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Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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4<head>
5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
6 <title>LLVM Bitcode File Format</title>
7 <link rel="stylesheet" href="llvm.css" type="text/css">
Reid Spencer2c1ce4f2007-01-20 23:21:08 +0000[diff] [blame]8</head>
9<body>
10<div class="doc_title"> LLVM Bitcode File Format </div>
11<ol>
12 <li><a href="#abstract">Abstract</a></li>
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]13 <li><a href="#overview">Overview</a></li>
14 <li><a href="#bitstream">Bitstream Format</a>
15 <ol>
16 <li><a href="#magic">Magic Numbers</a></li>
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]17 <li><a href="#primitives">Primitives</a></li>
18 <li><a href="#abbrevid">Abbreviation IDs</a></li>
19 <li><a href="#blocks">Blocks</a></li>
20 <li><a href="#datarecord">Data Records</a></li>
Chris Lattnerdaeb63c2007-05-12 07:49:15 +0000[diff] [blame]21 <li><a href="#abbreviations">Abbreviations</a></li>
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]22 <li><a href="#stdblocks">Standard Blocks</a></li>
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]23 </ol>
24 </li>
Chris Lattner6fa6a322008-07-09 05:14:23 +0000[diff] [blame]25 <li><a href="#wrapper">Bitcode Wrapper Format</a>
26 </li>
Chris Lattner69b3e402007-05-13 01:39:44 +0000[diff] [blame]27 <li><a href="#llvmir">LLVM IR Encoding</a>
28 <ol>
29 <li><a href="#basics">Basics</a></li>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]30 <li><a href="#MODULE_BLOCK">MODULE_BLOCK Contents</a></li>
31 <li><a href="#PARAMATTR_BLOCK">PARAMATTR_BLOCK Contents</a></li>
32 <li><a href="#TYPE_BLOCK">TYPE_BLOCK Contents</a></li>
33 <li><a href="#CONSTANTS_BLOCK">CONSTANTS_BLOCK Contents</a></li>
34 <li><a href="#FUNCTION_BLOCK">FUNCTION_BLOCK Contents</a></li>
35 <li><a href="#TYPE_SYMTAB_BLOCK">TYPE_SYMTAB_BLOCK Contents</a></li>
36 <li><a href="#VALUE_SYMTAB_BLOCK">VALUE_SYMTAB_BLOCK Contents</a></li>
37 <li><a href="#METADATA_BLOCK">METADATA_BLOCK Contents</a></li>
38 <li><a href="#METADATA_ATTACHMENT">METADATA_ATTACHMENT Contents</a></li>
Chris Lattner69b3e402007-05-13 01:39:44 +0000[diff] [blame]39 </ol>
40 </li>
Reid Spencer2c1ce4f2007-01-20 23:21:08 +0000[diff] [blame]41</ol>
42<div class="doc_author">
Chris Lattnerf19b8e42007-10-08 18:42:45 +0000[diff] [blame]43 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
44 and <a href="http://www.reverberate.org">Joshua Haberman</a>.
Reid Spencer2c1ce4f2007-01-20 23:21:08 +0000[diff] [blame]45</p>
46</div>
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]47
Reid Spencer2c1ce4f2007-01-20 23:21:08 +0000[diff] [blame]48<!-- *********************************************************************** -->
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]49<div class="doc_section"> <a name="abstract">Abstract</a></div>
Reid Spencer2c1ce4f2007-01-20 23:21:08 +0000[diff] [blame]50<!-- *********************************************************************** -->
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]51
Reid Spencer2c1ce4f2007-01-20 23:21:08 +0000[diff] [blame]52<div class="doc_text">
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]53
54<p>This document describes the LLVM bitstream file format and the encoding of
55the LLVM IR into it.</p>
56
Reid Spencer2c1ce4f2007-01-20 23:21:08 +0000[diff] [blame]57</div>
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]58
Reid Spencer2c1ce4f2007-01-20 23:21:08 +0000[diff] [blame]59<!-- *********************************************************************** -->
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]60<div class="doc_section"> <a name="overview">Overview</a></div>
Reid Spencer2c1ce4f2007-01-20 23:21:08 +0000[diff] [blame]61<!-- *********************************************************************** -->
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]62
Reid Spencer2c1ce4f2007-01-20 23:21:08 +0000[diff] [blame]63<div class="doc_text">
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]64
65<p>
66What is commonly known as the LLVM bitcode file format (also, sometimes
67anachronistically known as bytecode) is actually two things: a <a
68href="#bitstream">bitstream container format</a>
69and an <a href="#llvmir">encoding of LLVM IR</a> into the container format.</p>
70
71<p>
Reid Spencer58d05472007-05-12 08:01:52 +0000[diff] [blame]72The bitstream format is an abstract encoding of structured data, very
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]73similar to XML in some ways. Like XML, bitstream files contain tags, and nested
74structures, and you can parse the file without having to understand the tags.
75Unlike XML, the bitstream format is a binary encoding, and unlike XML it
76provides a mechanism for the file to self-describe "abbreviations", which are
77effectively size optimizations for the content.</p>
78
Chris Lattner6fa6a322008-07-09 05:14:23 +0000[diff] [blame]79<p>LLVM IR files may be optionally embedded into a <a
80href="#wrapper">wrapper</a> structure that makes it easy to embed extra data
81along with LLVM IR files.</p>
82
83<p>This document first describes the LLVM bitstream format, describes the
84wrapper format, then describes the record structure used by LLVM IR files.
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]85</p>
86
Reid Spencer2c1ce4f2007-01-20 23:21:08 +0000[diff] [blame]87</div>
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]88
89<!-- *********************************************************************** -->
90<div class="doc_section"> <a name="bitstream">Bitstream Format</a></div>
91<!-- *********************************************************************** -->
92
93<div class="doc_text">
94
95<p>
96The bitstream format is literally a stream of bits, with a very simple
97structure. This structure consists of the following concepts:
98</p>
99
100<ul>
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]101<li>A "<a href="#magic">magic number</a>" that identifies the contents of
102 the stream.</li>
103<li>Encoding <a href="#primitives">primitives</a> like variable bit-rate
104 integers.</li>
105<li><a href="#blocks">Blocks</a>, which define nested content.</li>
106<li><a href="#datarecord">Data Records</a>, which describe entities within the
107 file.</li>
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]108<li>Abbreviations, which specify compression optimizations for the file.</li>
109</ul>
110
111<p>Note that the <a
112href="CommandGuide/html/llvm-bcanalyzer.html">llvm-bcanalyzer</a> tool can be
113used to dump and inspect arbitrary bitstreams, which is very useful for
114understanding the encoding.</p>
115
116</div>
117
118<!-- ======================================================================= -->
119<div class="doc_subsection"><a name="magic">Magic Numbers</a>
120</div>
121
122<div class="doc_text">
123
Chris Lattnerf19b8e42007-10-08 18:42:45 +0000[diff] [blame]124<p>The first two bytes of a bitcode file are 'BC' (0x42, 0x43).
