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<h2>Section Example</h2> <div> <!-- h2+div is applied --> <p>Section preamble.</p> <h3>Subsection Example</h3> <p> <!-- h3+p is applied --> Subsection body </p> <!-- End of section body --> </div> git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129901 91177308-0d34-0410-b5e6-96231b3b80d8
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<!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="llvm.css" type="text/css">
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<title>LLVM 2.9 Release Notes</title>
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</head>
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<body>
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<h1>LLVM 2.9 Release Notes</h1>
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<img align=right src="http://llvm.org/img/DragonSmall.png"
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width="136" height="136" alt="LLVM Dragon Logo">
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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 2.9</a></li>
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<li><a href="#whatsnew">What's New in LLVM 2.9?</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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<!--
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<h1 style="color:red">These are in-progress notes for the upcoming LLVM 2.9
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release.<br>
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You may prefer the
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<a href="http://llvm.org/releases/2.8/docs/ReleaseNotes.html">LLVM 2.8
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Release Notes</a>.</h1>
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-->
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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 2.9. Here we describe the status of LLVM, including
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major improvements from the previous release and significant known problems.
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All LLVM releases may be downloaded from the <a
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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
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web site</a>. If you have questions or comments, the <a
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href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM Developer's
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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
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main 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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<!-- 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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-->
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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>
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The LLVM 2.9 distribution currently consists of code from the core LLVM
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repository (which roughly includes the LLVM optimizers, code generators
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and supporting tools), the Clang repository and the llvm-gcc repository. In
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addition to this code, the LLVM Project includes other sub-projects that are in
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development. Here we include updates on these subprojects.
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</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 experience
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through expressive diagnostics, a high level of conformance to language
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standards, fast compilation, and low memory use. Like LLVM, Clang provides a
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modular, library-based architecture that makes it suitable for creating or
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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 2.9 time-frame, the Clang team has made many improvements in C,
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C++ and Objective-C support. C++ support is now generally rock solid, has
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been exercised on a broad variety of code, and has several new <a
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href="http://clang.llvm.org/cxx_status.html#cxx0x">C++'0x features</a>
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implemented (such as rvalue references and variadic templates). LLVM 2.9 has
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also brought in a large range of bug fixes and minor features (e.g. __label__
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support), and is much more compatible with the Linux Kernel.</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 issue.
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</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>
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<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.
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Currently it requires a patched version of gcc-4.5.
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The plugin can target the x86-32 and x86-64 processor families and has been
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used successfully on the Darwin, FreeBSD and Linux platforms.
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The Ada, C, C++ and Fortran languages work well.
|
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The plugin is capable of compiling plenty of Obj-C, Obj-C++ and Java but it is
|
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not known whether the compiled code actually works or not!
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</p>
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<p>
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The 2.9 release has the following notable changes:
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<ul>
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<li>The plugin is much more stable when compiling Fortran.</li>
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<li>Inline assembly where an asm output is tied to an input of a different size
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is now supported in many more cases.</li>
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<li>Basic support for the __float128 type was added. It is now possible to
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generate LLVM IR from programs using __float128 but code generation does not
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work yet.</li>
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<li>Compiling Java programs no longer systematically crashes the plugin.</li>
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</ul>
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|
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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>
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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 components.
