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author: Chris Lattner <sabre@nondot.org> 2007-05-06 23:21:05 +0000
committer: Chris Lattner <sabre@nondot.org> 2007-05-06 23:21:05 +0000
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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 Bytecode File Format</title>
-  <link rel="stylesheet" href="llvm.css" type="text/css">
-  <style type="text/css">
-    TR, TD { border: 2px solid gray; padding-left: 4pt; padding-right: 4pt; 
-             padding-top: 2pt; padding-bottom: 2pt; }
-    TH { border: 2px solid gray; font-weight: bold; font-size: 105%; }
-    TABLE { text-align: center; border: 2px solid black; 
-      border-collapse: collapse; margin-top: 1em; margin-left: 1em; 
-      margin-right: 1em; margin-bottom: 1em; }
-    .td_left { border: 2px solid gray; text-align: left; }
-  </style>
-</head>
-<body>
-<div class="doc_title"> LLVM Bytecode File Format </div>
-<ol>
-  <li><a href="#abstract">Abstract</a></li>
-  <li><a href="#concepts">Concepts</a>
-    <ol>
-      <li><a href="#blocks">Blocks</a></li>
-      <li><a href="#lists">Lists</a></li>
-      <li><a href="#fields">Fields</a></li>
-      <li><a href="#align">Alignment</a></li>
-      <li><a href="#vbr">Variable Bit-Rate Encoding</a></li>
-      <li><a href="#encoding">Encoding Primitives</a></li>
-      <li><a href="#slots">Slots</a></li>
-    </ol>
-  </li>
-  <li><a href="#general">General Structure</a> </li>
-  <li><a href="#blockdefs">Block Definitions</a>
-    <ol>
-      <li><a href="#signature">Signature Block</a></li>
-      <li><a href="#module">Module Block</a></li>
-      <li><a href="#globaltypes">Global Type Pool</a></li>
-      <li><a href="#globalinfo">Module Info Block</a></li>
-      <li><a href="#constantpool">Global Constant Pool</a></li>
-      <li><a href="#functiondefs">Function Definition</a></li>
-      <li><a href="#instructionlist">Instructions List</a></li>
-      <li><a href="#instructions">Instructions</a></li>
-      <li><a href="#symtab">Symbol Table</a></li>
-    </ol>
-  </li>
-  <li><a href="#versiondiffs">Version Differences</a>
-    <ol>
-      <li><a href="#vers13">Version 1.3 Differences From 1.4</a></li>
-      <li><a href="#vers12">Version 1.2 Differences From 1.3</a></li>
-      <li><a href="#vers11">Version 1.1 Differences From 1.2</a></li>
-      <li><a href="#vers10">Version 1.0 Differences From 1.1</a></li>
-    </ol>
-  </li>
-</ol>
-<div class="doc_author">
-<p>Written by <a href="mailto:rspencer@x10sys.com">Reid Spencer</a>
-</p>
-</div>
-<!-- *********************************************************************** -->
-<div class="doc_section"> <a name="abstract">Abstract </a></div>
-<!-- *********************************************************************** -->
-<div class="doc_text">
-<p>This document describes the LLVM bytecode file format. It specifies
-the binary encoding rules of the bytecode file format so that
-equivalent systems can encode bytecode files correctly. The LLVM
-bytecode representation is used to store the intermediate
-representation on disk in compacted form.</p>
-<p>The LLVM bytecode format may change in the future, but LLVM will
-always be backwards compatible with older formats. This document will
-only describe the most current version of the bytecode format. See <a
- href="#versiondiffs">Version Differences</a> for the details on how
-the current version is different from previous versions.</p>
-</div>
-<!-- *********************************************************************** -->
-<div class="doc_section"> <a name="concepts">Concepts</a> </div>
-<!-- *********************************************************************** -->
-<div class="doc_text">
-<p>This section describes the general concepts of the bytecode file
-format without getting into specific layout details. It is recommended
-that you read this section thoroughly before interpreting the detailed
-descriptions.</p>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="blocks">Blocks</a> </div>
-<div class="doc_text">
-<p>LLVM bytecode files consist simply of a sequence of blocks of bytes
-using a binary encoding Each block begins with an header of two
-unsigned integers. The first value identifies the type of block and the
-second value provides the size of the block in bytes. The block
-identifier is used because it is possible for entire blocks to be
-omitted from the file if they are empty. The block identifier helps the
-reader determine which kind of block is next in the file. Note that
-blocks can be nested within other blocks.</p>
-<p> All blocks are variable length, and the block header specifies the
-size of the block. All blocks begin on a byte index that is aligned to
-an even 32-bit boundary. That is, the first block is 32-bit aligned
-because it starts at offset 0. Each block is padded with zero fill
-bytes to ensure that the next block also starts on a 32-bit boundary.</p>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="lists">Lists</a> </div>
-<div class="doc_text">
-<p>LLVM Bytecode blocks often contain lists of things of a similar
-type. For example, a function contains a list of instructions and a
-function type contains a list of argument types. There are two basic
-types of lists: length lists (<a href="#llist">llist</a>), and null
-terminated lists (<a href="#zlist">zlist</a>), as described below in
-the <a href="#encoding">Encoding Primitives</a>.</p>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="fields">Fields</a> </div>
-<div class="doc_text">
-<p>Fields are units of information that LLVM knows how to write atomically. Most 
-fields have a uniform length or some kind of length indication built into their 
-encoding. For example, a constant string (array of bytes) is written simply as 
-the length followed by the characters. Although this is similar to a list, 
-constant strings are treated atomically and are thus fields.</p>
-<p>Fields use a condensed bit format specific to the type of information
-they must contain. As few bits as possible are written for each field. The
-sections that follow will provide the details on how these fields are
-written and how the bits are to be interpreted.</p>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="align">Alignment</a> </div>
-<div class="doc_text">
-  <p>To support cross-platform differences, the bytecode file is aligned on 
-  certain boundaries. This means that a small amount of padding (at most 3 
-  bytes) will be added to ensure that the next entry is aligned to a 32-bit 
-  boundary.</p>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="vbr">Variable Bit-Rate Encoding</a>
-</div>
-<div class="doc_text">
-<p>Most of the values written to LLVM bytecode files are small integers. To 
-minimize the number of bytes written for these quantities, an encoding scheme 
-similar to UTF-8 is used to write integer data. The scheme is known as
-variable bit rate (vbr) encoding. In this encoding, the high bit of
-each byte is used to indicate if more bytes follow. If (byte &amp;
-0x80) is non-zero in any given byte, it means there is another byte
-immediately following that also contributes to the value. For the final
-byte (byte &amp; 0x80) is false (the high bit is not set). In each byte
-only the low seven bits contribute to the value. Consequently 32-bit
-quantities can take from one to <em>five</em> bytes to encode. In
-general, smaller quantities will encode in fewer bytes, as follows:</p>
-<table>
-  <tbody>
-    <tr>
-      <th>Byte #</th>
-      <th>Significant Bits</th>
-      <th>Maximum Value</th>
-    </tr>
-    <tr>
-      <td>1</td>
-      <td>0-6</td>
-      <td>127</td>
-    </tr>
-    <tr>
-      <td>2</td>
-      <td>7-13</td>
-      <td>16,383</td>
-    </tr>
-    <tr>
-      <td>3</td>
-      <td>14-20</td>
-      <td>2,097,151</td>
-    </tr>
-    <tr>
-      <td>4</td>
-      <td>21-27</td>
-      <td>268,435,455</td>
-    </tr>
-    <tr>
-      <td>5</td>
-      <td>28-34</td>
-      <td>34,359,738,367</td>
-    </tr>
-    <tr>
-      <td>6</td>
-      <td>35-41</td>
-      <td>4,398,046,511,103</td>
-    </tr>
-    <tr>
-      <td>7</td>
-      <td>42-48</td>
-      <td>562,949,953,421,311</td>
-    </tr>
-    <tr>
-      <td>8</td>
-      <td>49-55</td>
-      <td>72,057,594,037,927,935</td>
-    </tr>
-    <tr>
-      <td>9</td>
-      <td>56-62</td>
-      <td>9,223,372,036,854,775,807</td>
-    </tr>
-    <tr>
-      <td>10</td>
-      <td>63-69</td>
-      <td>1,180,591,620,717,411,303,423</td>
-    </tr>
-  </tbody>
-</table>
-<p>Note that in practice, the tenth byte could only encode bit 63 since
-the maximum quantity to use this encoding is a 64-bit integer.</p>
-<p><em>Signed</em> VBR values are encoded with the standard vbr
-encoding, but with the sign bit as the low order bit instead of the
-high order bit. This allows small negative quantities to be encoded
-efficiently. For example, -3
-is encoded as "((3 &lt;&lt; 1) | 1)" and 3 is encoded as "(3 &lt;&lt;
-1) | 0)", emitted with the standard vbr encoding above.</p>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="encoding">Encoding Primitives</a> </div>
-<div class="doc_text">
-<p>Each field in the bytecode format is encoded into the file using a
-small set of primitive formats. The table below defines the encoding
-rules for the various primitives used and gives them each a type name.