125The second two bytes are an application-specific magic number. Generic
126bitcode tools can look at only the first two bytes to verify the file is
127bitcode, while application-specific programs will want to look at all four.</p>
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]128
129</div>
130
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]131<!-- ======================================================================= -->
132<div class="doc_subsection"><a name="primitives">Primitives</a>
133</div>
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]134
135<div class="doc_text">
136
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]137<p>
Chris Lattnerf19b8e42007-10-08 18:42:45 +0000[diff] [blame]138A bitstream literally consists of a stream of bits, which are read in order
139starting with the least significant bit of each byte. The stream is made up of a
Chris Lattner69b3e402007-05-13 01:39:44 +0000[diff] [blame]140number of primitive values that encode a stream of unsigned integer values.
141These
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]142integers are are encoded in two ways: either as <a href="#fixedwidth">Fixed
143Width Integers</a> or as <a href="#variablewidth">Variable Width
144Integers</a>.
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]145</p>
146
147</div>
148
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]149<!-- _______________________________________________________________________ -->
150<div class="doc_subsubsection"> <a name="fixedwidth">Fixed Width Integers</a>
151</div>
152
153<div class="doc_text">
154
155<p>Fixed-width integer values have their low bits emitted directly to the file.
156 For example, a 3-bit integer value encodes 1 as 001. Fixed width integers
157 are used when there are a well-known number of options for a field. For
158 example, boolean values are usually encoded with a 1-bit wide integer.
159</p>
160
161</div>
162
163<!-- _______________________________________________________________________ -->
164<div class="doc_subsubsection"> <a name="variablewidth">Variable Width
165Integers</a></div>
166
167<div class="doc_text">
168
169<p>Variable-width integer (VBR) values encode values of arbitrary size,
170optimizing for the case where the values are small. Given a 4-bit VBR field,
171any 3-bit value (0 through 7) is encoded directly, with the high bit set to
172zero. Values larger than N-1 bits emit their bits in a series of N-1 bit
173chunks, where all but the last set the high bit.</p>
174
175<p>For example, the value 27 (0x1B) is encoded as 1011 0011 when emitted as a
176vbr4 value. The first set of four bits indicates the value 3 (011) with a
177continuation piece (indicated by a high bit of 1). The next word indicates a
178value of 24 (011 << 3) with no continuation. The sum (3+24) yields the value
17927.
180</p>
181
182</div>
183
184<!-- _______________________________________________________________________ -->
185<div class="doc_subsubsection"> <a name="char6">6-bit characters</a></div>
186
187<div class="doc_text">
188
189<p>6-bit characters encode common characters into a fixed 6-bit field. They
Chris Lattnerf1d64e92007-05-12 07:50:14 +0000[diff] [blame]190represent the following characters with the following 6-bit values:</p>
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]191
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]192<div class="doc_code">
193<pre>
194'a' .. 'z' &mdash; 0 .. 25
195'A' .. 'Z' &mdash; 26 .. 51
196'0' .. '9' &mdash; 52 .. 61
197 '.' &mdash; 62
198 '_' &mdash; 63
199</pre>
200</div>
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]201
202<p>This encoding is only suitable for encoding characters and strings that
203consist only of the above characters. It is completely incapable of encoding
204characters not in the set.</p>
205
206</div>
207
208<!-- _______________________________________________________________________ -->
209<div class="doc_subsubsection"> <a name="wordalign">Word Alignment</a></div>
210
211<div class="doc_text">
212
213<p>Occasionally, it is useful to emit zero bits until the bitstream is a
214multiple of 32 bits. This ensures that the bit position in the stream can be
215represented as a multiple of 32-bit words.</p>
216
217</div>
218
219
220<!-- ======================================================================= -->
221<div class="doc_subsection"><a name="abbrevid">Abbreviation IDs</a>
222</div>
223
224<div class="doc_text">
225
226<p>
227A bitstream is a sequential series of <a href="#blocks">Blocks</a> and
228<a href="#datarecord">Data Records</a>. Both of these start with an
229abbreviation ID encoded as a fixed-bitwidth field. The width is specified by
230the current block, as described below. The value of the abbreviation ID
231specifies either a builtin ID (which have special meanings, defined below) or
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]232one of the abbreviation IDs defined for the current block by the stream itself.
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]233</p>
234
235<p>
236The set of builtin abbrev IDs is:
237</p>
238
239<ul>
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]240<li><tt>0 - <a href="#END_BLOCK">END_BLOCK</a></tt> &mdash; This abbrev ID marks
241 the end of the current block.</li>
242<li><tt>1 - <a href="#ENTER_SUBBLOCK">ENTER_SUBBLOCK</a></tt> &mdash; This
243 abbrev ID marks the beginning of a new block.</li>
244<li><tt>2 - <a href="#DEFINE_ABBREV">DEFINE_ABBREV</a></tt> &mdash; This defines
245 a new abbreviation.</li>
246<li><tt>3 - <a href="#UNABBREV_RECORD">UNABBREV_RECORD</a></tt> &mdash; This ID
247 specifies the definition of an unabbreviated record.</li>
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]248</ul>
249
Chris Lattnerdaeb63c2007-05-12 07:49:15 +0000[diff] [blame]250<p>Abbreviation IDs 4 and above are defined by the stream itself, and specify
251an <a href="#abbrev_records">abbreviated record encoding</a>.</p>
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]252
253</div>
254
255<!-- ======================================================================= -->
256<div class="doc_subsection"><a name="blocks">Blocks</a>
257</div>
258
259<div class="doc_text">
260
261<p>
262Blocks in a bitstream denote nested regions of the stream, and are identified by
263a content-specific id number (for example, LLVM IR uses an ID of 12 to represent
Chris Lattnerf19b8e42007-10-08 18:42:45 +0000[diff] [blame]264function bodies). Block IDs 0-7 are reserved for <a href="#stdblocks">standard blocks</a>
265whose meaning is defined by Bitcode; block IDs 8 and greater are
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]266application specific. Nested blocks capture the hierarchical structure of the data
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]267encoded in it, and various properties are associated with blocks as the file is
268parsed. Block definitions allow the reader to efficiently skip blocks
269in constant time if the reader wants a summary of blocks, or if it wants to
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]270efficiently skip data it does not understand. The LLVM IR reader uses this
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]271mechanism to skip function bodies, lazily reading them on demand.
