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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>
42 <li><a href="#instructionlist">Instruction List</a></li>
43 <li><a href="#symtab">Symbol Table</a></li>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]44 </ol>
45 </li>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]46 <li><a href="#versiondiffs">Version Differences</a>
47 <ol>
Reid Spencer43dfdb72004-08-18 20:17:05 +0000[diff] [blame]48 <li><a href="#vers13">Version 1.3 Differences From 1.4</a></li>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]49 <li><a href="#vers12">Version 1.2 Differences From 1.3</a></li>
50 <li><a href="#vers11">Version 1.1 Differences From 1.2</a></li>
51 <li><a href="#vers10">Version 1.0 Differences From 1.1</a></li>
52 </ol>
53 </li>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]54</ol>
Chris Lattner8dabb502004-05-25 17:44:58 +0000[diff] [blame]55<div class="doc_author">
56<p>Written by <a href="mailto:rspencer@x10sys.com">Reid Spencer</a>
57</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]58</div>
59<!-- *********************************************************************** -->
60<div class="doc_section"> <a name="abstract">Abstract </a></div>
61<!-- *********************************************************************** -->
62<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]63<p>This document describes the LLVM bytecode file format. It specifies
64the binary encoding rules of the bytecode file format so that
65equivalent systems can encode bytecode files correctly. The LLVM
66bytecode representation is used to store the intermediate
67representation on disk in compacted form.</p>
68<p>The LLVM bytecode format may change in the future, but LLVM will
69always be backwards compatible with older formats. This document will
70only describe the most current version of the bytecode format. See <a
71 href="#versiondiffs">Version Differences</a> for the details on how
72the current version is different from previous versions.</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]73</div>
74<!-- *********************************************************************** -->
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]75<div class="doc_section"> <a name="concepts">Concepts</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]76<!-- *********************************************************************** -->
77<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]78<p>This section describes the general concepts of the bytecode file
79format without getting into specific layout details. It is recommended
80that you read this section thoroughly before interpreting the detailed
81descriptions.</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]82</div>
83<!-- _______________________________________________________________________ -->
84<div class="doc_subsection"><a name="blocks">Blocks</a> </div>
85<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]86<p>LLVM bytecode files consist simply of a sequence of blocks of bytes
87using a binary encoding Each block begins with an header of two
88unsigned integers. The first value identifies the type of block and the
89second value provides the size of the block in bytes. The block
90identifier is used because it is possible for entire blocks to be
91omitted from the file if they are empty. The block identifier helps the
92reader determine which kind of block is next in the file. Note that
93blocks can be nested within other blocks.</p>
94<p> All blocks are variable length, and the block header specifies the
95size of the block. All blocks begin on a byte index that is aligned to
96an even 32-bit boundary. That is, the first block is 32-bit aligned
97because it starts at offset 0. Each block is padded with zero fill
98bytes to ensure that the next block also starts on a 32-bit boundary.</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]99</div>
100<!-- _______________________________________________________________________ -->
101<div class="doc_subsection"><a name="lists">Lists</a> </div>
102<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]103<p>LLVM Bytecode blocks often contain lists of things of a similar
104type. For example, a function contains a list of instructions and a
105function type contains a list of argument types. There are two basic
106types of lists: length lists (<a href="#llist">llist</a>), and null
107terminated lists (<a href="#zlist">zlist</a>), as described below in
108the <a href="#encoding">Encoding Primitives</a>.</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]109</div>
110<!-- _______________________________________________________________________ -->
111<div class="doc_subsection"><a name="fields">Fields</a> </div>
112<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]113<p>Fields are units of information that LLVM knows how to write atomically. Most
114fields have a uniform length or some kind of length indication built into their
115encoding. For example, a constant string (array of bytes) is written simply as
116the length followed by the characters. Although this is similar to a list,
117constant strings are treated atomically and are thus fields.</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]118<p>Fields use a condensed bit format specific to the type of information
119they must contain. As few bits as possible are written for each field. The
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]120sections that follow will provide the details on how these fields are
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]121written and how the bits are to be interpreted.</p>
122</div>
123<!-- _______________________________________________________________________ -->
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]124<div class="doc_subsection"><a name="align">Alignment</a> </div>
Reid Spencer7aa940d2004-05-25 15:47:57 +0000[diff] [blame]125<div class="doc_text">
Reid Spencer267660f2004-08-03 20:33:56 +0000[diff] [blame]126 <p>To support cross-platform differences, the bytecode file is aligned on
127 certain boundaries. This means that a small amount of padding (at most 3
128 bytes) will be added to ensure that the next entry is aligned to a 32-bit
129 boundary.</p>
Chris Lattner8dabb502004-05-25 17:44:58 +0000[diff] [blame]130</div>
Reid Spencer7aa940d2004-05-25 15:47:57 +0000[diff] [blame]131<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]132<div class="doc_subsection"><a name="vbr">Variable Bit-Rate Encoding</a>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]133</div>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]134<div class="doc_text">
135<p>Most of the values written to LLVM bytecode files are small integers. To
136minimize the number of bytes written for these quantities, an encoding scheme
137similar to UTF-8 is used to write integer data. The scheme is known as
138variable bit rate (vbr) encoding. In this encoding, the high bit of
139each byte is used to indicate if more bytes follow. If (byte &amp;
1400x80) is non-zero in any given byte, it means there is another byte
141immediately following that also contributes to the value. For the final
142byte (byte &amp; 0x80) is false (the high bit is not set). In each byte
143only the low seven bits contribute to the value. Consequently 32-bit
144quantities can take from one to <em>five</em> bytes to encode. In
145general, smaller quantities will encode in fewer bytes, as follows:</p>
146<table>
147 <tbody>
148 <tr>
149 <th>Byte #</th>
150 <th>Significant Bits</th>
151 <th>Maximum Value</th>
152 </tr>
153 <tr>
154 <td>1</td>
155 <td>0-6</td>
156 <td>127</td>
157 </tr>
158 <tr>
159 <td>2</td>
160 <td>7-13</td>
161 <td>16,383</td>
162 </tr>
163 <tr>
164 <td>3</td>
165 <td>14-20</td>
166 <td>2,097,151</td>
167 </tr>
168 <tr>
169 <td>4</td>
170 <td>21-27</td>
171 <td>268,435,455</td>
172 </tr>
173 <tr>
174 <td>5</td>
175 <td>28-34</td>
176 <td>34,359,738,367</td>
177 </tr>
178 <tr>
179 <td>6</td>
180 <td>35-41</td>
181 <td>4,398,046,511,103</td>
182 </tr>
183 <tr>
184 <td>7</td>
185 <td>42-48</td>
186 <td>562,949,953,421,311</td>
187 </tr>
188 <tr>
189 <td>8</td>
190 <td>49-55</td>
191 <td>72,057,594,037,927,935</td>
192 </tr>
193 <tr>
194 <td>9</td>
195 <td>56-62</td>
196 <td>9,223,372,036,854,775,807</td>
197 </tr>
198 <tr>
199 <td>10</td>
200 <td>63-69</td>
201 <td>1,180,591,620,717,411,303,423</td>
202 </tr>
203 </tbody>
204</table>
205<p>Note that in practice, the tenth byte could only encode bit 63 since
206the maximum quantity to use this encoding is a 64-bit integer.</p>
207<p><em>Signed</em> VBR values are encoded with the standard vbr
208encoding, but with the sign bit as the low order bit instead of the
209high order bit. This allows small negative quantities to be encoded
210efficiently. For example, -3
211is encoded as "((3 &lt;&lt; 1) | 1)" and 3 is encoded as "(3 &lt;&lt;
2121) | 0)", emitted with the standard vbr encoding above.</p>
213</div>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]214<!-- _______________________________________________________________________ -->
215<div class="doc_subsection"><a name="encoding">Encoding Primitives</a> </div>
216<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]217<p>Each field in the bytecode format is encoded into the file using a
218small set of primitive formats. The table below defines the encoding
219rules for the various primitives used and gives them each a type name.
