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| <title>LLVM 2.9 Release Notes</title> |
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| |
| <h1 class="doc_title">LLVM 2.9 Release Notes</h1> |
| |
| <img align=right src="http://llvm.org/img/DragonSmall.png" |
| width="136" height="136" alt="LLVM Dragon Logo"> |
| |
| <ol> |
| <li><a href="#intro">Introduction</a></li> |
| <li><a href="#subproj">Sub-project Status Update</a></li> |
| <li><a href="#externalproj">External Projects Using LLVM 2.9</a></li> |
| <li><a href="#whatsnew">What's New in LLVM 2.9?</a></li> |
| <li><a href="GettingStarted.html">Installation Instructions</a></li> |
| <li><a href="#knownproblems">Known Problems</a></li> |
| <li><a href="#additionalinfo">Additional Information</a></li> |
| </ol> |
| |
| <div class="doc_author"> |
| <p>Written by the <a href="http://llvm.org">LLVM Team</a></p> |
| </div> |
| |
| <!-- |
| <h1 style="color:red">These are in-progress notes for the upcoming LLVM 2.9 |
| release.<br> |
| You may prefer the |
| <a href="http://llvm.org/releases/2.8/docs/ReleaseNotes.html">LLVM 2.8 |
| Release Notes</a>.</h1> |
| --> |
| |
| <!-- *********************************************************************** --> |
| <h1> |
| <a name="intro">Introduction</a> |
| </h1> |
| <!-- *********************************************************************** --> |
| |
| <div class="doc_text"> |
| |
| <p>This document contains the release notes for the LLVM Compiler |
| Infrastructure, release 2.9. 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 <a |
| href="http://llvm.org/releases/">LLVM releases web site</a>.</p> |
| |
| <p>For more information about LLVM, including information about the latest |
| release, please check out the <a href="http://llvm.org/">main LLVM |
| web site</a>. If you have questions or comments, the <a |
| href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM Developer's |
| Mailing List</a> is a good place to send them.</p> |
| |
| <p>Note that if you are reading this file from a Subversion checkout or the |
| main LLVM web page, this document applies to the <i>next</i> release, not the |
| current one. To see the release notes for a specific release, please see the |
| <a href="http://llvm.org/releases/">releases page</a>.</p> |
| |
| </div> |
| |
| <!-- Features that need text if they're finished for 3.1: |
| ARM EHABI |
| combiner-aa? |
| strong phi elim |
| loop dependence analysis |
| CorrelatedValuePropagation |
| lib/Transforms/IPO/MergeFunctions.cpp => consider for 3.1. |
| --> |
| |
| <!-- *********************************************************************** --> |
| <h1> |
| <a name="subproj">Sub-project Status Update</a> |
| </h1> |
| <!-- *********************************************************************** --> |
| |
| <div class="doc_text"> |
| <p> |
| The LLVM 2.9 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. |
| </p> |
| |
| </div> |
| |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a> |
| </h2> |
| |
| <div class="doc_text"> |
| |
| <p><a href="http://clang.llvm.org/">Clang</a> is an LLVM front end for the C, |
| C++, and Objective-C languages. Clang aims to provide a better user experience |
| through expressive diagnostics, a high level of conformance to language |
| standards, fast compilation, and low memory use. Like LLVM, Clang provides a |
| modular, library-based architecture that makes it suitable for creating or |
| integrating with other development tools. Clang is considered a |
| production-quality compiler for C, Objective-C, C++ and Objective-C++ on x86 |
| (32- and 64-bit), and for darwin/arm targets.</p> |
| |
| <p>In the LLVM 2.9 time-frame, the Clang team has made many improvements in C, |
| C++ and Objective-C support. C++ support is now generally rock solid, has |
| been exercised on a broad variety of code, and has several new <a |
| href="http://clang.llvm.org/cxx_status.html#cxx0x">C++'0x features</a> |
| implemented (such as rvalue references and variadic templates). LLVM 2.9 has |
| also brought in a large range of bug fixes and minor features (e.g. __label__ |
| support), and is much more compatible with the Linux Kernel.</p> |
| |
| <p>If Clang rejects your code but another compiler accepts it, please take a |
| look at the <a href="http://clang.llvm.org/compatibility.html">language |
| compatibility</a> guide to make sure this is not intentional or a known issue. |
| </p> |
| |
| <ul> |
| </ul> |
| </div> |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="dragonegg">DragonEgg: GCC front-ends, LLVM back-end</a> |
| </h2> |
| |
| <div class="doc_text"> |
| <p> |
| <a href="http://dragonegg.llvm.org/">DragonEgg</a> is a |
| <a href="http://gcc.gnu.org/wiki/plugins">gcc plugin</a> that replaces GCC's |
| optimizers and code generators with LLVM's. |
| Currently it requires a patched version of gcc-4.5. |
