d870a57563
EnumDecl's promotion type is set either to the parsed type or calculated type after completing its definition. When it's bool type and has no definition, its promotion type is bool which is not allowed by clang. Fixes #56560. Differential Revision: https://reviews.llvm.org/D130210
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ReStructuredText
===========================================
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Clang |release| |ReleaseNotesTitle|
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===========================================
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.. contents::
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:local:
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:depth: 2
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Written by the `LLVM Team <https://llvm.org/>`_
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.. only:: PreRelease
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.. warning::
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These are in-progress notes for the upcoming Clang |version| release.
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Release notes for previous releases can be found on
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`the Download Page <https://releases.llvm.org/download.html>`_.
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Introduction
|
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============
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This document contains the release notes for the Clang C/C++/Objective-C
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frontend, part of the LLVM Compiler Infrastructure, release |release|. Here we
|
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describe the status of Clang in some detail, including major
|
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improvements from the previous release and new feature work. For the
|
|
general LLVM release notes, see `the LLVM
|
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documentation <https://llvm.org/docs/ReleaseNotes.html>`_. All LLVM
|
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releases may be downloaded from the `LLVM releases web
|
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site <https://llvm.org/releases/>`_.
|
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|
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For more information about Clang or LLVM, including information about the
|
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latest release, please see the `Clang Web Site <https://clang.llvm.org>`_ or the
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`LLVM Web Site <https://llvm.org>`_.
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|
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Note that if you are reading this file from a Git checkout or the
|
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main Clang web page, this document applies to the *next* release, not
|
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the current one. To see the release notes for a specific release, please
|
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see the `releases page <https://llvm.org/releases/>`_.
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What's New in Clang |release|?
|
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==============================
|
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|
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Some of the major new features and improvements to Clang are listed
|
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here. Generic improvements to Clang as a whole or to its underlying
|
|
infrastructure are described first, followed by language-specific
|
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sections with improvements to Clang's support for those languages.
|
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|
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Major New Features
|
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------------------
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|
|
|
- Clang now supports the ``-fzero-call-used-regs`` feature for x86. The purpose
|
|
of this feature is to limit Return-Oriented Programming (ROP) exploits and
|
|
information leakage. It works by zeroing out a selected class of registers
|
|
before function return --- e.g., all GPRs that are used within the function.
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There is an analogous ``zero_call_used_regs`` attribute to allow for finer
|
|
control of this feature.
|
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|
|
- Clang now supports randomizing structure layout in C. This feature is a
|
|
compile-time hardening technique, making it more difficult for an attacker to
|
|
retrieve data from structures. Specify randomization with the
|
|
``randomize_layout`` attribute. The corresponding ``no_randomize_layout``
|
|
attribute can be used to turn the feature off.
|
|
|
|
A seed value is required to enable randomization, and is deterministic based
|
|
on a seed value. Use the ``-frandomize-layout-seed=`` or
|
|
``-frandomize-layout-seed-file=`` flags.
|
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|
|
.. note::
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|
|
Randomizing structure layout is a C-only feature.
|
|
|
|
- Clang now supports the ``-fstrict-flex-arrays=<arg>`` option to control which
|
|
array bounds lead to flexible array members. The option yields more accurate
|
|
``__builtin_object_size`` and ``__builtin_dynamic_object_size`` results in
|
|
most cases but may be overly conservative for some legacy code.
|
|
- Experimental support for HLSL has been added. The implementation is
|
|
incomplete and highly experimental. For more information about the ongoing
|
|
work to support HLSL see the `documentation
|
|
<https://clang.llvm.org/docs/HLSLSupport.html>`_, or the `GitHub project
|
|
<https://github.com/orgs/llvm/projects/4>`_.
|
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|
|
Bug Fixes
|
|
---------
|
|
- ``CXXNewExpr::getArraySize()`` previously returned a ``llvm::Optional``
|
|
wrapping a ``nullptr`` when the ``CXXNewExpr`` did not have an array
|
|
size expression. This was fixed and ``::getArraySize()`` will now always
|
|
either return ``None`` or a ``llvm::Optional`` wrapping a valid ``Expr*``.
|
|
This fixes `Issue 53742 <https://github.com/llvm/llvm-project/issues/53742>`_.
|
|
- We now ignore full expressions when traversing cast subexpressions. This
|
|
fixes `Issue 53044 <https://github.com/llvm/llvm-project/issues/53044>`_.
|
|
- Allow ``-Wno-gnu`` to silence GNU extension diagnostics for pointer
|
|
arithmetic diagnostics. Fixes `Issue 54444
|
|
<https://github.com/llvm/llvm-project/issues/54444>`_.
|
|
- Placeholder constraints, as in ``Concept auto x = f();``, were not checked
|
|
when modifiers like ``auto&`` or ``auto**`` were added. These constraints are
|
|
now checked.
|
|
This fixes `Issue 53911 <https://github.com/llvm/llvm-project/issues/53911>`_
|
|
and `Issue 54443 <https://github.com/llvm/llvm-project/issues/54443>`_.
|
|
- Previously invalid member variables with template parameters would crash clang.
|
|
Now fixed by setting identifiers for them.
|
|
This fixes `Issue 28475 (PR28101) <https://github.com/llvm/llvm-project/issues/28475>`_.
