LLVM 2.4 Release Notes

Introduction @@ -33,36 +43,59 @@

This document contains the release notes for the LLVM Compiler -Infrastructure, release 2.4. Here we describe the status of LLVM, including +Infrastructure, release 2.7. Here we describe the status of LLVM, including major improvements from the previous release and significant known problems. -All LLVM releases may be downloaded from the LLVM releases web site.

For more information about LLVM, including information about the latest release, please check out the main LLVM web site. If you have questions or comments, the LLVM Developer's Mailing -List is a good place to send them.

+href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM Developer's +Mailing List is a good place to send them.

Note that if you are reading this file from a Subversion checkout or the main LLVM web page, this document applies to the next release, not the current one. To see the release notes for a specific release, please see the releases page.

- + + + + Logo web page. + llvm devmtg + compiler_rt + KLEE web page at klee.llvm.org + Many new papers added to /pubs/ + Mention gcc plugin. + -->

@@ -72,12 +105,11 @@ current one. To see the release notes for a specific release, please see the

-The LLVM 2.4 distribution currently consists of code from the core LLVM -repository (which roughly includes the LLVM optimizers, code generators and -supporting tools) and the llvm-gcc repository. In addition to this code, the -LLVM Project includes other sub-projects that are in development. The two which -are the most actively developed are the Clang Project and -the VMKit Project. +The LLVM 2.7 distribution currently consists of code from the core LLVM +repository (which roughly includes the LLVM optimizers, code generators +and supporting tools), the Clang repository and the llvm-gcc repository. In +addition to this code, the LLVM Project includes other sub-projects that are in +development. Here we include updates on these subprojects.

@@ -90,38 +122,14 @@ the VMKit Project.

The Clang project is an effort to build -a set of new 'LLVM native' front-end technologies for the LLVM optimizer -and code generator. Clang is continuing to make major strides forward in all -areas. Its C and Objective-C parsing support is very solid, and the code -generation support is far enough along to build many C applications. While not -yet production quality, it is progressing very nicely. In addition, C++ -front-end work has started to make significant progress.

The Clang project is ...

-Clang, in conjunction with the ccc driver, is now usable as a -replacement for gcc for building some small- to medium-sized C applications. -Additionally, Clang now has code generation support for Objective-C on Mac OS X -platform. Major highlights include: -

Clang/ccc pass almost all of the LLVM test suite on Mac OS X and Linux -on the 32-bit x86 architecture. This includes significant C -applications such as sqlite3, -lua, and -Clam AntiVirus. - -
Clang can build the majority of Objective-C examples shipped with the -Mac OS X Developer Tools. -

In the LLVM 2.7 time-frame, the Clang team has made many improvements:

-Clang code generation still needs considerable testing and development, however. -Some areas under active development include:

Improved support for C and Objective-C features, for example - variable-length arrays, va_arg, exception handling (Obj-C), and garbage - collection (Obj-C). -
ABI compatibility, especially for platforms other than 32-bit x86. +
...

@@ -131,29 +139,13 @@ Some areas under active development include:

The Clang project also includes an early stage static source code analysis -tool for automatically -finding bugs in C and Objective-C programs. The tool performs a growing set -of checks to find bugs that occur on a specific path within a program. Examples -of bugs the tool finds include logic errors such as null dereferences, -violations of various API rules, dead code, and potential memory leaks in -Objective-C programs. Since its inception, public feedback on the tool has been -extremely positive, and conservative estimates put the number of real bugs it -has found in industrial-quality software on the order of thousands.

Previously announced in the 2.4, 2.5, and 2.6 LLVM releases, the Clang project also +includes an early stage static source code analysis tool for automatically finding bugs +in C and Objective-C programs. The tool performs checks to find +bugs that occur on a specific path within a program.

The tool also provides a simple web GUI to inspect potential bugs found by -the tool. While still early in development, the GUI illustrates some of the key -features of Clang: accurate source location information, which is used by the -GUI to highlight specific code expressions that relate to a bug (including those -that span multiple lines) and built-in knowledge of macros, which is used to -perform inline expansion of macros within the GUI itself.

- -

The set of checks performed by the static analyzer is gradually expanding, -and -future plans for the tool include full source-level inter-procedural analysis -and deeper checks such as buffer overrun detection. There are many opportunities -to extend and enhance the static analyzer, and anyone interested in working on -this project is encouraged to get involved!

