-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
- "http://www.w3.org/TR/html4/strict.dtd">
+<!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>
- table, tr, td { border: 2px solid gray }
- th { border: 2px sold gray; font-weight: bold; }
- table { border-collapse: collapse; margin-top: 1em margin-bottom: 1em }
+ <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>
+<div class="doc_title"> LLVM Bytecode File Format </div>
<ol>
<li><a href="#abstract">Abstract</a></li>
- <li><a href="#general">General Concepts</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><a href="#details">Detailed Layout</a>
+ </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="#compactiontable">Compaction Table</a></li>
+ <li><a href="#instructionlist">Instruction List</a></li>
+ <li><a href="#opcodes">Instruction Opcodes</a></li>
+ <li><a href="#symtab">Symbol Table</a></li>
+ </ol>
+ </li>
+ <li><a href="#versiondiffs">Version Differences</a>
<ol>
- <li><a href="#notation">Notation</a></li>
- <li><a href="#blocktypes">Blocks Types</a></li>
- <li><a href="#header">Header Block</a></li>
- <li><a href="#typeool">Global Type Pool</a></li>
- <li><a href="#modinfo">Module Info Block</a></li>
- <li><a href="#constants">Global Constant Pool</a></li>
- <li><a href="#functions">Function Blocks</a><li>
- <li><a href="#symtab">Module Symbol Table</a><li>
+ <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_text">
-<p><b>Written by <a href="mailto:rspencer@x10sys.com">Reid Spencer</a>
-and <a href="mailto:sabre@nondot.org">Chris Lattner</a></b></p>
-<p> </p>
+<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 is an (after the fact) specification of the LLVM bytecode
-file format. It documents 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>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="general">General Concepts</a> </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 bit and byte level specifics.</p>
+<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.
-Each block begins with an identification value that determines the type of
-the next block. The possible types of blocks are described below in the section
-<a href="#blockstypes">Block Types</a>. 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.</p>
-<p>The following block identifiers are currently in use
-(from llvm/Bytecode/Format.h):</p>
-<ol>
- <li><b>Module (0x01)</b>.</li>
- <li><b>Function (0x11)</b>.</li>
- <li><b>ConstantPool (0x12)</b>.</li>
- <li><b>SymbolTable (0x13)</b>.</li>
- <li><b>ModuleGlobalInfo (0x14)</b>.</li>
- <li><b>GlobalTypePlane (0x15)</b>.</li>
- <li><b>BasicBlock (0x31)</b>.</li>
- <li><b>InstructionList (0x32)</b>.</li>
- <li><b>CompactionTable (0x33)</b>.</li>
-</ol>
-<p> Except for the <a href="#header">Header Block</a> all blocks are variable
-length. They consume just enough bytes to express their contents.</p>
+<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>Most blocks are constructed of lists of information. Lists can be constructed
-of other lists, etc. This decomposition of information follows the containment
-hierarchy of the LLVM Intermediate Representation. For example, a function is
-composed of a list of basic blocks. Each basic block is composed of a set of
-instructions. This list of list nesting and hierarchy is maintained in the
-bytecode file.</p>
-<p>A list is encoded into the file simply by encoding the number of entries as
-an integer followed by each of the entries. The reader knows when the list is
-done because it will have filled the list with the required numbe of entries.
