forked from OSchip/llvm-project
333 lines
11 KiB
ReStructuredText
333 lines
11 KiB
ReStructuredText
========================================
|
|
Clang 10.0.0 (In-Progress) Release Notes
|
|
========================================
|
|
|
|
.. contents::
|
|
:local:
|
|
:depth: 2
|
|
|
|
Written by the `LLVM Team <https://llvm.org/>`_
|
|
|
|
.. warning::
|
|
|
|
These are in-progress notes for the upcoming Clang 10 release.
|
|
Release notes for previous releases can be found on
|
|
`the Download Page <https://releases.llvm.org/download.html>`_.
|
|
|
|
Introduction
|
|
============
|
|
|
|
This document contains the release notes for the Clang C/C++/Objective-C
|
|
frontend, part of the LLVM Compiler Infrastructure, release 10.0.0. 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 <https://llvm.org/docs/ReleaseNotes.html>`_. All LLVM
|
|
releases may be downloaded from the `LLVM releases web
|
|
site <https://llvm.org/releases/>`_.
|
|
|
|
For more information about Clang or LLVM, including information about the
|
|
latest release, please see the `Clang Web Site <https://clang.llvm.org>`_ or the
|
|
`LLVM Web Site <https://llvm.org>`_.
|
|
|
|
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 <https://llvm.org/releases/>`_.
|
|
|
|
What's New in Clang 10.0.0?
|
|
===========================
|
|
|
|
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
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
- -Wtautological-overlap-compare will warn on negative numbers and non-int
|
|
types.
|
|
- -Wtautological-compare for self comparisons and
|
|
-Wtautological-overlap-compare will now look through member and array
|
|
access to determine if two operand expressions are the same.
|
|
- -Wtautological-bitwise-compare is a new warning group. This group has the
|
|
current warning which diagnoses the tautological comparison of a bitwise
|
|
operation and a constant. The group also has the new warning which diagnoses
|
|
when a bitwise-or with a non-negative value is converted to a bool, since
|
|
that bool will always be true.
|
|
- -Wbitwise-conditional-parentheses will warn on operator precedence issues
|
|
when mixing bitwise-and (&) and bitwise-or (|) operator with the
|
|
conditional operator (?:).
|
|
|
|
Non-comprehensive list of changes in this release
|
|
-------------------------------------------------
|
|
|
|
* In both C and C++ (C17 ``6.5.6p8``, C++ ``[expr.add]``), pointer arithmetic is
|
|
only permitted within arrays. In particular, the behavior of a program is not
|
|
defined if it adds a non-zero offset (or in C, any offset) to a null pointer,
|
|
or if it forms a null pointer by subtracting an integer from a non-null
|
|
pointer, and the LLVM optimizer now uses those guarantees for transformations.
|
|
This may lead to unintended behavior in code that performs these operations.
|
|
The Undefined Behavior Sanitizer ``-fsanitize=pointer-overflow`` check has
|
|
been extended to detect these cases, so that code relying on them can be
|
|
detected and fixed.
|
|
|
|
- For X86 target, -march=skylake-avx512, -march=icelake-client,
|
|
-march=icelake-server, -march=cascadelake, -march=cooperlake will default to
|
|
not using 512-bit zmm registers in vectorized code unless 512-bit intrinsics
|
|
are used in the source code. 512-bit operations are known to cause the CPUs
|
|
to run at a lower frequency which can impact performance. This behavior can be
|
|
changed by passing -mprefer-vector-width=512 on the command line.
|
|
|
|
New Compiler Flags
|
|
------------------
|
|
|
|
- The -fgnuc-version= flag now controls the value of ``__GNUC__`` and related
|
|
macros. This flag does not enable or disable any GCC extensions implemented in
|
|
Clang. Setting the version to zero causes Clang to leave ``__GNUC__`` and
|
|
other GNU-namespaced macros, such as ``__GXX_WEAK__``, undefined.