| The plugin can target the x86-32 and x86-64 processor families and has been |
| used successfully on the Darwin, FreeBSD and Linux platforms. |
| The Ada, C, C++ and Fortran languages work well. |
| The plugin is capable of compiling plenty of Obj-C, Obj-C++ and Java but it is |
| not known whether the compiled code actually works or not! |
| </p> |
| |
| <p> |
| The 2.9 release has the following notable changes: |
| <ul> |
| <li>The plugin is much more stable when compiling Fortran.</li> |
| <li>Inline assembly where an asm output is tied to an input of a different size |
| is now supported in many more cases.</li> |
| <li>Basic support for the __float128 type was added. It is now possible to |
| generate LLVM IR from programs using __float128 but code generation does not |
| work yet.</li> |
| <li>Compiling Java programs no longer systematically crashes the plugin.</li> |
| </ul> |
| |
| </div> |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="compiler-rt">compiler-rt: Compiler Runtime Library</a> |
| </h2> |
| |
| <div class="doc_text"> |
| <p> |
| The new LLVM <a href="http://compiler-rt.llvm.org/">compiler-rt project</a> |
| 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).</p> |
| |
| <p>In the LLVM 2.9 timeframe, compiler_rt has had several minor changes for |
| better ARM support, and a fairly major license change. All of the code in the |
| compiler-rt project is now <a href="DeveloperPolicy.html#license">dual |
| licensed</a> under MIT and UIUC license, which allows you to use compiler-rt |
| in applications without the binary copyright reproduction clause. If you |
| prefer the LLVM/UIUC license, you are free to continue using it under that |
| license as well.</p> |
| |
| </div> |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="lldb">LLDB: Low Level Debugger</a> |
| </h2> |
| |
| <div class="doc_text"> |
| <p> |
| <a href="http://lldb.llvm.org/">LLDB</a> is a brand new member of the LLVM |
| umbrella of projects. LLDB is a next generation, high-performance debugger. It |
| is built as a set of reusable components which highly leverage existing |
| libraries in the larger LLVM Project, such as the Clang expression parser, the |
| LLVM disassembler and the LLVM JIT.</p> |
| |
| <p> |
| LLDB is has advanced by leaps and bounds in the 2.9 timeframe. It is |
| dramatically more stable and useful, and includes both a new <a |
| href="http://lldb.llvm.org/tutorial.html">tutorial</a> and a <a |
| href="http://lldb.llvm.org/lldb-gdb.html">side-by-side comparison with |
| GDB</a>.</p> |
| |
| </div> |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="libc++">libc++: C++ Standard Library</a> |
| </h2> |
| |
| <div class="doc_text"> |
| <p> |
| <a href="http://libcxx.llvm.org/">libc++</a> is another new member of the LLVM |
| family. It is an implementation of the C++ standard library, written from the |
| ground up to specifically target the forthcoming C++'0X standard and focus on |
| delivering great performance.</p> |
| |
| <p> |
| In the LLVM 2.9 timeframe, libc++ has had numerous bugs fixed, and is now being |
| co-developed with Clang's C++'0x mode.</p> |
| |
| <p> |
| Like compiler_rt, libc++ is now <a href="DeveloperPolicy.html#license">dual |
| licensed</a> under the MIT and UIUC license, allowing it to be used more |
| permissively. |
| </p> |
| |
| </div> |
| |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="LLBrowse">LLBrowse: IR Browser</a> |
| </h2> |
| |
| <div class="doc_text"> |
| <p> |
| <a href="http://llvm.org/svn/llvm-project/llbrowse/trunk/doc/LLBrowse.html"> |
| LLBrowse</a> is an interactive viewer for LLVM modules. It can load any LLVM |
| module and displays its contents as an expandable tree view, facilitating an |
| easy way to inspect types, functions, global variables, or metadata nodes. It |
| is fully cross-platform, being based on the popular wxWidgets GUI toolkit. |
| </p> |
| </div> |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="vmkit">VMKit</a> |
| </h2> |
| |
| <div class="doc_text"> |
| <p>The <a href="http://vmkit.llvm.org/">VMKit project</a> is an implementation |
| of a Java Virtual Machine (Java VM or JVM) that uses LLVM for static and |
| just-in-time compilation. As of LLVM 2.9, VMKit now supports generational |
| garbage collectors. The garbage collectors are provided by the MMTk framework, |
| and VMKit can be configured to use one of the numerous implemented collectors |
| of MMTk. |
| </p> |
| </div> |
| |
| |
| <!--=========================================================================--> |
| <!-- |
| <h2> |
| <a name="klee">KLEE: A Symbolic Execution Virtual Machine</a> |
| </h2> |
| |
| <div class="doc_text"> |
| <p> |
| <a href="http://klee.llvm.org/">KLEE</a> is a symbolic execution framework for |
| programs in LLVM bitcode form. KLEE tries to symbolically evaluate "all" paths |
| through the application and records state transitions that lead to fault |