|
|
- Now allow the ``restrict`` and ``_Atomic`` qualifiers to be used in
|
|
conjunction with ``__auto_type`` to match the behavior in GCC. This fixes
|
|
`Issue 53652 <https://github.com/llvm/llvm-project/issues/53652>`_.
|
|
- No longer crash when specifying a variably-modified parameter type in a
|
|
function with the ``naked`` attribute. This fixes
|
|
`Issue 50541 <https://github.com/llvm/llvm-project/issues/50541>`_.
|
|
- Allow multiple ``#pragma weak`` directives to name the same undeclared (if an
|
|
alias, target) identifier instead of only processing one such ``#pragma weak``
|
|
per identifier.
|
|
Fixes `Issue 28985 <https://github.com/llvm/llvm-project/issues/28985>`_.
|
|
- Assignment expressions in C11 and later mode now properly strip the _Atomic
|
|
qualifier when determining the type of the assignment expression. Fixes
|
|
`Issue 48742 <https://github.com/llvm/llvm-project/issues/48742>`_.
|
|
- Improved the diagnostic when accessing a member of an atomic structure or
|
|
union object in C; was previously an unhelpful error, but now issues a
|
|
``-Watomic-access`` warning which defaults to an error. Fixes
|
|
`Issue 54563 <https://github.com/llvm/llvm-project/issues/54563>`_.
|
|
- Unevaluated lambdas in dependant contexts no longer result in clang crashing.
|
|
This fixes Issues `50376 <https://github.com/llvm/llvm-project/issues/50376>`_,
|
|
`51414 <https://github.com/llvm/llvm-project/issues/51414>`_,
|
|
`51416 <https://github.com/llvm/llvm-project/issues/51416>`_,
|
|
and `51641 <https://github.com/llvm/llvm-project/issues/51641>`_.
|
|
- The builtin function __builtin_dump_struct would crash clang when the target
|
|
struct contains a bitfield. It now correctly handles bitfields.
|
|
This fixes Issue `Issue 54462 <https://github.com/llvm/llvm-project/issues/54462>`_.
|
|
- Statement expressions are now disabled in default arguments in general.
|
|
This fixes Issue `Issue 53488 <https://github.com/llvm/llvm-project/issues/53488>`_.
|
|
- According to `CWG 1394 <https://wg21.link/cwg1394>`_ and
|
|
`C++20 [dcl.fct.def.general]p2 <https://timsong-cpp.github.io/cppwp/n4868/dcl.fct.def#general-2.sentence-3>`_,
|
|
Clang should not diagnose incomplete types in function definitions if the function body is "= delete;".
|
|
This fixes Issue `Issue 52802 <https://github.com/llvm/llvm-project/issues/52802>`_.
|
|
- Unknown type attributes with a ``[[]]`` spelling are no longer diagnosed twice.
|
|
This fixes Issue `Issue 54817 <https://github.com/llvm/llvm-project/issues/54817>`_.
|
|
- Clang should no longer incorrectly diagnose a variable declaration inside of
|
|
a lambda expression that shares the name of a variable in a containing
|
|
if/while/for/switch init statement as a redeclaration.
|
|
This fixes `Issue 54913 <https://github.com/llvm/llvm-project/issues/54913>`_.
|
|
- Overload resolution for constrained function templates could use the partial
|
|
order of constraints to select an overload, even if the parameter types of
|
|
the functions were different. It now diagnoses this case correctly as an
|
|
ambiguous call and an error. Fixes
|
|
`Issue 53640 <https://github.com/llvm/llvm-project/issues/53640>`_.
|
|
- No longer crash when trying to determine whether the controlling expression
|
|
argument to a generic selection expression has side effects in the case where
|
|
the expression is result dependent. This fixes
|
|
`Issue 50227 <https://github.com/llvm/llvm-project/issues/50227>`_.
|
|
- Fixed an assertion when constant evaluating an initializer for a GCC/Clang
|
|
floating-point vector type when the width of the initialization is exactly
|
|
the same as the elements of the vector being initialized.
|
|
Fixes `Issue 50216 <https://github.com/llvm/llvm-project/issues/50216>`_.
|
|
- Fixed a crash when the ``__bf16`` type is used such that its size or
|
|
alignment is calculated on a target which does not support that type. This
|
|
fixes `Issue 50171 <https://github.com/llvm/llvm-project/issues/50171>`_.
|
|
- Fixed a false positive diagnostic about an unevaluated expression having no
|
|
side effects when the expression is of VLA type and is an operand of the
|
|
``sizeof`` operator. Fixes `Issue 48010 <https://github.com/llvm/llvm-project/issues/48010>`_.
|
|
- Fixed a false positive diagnostic about scoped enumerations being a C++11
|
|
extension in C mode. A scoped enumeration's enumerators cannot be named in C
|
|
because there is no way to fully qualify the enumerator name, so this
|
|
"extension" was unintentional and useless. This fixes
|
|
`Issue 42372 <https://github.com/llvm/llvm-project/issues/42372>`_.
|
|
- Clang will now find and emit a call to an allocation function in a
|
|
promise_type body for coroutines if there is any allocation function
|
|
declaration in the scope of promise_type. Additionally, to implement CWG2585,
|
|
a coroutine will no longer generate a call to a global allocation function
|
|
with the signature (std::size_t, p0, ..., pn).
