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17<body>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]18<div class="doc_title"> LLVM Bytecode File Format </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]19<ol>
20 <li><a href="#abstract">Abstract</a></li>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]21 <li><a href="#concepts">Concepts</a>
Reid Spencer50026612004-05-22 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 Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]27 <li><a href="#vbr">Variable Bit-Rate Encoding</a></li>
Reid Spencer1ab929c2004-07-05 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 Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]32 <li><a href="#general">General Structure</a> </li>
33 <li><a href="#blockdefs">Block Definitions</a>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]34 <ol>
Reid Spencerb39021b2004-05-23 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 Spencer1ab929c2004-07-05 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>
Chris Lattnerf97fa592005-11-05 22:20:06 +0000[diff] [blame^]42 <li><a href="#instructionlist">Instructions List</a></li>
43 <li><a href="#instructions">Instructions</a></li>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]44 <li><a href="#symtab">Symbol Table</a></li>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]45 </ol>
46 </li>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]47 <li><a href="#versiondiffs">Version Differences</a>
48 <ol>
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]49 <li><a href="#vers13">Version 1.3 Differences From 1.4</a></li>
Reid Spencer7c76d332004-06-08 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 Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]55</ol>
Chris Lattner8dabb502004-05-25 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 Spencer50026612004-05-22 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 Spencer9bd2be22004-07-29 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 Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]74</div>
75<!-- *********************************************************************** -->
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]76<div class="doc_section"> <a name="concepts">Concepts</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]77<!-- *********************************************************************** -->
78<div class="doc_text">
Reid Spencer9bd2be22004-07-29 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 Spencer50026612004-05-22 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 Spencer9bd2be22004-07-29 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 Spencer50026612004-05-22 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 Spencer9bd2be22004-07-29 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 Spencer50026612004-05-22 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 Spencer9bd2be22004-07-29 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 Spencer50026612004-05-22 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 Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]121sections that follow will provide the details on how these fields are
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]122written and how the bits are to be interpreted.</p>
123</div>
124<!-- _______________________________________________________________________ -->
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]125<div class="doc_subsection"><a name="align">Alignment</a> </div>
Reid Spencer7aa940d2004-05-25 15:47:57 +0000[diff] [blame]126<div class="doc_text">
Reid Spencer267660f2004-08-03 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 Lattner8dabb502004-05-25 17:44:58 +0000[diff] [blame]131</div>
Reid Spencer7aa940d2004-05-25 15:47:57 +0000[diff] [blame]132<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]133<div class="doc_subsection"><a name="vbr">Variable Bit-Rate Encoding</a>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]134</div>
Reid Spencer9bd2be22004-07-29 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 Spencer82c46712004-07-07 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 Spencer9bd2be22004-07-29 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 Spencerb39021b2004-05-23 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 Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]237 </tr>
238 <tr>
Reid Spencer301fe482004-08-03 20:57:56 +0000[diff] [blame]239 <td style="vertical-align: top;"><a name="uint24_vbr">
240 <b>uint24_vbr</b></a></td>
Reid Spencer9bd2be22004-07-29 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 Spencerf08561f2004-08-03 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 Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]249 </tr>
250 <tr>
251 <td><a name="uint64_vbr"><b>uint64_vbr</b></a></td>
Reid Spencerf08561f2004-08-03 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 Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]254 </tr>
255 <tr>
256 <td><a name="int64_vbr"><b>int64_vbr</b></a></td>
Reid Spencerf08561f2004-08-03 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 Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]259 </tr>
260 <tr>
261 <td><a name="char"><b>char</b></a></td>
Reid Spencerf08561f2004-08-03 19:20:18 +0000[diff] [blame]262 <td class="td_left">A single unsigned character encoded into one byte</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]263 </tr>
264 <tr>
265 <td><a name="bit"><b>bit(n-m)</b></a></td>
Reid Spencerf08561f2004-08-03 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 Spencer9bd2be22004-07-29 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 Spencerf08561f2004-08-03 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 Spencer9bd2be22004-07-29 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 Spencerf08561f2004-08-03 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 Spencer9bd2be22004-07-29 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 Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]320</table>
321</div>
322<!-- _______________________________________________________________________ -->
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]323<div class="doc_subsection"><a name="notation">Field Notation</a> </div>
324<div class="doc_text">
Reid Spencer9bd2be22004-07-29 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 Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]331 <tr>
332 <th><b>Character</b></th>
333 <th class="td_left"><b>Meaning</b></th>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]334 </tr>
335 <tr>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]336 <td><b><code>?</code></b></td>
Reid Spencer9bd2be22004-07-29 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 Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]341 <td><b><code>*</code></b></td>
Reid Spencer9bd2be22004-07-29 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 Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]346 <td><b><code>+</code></b></td>
Reid Spencer9bd2be22004-07-29 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 Spencer82c46712004-07-07 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 Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]353 </tr>
Reid Spencer9bd2be22004-07-29 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 Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]368</div>
Reid Spencer9bd2be22004-07-29 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 Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]378<!-- _______________________________________________________________________ -->
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]379<div class="doc_subsection"><a name="slots">Slots</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]380<div class="doc_text">
Reid Spencer9bd2be22004-07-29 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 Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]386</p>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]387<div class="doc_code"><code> %MyType = type { int, sbyte }<br>
388%MyVar = external global %MyType
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]389</code></div>
Reid Spencer9bd2be22004-07-29 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 Spencer1ab929c2004-07-05 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 Spencer9bd2be22004-07-29 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 Spencer09daa632004-08-18 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 Spencer9bd2be22004-07-29 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 Spencer09daa632004-08-18 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 Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]418</div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]419<!-- *********************************************************************** -->
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]420<div class="doc_section"> <a name="general">General Structure</a> </div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]421<!-- *********************************************************************** -->
422<div class="doc_text">
Reid Spencer9bd2be22004-07-29 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 Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]432<table>
Reid Spencer9bd2be22004-07-29 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 Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]563</table>
Reid Spencer9bd2be22004-07-29 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 Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]566</div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]567<!-- *********************************************************************** -->
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]568<div class="doc_section"> <a name="blockdefs">Block Definitions</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]569<!-- *********************************************************************** -->
570<div class="doc_text">
Reid Spencer9bd2be22004-07-29 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 Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]573</div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]574<!-- _______________________________________________________________________ -->
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]575<div class="doc_subsection"><a name="signature">Signature Block</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]576<div class="doc_text">
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]577<p>The signature occurs in every LLVM bytecode file and is always first.
Reid Spencerb39021b2004-05-23 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 Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]582</p>
Reid Spencerda794e72004-11-08 08:55:21 +0000[diff] [blame]583<p>There are two types of signatures for LLVM bytecode: uncompressed and
584compressed as shown in the table below. </p>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]585<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]586 <tbody>
587 <tr>
588 <th><b>Type</b></th>
Reid Spencerda794e72004-11-08 08:55:21 +0000[diff] [blame]589 <th class="td_left"><b>Uncompressed</b></th>
590 <th class="td_left"><b>Compressed</b></th>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]591 </tr>
592 <tr>
593 <td><a href="#char">char</a></td>
594 <td class="td_left">Constant "l" (0x6C)</td>
Reid Spencerda794e72004-11-08 08:55:21 +0000[diff] [blame]595 <td class="td_left">Constant "l" (0x6C)</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]596 </tr>
597 <tr>
598 <td><a href="#char">char</a></td>
599 <td class="td_left">Constant "l" (0x6C)</td>
Reid Spencerda794e72004-11-08 08:55:21 +0000[diff] [blame]600 <td class="td_left">Constant "l" (0x6C)</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]601 </tr>
602 <tr>
603 <td><a href="#char">char</a></td>
604 <td class="td_left">Constant "v" (0x76)</td>
Reid Spencerda794e72004-11-08 08:55:21 +0000[diff] [blame]605 <td class="td_left">Constant "v" (0x76)</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]606 </tr>
607 <tr>
608 <td><a href="#char">char</a></td>
609 <td class="td_left">Constant "m" (0x6D)</td>
Reid Spencerda794e72004-11-08 08:55:21 +0000[diff] [blame]610 <td class="td_left">Constant "c" (0x63)</td>
611 </tr>
612 <tr>
613 <td><a href="#char">char</a></td>
614 <td class="td_left">N/A</td>
615 <td class="td_left">'0'=null,'1'=gzip,'2'=bzip2</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]616 </tr>
617 </tbody>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]618</table>
Reid Spencerda794e72004-11-08 08:55:21 +0000[diff] [blame]619<p>In other words, the uncompressed signature is just the characters 'llvm'
620while the compressed signature is the characters 'llvc' followed by an ascii
621digit ('0', '1', or '2') that indicates the kind of compression used. A value of
622'0' indicates that null compression was used. This can happen when compression
623was requested on a platform that wasn't configured for gzip or bzip2. A value of
624'1' means that the rest of the file is compressed using the gzip algorithm and
625should be uncompressed before interpretation. A value of '2' means that the rest
626of the file is compressed using the bzip2 algorithm and should be uncompressed
627before interpretation. In all cases, the data resulting from uncompression
628should be interpreted as if it occurred immediately after the 'llvm'
629signature (i.e. the uncompressed data begins with the
630<a href="#module">Module Block</a></p>
631<p><b>NOTE:</b> As of LLVM 1.4, all bytecode files produced by the LLVM tools
Reid Spencera4213b22004-11-08 09:10:50 +0000[diff] [blame]632are compressed by default. To disable compression, pass the
Reid Spencerda794e72004-11-08 08:55:21 +0000[diff] [blame]633<tt>--disable-compression</tt> option to the tool, if it supports it.
