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              <title>LLVM 2.6 Release Notes</title>

            
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            <div class="doc_title">LLVM 2.6 Release Notes</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 2.6</a></li>

            
              <li><a href="#whatsnew">What's New in LLVM 2.6?</a></li>

            
              <li><a href="GettingStarted.html">Installation Instructions</a></li>

            
              <li><a href="#portability">Portability and Supported Platforms</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>


            <!-- *********************************************************************** -->

            
            <div class="doc_section">

            
              <a name="intro">Introduction</a>

            
            </div>

            
            <!-- *********************************************************************** -->


            <div class="doc_text">


            <p>This document contains the release notes for the LLVM Compiler

            
            Infrastructure, release 2.6.  Here we describe the status of LLVM, including

            
            major improvements from the previous release and significant known problems.

            
            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://mail.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>


            <!--

            
            Almost dead code.

            
              include/llvm/Analysis/LiveValues.h => Dan

            
              lib/Transforms/IPO/MergeFunctions.cpp => consider for 2.8.

            
              llvm/Analysis/PointerTracking.h => Edwin wants this, consider for 2.8.

            
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            <!-- Unfinished features in 2.6:

            
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              strong phi elim

            
              variable debug info for optimized code

            
              postalloc scheduler: anti dependence breaking, hazard recognizer?

            
              metadata

            
              loop dependence analysis

            
              ELF Writer?  How stable?

            
              <li>PostRA scheduler improvements, ARM adoption (David Goodwin).</li>

            
              2.7 supports the GDB 7.0 jit interfaces for debug info.

            
              2.7 eliminates ADT/iterator.h

            
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             <!-- for announcement email:

            
             Logo web page.

            
             llvm devmtg

            
             compiler_rt

            
             KLEE web page at klee.llvm.org

            
             Many new papers added to /pubs/

            
               Mention gcc plugin.


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            <div class="doc_section">

            
              <a name="subproj">Sub-project Status Update</a>

            
            </div>

            
            <!-- *********************************************************************** -->


            <div class="doc_text">

            
            <p>

            
            The LLVM 2.6 distribution currently consists of code from the core LLVM

            
            repository (which roughly includes the LLVM optimizers, code generators

            
            and supporting tools), the Clang repository and the llvm-gcc 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>


            </div>


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            <div class="doc_subsection">

            
            <a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>

            
            </div>


            <div class="doc_text">


            <p>The <a href="http://clang.llvm.org/">Clang project</a> is an effort to build

            
            a set of new 'LLVM native' front-end technologies for the C family of languages.

            
            LLVM 2.6 is the first release to officially include Clang, and it provides a

            
            production quality C and Objective-C compiler.  If you are interested in <a

            
            href="http://clang.llvm.org/performance.html">fast compiles</a> and

            
            <a href="http://clang.llvm.org/diagnostics.html">good diagnostics</a>, we

            
            encourage you to try it out.  Clang currently compiles typical Objective-C code

            
            3x faster than GCC and compiles C code about 30% faster than GCC at -O0 -g

            
            (which is when the most pressure is on the frontend).</p>


            <p>In addition to supporting these languages, C++ support is also <a

            
            href="http://clang.llvm.org/cxx_status.html">well under way</a>, and mainline

            
            Clang is able to parse the libstdc++ 4.2 headers and even codegen simple apps.

            
            If you are interested in Clang C++ support or any other Clang feature, we

            
            strongly encourage you to get involved on the <a

            
            href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">Clang front-end mailing

            
            list</a>.</p>


            <p>In the LLVM 2.6 time-frame, the Clang team has made many improvements:</p>


            <ul>

            
            <li>C and Objective-C support are now considered production quality.</li>

            
            <li>AuroraUX, FreeBSD and OpenBSD are now supported.</li>

            
            <li>Most of Objective-C 2.0 is now supported with the GNU runtime.</li>

            
            <li>Many many bugs are fixed and lots of features have been added.</li>

            
            </ul>

            
            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="clangsa">Clang Static Analyzer</a>

            
            </div>


            <div class="doc_text">


            <p>Previously announced in the 2.4 and 2.5 LLVM releases, the Clang project also

            
            includes an early stage static source code analysis tool for <a

            
            href="http://clang.llvm.org/StaticAnalysis.html">automatically finding bugs</a>

            
            in C and Objective-C programs. The tool performs checks to find

            
            bugs that occur on a specific path within a program.</p>


            <p>In the LLVM 2.6 time-frame, the analyzer core has undergone several important

            
            improvements and cleanups and now includes a new <em>Checker</em> interface that

            
            is intended to eventually serve as a basis for domain-specific checks. Further,

            
            in addition to generating HTML files for reporting analysis results, the

            
            analyzer can now also emit bug reports in a structured XML format that is

            
            intended to be easily readable by other programs.</p>


            <p>The set of checks performed by the static analyzer continues to expand, and

            
            future plans for the tool include full source-level inter-procedural analysis

            
            and deeper checks such as buffer overrun detection. There are many opportunities

            
            to extend and enhance the static analyzer, and anyone interested in working on

            
            this project is encouraged to get involved!</p>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="vmkit">VMKit: JVM/CLI Virtual Machine Implementation</a>

            
            </div>


            <div class="doc_text">

            
            <p>

            
            The <a href="http://vmkit.llvm.org/">VMKit project</a> is an implementation of

            
            a JVM and a CLI Virtual Machine (Microsoft .NET is an

            
            implementation of the CLI) using LLVM for static and just-in-time

            
            compilation.</p>


            <p>

            
            VMKit version 0.26 builds with LLVM 2.6 and you can find it on its

            
            <a href="http://vmkit.llvm.org/releases/">web page</a>. The release includes

            
            bug fixes, cleanup and new features. The major changes are:</p>


            <ul>


            <li>A new llcj tool to generate shared libraries or executables of Java

            
                files.</li>

            
            <li>Cooperative garbage collection. </li>

            
            <li>Fast subtype checking (paper from Click et al [JGI'02]). </li>

            
            <li>Implementation of a two-word header for Java objects instead of the original

            
                three-word header. </li>

            
            <li>Better Java specification-compliance: division by zero checks, stack

            
                overflow checks, finalization and references support. </li>


            </ul>

            
            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="compiler-rt">compiler-rt: Compiler Runtime Library</a>

            
            </div>


            <div class="doc_text">

            
            <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 "__fixunsdfdi"

