=========================================== Clang |release| |ReleaseNotesTitle| =========================================== .. contents:: :local: :depth: 2 Written by the `LLVM Team `_ .. 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 `_. 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 `_. 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 |release| because of the opportunity they pose for disruption to existing code bases. C/C++ Language Potentially Breaking Changes ------------------------------------------- - Indirect edges of asm goto statements under certain circumstances may now be split. In previous releases of clang, that means for the following code the two inputs may have compared equal in the inline assembly. This is no longer guaranteed (and necessary to support outputs along indirect edges, which is now supported as of this release). This change is more consistent with the behavior of GCC. .. code-block:: c foo: asm goto ("# %0 %1"::"i"(&&foo)::foo); C++ Specific Potentially Breaking Changes ----------------------------------------- - Clang won't search for coroutine_traits in std::experimental namespace any more. Clang will only search for std::coroutine_traits for coroutines then. ABI Changes in This Version --------------------------- - ``__is_trivial`` has changed for a small category of classes with constrained default constructors (`#60697 `_). *FIXME: Remove this note if we've backported this change to the Clang 16 branch.* 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 -------------------- - Improved ``-O0`` code generation for calls to ``std::forward_like``. Similarly to ``std::move, std::forward`` et al. it is now treated as a compiler builtin and implemented directly rather than instantiating the definition from the standard library. - Implemented `CWG2518 `_ which allows ``static_assert(false)`` to not be ill-formed when its condition is evaluated in the context of a template definition. C++20 Feature Support ^^^^^^^^^^^^^^^^^^^^^ - Support for out-of-line definitions of constrained templates has been improved. This partially fixes `#49620 `_. - Lambda templates with a requires clause directly after the template parameters now parse correctly if the requires clause consists of a variable with a dependent type. (`#61278 `_) - Announced C++20 Coroutines is fully supported on all targets except Windows, which still has some stability and ABI issues. - Downgraded use of a reserved identifier in a module export declaration from an error to a warning under the ``-Wreserved-module-identifier`` warning group. This warning is enabled by default. This addresses `#61446 `_ and allows easier building of standard modules. This diagnostic may be strengthened into an error again in the future once there is a less fragile way to mark a module as being part of the implementation rather than a user module. C++2b Feature Support ^^^^^^^^^^^^^^^^^^^^^ - Implemented `P2036R3: Change scope of lambda trailing-return-type `_ and `P2579R0 Mitigation strategies for P2036 `_. These proposals modify how variables captured in lambdas can appear in trailing return type expressions and how their types are deduced therein, in all C++ language versions. Resolutions to C++ Defect Reports ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - Implemented `DR2397 `_ which allows ``auto`` specifier for pointers and reference to arrays. C Language Changes ------------------ - Support for outputs from asm goto statements along indirect edges has been added. (`#53562 `_) - Fixed a bug that prevented initialization of an ``_Atomic``-qualified pointer from a null pointer constant. - Fixed a bug that prevented casting to an ``_Atomic``-qualified type. (`#39596 `_) C2x Feature Support ^^^^^^^^^^^^^^^^^^^ - Implemented the ``unreachable`` macro in freestanding ```` for `WG14 N2826 `_ - Removed the ``ATOMIC_VAR_INIT`` macro in C2x and later standards modes, which implements `WG14 N2886 `_ - Implemented `WG14 N2934 `_ which introduces the ``bool``, ``static_assert``, ``alignas``, ``alignof``, and ``thread_local`` keywords in C2x. - Implemented `WG14 N2900 `_ and `WG14 N3011 `_ which allows for empty braced initialization in C. .. code-block:: c struct S { int x, y } s = {}; // Initializes s.x and s.y to 0 As part of this change, the ``-Wgnu-empty-initializer`` warning group was removed, as this is no longer a GNU extension but a C2x extension. You can use ``-Wno-c2x-extensions`` to silence the extension warning instead. - Updated the implementation