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diff --git a/docs/BytecodeFormat.html b/docs/BytecodeFormat.html new file mode 100644 index 0000000000..67ed8ba7c4 --- /dev/null +++ b/docs/BytecodeFormat.html @@ -0,0 +1,1943 @@ +<!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="#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="#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 & +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="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> +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 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, 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</li> + <li>#4: LLVM 1.3.x (not released)</li> + <li>#5: LLVM 1.4, 1.5, 1.6</li> + </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"> + Encodes the calling convention number of the function. If this number is + zero, this field is followed by a vbr indicating the CC#. Otherwise, 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.</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_subsubsection"><a name="constant">Constant Field</a></div> +<div class="doc_text"> +<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="functiondefs">Function Definition</a></div> +<div class="doc_text"> +<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>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="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>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="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 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+Volatile</td><td>62</td><td>3</td><td>1.3</td></tr> + <tr><td>Store+Volatile</td><td>63</td><td>3</td><td>1.3</td></tr> + </tbody> + </table> +</div> + +<p><b><a name="pi_note">* Note: </a></b> +These aren't really opcodes from an LLVM language prespeective. They encode +information into other opcodes without reserving space for that information. +For example, opcode=63 is a Volatile 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 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_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> |