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11 <h1>LLVM 3.0 Release Notes</h1>
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17 <li><a href="#intro">Introduction</a></li>
18 <li><a href="#subproj">Sub-project Status Update</a></li>
19 <li><a href="#externalproj">External Projects Using LLVM 3.0</a></li>
20 <li><a href="#whatsnew">What's New in LLVM 3.0?</a></li>
21 <li><a href="GettingStarted.html">Installation Instructions</a></li>
22 <li><a href="#knownproblems">Known Problems</a></li>
23 <li><a href="#additionalinfo">Additional Information</a></li>
26 <div class="doc_author">
27 <p>Written by the <a href="http://llvm.org/">LLVM Team</a></p>
31 <h1 style="color:red">These are in-progress notes for the upcoming LLVM 3.0
34 <a href="http://llvm.org/releases/2.9/docs/ReleaseNotes.html">LLVM 2.9
35 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 3.0. Here we describe the status of LLVM, including
48 major improvements from the previous release and significant known problems.
49 All LLVM releases may be downloaded from
50 the <a href="http://llvm.org/releases/">LLVM releases web site</a>.</p>
52 <p>For more information about LLVM, including information about the latest
53 release, please check out the <a href="http://llvm.org/">main LLVM web
54 site</a>. If you have questions or comments,
55 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM
56 Developer's Mailing List</a> is a good place to send them.</p>
58 <p>Note that if you are reading this file from a Subversion checkout or the main
59 LLVM web page, this document applies to the <i>next</i> release, not the
60 current one. To see the release notes for a specific release, please see the
61 <a href="http://llvm.org/releases/">releases page</a>.</p>
65 <!-- Features that need text if they're finished for 3.1:
69 loop dependence analysis
70 CorrelatedValuePropagation
71 lib/Transforms/IPO/MergeFunctions.cpp => consider for 3.1.
74 <!-- *********************************************************************** -->
76 <a name="subproj">Sub-project Status Update</a>
78 <!-- *********************************************************************** -->
82 <p>The LLVM 3.0 distribution currently consists of code from the core LLVM
83 repository (which roughly includes the LLVM optimizers, code generators and
84 supporting tools), and the Clang repository. In
85 addition to this code, the LLVM Project includes other sub-projects that are
86 in development. Here we include updates on these subprojects.</p>
88 <!--=========================================================================-->
90 <a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>
95 <p><a href="http://clang.llvm.org/">Clang</a> is an LLVM front end for the C,
96 C++, and Objective-C languages. Clang aims to provide a better user
97 experience through expressive diagnostics, a high level of conformance to
98 language standards, fast compilation, and low memory use. Like LLVM, Clang
99 provides a modular, library-based architecture that makes it suitable for
100 creating or integrating with other development tools. Clang is considered a
101 production-quality compiler for C, Objective-C, C++ and Objective-C++ on x86
102 (32- and 64-bit), and for darwin/arm targets.</p>
104 <p>In the LLVM 3.0 time-frame, the Clang team has made many improvements:</p>
107 <li>Greatly improved support for building C++ applications, with greater
108 stability and better diagnostics.</li>
110 <li><a href="http://clang.llvm.org/cxx_status.html">Improved support</a> for
111 the <a href="http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=50372">C++
112 2011</a> standard, including implementations of non-static data member
113 initializers, alias templates, delegating constructors, the range-based
114 for loop, and implicitly-generated move constructors and move assignment
115 operators, among others.</li>
117 <li>Implemented support for some features of the upcoming C1x standard,
118 including static assertions and generic selections.</li>
120 <li>Better detection of include and linking paths for system headers and
121 libraries, especially for Linux distributions.</li>
123 <li>Several improvements to Objective-C support, including:
126 <li><a href="http://clang.llvm.org/docs/AutomaticReferenceCounting.html">
127 Automatic Reference Counting</a> (ARC) and an improved memory model
128 cleanly separating object and C memory.</li>
130 <li>A migration tool for moving legacy code to ARC</li>
132 <li>Better support for data hiding, allowing instance variables to be
133 declared in implementation contexts or class extensions</li>
134 <li>Weak linking for classes</li>
135 <li>Improved static type checking by inferring the return type of methods
136 such as +alloc and -init.</li>
139 Some new features require either the Mac OS X 10.7 / iOS 5 Objective-C
140 runtime, or version 1.6 or later of the GNUstep Objective-C runtime
143 <li>Implemented a number of optimizations in <tt>libclang</tt>, the Clang C
144 interface, to improve the performance of code completion and the mapping
145 from source locations to abstract syntax tree nodes.</li>
149 <p>If Clang rejects your code but another compiler accepts it, please take a
150 look at the <a href="http://clang.llvm.org/compatibility.html">language
151 compatibility</a> guide to make sure this is not intentional or a known
156 <!--=========================================================================-->
158 <a name="dragonegg">DragonEgg: GCC front-ends, LLVM back-end</a>
162 <p><a href="http://dragonegg.llvm.org/">DragonEgg</a> is a
163 <a href="http://gcc.gnu.org/wiki/plugins">gcc plugin</a> that replaces GCC's
164 optimizers and code generators with LLVM's. It works with gcc-4.5 or gcc-4.6,
165 targets the x86-32 and x86-64 processor families, and has been successfully
166 used on the Darwin, FreeBSD, KFreeBSD, Linux and OpenBSD platforms. It fully
167 supports Ada, C, C++ and Fortran. It has partial support for Go, Java, Obj-C
170 <p>The 3.0 release has the following notable changes:</p>
172 <li>GCC version 4.6 is now fully supported.</li>
174 <li>Patching and building GCC is no longer required: the plugin should work
175 with your system GCC (version 4.5 or 4.6; on Debian/Ubuntu systems the
176 gcc-4.5-plugin-dev or gcc-4.6-plugin-dev package is also needed).</li>
178 <li>The <tt>-fplugin-arg-dragonegg-enable-gcc-optzns</tt> option, which runs
179 GCC's optimizers as well as LLVM's, now works much better. This is the
180 option to use if you want ultimate performance! It not yet completely
181 stable: it may cause the plugin to crash.</li>
183 <li>The type and constant conversion logic has been almost entirely rewritten,
184 fixing a multitude of obscure bugs.</li>
194 <!--=========================================================================-->
196 <a name="compiler-rt">compiler-rt: Compiler Runtime Library</a>
201 <p>The new LLVM <a href="http://compiler-rt.llvm.org/">compiler-rt project</a>
202 is a simple library that provides an implementation of the low-level
203 target-specific hooks required by code generation and other runtime
204 components. For example, when compiling for a 32-bit target, converting a
205 double to a 64-bit unsigned integer is compiled into a runtime call to the
206 "__fixunsdfdi" function. The compiler-rt library provides highly optimized
