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| <title>LLVM 2.7 Release Notes</title> | |
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| <body> | |
| <div class="doc_title">LLVM 2.7 Release Notes</div> | |
| <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 2.7</a></li> | |
| <li><a href="#whatsnew">What's New in LLVM 2.7?</a></li> | |
| <li><a href="GettingStarted.html">Installation Instructions</a></li> | |
| <li><a href="#portability">Portability and Supported Platforms</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 2.8 | |
| release.<br> | |
| You may prefer the | |
| <a href="http://llvm.org/releases/2.6/docs/ReleaseNotes.html">LLVM 2.7 | |
| Release Notes</a>.</h1>--> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_section"> | |
| <a name="intro">Introduction</a> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_text"> | |
| <p>This document contains the release notes for the LLVM Compiler | |
| 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 <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> | |
| <!-- | |
| Almost dead code. | |
| include/llvm/Analysis/LiveValues.h => Dan | |
| lib/Transforms/IPO/MergeFunctions.cpp => consider for 2.8. | |
| llvm/Analysis/PointerTracking.h => Edwin wants this, consider for 2.8. | |
| ABCD, GEPSplitterPass | |
| MSIL backend? | |
| lib/Transforms/Utils/SSI.cpp -> ABCD depends on it. | |
| --> | |
| <!-- Features that need text if they're finished for 2.7: | |
| combiner-aa? | |
| strong phi elim | |
| llvm.dbg.value: variable debug info for optimized code | |
| loop dependence analysis | |
| --> | |
| <!-- for announcement email: | |
| Logo web page. | |
| llvm devmtg | |
| compiler_rt | |
| KLEE web page at klee.llvm.org | |
| Many new papers added to /pubs/ | |
| Mention gcc plugin. | |
| --> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_section"> | |
| <a name="subproj">Sub-project Status Update</a> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_text"> | |
| <p> | |
| 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. | |
| </p> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a> | |
| </div> | |
| <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 and Objective-C on x86 (32- and 64-bit).</p> | |
| <p>In the LLVM 2.7 time-frame, the Clang team has made many improvements:</p> | |
| <ul> | |
| <li>C++ Support: Clang is now capable of self-hosting! While still | |
| alpha-quality, Clang's C++ support has matured enough to build LLVM and Clang, | |
| and C++ is now enabled by default. See the <a | |
| href="http://clang.llvm.org/cxx_compatibility.html">Clang C++ compatibility | |
| page</a> for common C++ migration issues.</li> | |
| <li>Objective-C: Clang now includes experimental support for an updated | |
| Objective-C ABI on non-Darwin platforms. This includes support for non-fragile | |
| instance variables and accelerated proxies, as well as greater potential for | |
| future optimisations. The new ABI is used when compiling with the | |
| -fobjc-nonfragile-abi and -fgnu-runtime options. Code compiled with these | |
| options may be mixed with code compiled with GCC or clang using the old GNU ABI, | |
| but requires the libobjc2 runtime from the GNUstep project.</li> | |
| <li>New warnings: Clang contains a number of new warnings, including | |
| control-flow warnings (unreachable code, missing return statements in a | |
| non-<code>void</code> function, etc.), sign-comparison warnings, and improved | |
| format-string warnings.</li> | |
| <li>CIndex API and Python bindings: Clang now includes a C API as part of the | |
| CIndex library. Although we may make some changes to the API in the future, it | |
| is intended to be stable and has been designed for use by external projects. See | |
| the Clang | |
| doxygen <a href="http://clang.llvm.org/doxygen/group__CINDEX.html">CIndex</a> | |
| documentation for more details. The CIndex API also includes a preliminary | |
| set of Python bindings.</li> | |
| <li>ARM Support: Clang now has ABI support for both the Darwin and Linux ARM | |
| ABIs. Coupled with many improvements to the LLVM ARM backend, Clang is now | |
| suitable for use as a beta quality ARM compiler.</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="clangsa">Clang Static Analyzer</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>The <a href="http://clang-analyzer.llvm.org/">Clang Static Analyzer</a> | |
| project is an effort to use static source code analysis techniques to | |
| automatically find bugs in C and Objective-C programs (and hopefully <a | |
| href="http://clang-analyzer.llvm.org/dev_cxx.html">C++ in the | |
| future</a>!). The tool is very good at finding bugs that occur on specific | |
| paths through code, such as on error conditions.</p> | |
| <p>In the LLVM 2.7 time-frame, the analyzer core has made several major and | |
| minor improvements, including better support for tracking the fields of | |
| structures, initial support (not enabled by default yet) for doing | |
| interprocedural (cross-function) analysis, and new checks have been added. | |
| </p> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="vmkit">VMKit: JVM/CLI Virtual Machine Implementation</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p> | |