272</p>
273
274<p>
275When reading and encoding the stream, several properties are maintained for the
276block. In particular, each block maintains:
277</p>
278
279<ol>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]280<li>A current abbrev id width. This value starts at 2 at the beginning of
281 the stream, and is set every time a
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]282 block record is entered. The block entry specifies the abbrev id width for
283 the body of the block.</li>
284
Chris Lattnerf19b8e42007-10-08 18:42:45 +0000[diff] [blame]285<li>A set of abbreviations. Abbreviations may be defined within a block, in
286 which case they are only defined in that block (neither subblocks nor
287 enclosing blocks see the abbreviation). Abbreviations can also be defined
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]288 inside a <tt><a href="#BLOCKINFO">BLOCKINFO</a></tt> block, in which case
289 they are defined in all blocks that match the ID that the BLOCKINFO block is
290 describing.
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]291</li>
292</ol>
293
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]294<p>
295As sub blocks are entered, these properties are saved and the new sub-block has
296its own set of abbreviations, and its own abbrev id width. When a sub-block is
297popped, the saved values are restored.
298</p>
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]299
300</div>
301
302<!-- _______________________________________________________________________ -->
303<div class="doc_subsubsection"> <a name="ENTER_SUBBLOCK">ENTER_SUBBLOCK
304Encoding</a></div>
305
306<div class="doc_text">
307
308<p><tt>[ENTER_SUBBLOCK, blockid<sub>vbr8</sub>, newabbrevlen<sub>vbr4</sub>,
309 &lt;align32bits&gt;, blocklen<sub>32</sub>]</tt></p>
310
311<p>
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]312The <tt>ENTER_SUBBLOCK</tt> abbreviation ID specifies the start of a new block
313record. The <tt>blockid</tt> value is encoded as an 8-bit VBR identifier, and
314indicates the type of block being entered, which can be
315a <a href="#stdblocks">standard block</a> or an application-specific block.
316The <tt>newabbrevlen</tt> value is a 4-bit VBR, which specifies the abbrev id
317width for the sub-block. The <tt>blocklen</tt> value is a 32-bit aligned value
318that specifies the size of the subblock in 32-bit words. This value allows the
319reader to skip over the entire block in one jump.
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]320</p>
321
322</div>
323
324<!-- _______________________________________________________________________ -->
325<div class="doc_subsubsection"> <a name="END_BLOCK">END_BLOCK
326Encoding</a></div>
327
328<div class="doc_text">
329
330<p><tt>[END_BLOCK, &lt;align32bits&gt;]</tt></p>
331
332<p>
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]333The <tt>END_BLOCK</tt> abbreviation ID specifies the end of the current block
334record. Its end is aligned to 32-bits to ensure that the size of the block is
335an even multiple of 32-bits.
336</p>
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]337
338</div>
339
340
341
342<!-- ======================================================================= -->
343<div class="doc_subsection"><a name="datarecord">Data Records</a>
344</div>
345
346<div class="doc_text">
Chris Lattnerdaeb63c2007-05-12 07:49:15 +0000[diff] [blame]347<p>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]348Data records consist of a record code and a number of (up to) 64-bit
349integer values. The interpretation of the code and values is
350application specific and may vary between different block types.
351Records can be encoded either using an unabbrev record, or with an
352abbreviation. In the LLVM IR format, for example, there is a record
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]353which encodes the target triple of a module. The code is
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]354<tt>MODULE_CODE_TRIPLE</tt>, and the values of the record are the
355ASCII codes for the characters in the string.
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]356</p>
Chris Lattnerdaeb63c2007-05-12 07:49:15 +0000[diff] [blame]357
358</div>
359
360<!-- _______________________________________________________________________ -->
361<div class="doc_subsubsection"> <a name="UNABBREV_RECORD">UNABBREV_RECORD
362Encoding</a></div>
363
364<div class="doc_text">
365
366<p><tt>[UNABBREV_RECORD, code<sub>vbr6</sub>, numops<sub>vbr6</sub>,
367 op0<sub>vbr6</sub>, op1<sub>vbr6</sub>, ...]</tt></p>
368
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]369<p>
370An <tt>UNABBREV_RECORD</tt> provides a default fallback encoding, which is both
371completely general and extremely inefficient. It can describe an arbitrary
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]372record by emitting the code and operands as VBRs.
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]373</p>
Chris Lattnerdaeb63c2007-05-12 07:49:15 +0000[diff] [blame]374
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]375<p>
376For example, emitting an LLVM IR target triple as an unabbreviated record
377requires emitting the <tt>UNABBREV_RECORD</tt> abbrevid, a vbr6 for the
378<tt>MODULE_CODE_TRIPLE</tt> code, a vbr6 for the length of the string, which is
379equal to the number of operands, and a vbr6 for each character. Because there
380are no letters with values less than 32, each letter would need to be emitted as
381at least a two-part VBR, which means that each letter would require at least 12
382bits. This is not an efficient encoding, but it is fully general.
383</p>
Chris Lattnerdaeb63c2007-05-12 07:49:15 +0000[diff] [blame]384
385</div>
386
387<!-- _______________________________________________________________________ -->
388<div class="doc_subsubsection"> <a name="abbrev_records">Abbreviated Record
389Encoding</a></div>
390
391<div class="doc_text">
392
393<p><tt>[&lt;abbrevid&gt;, fields...]</tt></p>
394
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]395<p>
396An abbreviated record is a abbreviation id followed by a set of fields that are
397encoded according to the <a href="#abbreviations">abbreviation definition</a>.
398This allows records to be encoded significantly more densely than records
399encoded with the <tt><a href="#UNABBREV_RECORD">UNABBREV_RECORD</a></tt> type,
400and allows the abbreviation types to be specified in the stream itself, which
401allows the files to be completely self describing. The actual encoding of
402abbreviations is defined below.
Chris Lattnerdaeb63c2007-05-12 07:49:15 +0000[diff] [blame]403</p>
404
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]405<p>The record code, which is the first field of an abbreviated record,
406may be encoded in the abbreviation definition (as a literal
407operand) or supplied in the abbreviated record (as a Fixed or VBR
408operand value).</p>
409
Chris Lattnerdaeb63c2007-05-12 07:49:15 +0000[diff] [blame]410</div>
411
412<!-- ======================================================================= -->
413<div class="doc_subsection"><a name="abbreviations">Abbreviations</a>
414</div>
415
416<div class="doc_text">
417<p>
418Abbreviations are an important form of compression for bitstreams. The idea is
419to specify a dense encoding for a class of records once, then use that encoding
420to emit many records. It takes space to emit the encoding into the file, but
421the space is recouped (hopefully plus some) when the records that use it are
422emitted.
423</p>
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]424
425<p>
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]426Abbreviations can be determined dynamically per client, per file. Because the
Chris Lattnerdaeb63c2007-05-12 07:49:15 +0000[diff] [blame]427abbreviations are stored in the bitstream itself, different streams of the same
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]428format can contain different sets of abbreviations according to the needs
429of the specific stream.
