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11 <h1>LLVM 3.1 Release Notes</h1>
14 <img style="float:right" src="http://llvm.org/img/DragonSmall.png"
15 width="136" height="136" alt="LLVM Dragon Logo">
19 <li><a href="#intro">Introduction</a></li>
20 <li><a href="#subproj">Sub-project Status Update</a></li>
21 <li><a href="#externalproj">External Projects Using LLVM 3.1</a></li>
22 <li><a href="#whatsnew">What's New in LLVM?</a></li>
23 <li><a href="GettingStarted.html">Installation Instructions</a></li>
24 <li><a href="#knownproblems">Known Problems</a></li>
25 <li><a href="#additionalinfo">Additional Information</a></li>
28 <div class="doc_author">
29 <p>Written by the <a href="http://llvm.org/">LLVM Team</a></p>
32 <h1 style="color:red">These are in-progress notes for the upcoming LLVM 3.1
35 <a href="http://llvm.org/releases/3.0/docs/ReleaseNotes.html">LLVM 3.0
36 Release Notes</a>.</h1>
38 <!-- *********************************************************************** -->
40 <a name="intro">Introduction</a>
42 <!-- *********************************************************************** -->
46 <p>This document contains the release notes for the LLVM Compiler
47 Infrastructure, release 3.1. Here we describe the status of LLVM, including
48 major improvements from the previous release, improvements in various
49 subprojects of LLVM, and some of the current users of the code.
50 All LLVM releases may be downloaded from
51 the <a href="http://llvm.org/releases/">LLVM releases web site</a>.</p>
53 <p>For more information about LLVM, including information about the latest
54 release, please check out the <a href="http://llvm.org/">main LLVM web
55 site</a>. If you have questions or comments,
56 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM
57 Developer's Mailing List</a> is a good place to send them.</p>
59 <p>Note that if you are reading this file from a Subversion checkout or the main
60 LLVM web page, this document applies to the <i>next</i> release, not the
61 current one. To see the release notes for a specific release, please see the
62 <a href="http://llvm.org/releases/">releases page</a>.</p>
67 <!-- *********************************************************************** -->
69 <a name="subproj">Sub-project Status Update</a>
71 <!-- *********************************************************************** -->
75 <p>The LLVM 3.1 distribution currently consists of code from the core LLVM
76 repository (which roughly includes the LLVM optimizers, code generators and
77 supporting tools), and the Clang repository. In
78 addition to this code, the LLVM Project includes other sub-projects that are
79 in development. Here we include updates on these subprojects.</p>
81 <!--=========================================================================-->
83 <a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>
88 <p><a href="http://clang.llvm.org/">Clang</a> is an LLVM front end for the C,
89 C++, and Objective-C languages. Clang aims to provide a better user
90 experience through expressive diagnostics, a high level of conformance to
91 language standards, fast compilation, and low memory use. Like LLVM, Clang
92 provides a modular, library-based architecture that makes it suitable for
93 creating or integrating with other development tools. Clang is considered a
94 production-quality compiler for C, Objective-C, C++ and Objective-C++ on x86
95 (32- and 64-bit), and for Darwin/ARM targets.</p>
97 <p>In the LLVM 3.1 time-frame, the Clang team has made many improvements:</p>
99 <li>C++11 support is greatly expanded including lambdas, initializer lists, constexpr, user-defined literals, and atomics.</li>
103 <p>For more details about the changes to Clang since the 2.9 release, see the
104 <a href="http://clang.llvm.org/docs/ReleaseNotes.html">Clang release notes</a>
108 <p>If Clang rejects your code but another compiler accepts it, please take a
109 look at the <a href="http://clang.llvm.org/compatibility.html">language
110 compatibility</a> guide to make sure this is not intentional or a known
115 <!--=========================================================================-->
