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98062d8fef
The change causes some libcxx regressions This reverts commit eaf725bc9371a6699902d67d97662caaa3332799.
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===========================================
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Clang |release| |ReleaseNotesTitle|
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===========================================
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.. contents::
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:local:
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:depth: 2
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Written by the `LLVM Team <https://llvm.org/>`_
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.. only:: PreRelease
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.. warning::
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These are in-progress notes for the upcoming Clang |version| release.
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Release notes for previous releases can be found on
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`the Releases Page <https://llvm.org/releases/>`_.
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Introduction
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============
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This document contains the release notes for the Clang C/C++/Objective-C
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frontend, part of the LLVM Compiler Infrastructure, release |release|. Here we
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describe the status of Clang in some detail, including major
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improvements from the previous release and new feature work. For the
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general LLVM release notes, see `the LLVM
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documentation <https://llvm.org/docs/ReleaseNotes.html>`_. For the libc++ release notes,
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see `this page <https://libcxx.llvm.org/ReleaseNotes.html>`_. All LLVM releases
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may be downloaded from the `LLVM releases web site <https://llvm.org/releases/>`_.
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For more information about Clang or LLVM, including information about the
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latest release, please see the `Clang Web Site <https://clang.llvm.org>`_ or the
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`LLVM Web Site <https://llvm.org>`_.
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Potentially Breaking Changes
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============================
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These changes are ones which we think may surprise users when upgrading to
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Clang |release| because of the opportunity they pose for disruption to existing
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code bases.
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C/C++ Language Potentially Breaking Changes
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-------------------------------------------
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C++ Specific Potentially Breaking Changes
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-----------------------------------------
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ABI Changes in This Version
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---------------------------
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- Following the SystemV ABI for x86-64, ``__int128`` arguments will no longer
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be split between a register and a stack slot.
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What's New in Clang |release|?
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==============================
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Some of the major new features and improvements to Clang are listed
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here. Generic improvements to Clang as a whole or to its underlying
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infrastructure are described first, followed by language-specific
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sections with improvements to Clang's support for those languages.
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C++ Language Changes
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--------------------
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C++20 Feature Support
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^^^^^^^^^^^^^^^^^^^^^
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C++23 Feature Support
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^^^^^^^^^^^^^^^^^^^^^
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C++2c Feature Support
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^^^^^^^^^^^^^^^^^^^^^
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- Implemented `P2169R4: A nice placeholder with no name <https://wg21.link/P2169R4>`_. This allows using ``_``
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as a variable name multiple times in the same scope and is supported in all C++ language modes as an extension.
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An extension warning is produced when multiple variables are introduced by ``_`` in the same scope.
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Unused warnings are no longer produced for variables named ``_``.
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Currently, inspecting placeholders variables in a debugger when more than one are declared in the same scope
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is not supported.
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.. code-block:: cpp
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struct S {
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int _, _; // Was invalid, now OK
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};
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void func() {
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int _, _; // Was invalid, now OK
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}
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void other() {
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int _; // Previously diagnosed under -Wunused, no longer diagnosed
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}
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- Attributes now expect unevaluated strings in attributes parameters that are string literals.
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This is applied to both C++ standard attributes, and other attributes supported by Clang.
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This completes the implementation of `P2361R6 Unevaluated Strings <https://wg21.link/P2361R6>`_
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Resolutions to C++ Defect Reports
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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C Language Changes
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------------------
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- ``structs``, ``unions``, and ``arrays`` that are const may now be used as
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constant expressions. This change is more consistent with the behavior of
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GCC.
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C23 Feature Support
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^^^^^^^^^^^^^^^^^^^
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- Clang now accepts ``-std=c23`` and ``-std=gnu23`` as language standard modes,
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and the ``__STDC_VERSION__`` macro now expands to ``202311L`` instead of its
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previous placeholder value. Clang continues to accept ``-std=c2x`` and
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``-std=gnu2x`` as aliases for C23 and GNU C23, respectively.
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- Clang now supports `requires c23` for module maps.
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Non-comprehensive list of changes in this release
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-------------------------------------------------
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New Compiler Flags
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------------------
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Deprecated Compiler Flags
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-------------------------
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Modified Compiler Flags
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-----------------------
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* ``-Woverriding-t-option`` is renamed to ``-Woverriding-option``.