220The type names used in the descriptions of blocks and fields in the <a
221 href="#details">Detailed Layout</a>next section. Any type name with
222the suffix <em>_vbr</em> indicates a quantity that is encoded using
223variable bit rate encoding as described above.</p>
224<table class="doc_table">
225 <tbody>
226 <tr>
227 <th><b>Type</b></th>
228 <th class="td_left"><b>Rule</b></th>
229 </tr>
230 <tr>
231 <td><a name="unsigned"><b>unsigned</b></a></td>
232 <td class="td_left">A 32-bit unsigned integer that always occupies four
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]233 consecutive bytes. The unsigned integer is encoded using LSB first
234 ordering. That is bits 2<sup>0</sup> through 2<sup>7</sup> are in the
235 byte with the lowest file offset (little endian).</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]236 </tr>
237 <tr>
Reid Spencer301fe482004-08-03 20:57:56 +0000[diff] [blame]238 <td style="vertical-align: top;"><a name="uint24_vbr">
239 <b>uint24_vbr</b></a></td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]240 <td style="vertical-align: top; text-align: left;">A 24-bit unsigned
241 integer that occupies from one to four bytes using variable bit rate
242 encoding.</td>
243 </tr>
244 <tr>
245 <td><a name="uint32_vbr"><b>uint32_vbr</b></a></td>
Reid Spencerf08561f2004-08-03 19:20:18 +0000[diff] [blame]246 <td class="td_left">A 32-bit unsigned integer that occupies from one to
247 five bytes using variable bit rate encoding.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]248 </tr>
249 <tr>
250 <td><a name="uint64_vbr"><b>uint64_vbr</b></a></td>
Reid Spencerf08561f2004-08-03 19:20:18 +0000[diff] [blame]251 <td class="td_left">A 64-bit unsigned integer that occupies from one to ten
252 bytes using variable bit rate encoding.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]253 </tr>
254 <tr>
255 <td><a name="int64_vbr"><b>int64_vbr</b></a></td>
Reid Spencerf08561f2004-08-03 19:20:18 +0000[diff] [blame]256 <td class="td_left">A 64-bit signed integer that occupies from one to ten
257 bytes using the signed variable bit rate encoding.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]258 </tr>
259 <tr>
260 <td><a name="char"><b>char</b></a></td>
Reid Spencerf08561f2004-08-03 19:20:18 +0000[diff] [blame]261 <td class="td_left">A single unsigned character encoded into one byte</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]262 </tr>
263 <tr>
264 <td><a name="bit"><b>bit(n-m)</b></a></td>
Reid Spencerf08561f2004-08-03 19:20:18 +0000[diff] [blame]265 <td class="td_left">A set of bit within some larger integer field. The values
266 of <code>n</code> and <code>m</code> specify the inclusive range of bits
267 that define the subfield. The value for <code>m</code> may be omitted if
268 its the same as <code>n</code>.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]269 </tr>
270 <tr>
271 <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]272 <td style="vertical-align: top; text-align: left;">A floating point value encoded
273 as a 32-bit IEEE value written in little-endian form.<br>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]274 </td>
275 </tr>
276 <tr>
277 <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]278 <td style="vertical-align: top; text-align: left;">A floating point value encoded
279 as a64-bit IEEE value written in little-endian form</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]280 </tr>
281 <tr>
282 <td><a name="string"><b>string</b></a></td>
283 <td class="td_left">A uint32_vbr indicating the type of the
284constant string which also includes its length, immediately followed by
285the characters of the string. There is no terminating null byte in the
286string.</td>
287 </tr>
288 <tr>
289 <td><a name="data"><b>data</b></a></td>
290 <td class="td_left">An arbitrarily long segment of data to which
291no interpretation is implied. This is used for constant initializers.<br>
292 </td>
293 </tr>
294 <tr>
295 <td><a name="llist"><b>llist(x)</b></a></td>
296 <td class="td_left">A length list of x. This means the list is
297encoded as an <a href="#uint32_vbr">uint32_vbr</a> providing the
298length of the list, followed by a sequence of that many "x" items. This
299implies that the reader should iterate the number of times provided by
300the length.</td>
301 </tr>
302 <tr>
303 <td><a name="zlist"><b>zlist(x)</b></a></td>
304 <td class="td_left">A zero-terminated list of x. This means the
305list is encoded as a sequence of an indeterminate number of "x" items,
306followed by an <a href="#uint32_vbr">uint32_vbr</a> terminating value.
307This implies that none of the "x" items can have a zero value (or else
308the list terminates).</td>
309 </tr>
310 <tr>
311 <td><a name="block"><b>block</b></a></td>
312 <td class="td_left">A block of data that is logically related. A
313block is an unsigned 32-bit integer that encodes the type of the block
314in the low 5 bits and the size of the block in the high 27 bits. The
315length does not include the block header or any alignment bytes at the
316end of the block. Blocks may compose other blocks. </td>
317 </tr>
318 </tbody>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]319</table>
320</div>
321<!-- _______________________________________________________________________ -->
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]322<div class="doc_subsection"><a name="notation">Field Notation</a> </div>
323<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]324<p>In the detailed block and field descriptions that follow, a regex
325like notation is used to describe optional and repeated fields. A very
326limited subset of regex is used to describe these, as given in the
327following table: </p>
328<table class="doc_table">
329 <tbody>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]330 <tr>
331 <th><b>Character</b></th>
332 <th class="td_left"><b>Meaning</b></th>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]333 </tr>
334 <tr>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]335 <td><b><code>?</code></b></td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]336 <td class="td_left">The question mark indicates 0 or 1
337occurrences of the thing preceding it.</td>
338 </tr>
339 <tr>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]340 <td><b><code>*</code></b></td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]341 <td class="td_left">The asterisk indicates 0 or more occurrences
342of the thing preceding it.</td>
343 </tr>
344 <tr>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]345 <td><b><code>+</code></b></td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]346 <td class="td_left">The plus sign indicates 1 or more occurrences
347of the thing preceding it.</td>
348 </tr>
349 <tr>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]350 <td><b><code>()</code></b></td>
351 <td class="td_left">Parentheses are used for grouping.</td>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]352 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]353 <tr>
354 <td><b><code>,</code></b></td>
355 <td class="td_left">The comma separates sequential fields.</td>
356 </tr>
357 </tbody>
358</table>
359<p>So, for example, consider the following specifications:</p>
360<div class="doc_code">
361<ol>
362 <li><code>string?</code></li>
363 <li><code>(uint32_vbr,uin32_vbr)+</code></li>
364 <li><code>(unsigned?,uint32_vbr)*</code></li>
365 <li><code>(llist(unsigned))?</code></li>
366</ol>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]367</div>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]368<p>with the following interpretations:</p>
369<ol>
370 <li>An optional string. Matches either nothing or a single string</li>
371 <li>One or more pairs of uint32_vbr.</li>
372 <li>Zero or more occurrences of either an unsigned followed by a
373uint32_vbr or just a uint32_vbr.</li>
374 <li>An optional length list of unsigned values.</li>
375</ol>
376</div>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]377<!-- _______________________________________________________________________ -->
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]378<div class="doc_subsection"><a name="slots">Slots</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]379<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]380<p>The bytecode format uses the notion of a "slot" to reference Types
381and Values. Since the bytecode file is a <em>direct</em> representation of
382LLVM's intermediate representation, there is a need to represent pointers in
383the file. Slots are used for this purpose. For example, if one has the following
384assembly:
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]385</p>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]386<div class="doc_code"><code> %MyType = type { int, sbyte }<br>
387%MyVar = external global %MyType
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]388</code></div>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]389<p>there are two definitions. The definition of <tt>%MyVar</tt> uses <tt>%MyType</tt>.
390In the C++ IR this linkage between <tt>%MyVar</tt> and <tt>%MyType</tt>
391is explicit through the use of C++ pointers. In bytecode, however, there's no
392ability to store memory addresses. Instead, we compute and write out
393slot numbers for every Type and Value written to the file.</p>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]394<p>A slot number is simply an unsigned 32-bit integer encoded in the variable
395bit rate scheme (see <a href="#encoding">encoding</a>). This ensures that
396low slot numbers are encoded in one byte. Through various bits of magic LLVM
397attempts to always keep the slot numbers low. The first attempt is to associate
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]398slot numbers with their "type plane". That is, Values of the same type
399are written to the bytecode file in a list (sequentially). Their order in
400that list determines their slot number. This means that slot #1 doesn't mean
401anything unless you also specify for which type you want slot #1. Types are
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]402always written to the file first (in the <a href="#globaltypes">Global Type
403Pool</a>) and in such a way that both forward and backward references of the
404types can often be resolved with a single pass through the type pool. </p>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]405<p>Slot numbers are also kept small by rearranging their order. Because
406of the structure of LLVM, certain values are much more likely to be used
407frequently in the body of a function. For this reason, a compaction table is
408provided in the body of a function if its use would make the function body
409smaller. Suppose you have a function body that uses just the types "int*" and
410"{double}" but uses them thousands of time. Its worthwhile to ensure that the
411slot number for these types are low so they can be encoded in a single byte
412(via vbr). This is exactly what the compaction table does.</p>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]413<p>In summary then, a slot number can be though of as just a vbr encoded index
414into a list of Type* or Value*. To keep slot numbers low, Value* are indexed by
415two slot numbers: the "type plane index" (type slot) and the "value index"
416(value slot).</p>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]417</div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]418<!-- *********************************************************************** -->
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]419<div class="doc_section"> <a name="general">General Structure</a> </div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]420<!-- *********************************************************************** -->
421<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]422<p>This section provides the general structure of the LLVM bytecode
423file format. The bytecode file format requires blocks to be in a
424certain order and nested in a particular way so that an LLVM module can
425be constructed efficiently from the contents of the file. This ordering
426defines a general structure for bytecode files as shown below. The
427table below shows the order in which all block types may appear. Please