117 <a name="dragonegg">DragonEgg: GCC front-ends, LLVM back-end</a>
121 <p><a href="http://dragonegg.llvm.org/">DragonEgg</a> is a
122 <a href="http://gcc.gnu.org/wiki/plugins">gcc plugin</a> that replaces GCC's
123 optimizers and code generators with LLVM's. It works with gcc-4.5 and gcc-4.6
124 (and partially with gcc-4.7), can target the x86-32/x86-64 and ARM processor
125 families, and has been successfully used on the Darwin, FreeBSD, KFreeBSD,
126 Linux and OpenBSD platforms. It fully supports Ada, C, C++ and Fortran. It
127 has partial support for Go, Java, Obj-C and Obj-C++.</p>
129 <p>The 3.1 release has the following notable changes:</p>
133 <li>Partial support for gcc-4.7. Ada support is poor, but other languages work
136 <li>Support for ARM processors. Some essential gcc headers that are needed to
137 build DragonEgg for ARM are not installed by gcc. To work around this,
138 copy the missing headers from the gcc source tree.</li>
140 <li>Better optimization for Fortran by exploiting the fact that Fortran scalar
141 arguments have 'restrict' semantics.</li>
143 <li>Better optimization for all languages by passing information about type
144 aliasing and type ranges to the LLVM optimizers.</li>
146 <li>A regression test-suite was added.</li>
152 <!--=========================================================================-->
154 <a name="compiler-rt">compiler-rt: Compiler Runtime Library</a>
159 <p>The new LLVM <a href="http://compiler-rt.llvm.org/">compiler-rt project</a>
160 is a simple library that provides an implementation of the low-level
161 target-specific hooks required by code generation and other runtime
162 components. For example, when compiling for a 32-bit target, converting a
163 double to a 64-bit unsigned integer is compiled into a runtime call to the
164 "__fixunsdfdi" function. The compiler-rt library provides highly optimized
165 implementations of this and other low-level routines (some are 3x faster than
166 the equivalent libgcc routines).</p>
172 <!--=========================================================================-->
174 <a name="lldb">LLDB: Low Level Debugger</a>
179 <p><a href="http://lldb.llvm.org">LLDB</a> is a ground-up implementation of a
180 command line debugger, as well as a debugger API that can be used from other
181 applications. LLDB makes use of the Clang parser to provide high-fidelity
182 expression parsing (particularly for C++) and uses the LLVM JIT for target
189 <!--=========================================================================-->
191 <a name="libc++">libc++: C++ Standard Library</a>
196 <p>Like compiler_rt, libc++ is now <a href="DeveloperPolicy.html#license">dual
197 licensed</a> under the MIT and UIUC license, allowing it to be used more
204 <!--=========================================================================-->
206 <a name="vmkit">VMKit</a>
211 <p>The <a href="http://vmkit.llvm.org/">VMKit project</a> is an
212 implementation of a Java Virtual Machine (Java VM or JVM) that uses LLVM for
213 static and just-in-time compilation.
215 <p>In the LLVM 3.1 time-frame, VMKit has had significant improvements on both
216 runtime and startup performance:</p>
225 <!--=========================================================================-->
227 <a name="Polly">Polly: Polyhedral Optimizer</a>
232 <p><a href="http://polly.llvm.org/">Polly</a> is an <em>experimental</em>
233 optimizer for data locality and parallelism. It currently provides high-level
234 loop optimizations and automatic parallelisation (using the OpenMP run time).
235 Work in the area of automatic SIMD and accelerator code generation was
238 <p>Within the LLVM 3.1 time-frame there were the following highlights:</p>
241 <li>Polly became an official LLVM project</li>
242 <li>Polly can be loaded directly into clang (Enabled by '-O3 -mllvm -polly'
244 <li>An automatic scheduling optimizer (derived from <a
245 href="http://pluto-compiler.sourceforge.net/">Pluto</a>) was integrated. It
246 performs loop transformations to optimize for data-locality and parallelism.
247 The transformations include, but are not limited to interchange, fusion,
248 fission, skewing and tiling.
