1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
7 <link rel="stylesheet" href="llvm.css" type="text/css">
8 <title>LLVM 2.9 Release Notes</title>
12 <h1 class="doc_title">LLVM 2.9 Release Notes</h1>
14 <img align=right src="http://llvm.org/img/DragonSmall.png"
15 width="136" height="136" alt="LLVM Dragon Logo">
18 <li><a href="#intro">Introduction</a></li>
19 <li><a href="#subproj">Sub-project Status Update</a></li>
20 <li><a href="#externalproj">External Projects Using LLVM 2.9</a></li>
21 <li><a href="#whatsnew">What's New in LLVM 2.9?</a></li>
22 <li><a href="GettingStarted.html">Installation Instructions</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>
32 <h1 style="color:red">These are in-progress notes for the upcoming LLVM 2.9
35 <a href="http://llvm.org/releases/2.8/docs/ReleaseNotes.html">LLVM 2.8
36 Release Notes</a>.</h1>
39 <!-- *********************************************************************** -->
41 <a name="intro">Introduction</a>
43 <!-- *********************************************************************** -->
45 <div class="doc_text">
47 <p>This document contains the release notes for the LLVM Compiler
48 Infrastructure, release 2.9. Here we describe the status of LLVM, including
49 major improvements from the previous release and significant known problems.
50 All LLVM releases may be downloaded from the <a
51 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
55 web site</a>. If you have questions or comments, the <a
56 href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM Developer's
57 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
60 main 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>
66 <!-- Features that need text if they're finished for 3.1:
70 loop dependence analysis
71 CorrelatedValuePropagation
72 lib/Transforms/IPO/MergeFunctions.cpp => consider for 3.1.
75 <!-- *********************************************************************** -->
77 <a name="subproj">Sub-project Status Update</a>
79 <!-- *********************************************************************** -->
81 <div class="doc_text">
83 The LLVM 2.9 distribution currently consists of code from the core LLVM
84 repository (which roughly includes the LLVM optimizers, code generators
85 and supporting tools), the Clang repository and the llvm-gcc repository. In
86 addition to this code, the LLVM Project includes other sub-projects that are in
87 development. Here we include updates on these subprojects.
93 <!--=========================================================================-->
95 <a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>
98 <div class="doc_text">
100 <p><a href="http://clang.llvm.org/">Clang</a> is an LLVM front end for the C,
101 C++, and Objective-C languages. Clang aims to provide a better user experience
102 through expressive diagnostics, a high level of conformance to language
103 standards, fast compilation, and low memory use. Like LLVM, Clang provides a
104 modular, library-based architecture that makes it suitable for creating or
105 integrating with other development tools. Clang is considered a
106 production-quality compiler for C, Objective-C, C++ and Objective-C++ on x86
107 (32- and 64-bit), and for darwin/arm targets.</p>
109 <p>In the LLVM 2.9 time-frame, the Clang team has made many improvements in C,
110 C++ and Objective-C support. C++ support is now generally rock solid, has
111 been exercised on a broad variety of code, and has several new <a
112 href="http://clang.llvm.org/cxx_status.html#cxx0x">C++'0x features</a>
113 implemented (such as rvalue references and variadic templates). LLVM 2.9 has
114 also brought in a large range of bug fixes and minor features (e.g. __label__
115 support), and is much more compatible with the Linux Kernel.</p>
117 <p>If Clang rejects your code but another compiler accepts it, please take a
118 look at the <a href="http://clang.llvm.org/compatibility.html">language
119 compatibility</a> guide to make sure this is not intentional or a known issue.
126 <!--=========================================================================-->
128 <a name="dragonegg">DragonEgg: GCC front-ends, LLVM back-end</a>
131 <div class="doc_text">
133 <a href="http://dragonegg.llvm.org/">DragonEgg</a> is a
134 <a href="http://gcc.gnu.org/wiki/plugins">gcc plugin</a> that replaces GCC's
135 optimizers and code generators with LLVM's.
136 Currently it requires a patched version of gcc-4.5.
137 The plugin can target the x86-32 and x86-64 processor families and has been
138 used successfully on the Darwin, FreeBSD and Linux platforms.
