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<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="#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="#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>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>
</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>
-Except for the <a href="#header">Header Block</a> all blocks are variable
-length. The 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
+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>
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>
+ <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>
+</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" >
+ <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><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><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 float, double, and constant
+ initializers.</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
+ begins with an <a href="#unsigned">unsigned</a> that provides the block
+ identifier (constant value) and an <a href="#unsigned">unsigned</a> that
+ provides the length of the block. Blocks may compose other blocks.
+ </td>
+ </tr>
+</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" >
+ <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>
+ </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 handled
+specially and 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>
</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>
+ <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.</li>
+ </tr>
+ <tr><td>0x15</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>0x14</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>0x12</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>0x11</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>0x12</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>0x33</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>0x32</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>0x13</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>0x13</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>
+</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="notation">Notation</a></div>
+<div class="doc_subsection"><a name="signature">Signature Block</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>Description</b>. Descripts the contents of the field.</li>
- </ol>
+<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.
+<table>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr><tr>
+ <td><a href="#char">char</a></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>
+ </tr><tr>
+ <td><a href="#char">char</a></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>
+ </tr>
+</table>
</div>
+
<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="blocktypes">Block Types</a></div>
+<div class="doc_subsection"><a name="module">Module Block</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>
-<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>
-</ol>
+<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>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr><tr>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Module Identifier (0x01)</td>
+ </tr><tr>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Size of the module block in bytes</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="#symboltable">Module Symbol Table</a></td>
+ </tr>
+</table>
+</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>
+ <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>
+</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 1.3</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="header">Header Block</a> </div>
+<div class="doc_subsection"><a name="globaltypes">Global Type Pool</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%">
+<p>The global type pool consists of type definitions. Their order of appearance
+in the file determines their 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>
<tr>
- <th><b>Byte(s)</b></th>
- <th><b>Bit(s)</b></th>
- <th><b>Align?</b></th>
- <th align="left"><b>Field Description</b></th>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr><tr>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Type Pool Identifier (0x15)</td>
+ </tr><tr>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Size in bytes of the type pool block.</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>
+</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</p>
+<table>
<tr>
- <td>00</td><td>00-07</td><td>No</td>
- <td align="left">Constant "l"</td>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr><tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Type ID for the primitive types (values 1 to 11)
+ <sup>1</sup></td>
</tr>
+</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>
<tr>
- <td>01</td><td>00-07</td><td>No</td>
- <td align="left">Constant "l"</td>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr><tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Type ID for function types (13)</td>
+ </tr><tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Slot number of function's return type.</td>
+ </tr><tr>
+ <td><a href="#llist">llist</a>(<a href="#uint32_vbr">uint32_vbr</a>)</td>
+ <td class="td_left">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>
+</table>
+<h3>Structure Types</h3>
+<table>
<tr>
- <td>02</td><td>00-07</td><td>No</td>
- <td align="left">Constant "v"</td>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr><tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Type ID for structure types (14)</td>
+ </tr><tr>
+ <td><a href="#zlist">zlist</a>(<a href="#uint32_vbr">uint32_vbr</a>)</td>
+ <td class="td_left">Slot number of each of the element's fields.</td>
</tr>
+</table>
+<h3>Array Types</h3>
+<table>
<tr>
- <td>03</td><td>00-07</td><td>No</td>
- <td align="left">Constant "m"</td>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr><tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Type ID for Array Types (15)</td>
+ </tr><tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">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>
+</table>
+<h3>Pointer Types</h3>
+<table>
<tr>
- <td>04-07</td><td>00</td><td>No</td>
- <td align="left">Target is big endian</td>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr><tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Type ID For Pointer Types (16)</td>
+ </tr><tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Slot number of pointer's element type.</td>
</tr>
+</table>
+<h3>Opaque Types</h3>
+<table>
<tr>
- <td>04-07</td><td>01</td><td>No</td>
- <td align="left">Target has long pointers</td>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Description</b></th>
+ </tr><tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Type ID For Opaque Types (17)</td>
</tr>
+</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>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr><tr>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Module global info identifier (0x14)</td>
+ </tr><tr>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Size in bytes of the module global info block.</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
+ occuring in the module.</td>
+ </tr><tr>
+ <td><a href="#zlist">zlist</a>(<a href="#uint32_vbr">uint32_vbr</a>)</td>
+ <td class="td_left">A zero terminated list of function types occuring in
+ the module.</td>
+ </tr>
+ </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>
<tr>
- <td>04-07</td><td>02</td><td>No</td>
- <td align="left">Target has no endianess</td>
+ <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.</li>
+ </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">Slot number of type for the global variable.</td>
</tr>
+ </table>
+ <p>The table below provides the format of the constant initializers for the
+ global variable field, if it has one.</p>
+ <table>
+ <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>))?
