======================
LLVM 3.4 Release Notes
======================

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

This document contains the release notes for the LLVM Compiler Infrastructure,
release 3.4.  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
=================================================

* This is expected to be the last release of LLVM which compiles using a C++98
  toolchain. We expect to start using some C++11 features in LLVM and other
  sub-projects starting after this release. That said, we are committed to
  supporting a reasonable set of modern C++ toolchains as the host compiler on
  all of the platforms. This will at least include Visual Studio 2012 on
  Windows, and Clang 3.1 or GCC 4.7.x on Mac and Linux. The final set of
  compilers (and the C++11 features they support) is not set in stone, but we
  wanted users of LLVM to have a heads up that the next release will involve
  a substantial change in the host toolchain requirements.

* The regression tests now fail if any command in a pipe fails. To disable it in
  a directory, just add ``config.pipefail = False`` to its ``lit.local.cfg``.
  See :doc:`Lit <CommandGuide/lit>` for the details.

* Support for exception handling has been removed from the old JIT. Use MCJIT
  if you need EH support.

* The R600 backend is not marked experimental anymore and is built by default.

* ``APFloat::isNormal()`` was renamed to ``APFloat::isFiniteNonZero()`` and
  ``APFloat::isIEEENormal()`` was renamed to ``APFloat::isNormal()``. This
  ensures that ``APFloat::isNormal()`` conforms to IEEE-754R-2008.

* The library call simplification pass has been removed.  Its functionality
  has been integrated into the instruction combiner and function attribute
  marking passes.

* Support for building using Visual Studio 2008 has been dropped. Use VS 2010
  or later instead. For more information, see the `Getting Started using Visual
  Studio <GettingStartedVS.html>`_ page.

* The Loop Vectorizer that was previously enabled for ``-O3`` is now enabled
  for ``-Os`` and ``-O2``.

* The new SLP Vectorizer is now enabled by default.

* ``llvm-ar`` now uses the new Object library and produces archives and
  symbol tables in the gnu format.

* FileCheck now allows specifing ``-check-prefix`` multiple times. This
  helps reduce duplicate check lines when using multiple RUN lines.

* The bitcast instruction no longer allows casting between pointers
   with different address spaces. To achieve this, use the new addrspacecast
   instruction.

* Different sized pointers for different address spaces should now
  generally work. This is primarily useful for GPU targets.

* OCaml bindings have been significantly extended to cover almost all of the
  LLVM libraries.

Mips Target
-----------

Support for the MIPS SIMD Architecture (MSA) has been added. MSA is supported
through inline assembly, intrinsics with the prefix '``__builtin_msa``', and
normal code generation.

For more information on MSA (including documentation for the instruction set),
see the `MIPS SIMD page at Imagination Technologies
<http://imgtec.com/mips/mips-simd.asp>`_

PowerPC Target
--------------

Changes in the PowerPC backend include:

* fast-isel support (for faster ``-O0`` code generation)
* many improvements to the builtin assembler
* support for generating unaligned (Altivec) vector loads
* support for generating the fcpsgn instruction
* generate ``frin`` for ``round()`` (not ``nearbyint()`` and ``rint()``, which
  had been done only in fast-math mode)
* improved instruction scheduling for embedded cores (such as the A2)
* improved prologue/epilogue generation (especially in 32-bit mode)
* support for dynamic stack alignment (and dynamic stack allocations with large alignments)
* improved generation of counter-register-based loops
* bug fixes

SPARC Target
------------

The SPARC backend got many improvements, namely

* experimental SPARC V9 backend
* JIT support for SPARC
* fp128 support
* exception handling
* TLS support
* leaf functions optimization
* bug fixes

SystemZ/s390x Backend
---------------------

LLVM and clang can now optimize for zEnterprise z196 and zEnterprise EC12
targets.  In clang these targets are selected using ``-march=z196`` and
``-march=zEC12`` respectively.

External Open Source Projects Using LLVM 3.4
============================================

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 3.4.

DXR
---

`DXR <https://wiki.mozilla.org/DXR>`_ is Mozilla's code search and navigation
tool, aimed at making sense of large projects like Firefox. It supports
full-text and regex searches as well as structural queries like "Find all the
callers of this function." Behind the scenes, it uses a custom trigram index,
the re2 library, and structural data collected by a clang compiler plugin.

