===========================================
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
============================
These changes are ones which we think may surprise users when upgrading to
Clang |release| because of the opportunity they pose for disruption to existing
code bases.

- Setting the deprecated CMake variable ``GCC_INSTALL_PREFIX`` (which sets the
  default ``--gcc-toolchain=``) now leads to a fatal error.

C/C++ Language Potentially Breaking Changes
-------------------------------------------

C++ Specific Potentially Breaking Changes
-----------------------------------------
- Clang now diagnoses function/variable templates that shadow their own template parameters, e.g. ``template<class T> void T();``.
  This error can be disabled via `-Wno-strict-primary-template-shadow` for compatibility with previous versions of clang.

- The behavior controlled by the `-frelaxed-template-template-args` flag is now
  on by default, and the flag is deprecated. Until the flag is finally removed,
  it's negative spelling can be used to obtain compatibility with previous
  versions of clang.

- Clang now rejects pointer to member from parenthesized expression in unevaluated context such as ``decltype(&(foo::bar))``. (#GH40906).

ABI Changes in This Version
---------------------------
- Fixed Microsoft name mangling of implicitly defined variables used for thread
  safe static initialization of static local variables. This change resolves
  incompatibilities with code compiled by MSVC but might introduce
  incompatibilities with code compiled by earlier versions of Clang when an
  inline member function that contains a static local variable with a dynamic
  initializer is declared with ``__declspec(dllimport)``. (#GH83616).

- Fixed Microsoft name mangling of lifetime extended temporary objects. This
  change corrects missing back reference registrations that could result in
  incorrect back reference indexes and suprising demangled name results. Since
  MSVC uses a different mangling for these objects, compatibility is not affected.
  (#GH85423).

- Fixed Microsoft calling convention for returning certain classes with a
  templated constructor. If a class has a templated constructor, it should
  be returned indirectly even if it meets all the other requirements for
  returning a class in a register. This affects some uses of std::pair.
  (#GH86384).

AST Dumping Potentially Breaking Changes
----------------------------------------

Clang Frontend Potentially Breaking Changes
-------------------------------------------
- Removed support for constructing on-stack ``TemplateArgumentList``\ s; interfaces should instead
  use ``ArrayRef<TemplateArgument>`` to pass template arguments. Transitioning internal uses to
  ``ArrayRef<TemplateArgument>`` reduces AST memory usage by 0.4% when compiling clang, and is
  expected to show similar improvements on other workloads.

- The ``-Wgnu-binary-literal`` diagnostic group no longer controls any
  diagnostics. Binary literals are no longer a GNU extension, they're now a C23
  extension which is controlled via ``-pedantic`` or ``-Wc23-extensions``. Use
  of ``-Wno-gnu-binary-literal`` will no longer silence this pedantic warning,
  which may break existing uses with ``-Werror``.

- The normalization of 3 element target triples where ``-none-`` is the middle
  element has changed. For example, ``armv7m-none-eabi`` previously normalized
  to ``armv7m-none-unknown-eabi``, with ``none`` for the vendor and ``unknown``
  for the operating system. It now normalizes to ``armv7m-unknown-none-eabi``,
  which has ``unknown`` vendor and ``none`` operating system.

  The affected triples are primarily for bare metal Arm where it is intended
  that ``none`` means that there is no operating system. As opposed to an unknown
  type of operating system.

  This change my cause clang to not find libraries, or libraries to be built at
  different file system locations. This can be fixed by changing your builds to
  use the new normalized triple. However, we recommend instead getting the
  normalized triple from clang itself, as this will make your builds more
  robust in case of future changes::

    $ clang --target=<your target triple> -print-target-triple
    <the normalized target triple>

What's New in Clang |release|?
==============================
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.

C++ Language Changes
--------------------
- C++17 support is now completed, with the enablement of the
  relaxed temlate template argument matching rules introduced in P0522,
  which was retroactively applied as a defect report.
  While the implementation already existed since Clang 4, it was turned off by
  default, and was controlled with the `-frelaxed-template-template-args` flag.
  In this release, we implement provisional wording for a core defect on
  P0522 (CWG2398), which avoids the most serious compatibility issues caused
  by it, allowing us to enable it by default in this release.
  The flag is now deprecated, and will be removed in the next release, but can
  still be used to turn it off and regain compatibility with previous versions
  (#GH36505).
- Implemented ``_BitInt`` literal suffixes ``__wb`` or ``__WB`` as a Clang extension with ``unsigned`` modifiers also allowed. (#GH85223).