            
            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>

            
            All of the code in the compiler-rt project is available under the standard LLVM

            
            License, a "BSD-style" license.</p>


            </div>


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            <div class="doc_subsection">

            
            <a name="klee">KLEE: Symbolic Execution and Automatic Test Case Generator</a>

            
            </div>


            <div class="doc_text">

            
            <p>

            
            The new LLVM <a href="http://klee.llvm.org/">KLEE project</a> is a symbolic

            
            execution framework for programs in LLVM bitcode form.  KLEE tries to

            
            symbolically evaluate "all" paths through the application and records state

            
            transitions that lead to fault states.  This allows it to construct testcases

            
            that lead to faults and can even be used to verify algorithms.  For more

            
            details, please see the <a

            
            href="http://llvm.org/pubs/2008-12-OSDI-KLEE.html">OSDI 2008 paper</a> about

            
            KLEE.</p>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="dragonegg">DragonEgg: GCC-4.5 as an LLVM frontend</a>

            
            </div>


            <div class="doc_text">

            
            <p>

            
            The goal of <a href="http://dragonegg.llvm.org/">DragonEgg</a> is to make

            
            gcc-4.5 act like llvm-gcc without requiring any gcc modifications whatsoever.

            
            <a href="http://dragonegg.llvm.org/">DragonEgg</a> is a shared library (dragonegg.so)

            
            that is loaded by gcc at runtime.  It uses the new gcc plugin architecture to

            
            disable the GCC optimizers and code generators, and schedule the LLVM optimizers

            
            and code generators (or direct output of LLVM IR) instead.  Currently only Linux

            
            and Darwin are supported, and only on x86-32 and x86-64.  It should be easy to

            
            add additional unix-like architectures and other processor families.  In theory

            
            it should be possible to use <a href="http://dragonegg.llvm.org/">DragonEgg</a>

            
            with any language supported by gcc, however only C and Fortran work well for the

            
            moment.  Ada and C++ work to some extent, while Java, Obj-C and Obj-C++ are so

            
            far entirely untested.  Since gcc-4.5 has not yet been released, neither has

            
            <a href="http://dragonegg.llvm.org/">DragonEgg</a>.  To build

            
            <a href="http://dragonegg.llvm.org/">DragonEgg</a> you will need to check out the

            
            development versions of <a href="http://gcc.gnu.org/svn.html/"> gcc</a>,

            
            <a href="http://llvm.org/docs/GettingStarted.html#checkout">llvm</a> and

            
            <a href="http://dragonegg.llvm.org/">DragonEgg</a> from their respective

            
            subversion repositories, and follow the instructions in the

            
            <a href="http://dragonegg.llvm.org/">DragonEgg</a> README.

            
            </p>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="mc">llvm-mc: Machine Code Toolkit</a>

            
            </div>


            <div class="doc_text">

            
            <p>

            
            The LLVM Machine Code (MC) Toolkit project is a (very early) effort to build

            
            better tools for dealing with machine code, object file formats, etc.  The idea

            
            is to be able to generate most of the target specific details of assemblers and

            
            disassemblers from existing LLVM target .td files (with suitable enhancements),

            
            and to build infrastructure for reading and writing common object file formats.

            
            One of the first deliverables is to build a full assembler and integrate it into

            
            the compiler, which is predicted to substantially reduce compile time in some

            
            scenarios.

            
            </p>


            <p>In the LLVM 2.6 timeframe, the MC framework has grown to the point where it

            
            can reliably parse and pretty print (with some encoding information) a

            
            darwin/x86 .s file successfully, and has the very early phases of a Mach-O

            
            assembler in progress.  Beyond the MC framework itself, major refactoring of the

            
            LLVM code generator has started.  The idea is to make the code generator reason

            
            about the code it is producing in a much more semantic way, rather than a

            
            textual way.  For example, the code generator now uses MCSection objects to

            
            represent section assignments, instead of text strings that print to .section

            
            directives.</p>


            <p>MC is an early and ongoing project that will hopefully continue to lead to

            
            many improvements in the code generator and build infrastructure useful for many

            
            other situations.

            
            </p>


            </div>


            <!-- *********************************************************************** -->

            
            <div class="doc_section">

            
              <a name="externalproj">External Open Source Projects Using LLVM 2.6</a>

            
            </div>

            
            <!-- *********************************************************************** -->


            <div class="doc_text">


            <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 2.6.</p>

            
            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="Rubinius">Rubinius</a>

            
            </div>


            <div class="doc_text">

            
            <p><a href="http://github.com/evanphx/rubinius">Rubinius</a> is an environment

            
            for running Ruby code which strives to write as much of the core class

            
            implementation in Ruby as possible. Combined with a bytecode interpreting VM, it

            
            uses LLVM to optimize and compile ruby code down to machine code. Techniques

            
            such as type feedback, method inlining, and uncommon traps are all used to

            
            remove dynamism from ruby execution and increase performance.</p>


            <p>Since LLVM 2.5, Rubinius has made several major leaps forward, implementing

            
            a counter based JIT, type feedback and speculative method inlining.

            
            </p>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="macruby">MacRuby</a>

            
            </div>


            <div class="doc_text">


            <p>

            
            <a href="http://macruby.org">MacRuby</a> is an implementation of Ruby on top of

            
            core Mac OS X technologies, such as the Objective-C common runtime and garbage

            
            collector and the CoreFoundation framework. It is principally developed by

            
            Apple and aims at enabling the creation of full-fledged Mac OS X applications.

            
            </p>


            <p>

            
            MacRuby uses LLVM for optimization passes, JIT and AOT compilation of Ruby

            
            expressions. It also uses zero-cost DWARF exceptions to implement Ruby exception

            
            handling.</p>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="pure">Pure</a>

            
            </div>


            <div class="doc_text">

            
            <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. 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 C interface. The interpreter uses LLVM as a backend to

            
             JIT-compile Pure programs to fast native code.</p>


            <p>Pure versions 0.31 and later have been tested and are known to work with

            
            LLVM 2.6 (and continue to work with older LLVM releases >= 2.3 as well).

            
            </p>

            
            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="ldc">LLVM D Compiler</a>

            
            </div>


            <div class="doc_text">

            
            <p>

            
            <a href="http://www.dsource.org/projects/ldc">LDC</a> is an implementation of

            
            the D Programming Language using the LLVM optimizer and code generator.

