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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>
66 lib/Transforms/IPO/MergeFunctions.cpp => consider for 3.0.
70 <!-- Features that need text if they're finished for 3.0:
73 loop dependence analysis
74 CorrelatedValuePropagation
77 <!-- *********************************************************************** -->
79 <a name="subproj">Sub-project Status Update</a>
81 <!-- *********************************************************************** -->
83 <div class="doc_text">
85 The LLVM 2.9 distribution currently consists of code from the core LLVM
86 repository (which roughly includes the LLVM optimizers, code generators
87 and supporting tools), the Clang repository and the llvm-gcc repository. In
88 addition to this code, the LLVM Project includes other sub-projects that are in
89 development. Here we include updates on these subprojects.
95 <!--=========================================================================-->
97 <a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>
100 <div class="doc_text">
102 <p><a href="http://clang.llvm.org/">Clang</a> is an LLVM front end for the C,
103 C++, and Objective-C languages. Clang aims to provide a better user experience
104 through expressive diagnostics, a high level of conformance to language
105 standards, fast compilation, and low memory use. Like LLVM, Clang provides a
106 modular, library-based architecture that makes it suitable for creating or
107 integrating with other development tools. Clang is considered a
108 production-quality compiler for C, Objective-C, C++ and Objective-C++ on x86
109 (32- and 64-bit), and for darwin-arm targets.</p>
111 <p>In the LLVM 2.9 time-frame, the Clang team has made many improvements in C,
112 C++ and Objective-C support. C++ support is now generally rock solid, has
113 been exercised on a broad variety of code, and has several new C++'0x features
114 implemented (such as rvalue references and variadic templates). LLVM 2.9 has
115 also brought in a large range of bug fixes and minor features (e.g. __label__
116 support), and is much more compatible with the Linux Kernel.</p>
118 <p>If Clang rejects your code that is built with another compiler, please take a
119 look at the <a href="http://clang.llvm.org/compatibility.html">language
120 compatibility</a> guide to make sure the issue isn't intentional or a known
128 <!--=========================================================================-->
130 <a name="dragonegg">DragonEgg: GCC front-ends, LLVM back-end</a>
133 <div class="doc_text">
135 <a href="http://dragonegg.llvm.org/">DragonEgg</a> is a
136 <a href="http://gcc.gnu.org/wiki/plugins">gcc plugin</a> that replaces GCC's
137 optimizers and code generators with LLVM's.
138 Currently it requires a patched version of gcc-4.5.
139 The plugin can target the x86-32 and x86-64 processor families and has been
140 used successfully on the Darwin, FreeBSD and Linux platforms.
141 The Ada, C, C++ and Fortran languages work well.
142 The plugin is capable of compiling plenty of Obj-C, Obj-C++ and Java but it is
143 not known whether the compiled code actually works or not!
147 The 2.9 release has the following notable changes:
149 <li>The plugin is much more stable when compiling Fortran.</li>
150 <li>Inline asm where an asm output is tied to an input of a different size is
151 now supported in many more cases.</li>
152 <li>Basic support for the __float128 type was added. It is now possible to
153 generate LLVM IR from programs using __float128 but code generation does not
155 <li>Compiling Java programs no longer systematically crashes the plugin.</li>
160 <!--=========================================================================-->
162 <a name="compiler-rt">compiler-rt: Compiler Runtime Library</a>
165 <div class="doc_text">
167 The new LLVM <a href="http://compiler-rt.llvm.org/">compiler-rt project</a>
168 is a simple library that provides an implementation of the low-level
169 target-specific hooks required by code generation and other runtime components.
170 For example, when compiling for a 32-bit target, converting a double to a 64-bit
171 unsigned integer is compiled into a runtime call to the "__fixunsdfdi"
172 function. The compiler-rt library provides highly optimized implementations of
