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7 <title>LLVM 2.7 Release Notes</title>
11 <div class="doc_title">LLVM 2.7 Release Notes</div>
13 <img align=right src="http://llvm.org/img/DragonSmall.png"
14 width="136" height="136">
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 2.7</a></li>
20 <li><a href="#whatsnew">What's New in LLVM 2.7?</a></li>
21 <li><a href="GettingStarted.html">Installation Instructions</a></li>
22 <li><a href="#portability">Portability and Supported Platforms</a></li>
23 <li><a href="#knownproblems">Known Problems</a></li>
24 <li><a href="#additionalinfo">Additional Information</a></li>
27 <div class="doc_author">
28 <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 2.7
34 <a href="http://llvm.org/releases/2.6/docs/ReleaseNotes.html">LLVM 2.6
35 Release Notes</a>.</h1>
37 <!-- *********************************************************************** -->
38 <div class="doc_section">
39 <a name="intro">Introduction</a>
41 <!-- *********************************************************************** -->
43 <div class="doc_text">
45 <p>This document contains the release notes for the LLVM Compiler
46 Infrastructure, release 2.7. Here we describe the status of LLVM, including
47 major improvements from the previous release and significant known problems.
48 All LLVM releases may be downloaded from the <a
49 href="http://llvm.org/releases/">LLVM releases web site</a>.</p>
51 <p>For more information about LLVM, including information about the latest
52 release, please check out the <a href="http://llvm.org/">main LLVM
53 web site</a>. If you have questions or comments, the <a
54 href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM Developer's
55 Mailing List</a> is a good place to send them.</p>
57 <p>Note that if you are reading this file from a Subversion checkout or the
58 main LLVM web page, this document applies to the <i>next</i> release, not the
59 current one. To see the release notes for a specific release, please see the
60 <a href="http://llvm.org/releases/">releases page</a>.</p>
63 <p>FIXME: llvm.org moved to new server, mention new logo, Ted and Doug new code
71 include/llvm/Analysis/LiveValues.h => Dan
72 lib/Transforms/IPO/MergeFunctions.cpp => consider for 2.8.
73 llvm/Analysis/PointerTracking.h => Edwin wants this, consider for 2.8.
74 ABCD, SCCVN, GEPSplitterPass
76 lib/Transforms/Utils/SSI.cpp -> ABCD depends on it.
80 <!-- Features that need text if they're finished for 2.7:
83 variable debug info for optimized code
84 postalloc scheduler: anti dependence breaking, hazard recognizer?
86 loop dependence analysis
87 ELF Writer? How stable?
88 <li>PostRA scheduler improvements, ARM adoption (David Goodwin).</li>
91 <!-- for announcement email:
95 KLEE web page at klee.llvm.org
96 Many new papers added to /pubs/
100 <!-- *********************************************************************** -->
101 <div class="doc_section">
102 <a name="subproj">Sub-project Status Update</a>
104 <!-- *********************************************************************** -->
106 <div class="doc_text">
108 The LLVM 2.7 distribution currently consists of code from the core LLVM
109 repository (which roughly includes the LLVM optimizers, code generators
110 and supporting tools), the Clang repository and the llvm-gcc repository. In
111 addition to this code, the LLVM Project includes other sub-projects that are in
112 development. Here we include updates on these subprojects.