|
|
|
|
Deprecated Compiler Flags
|
|
-------------------------
|
|
|
|
The following options are deprecated and ignored. They will be removed in
|
|
future versions of Clang.
|
|
|
|
- -mmpx used to enable the __MPX__ preprocessor define for the Intel MPX
|
|
instructions. There were no MPX intrinsics.
|
|
- -mno-mpx used to disable -mmpx and is the default behavior.
|
|
|
|
- ...
|
|
|
|
Modified Compiler Flags
|
|
-----------------------
|
|
|
|
- ...
|
|
|
|
New Pragmas in Clang
|
|
--------------------
|
|
|
|
- ...
|
|
|
|
Attribute Changes in Clang
|
|
--------------------------
|
|
|
|
- ...
|
|
|
|
Windows Support
|
|
---------------
|
|
|
|
- Previous Clang versions contained a work-around to avoid an issue with the
|
|
standard library headers in Visual Studio 2019 versions prior to 16.3. This
|
|
work-around has now been removed, and users of Visual Studio 2019 are
|
|
encouraged to upgrade to 16.3 or later, otherwise they may see link errors as
|
|
below:
|
|
|
|
.. code-block:: console
|
|
|
|
error LNK2005: "bool const std::_Is_integral<int>" (??$_Is_integral@H@std@@3_NB) already defined
|
|
|
|
|
|
|
|
|
|
C Language Changes in Clang
|
|
---------------------------
|
|
|
|
- ...
|
|
|
|
C11 Feature Support
|
|
^^^^^^^^^^^^^^^^^^^
|
|
|
|
...
|
|
|
|
C++ Language Changes in Clang
|
|
-----------------------------
|
|
|
|
- The behaviour of the `gnu_inline` attribute now matches GCC, for cases
|
|
where used without the `extern` keyword. As this is a change compared to
|
|
how it behaved in previous Clang versions, a warning is emitted for this
|
|
combination.
|
|
|
|
C++1z Feature Support
|
|
^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
...
|
|
|
|
Objective-C Language Changes in Clang
|
|
-------------------------------------
|
|
|
|
- ...
|
|
|
|
OpenCL C Language Changes in Clang
|
|
----------------------------------
|
|
|
|
...
|
|
|
|
ABI Changes in Clang
|
|
--------------------
|
|
|
|
- gcc passes vectors of __int128 in memory on X86-64. Clang historically
|
|
broke the vectors into multiple scalars using two 64-bit values for each
|
|
element. Clang now matches the gcc behavior on Linux and NetBSD. You can
|
|
switch back to old API behavior with flag: -fclang-abi-compat=9.0.
|
|
|
|
OpenMP Support in Clang
|
|
-----------------------
|
|
|
|
- ...
|
|
|
|
CUDA Support in Clang
|
|
---------------------
|
|
|
|
- ...
|
|
|
|
Internal API Changes
|
|
--------------------
|
|
|
|
These are major API changes that have happened since the 9.0.0 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.
|
|
|
|
- libTooling APIs that transfer ownership of `FrontendAction` objects now pass
|
|
them by `unique_ptr`, making the ownership transfer obvious in the type
|
|
system. `FrontendActionFactory::create()` now returns a
|
|
`unique_ptr<FrontendAction>`. `runToolOnCode`, `runToolOnCodeWithArgs`,
|
|
`ToolInvocation::ToolInvocation()` now take a `unique_ptr<FrontendAction>`.
|
|
|
|
Build System Changes
|
|
--------------------
|
|
|
|
These are major changes to the build system that have happened since the 9.0.0
|
|
release of Clang. Users of the build system should adjust accordingly.
|
|
|
|
- In 8.0.0 and below, the install-clang-headers target would install clang's
|
|
resource directory headers. This installation is now performed by the
|
|
install-clang-resource-headers target. Users of the old install-clang-headers
|
|
target should switch to the new install-clang-resource-headers target. The
|
|
install-clang-headers target now installs clang's API headers (corresponding
|
|
to its libraries), which is consistent with the install-llvm-headers target.