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For example, when compiling for a 32-bit target, converting a double to a 64-bit
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unsigned integer is compiled into a runtime call to the "__fixunsdfdi"
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function. The compiler-rt library provides highly optimized implementations of
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this and other low-level routines (some are 3x faster than the equivalent
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libgcc routines).</p>
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<p>In the LLVM 2.9 timeframe, compiler_rt has had several minor changes for
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better ARM support, and a fairly major license change. All of the code in the
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compiler-rt project is now <a href="DeveloperPolicy.html#license">dual
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licensed</a> under MIT and UIUC license, which allows you to use compiler-rt
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in applications without the binary copyright reproduction clause. If you
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prefer the LLVM/UIUC license, you are free to continue using it under that
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license as well.</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>
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<a href="http://lldb.llvm.org/">LLDB</a> is a brand new member of the LLVM
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umbrella of projects. LLDB is a next generation, high-performance debugger. It
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is built as a set of reusable components which highly leverage existing
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libraries in the larger LLVM Project, such as the Clang expression parser, the
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LLVM disassembler and the LLVM JIT.</p>
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<p>
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LLDB is has advanced by leaps and bounds in the 2.9 timeframe. It is
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dramatically more stable and useful, and includes both a new <a
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href="http://lldb.llvm.org/tutorial.html">tutorial</a> and a <a
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href="http://lldb.llvm.org/lldb-gdb.html">side-by-side comparison with
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GDB</a>.</p>
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|
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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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|
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<div>
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<p>
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<a href="http://libcxx.llvm.org/">libc++</a> is another new member of the LLVM
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family. It is an implementation of the C++ standard library, written from the
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ground up to specifically target the forthcoming C++'0X standard and focus on
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delivering great performance.</p>
|
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<p>
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In the LLVM 2.9 timeframe, libc++ has had numerous bugs fixed, and is now being
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co-developed with Clang's C++'0x mode.</p>
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<p>
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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.
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</p>
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</div>
|
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|
|
|
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<!--=========================================================================-->
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<h3>
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<a name="LLBrowse">LLBrowse: IR Browser</a>
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</h3>
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<div>
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<p>
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<a href="http://llvm.org/svn/llvm-project/llbrowse/trunk/doc/LLBrowse.html">
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LLBrowse</a> is an interactive viewer for LLVM modules. It can load any LLVM
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module and displays its contents as an expandable tree view, facilitating an
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easy way to inspect types, functions, global variables, or metadata nodes. It
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is fully cross-platform, being based on the popular wxWidgets GUI toolkit.
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</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 implementation
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of a Java Virtual Machine (Java VM or JVM) that uses LLVM for static and
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just-in-time compilation. As of LLVM 2.9, VMKit now supports generational
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garbage collectors. The garbage collectors are provided by the MMTk framework,
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and VMKit can be configured to use one of the numerous implemented collectors
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of MMTk.
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</p>
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</div>
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|
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<!--=========================================================================-->
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<!--
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<h3>
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<a name="klee">KLEE: A Symbolic Execution Virtual Machine</a>
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</h3>
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<div>
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<p>
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<a href="http://klee.llvm.org/">KLEE</a> is a symbolic execution framework for
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programs in LLVM bitcode form. KLEE tries to symbolically evaluate "all" paths
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through the application and records state transitions that lead to fault
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states. This allows it to construct testcases that lead to faults and can even
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be used to verify some algorithms.
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</p>
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<p>UPDATE!</p>
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</div>-->
|
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</div>
|
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|
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<!-- *********************************************************************** -->
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<h2>
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<a name="externalproj">External Open Source Projects Using LLVM 2.9</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 2.9.</p>
|
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|
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<!--=========================================================================-->
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<h3>Crack Programming Language</h3>
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<div>
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<p>