118 <!--=========================================================================-->
119 <div class="doc_subsection">
120 <a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>
123 <div class="doc_text">
125 <p>The <a href="http://clang.llvm.org/">Clang project</a> is ...</p>
127 <p>In the LLVM 2.7 time-frame, the Clang team has made many improvements:</p>
130 <li>FIXME: C++! Include a link to cxx_compatibility.html</li>
132 <li>FIXME: Static Analyzer improvements?</li>
134 <li>CIndex API and Python bindings: Clang now includes a C API as part of the
135 CIndex library. Although we make make some changes to the API in the future, it
136 is intended to be stable and has been designed for use by external projects. See
138 doxygen <a href="http://clang.llvm.org/doxygen/group__CINDEX.html">CIndex</a>
139 documentation for more details. The CIndex API also includings an preliminary
140 set of Python bindings.</li>
142 <li>ARM Support: Clang now has ABI support for both the Darwin and Linux ARM
143 ABIs. Coupled with many improvements to the LLVM ARM backend, Clang is now
144 suitable for use as a a beta quality ARM compiler.</li>
148 <!--=========================================================================-->
149 <div class="doc_subsection">
150 <a name="clangsa">Clang Static Analyzer</a>
153 <div class="doc_text">
155 <p>Previously announced in the 2.4, 2.5, and 2.6 LLVM releases, the Clang project also
156 includes an early stage static source code analysis tool for <a
157 href="http://clang.llvm.org/StaticAnalysis.html">automatically finding bugs</a>
158 in C and Objective-C programs. The tool performs checks to find
159 bugs that occur on a specific path within a program.</p>
161 <p>In the LLVM 2.7 time-frame, the analyzer core has sprouted legs and...</p>
165 <!--=========================================================================-->
166 <div class="doc_subsection">
167 <a name="vmkit">VMKit: JVM/CLI Virtual Machine Implementation</a>
170 <div class="doc_text">
172 The <a href="http://vmkit.llvm.org/">VMKit project</a> is an implementation of
173 a JVM and a CLI Virtual Machine (Microsoft .NET is an
174 implementation of the CLI) using LLVM for static and just-in-time
178 With the release of LLVM 2.7, VMKit has shifted to a great framework for writing
179 virtual machines. VMKit now offers precise and efficient garbage collection with
180 multi-threading support, thanks to the MMTk memory management toolkit, as well
181 as just in time and ahead of time compilation with LLVM. The major changes in
186 <li>Garbage collection: VMKit now uses the MMTk toolkit for garbage collectors.
187 The first collector to be ported is the MarkSweep collector, which is precise,
188 and drastically improves the performance of VMKit.</li>
189 <li>Line number information in the JVM: by using the debug metadata of LLVM, the
190 JVM now supports precise line number information, useful when printing a stack
192 <li>Interface calls in the JVM: we implemented a variant of the Interface Method
193 Table technique for interface calls in the JVM.
200 <!--=========================================================================-->
201 <div class="doc_subsection">
202 <a name="compiler-rt">compiler-rt: Compiler Runtime Library</a>
205 <div class="doc_text">
207 The new LLVM <a href="http://compiler-rt.llvm.org/">compiler-rt project</a>
208 is a simple library that provides an implementation of the low-level
209 target-specific hooks required by code generation and other runtime components.
210 For example, when compiling for a 32-bit target, converting a double to a 64-bit
211 unsigned integer is compiled into a runtime call to the "__fixunsdfdi"
212 function. The compiler-rt library provides highly optimized implementations of
213 this and other low-level routines (some are 3x faster than the equivalent
214 libgcc routines).</p>
217 All of the code in the compiler-rt project is available under the standard LLVM
218 License, a "BSD-style" license.</p>
222 <!--=========================================================================-->
223 <div class="doc_subsection">
224 <a name="dragonegg">DragonEgg: GCC-4.5 as an LLVM frontend</a>
227 <div class="doc_text">
229 The goal of <a href="http://dragonegg.llvm.org/">DragonEgg</a> is to make
230 gcc-4.5 act like llvm-gcc without requiring any gcc modifications whatsoever.
231 <a href="http://dragonegg.llvm.org/">DragonEgg</a> is a shared library (dragonegg.so)
232 that is loaded by gcc at runtime. It ...
238 <!--=========================================================================-->