C++17 Feature Support
^^^^^^^^^^^^^^^^^^^^^
- Clang now exposes ``__GCC_DESTRUCTIVE_SIZE`` and ``__GCC_CONSTRUCTIVE_SIZE``
  predefined macros to support standard library implementations of
  ``std::hardware_destructive_interference_size`` and
  ``std::hardware_constructive_interference_size``, respectively. These macros
  are predefined in all C and C++ language modes. The values the macros
  expand to are not stable between releases of Clang and do not need to match
  the values produced by GCC, so these macros should not be used from header
  files because they may not be stable across multiple TUs (the values may vary
  based on compiler version as well as CPU tuning). #GH60174

C++20 Feature Support
^^^^^^^^^^^^^^^^^^^^^

- Clang won't perform ODR checks for decls in the global module fragment any
  more to ease the implementation and improve the user's using experience.
  This follows the MSVC's behavior. Users interested in testing the more strict
  behavior can use the flag '-Xclang -fno-skip-odr-check-in-gmf'.
  (#GH79240).

- Implemented the `__is_layout_compatible` and `__is_pointer_interconvertible_base_of`
  intrinsics to support
  `P0466R5: Layout-compatibility and Pointer-interconvertibility Traits <https://wg21.link/P0466R5>`_.

- Clang now implements [module.import]p7 fully. Clang now will import module
  units transitively for the module units coming from the same module of the
  current module units. Fixes #GH84002

- Initial support for class template argument deduction (CTAD) for type alias
  templates (`P1814R0 <https://wg21.link/p1814r0>`_).
  (#GH54051).

- We have sufficient confidence and experience with the concepts implementation
  to update the ``__cpp_concepts`` macro to `202002L`. This enables
  ``<expected>`` from libstdc++ to work correctly with Clang.

C++23 Feature Support
^^^^^^^^^^^^^^^^^^^^^

- Implemented `P2718R0: Lifetime extension in range-based for loops <https://wg21.link/P2718R0>`_. Also
  materialize temporary object which is a prvalue in discarded-value expression.
- Implemented `P1774R8: Portable assumptions <https://wg21.link/P1774R8>`_.

- Implemented `P2448R2: Relaxing some constexpr restrictions <https://wg21.link/P2448R2>`_.

C++2c Feature Support
^^^^^^^^^^^^^^^^^^^^^

- Implemented `P2662R3 Pack Indexing <https://wg21.link/P2662R3>`_.

- Implemented `P2573R2: = delete("should have a reason"); <https://wg21.link/P2573R2>`_

- Implemented `P0609R3: Attributes for Structured Bindings <https://wg21.link/P0609R3>`_

- Implemented `P2748R5 Disallow Binding a Returned Glvalue to a Temporary <https://wg21.link/P2748R5>`_.

- Implemented `P2809R3: Trivial infinite loops are not Undefined Behavior <https://wg21.link/P2809R3>`_.


Resolutions to C++ Defect Reports
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
- Substitute template parameter pack, when it is not explicitly specified
  in the template parameters, but is deduced from a previous argument. (#GH78449)

- Type qualifications are now ignored when evaluating layout compatibility
  of two types.
  (`CWG1719: Layout compatibility and cv-qualification revisited <https://cplusplus.github.io/CWG/issues/1719.html>`_).

- Alignment of members is now respected when evaluating layout compatibility
  of structs.
  (`CWG2583: Common initial sequence should consider over-alignment <https://cplusplus.github.io/CWG/issues/2583.html>`_).

- ``[[no_unique_address]]`` is now respected when evaluating layout
  compatibility of two types.
  (`CWG2759: [[no_unique_address] and common initial sequence  <https://cplusplus.github.io/CWG/issues/2759.html>`_).

- Clang now diagnoses declarative nested-name-specifiers with pack-index-specifiers.
  (`CWG2858: Declarative nested-name-specifiers and pack-index-specifiers <https://cplusplus.github.io/CWG/issues/2858.html>`_).

- P0522 implementation is enabled by default in all language versions, and
  provisional wording for CWG2398 is implemented.

C Language Changes
------------------

C23 Feature Support
^^^^^^^^^^^^^^^^^^^
- No longer diagnose use of binary literals as an extension in C23 mode. Fixes
  #GH72017.

- Corrected parsing behavior for the ``alignas`` specifier/qualifier in C23. We
  previously handled it as an attribute as in C++, but there are parsing
  differences. The behavioral differences are:

  .. code-block:: c

     struct alignas(8) /* was accepted, now rejected */ S {
       char alignas(8) /* was rejected, now accepted */ C;
     };
     int i alignas(8) /* was accepted, now rejected */ ;

  Fixes (#GH81472).

- Clang now generates predefined macros of the form ``__TYPE_FMTB__`` and
  ``__TYPE_FMTb__`` (e.g., ``__UINT_FAST64_FMTB__``) in C23 mode for use with
  macros typically exposed from ``<inttypes.h>``, such as ``PRIb8``. (#GH81896)

- Clang now supports `N3018 The constexpr specifier for object definitions`
  <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3018.htm>`_.

- Properly promote bit-fields of bit-precise integer types to the field's type
  rather than to ``int``. #GH87641

Non-comprehensive list of changes in this release
-------------------------------------------------

- Added ``__builtin_readsteadycounter`` for reading fixed frequency hardware
  counters.

