| ======================================== |
| Clang 12.0.0 (In-Progress) Release Notes |
| ======================================== |
| |
| .. contents:: |
| :local: |
| :depth: 2 |
| |
| Written by the `LLVM Team <https://llvm.org/>`_ |
| |
| .. warning:: |
| |
| These are in-progress notes for the upcoming Clang 12 release. |
| Release notes for previous releases can be found on |
| `the Download Page <https://releases.llvm.org/download.html>`_. |
| |
| Introduction |
| ============ |
| |
| This document contains the release notes for the Clang C/C++/Objective-C |
| frontend, part of the LLVM Compiler Infrastructure, release 12.0.0. 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 <https://llvm.org/docs/ReleaseNotes.html>`_. All LLVM |
| releases may be downloaded from the `LLVM releases web |
| site <https://llvm.org/releases/>`_. |
| |
| For more information about Clang or LLVM, including information about the |
| latest release, please see the `Clang Web Site <https://clang.llvm.org>`_ or the |
| `LLVM Web Site <https://llvm.org>`_. |
| |
| Note that if you are reading this file from a Git checkout or the |
| main Clang web page, this document applies to the *next* release, not |
| the current one. To see the release notes for a specific release, please |
| see the `releases page <https://llvm.org/releases/>`_. |
| |
| What's New in Clang 12.0.0? |
| =========================== |
| |
| 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. |
| |
| Major New Features |
| ------------------ |
| |
| - ... |
| |
| Improvements to Clang's diagnostics |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| - ... |
| |
| Non-comprehensive list of changes in this release |
| ------------------------------------------------- |
| |
| - The builtin intrinsics ``__builtin_bitreverse8``, ``__builtin_bitreverse16``, |
| ``__builtin_bitreverse32`` and ``__builtin_bitreverse64`` may now be used |
| within constant expressions. |
| |
| - The builtin intrinsics ``__builtin_rotateleft8``, ``__builtin_rotateleft16``, |
| ``__builtin_rotateleft32`` and ``__builtin_rotateleft64`` may now be used |
| within constant expressions. |
| |
| - The builtin intrinsics ``__builtin_rotateright8``, ``__builtin_rotateright16``, |
| ``__builtin_rotateright32`` and ``__builtin_rotateright64`` may now be used |
| within constant expressions. |
| |
| New Compiler Flags |
| ------------------ |
| |
| - ... |
| |
| - AArch64 options ``-moutline-atomics``, ``-mno-outline-atomics`` to enable |
| and disable calls to helper functions implementing atomic operations. These |
| out-of-line helpers like '__aarch64_cas8_relax' will detect at runtime |
| AArch64 Large System Extensions (LSE) availability and either use their |
| atomic instructions, or falls back to LL/SC loop. These options do not apply |
| if the compilation target supports LSE. Atomic instructions are used directly |
| in that case. The option's behaviour mirrors GCC, the helpers are implemented |
| both in compiler-rt and libgcc. |
| |
| - New option ``-fbinutils-version=`` specifies the targeted binutils version. |
| For example, ``-fbinutils-version=2.35`` means compatibility with GNU as/ld |
| before 2.35 is not needed: new features can be used and there is no need to |
| work around old GNU as/ld bugs. |
| |
| Deprecated Compiler Flags |
| ------------------------- |
| |
| The following options are deprecated and ignored. They will be removed in |
| future versions of Clang. |
| |
| - The clang-cl ``/fallback`` flag, which made clang-cl invoke Microsoft Visual |
| C++ on files it couldn't compile itself, has been deprecated. It will be |
| removed in Clang 13. |
| |
| - ... |
| |
| Modified Compiler Flags |
| ----------------------- |
| |
| - On ELF, ``-gz`` now defaults to ``-gz=zlib`` with the integrated assembler. |
| It produces ``SHF_COMPRESSED`` style compression of debug information. GNU |
| binutils 2.26 or newer, or lld is required to link produced object files. Use |
| ``-gz=zlib-gnu`` to get the old behavior. |
| - Now that `this` pointers are tagged with `nonnull` and `dereferenceable(N)`, |
| `-fno-delete-null-pointer-checks` has gained the power to remove the |
| `nonnull` attribute on `this` for configurations that need it to be nullable. |
| - ``-gsplit-dwarf`` no longer implies ``-g2``. |