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* ``-Winterrupt-service-routine`` is renamed to ``-Wexcessive-regsave`` as a generalization
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Removed Compiler Flags
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-------------------------
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* ``-enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang`` has been removed.
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It has not been needed to enable ``-ftrivial-auto-var-init=zero`` since Clang 16.
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Attribute Changes in Clang
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--------------------------
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- On X86, a warning is now emitted if a function with ``__attribute__((no_caller_saved_registers))``
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calls a function without ``__attribute__((no_caller_saved_registers))``, and is not compiled with
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``-mgeneral-regs-only``
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- On X86, a function with ``__attribute__((interrupt))`` can now call a function without
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``__attribute__((no_caller_saved_registers))`` provided that it is compiled with ``-mgeneral-regs-only``
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- When a non-variadic function is decorated with the ``format`` attribute,
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Clang now checks that the format string would match the function's parameters'
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types after default argument promotion. As a result, it's no longer an
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automatic diagnostic to use parameters of types that the format style
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supports but that are never the result of default argument promotion, such as
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``float``. (`#59824: <https://github.com/llvm/llvm-project/issues/59824>`_)
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Improvements to Clang's diagnostics
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-----------------------------------
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- Clang constexpr evaluator now prints template arguments when displaying
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template-specialization function calls.
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- Clang contexpr evaluator now displays notes as well as an error when a constructor
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of a base class is not called in the constructor of its derived class.
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- Clang no longer emits ``-Wmissing-variable-declarations`` for variables declared
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with the ``register`` storage class.
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- Clang's ``-Wtautological-negation-compare`` flag now diagnoses logical
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tautologies like ``x && !x`` and ``!x || x`` in expressions. This also
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makes ``-Winfinite-recursion`` diagnose more cases.
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(`#56035: <https://github.com/llvm/llvm-project/issues/56035>`_).
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- Clang constexpr evaluator now diagnoses compound assignment operators against
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uninitialized variables as a read of uninitialized object.
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(`#51536 <https://github.com/llvm/llvm-project/issues/51536>`_)
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- Clang's ``-Wfortify-source`` now diagnoses ``snprintf`` call that is known to
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result in string truncation.
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(`#64871: <https://github.com/llvm/llvm-project/issues/64871>`_).
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Also clang no longer emits false positive warnings about the output length of
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``%g`` format specifier.
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- Clang now emits ``-Wcast-qual`` for functional-style cast expressions.
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Bug Fixes in This Version
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-------------------------
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- Fixed an issue where a class template specialization whose declaration is
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instantiated in one module and whose definition is instantiated in another
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module may end up with members associated with the wrong declaration of the
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class, which can result in miscompiles in some cases.
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- Fix crash on use of a variadic overloaded operator.
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(`#42535 <https://github.com/llvm/llvm-project/issues/42535>`_)
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- Fix a hang on valid C code passing a function type as an argument to
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``typeof`` to form a function declaration.
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(`#64713 <https://github.com/llvm/llvm-project/issues/64713>`_)
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- Clang now reports missing-field-initializers warning for missing designated
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initializers in C++.
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(`#56628 <https://github.com/llvm/llvm-project/issues/56628>`_)
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- Clang now respects ``-fwrapv`` and ``-ftrapv`` for ``__builtin_abs`` and
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``abs`` builtins.
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(`#45129 <https://github.com/llvm/llvm-project/issues/45129>`_,
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`#45794 <https://github.com/llvm/llvm-project/issues/45794>`_)
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- Fixed an issue where accesses to the local variables of a coroutine during
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``await_suspend`` could be misoptimized, including accesses to the awaiter
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object itself.
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(`#56301 <https://github.com/llvm/llvm-project/issues/56301>`_)
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The current solution may bring performance regressions if the awaiters have
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non-static data members. See
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`#64945 <https://github.com/llvm/llvm-project/issues/64945>`_ for details.
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- Clang now prints unnamed members in diagnostic messages instead of giving an
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empty ''. Fixes
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(`#63759 <https://github.com/llvm/llvm-project/issues/63759>`_)
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- Fix crash in __builtin_strncmp and related builtins when the size value
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exceeded the maximum value representable by int64_t. Fixes
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(`#64876 <https://github.com/llvm/llvm-project/issues/64876>`_)
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- Fixed an assertion if a function has cleanups and fatal erors.