139 The Ada, C, C++ and Fortran languages work well.
140 The plugin is capable of compiling plenty of Obj-C, Obj-C++ and Java but it is
141 not known whether the compiled code actually works or not!
145 The 2.9 release has the following notable changes:
147 <li>The plugin is much more stable when compiling Fortran.</li>
148 <li>Inline assembly where an asm output is tied to an input of a different size
149 is now supported in many more cases.</li>
150 <li>Basic support for the __float128 type was added. It is now possible to
151 generate LLVM IR from programs using __float128 but code generation does not
153 <li>Compiling Java programs no longer systematically crashes the plugin.</li>
158 <!--=========================================================================-->
160 <a name="compiler-rt">compiler-rt: Compiler Runtime Library</a>
163 <div class="doc_text">
165 The new LLVM <a href="http://compiler-rt.llvm.org/">compiler-rt project</a>
166 is a simple library that provides an implementation of the low-level
167 target-specific hooks required by code generation and other runtime components.
168 For example, when compiling for a 32-bit target, converting a double to a 64-bit
169 unsigned integer is compiled into a runtime call to the "__fixunsdfdi"
170 function. The compiler-rt library provides highly optimized implementations of
171 this and other low-level routines (some are 3x faster than the equivalent
172 libgcc routines).</p>
174 <p>In the LLVM 2.9 timeframe, compiler_rt has had several minor changes for
175 better ARM support, and a fairly major license change. All of the code in the
176 compiler-rt project is now <a href="DeveloperPolicy.html#license">dual
177 licensed</a> under MIT and UIUC license, which allows you to use compiler-rt
178 in applications without the binary copyright reproduction clause. If you
179 prefer the LLVM/UIUC license, you are free to continue using it under that
184 <!--=========================================================================-->
186 <a name="lldb">LLDB: Low Level Debugger</a>
189 <div class="doc_text">
191 <a href="http://lldb.llvm.org/">LLDB</a> is a brand new member of the LLVM
192 umbrella of projects. LLDB is a next generation, high-performance debugger. It
193 is built as a set of reusable components which highly leverage existing
194 libraries in the larger LLVM Project, such as the Clang expression parser, the
195 LLVM disassembler and the LLVM JIT.</p>
198 LLDB is has advanced by leaps and bounds in the 2.9 timeframe. It is
199 dramatically more stable and useful, and includes both a new <a
200 href="http://lldb.llvm.org/tutorial.html">tutorial</a> and a <a
201 href="http://lldb.llvm.org/lldb-gdb.html">side-by-side comparison with
206 <!--=========================================================================-->
208 <a name="libc++">libc++: C++ Standard Library</a>
211 <div class="doc_text">
213 <a href="http://libcxx.llvm.org/">libc++</a> is another new member of the LLVM
214 family. It is an implementation of the C++ standard library, written from the
215 ground up to specifically target the forthcoming C++'0X standard and focus on
216 delivering great performance.</p>
219 In the LLVM 2.9 timeframe, libc++ has had numerous bugs fixed, and is now being
220 co-developed with Clang's C++'0x mode.</p>
223 Like compiler_rt, libc++ is now <a href="DeveloperPolicy.html#license">dual
224 licensed</a> under the MIT and UIUC license, allowing it to be used more
231 <!--=========================================================================-->
233 <a name="LLBrowse">LLBrowse: IR Browser</a>
236 <div class="doc_text">
238 <a href="http://llvm.org/svn/llvm-project/llbrowse/trunk/doc/LLBrowse.html">
239 LLBrowse</a> is an interactive viewer for LLVM modules. It can load any LLVM
240 module and displays its contents as an expandable tree view, facilitating an
241 easy way to inspect types, functions, global variables, or metadata nodes. It
242 is fully cross-platform, being based on the popular wxWidgets GUI toolkit.
246 <!--=========================================================================-->
248 <a name="vmkit">VMKit</a>
251 <div class="doc_text">
252 <p>The <a href="http://vmkit.llvm.org/">VMKit project</a> is an implementation
253 of a Java Virtual Machine (Java VM or JVM) that uses LLVM for static and
254 just-in-time compilation. As of LLVM 2.9, VMKit now supports generational
255 garbage collectors. The garbage collectors are provided by the MMTk framework,
256 and VMKit can be configured to use one of the numerous implemented collectors
262 <!--=========================================================================-->
265 <a name="klee">KLEE: A Symbolic Execution Virtual Machine</a>
268 <div class="doc_text">
270 <a href="http://klee.llvm.org/">KLEE</a> is a symbolic execution framework for
271 programs in LLVM bitcode form. KLEE tries to symbolically evaluate "all" paths
272 through the application and records state transitions that lead to fault
273 states. This allows it to construct testcases that lead to faults and can even
274 be used to verify some algorithms.