173 this and other low-level routines (some are 3x faster than the equivalent
174 libgcc routines).</p>
177 All of the code in the compiler-rt project is available under the standard LLVM
178 License, a "BSD-style" license.
180 compiler_rt is now dual licensed under MIT and UIUC license
182 Several minor changes for better ARM support.
184 New in LLVM 2.9, UPDATE</p>
188 <!--=========================================================================-->
190 <a name="lldb">LLDB: Low Level Debugger</a>
193 <div class="doc_text">
195 <a href="http://lldb.llvm.org/">LLDB</a> is a brand new member of the LLVM
196 umbrella of projects. LLDB is a next generation, high-performance debugger. It
197 is built as a set of reusable components which highly leverage existing
198 libraries in the larger LLVM Project, such as the Clang expression parser, the
199 LLVM disassembler and the LLVM JIT.</p>
202 LLDB is in early development and not included as part of the LLVM 2.9 release,
207 but is mature enough to support basic debugging scenarios on Mac OS X in C,
208 Objective-C and C++. We'd really like help extending and expanding LLDB to
209 support new platforms, new languages, new architectures, and new features.-->
214 <!--=========================================================================-->
216 <a name="libc++">libc++: C++ Standard Library</a>
219 <div class="doc_text">
221 <a href="http://libcxx.llvm.org/">libc++</a> is another new member of the LLVM
222 family. It is an implementation of the C++ standard library, written from the
223 ground up to specifically target the forthcoming C++'0X standard and focus on
224 delivering great performance.</p>
227 As of the LLVM 2.9 release, UPDATE!
229 libc++ is now dual licensed under MIT and UIUC license
231 <!--libc++ is virtually feature complete, but would
232 benefit from more testing and better integration with Clang++. It is also
233 looking forward to the C++ committee finalizing the C++'0x standard.-->
240 <!--=========================================================================-->
243 <a name="klee">KLEE: A Symbolic Execution Virtual Machine</a>
246 <div class="doc_text">
248 <a href="http://klee.llvm.org/">KLEE</a> is a symbolic execution framework for
249 programs in LLVM bitcode form. KLEE tries to symbolically evaluate "all" paths
250 through the application and records state transitions that lead to fault
251 states. This allows it to construct testcases that lead to faults and can even
252 be used to verify some algorithms.
259 <!-- *********************************************************************** -->
261 <a name="externalproj">External Open Source Projects Using LLVM 2.9</a>
263 <!-- *********************************************************************** -->
265 <div class="doc_text">
267 <p>An exciting aspect of LLVM is that it is used as an enabling technology for
268 a lot of other language and tools projects. This section lists some of the
269 projects that have already been updated to work with LLVM 2.9.</p>
275 <!-- *********************************************************************** -->
277 <a name="whatsnew">What's New in LLVM 2.9?</a>
279 <!-- *********************************************************************** -->
281 <div class="doc_text">
283 <p>This release includes a huge number of bug fixes, performance tweaks and
284 minor improvements. Some of the major improvements and new features are listed
290 <!--=========================================================================-->
292 <a name="majorfeatures">Major New Features</a>
295 <div class="doc_text">
297 <p>LLVM 2.9 includes several major new capabilities:</p>
301 last release for llvm-gcc
302 TBAA: On by default in clang. Disable it with -fno-strict-aliasing.
303 Could be more aggressive for structs.
305 Triple::normalize is new, llvm triples are always stored in normalized form internally.
307 Triple x86_64--mingw64 is obsoleted. Use x86_64--mingw32 instead.
309 MC Assembler: X86 now generates much better diagnostics for common errors,
310 is much faster at matching instructions, is much more bug-compatible with
311 the GAS assembler, and is now generally useful for a broad range of X86
314 New Nvidia PTX backend, not generally useful in 2.9 though.
316 Much better debug info generated, particularly in optimized code situations.
320 ELF MC support: on by default in clang. There are still known missing features
321 for human written assembly.
323 X86: Reimplemented all of MMX to introduce a new LLVM IR x86_mmx type. Now
324 random types like <2 x i32> are not iseld to mmx without emms. The
325 -disable-mmx flag is gone now.
327 Some basic <a href="CodeGenerator.html#mc">internals documentation</a> for MC.
329 MC Assembler support for .file and .loc.
332 inline asm multiple alternative constraint support.
334 LoopIdiom: memset/memcpy formation. Build with -ffreestanding or -fno-builtin
335 if your memcpy is being compiled into infinite recursion.
340 X86 support for FS/GS relative loads and stores using address space 256/257 are
343 ARM: New code placement pass.
345 unnamed_addr + PR8927
347 PointerTracking has been removed from mainline, moved to ClamAV.
350 LoopInstSimplify pass.
352 - DIBuilder provides simpler interface for front ends like Clang to encode debug info in LLVM IR.
353 - This interface hides implementation details (e.g. DIDerivedType, existence of compile unit etc..) that any front end should not know about.