| - ``-fasynchronous-unwind-tables`` is now the default on Linux AArch64/PowerPC. |
| This behavior matches newer GCC. |
| (`D91760 <https://reviews.llvm.org/D91760>`_) |
| (`D92054 <https://reviews.llvm.org/D92054>`_) |
| - Support has been added for the following processors (command-line identifiers |
| in parentheses): |
| |
| - Arm Cortex-A78C (cortex-a78c). |
| - Arm Cortex-R82 (cortex-r82). |
| - Arm Neoverse V1 (neoverse-v1). |
| - Arm Neoverse N2 (neoverse-n2). |
| - Fujitsu A64FX (a64fx). |
| For example, to select architecture support and tuning for Neoverse-V1 based |
| systems, use ``-mcpu=neoverse-v1``. |
| |
| Removed Compiler Flags |
| ------------------------- |
| |
| The following options no longer exist. |
| |
| - clang-cl's ``/Zd`` flag no longer exist. But ``-gline-tables-only`` still |
| exists and does the same thing. |
| |
| New Pragmas in Clang |
| -------------------- |
| |
| - ... |
| |
| Modified Pragmas in Clang |
| ------------------------- |
| |
| - The "#pragma clang loop vectorize_width" has been extended to support an |
| optional 'fixed|scalable' argument, which can be used to indicate that the |
| compiler should use fixed-width or scalable vectorization. Fixed-width is |
| assumed by default. |
| |
| Scalable or vector length agnostic vectorization is an experimental feature |
| for targets that support scalable vectors. For more information please refer |
| to the Clang Language Extensions documentation. |
| |
| Attribute Changes in Clang |
| -------------------------- |
| |
| - Added support for the C++20 likelihood attributes ``[[likely]]`` and |
| ``[[unlikely]]``. As an extension they can be used in C++11 and newer. |
| This extension is enabled by default. |
| |
| Windows Support |
| --------------- |
| |
| - Implicitly add ``.exe`` suffix for MinGW targets, even when cross compiling. |
| (This matches a change from GCC 8.) |
| |
| - Windows on Arm64: programs using the C standard library's setjmp and longjmp |
| functions may crash with a "Security check failure or stack buffer overrun" |
| exception. To workaround (with reduced security), compile with |
| /guard:cf,nolongjmp. |
| |
| - Windows on Arm64: LLVM 12 adds official binary release hosted on |
| Windows on Arm64. The binary is built and tested by Linaro alongside |
| AArch64 and ARM 32-bit Linux binary releases. This first WoA release |
| includes Clang compiler, LLD Linker, and compiler-rt runtime libraries. |
| Work on LLDB, sanitizer support, OpenMP, and other features is in progress |
| and will be included in future Windows on Arm64 LLVM releases. |
| |
| C Language Changes in Clang |
| --------------------------- |
| |
| - ... |
| |
| C++ Language Changes in Clang |
| ----------------------------- |
| |
| - ... |
| |
| C++1z Feature Support |
| ^^^^^^^^^^^^^^^^^^^^^ |
| ... |
| |
| Objective-C Language Changes in Clang |
| ------------------------------------- |
| |
| OpenCL Kernel Language Changes in Clang |
| --------------------------------------- |
| |
| - Improved online documentation: :doc:`UsersManual` and :doc:`OpenCLSupport` |
| pages. |
| - Added ``-cl-std=CL3.0`` and predefined version macro for OpenCL 3.0. |
| - Added ``-cl-std=CL1.0`` and mapped to the existing OpenCL 1.0 functionality. |
| - Improved OpenCL extension handling per target. |
| - Added clang extension for function pointers ``__cl_clang_function_pointers`` |
| and variadic functions ``__cl_clang_variadic_functions``, more details can be |
| found in :doc:`LanguageExtensions`. |
| - Removed extensions without kernel language changes: |
| ``cl_khr_select_fprounding_mode``, ``cl_khr_gl_sharing``, ``cl_khr_icd``, |
| ``cl_khr_gl_event``, ``cl_khr_d3d10_sharing``, ``cl_khr_context_abort``, |
| ``cl_khr_d3d11_sharing``, ``cl_khr_dx9_media_sharing``, |
| ``cl_khr_image2d_from_buffer``, ``cl_khr_initialize_memory``, |
| ``cl_khr_gl_depth_images``, ``cl_khr_spir``, ``cl_khr_egl_event``, |
| ``cl_khr_egl_image``, ``cl_khr_terminate_context``. |
| - Improved diagnostics for unevaluated ``vec_step`` expression. |
| - Allow nested pointers (e.g. pointer-to-pointer) kernel arguments beyond OpenCL |
| 1.2. |
| - Added ``global_device`` and ``global_host`` address spaces for USM |
| allocations. |
| |
| Miscellaneous improvements in C++ for OpenCL support: |
| |