430As a concrete example, LLVM IR files usually emit an abbreviation
Chris Lattnerdaeb63c2007-05-12 07:49:15 +0000[diff] [blame]431for binary operators. If a specific LLVM module contained no or few binary
432operators, the abbreviation does not need to be emitted.
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]433</p>
Chris Lattnerdaeb63c2007-05-12 07:49:15 +0000[diff] [blame]434</div>
435
436<!-- _______________________________________________________________________ -->
437<div class="doc_subsubsection"><a name="DEFINE_ABBREV">DEFINE_ABBREV
438 Encoding</a></div>
439
440<div class="doc_text">
441
442<p><tt>[DEFINE_ABBREV, numabbrevops<sub>vbr5</sub>, abbrevop0, abbrevop1,
443 ...]</tt></p>
444
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]445<p>
446A <tt>DEFINE_ABBREV</tt> record adds an abbreviation to the list of currently
447defined abbreviations in the scope of this block. This definition only exists
448inside this immediate block &mdash; it is not visible in subblocks or enclosing
449blocks. Abbreviations are implicitly assigned IDs sequentially starting from 4
450(the first application-defined abbreviation ID). Any abbreviations defined in a
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]451<tt>BLOCKINFO</tt> record for the particular block type
452receive IDs first, in order, followed by any
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]453abbreviations defined within the block itself. Abbreviated data records
454reference this ID to indicate what abbreviation they are invoking.
455</p>
Chris Lattnerf19b8e42007-10-08 18:42:45 +0000[diff] [blame]456
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]457<p>
458An abbreviation definition consists of the <tt>DEFINE_ABBREV</tt> abbrevid
459followed by a VBR that specifies the number of abbrev operands, then the abbrev
Chris Lattnerdaeb63c2007-05-12 07:49:15 +0000[diff] [blame]460operands themselves. Abbreviation operands come in three forms. They all start
461with a single bit that indicates whether the abbrev operand is a literal operand
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]462(when the bit is 1) or an encoding operand (when the bit is 0).
463</p>
Chris Lattnerdaeb63c2007-05-12 07:49:15 +0000[diff] [blame]464
465<ol>
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]466<li>Literal operands &mdash; <tt>[1<sub>1</sub>, litvalue<sub>vbr8</sub>]</tt>
467&mdash; Literal operands specify that the value in the result is always a single
468specific value. This specific value is emitted as a vbr8 after the bit
469indicating that it is a literal operand.</li>
470<li>Encoding info without data &mdash; <tt>[0<sub>1</sub>,
471 encoding<sub>3</sub>]</tt> &mdash; Operand encodings that do not have extra
472 data are just emitted as their code.
Chris Lattnerdaeb63c2007-05-12 07:49:15 +0000[diff] [blame]473</li>
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]474<li>Encoding info with data &mdash; <tt>[0<sub>1</sub>, encoding<sub>3</sub>,
475value<sub>vbr5</sub>]</tt> &mdash; Operand encodings that do have extra data are
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]476emitted as their code, followed by the extra data.
Chris Lattnerdaeb63c2007-05-12 07:49:15 +0000[diff] [blame]477</li>
478</ol>
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]479
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]480<p>The possible operand encodings are:</p>
481
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]482<ul>
483<li>Fixed (code 1): The field should be emitted as
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]484 a <a href="#fixedwidth">fixed-width value</a>, whose width is specified by
485 the operand's extra data.</li>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]486<li>VBR (code 2): The field should be emitted as
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]487 a <a href="#variablewidth">variable-width value</a>, whose width is
488 specified by the operand's extra data.</li>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]489<li>Array (code 3): This field is an array of values. The array operand
490 has no extra data, but expects another operand to follow it, indicating
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]491 the element type of the array. When reading an array in an abbreviated
492 record, the first integer is a vbr6 that indicates the array length,
493 followed by the encoded elements of the array. An array may only occur as
494 the last operand of an abbreviation (except for the one final operand that
495 gives the array's type).</li>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]496<li>Char6 (code 4): This field should be emitted as
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]497 a <a href="#char6">char6-encoded value</a>. This operand type takes no
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]498 extra data. Char6 encoding is normally used as an array element type.
499 </li>
500<li>Blob (code 5): This field is emitted as a vbr6, followed by padding to a
Chris Lattnerdcd006b2009-04-06 21:50:39 +0000[diff] [blame]501 32-bit boundary (for alignment) and an array of 8-bit objects. The array of
502 bytes is further followed by tail padding to ensure that its total length is
503 a multiple of 4 bytes. This makes it very efficient for the reader to
504 decode the data without having to make a copy of it: it can use a pointer to
505 the data in the mapped in file and poke directly at it. A blob may only
506 occur as the last operand of an abbreviation.</li>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]507</ul>
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]508
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]509<p>
510For example, target triples in LLVM modules are encoded as a record of the
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]511form <tt>[TRIPLE, 'a', 'b', 'c', 'd']</tt>. Consider if the bitstream emitted
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]512the following abbrev entry:
513</p>
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]514
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]515<div class="doc_code">
516<pre>
517[0, Fixed, 4]
518[0, Array]
519[0, Char6]
520</pre>
521</div>
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]522
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]523<p>
524When emitting a record with this abbreviation, the above entry would be emitted
525as:
526</p>
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]527
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]528<div class="doc_code">
Bill Wendling903bcc42009-04-04 22:36:02 +0000[diff] [blame]529<p>
530<tt>[4<sub>abbrevwidth</sub>, 2<sub>4</sub>, 4<sub>vbr6</sub>, 0<sub>6</sub>,
5311<sub>6</sub>, 2<sub>6</sub>, 3<sub>6</sub>]</tt>
532</p>
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]533</div>
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]534
535<p>These values are:</p>
536
537<ol>
538<li>The first value, 4, is the abbreviation ID for this abbreviation.</li>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]539<li>The second value, 2, is the record code for <tt>TRIPLE</tt> records within LLVM IR file <tt>MODULE_BLOCK</tt> blocks.</li>
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]540<li>The third value, 4, is the length of the array.</li>
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]541<li>The rest of the values are the char6 encoded values
542 for <tt>"abcd"</tt>.</li>
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]543</ol>
544
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]545<p>
546With this abbreviation, the triple is emitted with only 37 bits (assuming a
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]547abbrev id width of 3). Without the abbreviation, significantly more space would
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]548be required to emit the target triple. Also, because the <tt>TRIPLE</tt> value
549is not emitted as a literal in the abbreviation, the abbreviation can also be
550used for any other string value.
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]551</p>
552
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]553</div>
554
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]555<!-- ======================================================================= -->
556<div class="doc_subsection"><a name="stdblocks">Standard Blocks</a>
557</div>
558
559<div class="doc_text">
560
561<p>
562In addition to the basic block structure and record encodings, the bitstream
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]563also defines specific built-in block types. These block types specify how the
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]564stream is to be decoded or other metadata. In the future, new standard blocks
Chris Lattnerf19b8e42007-10-08 18:42:45 +0000[diff] [blame]565may be added. Block IDs 0-7 are reserved for standard blocks.