428note that some of the blocks are optional and some may be repeated. The
429structure is fairly loose because optional blocks, if empty, are
430completely omitted from the file.</p>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]431<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]432 <tbody>
433 <tr>
434 <th>ID</th>
435 <th>Parent</th>
436 <th>Optional?</th>
437 <th>Repeated?</th>
438 <th>Level</th>
439 <th>Block Type</th>
440 <th>Description</th>
441 </tr>
442 <tr>
443 <td>N/A</td>
444 <td>File</td>
445 <td>No</td>
446 <td>No</td>
447 <td>0</td>
448 <td class="td_left"><a href="#signature">Signature</a></td>
449 <td class="td_left">This contains the file signature (magic
450number) that identifies the file as LLVM bytecode.</td>
451 </tr>
452 <tr>
453 <td>0x01</td>
454 <td>File</td>
455 <td>No</td>
456 <td>No</td>
457 <td>0</td>
458 <td class="td_left"><a href="#module">Module</a></td>
459 <td class="td_left">This is the top level block in a bytecode
460file. It contains all the other blocks. </td>
461 </tr>
462 <tr>
463 <td>0x06</td>
464 <td>Module</td>
465 <td>No</td>
466 <td>No</td>
467 <td>1</td>
468 <td class="td_left">&nbsp;&nbsp;&nbsp;<a href="#globaltypes">Global&nbsp;Type&nbsp;Pool</a></td>
469 <td class="td_left">This block contains all the global (module)
470level types.</td>
471 </tr>
472 <tr>
473 <td>0x05</td>
474 <td>Module</td>
475 <td>No</td>
476 <td>No</td>
477 <td>1</td>
478 <td class="td_left">&nbsp;&nbsp;&nbsp;<a href="#globalinfo">Module&nbsp;Globals&nbsp;Info</a></td>
479 <td class="td_left">This block contains the type, constness, and
480linkage for each of the global variables in the module. It also
481contains the type of the functions and the constant initializers.</td>
482 </tr>
483 <tr>
484 <td>0x03</td>
485 <td>Module</td>
486 <td>Yes</td>
487 <td>No</td>
488 <td>1</td>
489 <td class="td_left">&nbsp;&nbsp;&nbsp;<a href="#constantpool">Module&nbsp;Constant&nbsp;Pool</a></td>
490 <td class="td_left">This block contains all the global constants
491except function arguments, global values and constant strings.</td>
492 </tr>
493 <tr>
494 <td>0x02</td>
495 <td>Module</td>
496 <td>Yes</td>
497 <td>Yes</td>
498 <td>1</td>
499 <td class="td_left">&nbsp;&nbsp;&nbsp;<a href="#functiondefs">Function&nbsp;Definitions</a>*</td>
500 <td class="td_left">One function block is written for each
501function in the module. The function block contains the instructions,
502compaction table, type constant pool, and symbol table for the function.</td>
503 </tr>
504 <tr>
505 <td>0x03</td>
506 <td>Function</td>
507 <td>Yes</td>
508 <td>No</td>
509 <td>2</td>
510 <td class="td_left">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a
511 href="#constantpool">Function&nbsp;Constant&nbsp;Pool</a></td>
512 <td class="td_left">Any constants (including types) used solely
513within the function are emitted here in the function constant pool. </td>
514 </tr>
515 <tr>
516 <td>0x08</td>
517 <td>Function</td>
518 <td>Yes</td>
519 <td>No</td>
520 <td>2</td>
521 <td class="td_left">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a
522 href="#compactiontable">Compaction&nbsp;Table</a></td>
523 <td class="td_left">This table reduces bytecode size by providing
524a funtion-local mapping of type and value slot numbers to their global
525slot numbers</td>
526 </tr>
527 <tr>
528 <td>0x07</td>
529 <td>Function</td>
530 <td>No</td>
531 <td>No</td>
532 <td>2</td>
533 <td class="td_left">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a
534 href="#instructionlist">Instruction&nbsp;List</a></td>
535 <td class="td_left">This block contains all the instructions of
536the function. The basic blocks are inferred by terminating
537instructions. </td>
538 </tr>
539 <tr>
540 <td>0x04</td>
541 <td>Function</td>
542 <td>Yes</td>
543 <td>No</td>
544 <td>2</td>
545 <td class="td_left">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a
546 href="#symtab">Function&nbsp;Symbol&nbsp;Table</a></td>
547 <td class="td_left">This symbol table provides the names for the
548function specific values used (basic block labels mostly).</td>
549 </tr>
550 <tr>
551 <td>0x04</td>
552 <td>Module</td>
553 <td>Yes</td>
554 <td>No</td>
555 <td>1</td>
556 <td class="td_left">&nbsp;&nbsp;&nbsp;<a href="#symtab">Module&nbsp;Symbol&nbsp;Table</a></td>
557 <td class="td_left">This symbol table provides the names for the
558various entries in the file that are not function specific (global
559vars, and functions mostly).</td>
560 </tr>
561 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]562</table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]563<p>Use the links in the table for details about the contents of each of
564the block types.</p>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]565</div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]566<!-- *********************************************************************** -->
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]567<div class="doc_section"> <a name="blockdefs">Block Definitions</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]568<!-- *********************************************************************** -->
569<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]570<p>This section provides the detailed layout of the individual block
571types in the LLVM bytecode file format. </p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]572</div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]573<!-- _______________________________________________________________________ -->
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]574<div class="doc_subsection"><a name="signature">Signature Block</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]575<div class="doc_text">
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]576<p>The signature occurs in every LLVM bytecode file and is always first.
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]577It simply provides a few bytes of data to identify the file as being an LLVM
578bytecode file. This block is always four bytes in length and differs from the
579other blocks because there is no identifier and no block length at the start
580of the block. Essentially, this block is just the "magic number" for the file.
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]581</p>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]582<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]583 <tbody>
584 <tr>
585 <th><b>Type</b></th>
586 <th class="td_left"><b>Field Description</b></th>
587 </tr>
588 <tr>
589 <td><a href="#char">char</a></td>
590 <td class="td_left">Constant "l" (0x6C)</td>
591 </tr>
592 <tr>
593 <td><a href="#char">char</a></td>
594 <td class="td_left">Constant "l" (0x6C)</td>
595 </tr>
596 <tr>
597 <td><a href="#char">char</a></td>
598 <td class="td_left">Constant "v" (0x76)</td>
599 </tr>
600 <tr>
601 <td><a href="#char">char</a></td>
602 <td class="td_left">Constant "m" (0x6D)</td>
603 </tr>
604 </tbody>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]605</table>
606</div>
607<!-- _______________________________________________________________________ -->
608<div class="doc_subsection"><a name="module">Module Block</a> </div>
609<div class="doc_text">
610<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]611the file. The table below shows the structure of the module block. Note that it
612only provides the module identifier, size of the module block, and the format
613information. Everything else is contained in other blocks, described in other
614sections.</p>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]615<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]616 <tbody>
617 <tr>
618 <th><b>Type</b></th>
619 <th class="td_left"><b>Field Description</b></th>
620 </tr>
621 <tr>
Reid Spencer5bc74d52004-08-16 19:24:36 +0000[diff] [blame]622 <td><a href="#unsigned">unsigned</a><br></td>
623 <td class="td_left"><a href="#mod_header">Module Block Identifier
624 (0x01)</a></td>
625 </tr>
626 <tr>
627 <td><a href="#unsigned">unsigned</a></td>
628 <td class="td_left"><a href="#mod_header">Module Block Size</a></td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]629 </tr>
630 <tr>
631 <td><a href="#uint32_vbr">uint32_vbr</a></td>
632 <td class="td_left"><a href="#format">Format Information</a></td>
633 </tr>
634 <tr>
635 <td><a href="#block">block</a></td>
636 <td class="td_left"><a href="#globaltypes">Global Type Pool</a></td>
637 </tr>
638 <tr>
639 <td><a href="#block">block</a></td>
640 <td class="td_left"><a href="#globalinfo">Module Globals Info</a></td>
641 </tr>
642 <tr>
643 <td><a href="#block">block</a></td>
644 <td class="td_left"><a href="#constantpool">Module Constant Pool</a></td>
645 </tr>
646 <tr>
647 <td><a href="#block">block</a>*</td>
648 <td class="td_left"><a href="#functiondefs">Function Definitions</a></td>
649 </tr>
650 <tr>
651 <td><a href="#block">block</a></td>
Reid Spencer8996e552004-08-17 00:49:03 +0000[diff] [blame]652 <td class="td_left"><a href="#symtab">Module Symbol Table</a></td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]653 </tr>
654 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]655</table>
656</div>
Reid Spencer5bc74d52004-08-16 19:24:36 +0000[diff] [blame]657
658<!-- _______________________________________________________________________ -->
659<div class="doc_subsubsection"><a name="mod_header">Module Block Header</a></div>
660<div class="doc_text">
661 <p>The block header for the module block uses a longer format than the other
662 blocks in a bytecode file. Specifically, instead of encoding the type and size
663 of the block into a 32-bit integer with 5-bits for type and 27-bits for size,
664 the module block header uses two 32-bit unsigned values, one for type, and one
665 for size. While the 2<sup>27</sup> byte limit on block size is sufficient for the blocks
666 contained in the module, it isn't sufficient for the module block itself
667 because we want to ensure that bytecode files as large as 2<sup>32</sup> bytes
668 are possible. For this reason, the module block (and only the module block)
669 uses a long format header.</p>
670</div>
671
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]672<!-- _______________________________________________________________________ -->
673<div class="doc_subsubsection"><a name="format">Format Information</a></div>
674<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]675<p>The format information field is encoded into a <a href="#uint32_vbr">uint32_vbr</a>
676as shown in the following table.</p>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]677<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]678 <tbody>
679 <tr>
680 <th><b>Type</b></th>
681 <th class="td_left"><b>Description</b></th>
682 </tr>
683 <tr>
684 <td><a href="#bit">bit(0)</a></td>
685 <td class="td_left">Target is big endian?</td>
686 </tr>
687 <tr>
688 <td><a href="#bit">bit(1)</a></td>
689 <td class="td_left">On target pointers are 64-bit?</td>
690 </tr>
691 <tr>
692 <td><a href="#bit">bit(2)</a></td>
693 <td class="td_left">Target has no endianess?</td>
694 </tr>
695 <tr>
696 <td><a href="#bit">bit(3)</a></td>
697 <td class="td_left">Target has no pointer size?</td>
698 </tr>
699 <tr>
700 <td><a href="#bit">bit(4-31)</a></td>
701 <td class="td_left">Bytecode format version</td>
702 </tr>
703 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]704</table>
705<p>
706Of particular note, the bytecode format number is simply a 28-bit
707monotonically increase integer that identifies the version of the bytecode
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]708format (which is not directly related to the LLVM release number). The
709bytecode versions defined so far are (note that this document only
710describes the latest version, 1.3):</p>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]711<ul>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]712 <li>#0: LLVM 1.0 &amp; 1.1</li>
713 <li>#1: LLVM 1.2</li>
714 <li>#2: LLVM 1.2.5 (not released)</li>
715 <li>#3: LLVM 1.3<br>
716 </li>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]717</ul>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]718<p>Note that we plan to eventually expand the target description
719capabilities
720of bytecode files to <a href="http://llvm.cs.uiuc.edu/PR263">target
721triples</a>.