207 implementations of this and other low-level routines (some are 3x faster than
208 the equivalent libgcc routines).</p>
210 <p>In the LLVM 3.0 timeframe,</p>
214 <!--=========================================================================-->
216 <a name="lldb">LLDB: Low Level Debugger</a>
221 <p>LLDB has advanced by leaps and bounds in the 3.0 timeframe. It is
222 dramatically more stable and useful, and includes both a
223 new <a href="http://lldb.llvm.org/tutorial.html">tutorial</a> and
224 a <a href="http://lldb.llvm.org/lldb-gdb.html">side-by-side comparison with
229 <!--=========================================================================-->
231 <a name="libc++">libc++: C++ Standard Library</a>
236 <p>Like compiler_rt, libc++ is now <a href="DeveloperPolicy.html#license">dual
237 licensed</a> under the MIT and UIUC license, allowing it to be used more
240 <p>Libc++ has been ported to FreeBSD and imported into the base system. It is
241 planned to be the default STL implementation for FreeBSD 10.</p>
246 <!--=========================================================================-->
248 <a name="LLBrowse">LLBrowse: IR Browser</a>
253 <p><a href="http://llvm.org/svn/llvm-project/llbrowse/trunk/doc/LLBrowse.html">
254 LLBrowse</a> is an interactive viewer for LLVM modules. It can load any LLVM
255 module and displays its contents as an expandable tree view, facilitating an
256 easy way to inspect types, functions, global variables, or metadata nodes. It
257 is fully cross-platform, being based on the popular wxWidgets GUI
262 <!--=========================================================================-->
264 <a name="vmkit">VMKit</a>
269 <p>The <a href="http://vmkit.llvm.org/">VMKit project</a> is an
270 implementation of a Java Virtual Machine (Java VM or JVM) that uses LLVM for
271 static and just-in-time compilation.
273 <p>In the LLVM 3.0 time-frame, VMKit has had significant improvements on both
274 runtime and startup performance:</p>
277 <li>Precompilation: by compiling ahead of time a small subset of Java's core
278 library, the startup performance have been highly optimized to the point that
279 running a 'Hello World' program takes less than 30 milliseconds.</li>
281 <li>Customization: by customizing virtual methods for individual classes,
282 the VM can statically determine the target of a virtual call, and decide to
285 <li>Inlining: the VM does more inlining than it did before, by allowing more
286 bytecode instructions to be inlined, and thanks to customization. It also
287 inlines GC barriers, and object allocations.</li>
289 <li>New exception model: the generated code for a method that does not do
290 any try/catch is not penalized anymore by the eventuality of calling a
291 method that throws an exception. Instead, the method that throws the
292 exception jumps directly to the method that could catch it.</li>
298 <!--=========================================================================-->
301 <a name="klee">KLEE: A Symbolic Execution Virtual Machine</a>
306 <a href="http://klee.llvm.org/">KLEE</a> is a symbolic execution framework for
307 programs in LLVM bitcode form. KLEE tries to symbolically evaluate "all" paths
308 through the application and records state transitions that lead to fault
309 states. This allows it to construct testcases that lead to faults and can even
310 be used to verify some algorithms.
318 <!-- *********************************************************************** -->
320 <a name="externalproj">External Open Source Projects Using LLVM 3.0</a>
322 <!-- *********************************************************************** -->
326 <p>An exciting aspect of LLVM is that it is used as an enabling technology for
327 a lot of other language and tools projects. This section lists some of the
328 projects that have already been updated to work with LLVM 3.0.</p>
330 <!--=========================================================================-->
331 <h3>AddressSanitizer</h3>
335 <p><a href="http://code.google.com/p/address-sanitizer/">AddressSanitizer</a>
336 uses compiler instrumentation and a specialized malloc library to find C/C++
337 bugs such as use-after-free and out-of-bound accesses to heap, stack, and
338 globals. The key feature of the tool is speed: the average slowdown
339 introduced by AddressSanitizer is less than 2x.</p>
343 <!--=========================================================================-->
348 <p><a href="http://www.clamav.net">Clam AntiVirus</a> is an open source (GPL)
349 anti-virus toolkit for UNIX, designed especially for e-mail scanning on mail
352 <p>Since version 0.96 it
353 has <a href="http://vrt-sourcefire.blogspot.com/2010/09/introduction-to-clamavs-low-level.html">bytecode
354 signatures</a> that allow writing detections for complex malware.</p>
356 <p>It uses LLVM's JIT to speed up the execution of bytecode on X86, X86-64,
357 PPC32/64, falling back to its own interpreter otherwise. The git version was
358 updated to work with LLVM 3.0.</p>
362 <!--=========================================================================-->
363 <h3>clang_complete for VIM</h3>
367 <p><a href="https://github.com/Rip-Rip/clang_complete">clang_complete</a> is a
368 VIM plugin, that provides accurate C/C++ autocompletion using the clang front
369 end. The development version of clang complete, can directly use libclang
370 which can maintain a cache to speed up auto completion.</p>
374 <!--=========================================================================-->
379 <p><a href="https://bitbucket.org/dwilliamson/clreflect">clReflect</a> is a C++
380 parser that uses clang/LLVM to derive a light-weight reflection database
381 suitable for use in game development. It comes with a very simple runtime
382 library for loading and querying the database, requiring no external
383 dependencies (including CRT), and an additional utility library for object
384 management and serialisation.</p>
388 <!--=========================================================================-->
389 <h3>Cling C++ Interpreter</h3>
393 <p><a href="http://cern.ch/cling">Cling</a> is an interactive compiler interface
394 (aka C++ interpreter). It uses LLVM's JIT and clang; it currently supports
395 C++ and C. It has a prompt interface, runs source files, calls into shared
396 libraries, prints the value of expressions, even does runtime lookup of
397 identifiers (dynamic scopes). And it just behaves like one would expect from
402 <!--=========================================================================-->
403 <h3>Crack Programming Language</h3>
407 <p><a href="http://code.google.com/p/crack-language/">Crack</a> aims to provide
408 the ease of development of a scripting language with the performance of a
409 compiled language. The language derives concepts from C++, Java and Python,
410 incorporating object-oriented programming, operator overloading and strong
415 <!--=========================================================================-->
420 <p><a href="http://eerolanguage.org/">Eero</a> is a fully
421 header-and-binary-compatible dialect of Objective-C 2.0, implemented with a
422 patched version of the Clang/LLVM compiler. It features a streamlined syntax,
423 Python-like indentation, and new operators, for improved readability and
