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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>
31 <h1 style="color:red">These are in-progress notes for the upcoming LLVM 2.9
34 <a href="http://llvm.org/releases/2.8/docs/ReleaseNotes.html">LLVM 2.8
35 Release Notes</a>.</h1>
37 <!-- *********************************************************************** -->
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 2.9. 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>
64 <!-- Features that need text if they're finished for 3.1:
68 loop dependence analysis
69 CorrelatedValuePropagation
70 lib/Transforms/IPO/MergeFunctions.cpp => consider for 3.1.
73 <!-- *********************************************************************** -->
75 <a name="subproj">Sub-project Status Update</a>
77 <!-- *********************************************************************** -->
79 <div class="doc_text">
81 The LLVM 2.9 distribution currently consists of code from the core LLVM
82 repository (which roughly includes the LLVM optimizers, code generators
83 and supporting tools), the Clang repository and the llvm-gcc repository. In
84 addition to this code, the LLVM Project includes other sub-projects that are in
85 development. Here we include updates on these subprojects.
91 <!--=========================================================================-->
93 <a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>
96 <div class="doc_text">
98 <p><a href="http://clang.llvm.org/">Clang</a> is an LLVM front end for the C,
99 C++, and Objective-C languages. Clang aims to provide a better user experience
100 through expressive diagnostics, a high level of conformance to language
101 standards, fast compilation, and low memory use. Like LLVM, Clang provides a
102 modular, library-based architecture that makes it suitable for creating or
103 integrating with other development tools. Clang is considered a
104 production-quality compiler for C, Objective-C, C++ and Objective-C++ on x86
105 (32- and 64-bit), and for darwin/arm targets.</p>
107 <p>In the LLVM 2.9 time-frame, the Clang team has made many improvements in C,
108 C++ and Objective-C support. C++ support is now generally rock solid, has
109 been exercised on a broad variety of code, and has several new <a
110 href="http://clang.llvm.org/cxx_status.html#cxx0x">C++'0x features</a>
111 implemented (such as rvalue references and variadic templates). LLVM 2.9 has
112 also brought in a large range of bug fixes and minor features (e.g. __label__
113 support), and is much more compatible with the Linux Kernel.</p>
115 <p>If Clang rejects your code that is built with another compiler, please take a
116 look at the <a href="http://clang.llvm.org/compatibility.html">language
117 compatibility</a> guide to make sure the issue isn't intentional or a known
125 <!--=========================================================================-->
127 <a name="dragonegg">DragonEgg: GCC front-ends, LLVM back-end</a>
130 <div class="doc_text">
132 <a href="http://dragonegg.llvm.org/">DragonEgg</a> is a
133 <a href="http://gcc.gnu.org/wiki/plugins">gcc plugin</a> that replaces GCC's
134 optimizers and code generators with LLVM's.
135 Currently it requires a patched version of gcc-4.5.
136 The plugin can target the x86-32 and x86-64 processor families and has been
137 used successfully on the Darwin, FreeBSD and Linux platforms.
138 The Ada, C, C++ and Fortran languages work well.
139 The plugin is capable of compiling plenty of Obj-C, Obj-C++ and Java but it is
140 not known whether the compiled code actually works or not!
144 The 2.9 release has the following notable changes:
146 <li>The plugin is much more stable when compiling Fortran.</li>
147 <li>Inline assembly where an asm output is tied to an input of a different size
148 is now supported in many more cases.</li>
149 <li>Basic support for the __float128 type was added. It is now possible to
150 generate LLVM IR from programs using __float128 but code generation does not
152 <li>Compiling Java programs no longer systematically crashes the plugin.</li>
157 <!--=========================================================================-->
159 <a name="compiler-rt">compiler-rt: Compiler Runtime Library</a>
162 <div class="doc_text">
164 The new LLVM <a href="http://compiler-rt.llvm.org/">compiler-rt project</a>
165 is a simple library that provides an implementation of the low-level
166 target-specific hooks required by code generation and other runtime components.