| states. This allows it to construct testcases that lead to faults and can even |
| be used to verify some algorithms. |
| </p> |
| |
| <p>UPDATE!</p> |
| </div>--> |
| |
| |
| <!-- *********************************************************************** --> |
| <h1> |
| <a name="externalproj">External Open Source Projects Using LLVM 2.9</a> |
| </h1> |
| <!-- *********************************************************************** --> |
| |
| <div class="doc_text"> |
| |
| <p>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 2.9.</p> |
| </div> |
| |
| |
| <!--=========================================================================--> |
| <h2>Crack Programming Language</h2> |
| |
| <div class="doc_text"> |
| <p> |
| <a href="http://code.google.com/p/crack-language/">Crack</a> aims to provide the |
| ease of development of a scripting language with the performance of a compiled |
| language. The language derives concepts from C++, Java and Python, incorporating |
| object-oriented programming, operator overloading and strong typing.</p> |
| </div> |
| |
| |
| <!--=========================================================================--> |
| <h2>TTA-based Codesign Environment (TCE)</h2> |
| |
| <div class="doc_text"> |
| <p>TCE is a toolset for designing application-specific processors (ASP) based on |
| the Transport triggered architecture (TTA). The toolset provides a complete |
| co-design flow from C/C++ programs down to synthesizable VHDL and parallel |
| program binaries. Processor customization points include the register files, |
| function units, supported operations, and the interconnection network.</p> |
| |
| <p>TCE uses Clang and LLVM for C/C++ language support, target independent |
| optimizations and also for parts of code generation. It generates new LLVM-based |
| code generators "on the fly" for the designed TTA processors and loads them in |
| to the compiler backend as runtime libraries to avoid per-target recompilation |
| of larger parts of the compiler chain.</p> |
| </div> |
| |
| |
| |
| <!--=========================================================================--> |
| <h2>PinaVM</h2> |
| |
| <div class="doc_text"> |
| <p><a href="http://gitorious.org/pinavm/pages/Home">PinaVM</a> is an open |
| source, <a href="http://www.systemc.org/">SystemC</a> front-end. Unlike many |
| other front-ends, PinaVM actually executes the elaboration of the |
| program analyzed using LLVM's JIT infrastructure. It later enriches the |
| bitcode with SystemC-specific information.</p> |
| </div> |
| |
| <!--=========================================================================--> |
| <h2>Pure</h2> |
| |
| <div class="doc_text"> |
| <p><a href="http://pure-lang.googlecode.com/">Pure</a> 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. The interpreter uses LLVM as a backend to JIT-compile Pure |
| programs to fast native code. 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 interface to C and other |
| programming languages (including the ability to load LLVM bitcode |
| modules, and inline C, C++, Fortran and Faust code in Pure programs if |
| the corresponding LLVM-enabled compilers are installed).</p> |
| |
| <p>Pure version 0.47 has been tested and is known to work with LLVM 2.9 |
| (and continues to work with older LLVM releases >= 2.5).</p> |
| </div> |
| |
| <!--=========================================================================--> |
| <h2 id="icedtea">IcedTea Java Virtual Machine Implementation</h2> |
| |
| <div class="doc_text"> |
| <p> |
| <a href="http://icedtea.classpath.org/wiki/Main_Page">IcedTea</a> provides a |
| harness to build OpenJDK using only free software build tools and to provide |
| replacements for the not-yet free parts of OpenJDK. One of the extensions that |
| IcedTea provides is a new JIT compiler named <a |
| href="http://icedtea.classpath.org/wiki/ZeroSharkFaq">Shark</a> which uses LLVM |
| to provide native code generation without introducing processor-dependent |
| code. |
| </p> |
| |
| <p> OpenJDK 7 b112, IcedTea6 1.9 and IcedTea7 1.13 and later have been tested |
| and are known to work with LLVM 2.9 (and continue to work with older LLVM |
| releases >= 2.6 as well).</p> |
| </div> |
| |
| <!--=========================================================================--> |
| <h2>Glasgow Haskell Compiler (GHC)</h2> |
| |
| <div class="doc_text"> |
| <p>GHC is an open source, state-of-the-art programming suite for Haskell, |
| a standard lazy functional programming language. It includes an |
| optimizing static compiler generating good code for a variety of |
| platforms, together with an interactive system for convenient, quick |
| development.</p> |
| |
| <p>In addition to the existing C and native code generators, GHC 7.0 now |
| supports an LLVM code generator. GHC supports LLVM 2.7 and later.</p> |
| </div> |