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]634</div>
635<!-- _______________________________________________________________________ -->
636<div class="doc_subsection"><a name="module">Module Block</a> </div>
637<div class="doc_text">
638<p>The module block contains a small pre-amble and all the other blocks in
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]639the file. The table below shows the structure of the module block. Note that it
640only provides the module identifier, size of the module block, and the format
641information. Everything else is contained in other blocks, described in other
642sections.</p>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]643<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]644 <tbody>
645 <tr>
646 <th><b>Type</b></th>
647 <th class="td_left"><b>Field Description</b></th>
648 </tr>
649 <tr>
Reid Spencer5bc74d52004-08-16 19:24:36 +0000[diff] [blame]650 <td><a href="#unsigned">unsigned</a><br></td>
651 <td class="td_left"><a href="#mod_header">Module Block Identifier
652 (0x01)</a></td>
653 </tr>
654 <tr>
655 <td><a href="#unsigned">unsigned</a></td>
656 <td class="td_left"><a href="#mod_header">Module Block Size</a></td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]657 </tr>
658 <tr>
659 <td><a href="#uint32_vbr">uint32_vbr</a></td>
660 <td class="td_left"><a href="#format">Format Information</a></td>
661 </tr>
662 <tr>
663 <td><a href="#block">block</a></td>
664 <td class="td_left"><a href="#globaltypes">Global Type Pool</a></td>
665 </tr>
666 <tr>
667 <td><a href="#block">block</a></td>
668 <td class="td_left"><a href="#globalinfo">Module Globals Info</a></td>
669 </tr>
670 <tr>
671 <td><a href="#block">block</a></td>
672 <td class="td_left"><a href="#constantpool">Module Constant Pool</a></td>
673 </tr>
674 <tr>
675 <td><a href="#block">block</a>*</td>
676 <td class="td_left"><a href="#functiondefs">Function Definitions</a></td>
677 </tr>
678 <tr>
679 <td><a href="#block">block</a></td>
Reid Spencer8996e552004-08-17 00:49:03 +0000[diff] [blame]680 <td class="td_left"><a href="#symtab">Module Symbol Table</a></td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]681 </tr>
682 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]683</table>
684</div>
Reid Spencer5bc74d52004-08-16 19:24:36 +0000[diff] [blame]685
686<!-- _______________________________________________________________________ -->
687<div class="doc_subsubsection"><a name="mod_header">Module Block Header</a></div>
688<div class="doc_text">
689 <p>The block header for the module block uses a longer format than the other
690 blocks in a bytecode file. Specifically, instead of encoding the type and size
691 of the block into a 32-bit integer with 5-bits for type and 27-bits for size,
692 the module block header uses two 32-bit unsigned values, one for type, and one
693 for size. While the 2<sup>27</sup> byte limit on block size is sufficient for the blocks
694 contained in the module, it isn't sufficient for the module block itself
695 because we want to ensure that bytecode files as large as 2<sup>32</sup> bytes
696 are possible. For this reason, the module block (and only the module block)
697 uses a long format header.</p>
698</div>
699
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]700<!-- _______________________________________________________________________ -->
701<div class="doc_subsubsection"><a name="format">Format Information</a></div>
702<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]703<p>The format information field is encoded into a <a href="#uint32_vbr">uint32_vbr</a>
704as shown in the following table.</p>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]705<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]706 <tbody>
707 <tr>
708 <th><b>Type</b></th>
709 <th class="td_left"><b>Description</b></th>
710 </tr>
711 <tr>
712 <td><a href="#bit">bit(0)</a></td>
713 <td class="td_left">Target is big endian?</td>
714 </tr>
715 <tr>
716 <td><a href="#bit">bit(1)</a></td>
717 <td class="td_left">On target pointers are 64-bit?</td>
718 </tr>
719 <tr>
720 <td><a href="#bit">bit(2)</a></td>
721 <td class="td_left">Target has no endianess?</td>
722 </tr>
723 <tr>
724 <td><a href="#bit">bit(3)</a></td>
725 <td class="td_left">Target has no pointer size?</td>
726 </tr>
727 <tr>
728 <td><a href="#bit">bit(4-31)</a></td>
729 <td class="td_left">Bytecode format version</td>
730 </tr>
731 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]732</table>
733<p>
734Of particular note, the bytecode format number is simply a 28-bit
John Criswell611a8d12005-10-24 16:20:10 +0000[diff] [blame]735monotonically increasing integer that identifies the version of the bytecode
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]736format (which is not directly related to the LLVM release number). The
737bytecode versions defined so far are (note that this document only
738describes the latest version, 1.3):</p>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]739<ul>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]740 <li>#0: LLVM 1.0 &amp; 1.1</li>
741 <li>#1: LLVM 1.2</li>
742 <li>#2: LLVM 1.2.5 (not released)</li>
John Criswell1d9be9e2005-10-24 17:10:57 +0000[diff] [blame]743 <li>#3: LLVM 1.3</li>
744 <li>#4: LLVM 1.3.x (not released)</li>
745 <li>#5: LLVM 1.4, 1.5, 1.6</li>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]746 </li>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]747</ul>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]748<p>Note that we plan to eventually expand the target description
749capabilities
750of bytecode files to <a href="http://llvm.cs.uiuc.edu/PR263">target
751triples</a>.
