Clang 14.0.0 (In-Progress) Release Notes

Written by the LLVM Team

Warning

These are in-progress notes for the upcoming Clang 14 release. Release notes for previous releases can be found on the Download Page.

Introduction

This document contains the release notes for the Clang C/C++/Objective-C frontend, part of the LLVM Compiler Infrastructure, release 14.0.0. 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. 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 14.0.0?

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

  • -Wbitwise-instead-of-logical (part of -Wbool-operation) warns about use of bitwise operators with boolean operands which have side effects.

Non-comprehensive list of changes in this release

  • Maximum _ExtInt size was decreased from 16,777,215 bits to 8,388,608 bits. Motivation for this was discussed in PR51829.

Modified Compiler Flags

  • Support has been added for the following processors (-mcpu identifiers in parentheses):
    • RISC-V SiFive E20 (sifive-e20).
    • RISC-V SiFive E21 (sifive-e21).
    • RISC-V SiFive E24 (sifive-e24).
    • RISC-V SiFive E34 (sifive-e34).
    • RISC-V SiFive S21 (sifive-s21).
    • RISC-V SiFive S51 (sifive-s51).
    • RISC-V SiFive S54 (sifive-s54).
    • RISC-V SiFive S76 (sifive-s76).
  • Support has been added for the following architectures (-march identifiers in parentheses):
    • Armv9-A (armv9-a).
    • Armv9.1-A (armv9.1-a).
    • Armv9.2-A (armv9.2-a).

Attribute Changes in Clang

  • Attributes loaded as clang plugins which are sensitive to LangOpts must now override acceptsLangOpts instead of diagLangOpts. Returning false will produce a generic “attribute ignored” diagnostic, as with clang’s built-in attributes. If plugins want to provide richer diagnostics, they can do so when the attribute is handled instead, e.g. in handleDeclAttribute. (This was changed in order to better support attributes in code completion).
  • __has_cpp_attribute, __has_c_attribute, __has_attribute, and __has_declspec will now macro expand their argument. This causes a change in behavior for code using __has_cpp_attribute(__clang__::attr) (and same for __has_c_attribute) where it would previously expand to 0 for all attributes, but will now issue an error due to the expansion of the predefined __clang__ macro.

Windows Support

  • An MSVC compatibility workaround for C++ operator names was removed. As a result, the <query.h> Windows SDK header may not compile out of the box. Users should use a recent SDK and pass -DQUERY_H_RESTRICTION_PERMISSIVE or pass /permissive to disable C++ operator names altogether. See PR42427 <https://llvm.org/pr42427> for more info.

C Language Changes in Clang

  • The value of __STDC_VERSION__ has been bumped to 202000L when passing -std=c2x so that it can be distinguished from C17 mode. This value is expected to change again when C23 is published.
  • Wide multi-characters literals such as L'ab' that would previously be interpreted as L'b' are now ill-formed in all language modes. The motivation for this change is outlined in P2362.
  • Support for __attribute__((error(""))) and __attribute__((warning(""))) function attributes have been added.
  • The maximum allowed alignment has been increased from 2^29 to 2^32.

C++ Language Changes in Clang

C++20 Feature Support

CUDA Language Changes in Clang

  • Clang now supports CUDA versions up to 11.4.
  • Default GPU architecture has been changed from sm_20 to sm_35.

OpenMP Support in Clang

  • clang-nvlink-wrapper tool introduced to support linking of cubin files archived in an archive. See Clang Nvlink Wrapper.

X86 Support in Clang

  • Support for AVX512-FP16 instructions has been added.

Arm and AArch64 Support in Clang

  • Support has been added for the following processors (command-line identifiers in parentheses): - Arm Cortex-A510 (cortex-a510)
  • The -mtune flag is no longer ignored for AArch64. It is now possible to tune code generation for a particular CPU with -mtune without setting any architectural features. For example, compiling with “-mcpu=generic -mtune=cortex-a57” will not enable any Cortex-A57 specific architecture features, but will enable certain optimizations specific to Cortex-A57 CPUs and enable the use of a more accurate scheduling model.

AST Matchers

  • TypeLoc AST Matchers are now available. These matchers provide helpful utilities for matching TypeLoc nodes, such as the pointerTypeLoc matcher or the hasReturnTypeLoc matcher. The addition of these matchers was made possible by changes to the handling of TypeLoc nodes that allows them to enjoy the same static type checking as other AST node kinds.

clang-format

  • Option AllowShortEnumsOnASingleLine: false has been improved, it now correctly places the opening brace according to BraceWrapping.AfterEnum.
  • Option QualifierAligment has been added in order to auto-arrange the positioning of specifiers/qualifiers const volatile static inline constexpr restrict in variable and parameter declarations to be either Right aligned or Left aligned or Custom using QualifierOrder.
  • Option QualifierOrder has been added to allow the order const volatile static inline constexpr restrict to be controlled relative to the type.

New Issues Found

Python Binding Changes

The following methods have been added:

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.

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