2007-01-20 23:21:08 +00:00
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<title>LLVM Bitcode File Format</title>
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<link rel="stylesheet" href="llvm.css" type="text/css">
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<div class="doc_title"> LLVM Bitcode File Format </div>
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<ol>
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<li><a href="#abstract">Abstract</a></li>
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2007-05-12 03:23:40 +00:00
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<li><a href="#overview">Overview</a></li>
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<li><a href="#bitstream">Bitstream Format</a>
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<ol>
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<li><a href="#magic">Magic Numbers</a></li>
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</ol>
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</li>
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<li><a href="#llvmir">LLVM IR Encoding</a></li>
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2007-01-20 23:21:08 +00:00
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</ol>
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<div class="doc_author">
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2007-05-12 03:23:40 +00:00
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<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>.
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2007-01-20 23:21:08 +00:00
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</p>
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</div>
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2007-05-12 03:23:40 +00:00
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2007-01-20 23:21:08 +00:00
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<!-- *********************************************************************** -->
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2007-05-12 03:23:40 +00:00
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<div class="doc_section"> <a name="abstract">Abstract</a></div>
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2007-01-20 23:21:08 +00:00
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<!-- *********************************************************************** -->
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2007-05-12 03:23:40 +00:00
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2007-01-20 23:21:08 +00:00
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<div class="doc_text">
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2007-05-12 03:23:40 +00:00
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<p>This document describes the LLVM bitstream file format and the encoding of
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the LLVM IR into it.</p>
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2007-01-20 23:21:08 +00:00
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</div>
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2007-05-12 03:23:40 +00:00
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2007-01-20 23:21:08 +00:00
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<!-- *********************************************************************** -->
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2007-05-12 03:23:40 +00:00
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<div class="doc_section"> <a name="overview">Overview</a></div>
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2007-01-20 23:21:08 +00:00
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<!-- *********************************************************************** -->
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2007-05-12 03:23:40 +00:00
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2007-01-20 23:21:08 +00:00
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<div class="doc_text">
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2007-05-12 03:23:40 +00:00
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<p>
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What is commonly known as the LLVM bitcode file format (also, sometimes
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anachronistically known as bytecode) is actually two things: a <a
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href="#bitstream">bitstream container format</a>
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and an <a href="#llvmir">encoding of LLVM IR</a> into the container format.</p>
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<p>
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The bitstream format is an abstract encoding of structured data, like very
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similar to XML in some ways. Like XML, bitstream files contain tags, and nested
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structures, and you can parse the file without having to understand the tags.
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Unlike XML, the bitstream format is a binary encoding, and unlike XML it
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provides a mechanism for the file to self-describe "abbreviations", which are
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effectively size optimizations for the content.</p>
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<p>This document first describes the LLVM bitstream format, then describes the
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record structure used by LLVM IR files.
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</p>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section"> <a name="bitstream">Bitstream Format</a></div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>
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The bitstream format is literally a stream of bits, with a very simple
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structure. This structure consists of the following concepts:
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</p>
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<ul>
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<li>A magic number that identifies the stream.</li>
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<li>Encoding primitives like variable bit-rate integers.</li>
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<li>Blocks, which define nested content.</li>
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<li>Data Records, which describe entities within the file.</li>
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<li>Abbreviations, which specify compression optimizations for the file.</li>
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</ul>
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<p>Note that the <a
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href="CommandGuide/html/llvm-bcanalyzer.html">llvm-bcanalyzer</a> tool can be
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used to dump and inspect arbitrary bitstreams, which is very useful for
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understanding the encoding.</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection"><a name="magic">Magic Numbers</a>
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</div>
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<div class="doc_text">
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<p>LLVM </p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsubsection"> <a name="wellformed">Well-Formedness</a> </div>
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<div class="doc_text">
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<p>blah
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</p>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section"> <a name="llvmir">LLVM IR Encoding</a></div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p></p>
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2007-01-20 23:21:08 +00:00
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</div>
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2007-05-12 03:23:40 +00:00
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2007-01-20 23:21:08 +00:00
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<!-- *********************************************************************** -->
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2007-05-12 03:23:40 +00:00
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<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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2007-01-20 23:21:08 +00:00
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<a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
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Last modified: $Date$
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