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]752</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]753</div>
754<!-- _______________________________________________________________________ -->
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]755<div class="doc_subsection"><a name="globaltypes">Global Type Pool</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]756<div class="doc_text">
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]757<p>The global type pool consists of type definitions. Their order of appearance
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]758in the file determines their type slot number (0 based). Slot numbers are
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]759used to replace pointers in the intermediate representation. Each slot number
760uniquely identifies one entry in a type plane (a collection of values of the
761same type). Since all values have types and are associated with the order in
762which the type pool is written, the global type pool <em>must</em> be written
763as the first block of a module. If it is not, attempts to read the file will
764fail because both forward and backward type resolution will not be possible.</p>
765<p>The type pool is simply a list of type definitions, as shown in the
766table below.</p>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]767<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]768 <tbody>
769 <tr>
770 <th><b>Type</b></th>
771 <th class="td_left"><b>Field Description</b></th>
772 </tr>
773 <tr>
774 <td><a href="#unsigned">block</a></td>
775 <td class="td_left">Type Pool Identifier (0x06) + Size<br>
776 </td>
777 </tr>
778 <tr>
779 <td><a href="#llist">llist</a>(<a href="#type">type</a>)</td>
780 <td class="td_left">A length list of type definitions.</td>
781 </tr>
782 </tbody>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]783</table>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]784</div>
785<!-- _______________________________________________________________________ -->
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]786<div class="doc_subsubsection"><a name="type">Type Definitions</a></div>
787<div class="doc_text">
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]788<p>Types in the type pool are defined using a different format for each kind
789of type, as given in the following sections.</p>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]790<h3>Primitive Types</h3>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]791<p>The primitive types encompass the basic integer and floating point
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]792types. They are encoded simply as their TypeID.</p>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]793<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]794 <tbody>
795 <tr>
796 <th><b>Type</b></th>
797 <th class="td_left"><b>Description</b></th>
798 </tr>
799 <tr>
800 <td><a href="#uint24_vbr">uint24_vbr</a></td>
801 <td class="td_left">Type ID for the primitive types (values 1 to
80211) <sup>1</sup></td>
803 </tr>
804 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]805</table>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]806Notes:
807<ol>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]808 <li>The values for the Type IDs for the primitive types are provided
809by the definition of the <code>llvm::Type::TypeID</code> enumeration
810in <code>include/llvm/Type.h</code>. The enumeration gives the
811following mapping:
812 <ol>
813 <li>bool</li>
814 <li>ubyte</li>
815 <li>sbyte</li>
816 <li>ushort</li>
817 <li>short</li>
818 <li>uint</li>
819 <li>int</li>
820 <li>ulong</li>
821 <li>long</li>
822 <li>float</li>
823 <li>double</li>
824 </ol>
825 </li>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]826</ol>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]827<h3>Function Types</h3>
828<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]829 <tbody>
830 <tr>
831 <th><b>Type</b></th>
832 <th class="td_left"><b>Description</b></th>
833 </tr>
834 <tr>
835 <td><a href="#uint24_vbr">uint24_vbr</a></td>
836 <td class="td_left">Type ID for function types (13)</td>
837 </tr>
838 <tr>
839 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]840 <td class="td_left">Type slot number of function's return type.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]841 </tr>
842 <tr>
843 <td><a href="#llist">llist</a>(<a href="#uint24_vbr">uint24_vbr</a>)</td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]844 <td class="td_left">Type slot number of each argument's type.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]845 </tr>
846 <tr>
847 <td><a href="#uint32_vbr">uint32_vbr</a>?</td>
848 <td class="td_left">Value 0 if this is a varargs function,
849missing otherwise.</td>
850 </tr>
851 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]852</table>
853<h3>Structure Types</h3>
854<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]855 <tbody>
856 <tr>
857 <th><b>Type</b></th>
858 <th class="td_left"><b>Description</b></th>
859 </tr>
860 <tr>
861 <td><a href="#uint24_vbr">uint24_vbr</a></td>
862 <td class="td_left">Type ID for structure types (14)</td>
863 </tr>
864 <tr>
865 <td><a href="#zlist">zlist</a>(<a href="#uint24_vbr">uint24_vbr</a>)</td>
866 <td class="td_left">Slot number of each of the element's fields.</td>
867 </tr>
868 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]869</table>
870<h3>Array Types</h3>
871<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]872 <tbody>
873 <tr>
874 <th><b>Type</b></th>
875 <th class="td_left"><b>Description</b></th>
876 </tr>
877 <tr>
878 <td><a href="#uint24_vbr">uint24_vbr</a></td>
879 <td class="td_left">Type ID for Array Types (15)</td>
880 </tr>
881 <tr>
882 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]883 <td class="td_left">Type slot number of array's element type.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]884 </tr>
885 <tr>
886 <td><a href="#uint32_vbr">uint32_vbr</a></td>
887 <td class="td_left">The number of elements in the array.</td>
888 </tr>
889 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]890</table>
891<h3>Pointer Types</h3>
892<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]893 <tbody>
894 <tr>
895 <th><b>Type</b></th>
896 <th class="td_left"><b>Description</b></th>
897 </tr>
898 <tr>
899 <td><a href="#uint24_vbr">uint24_vbr</a></td>
900 <td class="td_left">Type ID For Pointer Types (16)</td>
901 </tr>
902 <tr>
903 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]904 <td class="td_left">Type slot number of pointer's element type.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]905 </tr>
906 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]907</table>
908<h3>Opaque Types</h3>
909<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]910 <tbody>
911 <tr>
912 <th><b>Type</b></th>
913 <th class="td_left"><b>Description</b></th>
914 </tr>
915 <tr>
916 <td><a href="#uint24_vbr">uint24_vbr</a></td>
917 <td class="td_left">Type ID For Opaque Types (17)</td>
918 </tr>
919 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]920</table>
Brian Gaeke715c90b2004-08-20 06:00:58 +0000[diff] [blame]921<h3>Packed Types</h3>
922<table>
923 <tbody>
924 <tr>
925 <th><b>Type</b></th>
926 <th class="td_left"><b>Description</b></th>
927 </tr>
928 <tr>
929 <td><a href="#uint24_vbr">uint24_vbr</a></td>
930 <td class="td_left">Type ID for Packed Types (18)</td>
931 </tr>
932 <tr>
933 <td><a href="#uint24_vbr">uint24_vbr</a></td>
934 <td class="td_left">Slot number of packed vector's element type.</td>
935 </tr>
936 <tr>
937 <td><a href="#uint32_vbr">uint32_vbr</a></td>
938 <td class="td_left">The number of elements in the packed vector.</td>
939 </tr>
940 </tbody>
941</table>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]942</div>
943<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]944<div class="doc_subsection"><a name="globalinfo">Module Global Info</a>
945</div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]946<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]947<p>The module global info block contains the definitions of all global
948variables including their initializers and the <em>declaration</em> of
949all functions. The format is shown in the table below:</p>
950<table>
951 <tbody>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]952 <tr>
953 <th><b>Type</b></th>
954 <th class="td_left"><b>Field Description</b></th>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]955 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]956 <tr>
957 <td><a href="#block">block</a></td>
958 <td class="td_left">Module global info identifier (0x05) + size<br>
959 </td>
960 </tr>
961 <tr>
962 <td><a href="#zlist">zlist</a>(<a href="#globalvar">globalvar</a>)</td>
963 <td class="td_left">A zero terminated list of global var
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]964definitions occurring in the module.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]965 </tr>
966 <tr>
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]967 <td><a href="#zlist">zlist</a>(<a href="#funcfield">funcfield</a>)</td>
968 <td class="td_left">A zero terminated list of function definitions
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]969occurring in the module.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]970 </tr>
971 <tr>
972 <td style="vertical-align: top;"><a href="#llist">llist</a>(<a
973 href="#string">string</a>)<br>
974 </td>
975 <td style="vertical-align: top; text-align: left;">A length list
976of strings that specify the names of the libraries that this module
977depends upon.<br>
978 </td>
979 </tr>
980 <tr>
981 <td style="vertical-align: top;"><a href="#string">string</a><br>
982 </td>
983 <td style="vertical-align: top; text-align: left;">The target
984triple for the module (blank means no target triple specified, i.e. a
985platform independent module).<br>
986 </td>
987 </tr>
988 </tbody>
989</table>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]990</div>
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]991
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]992<!-- _______________________________________________________________________ -->
993<div class="doc_subsubsection"><a name="globalvar">Global Variable Field</a>
994</div>
995<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]996<p>Global variables are written using an <a href="#uint32_vbr">uint32_vbr</a>
997that encodes information about the global variable and a list of the
998constant initializers for the global var, if any.</p>
999<p>The table below provides the bit layout of the first <a
1000 href="#uint32_vbr">uint32_vbr</a> that describes the global variable.</p>
1001<table>
1002 <tbody>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]1003 <tr>
1004 <th><b>Type</b></th>
1005 <th class="td_left"><b>Description</b></th>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]1006 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1007 <tr>
1008 <td><a href="#bit">bit(0)</a></td>
1009 <td class="td_left">Is constant?</td>
1010 </tr>
1011 <tr>
1012 <td><a href="#bit">bit(1)</a></td>
1013 <td class="td_left">Has initializer? Note that this bit
1014determines whether the constant initializer field (described below)
1015follows. </td>
1016 </tr>
1017 <tr>
1018 <td><a href="#bit">bit(2-4)</a></td>
1019 <td class="td_left">Linkage type: 0=External, 1=Weak,
10202=Appending, 3=Internal, 4=LinkOnce</td>
1021 </tr>
1022 <tr>
1023 <td><a href="#bit">bit(5-31)</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1024 <td class="td_left">Type slot number of type for the global variable.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1025 </tr>
1026 </tbody>
1027</table>
1028<p>The table below provides the format of the constant initializers for
1029the global variable field, if it has one.</p>
1030<table>
1031 <tbody>
1032 <tr>
1033 <th><b>Type</b></th>
1034 <th class="td_left"><b>Description</b></th>
1035 </tr>
1036 <tr>
1037 <td>(<a href="#zlist">zlist</a>(<a href="#uint32_vbr">uint32_vbr</a>))?