-The type names used in the descriptions of blocks and fields in the <a
- href="#details">Detailed Layout</a>next section. Any type name with
-the suffix <em>_vbr</em> indicates a quantity that is encoded using
-variable bit rate encoding as described above.</p>
-<table class="doc_table">
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Rule</b></th>
-    </tr>
-    <tr>
-      <td><a name="unsigned"><b>unsigned</b></a></td>
-      <td class="td_left">A 32-bit unsigned integer that always occupies four 
-      consecutive bytes. The unsigned integer is encoded using LSB first 
-      ordering. That is bits 2<sup>0</sup> through 2<sup>7</sup> are in the 
-      byte with the lowest file offset (little endian).</td>
-    </tr>
-    <tr>
-      <td style="vertical-align: top;"><a name="uint24_vbr">
-        <b>uint24_vbr</b></a></td>
-      <td style="vertical-align: top; text-align: left;">A 24-bit unsigned 
-      integer that occupies from one to four bytes using variable bit rate 
-      encoding.</td>
-    </tr>
-    <tr>
-      <td><a name="uint32_vbr"><b>uint32_vbr</b></a></td>
-      <td class="td_left">A 32-bit unsigned integer that occupies from one to 
-        five bytes using variable bit rate encoding.</td>
-    </tr>
-    <tr>
-      <td><a name="uint64_vbr"><b>uint64_vbr</b></a></td>
-      <td class="td_left">A 64-bit unsigned integer that occupies from one to 
-        ten bytes using variable bit rate encoding.</td>
-    </tr>
-    <tr>
-      <td><a name="int64_vbr"><b>int64_vbr</b></a></td>
-      <td class="td_left">A 64-bit signed integer that occupies from one to ten 
-        bytes using the signed variable bit rate encoding.</td>
-    </tr>
-    <tr>
-      <td><a name="char"><b>char</b></a></td>
-      <td class="td_left">A single unsigned character encoded into one byte</td>
-    </tr>
-    <tr>
-      <td><a name="bit"><b>bit(n-m)</b></a></td>
-      <td class="td_left">A set of bit within some larger integer field. The 
-        values of <code>n</code> and <code>m</code> specify the inclusive range
-        of bits that define the subfield. The value for <code>m</code> may be 
-        omitted if its the same as <code>n</code>.</td>
-    </tr>
-    <tr>
-      <td style="vertical-align: top;"><b><a name="float"><b>float</b></a></b>
-      </td>
-      <td style="vertical-align: top; text-align: left;">A floating point 
-        value encoded as a 32-bit IEEE value written in little-endian form.<br>
-      </td>
-    </tr>
-    <tr>
-      <td style="vertical-align: top;"><b><b><a name="double"><b>double</b></a>
-      </b></b></td>
-      <td style="vertical-align: top; text-align: left;">A floating point value
-        encoded as a64-bit IEEE value written in little-endian form</td>
-    </tr>
-    <tr>
-      <td><a name="string"><b>string</b></a></td>
-      <td class="td_left">A uint32_vbr indicating the type of the constant 
-        string which also includes its length, immediately followed by the 
-        characters of the string. There is no terminating null byte in the 
-        string.</td>
-    </tr>
-    <tr>
-      <td><a name="data"><b>data</b></a></td>
-      <td class="td_left">An arbitrarily long segment of data to which no 
-        interpretation is implied. This is used for constant initializers.<br>
-      </td>
-    </tr>
-    <tr>
-      <td><a name="llist"><b>llist(x)</b></a></td>
-      <td class="td_left">A length list of x. This means the list is encoded 
-        as an <a href="#uint32_vbr">uint32_vbr</a> providing the length of the 
-        list, followed by a sequence of that many "x" items. This implies that 
-        the reader should iterate the number of times provided by the length.
-      </td>
-    </tr>
-    <tr>
-      <td><a name="zlist"><b>zlist(x)</b></a></td>
-      <td class="td_left">A zero-terminated list of x. This means the list is 
-        encoded as a sequence of an indeterminate number of "x" items, followed
-        by an <a href="#uint32_vbr">uint32_vbr</a> terminating value.  This 
-        implies that none of the "x" items can have a zero value (or else the 
-        list terminates).</td>
-    </tr>
-    <tr>
-      <td><a name="block"><b>block</b></a></td>
-      <td class="td_left">A block of data that is logically related. A block 
-        is an unsigned 32-bit integer that encodes the type of the block in 
-        the low 5 bits and the size of the block in the high 27 bits. The 
-        length does not include the block header or any alignment bytes at the 
-        end of the block. Blocks may compose other blocks. </td>
-    </tr>
-  </tbody>
-</table>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="notation">Field Notation</a> </div>
-<div class="doc_text">
-<p>In the detailed block and field descriptions that follow, a regex
-like notation is used to describe optional and repeated fields. A very
-limited subset of regex is used to describe these, as given in the
-following table: </p>
-<table class="doc_table">
-  <tbody>
-    <tr>
-      <th><b>Character</b></th>
-      <th class="td_left"><b>Meaning</b></th>
-    </tr>
-    <tr>
-      <td><b><code>?</code></b></td>
-      <td class="td_left">The question mark indicates 0 or 1 occurrences of 
-        the thing preceding it.</td>
-    </tr>
-    <tr>
-      <td><b><code>*</code></b></td>
-      <td class="td_left">The asterisk indicates 0 or more occurrences of the 
-        thing preceding it.</td>
-    </tr>
-    <tr>
-      <td><b><code>+</code></b></td>
-      <td class="td_left">The plus sign indicates 1 or more occurrences of the 
-        thing preceding it.</td>
-    </tr>
-    <tr>
-      <td><b><code>()</code></b></td>
-      <td class="td_left">Parentheses are used for grouping.</td>
-    </tr>
-    <tr>
-      <td><b><code>,</code></b></td>
-      <td class="td_left">The comma separates sequential fields.</td>
-    </tr>
-  </tbody>
-</table>
-<p>So, for example, consider the following specifications:</p>
-<div class="doc_code">
-<ol>
-  <li><code>string?</code></li>
-  <li><code>(uint32_vbr,uin32_vbr)+</code></li>
-  <li><code>(unsigned?,uint32_vbr)*</code></li>
-  <li><code>(llist(unsigned))?</code></li>
-</ol>
-</div>
-<p>with the following interpretations:</p>
-<ol>
-  <li>An optional string. Matches either nothing or a single string</li>
-  <li>One or more pairs of uint32_vbr.</li>
-  <li>Zero or more occurrences of either an unsigned followed by a uint32_vbr 
-  or just a uint32_vbr.</li>
-  <li>An optional length list of unsigned values.</li>
-</ol>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="slots">Slots</a> </div>
-<div class="doc_text">
-<p>The bytecode format uses the notion of a "slot" to reference Types
-and Values. Since the bytecode file is a <em>direct</em> representation of
-LLVM's intermediate representation, there is a need to represent pointers in
-the file.  Slots are used for this purpose. For example, if one has the 
-following assembly:
-</p>
-<div class="doc_code"><code> %MyType = type { int, sbyte }<br>
-%MyVar = external global %MyType
-</code></div>
-<p>there are two definitions. The definition of <tt>%MyVar</tt> uses 
-<tt>%MyType</tt>.