|
|
This fixes Issue `Issue 54881 <https://github.com/llvm/llvm-project/issues/54881>`_.
|
|
- Implement `CWG 2394 <https://wg21.link/cwg2394>`_: Const class members
|
|
may be initialized with a defaulted default constructor under the same
|
|
conditions it would be allowed for a const object elsewhere.
|
|
- ``__has_unique_object_representations`` no longer reports that ``_BitInt`` types
|
|
have unique object representations if they have padding bits.
|
|
- Unscoped and scoped enumeration types can no longer be initialized from a
|
|
brace-init-list containing a single element of a different scoped enumeration
|
|
type.
|
|
- Allow use of an elaborated type specifier as a ``_Generic`` selection
|
|
association in C++ mode. This fixes
|
|
`Issue 55562 <https://github.com/llvm/llvm-project/issues/55562>`_.
|
|
- Clang will allow calling a ``consteval`` function in a default argument. This
|
|
fixes `Issue 48230 <https://github.com/llvm/llvm-project/issues/48230>`_.
|
|
- Fixed memory leak due to ``VarTemplateSpecializationDecl`` using
|
|
``TemplateArgumentListInfo`` instead of ``ASTTemplateArgumentListInfo``.
|
|
- An initializer for a static variable declaration, which is nested
|
|
inside a statement expression in an aggregate initializer, is now
|
|
emitted as a dynamic initializer. Previously the variable would
|
|
incorrectly be zero-initialized. In contexts where a dynamic
|
|
initializer is not allowed this is now diagnosed as an error.
|
|
- Clang now correctly emits symbols for implicitly instantiated constexpr
|
|
template function. Fixes `Issue 55560 <https://github.com/llvm/llvm-project/issues/55560>`_.
|
|
- Clang now checks ODR violations when merging concepts from different modules.
|
|
Note that this may possibly break existing code, and is done so intentionally.
|
|
Fixes `Issue 56310 <https://github.com/llvm/llvm-project/issues/56310>`_.
|
|
- Clang will now look through type sugar when checking a member function is a
|
|
move assignment operator. Fixes `Issue 56456 <https://github.com/llvm/llvm-project/issues/56456>`_.
|
|
- Fixed a crash when a variable with a bool enum type that has no definition
|
|
used in comparison operators. Fixes `Issue 56560 <https://github.com/llvm/llvm-project/issues/56560>`_.
|
|
|
|
Improvements to Clang's diagnostics
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
- ``-Wliteral-range`` will warn on floating-point equality comparisons with
|
|
constants that are not representable in a casted value. For example,
|
|
``(float) f == 0.1`` is always false.
|
|
- ``-Winline-namespace-reopened-noninline`` now takes into account that the
|
|
``inline`` keyword must appear on the original but not necessarily all
|
|
extension definitions of an inline namespace and therefore points its note
|
|
at the original definition. This fixes `Issue 50794 (PR51452)
|
|
<https://github.com/llvm/llvm-project/issues/50794>`_.
|
|
- ``-Wunused-but-set-variable`` now also warns if the variable is only used
|
|
by unary operators.
|
|
- ``-Wunused-variable`` no longer warn for references extending the lifetime
|
|
of temporaries with side effects. This fixes `Issue 54489
|
|
<https://github.com/llvm/llvm-project/issues/54489>`_.
|
|
- Modified the behavior of ``-Wstrict-prototypes`` and added a new, related
|
|
diagnostic ``-Wdeprecated-non-prototype``. The strict prototypes warning will
|
|
now only diagnose deprecated declarations and definitions of functions
|
|
without a prototype where the behavior in C2x will remain correct. This
|
|
diagnostic remains off by default but is now enabled via ``-pedantic`` due to
|
|
it being a deprecation warning. ``-Wstrict-prototypes`` has no effect in C2x
|
|
or when ``-fno-knr-functions`` is enabled. ``-Wdeprecated-non-prototype``
|
|
will diagnose cases where the deprecated declarations or definitions of a
|
|
function without a prototype will change behavior in C2x. Additionally, it
|
|
will diagnose calls which pass arguments to a function without a prototype.
|
|
This warning is enabled only when the ``-Wdeprecated-non-prototype`` option
|
|
is enabled at the function declaration site, which allows a developer to
|
|
disable the diagnostic for all callers at the point of declaration. This
|
|
diagnostic is grouped under the ``-Wstrict-prototypes`` warning group, but is
|
|
enabled by default. ``-Wdeprecated-non-prototype`` has no effect in C2x or
|
|
when ``-fno-knr-functions`` is enabled.
|
|
- Clang now appropriately issues an error in C when a definition of a function
|
|
without a prototype and with no arguments is an invalid redeclaration of a
|
|
function with a prototype. e.g., ``void f(int); void f() {}`` is now properly
|
|
diagnosed.
|
|
- The ``-Wimplicit-function-declaration`` warning diagnostic now defaults to
|
|
an error in C99 and later. Prior to C2x, it may be downgraded to a warning
|
|
with ``-Wno-error=implicit-function-declaration``, or disabled entirely with
|
|
``-Wno-implicit-function-declaration``. As of C2x, support for implicit
|
|
function declarations has been removed, and the warning options will have no
|
|
effect.