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<a href="http://code.google.com/p/crack-language/">Crack</a> aims to provide the
|
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ease of development of a scripting language with the performance of a compiled
|
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language. The language derives concepts from C++, Java and Python, incorporating
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object-oriented programming, operator overloading and strong typing.</p>
|
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</div>
|
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|
|
|
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<!--=========================================================================-->
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<h3>TTA-based Codesign Environment (TCE)</h3>
|
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|
|
<div>
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|
<p>TCE is a toolset for designing application-specific processors (ASP) based on
|
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the Transport triggered architecture (TTA). The toolset provides a complete
|
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co-design flow from C/C++ programs down to synthesizable VHDL and parallel
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program binaries. Processor customization points include the register files,
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function units, supported operations, and the interconnection network.</p>
|
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<p>TCE uses Clang and LLVM for C/C++ language support, target independent
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optimizations and also for parts of code generation. It generates new LLVM-based
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code generators "on the fly" for the designed TTA processors and loads them in
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to the compiler backend as runtime libraries to avoid per-target recompilation
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of larger parts of the compiler chain.</p>
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</div>
|
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|
|
|
|
|
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<!--=========================================================================-->
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<h3>PinaVM</h3>
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<div>
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<p><a href="http://gitorious.org/pinavm/pages/Home">PinaVM</a> is an open
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source, <a href="http://www.systemc.org/">SystemC</a> front-end. Unlike many
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other front-ends, PinaVM actually executes the elaboration of the
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program analyzed using LLVM's JIT infrastructure. It later enriches the
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bitcode with SystemC-specific information.</p>
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</div>
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<!--=========================================================================-->
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<h3>Pure</h3>
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<div>
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<p><a href="http://pure-lang.googlecode.com/">Pure</a> is an
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algebraic/functional
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programming language based on term rewriting. Programs are collections
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of equations which are used to evaluate expressions in a symbolic
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fashion. The interpreter uses LLVM as a backend to JIT-compile Pure
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programs to fast native code. Pure offers dynamic typing, eager and lazy
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evaluation, lexical closures, a hygienic macro system (also based on
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term rewriting), built-in list and matrix support (including list and
|
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matrix comprehensions) and an easy-to-use interface to C and other
|
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programming languages (including the ability to load LLVM bitcode
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modules, and inline C, C++, Fortran and Faust code in Pure programs if
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the corresponding LLVM-enabled compilers are installed).</p>
|
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<p>Pure version 0.47 has been tested and is known to work with LLVM 2.9
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(and continues to work with older LLVM releases >= 2.5).</p>
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</div>
|
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<!--=========================================================================-->
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<h3 id="icedtea">IcedTea Java Virtual Machine Implementation</h3>
|
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|
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<div>
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<p>
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<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
|
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IcedTea provides is a new JIT compiler named <a
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href="http://icedtea.classpath.org/wiki/ZeroSharkFaq">Shark</a> which uses LLVM
|
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to provide native code generation without introducing processor-dependent
|
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code.
|
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</p>
|
|
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<p> OpenJDK 7 b112, IcedTea6 1.9 and IcedTea7 1.13 and later have been tested
|
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and are known to work with LLVM 2.9 (and continue to work with older LLVM
|
|
releases >= 2.6 as well).</p>
|
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</div>
|
|
|
|
<!--=========================================================================-->
|
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<h3>Glasgow Haskell Compiler (GHC)</h3>
|
|
|
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<div>
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<p>GHC is an open source, state-of-the-art programming suite for Haskell,
|
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a standard lazy functional programming language. It includes an
|
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optimizing static compiler generating good code for a variety of
|
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platforms, together with an interactive system for convenient, quick
|
|
development.</p>
|
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|
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<p>In addition to the existing C and native code generators, GHC 7.0 now
|
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supports an LLVM code generator. GHC supports LLVM 2.7 and later.</p>
|
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</div>
|
|
|
|
<!--=========================================================================-->
|
|
<h3>Polly - Polyhedral optimizations for LLVM</h3>
|
|
|
|
<div>
|
|
<p>Polly is a project that aims to provide advanced memory access optimizations
|
|
to better take advantage of SIMD units, cache hierarchies, multiple cores or
|
|
even vector accelerators for LLVM. Built around an abstract mathematical
|
|
description based on Z-polyhedra, it provides the infrastructure to develop
|
|
advanced optimizations in LLVM and to connect complex external optimizers. In
|
|
its first year of existence Polly already provides an exact value-based
|
|
dependency analysis as well as basic SIMD and OpenMP code generation support.