281 <!-- *********************************************************************** -->
283 <a name="externalproj">External Open Source Projects Using LLVM 2.9</a>
285 <!-- *********************************************************************** -->
287 <div class="doc_text">
289 <p>An exciting aspect of LLVM is that it is used as an enabling technology for
290 a lot of other language and tools projects. This section lists some of the
291 projects that have already been updated to work with LLVM 2.9.</p>
295 <!--=========================================================================-->
296 <h2>Crack Programming Language</h2>
298 <div class="doc_text">
300 <a href="http://code.google.com/p/crack-language/">Crack</a> aims to provide the
301 ease of development of a scripting language with the performance of a compiled
302 language. The language derives concepts from C++, Java and Python, incorporating
303 object-oriented programming, operator overloading and strong typing.</p>
307 <!--=========================================================================-->
308 <h2>TTA-based Codesign Environment (TCE)</h2>
310 <div class="doc_text">
311 <p>TCE is a toolset for designing application-specific processors (ASP) based on
312 the Transport triggered architecture (TTA). The toolset provides a complete
313 co-design flow from C/C++ programs down to synthesizable VHDL and parallel
314 program binaries. Processor customization points include the register files,
315 function units, supported operations, and the interconnection network.</p>
317 <p>TCE uses Clang and LLVM for C/C++ language support, target independent
318 optimizations and also for parts of code generation. It generates new LLVM-based
319 code generators "on the fly" for the designed TTA processors and loads them in
320 to the compiler backend as runtime libraries to avoid per-target recompilation
321 of larger parts of the compiler chain.</p>
326 <!--=========================================================================-->
329 <div class="doc_text">
330 <p><a href="http://gitorious.org/pinavm/pages/Home">PinaVM</a> is an open
331 source, <a href="http://www.systemc.org/">SystemC</a> front-end. Unlike many
332 other front-ends, PinaVM actually executes the elaboration of the
333 program analyzed using LLVM's JIT infrastructure. It later enriches the
334 bitcode with SystemC-specific information.</p>
337 <!--=========================================================================-->
340 <div class="doc_text">
341 <p><a href="http://pure-lang.googlecode.com/">Pure</a> is an
343 programming language based on term rewriting. Programs are collections
344 of equations which are used to evaluate expressions in a symbolic
345 fashion. The interpreter uses LLVM as a backend to JIT-compile Pure
346 programs to fast native code. Pure offers dynamic typing, eager and lazy
347 evaluation, lexical closures, a hygienic macro system (also based on
348 term rewriting), built-in list and matrix support (including list and
349 matrix comprehensions) and an easy-to-use interface to C and other
350 programming languages (including the ability to load LLVM bitcode
351 modules, and inline C, C++, Fortran and Faust code in Pure programs if
352 the corresponding LLVM-enabled compilers are installed).</p>
354 <p>Pure version 0.47 has been tested and is known to work with LLVM 2.9
355 (and continues to work with older LLVM releases >= 2.5).</p>
358 <!--=========================================================================-->
359 <h2 id="icedtea">IcedTea Java Virtual Machine Implementation</h2>
361 <div class="doc_text">
363 <a href="http://icedtea.classpath.org/wiki/Main_Page">IcedTea</a> provides a
364 harness to build OpenJDK using only free software build tools and to provide
365 replacements for the not-yet free parts of OpenJDK. One of the extensions that
366 IcedTea provides is a new JIT compiler named <a
367 href="http://icedtea.classpath.org/wiki/ZeroSharkFaq">Shark</a> which uses LLVM
368 to provide native code generation without introducing processor-dependent
372 <p> OpenJDK 7 b112, IcedTea6 1.9 and IcedTea7 1.13 and later have been tested
373 and are known to work with LLVM 2.9 (and continue to work with older LLVM
374 releases >= 2.6 as well).</p>
377 <!--=========================================================================-->
378 <h2>Glasgow Haskell Compiler (GHC)</h2>
380 <div class="doc_text">
381 <p>GHC is an open source, state-of-the-art programming suite for Haskell,
382 a standard lazy functional programming language. It includes an
383 optimizing static compiler generating good code for a variety of
384 platforms, together with an interactive system for convenient, quick
387 <p>In addition to the existing C and native code generators, GHC 7.0 now
388 supports an LLVM code generator. GHC supports LLVM 2.7 and later.</p>
391 <!--=========================================================================-->
392 <h2>Polly - Polyhedral optimizations for LLVM</h2>
394 <div class="doc_text">
395 <p>Polly is a project that aims to provide advanced memory access optimizations
396 to better take advantage of SIMD units, cache hierarchies, multiple cores or
397 even vector accelerators for LLVM. Built around an abstract mathematical
398 description based on Z-polyhedra, it provides the infrastructure to develop
399 advanced optimizations in LLVM and to connect complex external optimizers. In
400 its first year of existence Polly already provides an exact value-based
401 dependency analysis as well as basic SIMD and OpenMP code generation support.
