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691 lines
23 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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"http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link rel="stylesheet" href="_static/llvm.css" type="text/css">
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<title>LLVM 3.1 Release Notes</title>
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</head>
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<body>
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<h1>LLVM 3.1 Release Notes</h1>
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<div>
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<img style="float:right" src="http://llvm.org/img/DragonSmall.png"
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width="136" height="136" alt="LLVM Dragon Logo">
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</div>
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<ol>
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<li><a href="#intro">Introduction</a></li>
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<li><a href="#subproj">Sub-project Status Update</a></li>
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<li><a href="#externalproj">External Projects Using LLVM 3.1</a></li>
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<li><a href="#whatsnew">What's New in LLVM?</a></li>
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<li><a href="GettingStarted.html">Installation Instructions</a></li>
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<li><a href="#knownproblems">Known Problems</a></li>
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<li><a href="#additionalinfo">Additional Information</a></li>
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</ol>
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<div class="doc_author">
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<p>Written by the <a href="http://llvm.org/">LLVM Team</a></p>
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</div>
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<h1 style="color:red">These are in-progress notes for the upcoming LLVM 3.1
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release.<br>
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You may prefer the
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<a href="http://llvm.org/releases/3.0/docs/ReleaseNotes.html">LLVM 3.0
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Release Notes</a>.</h1>
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<!-- *********************************************************************** -->
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<h2>
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<a name="intro">Introduction</a>
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</h2>
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<!-- *********************************************************************** -->
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<div>
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<p>This document contains the release notes for the LLVM Compiler
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Infrastructure, release 3.1. Here we describe the status of LLVM, including
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major improvements from the previous release, improvements in various
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subprojects of LLVM, and some of the current users of the code.
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All LLVM releases may be downloaded from
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the <a href="http://llvm.org/releases/">LLVM releases web site</a>.</p>
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<p>For more information about LLVM, including information about the latest
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release, please check out the <a href="http://llvm.org/">main LLVM web
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site</a>. If you have questions or comments,
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the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM
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Developer's Mailing List</a> is a good place to send them.</p>
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<p>Note that if you are reading this file from a Subversion checkout or the main
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LLVM web page, this document applies to the <i>next</i> release, not the
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current one. To see the release notes for a specific release, please see the
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<a href="http://llvm.org/releases/">releases page</a>.</p>
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</div>
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<!-- *********************************************************************** -->
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<h2>
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<a name="subproj">Sub-project Status Update</a>
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</h2>
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<!-- *********************************************************************** -->
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<div>
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<p>The LLVM 3.1 distribution currently consists of code from the core LLVM
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repository (which roughly includes the LLVM optimizers, code generators and
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supporting tools), and the Clang repository. In
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addition to this code, the LLVM Project includes other sub-projects that are
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in development. Here we include updates on these subprojects.</p>
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<!--=========================================================================-->
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<h3>
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<a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>
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</h3>
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<div>
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<p><a href="http://clang.llvm.org/">Clang</a> is an LLVM front end for the C,
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C++, and Objective-C languages. Clang aims to provide a better user
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experience through expressive diagnostics, a high level of conformance to
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language standards, fast compilation, and low memory use. Like LLVM, Clang
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provides a modular, library-based architecture that makes it suitable for
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creating or integrating with other development tools. Clang is considered a
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production-quality compiler for C, Objective-C, C++ and Objective-C++ on x86
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(32- and 64-bit), and for Darwin/ARM targets.</p>
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<p>In the LLVM 3.1 time-frame, the Clang team has made many improvements:</p>
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<ul>
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<li>...</li>
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</ul>
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<p>For more details about the changes to Clang since the 2.9 release, see the
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<a href="http://clang.llvm.org/docs/ReleaseNotes.html">Clang release notes</a>
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</p>
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<p>If Clang rejects your code but another compiler accepts it, please take a
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look at the <a href="http://clang.llvm.org/compatibility.html">language
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compatibility</a> guide to make sure this is not intentional or a known
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issue.</p>
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</div>
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<!--=========================================================================-->
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<h3>
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<a name="dragonegg">DragonEgg: GCC front-ends, LLVM back-end</a>
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</h3>
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<div>
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<p><a href="http://dragonegg.llvm.org/">DragonEgg</a> is a
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<a href="http://gcc.gnu.org/wiki/plugins">gcc plugin</a> that replaces GCC's
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optimizers and code generators with LLVM's. It works with gcc-4.5 or gcc-4.6,
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targets the x86-32 and x86-64 processor families, and has been successfully
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used on the Darwin, FreeBSD, KFreeBSD, Linux and OpenBSD platforms. It fully
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supports Ada, C, C++ and Fortran. It has partial support for Go, Java, Obj-C
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and Obj-C++.</p>
