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Nadav Rotem b08c1de748 Update the release notes about how to enable the loop vectorizer. 
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<title>LLVM 3.2 Release Notes</title>
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<body>
<h1>LLVM 3.2 Release Notes</h1>
<div>
<img style="float:right" src="http://llvm.org/img/DragonSmall.png"
width="136" height="136" alt="LLVM Dragon Logo">
</div>
<ol>
<li><a href="#intro">Introduction</a></li>
<li><a href="#subproj">Sub-project Status Update</a></li>
<li><a href="#externalproj">External Projects Using LLVM 3.2</a></li>
<li><a href="#whatsnew">What's New in LLVM?</a></li>
<li><a href="GettingStarted.html">Installation Instructions</a></li>
<li><a href="#knownproblems">Known Problems</a></li>
<li><a href="#additionalinfo">Additional Information</a></li>
</ol>
<div class="doc_author">
<p>Written by the <a href="http://llvm.org/">LLVM Team</a></p>
</div>
<h1 style="color:red">These are in-progress notes for the upcoming LLVM 3.2
release.<br>
You may prefer the
<a href="http://llvm.org/releases/3.1/docs/ReleaseNotes.html">LLVM 3.1
Release Notes</a>.</h1>
<!-- *********************************************************************** -->
<h2>
<a name="intro">Introduction</a>
</h2>
<!-- *********************************************************************** -->
<div>
<p>This document contains the release notes for the LLVM Compiler
Infrastructure, release 3.2. 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 <a href="http://llvm.org/releases/">LLVM
releases web site</a>.</p>
<p>For more information about LLVM, including information about the latest
release, please check out the <a href="http://llvm.org/">main LLVM web
site</a>. If you have questions or comments,
the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM
Developer's Mailing List</a> is a good place to send them.</p>
<p>Note that if you are reading this file from a Subversion checkout or the main
LLVM web page, this document applies to the <i>next</i> release, not the
current one. To see the release notes for a specific release, please see the
<a href="http://llvm.org/releases/">releases page</a>.</p>
</div>
<!-- *********************************************************************** -->
<h2>
<a name="subproj">Sub-project Status Update</a>
</h2>
<!-- *********************************************************************** -->
<div>
<p>The LLVM 3.2 distribution currently consists of code from the core LLVM
repository, which roughly includes the LLVM optimizers, code generators and
supporting tools, and the Clang repository. In addition to this code, the
LLVM Project includes other sub-projects that are in development. Here we
include updates on these subprojects.</p>
<!--=========================================================================-->
<h3>
<a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>
</h3>
<div>
<p><a href="http://clang.llvm.org/">Clang</a> is an LLVM front end for the C,
C++, and Objective-C languages. Clang aims to provide a better user
experience through expressive diagnostics, a high level of conformance to
language standards, fast compilation, and low memory use. Like LLVM, Clang
provides a modular, library-based architecture that makes it suitable for
creating or integrating with other development tools. Clang is considered a
production-quality compiler for C, Objective-C, C++ and Objective-C++ on x86
(32- and 64-bit), and for Darwin/ARM targets.</p>
<p>In the LLVM 3.2 time-frame, the Clang team has made many improvements.
Highlights include:</p>
<ul>
<li>...</li>
</ul>
<p>For more details about the changes to Clang since the 3.1 release, see the
<a href="http://clang.llvm.org/docs/ReleaseNotes.html">Clang release
notes.</a></p>
<p>If Clang rejects your code but another compiler accepts it, please take a
look at the <a href="http://clang.llvm.org/compatibility.html">language
compatibility</a> guide to make sure this is not intentional or a known
issue.</p>
</div>
<!--=========================================================================-->
<h3>
<a name="dragonegg">DragonEgg: GCC front-ends, LLVM back-end</a>
</h3>
<div>
<p><a href="http://dragonegg.llvm.org/">DragonEgg</a> is a
<a href="http://gcc.gnu.org/wiki/plugins">gcc plugin</a> that replaces GCC's
optimizers and code generators with LLVM's. It works with gcc-4.5 and gcc-4.6
(and partially with gcc-4.7), can target the x86-32/x86-64 and ARM processor
families, and has been successfully used on the Darwin, FreeBSD, KFreeBSD,
Linux and OpenBSD platforms. It fully supports Ada, C, C++ and Fortran. It
has partial support for Go, Java, Obj-C and Obj-C++.</p>
<p>The 3.2 release has the following notable changes:</p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="compiler-rt">compiler-rt: Compiler Runtime Library</a>
</h3>
<div>