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(`#48974 <https://github.com/llvm/llvm-project/issues/48974>`_)
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- Clang now emits an error if it is not possible to deduce array size for a
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variable with incomplete array type.
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(`#37257 <https://github.com/llvm/llvm-project/issues/37257>`_)
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- Clang's ``-Wunused-private-field`` no longer warns on fields whose type is
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declared with ``[[maybe_unused]]``.
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(`#61334 <https://github.com/llvm/llvm-project/issues/61334>`_)
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- For function multi-versioning using the ``target``, ``target_clones``, or
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``target_version`` attributes, remove comdat for internal linkage functions.
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(`#65114 <https://github.com/llvm/llvm-project/issues/65114>`_)
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- Clang now reports ``-Wformat`` for bool value and char specifier confusion
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in scanf. Fixes
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(`#64987 <https://github.com/llvm/llvm-project/issues/64987>`_)
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- Support MSVC predefined macro expressions in constant expressions and in
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local structs.
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- Correctly parse non-ascii identifiers that appear immediately after a line splicing
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(`#65156 <https://github.com/llvm/llvm-project/issues/65156>`_`)
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Bug Fixes to Compiler Builtins
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Bug Fixes to Attribute Support
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Bug Fixes to C++ Support
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^^^^^^^^^^^^^^^^^^^^^^^^
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- Clang limits the size of arrays it will try to evaluate at compile time
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to avoid memory exhaustion.
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This limit can be modified by `-fconstexpr-steps`.
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(`#63562 <https://github.com/llvm/llvm-project/issues/63562>`_)
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- Fix a crash caused by some named unicode escape sequences designating
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a Unicode character whose name contains a ``-``.
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(Fixes `#64161 <https://github.com/llvm/llvm-project/issues/64161>`_)
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- Fix cases where we ignore ambiguous name lookup when looking up members.
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(`#22413 <https://github.com/llvm/llvm-project/issues/22413>`_),
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(`#29942 <https://github.com/llvm/llvm-project/issues/29942>`_),
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(`#35574 <https://github.com/llvm/llvm-project/issues/35574>`_) and
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(`#27224 <https://github.com/llvm/llvm-project/issues/27224>`_).
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- Clang emits an error on substitution failure within lambda body inside a
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requires-expression. This fixes:
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(`#64138 <https://github.com/llvm/llvm-project/issues/64138>`_).
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- Update ``FunctionDeclBitfields.NumFunctionDeclBits``. This fixes:
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(`#64171 <https://github.com/llvm/llvm-project/issues/64171>`_).
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- Expressions producing ``nullptr`` are correctly evaluated
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by the constant interpreter when appearing as the operand
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of a binary comparison.
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(`#64923 <https://github.com/llvm/llvm-project/issues/64923>`_)
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- Fix a crash when an immediate invocation is not a constant expression
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and appear in an implicit cast.
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(`#64949 <https://github.com/llvm/llvm-project/issues/64949>`_).
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- Fix crash when parsing ill-formed lambda trailing return type. Fixes:
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(`#64962 <https://github.com/llvm/llvm-project/issues/64962>`_) and
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(`#28679 <https://github.com/llvm/llvm-project/issues/28679>`_).
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- Fix a crash caused by substitution failure in expression requirements.
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(`#64172 <https://github.com/llvm/llvm-project/issues/64172>`_) and
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(`#64723 <https://github.com/llvm/llvm-project/issues/64723>`_).
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- Fix crash when parsing the requires clause of some generic lambdas.
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(`#64689 <https://github.com/llvm/llvm-project/issues/64689>`_)
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Bug Fixes to AST Handling
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^^^^^^^^^^^^^^^^^^^^^^^^^
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- Fixed an import failure of recursive friend class template.
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`Issue 64169 <https://github.com/llvm/llvm-project/issues/64169>`_
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- Remove unnecessary RecordLayout computation when importing UnaryOperator. The
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computed RecordLayout is incorrect if fields are not completely imported and
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should not be cached.