In the LLVM 2.7 time-frame, the analyzer core has sprouted legs and...

@@ -165,168 +157,330 @@ this project is encouraged to get involved!

The VMKit project is an implementation of -a JVM and a CLI Virtual Machines (Microsoft .NET is an -implementation of the CLI) using the Just-In-Time compiler of LLVM.

+a JVM and a CLI Virtual Machine (Microsoft .NET is an +implementation of the CLI) using LLVM for static and just-in-time +compilation.

Following LLVM 2.4, VMKit has its first release 0.24 that you can find on -the release page. The release includes -bug fixes, cleanup and new features. The major changes include:

+VMKit version ?? builds with LLVM 2.7 and you can find it on its +web page. The release includes +bug fixes, cleanup and new features. The major changes are:

Support for generics in the .Net virtual machine. This was implemented -by Tilmann Scheller during his Google Summer of Code project. -
Initial support for the Mono class libraries. -
Support for MacOSX/x86, following LLVM's support for exceptions in -JIT on MacOSX/x86. -
A new vmkit driver: a program to run java or .net applications. The -driver supports llvm command line arguments including the new "-fast" option. -
A new memory allocation scheme in the JVM that makes unloading a -class loader very fast. -
VMKit now follows the LLVM Makefile machinery. +
...

+ +

+compiler-rt: Compiler Runtime Library +

+ +

+The new LLVM compiler-rt project +is a simple library that provides an implementation of the low-level +target-specific hooks required by code generation and other runtime components. +For example, when compiling for a 32-bit target, converting a double to a 64-bit +unsigned integer is compiled into a runtime call to the "__fixunsdfdi" +function. The compiler-rt library provides highly optimized implementations of +this and other low-level routines (some are 3x faster than the equivalent +libgcc routines).

+ +

+All of the code in the compiler-rt project is available under the standard LLVM +License, a "BSD-style" license.

+ +

+ + +

+DragonEgg: GCC-4.5 as an LLVM frontend +

+ +

+The goal of DragonEgg is to make +gcc-4.5 act like llvm-gcc without requiring any gcc modifications whatsoever. +DragonEgg is a shared library (dragonegg.so) +that is loaded by gcc at runtime. It ... +

+ +

+ + + +

+llvm-mc: Machine Code Toolkit +

+ +

+The LLVM Machine Code (MC) Toolkit project is ... +

+ +

- What's New in LLVM? + External Open Source Projects Using LLVM 2.7

This release includes a huge number of bug fixes, performance tweaks and -minor improvements. Some of the major improvements and new features are listed -in this section. +

An exciting aspect of LLVM is that it is used as an enabling technology for + a lot of other language and tools projects. This section lists some of the + projects that have already been updated to work with LLVM 2.7.

+ + + +

+Rubinius +

+ +

+Need update. +

-Major New Features +MacRuby

LLVM 2.4 includes several major new capabilities:

+Need update. +

+ +

- + + +

+Pure +

+ +

+Pure +is an algebraic/functional programming language based on term rewriting. +Programs are collections of equations which are used to evaluate expressions in +a symbolic fashion. Pure offers dynamic typing, eager and lazy evaluation, +lexical closures, a hygienic macro system (also based on term rewriting), +built-in list and matrix support (including list and matrix comprehensions) and +an easy-to-use C interface. The interpreter uses LLVM as a backend to + JIT-compile Pure programs to fast native code.

+ +

Pure versions 0.43 and later have been tested and are known to work with +LLVM 2.7 (and continue to work with older LLVM releases >= 2.5).

-llvm-gcc 4.2 Improvements +LLVM D Compiler

+Need update. + +

LLVM fully supports the llvm-gcc 4.2 front-end, which marries the GCC -front-ends and driver with the LLVM optimizer and code generator. It currently -includes support for the C, C++, Objective-C, Ada, and Fortran front-ends.