256 <!-- *********************************************************************** -->
258 <a name="externalproj">External Open Source Projects Using LLVM 3.1</a>
260 <!-- *********************************************************************** -->
264 <p>An exciting aspect of LLVM is that it is used as an enabling technology for
265 a lot of other language and tools projects. This section lists some of the
266 projects that have already been updated to work with LLVM 3.1.</p>
272 <p><a href="http://faust.grame.fr/">FAUST</a> is a compiled language for
273 real-time audio signal processing. The name FAUST stands for Functional
274 AUdio STream. Its programming model combines two approaches: functional
275 programming and block diagram composition. In addition with the C, C++, Java,
276 JavaScript output formats, the Faust compiler can generate LLVM bitcode, and
277 works with LLVM 2.7-3.1.</p>
281 <h3>Glasgow Haskell Compiler (GHC)</h3>
285 <p><a href="http://www.haskell.org/ghc/">GHC</a> is an open source compiler and
286 programming suite for Haskell, a lazy functional programming language. It
287 includes an optimizing static compiler generating good code for a variety of
288 platforms, together with an interactive system for convenient, quick
291 <p>GHC 7.0 and onwards include an LLVM code generator, supporting LLVM 2.8 and
296 <h3>LLVM D Compiler</h3>
300 <p><a href="https://github.com/ldc-developers/ldc">LLVM D Compiler</a> (LDC) is
301 a compiler for the D programming Language. It is based on the DMD frontend
302 and uses LLVM as backend.</p>
306 <h3>Open Shading Language</h3>
310 <p><a href="https://github.com/imageworks/OpenShadingLanguage/">Open Shading
311 Language (OSL)</a> is a small but rich language for programmable shading in
312 advanced global illumination renderers and other applications, ideal for
313 describing materials, lights, displacement, and pattern generation. It uses
314 LLVM to JIT complex shader networks to x86 code at runtime.</p>
316 <p>OSL was developed by Sony Pictures Imageworks for use in its in-house
317 renderer used for feature film animation and visual effects, and is
318 distributed as open source software with the "New BSD" license.</p>
322 <h3>Portable OpenCL (pocl)</h3>
326 <p>In addition to producing an easily portable open source OpenCL
327 implementation, another major goal of <a href="http://pocl.sourceforge.net/">
328 pocl</a> is improving performance portability of OpenCL programs with
329 compiler optimizations, reducing the need for target-dependent manual
330 optimizations. An important part of pocl is a set of LLVM passes used to
331 statically parallelize multiple work-items with the kernel compiler, even in
332 the presence of work-group barriers. This enables static parallelization of
333 the fine-grained static concurrency in the work groups in multiple ways
334 (SIMD, VLIW, superscalar,...).</p>
342 <p><a href="http://pure-lang.googlecode.com/">Pure</a> is an
343 algebraic/functional programming language based on term rewriting. Programs
344 are collections of equations which are used to evaluate expressions in a
345 symbolic fashion. The interpreter uses LLVM as a backend to JIT-compile Pure
346 programs to fast native code. Pure offers dynamic typing, eager and lazy
347 evaluation, lexical closures, a hygienic macro system (also based on term
348 rewriting), built-in list and matrix support (including list and matrix
349 comprehensions) and an easy-to-use interface to C and other programming
350 languages (including the ability to load LLVM bitcode modules, and inline C,
351 C++, Fortran and Faust code in Pure programs if the corresponding
352 LLVM-enabled compilers are installed).</p>
354 <p>Pure version 0.54 has been tested and is known to work with LLVM 3.1 (and
355 continues to work with older LLVM releases >= 2.5).</p>
359 <h3>TTA-based Co-design Environment (TCE)</h3>
363 <p><a href="http://tce.cs.tut.fi/">TCE</a> is a toolset for designing
364 application-specific processors (ASP) based on the Transport triggered
365 architecture (TTA). The toolset provides a complete co-design flow from C/C++
366 programs down to synthesizable VHDL/Verilog and parallel program binaries.
367 Processor customization points include the register files, function units,
368 supported operations, and the interconnection network.</p>
370 <p>TCE uses Clang and LLVM for C/C++ language support, target independent
371 optimizations and also for parts of code generation. It generates new
372 LLVM-based code generators "on the fly" for the designed TTA processors and
373 loads them in to the compiler backend as runtime libraries to avoid
374 per-target recompilation of larger parts of the compiler chain.</p>
380 <!-- *********************************************************************** -->
382 <a name="whatsnew">What's New in LLVM 3.1?</a>
384 <!-- *********************************************************************** -->
388 <p>This release includes a huge number of bug fixes, performance tweaks and
389 minor improvements. Some of the major improvements and new features are
390 listed in this section.</p>
392 <!--=========================================================================-->
394 <a name="majorfeatures">Major New Features</a>
399 <!-- Features that need text if they're finished for 3.1:
403 loop dependence analysis
404 CorrelatedValuePropagation
405 lib/Transforms/IPO/MergeFunctions.cpp => consider for 3.1.