|
|
- The ``-Wimplicit-int`` warning diagnostic now defaults to an error in C99 and
|
|
later. Prior to C2x, it may be downgraded to a warning with
|
|
``-Wno-error=implicit-int``, or disabled entirely with ``-Wno-implicit-int``.
|
|
As of C2x, support for implicit int has been removed, and the warning options
|
|
will have no effect. Specifying ``-Wimplicit-int`` in C89 mode will now issue
|
|
warnings instead of being a noop.
|
|
- No longer issue a "declaration specifiers missing, defaulting to int"
|
|
diagnostic in C89 mode because it is not an extension in C89, it was valid
|
|
code. The diagnostic has been removed entirely as it did not have a
|
|
diagnostic group to disable it, but it can be covered wholly by
|
|
``-Wimplicit-int``.
|
|
- ``-Wmisexpect`` warns when the branch weights collected during profiling
|
|
conflict with those added by ``llvm.expect``.
|
|
- ``-Wthread-safety-analysis`` now considers overloaded compound assignment and
|
|
increment/decrement operators as writing to their first argument, thus
|
|
requiring an exclusive lock if the argument is guarded.
|
|
- ``-Wenum-conversion`` now warns on converting a signed enum of one type to an
|
|
unsigned enum of a different type (or vice versa) rather than
|
|
``-Wsign-conversion``.
|
|
- Added the ``-Wunreachable-code-generic-assoc`` diagnostic flag (grouped under
|
|
the ``-Wunreachable-code`` flag) which is enabled by default and warns the
|
|
user about ``_Generic`` selection associations which are unreachable because
|
|
the type specified is an array type or a qualified type.
|
|
- Added the ``-Wgnu-line-marker`` diagnostic flag (grouped under the ``-Wgnu``
|
|
flag) which is a portability warning about use of GNU linemarker preprocessor
|
|
directives. Fixes `Issue 55067 <https://github.com/llvm/llvm-project/issues/55067>`_.
|
|
- Using ``#elifdef`` and ``#elifndef`` that are incompatible with C/C++
|
|
standards before C2x/C++2b are now warned via ``-pedantic``. Additionally,
|
|
on such language mode, ``-Wpre-c2x-compat`` and ``-Wpre-c++2b-compat``
|
|
diagnostic flags report a compatibility issue.
|
|
Fixes `Issue 55306 <https://github.com/llvm/llvm-project/issues/55306>`_.
|
|
- Clang now checks for stack resource exhaustion when recursively parsing
|
|
declarators in order to give a diagnostic before we run out of stack space.
|
|
This fixes `Issue 51642 <https://github.com/llvm/llvm-project/issues/51642>`_.
|
|
- Unknown preprocessor directives in a skipped conditional block are now given
|
|
a typo correction suggestion if the given directive is sufficiently similar
|
|
to another preprocessor conditional directive. For example, if ``#esle``
|
|
appears in a skipped block, we will warn about the unknown directive and
|
|
suggest ``#else`` as an alternative. ``#elifdef`` and ``#elifndef`` are only
|
|
suggested when in C2x or C++2b mode. Fixes
|
|
`Issue 51598 <https://github.com/llvm/llvm-project/issues/51598>`_.
|
|
- The ``-Wdeprecated`` diagnostic will now warn on out-of-line ``constexpr``
|
|
declarations downgraded to definitions in C++1z, in addition to the
|
|
existing warning on out-of-line ``const`` declarations.
|
|
- ``-Wshift-overflow`` will not warn for signed left shifts in C++20 mode
|
|
(and newer), as it will always wrap and never overflow. This fixes
|
|
`Issue 52873 <https://github.com/llvm/llvm-project/issues/52873>`_.
|
|
- When using class templates without arguments, clang now tells developers
|
|
that template arguments are missing in certain contexts.
|
|
This fixes `Issue 55962 <https://github.com/llvm/llvm-project/issues/55962>`_.
|
|
- Printable Unicode characters within `static_assert` messages are no longer
|
|
escaped.
|
|
- The ``-Winfinite-recursion`` diagnostic no longer warns about
|
|
unevaluated operands of a ``typeid`` expression, as they are now
|
|
modeled correctly in the CFG. This fixes
|
|
`Issue 21668 <https://github.com/llvm/llvm-project/issues/21668>`_.
|
|
- ``-Wself-assign``, ``-Wself-assign-overloaded`` and ``-Wself-move`` will
|
|
suggest a fix if the decl being assigned is a parameter that shadows a data
|
|
member of the contained class.
|
|
- Added ``-Winvalid-utf8`` which diagnoses invalid UTF-8 code unit sequences in
|
|
comments.
|
|
|
|
Non-comprehensive list of changes in this release
|
|
-------------------------------------------------
|
|
|
|
- Improve __builtin_dump_struct:
|
|
|
|
- Support bitfields in struct and union.
|
|
- Improve the dump format, dump both bitwidth(if its a bitfield) and field
|
|
value.
|
|
- Remove anonymous tag locations and flatten anonymous struct members.
|
|
- Beautify dump format, add indent for struct members.
|
|
- Support passing additional arguments to the formatting function, allowing
|
|
use with ``fprintf`` and similar formatting functions.
