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17<body>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]18<div class="doc_title"> LLVM Bytecode File Format </div>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]19<ol>
20 <li><a href="#abstract">Abstract</a></li>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]21 <li><a href="#concepts">Concepts</a>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]22 <ol>
23 <li><a href="#blocks">Blocks</a></li>
24 <li><a href="#lists">Lists</a></li>
25 <li><a href="#fields">Fields</a></li>
26 <li><a href="#align">Alignment</a></li>
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]27 <li><a href="#vbr">Variable Bit-Rate Encoding</a></li>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]28 <li><a href="#encoding">Encoding Primitives</a></li>
29 <li><a href="#slots">Slots</a></li>
30 </ol>
31 </li>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]32 <li><a href="#general">General Structure</a> </li>
33 <li><a href="#blockdefs">Block Definitions</a>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]34 <ol>
Reid Spencereca340b2004-05-23 17:05:09 +0000[diff] [blame]35 <li><a href="#signature">Signature Block</a></li>
36 <li><a href="#module">Module Block</a></li>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]37 <li><a href="#globaltypes">Global Type Pool</a></li>
38 <li><a href="#globalinfo">Module Info Block</a></li>
39 <li><a href="#constantpool">Global Constant Pool</a></li>
40 <li><a href="#functiondefs">Function Definition</a></li>
41 <li><a href="#compactiontable">Compaction Table</a></li>
42 <li><a href="#instructionlist">Instruction List</a></li>
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]43 <li><a href="#opcodes">Instruction Opcodes</a></li>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]44 <li><a href="#symtab">Symbol Table</a></li>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]45 </ol>
46 </li>
Reid Spencerb14a0a62004-06-08 07:41:41 +0000[diff] [blame]47 <li><a href="#versiondiffs">Version Differences</a>
48 <ol>
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]49 <li><a href="#vers13">Version 1.3 Differences From 1.4</a></li>
Reid Spencerb14a0a62004-06-08 07:41:41 +0000[diff] [blame]50 <li><a href="#vers12">Version 1.2 Differences From 1.3</a></li>
51 <li><a href="#vers11">Version 1.1 Differences From 1.2</a></li>
52 <li><a href="#vers10">Version 1.0 Differences From 1.1</a></li>
53 </ol>
54 </li>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]55</ol>
Chris Lattnere7d5ec22004-05-25 17:44:58 +0000[diff] [blame]56<div class="doc_author">
57<p>Written by <a href="mailto:rspencer@x10sys.com">Reid Spencer</a>
58</p>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]59</div>
60<!-- *********************************************************************** -->
61<div class="doc_section"> <a name="abstract">Abstract </a></div>
62<!-- *********************************************************************** -->
63<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]64<p>This document describes the LLVM bytecode file format. It specifies
65the binary encoding rules of the bytecode file format so that
66equivalent systems can encode bytecode files correctly. The LLVM
67bytecode representation is used to store the intermediate
68representation on disk in compacted form.</p>
69<p>The LLVM bytecode format may change in the future, but LLVM will
70always be backwards compatible with older formats. This document will
71only describe the most current version of the bytecode format. See <a
72 href="#versiondiffs">Version Differences</a> for the details on how
73the current version is different from previous versions.</p>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]74</div>
75<!-- *********************************************************************** -->
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]76<div class="doc_section"> <a name="concepts">Concepts</a> </div>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]77<!-- *********************************************************************** -->
78<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]79<p>This section describes the general concepts of the bytecode file
80format without getting into specific layout details. It is recommended
81that you read this section thoroughly before interpreting the detailed
82descriptions.</p>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]83</div>
84<!-- _______________________________________________________________________ -->
85<div class="doc_subsection"><a name="blocks">Blocks</a> </div>
86<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]87<p>LLVM bytecode files consist simply of a sequence of blocks of bytes
88using a binary encoding Each block begins with an header of two
89unsigned integers. The first value identifies the type of block and the
90second value provides the size of the block in bytes. The block
91identifier is used because it is possible for entire blocks to be
92omitted from the file if they are empty. The block identifier helps the
93reader determine which kind of block is next in the file. Note that
94blocks can be nested within other blocks.</p>
95<p> All blocks are variable length, and the block header specifies the
96size of the block. All blocks begin on a byte index that is aligned to
97an even 32-bit boundary. That is, the first block is 32-bit aligned
98because it starts at offset 0. Each block is padded with zero fill
99bytes to ensure that the next block also starts on a 32-bit boundary.</p>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]100</div>
101<!-- _______________________________________________________________________ -->
102<div class="doc_subsection"><a name="lists">Lists</a> </div>
103<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]104<p>LLVM Bytecode blocks often contain lists of things of a similar
105type. For example, a function contains a list of instructions and a
106function type contains a list of argument types. There are two basic
107types of lists: length lists (<a href="#llist">llist</a>), and null
108terminated lists (<a href="#zlist">zlist</a>), as described below in
109the <a href="#encoding">Encoding Primitives</a>.</p>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]110</div>
111<!-- _______________________________________________________________________ -->
112<div class="doc_subsection"><a name="fields">Fields</a> </div>
113<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]114<p>Fields are units of information that LLVM knows how to write atomically. Most
115fields have a uniform length or some kind of length indication built into their
116encoding. For example, a constant string (array of bytes) is written simply as
117the length followed by the characters. Although this is similar to a list,
118constant strings are treated atomically and are thus fields.</p>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]119<p>Fields use a condensed bit format specific to the type of information
120they must contain. As few bits as possible are written for each field. The
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]121sections that follow will provide the details on how these fields are
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]122written and how the bits are to be interpreted.</p>
123</div>
124<!-- _______________________________________________________________________ -->
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]125<div class="doc_subsection"><a name="align">Alignment</a> </div>
Reid Spencer49ad21c2004-05-25 15:47:57 +0000[diff] [blame]126<div class="doc_text">
Reid Spencer40e93a42004-08-03 20:33:56 +0000[diff] [blame]127 <p>To support cross-platform differences, the bytecode file is aligned on
128 certain boundaries. This means that a small amount of padding (at most 3
129 bytes) will be added to ensure that the next entry is aligned to a 32-bit
130 boundary.</p>
Chris Lattnere7d5ec22004-05-25 17:44:58 +0000[diff] [blame]131</div>
Reid Spencer49ad21c2004-05-25 15:47:57 +0000[diff] [blame]132<!-- _______________________________________________________________________ -->
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]133<div class="doc_subsection"><a name="vbr">Variable Bit-Rate Encoding</a>
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]134</div>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]135<div class="doc_text">
136<p>Most of the values written to LLVM bytecode files are small integers. To
137minimize the number of bytes written for these quantities, an encoding scheme
138similar to UTF-8 is used to write integer data. The scheme is known as
139variable bit rate (vbr) encoding. In this encoding, the high bit of
140each byte is used to indicate if more bytes follow. If (byte &amp;
1410x80) is non-zero in any given byte, it means there is another byte
142immediately following that also contributes to the value. For the final
143byte (byte &amp; 0x80) is false (the high bit is not set). In each byte
144only the low seven bits contribute to the value. Consequently 32-bit
145quantities can take from one to <em>five</em> bytes to encode. In
146general, smaller quantities will encode in fewer bytes, as follows:</p>
147<table>
148 <tbody>
149 <tr>
150 <th>Byte #</th>
151 <th>Significant Bits</th>
152 <th>Maximum Value</th>
153 </tr>
154 <tr>
155 <td>1</td>
156 <td>0-6</td>
157 <td>127</td>
158 </tr>
159 <tr>
160 <td>2</td>
161 <td>7-13</td>
162 <td>16,383</td>
163 </tr>
164 <tr>
165 <td>3</td>
166 <td>14-20</td>
167 <td>2,097,151</td>
168 </tr>
169 <tr>
170 <td>4</td>
171 <td>21-27</td>
172 <td>268,435,455</td>
173 </tr>
174 <tr>
175 <td>5</td>
176 <td>28-34</td>
177 <td>34,359,738,367</td>
178 </tr>
179 <tr>
180 <td>6</td>
181 <td>35-41</td>
182 <td>4,398,046,511,103</td>
183 </tr>
184 <tr>
185 <td>7</td>
186 <td>42-48</td>
187 <td>562,949,953,421,311</td>
188 </tr>
189 <tr>
190 <td>8</td>
191 <td>49-55</td>
192 <td>72,057,594,037,927,935</td>
193 </tr>
194 <tr>
195 <td>9</td>
196 <td>56-62</td>
197 <td>9,223,372,036,854,775,807</td>
198 </tr>
199 <tr>
200 <td>10</td>
201 <td>63-69</td>
202 <td>1,180,591,620,717,411,303,423</td>
203 </tr>
204 </tbody>
205</table>
206<p>Note that in practice, the tenth byte could only encode bit 63 since
207the maximum quantity to use this encoding is a 64-bit integer.</p>
208<p><em>Signed</em> VBR values are encoded with the standard vbr
209encoding, but with the sign bit as the low order bit instead of the
210high order bit. This allows small negative quantities to be encoded
211efficiently. For example, -3
212is encoded as "((3 &lt;&lt; 1) | 1)" and 3 is encoded as "(3 &lt;&lt;
2131) | 0)", emitted with the standard vbr encoding above.</p>
214</div>
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]215<!-- _______________________________________________________________________ -->
216<div class="doc_subsection"><a name="encoding">Encoding Primitives</a> </div>
217<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]218<p>Each field in the bytecode format is encoded into the file using a
219small set of primitive formats. The table below defines the encoding
220rules for the various primitives used and gives them each a type name.