-</p>
+<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 SByte or UByte) 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 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
+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>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 &
+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 & 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 << 1) | 1)" and 3 is encoded as "(3 <<
+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>Slot numbers are also kept small by rearranging their order. Because
+of the structure of LLVM, certain values are much more likely to be used
+frequently in the body of a function. For this reason, a compaction table is
+provided in the body of a function if its use would make the function body
+smaller. Suppose you have a function body that uses just the types "int*" and
+"{double}" but uses them thousands of time. Its worthwhile to ensure that the
+slot number for these types are low so they can be encoded in a single byte
+(via vbr). This is exactly what the compaction table does.</p>
+<p>In summary then, a slot number can be though 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"> <a href="#globaltypes">Global Type 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"> <a href="#globalinfo">Module Globals 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"> <a href="#constantpool">Module Constant 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"> <a href="#functiondefs">Function Definitions</a>*</td>
+ <td class="td_left">One function block is written for each
+function in the module. The function block contains the instructions,
+compaction table, 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"> <a
+ href="#constantpool">Function Constant 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>0x08</td>
+ <td>Function</td>
+ <td>Yes</td>
+ <td>No</td>
+ <td>2</td>
+ <td class="td_left"> <a
+ href="#compactiontable">Compaction Table</a></td>
+ <td class="td_left">This table reduces bytecode size by providing
+a funtion-local mapping of type and value slot numbers to their global
+slot numbers</td>
+ </tr>
+ <tr>
+ <td>0x07</td>
+ <td>Function</td>
+ <td>No</td>
+ <td>No</td>
+ <td>2</td>
+ <td class="td_left"> <a
+ href="#instructionlist">Instruction 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"> <a
+ href="#symtab">Function Symbol 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"> <a href="#symtab">Module Symbol 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="details">Detailed Layout</a> </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 LLVM bytecode file format.
- bit and byte level specifics.</p>
+<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>
+as shown in the following table.</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">Target is big endian?</td>
+ </tr>
+ <tr>
+ <td><a href="#bit">bit(1)</a></td>
+ <td class="td_left">On target pointers are 64-bit?</td>
+ </tr>
+ <tr>
+ <td><a href="#bit">bit(2)</a></td>
+ <td class="td_left">Target has no endianess?</td>
+ </tr>
+ <tr>
+ <td><a href="#bit">bit(3)</a></td>
+ <td class="td_left">Target has no pointer size?</td>
+ </tr>
+ <tr>
+ <td><a href="#bit">bit(4-31)</a></td>
+ <td class="td_left">Bytecode format version</td>
+ </tr>
+ </tbody>
+</table>
+<p>
+Of particular note, the bytecode format number is simply a 28-bit
+monotonically increase 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, 1.3):</p>
+<ul>
+ <li>#0: LLVM 1.0 & 1.1</li>
+ <li>#1: LLVM 1.2</li>
+ <li>#2: LLVM 1.2.5 (not released)</li>
+ <li>#3: LLVM 1.3<br>
+ </li>
+</ul>
+<p>Note that we plan to eventually expand the target description
+capabilities
+of bytecode files to <a href="http://llvm.cs.uiuc.edu/PR263">target
+triples</a>.
+</p>
+</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>Packed 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 Types (18)</td>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a></td>
+ <td class="td_left">Slot number of packed 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 packed vector.</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<br>
+ </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 style="vertical-align: top;"><a href="#llist">llist</a>(<a
+ href="#string">string</a>)<br>
+ </td>
+ <td style="vertical-align: top; text-align: left;">A length list
+of strings that specify the names of the libraries that this module
+depends upon.<br>
+ </td>
+ </tr>
+ <tr>
+ <td style="vertical-align: top;"><a href="#string">string</a><br>
+ </td>
+ <td style="vertical-align: top; text-align: left;">The target
+triple for the module (blank means no target triple specified, i.e. a
+platform independent module).<br>
+ </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 and a list of the
+constant initializers for the global var, if any.</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</td>
+ </tr>
+ <tr>
+ <td><a href="#bit">bit(5-31)</a></td>
+ <td class="td_left">Type slot number of type for the global variable.</td>
+ </tr>
+ </tbody>
+</table>
+<p>The table below provides the format of the constant initializers for
+the global variable field, if it has one.</p>
+<table>
+ <tbody>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr>
+ <tr>
+ <td>(<a href="#zlist">zlist</a>(<a href="#uint32_vbr">uint32_vbr</a>))?
+ </td>
+ <td class="td_left">An optional zero-terminated list of value slot
+numbers of 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.</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">Reserved for future use. Currently set to 0001.</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.</td>
+ </tr>
+ <tr>
+ <td><a href="#bit">bit(5-)</a></td>
+ <td class="td_left">Type slot number of type for the function.</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_subsection"><a name="notation">Notation</a></div>
+<div class="doc_subsubsection"><a name="constant">Constant Field</a></div>
<div class="doc_text">
- <p>The descriptions of the bytecode format that follow describe the bit
- fields in detail. These descriptions are provided in tabular form. Each table
- has four columns that specify:</p>
- <ol>
- <li><b>Byte(s)</b>. The offset in bytes of the field from the start of
- its container (block, list, other field).<li>
- <li><b>Bit(s)</b>. The offset in bits of the field from the start of
- the byte field. Bits are always little endian. That is, bit addresses with
- smaller values have smaller address (i.e. 2^0 is at bit 0, 2^1 at 1, etc.)