+ +

+Roadsend PHP +

LLVM 2.4 supports the full set of atomic __sync_* builtins. LLVM -2.3 only supported those used by OpenMP, but 2.4 supports them all. While -llvm-gcc supports all of these builtins, note that not all targets do. X86 -support them all in both 32-bit and 64-bit mode and PowerPC supports them all -except for the 64-bit operations when in 32-bit mode.
llvm-gcc now supports an -flimited-precision option, which tells -the compiler that it is ok to use low-precision approximations of certain libm -functions (like tan, log, etc). This allows you to get high performance if you -only need (say) 14-bits of precision.
llvm-gcc now supports a C language extension known as "Blocks -". This feature is similar to nested functions and closures, but does not -require stack trampolines (with most ABIs) and supports returning closures -from functions that define them. Note that actually using Blocks -requires a small runtime that is not included with llvm-gcc.
llvm-gcc now supports a new -flto option. On systems that support -transparent Link Time Optimization (currently Darwin systems with Xcode 3.1 and -later) this allows the use of LTO with other optimization levels like -Os. -Previously, LTO could only be used with -O4, which implied optimizations in --O3 that can increase code size.

+Roadsend PHP (rphp) is an open +source implementation of the PHP programming +language that uses LLVM for its optimizer, JIT and static compiler. This is a +reimplementation of an earlier project that is now based on LLVM. +

+ + +

+Unladen Swallow +

+ +

+Unladen Swallow is a +branch of Python intended to be fully +compatible and significantly faster. It uses LLVM's optimization passes and JIT +compiler. +

+ +

+llvm-lua

+Need update. + +

-LLVM Core Improvements +IcedTea Java Virtual Machine Implementation

New features include: +

+Need update. +

+ + + + +

+ What's New in LLVM 2.7? +

+ + +

+ +

This release includes a huge number of bug fixes, performance tweaks and +minor improvements. Some of the major improvements and new features are listed +in this section. +

+ +

+ + +

+Major New Features +

+ +

LLVM 2.7 includes several major new capabilities:

A major change to the Use class landed, which shrank it by 25%. Since -this is a pervasive part of the LLVM, it ended up reducing the memory use of -LLVM IR in general by 15% for most programs.
...

Values with no names are now pretty printed by llvm-dis more -nicely. They now print as "%3 = add i32 %A, 4" instead of -"add i32 %A, 4 ; <i32>:3", which makes it much easier to read. -

+Extensible metadata solid. + +Debug info improvements: using metadata instead of llvm.dbg global variables. +This brings several enhancements including improved compile times. + +New instruction selector. +GHC Haskell ABI/ calling conv support. +Pre-Alpha support for unions in IR. +New InlineHint and StackAlignment function attributes +Code generator MC'ized except for debug info and EH. +New SCEV AA pass: -scev-aa +Inliner reuses arrays allocas when inlining multiple callers to reduce stack usage. +MC encoding and disassembler apis. +Optimal Edge Profiling? +Instcombine is now a library, has its own IRBuilder to simplify itself. +New llvm/Support/Regex.h API. FileCheck now does regex's +Many subtle pointer invalidation bugs in Callgraph have been fixed and it now uses asserting value handles. +MC Disassembler (with blog post), MCInstPrinter. Many X86 backend and AsmPrinter simplifications +Various tools like llc and opt now read either .ll or .bc files as input. +Malloc and free instructions got removed. +compiler-rt support for ARM. +completely llvm-gcc NEON support. +Can transcode from GAS to intel syntax with "llvm-mc foo.s -output-asm-variant=1" +JIT debug information with GDB 7.0 +New CodeGen Level CSE +CMake can now run tests, what other improvements? +ARM/Thumb using reg scavenging for stack object address materialization (PEI). +New SSAUpdater and MachineSSAUpdater classes for unstructured ssa updating, + changed jump threading, GVN, etc to use it which simplified them and speed + them up. +Combiner-AA improvements, why not on by default? +Pre-regalloc tail duplication +x86 sibcall optimization +New LSR with full strength reduction mode +The most awesome sext / zext optimization pass. ? + + + +CondProp pass removed (functionality merged into jump threading). +AndersAA got removed (from 2.7 or mainline?) +PredSimplify, LoopVR, GVNPRE got removed. +LLVM command line tools now overwrite their output, before they would only do this with -f. +DOUT removed, use DEBUG(errs() instead. +Much stuff converted to use raw_ostream instead of std::ostream. +TargetAsmInfo renamed to MCAsmInfo +llvm/ADT/iterator.h gone. + + +

+ + +

+LLVM IR and Core Improvements +

LLVM 2.4 includes some changes for better vector support. First, the shift -operations (shl, ashr, lshr) now all support vectors -and do an element-by-element shift (shifts of the whole vector can be -accomplished by bitcasting the vector to <1 x i128> for example). Second, -there is initial support in development for vector comparisons with the -fcmp/icmp -instructions. These instructions compare two vectors and return a vector of -i1's for each result. Note that there is very little codegen support available -for any of these IR features though.

