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Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]5<title>"Clang" CFE Internals Manual</title>
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18<div id="content">
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]19
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]20<h1>"Clang" CFE Internals Manual</h1>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]21
22<ul>
23<li><a href="#intro">Introduction</a></li>
Peter Collingbourne967c1182011-10-15 16:59:24 +0000[diff] [blame]24<li><a href="#libsupport">LLVM Support Library</a></li>
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]25<li><a href="#libbasic">The Clang 'Basic' Library</a>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]26 <ul>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]27 <li><a href="#Diagnostics">The Diagnostics Subsystem</a></li>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]28 <li><a href="#SourceLocation">The SourceLocation and SourceManager
29 classes</a></li>
Douglas Gregor715c92a2010-10-27 16:02:28 +0000[diff] [blame]30 <li><a href="#SourceRange">SourceRange and CharSourceRange</a></li>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]31 </ul>
32</li>
Daniel Dunbar27d9e9f2009-03-30 06:50:01 +0000[diff] [blame]33<li><a href="#libdriver">The Driver Library</a>
Daniel Dunbar27d9e9f2009-03-30 06:50:01 +0000[diff] [blame]34</li>
Douglas Gregor32110df2009-05-20 00:16:32 +0000[diff] [blame]35<li><a href="#pch">Precompiled Headers</a>
Daniel Dunbar27d9e9f2009-03-30 06:50:01 +0000[diff] [blame]36<li><a href="#libfrontend">The Frontend Library</a>
Daniel Dunbar27d9e9f2009-03-30 06:50:01 +0000[diff] [blame]37</li>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]38<li><a href="#liblex">The Lexer and Preprocessor Library</a>
39 <ul>
40 <li><a href="#Token">The Token class</a></li>
41 <li><a href="#Lexer">The Lexer class</a></li>
Chris Lattner3932fe02009-01-06 06:02:08 +0000[diff] [blame]42 <li><a href="#AnnotationToken">Annotation Tokens</a></li>
Chris Lattner79281252008-03-09 02:27:26 +0000[diff] [blame]43 <li><a href="#TokenLexer">The TokenLexer class</a></li>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]44 <li><a href="#MultipleIncludeOpt">The MultipleIncludeOpt class</a></li>
45 </ul>
46</li>
47<li><a href="#libparse">The Parser Library</a>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]48</li>
49<li><a href="#libast">The AST Library</a>
50 <ul>
51 <li><a href="#Type">The Type class and its subclasses</a></li>
52 <li><a href="#QualType">The QualType class</a></li>
Douglas Gregor2e1cd422008-11-17 14:58:09 +0000[diff] [blame]53 <li><a href="#DeclarationName">Declaration names</a></li>
Douglas Gregor074149e2009-01-05 19:45:36 +0000[diff] [blame]54 <li><a href="#DeclContext">Declaration contexts</a>
55 <ul>
56 <li><a href="#Redeclarations">Redeclarations and Overloads</a></li>
57 <li><a href="#LexicalAndSemanticContexts">Lexical and Semantic
58 Contexts</a></li>
59 <li><a href="#TransparentContexts">Transparent Declaration Contexts</a></li>
60 <li><a href="#MultiDeclContext">Multiply-Defined Declaration Contexts</a></li>
61 </ul>
62 </li>
Ted Kremenek8bc05712007-10-10 23:01:43 +0000[diff] [blame]63 <li><a href="#CFG">The CFG class</a></li>
Chris Lattner7bad1992008-11-16 21:48:07 +0000[diff] [blame]64 <li><a href="#Constants">Constant Folding in the Clang AST</a></li>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]65 </ul>
66</li>
Jeffrey Yasskin28dadd62011-01-28 23:41:54 +0000[diff] [blame]67<li><a href="#Howtos">Howto guides</a>
68 <ul>
69 <li><a href="#AddingAttributes">How to add an attribute</a></li>
Douglas Gregor1f634c62011-09-30 21:32:37 +0000[diff] [blame]70 <li><a href="#AddingExprStmt">How to add a new expression or statement</a></li>
Jeffrey Yasskin28dadd62011-01-28 23:41:54 +0000[diff] [blame]71 </ul>
72</li>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]73</ul>
74
75
76<!-- ======================================================================= -->
77<h2 id="intro">Introduction</h2>
78<!-- ======================================================================= -->
79
80<p>This document describes some of the more important APIs and internal design
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]81decisions made in the Clang C front-end. The purpose of this document is to
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]82both capture some of this high level information and also describe some of the
83design decisions behind it. This is meant for people interested in hacking on
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]84Clang, not for end-users. The description below is categorized by
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]85libraries, and does not describe any of the clients of the libraries.</p>
86
87<!-- ======================================================================= -->
Peter Collingbourne967c1182011-10-15 16:59:24 +0000[diff] [blame]88<h2 id="libsupport">LLVM Support Library</h2>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]89<!-- ======================================================================= -->
90
Peter Collingbourne967c1182011-10-15 16:59:24 +0000[diff] [blame]91<p>The LLVM libsupport library provides many underlying libraries and
92<a href="http://llvm.org/docs/ProgrammersManual.html">data-structures</a>,
93including command line option processing, various containers and a system
94abstraction layer, which is used for file system access.</p>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]95
96<!-- ======================================================================= -->
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]97<h2 id="libbasic">The Clang 'Basic' Library</h2>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]98<!-- ======================================================================= -->
99
100<p>This library certainly needs a better name. The 'basic' library contains a
101number of low-level utilities for tracking and manipulating source buffers,
102locations within the source buffers, diagnostics, tokens, target abstraction,
103and information about the subset of the language being compiled for.</p>
104
105<p>Part of this infrastructure is specific to C (such as the TargetInfo class),
106other parts could be reused for other non-C-based languages (SourceLocation,
107SourceManager, Diagnostics, FileManager). When and if there is future demand
108we can figure out if it makes sense to introduce a new library, move the general
109classes somewhere else, or introduce some other solution.</p>
110
111<p>We describe the roles of these classes in order of their dependencies.</p>
112
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]113
114<!-- ======================================================================= -->
115<h3 id="Diagnostics">The Diagnostics Subsystem</h3>
116<!-- ======================================================================= -->
117
118<p>The Clang Diagnostics subsystem is an important part of how the compiler
119communicates with the human. Diagnostics are the warnings and errors produced
120when the code is incorrect or dubious. In Clang, each diagnostic produced has
Sebastian Redl9bc2a992010-07-07 23:42:27 +0000[diff] [blame]121(at the minimum) a unique ID, an English translation associated with it, a <a
122href="#SourceLocation">SourceLocation</a> to "put the caret", and a severity (e.g.
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]123<tt>WARNING</tt> or <tt>ERROR</tt>). They can also optionally include a number
124of arguments to the dianostic (which fill in "%0"'s in the string) as well as a
125number of source ranges that related to the diagnostic.</p>
126
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]127<p>In this section, we'll be giving examples produced by the Clang command line
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]128driver, but diagnostics can be <a href="#DiagnosticClient">rendered in many
129different ways</a> depending on how the DiagnosticClient interface is
Sebastian Redl9bc2a992010-07-07 23:42:27 +0000[diff] [blame]130implemented. A representative example of a diagnostic is:</p>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]131
132<pre>
133t.c:38:15: error: invalid operands to binary expression ('int *' and '_Complex float')
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]134 <span style="color:darkgreen">P = (P-42) + Gamma*4;</span>
135 <span style="color:blue">~~~~~~ ^ ~~~~~~~</span>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]136</pre>
137
138<p>In this example, you can see the English translation, the severity (error),
139you can see the source location (the caret ("^") and file/line/column info),
140the source ranges "~~~~", arguments to the diagnostic ("int*" and "_Complex
141float"). You'll have to believe me that there is a unique ID backing the
142diagnostic :).</p>
143
144<p>Getting all of this to happen has several steps and involves many moving
145pieces, this section describes them and talks about best practices when adding
146a new diagnostic.</p>
147
Chris Lattnercc2ac1e2011-02-14 06:42:50 +0000[diff] [blame]148<!-- ============================= -->
149<h4>The Diagnostic*Kinds.td files</h4>
150<!-- ============================= -->
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]151
Chris Lattner4c50b692010-05-01 17:35:19 +0000[diff] [blame]152<p>Diagnostics are created by adding an entry to one of the <tt>
Chris Lattnercc2ac1e2011-02-14 06:42:50 +0000[diff] [blame]153clang/Basic/Diagnostic*Kinds.td</tt> files, depending on what library will
154be using it. From this file, tblgen generates the unique ID of the diagnostic,
155the severity of the diagnostic and the English translation + format string.</p>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]156
157<p>There is little sanity with the naming of the unique ID's right now. Some
158start with err_, warn_, ext_ to encode the severity into the name. Since the
159enum is referenced in the C++ code that produces the diagnostic, it is somewhat
160useful for it to be reasonably short.</p>
161
162<p>The severity of the diagnostic comes from the set {<tt>NOTE</tt>,
163<tt>WARNING</tt>, <tt>EXTENSION</tt>, <tt>EXTWARN</tt>, <tt>ERROR</tt>}. The
164<tt>ERROR</tt> severity is used for diagnostics indicating the program is never
165acceptable under any circumstances. When an error is emitted, the AST for the
166input code may not be fully built. The <tt>EXTENSION</tt> and <tt>EXTWARN</tt>
167severities are used for extensions to the language that Clang accepts. This
168means that Clang fully understands and can represent them in the AST, but we
169produce diagnostics to tell the user their code is non-portable. The difference
170is that the former are ignored by default, and the later warn by default. The
171<tt>WARNING</tt> severity is used for constructs that are valid in the currently
172selected source language but that are dubious in some way. The <tt>NOTE</tt>
Daniel Dunbar426b8632009-02-17 15:49:03 +0000[diff] [blame]173level is used to staple more information onto previous diagnostics.</p>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]174
175<p>These <em>severities</em> are mapped into a smaller set (the
176Diagnostic::Level enum, {<tt>Ignored</tt>, <tt>Note</tt>, <tt>Warning</tt>,
Chris Lattner0aad2972009-02-05 22:49:08 +0000[diff] [blame]177<tt>Error</tt>, <tt>Fatal</tt> }) of output <em>levels</em> by the diagnostics
Chris Lattnera180fdd2009-02-17 07:07:29 +0000[diff] [blame]178subsystem based on various configuration options. Clang internally supports a
179fully fine grained mapping mechanism that allows you to map almost any
180diagnostic to the output level that you want. The only diagnostics that cannot
181be mapped are <tt>NOTE</tt>s, which always follow the severity of the previously
182emitted diagnostic and <tt>ERROR</tt>s, which can only be mapped to
183<tt>Fatal</tt> (it is not possible to turn an error into a warning,
184for example).</p>
185
186<p>Diagnostic mappings are used in many ways. For example, if the user
187specifies <tt>-pedantic</tt>, <tt>EXTENSION</tt> maps to <tt>Warning</tt>, if
188they specify <tt>-pedantic-errors</tt>, it turns into <tt>Error</tt>. This is
189used to implement options like <tt>-Wunused_macros</tt>, <tt>-Wundef</tt> etc.
190</p>
191
192<p>
193Mapping to <tt>Fatal</tt> should only be used for diagnostics that are
194considered so severe that error recovery won't be able to recover sensibly from
195them (thus spewing a ton of bogus errors). One example of this class of error
196are failure to #include a file.
197</p>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]198
199<!-- ================= -->
200<h4>The Format String</h4>
201<!-- ================= -->
202
203<p>The format string for the diagnostic is very simple, but it has some power.
