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37 KiB
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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 2.0 Release Notes</title>
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</head>
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<body>
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<div class="doc_title">LLVM 2.0 Release Notes</div>
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<ol>
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<li><a href="#intro">Introduction</a></li>
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<li><a href="#whatsnew">What's New?</a></li>
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<li><a href="GettingStarted.html">Installation Instructions</a></li>
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<li><a href="#portability">Portability and Supported Platforms</a></li>
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<li><a href="#knownproblems">Known Problems</a>
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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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<div class="doc_section">
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<a name="intro">Introduction</a>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>This document contains the release notes for the LLVM compiler
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infrastructure, release 2.0. Here we describe the status of LLVM, including
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major improvements from the previous release and any known problems. All LLVM
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releases may be downloaded from the <a href="http://llvm.org/releases/">LLVM
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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://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM developer's mailing
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list</a> is a good place to send them.</p>
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<p>Note that if you are reading this file from CVS or the main LLVM web page,
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this document applies to the <i>next</i> release, not the current one. To see
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the release notes for the current or previous releases, see the <a
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href="http://llvm.org/releases/">releases page</a>.</p>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section">
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<a name="whatsnew">What's New?</a>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>This is the eleventh public release of the LLVM Compiler Infrastructure.
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Being the first major release since 1.0, this release is different in several
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ways from our previous releases:</p>
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<ol>
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<li>We took this as an opportunity to
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break backwards compatibility with the LLVM 1.x bytecode and .ll file format.
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If you have LLVM 1.9 .ll files that you would like to upgrade to LLVM 2.x, we
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recommend the use of the stand alone <a href="#llvm-upgrade">llvm-upgrade</a>
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tool (which is included with 2.0). We intend to keep compatibility with .ll
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and .bc formats within the 2.x release series, like we did within the 1.x
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series.</li>
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<li>There are several significant change to the LLVM IR and internal APIs, such
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as a major overhaul of the type system, the completely new bitcode file
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format, etc (described below).</li>
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<li>We designed the release around a 6 month release cycle instead of the usual
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3-month cycle. This gave us extra time to develop and test some of the
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more invasive features in this release.</li>
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<li>LLVM 2.0 no longer supports the llvm-gcc3 front-end. Users are required to
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upgrade to llvm-gcc4. llvm-gcc4 includes many features over
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llvm-gcc3, is faster, and is <a href="CFEBuildInstrs.html">much easier to
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build from source</a>.</li>
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</ol>
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<p>Note that while this is a major version bump, this release has been
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extensively tested on a wide range of software. It is easy to say that this
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is our best release yet, in terms of both features and correctness. This is
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the first LLVM release to correctly compile and optimize major software like
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LLVM itself, Mozilla/Seamonkey, Qt 4.3rc1, kOffice, etc out of the box on
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linux/x86.
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</p>
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</div>
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<!--=========================================================================-->
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<div class="doc_subsection">
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<a name="newfeatures">New Features in LLVM 2.0</a>
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</div>
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<!--_________________________________________________________________________-->
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<div class="doc_subsubsection"><a name="majorchanges">Major Changes</a></div>
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<div class="doc_text">
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<p>Changes to the LLVM IR itself:</p>
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<ul>
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<li>Integer types are now completely signless. This means that we
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have types like i8/i16/i32 instead of ubyte/sbyte/short/ushort/int
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etc. LLVM operations that depend on sign have been split up into
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separate instructions (<a href="http://llvm.org/PR950">PR950</a>). This
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eliminates cast instructions that just change the sign of the operands (e.g.
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int -> uint), which reduces the size of the IR and makes optimizers
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simpler to write.</li>
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<li>Integer types with arbitrary bitwidths (e.g. i13, i36, i42, i1057, etc) are
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now supported in the LLVM IR and optimizations (<a
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href="http://llvm.org/PR1043">PR1043</a>). However, neither llvm-gcc
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(<a href="http://llvm.org/PR1284">PR1284</a>) nor the native code generators
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(<a href="http://llvm.org/PR1270">PR1270</a>) support non-standard width
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integers yet.</li>
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<li>'Type planes' have been removed (<a href="http://llvm.org/PR411">PR411</a>).