            
            The LDC project works great with the LLVM 2.6 release.  General improvements in

            
            this

            
            cycle have included new inline asm constraint handling, better debug info

            
            support, general bug fixes and better x86-64 support.  This has allowed

            
            some major improvements in LDC, getting it much closer to being as

            
            fully featured as the original DMD compiler from DigitalMars.

            
            </p>

            
            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="RoadsendPHP">Roadsend PHP</a>

            
            </div>


            <div class="doc_text">

            
            <p>

            
            <a href="http://code.roadsend.com/rphp">Roadsend PHP</a> (rphp) is an open

            
            source implementation of the PHP programming

            
            language that uses LLVM for its optimizer, JIT and static compiler. This is a

            
            reimplementation of an earlier project that is now based on LLVM.</p>

            
            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="UnladenSwallow">Unladen Swallow</a>

            
            </div>


            <div class="doc_text">

            
            <p>

            
            <a href="http://code.google.com/p/unladen-swallow/">Unladen Swallow</a> is a

            
            branch of <a href="http://python.org/">Python</a> intended to be fully

            
            compatible and significantly faster.  It uses LLVM's optimization passes and JIT

            
            compiler.</p>

            
            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="llvm-lua">llvm-lua</a>

            
            </div>


            <div class="doc_text">

            
            <p>

            
            <a href="http://code.google.com/p/llvm-lua/">LLVM-Lua</a> uses LLVM to add JIT

            
            and static compiling support to the Lua VM.  Lua bytecode is analyzed to

            
            remove type checks, then LLVM is used to compile the bytecode down to machine

            
            code.</p>

            
            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="icedtea">IcedTea Java Virtual Machine Implementation</a>

            
            </div>


            <div class="doc_text">

            
            <p>

            
            <a href="http://icedtea.classpath.org/wiki/Main_Page">IcedTea</a> provides a

            
            harness to build OpenJDK using only free software build tools and to provide

            
            replacements for the not-yet free parts of OpenJDK.  One of the extensions that

            
            IcedTea provides is a new JIT compiler named <a

            
            href="http://icedtea.classpath.org/wiki/ZeroSharkFaq">Shark</a> which uses LLVM

            
            to provide native code generation without introducing processor-dependent

            
            code.

            
            </p>

            
            </div>


            <!-- *********************************************************************** -->

            
            <div class="doc_section">

            
              <a name="whatsnew">What's New in LLVM 2.6?</a>

            
            </div>

            
            <!-- *********************************************************************** -->


            <div class="doc_text">


            <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>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="majorfeatures">Major New Features</a>

            
            </div>


            <div class="doc_text">


            <p>LLVM 2.6 includes several major new capabilities:</p>


            <ul>

            
            <li>New <a href="#compiler-rt">compiler-rt</a>, <A href="#klee">KLEE</a>

            
                and <a href="#mc">machine code toolkit</a> sub-projects.</li>

            
            <li>Debug information now includes line numbers when optimizations are enabled.

            
                This allows statistical sampling tools like OProfile and Shark to map

            
                samples back to source lines.</li>

            
            <li>LLVM now includes new experimental backends to support the MSP430, SystemZ

            
                and BlackFin architectures.</li>

            
            <li>LLVM supports a new <a href="GoldPlugin.html">Gold Linker Plugin</a> which

            
                enables support for <a href="LinkTimeOptimization.html">transparent

            
                link-time optimization</a> on ELF targets when used with the Gold binutils

            
                linker.</li>

            
            <li>LLVM now supports doing optimization and code generation on multiple

            
                threads.  Please see the <a href="ProgrammersManual.html#threading">LLVM

            
                Programmer's Manual</a> for more information.</li>

            
            <li>LLVM now has experimental support for <a

            
                href="http://nondot.org/~sabre/LLVMNotes/EmbeddedMetadata.txt">embedded

            
                metadata</a> in LLVM IR, though the implementation is not guaranteed to be

            
                final and the .bc file format may change in future releases.  Debug info

            
                does not yet use this format in LLVM 2.6.</li>

            
            </ul>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="coreimprovements">LLVM IR and Core Improvements</a>

            
            </div>


            <div class="doc_text">

            
            <p>LLVM IR has several new features for better support of new targets and that

            
            expose new optimization opportunities:</p>


            <ul>

            
            <li>The <a href="LangRef.html#i_add">add</a>, <a

            
                href="LangRef.html#i_sub">sub</a> and <a href="LangRef.html#i_mul">mul</a>

            
                instructions have been split into integer and floating point versions (like

            
                divide and remainder), introducing new <a

            
                href="LangRef.html#i_fadd">fadd</a>, <a href="LangRef.html#i_fsub">fsub</a>,

            
                and <a href="LangRef.html#i_fmul">fmul</a> instructions.</li>

            
            <li>The <a href="LangRef.html#i_add">add</a>, <a

            
                href="LangRef.html#i_sub">sub</a> and <a href="LangRef.html#i_mul">mul</a>

            
                instructions now support optional "nsw" and "nuw" bits which indicate that

            
                the operation is guaranteed to not overflow (in the signed or

            
                unsigned case, respectively).  This gives the optimizer more information and

            
                can be used for things like C signed integer values, which are undefined on

            
                overflow.</li>

            
            <li>The <a href="LangRef.html#i_sdiv">sdiv</a> instruction now supports an

            
                optional "exact" flag which indicates that the result of the division is

            
                guaranteed to have a remainder of zero.  This is useful for optimizing pointer

            
                subtraction in C.</li>

            
            <li>The <a href="LangRef.html#i_getelementptr">getelementptr</a> instruction now

            
                supports arbitrary integer index values for array/pointer indices.  This

            
                allows for better code generation on 16-bit pointer targets like PIC16.</li>

            
            <li>The <a href="LangRef.html#i_getelementptr">getelementptr</a> instruction now

            
                supports an "inbounds" optimization hint that tells the optimizer that the

            
                pointer is guaranteed to be within its allocated object.</li>

            
            <li>LLVM now support a series of new linkage types for global values which allow

            
                for better optimization and new capabilities:

            
                <ul>

            
                <li><a href="LangRef.html#linkage_linkonce">linkonce_odr</a> and

            
                    <a href="LangRef.html#linkage_weak">weak_odr</a> have the same linkage

            
                    semantics as the non-"odr" linkage types.  The difference is that these

            
                    linkage types indicate that all definitions of the specified function

            
                    are guaranteed to have the same semantics.  This allows inlining

            
                    templates functions in C++ but not inlining weak functions in C,

            
                    which previously both got the same linkage type.</li>

            
                <li><a href="LangRef.html#linkage_available_externally">available_externally

            
                    </a> is a new linkage type that gives the optimizer visibility into the

            
                    definition of a function (allowing inlining and side effect analysis)