204It takes the form of a string in English with markers that indicate where and
205how arguments to the diagnostic are inserted and formatted. For example, here
206are some simple format strings:</p>
207
208<pre>
209 "binary integer literals are an extension"
210 "format string contains '\\0' within the string body"
211 "more '<b>%%</b>' conversions than data arguments"
Chris Lattner545b3682008-11-23 20:27:13 +0000[diff] [blame]212 "invalid operands to binary expression (<b>%0</b> and <b>%1</b>)"
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]213 "overloaded '<b>%0</b>' must be a <b>%select{unary|binary|unary or binary}2</b> operator"
214 " (has <b>%1</b> parameter<b>%s1</b>)"
215</pre>
216
217<p>These examples show some important points of format strings. You can use any
218 plain ASCII character in the diagnostic string except "%" without a problem,
219 but these are C strings, so you have to use and be aware of all the C escape
220 sequences (as in the second example). If you want to produce a "%" in the
221 output, use the "%%" escape sequence, like the third diagnostic. Finally,
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]222 Clang uses the "%...[digit]" sequences to specify where and how arguments to
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]223 the diagnostic are formatted.</p>
224
225<p>Arguments to the diagnostic are numbered according to how they are specified
226 by the C++ code that <a href="#producingdiag">produces them</a>, and are
227 referenced by <tt>%0</tt> .. <tt>%9</tt>. If you have more than 10 arguments
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]228 to your diagnostic, you are doing something wrong :). Unlike printf, there
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]229 is no requirement that arguments to the diagnostic end up in the output in
230 the same order as they are specified, you could have a format string with
231 <tt>"%1 %0"</tt> that swaps them, for example. The text in between the
232 percent and digit are formatting instructions. If there are no instructions,
233 the argument is just turned into a string and substituted in.</p>
234
235<p>Here are some "best practices" for writing the English format string:</p>
236
237<ul>
238<li>Keep the string short. It should ideally fit in the 80 column limit of the
Chris Lattnercc2ac1e2011-02-14 06:42:50 +0000[diff] [blame]239 <tt>DiagnosticKinds.td</tt> file. This avoids the diagnostic wrapping when
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]240 printed, and forces you to think about the important point you are conveying
241 with the diagnostic.</li>
242<li>Take advantage of location information. The user will be able to see the
243 line and location of the caret, so you don't need to tell them that the
244 problem is with the 4th argument to the function: just point to it.</li>
245<li>Do not capitalize the diagnostic string, and do not end it with a
246 period.</li>
247<li>If you need to quote something in the diagnostic string, use single
248 quotes.</li>
249</ul>
250
251<p>Diagnostics should never take random English strings as arguments: you
252shouldn't use <tt>"you have a problem with %0"</tt> and pass in things like
253<tt>"your argument"</tt> or <tt>"your return value"</tt> as arguments. Doing
Chris Lattnercc2ac1e2011-02-14 06:42:50 +0000[diff] [blame]254this prevents <a href="#translation">translating</a> the Clang diagnostics to
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]255other languages (because they'll get random English words in their otherwise
256localized diagnostic). The exceptions to this are C/C++ language keywords
257(e.g. auto, const, mutable, etc) and C/C++ operators (<tt>/=</tt>). Note
258that things like "pointer" and "reference" are not keywords. On the other
259hand, you <em>can</em> include anything that comes from the user's source code,
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]260including variable names, types, labels, etc. The 'select' format can be
261used to achieve this sort of thing in a localizable way, see below.</p>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]262
263<!-- ==================================== -->
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]264<h4>Formatting a Diagnostic Argument</h4>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]265<!-- ==================================== -->
266
267<p>Arguments to diagnostics are fully typed internally, and come from a couple
268different classes: integers, types, names, and random strings. Depending on
269the class of the argument, it can be optionally formatted in different ways.
270This gives the DiagnosticClient information about what the argument means
271without requiring it to use a specific presentation (consider this MVC for
272Clang :).</p>
273
274<p>Here are the different diagnostic argument formats currently supported by
275Clang:</p>
276
277<table>
278<tr><td colspan="2"><b>"s" format</b></td></tr>
279<tr><td>Example:</td><td><tt>"requires %1 parameter%s1"</tt></td></tr>
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]280<tr><td>Class:</td><td>Integers</td></tr>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]281<tr><td>Description:</td><td>This is a simple formatter for integers that is
282 useful when producing English diagnostics. When the integer is 1, it prints
283 as nothing. When the integer is not 1, it prints as "s". This allows some
Chris Lattner627b7052008-11-23 00:28:33 +0000[diff] [blame]284 simple grammatical forms to be to be handled correctly, and eliminates the
285 need to use gross things like <tt>"requires %1 parameter(s)"</tt>.</td></tr>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]286
287<tr><td colspan="2"><b>"select" format</b></td></tr>
288<tr><td>Example:</td><td><tt>"must be a %select{unary|binary|unary or binary}2
289 operator"</tt></td></tr>
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]290<tr><td>Class:</td><td>Integers</td></tr>
John McCall3a47e232010-01-14 19:12:17 +0000[diff] [blame]291<tr><td>Description:</td><td><p>This format specifier is used to merge multiple
Chris Lattnercc543342008-11-22 23:50:47 +0000[diff] [blame]292 related diagnostics together into one common one, without requiring the
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]293 difference to be specified as an English string argument. Instead of
Chris Lattnercc543342008-11-22 23:50:47 +0000[diff] [blame]294 specifying the string, the diagnostic gets an integer argument and the
295 format string selects the numbered option. In this case, the "%2" value
296 must be an integer in the range [0..2]. If it is 0, it prints 'unary', if
297 it is 1 it prints 'binary' if it is 2, it prints 'unary or binary'. This
298 allows other language translations to substitute reasonable words (or entire
299 phrases) based on the semantics of the diagnostic instead of having to do
John McCall3a47e232010-01-14 19:12:17 +0000[diff] [blame]300 things textually.</p>
301 <p>The selected string does undergo formatting.</p></td></tr>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]302
303<tr><td colspan="2"><b>"plural" format</b></td></tr>
Sebastian Redl68168562008-11-22 22:16:45 +0000[diff] [blame]304<tr><td>Example:</td><td><tt>"you have %1 %plural{1:mouse|:mice}1 connected to
305 your computer"</tt></td></tr>
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]306<tr><td>Class:</td><td>Integers</td></tr>
Sebastian Redl68168562008-11-22 22:16:45 +0000[diff] [blame]307<tr><td>Description:</td><td><p>This is a formatter for complex plural forms.
308 It is designed to handle even the requirements of languages with very
309 complex plural forms, as many Baltic languages have. The argument consists
310 of a series of expression/form pairs, separated by ':', where the first form
311 whose expression evaluates to true is the result of the modifier.</p>
312 <p>An expression can be empty, in which case it is always true. See the
313 example at the top. Otherwise, it is a series of one or more numeric
314 conditions, separated by ','. If any condition matches, the expression
315 matches. Each numeric condition can take one of three forms.</p>
316 <ul>
317 <li>number: A simple decimal number matches if the argument is the same
Chris Lattner627b7052008-11-23 00:28:33 +0000[diff] [blame]318 as the number. Example: <tt>"%plural{1:mouse|:mice}4"</tt></li>
Sebastian Redl68168562008-11-22 22:16:45 +0000[diff] [blame]319 <li>range: A range in square brackets matches if the argument is within
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]320 the range. Then range is inclusive on both ends. Example:
Chris Lattner627b7052008-11-23 00:28:33 +0000[diff] [blame]321 <tt>"%plural{0:none|1:one|[2,5]:some|:many}2"</tt></li>
322 <li>modulo: A modulo operator is followed by a number, and
323 equals sign and either a number or a range. The tests are the
324 same as for plain
Sebastian Redl68168562008-11-22 22:16:45 +0000[diff] [blame]325 numbers and ranges, but the argument is taken modulo the number first.
Chris Lattner627b7052008-11-23 00:28:33 +0000[diff] [blame]326 Example: <tt>"%plural{%100=0:even hundred|%100=[1,50]:lower half|:everything
327 else}1"</tt></li>
Sebastian Redl68168562008-11-22 22:16:45 +0000[diff] [blame]328 </ul>
329 <p>The parser is very unforgiving. A syntax error, even whitespace, will
330 abort, as will a failure to match the argument against any
331 expression.</p></td></tr>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]332
John McCall3a47e232010-01-14 19:12:17 +0000[diff] [blame]333<tr><td colspan="2"><b>"ordinal" format</b></td></tr>
334<tr><td>Example:</td><td><tt>"ambiguity in %ordinal0 argument"</tt></td></tr>
335<tr><td>Class:</td><td>Integers</td></tr>
336<tr><td>Description:</td><td><p>This is a formatter which represents the
337 argument number as an ordinal: the value <tt>1</tt> becomes <tt>1st</tt>,
338 <tt>3</tt> becomes <tt>3rd</tt>, and so on. Values less than <tt>1</tt>
339 are not supported.</p>
340 <p>This formatter is currently hard-coded to use English ordinals.</p></td></tr>
341
Chris Lattner077bf5e2008-11-24 03:33:13 +0000[diff] [blame]342<tr><td colspan="2"><b>"objcclass" format</b></td></tr>
343<tr><td>Example:</td><td><tt>"method %objcclass0 not found"</tt></td></tr>
344<tr><td>Class:</td><td>DeclarationName</td></tr>
345<tr><td>Description:</td><td><p>This is a simple formatter that indicates the
346 DeclarationName corresponds to an Objective-C class method selector. As
347 such, it prints the selector with a leading '+'.</p></td></tr>
348
349<tr><td colspan="2"><b>"objcinstance" format</b></td></tr>
350<tr><td>Example:</td><td><tt>"method %objcinstance0 not found"</tt></td></tr>
351<tr><td>Class:</td><td>DeclarationName</td></tr>
352<tr><td>Description:</td><td><p>This is a simple formatter that indicates the
353 DeclarationName corresponds to an Objective-C instance method selector. As
354 such, it prints the selector with a leading '-'.</p></td></tr>
355
Douglas Gregor47b9a1c2009-02-04 17:27:36 +0000[diff] [blame]356<tr><td colspan="2"><b>"q" format</b></td></tr>
357<tr><td>Example:</td><td><tt>"candidate found by name lookup is %q0"</tt></td></tr>
358<tr><td>Class:</td><td>NamedDecl*</td></tr>
359<tr><td>Description</td><td><p>This formatter indicates that the fully-qualified name of the declaration should be printed, e.g., "std::vector" rather than "vector".</p></td></tr>
Richard Trieue59331a2012-06-27 02:00:20 +0000[diff] [blame]360
361<tr><td colspan="2"><b>"diff" format</b></td></tr>
362<tr><td>Example:</td><td><tt>"no known conversion %diff{from | to | }1,2"</tt></td></tr>
363<tr><td>Class:</td><td>QualType</td></tr>
Sylvestre Ledrubed28ac2012-07-23 08:59:39 +0000[diff] [blame]364<tr><td>Description</td><td><p>This formatter takes two QualTypes and attempts to print a template difference between the two. If tree printing is off, the text inside the braces before the pipe is printed, with the formatted text replacing the $. If tree printing is on, the text after the pipe is printed and a type tree is printed after the diagnostic message.