167 For example, when compiling for a 32-bit target, converting a double to a 64-bit
168 unsigned integer is compiled into a runtime call to the "__fixunsdfdi"
169 function. The compiler-rt library provides highly optimized implementations of
170 this and other low-level routines (some are 3x faster than the equivalent
171 libgcc routines).</p>
173 <p>In the LLVM 2.9 timeframe, compiler_rt has had several minor changes for
174 better ARM support, and a fairly major license change. All of the code in the
175 compiler-rt project is now <a href="DeveloperPolicy.html#license">dual
176 licensed</a> under MIT and UIUC license, which allows you to use compiler-rt
177 in applications without the binary copyright reproduction clause. If you
178 prefer the LLVM/UIUC license, you are free to continue using it under that
183 <!--=========================================================================-->
185 <a name="lldb">LLDB: Low Level Debugger</a>
188 <div class="doc_text">
190 <a href="http://lldb.llvm.org/">LLDB</a> is a brand new member of the LLVM
191 umbrella of projects. LLDB is a next generation, high-performance debugger. It
192 is built as a set of reusable components which highly leverage existing
193 libraries in the larger LLVM Project, such as the Clang expression parser, the
194 LLVM disassembler and the LLVM JIT.</p>
197 LLDB is has advanced by leaps and bounds in the 2.9 timeframe. It is
198 dramatically more stable and useful, and includes both a new <a
199 href="http://lldb.llvm.org/tutorial.html">tutorial</a> and a <a
200 href="http://lldb.llvm.org/lldb-gdb.html">side-by-side comparison with
205 <!--=========================================================================-->
207 <a name="libc++">libc++: C++ Standard Library</a>
210 <div class="doc_text">
212 <a href="http://libcxx.llvm.org/">libc++</a> is another new member of the LLVM
213 family. It is an implementation of the C++ standard library, written from the
214 ground up to specifically target the forthcoming C++'0X standard and focus on
215 delivering great performance.</p>
218 In the LLVM 2.9 timeframe, libc++ has had numerous bugs fixed, and is now being
219 co-developed with Clang's C++'0x mode.</p>
222 Like compiler_rt, libc++ is now <a href="DeveloperPolicy.html#license">dual
223 licensed</a> under the MIT and UIUC license, allowing it to be used more
231 <!--=========================================================================-->
234 <a name="klee">KLEE: A Symbolic Execution Virtual Machine</a>
237 <div class="doc_text">
239 <a href="http://klee.llvm.org/">KLEE</a> is a symbolic execution framework for
240 programs in LLVM bitcode form. KLEE tries to symbolically evaluate "all" paths
241 through the application and records state transitions that lead to fault
242 states. This allows it to construct testcases that lead to faults and can even
243 be used to verify some algorithms.
250 <!-- *********************************************************************** -->
252 <a name="externalproj">External Open Source Projects Using LLVM 2.9</a>
254 <!-- *********************************************************************** -->
256 <div class="doc_text">
258 <p>An exciting aspect of LLVM is that it is used as an enabling technology for
259 a lot of other language and tools projects. This section lists some of the
260 projects that have already been updated to work with LLVM 2.9.</p>
264 <!--=========================================================================-->
265 <h2>Crack Programming Language</h2>
267 <div class="doc_text">
269 <a href="http://code.google.com/p/crack-language/">Crack</a> aims to provide the
270 ease of development of a scripting language with the performance of a compiled
271 language. The language derives concepts from C++, Java and Python, incorporating
272 object-oriented programming, operator overloading and strong typing.</p>
276 <!--=========================================================================-->
277 <h2>TTA-based Codesign Environment (TCE)</h2>
279 <div class="doc_text">
280 <p>TCE is a toolset for designing application-specific processors (ASP) based on
281 the Transport triggered architecture (TTA). The toolset provides a complete
282 co-design flow from C/C++ programs down to synthesizable VHDL and parallel
283 program binaries. Processor customization points include the register files,
284 function units, supported operations, and the interconnection network.</p>
286 <p>TCE uses Clang and LLVM for C/C++ language support, target independent
287 optimizations and also for parts of code generation. It generates new LLVM-based
288 code generators "on the fly" for the designed TTA processors and loads them in
289 to the compiler backend as runtime libraries to avoid per-target recompilation