402 Furthermore, Polly can use PoCC(Pluto) an advanced optimizer for data-locality
406 <!--=========================================================================-->
409 <div class="doc_text">
410 <p><a href="http://github.com/evanphx/rubinius">Rubinius</a> is an environment
411 for running Ruby code which strives to write as much of the implementation in
412 Ruby as possible. Combined with a bytecode interpreting VM, it uses LLVM to
413 optimize and compile ruby code down to machine code. Techniques such as type
414 feedback, method inlining, and deoptimization are all used to remove dynamism
415 from ruby execution and increase performance.</p>
420 <!-- *********************************************************************** -->
422 <a name="whatsnew">What's New in LLVM 2.9?</a>
424 <!-- *********************************************************************** -->
426 <div class="doc_text">
428 <p>This release includes a huge number of bug fixes, performance tweaks and
429 minor improvements. Some of the major improvements and new features are listed
435 <!--=========================================================================-->
437 <a name="majorfeatures">Major New Features</a>
440 <div class="doc_text">
442 <p>LLVM 2.9 includes several major new capabilities:</p>
446 <li>Type Based Alias Analysis (TBAA) is now implemented and turned on by default
447 in Clang. This allows substantially better load/store optimization in some
448 cases. TBAA can be disabled by passing -fno-strict-aliasing.
451 <li>This release has seen a continued focus on quality of debug information.
452 LLVM now generates much higher fidelity debug information, particularly when
453 debugging optimized code.</li>
455 <li>Inline assembly now supports multiple alternative constraints.</li>
457 <li>A new backend for the NVIDIA PTX virtual ISA (used to target its GPUs) is
458 under rapid development. It is not generally useful in 2.9, but is making
465 <!--=========================================================================-->
467 <a name="coreimprovements">LLVM IR and Core Improvements</a>
470 <div class="doc_text">
471 <p>LLVM IR has several new features for better support of new targets and that
472 expose new optimization opportunities:</p>
475 <li>The <a href="LangRef.html#bitwiseops">udiv, ashr, lshr, and shl</a>
476 instructions now have support exact and nuw/nsw bits to indicate that they
477 don't overflow or shift out bits. This is useful for optimization of <a
478 href="http://llvm.org/PR8862">pointer differences</a> and other cases.</li>
480 <li>LLVM IR now supports the <a href="LangRef.html#globalvars">unnamed_addr</a>
481 attribute to indicate that constant global variables with identical
482 initializers can be merged. This fixed <a href="http://llvm.org/PR8927">an
483 issue</a> where LLVM would incorrectly merge two globals which were supposed
484 to have distinct addresses.</li>
486 <li>The new <a href="LangRef.html#fnattrs">hotpatch attribute</a> has been added
487 to allow runtime patching of functions.</li>
492 <!--=========================================================================-->
494 <a name="optimizer">Optimizer Improvements</a>
497 <div class="doc_text">
499 <p>In addition to a large array of minor performance tweaks and bug fixes, this
500 release includes a few major enhancements and additions to the optimizers:</p>
503 <li>Link Time Optimization (LTO) has been improved to use MC for parsing inline
504 assembly and now can build large programs like Firefox 4 on both Mac OS X and
507 <li>The new -loop-idiom pass recognizes memset/memcpy loops (and memset_pattern
508 on darwin), turning them into library calls, which are typically better
509 optimized than inline code. If you are building a libc and notice that your
510 memcpy and memset functions are compiled into infinite recursion, please build
511 with -ffreestanding or -fno-builtin to disable this pass.</li>
513 <li>A new -early-cse pass does a fast pass over functions to fold constants,
514 simplify expressions, perform simple dead store elimination, and perform
515 common subexpression elimination. It does a good job at catching some of the
516 trivial redundancies that exist in unoptimized code, making later passes more
519 <li>A new -loop-instsimplify pass is used to clean up loop bodies in the loop
522 <li>The new TargetLibraryInfo interface allows mid-level optimizations to know
523 whether the current target's runtime library has certain functions. For
524 example, the optimizer can now transform integer-only printf calls to call
525 iprintf, allowing reduced code size for embedded C libraries (e.g. newlib).
