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¶
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¶
C++23 Feature Support¶
C++2c Feature Support¶
Implemented P2169R4: A nice placeholder with no name. This allows using
_
as a variable name multiple times in the same scope and is supported in all C++ language modes as an extension. An extension warning is produced when multiple variables are introduced by_
in the same scope. Unused warnings are no longer produced for variables named_
. Currently, inspecting placeholders variables in a debugger when more than one are declared in the same scope is not supported.struct S { int _, _; // Was invalid, now OK }; void func() { int _, _; // Was invalid, now OK } void other() { int _; // Previously diagnosed under -Wunused, no longer diagnosed }
Attributes now expect unevaluated strings in attributes parameters that are string literals. This is applied to both C++ standard attributes, and other attributes supported by Clang. This completes the implementation of P2361R6 Unevaluated Strings
Resolutions to C++ Defect Reports¶
Implemented CWG1473 which allows spaces after
operator""
. Clang used to err on the lack of space when the literal suffix identifier was invalid in all the language modes, which contradicted the deprecation of the whitespaces. Also turn on-Wdeprecated-literal-operator
by default in all the language modes.
C Language Changes¶
structs
,unions
, andarrays
that are const may now be used as constant expressions. This change is more consistent with the behavior of GCC.
C23 Feature Support¶
Clang now accepts
-std=c23
and-std=gnu23
as language standard modes, and the__STDC_VERSION__
macro now expands to202311L
instead of its previous placeholder value. Clang continues to accept-std=c2x
and-std=gnu2x
as aliases for C23 and GNU C23, respectively.
Non-comprehensive list of changes in this release¶
New Compiler Flags¶
Deprecated Compiler Flags¶
Modified Compiler Flags¶
Removed Compiler Flags¶
Attribute Changes in Clang¶
Improvements to Clang’s diagnostics¶
Clang constexpr evaluator now prints template arguments when displaying template-specialization function calls.
Clang contexpr evaluator now displays notes as well as an error when a constructor of a base class is not called in the constructor of its derived class.
Clang no longer emits
-Wmissing-variable-declarations
for variables declared with theregister
storage class.Clang’s
-Wtautological-negation-compare
flag now diagnoses logical tautologies likex && !x
and!x || x
in expressions. This also makes-Winfinite-recursion
diagnose more cases. (#56035:).
Bug Fixes in This Version¶
Fixed an issue where a class template specialization whose declaration is instantiated in one module and whose definition is instantiated in another module may end up with members associated with the wrong declaration of the class, which can result in miscompiles in some cases.
Fix crash on use of a variadic overloaded operator. (#42535 <https://github.com/llvm/llvm-project/issues/42535>_)
Fix a hang on valid C code passing a function type as an argument to
typeof
to form a function declaration. (#64713 <https://github.com/llvm/llvm-project/issues/64713>_)Clang now respects
-fwrapv
and-ftrapv
for__builtin_abs
andabs
builtins. (#45129, #45794)
Bug Fixes to Compiler Builtins¶
Bug Fixes to Attribute Support¶
Bug Fixes to C++ Support¶
Clang limits the size of arrays it will try to evaluate at compile time to avoid memory exhaustion. This limit can be modified by -fconstexpr-steps. (#63562)
Fix a crash caused by some named unicode escape sequences designating a Unicode character whose name contains a
-
. (Fixes #64161)Fix cases where we ignore ambiguous name lookup when looking up memebers. (#22413), (#29942), (#35574) and (#27224).
Clang emits an error on substitution failure within lambda body inside a requires-expression. This fixes: (#64138).
Update
FunctionDeclBitfields.NumFunctionDeclBits
. This fixes: (#64171).
Bug Fixes to AST Handling¶
Fixed an import failure of recursive friend class template. Issue 64169
Remove unnecessary RecordLayout computation when importing UnaryOperator. The computed RecordLayout is incorrect if fields are not completely imported and should not be cached. Issue 64170
Miscellaneous Bug Fixes¶
Miscellaneous Clang Crashes Fixed¶
Fixed a crash when parsing top-level ObjC blocks that aren’t properly terminated. Clang should now also recover better when an @end is missing between blocks. Issue 64065
Fixed a crash when check array access on zero-length element. Issue 64564
Target Specific Changes¶
AMDGPU Support¶
Use pass-by-reference (byref) in stead of pass-by-value (byval) for struct arguments in C ABI. Callee is responsible for allocating stack memory and copying the value of the struct if modified. Note that AMDGPU backend still supports byval for struct arguments.
X86 Support¶
Arm and AArch64 Support¶
Windows Support¶
LoongArch Support¶
RISC-V Support¶
Unaligned memory accesses can be toggled by
-m[no-]unaligned-access
or the aliases-m[no-]strict-align
.
CUDA/HIP Language Changes¶
CUDA Support¶
AIX Support¶
WebAssembly Support¶
AVR Support¶
DWARF Support in Clang¶
Floating Point Support in Clang¶
Add
__builtin_elementwise_log
builtin for floating point types only.Add
__builtin_elementwise_log10
builtin for floating point types only.Add
__builtin_elementwise_log2
builtin for floating point types only.Add
__builtin_elementwise_exp
builtin for floating point types only.Add
__builtin_elementwise_exp2
builtin for floating point types only.Add
__builtin_set_flt_rounds
builtin for X86, x86_64, Arm and AArch64 only.Add
__builtin_elementwise_pow
builtin for floating point types only.Add
__builtin_elementwise_bitreverse
builtin for integer types only.Add
__builtin_elementwise_sqrt
builtin for floating point types only.
AST Matchers¶
Add
convertVectorExpr
.Add
dependentSizedExtVectorType
.Add
macroQualifiedType
.
clang-format¶
libclang¶
Exposed arguments of
clang::annotate
.
Static Analyzer¶
Added a new checker
core.BitwiseShift
which reports situations where bitwise shift operators produce undefined behavior (because some operand is negative or too large).
Sanitizers¶
-fsanitize=signed-integer-overflow
now instruments__builtin_abs
andabs
builtins.
Python Binding Changes¶
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).