406 Integrated assembler on by default for arm/thumb?
411 Analysis/RegionInfo.h + Dom Frontiers
412 SparseBitVector: used in LiveVar.
413 llvm/lib/Archive - replace with lib object?
416 <p>LLVM 3.1 includes several major changes and big features:</p>
419 <li><a href="../tools/clang/docs/AddressSanitizer.html">AddressSanitizer</a>,
420 a fast memory error detector.</li>
421 <li><a href="CodeGenerator.html#machineinstrbundle">MachineInstr Bundles</a>,
422 Support to model instruction bundling / packing.</li>
423 <li><a href="#armintegratedassembler">ARM Integrated Assembler</a>,
424 A full featured assembler and direct-to-object support for ARM.</li>
425 <li><a href="#blockplacement">Basic Block Placement</a>
426 Probability driven basic block placement.</li>
433 <!--=========================================================================-->
435 <a name="coreimprovements">LLVM IR and Core Improvements</a>
440 <p>LLVM IR has several new features for better support of new targets and that
441 expose new optimization opportunities:</p>
444 <li>IR support for half float</li>
445 <li>IR support for vectors of pointers, including vector GEPs.</li>
446 <li>Module flags have been introduced. They convey information about the
447 module as a whole to LLVM subsystems.</li>
448 <li>Loads can now have range metadata attached to them to describe the
449 possible values being loaded.</li>
450 <li>Inline cost heuristics have been completely overhauled and now closely
451 model constant propagation through call sites, disregard trivially dead
452 code costs, and can model C++ STL iterator patterns.</li>
457 <!--=========================================================================-->
459 <a name="optimizer">Optimizer Improvements</a>
464 <p>In addition to many minor performance tweaks and bug fixes, this
465 release includes a few major enhancements and additions to the
469 <li>The loop unroll pass now is able to unroll loops with run-time trip counts.
470 This feature is turned off by default, and is enabled with the
471 <code>-unroll-runtime</code> flag.</li>
472 <li>A new basic-block autovectorization pass is available. Pass
473 <code>-vectorize</code> to run this pass along with some associated
474 post-vectorization cleanup passes. For more information, see the EuroLLVM
475 2012 slides: <a href="http://llvm.org/devmtg/2012-04-12/Slides/Hal_Finkel.pdf">
476 Autovectorization with LLVM</a>.</li>
482 <!--=========================================================================-->
484 <a name="mc">MC Level Improvements</a>
489 <p>The LLVM Machine Code (aka MC) subsystem was created to solve a number of
490 problems in the realm of assembly, disassembly, object file format handling,
491 and a number of other related areas that CPU instruction-set level tools work
492 in. For more information, please see
493 the <a href="http://blog.llvm.org/2010/04/intro-to-llvm-mc-project.html">Intro
494 to the LLVM MC Project Blog Post</a>.</p>
502 <!--=========================================================================-->
504 <a name="codegen">Target Independent Code Generator Improvements</a>
509 <p>We have changed the way that the Type Legalizer legalizes vectors. The type
510 legalizer now attempts to promote integer elements. This enabled the
511 implementation of vector-select. Additionally, we see a performance boost on
512 workloads which use vectors of chars and shorts, since they are now promoted
513 to 32-bit types, which are better supported by the SIMD instruction set.
514 Floating point types are still widened as before.</p>
517 <p>We have put a significant amount of work into the code generator
518 infrastructure, which allows us to implement more aggressive algorithms and
519 make it run faster:</p>
522 <li>TableGen can now synthesize register classes that are only needed to
523 represent combinations of constraints from instructions and sub-registers.
