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llvm-project/clang/docs/ReleaseNotes.rst
Craig Topper 92a966bd8f
[RISCV] Add -march=unset to cancel and ignore a previous -march. (#148321) 
-mcpu is used to determine the ISA string if an explicit -march is not
present on the command line. If there is a -march present it always has
priority over -mcpu regardless of where it appears in the command line.

This can cause issues if -march appears in a Makefile and a user wants
to override it with an -mcpu on the command line. The user would need to
provide a potentially long ISA string to -march that matches the -mcpu
in order to override the MakeFile.

This issue can also be seen on Compiler Explorer where the rv64gc
toolchain is passed -march=rv64gc before any user command line options
are added. If you pass -mcpu=spacemit-x60, vectors will not be enabled
due to the hidden -march.

This patch adds a new option for -march, "unset" that makes the -march
ignored for purposes of prioritizing over -mcpu. Now a user can write
-march=unset -mcpu=<cpu_name>. This is also implemented by gcc for
ARM32.

An alternative would be to allow -march to take a cpu name, but that
requires "-march=<cpu_name> -mcpu=<cpu_name>" or "-march=<cpu_name>
-mtune=<cpu_name>" to ensure the tune cpu also gets updated. IMHO,
needing to repeat the CPU name twice isn't friendly and invites
mistakes.