- ``__builtin_addc``, ``__builtin_subc``, and the other sizes of those
  builtins are now constexpr and may be used in constant expressions.

- Added ``__builtin_popcountg`` as a type-generic alternative to
  ``__builtin_popcount{,l,ll}`` with support for any unsigned integer type. Like
  the previous builtins, this new builtin is constexpr and may be used in
  constant expressions.

- Lambda expressions are now accepted in C++03 mode as an extension.

- Added ``__builtin_clzg`` and ``__builtin_ctzg`` as type-generic alternatives
  to ``__builtin_clz{,s,l,ll}`` and ``__builtin_ctz{,s,l,ll}`` respectively,
  with support for any unsigned integer type. Like the previous builtins, these
  new builtins are constexpr and may be used in constant expressions.

- ``__typeof_unqual__`` is available in all C modes as an extension, which behaves
  like ``typeof_unqual`` from C23, similar to ``__typeof__`` and ``typeof``.

- ``__builtin_reduce_{add|mul|xor|or|and|min|max}`` builtins now support scalable vectors.

* Shared libraries linked with either the ``-ffast-math``, ``-Ofast``, or
  ``-funsafe-math-optimizations`` flags will no longer enable flush-to-zero
  floating-point mode by default. This decision can be overridden with use of
  ``-mdaz-ftz``. This behavior now matches GCC's behavior.
  (`#57589 <https://github.com/llvm/llvm-project/issues/57589>`_)

* ``-fdenormal-fp-math=preserve-sign`` is no longer implied by ``-ffast-math``
  on x86 systems.

- Builtins ``__builtin_shufflevector()`` and ``__builtin_convertvector()`` may
  now be used within constant expressions.

New Compiler Flags
------------------
- ``-fsanitize=implicit-bitfield-conversion`` checks implicit truncation and
  sign change.
- ``-fsanitize=implicit-integer-conversion`` a group that replaces the previous
  group ``-fsanitize=implicit-conversion``.

- ``-Wmissing-designated-field-initializers``, grouped under ``-Wmissing-field-initializers``.
  This diagnostic can be disabled to make ``-Wmissing-field-initializers`` behave
  like it did before Clang 18.x. Fixes #GH56628

- ``-fexperimental-modules-reduced-bmi`` enables the Reduced BMI for C++20 named modules.
  See the document of standard C++ modules for details.

- ``-fexperimental-late-parse-attributes`` enables an experimental feature to
  allow late parsing certain attributes in specific contexts where they would
  not normally be late parsed.

Deprecated Compiler Flags
-------------------------

Modified Compiler Flags
-----------------------
- Added a new diagnostic flag ``-Wreturn-mismatch`` which is grouped under
  ``-Wreturn-type``, and moved some of the diagnostics previously controlled by
  ``-Wreturn-type`` under this new flag. Fixes #GH72116.
- ``-fsanitize=implicit-conversion`` is now a group for both
  ``-fsanitize=implicit-integer-conversion`` and
  ``-fsanitize=implicit-bitfield-conversion``.

- Added ``-Wcast-function-type-mismatch`` under the ``-Wcast-function-type``
  warning group. Moved the diagnostic previously controlled by
  ``-Wcast-function-type`` to the new warning group and added
  ``-Wcast-function-type-mismatch`` to ``-Wextra``. #GH76872

  .. code-block:: c

     int x(long);
     typedef int (f2)(void*);
     typedef int (f3)();

     void func(void) {
       // Diagnoses under -Wcast-function-type, -Wcast-function-type-mismatch,
       // -Wcast-function-type-strict, -Wextra
       f2 *b = (f2 *)x;
       // Diagnoses under -Wcast-function-type, -Wcast-function-type-strict
       f3 *c = (f3 *)x;
     }

- Carved out ``-Wformat`` warning about scoped enums into a subwarning and
  make it controlled by ``-Wformat-pedantic``. Fixes #GH88595.

- Trivial infinite loops (i.e loops with a constant controlling expresion
  evaluating to ``true`` and an empty body such as ``while(1);``)
  are considered infinite, even when the ``-ffinite-loop`` flag is set.

Removed Compiler Flags
-------------------------

- The ``-freroll-loops`` flag has been removed. It had no effect since Clang 13.
- ``-m[no-]unaligned-access`` is removed for RISC-V and LoongArch.
  ``-m[no-]strict-align``, also supported by GCC, should be used instead. (#GH85350)

Attribute Changes in Clang
--------------------------
- Introduced a new function attribute ``__attribute__((amdgpu_max_num_work_groups(x, y, z)))`` or
  ``[[clang::amdgpu_max_num_work_groups(x, y, z)]]`` for the AMDGPU target. This attribute can be
  attached to HIP or OpenCL kernel function definitions to provide an optimization hint. The parameters
  ``x``, ``y``, and ``z`` specify the maximum number of workgroups for the respective dimensions,
  and each must be a positive integer when provided. The parameter ``x`` is required, while ``y`` and
  ``z`` are optional with default value of 1.