524 The synthetic register classes inherit most of their properties form their
525 closest user-defined super-class.</li>
526 <li><code>MachineRegisterInfo</code> now allows the reserved registers to be
527 frozen when register allocation starts. Target hooks should use the
528 <code>MRI->canReserveReg(FramePtr)</code> method to avoid accidentally
529 disabling frame pointer elimination during register allocation.</li>
530 <li>A new kind of <code>MachineOperand</code> provides a compact
531 representation of large clobber lists on call instructions. The register
532 mask operand references a bit mask of preserved registers. Everything else
536 <p> We added new TableGen infrastructure to support bundling for
537 Very Long Instruction Word (VLIW) architectures. TableGen can now
538 automatically generate a deterministic finite automaton from a VLIW
539 target's schedule description which can be queried to determine
540 legal groupings of instructions in a bundle.</p>
542 <p> We have added a new target independent VLIW packetizer based on the
543 DFA infrastructure to group machine instructions into bundles.</p>
548 <a name="blockplacement">Basic Block Placement</a>
551 <p>A probability based block placement and code layout algorithm was added to
552 LLVM's code generator. This layout pass supports probabilities derived from
553 static heuristics as well as source code annotations such as
554 <code>__builtin_expect</code>.</p>
557 <!--=========================================================================-->
559 <a name="x86">X86-32 and X86-64 Target Improvements</a>
564 <p>New features and major changes in the X86 target include:</p>
567 <li>Bug fixes and improved support for AVX1</li>
568 <li>Support for AVX2 (still incomplete at this point)</li>
569 <li>Call instructions use the new register mask operands for faster compile
570 times and better support for different calling conventions. The old WINCALL
571 instructions are no longer needed.</li>
572 <li>DW2 Exception Handling is enabled on Cygwin and MinGW.</li>
573 <li>Support for implicit TLS model used with MS VC runtime</li>
578 <!--=========================================================================-->
580 <a name="ARM">ARM Target Improvements</a>
585 <p>New features of the ARM target include:</p>
588 <li>The constant island pass now supports basic block and constant pool entry
589 alignments greater than 4 bytes.</li>
590 <li>On Darwin, the ARM target now has a full-featured integrated assembler.
595 <a name="armintegratedassembler">ARM Integrated Assembler</a>
598 <p>The ARM target now includes a full featured macro assembler, including
599 direct-to-object module support for clang. The assembler is currently enabled
600 by default for Darwin only pending testing and any additional necessary
601 platform specific support for Linux.</p>
603 <p>Full support is included for Thumb1, Thumb2 and ARM modes, along with
604 subtarget and CPU specific extensions for VFP2, VFP3 and NEON.</p>
606 <p>The assembler is Unified Syntax only (see ARM Architecural Reference Manual
607 for details). While there is some, and growing, support for pre-unfied (divided)
608 syntax, there are still significant gaps in that support.</p>
612 <!--=========================================================================-->
614 <a name="MIPS">MIPS Target Improvements</a>
619 <p>This release has seen major new work on just about every aspect of the MIPS
620 backend. Some of the major new features include:</p>
627 <!--=========================================================================-->
629 <a name="OtherTS">Other Target Specific Improvements</a>
634 <p>Support for Qualcomm's Hexagon VLIW processor has been added.</p>
644 <!--=========================================================================-->
646 <a name="changes">Major Changes and Removed Features</a>
651 <p>If you're already an LLVM user or developer with out-of-tree changes based on
652 LLVM 3.1, this section lists some "gotchas" that you may run into upgrading
653 from the previous release.</p>
656 <li>LLVM 3.1 removes support for reading LLVM 2.9 bitcode files. Going
657 forward, we aim for all future versions of LLVM to read bitcode files and
658 <tt>.ll</tt> files produced by LLVM 3.0 and later.</li>
659 <li>The <tt>unwind</tt> instruction is now gone. With the introduction of the
660 new exception handling system in LLVM 3.0, the <tt>unwind</tt> instruction
661 became obsolete.</li>
662 <li>LLVM 3.0 and earlier automatically added the returns_twice fo functions
663 like setjmp based on the name. This functionality was removed in 3.1.