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<p>The 3.1 release has the following notable changes:</p>
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<ul>
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<li>...</li>
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</ul>
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</div>
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<!--=========================================================================-->
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<h3>
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<a name="compiler-rt">compiler-rt: Compiler Runtime Library</a>
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</h3>
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<div>
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<p>The new LLVM <a href="http://compiler-rt.llvm.org/">compiler-rt project</a>
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is a simple library that provides an implementation of the low-level
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target-specific hooks required by code generation and other runtime
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components. For example, when compiling for a 32-bit target, converting a
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double to a 64-bit unsigned integer is compiled into a runtime call to the
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"__fixunsdfdi" function. The compiler-rt library provides highly optimized
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implementations of this and other low-level routines (some are 3x faster than
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the equivalent libgcc routines).</p>
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<p>....</p>
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</div>
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<!--=========================================================================-->
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<h3>
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<a name="lldb">LLDB: Low Level Debugger</a>
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</h3>
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<div>
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<p>LLDB is a ground-up implementation of a command line debugger, as well as a
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debugger API that can be used from other applications. LLDB makes use of the
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Clang parser to provide high-fidelity expression parsing (particularly for
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C++) and uses the LLVM JIT for target support.</p>
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<p>...</p>
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</div>
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<!--=========================================================================-->
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<h3>
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<a name="libc++">libc++: C++ Standard Library</a>
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</h3>
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<div>
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<p>Like compiler_rt, libc++ is now <a href="DeveloperPolicy.html#license">dual
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licensed</a> under the MIT and UIUC license, allowing it to be used more
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permissively.</p>
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<p>...</p>
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</div>
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<!--=========================================================================-->
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<h3>
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<a name="vmkit">VMKit</a>
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</h3>
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<div>
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<p>The <a href="http://vmkit.llvm.org/">VMKit project</a> is an
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implementation of a Java Virtual Machine (Java VM or JVM) that uses LLVM for
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static and just-in-time compilation.
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<p>In the LLVM 3.1 time-frame, VMKit has had significant improvements on both
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runtime and startup performance:</p>
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<ul>
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<li>...</li>
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</ul>
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</div>
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<!--=========================================================================-->
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<h3>
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<a name="Polly">Polly: Polyhedral Optimizer</a>
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</h3>
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<div>
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<p><a href="http://polly.llvm.org/">Polly</a> is an <em>experimental</em>
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optimizer for data locality and parallelism. It currently provides high-level
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loop optimizations and automatic parallelisation (using the OpenMP run time).
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Work in the area of automatic SIMD and accelerator code generation was
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started.
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<p>Within the LLVM 3.1 time-frame there were the following highlights:</p>
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<ul>
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<li>Polly became an official LLVM project</li>
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<li>Polly can be loaded directly into clang (Enabled by '-O3 -mllvm -polly'
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)</li>
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<li>An automatic scheduling optimizer (derived from <a
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href="http://pluto-compiler.sourceforge.net/">Pluto</a>) was integrated. It
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performs loop transformations to optimize for data-locality and parallelism.
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The transformations include, but are not limited to interchange, fusion,
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fission, skewing and tiling.
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</li>
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</ul>
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</div>
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</div>
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<!-- *********************************************************************** -->
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<h2>
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<a name="externalproj">External Open Source Projects Using LLVM 3.1</a>
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</h2>
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<!-- *********************************************************************** -->
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<div>
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<p>An exciting aspect of LLVM is that it is used as an enabling technology for
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a lot of other language and tools projects. This section lists some of the
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projects that have already been updated to work with LLVM 3.1.</p>
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... to be filled in right before the release ...
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</div>
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<!-- *********************************************************************** -->
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<h2>
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<a name="whatsnew">What's New in LLVM 3.1?</a>
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</h2>
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<!-- *********************************************************************** -->
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<div>
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<p>This release includes a huge number of bug fixes, performance tweaks and
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minor improvements. Some of the major improvements and new features are
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listed in this section.</p>
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<!--=========================================================================-->
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<h3>
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<a name="majorfeatures">Major New Features</a>
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</h3>
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<div>
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<!-- Features that need text if they're finished for 3.1:
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ARM EHABI
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combiner-aa?