- The ``swiftasynccc`` attribute is now considered to be a Clang extension
  rather than a language standard feature. Please use
  ``__has_extension(swiftasynccc)`` to check the availability of this attribute
  for the target platform instead of ``__has_feature(swiftasynccc)``. Also,
  added a new extension query ``__has_extension(swiftcc)`` corresponding to the
  ``__attribute__((swiftcc))`` attribute.

- The ``_Nullable`` and ``_Nonnull`` family of type attributes can now apply
  to certain C++ class types, such as smart pointers:
  ``void useObject(std::unique_ptr<Object> _Nonnull obj);``.

  This works for standard library types including ``unique_ptr``, ``shared_ptr``,
  and ``function``. See
  `the attribute reference documentation <https://llvm.org/docs/AttributeReference.html#nullability-attributes>`_
  for the full list.

- The ``_Nullable`` attribute can be applied to C++ class declarations:
  ``template <class T> class _Nullable MySmartPointer {};``.

  This allows the ``_Nullable`` and ``_Nonnull`` family of type attributes to
  apply to this class.

- Clang now warns that the ``exclude_from_explicit_instantiation`` attribute
  is ignored when applied to a local class or a member thereof.

Improvements to Clang's diagnostics
-----------------------------------
- Clang now applies syntax highlighting to the code snippets it
  prints.

- Clang now diagnoses member template declarations with multiple declarators.

- Clang now diagnoses use of the ``template`` keyword after declarative nested
  name specifiers.

- The ``-Wshorten-64-to-32`` diagnostic is now grouped under ``-Wimplicit-int-conversion`` instead
   of ``-Wconversion``. Fixes #GH69444.

- Clang now uses thousand separators when printing large numbers in integer overflow diagnostics.
  Fixes #GH80939.

- Clang now diagnoses friend declarations with an ``enum`` elaborated-type-specifier in language modes after C++98.

- Added diagnostics for C11 keywords being incompatible with language standards
  before C11, under a new warning group: ``-Wpre-c11-compat``.

- Now diagnoses an enumeration constant whose value is larger than can be
  represented by ``unsigned long long``, which can happen with a large constant
  using the ``wb`` or ``uwb`` suffix. The maximal underlying type is currently
  ``unsigned long long``, but this behavior may change in the future when Clang
  implements
  `WG14 N3029 <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3029.htm>`_.
  (#GH69352).

- Clang now diagnoses extraneous template parameter lists as a language extension.

- Clang now diagnoses declarative nested name specifiers that name alias templates.

- Clang now diagnoses lambda function expressions being implicitly cast to boolean values, under ``-Wpointer-bool-conversion``.
  Fixes #GH82512.

- Clang now provides improved warnings for the ``cleanup`` attribute to detect misuse scenarios,
  such as attempting to call ``free`` on an unallocated object. Fixes #GH79443.

- Clang no longer warns when the ``bitand`` operator is used with boolean
  operands, distinguishing it from potential typographical errors or unintended
  bitwise operations. Fixes #GH77601.

- Clang now correctly diagnoses no arguments to a variadic macro parameter as a C23/C++20 extension.
  Fixes #GH84495.

- Clang no longer emits a ``-Wexit-time destructors`` warning on static variables explicitly
  annotated with the ``clang::always_destroy`` attribute.
  Fixes #GH68686, #GH86486

- ``-Wmicrosoft``, ``-Wgnu``, or ``-pedantic`` is now required to diagnose C99
  flexible array members in a union or alone in a struct. Fixes GH#84565.

- Clang now no longer diagnoses type definitions in ``offsetof`` in C23 mode.
  Fixes #GH83658.

- New ``-Wformat-signedness`` diagnostic that warn if the format string requires an
  unsigned argument and the argument is signed and vice versa.

- Clang now emits ``unused argument`` warning when the -fmodule-output flag is used
  with an input that is not of type c++-module.

- Clang emits a ``-Wreturn-stack-address`` warning if a function returns a pointer or
  reference to a struct literal. Fixes #GH8678

- Clang emits a ``-Wunused-but-set-variable`` warning on C++ variables whose declaration
  (with initializer) entirely consist the condition expression of a if/while/for construct
  but are not actually used in the body of the if/while/for construct. Fixes #GH41447

- Clang emits a diagnostic when a tentative array definition is assumed to have
  a single element, but that diagnostic was never given a diagnostic group.
  Added the ``-Wtentative-definition-array`` warning group to cover this.
  Fixes #GH87766

- Clang now uses the correct type-parameter-key (``class`` or ``typename``) when printing
  template template parameter declarations.

- Clang now diagnoses requires expressions with explicit object parameters.

- Clang now looks up members of the current instantiation in the template definition context
  if the current instantiation has no dependent base classes.