| The <a href="http://vmkit.llvm.org/">VMKit project</a> is an implementation of | |
| a JVM and a CLI Virtual Machine (Microsoft .NET is an | |
| implementation of the CLI) using LLVM for static and just-in-time | |
| compilation.</p> | |
| <p> | |
| With the release of LLVM 2.7, VMKit has shifted to a great framework for writing | |
| virtual machines. VMKit now offers precise and efficient garbage collection with | |
| multi-threading support, thanks to the MMTk memory management toolkit, as well | |
| as just in time and ahead of time compilation with LLVM. The major changes in | |
| VMKit 0.27 are:</p> | |
| <ul> | |
| <li>Garbage collection: VMKit now uses the MMTk toolkit for garbage collectors. | |
| The first collector to be ported is the MarkSweep collector, which is precise, | |
| and drastically improves the performance of VMKit.</li> | |
| <li>Line number information in the JVM: by using the debug metadata of LLVM, the | |
| JVM now supports precise line number information, useful when printing a stack | |
| trace.</li> | |
| <li>Interface calls in the JVM: we implemented a variant of the Interface Method | |
| Table technique for interface calls in the JVM. | |
| </li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="compiler-rt">compiler-rt: Compiler Runtime Library</a> | |
| </div> | |
| <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> | |
| All of the code in the compiler-rt project is available under the standard LLVM | |
| License, a "BSD-style" license. New in LLVM 2.7: compiler_rt now | |
| supports ARM targets.</p> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="dragonegg">DragonEgg: llvm-gcc ported to gcc-4.5</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p> | |
| <a href="http://dragonegg.llvm.org/">DragonEgg</a> is a port of llvm-gcc to | |
| gcc-4.5. Unlike llvm-gcc, which makes many intrusive changes to the underlying | |
| gcc-4.2 code, dragonegg in theory does not require any gcc-4.5 modifications | |
| whatsoever (currently one small patch is needed). This is thanks to the new | |
| <a href="http://gcc.gnu.org/wiki/plugins">gcc plugin architecture</a>, which | |
| makes it possible to modify the behaviour of gcc at runtime by loading a plugin, | |
| which is nothing more than a dynamic library which conforms to the gcc plugin | |
| interface. DragonEgg is a gcc plugin that causes the LLVM optimizers to be run | |
| instead of the gcc optimizers, and the LLVM code generators instead of the gcc | |
| code generators, just like llvm-gcc. To use it, you add | |
| "-fplugin=path/dragonegg.so" to the gcc-4.5 command line, and gcc-4.5 magically | |
| becomes llvm-gcc-4.5! | |
| </p> | |
| <p> | |
| DragonEgg is still a work in progress. Currently C works very well, while C++, | |
| Ada and Fortran work fairly well. All other languages either don't work at all, | |
| or only work poorly. For the moment only the x86-32 and x86-64 targets are | |
| supported, and only on linux and darwin (darwin needs an additional gcc patch). | |
| </p> | |
| <p> | |
| DragonEgg is a new project which is seeing its first release with llvm-2.7. | |
| </p> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="mc">llvm-mc: Machine Code Toolkit</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p> | |
| The LLVM Machine Code (aka MC) sub-project of LLVM 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. It is a sub-project of LLVM which provides it with a number of advantages | |
| over other compilers that do not have tightly integrated assembly-level tools. | |
| For a gentle introduction, 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> | |
| <p>2.7 includes major parts of the work required by the new MC Project. A few | |
| targets have been refactored to support it, and work is underway to support a | |
| native assembler in LLVM. This work is not complete in LLVM 2.7, but it has | |
| made substantially more progress on LLVM mainline.</p> | |
| <p>One minor example of what MC can do is to transcode an AT&T syntax | |
| X86 .s file into intel syntax. You can do this with something like:</p> | |
| <pre> | |
| llvm-mc foo.s -output-asm-variant=1 -o foo-intel.s | |
| </pre> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_section"> | |
| <a name="externalproj">External Open Source Projects Using LLVM 2.7</a> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <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 2.7.</p> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="pure">Pure</a> | |
| </div> | |
| <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. 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.</p> | |
| <p>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).</p> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="RoadsendPHP">Roadsend PHP</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p> | |
| <a href="http://code.roadsend.com/rphp">Roadsend PHP</a> (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. | |
| </p> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="UnladenSwallow">Unladen Swallow</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p> | |
| <a href="http://code.google.com/p/unladen-swallow/">Unladen Swallow</a> is a | |