-In the C++ IR this linkage between <tt>%MyVar</tt> and <tt>%MyType</tt>
-is explicit through the use of C++ pointers. In bytecode, however, there's no
-ability to store memory addresses. Instead, we compute and write out
-slot numbers for every Type and Value written to the file.</p>
-<p>A slot number is simply an unsigned 32-bit integer encoded in the variable
-bit rate scheme (see <a href="#encoding">encoding</a>). This ensures that
-low slot numbers are encoded in one byte. Through various bits of magic LLVM
-attempts to always keep the slot numbers low. The first attempt is to associate
-slot numbers with their "type plane". That is, Values of the same type
-are written to the bytecode file in a list (sequentially). Their order in 
-that list determines their slot number. This means that slot #1 doesn't mean
-anything unless you also specify for which type you want slot #1. Types are
-always written to the file first (in the <a href="#globaltypes">Global Type 
-Pool</a>) and in such a way that both forward and backward references of the 
-types can often be resolved with a single pass through the type pool. </p>
-<p>In summary then, a slot number can be thought of as just a vbr encoded index 
-into a list of Type* or Value*. To keep slot numbers low, Value* are indexed by
-two slot numbers: the "type plane index" (type slot) and the "value index"
-(value slot).</p>
-</div>
-<!-- *********************************************************************** -->
-<div class="doc_section"> <a name="general">General Structure</a> </div>
-<!-- *********************************************************************** -->
-<div class="doc_text">
-<p>This section provides the general structure of the LLVM bytecode
-file format. The bytecode file format requires blocks to be in a
-certain order and nested in a particular way so that an LLVM module can
-be constructed efficiently from the contents of the file. This ordering
-defines a general structure for bytecode files as shown below. The
-table below shows the order in which all block types may appear. Please
-note that some of the blocks are optional and some may be repeated. The
-structure is fairly loose because optional blocks, if empty, are
-completely omitted from the file.</p>
-<table>
-  <tbody>
-    <tr>
-      <th>ID</th>
-      <th>Parent</th>
-      <th>Optional?</th>
-      <th>Repeated?</th>
-      <th>Level</th>
-      <th>Block Type</th>
-      <th>Description</th>
-    </tr>
-    <tr>
-      <td>N/A</td>
-      <td>File</td>
-      <td>No</td>
-      <td>No</td>
-      <td>0</td>
-      <td class="td_left"><a href="#signature">Signature</a></td>
-      <td class="td_left">This contains the file signature (magic
-number) that identifies the file as LLVM bytecode.</td>
-    </tr>
-    <tr>
-      <td>0x01</td>
-      <td>File</td>
-      <td>No</td>
-      <td>No</td>
-      <td>0</td>
-      <td class="td_left"><a href="#module">Module</a></td>
-      <td class="td_left">This is the top level block in a bytecode
-file. It contains all the other blocks. </td>
-    </tr>
-    <tr>
-      <td>0x06</td>
-      <td>Module</td>
-      <td>No</td>
-      <td>No</td>
-      <td>1</td>
-      <td class="td_left">&nbsp;&nbsp;&nbsp;<a href="#globaltypes">Global&nbsp;Type&nbsp;Pool</a></td>
-      <td class="td_left">This block contains all the global (module)
-level types.</td>
-    </tr>
-    <tr>
-      <td>0x05</td>
-      <td>Module</td>
-      <td>No</td>
-      <td>No</td>
-      <td>1</td>
-      <td class="td_left">&nbsp;&nbsp;&nbsp;<a href="#globalinfo">Module&nbsp;Globals&nbsp;Info</a></td>
-      <td class="td_left">This block contains the type, constness, and
-linkage for each of the global variables in the module. It also
-contains the type of the functions and the constant initializers.</td>
-    </tr>
-    <tr>
-      <td>0x03</td>
-      <td>Module</td>
-      <td>Yes</td>
-      <td>No</td>
-      <td>1</td>
-      <td class="td_left">&nbsp;&nbsp;&nbsp;<a href="#constantpool">Module&nbsp;Constant&nbsp;Pool</a></td>
-      <td class="td_left">This block contains all the global constants
-except function arguments, global values and constant strings.</td>
-    </tr>
-    <tr>
-      <td>0x02</td>
-      <td>Module</td>
-      <td>Yes</td>
-      <td>Yes</td>
-      <td>1</td>
-      <td class="td_left">&nbsp;&nbsp;&nbsp;<a href="#functiondefs">Function&nbsp;Definitions</a>*</td>
-      <td class="td_left">One function block is written for each
-function in the module. The function block contains the instructions,
-type constant pool, and symbol table for the function.</td>
-    </tr>
-    <tr>
-      <td>0x03</td>
-      <td>Function</td>
-      <td>Yes</td>
-      <td>No</td>
-      <td>2</td>
-      <td class="td_left">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a
- href="#constantpool">Function&nbsp;Constant&nbsp;Pool</a></td>
-      <td class="td_left">Any constants (including types) used solely within 
-        the function are emitted here in the function constant pool. </td>
-    </tr>
-    <tr>
-      <td>0x07</td>
-      <td>Function</td>
-      <td>No</td>
-      <td>No</td>
-      <td>2</td>
-      <td class="td_left">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a
- href="#instructionlist">Instruction&nbsp;List</a></td>
-      <td class="td_left">This block contains all the instructions of the 
-        function. The basic blocks are inferred by terminating instructions.
-      </td>
-    </tr>
-    <tr>
-      <td>0x04</td>
-      <td>Function</td>
-      <td>Yes</td>
-      <td>No</td>
-      <td>2</td>
-      <td class="td_left">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a
- href="#symtab">Function&nbsp;Symbol&nbsp;Table</a></td>
-      <td class="td_left">This symbol table provides the names for the function
-        specific values used (basic block labels mostly).</td>
-    </tr>
-    <tr>
-      <td>0x04</td>
-      <td>Module</td>
-      <td>Yes</td>
-      <td>No</td>
-      <td>1</td>
-      <td class="td_left">&nbsp;&nbsp;&nbsp;<a href="#symtab">Module&nbsp;Symbol&nbsp;Table</a></td>
-      <td class="td_left">This symbol table provides the names for the various 
-        entries in the file that are not function specific (global vars, and 
-        functions mostly).</td>
-    </tr>
-  </tbody>
-</table>
-<p>Use the links in the table for details about the contents of each of
-the block types.</p>
-</div>
-<!-- *********************************************************************** -->
-<div class="doc_section"> <a name="blockdefs">Block Definitions</a> </div>
-<!-- *********************************************************************** -->
-<div class="doc_text">
-<p>This section provides the detailed layout of the individual block
-types in the LLVM bytecode file format. </p>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="signature">Signature Block</a> </div>
-<div class="doc_text">
-<p>The signature occurs in every LLVM bytecode file and is always first.
-It simply provides a few bytes of data to identify the file as being an LLVM
-bytecode file. This block is always four bytes in length and differs from the
-other blocks because there is no identifier and no block length at the start
-of the block. Essentially, this block is just the "magic number" for the file.
-</p>
-<p>There are two types of signatures for LLVM bytecode: uncompressed and
-compressed as shown in the table below. </p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Uncompressed</b></th>
-      <th class="td_left"><b>Compressed</b></th>
-    </tr>
-    <tr>
-      <td><a href="#char">char</a></td>
-      <td class="td_left">Constant "l" (0x6C)</td>
-      <td class="td_left">Constant "l" (0x6C)</td>
-    </tr>
-    <tr>
-      <td><a href="#char">char</a></td>
-      <td class="td_left">Constant "l" (0x6C)</td>
-      <td class="td_left">Constant "l" (0x6C)</td>
-    </tr>
-    <tr>
-      <td><a href="#char">char</a></td>
-      <td class="td_left">Constant "v" (0x76)</td>
-      <td class="td_left">Constant "v" (0x76)</td>
-    </tr>
-    <tr>
-      <td><a href="#char">char</a></td>
-      <td class="td_left">Constant "m" (0x6D)</td>
-      <td class="td_left">Constant "c" (0x63)</td>
-    </tr>
-    <tr>
-      <td><a href="#char">char</a></td>
-      <td class="td_left">N/A</td>
-      <td class="td_left">'0'=null,'1'=gzip,'2'=bzip2</td>
-    </tr>
-  </tbody>
-</table>
-<p>In other words, the uncompressed signature is just the characters 'llvm'
-while the compressed signature is the characters 'llvc' followed by an ascii
-digit ('0', '1', or '2') that indicates the kind of compression used. A value of
-'0' indicates that null compression was used. This can happen when compression
-was requested on a platform that wasn't configured for gzip or bzip2. A value of
-'1' means that the rest of the file is compressed using the gzip algorithm and
-should be uncompressed before interpretation. A value of '2' means that the rest
-of the file is compressed using the bzip2 algorithm and should be uncompressed
-before interpretation. In all cases, the data resulting from uncompression
-should be interpreted as if it occurred immediately after the 'llvm'
-signature (i.e. the uncompressed data begins with the 
-<a href="#module">Module Block</a></p>
-<p><b>NOTE:</b> As of LLVM 1.4, all bytecode files produced by the LLVM tools
-are compressed by default. To disable compression, pass the 
-<tt>--disable-compression</tt> option to the tool, if it supports it.