of `WG14 N3042 `_ based on decisions reached during the WG14 CD Ballot Resolution meetings held in Jan and Feb 2023. This should complete the implementation of ``nullptr`` and ``nullptr_t`` in C. The specific changes are: .. code-block:: c void func(nullptr_t); func(0); // Previously required to be rejected, is now accepted. func((void *)0); // Previously required to be rejected, is now accepted. nullptr_t val; val = 0; // Previously required to be rejected, is now accepted. val = (void *)0; // Previously required to be rejected, is now accepted. bool b = nullptr; // Was incorrectly rejected by Clang, is now accepted. Non-comprehensive list of changes in this release ------------------------------------------------- - Clang now saves the address of ABI-indirect function parameters on the stack, improving the debug information available in programs compiled without optimizations. - Clang now supports ``__builtin_nondeterministic_value`` that returns a nondeterministic value of the same type as the provided argument. - Clang now supports ``__builtin_FILE_NAME()`` which returns the same information as the ``__FILE_NAME__`` macro (the presumed file name from the invocation point, with no path components included). - Clang now supports ``__builtin_assume_separate_storage`` that indicates that its arguments point to objects in separate storage allocations. - Clang now supports expressions in ``#pragma clang __debug dump``. - Clang now supports declaration of multi-dimensional arrays with ``__declspec(property)``. - A new builtin type trait ``__is_trivially_equaltiy_comparable`` has been added, which checks whether comparing two instances of a type is equivalent to ``memcmp(&lhs, &rhs, sizeof(T)) == 0``. - Clang now ignores null directives outside of the include guard when deciding whether a file can be enabled for the multiple-include optimization. New Compiler Flags ------------------ Deprecated Compiler Flags ------------------------- Modified Compiler Flags ----------------------- Removed Compiler Flags ------------------------- - The deprecated flag `-fmodules-ts` is removed. Please use ``-std=c++20`` or higher to use standard C++ modules instead. - The deprecated flag `-fcoroutines-ts` is removed. Please use ``-std=c++20`` or higher to use standard C++ coroutines instead. - The CodeGen flag `-lower-global-dtors-via-cxa-atexit` which affects how global destructors are lowered for MachO is removed without replacement. The default of `-lower-global-dtors-via-cxa-atexit=true` is now the only supported way. Attribute Changes in Clang -------------------------- - Introduced a new function attribute ``__attribute__((unsafe_buffer_usage))`` to be worn by functions containing buffer operations that could cause out of bounds memory accesses. It emits warnings at call sites to such functions when the flag ``-Wunsafe-buffer-usage`` is enabled. - ``__declspec`` attributes can now be used together with the using keyword. Before the attributes on ``__declspec`` was ignored, while now it will be forwarded to the point where the alias is used. - Introduced a new ``USR`` (unified symbol resolution) clause inside of the existing ``__attribute__((external_source_symbol))`` attribute. Clang's indexer uses the optional USR value when indexing Clang's AST. This value is expected to be generated by an external compiler when generating C++ bindings during the compilation of the foreign language sources (e.g. Swift). - The ``__has_attribute``, ``__has_c_attribute`` and ``__has_cpp_attribute`` preprocessor operators now return 1 also for attributes defined by plugins. Improvements to Clang's diagnostics ----------------------------------- - We now generate a diagnostic for signed integer overflow due to unary minus in a non-constant expression context. (`#31643 `_) - Clang now warns by default for C++20 and later about deprecated capture of ``this`` with a capture default of ``=``. This warning can be disabled with ``-Wno-deprecated-this-capture``. - Clang had failed to emit some ``-Wundefined-internal`` for members of a local class if that class was first introduced with a forward declaration. - Diagnostic notes and fix-its are now generated for ``ifunc``/``alias`` attributes which point to functions whose names are mangled. - Diagnostics relating to macros on the command line of a preprocessed assembly file or precompiled header are now reported as coming from the file ```` instead of ````. - Clang constexpr evaluator now provides a more concise diagnostic when calling