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llvm-project/clang/docs/ReleaseNotes.rst
Alejandro Álvarez Ayllón 252c83bc9e
[clang][Sema] Fix type of an statement expression ending with an atomic type (#119711) 
When a statement expression's last statement is an atomic variable, GCC
and Clang disagree on the type of the expression. This can be made
apparent using `typeof` and forcing a diagnostic message:

```cpp
_Atomic int a = 0;
typeof(({a;})) x = "0";
```

* GCC complains about initializing `int` with `char*`
* Clang complains about initializing `_Atomic(int)` with a `char[2]`

Due to the type of the statement expression being deduced to be atomic,
we end with three implicit casts inside the `StmtExpr` on the AST:

* `LValueToRValue` -> `AtomicToNonAtomic`  ->  `NonAtomicToAtomic`

In some situations, this can end on an assertion inside
`IntExprEvaluator`, as reported in #106576.

With this patch, we now have two implicit casts, since the type of the
statement expression is deduced to be non-atomic:

* `LValueToRValue` -> `AtomicToNonAtomic`

This is consistent with the C standard (6.7.2.4, p4)

> The properties associated with atomic types are meaningful only for
expressions that are lvalues.

But a statement expression is an rvalue.

`IntExprEvaluator` assumptions are now satisfied and there is no
assertion error.
Additionally, the `typeof` trick mentioned above shows that the type is
consistently deduced between GCC and Clang.