1038 </td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1039 <td class="td_left">An optional zero-terminated list of value slot
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1040numbers of the global variable's constant initializer.</td>
1041 </tr>
1042 </tbody>
1043</table>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1044</div>
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]1045
1046<!-- _______________________________________________________________________ -->
1047<div class="doc_subsubsection"><a name="funcfield">Function Field</a>
1048</div>
1049<div class="doc_text">
1050<p>Functions are written using an <a href="#uint32_vbr">uint32_vbr</a>
1051that encodes information about the function and a set of flags.</p>
1052
1053<p>The table below provides the bit layout of the <a
1054href="#uint32_vbr">uint32_vbr</a> that describes the function.</p>
1055
1056<table>
1057 <tbody>
1058 <tr>
1059 <th><b>Type</b></th>
1060 <th class="td_left"><b>Description</b></th>
1061 </tr>
1062 <tr>
Chris Lattnerced62222004-11-15 22:54:50 +0000[diff] [blame]1063 <td><a href="#bit">bit(0-3)</a></td>
Chris Lattnerbad10ee2005-05-06 22:57:40 +0000[diff] [blame]1064 <td class="td_left">
1065 Encodes the calling convention number of the function. If this number is
1066 zero, this field is followed by a vbr indicating the CC#. Otherwise, the
1067 CC number of the function is the value of this field minus one.
1068 </td>
Chris Lattnerced62222004-11-15 22:54:50 +0000[diff] [blame]1069 </tr>
1070 <tr>
1071 <td><a href="#bit">bit(4)</a></td>
1072 <td class="td_left">If this bit is set to 1, the indicated function is
1073 external, and there is no <a href="#functiondefs">Function Definiton
1074 Block</a> in the bytecode file for the function.</td>
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]1075 </tr>
1076 <tr>
1077 <td><a href="#bit">bit(5-)</a></td>
1078 <td class="td_left">Type slot number of type for the function.</td>
1079 </tr>
1080 </tbody>
1081</table>
1082
1083</div>
1084
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1085<!-- _______________________________________________________________________ -->
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1086<div class="doc_subsection"><a name="constantpool">Constant Pool</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1087<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1088<p>A constant pool defines as set of constant values. There are
1089actually two types of constant pool blocks: one for modules and one for
1090functions. For modules, the block begins with the constant strings
1091encountered anywhere in the module. For functions, the block begins
1092with types only encountered in the function. In both cases the header
1093is identical. The tables that follow, show the header, module constant
1094pool preamble, function constant pool preamble, and the part common to
1095both function and module constant pools.</p>
1096<p><b>Common Block Header</b></p>
1097<table>
1098 <tbody>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1099 <tr>
1100 <th><b>Type</b></th>
1101 <th class="td_left"><b>Field Description</b></th>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1102 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1103 <tr>
1104 <td><a href="#block">block</a></td>
1105 <td class="td_left">Constant pool identifier (0x03) + size<br>
1106 </td>
1107 </tr>
1108 </tbody>
1109</table>
1110<p><b>Module Constant Pool Preamble (constant strings)</b></p>
1111<table>
1112 <tbody>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1113 <tr>
1114 <th><b>Type</b></th>
1115 <th class="td_left"><b>Field Description</b></th>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1116 </tr>
1117 <tr>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1118 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1119 <td class="td_left">The number of constant strings that follow.</td>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1120 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1121 <tr>
1122 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1123 <td class="td_left">Zero. This identifies the following "plane"
1124as containing the constant strings. This is needed to identify it
1125uniquely from other constant planes that follow. </td>
1126 </tr>
1127 <tr>
1128 <td><a href="#uint24_vbr">uint24_vbr</a>+</td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1129 <td class="td_left">Type slot number of the constant string's type.
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1130Note that the constant string's type implicitly defines the length of
1131the string. </td>
1132 </tr>
1133 </tbody>
1134</table>
1135<p><b>Function Constant Pool Preamble (function types)</b></p>
1136<p>The structure of the types for functions is identical to the <a
1137 href="#globaltypes">Global Type Pool</a>. Please refer to that section
1138for the details. </p>
1139<p><b>Common Part (other constants)</b></p>
1140<table>
1141 <tbody>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1142 <tr>
1143 <th><b>Type</b></th>
1144 <th class="td_left"><b>Field Description</b></th>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1145 </tr>
1146 <tr>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1147 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1148 <td class="td_left">Number of entries in this type plane.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1149 </tr>
1150 <tr>
1151 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1152 <td class="td_left">Type slot number of this plane.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1153 </tr>
1154 <tr>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]1155 <td><a href="#constant">constant</a>+</td>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1156 <td class="td_left">The definition of a constant (see below).</td>
1157 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1158 </tbody>
1159</table>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1160</div>
1161<!-- _______________________________________________________________________ -->
1162<div class="doc_subsubsection"><a name="constant">Constant Field</a></div>
1163<div class="doc_text">
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1164<p>Constants come in many shapes and flavors. The sections that follow
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1165define the format for each of them. All constants start with a <a
1166 href="#uint32_vbr">uint32_vbr</a> encoded integer that provides the
1167number of operands for the constant. For primitive, structure, and
1168array constants, this will always be zero since those types of
1169constants have no operands. In this case, we have the following field
1170definitions:</p>
1171<ul>
1172 <li><b>Bool</b>. This is written as an <a href="#uint32_vbr">uint32_vbr</a>
1173of value 1U or 0U.</li>
1174 <li><b>Signed Integers (sbyte,short,int,long)</b>. These are written
1175as an <a href="#int64_vbr">int64_vbr</a> with the corresponding value.</li>
1176 <li><b>Unsigned Integers (ubyte,ushort,uint,ulong)</b>. These are
1177written as an <a href="#uint64_vbr">uint64_vbr</a> with the
1178corresponding value. </li>
1179 <li><b>Floating Point</b>. Both the float and double types are
1180written literally in binary format.</li>
1181 <li><b>Arrays</b>. Arrays are written simply as a list of <a
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1182 href="#uint32_vbr">uint32_vbr</a> encoded value slot numbers to the constant
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1183element values.</li>
1184 <li><b>Structures</b>. Structures are written simply as a list of <a
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1185 href="#uint32_vbr">uint32_vbr</a> encoded value slot numbers to the constant
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1186field values of the structure.</li>
1187</ul>
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]1188
1189<p>When the number of operands to the constant is one, we have an 'undef' value
1190of the specified type.</p>
1191
1192<p>When the number of operands to the constant is greater than one, we have a
1193constant expression and its field format is provided in the table below, and the
1194number is equal to the number of operands+1.</p>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1195<table>
1196 <tbody>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1197 <tr>
1198 <th><b>Type</b></th>
1199 <th class="td_left"><b>Field Description</b></th>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1200 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1201 <tr>
1202 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1203 <td class="td_left">Op code of the instruction for the constant
1204expression.</td>
1205 </tr>
1206 <tr>
1207 <td><a href="#uint32_vbr">uint32_vbr</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1208 <td class="td_left">The value slot number of the constant value for an
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1209operand.<sup>1</sup></td>
1210 </tr>
1211 <tr>
1212 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1213 <td class="td_left">The type slot number for the type of the constant
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1214value for an operand.<sup>1</sup></td>
1215 </tr>
1216 </tbody>
1217</table>
1218Notes:
1219<ol>
1220 <li>Both these fields are repeatable but only in pairs.</li>
1221</ol>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1222</div>
1223<!-- _______________________________________________________________________ -->
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1224<div class="doc_subsection"><a name="functiondefs">Function Definition</a></div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1225<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1226<p>Function definitions contain the linkage, constant pool or
1227compaction table, instruction list, and symbol table for a function.