<p>The new LLVM <a href="http://compiler-rt.llvm.org/">compiler-rt project</a>
is a simple library that provides an implementation of the low-level
target-specific hooks required by code generation and other runtime
components. For example, when compiling for a 32-bit target, converting a
double to a 64-bit unsigned integer is compiled into a runtime call to the
<code>__fixunsdfdi</code> function. The compiler-rt library provides highly
optimized implementations of this and other low-level routines (some are 3x
faster than the equivalent libgcc routines).</p>
<p>The 3.2 release has the following notable changes:</p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="lldb">LLDB: Low Level Debugger</a>
</h3>
<div>
<p><a href="http://lldb.llvm.org">LLDB</a> is a ground-up implementation of a
command line debugger, as well as a debugger API that can be used from other
applications. LLDB makes use of the Clang parser to provide high-fidelity
expression parsing (particularly for C++) and uses the LLVM JIT for target
support.</p>
<p>The 3.2 release has the following notable changes:</p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="libc++">libc++: C++ Standard Library</a>
</h3>
<div>
<p>Like compiler_rt, libc++ is now <a href="DeveloperPolicy.html#license">dual
licensed</a> under the MIT and UIUC license, allowing it to be used more
permissively.</p>
<p>Within the LLVM 3.2 time-frame there were the following highlights:</p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="vmkit">VMKit</a>
</h3>
<div>
<p>The <a href="http://vmkit.llvm.org/">VMKit project</a> is an implementation
of a Java Virtual Machine (Java VM or JVM) that uses LLVM for static and
just-in-time compilation.</p>
<p>The 3.2 release has the following notable changes:</p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="Polly">Polly: Polyhedral Optimizer</a>
</h3>
<div>
<p><a href="http://polly.llvm.org/">Polly</a> is an <em>experimental</em>
optimizer for data locality and parallelism. It currently provides high-level
loop optimizations and automatic parallelisation (using the OpenMP run time).
Work in the area of automatic SIMD and accelerator code generation was
started.</p>
<p>Within the LLVM 3.2 time-frame there were the following highlights:</p>
<ul>
<li>...</li>
</ul>
</div>
</div>
<!-- *********************************************************************** -->
<h2>
<a name="externalproj">External Open Source Projects Using LLVM 3.2</a>
</h2>
<!-- *********************************************************************** -->
<div>
<p>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 3.2.</p>
<h3>Crack</h3>
<div>
<p><a href="http://code.google.com/p/crack-language/">Crack</a> aims to provide
the ease of development of a scripting language with the performance of a
compiled language. The language derives concepts from C++, Java and Python,
incorporating object-oriented programming, operator overloading and strong
typing.</p>
</div>
<h3>FAUST</h3>
<div>
<p><a href="http://faust.grame.fr/">FAUST</a> is a compiled language for
real-time audio signal processing. The name FAUST stands for Functional
AUdio STream. Its programming model combines two approaches: functional
programming and block diagram composition. In addition with the C, C++, Java,
JavaScript output formats, the Faust compiler can generate LLVM bitcode, and
works with LLVM 2.7-3.1.</p>
</div>
<h3>Glasgow Haskell Compiler (GHC)</h3>
<div>
<p><a href="http://www.haskell.org/ghc/">GHC</a> is an open source compiler and
programming suite for Haskell, a lazy functional programming language. It
includes an optimizing static compiler generating good code for a variety of
platforms, together with an interactive system for convenient, quick
development.</p>
<p>GHC 7.0 and onwards include an LLVM code generator, supporting LLVM 2.8 and
later.</p>
</div>
<h3>Julia</h3>
<div>
<p><a href="https://github.com/JuliaLang/julia">Julia</a> is a high-level,
high-performance dynamic language for technical computing. It provides a
sophisticated compiler, distributed parallel execution, numerical accuracy,
and an extensive mathematical function library. The compiler uses type
inference to generate fast code without any type declarations, and uses
LLVM's optimization passes and JIT compiler. The
<a href="http://julialang.org/"> Julia Language</a> is designed
around multiple dispatch, giving programs a large degree of flexibility. It
is ready for use on many kinds of problems.</p>
</div>
<h3>LLVM D Compiler</h3>
<div>
<p><a href="https://github.com/ldc-developers/ldc">LLVM D Compiler</a> (LDC) is
a compiler for the D programming Language. It is based on the DMD frontend
and uses LLVM as backend.</p>
</div>
<h3>Open Shading Language</h3>
<div>
<p><a href="https://github.com/imageworks/OpenShadingLanguage/">Open Shading
Language (OSL)</a> is a small but rich language for programmable shading in