| |
| <!--=========================================================================--> |
| <h2>Polly - Polyhedral optimizations for LLVM</h2> |
| |
| <div class="doc_text"> |
| <p>Polly is a project that aims to provide advanced memory access optimizations |
| to better take advantage of SIMD units, cache hierarchies, multiple cores or |
| even vector accelerators for LLVM. Built around an abstract mathematical |
| description based on Z-polyhedra, it provides the infrastructure to develop |
| advanced optimizations in LLVM and to connect complex external optimizers. In |
| its first year of existence Polly already provides an exact value-based |
| dependency analysis as well as basic SIMD and OpenMP code generation support. |
| Furthermore, Polly can use PoCC(Pluto) an advanced optimizer for data-locality |
| and parallelism.</p> |
| </div> |
| |
| <!--=========================================================================--> |
| <h2>Rubinius</h2> |
| |
| <div class="doc_text"> |
| <p><a href="http://github.com/evanphx/rubinius">Rubinius</a> is an environment |
| for running Ruby code which strives to write as much of the implementation in |
| Ruby as possible. Combined with a bytecode interpreting VM, it uses LLVM to |
| optimize and compile ruby code down to machine code. Techniques such as type |
| feedback, method inlining, and deoptimization are all used to remove dynamism |
| from ruby execution and increase performance.</p> |
| </div> |
| |
| |
| <!--=========================================================================--> |
| <div class="doc_subsection"> |
| <a name="FAUST">FAUST Real-Time Audio Signal Processing Language</a> |
| </div> |
| |
| <div class="doc_text"> |
| <p> |
| <a href="http://faust.grame.fr">FAUST</a> is a compiled language for real-time |
| audio signal processing. The name FAUST stands for Functional AUdio STream. Its |
| programming model combines two approaches: functional programming and block |
| diagram composition. In addition with the C, C++, JAVA output formats, the |
| Faust compiler can now generate LLVM bitcode, and works with LLVM 2.7-2.9.</p> |
| |
| </div> |
| |
| <!-- *********************************************************************** --> |
| <h1> |
| <a name="whatsnew">What's New in LLVM 2.9?</a> |
| </h1> |
| <!-- *********************************************************************** --> |
| |
| <div class="doc_text"> |
| |
| <p>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. |
| </p> |
| |
| </div> |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="majorfeatures">Major New Features</a> |
| </h2> |
| |
| <div class="doc_text"> |
| |
| <p>LLVM 2.9 includes several major new capabilities:</p> |
| |
| <ul> |
| |
| <li>Type Based Alias Analysis (TBAA) is now implemented and turned on by default |
| in Clang. This allows substantially better load/store optimization in some |
| cases. TBAA can be disabled by passing -fno-strict-aliasing. |
| </li> |
| |
| <li>This release has seen a continued focus on quality of debug information. |
| LLVM now generates much higher fidelity debug information, particularly when |
| debugging optimized code.</li> |
| |
| <li>Inline assembly now supports multiple alternative constraints.</li> |
| |
| <li>A new backend for the NVIDIA PTX virtual ISA (used to target its GPUs) is |
| under rapid development. It is not generally useful in 2.9, but is making |
| rapid progress.</li> |
| |
| </ul> |
| |
| </div> |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="coreimprovements">LLVM IR and Core Improvements</a> |
| </h2> |
| |
| <div class="doc_text"> |
| <p>LLVM IR has several new features for better support of new targets and that |
| expose new optimization opportunities:</p> |
| |
| <ul> |
| <li>The <a href="LangRef.html#bitwiseops">udiv, ashr, lshr, and shl</a> |
| instructions now have support exact and nuw/nsw bits to indicate that they |
| don't overflow or shift out bits. This is useful for optimization of <a |
| href="http://llvm.org/PR8862">pointer differences</a> and other cases.</li> |
| |
| <li>LLVM IR now supports the <a href="LangRef.html#globalvars">unnamed_addr</a> |
| attribute to indicate that constant global variables with identical |
| initializers can be merged. This fixed <a href="http://llvm.org/PR8927">an |
| issue</a> where LLVM would incorrectly merge two globals which were supposed |
| to have distinct addresses.</li> |
| |
| <li>The new <a href="LangRef.html#fnattrs">hotpatch attribute</a> has been added |
| to allow runtime patching of functions.</li> |
| </ul> |
| |
| </div> |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="optimizer">Optimizer Improvements</a> |
| </h2> |
| |
| <div class="doc_text"> |
| |
| <p>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:</p> |
| |
| <ul> |
| <li>Link Time Optimization (LTO) has been improved to use MC for parsing inline |