Fixes #106576

---------

Co-authored-by: John McCall <rjmccall@gmail.com>
2025-02-18 09:52:31 +01:00

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===========================================
Clang |release| |ReleaseNotesTitle|
===========================================
.. contents::
:local:
:depth: 2
Written by the `LLVM Team <https://llvm.org/>`_
.. only:: PreRelease
.. warning::
These are in-progress notes for the upcoming Clang |version| release.
Release notes for previous releases can be found on
`the Releases Page <https://llvm.org/releases/>`_.
Introduction
============
This document contains the release notes for the Clang C/C++/Objective-C
frontend, part of the LLVM Compiler Infrastructure, release |release|. 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>`_. For the libc++ release notes,
see `this page <https://libcxx.llvm.org/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>`_.
Potentially Breaking Changes
============================
- The Objective-C ARC migrator (ARCMigrate) has been removed.
C/C++ Language Potentially Breaking Changes
-------------------------------------------
C++ Specific Potentially Breaking Changes
-----------------------------------------
- The type trait builtin ``__is_referenceable`` has been removed, since it has
very few users and all the type traits that could benefit from it in the
standard library already have their own bespoke builtins.
ABI Changes in This Version
---------------------------
- Return larger CXX records in memory instead of using AVX registers. Code compiled with older clang will be incompatible with newer version of the clang unless -fclang-abi-compat=20 is provided. (#GH120670)
AST Dumping Potentially Breaking Changes
----------------------------------------
- Added support for dumping template arguments of structural value kinds.
Clang Frontend Potentially Breaking Changes
-------------------------------------------
Clang Python Bindings Potentially Breaking Changes
--------------------------------------------------
What's New in Clang |release|?
==============================
C++ Language Changes
--------------------
C++2c Feature Support
^^^^^^^^^^^^^^^^^^^^^
C++23 Feature Support
^^^^^^^^^^^^^^^^^^^^^
C++20 Feature Support
^^^^^^^^^^^^^^^^^^^^^
C++17 Feature Support
^^^^^^^^^^^^^^^^^^^^^
Resolutions to C++ Defect Reports
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
- The flag `-frelaxed-template-template-args`
and its negation have been removed, having been deprecated since the previous
two releases. The improvements to template template parameter matching implemented
in the previous release, as described in P3310 and P3579, made this flag unnecessary.
C Language Changes
------------------
- Clang now allows an ``inline`` specifier on a typedef declaration of a
function type in Microsoft compatibility mode. #GH124869
- Clang now allows ``restrict`` qualifier for array types with pointer elements (#GH92847).
C2y Feature Support
^^^^^^^^^^^^^^^^^^^
C23 Feature Support
^^^^^^^^^^^^^^^^^^^
Non-comprehensive list of changes in this release
-------------------------------------------------
New Compiler Flags
------------------
- New option ``-fprofile-continuous`` added to enable continuous profile syncing to file (#GH124353, `docs <https://clang.llvm.org/docs/UsersManual.html#cmdoption-fprofile-continuous>`_).
The feature has `existed <https://clang.llvm.org/docs/SourceBasedCodeCoverage.html#running-the-instrumented-program>`_)
for a while and this is just a user facing option.
Deprecated Compiler Flags
-------------------------
Modified Compiler Flags
-----------------------
Removed Compiler Flags
-------------------------
Attribute Changes in Clang
--------------------------
- The ``no_sanitize`` attribute now accepts both ``gnu`` and ``clang`` names.
- Clang now diagnoses use of declaration attributes on void parameters. (#GH108819)
- Clang now allows ``__attribute__((model("small")))`` and
``__attribute__((model("large")))`` on non-TLS globals in x86-64 compilations.
This forces the global to be considered small or large in regards to the
x86-64 code model, regardless of the code model specified for the compilation.
Improvements to Clang's diagnostics
-----------------------------------
- Improve the diagnostics for deleted default constructor errors for C++ class
initializer lists that don't explicitly list a class member and thus attempt
to implicitly default construct that member.
- The ``-Wunique-object-duplication`` warning has been added to warn about objects
which are supposed to only exist once per program, but may get duplicated when
built into a shared library.
- Fixed a bug where Clang's Analysis did not correctly model the destructor behavior of ``union`` members (#GH119415).
- A statement attribute applied to a ``case`` label no longer suppresses
'bypassing variable initialization' diagnostics (#84072).
Improvements to Clang's time-trace
----------------------------------
Improvements to Coverage Mapping
--------------------------------
Bug Fixes in This Version
-------------------------
- Clang now outputs correct values when #embed data contains bytes with negative
signed char values (#GH102798).
Bug Fixes to Compiler Builtins
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
- The behvaiour of ``__add_pointer`` and ``__remove_pointer`` for Objective-C++'s ``id`` and interfaces has been fixed.
Bug Fixes to Attribute Support
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
- Fixed crash when a parameter to the ``clang::annotate`` attribute evaluates to ``void``. See #GH119125
Bug Fixes to C++ Support
^^^^^^^^^^^^^^^^^^^^^^^^
- Clang is now better at keeping track of friend function template instance contexts. (#GH55509)
- The initialization kind of elements of structured bindings
direct-list-initialized from an array is corrected to direct-initialization.
Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
- Fixed type checking when a statement expression ends in an l-value of atomic type. (#GH106576)
Miscellaneous Bug Fixes
^^^^^^^^^^^^^^^^^^^^^^^
- HTML tags in comments that span multiple lines are now parsed correctly by Clang's comment parser. (#GH120843)
Miscellaneous Clang Crashes Fixed
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
OpenACC Specific Changes
------------------------
Target Specific Changes
-----------------------
AMDGPU Support
^^^^^^^^^^^^^^
NVPTX Support
^^^^^^^^^^^^^^
Hexagon Support
^^^^^^^^^^^^^^^
- The default compilation target has been changed from V60 to V68.
X86 Support
^^^^^^^^^^^
- Disable ``-m[no-]avx10.1`` and switch ``-m[no-]avx10.2`` to alias of 512 bit
options.
- Change ``-mno-avx10.1-512`` to alias of ``-mno-avx10.1-256`` to disable both
256 and 512 bit instructions.
Arm and AArch64 Support
^^^^^^^^^^^^^^^^^^^^^^^
Android Support
^^^^^^^^^^^^^^^
Windows Support
^^^^^^^^^^^^^^^
LoongArch Support
^^^^^^^^^^^^^^^^^
RISC-V Support
^^^^^^^^^^^^^^
- Add support for `-mtune=generic-ooo` (a generic out-of-order model).
CUDA/HIP Language Changes
^^^^^^^^^^^^^^^^^^^^^^^^^
CUDA Support
^^^^^^^^^^^^
AIX Support
^^^^^^^^^^^
NetBSD Support
^^^^^^^^^^^^^^
WebAssembly Support
^^^^^^^^^^^^^^^^^^^
AVR Support
^^^^^^^^^^^
DWARF Support in Clang
----------------------
Floating Point Support in Clang
-------------------------------
Fixed Point Support in Clang
----------------------------
AST Matchers
------------
clang-format
------------
- Adds ``BreakBeforeTemplateCloser`` option.
- Adds ``BinPackLongBracedList`` option to override bin packing options in
long (20 item or more) braced list initializer lists.
libclang
--------
Code Completion
---------------
Static Analyzer
---------------
- Clang currently support extending lifetime of object bound to
reference members of aggregates in CFG and ExprEngine, that are
created from default member initializer.
New features
^^^^^^^^^^^^
A new flag - `-static-libclosure` was introduced to support statically linking
the runtime for the Blocks extension on Windows. This flag currently only
changes the code generation, and even then, only on Windows. This does not
impact the linker behaviour like the other `-static-*` flags.
Crash and bug fixes
^^^^^^^^^^^^^^^^^^^
Improvements
^^^^^^^^^^^^
Moved checkers
^^^^^^^^^^^^^^
- After lots of improvements, the checker ``alpha.security.ArrayBoundV2`` is
renamed to ``security.ArrayBound``. As this checker is stable now, the old
checker ``alpha.security.ArrayBound`` (which was searching for the same kind
of bugs with an different, simpler and less accurate algorithm) is removed.
.. _release-notes-sanitizers:
Sanitizers
----------
Python Binding Changes
----------------------
OpenMP Support
--------------
- Added support 'no_openmp_constructs' assumption clause.
- Added support for 'omp stripe' directive.
Improvements
^^^^^^^^^^^^
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 Git 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 on the `Discourse forums (Clang Frontend category)
<https://discourse.llvm.org/c/clang/6>`_.
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