|
|
Furthermore, Polly can use PoCC(Pluto) an advanced optimizer for data-locality
|
|
and parallelism.</p>
|
|
</div>
|
|
|
|
<!--=========================================================================-->
|
|
<h3>Rubinius</h3>
|
|
|
|
<div>
|
|
<p><a href="http://github.com/evanphx/rubinius">Rubinius</a> is an environment
|
|
for running Ruby code which strives to write as much of the implementation in
|
|
Ruby as possible. Combined with a bytecode interpreting VM, it uses LLVM to
|
|
optimize and compile ruby code down to machine code. Techniques such as type
|
|
feedback, method inlining, and deoptimization are all used to remove dynamism
|
|
from ruby execution and increase performance.</p>
|
|
</div>
|
|
|
|
|
|
<!--=========================================================================-->
|
|
<h3>
|
|
<a name="FAUST">FAUST Real-Time Audio Signal Processing Language</a>
|
|
</h3>
|
|
|
|
<div>
|
|
<p>
|
|
<a href="http://faust.grame.fr">FAUST</a> is a compiled language for real-time
|
|
audio signal processing. The name FAUST stands for Functional AUdio STream. Its
|
|
programming model combines two approaches: functional programming and block
|
|
diagram composition. In addition with the C, C++, JAVA output formats, the
|
|
Faust compiler can now generate LLVM bitcode, and works with LLVM 2.7-2.9.</p>
|
|
|
|
</div>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<h2>
|
|
<a name="whatsnew">What's New in LLVM 2.9?</a>
|
|
</h2>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div>
|
|
|
|
<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>
|
|
|
|
<!--=========================================================================-->
|
|
<h3>
|
|
<a name="majorfeatures">Major New Features</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>LLVM 2.9 includes several major new capabilities:</p>
|
|
|
|
<ul>
|
|
|
|
<li>Type Based Alias Analysis (TBAA) is now implemented and turned on by default
|
|
in Clang. This allows substantially better load/store optimization in some
|
|
cases. TBAA can be disabled by passing -fno-strict-aliasing.
|
|
</li>
|
|
|
|
<li>This release has seen a continued focus on quality of debug information.
|
|
LLVM now generates much higher fidelity debug information, particularly when
|
|
debugging optimized code.</li>
|
|
|
|
<li>Inline assembly now supports multiple alternative constraints.</li>
|
|
|
|
<li>A new backend for the NVIDIA PTX virtual ISA (used to target its GPUs) is
|
|
under rapid development. It is not generally useful in 2.9, but is making
|
|
rapid progress.</li>
|
|
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!--=========================================================================-->
|
|
<h3>
|
|
<a name="coreimprovements">LLVM IR and Core Improvements</a>
|
|
</h3>
|
|
|
|
<div>
|
|
<p>LLVM IR has several new features for better support of new targets and that
|
|
expose new optimization opportunities:</p>
|
|
|
|
<ul>
|
|
<li>The <a href="LangRef.html#bitwiseops">udiv, ashr, lshr, and shl</a>
|
|
instructions now have support exact and nuw/nsw bits to indicate that they
|
|
don't overflow or shift out bits. This is useful for optimization of <a
|
|
href="http://llvm.org/PR8862">pointer differences</a> and other cases.</li>
|
|
|
|
<li>LLVM IR now supports the <a href="LangRef.html#globalvars">unnamed_addr</a>
|
|
attribute to indicate that constant global variables with identical
|
|
initializers can be merged. This fixed <a href="http://llvm.org/PR8927">an
|
|
issue</a> where LLVM would incorrectly merge two globals which were supposed
|
|
to have distinct addresses.</li>
|
|
|
|
<li>The new <a href="LangRef.html#fnattrs">hotpatch attribute</a> has been added
|
|
to allow runtime patching of functions.</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!--=========================================================================-->
|
|
<h3>
|
|
<a name="optimizer">Optimizer Improvements</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>In addition to a large array of minor performance tweaks and bug fixes, this
|
|
release includes a few major enhancements and additions to the optimizers:</p>
|
|
|
|
<ul>
|
|
<li>Link Time Optimization (LTO) has been improved to use MC for parsing inline
|
|
assembly and now can build large programs like Firefox 4 on both Mac OS X and
|
|
Linux.</li>
|
|
|
|
<li>The new -loop-idiom pass recognizes memset/memcpy loops (and memset_pattern
|
|
on darwin), turning them into library calls, which are typically better
|
|
optimized than inline code. If you are building a libc and notice that your
|
|
memcpy and memset functions are compiled into infinite recursion, please build
|
|
with -ffreestanding or -fno-builtin to disable this pass.</li>
|
|
|
|
<li>A new -early-cse pass does a fast pass over functions to fold constants,
|
|
simplify expressions, perform simple dead store elimination, and perform
|
|
common subexpression elimination. It does a good job at catching some of the
|
|
trivial redundancies that exist in unoptimized code, making later passes more
|
|
effective.</li>
|
|
|
|
<li>A new -loop-instsimplify pass is used to clean up loop bodies in the loop
|
|
optimizer.</li>
|
|
|
|
<li>The new TargetLibraryInfo interface allows mid-level optimizations to know
|
|
whether the current target's runtime library has certain functions. For
|
|
example, the optimizer can now transform integer-only printf calls to call
|
|
iprintf, allowing reduced code size for embedded C libraries (e.g. newlib).