- </li>
- <li><b>Align?</b> Indicates if this field is aligned to 32 bits or not.
- This indicates where the <em>next</em> field starts, always on a 32 bit
- boundary.</li>
- <li><b>Type</b>. The basic type of information contained in the field.</li>
- <li><b>Description</b>. Descripts the contents of the field.</li>
- </ol>
+<p>Constants 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 since those types of
+constants have no operands. In this case, we have the following field
+definitions:</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)</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)</b>. These are
+written as an <a href="#uint64_vbr">uint64_vbr</a> with the
+corresponding value. </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>
+
+<p>When the number of operands to the constant is one, we have an 'undef' value
+of the specified type.</p>
+
+<p>When the number of operands to the constant is greater than one, we have a
+constant expression and its field format is provided 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="blocktypes">Block Types</a></div>
+<div class="doc_subsection"><a name="functiondefs">Function Definition</a></div>
<div class="doc_text">
- <p>The bytecode format encodes the intermediate representation into groups
- of bytes known as blocks. The blocks are written sequentially to the file in
- the following order:</p>
+<p>Function definitions contain the linkage, constant pool or
+compaction table, 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">The linkage type of the function: 0=External,
+1=Weak, 2=Appending, 3=Internal, 4=LinkOnce<sup>1</sup></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="#compactiontable">compaction
+table</a> block for the 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><a href="#header">Header</a>. This block contains the file signature
- (magic number), machine description and file format version (not LLVM
- version).</li>
- <li><a href="#gtypepool">Global Type Pool</a>. This block contains all the
- global (module) level types.</li>
- <li><a href="#modinfo">Module Info</a>. This block contains the types of the
- global variables and functions in the module as well as the constant
- initializers for the global variables</li>
- <li><a href="#constants">Constants</a>. This block contains all the global
- constants except function arguments, global values and constant strings.</li>
- <li><a href="#functions">Functions</a>. One function block is written for
- each function in the module. </li>
- <li><a href="$symtab">Symbol Table</a>. The module level symbol table that
- provides names for the various other entries in the file is the final block
- written.</li>
+ <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>
+ <li>Note that only one of the constant pool or compaction table will
+be written. Compaction tables are only written if they will actually
+save bytecode space. If not, then a regular constant pool is written.</li>
</ol>
</div>
<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="header">Header Block</a> </div>
+<div class="doc_subsection"><a name="compactiontable">Compaction Table</a>
+</div>
+<div class="doc_text">
+<p>Compaction tables are part of a function definition. They are merely
+a device for reducing the size of bytecode files. The size of a
+bytecode file is dependent on the <em>values</em> of the slot numbers
+used because larger values use more bytes in the variable bit rate
+encoding scheme. Furthermore, the compressed instruction format
+reserves only six bits for the type of the instruction. In large
+modules, declaring hundreds or thousands of types, the values of the
+slot numbers can be quite large. However, functions may use only a
+small fraction of the global types. In such cases a compaction table is
+created that maps the global type and value slot numbers to smaller
+values used by a function. Functions will contain either a
+function-specific constant pool <em>or</em> a compaction table but not
+both. Compaction tables have the format 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="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">The number of types that follow</td>
+ </tr>
+ <tr>
+ <td><a href="#uint24_vbr">uint24_vbr</a>+</td>