424 reduced code clutter. It also has new features such as limited forms of
425 operator overloading and namespaces, and strict (type-and-operator-safe)
426 enumerations. It is inspired by languages such as Smalltalk, Python, and
431 <!--=========================================================================-->
432 <h3>FAUST Real-Time Audio Signal Processing Language</h3>
436 <p><a href="http://faust.grame.fr/">FAUST</a> is a compiled language for
437 real-time audio signal processing. The name FAUST stands for Functional
438 AUdio STream. Its programming model combines two approaches: functional
439 programming and block diagram composition. In addition with the C, C++, Java
440 output formats, the Faust compiler can now generate LLVM bitcode, and works
446 <!--=========================================================================-->
447 <h3>Glasgow Haskell Compiler (GHC)</h3>
451 <p>GHC is an open source, state-of-the-art programming suite for Haskell, a
452 standard lazy functional programming language. It includes an optimizing
453 static compiler generating good code for a variety of platforms, together
454 with an interactive system for convenient, quick development.</p>
456 <p>GHC 7.0 and onwards include an LLVM code generator, supporting LLVM 2.8 and
457 later. Since LLVM 2.9, GHC now includes experimental support for the ARM
458 platform with LLVM 3.0.</p>
462 <!--=========================================================================-->
467 <p><a href="http://botwars.tk/gwscript/">gwXscript</a> is an object oriented,
468 aspect oriented programming language which can create both executables (ELF,
469 EXE) and shared libraries (DLL, SO, DYNLIB). The compiler is implemented in
470 its own language and translates scripts into LLVM-IR which can be optimized
471 and translated into native code by the LLVM framework. Source code in
472 gwScript contains definitions that expand the namespaces. So you can build
473 your project and simply 'plug out' features by removing a file. The remaining
474 project does not leave scars since you directly separate concerns by the
475 'template' feature of gwX. It is also possible to add new features to a
476 project by just adding files and without editing the original project. This
477 language is used for example to create games or content management systems
478 that should be extendable.</p>
480 <p>gwXscript is strongly typed and offers comfort with its native types string,
481 hash and array. You can easily write new libraries in gwXscript or native
482 code. gwXscript is type safe and users should not be able to crash your
483 program or execute malicious code except code that is eating CPU time.</p>
487 <!--=========================================================================-->
488 <h3>include-what-you-use</h3>
492 <p><a href="http://code.google.com/p/include-what-you-use">include-what-you-use</a>
493 is a tool to ensure that a file directly <code>#include</code>s
494 all <code>.h</code> files that provide a symbol that the file uses. It also
495 removes superfluous <code>#include</code>s from source files.</p>
499 <!--=========================================================================-->
500 <h3>ispc: The Intel SPMD Program Compiler</h3>
504 <p><a href="http://ispc.github.com">ispc</a> is a compiler for "single program,
505 multiple data" (SPMD) programs. It compiles a C-based SPMD programming
506 language to run on the SIMD units of CPUs; it often delivers 5-6x speedups on
507 a single core of a CPU with an 8-wide SIMD unit compared to serial code,
508 while still providing a clean and easy-to-understand programming model. For
509 an introduction to the language and its performance,
510 see <a href="http://ispc.github.com/example.html">the walkthrough</a> of a short
511 example program. ispc is licensed under the BSD license.</p>
515 <!--=========================================================================-->
516 <h3>The Julia Programming Language</h3>
520 <p><a href="http://github.com/JuliaLang/julia">Julia</a> is a high-level,
521 high-performance dynamic language for technical
522 computing. It provides a sophisticated compiler, distributed parallel
523 execution, numerical accuracy, and an extensive mathematical function
524 library. The compiler uses type inference to generate fast code
525 without any type declarations, and uses LLVM's optimization passes and
526 JIT compiler. The language is designed around multiple dispatch,
527 giving programs a large degree of flexibility. It is ready for use on many
528 kinds of problems.</p>
531 <!--=========================================================================-->
532 <h3>LanguageKit and Pragmatic Smalltalk</h3>
536 <p><a href="http://etoileos.com/etoile/features/languagekit/">LanguageKit</a> is
537 a framework for implementing dynamic languages sharing an object model with
538 Objective-C. It provides static and JIT compilation using LLVM along with
539 its own interpreter. Pragmatic Smalltalk is a dialect of Smalltalk, built on
540 top of LanguageKit, that interfaces directly with Objective-C, sharing the
541 same object representation and message sending behaviour. These projects are
542 developed as part of the Étoilé desktop environment.</p>
546 <!--=========================================================================-->
551 <p><a href="http://lua-av.mat.ucsb.edu/blog/">LuaAV</a> is a real-time
552 audiovisual scripting environment based around the Lua language and a
553 collection of libraries for sound, graphics, and other media protocols. LuaAV
554 uses LLVM and Clang to JIT compile efficient user-defined audio synthesis
555 routines specified in a declarative syntax.</p>
559 <!--=========================================================================-->
564 <p>An open source, cross-platform implementation of C# and the CLR that is
565 binary compatible with Microsoft.NET. Has an optional, dynamically-loaded
566 LLVM code generation backend in Mini, the JIT compiler.</p>
568 <p>Note that we use a Git mirror of LLVM with some patches. See:
569 https://github.com/mono/llvm</p>
573 <!--=========================================================================-->
578 <p><a href="http://polly.grosser.es">Polly</a> is an advanced data-locality
579 optimizer and automatic parallelizer. It uses an advanced, mathematical
580 model to calculate detailed data dependency information which it uses to
581 optimize the loop structure of a program. Polly can speed up sequential code
582 by improving memory locality and consequently the cache use. Furthermore,
583 Polly is able to expose different kind of parallelism which it exploits by
584 introducing (basic) OpenMP and SIMD code. A mid-term goal of Polly is to
585 automatically create optimized GPU code.</p>
589 <!--=========================================================================-->
590 <h3>Portable OpenCL (pocl)</h3>
594 <p>Portable OpenCL is an open source implementation of the OpenCL standard which
595 can be easily adapted for new targets. One of the goals of the project is
596 improving performance portability of OpenCL programs, avoiding the need for
597 target-dependent manual optimizations. A "native" target is included, which
598 allows running OpenCL kernels on the host (CPU).</p>
602 <!--=========================================================================-->