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="module">Module Block</a> </div>
-<div class="doc_text">
-<p>The module block contains a small pre-amble and all the other blocks in
-the file. The table below shows the structure of the module block. Note that it
-only provides the module identifier, size of the module block, and the format
-information. Everything else is contained in other blocks, described in other
-sections.</p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#unsigned">unsigned</a><br></td>
-      <td class="td_left"><a href="#mod_header">Module Block Identifier
-          (0x01)</a></td>
-    </tr>
-    <tr>
-      <td><a href="#unsigned">unsigned</a></td>
-      <td class="td_left"><a href="#mod_header">Module Block Size</a></td>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left"><a href="#format">Format Information</a></td>
-    </tr>
-    <tr>
-      <td><a href="#block">block</a></td>
-      <td class="td_left"><a href="#globaltypes">Global Type Pool</a></td>
-    </tr>
-    <tr>
-      <td><a href="#block">block</a></td>
-      <td class="td_left"><a href="#globalinfo">Module Globals Info</a></td>
-    </tr>
-    <tr>
-      <td><a href="#block">block</a></td>
-      <td class="td_left"><a href="#constantpool">Module Constant Pool</a></td>
-    </tr>
-    <tr>
-      <td><a href="#block">block</a>*</td>
-      <td class="td_left"><a href="#functiondefs">Function Definitions</a></td>
-    </tr>
-    <tr>
-      <td><a href="#block">block</a></td>
-      <td class="td_left"><a href="#symtab">Module Symbol Table</a></td>
-    </tr>
-  </tbody>
-</table>
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection"><a name="mod_header">Module Block Header</a></div>
-<div class="doc_text">
-  <p>The block header for the module block uses a longer format than the other
-  blocks in a bytecode file. Specifically, instead of encoding the type and size
-  of the block into a 32-bit integer with 5-bits for type and 27-bits for size,
-  the module block header uses two 32-bit unsigned values, one for type, and one
-  for size. While the 2<sup>27</sup> byte limit on block size is sufficient 
-  for the blocks contained in the module, it isn't sufficient for the module 
-  block itself because we want to ensure that bytecode files as large as 
-  2<sup>32</sup> bytes are possible. For this reason, the module block (and 
-  only the module block) uses a long format header.</p>
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection"><a name="format">Format Information</a></div>
-<div class="doc_text">
-<p>The format information field is encoded into a <a href="#uint32_vbr">uint32_vbr</a>.</p>
-
-<p>Of particular note, the bytecode format number is simply a 32-bit
-monotonically increasing integer that identifies the version of the bytecode
-format (which is not directly related to the LLVM release number). The
-bytecode versions defined so far are (note that this document only
-describes the latest version, 2.0):</p>
-<ul>
-  <li>#0: LLVM 1.0 &amp; 1.1</li>
-  <li>#1: LLVM 1.2</li>
-  <li>#2: LLVM 1.2.5 (not released)</li>
-  <li>#3: LLVM 1.3</li>
-  <li>#4: LLVM 1.3.x (not released)</li>
-  <li>#5: LLVM 1.4 through 1.8</li>
-  <li>#6: LLVM 1.9</li>
-  <li>#7: LLVM 2.0 and newer</li>
-</ul>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="globaltypes">Global Type Pool</a> </div>
-<div class="doc_text">
-<p>The global type pool consists of type definitions. Their order of appearance
-in the file determines their type slot number (0 based). Slot numbers are
-used to replace pointers in the intermediate representation. Each slot number 
-uniquely identifies one entry in a type plane (a collection of values of the
-same type).  Since all values have types and are associated with the order in 
-which the type pool is written, the global type pool <em>must</em> be written 
-as the first block of a module. If it is not, attempts to read the file will
-fail because both forward and backward type resolution will not be possible.</p>
-<p>The type pool is simply a list of type definitions, as shown in the
-table below.</p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#unsigned">block</a></td>
-      <td class="td_left">Type Pool Identifier (0x06) + Size<br>
-      </td>
-    </tr>
-    <tr>
-      <td><a href="#llist">llist</a>(<a href="#type">type</a>)</td>
-      <td class="td_left">A length list of type definitions.</td>
-    </tr>
-  </tbody>
-</table>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection"><a name="type">Type Definitions</a></div>
-<div class="doc_text">
-<p>Types in the type pool are defined using a different format for each kind
-of type, as given in the following sections.</p>
-<h3>Primitive Types</h3>
-<p>The primitive types encompass the basic integer and floating point
-types. They are encoded simply as their TypeID.</p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a></td>
-      <td class="td_left">Type ID for the primitive types (values 1 to 11) 
-        <sup>1</sup></td>
-    </tr>
-  </tbody>
-</table>
-Notes:
-<ol>
-  <li>The values for the Type IDs for the primitive types are provided by the 
-  definition of the <code>llvm::Type::TypeID</code> enumeration in 
-  <code>include/llvm/Type.h</code>. The enumeration gives the following mapping:
-    <ol>
-      <li>bool</li>
-      <li>ubyte</li>
-      <li>sbyte</li>
-      <li>ushort</li>
-      <li>short</li>
-      <li>uint</li>
-      <li>int</li>
-      <li>ulong</li>
-      <li>long</li>
-      <li>float</li>
-      <li>double</li>
-    </ol>
-  </li>
-</ol>
-<h3>Function Types</h3>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a></td>
-      <td class="td_left">Type ID for function types (13)</td>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a></td>
-      <td class="td_left">Type slot number of function's return type.</td>
-    </tr>
-    <tr>
-      <td><a href="#llist">llist</a>(<a href="#uint24_vbr">uint24_vbr</a>)</td>
-      <td class="td_left">Type slot number of each argument's type.</td>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a>?</td>
-      <td class="td_left">Value 0 if this is a varargs function, missing 
-        otherwise.</td>
-    </tr>
-  </tbody>
-</table>
-<h3>Structure Types</h3>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a></td>
-      <td class="td_left">Type ID for structure types (14)</td>
-    </tr>
-    <tr>
-      <td><a href="#zlist">zlist</a>(<a href="#uint24_vbr">uint24_vbr</a>)</td>
-      <td class="td_left">Slot number of each of the element's fields.</td>
-    </tr>
-  </tbody>
-</table>
-<h3>Array Types</h3>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a></td>
-      <td class="td_left">Type ID for Array Types (15)</td>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a></td>
-      <td class="td_left">Type slot number of array's element type.</td>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">The number of elements in the array.</td>
-    </tr>
-  </tbody>
-</table>
-<h3>Pointer Types</h3>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a></td>
-      <td class="td_left">Type ID For Pointer Types (16)</td>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a></td>
-      <td class="td_left">Type slot number of pointer's element type.</td>
-    </tr>
-  </tbody>
-</table>
-<h3>Opaque Types</h3>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a></td>
-      <td class="td_left">Type ID For Opaque Types (17)</td>
-    </tr>
-  </tbody>
-</table>
-<h3>Vector Types</h3>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a></td>
-      <td class="td_left">Type ID for Vector Types (18)</td>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a></td>
-      <td class="td_left">Slot number of the vector's element type.</td>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">The number of elements in the vector.</td>
-    </tr>
-  </tbody>
-</table>
-<h3>Packed Structure Types</h3>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a></td>
-      <td class="td_left">Type ID for packed structure types (19)</td>
-    </tr>
-    <tr>
-      <td><a href="#zlist">zlist</a>(<a href="#uint24_vbr">uint24_vbr</a>)</td>
-      <td class="td_left">Slot number of each of the element's fields.</td>
-    </tr>
-  </tbody>
-</table>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="globalinfo">Module Global Info</a>
-</div>
-<div class="doc_text">
-<p>The module global info block contains the definitions of all global
-variables including their initializers and the <em>declaration</em> of
-all functions. The format is shown in the table below:</p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#block">block</a></td>
-      <td class="td_left">Module global info identifier (0x05) + size</td>
-    </tr>
-    <tr>
-      <td><a href="#zlist">zlist</a>(<a href="#globalvar">globalvar</a>)</td>
-      <td class="td_left">A zero terminated list of global var definitions 
-        occurring in the module.</td>
-    </tr>
-    <tr>
-      <td><a href="#zlist">zlist</a>(<a href="#funcfield">funcfield</a>)</td>
-      <td class="td_left">A zero terminated list of function definitions 
-        occurring in the module.</td>
-    </tr>
-    <tr>
-      <td><a href="#llist">llist</a>(<a href="#string">string</a>)</td>
-      <td class="td_left">A length list of strings that specify the names of 
-        the libraries that this module depends upon.</td>
-    </tr>
-    <tr>
-      <td><a href="#string">string</a></td>
-      <td class="td_left">The target triple for the module (blank means no 
-        target triple specified, i.e. a platform-independent module).</td>
-    </tr>
-    <tr>
-      <td><a href="#string">string</a></td>
-      <td class="td_left">The data layout string describing the endianness,
-        pointer size, and type alignments for which the module was written 
-        (blank means no data layout specified, i.e. a platform-independent 
-        module).</td>
-    </tr>
-    <tr>
-      <td><a href="#llist">llist</a>(<a href="#string">string</a>)</td>
-      <td class="td_left">A length list of strings that defines a table of 
-        section strings for globals.  A global's SectionID is an index into 
-        this table.</td>
-    </tr>
-    <tr>
-      <td><a href="#string">string</a></td>
-      <td class="td_left">The inline asm block for this module.</td>
-    </tr>
-    <tr>
-      <td><a href="#zlist">zlist</a>(<a href="#alias">alias</a>)</td>
-      <td class="td_left">A zero terminated list of aliases occurring in the
-      module.</td>
-    </tr>
-  </tbody>
-</table>
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection"><a name="globalvar">Global Variable Field</a>
-</div>
-
-<div class="doc_text">
-
-<p>Global variables are written using an <a href="#uint32_vbr">uint32_vbr</a>
-that encodes information about the global variable, an optional extension vbr,
-and a an optional initializers for the global var.</p>
-
-<p>The table below provides the bit layout of the first <a
- href="#uint32_vbr">uint32_vbr</a> that describes the global variable.</p>
- 
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(0)</a></td>
-      <td class="td_left">Is constant?</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(1)</a></td>
-      <td class="td_left">Has initializer? Note that this bit determines 
-        whether the constant initializer field (described below) follows.</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(2-4)</a></td>
-      <td class="td_left">Linkage type: 0=External, 1=Weak,
-        2=Appending, 3=Internal, 4=LinkOnce, 5=DllImport, 
-        6=DllExport, 7=ExternWeak</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(5)</a></td>
-      <td class="td_left">Is Thread Local?</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(6-31)</a></td>
-      <td class="td_left">Type slot number of type for the global variable.</td>
-    </tr>
-  </tbody>
-</table>
-
-<p>When the Linkage type is set to 3 (internal) and the initializer field is set
-to 0 (an invalid combination), an extension word follows the first <a
-href="#uint32_vbr">uint32_vbr</a> which encodes the real linkage and init flag,
-and can includes more information:</p>
-
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(0)</a></td>
-      <td class="td_left">Has initializer?  Indicates the real value of the "Has
-        initializer" field for the global. </td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(2-4)</a></td>
-      <td class="td_left">Linkage type: Indicates the real value of the "linkage
-        type" field for the global.</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(4-8)</a></td>
-      <td class="td_left">The log-base-2 of the alignment for the global.</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(9)</a></td>
-      <td class="td_left">If this bit is set, a SectionID follows this vbr.</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(10-12)</a></td>
-      <td class="td_left">Visibility style: 0=Default, 1=Hidden, 2=Protected.</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(13-31)</a></td>
-      <td class="td_left">Currently unassigned.</td>
-    </tr>
-  </tbody>
-</table>
-
-<p>If the SectionID bit is set above, the following field is included:</p>
-
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a>
-      </td>
-      <td class="td_left">An optional section ID number, specifying the string
-        to use for the section of the global.  This an index (+1) of an entry
-        into the SectionID llist in the 
-        <a href="#globalinfo">Module Global Info</a> block.  If this value is 
-        0 or not present, the global has an empty section string.</td>
-    </tr>
-  </tbody>
-</table>
-
-<p>If the "Has initializer" field is set, the following field is included:</p>
-
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a>
-      </td>
-      <td class="td_left">An optional value slot number for the global 
-          variable's constant initializer.</td>
-    </tr>
-  </tbody>
-</table>
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection"><a name="funcfield">Function Field</a>
-</div>
-<div class="doc_text">
-<p>Functions are written using an <a href="#uint32_vbr">uint32_vbr</a>
-that encodes information about the function and a set of flags.  If needed,
-an extension word may follow this first field.</p>
-
-<p>The table below provides the bit layout of the <a
-href="#uint32_vbr">uint32_vbr</a> that describes the function.</p>
-
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(0-3)</a></td>
-      <td class="td_left">
-      Encodes the calling convention number of the function. The
-      CC number of the function is the value of this field minus one.