221The type names used in the descriptions of blocks and fields in the <a
222 href="#details">Detailed Layout</a>next section. Any type name with
223the suffix <em>_vbr</em> indicates a quantity that is encoded using
224variable bit rate encoding as described above.</p>
225<table class="doc_table">
226 <tbody>
227 <tr>
228 <th><b>Type</b></th>
229 <th class="td_left"><b>Rule</b></th>
230 </tr>
231 <tr>
232 <td><a name="unsigned"><b>unsigned</b></a></td>
233 <td class="td_left">A 32-bit unsigned integer that always occupies four
Reid Spencereca340b2004-05-23 17:05:09 +0000[diff] [blame]234 consecutive bytes. The unsigned integer is encoded using LSB first
235 ordering. That is bits 2<sup>0</sup> through 2<sup>7</sup> are in the
236 byte with the lowest file offset (little endian).</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]237 </tr>
238 <tr>
Reid Spencer02d7f922004-08-03 20:57:56 +0000[diff] [blame]239 <td style="vertical-align: top;"><a name="uint24_vbr">
240 <b>uint24_vbr</b></a></td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]241 <td style="vertical-align: top; text-align: left;">A 24-bit unsigned
242 integer that occupies from one to four bytes using variable bit rate
243 encoding.</td>
244 </tr>
245 <tr>
246 <td><a name="uint32_vbr"><b>uint32_vbr</b></a></td>
Reid Spencera54f1102004-08-03 19:20:18 +0000[diff] [blame]247 <td class="td_left">A 32-bit unsigned integer that occupies from one to
248 five bytes using variable bit rate encoding.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]249 </tr>
250 <tr>
251 <td><a name="uint64_vbr"><b>uint64_vbr</b></a></td>
Reid Spencera54f1102004-08-03 19:20:18 +0000[diff] [blame]252 <td class="td_left">A 64-bit unsigned integer that occupies from one to ten
253 bytes using variable bit rate encoding.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]254 </tr>
255 <tr>
256 <td><a name="int64_vbr"><b>int64_vbr</b></a></td>
Reid Spencera54f1102004-08-03 19:20:18 +0000[diff] [blame]257 <td class="td_left">A 64-bit signed integer that occupies from one to ten
258 bytes using the signed variable bit rate encoding.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]259 </tr>
260 <tr>
261 <td><a name="char"><b>char</b></a></td>
Reid Spencera54f1102004-08-03 19:20:18 +0000[diff] [blame]262 <td class="td_left">A single unsigned character encoded into one byte</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]263 </tr>
264 <tr>
265 <td><a name="bit"><b>bit(n-m)</b></a></td>
Reid Spencera54f1102004-08-03 19:20:18 +0000[diff] [blame]266 <td class="td_left">A set of bit within some larger integer field. The values
267 of <code>n</code> and <code>m</code> specify the inclusive range of bits
268 that define the subfield. The value for <code>m</code> may be omitted if
269 its the same as <code>n</code>.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]270 </tr>
271 <tr>
272 <td style="vertical-align: top;"><b><a name="float"><b>float</b></a></b></td>
Reid Spencera54f1102004-08-03 19:20:18 +0000[diff] [blame]273 <td style="vertical-align: top; text-align: left;">A floating point value encoded
274 as a 32-bit IEEE value written in little-endian form.<br>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]275 </td>
276 </tr>
277 <tr>
278 <td style="vertical-align: top;"><b><b><a name="double"><b>double</b></a></b></b></td>
Reid Spencera54f1102004-08-03 19:20:18 +0000[diff] [blame]279 <td style="vertical-align: top; text-align: left;">A floating point value encoded
280 as a64-bit IEEE value written in little-endian form</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]281 </tr>
282 <tr>
283 <td><a name="string"><b>string</b></a></td>
284 <td class="td_left">A uint32_vbr indicating the type of the
285constant string which also includes its length, immediately followed by
286the characters of the string. There is no terminating null byte in the
287string.</td>
288 </tr>
289 <tr>
290 <td><a name="data"><b>data</b></a></td>
291 <td class="td_left">An arbitrarily long segment of data to which
292no interpretation is implied. This is used for constant initializers.<br>
293 </td>
294 </tr>
295 <tr>
296 <td><a name="llist"><b>llist(x)</b></a></td>
297 <td class="td_left">A length list of x. This means the list is
298encoded as an <a href="#uint32_vbr">uint32_vbr</a> providing the
299length of the list, followed by a sequence of that many "x" items. This
300implies that the reader should iterate the number of times provided by
301the length.</td>
302 </tr>
303 <tr>
304 <td><a name="zlist"><b>zlist(x)</b></a></td>
305 <td class="td_left">A zero-terminated list of x. This means the
306list is encoded as a sequence of an indeterminate number of "x" items,
307followed by an <a href="#uint32_vbr">uint32_vbr</a> terminating value.
308This implies that none of the "x" items can have a zero value (or else
309the list terminates).</td>
310 </tr>
311 <tr>
312 <td><a name="block"><b>block</b></a></td>
313 <td class="td_left">A block of data that is logically related. A
314block is an unsigned 32-bit integer that encodes the type of the block
315in the low 5 bits and the size of the block in the high 27 bits. The
316length does not include the block header or any alignment bytes at the
317end of the block. Blocks may compose other blocks. </td>
318 </tr>
319 </tbody>
Reid Spencereca340b2004-05-23 17:05:09 +0000[diff] [blame]320</table>
321</div>
322<!-- _______________________________________________________________________ -->
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]323<div class="doc_subsection"><a name="notation">Field Notation</a> </div>
324<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]325<p>In the detailed block and field descriptions that follow, a regex
326like notation is used to describe optional and repeated fields. A very
327limited subset of regex is used to describe these, as given in the
328following table: </p>
329<table class="doc_table">
330 <tbody>
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]331 <tr>
332 <th><b>Character</b></th>
333 <th class="td_left"><b>Meaning</b></th>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]334 </tr>
335 <tr>
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]336 <td><b><code>?</code></b></td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]337 <td class="td_left">The question mark indicates 0 or 1
338occurrences of the thing preceding it.</td>
339 </tr>
340 <tr>
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]341 <td><b><code>*</code></b></td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]342 <td class="td_left">The asterisk indicates 0 or more occurrences
343of the thing preceding it.</td>
344 </tr>
345 <tr>
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]346 <td><b><code>+</code></b></td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]347 <td class="td_left">The plus sign indicates 1 or more occurrences
348of the thing preceding it.</td>
349 </tr>
350 <tr>
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]351 <td><b><code>()</code></b></td>
352 <td class="td_left">Parentheses are used for grouping.</td>
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]353 </tr>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]354 <tr>
355 <td><b><code>,</code></b></td>
356 <td class="td_left">The comma separates sequential fields.</td>
357 </tr>
358 </tbody>
359</table>
360<p>So, for example, consider the following specifications:</p>
361<div class="doc_code">
362<ol>
363 <li><code>string?</code></li>
364 <li><code>(uint32_vbr,uin32_vbr)+</code></li>
365 <li><code>(unsigned?,uint32_vbr)*</code></li>
366 <li><code>(llist(unsigned))?</code></li>
367</ol>
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]368</div>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]369<p>with the following interpretations:</p>
370<ol>
371 <li>An optional string. Matches either nothing or a single string</li>
372 <li>One or more pairs of uint32_vbr.</li>
373 <li>Zero or more occurrences of either an unsigned followed by a
374uint32_vbr or just a uint32_vbr.</li>
375 <li>An optional length list of unsigned values.</li>
376</ol>
377</div>
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]378<!-- _______________________________________________________________________ -->
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]379<div class="doc_subsection"><a name="slots">Slots</a> </div>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]380<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]381<p>The bytecode format uses the notion of a "slot" to reference Types
382and Values. Since the bytecode file is a <em>direct</em> representation of
383LLVM's intermediate representation, there is a need to represent pointers in
384the file. Slots are used for this purpose. For example, if one has the following
385assembly:
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]386</p>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]387<div class="doc_code"><code> %MyType = type { int, sbyte }<br>
388%MyVar = external global %MyType
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]389</code></div>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]390<p>there are two definitions. The definition of <tt>%MyVar</tt> uses <tt>%MyType</tt>.