606 <p><a href="http://pure-lang.googlecode.com/">Pure</a> is an
607 algebraic/functional programming language based on term rewriting. Programs
608 are collections of equations which are used to evaluate expressions in a
609 symbolic fashion. The interpreter uses LLVM as a backend to JIT-compile Pure
610 programs to fast native code. Pure offers dynamic typing, eager and lazy
611 evaluation, lexical closures, a hygienic macro system (also based on term
612 rewriting), built-in list and matrix support (including list and matrix
613 comprehensions) and an easy-to-use interface to C and other programming
614 languages (including the ability to load LLVM bitcode modules, and inline C,
615 C++, Fortran and Faust code in Pure programs if the corresponding LLVM-enabled
616 compilers are installed).</p>
618 <p>Pure version 0.48 has been tested and is known to work with LLVM 3.0
619 (and continues to work with older LLVM releases >= 2.5).</p>
623 <!--=========================================================================-->
624 <h3>Renderscript</h3>
628 <p><a href="http://developer.android.com/guide/topics/renderscript/index.html">Renderscript</a>
629 is Android's advanced 3D graphics rendering and compute API. It provides a
630 portable C99-based language with extensions to facilitate common use cases
631 for enhancing graphics and thread level parallelism. The Renderscript
632 compiler frontend is based on Clang/LLVM. It emits a portable bitcode format
633 for the actual compiled script code, as well as reflects a Java interface for
634 developers to control the execution of the compiled bitcode. Executable
635 machine code is then generated from this bitcode by an LLVM backend on the
636 device. Renderscript is thus able to provide a mechanism by which Android
637 developers can improve performance of their applications while retaining
642 <!--=========================================================================-->
647 <p><a href="http://safecode.cs.illinois.edu">SAFECode</a> is a memory safe C/C++
648 compiler built using LLVM. It takes standard, unannotated C/C++ code,
649 analyzes the code to ensure that memory accesses and array indexing
650 operations are safe, and instruments the code with run-time checks when
651 safety cannot be proven statically. SAFECode can be used as a debugging aid
652 (like Valgrind) to find and repair memory safety bugs. It can also be used
653 to protect code from security attacks at run-time.</p>
657 <!--=========================================================================-->
658 <h3>The Stupid D Compiler (SDC)</h3>
662 <p><a href="https://github.com/bhelyer/SDC">The Stupid D Compiler</a> is a
663 project seeking to write a self-hosting compiler for the D programming
664 language without using the frontend of the reference compiler (DMD).</p>
668 <!--=========================================================================-->
669 <h3>TTA-based Co-design Environment (TCE)</h3>
673 <p>TCE is a toolset for designing application-specific processors (ASP) based on
674 the Transport triggered architecture (TTA). The toolset provides a complete
675 co-design flow from C/C++ programs down to synthesizable VHDL and parallel
676 program binaries. Processor customization points include the register files,
677 function units, supported operations, and the interconnection network.</p>
679 <p>TCE uses Clang and LLVM for C/C++ language support, target independent
680 optimizations and also for parts of code generation. It generates new
681 LLVM-based code generators "on the fly" for the designed TTA processors and
682 loads them in to the compiler backend as runtime libraries to avoid
683 per-target recompilation of larger parts of the compiler chain.</p>
687 <!--=========================================================================-->
688 <h3>Tart Programming Language</h3>
692 <p><a href="http://code.google.com/p/tart/">Tart</a> is a general-purpose,
693 strongly typed programming language designed for application
694 developers. Strongly inspired by Python and C#, Tart focuses on practical
695 solutions for the professional software developer, while avoiding the clutter
696 and boilerplate of legacy languages like Java and C++. Although Tart is still
697 in development, the current implementation supports many features expected of
698 a modern programming language, such as garbage collection, powerful
699 bidirectional type inference, a greatly simplified syntax for template
700 metaprogramming, closures and function literals, reflection, operator
701 overloading, explicit mutability and immutability, and much more. Tart is
702 flexible enough to accommodate a broad range of programming styles and
703 philosophies, while maintaining a strong commitment to simplicity, minimalism
704 and elegance in design.</p>
708 <!--=========================================================================-->
709 <h3>ThreadSanitizer</h3>
713 <p><a href="http://code.google.com/p/data-race-test/">ThreadSanitizer</a> is a
714 data race detector for (mostly) C and C++ code, available for Linux, Mac OS
715 and Windows. On different systems, we use binary instrumentation frameworks
716 (Valgrind and Pin) as frontends that generate the program events for the race
717 detection algorithm. On Linux, there's an option of using LLVM-based
718 compile-time instrumentation.</p>
724 <!-- *********************************************************************** -->
726 <a name="whatsnew">What's New in LLVM 3.0?</a>
728 <!-- *********************************************************************** -->
732 <p>This release includes a huge number of bug fixes, performance tweaks and
733 minor improvements. Some of the major improvements and new features are
734 listed in this section.</p>
736 <!--=========================================================================-->
738 <a name="majorfeatures">Major New Features</a>
743 <p><b>llvm-gcc is gone</b>. LLVM's configure script doesn't depend on llvm-gcc anymore, clean layering.</p>
745 <p>LLVM 3.0 includes several major new capabilities:</p>
748 Analysis/RegionInfo.h + Dom Frontiers
749 SparseBitVector: used in LiveVar.
750 llvm/lib/Archive - replace with lib object?
754 Type system rewrite: http://blog.llvm.org/2011/11/llvm-30-type-system-rewrite.html
755 Better performance for Neon code in clang due to SRoA improvements.
756 New regalloc on by default. Lin scan going away in 3.1
757 PGO / builtin_expect improvements (summary needed)
759 AVX support, assembler, compiler and disassembler.
760 IndVar improvements: andy
761 PTX backend improvements: Justin
762 llvm-rtdyld & MC JIT: JimG
763 InstAliases now automatically used in the asmprinter where they are shorter.
764 Integrated assembler on by default for arm/thumb?
765 PostOrder Dominator frontiers were removed.
766 Line Profiling / gcov support
767 EH and debug information produced with CFI directives, yielding smaller executables: http://blog.mozilla.com/respindola/2011/05/12/cfi-directives/
768 X86-64 generates smaller and faster code at -O0 (fast isel improvements)
769 Better code generation for Cortex-A9
770 Many APIs take ArrayRef's now.
771 Pass manager extension API.
772 ARM inline asm constraints implemented.
773 LangRef.html#fnattrs uwtable attribute for asynch unwind tables.
774 better performance for indirect gotos.