|
|
</li>
|
|
|
|
<li>LLVM has a new <a href="WritingAnLLVMPass.html#RegionPass">RegionPass</a>
|
|
infrastructure for region-based optimizations.</li>
|
|
|
|
<li>Several optimizer passes have been substantially sped up:
|
|
GVN is much faster on functions with deep dominator trees and lots of basic
|
|
blocks. The dominator tree and dominance frontier passes are much faster to
|
|
compute, and preserved by more passes (so they are computed less often). The
|
|
-scalar-repl pass is also much faster and doesn't use DominanceFrontier.
|
|
</li>
|
|
|
|
<li>The Dead Store Elimination pass is more aggressive optimizing stores of
|
|
different types: e.g. a large store following a small one to the same address.
|
|
The MemCpyOptimizer pass handles several new forms of memcpy elimination.</li>
|
|
|
|
<li>LLVM now optimizes various idioms for overflow detection into check of the
|
|
flag register on various CPUs. For example, we now compile:
|
|
|
|
<pre>
|
|
unsigned long t = a+b;
|
|
if (t < a) ...
|
|
</pre>
|
|
into:
|
|
<pre>
|
|
addq %rdi, %rbx
|
|
jno LBB0_2
|
|
</pre>
|
|
</li>
|
|
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!--=========================================================================-->
|
|
<h3>
|
|
<a name="mc">MC Level Improvements</a>
|
|
</h3>
|
|
|
|
<div>
|
|
<p>
|
|
The LLVM Machine Code (aka MC) subsystem was created to solve a number
|
|
of problems in the realm of assembly, disassembly, object file format handling,
|
|
and a number of other related areas that CPU instruction-set level tools work
|
|
in.</p>
|
|
|
|
<ul>
|
|
<li>ELF MC support has matured enough for the integrated assembler to be turned
|
|
on by default in Clang on X86-32 and X86-64 ELF systems.</li>
|
|
|
|
<li>MC supports and CodeGen uses the <tt>.file</tt> and <tt>.loc</tt> directives
|
|
for producing line number debug info. This produces more compact line
|
|
tables and easier to read .s files.</li>
|
|
|
|
<li>MC supports the <tt>.cfi_*</tt> directives for producing DWARF
|
|
frame information, but it is still not used by CodeGen by default.</li>
|
|
|
|
|
|
<li>The MC assembler now generates much better diagnostics for common errors,
|
|
is much faster at matching instructions, is much more bug-compatible with
|
|
the GAS assembler, and is now generally useful for a broad range of X86
|
|
assembly.</li>
|
|
|
|
<li>We now have some basic <a href="CodeGenerator.html#mc">internals
|
|
documentation</a> for MC.</li>
|
|
|
|
<li>.td files can now specify assembler aliases directly with the <a
|
|
href="CodeGenerator.html#na_instparsing">MnemonicAlias and InstAlias</a>
|
|
tblgen classes.</li>
|
|
|
|
<li>LLVM now has an experimental format-independent object file manipulation
|
|
library (lib/Object). It supports both PE/COFF and ELF. The llvm-nm tool has
|
|
been extended to work with native object files, and the new llvm-objdump tool
|
|
supports disassembly of object files (but no relocations are displayed yet).
|
|
</li>
|
|
|
|
<li>Win32 PE-COFF support in the MC assembler has made a lot of progress in the
|
|
2.9 timeframe, but is still not generally useful.</li>
|
|
|
|
</ul>
|
|
|
|
<p>For more information, please see the <a
|
|
href="http://blog.llvm.org/2010/04/intro-to-llvm-mc-project.html">Intro to the
|
|
LLVM MC Project Blog Post</a>.