| branch of <a href="http://python.org/">Python</a> intended to be fully | |
| compatible and significantly faster. It uses LLVM's optimization passes and JIT | |
| compiler. | |
| </p> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="tce">TTA-based Codesign Environment (TCE)</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p> | |
| <a href="http://tce.cs.tut.fi/">TCE</a> 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 llvm-gcc/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> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="safecode">SAFECode Compiler</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p> | |
| <a href="http://safecode.cs.illinois.edu">SAFECode</a> is a memory safe C | |
| compiler built using LLVM. It takes standard, unannotated C code, analyzes the | |
| code to ensure that memory accesses and array indexing operations are safe, and | |
| instruments the code with run-time checks when safety cannot be proven | |
| statically. | |
| </p> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="icedtea">IcedTea Java Virtual Machine Implementation</a> | |
| </div> | |
| <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>Icedtea6 1.8 and later have been tested and are known to work with | |
| LLVM 2.7 (and continue to work with older LLVM releases >= 2.6 as well). | |
| </p> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="llvm-lua">LLVM-Lua</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p> | |
| <a href="http://code.google.com/p/llvm-lua/">LLVM-Lua</a> uses LLVM | |
| to add JIT and static compiling support to the Lua VM. Lua | |
| bytecode is analyzed to remove type checks, then LLVM is used to compile the | |
| bytecode down to machine code. | |
| </p> | |
| <p>LLVM-Lua 1.2.0 have been tested and is known to work with LLVM 2.7. | |
| </p> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="MacRuby">MacRuby</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p> | |
| <a href="http://macruby.org">MacRuby</a> is an implementation of Ruby based on | |
| core Mac OS technologies, sponsored by Apple Inc. It uses LLVM at runtime for | |
| optimization passes, JIT compilation and exception handling. It also allows | |
| static (ahead-of-time) compilation of Ruby code straight to machine code. | |
| </p> | |
| <p>The upcoming MacRuby 0.6 release works with LLVM 2.7. | |
| </p> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="GHC">Glasgow Haskell Compiler (GHC)</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p> | |
| <a href="http://www.haskell.org/ghc/">GHC</a> 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 now | |
| supports an <a | |
| href="http://hackage.haskell.org/trac/ghc/wiki/Commentary/Compiler/Backends/LLVM">LLVM | |
| code generator</a>. GHC supports LLVM 2.7.</p> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_section"> | |
| <a name="whatsnew">What's New in LLVM 2.7?</a> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <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> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="orgchanges">LLVM Community Changes</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>In addition to changes to the code, between LLVM 2.6 and 2.7, a number of | |
| organization changes have happened: | |
| </p> | |
| <ul> | |
| <li>LLVM has a new <a href="http://llvm.org/Logo.html">official logo</a>!</li> | |
| <li>Ted Kremenek and Doug Gregor have stepped forward as <a | |
| href="http://llvm.org/docs/DeveloperPolicy.html#owners">Code Owners</a> of the | |
| Clang static analyzer and the Clang frontend, respectively.</li> | |
| <li>LLVM now has an <a href="http://blog.llvm.org">official Blog</a> at | |
| <a href="http://blog.llvm.org">http://blog.llvm.org</a>. This is a great way | |
| to learn about new LLVM-related features as they are implemented. Several | |
| features in this release are already explained on the blog.</li> | |
| <li>The LLVM web pages are now checked into the SVN server, in the "www", | |
| "www-pubs" and "www-releases" SVN modules. Previously they were hidden in a | |
| largely inaccessible old CVS server.</li> | |
| <li><a href="http://llvm.org">llvm.org</a> is now hosted on a new (and much | |
| faster) server. It is still graciously hosted at the University of Illinois | |
| of Urbana Champaign.</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="majorfeatures">Major New Features</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>LLVM 2.7 includes several major new capabilities:</p> | |
| <ul> | |
| <li>2.7 includes initial support for the <a | |
| href="http://en.wikipedia.org/wiki/MicroBlaze">MicroBlaze</a> target. | |
| MicroBlaze is a soft processor core designed for Xilinx FPGAs.</li> | |
| <li>2.7 includes a new LLVM IR "extensible metadata" feature. This feature | |
| supports many different use cases, including allowing front-end authors to | |
| encode source level information into LLVM IR, which is consumed by later | |
| language-specific passes. This is a great way to do high-level optimizations | |
| like devirtualization, type-based alias analysis, etc. See the <a | |
| href="http://blog.llvm.org/2010/04/extensible-metadata-in-llvm-ir.html"> | |
| Extensible Metadata Blog Post</a> for more information.</li> | |