- -

A new DebugInfoBuilder class is available, which makes it much -easier for front-ends to create debug info descriptors, similar to the way that -IRBuilder makes it easier to create LLVM IR.

- -

The IRBuilder class is now parameterized by a class responsible -for constant folding. The default ConstantFolder class does target independent -constant folding. The NoFolder class does no constant folding at all, which is -useful when learning how LLVM works. The TargetFolder class folds the most, -doing target dependent constant folding.

- -

LLVM now supports "function attributes", which allows us to separate return -value attributes from function attributes. LLVM now supports attributes on a -function itself, a return value, and its parameters. New supported function -attributes include noinline/alwaysinline and the "opt-size" flag which says the -function should be optimized for code size.

- -

LLVM IR now directly represents "common" linkage, instead of - representing it as a form of weak linkage.

- +

LLVM IR has several new features for better support of new targets and that +expose new optimization opportunities:

+ +

@@ -338,218 +492,214 @@ function should be optimized for code size.

In addition to a huge array of bug fixes and minor performance tweaks, this +

In addition to a large array of minor performance tweaks and bug fixes, this release includes a few major enhancements and additions to the optimizers:

The Global Value Numbering (GVN) pass now does local Partial Redundancy -Elimination (PRE) to eliminate some partially redundant expressions in cases -where doing so won't grow code size.
...
LLVM 2.4 includes a new loop deletion pass (which removes output-free -provably-finite loops) and a rewritten Aggressive Dead Code Elimination (ADCE) -pass that no longer uses control dependence information. These changes speed up -the optimizer and also prevent it from deleting output-free infinite -loops.

The new AddReadAttrs pass works out which functions are read-only or -read-none (these correspond to 'pure' and 'const' in GCC) and marks them -with the appropriate attribute.

Also, -anders-aa was removed

LLVM 2.4 now includes a new SparsePropagation framework, which makes it -trivial to build lattice-based dataflow solvers that operate over LLVM IR. Using -this interface means that you just define objects to represent your lattice -values and the transfer functions that operate on them. It handles the -mechanics of worklist processing, liveness tracking, handling PHI nodes, -etc.

The Loop Strength Reduction and induction variable optimization passes have -several improvements to avoid inserting MAX expressions, to optimize simple -floating point induction variables and to analyze trip counts of more -loops.

Various helper functions (ComputeMaskedBits, ComputeNumSignBits, etc) were -pulled out of the Instruction Combining pass and put into a new -ValueTracking.h header, where they can be reused by other passes.

+ +

+Interpreter and JIT Improvements +

The tail duplication pass has been removed from the standard optimizer -sequence used by llvm-gcc. This pass still exists, but the benefits it once -provided are now achieved by other passes.

The JIT now defaults +to compiling eagerly to avoid a race condition in the lazy JIT. +Clients that still want the lazy JIT can switch it on by calling +ExecutionEngine::DisableLazyCompilation(false).
It is now possible to create more than one JIT instance in the same process. +These JITs can generate machine code in parallel, +although you +still have to obey the other threading restrictions.

-Code Generator Improvements +Target Independent Code Generator Improvements

We have put a significant amount of work into the code generator infrastructure, -which allows us to implement more aggressive algorithms and make it run -faster:

We have put a significant amount of work into the code generator +infrastructure, which allows us to implement more aggressive algorithms and make +it run faster:

The target-independent code generator supports (and the X86 backend - currently implements) a new interface for "fast" instruction selection. This - interface is optimized to produce code as quickly as possible, sacrificing - code quality to do it. This is used by default at -O0 or when using - "llc -fast" on X86. It is straight-forward to add support for - other targets if faster -O0 compilation is desired.
In addition to the new 'fast' instruction selection path, many existing - pieces of the code generator have been optimized in significant ways. - SelectionDAG's are now pool allocated and use better algorithms in many - places, the ".s" file printers now use raw_ostream to emit text much faster, - etc. The end result of these improvements is that the compiler also takes - substantially less time to generate code that is just as good (and often - better) than before.
Each target has been split to separate the ".s" file printing logic from the - rest of the target. This enables JIT compilers that don't link in the - (somewhat large) code and data tables used for printing a ".s" file.
The code generator now includes a "stack slot coloring" pass, which packs - together individual spilled values into common stack slots. This reduces - the size of stack frames with many spills, which tends to increase L1 cache - effectiveness.
Various pieces of the register allocator (e.g. the coalescer and two-address - operation elimination pass) now know how to rematerialize trivial operations - to avoid copies and include several other optimizations.
The graphs produced by - the llc -view-*-dags options are now significantly prettier and - easier to read.
LLVM 2.4 includes a new register allocator based on Partitioned Boolean - Quadratic Programming (PBQP). This register allocator is still in - development, but is very simple and clean.
...