|
|
</p>
|
|
|
|
</div>
|
|
|
|
<!--=========================================================================-->
|
|
<h3>
|
|
<a name="codegen">Target Independent Code Generator Improvements</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>We have put a significant amount of work into the code generator
|
|
infrastructure, which allows us to implement more aggressive algorithms and make
|
|
it run faster:</p>
|
|
|
|
<ul>
|
|
<li>The pre-register-allocation (preRA) instruction scheduler models register
|
|
pressure much more accurately in some cases. This allows the adoption of more
|
|
aggressive scheduling heuristics without causing spills to be generated.
|
|
</li>
|
|
|
|
<li>LiveDebugVariables is a new pass that keeps track of debugging information
|
|
for user variables that are promoted to registers in optimized builds.</li>
|
|
|
|
<li>The scheduler now models operand latency and pipeline forwarding.</li>
|
|
|
|
<li>A major register allocator infrastructure rewrite is underway. It is not on
|
|
by default for 2.9 and you are not advised to use it, but it has made
|
|
substantial progress in the 2.9 timeframe:
|
|
<ul>
|
|
<li>A new -regalloc=basic "basic" register allocator can be used as a simple
|
|
fallback when debugging. It uses the new infrastructure.</li>
|
|
<li>New infrastructure is in place for live range splitting. "SplitKit" can
|
|
break a live interval into smaller pieces while preserving SSA form, and
|
|
SpillPlacement can help find the best split points. This is a work in
|
|
progress so the API is changing quickly.</li>
|
|
<li>The inline spiller has learned to clean up after live range splitting. It
|
|
can hoist spills out of loops, and it can eliminate redundant spills.</li>
|
|
<li>Rematerialization works with live range splitting.</li>
|
|
<li>The new "greedy" register allocator using live range splitting. This will
|
|
be the default register allocator in the next LLVM release, but it is not
|
|
turned on by default in 2.9.</li>
|
|
</ul>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
|
|
<!--=========================================================================-->
|
|
<h3>
|
|
<a name="x86">X86-32 and X86-64 Target Improvements</a>
|
|
</h3>
|
|
|
|
<div>
|
|
<p>New features and major changes in the X86 target include:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>LLVM 2.9 includes a complete reimplementation of the MMX instruction set.
|
|
The reimplementation uses a new LLVM IR <a
|
|
href="LangRef.html#t_x86mmx">x86_mmx</a> type to ensure that MMX operations
|
|
are <em>only</em> generated from source that uses MMX builtin operations. With
|
|
this, random types like <2 x i32> are not turned into MMX operations
|
|
(which can be catastrophic without proper "emms" insertion). Because the X86
|
|
code generator always generates reliable code, the -disable-mmx flag is now
|
|
removed.
|
|
</li>
|
|
|
|
<li>X86 support for FS/GS relative loads and stores using <a
|
|
href="CodeGenerator.html#x86_memory">address space 256/257</a> works reliably
|
|
now.</li>
|
|
|
|
<li>LLVM 2.9 generates much better code in several cases by using adc/sbb to
|
|
avoid generation of conditional move instructions for conditional increment
|
|
and other idioms.</li>
|
|
|
|
<li>The X86 backend has adopted a new preRA scheduling mode, "list-ilp", to
|
|
shorten the height of instruction schedules without inducing register spills.