664 This affects Clang users, if -ffreestanding is used.</li>
670 <!--=========================================================================-->
672 <a name="api_changes">Internal API Changes</a>
677 <p>In addition, many APIs have changed in this release. Some of the major
678 LLVM API changes are:</p>
681 <li>Target specific options have been moved from global variables to members
682 on the new <code>TargetOptions</code> class, which is local to each
683 <code>TargetMachine</code>. As a consequence, the associated flags will
684 no longer be accepted by <tt>clang -mllvm</tt>. This includes:
686 <li><code>llvm::PrintMachineCode</code></li>
687 <li><code>llvm::NoFramePointerElim</code></li>
688 <li><code>llvm::NoFramePointerElimNonLeaf</code></li>
689 <li><code>llvm::DisableFramePointerElim(const MachineFunction &)</code></li>
690 <li><code>llvm::LessPreciseFPMADOption</code></li>
691 <li><code>llvm::LessPrecideFPMAD()</code></li>
692 <li><code>llvm::NoExcessFPPrecision</code></li>
693 <li><code>llvm::UnsafeFPMath</code></li>
694 <li><code>llvm::NoInfsFPMath</code></li>
695 <li><code>llvm::NoNaNsFPMath</code></li>
696 <li><code>llvm::HonorSignDependentRoundingFPMathOption</code></li>
697 <li><code>llvm::HonorSignDependentRoundingFPMath()</code></li>
698 <li><code>llvm::UseSoftFloat</code></li>
699 <li><code>llvm::FloatABIType</code></li>
700 <li><code>llvm::NoZerosInBSS</code></li>
701 <li><code>llvm::JITExceptionHandling</code></li>
702 <li><code>llvm::JITEmitDebugInfo</code></li>
703 <li><code>llvm::JITEmitDebugInfoToDisk</code></li>
704 <li><code>llvm::GuaranteedTailCallOpt</code></li>
705 <li><code>llvm::StackAlignmentOverride</code></li>
706 <li><code>llvm::RealignStack</code></li>
707 <li><code>llvm::DisableJumpTables</code></li>
708 <li><code>llvm::EnableFastISel</code></li>
709 <li><code>llvm::getTrapFunctionName()</code></li>
710 <li><code>llvm::EnableSegmentedStacks</code></li>
712 <li>The MDBuilder class has been added to simplify the creation of
719 <!--=========================================================================-->
721 <a name="tools_changes">Tools Changes</a>
726 <p>In addition, some tools have changed in this release. Some of the changes
731 <li>llvm-stress is a command line tool for generating random .ll files to fuzz
732 different LLVM components. </li>
733 <li>llvm-ld has been removed. Use llvm-link or Clang instead.</li>
744 <!--=========================================================================-->
746 <a name="python">Python Bindings</a>
751 <p>Officially supported Python bindings have been added! Feature support is far
752 from complete. The current bindings support interfaces to:</p>
754 <li>Object File Interface</li>
755 <li>Disassembler</li>
758 <p>Using the Object File Interface, it is possible to inspect binary object files.
759 Think of it as a Python version of readelf or llvm-objdump.</p>
761 <p>Support for additional features is currently being developed by community
762 contributors. If you are interested in shaping the direction of the Python
763 bindings, please express your intent on IRC or the developers list.</p>
769 <!-- *********************************************************************** -->
771 <a name="knownproblems">Known Problems</a>
773 <!-- *********************************************************************** -->
777 <p>LLVM is generally a production quality compiler, and is used by a broad range
778 of applications and shipping in many products. That said, not every
779 subsystem is as mature as the aggregate, particularly the more obscure
780 targets. If you run into a problem, please check the <a
781 href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
782 there isn't already one or ask on the <a
783 href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev
786 <p>Known problem areas include:</p>
789 <li>The Alpha, Blackfin, CellSPU, MSP430, PTX, SystemZ and
790 XCore backends are experimental, and the Alpha, Blackfin and SystemZ
791 targets have already been removed from mainline.</li>
793 <li>The integrated assembler, disassembler, and JIT is not supported by
794 several targets. If an integrated assembler is not supported, then a
795 system assembler is required. For more details, see the <a
796 href="CodeGenerator.html#targetfeatures">Target Features Matrix</a>.
799 <li>The C backend has numerous problems and is not being actively maintained.
800 Depending on it for anything serious is not advised.</li>
805 <!-- *********************************************************************** -->
807 <a name="additionalinfo">Additional Information</a>
809 <!-- *********************************************************************** -->
813 <p>A wide variety of additional information is available on
814 the <a href="http://llvm.org/">LLVM web page</a>, in particular in
815 the <a href="http://llvm.org/docs/">documentation</a> section. The web page
816 also contains versions of the API documentation which is up-to-date with the
817 Subversion version of the source code. You can access versions of these
818 documents specific to this release by going into the "<tt>llvm/doc/</tt>"
819 directory in the LLVM tree.</p>
821 <p>If you have any questions or comments about LLVM, please feel free to contact
822 us via the <a href="http://llvm.org/docs/#maillist"> mailing lists</a>.</p>
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