391In the C++ IR this linkage between <tt>%MyVar</tt> and <tt>%MyType</tt>
392is explicit through the use of C++ pointers. In bytecode, however, there's no
393ability to store memory addresses. Instead, we compute and write out
394slot numbers for every Type and Value written to the file.</p>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]395<p>A slot number is simply an unsigned 32-bit integer encoded in the variable
396bit rate scheme (see <a href="#encoding">encoding</a>). This ensures that
397low slot numbers are encoded in one byte. Through various bits of magic LLVM
398attempts to always keep the slot numbers low. The first attempt is to associate
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]399slot numbers with their "type plane". That is, Values of the same type
400are written to the bytecode file in a list (sequentially). Their order in
401that list determines their slot number. This means that slot #1 doesn't mean
402anything unless you also specify for which type you want slot #1. Types are
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]403always written to the file first (in the <a href="#globaltypes">Global Type
404Pool</a>) and in such a way that both forward and backward references of the
405types can often be resolved with a single pass through the type pool. </p>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]406<p>Slot numbers are also kept small by rearranging their order. Because
407of the structure of LLVM, certain values are much more likely to be used
408frequently in the body of a function. For this reason, a compaction table is
409provided in the body of a function if its use would make the function body
410smaller. Suppose you have a function body that uses just the types "int*" and
411"{double}" but uses them thousands of time. Its worthwhile to ensure that the
412slot number for these types are low so they can be encoded in a single byte
413(via vbr). This is exactly what the compaction table does.</p>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]414<p>In summary then, a slot number can be though of as just a vbr encoded index
415into a list of Type* or Value*. To keep slot numbers low, Value* are indexed by
416two slot numbers: the "type plane index" (type slot) and the "value index"
417(value slot).</p>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]418</div>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]419<!-- *********************************************************************** -->
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]420<div class="doc_section"> <a name="general">General Structure</a> </div>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]421<!-- *********************************************************************** -->
422<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]423<p>This section provides the general structure of the LLVM bytecode
424file format. The bytecode file format requires blocks to be in a
425certain order and nested in a particular way so that an LLVM module can
426be constructed efficiently from the contents of the file. This ordering
427defines a general structure for bytecode files as shown below. The
428table below shows the order in which all block types may appear. Please
429note that some of the blocks are optional and some may be repeated. The
430structure is fairly loose because optional blocks, if empty, are
431completely omitted from the file.</p>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]432<table>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]433 <tbody>
434 <tr>
435 <th>ID</th>
436 <th>Parent</th>
437 <th>Optional?</th>
438 <th>Repeated?</th>
439 <th>Level</th>
440 <th>Block Type</th>
441 <th>Description</th>
442 </tr>
443 <tr>
444 <td>N/A</td>
445 <td>File</td>
446 <td>No</td>
447 <td>No</td>
448 <td>0</td>
449 <td class="td_left"><a href="#signature">Signature</a></td>
450 <td class="td_left">This contains the file signature (magic
451number) that identifies the file as LLVM bytecode.</td>
452 </tr>
453 <tr>
454 <td>0x01</td>
455 <td>File</td>
456 <td>No</td>
457 <td>No</td>
458 <td>0</td>
459 <td class="td_left"><a href="#module">Module</a></td>
460 <td class="td_left">This is the top level block in a bytecode
461file. It contains all the other blocks. </td>
462 </tr>
463 <tr>
464 <td>0x06</td>
465 <td>Module</td>
466 <td>No</td>
467 <td>No</td>
468 <td>1</td>
469 <td class="td_left">&nbsp;&nbsp;&nbsp;<a href="#globaltypes">Global&nbsp;Type&nbsp;Pool</a></td>
470 <td class="td_left">This block contains all the global (module)
471level types.</td>
472 </tr>
473 <tr>
474 <td>0x05</td>
475 <td>Module</td>
476 <td>No</td>
477 <td>No</td>
478 <td>1</td>
479 <td class="td_left">&nbsp;&nbsp;&nbsp;<a href="#globalinfo">Module&nbsp;Globals&nbsp;Info</a></td>
480 <td class="td_left">This block contains the type, constness, and
481linkage for each of the global variables in the module. It also
482contains the type of the functions and the constant initializers.</td>
483 </tr>
484 <tr>
485 <td>0x03</td>
486 <td>Module</td>
487 <td>Yes</td>
488 <td>No</td>
489 <td>1</td>
490 <td class="td_left">&nbsp;&nbsp;&nbsp;<a href="#constantpool">Module&nbsp;Constant&nbsp;Pool</a></td>
491 <td class="td_left">This block contains all the global constants
492except function arguments, global values and constant strings.</td>
493 </tr>
494 <tr>
495 <td>0x02</td>
496 <td>Module</td>
497 <td>Yes</td>
498 <td>Yes</td>
499 <td>1</td>
500 <td class="td_left">&nbsp;&nbsp;&nbsp;<a href="#functiondefs">Function&nbsp;Definitions</a>*</td>
501 <td class="td_left">One function block is written for each
502function in the module. The function block contains the instructions,
503compaction table, type constant pool, and symbol table for the function.</td>
504 </tr>
505 <tr>
506 <td>0x03</td>
507 <td>Function</td>
508 <td>Yes</td>
509 <td>No</td>
510 <td>2</td>
511 <td class="td_left">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a
512 href="#constantpool">Function&nbsp;Constant&nbsp;Pool</a></td>
513 <td class="td_left">Any constants (including types) used solely
514within the function are emitted here in the function constant pool. </td>
515 </tr>
516 <tr>
517 <td>0x08</td>
518 <td>Function</td>
519 <td>Yes</td>
520 <td>No</td>
521 <td>2</td>
522 <td class="td_left">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a
523 href="#compactiontable">Compaction&nbsp;Table</a></td>
524 <td class="td_left">This table reduces bytecode size by providing
525a funtion-local mapping of type and value slot numbers to their global
526slot numbers</td>
527 </tr>
528 <tr>
529 <td>0x07</td>
530 <td>Function</td>
531 <td>No</td>
532 <td>No</td>
533 <td>2</td>
534 <td class="td_left">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a
535 href="#instructionlist">Instruction&nbsp;List</a></td>
536 <td class="td_left">This block contains all the instructions of
537the function. The basic blocks are inferred by terminating
538instructions. </td>
539 </tr>
540 <tr>
541 <td>0x04</td>
542 <td>Function</td>
543 <td>Yes</td>
544 <td>No</td>
545 <td>2</td>
546 <td class="td_left">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a
547 href="#symtab">Function&nbsp;Symbol&nbsp;Table</a></td>
548 <td class="td_left">This symbol table provides the names for the
549function specific values used (basic block labels mostly).</td>
550 </tr>
551 <tr>
552 <td>0x04</td>
553 <td>Module</td>
554 <td>Yes</td>
555 <td>No</td>
556 <td>1</td>
557 <td class="td_left">&nbsp;&nbsp;&nbsp;<a href="#symtab">Module&nbsp;Symbol&nbsp;Table</a></td>
558 <td class="td_left">This symbol table provides the names for the
559various entries in the file that are not function specific (global
560vars, and functions mostly).</td>
561 </tr>
562 </tbody>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]563</table>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]564<p>Use the links in the table for details about the contents of each of
565the block types.</p>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]566</div>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]567<!-- *********************************************************************** -->
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]568<div class="doc_section"> <a name="blockdefs">Block Definitions</a> </div>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]569<!-- *********************************************************************** -->
570<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]571<p>This section provides the detailed layout of the individual block
572types in the LLVM bytecode file format. </p>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]573</div>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]574<!-- _______________________________________________________________________ -->
Reid Spencereca340b2004-05-23 17:05:09 +0000[diff] [blame]575<div class="doc_subsection"><a name="signature">Signature Block</a> </div>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]576<div class="doc_text">
Chris Lattnera0390ec2004-05-24 05:35:17 +0000[diff] [blame]577<p>The signature occurs in every LLVM bytecode file and is always first.
Reid Spencereca340b2004-05-23 17:05:09 +0000[diff] [blame]578It simply provides a few bytes of data to identify the file as being an LLVM
579bytecode file. This block is always four bytes in length and differs from the
580other blocks because there is no identifier and no block length at the start
581of the block. Essentially, this block is just the "magic number" for the file.
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]582</p>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]583<table>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]584 <tbody>
585 <tr>
586 <th><b>Type</b></th>
587 <th class="td_left"><b>Field Description</b></th>
588 </tr>
589 <tr>
590 <td><a href="#char">char</a></td>
591 <td class="td_left">Constant "l" (0x6C)</td>
592 </tr>
593 <tr>
594 <td><a href="#char">char</a></td>
595 <td class="td_left">Constant "l" (0x6C)</td>
596 </tr>
597 <tr>
598 <td><a href="#char">char</a></td>
599 <td class="td_left">Constant "v" (0x76)</td>
600 </tr>
601 <tr>
602 <td><a href="#char">char</a></td>
603 <td class="td_left">Constant "m" (0x6D)</td>
604 </tr>
605 </tbody>
Reid Spencereca340b2004-05-23 17:05:09 +0000[diff] [blame]606</table>
607</div>
608<!-- _______________________________________________________________________ -->
609<div class="doc_subsection"><a name="module">Module Block</a> </div>
610<div class="doc_text">
611<p>The module block contains a small pre-amble and all the other blocks in
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]612the file. The table below shows the structure of the module block. Note that it
613only provides the module identifier, size of the module block, and the format
614information. Everything else is contained in other blocks, described in other
615sections.</p>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]616<table>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]617 <tbody>
618 <tr>
619 <th><b>Type</b></th>
620 <th class="td_left"><b>Field Description</b></th>
621 </tr>
622 <tr>
Reid Spencerf57b8b92004-08-16 19:24:36 +0000[diff] [blame]623 <td><a href="#unsigned">unsigned</a><br></td>
624 <td class="td_left"><a href="#mod_header">Module Block Identifier
625 (0x01)</a></td>
626 </tr>
627 <tr>
628 <td><a href="#unsigned">unsigned</a></td>
629 <td class="td_left"><a href="#mod_header">Module Block Size</a></td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]630 </tr>
631 <tr>
632 <td><a href="#uint32_vbr">uint32_vbr</a></td>
633 <td class="td_left"><a href="#format">Format Information</a></td>
634 </tr>
635 <tr>
636 <td><a href="#block">block</a></td>
637 <td class="td_left"><a href="#globaltypes">Global Type Pool</a></td>
638 </tr>
639 <tr>
640 <td><a href="#block">block</a></td>
641 <td class="td_left"><a href="#globalinfo">Module Globals Info</a></td>
642 </tr>
643 <tr>
644 <td><a href="#block">block</a></td>
645 <td class="td_left"><a href="#constantpool">Module Constant Pool</a></td>
646 </tr>
647 <tr>
648 <td><a href="#block">block</a>*</td>
649 <td class="td_left"><a href="#functiondefs">Function Definitions</a></td>
650 </tr>
651 <tr>
652 <td><a href="#block">block</a></td>
Reid Spencer9a910812004-08-17 00:49:03 +0000[diff] [blame]653 <td class="td_left"><a href="#symtab">Module Symbol Table</a></td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]654 </tr>
655 </tbody>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]656</table>
657</div>
Reid Spencerf57b8b92004-08-16 19:24:36 +0000[diff] [blame]658
659<!-- _______________________________________________________________________ -->
660<div class="doc_subsubsection"><a name="mod_header">Module Block Header</a></div>
661<div class="doc_text">
662 <p>The block header for the module block uses a longer format than the other
663 blocks in a bytecode file. Specifically, instead of encoding the type and size
664 of the block into a 32-bit integer with 5-bits for type and 27-bits for size,
665 the module block header uses two 32-bit unsigned values, one for type, and one
666 for size. While the 2<sup>27</sup> byte limit on block size is sufficient for the blocks
667 contained in the module, it isn't sufficient for the module block itself
668 because we want to ensure that bytecode files as large as 2<sup>32</sup> bytes
669 are possible. For this reason, the module block (and only the module block)
670 uses a long format header.</p>
671</div>
672
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]673<!-- _______________________________________________________________________ -->
674<div class="doc_subsubsection"><a name="format">Format Information</a></div>
675<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]676<p>The format information field is encoded into a <a href="#uint32_vbr">uint32_vbr</a>
677as shown in the following table.</p>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]678<table>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]679 <tbody>
680 <tr>
681 <th><b>Type</b></th>
682 <th class="td_left"><b>Description</b></th>
683 </tr>
684 <tr>
685 <td><a href="#bit">bit(0)</a></td>
686 <td class="td_left">Target is big endian?</td>
687 </tr>
688 <tr>
689 <td><a href="#bit">bit(1)</a></td>
690 <td class="td_left">On target pointers are 64-bit?</td>
691 </tr>
692 <tr>
693 <td><a href="#bit">bit(2)</a></td>
694 <td class="td_left">Target has no endianess?</td>
695 </tr>
696 <tr>
697 <td><a href="#bit">bit(3)</a></td>
698 <td class="td_left">Target has no pointer size?</td>
699 </tr>
700 <tr>
701 <td><a href="#bit">bit(4-31)</a></td>
702 <td class="td_left">Bytecode format version</td>
703 </tr>
704 </tbody>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]705</table>
706<p>
707Of particular note, the bytecode format number is simply a 28-bit
708monotonically increase integer that identifies the version of the bytecode
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]709format (which is not directly related to the LLVM release number). The
710bytecode versions defined so far are (note that this document only
711describes the latest version, 1.3):</p>
Chris Lattnera0390ec2004-05-24 05:35:17 +0000[diff] [blame]712<ul>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]713 <li>#0: LLVM 1.0 &amp; 1.1</li>
714 <li>#1: LLVM 1.2</li>
715 <li>#2: LLVM 1.2.5 (not released)</li>
716 <li>#3: LLVM 1.3<br>
717 </li>
Chris Lattnera0390ec2004-05-24 05:35:17 +0000[diff] [blame]718</ul>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]719<p>Note that we plan to eventually expand the target description
720capabilities
721of bytecode files to <a href="http://llvm.cs.uiuc.edu/PR263">target
722triples</a>.
