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llvm-project/clang/docs/ReleaseNotes.rst
cor3ntin dd32c3d36f
[Clang] Only check exprs that might be immediate escalating in evaluated contexts (#93187) 
As per https://eel.is/c++draft/expr.const#17

Fixes #91308

---------

Co-authored-by: Mariya Podchishchaeva <mariya.podchishchaeva@intel.com>
2024-05-23 17:53:07 +02:00

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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
============================
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. The deprecation warning for the negative spelling can be
disabled with `-Wno-deprecated-no-relaxed-template-template-args`.
- Clang now rejects pointer to member from parenthesized expression in unevaluated context such as ``decltype(&(foo::bar))``. (#GH40906).
- Clang now performs semantic analysis for unary operators with dependent operands
that are known to be of non-class non-enumeration type prior to instantiation.
This change uncovered a bug in libstdc++ 14.1.0 which may cause compile failures
on systems using that version of libstdc++ and Clang 19, with an error that looks
something like this:
.. code-block:: text
<source>:4:5: error: expression is not assignable
4 | ++this;
| ^ ~~~~
To fix this, update libstdc++ to version 14.1.1 or greater.
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).
- Fixed Microsoft calling convention when returning classes that have a deleted
copy assignment operator. Such a class should be returned indirectly.
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>
- The ``hasTypeLoc`` AST matcher will no longer match a ``classTemplateSpecializationDecl``;
existing uses should switch to ``templateArgumentLoc`` or ``hasAnyTemplateArgumentLoc`` instead.
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++14 Feature Support
^^^^^^^^^^^^^^^^^^^^^
- Sized deallocation is enabled by default in C++14 onwards. The user may specify
``-fno-sized-deallocation`` to disable it if there are some regressions.
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>`_.
- Added a ``__reference_converts_from_temporary`` builtin, completing the necessary compiler support for
`P2255R2: Type trait to determine if a reference binds to a temporary <https://wg21.link/P2255R2>`_.
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>`_).
- Clang now allows attributes on concepts.
(`CWG2428: Deprecating a concept <https://cplusplus.github.io/CWG/issues/2428.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.
- ``-fseparate-named-sections`` uses separate unique sections for global
symbols in named special sections (i.e. symbols annotated with
``__attribute__((section(...)))``. This enables linker GC to collect unused
symbols without having to use a per-symbol section.
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.
- The ``clspv_libclc_builtin`` attribute has been added to allow clspv
(`OpenCL-C to Vulkan SPIR-V compiler <https://github.com/google/clspv>`_) to identify functions coming from libclc
(`OpenCL-C builtin library <https://libclc.llvm.org>`_).
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>'
}
};
- Clang emits a ``-Wparentheses`` warning for expressions with consecutive comparisons like ``x < y < z``.
Fixes #GH20456.
Improvements to Clang's time-trace
----------------------------------
- Clang now specifies that using ``auto`` in a lambda parameter is a C++14 extension when
appropriate. (`#46059: <https://github.com/llvm/llvm-project/issues/46059>`_).
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)
- Clang now correctly disallows VLA type compound literals, e.g. ``(int[size]){}``,
as the C standard mandates. (#GH89835)
- ``__is_array`` and ``__is_bounded_array`` no longer return ``true`` for
zero-sized arrays. Fixes (#GH54705).
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).
- Clang now defers all substitution into the exception specification of a function template specialization
until the noexcept-specifier is instantiated.
- Fix a crash when an implicitly declared ``operator==`` function with a trailing requires-clause has its
constraints compared to that of another declaration.
- Fix a bug where explicit specializations of member functions/function templates would have substitution
performed incorrectly when checking constraints. Fixes (#GH90349).
- Clang now allows constrained member functions to be explicitly specialized for an implicit instantiation
of a class template.
- Fix a C++23 bug in implementation of P2564R3 which evaluates immediate invocations in place
within initializers for variables that are usable in constant expressions or are constant
initialized, rather than evaluating them as a part of the larger manifestly constant evaluated
expression.
- Fix a bug in access control checking due to dealyed checking of friend declaration. Fixes (#GH12361).
- Correctly treat the compound statement of an ``if consteval`` as an immediate context. Fixes (#GH91509).
- When partial ordering alias templates against template template parameters,
allow pack expansions when the alias has a fixed-size parameter list. Fixes (#GH62529).
- Clang now ignores template parameters only used within the exception specification of candidate function
templates during partial ordering when deducing template arguments from a function declaration or when
taking the address of a function template.
- Fix a bug with checking constrained non-type template parameters for equivalence. Fixes (#GH77377).
- Fix a bug where the last argument was not considered when considering the most viable function for
explicit object argument member functions. Fixes (#GH92188).
- Fix a C++11 crash when a non-const non-static member function is defined out-of-line with
the ``constexpr`` specifier. Fixes (#GH61004).
- Clang no longer transforms dependent qualified names into implicit class member access expressions
until it can be determined whether the name is that of a non-static member.
- Clang now correctly diagnoses when the current instantiation is used as an incomplete base class.
- Clang no longer treats ``constexpr`` class scope function template specializations of non-static members
as implicitly ``const`` in language modes after C++11.
- Fixed a crash when trying to emit captures in a lambda call operator with an explicit object
parameter that is called on a derived type of the lambda.
Fixes (#GH87210), (GH89541).
- Clang no longer tries to check if an expression is immediate-escalating in an unevaluated context.
Fixes (#GH91308).
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``.
- Fixed malformed AST generated for anonymous union access in templates. (#GH90842)
Miscellaneous Bug Fixes
^^^^^^^^^^^^^^^^^^^^^^^
- Fixed an infinite recursion in ASTImporter, on return type declared inside
body of C++11 lambda without trailing return (#GH68775).
- Fixed declaration name source location of instantiated function definitions (GH71161).
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
^^^^^^^^^^^^
- Clang now supports CUDA SDK up to 12.4
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``.
- Handles Java ``switch`` expressions.
- Adds ``AllowShortCaseExpressionOnASingleLine`` option.
- Adds ``AlignCaseArrows`` suboption to ``AlignConsecutiveShortCaseStatements``.
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>`_.
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