| assembly and now can build large programs like Firefox 4 on both Mac OS X and |
| Linux.</li> |
| |
| <li>The new -loop-idiom pass recognizes memset/memcpy loops (and memset_pattern |
| on darwin), turning them into library calls, which are typically better |
| optimized than inline code. If you are building a libc and notice that your |
| memcpy and memset functions are compiled into infinite recursion, please build |
| with -ffreestanding or -fno-builtin to disable this pass.</li> |
| |
| <li>A new -early-cse pass does a fast pass over functions to fold constants, |
| simplify expressions, perform simple dead store elimination, and perform |
| common subexpression elimination. It does a good job at catching some of the |
| trivial redundancies that exist in unoptimized code, making later passes more |
| effective.</li> |
| |
| <li>A new -loop-instsimplify pass is used to clean up loop bodies in the loop |
| optimizer.</li> |
| |
| <li>The new TargetLibraryInfo interface allows mid-level optimizations to know |
| whether the current target's runtime library has certain functions. For |
| example, the optimizer can now transform integer-only printf calls to call |
| iprintf, allowing reduced code size for embedded C libraries (e.g. newlib). |
| </li> |
| |
| <li>LLVM has a new <a href="WritingAnLLVMPass.html#RegionPass">RegionPass</a> |
| infrastructure for region-based optimizations.</li> |
| |
| <li>Several optimizer passes have been substantially sped up: |
| GVN is much faster on functions with deep dominator trees and lots of basic |
| blocks. The dominator tree and dominance frontier passes are much faster to |
| compute, and preserved by more passes (so they are computed less often). The |
| -scalar-repl pass is also much faster and doesn't use DominanceFrontier. |
| </li> |
| |
| <li>The Dead Store Elimination pass is more aggressive optimizing stores of |
| different types: e.g. a large store following a small one to the same address. |
| The MemCpyOptimizer pass handles several new forms of memcpy elimination.</li> |
| |
| <li>LLVM now optimizes various idioms for overflow detection into check of the |
| flag register on various CPUs. For example, we now compile: |
| |
| <pre> |
| unsigned long t = a+b; |
| if (t < a) ... |
| </pre> |
| into: |
| <pre> |
| addq %rdi, %rbx |
| jno LBB0_2 |
| </pre> |
| </li> |
| |
| </ul> |
| |
| </div> |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="mc">MC Level Improvements</a> |
| </h2> |
| |
| <div class="doc_text"> |
| <p> |
| The LLVM Machine Code (aka MC) subsystem was created to solve a number |
| of problems in the realm of assembly, disassembly, object file format handling, |
| and a number of other related areas that CPU instruction-set level tools work |
| in.</p> |
| |
| <ul> |
| <li>ELF MC support has matured enough for the integrated assembler to be turned |
| on by default in Clang on X86-32 and X86-64 ELF systems.</li> |
| |
| <li>MC supports and CodeGen uses the <tt>.file</tt> and <tt>.loc</tt> directives |
| for producing line number debug info. This produces more compact line |
| tables and easier to read .s files.</li> |
| |
| <li>MC supports the <tt>.cfi_*</tt> directives for producing DWARF |
| frame information, but it is still not used by CodeGen by default.</li> |
| |
| |
| <li>The MC assembler now generates much better diagnostics for common errors, |
| is much faster at matching instructions, is much more bug-compatible with |
| the GAS assembler, and is now generally useful for a broad range of X86 |
| assembly.</li> |
| |
| <li>We now have some basic <a href="CodeGenerator.html#mc">internals |
| documentation</a> for MC.</li> |
| |
| <li>.td files can now specify assembler aliases directly with the <a |
| href="CodeGenerator.html#na_instparsing">MnemonicAlias and InstAlias</a> |
| tblgen classes.</li> |
| |
| <li>LLVM now has an experimental format-independent object file manipulation |
| library (lib/Object). It supports both PE/COFF and ELF. The llvm-nm tool has |
| been extended to work with native object files, and the new llvm-objdump tool |
| supports disassembly of object files (but no relocations are displayed yet). |
| </li> |
| |
| <li>Win32 PE-COFF support in the MC assembler has made a lot of progress in the |
| 2.9 timeframe, but is still not generally useful.</li> |
| |
| </ul> |
| |
| <p>For more information, please see the <a |
| href="http://blog.llvm.org/2010/04/intro-to-llvm-mc-project.html">Intro to the |
| LLVM MC Project Blog Post</a>. |
| </p> |
| |
| </div> |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="codegen">Target Independent Code Generator Improvements</a> |
| </h2> |
| |
| <div class="doc_text"> |
| |
| <p>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:</p> |
| |
| <ul> |
| <li>The pre-register-allocation (preRA) instruction scheduler models register |