| <li>2.7 encodes <a href="SourceLevelDebugging.html">debug information</a> | |
| in a completely new way, built on extensible metadata. The new implementation | |
| is much more memory efficient and paves the way for improvements to optimized | |
| code debugging experience.</li> | |
| <li>2.7 now directly supports taking the address of a label and doing an | |
| indirect branch through a pointer. This is particularly useful for | |
| interpreter loops, and is used to implement the GCC "address of label" | |
| extension. For more information, see the <a | |
| href="http://blog.llvm.org/2010/01/address-of-label-and-indirect-branches.html"> | |
| Address of Label and Indirect Branches in LLVM IR Blog Post</a>. | |
| <li>2.7 is the first release to start supporting APIs for assembling and | |
| disassembling target machine code. These APIs are useful for a variety of | |
| low level clients, and are surfaced in the new "enhanced disassembly" API. | |
| For more information see the <a | |
| href="http://blog.llvm.org/2010/01/x86-disassembler.html">The X86 | |
| Disassembler Blog Post</a> for more information.</li> | |
| <li>2.7 includes major parts of the work required by the new MC Project, | |
| see the <a href="#mc">MC update above</a> for more information.</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="coreimprovements">LLVM IR and Core Improvements</a> | |
| </div> | |
| <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>LLVM IR now supports a 16-bit "half float" data type through <a | |
| href="LangRef.html#int_fp16">two new intrinsics</a> and APFloat support.</li> | |
| <li>LLVM IR supports two new <a href="LangRef.html#fnattrs">function | |
| attributes</a>: inlinehint and alignstack(n). The former is a hint to the | |
| optimizer that a function was declared 'inline' and thus the inliner should | |
| weight it higher when considering inlining it. The later | |
| indicates to the code generator that the function diverges from the platform | |
| ABI on stack alignment.</li> | |
| <li>The new <a href="LangRef.html#int_objectsize">llvm.objectsize</a> intrinsic | |
| allows the optimizer to infer the sizes of memory objects in some cases. | |
| This intrinsic is used to implement the GCC <tt>__builtin_object_size</tt> | |
| extension.</li> | |
| <li>LLVM IR now supports marking load and store instructions with <a | |
| href="LangRef.html#i_load">"non-temporal" hints</a> (building on the new | |
| metadata feature). This hint encourages the code | |
| generator to generate non-temporal accesses when possible, which are useful | |
| for code that is carefully managing cache behavior. Currently, only the | |
| X86 backend provides target support for this feature.</li> | |
| <li>LLVM 2.7 has pre-alpha support for <a | |
| href="LangRef.html#t_union">unions in LLVM IR</a>. | |
| Unfortunately, this support is not really usable in 2.7, so if you're | |
| interested in pushing it forward, please help contribute to LLVM mainline.</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="optimizer">Optimizer Improvements</a> | |
| </div> | |
| <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>The inliner reuses now merges arrays stack objects in different callees when | |
| inlining multiple call sites into one function. This reduces the stack size | |
| of the resultant function.</li> | |
| <li>The -basicaa alias analysis pass (which is the default) has been improved to | |
| be less dependent on "type safe" pointers. It can now look through bitcasts | |
| and other constructs more aggressively, allowing better load/store | |
| optimization.</li> | |
| <li>The load elimination optimization in the GVN Pass [<a | |
| href="http://blog.llvm.org/2009/12/introduction-to-load-elimination-in-gvn.html">intro | |
| blog post</a>] has been substantially improved to be more aggressive about | |
| partial redundancy elimination and do more aggressive phi translation. Please | |
| see the <a | |
| href="http://blog.llvm.org/2009/12/advanced-topics-in-redundant-load.html"> | |
| Advanced Topics in Redundant Load Elimination with a Focus on PHI Translation | |
| Blog Post</a> for more details.</li> | |
| <li>The module <a href="LangRef.html#datalayout">target data string</a> now | |
| includes a notion of 'native' integer data types for the target. This | |
| helps mid-level optimizations avoid promoting complex sequences of | |
| operations to data types that are not natively supported (e.g. converting | |
| i32 operations to i64 on 32-bit chips).</li> | |
| <li>The mid-level optimizer is now conservative when operating on a module with | |
| no target data. Previously, it would default to SparcV9 settings, which is | |
| not what most people expected.</li> | |
| <li>Jump threading is now much more aggressive at simplifying correlated | |
| conditionals and threading blocks with otherwise complex logic. It has | |
| subsumed the old "Conditional Propagation" pass, and -condprop has been | |
| removed from LLVM 2.7.</li> | |
| <li>The -instcombine pass has been refactored from being one huge file to being | |
| a library of its own. Internally, it uses a customized IRBuilder to clean | |
| it up and simplify it.</li> | |
| <li>The optimal edge profiling pass is reliable and much more complete than in | |