-      </td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(4)</a></td>
-      <td class="td_left">If this bit is set to 1, the indicated function is
-        external, and there is no 
-        <a href="#functiondefs">Function Definiton Block</a> in the bytecode 
-        file for the function. If the function is external and has 
-        <tt>dllimport or extern_weak</tt> linkage additional field in the 
-        extension word is used to indicate the actual linkage type.</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(5-30)</a></td>
-      <td class="td_left">Type slot number of type for the function.</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(31)</a></td>
-      <td class="td_left">Indicates whether an extension word follows.</td>
-    </tr>
-  </tbody>
-</table>
-
-<p>If bit(31) is set, an additional <a href="#uint32_vbr">uint32_vbr</a> word
-follows with the following fields:</p>
-
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(0-4)</a></td>
-      <td class="td_left">The log-base-2 of the alignment for the function.</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(5-9)</a></td>
-      <td class="td_left">The top nibble of the calling convention.</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(10)</a></td>
-      <td class="td_left">If this bit is set, a SectionID follows this vbr.</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(11-12)</a></td>
-      <td class="td_left">Linkage type for external functions. 0 - External
-        linkage, 1 - DLLImport linkage, 2 - External weak linkage.</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(13-31)</a></td>
-      <td class="td_left">Currently unassigned.</td>
-    </tr>
-  </tbody>
-</table>
-
-<p>If the SectionID bit is set above, the following field is included:</p>
-
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a>
-      </td>
-      <td class="td_left">An optional section ID number, specifying the string
-        to use for the section of the function.  This an index (+1) of an entry
-        into the SectionID llist in the 
-        <a href="#globalinfo">Module Global Info</a> block.  If this value is 
-        0 or not present, the function has an empty section string.</td>
-    </tr>
-  </tbody>
-</table>
-
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection"><a name="alias">Alias Field</a>
-</div>
-<div class="doc_text">
-<p>Aliases are written using 3 <a href="#uint32_vbr">uint32_vbr</a>
-that encode information about alias itself and aliasee.</p>
-
-<p>The table below provides the bit layout of
-the first <a href="#uint32_vbr">uint32_vbr</a> which describes alias itself.</p>
-
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(0-1)</a></td>
-      <td class="td_left">Alias linkage. 0 - External linkage, 1 - Internal
-      linkage, 2 - Weak linkage.</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(2)</a></td>
-      <td class="td_left">0 - Aliasee is global value. 1 - Aliasee is constant
-      expression (bitcast of global value)</td>
-    </tr>    
-    <tr>
-      <td><a href="#bit">bit(3-31)</a></td>
-      <td class="td_left">Type slot number of type for the alias itself.</td>
-    </tr>
-  </tbody>
-</table>
-
-  <p>The next <a href="#uint32_vbr">uint32_vbr</a> describes the aliasee. </p>
-
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">Slot number of the aliasee.</td>
-    </tr>
-  </tbody>
-</table>
-
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="constantpool">Constant Pool</a> </div>
-<div class="doc_text">
-<p>A constant pool defines as set of constant values. There are
-actually two types of constant pool blocks: one for modules and one for
-functions. For modules, the block begins with the constant strings
-encountered anywhere in the module. For functions, the block begins
-with types only encountered in the function. In both cases the header
-is identical. The tables that follow, show the header, module constant
-pool preamble, function constant pool preamble, and the part common to
-both function and module constant pools.</p>
-<p><b>Common Block Header</b></p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#block">block</a></td>
-      <td class="td_left">Constant pool identifier (0x03) + size<br>
-      </td>
-    </tr>
-  </tbody>
-</table>
-<p><b>Module Constant Pool Preamble (constant strings)</b></p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">The number of constant strings that follow.</td>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">Zero. This identifies the following "plane" as 
-        containing the constant strings. This is needed to identify it uniquely
-        from other constant planes that follow. </td>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a>+</td>
-      <td class="td_left">Type slot number of the constant string's type.  Note
-        that the constant string's type implicitly defines the length of the 
-        string. </td>
-    </tr>
-  </tbody>
-</table>
-<p><b>Function Constant Pool Preamble (function types)</b></p>
-<p>The structure of the types for functions is identical to the <a
- href="#globaltypes">Global Type Pool</a>. Please refer to that section
-for the details. </p>
-<p><b>Common Part (other constants)</b></p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">Number of entries in this type plane.</td>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a></td>
-      <td class="td_left">Type slot number of this plane.</td>
-    </tr>
-    <tr>
-      <td><a href="#constant">constant</a>+</td>
-      <td class="td_left">The definition of a constant (see below).</td>
-    </tr>
-  </tbody>
-</table>
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection"><a name="constant">Simple Constant Pool
-Entries</a></div>
-
-<div class="doc_text">
-
-<p>Constant pool entries come in many shapes and flavors. The sections that
-follow define the format for each of them. All constants start with a <a
- href="#uint32_vbr">uint32_vbr</a> encoded integer that provides the
-number of operands for the constant. For primitive, structure, and
-array constants, this will always be zero to indicate that the form of the 
-constant is solely determined by its type. In this case, we have the following
-field definitions, based on type:</p>
-
-<ul>
-  <li><b>Bool</b>. This is written as an <a href="#uint32_vbr">uint32_vbr</a> of
-  value 1U or 0U.</li>
-  <li><b>Signed Integers (sbyte,short,int,long) &le; 64 bits</b>. These are 
-  written as an <a href="#int64_vbr">int64_vbr</a> with the corresponding 
-  value.</li>
-  <li><b>Unsigned Integers (ubyte,ushort,uint,ulong) &le; 64 bits</b>. These 
-  are written as an <a href="#uint64_vbr">uint64_vbr</a> with the corresponding
-  value. </li>
-  <li><b>Integers &gt; 64 bits</b>. These are written as a length followed by a
-  series of 64-bit words. The length specifies the number of words that follow.