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It is no longer possible to have two values with the same name in the
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same symbol table. This simplifies LLVM internals, allowing significant
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speedups.</li>
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<li>Global variables and functions in .ll files are now prefixed with
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@ instead of % (<a href="http://llvm.org/PR645">PR645</a>).</li>
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<li>The LLVM 1.x "bytecode" format has been replaced with a
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completely new binary representation, named 'bitcode'. The <a
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href="BitCodeFormat.html">Bitcode Format</a> brings a
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number of advantages to the LLVM over the old bytecode format: it is denser
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(files are smaller), more extensible, requires less memory to read,
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is easier to keep backwards compatible (so LLVM 2.5 will read 2.0 .bc
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files), and has many other nice features.</li>
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<li>Load and store instructions now track the alignment of their pointer
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(<a href="http://www.llvm.org/PR400">PR400</a>). This allows the IR to
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express loads that are not sufficiently aligned (e.g. due to '<tt>#pragma
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packed</tt>') or to capture extra alignment information.</li>
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</ul>
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<p>Major new features:</p>
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<ul>
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<li>A number of ELF features are now supported by LLVM, including 'visibility',
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extern weak linkage, Thread Local Storage (TLS) with the <tt>__thread</tt>
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keyword, and symbol aliases.
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Among other things, this means that many of the special options needed to
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configure llvm-gcc on linux are no longer needed, and special hacks to build
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large C++ libraries like Qt are not needed.</li>
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<li>LLVM now has a new MSIL backend. <tt>llc -march=msil</tt> will now turn LLVM
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into MSIL (".net") bytecode. This is still fairly early development
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with a number of limitations.</li>
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<li>A new <a href="CommandGuide/html/llvm-upgrade.html">llvm-upgrade</a> tool
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exists to migrates LLVM 1.9 .ll files to LLVM 2.0 syntax.</li>
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</ul>
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</div>
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<!--_________________________________________________________________________-->
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<div class="doc_subsubsection"><a name="llvmgccfeatures">llvm-gcc
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Improvements</a></div>
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<div class="doc_text">
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<p>New features include:
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</p>
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<ul>
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<li>Precompiled Headers (PCH) are now supported.</li>
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<li>"<tt>#pragma packed</tt>" is now supported, as are the various features
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described above (visibility, extern weak linkage, __thread, aliases,
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etc).</li>
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<li>Tracking function parameter/result attributes is now possible.</li>
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<li>Many internal enhancements have been added, such as improvements to
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NON_LVALUE_EXPR, arrays with non-zero base, structs with variable sized
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fields, VIEW_CONVERT_EXPR, CEIL_DIV_EXPR, nested functions, and many other
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things. This is primarily to supports non-C GCC front-ends, like Ada.</li>
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<li>It is simpler to configure llvm-gcc for linux.</li>
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</ul>
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</div>
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<!--_________________________________________________________________________-->
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<div class="doc_subsubsection"><a name="optimizer">Optimizer
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Improvements</a></div>
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<div class="doc_text">
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<p>New features include:
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</p>
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<ul>
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<li>The <a href="WritingAnLLVMPass.html">pass manager</a> has been entirely
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rewritten, making it significantly smaller, simpler, and more extensible.