  .. code-block:: c++

     template<typename T>
     struct A {
       int f() {
         return this->x; // error: no member named 'x' in 'A<T>'
       }
     };

Improvements to Clang's time-trace
----------------------------------

Bug Fixes in This Version
-------------------------
- Clang's ``-Wundefined-func-template`` no longer warns on pure virtual
  functions. (#GH74016)

- Fixed missing warnings when comparing mismatched enumeration constants
  in C (#GH29217)

- Clang now accepts elaborated-type-specifiers that explicitly specialize
  a member class template for an implicit instantiation of a class template.

- Fixed missing warnings when doing bool-like conversions in C23 (#GH79435).
- Clang's ``-Wshadow`` no longer warns when an init-capture is named the same as
  a class field unless the lambda can capture this.
  Fixes (#GH71976)

- Clang now accepts qualified partial/explicit specializations of variable templates that
  are not nominable in the lookup context of the specialization.

- Clang now doesn't produce false-positive warning `-Wconstant-logical-operand`
  for logical operators in C23.
  Fixes (#GH64356).

- ``__is_trivially_relocatable`` no longer returns ``false`` for volatile-qualified types.
  Fixes (#GH77091).

- Clang no longer produces a false-positive `-Wunused-variable` warning
  for variables created through copy initialization having side-effects in C++17 and later.
  Fixes (#GH64356) (#GH79518).

- Fix value of predefined macro ``__FUNCTION__`` in MSVC compatibility mode.
  Fixes (#GH66114).

- Clang now emits errors for explicit specializations/instatiations of lambda call
  operator.
  Fixes (#GH83267).

- Fix crash on ill-formed partial specialization with CRTP.
  Fixes (#GH89374).

- Clang now correctly generates overloads for bit-precise integer types for
  builtin operators in C++. Fixes #GH82998.

- Fix crash when destructor definition is preceded with an equals sign.
  Fixes (#GH89544).

- When performing mixed arithmetic between ``_Complex`` floating-point types and integers,
  Clang now correctly promotes the integer to its corresponding real floating-point
  type only rather than to the complex type (e.g. ``_Complex float / int`` is now evaluated
  as ``_Complex float / float`` rather than ``_Complex float / _Complex float``), as mandated
  by the C standard. This significantly improves codegen of `*` and `/` especially.
  Fixes #GH31205.

- Fixes an assertion failure on invalid code when trying to define member
  functions in lambdas.

- Fixed a regression in CTAD that a friend declaration that befriends itself may cause
  incorrect constraint substitution. (#GH86769).

- Fixed an assertion failure on invalid InitListExpr in C89 mode (#GH88008).

- Fixed missing destructor calls when we branch from middle of an expression.
  This could happen through a branch in stmt-expr or in an expression containing a coroutine
  suspension. Fixes (#GH63818) (#GH88478).

- Clang will no longer diagnose an erroneous non-dependent ``switch`` condition
  during instantiation, and instead will only diagnose it once, during checking
  of the function template.

- Clang now allows the value of unroll count to be zero in ``#pragma GCC unroll`` and ``#pragma unroll``.
  The values of 0 and 1 block any unrolling of the loop. This keeps the same behavior with GCC.
  Fixes (`#88624 <https://github.com/llvm/llvm-project/issues/88624>`_).

- Clang will no longer emit a duplicate -Wunused-value warning for an expression
  `(A, B)` which evaluates to glvalue `B` that can be converted to non ODR-use. (#GH45783)

Bug Fixes to Compiler Builtins
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Bug Fixes to Attribute Support
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Bug Fixes to C++ Support
^^^^^^^^^^^^^^^^^^^^^^^^