| 2.6. It can be used with the llvm-prof tool but isn't wired up to the | |
| llvm-gcc and clang command line options yet.</li> | |
| <li>A new experimental alias analysis implementation, -scev-aa, has been added. | |
| It uses LLVM's Scalar Evolution implementation to do symbolic analysis of | |
| pointer offset expressions to disambiguate pointers. It can catch a few | |
| cases that basicaa cannot, particularly in complex loop nests.</li> | |
| <li>The default pass ordering has been tweaked for improved optimization | |
| effectiveness.</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="executionengine">Interpreter and JIT Improvements</a> | |
| </div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li>The JIT now supports generating debug information and is compatible with | |
| the new GDB 7.0 (and later) interfaces for registering dynamically generated | |
| debug info.</li> | |
| <li>The JIT now <a href="http://llvm.org/PR5184">defaults | |
| to compiling eagerly</a> to avoid a race condition in the lazy JIT. | |
| Clients that still want the lazy JIT can switch it on by calling | |
| <tt>ExecutionEngine::DisableLazyCompilation(false)</tt>.</li> | |
| <li>It is now possible to create more than one JIT instance in the same process. | |
| These JITs can generate machine code in parallel, | |
| although <a href="http://llvm.org/docs/ProgrammersManual.html#jitthreading">you | |
| still have to obey the other threading restrictions</a>.</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="codegen">Target Independent Code Generator Improvements</a> | |
| </div> | |
| <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 'llc -asm-verbose' option (which is now the default) has been enhanced | |
| to emit many useful comments to .s files indicating information about spill | |
| slots and loop nest structure. This should make it much easier to read and | |
| understand assembly files. This is wired up in llvm-gcc and clang to | |
| the <tt>-fverbose-asm</tt> option.</li> | |
| <li>New LSR with "full strength reduction" mode, which can reduce address | |
| register pressure in loops where address generation is important.</li> | |
| <li>A new codegen level Common Subexpression Elimination pass (MachineCSE) | |
| is available and enabled by default. It catches redundancies exposed by | |
| lowering.</li> | |
| <li>A new pre-register-allocation tail duplication pass is available and enabled | |
| by default, it can substantially improve branch prediction quality in some | |
| cases.</li> | |
| <li>A new sign and zero extension optimization pass (OptimizeExtsPass) | |
| is available and enabled by default. This pass can takes advantage | |
| architecture features like x86-64 implicit zero extension behavior and | |
| sub-registers.</li> | |
| <li>The code generator now supports a mode where it attempts to preserve the | |
| order of instructions in the input code. This is important for source that | |
| is hand scheduled and extremely sensitive to scheduling. It is compatible | |
| with the GCC <tt>-fno-schedule-insns</tt> option.</li> | |
| <li>The target-independent code generator now supports generating code with | |
| arbitrary numbers of result values. Returning more values than was | |
| previously supported is handled by returning through a hidden pointer. In | |
| 2.7, only the X86 and XCore targets have adopted support for this | |
| though.</li> | |
| <li>The code generator now supports generating code that follows the | |
| <a href="LangRef.html#callingconv">Glasgow Haskell Compiler Calling | |
| Convention</a> and ABI.</li> | |
| <li>The "<a href="CodeGenerator.html#selectiondag_select">DAG instruction | |
| selection</a>" phase of the code generator has been largely rewritten for | |
| 2.7. Previously, tblgen spit out tons of C++ code which was compiled and | |
| linked into the target to do the pattern matching, now it emits a much | |
| smaller table which is read by the target-independent code. The primary | |
| advantages of this approach is that the size and compile time of various | |
| targets is much improved. The X86 code generator shrunk by 1.5MB of code, | |
| for example.</li> | |
| <li>Almost the entire code generator has switched to emitting code through the | |
| MC interfaces instead of printing textually to the .s file. This led to a | |
| number of cleanups and speedups. In 2.7, debug an exception handling | |
| information does not go through MC yet.</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="x86">X86-32 and X86-64 Target Improvements</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>New features of the X86 target include: | |
| </p> | |
| <ul> | |
| <li>The X86 backend now optimizes tails calls much more aggressively for | |
| functions that use the standard C calling convention.</li> | |
| <li>The X86 backend now models scalar SSE registers as subregs of the SSE vector | |
| registers, making the code generator more aggressive in cases where scalars | |
| and vector types are mixed.</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="ARM">ARM Target Improvements</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>New features of the ARM target include: | |
| </p> | |
| <ul> | |