LDC - the LLVM-based D compiler
-------------------------------

`D <http://dlang.org>`_ is a language with C-like syntax and static typing. It
pragmatically combines efficiency, control, and modeling power, with safety and
programmer productivity. D supports powerful concepts like Compile-Time Function
Execution (CTFE) and Template Meta-Programming, provides an innovative approach
to concurrency and offers many classical paradigms.

`LDC <http://wiki.dlang.org/LDC>`_ uses the frontend from the reference compiler
combined with LLVM as backend to produce efficient native code. LDC targets
x86/x86_64 systems like Linux, OS X, FreeBSD and Windows and also Linux/PPC64.
Ports to other architectures like ARM and AArch64 are underway.

LibBeauty
---------

The `LibBeauty <http://www.libbeauty.com>`_ decompiler and reverse
engineering tool currently utilises the LLVM disassembler and the LLVM IR
Builder. The current aim of the project is to take a x86_64 binary ``.o`` file
as input, and produce an equivalent LLVM IR ``.bc`` or ``.ll`` file as
output. Support for ARM binary ``.o`` file as input will be added later.

Likely
------

`Likely <http://www.liblikely.org/>`_ is an open source domain specific
language for image recognition.  Algorithms are just-in-time compiled using
LLVM's MCJIT infrastructure to execute on single or multi-threaded CPUs as well
as OpenCL SPIR or CUDA enabled GPUs. Likely exploits the observation that while
image processing and statistical learning kernels must be written generically
to handle any matrix datatype, at runtime they tend to be executed repeatedly
on the same type.

Portable Computing Language (pocl)
----------------------------------

In addition to producing an easily portable open source OpenCL
implementation, another major goal of `pocl <http://portablecl.org/>`_
is improving performance portability of OpenCL programs with
compiler optimizations, reducing the need for target-dependent manual
optimizations. An important part of pocl is a set of LLVM passes used to
statically parallelize multiple work-items with the kernel compiler, even in
the presence of work-group barriers. This enables static parallelization of
the fine-grained static concurrency in the work groups in multiple ways. 

Portable Native Client (PNaCl)
------------------------------

`Portable Native Client (PNaCl) <http://www.chromium.org/nativeclient/pnacl>`_
is a Chrome initiative to bring the performance and low-level control of native
code to modern web browsers, without sacrificing the security benefits and
portability of web applications. PNaCl works by compiling native C and C++ code
to an intermediate representation using the LLVM clang compiler. This
intermediate representation is a subset of LLVM bytecode that is wrapped into a
portable executable, which can be hosted on a web server like any other website
asset. When the site is accessed, Chrome fetches and translates the portable
executable into an architecture-specific machine code optimized directly for
the underlying device. PNaCl lets developers compile their code once to run on
any hardware platform and embed their PNaCl application in any website,
enabling developers to directly leverage the power of the underlying CPU and
GPU.

TTA-based Co-design Environment (TCE)
-------------------------------------

`TCE <http://tce.cs.tut.fi/>`_ is a toolset for designing new
exposed datapath processors based on the Transport triggered architecture (TTA). 
The toolset provides a complete co-design flow from C/C++
programs down to synthesizable VHDL/Verilog and parallel program binaries.
Processor customization points include the register files, function units,
supported operations, and the interconnection network.

TCE uses Clang and LLVM for C/C++/OpenCL C language support, target independent 
optimizations and also for parts of code generation. It generates
new LLVM-based code generators "on the fly" for the designed processors and
loads them in to the compiler backend as runtime libraries to avoid
per-target recompilation of larger parts of the compiler chain. 

WebCL Validator
---------------

`WebCL Validator <https://github.com/KhronosGroup/webcl-validator>`_ implements
validation for WebCL C language which is a subset of OpenCL ES 1.1. Validator
checks the correctness of WebCL C, and implements memory protection for it as a
source-2-source transformation. The transformation converts WebCL to memory
protected OpenCL. The protected OpenCL cannot access any memory ranges which
were not allocated for it, and its memory is always initialized to prevent
information leakage from other programs.


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>`_.
