Clang 9.0.0 (In-Progress) Release Notes

Written by the LLVM Team


These are in-progress notes for the upcoming Clang 9 release. Release notes for previous releases can be found on the Download Page.


This document contains the release notes for the Clang C/C++/Objective-C frontend, part of the LLVM Compiler Infrastructure, release 9.0.0. 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 Subversion 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 9.0.0?

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 __VERSION__ macro has been updated. Previously this macro contained the string ‘4.2.1 Compatible’ to achieve compatibility with GCC 4.2.1, but that should no longer be necessary. However, to retrieve Clang’s version, please favor the one of the macro defined in clang namespaced version macros.

Deprecated Compiler Flags

The following options are deprecated and ignored. They will be removed in future versions of Clang.

Modified Compiler Flags

  • clang -dumpversion now returns the version of Clang itself.

Windows Support

  • clang-cl now treats non-existent files as possible typos for flags, clang-cl /diagnostic:caret /c for example now produces clang: error: no such file or directory: '/diagnostic:caret'; did you mean '/diagnostics:caret'?
  • The -print-search-dirs option now separates elements with semicolons, as is the norm for path lists on Windows
  • Improved handling of dllexport in conjunction with explicit template instantiations for MinGW, to allow building a shared libc++ for MinGW without --export-all-symbols to override the dllexport attributes

C Language Changes in Clang

  • __FILE_NAME__ macro has been added as a Clang specific extension supported in all C-family languages. This macro is similar to __FILE__ except it will always provide the last path component when possible.
  • Initial support for asm goto statements (a GNU C extension) has been added for control flow from inline assembly to labels. The main consumers of this construct are the Linux kernel (CONFIG_JUMP_LABEL=y) and glib. There are still a few unsupported corner cases in Clang’s integrated assembler and IfConverter. Please file bugs for any issues you run into.

C11 Feature Support

C++ Language Changes in Clang

C++1z Feature Support

Objective-C Language Changes in Clang

  • Fixed encoding of ObjC pointer types that are pointers to typedefs.
typedef NSArray<NSObject *> MyArray;

// clang used to encode this as "^{NSArray=#}" instead of "@".
const char *s0 = @encode(MyArray *);

OpenMP Support in Clang

  • Added emission of the debug information for NVPTX target devices.

CUDA Support in Clang

  • Added emission of the debug information for the device code.

Internal API Changes

These are major API changes that have happened since the 8.0.0 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 8.0.0 release of Clang. Users of the build system should adjust accordingly.

  • In 8.0.0 and below, the install-clang-headers target would install clang’s resource directory headers. This installation is now performed by the install-clang-resource-headers target. Users of the old install-clang-headers target should switch to the new install-clang-resource-headers target. The install-clang-headers target now installs clang’s API headers (corresponding to its libraries), which is consistent with the install-llvm-headers target.


  • Add language support for clang-formatting C# files.
  • Add Microsoft coding style to encapsulate default C# formatting style.
  • Added new option PPDIS_BeforeHash (in configuration: BeforeHash) to IndentPPDirectives which indents preprocessor directives before the hash.
  • Added new option AlignConsecutiveMacros to align the C/C++ preprocessor macros of consecutive lines.


  • When CINDEXTEST_INCLUDE_ATTRIBUTED_TYPES is not provided when making a CXType, the equivalent type of the AttributedType is returned instead of the modified type if the user does not want attribute sugar. The equivalent type represents the minimally-desugared type which the AttributedType is canonically equivalent to.

Static Analyzer

  • The UninitializedObject checker is now considered as stable. (moved from the ‘alpha.cplusplus’ to the ‘optin.cplusplus’ package)

New Issues Found

Python Binding Changes

The following methods have been added:

Linux Kernel

With support for asm goto, the mainline Linux kernel for x86_64 is now buildable (and bootable) with Clang 9. Other architectures that don’t require CONFIG_JUMP_LABEL=y such as arm, aarch64, ppc32, ppc64le, (and possibly mips) have been supported with older releases of Clang (Clang 4 was first used with aarch64).

The Android and ChromeOS Linux distributions have moved to building their Linux kernels with Clang, and Google is currently testing Clang built kernels for their production Linux kernels.

Further, LLD, llvm-objcopy, llvm-ar, llvm-nm, llvm-objdump can all be used to build a working Linux kernel.

More information about building Linux kernels with Clang can be found:

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 Subversion 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.