| pressure much more accurately in some cases. This allows the adoption of more |
| aggressive scheduling heuristics without causing spills to be generated. |
| </li> |
| |
| <li>LiveDebugVariables is a new pass that keeps track of debugging information |
| for user variables that are promoted to registers in optimized builds.</li> |
| |
| <li>The scheduler now models operand latency and pipeline forwarding.</li> |
| |
| <li>A major register allocator infrastructure rewrite is underway. It is not on |
| by default for 2.9 and you are not advised to use it, but it has made |
| substantial progress in the 2.9 timeframe: |
| <ul> |
| <li>A new -regalloc=basic "basic" register allocator can be used as a simple |
| fallback when debugging. It uses the new infrastructure.</li> |
| <li>New infrastructure is in place for live range splitting. "SplitKit" can |
| break a live interval into smaller pieces while preserving SSA form, and |
| SpillPlacement can help find the best split points. This is a work in |
| progress so the API is changing quickly.</li> |
| <li>The inline spiller has learned to clean up after live range splitting. It |
| can hoist spills out of loops, and it can eliminate redundant spills.</li> |
| <li>Rematerialization works with live range splitting.</li> |
| <li>The new "greedy" register allocator using live range splitting. This will |
| be the default register allocator in the next LLVM release, but it is not |
| turned on by default in 2.9.</li> |
| </ul> |
| </li> |
| </ul> |
| </div> |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="x86">X86-32 and X86-64 Target Improvements</a> |
| </h2> |
| |
| <div class="doc_text"> |
| <p>New features and major changes in the X86 target include: |
| </p> |
| |
| <ul> |
| <li>LLVM 2.9 includes a complete reimplementation of the MMX instruction set. |
| The reimplementation uses a new LLVM IR <a |
| href="LangRef.html#t_x86mmx">x86_mmx</a> type to ensure that MMX operations |
| are <em>only</em> generated from source that uses MMX builtin operations. With |
| this, random types like <2 x i32> are not turned into MMX operations |
| (which can be catastrophic without proper "emms" insertion). Because the X86 |
| code generator always generates reliable code, the -disable-mmx flag is now |
| removed. |
| </li> |
| |
| <li>X86 support for FS/GS relative loads and stores using <a |
| href="CodeGenerator.html#x86_memory">address space 256/257</a> works reliably |
| now.</li> |
| |
| <li>LLVM 2.9 generates much better code in several cases by using adc/sbb to |
| avoid generation of conditional move instructions for conditional increment |
| and other idioms.</li> |
| |
| <li>The X86 backend has adopted a new preRA scheduling mode, "list-ilp", to |
| shorten the height of instruction schedules without inducing register spills. |
| </li> |
| |
| <li>The MC assembler supports 3dNow! and 3DNowA instructions.</li> |
| |
| <li>Several bugs have been fixed for Windows x64 code generator.</li> |
| </ul> |
| |
| </div> |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="ARM">ARM Target Improvements</a> |
| </h2> |
| |
| <div class="doc_text"> |
| <p>New features of the ARM target include: |
| </p> |
| |
| <ul> |
| <li>The ARM backend now has a fast instruction selector, which dramatically |
| improves -O0 compile times.</li> |
| <li>The ARM backend has new tuning for Cortex-A8 and Cortex-A9 CPUs.</li> |
| <li>The __builtin_prefetch builtin (and llvm.prefetch intrinsic) is compiled |
| into prefetch instructions instead of being discarded.</li> |
| |
| <li> The ARM backend preRA scheduler now models machine resources at cycle |
| granularity. This allows the scheduler to both accurately model |
| instruction latency and avoid overcommitting functional units.</li> |
| |
| <li>Countless ARM microoptimizations have landed in LLVM 2.9.</li> |
| </ul> |
| </div> |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="OtherTS">Other Target Specific Improvements</a> |
| </h2> |
| |
| <div class="doc_text"> |
| <ul> |
| <li>MicroBlaze: major updates for aggressive delay slot filler, MC-based |
| assembly printing, assembly instruction parsing, ELF .o file emission, and MC |
| instruction disassembler have landed.</li> |
| |
| <li>SPARC: Many improvements, including using the Y registers for |
| multiplications and addition of a simple delay slot filler.</li> |
| |
| <li>PowerPC: The backend has been largely MC'ized and is ready to support |
| directly writing out mach-o object files. No one seems interested in finishing |
| this final step though.</li> |
| |
| </ul> |
| </div> |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="changes">Major Changes and Removed Features</a> |
| </h2> |
| |
| <div class="doc_text"> |
| |
| <p>If you're already an LLVM user or developer with out-of-tree changes based |
| on LLVM 2.8, this section lists some "gotchas" that you may run into upgrading |
