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¶
The Objective-C ARC migrator (ARCMigrate) has been removed.
Fix missing diagnostics for uses of declarations when performing typename access, such as when performing member access on a ‘[[deprecated]]’ type alias. (#58547)
C/C++ Language Potentially Breaking Changes¶
C++ Specific Potentially Breaking Changes¶
The type trait builtin
__is_referenceable
has been removed, since it has very few users and all the type traits that could benefit from it in the standard library already have their own bespoke builtins.
ABI Changes in This Version¶
Return larger CXX records in memory instead of using AVX registers. Code compiled with older clang will be incompatible with newer version of the clang unless -fclang-abi-compat=20 is provided. (#120670)
AST Dumping Potentially Breaking Changes¶
Added support for dumping template arguments of structural value kinds.
Clang Frontend Potentially Breaking Changes¶
The
-Wglobal-constructors
flag now applies to[[gnu::constructor]]
and[[gnu::destructor]]
attributes.
Clang Python Bindings Potentially Breaking Changes¶
What’s New in Clang 15?¶
C++ Language Changes¶
C++2c Feature Support¶
Implemented P1061R10 Structured Bindings can introduce a Pack.
Implemented P0963R3 Structured binding declaration as a condition.
C++23 Feature Support¶
C++20 Feature Support¶
C++17 Feature Support¶
Resolutions to C++ Defect Reports¶
The flag -frelaxed-template-template-args and its negation have been removed, having been deprecated since the previous two releases. The improvements to template template parameter matching implemented in the previous release, as described in P3310 and P3579, made this flag unnecessary.
Implemented CWG2918 Consideration of constraints for address of overloaded ` `function
Bumped the
__cpp_constexpr
feature-test macro to202002L
in C++20 mode as indicated in P2493R0.
C Language Changes¶
Clang now allows an
inline
specifier on a typedef declaration of a function type in Microsoft compatibility mode. #124869Clang now allows
restrict
qualifier for array types with pointer elements (#92847).
C2y Feature Support¶
Implement WG14 N3409 which removes UB around use of
void
expressions. In practice, this means that_Generic
selection associations may now havevoid
type, but it also removes UB with code like(void)(void)1;
.Implemented WG14 N3411 which allows a source file to not end with a newline character. This is still reported as a conforming extension in earlier language modes.
C23 Feature Support¶
Non-comprehensive list of changes in this release¶
Support parsing the cc operand modifier and alias it to the c modifier (#127719).
Added __builtin_elementwise_exp10.
New Compiler Flags¶
New option
-Wundef-true
added and enabled by default to warn when true is used in the C preprocessor without being defined before C23.New option
-fprofile-continuous
added to enable continuous profile syncing to file (#124353, docs). The feature has existed) for a while and this is just a user facing option.
Deprecated Compiler Flags¶
Modified Compiler Flags¶
The ARM AArch32
-mtp
option accepts and defaults toauto
, a value ofauto
uses the best available method of providing the frame pointer supported by the hardware. This matches the behavior of-mtp
in gcc. This changes the default behavior for ARM targets that provide theTPIDRURO
register as this will be used instead of a call to the__aeabi_read_tp
. Programs that use__aeabi_read_tp
but do not use theTPIDRURO
register must use-mtp=soft
. Fixes #123864
Removed Compiler Flags¶
Attribute Changes in Clang¶
Adding [[clang::unsafe_buffer_usage]] attribute to a method definition now turns off all -Wunsafe-buffer-usage related warnings within the method body.