            
                    but that does not cause code to be generated.  This allows better

            
                    optimization of "GNU inline" functions, extern templates, etc.</li>

            
                <li><a href="LangRef.html#linkage_linker_private">linker_private</a> is a

            
                    new linkage type (which is only useful on Mac OS X) that is used for

            
                    some metadata generation and other obscure things.</li>

            
                </ul></li>

            
            <li>Finally, target-specific intrinsics can now return multiple values, which

            
                is useful for modeling target operations with multiple results.</li>

            
            </ul>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="optimizer">Optimizer Improvements</a>

            
            </div>


            <div class="doc_text">


            <p>In addition to a large array of minor performance tweaks and bug fixes, this

            
            release includes a few major enhancements and additions to the optimizers:</p>


            <ul>


            <li>The <a href="Passes.html#scalarrepl">Scalar Replacement of Aggregates</a>

            
                pass has many improvements that allow it to better promote vector unions,

            
                variables which are memset, and much more strange code that can happen to

            
                do bitfield accesses to register operations.  An interesting change is that

            
                it now produces "unusual" integer sizes (like i1704) in some cases and lets

            
                other optimizers clean things up.</li>

            
            <li>The <a href="Passes.html#loop-reduce">Loop Strength Reduction</a> pass now

            
                promotes small integer induction variables to 64-bit on 64-bit targets,

            
                which provides a major performance boost for much numerical code.  It also

            
                promotes shorts to int on 32-bit hosts, etc.  LSR now also analyzes pointer

            
                expressions (e.g. getelementptrs), as well as integers.</li>

            
            <li>The <a href="Passes.html#gvn">GVN</a> pass now eliminates partial

            
                redundancies of loads in simple cases.</li>

            
            <li>The <a href="Passes.html#inline">Inliner</a> now reuses stack space when

            
                inlining similar arrays from multiple callees into one caller.</li>

            
            <li>LLVM includes a new experimental Static Single Information (SSI)

            
                construction pass.</li>


            </ul>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="executionengine">Interpreter and JIT Improvements</a>

            
            </div>


            <div class="doc_text">


            <ul>

            
            <li>LLVM has a new "EngineBuilder" class which makes it more obvious how to

            
                set up and configure an ExecutionEngine (a JIT or interpreter).</li>

            
            <li>The JIT now supports generating more than 16M of code.</li>

            
            <li>When configured with <tt>--with-oprofile</tt>, the JIT can now inform

            
                 OProfile about JIT'd code, allowing OProfile to get line number and function

            
                 name information for JIT'd functions.</li>

            
            <li>When "libffi" is available, the LLVM interpreter now uses it, which supports

            
                calling almost arbitrary external (natively compiled) functions.</li>

            
            <li>Clients of the JIT can now register a 'JITEventListener' object to receive

            
                callbacks when the JIT emits or frees machine code. The OProfile support

            
                uses this mechanism.</li>

            
            </ul>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="codegen">Target Independent Code Generator Improvements</a>

            
            </div>


            <div class="doc_text">


            <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>The <tt>llc -asm-verbose</tt> option (exposed from llvm-gcc as <tt>-dA</tt>

            
                and clang as <tt>-fverbose-asm</tt> or <tt>-dA</tt>) now adds a lot of

            
                useful information in comments to

            
                the generated .s file.  This information includes location information (if

            
                built with <tt>-g</tt>) and loop nest information.</li>

            
            <li>The code generator now supports a new MachineVerifier pass which is useful

            
                for finding bugs in targets and codegen passes.</li>

            
            <li>The Machine LICM is now enabled by default.  It hoists instructions out of

            
                loops (such as constant pool loads, loads from read-only stubs, vector

            
                constant synthesization code, etc.) and is currently configured to only do

            
                so when the hoisted operation can be rematerialized.</li>

            
            <li>The Machine Sinking pass is now enabled by default.  This pass moves

            
                side-effect free operations down the CFG so that they are executed on fewer

            
                paths through a function.</li>

            
            <li>The code generator now performs "stack slot coloring" of register spills,

            
                which allows spill slots to be reused.  This leads to smaller stack frames

            
                in cases where there are lots of register spills.</li>

            
            <li>The register allocator has many improvements to take better advantage of

            
                commutable operations, various spiller peephole optimizations, and can now

            
                coalesce cross-register-class copies.</li>

            
            <li>Tblgen now supports multiclass inheritance and a number of new string and

            
                list operations like <tt>!(subst)</tt>, <tt>!(foreach)</tt>, <tt>!car</tt>,

            
                <tt>!cdr</tt>, <tt>!null</tt>, <tt>!if</tt>, <tt>!cast</tt>.

            
                These make the .td files more expressive and allow more aggressive factoring

            
                of duplication across instruction patterns.</li>

            
            <li>Target-specific intrinsics can now be added without having to hack VMCore to

            
                add them.  This makes it easier to maintain out-of-tree targets.</li>

            
            <li>The instruction selector is better at propagating information about values

            
                (such as whether they are sign/zero extended etc.) across basic block

            
                boundaries.</li>

            
            <li>The SelectionDAG datastructure has new nodes for representing buildvector

            
                and <a href="http://llvm.org/PR2957">vector shuffle</a> operations.  This

            
                makes operations and pattern matching more efficient and easier to get

            
                right.</li>

            
            <li>The Prolog/Epilog Insertion Pass now has experimental support for performing

            
                the "shrink wrapping" optimization, which moves spills and reloads around in

            
                the CFG to avoid doing saves on paths that don't need them.</li>

            
            <li>LLVM includes new experimental support for writing ELF .o files directly

            
                from the compiler.  It works well for many simple C testcases, but doesn't

            
                support exception handling, debug info, inline assembly, etc.</li>

            
            <li>Targets can now specify register allocation hints through

            
                <tt>MachineRegisterInfo::setRegAllocationHint</tt>. A regalloc hint consists

            
                of hint type and physical register number. A hint type of zero specifies a

            
                register allocation preference. Other hint type values are target specific

            
                which are resolved by <tt>TargetRegisterInfo::ResolveRegAllocHint</tt>. An

            
                example is the ARM target which uses register hints to request that the

            
                register allocator provide an even / odd register pair to two virtual

            
                registers.</li>

            
            </ul>

            
            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="x86">X86-32 and X86-64 Target Improvements</a>

