forked from OSchip/llvm-project
Update docs version and clear release notes after 8.0.0 version bump
llvm-svn: 338557
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Hans Wennborg
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=======================================
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Clang 7.0.0 (In-Progress) Release Notes
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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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@ -10,7 +10,7 @@ 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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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 <http://releases.llvm.org/download.html>`_.
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@ -18,7 +18,7 @@ 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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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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@ -35,7 +35,7 @@ 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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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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@ -46,87 +46,19 @@ 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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- A new Implicit Conversion Sanitizer (``-fsanitize=implicit-conversion``) group
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was added. Please refer to the :ref:`release-notes-ubsan` section of the
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release notes for the details.
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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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- By default, Clang emits an address-significance table into
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every ELF object file when using the integrated assembler.
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Address-significance tables allow linkers to implement `safe ICF
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<https://research.google.com/pubs/archive/36912.pdf>`_ without the false
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positives that can result from other implementation techniques such as
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relocation scanning. The ``-faddrsig`` and ``-fno-addrsig`` flags can be
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used to control whether to emit the address-significance table.
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- ...
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New Compiler Flags
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------------------
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- ``-fstrict-float-cast-overflow`` and ``-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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- ``-fforce-emit-vtables`` and ``-fno-force-emit-vtables``.
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In order to improve devirtualization, forces emitting of vtables even in
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modules where it isn't necessary. It causes more inline virtual functions
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to be emitted.
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- ...
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Deprecated Compiler Flags
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@ -140,12 +72,6 @@ future versions of Clang.
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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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@ -156,30 +82,11 @@ 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-cl's support for precompiled headers has been much improved:
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- When using a pch file, clang-cl now no longer redundantly emits inline
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methods that are already stored in the obj that was built together with
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the pch file (matching cl.exe). This speeds up builds using pch files
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by around 30%.
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- The /Ycfoo.h and /Yufoo.h flags can now be used without /FIfoo.h when
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foo.h is instead included by an explicit `#include` directive. This means
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Visual Studio's default stdafx.h setup now uses precompiled headers with
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clang-cl.
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- ...
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@ -218,38 +125,15 @@ OpenCL C Language Changes in Clang
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OpenMP Support in Clang
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----------------------------------
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- Clang gained basic support for OpenMP 4.5 offloading for NVPTX target.
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To compile your program for NVPTX target use the following options:
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`-fopenmp -fopenmp-targets=nvptx64-nvidia-cuda` for 64 bit platforms or
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`-fopenmp -fopenmp-targets=nvptx-nvidia-cuda` for 32 bit platform.
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- Passing options to the OpenMP device offloading toolchain can be done using
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the `-Xopenmp-target=<triple> -opt=val` flag. In this way the `-opt=val`
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option will be forwarded to the respective OpenMP device offloading toolchain
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described by the triple. For example passing the compute capability to
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the OpenMP NVPTX offloading toolchain can be done as follows:
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`-Xopenmp-target=nvptx64-nvidia-cuda -march=sm_60`. For the case when only one
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target offload toolchain is specified under the `-fopenmp-targets=<triples>`
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option, then the triple can be skipped: `-Xopenmp-target -march=sm_60`.
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- Other bugfixes.
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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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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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@ -263,9 +147,6 @@ AST Matchers
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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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@ -287,31 +168,6 @@ Static Analyzer
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Undefined Behavior Sanitizer (UBSan)
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------------------------------------
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* A new Implicit Conversion Sanitizer (``-fsanitize=implicit-conversion``) group
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was added.
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Currently, only one type of issues is caught - implicit integer truncation
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(``-fsanitize=implicit-integer-truncation``), also known as integer demotion.
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While there is a ``-Wconversion`` diagnostic group that catches this kind of
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issues, it is both noisy, and does not catch **all** the cases.
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.. code-block:: c++
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unsigned char store = 0;
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bool consume(unsigned int val);
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void test(unsigned long val) {
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if (consume(val)) // the value may have been silently truncated.
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store = store + 768; // before addition, 'store' was promoted to int.
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(void)consume((unsigned int)val); // OK, the truncation is explicit.
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}
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Just like 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-truncation`` check
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is enabled by ``-fsanitize=integer``.
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Core Analysis Improvements
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==========================
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@ -49,9 +49,9 @@ copyright = u'2007-%d, The Clang Team' % date.today().year
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# built documents.
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#
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# The short version.
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version = '7'
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version = '8'
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# The full version, including alpha/beta/rc tags.
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release = '7'
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release = '8'
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# The language for content autogenerated by Sphinx. Refer to documentation
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# for a list of supported languages.
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