- Fix crash when calling the constructor of an invalid class.
  (#GH10518) (#GH67914) (#GH78388)
- Fix crash when using lifetimebound attribute in function with trailing return.
  (#GH73619)
- Addressed an issue where constraints involving injected class types are perceived
  distinct from its specialization types. (#GH56482)
- Fixed a bug where variables referenced by requires-clauses inside
  nested generic lambdas were not properly injected into the constraint scope. (#GH73418)
- Fixed a crash where substituting into a requires-expression that refers to function
  parameters during the equivalence determination of two constraint expressions.
  (#GH74447)
- Fixed deducing auto& from const int in template parameters of partial
  specializations. (#GH77189)
- Fix for crash when using a erroneous type in a return statement.
  (#GH63244) (#GH79745)
- Fixed an out-of-bounds error caused by building a recovery expression for ill-formed
  function calls while substituting into constraints. (#GH58548)
- Fix incorrect code generation caused by the object argument
  of ``static operator()`` and ``static operator[]`` calls not being evaluated. (#GH67976)
- Fix crash and diagnostic with const qualified member operator new.
  Fixes (#GH79748)
- Fixed a crash where substituting into a requires-expression that involves parameter packs
  during the equivalence determination of two constraint expressions. (#GH72557)
- Fix a crash when specializing an out-of-line member function with a default
  parameter where we did an incorrect specialization of the initialization of
  the default parameter. (#GH68490)
- Fix a crash when trying to call a varargs function that also has an explicit object parameter.
  Fixes (#GH80971)
- Reject explicit object parameters on `new` and `delete` operators. (#GH82249)
- Fix a crash when trying to call a varargs function that also has an explicit object parameter. (#GH80971)
- Fixed a bug where abbreviated function templates would append their invented template parameters to
  an empty template parameter lists.
- Fix parsing of abominable function types inside type traits. Fixes #GH77585
- Clang now classifies aggregate initialization in C++17 and newer as constant
  or non-constant more accurately. Previously, only a subset of the initializer
  elements were considered, misclassifying some initializers as constant. Partially fixes
  #GH80510.
- Clang now ignores top-level cv-qualifiers on function parameters in template partial orderings. (#GH75404)
- No longer reject valid use of the ``_Alignas`` specifier when declaring a
  local variable, which is supported as a C11 extension in C++. Previously, it
  was only accepted at namespace scope but not at local function scope.
- Clang no longer tries to call consteval constructors at runtime when they appear in a member initializer. (#GH82154)
- Fix crash when using an immediate-escalated function at global scope. (#GH82258)
- Correctly immediate-escalate lambda conversion functions. (#GH82258)
- Fixed an issue where template parameters of a nested abbreviated generic lambda within
  a requires-clause lie at the same depth as those of the surrounding lambda. This,
  in turn, results in the wrong template argument substitution during constraint checking.
  (#GH78524)
- Clang no longer instantiates the exception specification of discarded candidate function
  templates when determining the primary template of an explicit specialization.
- Fixed a crash in Microsoft compatibility mode where unqualified dependent base class
  lookup searches the bases of an incomplete class.
- Fix a crash when an unresolved overload set is encountered on the RHS of a ``.*`` operator.
  (#GH53815)
- In ``__restrict``-qualified member functions, attach ``__restrict`` to the pointer type of
  ``this`` rather than the pointee type.
  Fixes (#GH82941), (#GH42411) and (#GH18121).
- Clang now properly reports supported C++11 attributes when using
  ``__has_cpp_attribute`` and parses attributes with arguments in C++03 (#GH82995)
- Clang now properly diagnoses missing 'default' template arguments on a variety
  of templates. Previously we were diagnosing on any non-function template
  instead of only on class, alias, and variable templates, as last updated by
  CWG2032. Fixes (#GH83461)
- Fixed an issue where an attribute on a declarator would cause the attribute to
  be destructed prematurely. This fixes a pair of Chromium that were brought to
  our attention by an attempt to fix in (#GH77703). Fixes (#GH83385).
- Fix evaluation of some immediate calls in default arguments.
  Fixes (#GH80630)
- Fixed an issue where the ``RequiresExprBody`` was involved in the lambda dependency
  calculation. (#GH56556), (#GH82849).
- Fix a bug where overload resolution falsely reported an ambiguity when it was comparing
  a member-function against a non member function or a member-function with an
  explicit object parameter against a member function with no explicit object parameter
  when one of the function had more specialized templates. Fixes #GH82509 and #GH74494
- Clang now supports direct lambda calls inside of a type alias template declarations.
  This addresses (#GH70601), (#GH76674), (#GH79555), (#GH81145) and (#GH82104).
- Allow access to a public template alias declaration that refers to friend's
  private nested type. (#GH25708).
- Fixed a crash in constant evaluation when trying to access a
  captured ``this`` pointer in a lambda with an explicit object parameter.
  Fixes (#GH80997)
- Fix an issue where missing set friend declaration in template class instantiation.
  Fixes (#GH84368).
- Fixed a crash while checking constraints of a trailing requires-expression of a lambda, that the
  expression references to an entity declared outside of the lambda. (#GH64808)
- Clang's __builtin_bit_cast will now produce a constant value for records with empty bases. See:
  (#GH82383)
- Fix a crash when instantiating a lambda that captures ``this`` outside of its context. Fixes (#GH85343).
- Fix an issue where a namespace alias could be defined using a qualified name (all name components
  following the first `::` were ignored).
- Fix an out-of-bounds crash when checking the validity of template partial specializations. (part of #GH86757).
- Fix an issue caused by not handling invalid cases when substituting into the parameter mapping of a constraint. Fixes (#GH86757).
- Fixed a bug that prevented member function templates of class templates declared with a deduced return type
  from being explicitly specialized for a given implicit instantiation of the class template.
- Fixed a crash when ``this`` is used in a dependent class scope function template specialization
  that instantiates to a static member function.