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]723</p>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]724</div>
725<!-- _______________________________________________________________________ -->
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]726<div class="doc_subsection"><a name="globaltypes">Global Type Pool</a> </div>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]727<div class="doc_text">
Chris Lattnera0390ec2004-05-24 05:35:17 +0000[diff] [blame]728<p>The global type pool consists of type definitions. Their order of appearance
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]729in the file determines their type slot number (0 based). Slot numbers are
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]730used to replace pointers in the intermediate representation. Each slot number
731uniquely identifies one entry in a type plane (a collection of values of the
732same type). Since all values have types and are associated with the order in
733which the type pool is written, the global type pool <em>must</em> be written
734as the first block of a module. If it is not, attempts to read the file will
735fail because both forward and backward type resolution will not be possible.</p>
736<p>The type pool is simply a list of type definitions, as shown in the
737table below.</p>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]738<table>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]739 <tbody>
740 <tr>
741 <th><b>Type</b></th>
742 <th class="td_left"><b>Field Description</b></th>
743 </tr>
744 <tr>
745 <td><a href="#unsigned">block</a></td>
746 <td class="td_left">Type Pool Identifier (0x06) + Size<br>
747 </td>
748 </tr>
749 <tr>
750 <td><a href="#llist">llist</a>(<a href="#type">type</a>)</td>
751 <td class="td_left">A length list of type definitions.</td>
752 </tr>
753 </tbody>
Reid Spencereca340b2004-05-23 17:05:09 +0000[diff] [blame]754</table>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]755</div>
756<!-- _______________________________________________________________________ -->
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]757<div class="doc_subsubsection"><a name="type">Type Definitions</a></div>
758<div class="doc_text">
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]759<p>Types in the type pool are defined using a different format for each kind
760of type, as given in the following sections.</p>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]761<h3>Primitive Types</h3>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]762<p>The primitive types encompass the basic integer and floating point
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]763types. They are encoded simply as their TypeID.</p>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]764<table>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]765 <tbody>
766 <tr>
767 <th><b>Type</b></th>
768 <th class="td_left"><b>Description</b></th>
769 </tr>
770 <tr>
771 <td><a href="#uint24_vbr">uint24_vbr</a></td>
772 <td class="td_left">Type ID for the primitive types (values 1 to
77311) <sup>1</sup></td>
774 </tr>
775 </tbody>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]776</table>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]777Notes:
778<ol>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]779 <li>The values for the Type IDs for the primitive types are provided
780by the definition of the <code>llvm::Type::TypeID</code> enumeration
781in <code>include/llvm/Type.h</code>. The enumeration gives the
782following mapping:
783 <ol>
784 <li>bool</li>
785 <li>ubyte</li>
786 <li>sbyte</li>
787 <li>ushort</li>
788 <li>short</li>
789 <li>uint</li>
790 <li>int</li>
791 <li>ulong</li>
792 <li>long</li>
793 <li>float</li>
794 <li>double</li>
795 </ol>
796 </li>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]797</ol>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]798<h3>Function Types</h3>
799<table>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]800 <tbody>
801 <tr>
802 <th><b>Type</b></th>
803 <th class="td_left"><b>Description</b></th>
804 </tr>
805 <tr>
806 <td><a href="#uint24_vbr">uint24_vbr</a></td>
807 <td class="td_left">Type ID for function types (13)</td>
808 </tr>
809 <tr>
810 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]811 <td class="td_left">Type slot number of function's return type.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]812 </tr>
813 <tr>
814 <td><a href="#llist">llist</a>(<a href="#uint24_vbr">uint24_vbr</a>)</td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]815 <td class="td_left">Type slot number of each argument's type.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]816 </tr>
817 <tr>
818 <td><a href="#uint32_vbr">uint32_vbr</a>?</td>
819 <td class="td_left">Value 0 if this is a varargs function,
820missing otherwise.</td>
821 </tr>
822 </tbody>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]823</table>
824<h3>Structure Types</h3>
825<table>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]826 <tbody>
827 <tr>
828 <th><b>Type</b></th>
829 <th class="td_left"><b>Description</b></th>
830 </tr>
831 <tr>
832 <td><a href="#uint24_vbr">uint24_vbr</a></td>
833 <td class="td_left">Type ID for structure types (14)</td>
834 </tr>
835 <tr>
836 <td><a href="#zlist">zlist</a>(<a href="#uint24_vbr">uint24_vbr</a>)</td>
837 <td class="td_left">Slot number of each of the element's fields.</td>
838 </tr>
839 </tbody>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]840</table>
841<h3>Array Types</h3>
842<table>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]843 <tbody>
844 <tr>
845 <th><b>Type</b></th>
846 <th class="td_left"><b>Description</b></th>
847 </tr>
848 <tr>
849 <td><a href="#uint24_vbr">uint24_vbr</a></td>
850 <td class="td_left">Type ID for Array Types (15)</td>
851 </tr>
852 <tr>
853 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]854 <td class="td_left">Type slot number of array's element type.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]855 </tr>
856 <tr>
857 <td><a href="#uint32_vbr">uint32_vbr</a></td>
858 <td class="td_left">The number of elements in the array.</td>
859 </tr>
860 </tbody>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]861</table>
862<h3>Pointer Types</h3>
863<table>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]864 <tbody>
865 <tr>
866 <th><b>Type</b></th>
867 <th class="td_left"><b>Description</b></th>
868 </tr>
869 <tr>
870 <td><a href="#uint24_vbr">uint24_vbr</a></td>
871 <td class="td_left">Type ID For Pointer Types (16)</td>
872 </tr>
873 <tr>
874 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]875 <td class="td_left">Type slot number of pointer's element type.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]876 </tr>
877 </tbody>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]878</table>
879<h3>Opaque Types</h3>
880<table>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]881 <tbody>
882 <tr>
883 <th><b>Type</b></th>
884 <th class="td_left"><b>Description</b></th>
885 </tr>
886 <tr>
887 <td><a href="#uint24_vbr">uint24_vbr</a></td>
888 <td class="td_left">Type ID For Opaque Types (17)</td>
889 </tr>
890 </tbody>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]891</table>
Brian Gaeke02209042004-08-20 06:00:58 +0000[diff] [blame]892<h3>Packed Types</h3>
893<table>
894 <tbody>
895 <tr>
896 <th><b>Type</b></th>
897 <th class="td_left"><b>Description</b></th>
898 </tr>
899 <tr>
900 <td><a href="#uint24_vbr">uint24_vbr</a></td>
901 <td class="td_left">Type ID for Packed Types (18)</td>
902 </tr>
903 <tr>
904 <td><a href="#uint24_vbr">uint24_vbr</a></td>
905 <td class="td_left">Slot number of packed vector's element type.</td>
906 </tr>
907 <tr>
908 <td><a href="#uint32_vbr">uint32_vbr</a></td>
909 <td class="td_left">The number of elements in the packed vector.</td>
910 </tr>
911 </tbody>
912</table>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]913</div>
914<!-- _______________________________________________________________________ -->
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]915<div class="doc_subsection"><a name="globalinfo">Module Global Info</a>
916</div>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]917<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]918<p>The module global info block contains the definitions of all global
919variables including their initializers and the <em>declaration</em> of
920all functions. The format is shown in the table below:</p>
921<table>
922 <tbody>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]923 <tr>
924 <th><b>Type</b></th>
925 <th class="td_left"><b>Field Description</b></th>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]926 </tr>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]927 <tr>
928 <td><a href="#block">block</a></td>
929 <td class="td_left">Module global info identifier (0x05) + size<br>
930 </td>
931 </tr>
932 <tr>
933 <td><a href="#zlist">zlist</a>(<a href="#globalvar">globalvar</a>)</td>
934 <td class="td_left">A zero terminated list of global var
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]935definitions occurring in the module.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]936 </tr>
937 <tr>
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]938 <td><a href="#zlist">zlist</a>(<a href="#funcfield">funcfield</a>)</td>
939 <td class="td_left">A zero terminated list of function definitions
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]940occurring in the module.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]941 </tr>
942 <tr>
943 <td style="vertical-align: top;"><a href="#llist">llist</a>(<a
944 href="#string">string</a>)<br>
945 </td>
946 <td style="vertical-align: top; text-align: left;">A length list
947of strings that specify the names of the libraries that this module
948depends upon.<br>
949 </td>
950 </tr>
951 <tr>
952 <td style="vertical-align: top;"><a href="#string">string</a><br>
953 </td>
954 <td style="vertical-align: top; text-align: left;">The target
955triple for the module (blank means no target triple specified, i.e. a
956platform independent module).<br>
957 </td>
958 </tr>
959 </tbody>
960</table>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]961</div>
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]962
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]963<!-- _______________________________________________________________________ -->
964<div class="doc_subsubsection"><a name="globalvar">Global Variable Field</a>
965</div>
966<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]967<p>Global variables are written using an <a href="#uint32_vbr">uint32_vbr</a>
968that encodes information about the global variable and a list of the
969constant initializers for the global var, if any.</p>
970<p>The table below provides the bit layout of the first <a
971 href="#uint32_vbr">uint32_vbr</a> that describes the global variable.</p>
972<table>
973 <tbody>
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]974 <tr>
975 <th><b>Type</b></th>
976 <th class="td_left"><b>Description</b></th>
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]977 </tr>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]978 <tr>
979 <td><a href="#bit">bit(0)</a></td>
980 <td class="td_left">Is constant?</td>
981 </tr>
982 <tr>
983 <td><a href="#bit">bit(1)</a></td>
984 <td class="td_left">Has initializer? Note that this bit
985determines whether the constant initializer field (described below)
986follows. </td>
987 </tr>
988 <tr>
989 <td><a href="#bit">bit(2-4)</a></td>
990 <td class="td_left">Linkage type: 0=External, 1=Weak,
9912=Appending, 3=Internal, 4=LinkOnce</td>
992 </tr>
993 <tr>
994 <td><a href="#bit">bit(5-31)</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]995 <td class="td_left">Type slot number of type for the global variable.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]996 </tr>
997 </tbody>
998</table>
999<p>The table below provides the format of the constant initializers for
1000the global variable field, if it has one.</p>
1001<table>
1002 <tbody>
1003 <tr>
1004 <th><b>Type</b></th>
1005 <th class="td_left"><b>Description</b></th>
1006 </tr>
1007 <tr>
1008 <td>(<a href="#zlist">zlist</a>(<a href="#uint32_vbr">uint32_vbr</a>))?