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Support has been added to run <tt>FunctionPass</tt>es interlaced with
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<tt>CallGraphSCCPass</tt>es, we now support loop transformations
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explicitly with <tt>LoopPass</tt>, and <tt>ModulePass</tt>es may now use the
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result of <tt>FunctionPass</tt>es.</li>
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<li>LLVM 2.0 includes a new loop rotation pass, which converts "for loops" into
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"do/while loops", where the condition is at the bottom of the loop.</li>
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<li>The Loop Strength Reduction pass has been improved, and we now support
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sinking expressions across blocks to reduce register pressure.</li>
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<li>The <tt>-scalarrepl</tt> pass can now promote unions containing FP values
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into a register, it can also handle unions of vectors of the same
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size.</li>
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<li>The [Post]DominatorSet classes have been removed from LLVM and clients
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switched to use the more-efficient ETForest class instead.</li>
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<li>The ImmediateDominator class has also been removed, and clients have been
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switched to use DominatorTree instead.</li>
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<li>The predicate simplifier pass has been improved, making it able to do
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simple value range propagation and eliminate more conditionals. However,
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note that predsimplify is not enabled by default in llvm-gcc.</li>
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</ul>
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</div>
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<!--_________________________________________________________________________-->
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<div class="doc_subsubsection"><a name="codegen">Code
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Generator Enhancements</a></div>
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<div class="doc_text">
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<p>
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New features include:
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</p>
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<ul>
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<li>LLVM now supports software floating point, which allows LLVM to target
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chips that don't have hardware FPUs (e.g. ARM thumb mode).</li>
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<li>A new register scavenger has been implemented, which is useful for
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finding free registers after register allocation. This is useful when
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rewriting frame references on RISC targets, for example.</li>
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<li>Heuristics have been added to avoid coalescing vregs with very large live
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ranges to physregs. This was bad because it effectively pinned the physical
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register for the entire lifetime of the virtual register (<a
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href="http://llvm.org/PR711">PR711</a>).</li>
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<li>Support now exists for very simple (but still very useful)
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rematerialization the register allocator, enough to move
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instructions like "load immediate" and constant pool loads.</li>
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<li>Switch statement lowering is significantly better, improving codegen for
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sparse switches that have dense subregions, and implemented support
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for the shift/and trick.</li>
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<li>LLVM now supports tracking physreg sub-registers and super-registers
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in the code generator, and includes extensive register
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allocator changes to track them.</li>
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<li>There is initial support for virtreg sub-registers
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(<a href="http://llvm.org/PR1350">PR1350</a>).</li>
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</ul>
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<p>
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Other improvements include:
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</p>
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<ul>
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<li>Inline assembly support is much more solid that before.
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The two primary features still missing are support for 80-bit floating point
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stack registers on X86 (<a href="http://llvm.org/PR879">PR879</a>), and
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support for inline asm in the C backend (<a
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href="http://llvm.org/PR802">PR802</a>).</li>
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<li>DWARF debug information generation has been improved. LLVM now passes
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most of the GDB testsuite on MacOS and debug info is more dense.</li>
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<li>Codegen support for Zero-cost DWARF exception handling has been added (<a
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href="http://llvm.org/PR592">PR592</a>). It is mostly
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complete and just in need of continued bug fixes and optimizations at
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this point. However, support in llvm-g++ is disabled with an
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#ifdef for the 2.0 release (<a
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href="http://llvm.org/PR870">PR870</a>).</li>
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<li>The code generator now has more accurate and general hooks for
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describing addressing modes ("isLegalAddressingMode") to
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optimizations like loop strength reduction and code sinking.</li>
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<li>Progress has been made on a direct Mach-o .o file writer. Many small
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apps work, but it is still not quite complete.</li>
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</ul>
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<p>In addition, the LLVM target description format has itself been extended in
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several ways:</p>
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<ul>
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<li>TargetData now supports better target parameterization in
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the .ll/.bc files, eliminating the 'pointersize/endianness' attributes
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in the files (<a href="http://llvm.org/PR761">PR761</a>).</li>
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<li>TargetData was generalized for finer grained alignment handling,
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handling of vector alignment, and handling of preferred alignment</li>
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<li>LLVM now supports describing target calling conventions
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explicitly in .td files, reducing the amount of C++ code that needs
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to be written for a port.</li>
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</ul>
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</div>
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<!--_________________________________________________________________________-->
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<div class="doc_subsubsection"><a name="specifictargets">Target-Specific
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Improvements</a></div>
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<div class="doc_text">
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<p>X86-specific Code Generator Enhancements:
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</p>