- Fix crash when inheriting from a cv-qualified type. Fixes #GH35603
- Fix a crash when the using enum declaration uses an anonymous enumeration. Fixes (#GH86790).
- Handled an edge case in ``getFullyPackExpandedSize`` so that we now avoid a false-positive diagnostic. (#GH84220)
- Clang now correctly tracks type dependence of by-value captures in lambdas with an explicit
  object parameter.
  Fixes (#GH70604), (#GH79754), (#GH84163), (#GH84425), (#GH86054), (#GH86398), and (#GH86399).
- Fix a crash when deducing ``auto`` from an invalid dereference (#GH88329).
- Fix a crash in requires expression with templated base class member function. Fixes (#GH84020).
- Fix a crash caused by defined struct in a type alias template when the structure
  has fields with dependent type. Fixes (#GH75221).
- Fix the Itanium mangling of lambdas defined in a member of a local class (#GH88906)
- Fixed a crash when trying to evaluate a user-defined ``static_assert`` message whose ``size()``
  function returns a large or negative value. Fixes (#GH89407).
- Fixed a use-after-free bug in parsing of type constraints with default arguments that involve lambdas. (#GH67235)
- Fixed bug in which the body of a consteval lambda within a template was not parsed as within an
  immediate function context.
- Fix CTAD for ``std::initializer_list``. This allows ``std::initializer_list{1, 2, 3}`` to be deduced as
  ``std::initializer_list<int>`` as intended.
- Fix a bug on template partial specialization whose template parameter is `decltype(auto)`.
- Fix a bug on template partial specialization with issue on deduction of nontype template parameter
  whose type is `decltype(auto)`. Fixes (#GH68885).
- Clang now correctly treats the noexcept-specifier of a friend function to be a complete-class context.
- Fix an assertion failure when parsing an invalid members of an anonymous class. (#GH85447)
- Fixed a misuse of ``UnresolvedLookupExpr`` for ill-formed templated expressions. Fixes (#GH48673), (#GH63243)
  and (#GH88832).

Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
- Clang now properly preserves ``FoundDecls`` within a ``ConceptReference``. (#GH82628)
- The presence of the ``typename`` keyword is now stored in ``TemplateTemplateParmDecl``.

Miscellaneous Bug Fixes
^^^^^^^^^^^^^^^^^^^^^^^

- Fixed an infinite recursion in ASTImporter, on return type declared inside
  body of C++11 lambda without trailing return (#GH68775).

Miscellaneous Clang Crashes Fixed
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

- Do not attempt to dump the layout of dependent types or invalid declarations
  when ``-fdump-record-layouts-complete`` is passed. Fixes #GH83684.

OpenACC Specific Changes
------------------------

Target Specific Changes
-----------------------

AMDGPU Support
^^^^^^^^^^^^^^

X86 Support
^^^^^^^^^^^

Arm and AArch64 Support
^^^^^^^^^^^^^^^^^^^^^^^

- ARMv7+ targets now default to allowing unaligned access, except Armv6-M, and
  Armv8-M without the Main Extension. Baremetal targets should check that the
  new default will work with their system configurations, since it requires
  that SCTLR.A is 0, SCTLR.U is 1, and that the memory in question is
  configured as "normal" memory. This brings Clang in-line with the default
  settings for GCC and Arm Compiler. Aside from making Clang align with other
  compilers, changing the default brings major performance and code size
  improvements for most targets. We have not changed the default behavior for
  ARMv6, but may revisit that decision in the future. Users can restore the old
  behavior with -m[no-]unaligned-access.
- An alias identifier (rdma) has been added for targeting the AArch64
  Architecture Extension which uses Rounding Doubling Multiply Accumulate
  instructions (rdm). The identifier is available on the command line as
  a feature modifier for -march and -mcpu as well as via target attributes
  like ``target_version`` or ``target_clones``.
- Support has been added for the following processors (-mcpu identifiers in parenthesis):
    * Arm Cortex-A78AE (cortex-a78ae).
    * Arm Cortex-A520AE (cortex-a520ae).
    * Arm Cortex-A720AE (cortex-a720ae).
    * Arm Cortex-R82AE (cortex-r82ae).
    * Arm Neoverse-N3 (neoverse-n3).
    * Arm Neoverse-V3 (neoverse-v3).
    * Arm Neoverse-V3AE (neoverse-v3ae).

Android Support
^^^^^^^^^^^^^^^

Windows Support
^^^^^^^^^^^^^^^

- Clang-cl now supports function targets with intrinsic headers. This allows
  for runtime feature detection of intrinsics. Previously under clang-cl
  ``immintrin.h`` and similar intrinsic headers would only include the intrinsics
  if building with that feature enabled at compile time, e.g. ``avxintrin.h``
  would only be included if AVX was enabled at compile time. This was done to work
  around include times from MSVC STL including ``intrin.h`` under clang-cl.
  Clang-cl now provides ``intrin0.h`` for MSVC STL and therefore all intrinsic
  features without requiring enablement at compile time. Fixes #GH53520

- Improved compile times with MSVC STL. MSVC provides ``intrin0.h`` which is a
  header that only includes intrinsics that are used by MSVC STL to avoid the
  use of ``intrin.h``. MSVC STL when compiled under clang uses ``intrin.h``
  instead. Clang-cl now provides ``intrin0.h`` for the same compiler throughput
  purposes as MSVC. Clang-cl also provides ``yvals_core.h`` to redefine
  ``_STL_INTRIN_HEADER`` to expand to ``intrin0.h`` instead of ``intrin.h``.
  This also means that if all intrinsic features are enabled at compile time
  including STL headers will no longer slow down compile times since ``intrin.h``
  is not included from MSVC STL.