+ <td class="td_left">The type slot number in the global types of
+the type that will be referenced in the function with the index of this
+entry in the compaction table.</td>
+ </tr>
+ <tr>
+ <td><a href="#type_len">type_len</a></td>
+ <td class="td_left">An encoding of the type and number of values
+that follow. This field's encoding varies depending on the size of the
+type plane. See <a href="#type_len">Type and Length</a> for further
+details.</td>
+ </tr>
+ <tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a>+</td>
+ <td class="td_left">The value slot number in the global values
+that will be referenced in the function with the index of this entry in
+the compaction table.</td>
+ </tr>
+ </tbody>
+</table>
+</div>
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection"><a name="type_len">Type and Length</a></div>
+<div class="doc_text">
+<p>The type and length of a compaction table type plane is encoded
+differently depending on the length of the plane. For planes of length
+1 or 2, the length is encoded into bits 0 and 1 of a <a
+ href="#uint32_vbr">uint32_vbr</a> and the type is encoded into bits
+2-31. Because type numbers are often small, this often saves an extra
+byte per plane. If the length of the plane is greater than 2 then the
+encoding uses a <a href="#uint32_vbr">uint32_vbr</a> for each of the
+length and type, in that order.</p>
+</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_subsubsection"><a name="instruction">Instructions</a></div>
<div class="doc_text">
-<p>The Header Block occurs in every LLVM bytecode file and is always first. It
-simply provides a few bytes of data to identify the file, its format, and the
-bytecode version. This block is fixed length and always eight bytes, as follows:
-<table class="doc_table" width="90%">
- <tr>
- <th><b>Byte(s)</b></th>
- <th><b>Bit(s)</b></th>
- <th><b>Align?</b></th>
- <th><b>Type</b></th>
- <th align="left"><b>Field Description</b></th>
- </tr>
- <tr>
- <td>00</td><td>00-07</td><td>No</td><td>Char</td>
- <td align="left">Constant "l" (0x6C)</td>
- </tr>
- <tr>
- <td>01</td><td>00-07</td><td>No</td><td>Char</td>
- <td align="left">Constant "l" (0x6C)</td>
- </tr>
- <tr>
- <td>02</td><td>00-07</td><td>No</td><td>Char</td>
- <td align="left">Constant "v" (0x76)</td>
- </tr>
- <tr>
- <td>03</td><td>00-07</td><td>No</td><td>Char</td>
- <td align="left">Constant "m" (0x6D)</td>
- </tr>
- <tr>
- <td>04-07</td><td>00</td><td>No</td><td>Bool</td>
- <td align="left">Target is big endian?</td>
- </tr>
- <tr>
- <td>04-07</td><td>01</td><td>No</td><td>Bool</td>
- <td align="left">Target has long pointers?</td>
- </tr>
- <tr>
- <td>04-07</td><td>02</td><td>No</td><td>Bool</td>
- <td align="left">Target has no endianess?</td>
- </tr>
- <tr>
- <td>04-07</td><td>03</td><td>No</td><td>Bool</td>
- <td align="left">Target has no pointer size?</td>
- </tr>
- <tr>
- <td>04-07</td><td>04-31</td><td>Yes</td><td>Unsigned</td>
- <td align="left">The LLVM bytecode format version number</td>
- </tr>
+<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).
+ <sup>1</sup></td>
+ </tr>
+ </tbody>
+</table>
+Notes:
+<ol>
+ <li>Note that if the instruction is a getelementptr and the type of
+the operand is a sequential type (array or pointer) then the slot
+number is shifted up two bits and the low order bits will encode the
+type of index used, as follows: 0=uint, 1=int, 2=ulong, 3=long.</li>
+</ol>
+<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="#opcode">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="#opcodes">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="#opcodes">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="gtypepool">Global Type Pool</a> </div>
+<div class="doc_subsection"><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.cs.uiuc.edu/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>Div</td><td>10</td><td>1</td><td>1.0</td></tr>
+ <tr><td>Rem</td><td>11</td><td>1</td><td>1.0</td></tr>
+ <tr><td colspan="4"><b>Logical Operators</b></td></tr>
+ <tr><td>And</td><td>12</td><td>1</td><td>1.0</td></tr>
+ <tr><td>Or</td><td>13</td><td>1</td><td>1.0</td></tr>
+ <tr><td>Xor</td><td>14</td><td>1</td><td>1.0</td></tr>
+ <tr><td colspan="4"><b>Binary Comparison Operators</b></td></tr>
+ <tr><td>SetEQ</td><td>15</td><td>1</td><td>1.0</td></tr>