1009 </td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1010 <td class="td_left">An optional zero-terminated list of value slot
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1011numbers of the global variable's constant initializer.</td>
1012 </tr>
1013 </tbody>
1014</table>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1015</div>
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]1016
1017<!-- _______________________________________________________________________ -->
1018<div class="doc_subsubsection"><a name="funcfield">Function Field</a>
1019</div>
1020<div class="doc_text">
1021<p>Functions are written using an <a href="#uint32_vbr">uint32_vbr</a>
1022that encodes information about the function and a set of flags.</p>
1023
1024<p>The table below provides the bit layout of the <a
1025href="#uint32_vbr">uint32_vbr</a> that describes the function.</p>
1026
1027<table>
1028 <tbody>
1029 <tr>
1030 <th><b>Type</b></th>
1031 <th class="td_left"><b>Description</b></th>
1032 </tr>
1033 <tr>
1034 <td><a href="#bit">bit(0-4)</a></td>
1035 <td class="td_left">Reserved for future use. Currently set to 00001.</td>
1036 </tr>
1037 <tr>
1038 <td><a href="#bit">bit(5-)</a></td>
1039 <td class="td_left">Type slot number of type for the function.</td>
1040 </tr>
1041 </tbody>
1042</table>
1043
1044</div>
1045
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]1046<!-- _______________________________________________________________________ -->
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]1047<div class="doc_subsection"><a name="constantpool">Constant Pool</a> </div>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]1048<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1049<p>A constant pool defines as set of constant values. There are
1050actually two types of constant pool blocks: one for modules and one for
1051functions. For modules, the block begins with the constant strings
1052encountered anywhere in the module. For functions, the block begins
1053with types only encountered in the function. In both cases the header
1054is identical. The tables that follow, show the header, module constant
1055pool preamble, function constant pool preamble, and the part common to
1056both function and module constant pools.</p>
1057<p><b>Common Block Header</b></p>
1058<table>
1059 <tbody>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1060 <tr>
1061 <th><b>Type</b></th>
1062 <th class="td_left"><b>Field Description</b></th>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1063 </tr>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1064 <tr>
1065 <td><a href="#block">block</a></td>
1066 <td class="td_left">Constant pool identifier (0x03) + size<br>
1067 </td>
1068 </tr>
1069 </tbody>
1070</table>
1071<p><b>Module Constant Pool Preamble (constant strings)</b></p>
1072<table>
1073 <tbody>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1074 <tr>
1075 <th><b>Type</b></th>
1076 <th class="td_left"><b>Field Description</b></th>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1077 </tr>
1078 <tr>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1079 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1080 <td class="td_left">The number of constant strings that follow.</td>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1081 </tr>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1082 <tr>
1083 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1084 <td class="td_left">Zero. This identifies the following "plane"
1085as containing the constant strings. This is needed to identify it
1086uniquely from other constant planes that follow. </td>
1087 </tr>
1088 <tr>
1089 <td><a href="#uint24_vbr">uint24_vbr</a>+</td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1090 <td class="td_left">Type slot number of the constant string's type.
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1091Note that the constant string's type implicitly defines the length of
1092the string. </td>
1093 </tr>
1094 </tbody>
1095</table>
1096<p><b>Function Constant Pool Preamble (function types)</b></p>
1097<p>The structure of the types for functions is identical to the <a
1098 href="#globaltypes">Global Type Pool</a>. Please refer to that section
1099for the details. </p>
1100<p><b>Common Part (other constants)</b></p>
1101<table>
1102 <tbody>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1103 <tr>
1104 <th><b>Type</b></th>
1105 <th class="td_left"><b>Field Description</b></th>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1106 </tr>
1107 <tr>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1108 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1109 <td class="td_left">Number of entries in this type plane.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1110 </tr>
1111 <tr>
1112 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1113 <td class="td_left">Type slot number of this plane.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1114 </tr>
1115 <tr>
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]1116 <td><a href="#constant">constant</a>+</td>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1117 <td class="td_left">The definition of a constant (see below).</td>
1118 </tr>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1119 </tbody>
1120</table>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1121</div>
1122<!-- _______________________________________________________________________ -->
1123<div class="doc_subsubsection"><a name="constant">Constant Field</a></div>
1124<div class="doc_text">
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1125<p>Constants come in many shapes and flavors. The sections that follow
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1126define the format for each of them. All constants start with a <a
1127 href="#uint32_vbr">uint32_vbr</a> encoded integer that provides the
1128number of operands for the constant. For primitive, structure, and
1129array constants, this will always be zero since those types of
1130constants have no operands. In this case, we have the following field
1131definitions:</p>
1132<ul>
1133 <li><b>Bool</b>. This is written as an <a href="#uint32_vbr">uint32_vbr</a>
1134of value 1U or 0U.</li>
1135 <li><b>Signed Integers (sbyte,short,int,long)</b>. These are written
1136as an <a href="#int64_vbr">int64_vbr</a> with the corresponding value.</li>
1137 <li><b>Unsigned Integers (ubyte,ushort,uint,ulong)</b>. These are
1138written as an <a href="#uint64_vbr">uint64_vbr</a> with the
1139corresponding value. </li>
1140 <li><b>Floating Point</b>. Both the float and double types are
1141written literally in binary format.</li>
1142 <li><b>Arrays</b>. Arrays are written simply as a list of <a
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1143 href="#uint32_vbr">uint32_vbr</a> encoded value slot numbers to the constant
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1144element values.</li>
1145 <li><b>Structures</b>. Structures are written simply as a list of <a
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1146 href="#uint32_vbr">uint32_vbr</a> encoded value slot numbers to the constant
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1147field values of the structure.</li>
1148</ul>
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]1149
1150<p>When the number of operands to the constant is one, we have an 'undef' value
1151of the specified type.</p>
1152
1153<p>When the number of operands to the constant is greater than one, we have a
1154constant expression and its field format is provided in the table below, and the
1155number is equal to the number of operands+1.</p>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1156<table>
1157 <tbody>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1158 <tr>
1159 <th><b>Type</b></th>
1160 <th class="td_left"><b>Field Description</b></th>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1161 </tr>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1162 <tr>
1163 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1164 <td class="td_left">Op code of the instruction for the constant
1165expression.</td>
1166 </tr>
1167 <tr>
1168 <td><a href="#uint32_vbr">uint32_vbr</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1169 <td class="td_left">The value slot number of the constant value for an
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1170operand.<sup>1</sup></td>
1171 </tr>
1172 <tr>
1173 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1174 <td class="td_left">The type slot number for the type of the constant
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1175value for an operand.<sup>1</sup></td>
1176 </tr>
1177 </tbody>
1178</table>
1179Notes:
1180<ol>
1181 <li>Both these fields are repeatable but only in pairs.</li>
1182</ol>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]1183</div>
1184<!-- _______________________________________________________________________ -->
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1185<div class="doc_subsection"><a name="functiondefs">Function Definition</a></div>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]1186<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1187<p>Function definitions contain the linkage, constant pool or
1188compaction table, instruction list, and symbol table for a function.