Richard Trieu529cdf42012-06-29 21:12:16 +0000[diff] [blame]365</p></td></tr>
Douglas Gregor47b9a1c2009-02-04 17:27:36 +0000[diff] [blame]366
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]367</table>
368
Chris Lattnercc543342008-11-22 23:50:47 +0000[diff] [blame]369<p>It is really easy to add format specifiers to the Clang diagnostics system,
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]370but they should be discussed before they are added. If you are creating a lot
371of repetitive diagnostics and/or have an idea for a useful formatter, please
372bring it up on the cfe-dev mailing list.</p>
Chris Lattnercc543342008-11-22 23:50:47 +0000[diff] [blame]373
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]374<!-- ===================================================== -->
Chris Lattnercc2ac1e2011-02-14 06:42:50 +0000[diff] [blame]375<h4 id="producingdiag">Producing the Diagnostic</h4>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]376<!-- ===================================================== -->
377
Chris Lattnercc2ac1e2011-02-14 06:42:50 +0000[diff] [blame]378<p>Now that you've created the diagnostic in the DiagnosticKinds.td file, you
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]379need to write the code that detects the condition in question and emits the
380new diagnostic. Various components of Clang (e.g. the preprocessor, Sema,
Chris Lattner627b7052008-11-23 00:28:33 +0000[diff] [blame]381etc) provide a helper function named "Diag". It creates a diagnostic and
382accepts the arguments, ranges, and other information that goes along with
383it.</p>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]384
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]385<p>For example, the binary expression error comes from code like this:</p>
Chris Lattner627b7052008-11-23 00:28:33 +0000[diff] [blame]386
387<pre>
388 if (various things that are bad)
389 Diag(Loc, diag::err_typecheck_invalid_operands)
390 &lt;&lt; lex-&gt;getType() &lt;&lt; rex-&gt;getType()
391 &lt;&lt; lex-&gt;getSourceRange() &lt;&lt; rex-&gt;getSourceRange();
392</pre>
393
394<p>This shows that use of the Diag method: they take a location (a <a
395href="#SourceLocation">SourceLocation</a> object) and a diagnostic enum value
Chris Lattnercc2ac1e2011-02-14 06:42:50 +0000[diff] [blame]396(which matches the name from DiagnosticKinds.td). If the diagnostic takes
Chris Lattner627b7052008-11-23 00:28:33 +0000[diff] [blame]397arguments, they are specified with the &lt;&lt; operator: the first argument
398becomes %0, the second becomes %1, etc. The diagnostic interface allows you to
Chris Lattnerfd408ea2008-11-23 00:42:53 +0000[diff] [blame]399specify arguments of many different types, including <tt>int</tt> and
400<tt>unsigned</tt> for integer arguments, <tt>const char*</tt> and
401<tt>std::string</tt> for string arguments, <tt>DeclarationName</tt> and
402<tt>const IdentifierInfo*</tt> for names, <tt>QualType</tt> for types, etc.
403SourceRanges are also specified with the &lt;&lt; operator, but do not have a
404specific ordering requirement.</p>
Chris Lattner627b7052008-11-23 00:28:33 +0000[diff] [blame]405
406<p>As you can see, adding and producing a diagnostic is pretty straightforward.
407The hard part is deciding exactly what you need to say to help the user, picking
408a suitable wording, and providing the information needed to format it correctly.
Chris Lattnerfd408ea2008-11-23 00:42:53 +0000[diff] [blame]409The good news is that the call site that issues a diagnostic should be
410completely independent of how the diagnostic is formatted and in what language
411it is rendered.
Chris Lattner627b7052008-11-23 00:28:33 +0000[diff] [blame]412</p>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]413
Douglas Gregorb2fb6de2009-02-27 17:53:17 +0000[diff] [blame]414<!-- ==================================================== -->
Peter Collingbourne38448d32011-03-21 01:45:18 +0000[diff] [blame]415<h4 id="fix-it-hints">Fix-It Hints</h4>
Douglas Gregorb2fb6de2009-02-27 17:53:17 +0000[diff] [blame]416<!-- ==================================================== -->
417
418<p>In some cases, the front end emits diagnostics when it is clear
419that some small change to the source code would fix the problem. For
420example, a missing semicolon at the end of a statement or a use of
Chris Lattner34c05332009-02-27 19:31:12 +0000[diff] [blame]421deprecated syntax that is easily rewritten into a more modern form.
422Clang tries very hard to emit the diagnostic and recover gracefully
423in these and other cases.</p>
Douglas Gregorb2fb6de2009-02-27 17:53:17 +0000[diff] [blame]424
Peter Collingbourne38448d32011-03-21 01:45:18 +0000[diff] [blame]425<p>However, for these cases where the fix is obvious, the diagnostic
426can be annotated with a hint (referred to as a "fix-it hint") that
427describes how to change the code referenced by the diagnostic to fix
428the problem. For example, it might add the missing semicolon at the
429end of the statement or rewrite the use of a deprecated construct
430into something more palatable. Here is one such example from the C++
431front end, where we warn about the right-shift operator changing
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]432meaning from C++98 to C++11:</p>
Douglas Gregorb2fb6de2009-02-27 17:53:17 +0000[diff] [blame]433
434<pre>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]435test.cpp:3:7: warning: use of right-shift operator ('&gt;&gt;') in template argument will require parentheses in C++11
Douglas Gregorb2fb6de2009-02-27 17:53:17 +0000[diff] [blame]436A&lt;100 &gt;&gt; 2&gt; *a;
437 ^
438 ( )
439</pre>
440
Peter Collingbourne38448d32011-03-21 01:45:18 +0000[diff] [blame]441<p>Here, the fix-it hint is suggesting that parentheses be added,
442and showing exactly where those parentheses would be inserted into the
443source code. The fix-it hints themselves describe what changes to make
444to the source code in an abstract manner, which the text diagnostic
445printer renders as a line of "insertions" below the caret line. <a
446href="#DiagnosticClient">Other diagnostic clients</a> might choose
447to render the code differently (e.g., as markup inline) or even give
448the user the ability to automatically fix the problem.</p>
Douglas Gregorb2fb6de2009-02-27 17:53:17 +0000[diff] [blame]449
Nico Weber80039632012-06-04 21:56:14 +0000[diff] [blame]450<p>Fix-it hints on errors and warnings need to obey these rules:</p>
451
452<ul>
453<li>Since they are automatically applied if <code>-Xclang -fixit</code>
454is passed to the driver, they should only be used when it's very likely they
455match the user's intent.</li>
Chris Lattnerf6385a52012-07-10 05:03:05 +0000[diff] [blame]456<li>Clang must recover from errors as if the fix-it had been applied.</li>
Nico Weber80039632012-06-04 21:56:14 +0000[diff] [blame]457</ul>
458
459<p>If a fix-it can't obey these rules, put the fix-it on a note. Fix-its on
460notes are not applied automatically.</p>
461
Peter Collingbourne38448d32011-03-21 01:45:18 +0000[diff] [blame]462<p>All fix-it hints are described by the <code>FixItHint</code> class,
463instances of which should be attached to the diagnostic using the
464&lt;&lt; operator in the same way that highlighted source ranges and
465arguments are passed to the diagnostic. Fix-it hints can be created
466with one of three constructors:</p>
Douglas Gregorb2fb6de2009-02-27 17:53:17 +0000[diff] [blame]467
468<dl>
Peter Collingbourne38448d32011-03-21 01:45:18 +0000[diff] [blame]469 <dt><code>FixItHint::CreateInsertion(Loc, Code)</code></dt>
Douglas Gregorb2fb6de2009-02-27 17:53:17 +0000[diff] [blame]470 <dd>Specifies that the given <code>Code</code> (a string) should be inserted
471 before the source location <code>Loc</code>.</dd>
472
Peter Collingbourne38448d32011-03-21 01:45:18 +0000[diff] [blame]473 <dt><code>FixItHint::CreateRemoval(Range)</code></dt>
Douglas Gregorb2fb6de2009-02-27 17:53:17 +0000[diff] [blame]474 <dd>Specifies that the code in the given source <code>Range</code>
475 should be removed.</dd>
476
Peter Collingbourne38448d32011-03-21 01:45:18 +0000[diff] [blame]477 <dt><code>FixItHint::CreateReplacement(Range, Code)</code></dt>
Douglas Gregorb2fb6de2009-02-27 17:53:17 +0000[diff] [blame]478 <dd>Specifies that the code in the given source <code>Range</code>
479 should be removed, and replaced with the given <code>Code</code> string.</dd>
480</dl>
481
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]482<!-- ============================================================= -->
483<h4><a name="DiagnosticClient">The DiagnosticClient Interface</a></h4>
484<!-- ============================================================= -->
485
Chris Lattner627b7052008-11-23 00:28:33 +0000[diff] [blame]486<p>Once code generates a diagnostic with all of the arguments and the rest of
487the relevant information, Clang needs to know what to do with it. As previously
488mentioned, the diagnostic machinery goes through some filtering to map a
489severity onto a diagnostic level, then (assuming the diagnostic is not mapped to
490"<tt>Ignore</tt>") it invokes an object that implements the DiagnosticClient
491interface with the information.</p>
492
493<p>It is possible to implement this interface in many different ways. For
494example, the normal Clang DiagnosticClient (named 'TextDiagnosticPrinter') turns
495the arguments into strings (according to the various formatting rules), prints
496out the file/line/column information and the string, then prints out the line of
497code, the source ranges, and the caret. However, this behavior isn't required.
498</p>
499
500<p>Another implementation of the DiagnosticClient interface is the
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]501'TextDiagnosticBuffer' class, which is used when Clang is in -verify mode.
Chris Lattnerfd408ea2008-11-23 00:42:53 +0000[diff] [blame]502Instead of formatting and printing out the diagnostics, this implementation just
503captures and remembers the diagnostics as they fly by. Then -verify compares
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]504the list of produced diagnostics to the list of expected ones. If they disagree,
Chris Lattnerfd408ea2008-11-23 00:42:53 +0000[diff] [blame]505it prints out its own output.
Chris Lattner627b7052008-11-23 00:28:33 +0000[diff] [blame]506</p>
507
Chris Lattnerfd408ea2008-11-23 00:42:53 +0000[diff] [blame]508<p>There are many other possible implementations of this interface, and this is
509why we prefer diagnostics to pass down rich structured information in arguments.
510For example, an HTML output might want declaration names be linkified to where
511they come from in the source. Another example is that a GUI might let you click
512on typedefs to expand them. This application would want to pass significantly
513more information about types through to the GUI than a simple flat string. The
514interface allows this to happen.</p>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]515
516<!-- ====================================================== -->
517<h4><a name="translation">Adding Translations to Clang</a></h4>
518<!-- ====================================================== -->
519
Chris Lattner627b7052008-11-23 00:28:33 +0000[diff] [blame]520<p>Not possible yet! Diagnostic strings should be written in UTF-8, the client
Chris Lattnerfd408ea2008-11-23 00:42:53 +0000[diff] [blame]521can translate to the relevant code page if needed. Each translation completely
522replaces the format string for the diagnostic.</p>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]523
524
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]525<!-- ======================================================================= -->
526<h3 id="SourceLocation">The SourceLocation and SourceManager classes</h3>
527<!-- ======================================================================= -->
528
529<p>Strangely enough, the SourceLocation class represents a location within the
530source code of the program. Important design points include:</p>
531
532<ol>
533<li>sizeof(SourceLocation) must be extremely small, as these are embedded into
534 many AST nodes and are passed around often. Currently it is 32 bits.</li>
535<li>SourceLocation must be a simple value object that can be efficiently
536 copied.</li>
537<li>We should be able to represent a source location for any byte of any input
538 file. This includes in the middle of tokens, in whitespace, in trigraphs,
539 etc.</li>
540<li>A SourceLocation must encode the current #include stack that was active when
541 the location was processed. For example, if the location corresponds to a
542 token, it should contain the set of #includes active when the token was
543 lexed. This allows us to print the #include stack for a diagnostic.</li>
544<li>SourceLocation must be able to describe macro expansions, capturing both
545 the ultimate instantiation point and the source of the original character
546 data.</li>
547</ol>
548
549<p>In practice, the SourceLocation works together with the SourceManager class
Nick Lewycky77561e52010-05-26 21:48:10 +0000[diff] [blame]550to encode two pieces of information about a location: its spelling location
551and its instantiation location. For most tokens, these will be the same.