290 of larger parts of the compiler chain.</p>
295 <!--=========================================================================-->
298 <div class="doc_text">
299 <p><a href="http://gitorious.org/pinavm/pages/Home">PinaVM</a> is an open
300 source, <a href="http://www.systemc.org/">SystemC</a> front-end. Unlike many
301 other front-ends, PinaVM actually executes the elaboration of the
302 program analyzed using LLVM's JIT infrastructure. It later enriches the
303 bitcode with SystemC-specific information.</p>
306 <!--=========================================================================-->
309 <div class="doc_text">
310 <p><a href="http://pure-lang.googlecode.com/">Pure</a> is an
312 programming language based on term rewriting. Programs are collections
313 of equations which are used to evaluate expressions in a symbolic
314 fashion. The interpreter uses LLVM as a backend to JIT-compile Pure
315 programs to fast native code. Pure offers dynamic typing, eager and lazy
316 evaluation, lexical closures, a hygienic macro system (also based on
317 term rewriting), built-in list and matrix support (including list and
318 matrix comprehensions) and an easy-to-use interface to C and other
319 programming languages (including the ability to load LLVM bitcode
320 modules, and inline C, C++, Fortran and Faust code in Pure programs if
321 the corresponding LLVM-enabled compilers are installed).</p>
323 <p>Pure version 0.47 has been tested and is known to work with LLVM 2.9
324 (and continues to work with older LLVM releases >= 2.5).</p>
327 <!--=========================================================================-->
328 <h2 id="icedtea">IcedTea Java Virtual Machine Implementation</h2>
330 <div class="doc_text">
332 <a href="http://icedtea.classpath.org/wiki/Main_Page">IcedTea</a> provides a
333 harness to build OpenJDK using only free software build tools and to provide
334 replacements for the not-yet free parts of OpenJDK. One of the extensions that
335 IcedTea provides is a new JIT compiler named <a
336 href="http://icedtea.classpath.org/wiki/ZeroSharkFaq">Shark</a> which uses LLVM
337 to provide native code generation without introducing processor-dependent
341 <p> OpenJDK 7 b112, IcedTea6 1.9 and IcedTea7 1.13 and later have been tested
342 and are known to work with LLVM 2.9 (and continue to work with older LLVM
343 releases >= 2.6 as well).</p>
346 <!--=========================================================================-->
347 <h2>Glasgow Haskell Compiler (GHC)</h2>
349 <div class="doc_text">
350 <p>GHC is an open source, state-of-the-art programming suite for Haskell,
351 a standard lazy functional programming language. It includes an
352 optimizing static compiler generating good code for a variety of
353 platforms, together with an interactive system for convenient, quick
356 <p>In addition to the existing C and native code generators, GHC 7.0 now
357 supports an LLVM code generator. GHC supports LLVM 2.7 and later.</p>
360 <!--=========================================================================-->
361 <h2>Polly - Polyhedral optimizations for LLVM</h2>
363 <div class="doc_text">
364 <p>Polly is a project that aims to provide advanced memory access optimizations
365 to better take advantage of SIMD units, cache hierarchies, multiple cores or
366 even vector accelerators for LLVM. Built around an abstract mathematical
367 description based on Z-polyhedra, it provides the infrastructure to develop
368 advanced optimizations in LLVM and to connect complex external optimizers. In
369 its first year of existence Polly already provides an exact value-based
370 dependency analysis as well as basic SIMD and OpenMP code generation support.
371 Furthermore, Polly can use PoCC(Pluto) an advanced optimizer for data-locality
376 <!-- *********************************************************************** -->
378 <a name="whatsnew">What's New in LLVM 2.9?</a>
380 <!-- *********************************************************************** -->
382 <div class="doc_text">
384 <p>This release includes a huge number of bug fixes, performance tweaks and
385 minor improvements. Some of the major improvements and new features are listed
391 <!--=========================================================================-->
393 <a name="majorfeatures">Major New Features</a>
396 <div class="doc_text">
398 <p>LLVM 2.9 includes several major new capabilities:</p>
402 <li>Type Based Alias Analysis (TBAA) is now implemented and turned on by default
403 in Clang. This allows substantially better load/store optimization in some
404 cases. TBAA can be disabled by passing -fno-strict-aliasing.
407 <li>This release has seen a continued focus on quality of debug information.