239 <div class="doc_subsection">
240 <a name="mc">llvm-mc: Machine Code Toolkit</a>
243 <div class="doc_text">
245 The LLVM Machine Code (MC) Toolkit project is ...
251 <!-- *********************************************************************** -->
252 <div class="doc_section">
253 <a name="externalproj">External Open Source Projects Using LLVM 2.7</a>
255 <!-- *********************************************************************** -->
257 <div class="doc_text">
259 <p>An exciting aspect of LLVM is that it is used as an enabling technology for
260 a lot of other language and tools projects. This section lists some of the
261 projects that have already been updated to work with LLVM 2.7.</p>
265 <!--=========================================================================-->
266 <div class="doc_subsection">
267 <a name="Rubinius">Rubinius</a>
270 <div class="doc_text">
273 <p><a href="http://github.com/evanphx/rubinius">Rubinius</a> is an environment
274 for running Ruby code which strives to write as much of the core class
275 implementation in Ruby as possible. Combined with a bytecode interpreting VM, it
276 uses LLVM to optimize and compile ruby code down to machine code. Techniques
277 such as type feedback, method inlining, and uncommon traps are all used to
278 remove dynamism from ruby execution and increase performance.</p>
280 <p>Since LLVM 2.5, Rubinius has made several major leaps forward, implementing
281 a counter based JIT, type feedback and speculative method inlining.
287 <!--=========================================================================-->
288 <div class="doc_subsection">
289 <a name="macruby">MacRuby</a>
292 <div class="doc_text">
297 <a href="http://macruby.org">MacRuby</a> is an implementation of Ruby on top of
298 core Mac OS X technologies, such as the Objective-C common runtime and garbage
299 collector and the CoreFoundation framework. It is principally developed by
300 Apple and aims at enabling the creation of full-fledged Mac OS X applications.
304 MacRuby uses LLVM for optimization passes, JIT and AOT compilation of Ruby
305 expressions. It also uses zero-cost DWARF exceptions to implement Ruby exception
311 <!--=========================================================================-->
312 <div class="doc_subsection">
313 <a name="pure">Pure</a>
316 <div class="doc_text">
318 <a href="http://pure-lang.googlecode.com/">Pure</a>
319 is an algebraic/functional programming language based on term rewriting.
320 Programs are collections of equations which are used to evaluate expressions in
321 a symbolic fashion. Pure offers dynamic typing, eager and lazy evaluation,
322 lexical closures, a hygienic macro system (also based on term rewriting),
323 built-in list and matrix support (including list and matrix comprehensions) and
324 an easy-to-use C interface. The interpreter uses LLVM as a backend to
325 JIT-compile Pure programs to fast native code.</p>
327 <p>Pure versions 0.43 and later have been tested and are known to work with
328 LLVM 2.7 (and continue to work with older LLVM releases >= 2.5).</p>
333 <!--=========================================================================-->
334 <div class="doc_subsection">
335 <a name="ldc">LLVM D Compiler</a>
338 <div class="doc_text">
342 <a href="http://www.dsource.org/projects/ldc">LDC</a> is an implementation of
343 the D Programming Language using the LLVM optimizer and code generator.
344 The LDC project works great with the LLVM 2.6 release. General improvements in
346 cycle have included new inline asm constraint handling, better debug info
347 support, general bug fixes and better x86-64 support. This has allowed
348 some major improvements in LDC, getting it much closer to being as
349 fully featured as the original DMD compiler from DigitalMars.-->
353 <!--=========================================================================-->
354 <div class="doc_subsection">
355 <a name="RoadsendPHP">Roadsend PHP</a>
358 <div class="doc_text">
360 <a href="http://code.roadsend.com/rphp">Roadsend PHP</a> (rphp) is an open
361 source implementation of the PHP programming
362 language that uses LLVM for its optimizer, JIT and static compiler. This is a
363 reimplementation of an earlier project that is now based on LLVM.
