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=======================================
Clang 4.0.0 (In-Progress) Release Notes
=======================================

.. contents::
   :local:
   :depth: 2

Written by the `LLVM Team <http://llvm.org/>`_

.. warning::

   These are in-progress notes for the upcoming Clang 4.0.0 release. You may
   prefer the `Clang 3.9 Release Notes
   <http://llvm.org/releases/3.9.0/tools/clang/docs/ReleaseNotes.html>`_.

Introduction
============

This document contains the release notes for the Clang C/C++/Objective-C
frontend, part of the LLVM Compiler Infrastructure, release 4.0.0. 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 <http://llvm.org/docs/ReleaseNotes.html>`_. All LLVM
releases may be downloaded from the `LLVM releases web
site <http://llvm.org/releases/>`_.

For more information about Clang or LLVM, including information about
the latest release, please check out the main please see the `Clang Web
Site <http://clang.llvm.org>`_ or the `LLVM Web
Site <http://llvm.org>`_.

What's New in Clang 4.0.0?
==========================

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
------------------

- The ``diagnose_if`` attribute has been added to clang. This attribute allows
  clang to emit a warning or error if a function call meets one or more
  user-specified conditions.

- Enhanced devirtualization with
  `-fstrict-vtable-pointers <UsersManual.html#cmdoption-fstrict-vtable-pointers>`_.
  Clang devirtualizes across different basic blocks, like loops:

  .. code-block:: c++

       struct A {
           virtual void foo();
       };
       void indirect(A &a, int n) {
           for (int i = 0 ; i < n; i++)
               a.foo();
       }
       void test(int n) {
           A a;
           indirect(a, n);
       }


-  ...

Improvements to ThinLTO (-flto=thin)
------------------------------------
- Integration with profile data (PGO). When available, profile data enables
  more accurate function importing decisions, as well as cross-module indirect
  call promotion.
- Significant build-time and binary-size improvements when compiling with debug
  info (-g).

Improvements to Clang's diagnostics
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

-  ...

New Compiler Flags
------------------

The option -Og has been added to optimize the debugging experience.
For now, this option is exactly the same as -O1. However, in the future,
some other optimizations might be enabled or disabled.

The option -MJ has been added to simplify adding JSON compilation
database output into existing build systems.

The option ....

New Pragmas in Clang
-----------------------

Clang now supports the ...


Attribute Changes in Clang
--------------------------

-  ...

Windows Support
---------------

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


C Language Changes in Clang
---------------------------

- ...

...

C11 Feature Support
^^^^^^^^^^^^^^^^^^^

...

C++ Language Changes in Clang
-----------------------------

...

C++1z Feature Support
^^^^^^^^^^^^^^^^^^^^^

...

Objective-C Language Changes in Clang
-------------------------------------

...

OpenCL C Language Changes in Clang
----------------------------------

...

OpenMP Support in Clang
----------------------------------

...

Internal API Changes
--------------------

These are major API changes that have happened since the 3.9 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
------------

...

libclang
--------

...

With the option --show-description, scan-build's list of defects will also
show the description of the defects.


Static Analyzer
---------------

...

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 <http://clang.llvm.org/>`_. 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 <http://lists.llvm.org/mailman/listinfo/cfe-dev>`_.