| - Added diagnostics for pointers to member functions and references to |
| functions. |
| - Added support of ``vec_step`` builtin. |
| - Fixed ICE on address spaces with forwarding references and templated copy |
| constructors. |
| - Removed warning for variadic macro use. |
| |
| ABI Changes in Clang |
| -------------------- |
| |
| OpenMP Support in Clang |
| ----------------------- |
| |
| - ... |
| |
| CUDA Support in Clang |
| --------------------- |
| |
| - ... |
| |
| X86 Support in Clang |
| -------------------- |
| |
| - The x86 intrinsics ``_mm_popcnt_u32``, ``_mm_popcnt_u64``, ``_popcnt32``, |
| ``_popcnt64``, ``__popcntd`` and ``__popcntq`` may now be used within |
| constant expressions. |
| |
| - The x86 intrinsics ``_bit_scan_forward``, ``__bsfd`` and ``__bsfq`` may now |
| be used within constant expressions. |
| |
| - The x86 intrinsics ``_bit_scan_reverse``, ``__bsrd`` and ``__bsrq`` may now |
| be used within constant expressions. |
| |
| - The x86 intrinsics ``__bswap``, ``__bswapd``, ``__bswap64`` and ``__bswapq`` |
| may now be used within constant expressions. |
| |
| - The x86 intrinsics ``_castf32_u32``, ``_castf64_u64``, ``_castu32_f32`` and |
| ``_castu64_f64`` may now be used within constant expressions. |
| |
| - The x86 intrinsics ``__rolb``, ``__rolw``, ``__rold``, ``__rolq`, ``_rotl``, |
| ``_rotwl`` and ``_lrotl`` may now be used within constant expressions. |
| |
| - The x86 intrinsics ``__rorb``, ``__rorw``, ``__rord``, ``__rorq`, ``_rotr``, |
| ``_rotwr`` and ``_lrotr`` may now be used within constant expressions. |
| |
| - Support for ``-march=alderlake``, ``-march=sapphirerapids`` and |
| ``-march=znver3`` was added. |
| |
| - Support for ``-march=x86-64-v[234]`` has been added. |
| See :doc:`UsersManual` for details about these micro-architecture levels. |
| |
| - The -mtune command line option is no longer ignored for X86. This can be used |
| to request microarchitectural optimizations independent on -march. -march=<cpu> |
| implies -mtune=<cpu>. -mtune=generic is the default with no -march or -mtune |
| specified. |
| |
| - Support for ``HRESET`` instructions has been added. |
| |
| - Support for ``UINTR`` instructions has been added. |
| |
| - Support for ``AVXVNNI`` instructions has been added. |
| |
| Internal API Changes |
| -------------------- |
| |
| These are major API changes that have happened since the 11.0.0 release of |
| Clang. If upgrading an external codebase that uses Clang as a library, |
| this section should help get you past the largest hurdles of upgrading. |
| |
| - ... |
| |
| Build System Changes |
| -------------------- |
| |
| These are major changes to the build system that have happened since the 11.0.0 |
| release of Clang. Users of the build system should adjust accordingly. |
| |
| - ... |
| |
| AST Matchers |
| ------------ |
| |
| - The ``mapAnyOf()`` matcher was added. This allows convenient matching of |
| different AST nodes which have a compatible matcher API. For example, |
| ``mapAnyOf(ifStmt, forStmt).with(hasCondition(integerLiteral()))`` |
| matches any ``IfStmt`` or ``ForStmt`` with a integer literal as the |
| condition. |
| |
| - The ``binaryOperation()`` matcher allows matching expressions which |
| appear like binary operators in the code, even if they are really |
| ``CXXOperatorCallExpr`` for example. It is based on the ``mapAnyOf()`` |
| matcher functionality. The matcher API for the latter node has been |
| extended with ``hasLHS()`` etc to facilitate the abstraction. |
| |
| - Matcher API for ``CXXRewrittenBinaryOperator`` has been added. In addition |
| to explicit matching with the ``cxxRewrittenBinaryOperator()`` matcher, the |
| ``binaryOperation()`` matches on nodes of this type. |
| |
| - The behavior of ``TK_IgnoreUnlessSpelledInSource`` with the ``traverse()`` |
| matcher has been changed to no longer match on template instantiations or on |
| implicit nodes which are not spelled in the source. |
| |
| - The ``TK_IgnoreImplicitCastsAndParentheses`` traversal kind was removed. It |
| is recommended to use ``TK_IgnoreUnlessSpelledInSource`` instead. |
| |
| - The behavior of the ``forEach()`` matcher was changed to not internally |
| ignore implicit and parenthesis nodes. This makes it consistent with |
| the ``has()`` matcher. Uses of ``forEach()`` relying on the old behavior |