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strong phi elim
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loop dependence analysis
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CorrelatedValuePropagation
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lib/Transforms/IPO/MergeFunctions.cpp => consider for 3.1.
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Integrated assembler on by default for arm/thumb?
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-->
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<!-- Near dead:
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Analysis/RegionInfo.h + Dom Frontiers
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SparseBitVector: used in LiveVar.
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llvm/lib/Archive - replace with lib object?
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-->
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<p>LLVM 3.1 includes several major changes and big features:</p>
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<ul>
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<li><a href="../tools/clang/docs/AddressSanitizer.html">AddressSanitizer</a>,
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a fast memory error detector.</li>
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<li><a href="CodeGenerator.html#machineinstrbundle">MachineInstr Bundles</a>,
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Support to model instruction bundling / packing.</li>
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<li><a href="#armintegratedassembler">ARM Integrated Assembler</a>,
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A full featured assembler and direct-to-object support for ARM.</li>
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<li><a href="#blockplacement">Basic Block Placement</a>
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Probability driven basic block placement.</li>
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<li>....</li>
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</ul>
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</div>
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|
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<!--=========================================================================-->
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<h3>
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<a name="coreimprovements">LLVM IR and Core Improvements</a>
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</h3>
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<div>
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<p>LLVM IR has several new features for better support of new targets and that
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expose new optimization opportunities:</p>
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<ul>
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<li>IR support for half float</li>
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<li>IR support for vectors of pointers, including vector GEPs.</li>
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<li>Module flags have been introduced. They convey information about the
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module as a whole to LLVM subsystems.</li>
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<li>Loads can now have range metadata attached to them to describe the
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possible values being loaded.</li>
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<li>Inline cost heuristics have been completely overhauled and now closely
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model constant propagation through call sites, disregard trivially dead
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code costs, and can model C++ STL iterator patterns.</li>
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<li>....</li>
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</ul>
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</div>
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<!--=========================================================================-->
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<h3>
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<a name="optimizer">Optimizer Improvements</a>
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</h3>
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<div>
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<p>In addition to many minor performance tweaks and bug fixes, this
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release includes a few major enhancements and additions to the
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optimizers:</p>
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<ul>
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<li>The loop unroll pass now is able to unroll loops with run-time trip counts.
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This feature is turned off by default, and is enabled with the
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<code>-unroll-runtime</code> flag.</li>
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<li>A new basic-block autovectorization pass is available. Pass
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<code>-vectorize</code> to run this pass along with some associated
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post-vectorization cleanup passes. For more information, see the EuroLLVM
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2012 slides: <a href="http://llvm.org/devmtg/2012-04-12/Slides/Hal_Finkel.pdf">
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Autovectorization with LLVM</a>.</li>
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<li>....</li>
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</ul>
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</div>
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<!--=========================================================================-->
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<h3>
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<a name="mc">MC Level Improvements</a>
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</h3>
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<div>
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<p>The LLVM Machine Code (aka MC) subsystem was created to solve a number of
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problems in the realm of assembly, disassembly, object file format handling,
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and a number of other related areas that CPU instruction-set level tools work
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in. For more information, please see
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the <a href="http://blog.llvm.org/2010/04/intro-to-llvm-mc-project.html">Intro
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to the LLVM MC Project Blog Post</a>.</p>
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<ul>
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<li>....</li>
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</ul>
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</div>
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<!--=========================================================================-->
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<h3>
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<a name="codegen">Target Independent Code Generator Improvements</a>
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</h3>
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<div>
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<p>We have changed the way that the Type Legalizer legalizes vectors. The type
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legalizer now attempts to promote integer elements. This enabled the
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implementation of vector-select. Additionally, we see a performance boost on
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workloads which use vectors of chars and shorts, since they are now promoted
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to 32-bit types, which are better supported by the SIMD instruction set.
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Floating point types are still widened as before.</p>
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<p>We have put a significant amount of work into the code generator
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infrastructure, which allows us to implement more aggressive algorithms and
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make it run faster:</p>
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<ul>
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<li>TableGen can now synthesize register classes that are only needed to
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represent combinations of constraints from instructions and sub-registers.