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`Issue 64170 <https://github.com/llvm/llvm-project/issues/64170>`_
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Miscellaneous Bug Fixes
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^^^^^^^^^^^^^^^^^^^^^^^
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Miscellaneous Clang Crashes Fixed
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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- Fixed a crash when parsing top-level ObjC blocks that aren't properly
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terminated. Clang should now also recover better when an @end is missing
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between blocks.
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`Issue 64065 <https://github.com/llvm/llvm-project/issues/64065>`_
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- Fixed a crash when check array access on zero-length element.
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`Issue 64564 <https://github.com/llvm/llvm-project/issues/64564>`_
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Target Specific Changes
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-----------------------
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AMDGPU Support
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^^^^^^^^^^^^^^
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- Use pass-by-reference (byref) in stead of pass-by-value (byval) for struct
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arguments in C ABI. Callee is responsible for allocating stack memory and
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copying the value of the struct if modified. Note that AMDGPU backend still
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supports byval for struct arguments.
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X86 Support
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^^^^^^^^^^^
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Arm and AArch64 Support
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^^^^^^^^^^^^^^^^^^^^^^^
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Windows Support
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^^^^^^^^^^^^^^^
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- Fixed an assertion failure that occurred due to a failure to propagate
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``MSInheritanceAttr`` attributes to class template instantiations created
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for explicit template instantiation declarations.
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- The ``-fno-auto-import`` option was added for MinGW targets. The option both
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affects code generation (inhibiting generating indirection via ``.refptr``
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stubs for potentially auto imported symbols, generating smaller and more
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efficient code) and linking (making the linker error out on such cases).
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If the option only is used during code generation but not when linking,
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linking may succeed but the resulting executables may expose issues at
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runtime.
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LoongArch Support
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^^^^^^^^^^^^^^^^^
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RISC-V Support
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^^^^^^^^^^^^^^
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- Unaligned memory accesses can be toggled by ``-m[no-]unaligned-access`` or the
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aliases ``-m[no-]strict-align``.
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CUDA/HIP Language Changes
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^^^^^^^^^^^^^^^^^^^^^^^^^
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CUDA Support
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^^^^^^^^^^^^
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AIX Support
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^^^^^^^^^^^
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WebAssembly Support
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^^^^^^^^^^^^^^^^^^^
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AVR Support
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^^^^^^^^^^^
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DWARF Support in Clang
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----------------------
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Floating Point Support in Clang
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-------------------------------
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- Add ``__builtin_elementwise_log`` builtin for floating point types only.
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- Add ``__builtin_elementwise_log10`` builtin for floating point types only.
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- Add ``__builtin_elementwise_log2`` builtin for floating point types only.
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- Add ``__builtin_elementwise_exp`` builtin for floating point types only.
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- Add ``__builtin_elementwise_exp2`` builtin for floating point types only.
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- Add ``__builtin_set_flt_rounds`` builtin for X86, x86_64, Arm and AArch64 only.
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- Add ``__builtin_elementwise_pow`` builtin for floating point types only.
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- Add ``__builtin_elementwise_bitreverse`` builtin for integer types only.
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- Add ``__builtin_elementwise_sqrt`` builtin for floating point types only.
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- ``__builtin_isfpclass`` builtin now supports vector types.
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AST Matchers
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------------
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- Add ``convertVectorExpr``.
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- Add ``dependentSizedExtVectorType``.
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- Add ``macroQualifiedType``.
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clang-format
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------------
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libclang
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--------
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- Exposed arguments of ``clang::annotate``.
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Static Analyzer
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---------------
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- Added a new checker ``core.BitwiseShift`` which reports situations where
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bitwise shift operators produce undefined behavior (because some operand is
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negative or too large).
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.. _release-notes-sanitizers:
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|
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Sanitizers
|
|
----------
|
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|
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- ``-fsanitize=signed-integer-overflow`` now instruments ``__builtin_abs`` and
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``abs`` builtins.
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Python Binding Changes
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----------------------
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Additional Information
|
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======================
|
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|
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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
|
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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.
|
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|
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If you have any questions or comments about Clang, please feel free to
|
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contact us on the `Discourse forums (Clang Frontend category)
|
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<https://discourse.llvm.org/c/clang/6>`_.
|