| <li>The ARM backend now generates instructions in unified assembly syntax.</li> | |
| <li>llvm-gcc now has complete support for the ARM v7 NEON instruction set. This | |
| support differs slightly from the GCC implementation. Please see the | |
| <a | |
| href="http://blog.llvm.org/2010/04/arm-advanced-simd-neon-intrinsics-and.html"> | |
| ARM Advanced SIMD (NEON) Intrinsics and Types in LLVM Blog Post</a> for | |
| helpful information if migrating code from GCC to LLVM-GCC.</li> | |
| <li>The ARM and Thumb code generators now use register scavenging for stack | |
| object address materialization. This allows the use of R3 as a general | |
| purpose register in Thumb1 code, as it was previous reserved for use in | |
| stack address materialization. Secondly, sequential uses of the same | |
| value will now re-use the materialized constant.</li> | |
| <li>The ARM backend now has good support for ARMv4 targets and has been tested | |
| on StrongARM hardware. Previously, LLVM only supported ARMv4T and | |
| newer chips.</li> | |
| <li>Atomic builtins are now supported for ARMv6 and ARMv7 (__sync_synchronize, | |
| __sync_fetch_and_add, etc.).</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="newapis">New Useful APIs</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>This release includes a number of new APIs that are used internally, which | |
| may also be useful for external clients. | |
| </p> | |
| <ul> | |
| <li>The optimizer uses the new CodeMetrics class to measure the size of code. | |
| Various passes (like the inliner, loop unswitcher, etc) all use this to make | |
| more accurate estimates of the code size impact of various | |
| optimizations.</li> | |
| <li>A new <a href="http://llvm.org/doxygen/InstructionSimplify_8h-source.html"> | |
| llvm/Analysis/InstructionSimplify.h</a> interface is available for doing | |
| symbolic simplification of instructions (e.g. <tt>a+0</tt> -> <tt>a</tt>) | |
| without requiring the instruction to exist. This centralizes a lot of | |
| ad-hoc symbolic manipulation code scattered in various passes.</li> | |
| <li>The optimizer now uses a new <a | |
| href="http://llvm.org/doxygen/SSAUpdater_8h-source.html">SSAUpdater</a> | |
| class which efficiently supports | |
| doing unstructured SSA update operations. This centralized a bunch of code | |
| scattered throughout various passes (e.g. jump threading, lcssa, | |
| loop rotate, etc) for doing this sort of thing. The code generator has a | |
| similar <a href="http://llvm.org/doxygen/MachineSSAUpdater_8h-source.html"> | |
| MachineSSAUpdater</a> class.</li> | |
| <li>The <a href="http://llvm.org/doxygen/Regex_8h-source.html"> | |
| llvm/Support/Regex.h</a> header exposes a platform independent regular | |
| expression API. Building on this, the <a | |
| href="TestingGuide.html#FileCheck">FileCheck</a> utility now supports | |
| regular exressions.</li> | |
| <li>raw_ostream now supports a circular "debug stream" accessed with "dbgs()". | |
| By default, this stream works the same way as "errs()", but if you pass | |
| <tt>-debug-buffer-size=1000</tt> to opt, the debug stream is capped to a | |
| fixed sized circular buffer and the output is printed at the end of the | |
| program's execution. This is helpful if you have a long lived compiler | |
| process and you're interested in seeing snapshots in time.</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="otherimprovements">Other Improvements and New Features</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>Other miscellaneous features include:</p> | |
| <ul> | |
| <li>You can now build LLVM as a big dynamic library (e.g. "libllvm2.7.so"). To | |
| get this, configure LLVM with the --enable-shared option.</li> | |
| <li>LLVM command line tools now overwrite their output by default. Previously, | |
| they would only do this with -f. This makes them more convenient to use, and | |
| behave more like standard unix tools.</li> | |
| <li>The opt and llc tools now autodetect whether their input is a .ll or .bc | |
| file, and automatically do the right thing. This means you don't need to | |
| explicitly use the llvm-as tool for most things.</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="changes">Major Changes and Removed Features</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>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.</p> | |
| <ul> | |
| <li> | |
| The Andersen's alias analysis ("anders-aa") pass, the Predicate Simplifier | |
| ("predsimplify") pass, the LoopVR pass, the GVNPRE pass, and the random sampling | |
| profiling ("rsprofiling") passes have all been removed. They were not being | |
| actively maintained and had substantial problems. If you are interested in | |
| these components, you are welcome to ressurect them from SVN, fix the | |
| correctness problems, and resubmit them to mainline.</li> | |
| <li>LLVM now defaults to building most libraries with RTTI turned off, providing | |
| a code size reduction. Packagers who are interested in building LLVM to support | |
| plugins that require RTTI information should build with "make REQUIRE_RTTI=1" | |
| and should read the new <a href="Packaging.html">Advice on Packaging LLVM</a> | |
| document.</li> | |