408 LLVM now generates much higher fidelity debug information, particularly when
409 debugging optimized code.</li>
411 <li>Inline assembly now supports multiple alternative constraints.</li>
413 <li>A new backend for the NVIDIA PTX virtual ISA (used to target its GPUs) is
414 under rapid development. It is not generally useful in 2.9, but is making
421 <!--=========================================================================-->
423 <a name="coreimprovements">LLVM IR and Core Improvements</a>
426 <div class="doc_text">
427 <p>LLVM IR has several new features for better support of new targets and that
428 expose new optimization opportunities:</p>
431 <li>The <a href="LangRef.html#bitwiseops">udiv, ashr, lshr, and shl</a>
432 instructions now have support exact and nuw/nsw bits to indicate that they
433 don't overflow or shift out bits. This is useful for optimization of <a
434 href="http://llvm.org/PR8862">pointer differences</a> and other cases.</li>
436 <li>LLVM IR now supports the <a href="LangRef.html#globalvars">unnamed_addr</a>
437 attribute to indicate that constant global variables with identical
438 initializers can be merged. This fixed <a href="http://llvm.org/PR8927">an
439 issue</a> where LLVM would incorrectly merge two globals which were supposed
440 to have distinct addresses.</li>
442 <li>The new <a href="LangRef.html#fnattrs">hotpatch attribute</a> has been added
443 to allow runtime patching of functions.</li>
448 <!--=========================================================================-->
450 <a name="optimizer">Optimizer Improvements</a>
453 <div class="doc_text">
455 <p>In addition to a large array of minor performance tweaks and bug fixes, this
456 release includes a few major enhancements and additions to the optimizers:</p>
459 <li>Link Time Optimization (LTO) has been improved to use MC for parsing inline
460 assembly and now can build large programs like Firefox 4 on both Mac OS X and
463 <li>The new -loop-idiom pass recognizes memset/memcpy loops (and memset_pattern
464 on darwin), turning them into library calls, which are typically better
465 optimized than inline code. If you are building a libc and notice that your
466 memcpy and memset functions are compiled into infinite recursion, please build
467 with -ffreestanding or -fno-builtin to disable this pass.</li>
469 <li>A new -early-cse pass does a fast pass over functions to fold constants,
470 simplify expressions, perform simple dead store elimination, and perform
471 common subexpression elimination. It does a good job at catching some of the
472 trivial redundancies that exist in unoptimized code, making later passes more
475 <li>A new -loop-instsimplify pass is used to clean up loop bodies in the loop
478 <li>The new TargetLibraryInfo interface allows mid-level optimizations to know
479 whether the current target's runtime library has certain functions. For
480 example, the optimizer can now transform integer-only printf calls to call
481 iprintf, allowing reduced code size for embedded C libraries (e.g. newlib).
484 <li>LLVM has a new <a href="WritingAnLLVMPass.html#RegionPass">RegionPass</a>
485 infrastructure for region-based optimizations.</li>
487 <li>Several optimizer passes have been substantially sped up:
488 GVN is much faster on functions with deep dominator trees and lots of basic
489 blocks. The dominator tree and dominance frontier passes are much faster to
490 compute, and preserved by more passes (so they are computed less often). The
491 -scalar-repl pass is also much faster and doesn't use DominanceFrontier.
494 <li>The Dead Store Elimination pass is more aggressive optimizing stores of
495 different types: e.g. a large store following a small one to the same address.
496 The MemCpyOptimizer pass handles several new forms of memcpy elimination.</li>
498 <li>LLVM now optimizes various idioms for overflow detection into check of the
499 flag register on various CPUs. For example, we now compile:
502 unsigned long t = a+b;
516 <!--=========================================================================-->
518 <a name="mc">MC Level Improvements</a>
521 <div class="doc_text">
523 The LLVM Machine Code (aka MC) subsystem was created to solve a number
524 of problems in the realm of assembly, disassembly, object file format handling,
525 and a number of other related areas that CPU instruction-set level tools work
529 <li>ELF MC support has matured enough for the integrated assembler to be turned
530 on by default in Clang on X86-32 and X86-64 ELF systems.</li>
532 <li>MC supports and CodeGen uses the <tt>.file</tt> and <tt>.loc</tt> directives
533 for producing line number debug info. This produces more compact line
534 tables and easier to read .s files.</li>
536 <li>MC supports the <tt>.cfi_*</tt> directives for producing DWARF
537 frame information, but it is still not used by CodeGen by default.</li>
540 <li>The MC assembler now generates much better diagnostics for common errors,
541 is much faster at matching instructions, is much more bug-compatible with
542 the GAS assembler, and is now generally useful for a broad range of X86
545 <li>We now have some basic <a href="CodeGenerator.html#mc">internals
546 documentation</a> for MC.</li>
548 <li>.td files can now specify assembler aliases directly with the <a
549 href="CodeGenerator.html#na_instparsing">MnemonicAlias and InstAlias</a>
552 <li>LLVM now has an experimental format-independent object file manipulation
553 library (lib/Object). It supports both PE/COFF and ELF. The llvm-nm tool has
554 been extended to work with native object files, and the new llvm-objdump tool
555 supports disassembly of object files (but no relocations are displayed yet).