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The synthetic register classes inherit most of their properties form their
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closest user-defined super-class.</li>
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<li><code>MachineRegisterInfo</code> now allows the reserved registers to be
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frozen when register allocation starts. Target hooks should use the
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<code>MRI->canReserveReg(FramePtr)</code> method to avoid accidentally
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disabling frame pointer elimination during register allocation.</li>
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<li>A new kind of <code>MachineOperand</code> provides a compact
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representation of large clobber lists on call instructions. The register
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mask operand references a bit mask of preserved registers. Everything else
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is clobbered.</li>
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</ul>
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<p> We added new TableGen infrastructure to support bundling for
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Very Long Instruction Word (VLIW) architectures. TableGen can now
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automatically generate a deterministic finite automaton from a VLIW
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target's schedule description which can be queried to determine
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legal groupings of instructions in a bundle.</p>
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<p> We have added a new target independent VLIW packetizer based on the
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DFA infrastructure to group machine instructions into bundles.</p>
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</div>
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<h4>
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<a name="blockplacement">Basic Block Placement</a>
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</h4>
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<div>
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<p>A probability based block placement and code layout algorithm was added to
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LLVM's code generator. This layout pass supports probabilities derived from
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static heuristics as well as source code annotations such as
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<code>__builtin_expect</code>.</p>
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</div>
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<!--=========================================================================-->
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<h3>
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<a name="x86">X86-32 and X86-64 Target Improvements</a>
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</h3>
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<div>
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<p>New features and major changes in the X86 target include:</p>
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<ul>
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<li>Bug fixes and improved support for AVX1</li>
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<li>Support for AVX2 (still incomplete at this point)</li>
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<li>Call instructions use the new register mask operands for faster compile
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times and better support for different calling conventions. The old WINCALL
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instructions are no longer needed.</li>
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<li>DW2 Exception Handling is enabled on Cygwin and MinGW.</li>
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<li>Support for implicit TLS model used with MS VC runtime</li>
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</ul>
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</div>
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<!--=========================================================================-->
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<h3>
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<a name="ARM">ARM Target Improvements</a>
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</h3>
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<div>
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<p>New features of the ARM target include:</p>
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<ul>
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<li>The constant island pass now supports basic block and constant pool entry
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alignments greater than 4 bytes.</li>
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<li>On Darwin, the ARM target now has a full-featured integrated assembler.
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</li>
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</ul>
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<h4>
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<a name="armintegratedassembler">ARM Integrated Assembler</a>
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</h4>
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<div>
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<p>The ARM target now includes a full featured macro assembler, including
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direct-to-object module support for clang. The assembler is currently enabled
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by default for Darwin only pending testing and any additional necessary
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platform specific support for Linux.</p>
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<p>Full support is included for Thumb1, Thumb2 and ARM modes, along with
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subtarget and CPU specific extensions for VFP2, VFP3 and NEON.</p>
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<p>The assembler is Unified Syntax only (see ARM Architecural Reference Manual
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for details). While there is some, and growing, support for pre-unfied (divided)
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syntax, there are still significant gaps in that support.</p>
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</div>