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]722</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]723</div>
724<!-- _______________________________________________________________________ -->
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]725<div class="doc_subsection"><a name="globaltypes">Global Type Pool</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]726<div class="doc_text">
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]727<p>The global type pool consists of type definitions. Their order of appearance
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]728in the file determines their type slot number (0 based). Slot numbers are
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]729used to replace pointers in the intermediate representation. Each slot number
730uniquely identifies one entry in a type plane (a collection of values of the
731same type). Since all values have types and are associated with the order in
732which the type pool is written, the global type pool <em>must</em> be written
733as the first block of a module. If it is not, attempts to read the file will
734fail because both forward and backward type resolution will not be possible.</p>
735<p>The type pool is simply a list of type definitions, as shown in the
736table below.</p>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]737<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]738 <tbody>
739 <tr>
740 <th><b>Type</b></th>
741 <th class="td_left"><b>Field Description</b></th>
742 </tr>
743 <tr>
744 <td><a href="#unsigned">block</a></td>
745 <td class="td_left">Type Pool Identifier (0x06) + Size<br>
746 </td>
747 </tr>
748 <tr>
749 <td><a href="#llist">llist</a>(<a href="#type">type</a>)</td>
750 <td class="td_left">A length list of type definitions.</td>
751 </tr>
752 </tbody>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]753</table>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]754</div>
755<!-- _______________________________________________________________________ -->
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]756<div class="doc_subsubsection"><a name="type">Type Definitions</a></div>
757<div class="doc_text">
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]758<p>Types in the type pool are defined using a different format for each kind
759of type, as given in the following sections.</p>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]760<h3>Primitive Types</h3>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]761<p>The primitive types encompass the basic integer and floating point
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]762types. They are encoded simply as their TypeID.</p>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]763<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]764 <tbody>
765 <tr>
766 <th><b>Type</b></th>
767 <th class="td_left"><b>Description</b></th>
768 </tr>
769 <tr>
770 <td><a href="#uint24_vbr">uint24_vbr</a></td>
771 <td class="td_left">Type ID for the primitive types (values 1 to
77211) <sup>1</sup></td>
773 </tr>
774 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]775</table>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]776Notes:
777<ol>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]778 <li>The values for the Type IDs for the primitive types are provided
779by the definition of the <code>llvm::Type::TypeID</code> enumeration
780in <code>include/llvm/Type.h</code>. The enumeration gives the
781following mapping:
782 <ol>
783 <li>bool</li>
784 <li>ubyte</li>
785 <li>sbyte</li>
786 <li>ushort</li>
787 <li>short</li>
788 <li>uint</li>
789 <li>int</li>
790 <li>ulong</li>
791 <li>long</li>
792 <li>float</li>
793 <li>double</li>
794 </ol>
795 </li>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]796</ol>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]797<h3>Function Types</h3>
798<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]799 <tbody>
800 <tr>
801 <th><b>Type</b></th>
802 <th class="td_left"><b>Description</b></th>
803 </tr>
804 <tr>
805 <td><a href="#uint24_vbr">uint24_vbr</a></td>
806 <td class="td_left">Type ID for function types (13)</td>
807 </tr>
808 <tr>
809 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]810 <td class="td_left">Type slot number of function's return type.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]811 </tr>
812 <tr>
813 <td><a href="#llist">llist</a>(<a href="#uint24_vbr">uint24_vbr</a>)</td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]814 <td class="td_left">Type slot number of each argument's type.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]815 </tr>
816 <tr>
817 <td><a href="#uint32_vbr">uint32_vbr</a>?</td>
818 <td class="td_left">Value 0 if this is a varargs function,
819missing otherwise.</td>
820 </tr>
821 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]822</table>
823<h3>Structure Types</h3>
824<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]825 <tbody>
826 <tr>
827 <th><b>Type</b></th>
828 <th class="td_left"><b>Description</b></th>
829 </tr>
830 <tr>
831 <td><a href="#uint24_vbr">uint24_vbr</a></td>
832 <td class="td_left">Type ID for structure types (14)</td>
833 </tr>
834 <tr>
835 <td><a href="#zlist">zlist</a>(<a href="#uint24_vbr">uint24_vbr</a>)</td>
836 <td class="td_left">Slot number of each of the element's fields.</td>
837 </tr>
838 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]839</table>
840<h3>Array Types</h3>
841<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]842 <tbody>
843 <tr>
844 <th><b>Type</b></th>
845 <th class="td_left"><b>Description</b></th>
846 </tr>
847 <tr>
848 <td><a href="#uint24_vbr">uint24_vbr</a></td>
849 <td class="td_left">Type ID for Array Types (15)</td>
850 </tr>
851 <tr>
852 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]853 <td class="td_left">Type slot number of array's element type.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]854 </tr>
855 <tr>
856 <td><a href="#uint32_vbr">uint32_vbr</a></td>
857 <td class="td_left">The number of elements in the array.</td>
858 </tr>
859 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]860</table>
861<h3>Pointer Types</h3>
862<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]863 <tbody>
864 <tr>
865 <th><b>Type</b></th>
866 <th class="td_left"><b>Description</b></th>
867 </tr>
868 <tr>
869 <td><a href="#uint24_vbr">uint24_vbr</a></td>
870 <td class="td_left">Type ID For Pointer Types (16)</td>
871 </tr>
872 <tr>
873 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]874 <td class="td_left">Type slot number of pointer's element type.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]875 </tr>
876 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]877</table>
878<h3>Opaque Types</h3>
879<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]880 <tbody>
881 <tr>
882 <th><b>Type</b></th>
883 <th class="td_left"><b>Description</b></th>
884 </tr>
885 <tr>
886 <td><a href="#uint24_vbr">uint24_vbr</a></td>
887 <td class="td_left">Type ID For Opaque Types (17)</td>
888 </tr>
889 </tbody>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]890</table>
Brian Gaeke715c90b2004-08-20 06:00:58 +0000[diff] [blame]891<h3>Packed Types</h3>
892<table>
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 Packed Types (18)</td>
901 </tr>
902 <tr>
903 <td><a href="#uint24_vbr">uint24_vbr</a></td>
904 <td class="td_left">Slot number of packed vector's element type.</td>
905 </tr>
906 <tr>
907 <td><a href="#uint32_vbr">uint32_vbr</a></td>
908 <td class="td_left">The number of elements in the packed vector.</td>
909 </tr>
910 </tbody>
911</table>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]912</div>
913<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]914<div class="doc_subsection"><a name="globalinfo">Module Global Info</a>
915</div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]916<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]917<p>The module global info block contains the definitions of all global
918variables including their initializers and the <em>declaration</em> of
919all functions. The format is shown in the table below:</p>
920<table>
921 <tbody>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]922 <tr>
923 <th><b>Type</b></th>
924 <th class="td_left"><b>Field Description</b></th>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]925 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]926 <tr>
927 <td><a href="#block">block</a></td>
928 <td class="td_left">Module global info identifier (0x05) + size<br>
929 </td>
930 </tr>
931 <tr>
932 <td><a href="#zlist">zlist</a>(<a href="#globalvar">globalvar</a>)</td>
933 <td class="td_left">A zero terminated list of global var
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]934definitions occurring in the module.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]935 </tr>
936 <tr>
937 <td><a href="#zlist">zlist</a>(<a href="#uint24_vbr">uint24_vbr</a>)</td>
938 <td class="td_left">A zero terminated list of function types
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]939occurring in the module.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]940 </tr>
941 <tr>
942 <td style="vertical-align: top;"><a href="#llist">llist</a>(<a
943 href="#string">string</a>)<br>
944 </td>
945 <td style="vertical-align: top; text-align: left;">A length list
946of strings that specify the names of the libraries that this module
947depends upon.<br>
948 </td>
949 </tr>
950 <tr>
951 <td style="vertical-align: top;"><a href="#string">string</a><br>
952 </td>
953 <td style="vertical-align: top; text-align: left;">The target
954triple for the module (blank means no target triple specified, i.e. a
955platform independent module).<br>
956 </td>
957 </tr>
958 </tbody>
959</table>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]960</div>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]961<!-- _______________________________________________________________________ -->
962<div class="doc_subsubsection"><a name="globalvar">Global Variable Field</a>
963</div>
964<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]965<p>Global variables are written using an <a href="#uint32_vbr">uint32_vbr</a>
966that encodes information about the global variable and a list of the
967constant initializers for the global var, if any.</p>
968<p>The table below provides the bit layout of the first <a
969 href="#uint32_vbr">uint32_vbr</a> that describes the global variable.</p>
970<table>
971 <tbody>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]972 <tr>
973 <th><b>Type</b></th>
974 <th class="td_left"><b>Description</b></th>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]975 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]976 <tr>
977 <td><a href="#bit">bit(0)</a></td>
978 <td class="td_left">Is constant?</td>
979 </tr>
980 <tr>
981 <td><a href="#bit">bit(1)</a></td>
982 <td class="td_left">Has initializer? Note that this bit
983determines whether the constant initializer field (described below)
984follows. </td>
985 </tr>
986 <tr>
987 <td><a href="#bit">bit(2-4)</a></td>
988 <td class="td_left">Linkage type: 0=External, 1=Weak,
9892=Appending, 3=Internal, 4=LinkOnce</td>
990 </tr>
991 <tr>
992 <td><a href="#bit">bit(5-31)</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]993 <td class="td_left">Type slot number of type for the global variable.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]994 </tr>
995 </tbody>
996</table>
997<p>The table below provides the format of the constant initializers for
998the global variable field, if it has one.</p>
999<table>
1000 <tbody>
1001 <tr>
1002 <th><b>Type</b></th>
1003 <th class="td_left"><b>Description</b></th>
1004 </tr>
1005 <tr>
1006 <td>(<a href="#zlist">zlist</a>(<a href="#uint32_vbr">uint32_vbr</a>))?
