Clang 3.9 documentation

Clang 3.9 (In-Progress) Release Notes

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Clang 3.9 (In-Progress) Release Notes

Written by the LLVM Team


These are in-progress notes for the upcoming Clang 3.9 release. You may prefer the Clang 3.8 Release Notes.


This document contains the release notes for the Clang C/C++/Objective-C frontend, part of the LLVM Compiler Infrastructure, release 3.9. 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 check out the main 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 3.9?

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 will no longer passes –build-id by default to the linker. In modern linkers that is a relatively expensive option. It can be passed explicitly with -Wl,–build-id. To have clang always pass it, build clang with -DENABLE_LINKER_BUILD_ID.

Improvements to Clang’s diagnostics

Clang’s diagnostics are constantly being improved to catch more issues, explain them more clearly, and provide more accurate source information about them. The improvements since the 3.7 release include:

  • ...

New Compiler Flags

The option ....

New Pragmas in Clang

Clang now supports the ...

Windows Support

Clang’s support for building native Windows programs ...

TLS is enabled for Cygwin defaults to -femulated-tls.

C Language Changes in Clang

The -faltivec and -maltivec flags no longer silently include altivec.h on Power platforms.

RenderScript support added to the Frontend and enabled by the ‘-x renderscript’ option or the ‘.rs’ file extension.


C11 Feature Support


C++ Language Changes in Clang

  • Clang now enforces the rule that a using-declaration cannot name an enumerator of a scoped enumeration.

    namespace Foo { enum class E { e }; }
    namespace Bar {
      using Foo::E::e; // error
      constexpr auto e = Foo::E::e; // ok
  • Clang now enforces the rule that an enumerator of an unscoped enumeration declared at class scope can only be named by a using-declaration in a derived class.

    class Foo { enum E { e }; }
    using Foo::e; // error
    static constexpr auto e = Foo::e; // ok


C++1z Feature Support

Clang’s experimental support for the upcoming C++1z standard can be enabled with -std=c++1z. Changes to C++1z features since Clang 3.8:

  • The [[fallthrough]], [[nodiscard]], and [[maybe_unused]] attributes are supported in C++11 onwards, and are largely synonymous with Clang’s existing attributes [[clang::fallthrough]], [[gnu::warn_unused_result]], and [[gnu::unused]]. Use -Wimplicit-fallthrough to warn on unannotated fallthrough within switch statements.

  • In C++1z mode, aggregate initialization can be performed for classes with base classes:

    struct A { int n; };
    struct B : A { int x, y; };
    B b = { 1, 2, 3 }; // b.n == 1, b.x == 2, b.y == 3
  • The range in a range-based for statement can have different types for its begin and end iterators. This is permitted as an extension in C++11 onwards.

  • Lambda-expressions can explicitly capture *this (to capture the surrounding object by copy). This is permitted as an extension in C++11 onwards.

  • Objects of enumeration type can be direct-list-initialized from a value of the underlying type. E{n} is equivalent to E(n), except that it implies a check for a narrowing conversion.

  • Unary fold-expressions over an empty pack are now rejected for all operators other than &&, ||, and ,.


OpenMP Support in Clang

Added support for all non-offloading features from OpenMP 4.5, including using data members in private clauses of non-static member functions. Additionally, data members can be used as loop control variables in loop-based directives.

Currently Clang supports OpenMP 3.1 and all non-offloading features of OpenMP 4.0/4.5. Offloading features are under development. Clang defines macro _OPENMP and sets it to OpenMP 3.1 (in accordance with OpenMP standard) by default. User may change this value using -fopenmp-version=[31|40|45] option.

The codegen for OpenMP constructs was significantly improved to produce much more stable and faster code.

Internal API Changes

These are major API changes that have happened since the 3.8 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.

  • ...

AST Matchers

  • has and hasAnyArgument: Matchers no longer ignores parentheses and implicit casts on the argument before applying the inner matcher. The fix was done to allow for greater control by the user. In all existing checkers that use this matcher all instances of code hasAnyArgument(<inner matcher>) or has(<inner matcher>) must be changed to hasAnyArgument(ignoringParenImpCasts(<inner matcher>)) or has(ignoringParenImpCasts(<inner matcher>)).


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 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.

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