docs/BitCodeFormat.html


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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
                      "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
  <title>LLVM Bitcode File Format</title>
  <link rel="stylesheet" href="llvm.css" type="text/css">
</head>
<body>
<div class="doc_title"> LLVM Bitcode File Format </div>
<ol>
  <li><a href="#abstract">Abstract</a></li>
  <li><a href="#overview">Overview</a></li>
  <li><a href="#bitstream">Bitstream Format</a>
    <ol>
    <li><a href="#magic">Magic Numbers</a></li>
    <li><a href="#primitives">Primitives</a></li>
    <li><a href="#abbrevid">Abbreviation IDs</a></li>
    <li><a href="#blocks">Blocks</a></li>
    <li><a href="#datarecord">Data Records</a></li>
    <li><a href="#abbreviations">Abbreviations</a></li>
    <li><a href="#stdblocks">Standard Blocks</a></li>
    </ol>
  </li>
  <li><a href="#wrapper">Bitcode Wrapper Format</a>
  </li>
  <li><a href="#llvmir">LLVM IR Encoding</a>
    <ol>
    <li><a href="#basics">Basics</a></li>
    <li><a href="#MODULE_BLOCK">MODULE_BLOCK Contents</a></li>
    <li><a href="#PARAMATTR_BLOCK">PARAMATTR_BLOCK Contents</a></li>
    <li><a href="#TYPE_BLOCK">TYPE_BLOCK Contents</a></li>
    <li><a href="#CONSTANTS_BLOCK">CONSTANTS_BLOCK Contents</a></li>
    <li><a href="#FUNCTION_BLOCK">FUNCTION_BLOCK Contents</a></li>
    <li><a href="#TYPE_SYMTAB_BLOCK">TYPE_SYMTAB_BLOCK Contents</a></li>
    <li><a href="#VALUE_SYMTAB_BLOCK">VALUE_SYMTAB_BLOCK Contents</a></li>
    <li><a href="#METADATA_BLOCK">METADATA_BLOCK Contents</a></li>
    <li><a href="#METADATA_ATTACHMENT">METADATA_ATTACHMENT Contents</a></li>
    </ol>
  </li>
</ol>
<div class="doc_author">
  <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
  and <a href="http://www.reverberate.org">Joshua Haberman</a>.
</p>
</div>

<!-- *********************************************************************** -->
<div class="doc_section"> <a name="abstract">Abstract</a></div>
<!-- *********************************************************************** -->

<div class="doc_text">

<p>This document describes the LLVM bitstream file format and the encoding of
the LLVM IR into it.</p>

</div>

<!-- *********************************************************************** -->
<div class="doc_section"> <a name="overview">Overview</a></div>
<!-- *********************************************************************** -->

<div class="doc_text">

<p>
What is commonly known as the LLVM bitcode file format (also, sometimes
anachronistically known as bytecode) is actually two things: a <a 
href="#bitstream">bitstream container format</a>
and an <a href="#llvmir">encoding of LLVM IR</a> into the container format.</p>

<p>
The bitstream format is an abstract encoding of structured data, very
similar to XML in some ways.  Like XML, bitstream files contain tags, and nested
structures, and you can parse the file without having to understand the tags.
Unlike XML, the bitstream format is a binary encoding, and unlike XML it
provides a mechanism for the file to self-describe "abbreviations", which are
effectively size optimizations for the content.</p>

<p>LLVM IR files may be optionally embedded into a <a 
href="#wrapper"