355 Ty = DebugFactory.CreateDerivedType(DW_TAG_volatile_type,
356 findRegion(TYPE_CONTEXT(type)),
358 getOrCreateFile(main_input_filename),
360 NodeSizeInBits(type),
361 NodeAlignInBits(type),
366 DbgTy = DBuilder.createQualifiedType(DW_TAG_volatile_type, MainTy);
368 PPC: Switched to MCInstPrinter, and MCCodeEmitter. Ready to implement support
369 for directly writing out mach-o object files, but noone seems interested.
371 ARM: Improved code generation for Cortex-A8 and Cortex-A9 CPUs.
373 Scheduler now models operand latency and pipeline forwarding.
375 error_code + libsystem + PathV2 changes
376 The system_error header from C++0x was added.
377 * Use if (error_code ec = function()) to check for error conditions
378 from functions which return it.
379 * error_code::message returns a human readable description of the error.
381 PathV1 has been deprecated in favor of PathV2 (sorry I didn't finish
382 this before the release).
383 * No Path class, use a r-value convertible to a twine instead.
384 * Assumes all paths are UTF-8.
388 Major regalloc rewrite, not on by default for 2.9 and not advised to use it.
389 * New basic register allocator that can be used as a safe fallback when
390 debugging. Enable with -regalloc=basic.
391 * New infrastructure for live range splitting. SplitKit can break a live
392 interval into smaller pieces while preserving SSA form, and SpillPlacement
393 can help find the best split points. This is a work in progress so the API
395 * The inline spiller has learned to clean up after live range splitting. It
396 can hoist spills out of loops, and it can eliminate redundant spills.
397 Rematerialization works with live range splitting.
398 * New greedy register allocator using live range splitting. This will be the
399 default register allocator in the next LLVM release, but it is not turned on
402 ARM: __builtin_prefetch turns into prefetch instructions.
404 MC assembler support for 3dNow! and 3DNowA instructions.
406 tblgen support for assembler aliases: <a
407 href="CodeGenerator.html#na_instparsing">MnemonicAlias and InstAlias</a>
409 LoopIndexSplit pass was removed, unmaintained.
411 include/llvm/System merged into include/llvm/Support.
413 Win32 PE-COFF support in the MC assembler has made a lot of progress in the 2.9
414 timeframe, but is still not generally useful. Please see
415 "http://llvm.org/bugs/showdependencytree.cgi?id=9100&hide_resolved=1" for open bugs?
417 New <a href="WritingAnLLVMPass.html#RegionPass">RegionPass</a> infrastructure
418 for region-based optimizations.
420 MicroBlaze: major updates for aggressive delay slot filler, MC-based assembly
421 printing, assembly instruction parsing, ELF .o file emission, and MC
422 instruction disassembler.
424 Countless ARM microoptimizations.
426 Speedups to various mid-level passes:
427 GVN is much faster on functions with deep dominator trees / lots of BBs.
428 DomTree and DominatorFrontier are much faster to compute, and preserved by
429 more passes (so they are computed less often)
430 SRoA is also much faster and doesn't use DominanceFrontier.
433 new 'hotpatch' attribute: LangRef.html#fnattrs
435 APInt API changes, see PR5207.
437 DSE is more aggressive with stores of different types: e.g. a large store
438 following a small one to the same address.
440 New naming rules in coding standards: CodingStandards.html#ll_naming
442 LiveDebugVariables is a new pass that keeps track of debugging information for
443 user variables that are kept in registers in optimized builds.
445 We now optimize various idioms for overflow detection into check of the flag
446 register on various CPUs, e.g.:
447 unsigned long t = a+b;
453 X86: Much better codegen for several cases using adc/sbb instead of cmovs for
454 conditional increment and other idioms.
456 MVT::Flag renamed to MVT::Glue
458 Removed the PartialSpecialization pass, it was unmaintained and buggy.
460 SPARC: Many improvements, including using the Y registers for multiplications
461 and addition of a simple delay slot filler.
466 Still todo: [110117-110228]
471 <!--=========================================================================-->
473 <a name="coreimprovements">LLVM IR and Core Improvements</a>
476 <div class="doc_text">
477 <p>LLVM IR has several new features for better support of new targets and that
478 expose new optimization opportunities:</p>
485 <!--=========================================================================-->
487 <a name="optimizer">Optimizer Improvements</a>
490 <div class="doc_text">
492 <p>In addition to a large array of minor performance tweaks and bug fixes, this
493 release includes a few major enhancements and additions to the optimizers:</p>