367 <!--=========================================================================-->
368 <div class="doc_subsection">
369 <a name="UnladenSwallow">Unladen Swallow</a>
372 <div class="doc_text">
374 <a href="http://code.google.com/p/unladen-swallow/">Unladen Swallow</a> is a
375 branch of <a href="http://python.org/">Python</a> intended to be fully
376 compatible and significantly faster. It uses LLVM's optimization passes and JIT
381 <!--=========================================================================-->
382 <div class="doc_subsection">
383 <a name="llvm-lua">llvm-lua</a>
386 <div class="doc_text">
390 <a href="http://code.google.com/p/llvm-lua/">LLVM-Lua</a> uses LLVM to add JIT
391 and static compiling support to the Lua VM. Lua bytecode is analyzed to
392 remove type checks, then LLVM is used to compile the bytecode down to machine
397 <!--=========================================================================-->
398 <div class="doc_subsection">
399 <a name="icedtea">IcedTea Java Virtual Machine Implementation</a>
402 <div class="doc_text">
406 <a href="http://icedtea.classpath.org/wiki/Main_Page">IcedTea</a> provides a
407 harness to build OpenJDK using only free software build tools and to provide
408 replacements for the not-yet free parts of OpenJDK. One of the extensions that
409 IcedTea provides is a new JIT compiler named <a
410 href="http://icedtea.classpath.org/wiki/ZeroSharkFaq">Shark</a> which uses LLVM
411 to provide native code generation without introducing processor-dependent
417 <!--=========================================================================-->
418 <div class="doc_subsection">
419 <a name="tce">TTA-based Codesign Environment (TCE)</a>
422 <div class="doc_text">
424 <a href="http://tce.cs.tut.fi/">TCE</a> is a toolset for designing
425 application-specific processors (ASP) based on the Transport triggered
426 architecture (TTA). The toolset provides a complete co-design flow from C/C++
427 programs down to synthesizable VHDL and parallel program binaries. Processor
428 customization points include the register files, function units, supported
429 operations, and the interconnection network.</p>
431 <p>TCE uses llvm-gcc/Clang and LLVM for C/C++ language support, target
432 independent optimizations and also for parts of code generation. It generates
433 new LLVM-based code generators "on the fly" for the designed TTA processors and
434 loads them in to the compiler backend as runtime libraries to avoid per-target
435 recompilation of larger parts of the compiler chain.</p>
439 <!-- *********************************************************************** -->
440 <div class="doc_section">
441 <a name="whatsnew">What's New in LLVM 2.7?</a>
443 <!-- *********************************************************************** -->
445 <div class="doc_text">
447 <p>This release includes a huge number of bug fixes, performance tweaks and
448 minor improvements. Some of the major improvements and new features are listed
454 <!--=========================================================================-->
455 <div class="doc_subsection">
456 <a name="majorfeatures">Major New Features</a>
459 <div class="doc_text">
461 <p>LLVM 2.7 includes several major new capabilities:</p>
467 Extensible metadata solid.
469 Debug info improvements: using metadata instead of llvm.dbg global variables.
470 This brings several enhancements including improved compile times.
472 New instruction selector.
473 GHC Haskell ABI/ calling conv support.
474 Pre-Alpha support for unions in IR.
475 New InlineHint and StackAlignment function attributes
476 Code generator MC'ized except for debug info and EH.
477 New SCEV AA pass: -scev-aa
478 Inliner reuses arrays allocas when inlining multiple callers to reduce stack usage.
479 MC encoding and disassembler apis.
480 Optimal Edge Profiling?
481 Instcombine is now a library, has its own IRBuilder to simplify itself.
482 New llvm/Support/Regex.h API. FileCheck now does regex's
483 Many subtle pointer invalidation bugs in Callgraph have been fixed and it now uses asserting value handles.
484 MC Disassembler (with blog post), MCInstPrinter. Many X86 backend and AsmPrinter simplifications
485 Various tools like llc and opt now read either .ll or .bc files as input.
486 Malloc and free instructions got removed, along with LowerAllocations pass.
487 compiler-rt support for ARM.
488 completely llvm-gcc NEON support.
489 Can transcode from GAS to intel syntax with "llvm-mc foo.s -output-asm-variant=1"
490 JIT debug information with GDB 7.0
491 New CodeGen Level CSE
492 CMake can now run tests, what other improvements?
493 ARM/Thumb using reg scavenging for stack object address materialization (PEI).
494 New SSAUpdater and MachineSSAUpdater classes for unstructured ssa updating,
495 changed jump threading, GVN, etc to use it which simplified them and speed
497 Combiner-AA improvements, why not on by default?
498 Pre-regalloc tail duplication
499 x86 sibcall optimization
500 New LSR with full strength reduction mode
501 The most awesome sext / zext optimization pass. ?
503 The ARM backend now has good support for ARMv4 backend (tested on StrongARM
504 hardware), previously only supported ARMv4T and newer.