+ </a>
+ </td>
+ <td class="td_left">An optional zero-terminated list of slot numbers of
+ the global variable's constant initializer.</td>
+ </tr>
+ </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>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr><tr>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Constant pool identifier (0x12)</td>
+ </tr><tr>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Size in bytes of the constant pool block.</td>
+ </tr>
+ </table>
+ <p><b>Module Constant Pool Preamble (constant strings)</b></p>
+ <table>
+ <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="#uint32_vbr">uint32_vbr</a>+</td>
+ <td class="td_left">Slot number of the constant string's type. Note
+ that the constant string's type implicitly defines the length of
+ the string.
+ </td>
+ </tr>
+ </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><b>Common Part (other constants)</b></p>
+ <table>
+ <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="#uint32_vbr">uint32_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>
+ </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 followe 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 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 slot numbers to the constant
+ field values of the structure.</li>
+ </ul>
+ <p>When the number of operands to the constant is non-zero, we have a
+ constant expression and its field format is provided in the table below.</p>
+ <table>
+ <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 slot number of the constant value for an
+ operand.<sup>1</sup></td>
+ </tr><tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">The slot number for the type of the constant value
+ for an operand.<sup>1</sup></td>
+ </tr>
+ </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>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr><tr>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Function definition block identifier (0x11)</td>
+ </tr><tr>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Size in bytes of the function definition block.</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="#symboltable">symbol table</a>
+ containing only those symbols pertinent to the function (mostly
+ block labels).</td>
+ </tr>
+ </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>value</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>
+ <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="#uint32_vbr">uint32_vbr</a>+</td>
+ <td class="td_left">The slot number in the global type plane 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 slot number in the globals of the value that
+ will be referenced in the function with the index of this entry in
+ the compaction table</td>
+ </tr>
+ </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>
+ <tr>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr><tr>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Instruction list identifier (0x33).</td>
+ </tr><tr>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Size in bytes of the instruction list.</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>
+ </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 word 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 optimized
+ because they have large numbers of operands (e.g. PHI Node or getelementptr).
+ Each of the opcode, type, and operand fields is as successive fields.</p>
+ <table>
+ <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="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Provides the 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>
+ </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>
+ <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>
+ </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>8-19</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>
+ </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>
+ <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>
+ </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>
+ </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>
+ <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>
+ </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>
+ </table>
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsection"><a name="symtab">Symbol Table</a> </div>
+<div class="doc_text">
+<p>A symbol table can be put out in conjunction with a module or a function.
+A symbol table is a list of type planes. Each type plane starts with the number
+of entries in the plane and the type plane's slot number (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>
<tr>
- <td>04-07</td><td>03</td><td>No</td>
- <td align="left">Target has no pointer size</td>
+ <th><b>Type</b></th>
+ <th class="td_left"><b>Field Description</b></th>
+ </tr><tr>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Symbol Table Identifier (0x13)</td>
+ </tr><tr>
+ <td><a href="#unsigned">unsigned</a></td>
+ <td class="td_left">Size in bytes of the symbol table block.</td>
+ </tr><tr>
+ <td><a href="#uint32_vbr">uint32_vbr</a></td>
+ <td class="td_left">Number of entries in type plane</td>
+ </tr><tr>
+ <td><a href="#symtab_entry">symtab_entry</a>*</td>
+ <td class="td_left">Provides the slot number of the type and its name.</td>
+ </tr><tr>
+ <td><a href="#symtab_plane">symtab_plane</a>*</td>
+ <td class="td_left">A type plane containing value slot number and name
+ for all values of the same type.</td>
</tr>
+</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>
<tr>
- <td>04-07</td><td>04-31</td><td>Yes</td>
- <td align="left">The LLVM bytecode format version number</td>
+ <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">Slot number of type for this plane.</td>
+ </tr><tr>
+ <td><a href="#symtab_entry">symtab_entry</a>+</td>
+ <td class="td_left">The symbol table entries for this plane.</td>
</tr>
</table>
</div>
+
<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="gtypepool">Global Type Pool</a> </div>
+<div class="doc_subsubsection"> <a name="symtab_entry">Symbol Table Entry</a>
+</div>
+<div class="doc_text">
+ <p>A symbol table entry provides the assocation between a type or value's
+ slot number and the name given to that type or value. The format is given
+ in the following table:</p>
+<table>
+ <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">Slot number of the type or 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>
+</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="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_subsection"><a name="modinfo">Module Info</a> </div>
+<div class="doc_subsubsection">Restricted getelementptr Types</a></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_subsection">
+<a name="vers11">Version 1.1 Differences From 1.2 </a></div>
<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="constants">Constants</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_subsection"><a name="functions">Functions</a> </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.</p>
</div>
+
<!-- _______________________________________________________________________ -->
-<div class="doc_subsection"><a name="symtab">Module Symbol Table</a> </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>
<!-- *********************************************************************** -->
projects / oota-llvm.git / blobdiff