1228The following table shows the structure of a function definition.</p>
1229<table>
1230 <tbody>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1231 <tr>
1232 <th><b>Type</b></th>
1233 <th class="td_left"><b>Field Description</b></th>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1234 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1235 <tr>
1236 <td><a href="#block">block</a><br>
1237 </td>
1238 <td class="td_left">Function definition block identifier (0x02) +
1239size<br>
1240 </td>
1241 </tr>
1242 <tr>
1243 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1244 <td class="td_left">The linkage type of the function: 0=External,
12451=Weak, 2=Appending, 3=Internal, 4=LinkOnce<sup>1</sup></td>
1246 </tr>
1247 <tr>
1248 <td><a href="#block">block</a></td>
1249 <td class="td_left">The <a href="#constantpool">constant pool</a>
1250block for this function.<sup>2</sup></td>
1251 </tr>
1252 <tr>
1253 <td><a href="#block">block</a></td>
1254 <td class="td_left">The <a href="#compactiontable">compaction
1255table</a> block for the function.<sup>2</sup></td>
1256 </tr>
1257 <tr>
1258 <td><a href="#block">block</a></td>
1259 <td class="td_left">The <a href="#instructionlist">instruction
1260list</a> for the function.</td>
1261 </tr>
1262 <tr>
1263 <td><a href="#block">block</a></td>
Reid Spencer8996e552004-08-17 00:49:03 +0000[diff] [blame]1264 <td class="td_left">The function's <a href="#symtab">symbol
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1265table</a> containing only those symbols pertinent to the function
1266(mostly block labels).</td>
1267 </tr>
1268 </tbody>
1269</table>
1270Notes:
1271<ol>
1272 <li>Note that if the linkage type is "External" then none of the
1273other fields will be present as the function is defined elsewhere.</li>
1274 <li>Note that only one of the constant pool or compaction table will
1275be written. Compaction tables are only written if they will actually
1276save bytecode space. If not, then a regular constant pool is written.</li>
1277</ol>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1278</div>
1279<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1280<div class="doc_subsection"><a name="compactiontable">Compaction Table</a>
1281</div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1282<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1283<p>Compaction tables are part of a function definition. They are merely
1284a device for reducing the size of bytecode files. The size of a
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1285bytecode file is dependent on the <em>values</em> of the slot numbers
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1286used because larger values use more bytes in the variable bit rate
1287encoding scheme. Furthermore, the compressed instruction format
1288reserves only six bits for the type of the instruction. In large
1289modules, declaring hundreds or thousands of types, the values of the
1290slot numbers can be quite large. However, functions may use only a
1291small fraction of the global types. In such cases a compaction table is
1292created that maps the global type and value slot numbers to smaller
1293values used by a function. Functions will contain either a
1294function-specific constant pool <em>or</em> a compaction table but not
1295both. Compaction tables have the format shown in the table below.</p>
1296<table>
1297 <tbody>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1298 <tr>
1299 <th><b>Type</b></th>
1300 <th class="td_left"><b>Field Description</b></th>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1301 </tr>
1302 <tr>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1303 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1304 <td class="td_left">The number of types that follow</td>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1305 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1306 <tr>
1307 <td><a href="#uint24_vbr">uint24_vbr</a>+</td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1308 <td class="td_left">The type slot number in the global types of
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1309the type that will be referenced in the function with the index of this
1310entry in the compaction table.</td>
1311 </tr>
1312 <tr>
1313 <td><a href="#type_len">type_len</a></td>
1314 <td class="td_left">An encoding of the type and number of values
1315that follow. This field's encoding varies depending on the size of the
1316type plane. See <a href="#type_len">Type and Length</a> for further
1317details.</td>
1318 </tr>
1319 <tr>
1320 <td><a href="#uint32_vbr">uint32_vbr</a>+</td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1321 <td class="td_left">The value slot number in the global values
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1322that will be referenced in the function with the index of this entry in
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1323the compaction table.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1324 </tr>
1325 </tbody>
1326</table>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1327</div>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1328<!-- _______________________________________________________________________ -->
1329<div class="doc_subsubsection"><a name="type_len">Type and Length</a></div>
1330<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1331<p>The type and length of a compaction table type plane is encoded
1332differently depending on the length of the plane. For planes of length
13331 or 2, the length is encoded into bits 0 and 1 of a <a
1334 href="#uint32_vbr">uint32_vbr</a> and the type is encoded into bits
13352-31. Because type numbers are often small, this often saves an extra
1336byte per plane. If the length of the plane is greater than 2 then the
1337encoding uses a <a href="#uint32_vbr">uint32_vbr</a> for each of the
1338length and type, in that order.</p>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1339</div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1340<!-- _______________________________________________________________________ -->
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1341<div class="doc_subsection"><a name="instructionlist">Instruction List</a></div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1342<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1343<p>The instructions in a function are written as a simple list. Basic
1344blocks are inferred by the terminating instruction types. The format of
1345the block is given in the following table.</p>
1346<table>
1347 <tbody>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1348 <tr>
1349 <th><b>Type</b></th>
1350 <th class="td_left"><b>Field Description</b></th>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1351 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1352 <tr>
1353 <td><a href="#block">block</a><br>
1354 </td>
1355 <td class="td_left">Instruction list identifier (0x07) + size<br>
1356 </td>
1357 </tr>
1358 <tr>
1359 <td><a href="#instruction">instruction</a>+</td>
1360 <td class="td_left">An instruction. Instructions have a variety
1361of formats. See <a href="#instruction">Instructions</a> for details.</td>
1362 </tr>
1363 </tbody>
1364</table>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1365</div>
Chris Lattnerf97fa592005-11-05 22:20:06 +0000[diff] [blame^]1366
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1367<!-- _______________________________________________________________________ -->
Chris Lattnerf97fa592005-11-05 22:20:06 +0000[diff] [blame^]1368<div class="doc_subsection"><a name="instructions">Instructions</a></div>
1369
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1370<div class="doc_text">
Chris Lattnerf97fa592005-11-05 22:20:06 +0000[diff] [blame^]1371<p>Instructions are written out one at a time as distinct units. Each
1372instruction
1373record contains at least an <a href="#opcodes">opcode</a> and a type field,
1374and may contain a list of operands (whose interpretation depends on the opcode).
1375Based on the number of operands, the
1376<a href="#instencode">instruction is encoded</a> in a
1377dense format that tries to encoded each instruction into 32-bits if
1378possible. </p>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1379</div>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1380
1381<!-- _______________________________________________________________________ -->
Chris Lattnerf97fa592005-11-05 22:20:06 +0000[diff] [blame^]1382<div class="doc_subsubsection"><a name="opcodes">Instruction Opcodes</a></div>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1383<div class="doc_text">