775 llvm.prefetch now takes a 4th argument that specifies whether the prefetch happens to the icache or dcache.
776 New PackedVector, TinyPtrVector class (see Programmer's Manual)
777 New nonlazybind function attribute.
778 ARC language specific optimizer (Transforms/ObjCARC) a decent example of language-specific transformation.
779 LLVM 3.0 removes support for reading LLVM 2.8 and earlier files. Aim to maintain compatibility all the way back to 3.0 "forever".
781 New llvm.expect intrinsic.
782 Table generated MC expansion logic for pseudo instructions that expand to multiple MC instructions through the PseudoInstExpansion class. (JimG)
783 New llvm.fma intrinsic.
785 Euro dev meeting and main one too.
786 New atomics instructions, "#i_fence" instruction, cmpxchg, atomicrmw too. What target support (X86/ARM)? Also 'atomic load/store'. See Atomics.html
787 X86: inline assembler supports .code32 and .code64.
788 Exception handling rewrite: new landingpad and resume instruction. Unwind gone.
789 LowerSetJmp pass removed, unused.
790 llvm-objdump / dwarf parser library / llvm-dwarfdump (d0k)
791 object file parsing stuff and llvm-size (mspencer)
793 Old arm disassembler replaced with a new one based on autogenerated encoding information from ARM .td files.
794 Frontend tests removed from llvm/test/Frontend* (was this completed for 3.0?)
795 Segmented stack support (X86 only?) Rafael and Sanjoy Das: docs/SegmentedStacks.html should be in CodeGen.html status table?
796 X86 backend support for NaCl (David Meyer / Nick L)
797 Codegen now supports vector "select" operations on vector comparisons, turning
798 them into various optimized code sequences (e.g. using the SSE4/AVX "blend"
800 #line directives in integrated assembler
801 SSE domain fixing code enabled for AVX (Bruno/Jakob). Domain fixing pass is
802 now target independent (ExecutionDepsFix pass). (Jakob)
803 X86 backend synthesizes horizontal add/sub instructions from generic code.
804 returns_twice attribute (rafael)
805 Tablegen has been split into a library, clang tblgen pieces now live in clang.
806 The llvm version is now named llvm-tblgen instead of tblgen.
807 X86: Tons of encoding improvements and new instructions (e.g. Atom, Ivy Bridge,
808 and BMI instructions)
809 added to assembler and disassembler (Craig Topper)
810 data layout string can encode the natural alignment of the target's stack for better optimization (LangRef.html#datalayout)
823 <!--=========================================================================-->
825 <a name="coreimprovements">LLVM IR and Core Improvements</a>
830 <p>LLVM IR has several new features for better support of new targets and that
831 expose new optimization opportunities:</p>
833 <p>One of the biggest changes is that 3.0 has a new exception handling
834 system. The old system used LLVM intrinsics to convey the exception handling
835 information to the code generator. It worked in most cases, but not
836 all. Inlining was especially difficult to get right. Also, the intrinsics
837 could be moved away from the <code>invoke</code> instruction, making it hard
838 to recover that information.</p>
840 <p>The new EH system makes exception handling a first-class member of the IR. It
841 adds two new instructions:</p>
844 <li><a href="LangRef.html#i_landingpad"><code>landingpad</code></a> —
845 this instruction defines a landing pad basic block. It contains all of the
846 information that's needed by the code generator. It's also required to be
847 the first non-PHI instruction in the landing pad. In addition, a landing
848 pad may be jumped to only by the unwind edge of an <code>invoke</code>
851 <li><a href="LangRef.html#i_resume"><code>resume</code></a> — this
852 instruction causes the current exception to resume traveling up the
853 stack. It replaces the <code>@llvm.eh.resume</code> intrinsic.</li>
856 <p>Converting from the old EH API to the new EH API is rather simple, because a
857 lot of complexity has been removed. The two intrinsics,
858 <code>@llvm.eh.exception</code> and <code>@llvm.eh.selector</code> have been
859 superseded by the <code>landingpad</code> instruction. Instead of generating
860 a call to <code>@llvm.eh.exception</code> and <code>@llvm.eh.selector</code>:
862 <div class="doc_code">
864 Function *ExcIntr = Intrinsic::getDeclaration(TheModule,
865 Intrinsic::eh_exception);
866 Function *SlctrIntr = Intrinsic::getDeclaration(TheModule,
867 Intrinsic::eh_selector);
869 // The exception pointer.
870 Value *ExnPtr = Builder.CreateCall(ExcIntr, "exc_ptr");
872 std::vector<Value*> Args;
873 Args.push_back(ExnPtr);
874 Args.push_back(Builder.CreateBitCast(Personality,
875 Type::getInt8PtrTy(Context)));
877 <i>// Add selector clauses to Args.</i>
879 // The selector call.