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<ul>
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<li>The MMX instruction set is now supported through intrinsics.</li>
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<li>The scheduler was improved to better reduce register pressure on
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X86 and other targets that are register pressure sensitive.</li>
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<li>Linux/x86-64 support is much better.</li>
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<li>PIC support for linux/x86 has been added.</li>
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<li>The X86 backend now supports the GCC regparm attribute.</li>
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<li>LLVM now supports inline asm with multiple constraint letters per operand
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(like "mri") which is common in X86 inline asms.</li>
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</ul>
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<p>ARM-specific Code Generator Enhancements:</p>
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<ul>
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<li>The ARM code generator is now stable and fully supported.</li>
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<li>There are major new features, including support for ARM
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v4-v6 chips, vfp support, soft float point support, pre/postinc support,
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load/store multiple generation, constant pool entry motion (to support
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large functions), inline asm support, weak linkage support, static
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ctor/dtor support and many bug fixes.</li>
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<li>Added support for Thumb code generation (<tt>llc -march=thumb</tt>).</li>
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<li>The ARM backend now supports the ARM AAPCS/EABI ABI and PIC codegen on
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arm/linux.</li>
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<li>Several bugs were fixed for DWARF debug info generation on arm/linux.</li>
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</ul>
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<p>PowerPC-specific Code Generator Enhancements:</p>
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<ul>
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<li>The PowerPC 64 JIT now supports addressing code loaded above the 2G
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boundary.</li>
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<li>Improved support for the Linux/ppc ABI and the linux/ppc JIT is fully
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functional now. llvm-gcc and static compilation are not fully supported
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yet though.</li>
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<li>Many PowerPC 64 bug fixes.</li>
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</ul>
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</div>
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<!--_________________________________________________________________________-->
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<div class="doc_subsubsection"><a name="other">Other Improvements</a></div>
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<div class="doc_text">
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<p>More specific changes include:</p>
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<ul>
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<li>LLVM no longer relies on static destructors to shut itself down. Instead,
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it lazily initializes itself and shuts down when <tt>llvm_shutdown()</tt> is
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explicitly called.</li>
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<li>LLVM now has significantly fewer static constructors, reducing startup time.
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</li>
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<li>Several classes have been refactored to reduce the amount of code that
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gets linked into apps that use the JIT.</li>
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<li>Construction of intrinsic function declarations has been simplified.</li>
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<li>The gccas/gccld tools have been replaced with small shell scripts.</li>
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<li>Support has been added to llvm-test for running on low-memory
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or slow machines (make SMALL_PROBLEM_SIZE=1).</li>
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</ul>
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</div>
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<!--_________________________________________________________________________-->
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<div class="doc_subsubsection"><a name="apichanges">API Changes</a></div>
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<div class="doc_text">
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<p>LLVM 2.0 contains a revamp of the type system and several other significant
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internal changes. If you are programming to the C++ API, be aware of the
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following major changes:</p>
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<ul>
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<li>Pass registration is slightly different in LLVM 2.0 (you now need an
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<tt>intptr_t</tt> in your constructor), as explained in the <a
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href="WritingAnLLVMPass.html#basiccode">Writing an LLVM Pass</a>
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document.</li>
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<li><tt>ConstantBool</tt>, <tt>ConstantIntegral</tt> and <tt>ConstantInt</tt>
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classes have been merged together, we now just have
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<tt>ConstantInt</tt>.</li>
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<li><tt>Type::IntTy</tt>, <tt>Type::UIntTy</tt>, <tt>Type::SByteTy</tt>, ... are
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replaced by <tt>Type::Int8Ty</tt>, <tt>Type::Int16Ty</tt>, etc. LLVM types
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have always corresponded to fixed size types
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(e.g. long was always 64-bits), but the type system no longer includes
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information about the sign of the type. Also, the
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<tt>Type::isPrimitiveType()</tt> method now returns false for integers.</li>
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<li>Several classes (<tt>CallInst</tt>, <tt>GetElementPtrInst</tt>,
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<tt>ConstantArray</tt>, etc), that once took <tt>std::vector</tt> as
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arguments now take ranges instead. For example, you can create a
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<tt>GetElementPtrInst</tt> with code like:
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<pre>
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Value *Ops[] = { Op1, Op2, Op3 };
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GEP = new GetElementPtrInst(BasePtr, Ops, 3);
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</pre>
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This avoids creation of a temporary vector (and a call to malloc/free). If
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you have an <tt>std::vector</tt>, use code like this:
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<pre>
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std::vector<Value*> Ops = ...;
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GEP = new GetElementPtrInst(BasePtr, &Ops[0], Ops.size());
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</pre>
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</li>
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<li><tt>CastInst</tt> is now abstract and its functionality is split into
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several parts, one for each of the <a href="LangRef.html#convertops">new
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cast instructions</a>.</li>
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<li><tt>Instruction::getNext()/getPrev()</tt> are now private (along with
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<tt>BasicBlock::getNext</tt>, etc), for efficiency reasons (they are now no
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longer just simple pointers). Please use <tt>BasicBlock::iterator</tt>, etc
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instead.