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]566</p>
567
568</div>
569
570<!-- _______________________________________________________________________ -->
571<div class="doc_subsubsection"><a name="BLOCKINFO">#0 - BLOCKINFO
572Block</a></div>
573
574<div class="doc_text">
575
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]576<p>
577The <tt>BLOCKINFO</tt> block allows the description of metadata for other
578blocks. The currently specified records are:
579</p>
580
581<div class="doc_code">
582<pre>
583[SETBID (#1), blockid]
584[DEFINE_ABBREV, ...]
Chris Lattnerf9a3ec82009-04-26 22:21:57 +0000[diff] [blame]585[BLOCKNAME, ...name...]
586[SETRECORDNAME, RecordID, ...name...]
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]587</pre>
588</div>
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]589
590<p>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]591The <tt>SETBID</tt> record (code 1) indicates which block ID is being
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]592described. <tt>SETBID</tt> records can occur multiple times throughout the
593block to change which block ID is being described. There must be
594a <tt>SETBID</tt> record prior to any other records.
Chris Lattnerf19b8e42007-10-08 18:42:45 +0000[diff] [blame]595</p>
596
597<p>
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]598Standard <tt>DEFINE_ABBREV</tt> records can occur inside <tt>BLOCKINFO</tt>
599blocks, but unlike their occurrence in normal blocks, the abbreviation is
600defined for blocks matching the block ID we are describing, <i>not</i> the
601<tt>BLOCKINFO</tt> block itself. The abbreviations defined
602in <tt>BLOCKINFO</tt> blocks receive abbreviation IDs as described
603in <tt><a href="#DEFINE_ABBREV">DEFINE_ABBREV</a></tt>.
Chris Lattnerf19b8e42007-10-08 18:42:45 +0000[diff] [blame]604</p>
605
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]606<p>The <tt>BLOCKNAME</tt> record (code 2) can optionally occur in this block. The elements of
607the record are the bytes of the string name of the block. llvm-bcanalyzer can use
Chris Lattnerf9a3ec82009-04-26 22:21:57 +0000[diff] [blame]608this to dump out bitcode files symbolically.</p>
609
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]610<p>The <tt>SETRECORDNAME</tt> record (code 3) can also optionally occur in this block. The
611first operand value is a record ID number, and the rest of the elements of the record are
612the bytes for the string name of the record. llvm-bcanalyzer can use
Chris Lattnerf9a3ec82009-04-26 22:21:57 +0000[diff] [blame]613this to dump out bitcode files symbolically.</p>
614
Chris Lattnerf19b8e42007-10-08 18:42:45 +0000[diff] [blame]615<p>
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]616Note that although the data in <tt>BLOCKINFO</tt> blocks is described as
617"metadata," the abbreviations they contain are essential for parsing records
618from the corresponding blocks. It is not safe to skip them.
Chris Lattner7300af52007-05-13 00:59:52 +0000[diff] [blame]619</p>
620
621</div>
Chris Lattner3a1716d2007-05-12 05:37:42 +0000[diff] [blame]622
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]623<!-- *********************************************************************** -->
Chris Lattner6fa6a322008-07-09 05:14:23 +0000[diff] [blame]624<div class="doc_section"> <a name="wrapper">Bitcode Wrapper Format</a></div>
625<!-- *********************************************************************** -->
626
627<div class="doc_text">
628
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]629<p>
630Bitcode files for LLVM IR may optionally be wrapped in a simple wrapper
Chris Lattner6fa6a322008-07-09 05:14:23 +0000[diff] [blame]631structure. This structure contains a simple header that indicates the offset
632and size of the embedded BC file. This allows additional information to be
633stored alongside the BC file. The structure of this file header is:
634</p>
635
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]636<div class="doc_code">
Bill Wendling903bcc42009-04-04 22:36:02 +0000[diff] [blame]637<p>
638<tt>[Magic<sub>32</sub>, Version<sub>32</sub>, Offset<sub>32</sub>,
639Size<sub>32</sub>, CPUType<sub>32</sub>]</tt>
640</p>
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]641</div>
Chris Lattner6fa6a322008-07-09 05:14:23 +0000[diff] [blame]642
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]643<p>
644Each of the fields are 32-bit fields stored in little endian form (as with
Chris Lattner6fa6a322008-07-09 05:14:23 +0000[diff] [blame]645the rest of the bitcode file fields). The Magic number is always
646<tt>0x0B17C0DE</tt> and the version is currently always <tt>0</tt>. The Offset
647field is the offset in bytes to the start of the bitcode stream in the file, and
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]648the Size field is the size in bytes of the stream. CPUType is a target-specific
Chris Lattner6fa6a322008-07-09 05:14:23 +0000[diff] [blame]649value that can be used to encode the CPU of the target.
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]650</p>
Chris Lattner6fa6a322008-07-09 05:14:23 +0000[diff] [blame]651
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]652</div>
Chris Lattner6fa6a322008-07-09 05:14:23 +0000[diff] [blame]653
654<!-- *********************************************************************** -->
Chris Lattnere9ef4572007-05-12 03:23:40 +0000[diff] [blame]655<div class="doc_section"> <a name="llvmir">LLVM IR Encoding</a></div>
656<!-- *********************************************************************** -->
657
658<div class="doc_text">
659
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]660<p>
661LLVM IR is encoded into a bitstream by defining blocks and records. It uses
Chris Lattner69b3e402007-05-13 01:39:44 +0000[diff] [blame]662blocks for things like constant pools, functions, symbol tables, etc. It uses
663records for things like instructions, global variable descriptors, type
664descriptions, etc. This document does not describe the set of abbreviations
665that the writer uses, as these are fully self-described in the file, and the
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]666reader is not allowed to build in any knowledge of this.
667</p>
Chris Lattner69b3e402007-05-13 01:39:44 +0000[diff] [blame]668
669</div>
670
671<!-- ======================================================================= -->
672<div class="doc_subsection"><a name="basics">Basics</a>
673</div>
674
675<!-- _______________________________________________________________________ -->
676<div class="doc_subsubsection"><a name="ir_magic">LLVM IR Magic Number</a></div>
677
678<div class="doc_text">
679
680<p>
681The magic number for LLVM IR files is:
682</p>
683
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]684<div class="doc_code">
Bill Wendling903bcc42009-04-04 22:36:02 +0000[diff] [blame]685<p>
686<tt>[0x0<sub>4</sub>, 0xC<sub>4</sub>, 0xE<sub>4</sub>, 0xD<sub>4</sub>]</tt>
687</p>
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]688</div>
Chris Lattner69b3e402007-05-13 01:39:44 +0000[diff] [blame]689
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]690<p>
691When combined with the bitcode magic number and viewed as bytes, this is
692<tt>"BC&nbsp;0xC0DE"</tt>.