558 <li>Win32 PE-COFF support in the MC assembler has made a lot of progress in the
559 2.9 timeframe, but is still not generally useful.</li>
563 <p>For more information, please see the <a
564 href="http://blog.llvm.org/2010/04/intro-to-llvm-mc-project.html">Intro to the
565 LLVM MC Project Blog Post</a>.
570 <!--=========================================================================-->
572 <a name="codegen">Target Independent Code Generator Improvements</a>
575 <div class="doc_text">
577 <p>We have put a significant amount of work into the code generator
578 infrastructure, which allows us to implement more aggressive algorithms and make
584 <li>The pre-register-allocation (preRA) instruction scheduler models register
585 pressure much more accurately in some cases. This allows the adoption of more
586 aggressive scheduling heuristics.
589 LiveDebugVariables is a new pass that keeps track of debugging information for
590 user variables that are kept in registers in optimized builds.
593 Scheduler now models operand latency and pipeline forwarding.
595 Major regalloc rewrite, not on by default for 2.9 and not advised to use it.
596 * New basic register allocator that can be used as a safe fallback when
597 debugging. Enable with -regalloc=basic.
598 * New infrastructure for live range splitting. SplitKit can break a live
599 interval into smaller pieces while preserving SSA form, and SpillPlacement
600 can help find the best split points. This is a work in progress so the API
602 * The inline spiller has learned to clean up after live range splitting. It
603 can hoist spills out of loops, and it can eliminate redundant spills.
604 Rematerialization works with live range splitting.
605 * New greedy register allocator using live range splitting. This will be the
606 default register allocator in the next LLVM release, but it is not turned on
614 <!--=========================================================================-->
616 <a name="x86">X86-32 and X86-64 Target Improvements</a>
619 <div class="doc_text">
620 <p>New features and major changes in the X86 target include:
625 X86: Reimplemented all of MMX to introduce a new LLVM IR x86_mmx type. Now
626 random types like <2 x i32> are not iseld to mmx without emms. The
627 -disable-mmx flag is gone now.
631 X86 support for FS/GS relative loads and stores using address space 256/257 are
636 X86: Much better codegen for several cases using adc/sbb instead of cmovs for
637 conditional increment and other idioms.
641 The X86 backend has adopted a new preRA scheduling
642 mode, "list-ilp", to shorten the height of instruction schedules
643 without inducing register spills.
646 MC assembler support for 3dNow! and 3DNowA instructions.
648 <li>Several bugs have been fixed for Windows x64 code generator.</li>
653 <!--=========================================================================-->
655 <a name="ARM">ARM Target Improvements</a>
658 <div class="doc_text">
659 <p>New features of the ARM target include:
663 <li>ARM Fast ISel</li>
664 <li>ARM: New code placement pass.</li>
665 <li>ARM: Improved code generation for Cortex-A8 and Cortex-A9 CPUs.</li>
666 <li>ARM: __builtin_prefetch turns into prefetch instructions.</li>
667 <li>Countless ARM microoptimizations.</li>
669 <li> The ARM backend preRA scheduler now models machine resources at cycle
670 granularity. This allows the scheduler to both accurately model
671 instruction latency and avoid overcommitting functional units.</li>
677 <!--=========================================================================-->
679 <a name="OtherTS">Other Target Specific Improvements</a>
682 <div class="doc_text">
684 PPC: Switched to MCInstPrinter, and MCCodeEmitter. Ready to implement support
685 for directly writing out mach-o object files, but noone seems interested.
687 MicroBlaze: major updates for aggressive delay slot filler, MC-based assembly
688 printing, assembly instruction parsing, ELF .o file emission, and MC
689 instruction disassembler.
691 SPARC: Many improvements, including using the Y registers for multiplications
692 and addition of a simple delay slot filler.