            
            </div>


            <div class="doc_text">

            
            <p>New features of the X86 target include:

            
            </p>


            <ul>


            <li>SSE 4.2 builtins are now supported.</li>

            
            <li>GCC-compatible soft float modes are now supported, which are typically used

            
                by OS kernels.</li>

            
            <li>X86-64 now models implicit zero extensions better, which allows the code

            
                generator to remove a lot of redundant zexts.  It also models the 8-bit "H"

            
                registers as subregs, which allows them to be used in some tricky

            
                situations.</li>

            
            <li>X86-64 now supports the "local exec" and "initial exec" thread local storage

            
                model.</li>

            
            <li>The vector forms of the <a href="LangRef.html#i_icmp">icmp</a> and <a

            
                href="LangRef.html#i_fcmp">fcmp</a> instructions now select to efficient

            
                SSE operations.</li>

            
            <li>Support for the win64 calling conventions have improved.  The primary

            
                missing feature is support for varargs function definitions.  It seems to

            
                work well for many win64 JIT purposes.</li>

            
            <li>The X86 backend has preliminary support for <a

            
                href="CodeGenerator.html#x86_memory">mapping address spaces to segment

            
                register references</a>.  This allows you to write GS or FS relative memory

            
                accesses directly in LLVM IR for cases where you know exactly what you're

            
                doing (such as in an OS kernel).  There are some known problems with this

            
                support, but it works in simple cases.</li>

            
            <li>The X86 code generator has been refactored to move all global variable

            
                reference logic to one place

            
                (<tt>X86Subtarget::ClassifyGlobalReference</tt>) which

            
                makes it easier to reason about.</li>


            </ul>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="pic16">PIC16 Target Improvements</a>

            
            </div>


            <div class="doc_text">

            
            <p>New features of the PIC16 target include:

            
            </p>


            <ul>

            
            <li>Support for floating-point, indirect function calls, and

            
                passing/returning aggregate types to functions.

            
            <li>The code generator is able to generate debug info into output COFF files.

            
            <li>Support for placing an object into a specific section or at a specific

            
                address in memory.</li>

            
            </ul>


            <p>Things not yet supported:</p>


            <ul>

            
            <li>Variable arguments.</li>

            
            <li>Interrupts/programs.</li>

            
            </ul>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="ARM">ARM Target Improvements</a>

            
            </div>


            <div class="doc_text">

            
            <p>New features of the ARM target include:

            
            </p>


            <ul>


            <li>Preliminary support for processors, such as the Cortex-A8 and Cortex-A9,

            
            that implement version v7-A of the ARM architecture.  The ARM backend now

            
            supports both the Thumb2 and Advanced SIMD (Neon) instruction sets.</li>


            <li>The AAPCS-VFP "hard float" calling conventions are also supported with the

            
            <tt>-float-abi=hard</tt> flag.</li>


            <li>The ARM calling convention code is now tblgen generated instead of resorting

            
                to C++ code.</li>

            
            </ul>


            <p>These features are still somewhat experimental

            
            and subject to change. The Neon intrinsics, in particular, may change in future

            
            releases of LLVM.  ARMv7 support has progressed a lot on top of tree since 2.6

            
            branched.</p>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="OtherTarget">Other Target Specific Improvements</a>

            
            </div>


            <div class="doc_text">

            
            <p>New features of other targets include:

            
            </p>


            <ul>

            
            <li>Mips now supports O32 Calling Convention.</li>

            
            <li>Many improvements to the 32-bit PowerPC SVR4 ABI (used on powerpc-linux)

            
                support, lots of bugs fixed.</li>

            
            <li>Added support for the 64-bit PowerPC SVR4 ABI (used on powerpc64-linux).

            
                Needs more testing.</li>

            
            </ul>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="newapis">New Useful APIs</a>

            
            </div>


            <div class="doc_text">


            <p>This release includes a number of new APIs that are used internally, which

            
               may also be useful for external clients.

            
            </p>


            <ul>

            
            <li>New <a href="http://llvm.org/doxygen/PrettyStackTrace_8h-source.html">

            
                <tt>PrettyStackTrace</tt> class</a> allows crashes of llvm tools (and applications

            
                that integrate them) to provide more detailed indication of what the

            
                compiler was doing at the time of the crash (e.g. running a pass).

            
                At the top level for each LLVM tool, it includes the command line arguments.

            
                </li>

            
            <li>New <a href="http://llvm.org/doxygen/StringRef_8h-source.html">StringRef</a>

            
                and <a href="http://llvm.org/doxygen/Twine_8h-source.html">Twine</a> classes

            
                make operations on character ranges and

            
                string concatenation to be more efficient.  <tt>StringRef</tt> is just a <tt>const

            
                char*</tt> with a length, <tt>Twine</tt> is a light-weight rope.</li>

            
            <li>LLVM has new <tt>WeakVH</tt>, <tt>AssertingVH</tt> and <tt>CallbackVH</tt>

            
                classes, which make it easier to write LLVM IR transformations.  <tt>WeakVH</tt>

            
                is automatically drops to null when the referenced <tt>Value</tt> is deleted,

            
                and is updated across a <tt>replaceAllUsesWith</tt> operation.

            
                <tt>AssertingVH</tt> aborts the program if the

            
                referenced value is destroyed while it is being referenced.  <tt>CallbackVH</tt>

            
                is a customizable class for handling value references.  See <a

            
                href="http://llvm.org/doxygen/ValueHandle_8h-source.html">ValueHandle.h</a>

            
                for more information.</li>

            
            <li>The new '<a href="http://llvm.org/doxygen/Triple_8h-source.html">Triple

            
                </a>' class centralizes a lot of logic that reasons about target

            
                triples.</li>

            
            <li>The new '<a href="http://llvm.org/doxygen/ErrorHandling_8h-source.html">

            
                llvm_report_error()</a>' set of APIs allows tools to embed the LLVM

            
                optimizer and backend and recover from previously unrecoverable errors.</li>

            
            <li>LLVM has new abstractions for <a

            
                href="http://llvm.org/doxygen/Atomic_8h-source.html">atomic operations</a>

            
                and <a href="http://llvm.org/doxygen/RWMutex_8h-source.html">reader/writer

            
                locks</a>.</li>

            
            <li>LLVM has new <a href="http://llvm.org/doxygen/SourceMgr_8h-source.html">

            
                <tt>SourceMgr</tt> and <tt>SMLoc</tt> classes</a> which implement caret

            
                diagnostics and basic include stack processing for simple parsers. It is

            
                used by tablegen, llvm-mc, the .ll parser and FileCheck.</li>

            
            </ul>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="otherimprovements">Other Improvements and New Features</a>