528 <li>LLVM has a new <a href="WritingAnLLVMPass.html#RegionPass">RegionPass</a>
529 infrastructure for region-based optimizations.</li>
531 <li>Several optimizer passes have been substantially sped up:
532 GVN is much faster on functions with deep dominator trees and lots of basic
533 blocks. The dominator tree and dominance frontier passes are much faster to
534 compute, and preserved by more passes (so they are computed less often). The
535 -scalar-repl pass is also much faster and doesn't use DominanceFrontier.
538 <li>The Dead Store Elimination pass is more aggressive optimizing stores of
539 different types: e.g. a large store following a small one to the same address.
540 The MemCpyOptimizer pass handles several new forms of memcpy elimination.</li>
542 <li>LLVM now optimizes various idioms for overflow detection into check of the
543 flag register on various CPUs. For example, we now compile:
546 unsigned long t = a+b;
560 <!--=========================================================================-->
562 <a name="mc">MC Level Improvements</a>
565 <div class="doc_text">
567 The LLVM Machine Code (aka MC) subsystem was created to solve a number
568 of problems in the realm of assembly, disassembly, object file format handling,
569 and a number of other related areas that CPU instruction-set level tools work
573 <li>ELF MC support has matured enough for the integrated assembler to be turned
574 on by default in Clang on X86-32 and X86-64 ELF systems.</li>
576 <li>MC supports and CodeGen uses the <tt>.file</tt> and <tt>.loc</tt> directives
577 for producing line number debug info. This produces more compact line
578 tables and easier to read .s files.</li>
580 <li>MC supports the <tt>.cfi_*</tt> directives for producing DWARF
581 frame information, but it is still not used by CodeGen by default.</li>
584 <li>The MC assembler now generates much better diagnostics for common errors,
585 is much faster at matching instructions, is much more bug-compatible with
586 the GAS assembler, and is now generally useful for a broad range of X86
589 <li>We now have some basic <a href="CodeGenerator.html#mc">internals
590 documentation</a> for MC.</li>
592 <li>.td files can now specify assembler aliases directly with the <a
593 href="CodeGenerator.html#na_instparsing">MnemonicAlias and InstAlias</a>
596 <li>LLVM now has an experimental format-independent object file manipulation
597 library (lib/Object). It supports both PE/COFF and ELF. The llvm-nm tool has
598 been extended to work with native object files, and the new llvm-objdump tool
599 supports disassembly of object files (but no relocations are displayed yet).
602 <li>Win32 PE-COFF support in the MC assembler has made a lot of progress in the
603 2.9 timeframe, but is still not generally useful.</li>
607 <p>For more information, please see the <a
608 href="http://blog.llvm.org/2010/04/intro-to-llvm-mc-project.html">Intro to the
609 LLVM MC Project Blog Post</a>.
614 <!--=========================================================================-->
616 <a name="codegen">Target Independent Code Generator Improvements</a>
619 <div class="doc_text">
621 <p>We have put a significant amount of work into the code generator
622 infrastructure, which allows us to implement more aggressive algorithms and make
626 <li>The pre-register-allocation (preRA) instruction scheduler models register
627 pressure much more accurately in some cases. This allows the adoption of more
628 aggressive scheduling heuristics without causing spills to be generated.