| <li>The LLVM interpreter now defaults to <em>not</em> using <tt>libffi</tt> 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 <tt>libffi</tt>, | |
| configure with <tt>--enable-libffi</tt>.</li> | |
| <li>Debug information uses a completely different representation, an LLVM 2.6 | |
| .bc file should work with LLVM 2.7, but debug info won't come forward.</li> | |
| <li>The LLVM 2.6 (and earlier) "malloc" and "free" instructions got removed, | |
| along with LowerAllocations pass. Now you should just use a call to the | |
| malloc and free functions in libc. These calls are optimized as well as | |
| the old instructions were.</li> | |
| </ul> | |
| <p>In addition, many APIs have changed in this release. Some of the major LLVM | |
| API changes are:</p> | |
| <ul> | |
| <li>Just about everything has been converted to use <tt>raw_ostream</tt> instead of | |
| <tt>std::ostream</tt>.</li> | |
| <li><tt>llvm/ADT/iterator.h</tt> has been removed, just use <tt><iterator></tt> | |
| instead.</li> | |
| <li>The <tt>Streams.h</tt> file and <tt>DOUT</tt> got removed, use <tt>DEBUG(errs() << ...);</tt> | |
| instead.</li> | |
| <li>The <tt>TargetAsmInfo</tt> interface was renamed to <tt>MCAsmInfo</tt>.</li> | |
| <li><tt>ModuleProvider</tt> has been <a | |
| href="http://llvm.org/viewvc/llvm-project?view=rev&revision=94686">removed</a> | |
| and its methods moved to <tt>Module</tt> and <tt>GlobalValue</tt>. | |
| Most clients can remove uses of <tt>ExistingModuleProvider</tt>, | |
| replace <tt>getBitcodeModuleProvider</tt> with | |
| <tt>getLazyBitcodeModule</tt>, and pass their <tt>Module</tt> to | |
| functions that used to accept <tt>ModuleProvider</tt>. Clients who | |
| wrote their own <tt>ModuleProvider</tt>s will need to derive from | |
| <tt>GVMaterializer</tt> instead and use | |
| <tt>Module::setMaterializer</tt> to attach it to a | |
| <tt>Module</tt>.</li> | |
| <li><tt>GhostLinkage</tt> has given up the ghost. | |
| <tt>GlobalValue</tt>s 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 | |
| <tt>GlobalValue::hasNotBeenReadFromBitcode</tt> with | |
| <tt>GlobalValue::isMaterializable</tt>.</li> | |
| <li>The <tt>isInteger</tt>, <tt>isIntOrIntVector</tt>, <tt>isFloatingPoint</tt>, | |
| <tt>isFPOrFPVector</tt> and <tt>isFPOrFPVector</tt> methods have been renamed | |
| <tt>isIntegerTy</tt>, <tt>isIntOrIntVectorTy</tt>, <tt>isFloatingPointTy</tt>, | |
| <tt>isFPOrFPVectorTy</tt> and <tt>isFPOrFPVectorTy</tt> respectively.</li> | |
| <li><tt>llvm::Instruction::clone()</tt> no longer takes argument.</li> | |
| <li><tt>raw_fd_ostream</tt>'s constructor now takes a flag argument, not individual | |
| booleans (see <tt>include/llvm/Support/raw_ostream.h</tt> for details).</li> | |
| <li>Some header files have been renamed: | |
| <ul> | |
| <li><tt>llvm/Support/AIXDataTypesFix.h</tt> to | |
| <tt>llvm/System/AIXDataTypesFix.h</tt></li> | |
| <li><tt>llvm/Support/DataTypes.h</tt> to <tt>llvm/System/DataTypes.h</tt></li> | |
| <li><tt>llvm/Transforms/Utils/InlineCost.h</tt> to | |
| <tt>llvm/Analysis/InlineCost.h</tt></li> | |
| <li><tt>llvm/Support/Mangler.h</tt> to <tt>llvm/Target/Mangler.h</tt></li> | |
| <li><tt>llvm/Analysis/Passes.h</tt> to <tt>llvm/CodeGen/Passes.h</tt></li> | |
| </ul></li> | |
| </ul> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_section"> | |
| <a name="portability">Portability and Supported Platforms</a> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_text"> | |
| <p>LLVM is known to work on the following platforms:</p> | |
| <ul> | |
| <li>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).</li> | |
| <li>PowerPC and X86-based Mac OS X systems, running 10.4 and above in 32-bit | |
| and 64-bit modes.</li> | |
| <li>Intel and AMD machines running on Win32 using MinGW libraries (native).</li> | |
| <li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited | |
| support is available for native builds with Visual C++).</li> | |
| <li>Sun x86 and AMD64 machines running Solaris 10, OpenSolaris 0906.</li> | |
| <li>Alpha-based machines running Debian GNU/Linux.</li> | |
| </ul> | |
| <p>The core LLVM infrastructure uses GNU autoconf to adapt itself | |
| to the machine and operating system on which it is built. However, minor | |
| porting may be required to get LLVM to work on new platforms. We welcome your | |
| portability patches and reports of successful builds or error messages.</p> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_section"> | |
| <a name="knownproblems">Known Problems</a> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <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> | |
| <ul> | |
| <li>LLVM will not correctly compile on Solaris and/or OpenSolaris | |
| using the stock GCC 3.x.x series 'out the box', | |
| See: <a href="GettingStarted.html#brokengcc">Broken versions of GCC and other tools</a>. | |
| However, A <a href="http://pkg.auroraux.org/GCC">Modern GCC Build</a> | |
| for x86/x86-64 has been made available from the third party AuroraUX Project | |
| that has been meticulously tested for bootstrapping LLVM & Clang.</li> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="experimental">Experimental features included with this release</a> | |
| </div> | |