|
|
</li>
|
|
|
|
<li>The MC assembler supports 3dNow! and 3DNowA instructions.</li>
|
|
|
|
<li>Several bugs have been fixed for Windows x64 code generator.</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!--=========================================================================-->
|
|
<h3>
|
|
<a name="ARM">ARM Target Improvements</a>
|
|
</h3>
|
|
|
|
<div>
|
|
<p>New features of the ARM target include:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>The ARM backend now has a fast instruction selector, which dramatically
|
|
improves -O0 compile times.</li>
|
|
<li>The ARM backend has new tuning for Cortex-A8 and Cortex-A9 CPUs.</li>
|
|
<li>The __builtin_prefetch builtin (and llvm.prefetch intrinsic) is compiled
|
|
into prefetch instructions instead of being discarded.</li>
|
|
|
|
<li> The ARM backend preRA scheduler now models machine resources at cycle
|
|
granularity. This allows the scheduler to both accurately model
|
|
instruction latency and avoid overcommitting functional units.</li>
|
|
|
|
<li>Countless ARM microoptimizations have landed in LLVM 2.9.</li>
|
|
</ul>
|
|
</div>
|
|
|
|
<!--=========================================================================-->
|
|
<h3>
|
|
<a name="OtherTS">Other Target Specific Improvements</a>
|
|
</h3>
|
|
|
|
<div>
|
|
<ul>
|
|
<li>MicroBlaze: major updates for aggressive delay slot filler, MC-based
|
|
assembly printing, assembly instruction parsing, ELF .o file emission, and MC
|
|
instruction disassembler have landed.</li>
|
|
|
|
<li>SPARC: Many improvements, including using the Y registers for
|
|
multiplications and addition of a simple delay slot filler.</li>
|
|
|
|
<li>PowerPC: The backend has been largely MC'ized and is ready to support
|
|
directly writing out mach-o object files. No one seems interested in finishing
|
|
this final step though.</li>
|
|
|
|
<li>Mips: Improved o32 ABI support, including better varags handling.
|
|
More instructions supported in codegen: madd, msub, rotr, rotrv and clo.
|
|
It also now supports lowering block addresses.</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 2.8, this section lists some "gotchas" that you may run into upgrading
|
|
from the previous release.</p>
|
|
|
|
<ul>
|
|
<li><b>This is the last release to support the llvm-gcc frontend.</b></li>
|
|
|
|
<li>LLVM has a new <a href="CodingStandards.html#ll_naming">naming
|
|
convention standard</a>, though the codebase hasn't fully adopted it yet.</li>
|
|
|
|
<li>The new DIBuilder class provides a simpler interface for front ends to
|
|
encode debug info in LLVM IR, and has replaced DIFactory.</li>
|
|
|
|
<li>LLVM IR and other tools always work on normalized target triples (which have
|
|
been run through <tt>Triple::normalize</tt>).</li>
|
|
|
|
<li>The target triple x86_64--mingw64 is obsoleted. Use x86_64--mingw32
|
|
instead.</li>
|
|
|
|
<li>The PointerTracking pass has been removed from mainline, and moved to The
|
|
ClamAV project (its only client).</li>
|
|
|
|
<li>The LoopIndexSplit, LiveValues, SimplifyHalfPowrLibCalls, GEPSplitter, and
|
|
PartialSpecialization passes were removed. They were unmaintained,
|
|
buggy, or deemed to be a bad idea.</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!--=========================================================================-->
|
|
<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>include/llvm/System merged into include/llvm/Support.</li>
|
|
<li>The <a href="http://llvm.org/PR5207">llvm::APInt API</a> was significantly
|
|
cleaned up.</li>
|
|
|
|
<li>In the code generator, MVT::Flag was renamed to MVT::Glue to more accurately
|
|
describe its behavior.</li>
|
|
|
|
<li>The system_error header from C++0x was added, and is now pervasively used to
|
|
capture and handle i/o and other errors in LLVM.</li>
|
|
|
|
<li>The old sys::Path API has been deprecated in favor of the new PathV2 API,
|
|
which is more efficient and flexible.</li>
|
|
</ul>
|
|
</div>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<h2>
|
|
<a name="knownproblems">Known Problems</a>
|
|
</h2>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div>
|
|
|
|
<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>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="experimental">Experimental features included with this release</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>The following components of this LLVM release are either untested, known to
|
|
be broken or unreliable, or are in early development. These components should
|
|
not be relied on, and bugs should not be filed against them, but they may be
|
|
useful to some people. In particular, if you would like to work on one of these
|
|
components, please contact us on the <a
|
|
href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
|
|
|
|
<ul>
|
|
<li>The Alpha, Blackfin, CellSPU, MicroBlaze, MSP430, MIPS, PTX, SystemZ
|
|
and XCore backends are experimental.</li>
|
|
<li><tt>llc</tt> "<tt>-filetype=obj</tt>" is experimental on all targets
|
|
other than darwin and ELF X86 systems.</li>
|
|
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="x86-be">Known problems with the X86 back-end</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<ul>
|
|
<li>The X86 backend does not yet support
|
|
all <a href="http://llvm.org/PR879">inline assembly that uses the X86
|
|
floating point stack</a>. It supports the 'f' and 't' constraints, but not
|
|
'u'.</li>
|
|
<li>The X86-64 backend does not yet support the LLVM IR instruction
|
|
<tt>va_arg</tt>. Currently, front-ends support variadic
|
|
argument constructs on X86-64 by lowering them manually.</li>
|
|
<li>Windows x64 (aka Win64) code generator has a few issues.