631 <li>LiveDebugVariables is a new pass that keeps track of debugging information
632 for user variables that are promoted to registers in optimized builds.</li>
634 <li>The scheduler now models operand latency and pipeline forwarding.</li>
636 <li>A major register allocator infrastructure rewrite is underway. It is not on
637 by default for 2.9 and you are not advised to use it, but it has made
638 substantial progress in the 2.9 timeframe:
640 <li>A new -regalloc=basic "basic" register allocator can be used as a simple
641 fallback when debugging. It uses the new infrastructure.</li>
642 <li>New infrastructure is in place for live range splitting. "SplitKit" can
643 break a live interval into smaller pieces while preserving SSA form, and
644 SpillPlacement can help find the best split points. This is a work in
645 progress so the API is changing quickly.</li>
646 <li>The inline spiller has learned to clean up after live range splitting. It
647 can hoist spills out of loops, and it can eliminate redundant spills.</li>
648 <li>Rematerialization works with live range splitting.</li>
649 <li>The new "greedy" register allocator using live range splitting. This will
650 be the default register allocator in the next LLVM release, but it is not
651 turned on by default in 2.9.</li>
657 <!--=========================================================================-->
659 <a name="x86">X86-32 and X86-64 Target Improvements</a>
662 <div class="doc_text">
663 <p>New features and major changes in the X86 target include:
667 <li>LLVM 2.9 includes a complete reimplementation of the MMX instruction set.
668 The reimplementation uses a new LLVM IR <a
669 href="LangRef.html#t_x86mmx">x86_mmx</a> type to ensure that MMX operations
670 are <em>only</em> generated from source that uses MMX builtin operations. With
671 this, random types like <2 x i32> are not turned into MMX operations
672 (which can be catastrophic without proper "emms" insertion). Because the X86
673 code generator always generates reliable code, the -disable-mmx flag is now
677 <li>X86 support for FS/GS relative loads and stores using <a
678 href="CodeGenerator.html#x86_memory">address space 256/257</a> works reliably
681 <li>LLVM 2.9 generates much better code in several cases by using adc/sbb to
682 avoid generation of conditional move instructions for conditional increment
683 and other idioms.</li>
685 <li>The X86 backend has adopted a new preRA scheduling mode, "list-ilp", to
686 shorten the height of instruction schedules without inducing register spills.
689 <li>The MC assembler supports 3dNow! and 3DNowA instructions.</li>
691 <li>Several bugs have been fixed for Windows x64 code generator.</li>
696 <!--=========================================================================-->
698 <a name="ARM">ARM Target Improvements</a>
701 <div class="doc_text">
702 <p>New features of the ARM target include:
706 <li>The ARM backend now has a fast instruction selector, which dramatically
707 improves -O0 compile times.</li>
708 <li>The ARM backend has new tuning for Cortex-A8 and Cortex-A9 CPUs.</li>
709 <li>The __builtin_prefetch builtin (and llvm.prefetch intrinsic) is compiled
710 into prefetch instructions instead of being discarded.</li>
712 <li> The ARM backend preRA scheduler now models machine resources at cycle
713 granularity. This allows the scheduler to both accurately model
714 instruction latency and avoid overcommitting functional units.</li>
716 <li>Countless ARM microoptimizations have landed in LLVM 2.9.</li>
720 <!--=========================================================================-->
722 <a name="OtherTS">Other Target Specific Improvements</a>
725 <div class="doc_text">
727 <li>MicroBlaze: major updates for aggressive delay slot filler, MC-based
728 assembly printing, assembly instruction parsing, ELF .o file emission, and MC
729 instruction disassembler have landed.</li>
731 <li>SPARC: Many improvements, including using the Y registers for
732 multiplications and addition of a simple delay slot filler.</li>
734 <li>PowerPC: The backend has been largely MC'ized and is ready to support
735 directly writing out mach-o object files. No one seems interested in finishing
736 this final step though.</li>
741 <!--=========================================================================-->