            
            </div>


            <div class="doc_text">

            
            <p>Other miscellaneous features include:</p>


            <ul>

            
            <li>LLVM now includes a new internal '<a

            
                href="http://llvm.org/cmds/FileCheck.html">FileCheck</a>' tool which allows

            
                writing much more accurate regression tests that run faster.  Please see the

            
                <a href="TestingGuide.html#FileCheck">FileCheck section of the Testing

            
                Guide</a> for more information.</li>

            
            <li>LLVM profile information support has been significantly improved to produce

            
            correct use counts, and has support for edge profiling with reduced runtime

            
            overhead.  Combined, the generated profile information is both more correct and

            
            imposes about half as much overhead (2.6. from 12% to 6% overhead on SPEC

            
            CPU2000).</li>

            
            <li>The C bindings (in the llvm/include/llvm-c directory) include many newly

            
                supported APIs.</li>

            
            <li>LLVM 2.6 includes a brand new experimental LLVM bindings to the Ada2005

            
                programming language.</li>


            <li>The LLVMC driver has several new features:

            
              <ul>

            
              <li>Dynamic plugins now work on Windows.</li>

            
              <li>New option property: init. Makes possible to provide default values for

            
                  options defined in plugins (interface to <tt>cl::init</tt>).</li>

            
              <li>New example: Skeleton, shows how to create a standalone LLVMC-based

            
                  driver.</li>

            
              <li>New example: mcc16, a driver for the PIC16 toolchain.</li>

            
              </ul>

            
            </li>


            </ul>


            </div>


            <!--=========================================================================-->

            
            <div class="doc_subsection">

            
            <a name="changes">Major Changes and Removed Features</a>

            
            </div>


            <div class="doc_text">


            <p>If you're already an LLVM user or developer with out-of-tree changes based

            
            on LLVM 2.5, this section lists some "gotchas" that you may run into upgrading

            
            from the previous release.</p>


            <ul>

            
            <li>The Itanium (IA64) backend has been removed.  It was not actively supported

            
                and had bitrotted.</li>

            
            <li>The BigBlock register allocator has been removed, it had also bitrotted.</li>

            
            <li>The C Backend (<tt>-march=c</tt>) is no longer considered part of the LLVM release

            
            criteria.  We still want it to work, but no one is maintaining it and it lacks

            
            support for arbitrary precision integers and other important IR features.</li>


            <li>All LLVM tools now default to overwriting their output file, behaving more

            
                like standard unix tools.  Previously, this only happened with the '<tt>-f</tt>'

            
                option.</li>

            
            <li>LLVM build now builds all libraries as .a files instead of some

            
              libraries as relinked .o files.  This requires some APIs like

            
              InitializeAllTargets.h.

            
              </li>

            
            </ul>


            <p>In addition, many APIs have changed in this release.  Some of the major LLVM

            
            API changes are:</p>


            <ul>

            
            <li>All uses of <tt>hash_set</tt> and <tt>hash_map</tt> have been removed from

            
                the LLVM tree and the wrapper headers have been removed.</li>

            
            <li>The llvm/Streams.h and <tt>DOUT</tt> member of Debug.h have been removed.  The

            
                <tt>llvm::Ostream</tt> class has been completely removed and replaced with

            
                uses of <tt>raw_ostream</tt>.</li>

            
            <li>LLVM's global uniquing tables for <tt>Type</tt>s and <tt>Constant</tt>s have

            
                been privatized into members of an <tt>LLVMContext</tt>.  A number of APIs

            
                now take an <tt>LLVMContext</tt> as a parameter.  To smooth the transition

            
                for clients that will only ever use a single context, the new

            
                <tt>getGlobalContext()</tt> API can be used to access a default global

            
                context which can be passed in any and all cases where a context is

            
                required.

            
            <li>The <tt>getABITypeSize</tt> methods are now called <tt>getAllocSize</tt>.</li>

            
            <li>The <tt>Add</tt>, <tt>Sub</tt> and <tt>Mul</tt> operators are no longer

            
                overloaded for floating-point types. Floating-point addition, subtraction

            
                and multiplication are now represented with new operators <tt>FAdd</tt>,

            
                <tt>FSub</tt> and <tt>FMul</tt>. In the <tt>IRBuilder</tt> API,

            
                <tt>CreateAdd</tt>, <tt>CreateSub</tt>, <tt>CreateMul</tt> and

            
                <tt>CreateNeg</tt> should only be used for integer arithmetic now;

            
                <tt>CreateFAdd</tt>, <tt>CreateFSub</tt>, <tt>CreateFMul</tt> and

            
                <tt>CreateFNeg</tt> should now be used for floating-point arithmetic.</li>

            
            <li>The <tt>DynamicLibrary</tt> class can no longer be constructed, its functionality has

            
                moved to static member functions.</li>

            
            <li><tt>raw_fd_ostream</tt>'s constructor for opening a given filename now

            
                takes an extra <tt>Force</tt> argument. If <tt>Force</tt> is set to

            
                <tt>false</tt>, an error will be reported if a file with the given name

            
                already exists. If <tt>Force</tt> is set to <tt>true</tt>, the file will

            
                be silently truncated (which is the behavior before this flag was

            
                added).</li>

            
            <li><tt>SCEVHandle</tt> no longer exists, because reference counting is no

            
                longer done for <tt>SCEV*</tt> objects, instead <tt>const SCEV*</tt>

            
                should be used.</li>


            <li>Many APIs, notably <tt>llvm::Value</tt>, now use the <tt>StringRef</tt>

            
            and <tt>Twine</tt> classes instead of passing <tt>const char*</tt>

            
            or <tt>std::string</tt>, as described in

            
            the <a href="ProgrammersManual.html#string_apis">Programmer's Manual</a>. Most

            
            clients should be unaffected by this transition, unless they are used to

            
            <tt>Value::getName()</tt> returning a string. Here are some tips on updating to

            
            2.6:

            
              <ul>

            
                <li><tt>getNameStr()</tt> is still available, and matches the old

            
                  behavior. Replacing <tt>getName()</tt> calls with this is an safe option,

            
                  although more efficient alternatives are now possible.</li>


                <li>If you were just relying on <tt>getName()</tt> being able to be sent to

            
                  a <tt>std::ostream</tt>, consider migrating

            
                  to <tt>llvm::raw_ostream</tt>.</li>


                <li>If you were using <tt>getName().c_str()</tt> to get a <tt>const

            
                    char*</tt> pointer to the name, you can use <tt>getName().data()</tt>.