|
|
- Support use within constant evaluation in C++, if a ``constexpr``
|
|
formatting function is provided.
|
|
- Support formatting of base classes in C++.
|
|
- Support calling a formatting function template in C++, which can provide
|
|
custom formatting for non-aggregate types.
|
|
|
|
- Previously disabled sanitizer options now enabled by default:
|
|
- ASAN_OPTIONS=detect_stack_use_after_return=1 (only on Linux).
|
|
- MSAN_OPTIONS=poison_in_dtor=1.
|
|
|
|
- Some type-trait builtins, such as ``__has_trivial_assign``, have been documented
|
|
as deprecated for a while because their semantics don't mix well with post-C++11 type-traits.
|
|
Clang now emits deprecation warnings for them under the flag ``-Wdeprecated-builtins``.
|
|
|
|
New Compiler Flags
|
|
------------------
|
|
- Added the ``-fno-knr-functions`` flag to allow users to opt into the C2x
|
|
behavior where a function with an empty parameter list is treated as though
|
|
the parameter list were ``void``. There is no ``-fknr-functions`` or
|
|
``-fno-no-knr-functions`` flag; this feature cannot be disabled in language
|
|
modes where it is required, such as C++ or C2x.
|
|
- A new ARM pass to workaround Cortex-A57 Erratum 1742098 and Cortex-A72 Erratum
|
|
1655431 can be enabled using ``-mfix-cortex-a57-aes-1742098`` or
|
|
``-mfix-cortex-a72-aes-1655431``. The pass is enabled when using either of
|
|
these cpus with ``-mcpu=`` and can be disabled using
|
|
``-mno-fix-cortex-a57-aes-1742098`` or ``-mno-fix-cortex-a72-aes-1655431``.
|
|
- Added the ``-fexperimental-max-bitint-width=`` option to increase the maximum
|
|
allowed bit width of ``_BitInt`` types beyond the default of 128 bits. Some
|
|
operations, such as division or float-to-integer conversion, on ``_BitInt``
|
|
types with more than 128 bits currently crash clang. This option will be
|
|
removed in the future once clang supports all such operations.
|
|
- Added the ``-print-diagnostic-options`` option, which prints a list of
|
|
warnings the compiler supports.
|
|
- Added the ``-Warray-parameter`` warning. It diagnoses differences between
|
|
array parameters between function redeclarations (arrays of different extents,
|
|
etc). This flag is related to the same flag in GCC, but is different in that
|
|
it does not accept an explicitly- specified warning level and use of this flag
|
|
has no effect on ``-Warray-bounds``.
|
|
|
|
Deprecated Compiler Flags
|
|
-------------------------
|
|
|
|
Modified Compiler Flags
|
|
-----------------------
|
|
|
|
Removed Compiler Flags
|
|
-------------------------
|
|
- Removed the ``-fno-concept-satisfaction-caching`` flag. The flag was added
|
|
at the time when the draft of C++20 standard did not permit caching of
|
|
atomic constraints. The final standard permits such caching, see
|
|
`WG21 P2104R0 <http://wg21.link/p2104r0>`_.
|
|
|
|
New Pragmas in Clang
|
|
--------------------
|
|
- Added support for MSVC's ``#pragma function``, which tells the compiler to
|
|
generate calls to functions listed in the pragma instead of using the
|
|
builtins.
|
|
- Added support for MSVC's ``#pragma alloc_text``. The pragma names the code
|
|
section functions are placed in. The pragma only applies to functions with
|
|
C linkage.
|
|
- Added support for an empty optimization list for MSVC's ``#pragma optimize``.
|
|
The pragma takes a list of optimizations to turn on or off which applies to
|
|
all functions following the pragma. At the moment, only an empty list is
|
|
supported.
|
|
|
|
- ...
|
|
|
|
Attribute Changes in Clang
|
|
--------------------------
|
|
|
|
- Added support for parameter pack expansion in ``clang::annotate``.
|
|
|
|
- The ``overloadable`` attribute can now be written in all of the syntactic
|
|
locations a declaration attribute may appear.
|
|
This fixes `Issue 53805 <https://github.com/llvm/llvm-project/issues/53805>`_.
|
|
|
|
- Improved namespace attributes handling:
|
|
|
|
- Handle GNU attributes before a namespace identifier and subsequent
|
|
attributes of different kinds.
|
|
- Emit error on GNU attributes for a nested namespace definition.
|
|
|
|
- Statement attributes ``[[clang::noinline]]`` and ``[[clang::always_inline]]``
|
|
can be used to control inlining decisions at callsites.
|
|
|
|
- ``#pragma clang attribute push`` now supports multiple attributes within a single directive.
|
|
|
|
- The ``__declspec(naked)`` attribute can no longer be written on a member
|
|
function in Microsoft compatibility mode, matching the behavior of cl.exe.
|
|
|
|
- Attribute ``no_builtin`` should now affect the generated code. It now disables
|
|
builtins (corresponding to the specific names listed in the attribute) in the
|
|
body of the function the attribute is on.
|
|
|
|
- When the ``weak`` attribute is applied to a const qualified variable clang no longer
|
|
tells the backend it is allowed to optimize based on initializer value.