advanced global illumination renderers and other applications, ideal for
describing materials, lights, displacement, and pattern generation. It uses
LLVM to JIT complex shader networks to x86 code at runtime.</p>
<p>OSL was developed by Sony Pictures Imageworks for use in its in-house
renderer used for feature film animation and visual effects, and is
distributed as open source software with the "New BSD" license.</p>
</div>
<h3>Portable OpenCL (pocl)</h3>
<div>
<p>In addition to producing an easily portable open source OpenCL
implementation, another major goal of <a href="http://pocl.sourceforge.net/">
pocl</a> 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
(SIMD, VLIW, superscalar,...).</p>
</div>
<h3>Pure</h3>
<div>
<p><a href="http://pure-lang.googlecode.com/">Pure</a> is an
algebraic/functional programming language based on term rewriting. Programs
are collections of equations which are used to evaluate expressions in a
symbolic fashion. The interpreter uses LLVM as a backend to JIT-compile Pure
programs to fast native code. Pure offers dynamic typing, eager and lazy
evaluation, lexical closures, a hygienic macro system (also based on term
rewriting), built-in list and matrix support (including list and matrix
comprehensions) and an easy-to-use interface to C and other programming
languages (including the ability to load LLVM bitcode modules, and inline C,
C++, Fortran and Faust code in Pure programs if the corresponding
LLVM-enabled compilers are installed).</p>
<p>Pure version 0.54 has been tested and is known to work with LLVM 3.1 (and
continues to work with older LLVM releases >= 2.5).</p>
</div>
<h3>TTA-based Co-design Environment (TCE)</h3>
<div>
<p><a href="http://tce.cs.tut.fi/">TCE</a> is a toolset for designing
application-specific processors (ASP) 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.</p>
<p>TCE uses Clang and LLVM for C/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 TTA processors and
loads them in to the compiler backend as runtime libraries to avoid
per-target recompilation of larger parts of the compiler chain.</p>
</div>
</div>
<!-- *********************************************************************** -->
<h2>
<a name="whatsnew">What's New in LLVM 3.2?</a>
</h2>
<!-- *********************************************************************** -->
<div>
<p>This release includes a huge number of bug fixes, performance tweaks and
minor improvements. Some of the major improvements and new features are
listed in this section.</p>
<!--=========================================================================-->
<h3>
<a name="majorfeatures">Major New Features</a>
</h3>
<div>
<!-- Features that need text if they're finished for 3.2:
ARM EHABI
combiner-aa?
strong phi elim
loop dependence analysis
CorrelatedValuePropagation
lib/Transforms/IPO/MergeFunctions.cpp => consider for 3.2.
Integrated assembler on by default for arm/thumb?
-->
<!-- Near dead:
Analysis/RegionInfo.h + Dom Frontiers
SparseBitVector: used in LiveVar.
llvm/lib/Archive - replace with lib object?
-->
<p>LLVM 3.2 includes several major changes and big features:</p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="coreimprovements">LLVM IR and Core Improvements</a>
</h3>
<div>
<p>LLVM IR has several new features for better support of new targets and that
expose new optimization opportunities:</p>
<ul>
<li>Thread local variables may have a specified TLS model. See the
<a href="LangRef.html#globalvars">Language Reference Manual</a>.</li>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="optimizer">Optimizer Improvements</a>
</h3>
<div>
<p>In addition to many minor performance tweaks and bug fixes, this release
includes a few major enhancements and additions to the optimizers:</p>
<p> Loop Vectorizer - We've added a basic loop vectorizer and we are now able
to vectorize small loops. The loop vectorizer is disabled by default and
can be enabled using the -mllvm -vectorize flags. </p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="mc">MC Level Improvements</a>
</h3>
<div>
<p>The LLVM Machine Code (aka MC) subsystem was created to solve a number of
problems in the realm of assembly, disassembly, object file format handling,
and a number of other related areas that CPU instruction-set level tools work
in. For more information, please see the
<a href="http://blog.llvm.org/2010/04/intro-to-llvm-mc-project.html">Intro
to the LLVM MC Project Blog Post</a>.</p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="codegen">Target Independent Code Generator Improvements</a>
</h3>
<div>
<p>Stack Coloring - We have implemented a new optimization pass
to merge stack objects which are used in disjoin areas of the code.
This optimization reduces the required stack space significantly, in cases
where it is clear to the optimizer that the stack slot is not shared.