880 Builder.CreateCall(SlctrIntr, Args, "exc_sel");
884 <p>You should instead generate a <code>landingpad</code> instruction, that
885 returns an exception object and selector value:</p>
887 <div class="doc_code">
889 LandingPadInst *LPadInst =
890 Builder.CreateLandingPad(StructType::get(Int8PtrTy, Int32Ty, NULL),
893 Value *LPadExn = Builder.CreateExtractValue(LPadInst, 0);
894 Builder.CreateStore(LPadExn, getExceptionSlot());
896 Value *LPadSel = Builder.CreateExtractValue(LPadInst, 1);
897 Builder.CreateStore(LPadSel, getEHSelectorSlot());
901 <p>It's now trivial to add the individual clauses to the <code>landingpad</code>
904 <div class="doc_code">
906 <i><b>// Adding a catch clause</b></i>
907 Constant *TypeInfo = getTypeInfo();
908 LPadInst->addClause(TypeInfo);
910 <i><b>// Adding a C++ catch-all</b></i>
911 LPadInst->addClause(Constant::getNullValue(Builder.getInt8PtrTy()));
913 <i><b>// Adding a cleanup</b></i>
914 LPadInst->setCleanup(true);
916 <i><b>// Adding a filter clause</b></i>
917 std::vector<Constant*> TypeInfos;
918 Constant *TypeInfo = getFilterTypeInfo();
919 TypeInfos.push_back(Builder.CreateBitCast(TypeInfo, Builder.getInt8PtrTy()));
921 ArrayType *FilterTy = ArrayType::get(Int8PtrTy, TypeInfos.size());
922 LPadInst->addClause(ConstantArray::get(FilterTy, TypeInfos));
926 <p>Converting from using the <code>@llvm.eh.resume</code> intrinsic to
927 the <code>resume</code> instruction is trivial. It takes the exception
928 pointer and exception selector values returned by
929 the <code>landingpad</code> instruction:</p>
931 <div class="doc_code">
933 Type *UnwindDataTy = StructType::get(Builder.getInt8PtrTy(),
934 Builder.getInt32Ty(), NULL);
935 Value *UnwindData = UndefValue::get(UnwindDataTy);
936 Value *ExcPtr = Builder.CreateLoad(getExceptionObjSlot());
937 Value *ExcSel = Builder.CreateLoad(getExceptionSelSlot());
938 UnwindData = Builder.CreateInsertValue(UnwindData, ExcPtr, 0, "exc_ptr");
939 UnwindData = Builder.CreateInsertValue(UnwindData, ExcSel, 1, "exc_sel");
940 Builder.CreateResume(UnwindData);
946 <!--=========================================================================-->
948 <a name="loopoptimization">Loop Optimization Improvements</a>
952 <p>The induction variable simplification pass in 3.0 only modifies
953 induction variables when profitable. Sign and zero extension
954 elimination, linear function test replacement, loop unrolling, and
955 other simplifications that require induction variable analysis have
956 been generalized so they no longer require loops to be rewritten in a
957 typically suboptimal form prior to optimization. This new design
958 preserves more IR level information, avoids undoing earlier loop
959 optimizations (particularly hand-optimized loops), and no longer
960 strongly depends on the code generator rewriting loops a second time
961 in a now optimal form--an intractable problem.</p>
963 <p>The original behavior can be restored with -mllvm -enable-iv-rewrite;
964 however, support for this mode will be short lived. As such, bug
965 reports should be filed for any significant performance regressions
966 when moving from -mllvm -enable-iv-rewrite to the 3.0 default mode.</p>
969 <!--=========================================================================-->
971 <a name="optimizer">Optimizer Improvements</a>
976 <p>In addition to a large array of minor performance tweaks and bug fixes, this
977 release includes a few major enhancements and additions to the
981 <li>Information about <a href="BranchWeightMetadata.html">branch probability</a>
982 and basic block frequency is now available within LLVM, based on a
983 combination of static branch prediction heuristics and
984 <code>__builtin_expect</code> calls. That information is currently used for
985 register spill placement and if-conversion, with additional optimizations
986 planned for future releases. The same framework is intended for eventual
987 use with profile-guided optimization.</li>
994 <!--=========================================================================-->
996 <a name="mc">MC Level Improvements</a>
1001 <p>The LLVM Machine Code (aka MC) subsystem was created to solve a number of
1002 problems in the realm of assembly, disassembly, object file format handling,
1003 and a number of other related areas that CPU instruction-set level tools work
1007 <li>The ELF object streamers are much more full featured.</li>
1008 <li>Target dependent relocation handling has been refactored into the Targets.</li>
1009 <li>Early stage MC-JIT infrastructure has been implemented.</li>
1012 <p>The MC-JIT is a major new feature for MC, and will eventually grow to replace
1013 the current JIT implementation. It emits object files direct to memory and
1014 uses a runtime dynamic linker to resolve references and drive lazy compilation.
1015 The MC-JIT enables much greater code reuse between the JIT and the static
1016 compiler and provides better integration with the platform ABI as a result.</p>
1018 <p>For more information, please see
1019 the <a href="http://blog.llvm.org/2010/04/intro-to-llvm-mc-project.html">Intro
1020 to the LLVM MC Project Blog Post</a>.</p>
1024 <!--=========================================================================-->
1026 <a name="codegen">Target Independent Code Generator Improvements</a>
1031 <p>We have put a significant amount of work into the code generator
1032 infrastructure, which allows us to implement more aggressive algorithms and
1033 make it run faster:</p>
1042 <!--=========================================================================-->
1044 <a name="x86">X86-32 and X86-64 Target Improvements</a>
1049 <p>New features and major changes in the X86 target include:</p>
1052 <li>The X86 backend, assembler and disassembler now completely support AVX.
1053 To enable it pass <code>-mavx</code> to the compiler.</li>
1055 <li>The X86 backend now supports
1056 all <a href="http://llvm.org/PR879">inline assembly that uses the X86
1057 floating point stack</a>.</li>
1059 <li>The CRC32 intrinsics have been renamed. The intrinsics were previously
1060 <code>@llvm.x86.sse42.crc32.[8|16|32]</code>
1061 and <code>@llvm.x86.sse42.crc64.[8|64]</code>. They have been renamed to
1062 <code>@llvm.x86.sse42.crc32.32.[8|16|32]</code> and
1063 <code>@llvm.x86.sse42.crc32.64.[8|64]</code>.</li>
1069 <!--=========================================================================-->
1071 <a name="ARM">ARM Target Improvements</a>
1076 <p>New features of the ARM target include:</p>
1079 <li>Reworked Set Jump Long Jump EH Lowering,</li>
1080 <li>improved support for Cortex-M series processors, and</li>
1081 <li>beta quality integrated assembler support.</li>
1086 <!--=========================================================================-->
1088 <a name="MIPS">MIPS Target Improvements</a>
1093 <p>New features and major changes in the MIPS target include:</p>
1096 <li>Most MIPS32r1 and r2 instructions are now supported.</li>
1097 <li>LE/BE MIPS32r1/r2 has been tested extensively.</li>
1098 <li>O32 ABI has been fully tested.</li>
1099 <li>MIPS backend has migrated to using the MC infrastructure for assembly printing. Initial support for direct object code emission has been implemented too.</li>
1100 <li>Delay slot filler has been updated. Now it tries to fill delay slots with useful instructions instead of always filling them with NOPs.</li>
1101 <li>Support for old-style JIT is complete.</li>
1102 <li>Support for old architectures (MIPS1 and MIPS2) has been removed.</li>
1103 <li>Initial support for MIPS64 has been added.</li>
1107 <!--=========================================================================-->
1109 <a name="PTX">PTX Target Improvements</a>
1115 The PTX back-end is still experimental, but is fairly usable for compute kernels
1116 in LLVM 3.0. Most scalar arithmetic is implemented, as well as intrinsics to
1117 access the special PTX registers and sync instructions. The major missing
1118 pieces are texture/sampler support and some vector operations.</p>
1120 <p>That said, the backend is already being used for domain-specific languages
1121 and works well with the <a href="http://www.pcc.me.uk/~peter/libclc/">libclc
1122 library</a> to supply OpenCL built-ins. With it, you can use Clang to compile
1123 OpenCL code into PTX and execute it by loading the resulting PTX as a binary
1124 blob using the nVidia OpenCL library. It has been tested with several OpenCL
1125 programs, including some from the nVidia GPU Computing SDK, and the performance
1126 is on par with the nVidia compiler.</p>
1130 <!--=========================================================================-->
1132 <a name="OtherTS">Other Target Specific Improvements</a>
1137 <p>PPC32/ELF va_arg was implemented.</p>
1138 <p>PPC32 initial support for .o file writing was implemented.</p>
1139 <p>MicroBlaze scheduling itineraries were added that model the
1140 3-stage and the 5-stage pipeline architectures. The 3-stage
1141 pipeline model can be selected with <code>-mcpu=mblaze3</code>
1142 and the 5-stage pipeline model can be selected with
1143 <code>-mcpu=mblaze5</code>.</p>
1153 <!--=========================================================================-->
1155 <a name="changes">Major Changes and Removed Features</a>
1160 <p>If you're already an LLVM user or developer with out-of-tree changes based on
1161 LLVM 2.9, this section lists some "gotchas" that you may run into upgrading
1162 from the previous release.</p>
1165 <li>The <code>LLVMC</code> meta compiler driver was removed.</li>
1166 <li>The <code>LowerSetJmp</code> pass wasn't used effectively by any
1167 target and has been removed.</li>
1168 <li>The old <code>TailDup</code> pass was not used in the standard pipeline
1169 and was unable to update ssa form, so it has been removed.