743 <a name="changes">Major Changes and Removed Features</a>
746 <div class="doc_text">
748 <p>If you're already an LLVM user or developer with out-of-tree changes based
749 on LLVM 2.8, this section lists some "gotchas" that you may run into upgrading
750 from the previous release.</p>
753 <li><b>This is the last release to support the llvm-gcc frontend.</b></li>
755 <li>LLVM has a new <a href="CodingStandards.html#ll_naming">naming
756 convention standard</a>, though the codebase hasn't fully adopted it yet.</li>
758 <li>The new DIBuilder class provides a simpler interface for front ends to
759 encode debug info in LLVM IR, and has replaced DIFactory.</li>
761 <li>LLVM IR and other tools always work on normalized target triples (which have
762 been run through <tt>Triple::normalize</tt>).</li>
764 <li>The target triple x86_64--mingw64 is obsoleted. Use x86_64--mingw32
767 <li>The PointerTracking pass has been removed from mainline, and moved to The
768 ClamAV project (its only client).</li>
770 <li>The LoopIndexSplit, LiveValues, SimplifyHalfPowrLibCalls, GEPSplitter, and
771 PartialSpecialization passes were removed. They were unmaintained,
772 buggy, or deemed to be a bad idea.</li>
777 <!--=========================================================================-->
779 <a name="api_changes">Internal API Changes</a>
782 <div class="doc_text">
784 <p>In addition, many APIs have changed in this release. Some of the major
785 LLVM API changes are:</p>
788 <li>include/llvm/System merged into include/llvm/Support.</li>
789 <li>The <a href="http://llvm.org/PR5207">llvm::APInt API</a> was significantly
792 <li>In the code generator, MVT::Flag was renamed to MVT::Glue to more accurately
793 describe its behavior.</li>
795 <li>The system_error header from C++0x was added, and is now pervasively used to
796 capture and handle i/o and other errors in LLVM.</li>
798 <li>The old sys::Path API has been deprecated in favor of the new PathV2 API,
799 which is more efficient and flexible.</li>
803 <!-- *********************************************************************** -->
805 <a name="knownproblems">Known Problems</a>
807 <!-- *********************************************************************** -->
809 <div class="doc_text">
811 <p>This section contains significant known problems with the LLVM system,
812 listed by component. If you run into a problem, please check the <a
813 href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
814 there isn't already one.</p>
818 <!-- ======================================================================= -->
820 <a name="experimental">Experimental features included with this release</a>
823 <div class="doc_text">
825 <p>The following components of this LLVM release are either untested, known to
826 be broken or unreliable, or are in early development. These components should
827 not be relied on, and bugs should not be filed against them, but they may be
828 useful to some people. In particular, if you would like to work on one of these
829 components, please contact us on the <a
830 href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
833 <li>The Alpha, Blackfin, CellSPU, MicroBlaze, MSP430, MIPS, PTX, SystemZ
834 and XCore backends are experimental.</li>
835 <li><tt>llc</tt> "<tt>-filetype=obj</tt>" is experimental on all targets
836 other than darwin and ELF X86 systems.</li>
842 <!-- ======================================================================= -->
844 <a name="x86-be">Known problems with the X86 back-end</a>
847 <div class="doc_text">
850 <li>The X86 backend does not yet support
851 all <a href="http://llvm.org/PR879">inline assembly that uses the X86
852 floating point stack</a>. It supports the 'f' and 't' constraints, but not
854 <li>The X86-64 backend does not yet support the LLVM IR instruction
855 <tt>va_arg</tt>. Currently, front-ends support variadic
856 argument constructs on X86-64 by lowering them manually.</li>
857 <li>Windows x64 (aka Win64) code generator has a few issues.
859 <li>llvm-gcc cannot build the mingw-w64 runtime currently
860 due to lack of support for the 'u' inline assembly
861 constraint and for X87 floating point inline assembly.</li>
862 <li>On mingw-w64, you will see unresolved symbol <tt>__chkstk</tt>
863 due to <a href="http://llvm.org/bugs/show_bug.cgi?id=8919">Bug 8919</a>.
