llvm/docs/ReleaseNotes.rst

======================
LLVM 3.5 Release Notes
======================

.. contents::
    :local:

.. warning::
   These are in-progress notes for the upcoming LLVM 3.5 release.  You may
   prefer the `LLVM 3.4 Release Notes <http://llvm.org/releases/3.4/docs
   /ReleaseNotes.html>`_.


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

This document contains the release notes for the LLVM Compiler Infrastructure,
release 3.5.  Here we describe the status of LLVM, including major improvements
from the previous release, improvements in various subprojects of LLVM, and
some of the current users of the code.  All LLVM releases may be downloaded
from the `LLVM releases web site <http://llvm.org/releases/>`_.

For more information about LLVM, including information about the latest
release, please check out the `main LLVM web site <http://llvm.org/>`_.  If you
have questions or comments, the `LLVM Developer's Mailing List
<http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev>`_ is a good place to send
them.

Note that if you are reading this file from a Subversion checkout or the main
LLVM 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 <http://llvm.org/releases/>`_.

Non-comprehensive list of changes in this release
=================================================

* All backends have been changed to use the MC asm printer and support for the
  non MC one has been removed.

* Clang can now successfully self-host itself on Linux/Sparc64 and on
  FreeBSD/Sparc64.

* LLVM now assumes the assembler supports ``.loc`` for generating debug line
  numbers. The old support for printing the debug line info directly was only
  used by ``llc`` and has been removed.

* All inline assembly is parsed by the integrated assembler when it is enabled.
  Previously this was only the case for object-file output. It is now the case
  for assembly output as well. The integrated assembler can be disabled with
  the ``-no-integrated-as`` option,

* llvm-ar now handles IR files like regular object files. In particular, a
  regular symbol table is created for symbols defined in IR files, including
  those in file scope inline assembly.

* LLVM now always uses cfi directives for producing most stack
  unwinding information.

* The prefix for loop vectorizer hint metadata has been changed from
  ``llvm.vectorizer`` to ``llvm.loop.vectorize``.

* Some backends previously implemented Atomic NAND(x,y) as ``x & ~y``. Now 
  all backends implement it as ``~(x & y)``, matching the semantics of GCC 4.4
  and later.

.. NOTE
   For small 1-3 sentence descriptions, just add an entry at the end of
   this list. If your description won't fit comfortably in one bullet
   point (e.g. maybe you would like to give an example of the
   functionality, or simply have a lot to talk about), see the `NOTE` below
   for adding a new subsection.

* ... next change ...

.. NOTE
   If you would like to document a larger change, then you can add a
   subsection about it right here. You can copy the following boilerplate
   and un-indent it (the indentation causes it to be inside this comment).

   Special New Feature
   -------------------

   Makes programs 10x faster by doing Special New Thing.

Changes to the ARM Backend
--------------------------

Since release 3.3, a lot of new features have been included in the ARM
back-end but weren't production ready (ie. well tested) on release 3.4.
Just after the 3.4 release, we started heavily testing two major parts
of the back-end: the integrated assembler (IAS) and the ARM exception
handling (EHABI), and now they are enabled by default on LLVM/Clang.

The IAS received a lot of GNU extensions and directives, as well as some
specific pre-UAL instructions. Not all remaining directives will be
implemented, as we made judgement calls on the need versus the complexity,
and have chosen simplicity and future compatibility where hard decisions
had to be made. The major difference is, as stated above, the IAS validates
all inline ASM, not just for object emission, and that cause trouble with
some uses of inline ASM as pre-processor magic.

So, while the IAS is good enough to compile large projects (including most
of the Linux kernel), there are a few things that we can't (and probably
won't) do. For those cases, please use ``-fno-integrated-as`` in Clang.

Exception handling is another big change. After extensive testing and
changes to cooperate with Dwarf unwinding, EHABI is enabled by default.
The options ``-arm-enable-ehabi`` and ``-arm-enable-ehabi-descriptors``,
which were used to enable EHABI in the previous releases, are removed now.

This means all ARM code will emit EH unwind tables, or CFI unwinding (for
debug/profiling), or both. To avoid run-time inconsistencies, C code will
also emit EH tables (in case they interoperate with C++ code), as is the
case for other architectures (ex. x86_64).

External Open Source Projects Using LLVM 3.5
============================================

An exciting aspect of LLVM is that it is used as an enabling technology for
a lot of other language and tools projects. This section lists some of the
projects that have already been updated to work with LLVM 3.5.


Additional Information
======================

A wide variety of additional information is available on the `LLVM web page
<http://llvm.org/>`_, in particular in the `documentation
<http://llvm.org/docs/>`_ section.  The web page also contains versions of the
API documentation which is 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 ``llvm/docs/`` directory in the LLVM tree.

If you have any questions or comments about LLVM, please feel free to contact
us via the `mailing lists <http://llvm.org/docs/#maillist>`_.