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11 <h1>LLVM 3.1 Release Notes</h1>
14 <img style="float:right" src="http://llvm.org/img/DragonSmall.png"
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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>
102 <p>For more details about the changes to Clang since the 2.9 release, see the
103 <a href="http://clang.llvm.org/docs/ReleaseNotes.html">Clang release notes</a>
107 <p>If Clang rejects your code but another compiler accepts it, please take a
108 look at the <a href="http://clang.llvm.org/compatibility.html">language
109 compatibility</a> guide to make sure this is not intentional or a known
114 <!--=========================================================================-->
116 <a name="dragonegg">DragonEgg: GCC front-ends, LLVM back-end</a>
120 <p><a href="http://dragonegg.llvm.org/">DragonEgg</a> is a
121 <a href="http://gcc.gnu.org/wiki/plugins">gcc plugin</a> that replaces GCC's
122 optimizers and code generators with LLVM's. It works with gcc-4.5 or gcc-4.6,
123 targets the x86-32 and x86-64 processor families, and has been successfully
124 used on the Darwin, FreeBSD, KFreeBSD, Linux and OpenBSD platforms. It fully
125 supports Ada, C, C++ and Fortran. It has partial support for Go, Java, Obj-C
128 <p>The 3.1 release has the following notable changes:</p>
138 <!--=========================================================================-->
140 <a name="compiler-rt">compiler-rt: Compiler Runtime Library</a>
145 <p>The new LLVM <a href="http://compiler-rt.llvm.org/">compiler-rt project</a>
146 is a simple library that provides an implementation of the low-level
147 target-specific hooks required by code generation and other runtime
148 components. For example, when compiling for a 32-bit target, converting a
149 double to a 64-bit unsigned integer is compiled into a runtime call to the
150 "__fixunsdfdi" function. The compiler-rt library provides highly optimized
151 implementations of this and other low-level routines (some are 3x faster than
152 the equivalent libgcc routines).</p>
158 <!--=========================================================================-->
160 <a name="lldb">LLDB: Low Level Debugger</a>
165 <p>LLDB is a ground-up implementation of a command line debugger, as well as a
166 debugger API that can be used from other applications. LLDB makes use of the
167 Clang parser to provide high-fidelity expression parsing (particularly for
168 C++) and uses the LLVM JIT for target support.</p>
174 <!--=========================================================================-->
176 <a name="libc++">libc++: C++ Standard Library</a>
181 <p>Like compiler_rt, libc++ is now <a href="DeveloperPolicy.html#license">dual
182 licensed</a> under the MIT and UIUC license, allowing it to be used more
189 <!--=========================================================================-->
191 <a name="vmkit">VMKit</a>
196 <p>The <a href="http://vmkit.llvm.org/">VMKit project</a> is an
197 implementation of a Java Virtual Machine (Java VM or JVM) that uses LLVM for
198 static and just-in-time compilation.
200 <p>In the LLVM 3.1 time-frame, VMKit has had significant improvements on both
201 runtime and startup performance:</p>
211 <!-- *********************************************************************** -->
213 <a name="externalproj">External Open Source Projects Using LLVM 3.1</a>
215 <!-- *********************************************************************** -->
219 <p>An exciting aspect of LLVM is that it is used as an enabling technology for
220 a lot of other language and tools projects. This section lists some of the
221 projects that have already been updated to work with LLVM 3.1.</p>
223 ... to be filled in right before the release ...
227 <!-- *********************************************************************** -->
229 <a name="whatsnew">What's New in LLVM 3.1?</a>
231 <!-- *********************************************************************** -->
235 <p>This release includes a huge number of bug fixes, performance tweaks and
236 minor improvements. Some of the major improvements and new features are
237 listed in this section.</p>
239 <!--=========================================================================-->
241 <a name="majorfeatures">Major New Features</a>
246 <!-- Features that need text if they're finished for 3.1:
250 loop dependence analysis
251 CorrelatedValuePropagation
252 lib/Transforms/IPO/MergeFunctions.cpp => consider for 3.1.
253 Integrated assembler on by default for arm/thumb?
258 Analysis/RegionInfo.h + Dom Frontiers
259 SparseBitVector: used in LiveVar.
260 llvm/lib/Archive - replace with lib object?
263 <p>LLVM 3.1 includes several major changes and big features:</p>
266 <li><a href="../tools/clang/docs/AddressSanitizer.html">AddressSanitizer</a>,
267 a fast memory error detector.</li>
268 <li><a href="CodeGenerator.html#machineinstrbundle">MachineInstr Bundles</a>,
269 Support to model instruction bundling / packing.</li>
276 <!--=========================================================================-->
278 <a name="coreimprovements">LLVM IR and Core Improvements</a>
283 <p>LLVM IR has several new features for better support of new targets and that
284 expose new optimization opportunities:</p>
287 <li>IR support for half float</li>
288 <li>IR support for vectors of pointers, including vector GEPs.</li>
289 <li>The <tt>unwind</tt> instruction is now gone. With the introduction of
290 the new exception handling system in LLVM 3.0, the <tt>unwind</tt>
291 instruction became obsolete.</li>
296 <!--=========================================================================-->
298 <a name="optimizer">Optimizer Improvements</a>
303 <p>In addition to many minor performance tweaks and bug fixes, this
304 release includes a few major enhancements and additions to the
313 <!--=========================================================================-->
315 <a name="mc">MC Level Improvements</a>
320 <p>The LLVM Machine Code (aka MC) subsystem was created to solve a number of
321 problems in the realm of assembly, disassembly, object file format handling,
322 and a number of other related areas that CPU instruction-set level tools work
323 in. For more information, please see
324 the <a href="http://blog.llvm.org/2010/04/intro-to-llvm-mc-project.html">Intro
325 to the LLVM MC Project Blog Post</a>.</p>
333 <!--=========================================================================-->
335 <a name="codegen">Target Independent Code Generator Improvements</a>
340 <p>We have changed the way that the Type Legalizer legalizes vectors.