|
|
|
|
- Added the ``clang::annotate_type`` attribute, which can be used to add
|
|
annotations to types (see documentation for details).
|
|
|
|
- Added half float to types that can be represented by ``__attribute__((mode(XX)))``.
|
|
|
|
- The ``format`` attribute can now be applied to non-variadic functions. The
|
|
format string must correctly format the fixed parameter types of the function.
|
|
Using the attribute this way emits a GCC compatibility diagnostic.
|
|
|
|
- Support was added for ``__attribute__((function_return("thunk-extern")))``
|
|
to X86 to replace ``ret`` instructions with ``jmp __x86_return_thunk``. The
|
|
corresponding attribute to disable this,
|
|
``__attribute__((function_return("keep")))`` was added. This is intended to
|
|
be used by the Linux kernel to mitigate RETBLEED.
|
|
|
|
Windows Support
|
|
---------------
|
|
|
|
- Add support for MSVC-compatible ``/JMC``/``/JMC-`` flag in clang-cl (supports
|
|
X86/X64/ARM/ARM64). ``/JMC`` could only be used when ``/Zi`` or ``/Z7`` is
|
|
turned on. With this addition, clang-cl can be used in Visual Studio for the
|
|
JustMyCode feature. Note, you may need to manually add ``/JMC`` as additional
|
|
compile options in the Visual Studio since it currently assumes clang-cl does not support ``/JMC``.
|
|
|
|
- Implemented generation of SEH unwind information on ARM. (C++ exception
|
|
handling in MSVC mode is still unimplemented though.)
|
|
|
|
- Switched MinGW mode on ARM to use SEH instead of DWARF for unwind information.
|
|
|
|
AIX Support
|
|
-----------
|
|
|
|
- The driver no longer adds ``-mignore-xcoff-visibility`` by default for AIX
|
|
targets when no other visibility command-line options are in effect, as
|
|
ignoring hidden visibility can silently have undesirable side effects (e.g
|
|
when libraries depend on visibility to hide non-ABI facing entities). The
|
|
``-mignore-xcoff-visibility`` option can be manually specified on the
|
|
command-line to recover the previous behavior if desired.
|
|
|
|
C Language Changes in Clang
|
|
---------------------------
|
|
|
|
C2x Feature Support
|
|
-------------------
|
|
|
|
- Implemented `WG14 N2674 The noreturn attribute <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2764.pdf>`_.
|
|
- Implemented `WG14 N2935 Make false and true first-class language features <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2935.pdf>`_.
|
|
- Implemented `WG14 N2763 Adding a fundamental type for N-bit integers <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2763.pdf>`_.
|
|
- Implemented `WG14 N2775 Literal suffixes for bit-precise integers <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2775.pdf>`_.
|
|
- Implemented the ``*_WIDTH`` macros to complete support for
|
|
`WG14 N2412 Two's complement sign representation for C2x <https://www9.open-std.org/jtc1/sc22/wg14/www/docs/n2412.pdf>`_.
|
|
- Implemented `WG14 N2418 Adding the u8 character prefix <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2418.pdf>`_.
|
|
- Removed support for implicit function declarations. This was a C89 feature
|
|
that was removed in C99, but cannot be supported in C2x because it requires
|
|
support for functions without prototypes, which no longer exist in C2x.
|
|
- Implemented `WG14 N2841 No function declarators without prototypes <https://www9.open-std.org/jtc1/sc22/wg14/www/docs/n2841.htm>`_
|
|
and `WG14 N2432 Remove support for function definitions with identifier lists <https://www9.open-std.org/jtc1/sc22/wg14/www/docs/n2432.pdf>`_.
|
|
|
|
C++ Language Changes in Clang
|
|
-----------------------------
|
|
|
|
- Improved ``-O0`` code generation for calls to ``std::move``, ``std::forward``,
|
|
``std::move_if_noexcept``, ``std::addressof``, and ``std::as_const``. These
|
|
are now treated as compiler builtins and implemented directly, rather than
|
|
instantiating the definition from the standard library.
|
|
- Fixed mangling of nested dependent names such as ``T::a::b``, where ``T`` is a
|
|
template parameter, to conform to the Itanium C++ ABI and be compatible with
|
|
GCC. This breaks binary compatibility with code compiled with earlier versions
|
|
of clang; use the ``-fclang-abi-compat=14`` option to get the old mangling.
|
|
- Preprocessor character literals with a ``u8`` prefix are now correctly treated as
|
|
unsigned character literals. This fixes `Issue 54886 <https://github.com/llvm/llvm-project/issues/54886>`_.
|
|
- Stopped allowing constraints on non-template functions to be compliant with
|
|
dcl.decl.general p4.
|
|
|
|
C++20 Feature Support
|
|
^^^^^^^^^^^^^^^^^^^^^
|
|
- Diagnose consteval and constexpr issues that happen at namespace scope. This
|
|
partially addresses `Issue 51593 <https://github.com/llvm/llvm-project/issues/51593>`_.
|
|
- No longer attempt to evaluate a consteval UDL function call at runtime when
|
|
it is called through a template instantiation. This fixes
|
|
`Issue 54578 <https://github.com/llvm/llvm-project/issues/54578>`_.
|
|
|
|
- Implemented ``__builtin_source_location()``, which enables library support
|
|
for ``std::source_location``.