508 Defaults to RTTI off, packagers should build with make REQUIRE_RTTI=1.
509 CondProp pass removed (functionality merged into jump threading).
510 AndersAA got removed (from 2.7 or mainline?)
511 PredSimplify, LoopVR, GVNPRE got removed.
512 LLVM command line tools now overwrite their output, before they would only do this with -f.
513 DOUT removed, use DEBUG(errs() instead.
514 Much stuff converted to use raw_ostream instead of std::ostream.
515 TargetAsmInfo renamed to MCAsmInfo
516 llvm/ADT/iterator.h gone.
521 <!--=========================================================================-->
522 <div class="doc_subsection">
523 <a name="coreimprovements">LLVM IR and Core Improvements</a>
526 <div class="doc_text">
527 <p>LLVM IR has several new features for better support of new targets and that
528 expose new optimization opportunities:</p>
536 <!--=========================================================================-->
537 <div class="doc_subsection">
538 <a name="optimizer">Optimizer Improvements</a>
541 <div class="doc_text">
543 <p>In addition to a large array of minor performance tweaks and bug fixes, this
544 release includes a few major enhancements and additions to the optimizers:</p>
552 <p>Also, -anders-aa was removed</p>
557 <!--=========================================================================-->
558 <div class="doc_subsection">
559 <a name="executionengine">Interpreter and JIT Improvements</a>
562 <div class="doc_text">
566 href="http://llvm.org/viewvc/llvm-project?view=rev&revision=85295">defaults
567 to compiling eagerly</a> to avoid a race condition in the lazy JIT.
568 Clients that still want the lazy JIT can switch it on by calling
569 <tt>ExecutionEngine::DisableLazyCompilation(false)</tt>.</li>
570 <li>It is now possible to create more than one JIT instance in the same process.
571 These JITs can generate machine code in parallel,
572 although <a href="http://llvm.org/docs/ProgrammersManual.html#jitthreading">you
573 still have to obey the other threading restrictions</a>.</li>
578 <!--=========================================================================-->
579 <div class="doc_subsection">
580 <a name="codegen">Target Independent Code Generator Improvements</a>
583 <div class="doc_text">
585 <p>We have put a significant amount of work into the code generator
586 infrastructure, which allows us to implement more aggressive algorithms and make
595 <!--=========================================================================-->
596 <div class="doc_subsection">
597 <a name="x86">X86-32 and X86-64 Target Improvements</a>
600 <div class="doc_text">
601 <p>New features of the X86 target include:
612 <!--=========================================================================-->
613 <div class="doc_subsection">
614 <a name="pic16">PIC16 Target Improvements</a>
617 <div class="doc_text">
618 <p>New features of the PIC16 target include:
625 <p>Things not yet supported:</p>
628 <li>Variable arguments.</li>
629 <li>Interrupts/programs.</li>
634 <!--=========================================================================-->
635 <div class="doc_subsection">
636 <a name="ARM">ARM Target Improvements</a>
639 <div class="doc_text">
640 <p>New features of the ARM target include:
651 <!--=========================================================================-->
652 <div class="doc_subsection">
653 <a name="OtherTarget">Other Target Specific Improvements</a>
656 <div class="doc_text">
657 <p>New features of other targets include:
666 <!--=========================================================================-->
667 <div class="doc_subsection">
668 <a name="newapis">New Useful APIs</a>
671 <div class="doc_text">
673 <p>This release includes a number of new APIs that are used internally, which
674 may also be useful for external clients.
684 <!--=========================================================================-->
685 <div class="doc_subsection">
686 <a name="otherimprovements">Other Improvements and New Features</a>
689 <div class="doc_text">
690 <p>Other miscellaneous features include:</p>
699 <!--=========================================================================-->
700 <div class="doc_subsection">
701 <a name="changes">Major Changes and Removed Features</a>
704 <div class="doc_text">
706 <p>If you're already an LLVM user or developer with out-of-tree changes based
707 on LLVM 2.6, this section lists some "gotchas" that you may run into upgrading
708 from the previous release.</p>
711 <li>The LLVM interpreter now defaults to <em>not</em> using <tt>libffi</tt> even
712 if you have it installed. This makes it more likely that an LLVM built on one
713 system will work when copied to a similar system. To use <tt>libffi</tt>,
714 configure with <tt>--enable-libffi</tt>.