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</li>
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<li><tt>Module::getNamedFunction()</tt> is now called
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<tt>Module::getFunction()</tt>.</li>
|
|
|
|
<li><tt>SymbolTable.h</tt> has been split into <tt>ValueSymbolTable.h</tt> and
|
|
<tt>TypeSymbolTable.h</tt>.</li>
|
|
</ul>
|
|
</div>
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section">
|
|
<a name="portability">Portability and Supported Platforms</a>
|
|
</div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>LLVM is known to work on the following platforms:</p>
|
|
|
|
<ul>
|
|
<li>Intel and AMD machines running Red Hat Linux, Fedora Core and FreeBSD
|
|
(and probably other unix-like systems).</li>
|
|
<li>PowerPC and X86-based Mac OS X systems, running 10.2 and above in 32-bit and
|
|
64-bit modes.</li>
|
|
<li>Intel and AMD machines running on Win32 using MinGW libraries (native)</li>
|
|
<li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited
|
|
support is available for native builds with Visual C++).</li>
|
|
<li>Sun UltraSPARC workstations running Solaris 8.</li>
|
|
<li>Alpha-based machines running Debian GNU/Linux.</li>
|
|
<li>Itanium-based machines running Linux and HP-UX.</li>
|
|
</ul>
|
|
|
|
<p>The core LLVM infrastructure uses
|
|
<a href="http://www.gnu.org/software/autoconf/">GNU autoconf</a> to adapt itself
|
|
to the machine and operating system on which it is built. However, minor
|
|
porting may be required to get LLVM to work on new platforms. We welcome your
|
|
portability patches and reports of successful builds or error messages.</p>
|
|
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section">
|
|
<a name="knownproblems">Known Problems</a>
|
|
</div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>This section contains all known problems with the LLVM system, listed by
|
|
component. As new problems are discovered, they will be added to these
|
|
sections. If you run into a problem, please check the <a
|
|
href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
|
|
there isn't already one.</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="experimental">Experimental features included with this release</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>The following components of this LLVM release are either untested, known to
|
|
be broken or unreliable, or are in early development. These components should
|
|
not be relied on, and bugs should not be filed against them, but they may be
|
|
useful to some people. In particular, if you would like to work on one of these
|
|
components, please contact us on the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
|
|
|
|
<ul>
|
|
<li>The <tt>-cee</tt> pass is known to be buggy, and may be removed in in a
|
|
future release.</li>
|
|
<li>C++ EH support is disabled for this release.</li>
|
|
<li>The MSIL backend is experimental.</li>
|
|
<li>The IA64 code generator is experimental.</li>
|
|
<li>The Alpha JIT is experimental.</li>
|
|
<li>"<tt>-filetype=asm</tt>" (the default) is the only supported value for the
|
|
<tt>-filetype</tt> llc option.</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="x86-be">Known problems with the X86 back-end</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<ul>
|
|
<li>The X86 backend does not yet support <a href="http://llvm.org/PR879">inline
|
|
assembly that uses the X86 floating point stack</a>.</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="ppc-be">Known problems with the PowerPC back-end</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<ul>