+ <tr><td>SetNE</td><td>16</td><td>1</td><td>1.0</td></tr>
+ <tr><td>SetLE</td><td>17</td><td>1</td><td>1.0</td></tr>
+ <tr><td>SetGE</td><td>18</td><td>1</td><td>1.0</td></tr>
+ <tr><td>SetLT</td><td>19</td><td>1</td><td>1.0</td></tr>
+ <tr><td>SetGT</td><td>20</td><td>1</td><td>1.0</td></tr>
+ <tr><td colspan="4"><b>Memory Operators</b></td></tr>
+ <tr><td>Malloc</td><td>21</td><td>1</td><td>1.0</td></tr>
+ <tr><td>Free</td><td>22</td><td>1</td><td>1.0</td></tr>
+ <tr><td>Alloca</td><td>23</td><td>1</td><td>1.0</td></tr>
+ <tr><td>Load</td><td>24</td><td>1</td><td>1.0</td></tr>
+ <tr><td>Store</td><td>25</td><td>1</td><td>1.0</td></tr>
+ <tr><td>GetElementPtr</td><td>26</td><td>1</td><td>1.0</td></tr>
+ <tr><td colspan="4"><b>Other Operators</b></td></tr>
+ <tr><td>PHI</td><td>27</td><td>1</td><td>1.0</td></tr>
+ <tr><td>Cast</td><td>28</td><td>1</td><td>1.0</td></tr>
+ <tr><td>Call</td><td>29</td><td>1</td><td>1.0</td></tr>
+ <tr><td>Shl</td><td>30</td><td>1</td><td>1.0</td></tr>
+ <tr><td>Shr</td><td>31</td><td>1</td><td>1.0</td></tr>
+ <tr><td>VANext</td><td>32</td><td>1</td><td>1.0</td></tr>
+ <tr><td>VAArg</td><td>33</td><td>1</td><td>1.0</td></tr>
+ <tr><td>Select</td><td>34</td><td>2</td><td>1.2</td></tr>
+ <tr><td>UserOp1</td><td>35</td><td>1</td><td>1.0</td></tr>
+ <tr><td>UserOp2</td><td>36</td><td>1</td><td>1.0</td></tr>
+ </tbody>
+ </table>
</div>
+
<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="modinfo">Module Info</a> </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_subsection"><a name="constants">Constants</a> </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_subsection"><a name="functions">Functions</a> </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_subsection"><a name="symtab">Module Symbol Table</a> </div>
+<div class="doc_subsubsection"><a name="value_entry">Symbol Table Value
+Entry</a>
+</div>
<div class="doc_text">
-<p>The module symbol table is a list of
+<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>
<!-- *********************************************************************** -->
-<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>
- <a href="http://validator.w3.org/check/referer"><img
- src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
+<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>
- <a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
- <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
- <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
- Last modified: $Date$
+<!-- _______________________________________________________________________ -->
+<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_subsubsection">Aligned Data</div>
+<div class="doc_text">
+ <p>In version 1.3, certain data items were aligned to 32-bit boundaries. In
+ version 1.4, alignment of data was done away with completely. The need for
+ alignment has gone away and the only thing it adds is bytecode file size
+ overhead. In most cases this overhead was small. However, in functions with
+ large numbers of format 0 instructions (GEPs and PHIs with lots of parameters)
+ or regular instructions with large valued operands (e.g. because there's just
+ a lot of instructions in the function) the overhead can be extreme. In one
+ test case, the overhead was 44,000 bytes (34% of the total file size).
+ Consequently in release 1.4, the decision was made to eliminate alignment
+ altogether.</p>
+ <p>In version 1.3 format, the following bytecode constructs were aligned (i.e.
+ they were followed by one to three bytes of padding):</p>
+ <ul>
+ <li>All blocks.</li>
+ <li>Instructions using the long format (format 0).</li>
+ <li>All call instructions that called a var args function.</li>
+ <li>The target triple (a string field at the end of the module block).</li>
+ <li>The version field (immediately following the signature).</li>
+ </ul>
+ <p>None of these constructs are aligned in version 1.4</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>
+<a href="http://validator.w3.org/check/referer"><img
+ 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.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
+Last modified: $Date$
</address>
</body>
</html>
-<!-- vim: sw=2
--->
projects / oota-llvm.git / blobdiff