+ +

+X86-32 and X86-64 Target Improvements

New features of the X86 target include: +

+ +

-Target Specific Improvements +PIC16 Target Improvements

New target-specific features include: +

New features of the PIC16 target include:

Exception handling is supported by default on Linux/x86-64.
Position Independent Code (PIC) is now supported on Linux/x86-64.
@llvm.frameaddress now supports getting the frame address of stack frames - > 0 on x86/x86-64.
MIPS floating point support? [BRUNO]
The PowerPC backend now supports trampolines.
...

Things not yet supported:

Variable arguments.
Interrupts/programs.

+ +

-Other Improvements +ARM Target Improvements

New features include: +

New features of the ARM target include:

llvmc2 (the generic compiler driver) gained plugin - support. It is now easier to experiment with llvmc2 and - build your own tools based on it.
LLVM 2.4 includes a number of new generic algorithms and data structures, - include a scoped hash table, 'immutable' data structures, a simple - free-list manager, and a raw_ostream class. - The raw_ostream class and - format allow for efficient file output, and various pieces of LLVM - have switched over to use it. The eventual goal is to eliminate - std::ostream in favor of it.
...

-Major Changes and Removed Features +Other Target Specific Improvements

- -

If you're already an LLVM user or developer with out-of-tree changes based -on LLVM 2.3, this section lists some "gotchas" that you may run into upgrading -from the previous release.

New features of other targets include: +

+ +

The LLVM IR generated by llvm-gcc no longer names all instructions. This - makes it run faster, but may be more confusing to some people. If you - prefer to have names, the 'opt -instnamer' pass will add names to - all instructions.

+ +

+New Useful APIs +

+ +

This release includes a number of new APIs that are used internally, which + may also be useful for external clients. +

The LoadVN and GCSE passes have been removed from the tree. They are - obsolete and have been replaced with the GVN and MemoryDependence passes. -

In addition, many APIs have changed in this release. Some of the major LLVM -API changes are:

+ + +

+Other Improvements and New Features +

+ +

Other miscellaneous features include:

+ +

+ + + +

+Major Changes and Removed Features +

+ +

If you're already an LLVM user or developer with out-of-tree changes based +on LLVM 2.6, this section lists some "gotchas" that you may run into upgrading +from the previous release.

Now, function attributes and return value attributes are managed -sepearately. Interface exported by ParameterAttributes.h header is now -experted by Attributes.h header. The new attributes interface changes are:

getParamAttrs method is now replaced by -getParamAttributes, getRetAttributes and -getFnAttributes methods.
Return value attributes are stored at index 0. Function attributes are -stored at index ~0U. Parameter attributes are stored at index that matches -parameter number.
ParamAttr namespace is now renamed as Attribute.
The name of the class that manages reference count of opaque -attributes is changed from PAListPtr to AttrListPtr.
ParamAttrsWithIndex is now renamed as AttributeWithIndex. +
The LLVM interpreter now defaults to not using libffi even +if you have it installed. This makes it more likely that an LLVM built on one +system will work when copied to a similar system. To use libffi, +configure with --enable-libffi.

The DbgStopPointInst methods getDirectory and -getFileName now return Value* instead of strings. These can be -converted to strings using llvm::GetConstantStringInfo defined via -"llvm/Analysis/ValueTracking.h".

- -

The APIs to create various instructions have changed from lower case - "create" methods to upper case "Create" methods (e.g. - BinaryOperator::create). LLVM 2.4 includes both cases, but the - lower case ones are removed in mainline, please migrate.

- -

Various header files like "llvm/ADT/iterator" were given a ".h" suffix. - Change your code to #include "llvm/ADT/iterator.h" instead.