1170 <li>The syntax of volatile loads and stores in IR has been changed to
1171 "<code>load volatile</code>"/"<code>store volatile</code>". The old
1172 syntax ("<code>volatile load</code>"/"<code>volatile store</code>")
1173 is still accepted, but is now considered deprecated.</li>
1174 <li>The old atomic intrinsics (<code>llvm.memory.barrier</code> and
1175 <code>llvm.atomic.*</code>) are now gone. Please use the new atomic
1176 instructions, described in the <a href="Atomics.html">atomics guide</a>.
1179 <h4>Windows (32-bit)</h4>
1183 <li>On Win32(MinGW32 and MSVC), Windows 2000 will not be supported.
1184 Windows XP or higher is required.</li>
1191 <!--=========================================================================-->
1193 <a name="api_changes">Internal API Changes</a>
1198 <p>In addition, many APIs have changed in this release. Some of the major
1199 LLVM API changes are:</p>
1202 <li>The biggest and most pervasive change is that llvm::Types are no longer
1203 returned or accepted as 'const' values. Instead, just pass around
1204 non-const Types.</li>
1206 <li><code>PHINode::reserveOperandSpace</code> has been removed. Instead, you
1207 must specify how many operands to reserve space for when you create the
1208 PHINode, by passing an extra argument
1209 into <code>PHINode::Create</code>.</li>
1211 <li>PHINodes no longer store their incoming BasicBlocks as operands. Instead,
1212 the list of incoming BasicBlocks is stored separately, and can be accessed
1213 with new functions <code>PHINode::block_begin</code>
1214 and <code>PHINode::block_end</code>.</li>
1216 <li>Various functions now take an <code>ArrayRef</code> instead of either a
1217 pair of pointers (or iterators) to the beginning and end of a range, or a
1218 pointer and a length. Others now return an <code>ArrayRef</code> instead
1219 of a reference to a <code>SmallVector</code>
1220 or <code>std::vector</code>. These include:
1222 <!-- Please keep this list sorted. -->
1223 <li><code>CallInst::Create</code></li>
1224 <li><code>ComputeLinearIndex</code> (in <code>llvm/CodeGen/Analysis.h</code>)</li>
1225 <li><code>ConstantArray::get</code></li>
1226 <li><code>ConstantExpr::getExtractElement</code></li>
1227 <li><code>ConstantExpr::getGetElementPtr</code></li>
1228 <li><code>ConstantExpr::getInBoundsGetElementPtr</code></li>
1229 <li><code>ConstantExpr::getIndices</code></li>
1230 <li><code>ConstantExpr::getInsertElement</code></li>
1231 <li><code>ConstantExpr::getWithOperands</code></li>
1232 <li><code>ConstantFoldCall</code> (in <code>llvm/Analysis/ConstantFolding.h</code>)</li>
1233 <li><code>ConstantFoldInstOperands</code> (in <code>llvm/Analysis/ConstantFolding.h</code>)</li>
1234 <li><code>ConstantVector::get</code></li>
1235 <li><code>DIBuilder::createComplexVariable</code></li>
1236 <li><code>DIBuilder::getOrCreateArray</code></li>
1237 <li><code>ExtractValueInst::Create</code></li>
1238 <li><code>ExtractValueInst::getIndexedType</code></li>
1239 <li><code>ExtractValueInst::getIndices</code></li>
1240 <li><code>FindInsertedValue</code> (in <code>llvm/Analysis/ValueTracking.h</code>)</li>
1241 <li><code>gep_type_begin</code> (in <code>llvm/Support/GetElementPtrTypeIterator.h</code>)</li>
1242 <li><code>gep_type_end</code> (in <code>llvm/Support/GetElementPtrTypeIterator.h</code>)</li>
1243 <li><code>GetElementPtrInst::Create</code></li>
1244 <li><code>GetElementPtrInst::CreateInBounds</code></li>
1245 <li><code>GetElementPtrInst::getIndexedType</code></li>
1246 <li><code>InsertValueInst::Create</code></li>
1247 <li><code>InsertValueInst::getIndices</code></li>
1248 <li><code>InvokeInst::Create</code></li>
1249 <li><code>IRBuilder::CreateCall</code></li>
1250 <li><code>IRBuilder::CreateExtractValue</code></li>
1251 <li><code>IRBuilder::CreateGEP</code></li>
1252 <li><code>IRBuilder::CreateInBoundsGEP</code></li>
1253 <li><code>IRBuilder::CreateInsertValue</code></li>
1254 <li><code>IRBuilder::CreateInvoke</code></li>
1255 <li><code>MDNode::get</code></li>
1256 <li><code>MDNode::getIfExists</code></li>
1257 <li><code>MDNode::getTemporary</code></li>
1258 <li><code>MDNode::getWhenValsUnresolved</code></li>
1259 <li><code>SimplifyGEPInst</code> (in <code>llvm/Analysis/InstructionSimplify.h</code>)</li>
1260 <li><code>TargetData::getIndexedOffset</code></li>
1263 <li>All forms of <code>StringMap::getOrCreateValue</code> have been remove
1264 except for the one which takes a <code>StringRef</code>.</li>
1266 <li>The <code>LLVMBuildUnwind</code> function from the C API was removed. The
1267 LLVM <code>unwind</code> instruction has been deprecated for a long time
1268 and isn't used by the current front-ends. So this was removed during the
1269 exception handling rewrite.</li>
1271 <li>The <code>LLVMAddLowerSetJmpPass</code> function from the C API was
1272 removed because the <code>LowerSetJmp</code> pass was removed.</li>
1274 <li>The <code>DIBuilder</code> interface used by front ends to encode
1275 debugging information in the LLVM IR now expects clients to
1276 use <code>DIBuilder::finalize()</code> at the end of translation unit to
1277 complete debugging information encoding.</li>
1279 <li>The way the type system works has been
1280 rewritten: <code>PATypeHolder</code> and <code>OpaqueType</code> are gone,
1281 and all APIs deal with <code>Type*</code> instead of <code>const
1282 Type*</code>. If you need to create recursive structures, then create a
1283 named structure, and use <code>setBody()</code> when all its elements are
1284 built. Type merging and refining is gone too: named structures are not
1285 merged with other structures, even if their layout is identical. (of