| can now use the ``traverse()`` matcher or ``ignoringParenCasts()``. |
| |
| - Several AST Matchers have been changed to match based on the active |
| traversal mode. For example, ``argumentCountIs()`` matches the number of |
| arguments written in the source, ignoring default arguments represented |
| by ``CXXDefaultArgExpr`` nodes. |
| |
| - Improvements in AST Matchers allow more matching of template declarations, |
| independent of their template instantations. |
| |
| clang-format |
| ------------ |
| |
| - Option ``BitFieldColonSpacing`` has been added that decides how |
| space should be added around identifier, colon and bit-width in |
| bitfield definitions. |
| |
| .. code-block:: c++ |
| |
| // Both (default) |
| struct F { |
| unsigned dscp : 6; |
| unsigned ecn : 2; // AlignConsecutiveBitFields=true |
| }; |
| // None |
| struct F { |
| unsigned dscp:6; |
| unsigned ecn :2; |
| }; |
| // Before |
| struct F { |
| unsigned dscp :6; |
| unsigned ecn :2; |
| }; |
| // After |
| struct F { |
| unsigned dscp: 6; |
| unsigned ecn : 2; |
| }; |
| |
| |
| - Experimental Support in clang-format for concepts has been improved, to |
| aid this the follow options have been added |
| |
| - Option ``IndentRequires`` has been added to indent the ``requires`` keyword |
| in templates. |
| |
| - Option ``BreakBeforeConceptDeclarations`` has been added to aid the formatting of concepts. |
| |
| - Option ``IndentPragmas`` has been added to allow #pragma to indented with the current scope |
| level. This is especially useful when using #pragma to mark OpenMP sections of code. |
| |
| - Option ``SpaceBeforeCaseColon`` has been added to add a space before the |
| colon in a case or default statement. |
| |
| - Option ``StatementAttributeLikeMacros`` has been added to declare |
| macros which are not parsed as a type in front of a statement. See |
| the documentation for an example. |
| |
| - Options ``AlignConsecutiveAssignments``, ``AlignConsecutiveBitFields``, |
| ``AlignConsecutiveDeclarations`` and ``AlignConsecutiveMacros`` have been modified to allow |
| alignment across empty lines and/or comments. |
| |
| libclang |
| -------- |
| |
| - ... |
| |
| Static Analyzer |
| --------------- |
| |
| .. 3ff220de9009 [analyzer][StdLibraryFunctionsChecker] Add POSIX networking functions |
| .. ...And a million other patches. |
| - Improve the analyzer's understanding of several POSIX functions. |
| |
| .. https://reviews.llvm.org/D86533#2238207 |
| - Greatly improved the analyzer’s constraint solver by better understanding |
| when constraints are imposed on multiple symbolic values that are known to be |
| equal or known to be non-equal. It will now also efficiently reject impossible |
| if-branches between known comparison expressions. (Incorrectly stated as a |
| 11.0.0 feature in the previous release notes) |
| |
| .. 820e8d8656ec [Analyzer][WebKit] UncountedLambdaCaptureChecker |
| - New checker: :ref:`webkit.UncountedLambdaCapturesChecker<webkit-UncountedLambdaCapturesChecker>` |
| is a WebKit coding convention checker that flags raw pointers to |
| reference-counted objects captured by lambdas and suggests using intrusive |
| reference-counting smart pointers instead. |
| |
| .. 8a64689e264c [Analyzer][WebKit] UncountedLocalVarsChecker |
| - New checker: :ref:`alpha.webkit.UncountedLocalVarsChecker<alpha-webkit-UncountedLocalVarsChecker>` |
| is a WebKit coding convention checker that intends to make sure that any |
| uncounted local variable is backed by a ref-counted object with lifetime that |
| is strictly larger than the scope of the uncounted local variable. |
| |
| .. i914f6c4ff8a4 [StaticAnalyzer] Support struct annotations in FuchsiaHandleChecker |
| - ``fuchia.HandleChecker`` now recognizes handles in structs; All the handles |
| referenced by the structure (direct value or ptr) would be treated as |
| containing the release/use/acquire annotations directly. |
| |
| .. 8deaec122ec6 [analyzer] Update Fuchsia checker to catch releasing unowned handles. |
| - Fuchsia checkers can detect the release of an unowned handle. |
| |
| - Numerous fixes and improvements to bug report generation. |
| |
| .. _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 via the `mailing |
| list <https://lists.llvm.org/mailman/listinfo/cfe-dev>`_. |