552However, for a macro expansion (or tokens that came from a _Pragma directive)
553these will describe the location of the characters corresponding to the token
554and the location where the token was used (i.e. the macro instantiation point
555or the location of the _Pragma itself).</p>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]556
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]557<p>The Clang front-end inherently depends on the location of a token being
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]558tracked correctly. If it is ever incorrect, the front-end may get confused and
559die. The reason for this is that the notion of the 'spelling' of a Token in
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]560Clang depends on being able to find the original input characters for the token.
Chris Lattner18376dd2009-01-16 07:00:50 +0000[diff] [blame]561This concept maps directly to the "spelling location" for the token.</p>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]562
Douglas Gregor715c92a2010-10-27 16:02:28 +0000[diff] [blame]563
564<!-- ======================================================================= -->
565<h3 id="SourceRange">SourceRange and CharSourceRange</h3>
566<!-- ======================================================================= -->
567<!-- mostly taken from
568 http://lists.cs.uiuc.edu/pipermail/cfe-dev/2010-August/010595.html -->
569
570<p>Clang represents most source ranges by [first, last], where first and last
571each point to the beginning of their respective tokens. For example
572consider the SourceRange of the following statement:</p>
573<pre>
574x = foo + bar;
575^first ^last
576</pre>
577
578<p>To map from this representation to a character-based
579representation, the 'last' location needs to be adjusted to point to
580(or past) the end of that token with either
581<code>Lexer::MeasureTokenLength()</code> or
Chris Lattner7ef5c272010-11-17 07:05:50 +0000[diff] [blame]582<code>Lexer::getLocForEndOfToken()</code>. For the rare cases
Douglas Gregor715c92a2010-10-27 16:02:28 +0000[diff] [blame]583where character-level source ranges information is needed we use
584the <code>CharSourceRange</code> class.</p>
585
586
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]587<!-- ======================================================================= -->
Daniel Dunbar27d9e9f2009-03-30 06:50:01 +0000[diff] [blame]588<h2 id="libdriver">The Driver Library</h2>
589<!-- ======================================================================= -->
590
Ted Kremenekcfa8d572009-04-09 18:08:18 +0000[diff] [blame]591<p>The clang Driver and library are documented <a
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]592href="DriverInternals.html">here</a>.<p>
Ted Kremenekcfa8d572009-04-09 18:08:18 +0000[diff] [blame]593
594<!-- ======================================================================= -->
Douglas Gregor32110df2009-05-20 00:16:32 +0000[diff] [blame]595<h2 id="pch">Precompiled Headers</h2>
Ted Kremenekcfa8d572009-04-09 18:08:18 +0000[diff] [blame]596<!-- ======================================================================= -->
597
Douglas Gregor32110df2009-05-20 00:16:32 +0000[diff] [blame]598<p>Clang supports two implementations of precompiled headers. The
599 default implementation, precompiled headers (<a
600 href="PCHInternals.html">PCH</a>) uses a serialized representation
601 of Clang's internal data structures, encoded with the <a
602 href="http://llvm.org/docs/BitCodeFormat.html">LLVM bitstream
603 format</a>. Pretokenized headers (<a
604 href="PTHInternals.html">PTH</a>), on the other hand, contain a
605 serialized representation of the tokens encountered when
606 preprocessing a header (and anything that header includes).</p>
607
Daniel Dunbar27d9e9f2009-03-30 06:50:01 +0000[diff] [blame]608
609<!-- ======================================================================= -->
610<h2 id="libfrontend">The Frontend Library</h2>
611<!-- ======================================================================= -->
612
613<p>The Frontend library contains functionality useful for building
614tools on top of the clang libraries, for example several methods for
615outputting diagnostics.</p>
616
617<!-- ======================================================================= -->
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]618<h2 id="liblex">The Lexer and Preprocessor Library</h2>
619<!-- ======================================================================= -->
620
621<p>The Lexer library contains several tightly-connected classes that are involved
622with the nasty process of lexing and preprocessing C source code. The main
623interface to this library for outside clients is the large <a
624href="#Preprocessor">Preprocessor</a> class.
625It contains the various pieces of state that are required to coherently read
626tokens out of a translation unit.</p>
627
628<p>The core interface to the Preprocessor object (once it is set up) is the
629Preprocessor::Lex method, which returns the next <a href="#Token">Token</a> from
630the preprocessor stream. There are two types of token providers that the
631preprocessor is capable of reading from: a buffer lexer (provided by the <a
632href="#Lexer">Lexer</a> class) and a buffered token stream (provided by the <a
Chris Lattner79281252008-03-09 02:27:26 +0000[diff] [blame]633href="#TokenLexer">TokenLexer</a> class).
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]634
635
636<!-- ======================================================================= -->
637<h3 id="Token">The Token class</h3>
638<!-- ======================================================================= -->
639
640<p>The Token class is used to represent a single lexed token. Tokens are
641intended to be used by the lexer/preprocess and parser libraries, but are not
642intended to live beyond them (for example, they should not live in the ASTs).<p>
643
644<p>Tokens most often live on the stack (or some other location that is efficient
645to access) as the parser is running, but occasionally do get buffered up. For
646example, macro definitions are stored as a series of tokens, and the C++
Chris Lattner3fcbb892008-11-23 08:32:53 +0000[diff] [blame]647front-end periodically needs to buffer tokens up for tentative parsing and
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]648various pieces of look-ahead. As such, the size of a Token matter. On a 32-bit
649system, sizeof(Token) is currently 16 bytes.</p>
650
Chris Lattner3932fe02009-01-06 06:02:08 +0000[diff] [blame]651<p>Tokens occur in two forms: "<a href="#AnnotationToken">Annotation
652Tokens</a>" and normal tokens. Normal tokens are those returned by the lexer,
653annotation tokens represent semantic information and are produced by the parser,
654replacing normal tokens in the token stream. Normal tokens contain the
655following information:</p>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]656
657<ul>
658<li><b>A SourceLocation</b> - This indicates the location of the start of the
659token.</li>
660
661<li><b>A length</b> - This stores the length of the token as stored in the
662SourceBuffer. For tokens that include them, this length includes trigraphs and
663escaped newlines which are ignored by later phases of the compiler. By pointing
664into the original source buffer, it is always possible to get the original
665spelling of a token completely accurately.</li>
666
667<li><b>IdentifierInfo</b> - If a token takes the form of an identifier, and if
668identifier lookup was enabled when the token was lexed (e.g. the lexer was not
669reading in 'raw' mode) this contains a pointer to the unique hash value for the
670identifier. Because the lookup happens before keyword identification, this
671field is set even for language keywords like 'for'.</li>
672
673<li><b>TokenKind</b> - This indicates the kind of token as classified by the
674lexer. This includes things like <tt>tok::starequal</tt> (for the "*="
675operator), <tt>tok::ampamp</tt> for the "&amp;&amp;" token, and keyword values
676(e.g. <tt>tok::kw_for</tt>) for identifiers that correspond to keywords. Note
677that some tokens can be spelled multiple ways. For example, C++ supports
678"operator keywords", where things like "and" are treated exactly like the
679"&amp;&amp;" operator. In these cases, the kind value is set to
680<tt>tok::ampamp</tt>, which is good for the parser, which doesn't have to
681consider both forms. For something that cares about which form is used (e.g.
682the preprocessor 'stringize' operator) the spelling indicates the original
683form.</li>
684
685<li><b>Flags</b> - There are currently four flags tracked by the
686lexer/preprocessor system on a per-token basis:
687
688 <ol>
689 <li><b>StartOfLine</b> - This was the first token that occurred on its input
690 source line.</li>
691 <li><b>LeadingSpace</b> - There was a space character either immediately
692 before the token or transitively before the token as it was expanded
693 through a macro. The definition of this flag is very closely defined by
694 the stringizing requirements of the preprocessor.</li>
695 <li><b>DisableExpand</b> - This flag is used internally to the preprocessor to
696 represent identifier tokens which have macro expansion disabled. This
697 prevents them from being considered as candidates for macro expansion ever
698 in the future.</li>
699 <li><b>NeedsCleaning</b> - This flag is set if the original spelling for the
700 token includes a trigraph or escaped newline. Since this is uncommon,
701 many pieces of code can fast-path on tokens that did not need cleaning.
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]702 </ol>
703</li>
704</ul>
705
Chris Lattner3932fe02009-01-06 06:02:08 +0000[diff] [blame]706<p>One interesting (and somewhat unusual) aspect of normal tokens is that they
707don't contain any semantic information about the lexed value. For example, if
708the token was a pp-number token, we do not represent the value of the number
709that was lexed (this is left for later pieces of code to decide). Additionally,
710the lexer library has no notion of typedef names vs variable names: both are
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]711returned as identifiers, and the parser is left to decide whether a specific
712identifier is a typedef or a variable (tracking this requires scope information
Chris Lattner3932fe02009-01-06 06:02:08 +0000[diff] [blame]713among other things). The parser can do this translation by replacing tokens
714returned by the preprocessor with "Annotation Tokens".</p>
715
716<!-- ======================================================================= -->
717<h3 id="AnnotationToken">Annotation Tokens</h3>
718<!-- ======================================================================= -->
719
720<p>Annotation Tokens are tokens that are synthesized by the parser and injected
721into the preprocessor's token stream (replacing existing tokens) to record
722semantic information found by the parser. For example, if "foo" is found to be
723a typedef, the "foo" <tt>tok::identifier</tt> token is replaced with an
724<tt>tok::annot_typename</tt>. This is useful for a couple of reasons: 1) this
725makes it easy to handle qualified type names (e.g. "foo::bar::baz&lt;42&gt;::t")
726in C++ as a single "token" in the parser. 2) if the parser backtracks, the
727reparse does not need to redo semantic analysis to determine whether a token
728sequence is a variable, type, template, etc.</p>
729
730<p>Annotation Tokens are created by the parser and reinjected into the parser's
731token stream (when backtracking is enabled). Because they can only exist in
732tokens that the preprocessor-proper is done with, it doesn't need to keep around
733flags like "start of line" that the preprocessor uses to do its job.