- -

In the code generator, many MachineOperand predicates were renamed to be - shorter (e.g. isFrameIndex() -> isFI()), - SDOperand was renamed to SDValue (and the "Val" - member was changed to be the getNode() accessor), and the - MVT::ValueType enum has been replaced with an "MVT" - struct. The getSignExtended and getValue methods in the - ConstantSDNode class were renamed to getSExtValue and - getZExtValue respectively, to be more consistent with - the ConstantInt class.

+ +

In addition, many APIs have changed in this release. Some of the major LLVM +API changes are:

+ +

ModuleProvider has been removed +and its methods moved to Module and GlobalValue. +Most clients can remove uses of ExistingModuleProvider, +replace getBitcodeModuleProvider with +getLazyBitcodeModule, and pass their Module to +functions that used to accept ModuleProvider. Clients who +wrote their own ModuleProviders will need to derive from +GVMaterializer instead and use +Module::setMaterializer to attach it to a +Module.
GhostLinkage has given up the ghost. +GlobalValues that have not yet been read from their backing +storage have the same linkage they will have after being read in. +Clients must replace calls to +GlobalValue::hasNotBeenReadFromBitcode with +GlobalValue::isMaterializable.
FIXME: Debug info has been totally redone. Add pointers to new APIs. Substantial caveats about compatibility of .ll and .bc files.
The llvm/Support/DataTypes.h header has moved +to llvm/System/DataTypes.h.
The isInteger, isIntOrIntVector, isFloatingPoint, +isFPOrFPVector and isFPOrFPVector methods have been renamed +isIntegerTy, isIntOrIntVectorTy, isFloatingPointTy, +isFPOrFPVectorTy and isFPOrFPVectorTy respectively.

@@ -567,16 +717,16 @@ converted to strings using llvm::GetConstantStringInfo defined via

LLVM is known to work on the following platforms:

Intel and AMD machines (IA32) running Red Hat Linux, Fedora Core and FreeBSD - (and probably other unix-like systems).
PowerPC and X86-based Mac OS X systems, running 10.3 and above in 32-bit and - 64-bit modes.
Intel and AMD machines (IA32, X86-64, AMD64, EMT-64) running Red Hat + Linux, Fedora Core, FreeBSD and AuroraUX (and probably other unix-like + systems).
PowerPC and X86-based Mac OS X systems, running 10.3 and above in 32-bit + and 64-bit modes.
Intel and AMD machines running on Win32 using MinGW libraries (native).
Intel and AMD machines running on Win32 with the Cygwin libraries (limited support is available for native builds with Visual C++).
Sun UltraSPARC workstations running Solaris 10.
Sun x86 and AMD64 machines running Solaris 10, OpenSolaris 0906.
Alpha-based machines running Debian GNU/Linux.
Itanium-based (IA64) machines running Linux and HP-UX.

The core LLVM infrastructure uses GNU autoconf to adapt itself @@ -594,12 +744,20 @@ portability patches and reports of successful builds or error messages.

This section contains all known problems with the LLVM system, listed by -component. As new problems are discovered, they will be added to these -sections. If you run into a problem, please check the This section contains significant known problems with the LLVM system, +listed by component. If you run into a problem, please check the LLVM bug database and submit a bug if there isn't already one.

LLVM will not correctly compile on Solaris and/or OpenSolaris +using the stock GCC 3.x.x series 'out the box', +See: Broken versions of GCC and other tools. +However, A Modern GCC Build +for x86/x86-64 has been made available from the third party AuroraUX Project +that has been meticulously tested for bootstrapping LLVM & Clang.

@@ -617,9 +775,11 @@ components, please contact us on the LLVMdev list.

The MSIL, IA64, Alpha, SPU, MIPS, and PIC16 backends are experimental.
The llc "-filetype=asm" (the default) is the only supported - value for this option.
The MSIL, Alpha, SPU, MIPS, PIC16, Blackfin, MSP430, SystemZ and MicroBlaze + backends are experimental.
The llc "-filetype=asm" (the default) is the only + supported value for this option. The MachO writer is experimental, and + works much better in mainline SVN.

These are in-progress notes for the upcoming LLVM 2.7 +release. +You may prefer the +LLVM 2.6 +Release Notes.

These are in-progress notes for the upcoming LLVM 2.7 +release.
+You may prefer the +LLVM 2.6 +Release Notes.