gcc has implemented this as well.
2025-08-09 09:23:04 -05:00

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===========================================
Clang |release| |ReleaseNotesTitle|
===========================================
.. contents::
:local:
:depth: 2
Written by the `LLVM Team <https://llvm.org/>`_
.. 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 <https://llvm.org/releases/>`_.
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 <https://llvm.org/docs/ReleaseNotes.html>`_. For the libc++ release notes,
see `this page <https://libcxx.llvm.org/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>`_.
Potentially Breaking Changes
============================
C/C++ Language Potentially Breaking Changes
-------------------------------------------
- The ``__has_builtin`` function now only considers the currently active target when being used with target offloading.
C++ Specific Potentially Breaking Changes
-----------------------------------------
- For C++20 modules, the Reduced BMI mode will be the default option. This may introduce
regressions if your build system supports two-phase compilation model but haven't support
reduced BMI or it is a compiler bug or a bug in users code.
- Clang now correctly diagnoses during constant expression evaluation undefined behavior due to member
pointer access to a member which is not a direct or indirect member of the most-derived object
of the accessed object but is instead located directly in a sibling class to one of the classes
along the inheritance hierarchy of the most-derived object as ill-formed.
Other scenarios in which the member is not member of the most derived object were already
diagnosed previously. (#GH150709)
.. code-block:: c++
struct A {};
struct B : A {};
struct C : A { constexpr int foo() const { return 1; } };
constexpr A a;
constexpr B b;
constexpr C c;
constexpr auto mp = static_cast<int(A::*)() const>(&C::foo);
static_assert((a.*mp)() == 1); // continues to be rejected
static_assert((b.*mp)() == 1); // newly rejected
static_assert((c.*mp)() == 1); // accepted
ABI Changes in This Version
---------------------------
AST Dumping Potentially Breaking Changes
----------------------------------------
- How nested name specifiers are dumped and printed changes, keeping track of clang AST changes.
Clang Frontend Potentially Breaking Changes
-------------------------------------------
Clang Python Bindings Potentially Breaking Changes
--------------------------------------------------
- TypeKind ``ELABORATED`` is not used anymore, per clang AST changes removing
ElaboratedTypes. The value becomes unused, and all the existing users should
expect the former underlying type to be reported instead.
What's New in Clang |release|?
==============================
C++ Language Changes
--------------------
C++2c Feature Support
^^^^^^^^^^^^^^^^^^^^^
C++23 Feature Support
^^^^^^^^^^^^^^^^^^^^^
C++20 Feature Support
^^^^^^^^^^^^^^^^^^^^^
C++17 Feature Support
^^^^^^^^^^^^^^^^^^^^^
Resolutions to C++ Defect Reports
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
C Language Changes
------------------
C2y Feature Support
^^^^^^^^^^^^^^^^^^^
C23 Feature Support
^^^^^^^^^^^^^^^^^^^
Non-comprehensive list of changes in this release
-------------------------------------------------
- Added ``__builtin_elementwise_minnumnum`` and ``__builtin_elementwise_maxnumnum``.
- Trapping UBSan (e.g. ``-fsanitize-trap=undefined``) now emits a string describing the reason for
trapping into the generated debug info. This feature allows debuggers (e.g. LLDB) to display
the reason for trapping if the trap is reached. The string is currently encoded in the debug
info as an artificial frame that claims to be inlined at the trap location. The function used
for the artificial frame is an artificial function whose name encodes the reason for trapping.
The encoding used is currently the same as ``__builtin_verbose_trap`` but might change in the future.
This feature is enabled by default but can be disabled by compiling with
``-fno-sanitize-annotate-debug-info-traps``.
New Compiler Flags
------------------
- New option ``-fno-sanitize-annotate-debug-info-traps`` added to disable emitting trap reasons into the debug info when compiling with trapping UBSan (e.g. ``-fsanitize-trap=undefined``).
Deprecated Compiler Flags
-------------------------
Modified Compiler Flags
-----------------------
Removed Compiler Flags
-------------------------
Attribute Changes in Clang
--------------------------
Improvements to Clang's diagnostics
-----------------------------------
- Added a separate diagnostic group ``-Wfunction-effect-redeclarations``, for the more pedantic
diagnostics for function effects (``[[clang::nonblocking]]`` and ``[[clang::nonallocating]]``).
Moved the warning for a missing (though implied) attribute on a redeclaration into this group.
Added a new warning in this group for the case where the attribute is missing/implicit on
an override of a virtual method.
- Fixed fix-it hint for fold expressions. Clang now correctly places the suggested right
parenthesis when diagnosing malformed fold expressions. (#GH151787)
Improvements to Clang's time-trace
----------------------------------
Improvements to Coverage Mapping
--------------------------------
Bug Fixes in This Version
-------------------------
- Fix a crash when marco name is empty in ``#pragma push_macro("")`` or
``#pragma pop_macro("")``. (#GH149762).
- `-Wunreachable-code`` now diagnoses tautological or contradictory
comparisons such as ``x != 0 || x != 1.0`` and ``x == 0 && x == 1.0`` on
targets that treat ``_Float16``/``__fp16`` as native scalar types. Previously
the warning was silently lost because the operands differed only by an implicit
cast chain. (#GH149967).
Bug Fixes to Compiler Builtins
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
- Fix an ambiguous reference to the builtin `type_info` (available when using
`-fms-compatibility`) with modules. (#GH38400)
Bug Fixes to Attribute Support
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
- ``[[nodiscard]]`` is now respected on Objective-C and Objective-C++ methods.
(#GH141504)
- Using ``[[gnu::cleanup(some_func)]]`` where some_func is annotated with
``[[gnu::error("some error")]]`` now correctly triggers an error. (#GH146520)
Bug Fixes to C++ Support
^^^^^^^^^^^^^^^^^^^^^^^^
- Diagnose binding a reference to ``*nullptr`` during constant evaluation. (#GH48665)
- Suppress ``-Wdeprecated-declarations`` in implicitly generated functions. (#GH147293)
- Fix a crash when deleting a pointer to an incomplete array (#GH150359).
- Fix an assertion failure when expression in assumption attribute
(``[[assume(expr)]]``) creates temporary objects.
- Fix the dynamic_cast to final class optimization to correctly handle
casts that are guaranteed to fail (#GH137518).
Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
- Fix incorrect name qualifiers applied to alias CTAD. (#GH136624)
- Fixed ElaboratedTypes appearing within NestedNameSpecifier, which was not a
legal representation. This is fixed because ElaboratedTypes don't exist anymore. (#GH43179) (#GH68670) (#GH92757)
Miscellaneous Bug Fixes
^^^^^^^^^^^^^^^^^^^^^^^
Miscellaneous Clang Crashes Fixed
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
OpenACC Specific Changes
------------------------
Target Specific Changes
-----------------------
AMDGPU Support
^^^^^^^^^^^^^^
NVPTX Support
^^^^^^^^^^^^^^
X86 Support
^^^^^^^^^^^
Arm and AArch64 Support
^^^^^^^^^^^^^^^^^^^^^^^
Android Support
^^^^^^^^^^^^^^^
Windows Support
^^^^^^^^^^^^^^^
LoongArch Support
^^^^^^^^^^^^^^^^^
RISC-V Support
^^^^^^^^^^^^^^
- Add support for `__attribute__((interrupt("rnmi")))` to be used with the `Smrnmi` extension.
With this the `Smrnmi` extension is fully supported.
- Add `-march=unset` to clear any previous `-march=` value. This ISA string will
be computed from `-mcpu` or the platform default.
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
------------
- Removed elaboratedType matchers, and related nested name specifier changes,
following the corresponding changes in the clang AST.
- Ensure ``hasBitWidth`` doesn't crash on bit widths that are dependent on template
parameters.
clang-format
------------
libclang
--------
Code Completion
---------------
Static Analyzer
---------------
- The Clang Static Analyzer now handles parenthesized initialization.
(#GH148875)
- ``__datasizeof`` (C++) and ``_Countof`` (C) no longer cause a failed assertion
when given an operand of VLA type. (#GH151711)
New features
^^^^^^^^^^^^
Crash and bug fixes
^^^^^^^^^^^^^^^^^^^
- Fixed a crash in the static analyzer that when the expression in an
``[[assume(expr)]]`` attribute was enclosed in parentheses. (#GH151529)
Improvements
^^^^^^^^^^^^
Moved checkers
^^^^^^^^^^^^^^
.. _release-notes-sanitizers:
Sanitizers
----------
Python Binding Changes
----------------------
OpenMP Support
--------------
- Added parsing and semantic analysis support for the ``need_device_addr``
modifier in the ``adjust_args`` clause.
- Allow array length to be omitted in array section subscript expression.
Improvements
^^^^^^^^^^^^
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 on the `Discourse forums (Clang Frontend category)
<https://discourse.llvm.org/c/clang/6>`_.
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