719 <p>In addition, many APIs have changed in this release. Some of the major LLVM
723 <li><tt>ModuleProvider</tt> has been <a
724 href="http://llvm.org/viewvc/llvm-project?view=rev&revision=94686">removed</a>
725 and its methods moved to <tt>Module</tt> and <tt>GlobalValue</tt>.
726 Most clients can remove uses of <tt>ExistingModuleProvider</tt>,
727 replace <tt>getBitcodeModuleProvider</tt> with
728 <tt>getLazyBitcodeModule</tt>, and pass their <tt>Module</tt> to
729 functions that used to accept <tt>ModuleProvider</tt>. Clients who
730 wrote their own <tt>ModuleProvider</tt>s will need to derive from
731 <tt>GVMaterializer</tt> instead and use
732 <tt>Module::setMaterializer</tt> to attach it to a
733 <tt>Module</tt>.</li>
735 <li><tt>GhostLinkage</tt> has given up the ghost.
736 <tt>GlobalValue</tt>s that have not yet been read from their backing
737 storage have the same linkage they will have after being read in.
738 Clients must replace calls to
739 <tt>GlobalValue::hasNotBeenReadFromBitcode</tt> with
740 <tt>GlobalValue::isMaterializable</tt>.</li>
742 <li>FIXME: Debug info has been totally redone. Add pointers to new APIs. Substantial caveats about compatibility of .ll and .bc files.</li>
744 <li>The <tt>llvm/Support/DataTypes.h</tt> header has moved
745 to <tt>llvm/System/DataTypes.h</tt>.</li>
747 <li>The <tt>isInteger</tt>, <tt>isIntOrIntVector</tt>, <tt>isFloatingPoint</tt>,
748 <tt>isFPOrFPVector</tt> and <tt>isFPOrFPVector</tt> methods have been renamed
749 <tt>isIntegerTy</tt>, <tt>isIntOrIntVectorTy</tt>, <tt>isFloatingPointTy</tt>,
750 <tt>isFPOrFPVectorTy</tt> and <tt>isFPOrFPVectorTy</tt> respectively.</li>
757 <!-- *********************************************************************** -->
758 <div class="doc_section">
759 <a name="portability">Portability and Supported Platforms</a>
761 <!-- *********************************************************************** -->
763 <div class="doc_text">
765 <p>LLVM is known to work on the following platforms:</p>
768 <li>Intel and AMD machines (IA32, X86-64, AMD64, EMT-64) running Red Hat
769 Linux, Fedora Core, FreeBSD and AuroraUX (and probably other unix-like
771 <li>PowerPC and X86-based Mac OS X systems, running 10.3 and above in 32-bit
772 and 64-bit modes.</li>
773 <li>Intel and AMD machines running on Win32 using MinGW libraries (native).</li>
774 <li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited
775 support is available for native builds with Visual C++).</li>
776 <li>Sun x86 and AMD64 machines running Solaris 10, OpenSolaris 0906.</li>
777 <li>Alpha-based machines running Debian GNU/Linux.</li>
780 <p>The core LLVM infrastructure uses GNU autoconf to adapt itself
781 to the machine and operating system on which it is built. However, minor
782 porting may be required to get LLVM to work on new platforms. We welcome your
783 portability patches and reports of successful builds or error messages.</p>
787 <!-- *********************************************************************** -->
788 <div class="doc_section">
789 <a name="knownproblems">Known Problems</a>
791 <!-- *********************************************************************** -->