1189The following table shows the structure of a function definition.</p>
1190<table>
1191 <tbody>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1192 <tr>
1193 <th><b>Type</b></th>
1194 <th class="td_left"><b>Field Description</b></th>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1195 </tr>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1196 <tr>
1197 <td><a href="#block">block</a><br>
1198 </td>
1199 <td class="td_left">Function definition block identifier (0x02) +
1200size<br>
1201 </td>
1202 </tr>
1203 <tr>
1204 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1205 <td class="td_left">The linkage type of the function: 0=External,
12061=Weak, 2=Appending, 3=Internal, 4=LinkOnce<sup>1</sup></td>
1207 </tr>
1208 <tr>
1209 <td><a href="#block">block</a></td>
1210 <td class="td_left">The <a href="#constantpool">constant pool</a>
1211block for this function.<sup>2</sup></td>
1212 </tr>
1213 <tr>
1214 <td><a href="#block">block</a></td>
1215 <td class="td_left">The <a href="#compactiontable">compaction
1216table</a> block for the function.<sup>2</sup></td>
1217 </tr>
1218 <tr>
1219 <td><a href="#block">block</a></td>
1220 <td class="td_left">The <a href="#instructionlist">instruction
1221list</a> for the function.</td>
1222 </tr>
1223 <tr>
1224 <td><a href="#block">block</a></td>
Reid Spencer9a910812004-08-17 00:49:03 +0000[diff] [blame]1225 <td class="td_left">The function's <a href="#symtab">symbol
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1226table</a> containing only those symbols pertinent to the function
1227(mostly block labels).</td>
1228 </tr>
1229 </tbody>
1230</table>
1231Notes:
1232<ol>
1233 <li>Note that if the linkage type is "External" then none of the
1234other fields will be present as the function is defined elsewhere.</li>
1235 <li>Note that only one of the constant pool or compaction table will
1236be written. Compaction tables are only written if they will actually
1237save bytecode space. If not, then a regular constant pool is written.</li>
1238</ol>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]1239</div>
1240<!-- _______________________________________________________________________ -->
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1241<div class="doc_subsection"><a name="compactiontable">Compaction Table</a>
1242</div>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]1243<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1244<p>Compaction tables are part of a function definition. They are merely
1245a device for reducing the size of bytecode files. The size of a
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1246bytecode file is dependent on the <em>values</em> of the slot numbers
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1247used because larger values use more bytes in the variable bit rate
1248encoding scheme. Furthermore, the compressed instruction format
1249reserves only six bits for the type of the instruction. In large
1250modules, declaring hundreds or thousands of types, the values of the
1251slot numbers can be quite large. However, functions may use only a
1252small fraction of the global types. In such cases a compaction table is
1253created that maps the global type and value slot numbers to smaller
1254values used by a function. Functions will contain either a
1255function-specific constant pool <em>or</em> a compaction table but not
1256both. Compaction tables have the format shown in the table below.</p>
1257<table>
1258 <tbody>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1259 <tr>
1260 <th><b>Type</b></th>
1261 <th class="td_left"><b>Field Description</b></th>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1262 </tr>
1263 <tr>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1264 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1265 <td class="td_left">The number of types that follow</td>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1266 </tr>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1267 <tr>
1268 <td><a href="#uint24_vbr">uint24_vbr</a>+</td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1269 <td class="td_left">The type slot number in the global types of
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1270the type that will be referenced in the function with the index of this
1271entry in the compaction table.</td>
1272 </tr>
1273 <tr>
1274 <td><a href="#type_len">type_len</a></td>
1275 <td class="td_left">An encoding of the type and number of values
1276that follow. This field's encoding varies depending on the size of the
1277type plane. See <a href="#type_len">Type and Length</a> for further
1278details.</td>
1279 </tr>
1280 <tr>
1281 <td><a href="#uint32_vbr">uint32_vbr</a>+</td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1282 <td class="td_left">The value slot number in the global values
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1283that will be referenced in the function with the index of this entry in
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1284the compaction table.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1285 </tr>
1286 </tbody>
1287</table>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]1288</div>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1289<!-- _______________________________________________________________________ -->
1290<div class="doc_subsubsection"><a name="type_len">Type and Length</a></div>
1291<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1292<p>The type and length of a compaction table type plane is encoded
1293differently depending on the length of the plane. For planes of length
12941 or 2, the length is encoded into bits 0 and 1 of a <a
1295 href="#uint32_vbr">uint32_vbr</a> and the type is encoded into bits
12962-31. Because type numbers are often small, this often saves an extra
1297byte per plane. If the length of the plane is greater than 2 then the
1298encoding uses a <a href="#uint32_vbr">uint32_vbr</a> for each of the
1299length and type, in that order.</p>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1300</div>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]1301<!-- _______________________________________________________________________ -->
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1302<div class="doc_subsection"><a name="instructionlist">Instruction List</a></div>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]1303<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1304<p>The instructions in a function are written as a simple list. Basic
1305blocks are inferred by the terminating instruction types. The format of
1306the block is given in the following table.</p>
1307<table>
1308 <tbody>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1309 <tr>
1310 <th><b>Type</b></th>
1311 <th class="td_left"><b>Field Description</b></th>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1312 </tr>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1313 <tr>
1314 <td><a href="#block">block</a><br>
1315 </td>
1316 <td class="td_left">Instruction list identifier (0x07) + size<br>
1317 </td>
1318 </tr>
1319 <tr>
1320 <td><a href="#instruction">instruction</a>+</td>
1321 <td class="td_left">An instruction. Instructions have a variety
1322of formats. See <a href="#instruction">Instructions</a> for details.</td>
1323 </tr>
1324 </tbody>
1325</table>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]1326</div>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1327<!-- _______________________________________________________________________ -->
1328<div class="doc_subsubsection"><a name="instruction">Instructions</a></div>
1329<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1330<p>For brevity, instructions are written in one of four formats,
1331depending on the number of operands to the instruction. Each
1332instruction begins with a <a href="#uint32_vbr">uint32_vbr</a> that
1333encodes the type of the instruction as well as other things. The tables
Reid Spencer9a910812004-08-17 00:49:03 +0000[diff] [blame]1334that follow describe the format of this first part of each instruction.</p>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1335<p><b>Instruction Format 0</b></p>
1336<p>This format is used for a few instructions that can't easily be
Reid Spencer9a910812004-08-17 00:49:03 +0000[diff] [blame]1337shortened because they have large numbers of operands (e.g. PHI Node or
1338getelementptr). Each of the opcode, type, and operand fields is found in
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1339successive fields.</p>
1340<table>
1341 <tbody>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1342 <tr>
1343 <th><b>Type</b></th>
1344 <th class="td_left"><b>Field Description</b></th>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1345 </tr>
1346 <tr>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1347 <td><a href="#uint32_vbr">uint32_vbr</a></td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1348 <td class="td_left">Specifies the opcode of the instruction. Note
1349that for compatibility with the other instruction formats, the opcode
1350is shifted left by 2 bits. Bits 0 and 1 must have value zero for this
1351format.</td>
1352 </tr>
1353 <tr>
1354 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1355 <td class="td_left">Provides the type slot number of the result type of
1356 the instruction.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1357 </tr>
1358 <tr>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1359 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1360 <td class="td_left">The number of operands that follow.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1361 </tr>
1362 <tr>
Reid Spencer8e32af02004-07-07 13:34:26 +0000[diff] [blame]1363 <td><a href="#uint32_vbr">uint32_vbr</a>+</td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1364 <td class="td_left">The slot number of the value(s) for the operand(s).
1365 <sup>1</sup></td>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1366 </tr>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1367 </tbody>
1368</table>
1369Notes:
1370<ol>
1371 <li>Note that if the instruction is a getelementptr and the type of
1372the operand is a sequential type (array or pointer) then the slot
1373number is shifted up two bits and the low order bits will encode the
1374type of index used, as follows: 0=uint, 1=int, 2=ulong, 3=long.</li>
1375</ol>
1376<p><b>Instruction Format 1</b></p>
1377<p>This format encodes the opcode, type and a single operand into a
1378single <a href="#uint32_vbr">uint32_vbr</a> as follows:</p>
1379<table>
1380 <tbody>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1381 <tr>
1382 <th><b>Bits</b></th>
1383 <th><b>Type</b></th>
1384 <th class="td_left"><b>Field Description</b></th>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1385 </tr>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1386 <tr>
1387 <td>0-1</td>
1388 <td>constant "1"</td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1389 <td class="td_left">These two bits must be the value 1 which identifies
1390 this as an instruction of format 1.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1391 </tr>
1392 <tr>
1393 <td>2-7</td>
Reid Spencer9a910812004-08-17 00:49:03 +0000[diff] [blame]1394 <td><a href="#opcode">opcode</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1395 <td class="td_left">Specifies the opcode of the instruction. Note that
1396 the maximum opcode value is 63.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1397 </tr>
1398 <tr>
1399 <td>8-19</td>
1400 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1401 <td class="td_left">Specifies the slot number of the type for this
1402 instruction. Maximum slot number is 2<sup>12</sup>-1=4095.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1403 </tr>
1404 <tr>
1405 <td>20-31</td>
1406 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1407 <td class="td_left">Specifies the slot number of the value for the
1408 first operand. Maximum slot number is 2<sup>12</sup>-1=4095. Note that
1409 the value 2<sup>12</sup>-1 denotes zero operands.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1410 </tr>
1411 </tbody>
1412</table>
1413<p><b>Instruction Format 2</b></p>
1414<p>This format encodes the opcode, type and two operands into a single <a
1415 href="#uint32_vbr">uint32_vbr</a> as follows:</p>
1416<table>
1417 <tbody>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1418 <tr>
1419 <th><b>Bits</b></th>
1420 <th><b>Type</b></th>
1421 <th class="td_left"><b>Field Description</b></th>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1422 </tr>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1423 <tr>
1424 <td>0-1</td>
1425 <td>constant "2"</td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1426 <td class="td_left">These two bits must be the value 2 which identifies
1427 this as an instruction of format 2.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1428 </tr>
1429 <tr>
1430 <td>2-7</td>
1431 <td><a href="#opcodes">opcode</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1432 <td class="td_left">Specifies the opcode of the instruction. Note that
1433 the maximum opcode value is 63.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1434 </tr>
1435 <tr>
1436 <td>8-15</td>
1437 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1438 <td class="td_left">Specifies the slot number of the type for this
1439 instruction. Maximum slot number is 2<sup>8</sup>-1=255.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1440 </tr>
1441 <tr>
1442 <td>16-23</td>
1443 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1444 <td class="td_left">Specifies the slot number of the value for the first
1445 operand. Maximum slot number is 2<sup>8</sup>-1=255.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1446 </tr>
1447 <tr>
1448 <td>24-31</td>
1449 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1450 <td class="td_left">Specifies the slot number of the value for the second
1451 operand. Maximum slot number is 2<sup>8</sup>-1=255.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1452 </tr>
1453 </tbody>
1454</table>
1455<p><b>Instruction Format 3</b></p>
1456<p>This format encodes the opcode, type and three operands into a
1457single <a href="#uint32_vbr">uint32_vbr</a> as follows:</p>
1458<table>
1459 <tbody>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1460 <tr>
1461 <th><b>Bits</b></th>
1462 <th><b>Type</b></th>
1463 <th class="td_left"><b>Field Description</b></th>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1464 </tr>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1465 <tr>
1466 <td>0-1</td>
1467 <td>constant "3"</td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1468 <td class="td_left">These two bits must be the value 3 which identifies
1469 this as an instruction of format 3.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1470 </tr>
1471 <tr>
1472 <td>2-7</td>
1473 <td><a href="#opcodes">opcode</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1474 <td class="td_left">Specifies the opcode of the instruction. Note that
1475 the maximum opcode value is 63.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1476 </tr>
1477 <tr>
1478 <td>8-13</td>
1479 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1480 <td class="td_left">Specifies the slot number of the type for this
1481 instruction. Maximum slot number is 2<sup>6</sup>-1=63.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1482 </tr>
1483 <tr>
1484 <td>14-19</td>
1485 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1486 <td class="td_left">Specifies the slot number of the value for the first
1487 operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1488 </tr>
1489 <tr>
1490 <td>20-25</td>
1491 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1492 <td class="td_left">Specifies the slot number of the value for the second
1493 operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1494 </tr>
1495 <tr>
1496 <td>26-31</td>
1497 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1498 <td class="td_left">Specifies the slot number of the value for the third
1499 operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1500 </tr>
1501 </tbody>
1502</table>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1503</div>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1504
1505<!-- _______________________________________________________________________ -->
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]1506<div class="doc_subsection"><a name="opcodes">Instruction Opcodes</a></div>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1507<div class="doc_text">
1508 <p>Instructions encode an opcode that identifies the kind of instruction.