697 <!--=========================================================================-->
699 <a name="changes">Major Changes and Removed Features</a>
702 <div class="doc_text">
704 <p>If you're already an LLVM user or developer with out-of-tree changes based
705 on LLVM 2.8, this section lists some "gotchas" that you may run into upgrading
706 from the previous release.</p>
709 last release for llvm-gcc
712 New naming rules in coding standards: CodingStandards.html#ll_naming
717 - DIBuilder provides simpler interface for front ends like Clang to encode debug info in LLVM IR.
718 - This interface hides implementation details (e.g. DIDerivedType, existence of compile unit etc..) that any front end should not know about.
719 For example, DIFactory DebugFactory;
720 Ty = DebugFactory.CreateDerivedType(DW_TAG_volatile_type,
721 findRegion(TYPE_CONTEXT(type)),
723 getOrCreateFile(main_input_filename),
725 NodeSizeInBits(type),
726 NodeAlignInBits(type),
731 DbgTy = DBuilder.createQualifiedType(DW_TAG_volatile_type, MainTy);
732 DIFactory is gone now.
739 LoopIndexSplit pass was removed, unmaintained.
740 LiveValues, SimplifyHalfPowrLibCalls, and GEPSplitter were removed.
741 Removed the PartialSpecialization pass, it was unmaintained and buggy.
743 DIFactory removed, use DIBuilder instead.
745 Triple::normalize is new, llvm triples are always stored in normalized form internally.
747 Triple x86_64--mingw64 is obsoleted. Use x86_64--mingw32 instead.
749 PointerTracking has been removed from mainline, moved to ClamAV.
755 <!--=========================================================================-->
757 <a name="api_changes">Internal API Changes</a>
760 <div class="doc_text">
762 <p>In addition, many APIs have changed in this release. Some of the major
763 LLVM API changes are:</p>
767 include/llvm/System merged into include/llvm/Support.
770 APInt API changes, see PR5207.
772 MVT::Flag renamed to MVT::Glue
775 error_code + libsystem + PathV2 changes
776 The system_error header from C++0x was added.
777 * Use if (error_code ec = function()) to check for error conditions
778 from functions which return it.
779 * error_code::message returns a human readable description of the error.
781 PathV1 has been deprecated in favor of PathV2 (sorry I didn't finish
782 this before the release).
783 * No Path class, use a r-value convertible to a twine instead.
784 * Assumes all paths are UTF-8.
790 <!-- *********************************************************************** -->
792 <a name="knownproblems">Known Problems</a>
794 <!-- *********************************************************************** -->
796 <div class="doc_text">
798 <p>This section contains significant known problems with the LLVM system,
799 listed by component. If you run into a problem, please check the <a
800 href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
801 there isn't already one.</p>
805 <!-- ======================================================================= -->
807 <a name="experimental">Experimental features included with this release</a>
810 <div class="doc_text">
812 <p>The following components of this LLVM release are either untested, known to
813 be broken or unreliable, or are in early development. These components should
814 not be relied on, and bugs should not be filed against them, but they may be
815 useful to some people. In particular, if you would like to work on one of these
816 components, please contact us on the <a
817 href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
820 <li>The Alpha, Blackfin, CellSPU, MicroBlaze, MSP430, MIPS, PTX, SystemZ
821 and XCore backends are experimental.</li>
822 <li><tt>llc</tt> "<tt>-filetype=obj</tt>" is experimental on all targets
823 other than darwin-i386 and darwin-x86_64. FIXME: Not true on ELF anymore?</li>
829 <!-- ======================================================================= -->
831 <a name="x86-be">Known problems with the X86 back-end</a>
834 <div class="doc_text">
837 <li>The X86 backend does not yet support
838 all <a href="http://llvm.org/PR879">inline assembly that uses the X86
839 floating point stack</a>. It supports the 'f' and 't' constraints, but not
841 <li>The X86-64 backend does not yet support the LLVM IR instruction
842 <tt>va_arg</tt>. Currently, front-ends support variadic
843 argument constructs on X86-64 by lowering them manually.</li>
844 <li>Windows x64 (aka Win64) code generator has a few issues.