734Additionally, an annotation token may "cover" a sequence of preprocessor tokens
735(e.g. <tt>a::b::c</tt> is five preprocessor tokens). As such, the valid fields
736of an annotation token are different than the fields for a normal token (but
737they are multiplexed into the normal Token fields):</p>
738
739<ul>
740<li><b>SourceLocation "Location"</b> - The SourceLocation for the annotation
741token indicates the first token replaced by the annotation token. In the example
742above, it would be the location of the "a" identifier.</li>
743
744<li><b>SourceLocation "AnnotationEndLoc"</b> - This holds the location of the
745last token replaced with the annotation token. In the example above, it would
746be the location of the "c" identifier.</li>
747
John McCall027ac442010-09-03 05:07:55 +0000[diff] [blame]748<li><b>void* "AnnotationValue"</b> - This contains an opaque object
749that the parser gets from Sema. The parser merely preserves the
750information for Sema to later interpret based on the annotation token
751kind.</li>
Chris Lattner3932fe02009-01-06 06:02:08 +0000[diff] [blame]752
753<li><b>TokenKind "Kind"</b> - This indicates the kind of Annotation token this
754is. See below for the different valid kinds.</li>
755</ul>
756
757<p>Annotation tokens currently come in three kinds:</p>
758
759<ol>
760<li><b>tok::annot_typename</b>: This annotation token represents a
John McCall027ac442010-09-03 05:07:55 +0000[diff] [blame]761resolved typename token that is potentially qualified. The
762AnnotationValue field contains the <tt>QualType</tt> returned by
763Sema::getTypeName(), possibly with source location information
764attached.</li>
Chris Lattner3932fe02009-01-06 06:02:08 +0000[diff] [blame]765
John McCall027ac442010-09-03 05:07:55 +0000[diff] [blame]766<li><b>tok::annot_cxxscope</b>: This annotation token represents a C++
767scope specifier, such as "A::B::". This corresponds to the grammar
768productions "::" and ":: [opt] nested-name-specifier". The
769AnnotationValue pointer is a <tt>NestedNameSpecifier*</tt> returned by
770the Sema::ActOnCXXGlobalScopeSpecifier and
771Sema::ActOnCXXNestedNameSpecifier callbacks.</li>
Chris Lattner3932fe02009-01-06 06:02:08 +0000[diff] [blame]772
Douglas Gregor39a8de12009-02-25 19:37:18 +0000[diff] [blame]773<li><b>tok::annot_template_id</b>: This annotation token represents a
774C++ template-id such as "foo&lt;int, 4&gt;", where "foo" is the name
775of a template. The AnnotationValue pointer is a pointer to a malloc'd
John McCall027ac442010-09-03 05:07:55 +0000[diff] [blame]776TemplateIdAnnotation object. Depending on the context, a parsed
777template-id that names a type might become a typename annotation token
778(if all we care about is the named type, e.g., because it occurs in a
779type specifier) or might remain a template-id token (if we want to
780retain more source location information or produce a new type, e.g.,
781in a declaration of a class template specialization). template-id
782annotation tokens that refer to a type can be "upgraded" to typename
783annotation tokens by the parser.</li>
Chris Lattner3932fe02009-01-06 06:02:08 +0000[diff] [blame]784
785</ol>
786
Cedric Venetda76b282009-01-06 16:22:54 +0000[diff] [blame]787<p>As mentioned above, annotation tokens are not returned by the preprocessor,
Chris Lattner3932fe02009-01-06 06:02:08 +0000[diff] [blame]788they are formed on demand by the parser. This means that the parser has to be
789aware of cases where an annotation could occur and form it where appropriate.
790This is somewhat similar to how the parser handles Translation Phase 6 of C99:
791String Concatenation (see C99 5.1.1.2). In the case of string concatenation,
792the preprocessor just returns distinct tok::string_literal and
793tok::wide_string_literal tokens and the parser eats a sequence of them wherever
794the grammar indicates that a string literal can occur.</p>
795
796<p>In order to do this, whenever the parser expects a tok::identifier or
797tok::coloncolon, it should call the TryAnnotateTypeOrScopeToken or
798TryAnnotateCXXScopeToken methods to form the annotation token. These methods
799will maximally form the specified annotation tokens and replace the current
800token with them, if applicable. If the current tokens is not valid for an
801annotation token, it will remain an identifier or :: token.</p>
802
803
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]804
805<!-- ======================================================================= -->
806<h3 id="Lexer">The Lexer class</h3>
807<!-- ======================================================================= -->
808
809<p>The Lexer class provides the mechanics of lexing tokens out of a source
810buffer and deciding what they mean. The Lexer is complicated by the fact that
811it operates on raw buffers that have not had spelling eliminated (this is a
812necessity to get decent performance), but this is countered with careful coding
813as well as standard performance techniques (for example, the comment handling
814code is vectorized on X86 and PowerPC hosts).</p>
815
816<p>The lexer has a couple of interesting modal features:</p>
817
818<ul>
819<li>The lexer can operate in 'raw' mode. This mode has several features that
820 make it possible to quickly lex the file (e.g. it stops identifier lookup,
821 doesn't specially handle preprocessor tokens, handles EOF differently, etc).
822 This mode is used for lexing within an "<tt>#if 0</tt>" block, for
823 example.</li>
824<li>The lexer can capture and return comments as tokens. This is required to
825 support the -C preprocessor mode, which passes comments through, and is
826 used by the diagnostic checker to identifier expect-error annotations.</li>
827<li>The lexer can be in ParsingFilename mode, which happens when preprocessing
Chris Lattner84386242007-09-16 19:25:23 +0000[diff] [blame]828 after reading a #include directive. This mode changes the parsing of '&lt;'
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]829 to return an "angled string" instead of a bunch of tokens for each thing
830 within the filename.</li>
831<li>When parsing a preprocessor directive (after "<tt>#</tt>") the
832 ParsingPreprocessorDirective mode is entered. This changes the parser to
Peter Collingbourne84021552011-02-28 02:37:51 +0000[diff] [blame]833 return EOD at a newline.</li>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]834<li>The Lexer uses a LangOptions object to know whether trigraphs are enabled,
835 whether C++ or ObjC keywords are recognized, etc.</li>
836</ul>
837
838<p>In addition to these modes, the lexer keeps track of a couple of other
839 features that are local to a lexed buffer, which change as the buffer is
840 lexed:</p>
841
842<ul>
843<li>The Lexer uses BufferPtr to keep track of the current character being
844 lexed.</li>
845<li>The Lexer uses IsAtStartOfLine to keep track of whether the next lexed token
846 will start with its "start of line" bit set.</li>
847<li>The Lexer keeps track of the current #if directives that are active (which
848 can be nested).</li>
849<li>The Lexer keeps track of an <a href="#MultipleIncludeOpt">
850 MultipleIncludeOpt</a> object, which is used to
851 detect whether the buffer uses the standard "<tt>#ifndef XX</tt> /
852 <tt>#define XX</tt>" idiom to prevent multiple inclusion. If a buffer does,
853 subsequent includes can be ignored if the XX macro is defined.</li>
854</ul>
855
856<!-- ======================================================================= -->
Chris Lattner79281252008-03-09 02:27:26 +0000[diff] [blame]857<h3 id="TokenLexer">The TokenLexer class</h3>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]858<!-- ======================================================================= -->
859
Chris Lattner79281252008-03-09 02:27:26 +0000[diff] [blame]860<p>The TokenLexer class is a token provider that returns tokens from a list
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]861of tokens that came from somewhere else. It typically used for two things: 1)
862returning tokens from a macro definition as it is being expanded 2) returning
863tokens from an arbitrary buffer of tokens. The later use is used by _Pragma and
864will most likely be used to handle unbounded look-ahead for the C++ parser.</p>
865
866<!-- ======================================================================= -->
867<h3 id="MultipleIncludeOpt">The MultipleIncludeOpt class</h3>
868<!-- ======================================================================= -->
869
870<p>The MultipleIncludeOpt class implements a really simple little state machine
871that is used to detect the standard "<tt>#ifndef XX</tt> / <tt>#define XX</tt>"
872idiom that people typically use to prevent multiple inclusion of headers. If a
873buffer uses this idiom and is subsequently #include'd, the preprocessor can
874simply check to see whether the guarding condition is defined or not. If so,
875the preprocessor can completely ignore the include of the header.</p>
876
877
878
879<!-- ======================================================================= -->
880<h2 id="libparse">The Parser Library</h2>
881<!-- ======================================================================= -->
882
883<!-- ======================================================================= -->
884<h2 id="libast">The AST Library</h2>
885<!-- ======================================================================= -->
886
887<!-- ======================================================================= -->
888<h3 id="Type">The Type class and its subclasses</h3>
889<!-- ======================================================================= -->
890
891<p>The Type class (and its subclasses) are an important part of the AST. Types
892are accessed through the ASTContext class, which implicitly creates and uniques
893them as they are needed. Types have a couple of non-obvious features: 1) they
894do not capture type qualifiers like const or volatile (See
895<a href="#QualType">QualType</a>), and 2) they implicitly capture typedef
Chris Lattner8a2bc622007-07-31 06:37:39 +0000[diff] [blame]896information. Once created, types are immutable (unlike decls).</p>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]897
898<p>Typedefs in C make semantic analysis a bit more complex than it would
899be without them. The issue is that we want to capture typedef information
900and represent it in the AST perfectly, but the semantics of operations need to
901"see through" typedefs. For example, consider this code:</p>
902
903<code>
904void func() {<br>
Bill Wendling30d17752007-10-06 01:56:01 +0000[diff] [blame]905&nbsp;&nbsp;typedef int foo;<br>
906&nbsp;&nbsp;foo X, *Y;<br>
907&nbsp;&nbsp;typedef foo* bar;<br>
908&nbsp;&nbsp;bar Z;<br>
909&nbsp;&nbsp;*X; <i>// error</i><br>
910&nbsp;&nbsp;**Y; <i>// error</i><br>
911&nbsp;&nbsp;**Z; <i>// error</i><br>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]912}<br>
913</code>
914
915<p>The code above is illegal, and thus we expect there to be diagnostics emitted
916on the annotated lines. In this example, we expect to get:</p>
917
918<pre>
Chris Lattner8a2bc622007-07-31 06:37:39 +0000[diff] [blame]919<b>test.c:6:1: error: indirection requires pointer operand ('foo' invalid)</b>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]920*X; // error
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]921<span style="color:blue">^~</span>
Chris Lattner8a2bc622007-07-31 06:37:39 +0000[diff] [blame]922<b>test.c:7:1: error: indirection requires pointer operand ('foo' invalid)</b>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]923**Y; // error
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]924<span style="color:blue">^~~</span>
Chris Lattner8a2bc622007-07-31 06:37:39 +0000[diff] [blame]925<b>test.c:8:1: error: indirection requires pointer operand ('foo' invalid)</b>
926**Z; // error
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]927<span style="color:blue">^~~</span>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]928</pre>
929
930<p>While this example is somewhat silly, it illustrates the point: we want to
931retain typedef information where possible, so that we can emit errors about
932"<tt>std::string</tt>" instead of "<tt>std::basic_string&lt;char, std:...</tt>".
933Doing this requires properly keeping typedef information (for example, the type
934of "X" is "foo", not "int"), and requires properly propagating it through the
Chris Lattner8a2bc622007-07-31 06:37:39 +0000[diff] [blame]935various operators (for example, the type of *Y is "foo", not "int"). In order
936to retain this information, the type of these expressions is an instance of the
937TypedefType class, which indicates that the type of these expressions is a
938typedef for foo.