            
                    Note that this string (as before), may not be the entire name if the

            
                    name contains embedded null characters.</li>


                <li>If you were using <tt>operator +</tt> on the result of <tt>getName()</tt> and

            
                  treating the result as an <tt>std::string</tt>, you can either

            
                  use <tt>Twine::str</tt> to get the result as an <tt>std::string</tt>, or

            
                  could move to a <tt>Twine</tt> based design.</li>


                <li><tt>isName()</tt> should be replaced with comparison

            
                  against <tt>getName()</tt> (this is now efficient).

            
              </ul>

            
            </li>


            <li>The registration interfaces for backend Targets has changed (what was

            
            previously <tt>TargetMachineRegistry</tt>). For backend authors, see the <a

            
            href="WritingAnLLVMBackend.html#TargetRegistration">Writing An LLVM Backend</a>

            
            guide. For clients, the notable API changes are:

            
              <ul>

            
                <li><tt>TargetMachineRegistry</tt> has been renamed

            
                  to <tt>TargetRegistry</tt>.</li>


                <li>Clients should move to using the <tt>TargetRegistry::lookupTarget()</tt>

            
                  function to find targets.</li>

            
              </ul>

            
            </li>

            
            </ul>


            </div>


            <!-- *********************************************************************** -->

            
            <div class="doc_section">

            
              <a name="portability">Portability and Supported Platforms</a>

            
            </div>

            
            <!-- *********************************************************************** -->


            <div class="doc_text">


            <p>LLVM is known to work on the following platforms:</p>


            <ul>

            
            <li>Intel and AMD machines (IA32, X86-64, AMD64, EMT-64) running Red Hat

            
                Linux, Fedora Core, FreeBSD and AuroraUX (and probably other unix-like

            
                systems).</li>

            
            <li>PowerPC and X86-based Mac OS X systems, running 10.3 and above in 32-bit

            
                and 64-bit modes.</li>

            
            <li>Intel and AMD machines running on Win32 using MinGW libraries (native).</li>

            
            <li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited

            
                support is available for native builds with Visual C++).</li>

            
            <li>Sun x86 and AMD64 machines running Solaris 10, OpenSolaris 0906.</li>

            
            <li>Alpha-based machines running Debian GNU/Linux.</li>

            
            </ul>


            <p>The core LLVM infrastructure uses GNU autoconf to adapt itself

            
            to the machine and operating system on which it is built.  However, minor

            
            porting may be required to get LLVM to work on new platforms.  We welcome your

            
            portability patches and reports of successful builds or error messages.</p>


            </div>


            <!-- *********************************************************************** -->

            
            <div class="doc_section">

            
              <a name="knownproblems">Known Problems</a>

            
            </div>

            
            <!-- *********************************************************************** -->


            <div class="doc_text">


            <p>This section contains significant known problems with the LLVM system,

            
            listed by component.  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.</p>


            <ul>

            
            <li>The llvm-gcc bootstrap will fail with some versions of binutils (e.g. 2.15)

            
                with a message of "<tt><a href="http://llvm.org/PR5004">Error: can not do 8

            
                byte pc-relative relocation</a></tt>" when building C++ code.  We intend to

            
                fix this on mainline, but a workaround for 2.6 is to upgrade to binutils

            
                2.17 or later.</li>


            <li>LLVM will not correctly compile on Solaris and/or OpenSolaris

            
            using the stock GCC 3.x.x series 'out the box',

            
            See: <a href="#brokengcc">Broken versions of GCC and other tools</a>.

            
            However, A <a href="http://pkg.auroraux.org/GCC">Modern GCC Build</a>

            
            for x86/x86-64 has been made available from the third party AuroraUX Project

            
            that has been meticulously tested for bootstrapping LLVM &amp; Clang.</li>

            
            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="experimental">Experimental features included with this release</a>

            
            </div>


            <div class="doc_text">


            <p>The following components of this LLVM release are either untested, known to

            
            be broken or unreliable, or are in early development.  These components should

            
            not be relied on, and bugs should not be filed against them, but they may be

            
            useful to some people.  In particular, if you would like to work on one of these

            
            components, please contact us on the <a

            
            href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>


            <ul>

            
            <li>The MSIL, Alpha, SPU, MIPS, PIC16, Blackfin, MSP430 and SystemZ backends are

            
                experimental.</li>

            
            <li>The <tt>llc</tt> "<tt>-filetype=asm</tt>" (the default) is the only

            
                supported value for this option.  The ELF writer is experimental.</li>

            
            <li>The implementation of Andersen's Alias Analysis has many known bugs.</li>

            
            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="x86-be">Known problems with the X86 back-end</a>

            
            </div>


            <div class="doc_text">


            <ul>

            
              <li>The X86 backend does not yet support

            
                all <a href="http://llvm.org/PR879">inline assembly that uses the X86

            
                floating point stack</a>.  It supports the 'f' and 't' constraints, but not

            
                'u'.</li>

            
              <li>The X86 backend generates inefficient floating point code when configured

            
                to generate code for systems that don't have SSE2.</li>

            
              <li>Win64 code generation wasn't widely tested. Everything should work, but we

            
                expect small issues to happen. Also, llvm-gcc cannot build the mingw64

            
                runtime currently due

            
                to <a href="http://llvm.org/PR2255">several</a>

            
                <a href="http://llvm.org/PR2257">bugs</a> and due to lack of support for

            
                the

            
                'u' inline assembly constraint and for X87 floating point inline assembly.</li>

            
              <li>The X86-64 backend does not yet support the LLVM IR instruction

            
                  <tt>va_arg</tt>. Currently, the llvm-gcc and front-ends support variadic

            
                  argument constructs on X86-64 by lowering them manually.</li>

            
            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="ppc-be">Known problems with the PowerPC back-end</a>

            
            </div>


            <div class="doc_text">


            <ul>

            
            <li>The Linux PPC32/ABI support needs testing for the interpreter and static

            
            compilation, and lacks support for debug information.</li>

            
            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="arm-be">Known problems with the ARM back-end</a>

            
            </div>


            <div class="doc_text">


            <ul>

            
            <li>Support for the Advanced SIMD (Neon) instruction set is still incomplete

            
            and not well tested.  Some features may not work at all, and the code quality

            
            may be poor in some cases.</li>

            
            <li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6

            
            processors, thumb programs can crash or produce wrong

            
            results (<a href="http://llvm.org/PR1388">PR1388</a>).</li>

            
            <li>Compilation for ARM Linux OABI (old ABI) is supported but not fully tested.