693</p>
Chris Lattner69b3e402007-05-13 01:39:44 +0000[diff] [blame]694
695</div>
696
697<!-- _______________________________________________________________________ -->
698<div class="doc_subsubsection"><a name="ir_signed_vbr">Signed VBRs</a></div>
699
700<div class="doc_text">
701
702<p>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]703<a href="#variablewidth">Variable Width Integer</a> encoding is an efficient way to
704encode arbitrary sized unsigned values, but is an extremely inefficient for
705encoding signed values, as signed values are otherwise treated as maximally large
706unsigned values.
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]707</p>
Chris Lattner69b3e402007-05-13 01:39:44 +0000[diff] [blame]708
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]709<p>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]710As such, signed VBR values of a specific width are emitted as follows:
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]711</p>
Chris Lattner69b3e402007-05-13 01:39:44 +0000[diff] [blame]712
713<ul>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]714<li>Positive values are emitted as VBRs of the specified width, but with their
Chris Lattner69b3e402007-05-13 01:39:44 +0000[diff] [blame]715 value shifted left by one.</li>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]716<li>Negative values are emitted as VBRs of the specified width, but the negated
Chris Lattner69b3e402007-05-13 01:39:44 +0000[diff] [blame]717 value is shifted left by one, and the low bit is set.</li>
718</ul>
719
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]720<p>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]721With this encoding, small positive and small negative values can both
722be emitted efficiently. Signed VBR encoding is used in
723<tt>CST_CODE_INTEGER</tt> and <tt>CST_CODE_WIDE_INTEGER</tt> records
724within <tt>CONSTANTS_BLOCK</tt> blocks.
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]725</p>
Chris Lattner69b3e402007-05-13 01:39:44 +0000[diff] [blame]726
727</div>
728
729
730<!-- _______________________________________________________________________ -->
731<div class="doc_subsubsection"><a name="ir_blocks">LLVM IR Blocks</a></div>
732
733<div class="doc_text">
734
735<p>
736LLVM IR is defined with the following blocks:
737</p>
738
739<ul>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]740<li>8 &mdash; <a href="#MODULE_BLOCK"><tt>MODULE_BLOCK</tt></a> &mdash; This is the top-level block that
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]741 contains the entire module, and describes a variety of per-module
742 information.</li>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]743<li>9 &mdash; <a href="#PARAMATTR_BLOCK"><tt>PARAMATTR_BLOCK</tt></a> &mdash; This enumerates the parameter
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]744 attributes.</li>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]745<li>10 &mdash; <a href="#TYPE_BLOCK"><tt>TYPE_BLOCK</tt></a> &mdash; This describes all of the types in
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]746 the module.</li>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]747<li>11 &mdash; <a href="#CONSTANTS_BLOCK"><tt>CONSTANTS_BLOCK</tt></a> &mdash; This describes constants for a
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]748 module or function.</li>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]749<li>12 &mdash; <a href="#FUNCTION_BLOCK"><tt>FUNCTION_BLOCK</tt></a> &mdash; This describes a function
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]750 body.</li>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]751<li>13 &mdash; <a href="#TYPE_SYMTAB_BLOCK"><tt>TYPE_SYMTAB_BLOCK</tt></a> &mdash; This describes the type symbol
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]752 table.</li>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]753<li>14 &mdash; <a href="#VALUE_SYMTAB_BLOCK"><tt>VALUE_SYMTAB_BLOCK</tt></a> &mdash; This describes a value symbol
Bill Wendlingbb7425f2009-04-04 22:27:03 +0000[diff] [blame]754 table.</li>
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]755<li>15 &mdash; <a href="#METADATA_BLOCK"><tt>METADATA_BLOCK</tt></a> &mdash; This describes metadata items.</li>
756<li>16 &mdash; <a href="#METADATA_ATTACHMENT"><tt>METADATA_ATTACHMENT</tt></a> &mdash; This contains records associating metadata with function instruction values.</li>
Chris Lattner69b3e402007-05-13 01:39:44 +0000[diff] [blame]757</ul>
758
759</div>
760
761<!-- ======================================================================= -->
762<div class="doc_subsection"><a name="MODULE_BLOCK">MODULE_BLOCK Contents</a>
763</div>
764
765<div class="doc_text">
766
Chris Lattner5c303e82009-10-29 04:25:46 +0000[diff] [blame]767<p>The <tt>MODULE_BLOCK</tt> block (id 8) is the top-level block for LLVM
768bitcode files, and each bitcode file must contain exactly one. In
769addition to records (described below) containing information
770about the module, a <tt>MODULE_BLOCK</tt> block may contain the
771following sub-blocks:
772</p>
773
774<ul>
775<li><a href="#BLOCKINFO"><tt>BLOCKINFO</tt></a></li>
776<li><a href="#PARAMATTR_BLOCK"><tt>PARAMATTR_BLOCK</tt></a></li>
777<li><a href="#TYPE_BLOCK"><tt>TYPE_BLOCK</tt></a></li>
778<li><a href="#TYPE_SYMTAB_BLOCK"><tt>TYPE_SYMTAB_BLOCK</tt></a></li>
779<li><a href="#VALUE_SYMTAB_BLOCK"><tt>VALUE_SYMTAB_BLOCK</tt></a></li>
780<li><a href="#CONSTANTS_BLOCK"><tt>CONSTANTS_BLOCK</tt></a></li>
781<li><a href="#FUNCTION_BLOCK"><tt>FUNCTION_BLOCK</tt></a></li>
782<li><a href="#METADATA_BLOCK"><tt>METADATA_BLOCK</tt></a></li>
783</ul>
784
785</div>
786
787<!-- _______________________________________________________________________ -->
788<div class="doc_subsubsection"><a name="MODULE_CODE_VERSION">MODULE_CODE_VERSION Record</a>
789</div>
790
791<div class="doc_text">
792
793<p><tt>[VERSION, version#]</tt></p>
794
795<p>The <tt>VERSION</tt> record (code 1) contains a single value
796indicating the format version. Only version 0 is supported at this
797time.</p>
798</div>
799
800<!-- _______________________________________________________________________ -->