1007 </td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1008 <td class="td_left">An optional zero-terminated list of value slot
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1009numbers of the global variable's constant initializer.</td>
1010 </tr>
1011 </tbody>
1012</table>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1013</div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1014<!-- _______________________________________________________________________ -->
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1015<div class="doc_subsection"><a name="constantpool">Constant Pool</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1016<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1017<p>A constant pool defines as set of constant values. There are
1018actually two types of constant pool blocks: one for modules and one for
1019functions. For modules, the block begins with the constant strings
1020encountered anywhere in the module. For functions, the block begins
1021with types only encountered in the function. In both cases the header
1022is identical. The tables that follow, show the header, module constant
1023pool preamble, function constant pool preamble, and the part common to
1024both function and module constant pools.</p>
1025<p><b>Common Block Header</b></p>
1026<table>
1027 <tbody>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1028 <tr>
1029 <th><b>Type</b></th>
1030 <th class="td_left"><b>Field Description</b></th>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1031 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1032 <tr>
1033 <td><a href="#block">block</a></td>
1034 <td class="td_left">Constant pool identifier (0x03) + size<br>
1035 </td>
1036 </tr>
1037 </tbody>
1038</table>
1039<p><b>Module Constant Pool Preamble (constant strings)</b></p>
1040<table>
1041 <tbody>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1042 <tr>
1043 <th><b>Type</b></th>
1044 <th class="td_left"><b>Field Description</b></th>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1045 </tr>
1046 <tr>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1047 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1048 <td class="td_left">The number of constant strings that follow.</td>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1049 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1050 <tr>
1051 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1052 <td class="td_left">Zero. This identifies the following "plane"
1053as containing the constant strings. This is needed to identify it
1054uniquely from other constant planes that follow. </td>
1055 </tr>
1056 <tr>
1057 <td><a href="#uint24_vbr">uint24_vbr</a>+</td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1058 <td class="td_left">Type slot number of the constant string's type.
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1059Note that the constant string's type implicitly defines the length of
1060the string. </td>
1061 </tr>
1062 </tbody>
1063</table>
1064<p><b>Function Constant Pool Preamble (function types)</b></p>
1065<p>The structure of the types for functions is identical to the <a
1066 href="#globaltypes">Global Type Pool</a>. Please refer to that section
1067for the details. </p>
1068<p><b>Common Part (other constants)</b></p>
1069<table>
1070 <tbody>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1071 <tr>
1072 <th><b>Type</b></th>
1073 <th class="td_left"><b>Field Description</b></th>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1074 </tr>
1075 <tr>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1076 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1077 <td class="td_left">Number of entries in this type plane.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1078 </tr>
1079 <tr>
1080 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1081 <td class="td_left">Type slot number of this plane.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1082 </tr>
1083 <tr>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]1084 <td><a href="#constant">constant</a>+</td>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1085 <td class="td_left">The definition of a constant (see below).</td>
1086 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1087 </tbody>
1088</table>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1089</div>
1090<!-- _______________________________________________________________________ -->
1091<div class="doc_subsubsection"><a name="constant">Constant Field</a></div>
1092<div class="doc_text">
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1093<p>Constants come in many shapes and flavors. The sections that follow
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1094define the format for each of them. All constants start with a <a
1095 href="#uint32_vbr">uint32_vbr</a> encoded integer that provides the
1096number of operands for the constant. For primitive, structure, and
1097array constants, this will always be zero since those types of
1098constants have no operands. In this case, we have the following field
1099definitions:</p>
1100<ul>
1101 <li><b>Bool</b>. This is written as an <a href="#uint32_vbr">uint32_vbr</a>
1102of value 1U or 0U.</li>
1103 <li><b>Signed Integers (sbyte,short,int,long)</b>. These are written
1104as an <a href="#int64_vbr">int64_vbr</a> with the corresponding value.</li>
1105 <li><b>Unsigned Integers (ubyte,ushort,uint,ulong)</b>. These are
1106written as an <a href="#uint64_vbr">uint64_vbr</a> with the
1107corresponding value. </li>
1108 <li><b>Floating Point</b>. Both the float and double types are
1109written literally in binary format.</li>
1110 <li><b>Arrays</b>. Arrays are written simply as a list of <a
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1111 href="#uint32_vbr">uint32_vbr</a> encoded value slot numbers to the constant
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1112element values.</li>
1113 <li><b>Structures</b>. Structures are written simply as a list of <a
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1114 href="#uint32_vbr">uint32_vbr</a> encoded value slot numbers to the constant
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1115field values of the structure.</li>
1116</ul>
1117<p>When the number of operands to the constant is non-zero, we have a
1118constant expression and its field format is provided in the table below.</p>
1119<table>
1120 <tbody>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1121 <tr>
1122 <th><b>Type</b></th>
1123 <th class="td_left"><b>Field Description</b></th>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1124 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1125 <tr>
1126 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1127 <td class="td_left">Op code of the instruction for the constant
1128expression.</td>
1129 </tr>
1130 <tr>
1131 <td><a href="#uint32_vbr">uint32_vbr</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1132 <td class="td_left">The value slot number of the constant value for an
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1133operand.<sup>1</sup></td>
1134 </tr>
1135 <tr>
1136 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1137 <td class="td_left">The type slot number for the type of the constant
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1138value for an operand.<sup>1</sup></td>
1139 </tr>
1140 </tbody>
1141</table>
1142Notes:
1143<ol>
1144 <li>Both these fields are repeatable but only in pairs.</li>
1145</ol>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1146</div>
1147<!-- _______________________________________________________________________ -->
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1148<div class="doc_subsection"><a name="functiondefs">Function Definition</a></div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1149<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1150<p>Function definitions contain the linkage, constant pool or
1151compaction table, instruction list, and symbol table for a function.