| from the previous release.</p> |
| |
| <ul> |
| <li><b>This is the last release to support the llvm-gcc frontend.</b></li> |
| |
| <li>LLVM has a new <a href="CodingStandards.html#ll_naming">naming |
| convention standard</a>, though the codebase hasn't fully adopted it yet.</li> |
| |
| <li>The new DIBuilder class provides a simpler interface for front ends to |
| encode debug info in LLVM IR, and has replaced DIFactory.</li> |
| |
| <li>LLVM IR and other tools always work on normalized target triples (which have |
| been run through <tt>Triple::normalize</tt>).</li> |
| |
| <li>The target triple x86_64--mingw64 is obsoleted. Use x86_64--mingw32 |
| instead.</li> |
| |
| <li>The PointerTracking pass has been removed from mainline, and moved to The |
| ClamAV project (its only client).</li> |
| |
| <li>The LoopIndexSplit, LiveValues, SimplifyHalfPowrLibCalls, GEPSplitter, and |
| PartialSpecialization passes were removed. They were unmaintained, |
| buggy, or deemed to be a bad idea.</li> |
| </ul> |
| |
| </div> |
| |
| <!--=========================================================================--> |
| <h2> |
| <a name="api_changes">Internal API Changes</a> |
| </h2> |
| |
| <div class="doc_text"> |
| |
| <p>In addition, many APIs have changed in this release. Some of the major |
| LLVM API changes are:</p> |
| |
| <ul> |
| <li>include/llvm/System merged into include/llvm/Support.</li> |
| <li>The <a href="http://llvm.org/PR5207">llvm::APInt API</a> was significantly |
| cleaned up.</li> |
| |
| <li>In the code generator, MVT::Flag was renamed to MVT::Glue to more accurately |
| describe its behavior.</li> |
| |
| <li>The system_error header from C++0x was added, and is now pervasively used to |
| capture and handle i/o and other errors in LLVM.</li> |
| |
| <li>The old sys::Path API has been deprecated in favor of the new PathV2 API, |
| which is more efficient and flexible.</li> |
| </ul> |
| </div> |
| |
| <!-- *********************************************************************** --> |
| <h1> |
| <a name="knownproblems">Known Problems</a> |
| </h1> |
| <!-- *********************************************************************** --> |
| |
| <div class="doc_text"> |
| |
| <p>This section contains significant known problems with the LLVM system, |
| listed by component. If you run into a problem, please check the <a |
| href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if |
| there isn't already one.</p> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <h2> |
| <a name="experimental">Experimental features included with this release</a> |
| </h2> |
| |
| <div class="doc_text"> |
| |
| <p>The following components of this LLVM release are either untested, known to |
| be broken or unreliable, or are in early development. These components should |
| not be relied on, and bugs should not be filed against them, but they may be |
| useful to some people. In particular, if you would like to work on one of these |
| components, please contact us on the <a |
| href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p> |
| |
| <ul> |
| <li>The Alpha, Blackfin, CellSPU, MicroBlaze, MSP430, MIPS, PTX, SystemZ |
| and XCore backends are experimental.</li> |
| <li><tt>llc</tt> "<tt>-filetype=obj</tt>" is experimental on all targets |
| other than darwin and ELF X86 systems.</li> |
| |
| </ul> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <h2> |
| <a name="x86-be">Known problems with the X86 back-end</a> |
| </h2> |
| |
| <div class="doc_text"> |
| |
| <ul> |
| <li>The X86 backend does not yet support |
| all <a href="http://llvm.org/PR879">inline assembly that uses the X86 |
| floating point stack</a>. It supports the 'f' and 't' constraints, but not |
| 'u'.</li> |
| <li>The X86-64 backend does not yet support the LLVM IR instruction |
| <tt>va_arg</tt>. Currently, front-ends support variadic |
| argument constructs on X86-64 by lowering them manually.</li> |
| <li>Windows x64 (aka Win64) code generator has a few issues. |
| <ul> |
| <li>llvm-gcc cannot build the mingw-w64 runtime currently |
| due to lack of support for the 'u' inline assembly |
| constraint and for X87 floating point inline assembly.</li> |
| <li>On mingw-w64, you will see unresolved symbol <tt>__chkstk</tt> |
| due to <a href="http://llvm.org/bugs/show_bug.cgi?id=8919">Bug 8919</a>. |
| It is fixed in <a href="http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110321/118499.html">r128206</a>.</li> |
| <li>Miss-aligned MOVDQA might crash your program. It is due to |
| <a href="http://llvm.org/bugs/show_bug.cgi?id=9483">Bug 9483</a>, |
| lack of handling aligned internal globals.</li> |
| </ul> |
| </li> |
| |
| </ul> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <h2> |
| <a name="ppc-be">Known problems with the PowerPC back-end</a> |
| </h2> |
| |
| <div class="doc_text"> |
| |
| <ul> |