-  Any zero-valued high order words are elided. Words with the least significant
-  bits are written to the lowest file offsets (little endian). The length is 
-  written as an <a href="#uint32_vbr">uint32_vbr</a>. Each word of the value
-  is written as an <a href="#uint64_vbr">uint64_vbr</a>.</li>
-  <li><b>Floating Point</b>. Both the float and double types are written 
-  literally in binary format.</li>
-  <li><b>Arrays</b>. Arrays are written simply as a list of 
-  <a href="#uint32_vbr">uint32_vbr</a> encoded value slot numbers to the 
-  constant element values.</li>
-  <li><b>Structures</b>. Structures are written simply as a list of 
-  <a href="#uint32_vbr">uint32_vbr</a> encoded value slot numbers to the 
-  constant field values of the structure.</li>
-</ul>
-
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">Undef Entries</div>
-
-<div class="doc_text">
-<p>When the number of operands to the constant is one, we have an 'undef' value
-of the specified type.</p>
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">Inline Assembler Entries</div>
-
-<div class="doc_text">
-<p>Inline Assembler entries are stored in the constant pool, though they are not
-   officially LLVM constants.  These entries are marked with a value of
-   "4294967295" (all ones) for the number of operands.  They are encoded as
-   follows:</p>
-   
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#string">string</a></td>
-      <td class="td_left">The asm string.</td>
-    </tr>
-    <tr>
-      <td><a href="#string">string</a></td>
-      <td class="td_left">The constraints string.</td>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">Flags</td>
-    </tr>
-  </tbody>
-</table>
-
-<p>Currently, the only defined flag, the low bit, indicates whether or not the
-   inline assembler has side effects.</p>
-
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">Constant Expression Entries</div>
-
-<div class="doc_text">
-
-<p>Otherwise, we have a constant expression.  The format of the constant
-expression is specified in the table below, and the number is equal to the
-number of operands+1.</p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">Op code of the instruction for the constant 
-        expression.</td>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">The value slot number of the constant value for an 
-        operand.<sup>1</sup></td>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a></td>
-      <td class="td_left">The type slot number for the type of the constant 
-        value for an operand.<sup>1</sup></td>
-    </tr>
-  </tbody>
-</table>
-Notes:
-<ol>
-  <li>Both these fields are repeatable but only in pairs.</li>
-</ol>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="functiondefs">Function Definition</a></div>
-<div class="doc_text">
-<p>Function definitions contain the linkage, constant pool, instruction list, 
-and symbol table for a function.  The following table shows the structure of 
-a function definition.</p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#block">block</a><br>
-      </td>
-      <td class="td_left">Function definition block identifier (0x02) +
-size<br>
-      </td>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">
-        <a href="#funclinkage_and_visibility">The linkage and visibility</a> 
-        style field</td>
-    </tr>
-    <tr>
-      <td><a href="#block">block</a></td>
-      <td class="td_left">The <a href="#constantpool">constant pool</a> block 
-        for this function.<sup>2</sup></td>
-    </tr>
-    <tr>
-      <td><a href="#block">block</a></td>
-      <td class="td_left">The <a href="#instructionlist">instruction list</a> 
-        for the function.</td>
-    </tr>
-    <tr>
-      <td><a href="#block">block</a></td>
-      <td class="td_left">The function's <a href="#symtab">symbol table</a> 
-        containing only those symbols pertinent to the function (mostly block 
-        labels).</td>
-    </tr>
-  </tbody>
-</table>
-Notes:
-<ol>
-  <li>Note that if the linkage type is "External" then none of the
-other fields will be present as the function is defined elsewhere.</li>
-</ol>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection"><a name="funclinkage_and_visibility">Linkage and
-    visibility word</a>
-</div>
-<div class="doc_text">
-
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(0-15)</a></td>
-      <td class="td_left">The linkage type of the function: 0=External, 1=Weak,
-        2=Appending, 3=Internal, 4=LinkOnce, 5=DllImport, 
-        6=DllExport<sup>1</sup></td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(16-18)</a></td>
-      <td class="td_left">Visibility style: 0=Default, 1=Hidden, 2=Protected.</td>
-    </tr>
-    <tr>
-      <td><a href="#bit">bit(19-31)</a></td>
-      <td class="td_left">Currently unassigned.</td>
-    </tr>
-  </tbody>
-</table>
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="instructionlist">Instruction List</a></div>
-<div class="doc_text">
-<p>The instructions in a function are written as a simple list. Basic
-blocks are inferred by the terminating instruction types. The format of
-the block is given in the following table.</p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#block">block</a><br>
-      </td>
-      <td class="td_left">Instruction list identifier (0x07) + size<br>
-      </td>
-    </tr>
-    <tr>
-      <td><a href="#instruction">instruction</a>+</td>
-      <td class="td_left">An instruction. Instructions have a variety of 
-        formats. See <a href="#instruction">Instructions</a> for details.</td>
-    </tr>
-  </tbody>
-</table>
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="instructions">Instructions</a></div>
-
-<div class="doc_text">
-<p>Instructions are written out one at a time as distinct units.  Each
-instruction
-record contains at least an <a href="#opcodes">opcode</a> and a type field, 
-and may contain a <a href="#instoperands">list of operands</a> (whose
-interpretation depends on the opcode). Based on the number of operands, the
-<a href="#instencode">instruction is encoded</a> in a
-dense format that tries to encoded each instruction into 32-bits if 
-possible. </p>
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection"><a name="opcodes">Instruction Opcodes</a></div>
-<div class="doc_text">
-  <p>Instructions encode an opcode that identifies the kind of instruction.
-  Opcodes are an enumerated integer value. The specific values used depend on
-  the version of LLVM you're using. The opcode values are defined in the
-  <a href="http://llvm.org/cvsweb/cvsweb.cgi/llvm/include/llvm/Instruction.def">
-  <tt>include/llvm/Instruction.def</tt></a> file. You should check there for the
-  most recent definitions. The table below provides the opcodes defined as of
-  the writing of this document. The table associates each opcode mnemonic with
-  its enumeration value and the bytecode and LLVM version numbers in which the
-  opcode was introduced.</p>
-  <table>
-    <tbody>
-      <tr>
-        <th>Opcode</th>
-        <th>Number</th>
-        <th>Bytecode Version</th>
-        <th>LLVM Version</th>
-      </tr>
-      <tr><td colspan="4"><b>Terminator Instructions</b></td></tr>
-      <tr><td>Ret</td><td>1</td><td>1</td><td>1.0</td></tr>
-      <tr><td>Br</td><td>2</td><td>1</td><td>1.0</td></tr>
-      <tr><td>Switch</td><td>3</td><td>1</td><td>1.0</td></tr>
-      <tr><td>Invoke</td><td>4</td><td>1</td><td>1.0</td></tr>
-      <tr><td>Unwind</td><td>5</td><td>1</td><td>1.0</td></tr>
-      <tr><td>Unreachable</td><td>6</td><td>1</td><td>1.4</td></tr>
-      <tr><td colspan="4"><b>Binary Operators</b></td></tr>
-      <tr><td>Add</td><td>7</td><td>1</td><td>1.0</td></tr>
-      <tr><td>Sub</td><td>8</td><td>1</td><td>1.0</td></tr>
-      <tr><td>Mul</td><td>9</td><td>1</td><td>1.0</td></tr>
-      <tr><td>UDiv</td><td>10</td><td>6</td><td>1.9</td></tr>
-      <tr><td>SDiv</td><td>11</td><td>6</td><td>1.9</td></tr>
-      <tr><td>FDiv</td><td>12</td><td>6</td><td>1.9</td></tr>
-      <tr><td>URem</td><td>13</td><td>6</td><td>1.9</td></tr>
-      <tr><td>SRem</td><td>14</td><td>6</td><td>1.9</td></tr>
-      <tr><td>FRem</td><td>15</td><td>6</td><td>1.9</td></tr>
-      <tr><td colspan="4"><b>Logical Operators</b></td></tr>
-      <tr><td>Shl</td><td>16</td><td>1</td><td>1.0</td></tr>
-      <tr><td>LShr</td><td>17</td><td>6</td><td>1.9</td></tr>
-      <tr><td>AShr</td><td>18</td><td>6</td><td>1.9</td></tr>
-      <tr><td>And</td><td>19</td><td>1</td><td>1.0</td></tr>
-      <tr><td>Or</td><td>20</td><td>1</td><td>1.0</td></tr>
-      <tr><td>Xor</td><td>21</td><td>1</td><td>1.0</td></tr>
-      <tr><td colspan="4"><b>Memory Operators</b></td></tr>
-      <tr><td>Malloc</td><td>22</td><td>1</td><td>1.0</td></tr>
-      <tr><td>Free</td><td>23</td><td>1</td><td>1.0</td></tr>
-      <tr><td>Alloca</td><td>24</td><td>1</td><td>1.0</td></tr>
-      <tr><td>Load</td><td>25</td><td>1</td><td>1.0</td></tr>
-      <tr><td>Store</td><td>26</td><td>1</td><td>1.0</td></tr>
-      <tr><td>GetElementPtr</td><td>27</td><td>1</td><td>1.0</td></tr>
-      <tr><td colspan="4"><b>Cast Operators</b></td></tr>
-      <tr><td>Trunc</td><td>28</td><td>7</td><td>2.0</td></tr>
-      <tr><td>ZExt</td><td>29</td><td>7</td><td>2.0</td></tr>
-      <tr><td>SExt</td><td>30</td><td>7</td><td>2.0</td></tr>
-      <tr><td>FPToUI</td><td>31</td><td>7</td><td>2.0</td></tr>
-      <tr><td>FPToSI</td><td>32</td><td>7</td><td>2.0</td></tr>
-      <tr><td>UIToFP</td><td>33</td><td>7</td><td>2.0</td></tr>
-      <tr><td>SIToFP</td><td>34</td><td>7</td><td>2.0</td></tr>
-      <tr><td>FPTrunc</td><td>35</td><td>7</td><td>2.0</td></tr>
-      <tr><td>FPExt</td><td>36</td><td>7</td><td>2.0</td></tr>
-      <tr><td>PtrToInt</td><td>37</td><td>7</td><td>2.0</td></tr>
-      <tr><td>IntToPtr</td><td>38</td><td>7</td><td>2.0</td></tr>
-      <tr><td>BitCast</td><td>39</td><td>7</td><td>2.0</td></tr>
-      <tr><td colspan="4"><b>Other Operators</b></td></tr>
-      <tr><td>ICmp</td><td>40</td><td>7</td><td>2.0</td></tr>
-      <tr><td>FCmp</td><td>41</td><td>7</td><td>2.0</td></tr>
-      <tr><td>PHI</td><td>42</td><td>1</td><td>1.0</td></tr>
-      <tr><td>Call</td><td>43</td><td>1</td><td>1.0</td></tr>
-      <tr><td>Select</td><td>44</td><td>2</td><td>1.2</td></tr>
-      <tr><td>UserOp1</td><td>45</td><td>1</td><td>1.0</td></tr>
-      <tr><td>UserOp2</td><td>46</td><td>1</td><td>1.0</td></tr>
-      <tr><td>VAArg</td><td>47</td><td>5</td><td>1.5</td></tr>
-      <tr><td>ExtractElement</td><td>48</td><td>5</td><td>1.5</td></tr>
-      <tr><td>InsertElement</td><td>49</td><td>5</td><td>1.5</td></tr>
-      <tr><td>ShuffleElement</td><td>50</td><td>5</td><td>1.5</td></tr>
-      <tr><td colspan="4">
-          <b>Pseudo Instructions<a href="#pi_note">*</a></b>
-      </td></tr>
-      <tr><td>Invoke+CC </td><td>56</td><td>5</td><td>1.5</td></tr>
-      <tr><td>Invoke+FastCC</td><td>57</td><td>5</td><td>1.5</td></tr>
-      <tr><td>Call+CC</td><td>58</td><td>5</td><td>1.5</td></tr>
-      <tr><td>Call+FastCC+TailCall</td><td>59</td><td>5</td><td>1.5</td></tr>
-      <tr><td>Call+FastCC</td><td>60</td><td>5</td><td>1.5</td></tr>
-      <tr><td>Call+CCC+TailCall</td><td>61</td><td>5</td><td>1.5</td></tr>
-      <tr><td>Load+Attributes</td><td>62</td><td>7</td><td>2.0</td></tr>
-      <tr><td>Store+Attributes</td><td>63</td><td>7</td><td>2.0</td></tr>
-    </tbody>
-  </table>
-
-<p><b><a name="pi_note">* Note: </a></b>
-These aren't really opcodes from an LLVM language perspective. They encode
-information into other opcodes without reserving space for that information. 