1152The following table shows the structure of a function definition.</p>
1153<table>
1154 <tbody>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1155 <tr>
1156 <th><b>Type</b></th>
1157 <th class="td_left"><b>Field Description</b></th>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1158 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1159 <tr>
1160 <td><a href="#block">block</a><br>
1161 </td>
1162 <td class="td_left">Function definition block identifier (0x02) +
1163size<br>
1164 </td>
1165 </tr>
1166 <tr>
1167 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1168 <td class="td_left">The linkage type of the function: 0=External,
11691=Weak, 2=Appending, 3=Internal, 4=LinkOnce<sup>1</sup></td>
1170 </tr>
1171 <tr>
1172 <td><a href="#block">block</a></td>
1173 <td class="td_left">The <a href="#constantpool">constant pool</a>
1174block for this function.<sup>2</sup></td>
1175 </tr>
1176 <tr>
1177 <td><a href="#block">block</a></td>
1178 <td class="td_left">The <a href="#compactiontable">compaction
1179table</a> block for the function.<sup>2</sup></td>
1180 </tr>
1181 <tr>
1182 <td><a href="#block">block</a></td>
1183 <td class="td_left">The <a href="#instructionlist">instruction
1184list</a> for the function.</td>
1185 </tr>
1186 <tr>
1187 <td><a href="#block">block</a></td>
Reid Spencer8996e552004-08-17 00:49:03 +0000[diff] [blame]1188 <td class="td_left">The function's <a href="#symtab">symbol
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1189table</a> containing only those symbols pertinent to the function
1190(mostly block labels).</td>
1191 </tr>
1192 </tbody>
1193</table>
1194Notes:
1195<ol>
1196 <li>Note that if the linkage type is "External" then none of the
1197other fields will be present as the function is defined elsewhere.</li>
1198 <li>Note that only one of the constant pool or compaction table will
1199be written. Compaction tables are only written if they will actually
1200save bytecode space. If not, then a regular constant pool is written.</li>
1201</ol>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1202</div>
1203<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1204<div class="doc_subsection"><a name="compactiontable">Compaction Table</a>
1205</div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1206<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1207<p>Compaction tables are part of a function definition. They are merely
1208a device for reducing the size of bytecode files. The size of a
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1209bytecode file is dependent on the <em>values</em> of the slot numbers
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1210used because larger values use more bytes in the variable bit rate
1211encoding scheme. Furthermore, the compressed instruction format
1212reserves only six bits for the type of the instruction. In large
1213modules, declaring hundreds or thousands of types, the values of the
1214slot numbers can be quite large. However, functions may use only a
1215small fraction of the global types. In such cases a compaction table is
1216created that maps the global type and value slot numbers to smaller
1217values used by a function. Functions will contain either a
1218function-specific constant pool <em>or</em> a compaction table but not
1219both. Compaction tables have the format shown in the table below.</p>
1220<table>
1221 <tbody>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1222 <tr>
1223 <th><b>Type</b></th>
1224 <th class="td_left"><b>Field Description</b></th>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1225 </tr>
1226 <tr>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1227 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1228 <td class="td_left">The number of types that follow</td>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1229 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1230 <tr>
1231 <td><a href="#uint24_vbr">uint24_vbr</a>+</td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1232 <td class="td_left">The type slot number in the global types of
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1233the type that will be referenced in the function with the index of this
1234entry in the compaction table.</td>
1235 </tr>
1236 <tr>
1237 <td><a href="#type_len">type_len</a></td>
1238 <td class="td_left">An encoding of the type and number of values
1239that follow. This field's encoding varies depending on the size of the
1240type plane. See <a href="#type_len">Type and Length</a> for further
1241details.</td>
1242 </tr>
1243 <tr>
1244 <td><a href="#uint32_vbr">uint32_vbr</a>+</td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1245 <td class="td_left">The value slot number in the global values
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1246that will be referenced in the function with the index of this entry in
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1247the compaction table.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1248 </tr>
1249 </tbody>
1250</table>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1251</div>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1252<!-- _______________________________________________________________________ -->
1253<div class="doc_subsubsection"><a name="type_len">Type and Length</a></div>
1254<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1255<p>The type and length of a compaction table type plane is encoded
1256differently depending on the length of the plane. For planes of length
12571 or 2, the length is encoded into bits 0 and 1 of a <a
1258 href="#uint32_vbr">uint32_vbr</a> and the type is encoded into bits
12592-31. Because type numbers are often small, this often saves an extra
1260byte per plane. If the length of the plane is greater than 2 then the
1261encoding uses a <a href="#uint32_vbr">uint32_vbr</a> for each of the
1262length and type, in that order.</p>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1263</div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1264<!-- _______________________________________________________________________ -->
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1265<div class="doc_subsection"><a name="instructionlist">Instruction List</a></div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1266<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1267<p>The instructions in a function are written as a simple list. Basic
1268blocks are inferred by the terminating instruction types. The format of
1269the block is given in the following table.</p>
1270<table>
1271 <tbody>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1272 <tr>
1273 <th><b>Type</b></th>
1274 <th class="td_left"><b>Field Description</b></th>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1275 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1276 <tr>
1277 <td><a href="#block">block</a><br>
1278 </td>
1279 <td class="td_left">Instruction list identifier (0x07) + size<br>
1280 </td>
1281 </tr>
1282 <tr>
1283 <td><a href="#instruction">instruction</a>+</td>
1284 <td class="td_left">An instruction. Instructions have a variety
1285of formats. See <a href="#instruction">Instructions</a> for details.</td>
1286 </tr>
1287 </tbody>
1288</table>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1289</div>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1290<!-- _______________________________________________________________________ -->
1291<div class="doc_subsubsection"><a name="instruction">Instructions</a></div>
1292<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1293<p>For brevity, instructions are written in one of four formats,
1294depending on the number of operands to the instruction. Each
1295instruction begins with a <a href="#uint32_vbr">uint32_vbr</a> that
1296encodes the type of the instruction as well as other things. The tables
Reid Spencer8996e552004-08-17 00:49:03 +0000[diff] [blame]1297that follow describe the format of this first part of each instruction.</p>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1298<p><b>Instruction Format 0</b></p>
1299<p>This format is used for a few instructions that can't easily be
Reid Spencer8996e552004-08-17 00:49:03 +0000[diff] [blame]1300shortened because they have large numbers of operands (e.g. PHI Node or
1301getelementptr). Each of the opcode, type, and operand fields is found in
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1302successive fields.</p>
1303<table>
1304 <tbody>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1305 <tr>
1306 <th><b>Type</b></th>
1307 <th class="td_left"><b>Field Description</b></th>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1308 </tr>
1309 <tr>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1310 <td><a href="#uint32_vbr">uint32_vbr</a></td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1311 <td class="td_left">Specifies the opcode of the instruction. Note
1312that for compatibility with the other instruction formats, the opcode
1313is shifted left by 2 bits. Bits 0 and 1 must have value zero for this
1314format.</td>
1315 </tr>
1316 <tr>
1317 <td><a href="#uint24_vbr">uint24_vbr</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1318 <td class="td_left">Provides the type slot number of the result type of
1319 the instruction.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1320 </tr>
1321 <tr>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1322 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1323 <td class="td_left">The number of operands that follow.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1324 </tr>
1325 <tr>
Reid Spencer82c46712004-07-07 13:34:26 +0000[diff] [blame]1326 <td><a href="#uint32_vbr">uint32_vbr</a>+</td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1327 <td class="td_left">The slot number of the value(s) for the operand(s).
1328 <sup>1</sup></td>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1329 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1330 </tbody>
1331</table>
1332Notes:
1333<ol>
1334 <li>Note that if the instruction is a getelementptr and the type of
1335the operand is a sequential type (array or pointer) then the slot
1336number is shifted up two bits and the low order bits will encode the
1337type of index used, as follows: 0=uint, 1=int, 2=ulong, 3=long.</li>
1338</ol>
1339<p><b>Instruction Format 1</b></p>
1340<p>This format encodes the opcode, type and a single operand into a
1341single <a href="#uint32_vbr">uint32_vbr</a> as follows:</p>
1342<table>
1343 <tbody>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1344 <tr>
1345 <th><b>Bits</b></th>
1346 <th><b>Type</b></th>
1347 <th class="td_left"><b>Field Description</b></th>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1348 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1349 <tr>
1350 <td>0-1</td>
1351 <td>constant "1"</td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1352 <td class="td_left">These two bits must be the value 1 which identifies
1353 this as an instruction of format 1.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1354 </tr>
1355 <tr>
1356 <td>2-7</td>
Reid Spencer8996e552004-08-17 00:49:03 +0000[diff] [blame]1357 <td><a href="#opcode">opcode</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1358 <td class="td_left">Specifies the opcode of the instruction. Note that
1359 the maximum opcode value is 63.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1360 </tr>
1361 <tr>
1362 <td>8-19</td>
1363 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1364 <td class="td_left">Specifies the slot number of the type for this
1365 instruction. Maximum slot number is 2<sup>12</sup>-1=4095.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1366 </tr>
1367 <tr>
1368 <td>20-31</td>
1369 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1370 <td class="td_left">Specifies the slot number of the value for the
1371 first operand. Maximum slot number is 2<sup>12</sup>-1=4095. Note that
1372 the value 2<sup>12</sup>-1 denotes zero operands.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1373 </tr>
1374 </tbody>
1375</table>
1376<p><b>Instruction Format 2</b></p>
1377<p>This format encodes the opcode, type and two operands into a single <a
1378 href="#uint32_vbr">uint32_vbr</a> as follows:</p>
1379<table>
1380 <tbody>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1381 <tr>
1382 <th><b>Bits</b></th>
1383 <th><b>Type</b></th>
1384 <th class="td_left"><b>Field Description</b></th>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1385 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1386 <tr>
1387 <td>0-1</td>
1388 <td>constant "2"</td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1389 <td class="td_left">These two bits must be the value 2 which identifies
1390 this as an instruction of format 2.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1391 </tr>
1392 <tr>
1393 <td>2-7</td>
1394 <td><a href="#opcodes">opcode</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1395 <td class="td_left">Specifies the opcode of the instruction. Note that
1396 the maximum opcode value is 63.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1397 </tr>
1398 <tr>
1399 <td>8-15</td>
1400 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1401 <td class="td_left">Specifies the slot number of the type for this
1402 instruction. Maximum slot number is 2<sup>8</sup>-1=255.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1403 </tr>
1404 <tr>
1405 <td>16-23</td>
1406 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1407 <td class="td_left">Specifies the slot number of the value for the first
1408 operand. Maximum slot number is 2<sup>8</sup>-1=255.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1409 </tr>
1410 <tr>
1411 <td>24-31</td>
1412 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1413 <td class="td_left">Specifies the slot number of the value for the second
1414 operand. Maximum slot number is 2<sup>8</sup>-1=255.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1415 </tr>
1416 </tbody>
1417</table>
1418<p><b>Instruction Format 3</b></p>
1419<p>This format encodes the opcode, type and three operands into a
1420single <a href="#uint32_vbr">uint32_vbr</a> as follows:</p>
1421<table>
1422 <tbody>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1423 <tr>
1424 <th><b>Bits</b></th>
1425 <th><b>Type</b></th>
1426 <th class="td_left"><b>Field Description</b></th>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1427 </tr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1428 <tr>
1429 <td>0-1</td>
1430 <td>constant "3"</td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1431 <td class="td_left">These two bits must be the value 3 which identifies
1432 this as an instruction of format 3.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1433 </tr>
1434 <tr>
1435 <td>2-7</td>
1436 <td><a href="#opcodes">opcode</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1437 <td class="td_left">Specifies the opcode of the instruction. Note that
1438 the maximum opcode value is 63.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1439 </tr>
1440 <tr>
1441 <td>8-13</td>
1442 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1443 <td class="td_left">Specifies the slot number of the type for this
1444 instruction. Maximum slot number is 2<sup>6</sup>-1=63.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1445 </tr>
1446 <tr>
1447 <td>14-19</td>
1448 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1449 <td class="td_left">Specifies the slot number of the value for the first
1450 operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1451 </tr>
1452 <tr>
1453 <td>20-25</td>
1454 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1455 <td class="td_left">Specifies the slot number of the value for the second
1456 operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1457 </tr>
1458 <tr>
1459 <td>26-31</td>
1460 <td><a href="#unsigned">unsigned</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1461 <td class="td_left">Specifies the slot number of the value for the third
1462 operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1463 </tr>
1464 </tbody>
1465</table>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1466</div>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1467
1468<!-- _______________________________________________________________________ -->
1469<div class="doc_subsection"><a name="opcodes">Opcodes</a></div>
1470<div class="doc_text">
1471 <p>Instructions encode an opcode that identifies the kind of instruction.