function pointer that is known to be null. - Clang now avoids duplicate warnings on unreachable ``[[fallthrough]];`` statements previously issued from ``-Wunreachable-code`` and ``-Wunreachable-code-fallthrough`` by prioritizing ``-Wunreachable-code-fallthrough``. - Clang now correctly diagnoses statement attributes ``[[clang::always_inine]]`` and ``[[clang::noinline]]`` when used on a statement with dependent call expressions. - Clang now checks for completeness of the second and third arguments in the conditional operator. (`#59718 `_) - There were some cases in which the diagnostic for the unavailable attribute might not be issued, this fixes those cases. (`61815 `_) - Clang now avoids unnecessary diagnostic warnings for obvious expressions in the case of binary operators with logical OR operations. (`#57906 `_) - Clang's "static assertion failed" diagnostic now points to the static assertion expression instead of pointing to the ``static_assert`` token. (`#61951 `_) - ``-Wformat`` now recognizes ``%lb`` for the ``printf``/``scanf`` family of functions. (`#62247: `_). - Clang now diagnoses shadowing of lambda's template parameter by a capture. (`#61105: `_). Bug Fixes in This Version ------------------------- - Fix segfault while running clang-rename on a non existing file. (`#36471 `_) - Fix crash when diagnosing incorrect usage of ``_Nullable`` involving alias templates. (`#60344 `_) - Fix confusing warning message when ``/clang:-x`` is passed in ``clang-cl`` driver mode and emit an error which suggests using ``/TC`` or ``/TP`` ``clang-cl`` options instead. (`#59307 `_) - Fix assert that fails when the expression causing the this pointer to be captured by a block is part of a constexpr if statement's branch and instantiation of the enclosing method causes the branch to be discarded. - Fix __VA_OPT__ implementation so that it treats the concatenation of a non-placemaker token and placemaker token as a non-placemaker token. (`#60268 `_) - Fix crash when taking the address of a consteval lambda call operator. (`#57682 `_) - Clang now support export declarations in the language linkage. (`#60405 `_) - Fix aggregate initialization inside lambda constexpr. (`#60936 `_) - No longer issue a false positive diagnostic about a catch handler that cannot be reached despite being reachable. This fixes `#61177 `_ in anticipation of `CWG2699 _` being accepted by WG21. - Fix crash when parsing fold expression containing a delayed typo correction. (`#61326 `_) - Fix crash when dealing with some member accesses outside of class or member function context. (`#37792 `_) and (`#48405 `_) - Fix crash when using ``[[clang::always_inline]]`` or ``[[clang::noinline]]`` statement attributes on a call to a template function in the body of a template function. - Fix coroutines issue where ``get_return_object()`` result was always eargerly converted to the return type. Eager initialization (allowing RVO) is now only perfomed when these types match, otherwise deferred initialization is used, enabling short-circuiting coroutines use cases. This fixes (`#56532 `_) in antecipation of `CWG2563 _`. - Fix highlighting issue with ``_Complex`` and initialization list with more than 2 items. (`#61518 `_) - Fix ``getSourceRange`` on ``VarTemplateSpecializationDecl`` and ``VarTemplatePartialSpecializationDecl``, which represents variable with the initializer, so it behaves consistently with other ``VarDecls`` and ends on the last token of initializer, instead of right angle bracket of the template argument list. - Fix false-positive diagnostic issued for consteval initializers of temporary objects. (`#60286 `_) - Correct restriction of trailing requirements clauses on a templated function. Previously we only rejected non-'templated' things, but the restrictions ALSO need to limit non-defined/non-member functions as well. Additionally, we now diagnose requires on lambdas when not allowed, which we previously missed. (`#61748 `_) - Fix confusing diagnostic for incorrect use of qualified concepts names. - Fix handling of comments in function like macros so they are ignored in -CC mode. (`#60887 `_) - Fix incorrect merging of lambdas across modules. (`#60985 `_) - Fix crash when handling nested immediate invocations in initializers of global variables. (`#58207 `_) - Fix crash when generating code coverage information for `PseudoObjectExpr` in Clang AST. (`#45481 `_) - Fix the assertion hit when a template consteval function appears in a nested consteval/constexpr call chain. (`#61142 `_) - Clang now better diagnose placeholder types constrained with a concept that is not a type concept. - Fix crash when a doc comment contains a line splicing. (`#62054 `_) - Work around with a clang coverage crash which happens when visiting expressions/statements with invalid source locations in non-assert builds. Assert builds may still see assertions triggered from this. - Fix a failed assertion due to an invalid source location when trying to form a coverage report for an unresolved constructor expression. (`#62105 `_) - Fix defaulted equality operator so that it does not attempt to compare unnamed bit-fields. This fixes: (`#61355 `_) and (`#61417 `_) - Fix crash after suggesting typo correction to constexpr if condition. (`#61885 `_) - Clang constexpr evaluator now treats comparison of [[gnu::weak]]-attributed member pointer as an invalid expression. - Fix crash when member function contains invalid default argument. (`#62122 `_) - Fix crash when handling undefined template partial specialization (`#61356 `_) - Fix premature substitution into the constraints of an inherited constructor. - Fix crash when attempting to perform parenthesized initialization of an aggregate with a base class with only non-public constructors. (`#62296 `_) - Fix a stack overflow issue when evaluating ``consteval`` default arguments. (`#60082` `_) - Fix the assertion hit when generating code for global variable initializer of _BitInt(1) type. (`#62207 `_) - Fix lambdas and other anonymous function names not respecting ``-fdebug-prefix-map`` (`#62192 `_) Bug Fixes to Compiler Builtins ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Bug Fixes to Attribute Support ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - Fixed a bug where attribute annotations on type specifiers (enums, classes, structs, unions, and scoped enums) were not properly ignored, resulting in misleading warning messages. Now, such attribute annotations are correctly ignored. (`#61660 `_) Bug Fixes to C++ Support ^^^^^^^^^^^^^^^^^^^^^^^^ - Fix crash on invalid code when looking up a destructor in a templated class inside a namespace. (`#59446 `_) - Fix crash when evaluating consteval constructor of derived class whose base has more than one field. (`#60166 `_) - Fix an issue about ``decltype`` in the members of class templates derived from templates with related parameters. (`#58674 `_) - Fix incorrect deletion of the default constructor of unions in some cases. (`#48416 `_) - No longer issue a pre-C++2b compatibility warning in ``-pedantic`` mode regading overloaded `operator[]` with more than one parmeter or for static lambdas. (`#61582 `_) - Stop stripping CV qualifiers from the type of ``this`` when capturing it by value in a lambda. (`#50866 `_) - Fix ordering of function templates by constraints when they have template template parameters with different nested constraints. - Fix type equivalence comparison between auto types to take constraints into account. - Fix bug in the computation of the ``__has_unique_object_representations`` builtin for types with unnamed bitfields. (`#61336 `_) - Fix default member initializers sometimes being ignored when performing parenthesized aggregate initialization of templated types. (`#62266 `_) - Fix overly aggressive lifetime checks for parenthesized aggregate initialization. (`#61567 `_) - Fix a crash when expanding a pack as the index of a subscript expression. Bug Fixes to AST Handling ^^^^^^^^^^^^^^^^^^^^^^^^^ Miscellaneous Bug Fixes ^^^^^^^^^^^^^^^^^^^^^^^ Miscellaneous Clang Crashes Fixed ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - Dumping the AST to JSON no longer causes a failed assertion when targetting the Microsoft ABI and the AST to be dumped contains dependent names that would not typically be mangled. (`#61440 `_) Target Specific Changes ----------------------- AMDGPU Support ^^^^^^^^^^^^^^ - Linking for AMDGPU now uses ``--no-undefined`` by default. This causes undefined symbols in the created module to be a linker error. To prevent this, pass ``-Wl,--undefined`` if compiling directly, or ``-Xoffload-linker --undefined`` if using an offloading language. - The deprecated ``-mcode-object-v3`` and ``-mno-code-object-v3`` command-line options have been removed. X86 Support ^^^^^^^^^^^ - Add ISA of ``AMX-COMPLEX`` which supports ``tcmmimfp16ps`` and ``tcmmrlfp16ps``. Arm and AArch64 Support ^^^^^^^^^^^^^^^^^^^^^^^ - The hard-float ABI is now available in Armv8.1-M configurations that have integer MVE instructions (and