-For example, opcode=63 is an Attributed Store. The opcode for this
-instruction is 25 (Store) but we encode it as 63 to indicate that is a Volatile
-Store. The same is done for the calling conventions and tail calls.
-In each of these entries in range 56-63, the opcode is documented as the base
-opcode (Invoke, Call, Store) plus some set of modifiers, as follows:</p>
-<dl>
-  <dt>CC</dt>
-  <dd>This means an arbitrary calling convention is specified
-  in a VBR that follows the opcode. This is used when the instruction cannot
-  be encoded with one of the more compact forms.
-  </dd>
-  <dt>FastCC</dt>
-  <dd>This indicates that the Call or Invoke is using the FastCC calling 
-  convention.</dd>
-  <dt>CCC</dt>
-  <dd>This indicates that the Call or Invoke is using the native "C" calling 
-  convention.</dd>
-  <dt>TailCall</dt>
-  <dd>This indicates that the Call has the 'tail' modifier.</dd>
-</dl>
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection"><a name="instoperands">Instruction
-Operands</a></div>
-
-<div class="doc_text">
-<p>
-Based on the instruction opcode and type, the bytecode format implicitly (to 
-save space) specifies the interpretation of the operand list.  For most
-instructions, the type of each operand is implicit from the type of the 
-instruction itself (e.g. the type of operands of a binary operator must match
-the type of the instruction).  As such, the bytecode format generally only 
-encodes the value number of the operand, not the type.</p>
-
-<p>In some cases, however, this is not sufficient.  This section enumerates
-those cases:</p>
-
-<ul>
-  <li>getelementptr: the slot numbers for sequential type indexes are shifted 
-  up two bits.  This allows the low order bits will encode the type of index 
-  used, as follows: 0=uint, 1=int, 2=ulong, 3=long.</li>
-  <li>cast: the result type number is encoded as the second operand.</li>
-  <li>alloca/malloc: If the allocation has an explicit alignment, the log2 of 
-  the alignment is encoded as the second operand.</li>
-  <li>call: If the tail marker and calling convention cannot be 
-  <a href="#pi_note">encoded into the opcode</a> of the call, it is passed as 
-  an additional operand.  The low bit of the operand is a flag indicating 
-  whether the call is a tail call.  The rest of the bits contain the calling 
-  convention number (shifted left by one bit).</li>
-</ul>
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection"><a name="instencode">Instruction 
-Encoding</a></div>
-
-<div class="doc_text">
-<p>For brevity, instructions are written in one of four formats,
-depending on the number of operands to the instruction. Each
-instruction begins with a <a href="#uint32_vbr">uint32_vbr</a> that
-encodes the type of the instruction as well as other things. The tables
-that follow describe the format of this first part of each instruction.</p>
-<p><b>Instruction Format 0</b></p>
-<p>This format is used for a few instructions that can't easily be
-shortened because they have large numbers of operands (e.g. PHI Node or
-getelementptr). Each of the opcode, type, and operand fields is found in
-successive fields.</p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">Specifies the opcode of the instruction. Note that 
-        for compatibility with the other instruction formats, the opcode is 
-        shifted left by 2 bits. Bits 0 and 1 must have value zero for this 
-        format.</td>
-    </tr>
-    <tr>
-      <td><a href="#uint24_vbr">uint24_vbr</a></td>
-      <td class="td_left">Provides the type slot number of the result type of
-        the instruction.</td>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">The number of operands that follow.</td>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a>+</td>
-      <td class="td_left">The slot number of the value(s) for the operand(s).
-      </td>
-    </tr>
-  </tbody>
-</table>
-
-<p><b>Instruction Format 1</b></p>
-<p>This format encodes the opcode, type and a single operand into a
-single <a href="#uint32_vbr">uint32_vbr</a> as follows:</p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Bits</b></th>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td>0-1</td>
-      <td>constant "1"</td>
-      <td class="td_left">These two bits must be the value 1 which identifies 
-        this as an instruction of format 1.</td>
-    </tr>
-    <tr>
-      <td>2-7</td>
-      <td><a href="#instructions">opcode</a></td>
-      <td class="td_left">Specifies the opcode of the instruction. Note that 
-        the maximum opcode value is 63.</td>
-    </tr>
-    <tr>
-      <td>8-19</td>
-      <td><a href="#unsigned">unsigned</a></td>
-      <td class="td_left">Specifies the slot number of the type for this 
-        instruction. Maximum slot number is 2<sup>12</sup>-1=4095.</td>
-    </tr>
-    <tr>
-      <td>20-31</td>
-      <td><a href="#unsigned">unsigned</a></td>
-      <td class="td_left">Specifies the slot number of the value for the 
-        first operand. Maximum slot number is 2<sup>12</sup>-1=4095. Note that 
-        the value 2<sup>12</sup>-1 denotes zero operands.</td>
-    </tr>
-  </tbody>
-</table>
-<p><b>Instruction Format 2</b></p>
-<p>This format encodes the opcode, type and two operands into a single <a
- href="#uint32_vbr">uint32_vbr</a> as follows:</p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Bits</b></th>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td>0-1</td>
-      <td>constant "2"</td>
-      <td class="td_left">These two bits must be the value 2 which identifies 
-        this as an instruction of format 2.</td>
-    </tr>
-    <tr>
-      <td>2-7</td>
-      <td><a href="#instructions">opcode</a></td>
-      <td class="td_left">Specifies the opcode of the instruction. Note that 
-        the maximum opcode value is 63.</td>
-    </tr>
-    <tr>
-      <td>8-15</td>
-      <td><a href="#unsigned">unsigned</a></td>
-      <td class="td_left">Specifies the slot number of the type for this 
-        instruction. Maximum slot number is 2<sup>8</sup>-1=255.</td>
-    </tr>
-    <tr>
-      <td>16-23</td>
-      <td><a href="#unsigned">unsigned</a></td>
-      <td class="td_left">Specifies the slot number of the value for the first 
-        operand. Maximum slot number is 2<sup>8</sup>-1=255.</td>
-    </tr>
-    <tr>
-      <td>24-31</td>
-      <td><a href="#unsigned">unsigned</a></td>
-      <td class="td_left">Specifies the slot number of the value for the second 
-        operand. Maximum slot number is 2<sup>8</sup>-1=255.</td>
-    </tr>
-  </tbody>
-</table>
-<p><b>Instruction Format 3</b></p>
-<p>This format encodes the opcode, type and three operands into a
-single <a href="#uint32_vbr">uint32_vbr</a> as follows:</p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Bits</b></th>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td>0-1</td>
-      <td>constant "3"</td>
-      <td class="td_left">These two bits must be the value 3 which identifies 
-        this as an instruction of format 3.</td>
-    </tr>
-    <tr>
-      <td>2-7</td>
-      <td><a href="#instructions">opcode</a></td>
-      <td class="td_left">Specifies the opcode of the instruction. Note that 
-        the maximum opcode value is 63.</td>
-    </tr>
-    <tr>
-      <td>8-13</td>
-      <td><a href="#unsigned">unsigned</a></td>
-      <td class="td_left">Specifies the slot number of the type for this 
-        instruction. Maximum slot number is 2<sup>6</sup>-1=63.</td>
-    </tr>
-    <tr>
-      <td>14-19</td>
-      <td><a href="#unsigned">unsigned</a></td>
-      <td class="td_left">Specifies the slot number of the value for the first 
-        operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
-    </tr>
-    <tr>
-      <td>20-25</td>
-      <td><a href="#unsigned">unsigned</a></td>
-      <td class="td_left">Specifies the slot number of the value for the second
-        operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
-    </tr>
-    <tr>
-      <td>26-31</td>
-      <td><a href="#unsigned">unsigned</a></td>
-      <td class="td_left">Specifies the slot number of the value for the third
-        operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
-    </tr>
-  </tbody>
-</table>
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="symtab">Symbol Table</a> </div>
-<div class="doc_text">
-<p>A symbol table can be put out in conjunction with a module or a function. A
-symbol table has a list of name/type associations followed by a list of
-name/value associations. The name/value associations are organized into "type
-planes" so that all values of a common type are listed together.  Each type 
-plane starts with the number of entries in the plane and the type slot number
-for all the values in that plane (so the type can be looked up in the global 
-type pool). For each entry in a type plane, the slot number of the value and 
-the name associated with that value are written. The format is given in the 
-table below. </p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#block">block</a><br>
-      </td>
-      <td class="td_left">Symbol Table Identifier (0x04)</td>
-    </tr>
-    <tr>
-      <td><a href="#llist">llist</a>(<a href="#symtab_entry">type_entry</a>)
-      </td>
-      <td class="td_left">A length list of symbol table entries for
-        <tt>Type</tt>s
-      </td>
-    </tr>
-    <tr>
-      <td><a href="#zlist">llist</a>(<a href="#symtab_plane">symtab_plane</a>)
-      </td>
-      <td class="td_left">A length list of "type planes" of symbol table
-        entries for <tt>Value</tt>s</td>
-    </tr>
-  </tbody>
-</table>
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection"> <a name="type_entry">Symbol Table Type
-Entry</a>
-</div>
-<div class="doc_text">
-<p>A symbol table type entry associates a name with a type. The name is provided
-simply as an array of chars. The type is provided as a type slot number (index)
-into the global type pool. The format is given in the following table:</p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint24_vbr</a></td>
-      <td class="td_left">Type slot number of the type being given a
-        name relative to the global type pool.