1384 <p>Instructions encode an opcode that identifies the kind of instruction.
1385 Opcodes are an enumerated integer value. The specific values used depend on
1386 the version of LLVM you're using. The opcode values are defined in the
Misha Brukmana36b6e52004-11-07 00:59:58 +0000[diff] [blame]1387 <a href="http://llvm.cs.uiuc.edu/cvsweb/cvsweb.cgi/llvm/include/llvm/Instruction.def">
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1388 <tt>include/llvm/Instruction.def</tt></a> file. You should check there for the
1389 most recent definitions. The table below provides the opcodes defined as of
Nate Begeman52ca9e42004-08-27 07:59:37 +0000[diff] [blame]1390 the writing of this document. The table associates each opcode mnemonic with
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1391 its enumeration value and the bytecode and LLVM version numbers in which the
1392 opcode was introduced.</p>
1393 <table>
1394 <tbody>
1395 <tr>
1396 <th>Opcode</th>
1397 <th>Number</th>
1398 <th>Bytecode Version</th>
1399 <th>LLVM Version</th>
1400 </tr>
1401 <tr><td colspan="4"><b>Terminator Instructions</b></td></tr>
1402 <tr><td>Ret</td><td>1</td><td>1</td><td>1.0</td></tr>
1403 <tr><td>Br</td><td>2</td><td>1</td><td>1.0</td></tr>
1404 <tr><td>Switch</td><td>3</td><td>1</td><td>1.0</td></tr>
1405 <tr><td>Invoke</td><td>4</td><td>1</td><td>1.0</td></tr>
1406 <tr><td>Unwind</td><td>5</td><td>1</td><td>1.0</td></tr>
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]1407 <tr><td>Unreachable</td><td>6</td><td>1</td><td>1.4</td></tr>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1408 <tr><td colspan="4"><b>Binary Operators</b></td></tr>
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]1409 <tr><td>Add</td><td>7</td><td>1</td><td>1.0</td></tr>
1410 <tr><td>Sub</td><td>8</td><td>1</td><td>1.0</td></tr>
1411 <tr><td>Mul</td><td>9</td><td>1</td><td>1.0</td></tr>
1412 <tr><td>Div</td><td>10</td><td>1</td><td>1.0</td></tr>
1413 <tr><td>Rem</td><td>11</td><td>1</td><td>1.0</td></tr>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1414 <tr><td colspan="4"><b>Logical Operators</b></td></tr>
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]1415 <tr><td>And</td><td>12</td><td>1</td><td>1.0</td></tr>
1416 <tr><td>Or</td><td>13</td><td>1</td><td>1.0</td></tr>
1417 <tr><td>Xor</td><td>14</td><td>1</td><td>1.0</td></tr>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1418 <tr><td colspan="4"><b>Binary Comparison Operators</b></td></tr>
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]1419 <tr><td>SetEQ</td><td>15</td><td>1</td><td>1.0</td></tr>
1420 <tr><td>SetNE</td><td>16</td><td>1</td><td>1.0</td></tr>
1421 <tr><td>SetLE</td><td>17</td><td>1</td><td>1.0</td></tr>
1422 <tr><td>SetGE</td><td>18</td><td>1</td><td>1.0</td></tr>
1423 <tr><td>SetLT</td><td>19</td><td>1</td><td>1.0</td></tr>
1424 <tr><td>SetGT</td><td>20</td><td>1</td><td>1.0</td></tr>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1425 <tr><td colspan="4"><b>Memory Operators</b></td></tr>
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]1426 <tr><td>Malloc</td><td>21</td><td>1</td><td>1.0</td></tr>
1427 <tr><td>Free</td><td>22</td><td>1</td><td>1.0</td></tr>
1428 <tr><td>Alloca</td><td>23</td><td>1</td><td>1.0</td></tr>
1429 <tr><td>Load</td><td>24</td><td>1</td><td>1.0</td></tr>
1430 <tr><td>Store</td><td>25</td><td>1</td><td>1.0</td></tr>
1431 <tr><td>GetElementPtr</td><td>26</td><td>1</td><td>1.0</td></tr>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1432 <tr><td colspan="4"><b>Other Operators</b></td></tr>
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]1433 <tr><td>PHI</td><td>27</td><td>1</td><td>1.0</td></tr>
1434 <tr><td>Cast</td><td>28</td><td>1</td><td>1.0</td></tr>
1435 <tr><td>Call</td><td>29</td><td>1</td><td>1.0</td></tr>
1436 <tr><td>Shl</td><td>30</td><td>1</td><td>1.0</td></tr>
1437 <tr><td>Shr</td><td>31</td><td>1</td><td>1.0</td></tr>
1438 <tr><td>VANext</td><td>32</td><td>1</td><td>1.0</td></tr>
1439 <tr><td>VAArg</td><td>33</td><td>1</td><td>1.0</td></tr>
1440 <tr><td>Select</td><td>34</td><td>2</td><td>1.2</td></tr>
Reid Spencera5681772005-05-14 00:06:06 +0000[diff] [blame]1441 <tr><td colspan="4">
1442 <b>Pseudo Instructions<a href="#pi_note">*</a></b>
1443 </td></tr>
1444 <tr><td>Invoke+CC </td><td>56</td><td>5</td><td>1.5</td></tr>
1445 <tr><td>Invoke+FastCC</td><td>57</td><td>5</td><td>1.5</td></tr>
1446 <tr><td>Call+CC</td><td>58</td><td>5</td><td>1.5</td></tr>
1447 <tr><td>Call+FastCC+TailCall</td><td>59</td><td>5</td><td>1.5</td></tr>
1448 <tr><td>Call+FastCC</td><td>60</td><td>5</td><td>1.5</td></tr>
1449 <tr><td>Call+CCC+TailCall</td><td>61</td><td>5</td><td>1.5</td></tr>
1450 <tr><td>Load+Volatile</td><td>62</td><td>3</td><td>1.3</td></tr>
1451 <tr><td>Store+Volatile</td><td>63</td><td>3</td><td>1.3</td></tr>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1452 </tbody>
1453 </table>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1454
Reid Spencera5681772005-05-14 00:06:06 +0000[diff] [blame]1455<p><b><a name="pi_note">* Note: </a></b>
Chris Lattnerf97fa592005-11-05 22:20:06 +0000[diff] [blame^]1456These aren't really opcodes from an LLVM language perspective. They encode
Reid Spencera5681772005-05-14 00:06:06 +0000[diff] [blame]1457information into other opcodes without reserving space for that information.
1458For example, opcode=63 is a Volatile Store. The opcode for this
1459instruction is 25 (Store) but we encode it as 63 to indicate that is a Volatile
1460Store. The same is done for the calling conventions and tail calls.
1461In each of these entries in range 56-63, the opcode is documented as the base
1462opcode (Invoke, Call, Store) plus some set of modifiers, as follows:</p>
1463<dl>
1464 <dt>CC</dt>
Chris Lattner120bc6d2005-05-14 01:30:15 +0000[diff] [blame]1465 <dd>This means an arbitrary calling convention is specified
1466 in a VBR that follows the opcode. This is used when the instruction cannot
1467 be encoded with one of the more compact forms.
Reid Spencera5681772005-05-14 00:06:06 +0000[diff] [blame]1468 </dd>
1469 <dt>FastCC</dt>
1470 <dd>This indicates that the Call or Invoke is using the FastCC calling
Chris Lattner120bc6d2005-05-14 01:30:15 +0000[diff] [blame]1471 convention.</dd>
Reid Spencera5681772005-05-14 00:06:06 +0000[diff] [blame]1472 <dt>CCC</dt>
Chris Lattner120bc6d2005-05-14 01:30:15 +0000[diff] [blame]1473 <dd>This indicates that the Call or Invoke is using the native "C" calling
1474 convention.</dd>
Reid Spencera5681772005-05-14 00:06:06 +0000[diff] [blame]1475 <dt>TailCall</dt>
Chris Lattner120bc6d2005-05-14 01:30:15 +0000[diff] [blame]1476 <dd>This indicates that the Call has the 'tail' modifier.</dd>
Reid Spencera5681772005-05-14 00:06:06 +0000[diff] [blame]1477</dl>
Chris Lattnerf97fa592005-11-05 22:20:06 +0000[diff] [blame^]1478</div>
1479
1480
1481<!-- _______________________________________________________________________ -->
1482<div class="doc_subsubsection"><a name="instencode">Instruction
1483Encoding</a></div>
1484
1485<div class="doc_text">
1486<p>For brevity, instructions are written in one of four formats,
1487depending on the number of operands to the instruction. Each
1488instruction begins with a <a href="#uint32_vbr">uint32_vbr</a> that
1489encodes the type of the instruction as well as other things. The tables
1490that follow describe the format of this first part of each instruction.</p>
1491<p><b>Instruction Format 0</b></p>
1492<p>This format is used for a few instructions that can't easily be
1493shortened because they have large numbers of operands (e.g. PHI Node or
1494getelementptr). Each of the opcode, type, and operand fields is found in
1495successive fields.</p>
1496<table>
1497 <tbody>
1498 <tr>
1499 <th><b>Type</b></th>
1500 <th class="td_left"><b>Field Description</b></th>
1501 </tr>
1502 <tr>
1503 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1504 <td class="td_left">Specifies the opcode of the instruction. Note
1505that for compatibility with the other instruction formats, the opcode
1506is shifted left by 2 bits. Bits 0 and 1 must have value zero for this
1507format.</td>
1508 </tr>
1509 <tr>
1510 <td><a href="#uint24_vbr">uint24_vbr</a></td>
1511 <td class="td_left">Provides the type slot number of the result type of
1512 the instruction.</td>
1513 </tr>
1514 <tr>
1515 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1516 <td class="td_left">The number of operands that follow.</td>
1517 </tr>
1518 <tr>
1519 <td><a href="#uint32_vbr">uint32_vbr</a>+</td>
1520 <td class="td_left">The slot number of the value(s) for the operand(s).