|
|
<li><a href="http://llvm.org/PR642">PowerPC backend does not correctly
|
|
implement ordered FP comparisons</a>.</li>
|
|
<li>The Linux PPC32/ABI support needs testing for the interpreter and static
|
|
compilation, and lacks support for debug information.</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="arm-be">Known problems with the ARM back-end</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<ul>
|
|
<li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
|
|
processors, thumb program can crash or produces 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>
|
|
<li>There is a bug in QEMU-ARM (<= 0.9.0) which causes it to incorrectly execute
|
|
programs compiled with LLVM. Please use more recent versions of QEMU.</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="sparc-be">Known problems with the SPARC back-end</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<ul>
|
|
<li>The SPARC backend only supports the 32-bit SPARC ABI (-m32), it does not
|
|
support the 64-bit SPARC ABI (-m64).</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="alpha-be">Known problems with the Alpha back-end</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<ul>
|
|
|
|
<li>On 21164s, some rare FP arithmetic sequences which may trap do not have the
|
|
appropriate nops inserted to ensure restartability.</li>
|
|
|
|
</ul>
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="ia64-be">Known problems with the IA64 back-end</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<ul>
|
|
|
|
<li>C++ programs are likely to fail on IA64, as calls to <tt>setjmp</tt> are
|
|
made where the argument is not 16-byte aligned, as required on IA64. (Strictly
|
|
speaking this is not a bug in the IA64 back-end; it will also be encountered
|
|
when building C++ programs using the C back-end.)</li>
|
|
|
|
<li>The C++ front-end does not use <a href="http://llvm.org/PR406">IA64
|
|
ABI compliant layout of v-tables</a>. In particular, it just stores function
|
|
pointers instead of function descriptors in the vtable. This bug prevents
|
|
mixing C++ code compiled with LLVM with C++ objects compiled by other C++
|
|
compilers.</li>
|
|
|
|
<li>There are a few ABI violations which will lead to problems when mixing LLVM
|
|
output with code built with other compilers, particularly for floating-point
|
|
programs.</li>
|
|
|
|
<li>Defining vararg functions is not supported (but calling them is ok).</li>
|
|
|
|
<li>The Itanium backend has bitrotted somewhat.</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="c-be">Known problems with the C back-end</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<ul>
|
|
<li><a href="http://llvm.org/PR802">The C backend does not support inline
|
|
assembly code</a>.</li>
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="c-fe">Known problems with the C front-end</a>
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">Bugs</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>llvm-gcc4 does not currently support <a href="http://llvm.org/PR869">Link-Time
|
|
Optimization</a> on most platforms "out-of-the-box". Please inquire on the
|
|
llvmdev mailing list if you are interested.</p>
|
|
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">
|
|
Notes
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
<ul>
|
|
|
|
<li><p>"long double" is silently transformed by the front-end into "double". There
|
|
is no support for floating point data types of any size other than 32 and 64
|
|
bits.</p></li>
|
|
|
|
<li><p>llvm-gcc does <b>not</b> support <tt>__builtin_apply</tt> yet.