| <li>The Linux PPC32/ABI support needs testing for the interpreter and static |
| compilation, and lacks support for debug information.</li> |
| </ul> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <h2> |
| <a name="arm-be">Known problems with the ARM back-end</a> |
| </h2> |
| |
| <div class="doc_text"> |
| |
| <ul> |
| <li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6 |
| processors, thumb programs can crash or produce wrong |
| results (<a href="http://llvm.org/PR1388">PR1388</a>).</li> |
| <li>Compilation for ARM Linux OABI (old ABI) is supported but not fully tested. |
| </li> |
| </ul> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <h2> |
| <a name="sparc-be">Known problems with the SPARC back-end</a> |
| </h2> |
| |
| <div class="doc_text"> |
| |
| <ul> |
| <li>The SPARC backend only supports the 32-bit SPARC ABI (-m32); it does not |
| support the 64-bit SPARC ABI (-m64).</li> |
| </ul> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <h2> |
| <a name="mips-be">Known problems with the MIPS back-end</a> |
| </h2> |
| |
| <div class="doc_text"> |
| |
| <ul> |
| <li>64-bit MIPS targets are not supported yet.</li> |
| </ul> |
| |
| </div> |
| |
| <!-- ======================================================================= --> |
| <h2> |
| <a name="alpha-be">Known problems with the Alpha back-end</a> |
| </h2> |
| |
| <div class="doc_text"> |
| |
| <ul> |
| |
| <li>On 21164s, some rare FP arithmetic sequences which may trap do not have the |
| appropriate nops inserted to ensure restartability.</li> |
| |
| </ul> |
| </div> |
| |
| <!-- ======================================================================= --> |
| <h2> |
| <a name="c-be">Known problems with the C back-end</a> |
| </h2> |
| |
| <div class="doc_text"> |
| |
| <p>The C backend has numerous problems and is not being actively maintained. |
| Depending on it for anything serious is not advised.</p> |
| |
| <ul> |
| <li><a href="http://llvm.org/PR802">The C backend has only basic support for |
| inline assembly code</a>.</li> |
| <li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common |
| C++ programs</a>, preventing intermixing between C++ compiled by the CBE and |
| C++ code compiled with <tt>llc</tt> or native compilers.</li> |
| <li>The C backend does not support all exception handling constructs.</li> |
| <li>The C backend does not support arbitrary precision integers.</li> |
| </ul> |
| |
| </div> |
| |
| |
| <!-- ======================================================================= --> |
| <h2> |
| <a name="llvm-gcc">Known problems with the llvm-gcc front-end</a> |
| </h2> |
| |
| <div class="doc_text"> |
| |
| <p><b>LLVM 2.9 will be the last release of llvm-gcc.</b></p> |
| |
| <p>llvm-gcc is generally very stable for the C family of languages. The only |
| major language feature of GCC not supported by llvm-gcc is the |
| <tt>__builtin_apply</tt> family of builtins. However, some extensions |
| are only supported on some targets. For example, trampolines are only |
| supported on some targets (these are used when you take the address of a |
| nested function).</p> |
| |
| <p>Fortran support generally works, but there are still several unresolved bugs |
| in <a href="http://llvm.org/bugs/">Bugzilla</a>. Please see the |
| tools/gfortran component for details. Note that llvm-gcc is missing major |
| Fortran performance work in the frontend and library that went into GCC after |
| 4.2. If you are interested in Fortran, we recommend that you consider using |
| <a href="#dragonegg">dragonegg</a> instead.</p> |
| |
| <p>The llvm-gcc 4.2 Ada compiler has basic functionality, but is no longer being |
| actively maintained. If you are interested in Ada, we recommend that you |
| consider using <a href="#dragonegg">dragonegg</a> instead.</p> |
| </div> |
| |
| <!-- *********************************************************************** --> |
| <h1> |
| <a name="additionalinfo">Additional Information</a> |
| </h1> |
| <!-- *********************************************************************** --> |
| |
| <div class="doc_text"> |
| |
| <p>A wide variety of additional information is available on the <a |
| href="http://llvm.org">LLVM web page</a>, in particular in the <a |
| href="http://llvm.org/docs/">documentation</a> section. The web page also |
| contains versions of the API documentation which is up-to-date with the |
| Subversion version of the source code. |
| You can access versions of these documents specific to this release by going |
| into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p> |
| |
| <p>If you have any questions or comments about LLVM, please feel free to contact |
| us via the <a href="http://llvm.org/docs/#maillist"> mailing |
| lists</a>.</p> |
| |
| </div> |
| |
| <!-- *********************************************************************** --> |
| |
| <hr> |
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