497 <li>LTO has been improved to use MC for parsing inline asm and now
498 can build large programs like Firefox 4 on both OS X and Linux.</li>
502 <p>In addition to these features that are done in 2.8, there is preliminary
503 support in the release for Type Based Alias Analysis
504 Preliminary work on TBAA but not usable in 2.8.
505 New CorrelatedValuePropagation pass, not on by default in 2.8 yet.
510 <!--=========================================================================-->
512 <a name="mc">MC Level Improvements</a>
515 <div class="doc_text">
517 The LLVM Machine Code (aka MC) subsystem was created to solve a number
518 of problems in the realm of assembly, disassembly, object file format handling,
519 and a number of other related areas that CPU instruction-set level tools work
523 <li>MC is now used by default for ELF systems on x86 and
525 <li>MC supports and CodeGen uses the <tt>.loc</tt> directives for
526 producing line number debug info. This produces more compact line
528 <li>MC supports the <tt>.cfi_*</tt> directives for producing DWARF
529 frame information, but it is still not used by CodeGen by default.</li>
530 <li>COFF support?</li>
533 <p>For more information, please see the <a
534 href="http://blog.llvm.org/2010/04/intro-to-llvm-mc-project.html">Intro to the
535 LLVM MC Project Blog Post</a>.
540 <!--=========================================================================-->
542 <a name="codegen">Target Independent Code Generator Improvements</a>
545 <div class="doc_text">
547 <p>We have put a significant amount of work into the code generator
548 infrastructure, which allows us to implement more aggressive algorithms and make
557 <!--=========================================================================-->
559 <a name="x86">X86-32 and X86-64 Target Improvements</a>
562 <div class="doc_text">
563 <p>New features and major changes in the X86 target include:
567 <li>Several bugs have been fixed for Windows x64 code generator.</li>
572 <!--=========================================================================-->
574 <a name="ARM">ARM Target Improvements</a>
577 <div class="doc_text">
578 <p>New features of the ARM target include:
586 <!--=========================================================================-->
588 <a name="changes">Major Changes and Removed Features</a>
591 <div class="doc_text">
593 <p>If you're already an LLVM user or developer with out-of-tree changes based
594 on LLVM 2.8, this section lists some "gotchas" that you may run into upgrading
595 from the previous release.</p>
602 <p>In addition, many APIs have changed in this release. Some of the major LLVM
609 <!--=========================================================================-->
611 <a name="devtree_changes">Development Infrastructure Changes</a>
614 <div class="doc_text">
616 <p>This section lists changes to the LLVM development infrastructure. This
617 mostly impacts users who actively work on LLVM or follow development on
618 mainline, but may also impact users who leverage the LLVM build infrastructure
619 or are interested in LLVM qualification.</p>
625 <!-- *********************************************************************** -->
627 <a name="knownproblems">Known Problems</a>
629 <!-- *********************************************************************** -->
631 <div class="doc_text">
633 <p>This section contains significant known problems with the LLVM system,
634 listed by component. If you run into a problem, please check the <a
635 href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
636 there isn't already one.</p>
640 <!-- ======================================================================= -->
642 <a name="experimental">Experimental features included with this release</a>
645 <div class="doc_text">
647 <p>The following components of this LLVM release are either untested, known to
648 be broken or unreliable, or are in early development. These components should
649 not be relied on, and bugs should not be filed against them, but they may be
650 useful to some people. In particular, if you would like to work on one of these
651 components, please contact us on the <a
652 href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
655 <li>The Alpha, Blackfin, CellSPU, MicroBlaze, MSP430, MIPS, PTX, SystemZ
656 and XCore backends are experimental.</li>
657 <li><tt>llc</tt> "<tt>-filetype=obj</tt>" is experimental on all targets
658 other than darwin-i386 and darwin-x86_64. FIXME: Not true on ELF anymore?</li>
664 <!-- ======================================================================= -->
666 <a name="x86-be">Known problems with the X86 back-end</a>
669 <div class="doc_text">
672 <li>The X86 backend does not yet support
673 all <a href="http://llvm.org/PR879">inline assembly that uses the X86
674 floating point stack</a>. It supports the 'f' and 't' constraints, but not
676 <li>The X86-64 backend does not yet support the LLVM IR instruction
677 <tt>va_arg</tt>. Currently, front-ends support variadic
678 argument constructs on X86-64 by lowering them manually.</li>
679 <li>Windows x64 (aka Win64) code generator has a few issues.