|
|
See <a href="http://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing%20Calls">Constructing Calls</a>: Dispatching a call to another function.</p>
|
|
</li>
|
|
|
|
<li><p>llvm-gcc <b>partially</b> supports these GCC extensions:</p>
|
|
<ol>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html#Nested%20Functions">Nested Functions</a>: As in Algol and Pascal, lexical scoping of functions.<br>
|
|
Nested functions are supported, but llvm-gcc does not support non-local
|
|
gotos or taking the address of a nested function.</li>
|
|
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#Function%20Attributes">Function Attributes</a>:
|
|
|
|
Declaring that functions have no side effects or that they can never
|
|
return.<br>
|
|
|
|
<b>Supported:</b> <tt>alias</tt>, <tt>always_inline</tt>, <tt>cdecl</tt>,
|
|
<tt>constructor</tt>, <tt>destructor</tt>,
|
|
<tt>deprecated</tt>, <tt>fastcall</tt>, <tt>format</tt>,
|
|
<tt>format_arg</tt>, <tt>non_null</tt>, <tt>noreturn</tt>, <tt>regparm</tt>
|
|
<tt>section</tt>, <tt>stdcall</tt>, <tt>unused</tt>, <tt>used</tt>,
|
|
<tt>visibility</tt>, <tt>warn_unused_result</tt>, <tt>weak</tt><br>
|
|
|
|
<b>Ignored:</b> <tt>noinline</tt>, <tt>pure</tt>, <tt>const</tt>, <tt>nothrow</tt>,
|
|
<tt>malloc</tt>, <tt>no_instrument_function</tt></li>
|
|
</ol>
|
|
</li>
|
|
|
|
<li><p>llvm-gcc supports the vast majority of GCC extensions, including:</p>
|
|
|
|
<ol>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pragmas.html#Pragmas">Pragmas</a>: Pragmas accepted by GCC.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Local-Labels.html#Local%20Labels">Local Labels</a>: Labels local to a block.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other%20Builtins">Other Builtins</a>:
|
|
Other built-in functions.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable%20Attributes">Variable Attributes</a>:
|
|
Specifying attributes of variables.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html#Type%20Attributes">Type Attributes</a>: Specifying attributes of types.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Thread_002dLocal.html">Thread-Local</a>: Per-thread variables.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable%20Length">Variable Length</a>:
|
|
Arrays whose length is computed at run time.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html#Labels%20as%20Values">Labels as Values</a>: Getting pointers to labels and computed gotos.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement%20Exprs">Statement Exprs</a>: Putting statements and declarations inside expressions.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Typeof.html#Typeof">Typeof</a>: <code>typeof</code>: referring to the type of an expression.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc-3.4.0/gcc/Lvalues.html#Lvalues">Lvalues</a>: Using <code>?:</code>, "<code>,</code>" and casts in lvalues.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Conditionals.html#Conditionals">Conditionals</a>: Omitting the middle operand of a <code>?:</code> expression.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Long-Long.html#Long%20Long">Long Long</a>: Double-word integers.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Complex.html#Complex">Complex</a>: Data types for complex numbers.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Hex-Floats.html#Hex%20Floats">Hex Floats</a>:Hexadecimal floating-point constants.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html#Zero%20Length">Zero Length</a>: Zero-length arrays.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Empty-Structures.html#Empty%20Structures">Empty Structures</a>: Structures with no members.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variadic-Macros.html#Variadic%20Macros">Variadic Macros</a>: Macros with a variable number of arguments.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Escaped-Newlines.html#Escaped%20Newlines">Escaped Newlines</a>: Slightly looser rules for escaped newlines.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Extended%20Asm">Extended Asm</a>: Assembler instructions with C expressions as operands.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constraints.html#Constraints">Constraints</a>: Constraints for asm operands.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Asm-Labels.html#Asm%20Labels">Asm Labels</a>: Specifying the assembler name to use for a C symbol.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Explicit-Reg-Vars.html#Explicit%20Reg%20Vars">Explicit Reg Vars</a>: Defining variables residing in specified registers.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html#Vector%20Extensions">Vector Extensions</a>: Using vector instructions through built-in functions.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Target-Builtins.html#Target%20Builtins">Target Builtins</a>: Built-in functions specific to particular targets.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Subscripting.html#Subscripting">Subscripting</a>: Any array can be subscripted, even if not an lvalue.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pointer-Arith.html#Pointer%20Arith">Pointer Arith</a>: Arithmetic on <code>void</code>-pointers and function pointers.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Initializers.html#Initializers">Initializers</a>: Non-constant initializers.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Compound-Literals.html#Compound%20Literals">Compound Literals</a>: Compound literals give structures, unions,