The
no_sanitize
attribute now accepts bothgnu
andclang
names.The
ext_vector_type(n)
attribute can now be used as a generic type attribute.Clang now diagnoses use of declaration attributes on void parameters. (#108819)
Clang now allows
__attribute__((model("small")))
and__attribute__((model("large")))
on non-TLS globals in x86-64 compilations. This forces the global to be considered small or large in regards to the x86-64 code model, regardless of the code model specified for the compilation.Clang now emits a warning
-Wreserved-init-priority
instead of a hard error when__attribute__((init_priority(n)))
is used with values of n in the reserved range [0, 100]. The warning will be treated as an error by default.There is a new
format_matches
attribute to complement the existingformat
attribute.format_matches
allows the compiler to verify that a format string argument is equivalent to a reference format string: it is useful when a function accepts a format string without its accompanying arguments to format. For instance:static int status_code; static const char *status_string; void print_status(const char *fmt) { fprintf(stderr, fmt, status_code, status_string); // ^ warning: format string is not a string literal [-Wformat-nonliteral] } void stuff(void) { print_status("%s (%#08x)\n"); // order of %s and %x is swapped but there is no diagnostic }
Before the introducion of
format_matches
, this code cannot be verified at compile-time.format_matches
plugs that hole:__attribute__((format_matches(printf, 1, "%x %s"))) void print_status(const char *fmt) { fprintf(stderr, fmt, status_code, status_string); // ^ `fmt` verified as if it was "%x %s" here; no longer triggers // -Wformat-nonliteral, would warn if arguments did not match "%x %s" } void stuff(void) { print_status("%s (%#08x)\n"); // warning: format specifier 's' is incompatible with 'x' // warning: format specifier 'x' is incompatible with 's' }
Like with
format
, the first argument is the format string flavor and the second argument is the index of the format string parameter.format_matches
accepts an example valid format string as its third argument. For more information, see the Clang attributes documentation.Introduced a new statement attribute
[[clang::atomic]]
that enables fine-grained control over atomic code generation on a per-statement basis. Supported options include[no_]remote_memory
,[no_]fine_grained_memory
, and[no_]ignore_denormal_mode
. These are particularly relevant for AMDGPU targets, where they map to corresponding IR metadata.
Improvements to Clang’s diagnostics¶
Improve the diagnostics for deleted default constructor errors for C++ class initializer lists that don’t explicitly list a class member and thus attempt to implicitly default construct that member.
The
-Wunique-object-duplication
warning has been added to warn about objects which are supposed to only exist once per program, but may get duplicated when built into a shared library.Fixed a bug where Clang’s Analysis did not correctly model the destructor behavior of
union
members (#119415).A statement attribute applied to a
case
label no longer suppresses ‘bypassing variable initialization’ diagnostics (#84072).The
-Wunsafe-buffer-usage
warning has been updated to warn about unsafe libc function calls. Those new warnings are emitted under the subgroup-Wunsafe-buffer-usage-in-libc-call
.Diagnostics on chained comparisons (
a < b < c
) are now an error by default. This can be disabled with-Wno-error=parentheses
.The
-Wshift-bool
warning has been added to warn about shifting a boolean. (#28334)Fixed diagnostics adding a trailing
::
when printing some source code constructs, like base classes.The Thread Safety Analysis now supports
-Wthread-safety-pointer
, which enables warning on passing or returning pointers to guarded variables as function arguments or return value respectively. Note that Thread Safety Analysis still does not perform alias analysis. The feature will be default-enabled with-Wthread-safety
in a future release.The
-Wsign-compare
warning now treats expressions with bitwise not(~) and minus(-) as signed integers except for the case where the operand is an unsigned integer and throws warning if they are compared with unsigned integers (##18878).Improve the diagnostics for chained comparisons to report actual expressions and operators (#129069).
Improve the diagnostics for shadows template parameter to report correct location (#129060).
Improvements to Clang’s time-trace¶
Improvements to Coverage Mapping¶
Bug Fixes in This Version¶
Clang now outputs correct values when #embed data contains bytes with negative signed char values (#102798).
Fixed a crash when merging named enumerations in modules (#114240).
Fixed rejects-valid problem when #embed appears in std::initializer_list or when it can affect template argument deduction (#122306).
Fix crash on code completion of function calls involving partial order of function templates (#125500).
Fixed clang crash when #embed data does not fit into an array (#128987).
Non-local variable and non-variable declarations in the first clause of a
for
loop in C are no longer incorrectly considered an error in C23 mode and are allowed as an extension in earlier language modes.Remove the
static
specifier for the value of_FUNCTION_
for static functions, in MSVC compatibility mode.
Bug Fixes to Compiler Builtins¶
The behvaiour of
__add_pointer
and__remove_pointer
for Objective-C++’sid
and interfaces has been fixed.
Bug Fixes to Attribute Support¶
Fixed crash when a parameter to the
clang::annotate
attribute evaluates tovoid
. See #119125
Clang now emits a warning instead of an error when using the one or two argument form of GCC 11’s
__attribute__((malloc(deallocator)))
or__attribute__((malloc(deallocator, ptr-index)))
(#51607).