846 <li>llvm-gcc cannot build the mingw-w64 runtime currently
847 due to lack of support for the 'u' inline assembly
848 constraint and for X87 floating point inline assembly.</li>
849 <li>On mingw-w64, you will see unresolved symbol <tt>__chkstk</tt>
850 due to <a href="http://llvm.org/bugs/show_bug.cgi?id=8919">Bug 8919</a>.
851 It is fixed in <a href="http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110321/118499.html">r128206</a>.</li>
852 <li>Miss-aligned MOVDQA might crash your program. It is due to
853 <a href="http://llvm.org/bugs/show_bug.cgi?id=9483">Bug 9483</a>,
854 lack of handling aligned internal globals.</li>
862 <!-- ======================================================================= -->
864 <a name="ppc-be">Known problems with the PowerPC back-end</a>
867 <div class="doc_text">
870 <li>The Linux PPC32/ABI support needs testing for the interpreter and static
871 compilation, and lacks support for debug information.</li>
876 <!-- ======================================================================= -->
878 <a name="arm-be">Known problems with the ARM back-end</a>
881 <div class="doc_text">
884 <li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
885 processors, thumb programs can crash or produce wrong
886 results (<a href="http://llvm.org/PR1388">PR1388</a>).</li>
887 <li>Compilation for ARM Linux OABI (old ABI) is supported but not fully tested.
893 <!-- ======================================================================= -->
895 <a name="sparc-be">Known problems with the SPARC back-end</a>
898 <div class="doc_text">
901 <li>The SPARC backend only supports the 32-bit SPARC ABI (-m32); it does not
902 support the 64-bit SPARC ABI (-m64).</li>
907 <!-- ======================================================================= -->
909 <a name="mips-be">Known problems with the MIPS back-end</a>
912 <div class="doc_text">
915 <li>64-bit MIPS targets are not supported yet.</li>
920 <!-- ======================================================================= -->
922 <a name="alpha-be">Known problems with the Alpha back-end</a>
925 <div class="doc_text">
929 <li>On 21164s, some rare FP arithmetic sequences which may trap do not have the
930 appropriate nops inserted to ensure restartability.</li>
935 <!-- ======================================================================= -->
937 <a name="c-be">Known problems with the C back-end</a>
940 <div class="doc_text">
942 <p>The C backend has numerous problems and is not being actively maintained.
943 Depending on it for anything serious is not advised.</p>
946 <li><a href="http://llvm.org/PR802">The C backend has only basic support for
947 inline assembly code</a>.</li>
948 <li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common
949 C++ programs</a>, preventing intermixing between C++ compiled by the CBE and
950 C++ code compiled with <tt>llc</tt> or native compilers.</li>
951 <li>The C backend does not support all exception handling constructs.</li>
952 <li>The C backend does not support arbitrary precision integers.</li>
958 <!-- ======================================================================= -->
960 <a name="llvm-gcc">Known problems with the llvm-gcc front-end</a>
963 <div class="doc_text">
965 <p>llvm-gcc is generally very stable for the C family of languages. The only
966 major language feature of GCC not supported by llvm-gcc is the
967 <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>Fortran support generally works, but there are still several unresolved bugs
973 in <a href="http://llvm.org/bugs/">Bugzilla</a>. Please see the
974 tools/gfortran component for details. Note that llvm-gcc is missing major
975 Fortran performance work in the frontend and library that went into GCC after
976 4.2. If you are interested in Fortran, we recommend that you consider using
977 <a href="#dragonegg">dragonegg</a> instead.</p>
979 <p>The llvm-gcc 4.2 Ada compiler has basic functionality, but is no longer being
980 actively maintained. If you are interested in Ada, we recommend that you
981 consider using <a href="#dragonegg">dragonegg</a> instead.</p>
984 <!-- *********************************************************************** -->
986 <a name="additionalinfo">Additional Information</a>
988 <!-- *********************************************************************** -->
990 <div class="doc_text">
992 <p>A wide variety of additional information is available on the <a
993 href="http://llvm.org">LLVM web page</a>, in particular in the <a
994 href="http://llvm.org/docs/">documentation</a> section. The web page also
995 contains versions of the API documentation which is up-to-date with the
996 Subversion version of the source code.
997 You can access versions of these documents specific to this release by going
998 into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>
1000 <p>If you have any questions or comments about LLVM, please feel free to contact
1001 us via the <a href="http://llvm.org/docs/#maillist"> mailing
1006 <!-- *********************************************************************** -->
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