therefore have FP registers) but no scalar or vector floating point computation. Previously, trying to select the hard-float ABI on such a target (via ``-mfloat-abi=hard`` or a triple ending in ``hf``) would silently use the soft-float ABI instead. - Clang builtin ``__arithmetic_fence`` and the command line option ``-fprotect-parens`` are now enabled for AArch64. - Clang supports flag output operands by which conditions in the NZCV could be outputs of inline assembly for AArch64. This change is more consistent with the behavior of GCC. .. code-block:: c // int a = foo(); int* b = bar(); asm("ands %w[a], %w[a], #3" : [a] "+r"(a), "=@cceq"(*b)); - Fix a crash when ``preserve_all`` calling convention is used on AArch64. `Issue 58145 `_ Windows Support ^^^^^^^^^^^^^^^ LoongArch Support ^^^^^^^^^^^^^^^^^ - Patchable function entry (``-fpatchable-function-entry``) is now supported on LoongArch. RISC-V Support ^^^^^^^^^^^^^^ - Added ``-mrvv-vector-bits=`` option to give an upper and lower bound on vector length. Valid values are powers of 2 between 64 and 65536. A value of 32 should eventually be supported. We also accept "zvl" to use the Zvl*b extension from ``-march`` or ``-mcpu`` to the be the upper and lower bound. - Fixed incorrect ABI lowering of ``_Float16`` in the case of structs containing ``_Float16`` that are eligible for passing via GPR+FPR or FPR+FPR. - Removed support for ``__attribute__((interrupt("user")))``. User-level interrupts are not in version 1.12 of the privileged specification. - Added ``attribute(riscv_rvv_vector_bits(__riscv_v_fixed_vlen))`` to allow the size of a RVV (RISC-V Vector) scalable type to be specified. This allows RVV scalable vector types to be used in structs or in global variables. CUDA/HIP Language Changes ^^^^^^^^^^^^^^^^^^^^^^^^^ CUDA Support ^^^^^^^^^^^^ AIX Support ^^^^^^^^^^^ - Add an AIX-only link-time option, `-mxcoff-build-id=0xHEXSTRING`, to allow users to embed a hex id in their binary such that it's readable by the program itself. This option is an alternative to the `--build-id=0xHEXSTRING` GNU linker option which is currently not supported by the AIX linker. WebAssembly Support ^^^^^^^^^^^^^^^^^^^ AVR Support ^^^^^^^^^^^ - The definition of ``USHRT_MAX`` in the freestanding ```` no longer overflows on AVR (where ``sizeof(int) == sizeof(unsigned short)``). The type of ``USHRT_MAX`` is now ``unsigned int`` instead of ``int``, as required by the C standard. 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. AST Matchers ------------ - Add ``coroutineBodyStmt`` matcher. - The ``hasBody`` matcher now matches coroutine body nodes in ``CoroutineBodyStmts``. clang-format ------------ - Add ``NextLineOnly`` style to option ``PackConstructorInitializers``. Compared to ``NextLine`` style, ``NextLineOnly`` style will not try to put the initializers on the current line first, instead, it will try to put the initializers on the next line only. - Add additional Qualifier Ordering support for special cases such as templates, requires clauses, long qualified names. - Fix all known issues associated with ``LambdaBodyIndentation: OuterScope``. - Add ``BracedInitializerIndentWidth`` which can be used to configure the indentation level of the contents of braced init lists. libclang -------- - Introduced the new function ``clang_CXXMethod_isExplicit``, which identifies whether a constructor or conversion function cursor was marked with the explicit identifier. - Introduced the new ``CXIndex`` constructor function ``clang_createIndexWithOptions``, which allows storing precompiled preambles in memory or overriding the precompiled preamble storage path. - Deprecated two functions ``clang_CXIndex_setGlobalOptions`` and ``clang_CXIndex_setInvocationEmissionPathOption`` in favor of the new function ``clang_createIndexWithOptions`` in order to improve thread safety. - Added check in ``clang_getFieldDeclBitWidth`` for whether a bit-field has an evaluable bit width. Fixes undefined behavior when called on a bit-field whose width depends on a template paramter. Static Analyzer --------------- - Fix incorrect alignment attribute on the this parameter of certain non-complete destructors when using the Microsoft ABI. (`#60465 `_) .. _release-notes-sanitizers: Sanitizers ---------- Python Binding Changes ---------------------- The following methods have been added: - ``clang_Location_isInSystemHeader`` exposed via the ``is_in_system_header`` property of the `Location` class. 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) `_.