801<div class="doc_subsubsection"><a name="MODULE_CODE_TRIPLE">MODULE_CODE_TRIPLE Record</a>
802</div>
803
804<div class="doc_text">
805<p><tt>[TRIPLE, ...string...]</tt></p>
806
807<p>The <tt>TRIPLE</tt> record (code 2) contains a variable number of
808values representing the bytes of the <tt>target triple</tt>
809specification string.</p>
810</div>
811
812<!-- _______________________________________________________________________ -->
813<div class="doc_subsubsection"><a name="MODULE_CODE_DATALAYOUT">MODULE_CODE_DATALAYOUT Record</a>
814</div>
815
816<div class="doc_text">
817<p><tt>[DATALAYOUT, ...string...]</tt></p>
818
819<p>The <tt>DATALAYOUT</tt> record (code 3) contains a variable number of
820values representing the bytes of the <tt>target datalayout</tt>
821specification string.</p>
822</div>
823
824<!-- _______________________________________________________________________ -->
825<div class="doc_subsubsection"><a name="MODULE_CODE_ASM">MODULE_CODE_ASM Record</a>
826</div>
827
828<div class="doc_text">
829<p><tt>[ASM, ...string...]</tt></p>
830
831<p>The <tt>ASM</tt> record (code 4) contains a variable number of
832values representing the bytes of <tt>module asm</tt> strings, with
833individual assembly blocks separated by newline (ASCII 10) characters.</p>
834</div>
835
836<!-- _______________________________________________________________________ -->
837<div class="doc_subsubsection"><a name="MODULE_CODE_SECTIONNAME">MODULE_CODE_SECTIONNAME Record</a>
838</div>
839
840<div class="doc_text">
841<p><tt>[SECTIONNAME, ...string...]</tt></p>
842
843<p>The <tt>SECTIONNAME</tt> record (code 5) contains a variable number
844of values representing the bytes of a single section name
845string. There should be one <tt>SECTIONNAME</tt> record for each
846section name referenced (e.g., in global variable or function
847<tt>section</tt> attributes) within the module. These records can be
848referenced by the 1-based index in the <i>section</i> fields of
849<tt>GLOBALVAR</tt> or <tt>FUNCTION</tt> records.</p>
850</div>
851
852<!-- _______________________________________________________________________ -->
853<div class="doc_subsubsection"><a name="MODULE_CODE_DEPLIB">MODULE_CODE_DEPLIB Record</a>
854</div>
855
856<div class="doc_text">
857<p><tt>[DEPLIB, ...string...]</tt></p>
858
859<p>The <tt>DEPLIB</tt> record (code 6) contains a variable number of
860values representing the bytes of a single dependent library name
861string, one of the libraries mentioned in a <tt>deplibs</tt>
862declaration. There should be one <tt>DEPLIB</tt> record for each
863library name referenced.</p>
864</div>
865
866<!-- _______________________________________________________________________ -->
867<div class="doc_subsubsection"><a name="MODULE_CODE_GLOBALVAR">MODULE_CODE_GLOBALVAR Record</a>
868</div>
869
870<div class="doc_text">
871<p><tt>[GLOBALVAR, pointer type, isconst, initid, linkage, alignment, section, visibility, threadlocal]</tt></p>
872
873<p>The <tt>GLOBALVAR</tt> record (code 7) marks the declaration or
874definition of a global variable. The operand fields are:</p>
875
876<ul>
877<li><i>pointer type</i>: The type index of the pointer type used to point to
878this global variable</li>
879
880<li><i>isconst</i>: Non-zero if the variable is treated as constant within
881the module, or zero if it is not</li>
882
883<li><i>initid</i>: If non-zero, the value index of the initializer for this
884variable, plus 1.</li>
885
886<li><a name="linkage"><i>linkage</i></a>: An encoding of the linkage
887type for this variable:
888 <ul>
889 <li><tt>external</tt>: code 0</li>
890 <li><tt>weak</tt>: code 1</li>
891 <li><tt>appending</tt>: code 2</li>
892 <li><tt>internal</tt>: code 3</li>
893 <li><tt>linkonce</tt>: code 4</li>
894 <li><tt>dllimport</tt>: code 5</li>
895 <li><tt>dllexport</tt>: code 6</li>
896 <li><tt>extern_weak</tt>: code 7</li>
897 <li><tt>common</tt>: code 8</li>
898 <li><tt>private</tt>: code 9</li>
899 <li><tt>weak_odr</tt>: code 10</li>
900 <li><tt>linkonce_odr</tt>: code 11</li>
901 <li><tt>available_externally</tt>: code 12</li>
902 <li><tt>linker_private</tt>: code 13</li>
903 </ul>
904</li>
905
906<li><i>alignment</i>: The logarithm base 2 of the variable's requested
907alignment, plus 1</li>
908
909<li><i>section</i>: If non-zero, the 1-based section index in the
910table of <a href="#MODULE_CODE_SECTIONNAME">MODULE_CODE_SECTIONNAME</a>
911entries.</li>
912
913<li><a name="visibility"><i>visibility</i></a>: If present, an
914encoding of the visibility of this variable:
915 <ul>
916 <li><tt>default</tt>: code 0</li>
917 <li><tt>hidden</tt>: code 1</li>
918 <li><tt>protected</tt>: code 2</li>
919 </ul>
920</li>
921
922<li><i>threadlocal</i>: If present and non-zero, indicates that the variable
923is <tt>thread_local</tt></li>
924
925</ul>
926</div>
927
928<!-- _______________________________________________________________________ -->
929<div class="doc_subsubsection"><a name="MODULE_CODE_FUNCTION">MODULE_CODE_FUNCTION Record</a>
930</div>
931
932<div class="doc_text">
933
934<p><tt>[FUNCTION, type, callingconv, isproto, linkage, paramattr, alignment, section, visibility, gc]</tt></p>
935
936<p>The <tt>FUNCTION</tt> record (code 8) marks the declaration or
937definition of a function. The operand fields are:</p>
938
939<ul>
940<li><i>type</i>: The type index of the function type describing this function</li>
941
942<li><i>callingconv</i>: The calling convention number:
943 <ul>
944 <li><tt>ccc</tt>: code 0</li>
945 <li><tt>fastcc</tt>: code 8</li>
946 <li><tt>coldcc</tt>: code 9</li>
947 <li><tt>x86_stdcallcc</tt>: code 64</li>
948 <li><tt>x86_fastcallcc</tt>: code 65</li>
949 <li><tt>arm_apcscc</tt>: code 66</li>
950 <li><tt>arm_aapcscc</tt>: code 67</li>
951 <li><tt>arm_aapcs_vfpcc</tt>: code 68</li>
952 </ul>
953</li>
954
955<li><i>isproto</i>: Non-zero if this entry represents a declaration
956rather than a definition</li>
957
958<li><i>linkage</i>: An encoding of the <a href="#linkage">linkage type</a>
959for this function</li>
960
961<li><i>paramattr</i>: If nonzero, the 1-based parameter attribute index