-      </td>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">Length of the character array that follows.</td>
-    </tr>
-    <tr>
-      <td><a href="#char">char</a>+</td>
-      <td class="td_left">The characters of the name.</td>
-    </tr>
-  </tbody>
-</table>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection"> <a name="symtab_plane">Symbol Table
-Plane</a>
-</div>
-<div class="doc_text">
-<p>A symbol table plane provides the symbol table entries for all
-values of a common type. The encoding is given in the following table:</p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">Number of entries in this plane.</td>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">Type slot number of type for all values in this plane.
-      </td>
-    </tr>
-    <tr>
-      <td><a href="#value_entry">value_entry</a>+</td>
-      <td class="td_left">The symbol table entries for to associate values with
-        names.</td>
-    </tr>
-  </tbody>
-</table>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection"><a name="value_entry">Symbol Table Value
-Entry</a>
-</div>
-<div class="doc_text">
-<p>A symbol table value entry provides the assocation between a value and the
-name given to the value. The value is referenced by its slot number. The
-format is given in the following table:</p>
-<table>
-  <tbody>
-    <tr>
-      <th><b>Type</b></th>
-      <th class="td_left"><b>Field Description</b></th>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint24_vbr</a></td>
-      <td class="td_left">Value slot number of the value being given a name.
-      </td>
-    </tr>
-    <tr>
-      <td><a href="#uint32_vbr">uint32_vbr</a></td>
-      <td class="td_left">Length of the character array that follows.</td>
-    </tr>
-    <tr>
-      <td><a href="#char">char</a>+</td>
-      <td class="td_left">The characters of the name.</td>
-    </tr>
-  </tbody>
-</table>
-</div>
-
-<!-- *********************************************************************** -->
-<div class="doc_section"> <a name="versiondiffs">Version Differences</a>
-</div>
-<!-- *********************************************************************** -->
-<div class="doc_text">
-<p>This section describes the differences in the Bytecode Format across
-LLVM
-versions. The versions are listed in reverse order because it assumes
-the current version is as documented in the previous sections. Each
-section here
-describes the differences between that version and the one that <i>follows</i>.
-</p>
-</div>
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="vers13">Version 1.3 Differences From 
-    1.4</a></div>
-<!-- _______________________________________________________________________ -->
-
-<div class="doc_subsubsection">Unreachable Instruction</div>
-<div class="doc_text">
-  <p>The LLVM <a href="LangRef.html#i_unreachable">Unreachable</a> instruction
-  was added in version 1.4 of LLVM.  This caused all instruction numbers after
-  it to shift down by one.</p>
-</div>
-
-<div class="doc_subsubsection">Function Flags</div>
-<div class="doc_text">
-  <p>LLVM bytecode versions prior to 1.4 did not include the 5 bit offset 
-     in <a href="#funcfield">the function list</a> in the <a
-     href="#globalinfo">Module Global Info</a> block.</p>
-</div>
-
-<div class="doc_subsubsection">Function Flags</div>
-<div class="doc_text">
-  <p>LLVM bytecode versions prior to 1.4 did not include the 'undef' constant
-  value, which affects the encoding of <a href="#constant">Constant Fields</a>.
-  </p>
-</div>
-
-
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="vers12">Version 1.2 Differences
-From 1.3</a></div>
-<!-- _______________________________________________________________________ -->
-
-<div class="doc_subsubsection">Type Derives From Value</div>
-<div class="doc_text">
-<p>In version 1.2, the Type class in the LLVM IR derives from the Value
-class. This is not the case in version 1.3. Consequently, in version
-1.2 the notion of a "Type Type" was used to write out values that were
-Types. The types always occuped plane 12 (corresponding to the
-TypeTyID) of any type planed set of values. In 1.3 this representation
-is not convenient because the TypeTyID (12) is not present and its
-value is now used for LabelTyID. Consequently, the data structures
-written that involve types do so by writing all the types first and
-then each of the value planes according to those types. In version 1.2,
-the types would have been written intermingled with the values.</p>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">Restricted getelementptr Types</div>
-<div class="doc_text">
-<p>In version 1.2, the getelementptr instruction required a ubyte type
-index for accessing a structure field and a long type index for
-accessing an array element. Consequently, it was only possible to
-access structures of 255 or fewer elements. Starting in version 1.3,
-this restriction was lifted. Structures must now be indexed with uint
-constants. Arrays may now be indexed with int, uint, long, or ulong
-typed values. The consequence of this was that the bytecode format had
-to change in order to accommodate the larger range of structure indices.</p>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">Short Block Headers</div>
-<div class="doc_text">
-<p>In version 1.2, block headers were always 8 bytes being comprised of
-both an unsigned integer type and an unsigned integer size. For very
-small modules, these block headers turn out to be a large fraction of
-the total bytecode file size. In an attempt to make these small files
-smaller, the type and size information was encoded into a single
-unsigned integer (4 bytes) comprised of 5 bits for the block type
-(maximum 31 block types) and 27 bits for the block size (max
-~134MBytes). These limits seemed sufficient for any blocks or sizes
-forseen in the future. Note that the module block, which encloses all
-the other blocks is still written as 8 bytes since bytecode files
-larger than 134MBytes might be possible.</p>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">Dependent Libraries and Target Triples</div>
-<div class="doc_text">
-<p>In version 1.2, the bytecode format does not store module's target
-triple or dependent. These fields have been added to the end of the <a
- href="#globalinfo">module global info block</a>. The purpose of these
-fields is to allow a front end compiler to specifiy that the generated
-module is specific to a particular target triple (operating
-system/manufacturer/processor) which makes it non-portable; and to
-allow front end compilers to specify the list of libraries that the
-module depends on for successful linking.</p>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">Types Restricted to 24-bits</div>
-<div class="doc_text">
-<p>In version 1.2, type slot identifiers were written as 32-bit VBR
-quantities. In 1.3 this has been reduced to 24-bits in order to ensure
-that it is not possible to overflow the type field of a global variable
-definition. 24-bits for type slot numbers is deemed sufficient for any
-practical use of LLVM.</p>
-</div>
-<!-- _______________________________________________________________________ -->
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="vers11">Version 1.1 Differences
-From 1.2 </a></div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">Explicit Primitive Zeros</div>
-<div class="doc_text">
-<p>In version 1.1, the zero value for primitives was explicitly encoded
-into the bytecode format. Since these zero values are constant values
-in the LLVM IR and never change, there is no reason to explicitly
-encode them. This explicit encoding was removed in version 1.2.</p>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">Inconsistent Module Global Info</div>
-<div class="doc_text">
-<p>In version 1.1, the Module Global Info block was not aligned causing
-the next block to be read in on an unaligned boundary. This problem was
-corrected in version 1.2.<br>
-<br>
-</p>
-</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="vers10">Version 1.0 Differences
-From 1.1</a></div>
-<div class="doc_text">
-<p>None. Version 1.0 and 1.1 bytecode formats are identical.</p>
-</div>
-<!-- *********************************************************************** -->
-<hr>
-<address> <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
- src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
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- src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
-<a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and <a
- href="mailto:sabre@nondot.org">Chris Lattner</a><br>
-<a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
-Last modified: $Date$
-</address>
-</body>
-</html>
author	Chris Lattner <sabre@nondot.org>	2007-05-06 23:21:05 +0000
committer	Chris Lattner <sabre@nondot.org>	2007-05-06 23:21:05 +0000
commit	c9bafdaa752db1cbfe0354fd50b1735187980cdb (patch)
tree	bc5fb543c2c7d5e16ee0759e3a9d888ebe1fc0d5
parent	de36ffd2ca8304ddaf189cf3b1ef97f7b57c2cb3 (diff)
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