864 It is fixed in <a href="http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110321/118499.html">r128206</a>.</li>
865 <li>Miss-aligned MOVDQA might crash your program. It is due to
866 <a href="http://llvm.org/bugs/show_bug.cgi?id=9483">Bug 9483</a>,
867 lack of handling aligned internal globals.</li>
875 <!-- ======================================================================= -->
877 <a name="ppc-be">Known problems with the PowerPC back-end</a>
880 <div class="doc_text">
883 <li>The Linux PPC32/ABI support needs testing for the interpreter and static
884 compilation, and lacks support for debug information.</li>
889 <!-- ======================================================================= -->
891 <a name="arm-be">Known problems with the ARM back-end</a>
894 <div class="doc_text">
897 <li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
898 processors, thumb programs can crash or produce wrong
899 results (<a href="http://llvm.org/PR1388">PR1388</a>).</li>
900 <li>Compilation for ARM Linux OABI (old ABI) is supported but not fully tested.
906 <!-- ======================================================================= -->
908 <a name="sparc-be">Known problems with the SPARC back-end</a>
911 <div class="doc_text">
914 <li>The SPARC backend only supports the 32-bit SPARC ABI (-m32); it does not
915 support the 64-bit SPARC ABI (-m64).</li>
920 <!-- ======================================================================= -->
922 <a name="mips-be">Known problems with the MIPS back-end</a>
925 <div class="doc_text">
928 <li>64-bit MIPS targets are not supported yet.</li>
933 <!-- ======================================================================= -->
935 <a name="alpha-be">Known problems with the Alpha back-end</a>
938 <div class="doc_text">
942 <li>On 21164s, some rare FP arithmetic sequences which may trap do not have the
943 appropriate nops inserted to ensure restartability.</li>
948 <!-- ======================================================================= -->
950 <a name="c-be">Known problems with the C back-end</a>
953 <div class="doc_text">
955 <p>The C backend has numerous problems and is not being actively maintained.
956 Depending on it for anything serious is not advised.</p>
959 <li><a href="http://llvm.org/PR802">The C backend has only basic support for
960 inline assembly code</a>.</li>
961 <li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common
962 C++ programs</a>, preventing intermixing between C++ compiled by the CBE and
963 C++ code compiled with <tt>llc</tt> or native compilers.</li>
964 <li>The C backend does not support all exception handling constructs.</li>
965 <li>The C backend does not support arbitrary precision integers.</li>
971 <!-- ======================================================================= -->
973 <a name="llvm-gcc">Known problems with the llvm-gcc front-end</a>
976 <div class="doc_text">
978 <p><b>LLVM 2.9 will be the last release of llvm-gcc.</b></p>
980 <p>llvm-gcc is generally very stable for the C family of languages. The only
981 major language feature of GCC not supported by llvm-gcc is the
982 <tt>__builtin_apply</tt> family of builtins. However, some extensions
983 are only supported on some targets. For example, trampolines are only
984 supported on some targets (these are used when you take the address of a
985 nested function).</p>
987 <p>Fortran support generally works, but there are still several unresolved bugs
988 in <a href="http://llvm.org/bugs/">Bugzilla</a>. Please see the
989 tools/gfortran component for details. Note that llvm-gcc is missing major
990 Fortran performance work in the frontend and library that went into GCC after
991 4.2. If you are interested in Fortran, we recommend that you consider using
992 <a href="#dragonegg">dragonegg</a> instead.</p>
994 <p>The llvm-gcc 4.2 Ada compiler has basic functionality, but is no longer being
995 actively maintained. If you are interested in Ada, we recommend that you
996 consider using <a href="#dragonegg">dragonegg</a> instead.</p>
999 <!-- *********************************************************************** -->
1001 <a name="additionalinfo">Additional Information</a>
1003 <!-- *********************************************************************** -->
1005 <div class="doc_text">
1007 <p>A wide variety of additional information is available on the <a
1008 href="http://llvm.org">LLVM web page</a>, in particular in the <a
1009 href="http://llvm.org/docs/">documentation</a> section. The web page also
1010 contains versions of the API documentation which is up-to-date with the
1011 Subversion version of the source code.
1012 You can access versions of these documents specific to this release by going
1013 into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>
1015 <p>If you have any questions or comments about LLVM, please feel free to contact
1016 us via the <a href="http://llvm.org/docs/#maillist"> mailing
1021 <!-- *********************************************************************** -->
1025 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
1026 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
1027 <a href="http://validator.w3.org/check/referer"><img
1028 src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
1030 <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
1031 Last modified: $Date$