939</p>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]940
Chris Lattner8a2bc622007-07-31 06:37:39 +0000[diff] [blame]941<p>Representing types like this is great for diagnostics, because the
942user-specified type is always immediately available. There are two problems
943with this: first, various semantic checks need to make judgements about the
Douglas Gregor2d1e21a2011-12-19 19:50:23 +0000[diff] [blame]944<em>actual structure</em> of a type, ignoring typedefs. Second, we need an
Chris Lattner33fc68a2007-07-31 18:54:50 +0000[diff] [blame]945efficient way to query whether two types are structurally identical to each
946other, ignoring typedefs. The solution to both of these problems is the idea of
Chris Lattner8a2bc622007-07-31 06:37:39 +0000[diff] [blame]947canonical types.</p>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]948
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]949<!-- =============== -->
Chris Lattner8a2bc622007-07-31 06:37:39 +0000[diff] [blame]950<h4>Canonical Types</h4>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]951<!-- =============== -->
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]952
Chris Lattner8a2bc622007-07-31 06:37:39 +0000[diff] [blame]953<p>Every instance of the Type class contains a canonical type pointer. For
954simple types with no typedefs involved (e.g. "<tt>int</tt>", "<tt>int*</tt>",
955"<tt>int**</tt>"), the type just points to itself. For types that have a
956typedef somewhere in their structure (e.g. "<tt>foo</tt>", "<tt>foo*</tt>",
957"<tt>foo**</tt>", "<tt>bar</tt>"), the canonical type pointer points to their
958structurally equivalent type without any typedefs (e.g. "<tt>int</tt>",
959"<tt>int*</tt>", "<tt>int**</tt>", and "<tt>int*</tt>" respectively).</p>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]960
Chris Lattner8a2bc622007-07-31 06:37:39 +0000[diff] [blame]961<p>This design provides a constant time operation (dereferencing the canonical
962type pointer) that gives us access to the structure of types. For example,
963we can trivially tell that "bar" and "foo*" are the same type by dereferencing
964their canonical type pointers and doing a pointer comparison (they both point
965to the single "<tt>int*</tt>" type).</p>
966
967<p>Canonical types and typedef types bring up some complexities that must be
968carefully managed. Specifically, the "isa/cast/dyncast" operators generally
969shouldn't be used in code that is inspecting the AST. For example, when type
970checking the indirection operator (unary '*' on a pointer), the type checker
971must verify that the operand has a pointer type. It would not be correct to
972check that with "<tt>isa&lt;PointerType&gt;(SubExpr-&gt;getType())</tt>",
973because this predicate would fail if the subexpression had a typedef type.</p>
974
975<p>The solution to this problem are a set of helper methods on Type, used to
976check their properties. In this case, it would be correct to use
977"<tt>SubExpr-&gt;getType()-&gt;isPointerType()</tt>" to do the check. This
978predicate will return true if the <em>canonical type is a pointer</em>, which is
979true any time the type is structurally a pointer type. The only hard part here
980is remembering not to use the <tt>isa/cast/dyncast</tt> operations.</p>
981
982<p>The second problem we face is how to get access to the pointer type once we
983know it exists. To continue the example, the result type of the indirection
984operator is the pointee type of the subexpression. In order to determine the
985type, we need to get the instance of PointerType that best captures the typedef
986information in the program. If the type of the expression is literally a
987PointerType, we can return that, otherwise we have to dig through the
988typedefs to find the pointer type. For example, if the subexpression had type
989"<tt>foo*</tt>", we could return that type as the result. If the subexpression
990had type "<tt>bar</tt>", we want to return "<tt>foo*</tt>" (note that we do
991<em>not</em> want "<tt>int*</tt>"). In order to provide all of this, Type has
Chris Lattner11406c12007-07-31 16:50:51 +0000[diff] [blame]992a getAsPointerType() method that checks whether the type is structurally a
Chris Lattner8a2bc622007-07-31 06:37:39 +0000[diff] [blame]993PointerType and, if so, returns the best one. If not, it returns a null
994pointer.</p>
995
996<p>This structure is somewhat mystical, but after meditating on it, it will
997make sense to you :).</p>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]998
999<!-- ======================================================================= -->
1000<h3 id="QualType">The QualType class</h3>
1001<!-- ======================================================================= -->
1002
John McCall027ac442010-09-03 05:07:55 +0000[diff] [blame]1003<p>The QualType class is designed as a trivial value class that is
1004small, passed by-value and is efficient to query. The idea of
1005QualType is that it stores the type qualifiers (const, volatile,
1006restrict, plus some extended qualifiers required by language
1007extensions) separately from the types themselves. QualType is
1008conceptually a pair of "Type*" and the bits for these type qualifiers.</p>
Chris Lattner86920d32007-07-31 05:42:17 +0000[diff] [blame]1009
1010<p>By storing the type qualifiers as bits in the conceptual pair, it is
1011extremely efficient to get the set of qualifiers on a QualType (just return the
1012field of the pair), add a type qualifier (which is a trivial constant-time
1013operation that sets a bit), and remove one or more type qualifiers (just return
1014a QualType with the bitfield set to empty).</p>
1015
1016<p>Further, because the bits are stored outside of the type itself, we do not
1017need to create duplicates of types with different sets of qualifiers (i.e. there
1018is only a single heap allocated "int" type: "const int" and "volatile const int"
1019both point to the same heap allocated "int" type). This reduces the heap size
1020used to represent bits and also means we do not have to consider qualifiers when
1021uniquing types (<a href="#Type">Type</a> does not even contain qualifiers).</p>
1022
John McCall027ac442010-09-03 05:07:55 +0000[diff] [blame]1023<p>In practice, the two most common type qualifiers (const and
1024restrict) are stored in the low bits of the pointer to the Type
1025object, together with a flag indicating whether extended qualifiers
1026are present (which must be heap-allocated). This means that QualType
1027is exactly the same size as a pointer.</p>
Ted Kremenek8bc05712007-10-10 23:01:43 +0000[diff] [blame]1028
1029<!-- ======================================================================= -->
Douglas Gregor2e1cd422008-11-17 14:58:09 +0000[diff] [blame]1030<h3 id="DeclarationName">Declaration names</h3>
1031<!-- ======================================================================= -->
1032
1033<p>The <tt>DeclarationName</tt> class represents the name of a
1034 declaration in Clang. Declarations in the C family of languages can
Chris Lattner3fcbb892008-11-23 08:32:53 +0000[diff] [blame]1035 take several different forms. Most declarations are named by
Douglas Gregor2e1cd422008-11-17 14:58:09 +0000[diff] [blame]1036 simple identifiers, e.g., "<code>f</code>" and "<code>x</code>" in
1037 the function declaration <code>f(int x)</code>. In C++, declaration
1038 names can also name class constructors ("<code>Class</code>"
1039 in <code>struct Class { Class(); }</code>), class destructors
1040 ("<code>~Class</code>"), overloaded operator names ("operator+"),
1041 and conversion functions ("<code>operator void const *</code>"). In
1042 Objective-C, declaration names can refer to the names of Objective-C
1043 methods, which involve the method name and the parameters,
Chris Lattner3fcbb892008-11-23 08:32:53 +0000[diff] [blame]1044 collectively called a <i>selector</i>, e.g.,
Douglas Gregor2e1cd422008-11-17 14:58:09 +0000[diff] [blame]1045 "<code>setWidth:height:</code>". Since all of these kinds of
Chris Lattner3fcbb892008-11-23 08:32:53 +0000[diff] [blame]1046 entities - variables, functions, Objective-C methods, C++
1047 constructors, destructors, and operators - are represented as
Douglas Gregor2e1cd422008-11-17 14:58:09 +0000[diff] [blame]1048 subclasses of Clang's common <code>NamedDecl</code>
1049 class, <code>DeclarationName</code> is designed to efficiently
1050 represent any kind of name.</p>
1051
1052<p>Given
1053 a <code>DeclarationName</code> <code>N</code>, <code>N.getNameKind()</code>
Douglas Gregor2def4832008-11-17 20:34:05 +0000[diff] [blame]1054 will produce a value that describes what kind of name <code>N</code>
Douglas Gregore94ca9e42008-11-18 14:39:36 +0000[diff] [blame]1055 stores. There are 8 options (all of the names are inside
Douglas Gregor2e1cd422008-11-17 14:58:09 +0000[diff] [blame]1056 the <code>DeclarationName</code> class)</p>
1057<dl>
1058 <dt>Identifier</dt>
1059 <dd>The name is a simple
1060 identifier. Use <code>N.getAsIdentifierInfo()</code> to retrieve the
1061 corresponding <code>IdentifierInfo*</code> pointing to the actual
1062 identifier. Note that C++ overloaded operators (e.g.,
1063 "<code>operator+</code>") are represented as special kinds of
1064 identifiers. Use <code>IdentifierInfo</code>'s <code>getOverloadedOperatorID</code>
1065 function to determine whether an identifier is an overloaded
1066 operator name.</dd>
1067
1068 <dt>ObjCZeroArgSelector, ObjCOneArgSelector,
1069 ObjCMultiArgSelector</dt>
1070 <dd>The name is an Objective-C selector, which can be retrieved as a
1071 <code>Selector</code> instance
1072 via <code>N.getObjCSelector()</code>. The three possible name
1073 kinds for Objective-C reflect an optimization within
1074 the <code>DeclarationName</code> class: both zero- and
1075 one-argument selectors are stored as a
1076 masked <code>IdentifierInfo</code> pointer, and therefore require
1077 very little space, since zero- and one-argument selectors are far
1078 more common than multi-argument selectors (which use a different
1079 structure).</dd>
1080
1081 <dt>CXXConstructorName</dt>
1082 <dd>The name is a C++ constructor
1083 name. Use <code>N.getCXXNameType()</code> to retrieve
1084 the <a href="#QualType">type</a> that this constructor is meant to
1085 construct. The type is always the canonical type, since all
1086 constructors for a given type have the same name.</dd>
1087
1088 <dt>CXXDestructorName</dt>
1089 <dd>The name is a C++ destructor
1090 name. Use <code>N.getCXXNameType()</code> to retrieve
1091 the <a href="#QualType">type</a> whose destructor is being
1092 named. This type is always a canonical type.</dd>
1093
1094 <dt>CXXConversionFunctionName</dt>
1095 <dd>The name is a C++ conversion function. Conversion functions are
1096 named according to the type they convert to, e.g., "<code>operator void
1097 const *</code>". Use <code>N.getCXXNameType()</code> to retrieve
1098 the type that this conversion function converts to. This type is
1099 always a canonical type.</dd>
Douglas Gregore94ca9e42008-11-18 14:39:36 +0000[diff] [blame]1100
1101 <dt>CXXOperatorName</dt>
1102 <dd>The name is a C++ overloaded operator name. Overloaded operators
1103 are named according to their spelling, e.g.,
1104 "<code>operator+</code>" or "<code>operator new
1105 []</code>". Use <code>N.getCXXOverloadedOperator()</code> to
1106 retrieve the overloaded operator (a value of
1107 type <code>OverloadedOperatorKind</code>).</dd>
Douglas Gregor2e1cd422008-11-17 14:58:09 +0000[diff] [blame]1108</dl>
1109
1110<p><code>DeclarationName</code>s are cheap to create, copy, and
1111 compare. They require only a single pointer's worth of storage in