LoongArch Support
^^^^^^^^^^^^^^^^^

RISC-V Support
^^^^^^^^^^^^^^

- ``__attribute__((rvv_vector_bits(N)))`` is now supported for RVV vbool*_t types.
- Profile names in ``-march`` option are now supported.

CUDA/HIP Language Changes
^^^^^^^^^^^^^^^^^^^^^^^^^

- PTX is no longer included by default when compiling for CUDA. Using
  ``--cuda-include-ptx=all`` will return the old behavior.

CUDA Support
^^^^^^^^^^^^

AIX Support
^^^^^^^^^^^

- Introduced the ``-maix-small-local-dynamic-tls`` option to produce a faster
  access sequence for local-dynamic TLS variables where the offset from the TLS
  base is encoded as an immediate operand.
  This access sequence is not used for TLS variables larger than 32KB, and is
  currently only supported on 64-bit mode.

WebAssembly Support
^^^^^^^^^^^^^^^^^^^

The -mcpu=generic configuration now enables multivalue feature, which is
standardized and available in all major engines. Enabling multivalue here only
enables the language feature but does not turn on the multivalue ABI (this
enables non-ABI uses of multivalue, like exnref).

AVR Support
^^^^^^^^^^^

DWARF Support in Clang
----------------------

Floating Point Support in Clang
-------------------------------

Fixed Point Support in Clang
----------------------------

- Support fixed point precision macros according to ``7.18a.3`` of
  `ISO/IEC TR 18037:2008 <https://standards.iso.org/ittf/PubliclyAvailableStandards/c051126_ISO_IEC_TR_18037_2008.zip>`_.

AST Matchers
------------

- Fixes a long-standing performance issue in parent map generation for
  ancestry-based matchers such as ``hasParent`` and ``hasAncestor``, making
  them significantly faster.
- ``isInStdNamespace`` now supports Decl declared with ``extern "C++"``.
- Add ``isExplicitObjectMemberFunction``.
- Fixed ``forEachArgumentWithParam`` and ``forEachArgumentWithParamType`` to
  not skip the explicit object parameter for operator calls.
- Fixed captureVars assertion failure if not capturesVariables. (#GH76425)

clang-format
------------

- ``AlwaysBreakTemplateDeclarations`` is deprecated and renamed to
  ``BreakTemplateDeclarations``.
- ``AlwaysBreakAfterReturnType`` is deprecated and renamed to
  ``BreakAfterReturnType``.

libclang
--------

- ``clang_getSpellingLocation`` now correctly resolves macro expansions; that
  is, it returns the spelling location instead of the expansion location.

Static Analyzer
---------------

- Fixed crashing on loops if the loop variable was declared in switch blocks
  but not under any case blocks if ``unroll-loops=true`` analyzer config is
  set. (#GH68819)
- Support C++23 static operator calls. (#GH84972)
- Fixed a crash in ``security.cert.env.InvalidPtr`` checker when accidentally
  matched user-defined ``strerror`` and similar library functions. (GH#88181)
- Fixed a crash when storing through an address that refers to the address of
  a label. (GH#89185)

New features
^^^^^^^^^^^^

Crash and bug fixes
^^^^^^^^^^^^^^^^^^^

Improvements
^^^^^^^^^^^^

- Support importing C++20 modules in clang-repl.

- Added support for ``TypeLoc::dump()`` for easier debugging, and improved
  textual and JSON dumping for various ``TypeLoc``-related nodes.

Moved checkers
^^^^^^^^^^^^^^

.. _release-notes-sanitizers:

Sanitizers
----------

- ``-fsanitize=signed-integer-overflow`` now instruments signed arithmetic even
  when ``-fwrapv`` is enabled. Previously, only division checks were enabled.

  Users with ``-fwrapv`` as well as a sanitizer group like
  ``-fsanitize=undefined`` or ``-fsanitize=integer`` enabled may want to
  manually disable potentially noisy signed integer overflow checks with
  ``-fno-sanitize=signed-integer-overflow``

- ``-fsanitize=cfi -fsanitize-cfi-cross-dso`` (cross-DSO CFI instrumentation)
  now generates the ``__cfi_check`` function with proper target-specific
  attributes, for example allowing unwind table generation.

Python Binding Changes
----------------------

- Exposed `CXRewriter` API as `class Rewriter`.
- Add some missing kinds from Index.h (CursorKind: 149-156, 272-320, 420-437.
  TemplateArgumentKind: 5-9. TypeKind: 161-175 and 178).

OpenMP Support
--------------

- Added support for the `[[omp::assume]]` attribute.

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>`_.