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Clang 6.0.0 (In-Progress) Release Notes
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Written by the `LLVM Team <>`_
.. warning::
These are in-progress notes for the upcoming Clang 6 release.
Release notes for previous releases can be found on
`the Download Page <>`_.
This document contains the release notes for the Clang C/C++/Objective-C
frontend, part of the LLVM Compiler Infrastructure, release 6.0.0. Here we
describe the status of Clang in some detail, including major
improvements from the previous release and new feature work. For the
general LLVM release notes, see `the LLVM
documentation <>`_. All LLVM
releases may be downloaded from the `LLVM releases web
site <>`_.
For more information about Clang or LLVM, including information about the
latest release, please see the `Clang Web Site <>`_ or the
`LLVM Web Site <>`_.
Note that if you are reading this file from a Subversion checkout or the
main Clang web page, this document applies to the *next* release, not
the current one. To see the release notes for a specific release, please
see the `releases page <>`_.
What's New in Clang 6.0.0?
Some of the major new features and improvements to Clang are listed
here. Generic improvements to Clang as a whole or to its underlying
infrastructure are described first, followed by language-specific
sections with improvements to Clang's support for those languages.
Major New Features
- ...
Improvements to Clang's diagnostics
- ``-Wpragma-pack`` is a new warning that warns in the following cases:
- When a translation unit is missing terminating ``#pragma pack (pop)``
- When leaving an included file that changes the current alignment value,
i.e. when the alignment before ``#include`` is different to the alignment
after ``#include``.
- ``-Wpragma-pack-suspicious-include`` (disabled by default) warns on an
``#include`` when the included file contains structures or unions affected by
a non-default alignment that has been specified using a ``#pragma pack``
directive prior to the ``#include``.
- ``-Wobjc-messaging-id`` is a new, non-default warning that warns about
message sends to unqualified ``id`` in Objective-C. This warning is useful
for projects that would like to avoid any potential future compiler
errors/warnings, as the system frameworks might add a method with the same
selector which could make the message send to ``id`` ambiguous.
- ``-Wtautological-compare`` now warns when comparing an unsigned integer and 0
regardless of whether the constant is signed or unsigned."
- ``-Wtautological-compare`` now warns about comparing a signed integer and 0
when the signed integer is coerced to an unsigned type for the comparison.
``-Wsign-compare`` was adjusted not to warn in this case.
- ``-Wtautological-constant-compare`` is a new warning that warns on
tautological comparisons between integer variable of the type ``T`` and the
largest/smallest possible integer constant of that same type.
- For C code, ``-Wsign-compare``, ``-Wsign-conversion``,
``-Wtautological-constant-compare`` and
``-Wtautological-constant-out-of-range-compare`` were adjusted to use the
underlying datatype of ``enum``.
- ``-Wnull-pointer-arithmetic`` now warns about performing pointer arithmetic
on a null pointer. Such pointer arithmetic has an undefined behavior if the
offset is nonzero. It also now warns about arithmetic on a null pointer
treated as a cast from integer to pointer (GNU extension).
- ``-Wzero-as-null-pointer-constant`` was adjusted not to warn on null pointer
constants that originate from system macros, except ``NULL`` macro.
Non-comprehensive list of changes in this release
- Bitrig OS was merged back into OpenBSD, so Bitrig support has been
removed from Clang/LLVM.
- The default value of _MSC_VER was raised from 1800 to 1911, making it
compatible with the Visual Studio 2015 and 2017 C++ standard library headers.
Users should generally expect this to be regularly raised to match the most
recently released version of the Visual C++ compiler.
- clang now defaults to ``.init_array`` if no gcc installation can be found.
If a gcc installation is found, it still prefers ``.ctors`` if the found
gcc is older than 4.7.0.
New Compiler Flags
- --autocomplete was implemented to obtain a list of flags and its arguments. This is used for shell autocompletion.
- The ``-fdouble-square-bracket-attributes`` and corresponding
``-fno-double-square-bracket-attributes`` flags were added to enable or
disable [[]] attributes in any language mode. Currently, only a limited
number of attributes are supported outside of C++ mode. See the Clang
attribute documentation for more information about which attributes are
supported for each syntax.
Deprecated Compiler Flags
The following options are deprecated and ignored. They will be removed in
future versions of Clang.
- ...
New Pragmas in Clang
Clang now supports the ...
Attribute Changes in Clang
- The presence of __attribute__((availability(...))) on a declaration no longer
implies default visibility for that declaration on macOS.
- ...
Windows Support
Clang's support for building native Windows programs ...
C Language Changes in Clang
- ...
C11 Feature Support
C++ Language Changes in Clang
C++1z Feature Support
Objective-C Language Changes in Clang
OpenCL C Language Changes in Clang
OpenMP Support in Clang
Internal API Changes
These are major API changes that have happened since the 4.0.0 release of
Clang. If upgrading an external codebase that uses Clang as a library,
this section should help get you past the largest hurdles of upgrading.
- ...
AST Matchers
The hasDeclaration matcher now works the same for Type and QualType and only
ever looks through one level of sugaring in a limited number of cases.
There are two main patterns affected by this:
- qualType(hasDeclaration(recordDecl(...))): previously, we would look through
sugar like TypedefType to get at the underlying recordDecl; now, we need
to explicitly remove the sugaring:
- hasType(recordDecl(...)): hasType internally uses hasDeclaration; previously,
this matcher used to match for example TypedefTypes of the RecordType, but
after the change they don't; to fix, use:
- templateSpecializationType(hasDeclaration(classTemplateDecl(...))):
previously, we would directly match the underlying ClassTemplateDecl;
now, we can explicitly match the ClassTemplateSpecializationDecl, but that
requires to explicitly get the ClassTemplateDecl:
* Option *IndentPPDirectives* added to indent preprocessor directives on
| Before | After |
| .. code-block:: c++ | .. code-block:: c++ |
| | |
| #if FOO | #if FOO |
| #if BAR | # if BAR |
| #include <foo> | # include <foo> |
| #endif | # endif |
| #endif | #endif |
* Option -verbose added to the command line.
Shows the list of processed files.
Static Analyzer
Undefined Behavior Sanitizer (UBSan)
* A minimal runtime is now available. It is suitable for use in production
environments, and has a small attack surface. It only provides very basic
issue logging and deduplication, and does not support ``-fsanitize=vptr``
Core Analysis Improvements
- ...
New Issues Found
- ...
Python Binding Changes
The following methods have been added:
- ...
Significant Known Problems
Additional Information
A wide variety of additional information is available on the `Clang web
page <>`_. The web page contains versions of the
API documentation which are up-to-date with the Subversion version of
the source code. You can access versions of these documents specific to
this release by going into the "``clang/docs/``" directory in the Clang
If you have any questions or comments about Clang, please feel free to
contact us via the `mailing
list <>`_.