1509 Opcodes are an enumerated integer value. The specific values used depend on
1510 the version of LLVM you're using. The opcode values are defined in the
Misha Brukmanaeee58f2004-11-07 00:59:58 +0000[diff] [blame]1511 <a href="http://llvm.cs.uiuc.edu/cvsweb/cvsweb.cgi/llvm/include/llvm/Instruction.def">
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1512 <tt>include/llvm/Instruction.def</tt></a> file. You should check there for the
1513 most recent definitions. The table below provides the opcodes defined as of
Nate Begeman0c1e6802004-08-27 07:59:37 +0000[diff] [blame]1514 the writing of this document. The table associates each opcode mnemonic with
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1515 its enumeration value and the bytecode and LLVM version numbers in which the
1516 opcode was introduced.</p>
1517 <table>
1518 <tbody>
1519 <tr>
1520 <th>Opcode</th>
1521 <th>Number</th>
1522 <th>Bytecode Version</th>
1523 <th>LLVM Version</th>
1524 </tr>
1525 <tr><td colspan="4"><b>Terminator Instructions</b></td></tr>
1526 <tr><td>Ret</td><td>1</td><td>1</td><td>1.0</td></tr>
1527 <tr><td>Br</td><td>2</td><td>1</td><td>1.0</td></tr>
1528 <tr><td>Switch</td><td>3</td><td>1</td><td>1.0</td></tr>
1529 <tr><td>Invoke</td><td>4</td><td>1</td><td>1.0</td></tr>
1530 <tr><td>Unwind</td><td>5</td><td>1</td><td>1.0</td></tr>
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]1531 <tr><td>Unreachable</td><td>6</td><td>1</td><td>1.4</td></tr>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1532 <tr><td colspan="4"><b>Binary Operators</b></td></tr>
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]1533 <tr><td>Add</td><td>7</td><td>1</td><td>1.0</td></tr>
1534 <tr><td>Sub</td><td>8</td><td>1</td><td>1.0</td></tr>
1535 <tr><td>Mul</td><td>9</td><td>1</td><td>1.0</td></tr>
1536 <tr><td>Div</td><td>10</td><td>1</td><td>1.0</td></tr>
1537 <tr><td>Rem</td><td>11</td><td>1</td><td>1.0</td></tr>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1538 <tr><td colspan="4"><b>Logical Operators</b></td></tr>
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]1539 <tr><td>And</td><td>12</td><td>1</td><td>1.0</td></tr>
1540 <tr><td>Or</td><td>13</td><td>1</td><td>1.0</td></tr>
1541 <tr><td>Xor</td><td>14</td><td>1</td><td>1.0</td></tr>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1542 <tr><td colspan="4"><b>Binary Comparison Operators</b></td></tr>
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]1543 <tr><td>SetEQ</td><td>15</td><td>1</td><td>1.0</td></tr>
1544 <tr><td>SetNE</td><td>16</td><td>1</td><td>1.0</td></tr>
1545 <tr><td>SetLE</td><td>17</td><td>1</td><td>1.0</td></tr>
1546 <tr><td>SetGE</td><td>18</td><td>1</td><td>1.0</td></tr>
1547 <tr><td>SetLT</td><td>19</td><td>1</td><td>1.0</td></tr>
1548 <tr><td>SetGT</td><td>20</td><td>1</td><td>1.0</td></tr>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1549 <tr><td colspan="4"><b>Memory Operators</b></td></tr>
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]1550 <tr><td>Malloc</td><td>21</td><td>1</td><td>1.0</td></tr>
1551 <tr><td>Free</td><td>22</td><td>1</td><td>1.0</td></tr>
1552 <tr><td>Alloca</td><td>23</td><td>1</td><td>1.0</td></tr>
1553 <tr><td>Load</td><td>24</td><td>1</td><td>1.0</td></tr>
1554 <tr><td>Store</td><td>25</td><td>1</td><td>1.0</td></tr>
1555 <tr><td>GetElementPtr</td><td>26</td><td>1</td><td>1.0</td></tr>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1556 <tr><td colspan="4"><b>Other Operators</b></td></tr>
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]1557 <tr><td>PHI</td><td>27</td><td>1</td><td>1.0</td></tr>
1558 <tr><td>Cast</td><td>28</td><td>1</td><td>1.0</td></tr>
1559 <tr><td>Call</td><td>29</td><td>1</td><td>1.0</td></tr>
1560 <tr><td>Shl</td><td>30</td><td>1</td><td>1.0</td></tr>
1561 <tr><td>Shr</td><td>31</td><td>1</td><td>1.0</td></tr>
1562 <tr><td>VANext</td><td>32</td><td>1</td><td>1.0</td></tr>
1563 <tr><td>VAArg</td><td>33</td><td>1</td><td>1.0</td></tr>
1564 <tr><td>Select</td><td>34</td><td>2</td><td>1.2</td></tr>
1565 <tr><td>UserOp1</td><td>35</td><td>1</td><td>1.0</td></tr>
1566 <tr><td>UserOp2</td><td>36</td><td>1</td><td>1.0</td></tr>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1567 </tbody>
1568 </table>
1569</div>
1570
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]1571<!-- _______________________________________________________________________ -->
Reid Spencereca340b2004-05-23 17:05:09 +0000[diff] [blame]1572<div class="doc_subsection"><a name="symtab">Symbol Table</a> </div>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]1573<div class="doc_text">
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1574<p>A symbol table can be put out in conjunction with a module or a function. A
1575symbol table has a list of name/type associations followed by a list of
1576name/value associations. The name/value associations are organized into "type
1577planes" so that all values of a common type are listed together. Each type
1578plane starts with the number of entries in the plane and the type slot number
1579for all the values in that plane (so the type can be looked up in the global
1580type pool). For each entry in a type plane, the slot number of the value and
1581the name associated with that value are written. The format is given in the
1582table below. </p>
Reid Spencer9ce11e42004-07-05 19:04:27 +0000[diff] [blame]1583<table>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1584 <tbody>
1585 <tr>
1586 <th><b>Type</b></th>
1587 <th class="td_left"><b>Field Description</b></th>
1588 </tr>
1589 <tr>
1590 <td><a href="#block">block</a><br>
1591 </td>
1592 <td class="td_left">Symbol Table Identifier (0x04)</td>
1593 </tr>
1594 <tr>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1595 <td><a href="#llist">llist</a>(<a href="#symtab_entry">type_entry</a>)</td>
Reid Spencer9a910812004-08-17 00:49:03 +0000[diff] [blame]1596 <td class="td_left">A length list of symbol table entries for
1597 <tt>Type</tt>s
1598 </td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1599 </tr>
1600 <tr>
Reid Spencer9a910812004-08-17 00:49:03 +0000[diff] [blame]1601 <td><a href="#zlist">llist</a>(<a href="#symtab_plane">symtab_plane</a>)</td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1602 <td class="td_left">A length list of "type planes" of symbol table
Reid Spencer9a910812004-08-17 00:49:03 +0000[diff] [blame]1603 entries for <tt>Value</tt>s</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1604 </tr>
1605 </tbody>
Reid Spencereca340b2004-05-23 17:05:09 +0000[diff] [blame]1606</table>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]1607</div>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1608
1609<!-- _______________________________________________________________________ -->
1610<div class="doc_subsubsection"> <a name="type_entry">Symbol Table Type
1611Entry</a>
1612</div>
1613<div class="doc_text">
1614<p>A symbol table type entry associates a name with a type. The name is provided
1615simply as an array of chars. The type is provided as a type slot number (index)
1616into the global type pool. The format is given in the following table:</p>
1617<table>
1618 <tbody>
1619 <tr>
1620 <th><b>Type</b></th>
1621 <th class="td_left"><b>Field Description</b></th>
1622 </tr>
1623 <tr>
1624 <td><a href="#uint32_vbr">uint24_vbr</a></td>
1625 <td class="td_left">Type slot number of the type being given a
1626 name relative to the global type pool.
1627 </td>
1628 </tr>
1629 <tr>
1630 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1631 <td class="td_left">Length of the character array that follows.</td>
1632 </tr>
1633 <tr>
1634 <td><a href="#char">char</a>+</td>
1635 <td class="td_left">The characters of the name.</td>
1636 </tr>
1637 </tbody>
1638</table>
1639</div>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1640<!-- _______________________________________________________________________ -->
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1641<div class="doc_subsubsection"> <a name="symtab_plane">Symbol Table
1642Plane</a>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1643</div>
1644<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1645<p>A symbol table plane provides the symbol table entries for all
1646values of a common type. The encoding is given in the following table:</p>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1647<table>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1648 <tbody>
1649 <tr>
1650 <th><b>Type</b></th>
1651 <th class="td_left"><b>Field Description</b></th>
1652 </tr>
1653 <tr>
1654 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1655 <td class="td_left">Number of entries in this plane.</td>
1656 </tr>
1657 <tr>
1658 <td><a href="#uint32_vbr">uint32_vbr</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1659 <td class="td_left">Type slot number of type for all values in this plane..</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1660 </tr>
1661 <tr>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1662 <td><a href="#value_entry">value_entry</a>+</td>
1663 <td class="td_left">The symbol table entries for to associate values with
1664 names.</td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1665 </tr>
1666 </tbody>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1667</table>
1668</div>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1669<!-- _______________________________________________________________________ -->
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1670<div class="doc_subsubsection"><a name="value_entry">Symbol Table Value
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1671Entry</a>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1672</div>
1673<div class="doc_text">
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1674<p>A symbol table value entry provides the assocation between a value and the
1675name given to the value. The value is referenced by its slot number. The
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1676format is given in the following table:</p>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1677<table>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1678 <tbody>
1679 <tr>
1680 <th><b>Type</b></th>
1681 <th class="td_left"><b>Field Description</b></th>
1682 </tr>
1683 <tr>
1684 <td><a href="#uint32_vbr">uint24_vbr</a></td>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1685 <td class="td_left">Value slot number of the value being given a name.
