Clang 15 |ReleaseNotesTitle|¶
Written by the LLVM Team
Introduction¶
This document contains the release notes for the Clang C/C++/Objective-C frontend, part of the LLVM Compiler Infrastructure, release 15. 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. For the libc++ release notes, see this page. All LLVM releases may be downloaded from the LLVM releases web site.
For more information about Clang or LLVM, including information about the latest release, please see the Clang Web Site or the LLVM Web Site.
Potentially Breaking Changes¶
These changes are ones which we think may surprise users when upgrading to Clang 15 because of the opportunity they pose for disruption to existing code bases.
C/C++ Language Potentially Breaking Changes¶
C++ Specific Potentially Breaking Changes¶
ABI Changes in This Version¶
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 toArrayRef<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
.
What’s New in Clang 15?¶
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++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’. (#79240).
Implemented the __is_layout_compatible intrinsic to support P0466R5: Layout-compatibility and Pointer-interconvertibility Traits.
C++23 Feature Support¶
Implemented P2718R0: Lifetime extension in range-based for loops. Also materialize temporary object which is a prvalue in discarded-value expression.
C++2c Feature Support¶
Implemented P2662R3 Pack Indexing.
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. (#78449:).
Type qualifications are now ignored when evaluating layout compatibility of two types. (CWG1719: Layout compatibility and cv-qualification revisited).
[[no_unique_address]]
is now respected when evaluating layout compatibility of two types. (CWG2759: [[no_unique_address] and common initial sequence).
C Language Changes¶
C23 Feature Support¶
No longer diagnose use of binary literals as an extension in C23 mode. Fixes #72017.
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: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 (#81472).
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 asPRIb8
. (#81896:).
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.
New Compiler Flags¶
Deprecated Compiler Flags¶
Modified Compiler Flags¶
Removed Compiler Flags¶
The
-freroll-loops
flag has been removed. It had no effect since Clang 13.
Attribute Changes in Clang¶
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 #69444.
- The
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 thewb
oruwb
suffix. The maximal underlying type is currentlyunsigned long long
, but this behavior may change in the future when Clang implements WG14 N3029. Fixes #69352.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 #82512.
Improvements to Clang’s time-trace¶
Bug Fixes in This Version¶
Fixed missing warnings when comparing mismatched enumeration constants in C (#29217 <https://github.com/llvm/llvm-project/issues/29217>).
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 (#79435).
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 (#71976)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 (#64356).
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 (#79518).
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. Fixes (#10518), (#67914), and (#78388)
Fix crash when using lifetimebound attribute in function with trailing return. Fixes (#73619)
Addressed an issue where constraints involving injected class types are perceived distinct from its specialization types. (#56482)
Fixed a bug where variables referenced by requires-clauses inside nested generic lambdas were not properly injected into the constraint scope. (#73418)
Fixed a crash where substituting into a requires-expression that refers to function parameters during the equivalence determination of two constraint expressions. (#74447)
Fixed deducing auto& from const int in template parameters of partial specializations. (#77189)
Fix for crash when using a erroneous type in a return statement. Fixes (#63244) and (#79745)
Fixed an out-of-bounds error caused by building a recovery expression for ill-formed function calls while substituting into constraints. (#58548)
Fix incorrect code generation caused by the object argument of
static operator()
andstatic operator[]
calls not being evaluated. Fixes (#67976)Fix crash and diagnostic with const qualified member operator new. Fixes (#79748)
Fixed a crash where substituting into a requires-expression that involves parameter packs during the equivalence determination of two constraint expressions. (#72557)
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. Fixes (#68490)
Fix a crash when trying to call a varargs function that also has an explicit object parameter. Fixes (#80971 ICE when explicit object parameter be a function parameter pack)
Reject explicit object parameters on new and delete operators. Fixes (#82249 <https://github.com/llvm/llvm-project/issues/82249> _)
Fixed a bug where abbreviated function templates would append their invented template parameters to an empty template parameter lists.
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. Fixes some of (#80510 <https://github.com/llvm/llvm-project/issues/80510>).
Clang now ignores top-level cv-qualifiers on function parameters in template partial orderings. (#75404)
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. (#82154 <https://github.com/llvm/llvm-project/issues/82154>`_)
Fix crash when using an immediate-escalated function at global scope. (#82258)
Correctly immediate-escalate lambda conversion functions. (#82258)
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. (#78524)
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. (#53815)In
__restrict
-qualified member functions, attach__restrict
to the pointer type ofthis
rather than the pointee type. Fixes (#82941), (#42411), and (#18121).Clang now properly reports supported C++11 attributes when using
__has_cpp_attribute
and parses attributes with arguments in C++03 (#82995)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 (#83461)
Bug Fixes to AST Handling¶
Miscellaneous Bug Fixes¶
Miscellaneous Clang Crashes Fixed¶
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
ortarget_clones
.
Android Support¶
Windows Support¶
LoongArch Support¶
RISC-V Support¶
__attribute__((rvv_vector_bits(N)))
is now supported for RVV vbool*_t types.
CUDA/HIP Language Changes¶
CUDA Support¶
AIX Support¶
WebAssembly Support¶
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.
AST Matchers¶
isInStdNamespace
now supports Decl declared withextern "C++"
.
clang-format¶
AlwaysBreakTemplateDeclarations
is deprecated and renamed toBreakTemplateDeclarations
.AlwaysBreakAfterReturnType
is deprecated and renamed toBreakAfterReturnType
.
libclang¶
Static Analyzer¶
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 variousTypeLoc
-related nodes.
Moved checkers¶
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
Python Binding Changes¶
Exposed CXRewriter API as class Rewriter.
Additional Information¶
A wide variety of additional information is available on the Clang web
page. 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).