Bug Fixes to C++ Support¶
Clang now diagnoses copy constructors taking the class by value in template instantiations. (#130866)
Clang is now better at keeping track of friend function template instance contexts. (#55509)
Clang now prints the correct instantiation context for diagnostics suppressed by template argument deduction.
Clang is now better at instantiating the function definition after its use inside of a constexpr lambda. (#125747)
The initialization kind of elements of structured bindings direct-list-initialized from an array is corrected to direct-initialization.
Clang no longer crashes when a coroutine is declared
[[noreturn]]
. (#127327)Clang now uses the parameter location for abbreviated function templates in
extern "C"
. (#46386)Clang will emit an error instead of crash when use co_await or co_yield in C++26 braced-init-list template parameter initialization. (#78426)
Fixes matching of nested template template parameters. (#130362)
Correctly diagnoses template template paramters which have a pack parameter not in the last position.
Clang now correctly parses
if constexpr
expressions in immediate function context. (#123524)Fixed an assertion failure affecting code that uses C++23 “deducing this”. (#130272)
Clang now properly instantiates destructors for initialized members within non-delegating constructors. (#93251)
Bug Fixes to AST Handling¶
Miscellaneous Bug Fixes¶
HTML tags in comments that span multiple lines are now parsed correctly by Clang’s comment parser. (#120843)
Miscellaneous Clang Crashes Fixed¶
OpenACC Specific Changes¶
Target Specific Changes¶
AMDGPU Support¶
NVPTX Support¶
Hexagon Support¶
The default compilation target has been changed from V60 to V68.
X86 Support¶
Disable
-m[no-]avx10.1
and switch-m[no-]avx10.2
to alias of 512 bit options.Change
-mno-avx10.1-512
to alias of-mno-avx10.1-256
to disable both 256 and 512 bit instructions.
Arm and AArch64 Support¶
Android Support¶
Windows Support¶
Clang now defines
_CRT_USE_BUILTIN_OFFSETOF
macro in MSVC-compatible mode, which makesoffsetof
provided by Microsoft’s<stddef.h>
to be defined correctly. (#59689)
LoongArch Support¶
RISC-V Support¶
Add support for -mtune=generic-ooo (a generic out-of-order model).
CUDA/HIP Language Changes¶
CUDA Support¶
AIX Support¶
NetBSD Support¶
WebAssembly Support¶
AVR Support¶
DWARF Support in Clang¶
Floating Point Support in Clang¶
Fixed Point Support in Clang¶
AST Matchers¶
Ensure
isDerivedFrom
matches the correct base in case more than one alias exists.Extend
templateArgumentCountIs
to support function and variable template specialization.
clang-format¶
Adds
BreakBeforeTemplateCloser
option.Adds
BinPackLongBracedList
option to override bin packing options in long (20 item or more) braced list initializer lists.Add the C language instead of treating it like C++.
Allow specifying the language (C, C++, or Objective-C) for a
.h
file by adding a special comment (e.g.// clang-format Language: ObjC
) near the top of the file.
libclang¶
Added
clang_visitCXXMethods
, which allows visiting the methods of a class.Fixed a buffer overflow in
CXString
implementation. The fix may result in increased memory allocation.
Code Completion¶
Static Analyzer¶
New features¶
A new flag - -static-libclosure was introduced to support statically linking the runtime for the Blocks extension on Windows. This flag currently only changes the code generation, and even then, only on Windows. This does not impact the linker behaviour like the other -static-* flags.
Crash and bug fixes¶
Improvements¶
Moved checkers¶
After lots of improvements, the checker
alpha.security.ArrayBoundV2
is renamed tosecurity.ArrayBound
. As this checker is stable now, the old checkeralpha.security.ArrayBound
(which was searching for the same kind of bugs with an different, simpler and less accurate algorithm) is removed.
Sanitizers¶
-fsanitize=vptr
is no longer a part of-fsanitize=undefined
.
Python Binding Changes¶
Added
Type.get_methods
, a binding forclang_visitCXXMethods
, which allows visiting the methods of a class.
OpenMP Support¶
Added support ‘no_openmp_constructs’ assumption clause.
Added support for ‘self_maps’ in map and requirement clause.
Added support for ‘omp stripe’ directive.
Improvements¶
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).