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ReleaseNotes.rst 13.66 KiB

Clang |release| |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 |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. 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.

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.

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.

Major New Features

  • Clang now supports the -fzero-call-used-regs feature for x86. The purpose of this feature is to limit Return-Oriented Programming (ROP) exploits and information leakage. It works by zeroing out a selected class of registers before function return --- e.g., all GPRs that are used within the function. There is an analogous zero_call_used_regs attribute to allow for finer control of this feature.

Bug Fixes

  • CXXNewExpr::getArraySize() previously returned a llvm::Optional wrapping a nullptr when the CXXNewExpr did not have an array size expression. This was fixed and ::getArraySize() will now always either return None or a llvm::Optional wrapping a valid Expr*. This fixes Issue 53742.
  • We now ignore full expressions when traversing cast subexpressions. This fixes Issue 53044.
  • Allow -Wno-gnu to silence GNU extension diagnostics for pointer arithmetic diagnostics. Fixes Issue 54444.
  • Placeholder constraints, as in Concept auto x = f();, were not checked when modifiers like auto& or auto** were added. These constraints are now checked. This fixes Issue 53911 and Issue 54443.
  • Previously invalid member variables with template parameters would crash clang. Now fixed by setting identifiers for them. This fixes Issue 28475 (PR28101).
  • Now allow the restrict and _Atomic qualifiers to be used in conjunction with __auto_type to match the behavior in GCC. This fixes Issue 53652.
  • No longer crash when specifying a variably-modified parameter type in a function with the naked attribute. This fixes Issue 50541.
  • Allow multiple #pragma weak directives to name the same undeclared (if an alias, target) identifier instead of only processing one such #pragma weak per identifier. Fixes Issue 28985.
  • Assignment expressions in C11 and later mode now properly strip the _Atomic qualifier when determining the type of the assignment expression. Fixes Issue 48742.
  • Improved the diagnostic when accessing a member of an atomic structure or union object in C; was previously an unhelpful error, but now issues a -Watomic-access warning which defaults to an error. Fixes Issue 54563.
  • Unevaluated lambdas in dependant contexts no longer result in clang crashing. This fixes Issues 50376, 51414, 51416, and 51641.
  • The builtin function __builtin_dump_struct would crash clang when the target struct contains a bitfield. It now correctly handles bitfields. This fixes Issue Issue 54462.
  • Statement expressions are now disabled in default arguments in general. This fixes Issue Issue 53488.

Improvements to Clang's diagnostics

  • -Wliteral-range will warn on floating-point equality comparisons with constants that are not representable in a casted value. For example, (float) f == 0.1 is always false.
  • -Winline-namespace-reopened-noninline now takes into account that the inline keyword must appear on the original but not necessarily all extension definitions of an inline namespace and therefore points its note at the original definition. This fixes Issue 50794 (PR51452).
  • -Wunused-but-set-variable now also warns if the variable is only used by unary operators.
  • -Wunused-variable no longer warn for references extending the lifetime of temporaries with side effects. This fixes Issue 54489.

Non-comprehensive list of changes in this release

  • Improve __builtin_dump_struct: - Support bitfields in struct and union. - Improve the dump format, dump both bitwidth(if its a bitfield) and field value. - Remove anonymous tag locations. - Beautify dump format, add indent for nested struct and struct members.

New Compiler Flags

Deprecated Compiler Flags

Modified Compiler Flags

Removed Compiler Flags

New Pragmas in Clang

  • ...

Attribute Changes in Clang

  • Added support for parameter pack expansion in clang::annotate.
  • The overloadable attribute can now be written in all of the syntactic locations a declaration attribute may appear. This fixes Issue 53805.
  • Improved namespace attributes handling:
    • Handle GNU attributes before a namespace identifier and subsequent attributes of different kinds.
    • Emit error on GNU attributes for a nested namespace definition.
  • Statement attributes [[clang::noinline]] and [[clang::always_inline]] can be used to control inlining decisions at callsites.
  • #pragma clang attribute push now supports multiple attributes within a single directive.
  • The __declspec(naked) attribute can no longer be written on a member function in Microsoft compatibility mode, matching the behavior of cl.exe.

Windows Support

  • Add support for MSVC-compatible /JMC//JMC- flag in clang-cl (supports X86/X64/ARM/ARM64). /JMC could only be used when /Zi or /Z7 is turned on. With this addition, clang-cl can be used in Visual Studio for the JustMyCode feature. Note, you may need to manually add /JMC as additional compile options in the Visual Studio since it currently assumes clang-cl does not support /JMC.

C Language Changes in Clang

C2x Feature Support

C++ Language Changes in Clang

  • ...

C++20 Feature Support

  • Diagnose consteval and constexpr issues that happen at namespace scope. This partially addresses Issue 51593.
  • No longer attempt to evaluate a consteval UDL function call at runtime when it is called through a template instantiation. This fixes Issue 54578.
  • Implemented __builtin_source_location() which enables library support for std::source_location.
  • The mangling scheme for C++20 modules has incompatibly changed. The initial mangling was discovered not to be reversible, and the weak ownership design decision did not give the backwards compatibility that was hoped for. C++20 since added extern "C++" semantics that can be used for such compatibility. The demangler now demangles symbols with named module attachment.

C++2b Feature Support

CUDA Language Changes in Clang

Objective-C Language Changes in Clang

OpenCL C Language Changes in Clang

...

ABI Changes in Clang

OpenMP Support in Clang

  • clang-nvlink-wrapper tool introduced to support linking of cubin files archived in an archive. See :doc:`ClangNvlinkWrapper`.
  • clang-linker-wrapper tool introduced to support linking using a new OpenMP target offloading method. See :doc:`ClangLinkerWrapper`.
  • Support for a new driver for OpenMP target offloading has been added as an opt-in feature. The new driver can be selected using -fopenmp-new-driver with clang. Device-side LTO can also be enabled using the new driver by passing -foffload-lto= as well. The new driver supports the following features: - Linking AMDGPU and NVPTX offloading targets. - Static linking using archive files. - Device-side LTO.

CUDA Support in Clang

  • ...

X86 Support in Clang

DWARF Support in Clang

Arm and AArch64 Support in Clang

  • When using -mbranch-protection=bti with AArch64, calls to setjmp will now be followed by a BTI instruction. This is done to be compatible with setjmp implementations that return with a br instead of a ret. You can disable this behaviour using the -mno-bti-at-return-twice option.

Floating Point Support in Clang

Internal API Changes

  • Added a new attribute flag AcceptsExprPack that when set allows expression pack expansions in the parsed arguments of the corresponding attribute. Additionally it introduces delaying of attribute arguments, adding common handling for creating attributes that cannot be fully initialized prior to template instantiation.

Build System Changes

AST Matchers

  • Expanded isInline narrowing matcher to support c++17 inline variables.

clang-format

  • Important change: Renamed IndentRequires to IndentRequiresClause and changed the default for all styles from false to true.
  • Reworked and improved handling of concepts and requires. Added the RequiresClausePosition option as part of that.
  • Changed BreakBeforeConceptDeclarations from Boolean to an enum.
  • Option InsertBraces has been added to insert optional braces after control statements.

libclang

  • ...

Static Analyzer

  • ...

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. 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.