Reid Spencer9a910812004-08-17 00:49:03 +0000[diff] [blame]1686 </td>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1687 </tr>
1688 <tr>
1689 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1690 <td class="td_left">Length of the character array that follows.</td>
1691 </tr>
1692 <tr>
1693 <td><a href="#char">char</a>+</td>
1694 <td class="td_left">The characters of the name.</td>
1695 </tr>
1696 </tbody>
Reid Spencere2f97b32004-07-05 22:28:02 +0000[diff] [blame]1697</table>
1698</div>
Reid Spencer375d7842004-08-18 20:06:19 +0000[diff] [blame]1699
Reid Spencerb14a0a62004-06-08 07:41:41 +0000[diff] [blame]1700<!-- *********************************************************************** -->
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1701<div class="doc_section"> <a name="versiondiffs">Version Differences</a>
1702</div>
Reid Spencerb14a0a62004-06-08 07:41:41 +0000[diff] [blame]1703<!-- *********************************************************************** -->
1704<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1705<p>This section describes the differences in the Bytecode Format across
1706LLVM
1707versions. The versions are listed in reverse order because it assumes
1708the current version is as documented in the previous sections. Each
1709section here
Chris Lattnere5589ea2004-07-05 18:05:48 +0000[diff] [blame]1710describes the differences between that version and the one that <i>follows</i>.
Reid Spencerb14a0a62004-06-08 07:41:41 +0000[diff] [blame]1711</p>
1712</div>
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]1713
Reid Spencerb14a0a62004-06-08 07:41:41 +0000[diff] [blame]1714<!-- _______________________________________________________________________ -->
Reid Spencer3cff8a042004-08-18 20:17:05 +0000[diff] [blame]1715<div class="doc_subsection"><a name="vers13">Version 1.3 Differences From
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]1716 1.4</a></div>
Reid Spencer0b85d032004-08-17 07:43:43 +0000[diff] [blame]1717<!-- _______________________________________________________________________ -->
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]1718
1719<div class="doc_subsubsection">Unreachable Instruction</div>
1720<div class="doc_text">
1721 <p>The LLVM <a href="LangRef.html#i_unreachable">Unreachable</a> instruction
1722 was added in version 1.4 of LLVM. This caused all instruction numbers after
1723 it to shift down by one.</p>
1724</div>
1725
1726<div class="doc_subsubsection">Function Flags</div>
1727<div class="doc_text">
1728 <p>LLVM bytecode versions prior to 1.4 did not include the 5 bit offset
1729 in <a href="#funcfield">the function list</a> in the <a
1730 href="#globalinfo">Module Global Info</a> block.</p>
1731</div>
1732
1733<div class="doc_subsubsection">Function Flags</div>
1734<div class="doc_text">
1735 <p>LLVM bytecode versions prior to 1.4 did not include the 'undef' constant
1736 value, which affects the encoding of <a href="#constant">Constant
1737 Fields</a>.</p>
1738</div>
1739
Chris Lattnerdb6a9fd2004-10-16 00:29:30 +0000[diff] [blame]1740<!--
Reid Spencer0b85d032004-08-17 07:43:43 +0000[diff] [blame]1741<div class="doc_subsubsection">Aligned Data</div>
1742<div class="doc_text">
1743 <p>In version 1.3, certain data items were aligned to 32-bit boundaries. In
1744 version 1.4, alignment of data was done away with completely. The need for
1745 alignment has gone away and the only thing it adds is bytecode file size
1746 overhead. In most cases this overhead was small. However, in functions with
1747 large numbers of format 0 instructions (GEPs and PHIs with lots of parameters)
1748 or regular instructions with large valued operands (e.g. because there's just
1749 a lot of instructions in the function) the overhead can be extreme. In one
1750 test case, the overhead was 44,000 bytes (34% of the total file size).
1751 Consequently in release 1.4, the decision was made to eliminate alignment
1752 altogether.</p>
1753 <p>In version 1.3 format, the following bytecode constructs were aligned (i.e.
1754 they were followed by one to three bytes of padding):</p>
1755 <ul>
1756 <li>All blocks.</li>
1757 <li>Instructions using the long format (format 0).</li>
1758 <li>All call instructions that called a var args function.</li>
1759 <li>The target triple (a string field at the end of the module block).</li>
1760 <li>The version field (immediately following the signature).</li>
1761 </ul>
1762 <p>None of these constructs are aligned in version 1.4</p>
1763</div>
Chris Lattnerdb6a9fd2004-10-16 00:29:30 +0000[diff] [blame]1764-->
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]1765
Reid Spencer0b85d032004-08-17 07:43:43 +0000[diff] [blame]1766<!-- _______________________________________________________________________ -->
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1767<div class="doc_subsection"><a name="vers12">Version 1.2 Differences
1768From 1.3</a></div>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]1769<!-- _______________________________________________________________________ -->
Chris Lattnercd196a92004-10-16 18:03:55 +0000[diff] [blame]1770
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]1771<div class="doc_subsubsection">Type Derives From Value</div>
Reid Spencerb14a0a62004-06-08 07:41:41 +0000[diff] [blame]1772<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1773<p>In version 1.2, the Type class in the LLVM IR derives from the Value
1774class. This is not the case in version 1.3. Consequently, in version
17751.2 the notion of a "Type Type" was used to write out values that were
1776Types. The types always occuped plane 12 (corresponding to the
1777TypeTyID) of any type planed set of values. In 1.3 this representation
1778is not convenient because the TypeTyID (12) is not present and its
1779value is now used for LabelTyID. Consequently, the data structures
1780written that involve types do so by writing all the types first and
1781then each of the value planes according to those types. In version 1.2,
1782the types would have been written intermingled with the values.</p>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]1783</div>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]1784<!-- _______________________________________________________________________ -->
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1785<div class="doc_subsubsection">Restricted getelementptr Types</div>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]1786<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1787<p>In version 1.2, the getelementptr instruction required a ubyte type
1788index for accessing a structure field and a long type index for
1789accessing an array element. Consequently, it was only possible to
1790access structures of 255 or fewer elements. Starting in version 1.3,
1791this restriction was lifted. Structures must now be indexed with uint
1792constants. Arrays may now be indexed with int, uint, long, or ulong
1793typed values. The consequence of this was that the bytecode format had
1794to change in order to accommodate the larger range of structure indices.</p>
Reid Spencerb14a0a62004-06-08 07:41:41 +0000[diff] [blame]1795</div>
Reid Spencerb14a0a62004-06-08 07:41:41 +0000[diff] [blame]1796<!-- _______________________________________________________________________ -->
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1797<div class="doc_subsubsection">Short Block Headers</div>
1798<div class="doc_text">
1799<p>In version 1.2, block headers were always 8 bytes being comprised of
1800both an unsigned integer type and an unsigned integer size. For very
1801small modules, these block headers turn out to be a large fraction of
1802the total bytecode file size. In an attempt to make these small files
1803smaller, the type and size information was encoded into a single
1804unsigned integer (4 bytes) comprised of 5 bits for the block type
1805(maximum 31 block types) and 27 bits for the block size (max
1806~134MBytes). These limits seemed sufficient for any blocks or sizes
1807forseen in the future. Note that the module block, which encloses all
1808the other blocks is still written as 8 bytes since bytecode files
1809larger than 134MBytes might be possible.</p>
1810</div>
1811<!-- _______________________________________________________________________ -->
1812<div class="doc_subsubsection">Dependent Libraries and Target Triples</div>
1813<div class="doc_text">
1814<p>In version 1.2, the bytecode format does not store module's target
1815triple or dependent. These fields have been added to the end of the <a
1816 href="#globalinfo">module global info block</a>. The purpose of these
1817fields is to allow a front end compiler to specifiy that the generated
1818module is specific to a particular target triple (operating
1819system/manufacturer/processor) which makes it non-portable; and to
1820allow front end compilers to specify the list of libraries that the
1821module depends on for successful linking.</p>
1822</div>
1823<!-- _______________________________________________________________________ -->
1824<div class="doc_subsubsection">Types Restricted to 24-bits</div>
1825<div class="doc_text">
1826<p>In version 1.2, type slot identifiers were written as 32-bit VBR
1827quantities. In 1.3 this has been reduced to 24-bits in order to ensure
1828that it is not possible to overflow the type field of a global variable
1829definition. 24-bits for type slot numbers is deemed sufficient for any
1830practical use of LLVM.</p>
1831</div>
1832<!-- _______________________________________________________________________ -->
1833<!-- _______________________________________________________________________ -->
1834<div class="doc_subsection"><a name="vers11">Version 1.1 Differences
1835From 1.2 </a></div>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]1836<!-- _______________________________________________________________________ -->
1837<div class="doc_subsubsection">Explicit Primitive Zeros</div>
Reid Spencerb14a0a62004-06-08 07:41:41 +0000[diff] [blame]1838<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1839<p>In version 1.1, the zero value for primitives was explicitly encoded
1840into the bytecode format. Since these zero values are constant values
1841in the LLVM IR and never change, there is no reason to explicitly
1842encode them. This explicit encoding was removed in version 1.2.</p>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]1843</div>
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]1844<!-- _______________________________________________________________________ -->
1845<div class="doc_subsubsection">Inconsistent Module Global Info</div>
1846<div class="doc_text">
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1847<p>In version 1.1, the Module Global Info block was not aligned causing
1848the next block to be read in on an unaligned boundary. This problem was
1849corrected in version 1.2.<br>
1850<br>
1851</p>
Reid Spencerb14a0a62004-06-08 07:41:41 +0000[diff] [blame]1852</div>
Reid Spencerb14a0a62004-06-08 07:41:41 +0000[diff] [blame]1853<!-- _______________________________________________________________________ -->
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1854<div class="doc_subsection"><a name="vers10">Version 1.0 Differences
1855From 1.1</a></div>
Reid Spencerb14a0a62004-06-08 07:41:41 +0000[diff] [blame]1856<div class="doc_text">
Reid Spencer4e0352d2004-07-05 08:18:07 +0000[diff] [blame]1857<p>None. Version 1.0 and 1.1 bytecode formats are identical.</p>
Reid Spencerb14a0a62004-06-08 07:41:41 +0000[diff] [blame]1858</div>
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]1859<!-- *********************************************************************** -->
1860<hr>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1861<address> <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
1862 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
1863<a href="http://validator.w3.org/check/referer"><img
1864 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
1865<a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and <a
1866 href="mailto:sabre@nondot.org">Chris Lattner</a><br>
1867<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
1868Last modified: $Date$
Reid Spencer9acd4122004-05-22 02:28:36 +0000[diff] [blame]1869</address>
Reid Spencere831f0b2004-07-29 00:13:04 +0000[diff] [blame]1870</body>
1871</html>