|
|
<ul>
|
|
<li>llvm-gcc cannot build the mingw-w64 runtime currently
|
|
due to lack of support for the 'u' inline assembly
|
|
constraint and for X87 floating point inline assembly.</li>
|
|
<li>On mingw-w64, you will see unresolved symbol <tt>__chkstk</tt>
|
|
due to <a href="http://llvm.org/bugs/show_bug.cgi?id=8919">Bug 8919</a>.
|
|
It is fixed in <a href="http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110321/118499.html">r128206</a>.</li>
|
|
<li>Miss-aligned MOVDQA might crash your program. It is due to
|
|
<a href="http://llvm.org/bugs/show_bug.cgi?id=9483">Bug 9483</a>,
|
|
lack of handling aligned internal globals.</li>
|
|
</ul>
|
|
</li>
|
|
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="ppc-be">Known problems with the PowerPC back-end</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<ul>
|
|
<li>The Linux PPC32/ABI support needs testing for the interpreter and static
|
|
compilation, and lacks support for debug information.</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="arm-be">Known problems with the ARM back-end</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<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>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="sparc-be">Known problems with the SPARC back-end</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<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>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="mips-be">Known problems with the MIPS back-end</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<ul>
|
|
<li>64-bit MIPS targets are not supported yet.</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="alpha-be">Known problems with the Alpha back-end</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<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>
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="c-be">Known problems with the C back-end</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p>The C backend has numerous problems and is not being actively maintained.
|
|
Depending on it for anything serious is not advised.</p>
|
|
|
|
<ul>
|
|
<li><a href="http://llvm.org/PR802">The C backend has only basic support for
|
|
inline assembly code</a>.</li>
|
|
<li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common
|
|
C++ programs</a>, preventing intermixing between C++ compiled by the CBE and
|
|
C++ code compiled with <tt>llc</tt> or native compilers.</li>
|
|
<li>The C backend does not support all exception handling constructs.</li>
|
|
<li>The C backend does not support arbitrary precision integers.</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
<h3>
|
|
<a name="llvm-gcc">Known problems with the llvm-gcc front-end</a>
|
|
</h3>
|
|
|
|
<div>
|
|
|
|
<p><b>LLVM 2.9 will be the last release of llvm-gcc.</b></p>
|
|
|
|
<p>llvm-gcc is generally very stable for the C family of languages. The only
|
|
major language feature of GCC not supported by llvm-gcc is the
|
|
<tt>__builtin_apply</tt> family of builtins. However, some extensions
|
|
are only supported on some targets. For example, trampolines are only
|
|
supported on some targets (these are used when you take the address of a
|
|
nested function).</p>
|
|
|
|
<p>Fortran support generally works, but there are still several unresolved bugs
|
|
in <a href="http://llvm.org/bugs/">Bugzilla</a>. Please see the
|
|
tools/gfortran component for details. Note that llvm-gcc is missing major
|
|
Fortran performance work in the frontend and library that went into GCC after
|
|
4.2. If you are interested in Fortran, we recommend that you consider using
|
|
<a href="#dragonegg">dragonegg</a> instead.</p>
|
|
|
|
<p>The llvm-gcc 4.2 Ada compiler has basic functionality, but is no longer being
|
|
actively maintained. If you are interested in Ada, we recommend that you
|
|
consider using <a href="#dragonegg">dragonegg</a> instead.</p>
|
|
</div>
|
|
|
|
</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>
|
|
|
|
<!-- *********************************************************************** -->
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<a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
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