1521 <sup>1</sup></td>
1522 </tr>
1523 </tbody>
1524</table>
1525Notes:
1526<ol>
1527 <li>Note that if the instruction is a getelementptr and the type of
1528the operand is a sequential type (array or pointer) then the slot
1529number is shifted up two bits and the low order bits will encode the
1530type of index used, as follows: 0=uint, 1=int, 2=ulong, 3=long.</li>
1531</ol>
1532<p><b>Instruction Format 1</b></p>
1533<p>This format encodes the opcode, type and a single operand into a
1534single <a href="#uint32_vbr">uint32_vbr</a> as follows:</p>
1535<table>
1536 <tbody>
1537 <tr>
1538 <th><b>Bits</b></th>
1539 <th><b>Type</b></th>
1540 <th class="td_left"><b>Field Description</b></th>
1541 </tr>
1542 <tr>
1543 <td>0-1</td>
1544 <td>constant "1"</td>
1545 <td class="td_left">These two bits must be the value 1 which identifies
1546 this as an instruction of format 1.</td>
1547 </tr>
1548 <tr>
1549 <td>2-7</td>
1550 <td><a href="#instructions">opcode</a></td>
1551 <td class="td_left">Specifies the opcode of the instruction. Note that
1552 the maximum opcode value is 63.</td>
1553 </tr>
1554 <tr>
1555 <td>8-19</td>
1556 <td><a href="#unsigned">unsigned</a></td>
1557 <td class="td_left">Specifies the slot number of the type for this
1558 instruction. Maximum slot number is 2<sup>12</sup>-1=4095.</td>
1559 </tr>
1560 <tr>
1561 <td>20-31</td>
1562 <td><a href="#unsigned">unsigned</a></td>
1563 <td class="td_left">Specifies the slot number of the value for the
1564 first operand. Maximum slot number is 2<sup>12</sup>-1=4095. Note that
1565 the value 2<sup>12</sup>-1 denotes zero operands.</td>
1566 </tr>
1567 </tbody>
1568</table>
1569<p><b>Instruction Format 2</b></p>
1570<p>This format encodes the opcode, type and two operands into a single <a
1571 href="#uint32_vbr">uint32_vbr</a> as follows:</p>
1572<table>
1573 <tbody>
1574 <tr>
1575 <th><b>Bits</b></th>
1576 <th><b>Type</b></th>
1577 <th class="td_left"><b>Field Description</b></th>
1578 </tr>
1579 <tr>
1580 <td>0-1</td>
1581 <td>constant "2"</td>
1582 <td class="td_left">These two bits must be the value 2 which identifies
1583 this as an instruction of format 2.</td>
1584 </tr>
1585 <tr>
1586 <td>2-7</td>
1587 <td><a href="#instructions">opcode</a></td>
1588 <td class="td_left">Specifies the opcode of the instruction. Note that
1589 the maximum opcode value is 63.</td>
1590 </tr>
1591 <tr>
1592 <td>8-15</td>
1593 <td><a href="#unsigned">unsigned</a></td>
1594 <td class="td_left">Specifies the slot number of the type for this
1595 instruction. Maximum slot number is 2<sup>8</sup>-1=255.</td>
1596 </tr>
1597 <tr>
1598 <td>16-23</td>
1599 <td><a href="#unsigned">unsigned</a></td>
1600 <td class="td_left">Specifies the slot number of the value for the first
1601 operand. Maximum slot number is 2<sup>8</sup>-1=255.</td>
1602 </tr>
1603 <tr>
1604 <td>24-31</td>
1605 <td><a href="#unsigned">unsigned</a></td>
1606 <td class="td_left">Specifies the slot number of the value for the second
1607 operand. Maximum slot number is 2<sup>8</sup>-1=255.</td>
1608 </tr>
1609 </tbody>
1610</table>
1611<p><b>Instruction Format 3</b></p>
1612<p>This format encodes the opcode, type and three operands into a
1613single <a href="#uint32_vbr">uint32_vbr</a> as follows:</p>
1614<table>
1615 <tbody>
1616 <tr>
1617 <th><b>Bits</b></th>
1618 <th><b>Type</b></th>
1619 <th class="td_left"><b>Field Description</b></th>
1620 </tr>
1621 <tr>
1622 <td>0-1</td>
1623 <td>constant "3"</td>
1624 <td class="td_left">These two bits must be the value 3 which identifies
1625 this as an instruction of format 3.</td>
1626 </tr>
1627 <tr>
1628 <td>2-7</td>
1629 <td><a href="#instructions">opcode</a></td>
1630 <td class="td_left">Specifies the opcode of the instruction. Note that
1631 the maximum opcode value is 63.</td>
1632 </tr>
1633 <tr>
1634 <td>8-13</td>
1635 <td><a href="#unsigned">unsigned</a></td>
1636 <td class="td_left">Specifies the slot number of the type for this
1637 instruction. Maximum slot number is 2<sup>6</sup>-1=63.</td>
1638 </tr>
1639 <tr>
1640 <td>14-19</td>
1641 <td><a href="#unsigned">unsigned</a></td>
1642 <td class="td_left">Specifies the slot number of the value for the first
1643 operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
1644 </tr>
1645 <tr>
1646 <td>20-25</td>
1647 <td><a href="#unsigned">unsigned</a></td>
1648 <td class="td_left">Specifies the slot number of the value for the second
1649 operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
1650 </tr>
1651 <tr>
1652 <td>26-31</td>
1653 <td><a href="#unsigned">unsigned</a></td>
1654 <td class="td_left">Specifies the slot number of the value for the third
1655 operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
1656 </tr>
1657 </tbody>
1658</table>
1659</div>
Reid Spencera5681772005-05-14 00:06:06 +0000[diff] [blame]1660
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1661<!-- _______________________________________________________________________ -->
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]1662<div class="doc_subsection"><a name="symtab">Symbol Table</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1663<div class="doc_text">
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1664<p>A symbol table can be put out in conjunction with a module or a function. A
1665symbol table has a list of name/type associations followed by a list of
1666name/value associations. The name/value associations are organized into "type
1667planes" so that all values of a common type are listed together. Each type
1668plane starts with the number of entries in the plane and the type slot number
1669for all the values in that plane (so the type can be looked up in the global
1670type pool). For each entry in a type plane, the slot number of the value and
1671the name associated with that value are written. The format is given in the
1672table below. </p>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1673<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1674 <tbody>
1675 <tr>
1676 <th><b>Type</b></th>
1677 <th class="td_left"><b>Field Description</b></th>
1678 </tr>
1679 <tr>
1680 <td><a href="#block">block</a><br>
1681 </td>
1682 <td class="td_left">Symbol Table Identifier (0x04)</td>
1683 </tr>
1684 <tr>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1685 <td><a href="#llist">llist</a>(<a href="#symtab_entry">type_entry</a>)</td>
Reid Spencer8996e552004-08-17 00:49:03 +0000[diff] [blame]1686 <td class="td_left">A length list of symbol table entries for
1687 <tt>Type</tt>s
1688 </td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1689 </tr>
1690 <tr>
Reid Spencer8996e552004-08-17 00:49:03 +0000[diff] [blame]1691 <td><a href="#zlist">llist</a>(<a href="#symtab_plane">symtab_plane</a>)</td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1692 <td class="td_left">A length list of "type planes" of symbol table
Reid Spencer8996e552004-08-17 00:49:03 +0000[diff] [blame]1693 entries for <tt>Value</tt>s</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1694 </tr>
1695 </tbody>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]1696</table>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1697</div>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1698
1699<!-- _______________________________________________________________________ -->
1700<div class="doc_subsubsection"> <a name="type_entry">Symbol Table Type
1701Entry</a>
1702</div>
1703<div class="doc_text">
1704<p>A symbol table type entry associates a name with a type. The name is provided
1705simply as an array of chars. The type is provided as a type slot number (index)
1706into the global type pool. The format is given in the following table:</p>
1707<table>
1708 <tbody>
1709 <tr>
1710 <th><b>Type</b></th>
1711 <th class="td_left"><b>Field Description</b></th>
1712 </tr>
1713 <tr>
1714 <td><a href="#uint32_vbr">uint24_vbr</a></td>
1715 <td class="td_left">Type slot number of the type being given a
1716 name relative to the global type pool.
1717 </td>
1718 </tr>
1719 <tr>
1720 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1721 <td class="td_left">Length of the character array that follows.</td>
1722 </tr>
1723 <tr>
1724 <td><a href="#char">char</a>+</td>
1725 <td class="td_left">The characters of the name.</td>
1726 </tr>
1727 </tbody>
1728</table>
1729</div>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1730<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1731<div class="doc_subsubsection"> <a name="symtab_plane">Symbol Table
1732Plane</a>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1733</div>
1734<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1735<p>A symbol table plane provides the symbol table entries for all
1736values of a common type. The encoding is given in the following table:</p>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1737<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1738 <tbody>
1739 <tr>
1740 <th><b>Type</b></th>
1741 <th class="td_left"><b>Field Description</b></th>
1742 </tr>
1743 <tr>
1744 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1745 <td class="td_left">Number of entries in this plane.</td>
1746 </tr>
1747 <tr>
1748 <td><a href="#uint32_vbr">uint32_vbr</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1749 <td class="td_left">Type slot number of type for all values in this plane..</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1750 </tr>
1751 <tr>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1752 <td><a href="#value_entry">value_entry</a>+</td>
1753 <td class="td_left">The symbol table entries for to associate values with
1754 names.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1755 </tr>
1756 </tbody>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1757</table>
1758</div>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1759<!-- _______________________________________________________________________ -->
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1760<div class="doc_subsubsection"><a name="value_entry">Symbol Table Value
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1761Entry</a>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1762</div>
1763<div class="doc_text">
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1764<p>A symbol table value entry provides the assocation between a value and the
1765name given to the value. The value is referenced by its slot number. The
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1766format is given in the following table:</p>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1767<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1768 <tbody>
1769 <tr>
1770 <th><b>Type</b></th>
1771 <th class="td_left"><b>Field Description</b></th>
1772 </tr>
1773 <tr>
1774 <td><a href="#uint32_vbr">uint24_vbr</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1775 <td class="td_left">Value slot number of the value being given a name.
