole invocation including all flags to be passed to the `--autocomplete` like
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this: `clang --autocomplete=-cc1,-xc++,-fsyn`.
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New Pragmas in Clang
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--------------------
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Clang now supports the ...
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Attribute Changes in Clang
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--------------------------
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- Clang now supports function multiversioning with attribute 'target' on ELF
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based x86/x86-64 environments by using indirect functions. This implementation
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has a few minor limitations over the GCC implementation for the sake of AST
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sanity, however it is otherwise compatible with existing code using this
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feature for GCC. Consult the documentation for the target attribute for more
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information.
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- ...
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Windows Support
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---------------
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Clang's support for building native Windows programs ...
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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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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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- Clang will now try to locate the CUDA installation next to :program:`ptxas`
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in the `PATH` environment variable. This behavior can be turned off by passing
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the new flag `--cuda-path-ignore-env`.
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- Clang now supports generating object files with relocatable device code. This
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feature needs to be enabled with `-fcuda-rdc` and my result in performance
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penalties compared to whole program compilation. Please note that NVIDIA's
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:program:`nvcc` must be used for linking.
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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 6.0.0 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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- Clang-format will now support detecting and formatting code snippets in raw
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string literals. This is configured through the `RawStringFormats` style
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option.
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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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Undefined Behavior Sanitizer (UBSan)
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------------------------------------
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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 <http://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 <http://lists.llvm.org/mailman/listinfo/cfe-dev>`_.
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