We use the lifetime markers to tell the codegen that a certain alloca
is used within a region.</p>
<p> We now merge consecutive loads and stores. </p>
<p>We have put a significant amount of work into the code generator
infrastructure, which allows us to implement more aggressive algorithms and
make it run faster:</p>
<ul>
<li>...</li>
</ul>
<p> We added new TableGen infrastructure to support bundling for
Very Long Instruction Word (VLIW) architectures. TableGen can now
automatically generate a deterministic finite automaton from a VLIW
target's schedule description which can be queried to determine
legal groupings of instructions in a bundle.</p>
<p> We have added a new target independent VLIW packetizer based on the
DFA infrastructure to group machine instructions into bundles.</p>
</div>
<h4>
<a name="blockplacement">Basic Block Placement</a>
</h4>
<div>
<p>A probability based block placement and code layout algorithm was added to
LLVM's code generator. This layout pass supports probabilities derived from
static heuristics as well as source code annotations such as
<code>__builtin_expect</code>.</p>
</div>
<!--=========================================================================-->
<h3>
<a name="x86">X86-32 and X86-64 Target Improvements</a>
</h3>
<div>
<p>New features and major changes in the X86 target include:</p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="ARM">ARM Target Improvements</a>
</h3>
<div>
<p>New features of the ARM target include:</p>
<ul>
<li>...</li>
</ul>
<!--_________________________________________________________________________-->
<h4>
<a name="armintegratedassembler">ARM Integrated Assembler</a>
</h4>
<div>
<p>The ARM target now includes a full featured macro assembler, including
direct-to-object module support for clang. The assembler is currently enabled
by default for Darwin only pending testing and any additional necessary
platform specific support for Linux.</p>
<p>Full support is included for Thumb1, Thumb2 and ARM modes, along with
subtarget and CPU specific extensions for VFP2, VFP3 and NEON.</p>
<p>The assembler is Unified Syntax only (see ARM Architecural Reference Manual
for details). While there is some, and growing, support for pre-unfied
(divided) syntax, there are still significant gaps in that support.</p>
</div>
</div>
<!--=========================================================================-->
<h3>
<a name="MIPS">MIPS Target Improvements</a>
</h3>
<div>
<p>New features and major changes in the MIPS target include:</p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="OtherTS">Other Target Specific Improvements</a>
</h3>
<div>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="changes">Major Changes and Removed Features</a>
</h3>
<div>
<p>If you're already an LLVM user or developer with out-of-tree changes based on
LLVM 3.2, this section lists some "gotchas" that you may run into upgrading
from the previous release.</p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="api_changes">Internal API Changes</a>
</h3>
<div>
<p>In addition, many APIs have changed in this release. Some of the major
LLVM API changes are:</p>
<p> We've added a new interface for allowing IR-level passes to access
target-specific information. A new IR-level pass, called
"TargetTransformInfo" provides a number of low-level interfaces.
LSR and LowerInvoke already use the new interface. </p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="tools_changes">Tools Changes</a>
</h3>
<div>
<p>In addition, some tools have changed in this release. Some of the changes
are:</p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="python">Python Bindings</a>
</h3>
<div>
<p>Officially supported Python bindings have been added! Feature support is far
from complete. The current bindings support interfaces to:</p>
<ul>
<li>...</li>
</ul>
</div>
</div>
<!-- *********************************************************************** -->
<h2>
<a name="knownproblems">Known Problems</a>
</h2>
<!-- *********************************************************************** -->
<div>
<p>LLVM is generally a production quality compiler, and is used by a broad range
of applications and shipping in many products. That said, not every
subsystem is as mature as the aggregate, particularly the more obscure
targets. If you run into a problem, please check
the <a href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
there isn't already one or ask on
the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev
list</a>.</p>
<p>Known problem areas include:</p>
<ul>
<li>The CellSPU, MSP430, PTX and XCore backends are experimental.</li>
<li>The integrated assembler, disassembler, and JIT is not supported by
several targets. If an integrated assembler is not supported, then a
system assembler is required. For more details, see the <a
href="CodeGenerator.html#targetfeatures">Target Features Matrix</a>.
</li>
</ul>
</div>
<!-- *********************************************************************** -->
<h2>
<a name="additionalinfo">Additional Information</a>
</h2>
<!-- *********************************************************************** -->
<div>
<p>A wide variety of additional information is available on
the <a href="http://llvm.org/">LLVM web page</a>, in particular in
the <a href="http://llvm.org/docs/">documentation</a> 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 "<tt>llvm/doc/</tt>"
directory in the LLVM tree.</p>
<p>If you have any questions or comments about LLVM, please feel free to contact
us via the <a href="http://llvm.org/docs/#maillist"> mailing lists</a>.</p>
</div>
<!-- *********************************************************************** -->
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