Reid Spencer8996e552004-08-17 00:49:03 +0000[diff] [blame]1776 </td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1777 </tr>
1778 <tr>
1779 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1780 <td class="td_left">Length of the character array that follows.</td>
1781 </tr>
1782 <tr>
1783 <td><a href="#char">char</a>+</td>
1784 <td class="td_left">The characters of the name.</td>
1785 </tr>
1786 </tbody>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1787</table>
1788</div>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1789
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1790<!-- *********************************************************************** -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1791<div class="doc_section"> <a name="versiondiffs">Version Differences</a>
1792</div>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1793<!-- *********************************************************************** -->
1794<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1795<p>This section describes the differences in the Bytecode Format across
1796LLVM
1797versions. The versions are listed in reverse order because it assumes
1798the current version is as documented in the previous sections. Each
1799section here
Chris Lattner1cc070c2004-07-05 18:05:48 +0000[diff] [blame]1800describes the differences between that version and the one that <i>follows</i>.
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1801</p>
1802</div>
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]1803
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1804<!-- _______________________________________________________________________ -->
Reid Spencer43dfdb72004-08-18 20:17:05 +0000[diff] [blame]1805<div class="doc_subsection"><a name="vers13">Version 1.3 Differences From
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]1806 1.4</a></div>
Reid Spencercf549e12004-08-17 07:43:43 +0000[diff] [blame]1807<!-- _______________________________________________________________________ -->
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]1808
1809<div class="doc_subsubsection">Unreachable Instruction</div>
1810<div class="doc_text">
1811 <p>The LLVM <a href="LangRef.html#i_unreachable">Unreachable</a> instruction
1812 was added in version 1.4 of LLVM. This caused all instruction numbers after
1813 it to shift down by one.</p>
1814</div>
1815
1816<div class="doc_subsubsection">Function Flags</div>
1817<div class="doc_text">
1818 <p>LLVM bytecode versions prior to 1.4 did not include the 5 bit offset
1819 in <a href="#funcfield">the function list</a> in the <a
1820 href="#globalinfo">Module Global Info</a> block.</p>
1821</div>
1822
1823<div class="doc_subsubsection">Function Flags</div>
1824<div class="doc_text">
1825 <p>LLVM bytecode versions prior to 1.4 did not include the 'undef' constant
1826 value, which affects the encoding of <a href="#constant">Constant
1827 Fields</a>.</p>
1828</div>
1829
Chris Lattner1dfc8e52004-10-16 00:29:30 +0000[diff] [blame]1830<!--
Reid Spencercf549e12004-08-17 07:43:43 +0000[diff] [blame]1831<div class="doc_subsubsection">Aligned Data</div>
1832<div class="doc_text">
1833 <p>In version 1.3, certain data items were aligned to 32-bit boundaries. In
1834 version 1.4, alignment of data was done away with completely. The need for
1835 alignment has gone away and the only thing it adds is bytecode file size
1836 overhead. In most cases this overhead was small. However, in functions with
1837 large numbers of format 0 instructions (GEPs and PHIs with lots of parameters)
1838 or regular instructions with large valued operands (e.g. because there's just
1839 a lot of instructions in the function) the overhead can be extreme. In one
1840 test case, the overhead was 44,000 bytes (34% of the total file size).
1841 Consequently in release 1.4, the decision was made to eliminate alignment
1842 altogether.</p>
1843 <p>In version 1.3 format, the following bytecode constructs were aligned (i.e.
1844 they were followed by one to three bytes of padding):</p>
1845 <ul>
1846 <li>All blocks.</li>
1847 <li>Instructions using the long format (format 0).</li>
1848 <li>All call instructions that called a var args function.</li>
1849 <li>The target triple (a string field at the end of the module block).</li>
1850 <li>The version field (immediately following the signature).</li>
1851 </ul>
1852 <p>None of these constructs are aligned in version 1.4</p>
1853</div>
Chris Lattner1dfc8e52004-10-16 00:29:30 +0000[diff] [blame]1854-->
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]1855
Reid Spencercf549e12004-08-17 07:43:43 +0000[diff] [blame]1856<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1857<div class="doc_subsection"><a name="vers12">Version 1.2 Differences
1858From 1.3</a></div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1859<!-- _______________________________________________________________________ -->
Chris Lattnera1dad812004-10-16 18:03:55 +0000[diff] [blame]1860
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1861<div class="doc_subsubsection">Type Derives From Value</div>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1862<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1863<p>In version 1.2, the Type class in the LLVM IR derives from the Value
1864class. This is not the case in version 1.3. Consequently, in version
18651.2 the notion of a "Type Type" was used to write out values that were
1866Types. The types always occuped plane 12 (corresponding to the
1867TypeTyID) of any type planed set of values. In 1.3 this representation
1868is not convenient because the TypeTyID (12) is not present and its
1869value is now used for LabelTyID. Consequently, the data structures
1870written that involve types do so by writing all the types first and
1871then each of the value planes according to those types. In version 1.2,
1872the types would have been written intermingled with the values.</p>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1873</div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1874<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1875<div class="doc_subsubsection">Restricted getelementptr Types</div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1876<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1877<p>In version 1.2, the getelementptr instruction required a ubyte type
1878index for accessing a structure field and a long type index for
1879accessing an array element. Consequently, it was only possible to
1880access structures of 255 or fewer elements. Starting in version 1.3,
1881this restriction was lifted. Structures must now be indexed with uint
1882constants. Arrays may now be indexed with int, uint, long, or ulong
1883typed values. The consequence of this was that the bytecode format had
1884to change in order to accommodate the larger range of structure indices.</p>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1885</div>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1886<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1887<div class="doc_subsubsection">Short Block Headers</div>
1888<div class="doc_text">
1889<p>In version 1.2, block headers were always 8 bytes being comprised of
1890both an unsigned integer type and an unsigned integer size. For very
1891small modules, these block headers turn out to be a large fraction of
1892the total bytecode file size. In an attempt to make these small files
1893smaller, the type and size information was encoded into a single
1894unsigned integer (4 bytes) comprised of 5 bits for the block type
1895(maximum 31 block types) and 27 bits for the block size (max
1896~134MBytes). These limits seemed sufficient for any blocks or sizes
1897forseen in the future. Note that the module block, which encloses all
1898the other blocks is still written as 8 bytes since bytecode files
1899larger than 134MBytes might be possible.</p>
1900</div>
1901<!-- _______________________________________________________________________ -->
1902<div class="doc_subsubsection">Dependent Libraries and Target Triples</div>
1903<div class="doc_text">
1904<p>In version 1.2, the bytecode format does not store module's target
1905triple or dependent. These fields have been added to the end of the <a
1906 href="#globalinfo">module global info block</a>. The purpose of these
1907fields is to allow a front end compiler to specifiy that the generated
1908module is specific to a particular target triple (operating
1909system/manufacturer/processor) which makes it non-portable; and to
1910allow front end compilers to specify the list of libraries that the
1911module depends on for successful linking.</p>
1912</div>
1913<!-- _______________________________________________________________________ -->
1914<div class="doc_subsubsection">Types Restricted to 24-bits</div>
1915<div class="doc_text">
1916<p>In version 1.2, type slot identifiers were written as 32-bit VBR
1917quantities. In 1.3 this has been reduced to 24-bits in order to ensure
1918that it is not possible to overflow the type field of a global variable
1919definition. 24-bits for type slot numbers is deemed sufficient for any
1920practical use of LLVM.</p>
1921</div>
1922<!-- _______________________________________________________________________ -->
1923<!-- _______________________________________________________________________ -->
1924<div class="doc_subsection"><a name="vers11">Version 1.1 Differences
1925From 1.2 </a></div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1926<!-- _______________________________________________________________________ -->
1927<div class="doc_subsubsection">Explicit Primitive Zeros</div>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1928<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1929<p>In version 1.1, the zero value for primitives was explicitly encoded
1930into the bytecode format. Since these zero values are constant values
1931in the LLVM IR and never change, there is no reason to explicitly
1932encode them. This explicit encoding was removed in version 1.2.</p>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1933</div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1934<!-- _______________________________________________________________________ -->
1935<div class="doc_subsubsection">Inconsistent Module Global Info</div>
1936<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1937<p>In version 1.1, the Module Global Info block was not aligned causing
1938the next block to be read in on an unaligned boundary. This problem was
1939corrected in version 1.2.<br>
1940<br>
1941</p>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1942</div>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1943<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1944<div class="doc_subsection"><a name="vers10">Version 1.0 Differences
1945From 1.1</a></div>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1946<div class="doc_text">
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1947<p>None. Version 1.0 and 1.1 bytecode formats are identical.</p>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1948</div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1949<!-- *********************************************************************** -->
1950<hr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1951<address> <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
1952 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
1953<a href="http://validator.w3.org/check/referer"><img
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1955<a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and <a
1956 href="mailto:sabre@nondot.org">Chris Lattner</a><br>
1957<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
1958Last modified: $Date$
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1959</address>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1960</body>
1961</html>