|
|
|
|
- The mangling scheme for C++20 modules has incompatibly changed. The
|
|
initial mangling was discovered not to be reversible, and the weak
|
|
ownership design decision did not give the backwards compatibility
|
|
that was hoped for. C++20 since added ``extern "C++"`` semantics
|
|
that can be used for such compatibility. The demangler now demangles
|
|
symbols with named module attachment.
|
|
|
|
- As per "Conditionally Trivial Special Member Functions" (P0848), it is
|
|
now possible to overload destructors using concepts. Note that the rest
|
|
of the paper about other special member functions is not yet implemented.
|
|
|
|
C++2b Feature Support
|
|
^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
- Implemented `P2128R6: Multidimensional subscript operator <https://wg21.link/P2128R6>`_.
|
|
- Implemented `P0849R8: auto(x): decay-copy in the language <https://wg21.link/P0849R8>`_.
|
|
- Implemented `P2242R3: Non-literal variables (and labels and gotos) in constexpr functions <https://wg21.link/P2242R3>`_.
|
|
- Implemented `LWG3659: Consider ATOMIC_FLAG_INIT undeprecation <https://wg21.link/LWG3659>`_.
|
|
- Implemented `P2290 Delimited escape sequences <https://wg21.link/P2290R3>`_.
|
|
This feature is available as an extension in all C and C++ language modes.
|
|
- Implemented `P2071 Named universal character escapes <https://wg21.link/P2290R2>`_.
|
|
This feature is available as an extension in all C and C++ language modes.
|
|
|
|
CUDA/HIP Language Changes in Clang
|
|
----------------------------------
|
|
|
|
- Added `__noinline__` as a keyword to avoid diagnostics due to usage of
|
|
`__attribute__((__noinline__))` in CUDA/HIP programs.
|
|
|
|
Objective-C Language Changes in Clang
|
|
-------------------------------------
|
|
|
|
OpenCL C Language Changes in Clang
|
|
----------------------------------
|
|
|
|
...
|
|
|
|
ABI Changes in Clang
|
|
--------------------
|
|
|
|
- GCC doesn't pack non-POD members in packed structs unless the packed
|
|
attribute is also specified on the member. Clang historically did perform
|
|
such packing. Clang now matches the gcc behavior (except on Darwin and PS4).
|
|
You can switch back to the old ABI behavior with the flag:
|
|
``-fclang-abi-compat=14.0``.
|
|
- When compiling C for ARM or AArch64, a zero-length bitfield in a ``struct``
|
|
(e.g. ``int : 0``) no longer prevents the structure from being considered a
|
|
homogeneous floating-point or vector aggregate. The new behavior agrees with
|
|
the AAPCS specification, and matches the similar bug fix in GCC 12.1.
|
|
- Targeting AArch64, since D127209 LLVM now only preserves the z8-z23
|
|
and p4-p15 registers across a call if the registers z0-z7 or p0-p3 are
|
|
used to pass data into or out of a subroutine. The new behavior
|
|
matches the AAPCS. Previously LLVM preserved z8-z23 and p4-p15 across
|
|
a call if the callee had an SVE type anywhere in its signature. This
|
|
would cause an incorrect use of the caller-preserved z8-z23 and p4-p15
|
|
ABI for example if the 9th argument or greater were the first SVE type
|
|
in the signature of a function.
|
|
- All copy constructors can now be trivial if they are not user-provided,
|
|
regardless of the type qualifiers of the argument of the defaulted constructor,
|
|
fixing dr2171.
|
|
You can switch back to the old ABI behavior with the flag:
|
|
``-fclang-abi-compat=14.0``.
|
|
|
|
OpenMP Support in Clang
|
|
-----------------------
|
|
|
|
...
|
|
|
|
CUDA Support in Clang
|
|
---------------------
|
|
|
|
- ...
|
|
|
|
X86 Support in Clang
|
|
--------------------
|
|
|
|
- Support ``-mharden-sls=[none|all|return|indirect-jmp]`` for straight-line
|
|
speculation hardening.
|
|
- Support for the ``_Float16`` type has been added for all targets with SSE2.
|
|
When AVX512-FP16 is not available, arithmetic on ``_Float16`` is emulated
|
|
using ``float``.
|
|
- Added the ``-m[no-]rdpru`` flag to enable/disable the RDPRU instruction
|
|
provided by AMD Zen2 and later processors. Defined intrinsics for using
|
|
this instruction (see rdpruintrin.h).
|
|
- Support ``-mstack-protector-guard-symbol=[SymbolName]`` to use the given
|
|
symbol for addressing the stack protector guard.
|
|
- ``-mfunction-return=thunk-extern`` support was added to clang for x86. This
|
|
will be used by Linux kernel mitigations for RETBLEED. The corresponding flag
|
|
``-mfunction-return=keep`` may be appended to disable the feature.
|
|
|
|
DWARF Support in Clang
|
|
----------------------
|
|
|
|
- clang now adds DWARF information for inline strings in C/C++ programs,
|
|
allowing ``line:column`` symbolization of strings. Some debugging programs may
|
|
require updating, as this takes advantage of DWARF ``DW_TAG_variable``
|
|
structures *without* a ``DW_AT_name`` field, which is valid DWARF, but may be
|
|
handled incorrectly by some software (e.g. new failures with incorrect
|
|
assertions).