681 <li>llvm-gcc cannot build the mingw-w64 runtime currently
682 due to lack of support for the 'u' inline assembly
683 constraint and for X87 floating point inline assembly.</li>
684 <li>On mingw-w64, you will see unresolved symbol <tt>__chkstk</tt>
685 due to <a href="http://llvm.org/bugs/show_bug.cgi?id=8919">Bug 8919</a>.
686 It is fixed in <a href="http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110321/118499.html">r128206</a>.</li>
687 <li>Miss-aligned MOVDQA might crash your program. It is due to
688 <a href="http://llvm.org/bugs/show_bug.cgi?id=9483">Bug 9483</a>,
689 lack of handling aligned internal globals.</li>
697 <!-- ======================================================================= -->
699 <a name="ppc-be">Known problems with the PowerPC back-end</a>
702 <div class="doc_text">
705 <li>The Linux PPC32/ABI support needs testing for the interpreter and static
706 compilation, and lacks support for debug information.</li>
711 <!-- ======================================================================= -->
713 <a name="arm-be">Known problems with the ARM back-end</a>
716 <div class="doc_text">
719 <li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
720 processors, thumb programs can crash or produce wrong
721 results (<a href="http://llvm.org/PR1388">PR1388</a>).</li>
722 <li>Compilation for ARM Linux OABI (old ABI) is supported but not fully tested.
728 <!-- ======================================================================= -->
730 <a name="sparc-be">Known problems with the SPARC back-end</a>
733 <div class="doc_text">
736 <li>The SPARC backend only supports the 32-bit SPARC ABI (-m32); it does not
737 support the 64-bit SPARC ABI (-m64).</li>
742 <!-- ======================================================================= -->
744 <a name="mips-be">Known problems with the MIPS back-end</a>
747 <div class="doc_text">
750 <li>64-bit MIPS targets are not supported yet.</li>
755 <!-- ======================================================================= -->
757 <a name="alpha-be">Known problems with the Alpha back-end</a>
760 <div class="doc_text">
764 <li>On 21164s, some rare FP arithmetic sequences which may trap do not have the
765 appropriate nops inserted to ensure restartability.</li>
770 <!-- ======================================================================= -->
772 <a name="c-be">Known problems with the C back-end</a>
775 <div class="doc_text">
777 <p>The C backend has numerous problems and is not being actively maintained.
778 Depending on it for anything serious is not advised.</p>
781 <li><a href="http://llvm.org/PR802">The C backend has only basic support for
782 inline assembly code</a>.</li>
783 <li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common
784 C++ programs</a>, preventing intermixing between C++ compiled by the CBE and
785 C++ code compiled with <tt>llc</tt> or native compilers.</li>
786 <li>The C backend does not support all exception handling constructs.</li>
787 <li>The C backend does not support arbitrary precision integers.</li>
793 <!-- ======================================================================= -->
795 <a name="llvm-gcc">Known problems with the llvm-gcc front-end</a>
798 <div class="doc_text">
800 <p>llvm-gcc is generally very stable for the C family of languages. The only
801 major language feature of GCC not supported by llvm-gcc is the
802 <tt>__builtin_apply</tt> family of builtins. However, some extensions
803 are only supported on some targets. For example, trampolines are only
804 supported on some targets (these are used when you take the address of a
805 nested function).</p>
807 <p>Fortran support generally works, but there are still several unresolved bugs
808 in <a href="http://llvm.org/bugs/">Bugzilla</a>. Please see the
809 tools/gfortran component for details. Note that llvm-gcc is missing major
810 Fortran performance work in the frontend and library that went into GCC after
811 4.2. If you are interested in Fortran, we recommend that you consider using
812 <a href="#dragonegg">dragonegg</a> instead.</p>
814 <p>The llvm-gcc 4.2 Ada compiler has basic functionality, but is no longer being
815 actively maintained. If you are interested in Ada, we recommend that you
816 consider using <a href="#dragonegg">dragonegg</a> instead.</p>
819 <!-- *********************************************************************** -->
821 <a name="additionalinfo">Additional Information</a>
823 <!-- *********************************************************************** -->
825 <div class="doc_text">
827 <p>A wide variety of additional information is available on the <a
828 href="http://llvm.org">LLVM web page</a>, in particular in the <a
829 href="http://llvm.org/docs/">documentation</a> section. The web page also
830 contains versions of the API documentation which is up-to-date with the
831 Subversion version of the source code.
832 You can access versions of these documents specific to this release by going
833 into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>
835 <p>If you have any questions or comments about LLVM, please feel free to contact
836 us via the <a href="http://llvm.org/docs/#maillist"> mailing
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