1472 Opcodes are an enumerated integer value. The specific values used depend on
1473 the version of LLVM you're using. The opcode values are defined in the
1474 <a href="http://llvm.org/cvsweb/cvsweb.cgi/llvm/include/llvm/Instruction.def">
1475 <tt>include/llvm/Instruction.def</tt></a> file. You should check there for the
1476 most recent definitions. The table below provides the opcodes defined as of
Nate Begeman52ca9e42004-08-27 07:59:37 +0000[diff] [blame]1477 the writing of this document. The table associates each opcode mnemonic with
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1478 its enumeration value and the bytecode and LLVM version numbers in which the
1479 opcode was introduced.</p>
1480 <table>
1481 <tbody>
1482 <tr>
1483 <th>Opcode</th>
1484 <th>Number</th>
1485 <th>Bytecode Version</th>
1486 <th>LLVM Version</th>
1487 </tr>
1488 <tr><td colspan="4"><b>Terminator Instructions</b></td></tr>
1489 <tr><td>Ret</td><td>1</td><td>1</td><td>1.0</td></tr>
1490 <tr><td>Br</td><td>2</td><td>1</td><td>1.0</td></tr>
1491 <tr><td>Switch</td><td>3</td><td>1</td><td>1.0</td></tr>
1492 <tr><td>Invoke</td><td>4</td><td>1</td><td>1.0</td></tr>
1493 <tr><td>Unwind</td><td>5</td><td>1</td><td>1.0</td></tr>
1494 <tr><td colspan="4"><b>Binary Operators</b></td></tr>
1495 <tr><td>Add</td><td>6</td><td>1</td><td>1.0</td></tr>
1496 <tr><td>Sub</td><td>7</td><td>1</td><td>1.0</td></tr>
1497 <tr><td>Mul</td><td>8</td><td>1</td><td>1.0</td></tr>
1498 <tr><td>Div</td><td>9</td><td>1</td><td>1.0</td></tr>
1499 <tr><td>Rem</td><td>10</td><td>1</td><td>1.0</td></tr>
1500 <tr><td colspan="4"><b>Logical Operators</b></td></tr>
1501 <tr><td>And</td><td>11</td><td>1</td><td>1.0</td></tr>
1502 <tr><td>Or</td><td>12</td><td>1</td><td>1.0</td></tr>
1503 <tr><td>Xor</td><td>13</td><td>1</td><td>1.0</td></tr>
1504 <tr><td colspan="4"><b>Binary Comparison Operators</b></td></tr>
1505 <tr><td>SetEQ</td><td>14</td><td>1</td><td>1.0</td></tr>
1506 <tr><td>SetNE</td><td>15</td><td>1</td><td>1.0</td></tr>
1507 <tr><td>SetLE</td><td>16</td><td>1</td><td>1.0</td></tr>
1508 <tr><td>SetGE</td><td>17</td><td>1</td><td>1.0</td></tr>
1509 <tr><td>SetLT</td><td>18</td><td>1</td><td>1.0</td></tr>
1510 <tr><td>SetGT</td><td>19</td><td>1</td><td>1.0</td></tr>
1511 <tr><td colspan="4"><b>Memory Operators</b></td></tr>
1512 <tr><td>Malloc</td><td>20</td><td>1</td><td>1.0</td></tr>
1513 <tr><td>Free</td><td>21</td><td>1</td><td>1.0</td></tr>
1514 <tr><td>Alloca</td><td>22</td><td>1</td><td>1.0</td></tr>
1515 <tr><td>Load</td><td>23</td><td>1</td><td>1.0</td></tr>
1516 <tr><td>Store</td><td>24</td><td>1</td><td>1.0</td></tr>
1517 <tr><td>GetElementPtr</td><td>25</td><td>1</td><td>1.0</td></tr>
1518 <tr><td colspan="4"><b>Other Operators</b></td></tr>
1519 <tr><td>PHI</td><td>26</td><td>1</td><td>1.0</td></tr>
1520 <tr><td>Cast</td><td>27</td><td>1</td><td>1.0</td></tr>
1521 <tr><td>Call</td><td>28</td><td>1</td><td>1.0</td></tr>
1522 <tr><td>Shl</td><td>29</td><td>1</td><td>1.0</td></tr>
1523 <tr><td>Shr</td><td>30</td><td>1</td><td>1.0</td></tr>
1524 <tr><td>VANext</td><td>31</td><td>1</td><td>1.0</td></tr>
1525 <tr><td>VAArg</td><td>32</td><td>1</td><td>1.0</td></tr>
1526 <tr><td>Select</td><td>33</td><td>2</td><td>1.2</td></tr>
1527 <tr><td>UserOp1</td><td>34</td><td>1</td><td>1.0</td></tr>
1528 <tr><td>UserOp2</td><td>35</td><td>1</td><td>1.0</td></tr>
1529 </tbody>
1530 </table>
1531</div>
1532
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1533<!-- _______________________________________________________________________ -->
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]1534<div class="doc_subsection"><a name="symtab">Symbol Table</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1535<div class="doc_text">
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1536<p>A symbol table can be put out in conjunction with a module or a function. A
1537symbol table has a list of name/type associations followed by a list of
1538name/value associations. The name/value associations are organized into "type
1539planes" so that all values of a common type are listed together. Each type
1540plane starts with the number of entries in the plane and the type slot number
1541for all the values in that plane (so the type can be looked up in the global
1542type pool). For each entry in a type plane, the slot number of the value and
1543the name associated with that value are written. The format is given in the
1544table below. </p>
Reid Spencer2cc36152004-07-05 19:04:27 +0000[diff] [blame]1545<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1546 <tbody>
1547 <tr>
1548 <th><b>Type</b></th>
1549 <th class="td_left"><b>Field Description</b></th>
1550 </tr>
1551 <tr>
1552 <td><a href="#block">block</a><br>
1553 </td>
1554 <td class="td_left">Symbol Table Identifier (0x04)</td>
1555 </tr>
1556 <tr>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1557 <td><a href="#llist">llist</a>(<a href="#symtab_entry">type_entry</a>)</td>
Reid Spencer8996e552004-08-17 00:49:03 +0000[diff] [blame]1558 <td class="td_left">A length list of symbol table entries for
1559 <tt>Type</tt>s
1560 </td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1561 </tr>
1562 <tr>
Reid Spencer8996e552004-08-17 00:49:03 +0000[diff] [blame]1563 <td><a href="#zlist">llist</a>(<a href="#symtab_plane">symtab_plane</a>)</td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1564 <td class="td_left">A length list of "type planes" of symbol table
Reid Spencer8996e552004-08-17 00:49:03 +0000[diff] [blame]1565 entries for <tt>Value</tt>s</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1566 </tr>
1567 </tbody>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]1568</table>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1569</div>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1570
1571<!-- _______________________________________________________________________ -->
1572<div class="doc_subsubsection"> <a name="type_entry">Symbol Table Type
1573Entry</a>
1574</div>
1575<div class="doc_text">
1576<p>A symbol table type entry associates a name with a type. The name is provided
1577simply as an array of chars. The type is provided as a type slot number (index)
1578into the global type pool. The format is given in the following table:</p>
1579<table>
1580 <tbody>
1581 <tr>
1582 <th><b>Type</b></th>
1583 <th class="td_left"><b>Field Description</b></th>
1584 </tr>
1585 <tr>
1586 <td><a href="#uint32_vbr">uint24_vbr</a></td>
1587 <td class="td_left">Type slot number of the type being given a
1588 name relative to the global type pool.