1286 course anonymous structures are still uniqued by layout).</li>
1288 <li>TargetSelect.h moved to Support/ from Target/</li>
1290 <li>UpgradeIntrinsicCall no longer upgrades pre-2.9 intrinsic calls (for
1291 example <code>llvm.memset.i32</code>).</li>
1293 <li>It is mandatory to initialize all out-of-tree passes too and their dependencies now with
1294 <code>INITIALIZE_PASS{BEGIN,END,}</code>
1295 and <code>INITIALIZE_{PASS,AG}_DEPENDENCY</code>.</li>
1297 <li>The interface for MemDepResult in MemoryDependenceAnalysis has been
1298 enhanced with new return types Unknown and NonFuncLocal, in addition to
1299 the existing types Clobber, Def, and NonLocal.</li>
1306 <!-- *********************************************************************** -->
1308 <a name="knownproblems">Known Problems</a>
1310 <!-- *********************************************************************** -->
1314 <p>This section contains significant known problems with the LLVM system, listed
1315 by component. If you run into a problem, please check
1316 the <a href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
1317 there isn't already one.</p>
1319 <!-- ======================================================================= -->
1321 <a name="experimental">Experimental features included with this release</a>
1326 <p>The following components of this LLVM release are either untested, known to
1327 be broken or unreliable, or are in early development. These components
1328 should not be relied on, and bugs should not be filed against them, but they
1329 may be useful to some people. In particular, if you would like to work on
1330 one of these components, please contact us on
1331 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev
1335 <li>The Alpha, Blackfin, CellSPU, MicroBlaze, MSP430, MIPS, PTX, SystemZ and
1336 XCore backends are experimental.</li>
1338 <li><tt>llc</tt> "<tt>-filetype=obj</tt>" is experimental on all targets other
1339 than darwin and ELF X86 systems.</li>
1344 <!-- ======================================================================= -->
1346 <a name="x86-be">Known problems with the X86 back-end</a>
1352 <li>The X86-64 backend <a href="http://llvm.org/PR1740">does not yet support
1353 the <tt>va_arg</tt> LLVM IR instruction</a>. Currently, front-ends support
1354 variadic argument constructs on X86-64 by lowering them manually.</li>
1359 <!-- ======================================================================= -->
1361 <a name="ppc-be">Known problems with the PowerPC back-end</a>
1367 <li>The PPC32/ELF support lacks PIC support.</li>
1372 <!-- ======================================================================= -->
1374 <a name="arm-be">Known problems with the ARM back-end</a>
1380 <li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
1381 processors, thumb programs can crash or produce wrong results
1382 (<a href="http://llvm.org/PR1388">PR1388</a>).</li>
1384 <li>Compilation for ARM Linux OABI (old ABI) is supported but not fully
1390 <!-- ======================================================================= -->
1392 <a name="sparc-be">Known problems with the SPARC back-end</a>
1398 <li>The SPARC backend only supports the 32-bit SPARC ABI (-m32); it does not
1399 support the 64-bit SPARC ABI (-m64).</li>
1404 <!-- ======================================================================= -->
1406 <a name="mips-be">Known problems with the MIPS back-end</a>
1412 <li>64-bit MIPS targets are not supported yet.</li>
1417 <!-- ======================================================================= -->
1419 <a name="alpha-be">Known problems with the Alpha back-end</a>
1425 <li>On 21164s, some rare FP arithmetic sequences which may trap do not have
1426 the appropriate nops inserted to ensure restartability.</li>
1431 <!-- ======================================================================= -->
1433 <a name="c-be">Known problems with the C back-end</a>
1438 <p>The C backend has numerous problems and is not being actively maintained.
1439 Depending on it for anything serious is not advised.</p>
1442 <li><a href="http://llvm.org/PR802">The C backend has only basic support for
1443 inline assembly code</a>.</li>
1445 <li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common
1446 C++ programs</a>, preventing intermixing between C++ compiled by the CBE
1447 and C++ code compiled with <tt>llc</tt> or native compilers.</li>
1449 <li>The C backend does not support all exception handling constructs.</li>
1451 <li>The C backend does not support arbitrary precision integers.</li>
1458 <!-- *********************************************************************** -->
1460 <a name="additionalinfo">Additional Information</a>
1462 <!-- *********************************************************************** -->
1466 <p>A wide variety of additional information is available on
1467 the <a href="http://llvm.org/">LLVM web page</a>, in particular in
1468 the <a href="http://llvm.org/docs/">documentation</a> section. The web page
1469 also contains versions of the API documentation which is up-to-date with the
1470 Subversion version of the source code. You can access versions of these
1471 documents specific to this release by going into the "<tt>llvm/doc/</tt>"
1472 directory in the LLVM tree.</p>
1474 <p>If you have any questions or comments about LLVM, please feel free to contact
1475 us via the <a href="http://llvm.org/docs/#maillist"> mailing lists</a>.</p>
1479 <!-- *********************************************************************** -->
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