962into the table of <a href="#PARAMATTR_CODE_ENTRY">PARAMATTR_CODE_ENTRY</a>
963entries.</li>
964
965<li><i>alignment</i>: The logarithm base 2 of the function's requested
966alignment, plus 1</li>
967
968<li><i>section</i>: If non-zero, the 1-based section index in the
969table of <a href="#MODULE_CODE_SECTIONNAME">MODULE_CODE_SECTIONNAME</a>
970entries.</li>
971
972<li><i>visibility</i>: An encoding of the <a href="#visibility">visibility</a>
973 of this function</li>
974
975<li><i>gc</i>: If present and nonzero, the 1-based garbage collector
976index in the table of
977<a href="#MODULE_CODE_GCNAME">MODULE_CODE_GCNAME</a> entries.</li>
978</ul>
979</div>
980
981<!-- _______________________________________________________________________ -->
982<div class="doc_subsubsection"><a name="MODULE_CODE_ALIAS">MODULE_CODE_ALIAS Record</a>
983</div>
984
985<div class="doc_text">
986
987<p><tt>[ALIAS, alias type, aliasee val#, linkage, visibility]</tt></p>
988
989<p>The <tt>ALIAS</tt> record (code 9) marks the definition of an
990alias. The operand fields are</p>
991
992<ul>
993<li><i>alias type</i>: The type index of the alias</li>
994
995<li><i>aliasee val#</i>: The value index of the aliased value</li>
996
997<li><i>linkage</i>: An encoding of the <a href="#linkage">linkage type</a>
998for this alias</li>
999
1000<li><i>visibility</i>: If present, an encoding of the
1001<a href="#visibility">visibility</a> of the alias</li>
1002
1003</ul>
1004</div>
1005
1006<!-- _______________________________________________________________________ -->
1007<div class="doc_subsubsection"><a name="MODULE_CODE_PURGEVALS">MODULE_CODE_PURGEVALS Record</a>
1008</div>
1009
1010<div class="doc_text">
1011<p><tt>[PURGEVALS, numvals]</tt></p>
1012
1013<p>The <tt>PURGEVALS</tt> record (code 10) resets the module-level
1014value list to the size given by the single operand value. Module-level
1015value list items are added by <tt>GLOBALVAR</tt>, <tt>FUNCTION</tt>,
1016and <tt>ALIAS</tt> records. After a <tt>PURGEVALS</tt> record is seen,
1017new value indices will start from the given <i>numvals</i> value.</p>
1018</div>
1019
1020<!-- _______________________________________________________________________ -->
1021<div class="doc_subsubsection"><a name="MODULE_CODE_GCNAME">MODULE_CODE_GCNAME Record</a>
1022</div>
1023
1024<div class="doc_text">
1025<p><tt>[GCNAME, ...string...]</tt></p>
1026
1027<p>The <tt>GCNAME</tt> record (code 11) contains a variable number of
1028values representing the bytes of a single garbage collector name
1029string. There should be one <tt>GCNAME</tt> record for each garbage
1030collector name referenced in function <tt>gc</tt> attributes within
1031the module. These records can be referenced by 1-based index in the <i>gc</i>
1032fields of <tt>FUNCTION</tt> records.</p>
1033</div>
1034
1035<!-- ======================================================================= -->
1036<div class="doc_subsection"><a name="PARAMATTR_BLOCK">PARAMATTR_BLOCK Contents</a>
1037</div>
1038
1039<div class="doc_text">
1040
1041<p>The <tt>PARAMATTR_BLOCK</tt> block (id 9) ...
1042</p>
1043
1044</div>
1045
1046
1047<!-- _______________________________________________________________________ -->
1048<div class="doc_subsubsection"><a name="PARAMATTR_CODE_ENTRY">PARAMATTR_CODE_ENTRY Record</a>
1049</div>
1050
1051<div class="doc_text">
1052
1053<p><tt>[ENTRY, paramidx0, attr0, paramidx1, attr1...]</tt></p>
1054
1055<p>The <tt>ENTRY</tt> record (code 1) ...
1056</p>
1057</div>
1058
1059<!-- ======================================================================= -->
1060<div class="doc_subsection"><a name="TYPE_BLOCK">TYPE_BLOCK Contents</a>
1061</div>
1062
1063<div class="doc_text">
1064
1065<p>The <tt>TYPE_BLOCK</tt> block (id 10) ...
1066</p>
1067
1068</div>
1069
1070
1071<!-- ======================================================================= -->
1072<div class="doc_subsection"><a name="CONSTANTS_BLOCK">CONSTANTS_BLOCK Contents</a>
1073</div>
1074
1075<div class="doc_text">
1076
1077<p>The <tt>CONSTANTS_BLOCK</tt> block (id 11) ...
1078</p>
1079
1080</div>
1081
1082
1083<!-- ======================================================================= -->
1084<div class="doc_subsection"><a name="FUNCTION_BLOCK">FUNCTION_BLOCK Contents</a>
1085</div>
1086
1087<div class="doc_text">
1088
1089<p>The <tt>FUNCTION_BLOCK</tt> block (id 12) ...
1090</p>
1091
1092<p>In addition to the record types described below, a
1093<tt>FUNCTION_BLOCK</tt> block may contain the following sub-blocks:
1094</p>
1095
1096<ul>
1097<li><a href="#CONSTANTS_BLOCK"><tt>CONSTANTS_BLOCK</tt></a></li>
1098<li><a href="#VALUE_SYMTAB_BLOCK"><tt>VALUE_SYMTAB_BLOCK</tt></a></li>
1099<li><a href="#METADATA_ATTACHMENT"><tt>METADATA_ATTACHMENT</tt></a></li>
1100</ul>
1101
1102</div>
1103
1104
1105<!-- ======================================================================= -->
1106<div class="doc_subsection"><a name="TYPE_SYMTAB_BLOCK">TYPE_SYMTAB_BLOCK Contents</a>
1107</div>
1108
1109<div class="doc_text">
1110
1111<p>The <tt>TYPE_SYMTAB_BLOCK</tt> block (id 13) ...
1112</p>
1113
1114</div>
1115
1116
1117<!-- ======================================================================= -->
1118<div class="doc_subsection"><a name="VALUE_SYMTAB_BLOCK">VALUE_SYMTAB_BLOCK Contents</a>
1119</div>
1120
1121<div class="doc_text">
1122
1123<p>The <tt>VALUE_SYMTAB_BLOCK</tt> block (id 14) ...
1124</p>
1125
1126</div>
1127
1128
1129<!-- ======================================================================= -->
1130<div class="doc_subsection"><a name="METADATA_BLOCK">METADATA_BLOCK Contents</a>
1131</div>
1132
1133<div class="doc_text">
1134
1135<p>The <tt>METADATA_BLOCK</tt> block (id 15) ...
1136</p>
1137
1138</div>
1139
1140
1141<!-- ======================================================================= -->
1142<div class="doc_subsection"><a name="METADATA_ATTACHMENT">METADATA_ATTACHMENT Contents</a>
1143</div>
1144
1145<div class="doc_text">
1146
1147<p>The <tt>METADATA_ATTACHMENT</tt> block (id 16) ...
Chris Lattner69b3e402007-05-13 01:39:44 +0000[diff] [blame]1148</p>
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