341 The type legalizer now attempts to promote integer elements.
342 This enabled the implementation of vector-select.
343 Additionally, we see a performance boost on workloads which use vectors of chars and shorts, since they are now promoted
344 to 32-bit types, which are better supported by the SIMD instruction set.
345 Floating point types are still widened as before.</p>
348 <p>We have put a significant amount of work into the code generator
349 infrastructure, which allows us to implement more aggressive algorithms and
350 make it run faster:</p>
353 <li>TableGen can now synthesize register classes that are only needed to
354 represent combinations of constraints from instructions and sub-registers.
355 The synthetic register classes inherit most of their properties form their
356 closest user-defined super-class.</li>
357 <li><code>MachineRegisterInfo</code> now allows the reserved registers to be
358 frozen when register allocation starts. Target hooks should use the
359 <code>MRI->canReserveReg(FramePtr)</code> method to avoid accidentally
360 disabling frame pointer elimination during register allocation.</li>
361 <li>A new kind of <code>MachineOperand</code> provides a compact
362 representation of large clobber lists on call instructions. The register
363 mask operand references a bit mask of preserved registers. Everything else is
368 <!--=========================================================================-->
370 <a name="x86">X86-32 and X86-64 Target Improvements</a>
375 <p>New features and major changes in the X86 target include:</p>
378 <li>Bug fixes and improved support for AVX1</li>
379 <li>Support for AVX2 (still incomplete at this point)</li>
385 <!--=========================================================================-->
387 <a name="ARM">ARM Target Improvements</a>
392 <p>New features of the ARM target include:</p>
395 <li>The constant island pass now supports basic block and constant pool entry
396 alignments greater than 4 bytes.</li> </ul>
400 <!--=========================================================================-->
402 <a name="MIPS">MIPS Target Improvements</a>
407 <p>This release has seen major new work on just about every aspect of the MIPS
408 backend. Some of the major new features include:</p>
415 <!--=========================================================================-->
417 <a name="OtherTS">Other Target Specific Improvements</a>
430 <!--=========================================================================-->
432 <a name="changes">Major Changes and Removed Features</a>
437 <p>If you're already an LLVM user or developer with out-of-tree changes based on
438 LLVM 3.1, this section lists some "gotchas" that you may run into upgrading
439 from the previous release.</p>
442 <li>LLVM 3.1 removes support for reading LLVM 2.9 bitcode files. Going forward,
443 we aim for all future versions of LLVM to read bitcode files and .ll files
444 produced by LLVM 3.0 and later.</li>
450 <!--=========================================================================-->
452 <a name="api_changes">Internal API Changes</a>
457 <p>In addition, many APIs have changed in this release. Some of the major
458 LLVM API changes are:</p>
468 <!-- *********************************************************************** -->
470 <a name="knownproblems">Known Problems</a>
472 <!-- *********************************************************************** -->
476 <p>LLVM is generally a production quality compiler, and is used by a broad range
477 of applications and shipping in many products. That said, not every
478 subsystem is as mature as the aggregate, particularly the more obscure
479 targets. If you run into a problem, please check the <a
480 href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
481 there isn't already one or ask on the <a
482 href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev
485 <p>Known problem areas include:</p>
488 <li>The Alpha, Blackfin, CellSPU, MSP430, PTX, SystemZ and
489 XCore backends are experimental, and the Alpha, Blackfin and SystemZ
490 targets have already been removed from mainline.</li>
492 <li>The integrated assembler, disassembler, and JIT is not supported by
493 several targets. If an integrated assembler is not supported, then a
494 system assembler is required. For more details, see the <a
495 href="CodeGenerator.html#targetfeatures">Target Features Matrix</a>.
498 <li>The C backend has numerous problems and is not being actively maintained.
499 Depending on it for anything serious is not advised.</li>
504 <!-- *********************************************************************** -->
506 <a name="additionalinfo">Additional Information</a>
508 <!-- *********************************************************************** -->
512 <p>A wide variety of additional information is available on
513 the <a href="http://llvm.org/">LLVM web page</a>, in particular in
514 the <a href="http://llvm.org/docs/">documentation</a> section. The web page
515 also contains versions of the API documentation which is up-to-date with the
516 Subversion version of the source code. You can access versions of these
517 documents specific to this release by going into the "<tt>llvm/doc/</tt>"
518 directory in the LLVM tree.</p>
520 <p>If you have any questions or comments about LLVM, please feel free to contact
521 us via the <a href="http://llvm.org/docs/#maillist"> mailing lists</a>.</p>
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