|
|
|
|
Arm and AArch64 Support in Clang
|
|
--------------------------------
|
|
|
|
- clang now supports the Cortex-M85 CPU, which can be chosen with
|
|
`-mcpu=cortex-m85`. By default, this has PACBTI turned on, but it can be
|
|
disabled with `-mcpu=cortex-m85+nopacbti`.
|
|
|
|
Floating Point Support in Clang
|
|
-------------------------------
|
|
|
|
Internal API Changes
|
|
--------------------
|
|
|
|
- Added a new attribute flag ``AcceptsExprPack`` that when set allows
|
|
expression pack expansions in the parsed arguments of the corresponding
|
|
attribute. Additionally it introduces delaying of attribute arguments, adding
|
|
common handling for creating attributes that cannot be fully initialized
|
|
prior to template instantiation.
|
|
|
|
Build System Changes
|
|
--------------------
|
|
|
|
* CMake ``-DCLANG_DEFAULT_PIE_ON_LINUX=ON`` is now the default. This is used by
|
|
linux-gnu systems to decide whether ``-fPIE -pie`` is the default (instead of
|
|
``-fno-pic -no-pie``). This matches GCC installations on many Linux distros.
|
|
Note: linux-android and linux-musl always default to ``-fPIE -pie``, ignoring
|
|
this variable. ``-DCLANG_DEFAULT_PIE_ON_LINUX`` may be removed in the future.
|
|
|
|
AST Matchers
|
|
------------
|
|
|
|
- Expanded ``isInline`` narrowing matcher to support C++17 inline variables.
|
|
|
|
- Added ``forEachTemplateArgument`` matcher which creates a match every
|
|
time a ``templateArgument`` matches the matcher supplied to it.
|
|
|
|
- Added ``objcStringLiteral`` matcher which matches ObjectiveC String
|
|
literal expressions.
|
|
|
|
clang-format
|
|
------------
|
|
|
|
- **Important change**: Renamed ``IndentRequires`` to ``IndentRequiresClause``
|
|
and changed the default for all styles from ``false`` to ``true``.
|
|
|
|
- Reworked and improved handling of concepts and requires. Added the
|
|
``RequiresClausePosition`` option as part of that.
|
|
|
|
- Changed ``BreakBeforeConceptDeclarations`` from ``Boolean`` to an enum.
|
|
|
|
- Option ``InsertBraces`` has been added to insert optional braces after control
|
|
statements.
|
|
|
|
clang-extdef-mapping
|
|
--------------------
|
|
|
|
- clang-extdef-mapping now accepts .ast files as input. This is faster than to
|
|
recompile the files from sources when extracting method definitons. This can
|
|
be really beneficial when creating .ast files for input to the clang-static-analyzer.
|
|
|
|
libclang
|
|
--------
|
|
|
|
- ...
|
|
|
|
Static Analyzer
|
|
---------------
|
|
- `New CTU implementation
|
|
<https://discourse.llvm.org/t/rfc-much-faster-cross-translation-unit-ctu-analysis-implementation/61728>`_
|
|
that keeps the slow-down around 2x compared to the single-TU analysis, even
|
|
in case of complex C++ projects. Still, it finds the majority of the "old"
|
|
CTU findings. Besides, not more than ~3% of the bug reports are lost compared
|
|
to single-TU analysis, the lost reports are highly likely to be false
|
|
positives.
|
|
|
|
- Added a new checker ``alpha.unix.cstring.UninitializedRead`` this will check for uninitialized reads
|
|
from common memory copy/manipulation functions such as ``memcpy``, ``mempcpy``, ``memmove``, ``memcmp``, `
|
|
`strcmp``, ``strncmp``, ``strcpy``, ``strlen``, ``strsep`` and many more. Although
|
|
this checker currently is in list of alpha checkers due to a false positive.
|
|
|
|
- Added a new checker ``alpha.unix.Errno``. This can find the first read
|
|
of ``errno`` after successful standard function calls, such use of ``errno``
|
|
could be unsafe.
|
|
|
|
- Deprecate the ``-analyzer-store region`` and
|
|
``-analyzer-opt-analyze-nested-blocks`` analyzer flags.
|
|
These flags are still accepted, but a warning will be displayed.
|
|
These flags will be rejected, thus turned into a hard error starting with
|
|
``clang-16``.
|
|
|
|
.. _release-notes-ubsan:
|
|
|
|
Undefined Behavior Sanitizer (UBSan)
|
|
------------------------------------
|
|
|
|
Core Analysis Improvements
|
|
==========================
|
|
|
|
- ...
|
|
|
|
New Issues Found
|
|
================
|
|
|
|
- ...
|
|
|
|
Python Binding Changes
|
|
----------------------
|
|
|
|
The following methods have been added:
|
|
|
|
- ...
|
|
|
|
Significant Known Problems
|
|
==========================
|
|
|
|
Additional Information
|
|
======================
|
|
|
|
A wide variety of additional information is available on the `Clang web
|
|
page <https://clang.llvm.org/>`_. The web page contains versions of the
|
|
API documentation which are up-to-date with the 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>`_.
|