            
            </li>

            
            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="sparc-be">Known problems with the SPARC back-end</a>

            
            </div>


            <div class="doc_text">


            <ul>

            
            <li>The SPARC backend only supports the 32-bit SPARC ABI (-m32); it does not

            
                support the 64-bit SPARC ABI (-m64).</li>

            
            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="mips-be">Known problems with the MIPS back-end</a>

            
            </div>


            <div class="doc_text">


            <ul>

            
            <li>64-bit MIPS targets are not supported yet.</li>

            
            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="alpha-be">Known problems with the Alpha back-end</a>

            
            </div>


            <div class="doc_text">


            <ul>


            <li>On 21164s, some rare FP arithmetic sequences which may trap do not have the

            
            appropriate nops inserted to ensure restartability.</li>


            </ul>

            
            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="c-be">Known problems with the C back-end</a>

            
            </div>


            <div class="doc_text">


            <ul>

            
            <li><a href="http://llvm.org/PR802">The C backend has only basic support for

            
                inline assembly code</a>.</li>

            
            <li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common

            
                C++ programs</a>, preventing intermixing between C++ compiled by the CBE and

            
                C++ code compiled with <tt>llc</tt> or native compilers.</li>

            
            <li>The C backend does not support all exception handling constructs.</li>

            
            <li>The C backend does not support arbitrary precision integers.</li>

            
            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="c-fe">Known problems with the llvm-gcc C front-end</a>

            
            </div>


            <div class="doc_text">


            <p>The only major language feature of GCC not supported by llvm-gcc is

            
                the <tt>__builtin_apply</tt> family of builtins.   However, some extensions

            
                are only supported on some targets.  For example, trampolines are only

            
                supported on some targets (these are used when you take the address of a

            
                nested function).</p>


            <p>If you run into GCC extensions which are not supported, please let us know.

            
            </p>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="c++-fe">Known problems with the llvm-gcc C++ front-end</a>

            
            </div>


            <div class="doc_text">


            <p>The C++ front-end is considered to be fully

            
            tested and works for a number of non-trivial programs, including LLVM

            
            itself, Qt, Mozilla, etc.</p>


            <ul>

            
            <li>Exception handling works well on the X86 and PowerPC targets. Currently

            
              only Linux and Darwin targets are supported (both 32 and 64 bit).</li>

            
            </ul>


            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="fortran-fe">Known problems with the llvm-gcc Fortran front-end</a>

            
            </div>


            <div class="doc_text">

            
            <ul>

            
            <li>Fortran support generally works, but there are still several unresolved bugs

            
                in <a href="http://llvm.org/bugs/">Bugzilla</a>.  Please see the

            
                tools/gfortran component for details.</li>

            
            </ul>

            
            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
              <a name="ada-fe">Known problems with the llvm-gcc Ada front-end</a>

            
            </div>


            <div class="doc_text">

            
            The llvm-gcc 4.2 Ada compiler works fairly well; however, this is not a mature

            
            technology, and problems should be expected.

            
            <ul>

            
            <li>The Ada front-end currently only builds on X86-32.  This is mainly due

            
            to lack of trampoline support (pointers to nested functions) on other platforms.

            
            However, it <a href="http://llvm.org/PR2006">also fails to build on X86-64</a>

            
            which does support trampolines.</li>

            
            <li>The Ada front-end <a href="http://llvm.org/PR2007">fails to bootstrap</a>.

            
            This is due to lack of LLVM support for <tt>setjmp</tt>/<tt>longjmp</tt> style

            
            exception handling, which is used internally by the compiler.

            
            Workaround: configure with <tt>--disable-bootstrap</tt>.</li>

            
            <li>The c380004, <a href="http://llvm.org/PR2010">c393010</a>

            
            and <a href="http://llvm.org/PR2421">cxg2021</a> ACATS tests fail

            
            (c380004 also fails with gcc-4.2 mainline).

            
            If the compiler is built with checks disabled then <a href="http://llvm.org/PR2010">c393010</a>

            
            causes the compiler to go into an infinite loop, using up all system memory.</li>

            
            <li>Some GCC specific Ada tests continue to crash the compiler.</li>

            
            <li>The <tt>-E</tt> binder option (exception backtraces)

            
            <a href="http://llvm.org/PR1982">does not work</a> and will result in programs

            
            crashing if an exception is raised.  Workaround: do not use <tt>-E</tt>.</li>

            
            <li>Only discrete types <a href="http://llvm.org/PR1981">are allowed to start

            
            or finish at a non-byte offset</a> in a record.  Workaround: do not pack records

            
            or use representation clauses that result in a field of a non-discrete type

            
            starting or finishing in the middle of a byte.</li>

            
            <li>The <tt>lli</tt> interpreter <a href="http://llvm.org/PR2009">considers

            
            'main' as generated by the Ada binder to be invalid</a>.

            
            Workaround: hand edit the file to use pointers for <tt>argv</tt> and

            
            <tt>envp</tt> rather than integers.</li>

            
            <li>The <tt>-fstack-check</tt> option <a href="http://llvm.org/PR2008">is

            
            ignored</a>.</li>

            
            </ul>

            
            </div>


            <!-- ======================================================================= -->

            
            <div class="doc_subsection">

            
            	<a name="ocaml-bindings">Known problems with the O'Caml bindings</a>

            
            </div>


            <div class="doc_text">


            <p>The <tt>Llvm.Linkage</tt> module is broken, and has incorrect values. Only

            
            <tt>Llvm.Linkage.External</tt>, <tt>Llvm.Linkage.Available_externally</tt>, and

            
            <tt>Llvm.Linkage.Link_once</tt> will be correct. If you need any of the other linkage

            
            modes, you'll have to write an external C library in order to expose the

            
            functionality. This has been fixed in the trunk.</p>

            
            </div>


            <!-- *********************************************************************** -->

            
            <div class="doc_section">

            
              <a name="additionalinfo">Additional Information</a>

            
            </div>

            
            <!-- *********************************************************************** -->


            <div class="doc_text">


            <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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