|
|
or arrays as values.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html#Designated%20Inits">Designated Inits</a>: Labeling elements of initializers.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Cast-to-Union.html#Cast%20to%20Union">Cast to Union</a>: Casting to union type from any member of the union.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html#Case%20Ranges">Case Ranges</a>: `case 1 ... 9' and such.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Mixed-Declarations.html#Mixed%20Declarations">Mixed Declarations</a>: Mixing declarations and code.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Prototypes.html#Function%20Prototypes">Function Prototypes</a>: Prototype declarations and old-style definitions.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Comments.html#C_002b_002b-Comments">C++ Comments</a>: C++ comments are recognized.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html#Dollar%20Signs">Dollar Signs</a>: Dollar sign is allowed in identifiers.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Character-Escapes.html#Character%20Escapes">Character Escapes</a>: <code>\e</code> stands for the character <ESC>.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alignment.html#Alignment">Alignment</a>: Inquiring about the alignment of a type or variable.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Inline.html#Inline">Inline</a>: Defining inline functions (as fast as macros).</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alternate-Keywords.html#Alternate%20Keywords">Alternate Keywords</a>:<code>__const__</code>, <code>__asm__</code>, etc., for header files.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Incomplete-Enums.html#Incomplete%20Enums">Incomplete Enums</a>: <code>enum foo;</code>, with details to follow.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Names.html#Function%20Names">Function Names</a>: Printable strings which are the name of the current function.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Return-Address.html#Return%20Address">Return Address</a>: Getting the return or frame address of a function.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Unnamed-Fields.html#Unnamed%20Fields">Unnamed Fields</a>: Unnamed struct/union fields within structs/unions.</li>
|
|
<li><a href="http://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html#Attribute%20Syntax">Attribute Syntax</a>: Formal syntax for attributes.</li>
|
|
</ol></li>
|
|
|
|
</ul>
|
|
|
|
<p>If you run into GCC extensions which have not been included in any of these
|
|
lists, please let us know (also including whether or not they work).</p>
|
|
|
|
</div>
|
|
|
|
<!-- ======================================================================= -->
|
|
<div class="doc_subsection">
|
|
<a name="c++-fe">Known problems with the C++ front-end</a>
|
|
</div>
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>The C++ front-end is considered to be fully
|
|
tested and works for a number of non-trivial programs, including LLVM
|
|
itself, Qt, Mozilla, etc.</p>
|
|
|
|
<ul>
|
|
<li>llvm-gcc4 only has partial support for <a href="http://llvm.org/PR870">C++
|
|
Exception Handling</a>, and it is not enabled by default.</li>
|
|
|
|
<!-- NO EH Support!
|
|
|
|
<li>Destructors for local objects are not always run when a <tt>longjmp</tt> is
|
|
performed. In particular, destructors for objects in the <tt>longjmp</tt>ing
|
|
function and in the <tt>setjmp</tt> receiver function may not be run.
|
|
Objects in intervening stack frames will be destroyed, however (which is
|
|
better than most compilers).</li>
|
|
|
|
<li>The LLVM C++ front-end follows the <a
|
|
href="http://www.codesourcery.com/cxx-abi">Itanium C++ ABI</a>.
|
|
This document, which is not Itanium specific, specifies a standard for name
|
|
mangling, class layout, v-table layout, RTTI formats, and other C++
|
|
representation issues. Because we use this API, code generated by the LLVM
|
|
compilers should be binary compatible with machine code generated by other
|
|
Itanium ABI C++ compilers (such as G++, the Intel and HP compilers, etc).
|
|
<i>However</i>, the exception handling mechanism used by llvm-gcc3 is very
|
|
different from the model used in the Itanium ABI, so <b>exceptions will not
|
|
interact correctly</b>. </li>
|
|
-->
|
|
</ul>
|
|
|
|
</div>
|
|
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section">
|
|
<a name="additionalinfo">Additional Information</a>
|
|
</div>
|
|
<!-- *********************************************************************** -->
|
|
|
|
<div class="doc_text">
|
|
|
|
<p>A wide variety of additional information is available on the <a
|
|
href="http://llvm.org">LLVM web page</a>, in particular in the <a
|
|
href="http://llvm.org/docs/">documentation</a> section. The web page also
|
|
contains versions of the API documentation which is up-to-date with the CVS
|
|
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
|
|
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