| <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 MSIL, Alpha, SPU, MIPS, PIC16, Blackfin, MSP430, SystemZ and MicroBlaze | |
| backends are experimental.</li> | |
| <li><tt>llc</tt> "<tt>-filetype=asm</tt>" (the default) is the only | |
| supported value for this option. The MachO writer is experimental, and | |
| works much better in mainline SVN.</li> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="x86-be">Known problems with the X86 back-end</a> | |
| </div> | |
| <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 backend generates inefficient floating point code when configured | |
| to generate code for systems that don't have SSE2.</li> | |
| <li>Win64 code generation wasn't widely tested. Everything should work, but we | |
| expect small issues to happen. Also, llvm-gcc cannot build the mingw64 | |
| runtime currently due to lack of support for the 'u' inline assembly | |
| constraint and for X87 floating point inline assembly.</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> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="ppc-be">Known problems with the PowerPC back-end</a> | |
| </div> | |
| <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> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="arm-be">Known problems with the ARM back-end</a> | |
| </div> | |
| <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> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="sparc-be">Known problems with the SPARC back-end</a> | |
| </div> | |
| <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> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="mips-be">Known problems with the MIPS back-end</a> | |
| </div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li>64-bit MIPS targets are not supported yet.</li> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="alpha-be">Known problems with the Alpha back-end</a> | |
| </div> | |
| <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> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="c-be">Known problems with the C back-end</a> | |
| </div> | |
| <div class="doc_text"> | |
| <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> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="c-fe">Known problems with the llvm-gcc C and C++ front-end</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>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> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="fortran-fe">Known problems with the llvm-gcc Fortran front-end</a> | |
| </div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li>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.</li> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="ada-fe">Known problems with the llvm-gcc Ada front-end</a> | |
| </div> | |
| <div class="doc_text"> | |
| The llvm-gcc 4.2 Ada compiler works fairly well; however, this is not a mature | |
| technology, and problems should be expected. | |
| <ul> | |
| <li>The Ada front-end currently only builds on X86-32. This is mainly due | |
| to lack of trampoline support (pointers to nested functions) on other platforms. | |
| However, it <a href="http://llvm.org/PR2006">also fails to build on X86-64</a> | |
| which does support trampolines.</li> | |
| <li>The Ada front-end <a href="http://llvm.org/PR2007">fails to bootstrap</a>. | |
| This is due to lack of LLVM support for <tt>setjmp</tt>/<tt>longjmp</tt> style | |
| exception handling, which is used internally by the compiler. | |
| Workaround: configure with <tt>--disable-bootstrap</tt>.</li> | |
| <li>The c380004, <a href="http://llvm.org/PR2010">c393010</a> | |
| and <a href="http://llvm.org/PR2421">cxg2021</a> ACATS tests fail | |
| (c380004 also fails with gcc-4.2 mainline). | |
| If the compiler is built with checks disabled then <a href="http://llvm.org/PR2010">c393010</a> | |
| causes the compiler to go into an infinite loop, using up all system memory.</li> | |
| <li>Some GCC specific Ada tests continue to crash the compiler.</li> | |
| <li>The <tt>-E</tt> binder option (exception backtraces) | |
| <a href="http://llvm.org/PR1982">does not work</a> and will result in programs | |
| crashing if an exception is raised. Workaround: do not use <tt>-E</tt>.</li> | |
| <li>Only discrete types <a href="http://llvm.org/PR1981">are allowed to start | |
| or finish at a non-byte offset</a> in a record. Workaround: do not pack records | |
| or use representation clauses that result in a field of a non-discrete type | |
| starting or finishing in the middle of a byte.</li> | |
| <li>The <tt>lli</tt> interpreter <a href="http://llvm.org/PR2009">considers | |
| 'main' as generated by the Ada binder to be invalid</a>. | |
| Workaround: hand edit the file to use pointers for <tt>argv</tt> and | |
| <tt>envp</tt> rather than integers.</li> | |
| <li>The <tt>-fstack-check</tt> option <a href="http://llvm.org/PR2008">is | |
| ignored</a>.</li> | |
| </ul> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_section"> | |
| <a name="additionalinfo">Additional Information</a> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <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> | |
| <!-- *********************************************************************** --> | |
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