793 <div class="doc_text">
795 <p>This section contains significant known problems with the LLVM system,
796 listed by component. If you run into a problem, please check the <a
797 href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
798 there isn't already one.</p>
801 <li>LLVM will not correctly compile on Solaris and/or OpenSolaris
802 using the stock GCC 3.x.x series 'out the box',
803 See: <a href="GettingStarted.html#brokengcc">Broken versions of GCC and other tools</a>.
804 However, A <a href="http://pkg.auroraux.org/GCC">Modern GCC Build</a>
805 for x86/x86-64 has been made available from the third party AuroraUX Project
806 that has been meticulously tested for bootstrapping LLVM & Clang.</li>
811 <!-- ======================================================================= -->
812 <div class="doc_subsection">
813 <a name="experimental">Experimental features included with this release</a>
816 <div class="doc_text">
818 <p>The following components of this LLVM release are either untested, known to
819 be broken or unreliable, or are in early development. These components should
820 not be relied on, and bugs should not be filed against them, but they may be
821 useful to some people. In particular, if you would like to work on one of these
822 components, please contact us on the <a
823 href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
826 <li>The MSIL, Alpha, SPU, MIPS, PIC16, Blackfin, MSP430, SystemZ and MicroBlaze
827 backends are experimental.</li>
828 <li>The <tt>llc</tt> "<tt>-filetype=asm</tt>" (the default) is the only
829 supported value for this option. The MachO writer is experimental, and
830 works much better in mainline SVN.</li>
835 <!-- ======================================================================= -->
836 <div class="doc_subsection">
837 <a name="x86-be">Known problems with the X86 back-end</a>
840 <div class="doc_text">
843 <li>The X86 backend does not yet support
844 all <a href="http://llvm.org/PR879">inline assembly that uses the X86
845 floating point stack</a>. It supports the 'f' and 't' constraints, but not
847 <li>The X86 backend generates inefficient floating point code when configured
848 to generate code for systems that don't have SSE2.</li>
849 <li>Win64 code generation wasn't widely tested. Everything should work, but we
850 expect small issues to happen. Also, llvm-gcc cannot build the mingw64
851 runtime currently due
852 to <a href="http://llvm.org/PR2255">several</a>
853 <a href="http://llvm.org/PR2257">bugs</a> and due to lack of support for
855 'u' inline assembly constraint and for X87 floating point inline assembly.</li>
856 <li>The X86-64 backend does not yet support the LLVM IR instruction
857 <tt>va_arg</tt>. Currently, the llvm-gcc and front-ends support variadic
858 argument constructs on X86-64 by lowering them manually.</li>
863 <!-- ======================================================================= -->
864 <div class="doc_subsection">
865 <a name="ppc-be">Known problems with the PowerPC back-end</a>
868 <div class="doc_text">
871 <li>The Linux PPC32/ABI support needs testing for the interpreter and static
872 compilation, and lacks support for debug information.</li>
877 <!-- ======================================================================= -->
878 <div class="doc_subsection">
879 <a name="arm-be">Known problems with the ARM back-end</a>
882 <div class="doc_text">
885 <li>Support for the Advanced SIMD (Neon) instruction set is still incomplete
886 and not well tested. Some features may not work at all, and the code quality
887 may be poor in some cases.</li>
888 <li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
889 processors, thumb programs can crash or produce wrong
890 results (<a href="http://llvm.org/PR1388">PR1388</a>).</li>
891 <li>Compilation for ARM Linux OABI (old ABI) is supported but not fully tested.
897 <!-- ======================================================================= -->
898 <div class="doc_subsection">
899 <a name="sparc-be">Known problems with the SPARC back-end</a>
902 <div class="doc_text">
905 <li>The SPARC backend only supports the 32-bit SPARC ABI (-m32); it does not
906 support the 64-bit SPARC ABI (-m64).</li>
911 <!-- ======================================================================= -->
912 <div class="doc_subsection">
913 <a name="mips-be">Known problems with the MIPS back-end</a>
916 <div class="doc_text">
919 <li>64-bit MIPS targets are not supported yet.</li>
924 <!-- ======================================================================= -->
925 <div class="doc_subsection">
926 <a name="alpha-be">Known problems with the Alpha back-end</a>
929 <div class="doc_text">
933 <li>On 21164s, some rare FP arithmetic sequences which may trap do not have the
934 appropriate nops inserted to ensure restartability.</li>
939 <!-- ======================================================================= -->
940 <div class="doc_subsection">
941 <a name="c-be">Known problems with the C back-end</a>
944 <div class="doc_text">
947 <li><a href="http://llvm.org/PR802">The C backend has only basic support for
948 inline assembly code</a>.</li>
949 <li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common
950 C++ programs</a>, preventing intermixing between C++ compiled by the CBE and
951 C++ code compiled with <tt>llc</tt> or native compilers.</li>
952 <li>The C backend does not support all exception handling constructs.</li>
953 <li>The C backend does not support arbitrary precision integers.</li>
959 <!-- ======================================================================= -->
960 <div class="doc_subsection">
961 <a name="c-fe">Known problems with the llvm-gcc C and C++ front-end</a>
964 <div class="doc_text">
966 <p>The only major language feature of GCC not supported by llvm-gcc is
967 the <tt>__builtin_apply</tt> family of builtins. However, some extensions
968 are only supported on some targets. For example, trampolines are only
969 supported on some targets (these are used when you take the address of a
970 nested function).</p>
972 <p>If you run into GCC extensions which are not supported, please let us know.