Douglas Gregore94ca9e42008-11-18 14:39:36 +0000[diff] [blame]1112 the common cases (identifiers, zero-
Douglas Gregor2e1cd422008-11-17 14:58:09 +0000[diff] [blame]1113 and one-argument Objective-C selectors) and use dense, uniqued
1114 storage for the other kinds of
1115 names. Two <code>DeclarationName</code>s can be compared for
1116 equality (<code>==</code>, <code>!=</code>) using a simple bitwise
1117 comparison, can be ordered
1118 with <code>&lt;</code>, <code>&gt;</code>, <code>&lt;=</code>,
1119 and <code>&gt;=</code> (which provide a lexicographical ordering for
1120 normal identifiers but an unspecified ordering for other kinds of
1121 names), and can be placed into LLVM <code>DenseMap</code>s
1122 and <code>DenseSet</code>s.</p>
1123
1124<p><code>DeclarationName</code> instances can be created in different
1125 ways depending on what kind of name the instance will store. Normal
Douglas Gregore94ca9e42008-11-18 14:39:36 +0000[diff] [blame]1126 identifiers (<code>IdentifierInfo</code> pointers) and Objective-C selectors
Douglas Gregor2e1cd422008-11-17 14:58:09 +0000[diff] [blame]1127 (<code>Selector</code>) can be implicitly converted
1128 to <code>DeclarationName</code>s. Names for C++ constructors,
Douglas Gregore94ca9e42008-11-18 14:39:36 +0000[diff] [blame]1129 destructors, conversion functions, and overloaded operators can be retrieved from
Douglas Gregor2e1cd422008-11-17 14:58:09 +0000[diff] [blame]1130 the <code>DeclarationNameTable</code>, an instance of which is
1131 available as <code>ASTContext::DeclarationNames</code>. The member
1132 functions <code>getCXXConstructorName</code>, <code>getCXXDestructorName</code>,
Douglas Gregore94ca9e42008-11-18 14:39:36 +0000[diff] [blame]1133 <code>getCXXConversionFunctionName</code>, and <code>getCXXOperatorName</code>, respectively,
1134 return <code>DeclarationName</code> instances for the four kinds of
Douglas Gregor2e1cd422008-11-17 14:58:09 +0000[diff] [blame]1135 C++ special function names.</p>
1136
1137<!-- ======================================================================= -->
Douglas Gregor074149e2009-01-05 19:45:36 +0000[diff] [blame]1138<h3 id="DeclContext">Declaration contexts</h3>
1139<!-- ======================================================================= -->
1140<p>Every declaration in a program exists within some <i>declaration
1141 context</i>, such as a translation unit, namespace, class, or
1142 function. Declaration contexts in Clang are represented by
1143 the <code>DeclContext</code> class, from which the various
1144 declaration-context AST nodes
1145 (<code>TranslationUnitDecl</code>, <code>NamespaceDecl</code>, <code>RecordDecl</code>, <code>FunctionDecl</code>,
1146 etc.) will derive. The <code>DeclContext</code> class provides
1147 several facilities common to each declaration context:</p>
1148<dl>
1149 <dt>Source-centric vs. Semantics-centric View of Declarations</dt>
1150 <dd><code>DeclContext</code> provides two views of the declarations
1151 stored within a declaration context. The source-centric view
1152 accurately represents the program source code as written, including
1153 multiple declarations of entities where present (see the
1154 section <a href="#Redeclarations">Redeclarations and
1155 Overloads</a>), while the semantics-centric view represents the
1156 program semantics. The two views are kept synchronized by semantic
1157 analysis while the ASTs are being constructed.</dd>
1158
1159 <dt>Storage of declarations within that context</dt>
1160 <dd>Every declaration context can contain some number of
1161 declarations. For example, a C++ class (represented
1162 by <code>RecordDecl</code>) contains various member functions,
1163 fields, nested types, and so on. All of these declarations will be
1164 stored within the <code>DeclContext</code>, and one can iterate
1165 over the declarations via
1166 [<code>DeclContext::decls_begin()</code>,
1167 <code>DeclContext::decls_end()</code>). This mechanism provides
1168 the source-centric view of declarations in the context.</dd>
1169
1170 <dt>Lookup of declarations within that context</dt>
1171 <dd>The <code>DeclContext</code> structure provides efficient name
1172 lookup for names within that declaration context. For example,
1173 if <code>N</code> is a namespace we can look for the
1174 name <code>N::f</code>
1175 using <code>DeclContext::lookup</code>. The lookup itself is
1176 based on a lazily-constructed array (for declaration contexts
1177 with a small number of declarations) or hash table (for
1178 declaration contexts with more declarations). The lookup
1179 operation provides the semantics-centric view of the declarations
1180 in the context.</dd>
1181
1182 <dt>Ownership of declarations</dt>
1183 <dd>The <code>DeclContext</code> owns all of the declarations that
1184 were declared within its declaration context, and is responsible
1185 for the management of their memory as well as their
1186 (de-)serialization.</dd>
1187</dl>
1188
Douglas Gregor4afa39d2009-01-20 01:17:11 +0000[diff] [blame]1189<p>All declarations are stored within a declaration context, and one
1190 can query
1191 information about the context in which each declaration lives. One
Douglas Gregor074149e2009-01-05 19:45:36 +0000[diff] [blame]1192 can retrieve the <code>DeclContext</code> that contains a
Douglas Gregor4afa39d2009-01-20 01:17:11 +0000[diff] [blame]1193 particular <code>Decl</code>
1194 using <code>Decl::getDeclContext</code>. However, see the
Douglas Gregor074149e2009-01-05 19:45:36 +0000[diff] [blame]1195 section <a href="#LexicalAndSemanticContexts">Lexical and Semantic
1196 Contexts</a> for more information about how to interpret this
1197 context information.</p>
1198
1199<h4 id="Redeclarations">Redeclarations and Overloads</h4>
1200<p>Within a translation unit, it is common for an entity to be
1201declared several times. For example, we might declare a function "f"
1202 and then later re-declare it as part of an inlined definition:</p>
1203
1204<pre>
1205void f(int x, int y, int z = 1);
1206
1207inline void f(int x, int y, int z) { /* ... */ }
1208</pre>
1209
1210<p>The representation of "f" differs in the source-centric and
1211 semantics-centric views of a declaration context. In the
1212 source-centric view, all redeclarations will be present, in the
1213 order they occurred in the source code, making
1214 this view suitable for clients that wish to see the structure of
1215 the source code. In the semantics-centric view, only the most recent "f"
1216 will be found by the lookup, since it effectively replaces the first
1217 declaration of "f".</p>
1218
1219<p>In the semantics-centric view, overloading of functions is
1220 represented explicitly. For example, given two declarations of a
1221 function "g" that are overloaded, e.g.,</p>
1222<pre>
1223void g();
1224void g(int);
1225</pre>
1226<p>the <code>DeclContext::lookup</code> operation will return
Jonathan D. Turnerd3224292011-07-06 18:12:36 +0000[diff] [blame]1227 a <code>DeclContext::lookup_result</code> that contains a range of iterators
1228 over declarations of "g". Clients that perform semantic analysis on a
Douglas Gregor074149e2009-01-05 19:45:36 +0000[diff] [blame]1229 program that is not concerned with the actual source code will
1230 primarily use this semantics-centric view.</p>
1231
1232<h4 id="LexicalAndSemanticContexts">Lexical and Semantic Contexts</h4>
Douglas Gregor4afa39d2009-01-20 01:17:11 +0000[diff] [blame]1233<p>Each declaration has two potentially different
Douglas Gregor074149e2009-01-05 19:45:36 +0000[diff] [blame]1234 declaration contexts: a <i>lexical</i> context, which corresponds to
1235 the source-centric view of the declaration context, and
1236 a <i>semantic</i> context, which corresponds to the
1237 semantics-centric view. The lexical context is accessible
Douglas Gregor4afa39d2009-01-20 01:17:11 +0000[diff] [blame]1238 via <code>Decl::getLexicalDeclContext</code> while the
Douglas Gregor074149e2009-01-05 19:45:36 +0000[diff] [blame]1239 semantic context is accessible
Douglas Gregor4afa39d2009-01-20 01:17:11 +0000[diff] [blame]1240 via <code>Decl::getDeclContext</code>, both of which return
Douglas Gregor074149e2009-01-05 19:45:36 +0000[diff] [blame]1241 <code>DeclContext</code> pointers. For most declarations, the two
1242 contexts are identical. For example:</p>
1243
1244<pre>
1245class X {
1246public:
1247 void f(int x);
1248};
1249</pre>
1250
1251<p>Here, the semantic and lexical contexts of <code>X::f</code> are
1252 the <code>DeclContext</code> associated with the
1253 class <code>X</code> (itself stored as a <code>RecordDecl</code> AST
1254 node). However, we can now define <code>X::f</code> out-of-line:</p>
1255
1256<pre>
1257void X::f(int x = 17) { /* ... */ }
1258</pre>
1259
1260<p>This definition of has different lexical and semantic
1261 contexts. The lexical context corresponds to the declaration
1262 context in which the actual declaration occurred in the source
1263 code, e.g., the translation unit containing <code>X</code>. Thus,
1264 this declaration of <code>X::f</code> can be found by traversing
1265 the declarations provided by
1266 [<code>decls_begin()</code>, <code>decls_end()</code>) in the
1267 translation unit.</p>
1268
1269<p>The semantic context of <code>X::f</code> corresponds to the
1270 class <code>X</code>, since this member function is (semantically) a
1271 member of <code>X</code>. Lookup of the name <code>f</code> into
1272 the <code>DeclContext</code> associated with <code>X</code> will
1273 then return the definition of <code>X::f</code> (including
1274 information about the default argument).</p>
1275
1276<h4 id="TransparentContexts">Transparent Declaration Contexts</h4>
1277<p>In C and C++, there are several contexts in which names that are
1278 logically declared inside another declaration will actually "leak"
1279 out into the enclosing scope from the perspective of name
1280 lookup. The most obvious instance of this behavior is in
1281 enumeration types, e.g.,</p>
1282<pre>
1283enum Color {
1284 Red,
1285 Green,
1286 Blue
1287};
1288</pre>
1289
1290<p>Here, <code>Color</code> is an enumeration, which is a declaration
1291 context that contains the
1292 enumerators <code>Red</code>, <code>Green</code>,
1293 and <code>Blue</code>. Thus, traversing the list of declarations
1294 contained in the enumeration <code>Color</code> will
1295 yield <code>Red</code>, <code>Green</code>,
1296 and <code>Blue</code>. However, outside of the scope
1297 of <code>Color</code> one can name the enumerator <code>Red</code>
1298 without qualifying the name, e.g.,</p>
1299
1300<pre>
1301Color c = Red;
1302</pre>
1303
1304<p>There are other entities in C++ that provide similar behavior. For
1305 example, linkage specifications that use curly braces:</p>
1306
1307<pre>
1308extern "C" {
1309 void f(int);
1310 void g(int);
1311}
1312// f and g are visible here
1313</pre>
1314
1315<p>For source-level accuracy, we treat the linkage specification and
1316 enumeration type as a
1317 declaration context in which its enclosed declarations ("Red",
1318 "Green", and "Blue"; "f" and "g")
1319 are declared. However, these declarations are visible outside of the
1320 scope of the declaration context.</p>
1321
1322<p>These language features (and several others, described below) have
1323 roughly the same set of
1324 requirements: declarations are declared within a particular lexical
1325 context, but the declarations are also found via name lookup in
1326 scopes enclosing the declaration itself. This feature is implemented
1327 via <i>transparent</i> declaration contexts
1328 (see <code>DeclContext::isTransparentContext()</code>), whose
1329 declarations are visible in the nearest enclosing non-transparent