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</div>
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<!--=========================================================================-->
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<h3>
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<a name="MIPS">MIPS Target Improvements</a>
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</h3>
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<div>
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<p>This release has seen major new work on just about every aspect of the MIPS
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backend. Some of the major new features include:</p>
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<ul>
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<li>....</li>
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</ul>
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</div>
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<!--=========================================================================-->
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<h3>
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<a name="OtherTS">Other Target Specific Improvements</a>
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</h3>
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|
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<div>
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<p>Support for Qualcomm's Hexagon VLIW processor has been added.</p>
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<ul>
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|
<li>....</li>
|
|
|
|
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!--=========================================================================-->
|
|
<h3>
|
|
<a name="changes">Major Changes and Removed Features</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>If you're already an LLVM user or developer with out-of-tree changes based on
|
|
LLVM 3.1, this section lists some "gotchas" that you may run into upgrading
|
|
from the previous release.</p>
|
|
|
|
<ul>
|
|
<li>LLVM 3.1 removes support for reading LLVM 2.9 bitcode files. Going
|
|
forward, we aim for all future versions of LLVM to read bitcode files and
|
|
<tt>.ll</tt> files produced by LLVM 3.0 and later.</li>
|
|
<li>The <tt>unwind</tt> instruction is now gone. With the introduction of the
|
|
new exception handling system in LLVM 3.0, the <tt>unwind</tt> instruction
|
|
became obsolete.</li>
|
|
<li>....</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!--=========================================================================-->
|
|
<h3>
|
|
<a name="api_changes">Internal API Changes</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>In addition, many APIs have changed in this release. Some of the major
|
|
LLVM API changes are:</p>
|
|
|
|
<ul>
|
|
<li>Target specific options have been moved from global variables to members
|
|
on the new <code>TargetOptions</code> class, which is local to each
|
|
<code>TargetMachine</code>. As a consequence, the associated flags will
|
|
no longer be accepted by <tt>clang -mllvm</tt>. This includes:
|
|
<ul>
|
|
<li><code>llvm::PrintMachineCode</code></li>
|
|
<li><code>llvm::NoFramePointerElim</code></li>
|
|
<li><code>llvm::NoFramePointerElimNonLeaf</code></li>
|
|
<li><code>llvm::DisableFramePointerElim(const MachineFunction &)</code></li>
|
|
<li><code>llvm::LessPreciseFPMADOption</code></li>
|
|
<li><code>llvm::LessPrecideFPMAD()</code></li>
|
|
<li><code>llvm::NoExcessFPPrecision</code></li>
|
|
<li><code>llvm::UnsafeFPMath</code></li>
|
|
<li><code>llvm::NoInfsFPMath</code></li>
|
|
<li><code>llvm::NoNaNsFPMath</code></li>
|
|
<li><code>llvm::HonorSignDependentRoundingFPMathOption</code></li>
|
|
<li><code>llvm::HonorSignDependentRoundingFPMath()</code></li>
|
|
<li><code>llvm::UseSoftFloat</code></li>
|
|
<li><code>llvm::FloatABIType</code></li>
|
|
<li><code>llvm::NoZerosInBSS</code></li>
|
|
<li><code>llvm::JITExceptionHandling</code></li>
|
|
<li><code>llvm::JITEmitDebugInfo</code></li>
|
|
<li><code>llvm::JITEmitDebugInfoToDisk</code></li>
|
|
<li><code>llvm::GuaranteedTailCallOpt</code></li>
|
|
<li><code>llvm::StackAlignmentOverride</code></li>
|
|
<li><code>llvm::RealignStack</code></li>
|
|
<li><code>llvm::DisableJumpTables</code></li>
|
|
<li><code>llvm::EnableFastISel</code></li>
|
|
<li><code>llvm::getTrapFunctionName()</code></li>
|
|
<li><code>llvm::EnableSegmentedStacks</code></li>
|
|
</ul></li>
|
|
<li>The MDBuilder class has been added to simplify the creation of
|
|
metadata.</li>
|
|
<li>....</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!--=========================================================================-->
|
|
<h3>
|
|
<a name="tools_changes">Tools Changes</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>In addition, some tools have changed in this release. Some of the changes
|
|
are:</p>
|
|
|
|
|
|
<ul>
|
|
<li>llvm-stress is a command line tool for generating random .ll files to fuzz
|
|
different LLVM components. </li>
|
|
<li>llvm-ld has been removed. Use llvm-link or Clang instead.</li>
|
|
<li>....</li>
|
|
</ul>
|
|
|
|
<ul>
|
|
<li>....</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<h2>
|
|
<a name="knownproblems">Known Problems</a>
|
|
</h2>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div>
|
|
|
|
<p>LLVM is generally a production quality compiler, and is used by a broad range
|
|
of applications and shipping in many products. That said, not every
|
|
subsystem is as mature as the aggregate, particularly the more obscure
|
|
targets. 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 or ask on the <a
|
|
href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev
|
|
list</a>.</p>
|
|
|
|
<p>Known problem areas include:</p>
|
|
|
|
<ul>
|
|
<li>The Alpha, Blackfin, CellSPU, MSP430, PTX, SystemZ and
|
|
XCore backends are experimental, and the Alpha, Blackfin and SystemZ
|
|
targets have already been removed from mainline.</li>
|
|
|
|
<li>The integrated assembler, disassembler, and JIT is not supported by
|
|
several targets. If an integrated assembler is not supported, then a
|
|
system assembler is required. For more details, see the <a
|
|
href="CodeGenerator.html#targetfeatures">Target Features Matrix</a>.
|
|
</li>
|
|
|
|
<li>The C backend has numerous problems and is not being actively maintained.
|
|
Depending on it for anything serious is not advised.</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<h2>
|
|
<a name="additionalinfo">Additional Information</a>
|
|
</h2>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div>
|
|
|
|
<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>
|
|
<address>
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<a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
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