977 <!-- ======================================================================= -->
978 <div class="doc_subsection">
979 <a name="fortran-fe">Known problems with the llvm-gcc Fortran front-end</a>
982 <div class="doc_text">
984 <li>Fortran support generally works, but there are still several unresolved bugs
985 in <a href="http://llvm.org/bugs/">Bugzilla</a>. Please see the
986 tools/gfortran component for details.</li>
990 <!-- ======================================================================= -->
991 <div class="doc_subsection">
992 <a name="ada-fe">Known problems with the llvm-gcc Ada front-end</a>
995 <div class="doc_text">
996 The llvm-gcc 4.2 Ada compiler works fairly well; however, this is not a mature
997 technology, and problems should be expected.
999 <li>The Ada front-end currently only builds on X86-32. This is mainly due
1000 to lack of trampoline support (pointers to nested functions) on other platforms.
1001 However, it <a href="http://llvm.org/PR2006">also fails to build on X86-64</a>
1002 which does support trampolines.</li>
1003 <li>The Ada front-end <a href="http://llvm.org/PR2007">fails to bootstrap</a>.
1004 This is due to lack of LLVM support for <tt>setjmp</tt>/<tt>longjmp</tt> style
1005 exception handling, which is used internally by the compiler.
1006 Workaround: configure with <tt>--disable-bootstrap</tt>.</li>
1007 <li>The c380004, <a href="http://llvm.org/PR2010">c393010</a>
1008 and <a href="http://llvm.org/PR2421">cxg2021</a> ACATS tests fail
1009 (c380004 also fails with gcc-4.2 mainline).
1010 If the compiler is built with checks disabled then <a href="http://llvm.org/PR2010">c393010</a>
1011 causes the compiler to go into an infinite loop, using up all system memory.</li>
1012 <li>Some GCC specific Ada tests continue to crash the compiler.</li>
1013 <li>The <tt>-E</tt> binder option (exception backtraces)
1014 <a href="http://llvm.org/PR1982">does not work</a> and will result in programs
1015 crashing if an exception is raised. Workaround: do not use <tt>-E</tt>.</li>
1016 <li>Only discrete types <a href="http://llvm.org/PR1981">are allowed to start
1017 or finish at a non-byte offset</a> in a record. Workaround: do not pack records
1018 or use representation clauses that result in a field of a non-discrete type
1019 starting or finishing in the middle of a byte.</li>
1020 <li>The <tt>lli</tt> interpreter <a href="http://llvm.org/PR2009">considers
1021 'main' as generated by the Ada binder to be invalid</a>.
1022 Workaround: hand edit the file to use pointers for <tt>argv</tt> and
1023 <tt>envp</tt> rather than integers.</li>
1024 <li>The <tt>-fstack-check</tt> option <a href="http://llvm.org/PR2008">is
1029 <!-- *********************************************************************** -->
1030 <div class="doc_section">
1031 <a name="additionalinfo">Additional Information</a>
1033 <!-- *********************************************************************** -->
1035 <div class="doc_text">
1037 <p>A wide variety of additional information is available on the <a
1038 href="http://llvm.org">LLVM web page</a>, in particular in the <a
1039 href="http://llvm.org/docs/">documentation</a> section. The web page also
1040 contains versions of the API documentation which is up-to-date with the
1041 Subversion version of the source code.
1042 You can access versions of these documents specific to this release by going
1043 into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>
1045 <p>If you have any questions or comments about LLVM, please feel free to contact
1046 us via the <a href="http://llvm.org/docs/#maillist"> mailing
1051 <!-- *********************************************************************** -->
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