1589 </td>
1590 </tr>
1591 <tr>
1592 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1593 <td class="td_left">Length of the character array that follows.</td>
1594 </tr>
1595 <tr>
1596 <td><a href="#char">char</a>+</td>
1597 <td class="td_left">The characters of the name.</td>
1598 </tr>
1599 </tbody>
1600</table>
1601</div>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1602<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1603<div class="doc_subsubsection"> <a name="symtab_plane">Symbol Table
1604Plane</a>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1605</div>
1606<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1607<p>A symbol table plane provides the symbol table entries for all
1608values of a common type. The encoding is given in the following table:</p>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1609<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1610 <tbody>
1611 <tr>
1612 <th><b>Type</b></th>
1613 <th class="td_left"><b>Field Description</b></th>
1614 </tr>
1615 <tr>
1616 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1617 <td class="td_left">Number of entries in this plane.</td>
1618 </tr>
1619 <tr>
1620 <td><a href="#uint32_vbr">uint32_vbr</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1621 <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]1622 </tr>
1623 <tr>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1624 <td><a href="#value_entry">value_entry</a>+</td>
1625 <td class="td_left">The symbol table entries for to associate values with
1626 names.</td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1627 </tr>
1628 </tbody>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1629</table>
1630</div>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1631<!-- _______________________________________________________________________ -->
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1632<div class="doc_subsubsection"><a name="value_entry">Symbol Table Value
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1633Entry</a>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1634</div>
1635<div class="doc_text">
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1636<p>A symbol table value entry provides the assocation between a value and the
1637name given to the value. The value is referenced by its slot number. The
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1638format is given in the following table:</p>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1639<table>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1640 <tbody>
1641 <tr>
1642 <th><b>Type</b></th>
1643 <th class="td_left"><b>Field Description</b></th>
1644 </tr>
1645 <tr>
1646 <td><a href="#uint32_vbr">uint24_vbr</a></td>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1647 <td class="td_left">Value slot number of the value being given a name.
Reid Spencer8996e552004-08-17 00:49:03 +0000[diff] [blame]1648 </td>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1649 </tr>
1650 <tr>
1651 <td><a href="#uint32_vbr">uint32_vbr</a></td>
1652 <td class="td_left">Length of the character array that follows.</td>
1653 </tr>
1654 <tr>
1655 <td><a href="#char">char</a>+</td>
1656 <td class="td_left">The characters of the name.</td>
1657 </tr>
1658 </tbody>
Reid Spencer51f31e02004-07-05 22:28:02 +0000[diff] [blame]1659</table>
1660</div>
Reid Spencer09daa632004-08-18 20:06:19 +0000[diff] [blame]1661
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1662<!-- *********************************************************************** -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1663<div class="doc_section"> <a name="versiondiffs">Version Differences</a>
1664</div>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1665<!-- *********************************************************************** -->
1666<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1667<p>This section describes the differences in the Bytecode Format across
1668LLVM
1669versions. The versions are listed in reverse order because it assumes
1670the current version is as documented in the previous sections. Each
1671section here
Chris Lattner1cc070c2004-07-05 18:05:48 +0000[diff] [blame]1672describes the differences between that version and the one that <i>follows</i>.
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1673</p>
1674</div>
1675<!-- _______________________________________________________________________ -->
Reid Spencer43dfdb72004-08-18 20:17:05 +0000[diff] [blame]1676<div class="doc_subsection"><a name="vers13">Version 1.3 Differences From
Reid Spencercf549e12004-08-17 07:43:43 +0000[diff] [blame]1677 1.4</a></div>
1678<!-- _______________________________________________________________________ -->
1679<div class="doc_subsubsection">Aligned Data</div>
1680<div class="doc_text">
1681 <p>In version 1.3, certain data items were aligned to 32-bit boundaries. In
1682 version 1.4, alignment of data was done away with completely. The need for
1683 alignment has gone away and the only thing it adds is bytecode file size
1684 overhead. In most cases this overhead was small. However, in functions with
1685 large numbers of format 0 instructions (GEPs and PHIs with lots of parameters)
1686 or regular instructions with large valued operands (e.g. because there's just
1687 a lot of instructions in the function) the overhead can be extreme. In one
1688 test case, the overhead was 44,000 bytes (34% of the total file size).
1689 Consequently in release 1.4, the decision was made to eliminate alignment
1690 altogether.</p>
1691 <p>In version 1.3 format, the following bytecode constructs were aligned (i.e.
1692 they were followed by one to three bytes of padding):</p>
1693 <ul>
1694 <li>All blocks.</li>
1695 <li>Instructions using the long format (format 0).</li>
1696 <li>All call instructions that called a var args function.</li>
1697 <li>The target triple (a string field at the end of the module block).</li>
1698 <li>The version field (immediately following the signature).</li>
1699 </ul>
1700 <p>None of these constructs are aligned in version 1.4</p>
1701</div>
1702
1703<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1704<div class="doc_subsection"><a name="vers12">Version 1.2 Differences
1705From 1.3</a></div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1706<!-- _______________________________________________________________________ -->
1707<div class="doc_subsubsection">Type Derives From Value</div>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1708<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1709<p>In version 1.2, the Type class in the LLVM IR derives from the Value
1710class. This is not the case in version 1.3. Consequently, in version
17111.2 the notion of a "Type Type" was used to write out values that were
1712Types. The types always occuped plane 12 (corresponding to the
1713TypeTyID) of any type planed set of values. In 1.3 this representation
1714is not convenient because the TypeTyID (12) is not present and its
1715value is now used for LabelTyID. Consequently, the data structures
1716written that involve types do so by writing all the types first and
1717then each of the value planes according to those types. In version 1.2,
1718the types would have been written intermingled with the values.</p>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1719</div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1720<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1721<div class="doc_subsubsection">Restricted getelementptr Types</div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1722<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1723<p>In version 1.2, the getelementptr instruction required a ubyte type
1724index for accessing a structure field and a long type index for
1725accessing an array element. Consequently, it was only possible to
1726access structures of 255 or fewer elements. Starting in version 1.3,
1727this restriction was lifted. Structures must now be indexed with uint
1728constants. Arrays may now be indexed with int, uint, long, or ulong
1729typed values. The consequence of this was that the bytecode format had
1730to change in order to accommodate the larger range of structure indices.</p>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1731</div>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1732<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1733<div class="doc_subsubsection">Short Block Headers</div>
1734<div class="doc_text">
1735<p>In version 1.2, block headers were always 8 bytes being comprised of
1736both an unsigned integer type and an unsigned integer size. For very
1737small modules, these block headers turn out to be a large fraction of
1738the total bytecode file size. In an attempt to make these small files
1739smaller, the type and size information was encoded into a single
1740unsigned integer (4 bytes) comprised of 5 bits for the block type
1741(maximum 31 block types) and 27 bits for the block size (max
1742~134MBytes). These limits seemed sufficient for any blocks or sizes
1743forseen in the future. Note that the module block, which encloses all
1744the other blocks is still written as 8 bytes since bytecode files
1745larger than 134MBytes might be possible.</p>
1746</div>
1747<!-- _______________________________________________________________________ -->
1748<div class="doc_subsubsection">Dependent Libraries and Target Triples</div>
1749<div class="doc_text">
1750<p>In version 1.2, the bytecode format does not store module's target
1751triple or dependent. These fields have been added to the end of the <a
1752 href="#globalinfo">module global info block</a>. The purpose of these
1753fields is to allow a front end compiler to specifiy that the generated
1754module is specific to a particular target triple (operating
1755system/manufacturer/processor) which makes it non-portable; and to
1756allow front end compilers to specify the list of libraries that the
1757module depends on for successful linking.</p>
1758</div>
1759<!-- _______________________________________________________________________ -->
1760<div class="doc_subsubsection">Types Restricted to 24-bits</div>
1761<div class="doc_text">
1762<p>In version 1.2, type slot identifiers were written as 32-bit VBR
1763quantities. In 1.3 this has been reduced to 24-bits in order to ensure
1764that it is not possible to overflow the type field of a global variable
1765definition. 24-bits for type slot numbers is deemed sufficient for any
1766practical use of LLVM.</p>
1767</div>
1768<!-- _______________________________________________________________________ -->
1769<!-- _______________________________________________________________________ -->
1770<div class="doc_subsection"><a name="vers11">Version 1.1 Differences
1771From 1.2 </a></div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1772<!-- _______________________________________________________________________ -->
1773<div class="doc_subsubsection">Explicit Primitive Zeros</div>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1774<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1775<p>In version 1.1, the zero value for primitives was explicitly encoded
1776into the bytecode format. Since these zero values are constant values
1777in the LLVM IR and never change, there is no reason to explicitly
1778encode them. This explicit encoding was removed in version 1.2.</p>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1779</div>
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1780<!-- _______________________________________________________________________ -->
1781<div class="doc_subsubsection">Inconsistent Module Global Info</div>
1782<div class="doc_text">
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1783<p>In version 1.1, the Module Global Info block was not aligned causing
1784the next block to be read in on an unaligned boundary. This problem was
1785corrected in version 1.2.<br>
1786<br>
1787</p>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1788</div>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1789<!-- _______________________________________________________________________ -->
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1790<div class="doc_subsection"><a name="vers10">Version 1.0 Differences
1791From 1.1</a></div>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1792<div class="doc_text">
Reid Spencer1ab929c2004-07-05 08:18:07 +0000[diff] [blame]1793<p>None. Version 1.0 and 1.1 bytecode formats are identical.</p>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]1794</div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1795<!-- *********************************************************************** -->
1796<hr>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1797<address> <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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1801<a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and <a
1802 href="mailto:sabre@nondot.org">Chris Lattner</a><br>
1803<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
1804Last modified: $Date$
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]1805</address>
Reid Spencer9bd2be22004-07-29 00:13:04 +0000[diff] [blame]1806</body>
1807</html>