|
|
|
|
- In 9.0.0 and later Clang added a new target, clang-cpp, which generates a
|
|
shared library comprised of all the clang component libraries and exporting
|
|
the clang C++ APIs. Additionally the build system gained the new
|
|
"CLANG_LINK_CLANG_DYLIB" option, which defaults Off, and when set to On, will
|
|
force clang (and clang-based tools) to link the clang-cpp library instead of
|
|
statically linking clang's components. This option will reduce the size of
|
|
binary distributions at the expense of compiler performance.
|
|
|
|
- ...
|
|
|
|
AST Matchers
|
|
------------
|
|
|
|
- ...
|
|
|
|
clang-format
|
|
------------
|
|
|
|
- The ``Standard`` style option specifies which version of C++ should be used
|
|
when parsing and formatting C++ code. The set of allowed values has changed:
|
|
|
|
- ``Latest`` will always enable new C++ language features.
|
|
- ``c++03``, ``c++11``, ``c++14``, ``c++17``, ``c++20`` will pin to exactly
|
|
that language version.
|
|
- ``Auto`` is the default and detects style from the code (this is unchanged).
|
|
|
|
The previous values of ``Cpp03`` and ``Cpp11`` are deprecated. Note that
|
|
``Cpp11`` is treated as ``Latest``, as this was always clang-format's behavior.
|
|
(One motivation for this change is the new name describes the behavior better).
|
|
|
|
libclang
|
|
--------
|
|
|
|
- ...
|
|
|
|
|
|
Static Analyzer
|
|
---------------
|
|
|
|
- The Clang analyzer checker ``DeadStores`` gets a new option called
|
|
``WarnForDeadNestedAssignments`` to detect nested dead assignments
|
|
(enabled by default).
|
|
- ...
|
|
|
|
.. _release-notes-ubsan:
|
|
|
|
Undefined Behavior Sanitizer (UBSan)
|
|
------------------------------------
|
|
|
|
- * The ``pointer-overflow`` check was extended added to catch the cases where
|
|
a non-zero offset is applied to a null pointer, or the result of
|
|
applying the offset is a null pointer.
|
|
|
|
.. code-block:: c++
|
|
|
|
#include <cstdint> // for intptr_t
|
|
|
|
static char *getelementpointer_inbounds(char *base, unsigned long offset) {
|
|
// Potentially UB.
|
|
return base + offset;
|
|
}
|
|
|
|
char *getelementpointer_unsafe(char *base, unsigned long offset) {
|
|
// Always apply offset. UB if base is ``nullptr`` and ``offset`` is not
|
|
// zero, or if ``base`` is non-``nullptr`` and ``offset`` is
|
|
// ``-reinterpret_cast<intptr_t>(base)``.
|
|
return getelementpointer_inbounds(base, offset);
|
|
}
|
|
|
|
char *getelementpointer_safe(char *base, unsigned long offset) {
|
|
// Cast pointer to integer, perform usual arithmetic addition,
|
|
// and cast to pointer. This is legal.
|
|
char *computed =
|
|
reinterpret_cast<char *>(reinterpret_cast<intptr_t>(base) + offset);
|
|
// If either the pointer becomes non-``nullptr``, or becomes
|
|
// ``nullptr``, we must use ``computed`` result.
|
|
if (((base == nullptr) && (computed != nullptr)) ||
|
|
((base != nullptr) && (computed == nullptr)))
|
|
return computed;
|
|
// Else we can use ``getelementpointer_inbounds()``.
|
|
return getelementpointer_inbounds(base, offset);
|
|
}
|
|
|
|
|
|
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 <https://clang.llvm.org/>`_. 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
|
|
tree.
|
|
|
|
If you have any questions or comments about Clang, please feel free to
|
|
contact us via the `mailing
|
|
list <https://lists.llvm.org/mailman/listinfo/cfe-dev>`_.
|