1330 declaration context. This means that the lexical context of the
1331 declaration (e.g., an enumerator) will be the
1332 transparent <code>DeclContext</code> itself, as will the semantic
1333 context, but the declaration will be visible in every outer context
1334 up to and including the first non-transparent declaration context (since
1335 transparent declaration contexts can be nested).</p>
1336
1337<p>The transparent <code>DeclContexts</code> are:</p>
1338<ul>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]1339 <li>Enumerations (but not C++11 "scoped enumerations"):
Douglas Gregor074149e2009-01-05 19:45:36 +0000[diff] [blame]1340 <pre>
1341enum Color {
1342 Red,
1343 Green,
1344 Blue
1345};
1346// Red, Green, and Blue are in scope
1347 </pre></li>
1348 <li>C++ linkage specifications:
1349 <pre>
1350extern "C" {
1351 void f(int);
1352 void g(int);
1353}
1354// f and g are in scope
1355 </pre></li>
1356 <li>Anonymous unions and structs:
1357 <pre>
1358struct LookupTable {
1359 bool IsVector;
1360 union {
1361 std::vector&lt;Item&gt; *Vector;
1362 std::set&lt;Item&gt; *Set;
1363 };
1364};
1365
1366LookupTable LT;
1367LT.Vector = 0; // Okay: finds Vector inside the unnamed union
1368 </pre>
1369 </li>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]1370 <li>C++11 inline namespaces:
Douglas Gregor074149e2009-01-05 19:45:36 +0000[diff] [blame]1371<pre>
1372namespace mylib {
1373 inline namespace debug {
1374 class X;
1375 }
1376}
1377mylib::X *xp; // okay: mylib::X refers to mylib::debug::X
1378</pre>
1379</li>
1380</ul>
1381
1382
1383<h4 id="MultiDeclContext">Multiply-Defined Declaration Contexts</h4>
1384<p>C++ namespaces have the interesting--and, so far, unique--property that
1385the namespace can be defined multiple times, and the declarations
1386provided by each namespace definition are effectively merged (from
1387the semantic point of view). For example, the following two code
1388snippets are semantically indistinguishable:</p>
1389<pre>
1390// Snippet #1:
1391namespace N {
1392 void f();
1393}
1394namespace N {
1395 void f(int);
1396}
1397
1398// Snippet #2:
1399namespace N {
1400 void f();
1401 void f(int);
1402}
1403</pre>
1404
1405<p>In Clang's representation, the source-centric view of declaration
1406 contexts will actually have two separate <code>NamespaceDecl</code>
1407 nodes in Snippet #1, each of which is a declaration context that
1408 contains a single declaration of "f". However, the semantics-centric
1409 view provided by name lookup into the namespace <code>N</code> for
Jonathan D. Turnerd3224292011-07-06 18:12:36 +0000[diff] [blame]1410 "f" will return a <code>DeclContext::lookup_result</code> that contains
1411 a range of iterators over declarations of "f".</p>
Douglas Gregor074149e2009-01-05 19:45:36 +0000[diff] [blame]1412
1413<p><code>DeclContext</code> manages multiply-defined declaration
1414 contexts internally. The
1415 function <code>DeclContext::getPrimaryContext</code> retrieves the
1416 "primary" context for a given <code>DeclContext</code> instance,
1417 which is the <code>DeclContext</code> responsible for maintaining
1418 the lookup table used for the semantics-centric view. Given the
1419 primary context, one can follow the chain
1420 of <code>DeclContext</code> nodes that define additional
1421 declarations via <code>DeclContext::getNextContext</code>. Note that
1422 these functions are used internally within the lookup and insertion
1423 methods of the <code>DeclContext</code>, so the vast majority of
1424 clients can ignore them.</p>
1425
1426<!-- ======================================================================= -->
Ted Kremenek8bc05712007-10-10 23:01:43 +0000[diff] [blame]1427<h3 id="CFG">The <tt>CFG</tt> class</h3>
1428<!-- ======================================================================= -->
1429
1430<p>The <tt>CFG</tt> class is designed to represent a source-level
1431control-flow graph for a single statement (<tt>Stmt*</tt>). Typically
1432instances of <tt>CFG</tt> are constructed for function bodies (usually
1433an instance of <tt>CompoundStmt</tt>), but can also be instantiated to
1434represent the control-flow of any class that subclasses <tt>Stmt</tt>,
1435which includes simple expressions. Control-flow graphs are especially
1436useful for performing
1437<a href="http://en.wikipedia.org/wiki/Data_flow_analysis#Sensitivities">flow-
1438or path-sensitive</a> program analyses on a given function.</p>
1439
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]1440<!-- ============ -->
Ted Kremenek8bc05712007-10-10 23:01:43 +0000[diff] [blame]1441<h4>Basic Blocks</h4>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]1442<!-- ============ -->
Ted Kremenek8bc05712007-10-10 23:01:43 +0000[diff] [blame]1443
1444<p>Concretely, an instance of <tt>CFG</tt> is a collection of basic
1445blocks. Each basic block is an instance of <tt>CFGBlock</tt>, which
1446simply contains an ordered sequence of <tt>Stmt*</tt> (each referring
1447to statements in the AST). The ordering of statements within a block
1448indicates unconditional flow of control from one statement to the
1449next. <a href="#ConditionalControlFlow">Conditional control-flow</a>
1450is represented using edges between basic blocks. The statements
1451within a given <tt>CFGBlock</tt> can be traversed using
1452the <tt>CFGBlock::*iterator</tt> interface.</p>
1453
1454<p>
Ted Kremenek18e17e72007-10-18 22:50:52 +0000[diff] [blame]1455A <tt>CFG</tt> object owns the instances of <tt>CFGBlock</tt> within
Ted Kremenek8bc05712007-10-10 23:01:43 +0000[diff] [blame]1456the control-flow graph it represents. Each <tt>CFGBlock</tt> within a
1457CFG is also uniquely numbered (accessible
1458via <tt>CFGBlock::getBlockID()</tt>). Currently the number is
1459based on the ordering the blocks were created, but no assumptions
1460should be made on how <tt>CFGBlock</tt>s are numbered other than their
1461numbers are unique and that they are numbered from 0..N-1 (where N is
1462the number of basic blocks in the CFG).</p>
1463
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]1464<!-- ===================== -->
Ted Kremenek8bc05712007-10-10 23:01:43 +0000[diff] [blame]1465<h4>Entry and Exit Blocks</h4>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]1466<!-- ===================== -->
Ted Kremenek8bc05712007-10-10 23:01:43 +0000[diff] [blame]1467
1468Each instance of <tt>CFG</tt> contains two special blocks:
1469an <i>entry</i> block (accessible via <tt>CFG::getEntry()</tt>), which
1470has no incoming edges, and an <i>exit</i> block (accessible
1471via <tt>CFG::getExit()</tt>), which has no outgoing edges. Neither
1472block contains any statements, and they serve the role of providing a
1473clear entrance and exit for a body of code such as a function body.
1474The presence of these empty blocks greatly simplifies the
1475implementation of many analyses built on top of CFGs.
1476
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]1477<!-- ===================================================== -->
Ted Kremenek8bc05712007-10-10 23:01:43 +0000[diff] [blame]1478<h4 id ="ConditionalControlFlow">Conditional Control-Flow</h4>
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]1479<!-- ===================================================== -->
Ted Kremenek8bc05712007-10-10 23:01:43 +0000[diff] [blame]1480
1481<p>Conditional control-flow (such as those induced by if-statements
1482and loops) is represented as edges between <tt>CFGBlock</tt>s.
1483Because different C language constructs can induce control-flow,
1484each <tt>CFGBlock</tt> also records an extra <tt>Stmt*</tt> that
1485represents the <i>terminator</i> of the block. A terminator is simply
1486the statement that caused the control-flow, and is used to identify
1487the nature of the conditional control-flow between blocks. For
1488example, in the case of an if-statement, the terminator refers to
1489the <tt>IfStmt</tt> object in the AST that represented the given
1490branch.</p>
1491
1492<p>To illustrate, consider the following code example:</p>
1493
1494<code>
1495int foo(int x) {<br>
1496&nbsp;&nbsp;x = x + 1;<br>
1497<br>
1498&nbsp;&nbsp;if (x > 2) x++;<br>
1499&nbsp;&nbsp;else {<br>
1500&nbsp;&nbsp;&nbsp;&nbsp;x += 2;<br>
1501&nbsp;&nbsp;&nbsp;&nbsp;x *= 2;<br>
1502&nbsp;&nbsp;}<br>
1503<br>
1504&nbsp;&nbsp;return x;<br>
1505}
1506</code>
1507
1508<p>After invoking the parser+semantic analyzer on this code fragment,
1509the AST of the body of <tt>foo</tt> is referenced by a
1510single <tt>Stmt*</tt>. We can then construct an instance
1511of <tt>CFG</tt> representing the control-flow graph of this function
1512body by single call to a static class method:</p>
1513
1514<code>
1515&nbsp;&nbsp;Stmt* FooBody = ...<br>
1516&nbsp;&nbsp;CFG* FooCFG = <b>CFG::buildCFG</b>(FooBody);
1517</code>
1518
1519<p>It is the responsibility of the caller of <tt>CFG::buildCFG</tt>
1520to <tt>delete</tt> the returned <tt>CFG*</tt> when the CFG is no
1521longer needed.</p>
1522
1523<p>Along with providing an interface to iterate over
1524its <tt>CFGBlock</tt>s, the <tt>CFG</tt> class also provides methods
1525that are useful for debugging and visualizing CFGs. For example, the
1526method
1527<tt>CFG::dump()</tt> dumps a pretty-printed version of the CFG to
1528standard error. This is especially useful when one is using a
1529debugger such as gdb. For example, here is the output
1530of <tt>FooCFG->dump()</tt>:</p>
1531
1532<code>
1533&nbsp;[ B5 (ENTRY) ]<br>
1534&nbsp;&nbsp;&nbsp;&nbsp;Predecessors (0):<br>
1535&nbsp;&nbsp;&nbsp;&nbsp;Successors (1): B4<br>
1536<br>
1537&nbsp;[ B4 ]<br>
1538&nbsp;&nbsp;&nbsp;&nbsp;1: x = x + 1<br>
1539&nbsp;&nbsp;&nbsp;&nbsp;2: (x > 2)<br>
1540&nbsp;&nbsp;&nbsp;&nbsp;<b>T: if [B4.2]</b><br>
1541&nbsp;&nbsp;&nbsp;&nbsp;Predecessors (1): B5<br>
1542&nbsp;&nbsp;&nbsp;&nbsp;Successors (2): B3 B2<br>
1543<br>
1544&nbsp;[ B3 ]<br>
1545&nbsp;&nbsp;&nbsp;&nbsp;1: x++<br>
1546&nbsp;&nbsp;&nbsp;&nbsp;Predecessors (1): B4<br>
1547&nbsp;&nbsp;&nbsp;&nbsp;Successors (1): B1<br>
1548<br>
1549&nbsp;[ B2 ]<br>
1550&nbsp;&nbsp;&nbsp;&nbsp;1: x += 2<br>
1551&nbsp;&nbsp;&nbsp;&nbsp;2: x *= 2<br>
1552&nbsp;&nbsp;&nbsp;&nbsp;Predecessors (1): B4<br>
1553&nbsp;&nbsp;&nbsp;&nbsp;Successors (1): B1<br>
1554<br>
1555&nbsp;[ B1 ]<br>
1556&nbsp;&nbsp;&nbsp;&nbsp;1: return x;<br>
1557&nbsp;&nbsp;&nbsp;&nbsp;Predecessors (2): B2 B3<br>
1558&nbsp;&nbsp;&nbsp;&nbsp;Successors (1): B0<br>
1559<br>
1560&nbsp;[ B0 (EXIT) ]<br>
1561&nbsp;&nbsp;&nbsp;&nbsp;Predecessors (1): B1<br>
1562&nbsp;&nbsp;&nbsp;&nbsp;Successors (0):
1563</code>
1564
1565<p>For each block, the pretty-printed output displays for each block
1566the number of <i>predecessor</i> blocks (blocks that have outgoing
1567control-flow to the given block) and <i>successor</i> blocks (blocks
1568that have control-flow that have incoming control-flow from the given
1569block). We can also clearly see the special entry and exit blocks at
1570the beginning and end of the pretty-printed output. For the entry
1571block (block B5), the number of predecessor blocks is 0, while for the
1572exit block (block B0) the number of successor blocks is 0.</p>
1573
1574<p>The most interesting block here is B4, whose outgoing control-flow
1575represents the branching caused by the sole if-statement
1576in <tt>foo</tt>. Of particular interest is the second statement in
1577the block, <b><tt>(x > 2)</tt></b>, and the terminator, printed
1578as <b><tt>if [B4.2]</tt></b>. The second statement represents the
1579evaluation of the condition of the if-statement, which occurs before
1580the actual branching of control-flow. Within the <tt>CFGBlock</tt>
1581for B4, the <tt>Stmt*</tt> for the second statement refers to the
1582actual expression in the AST for <b><tt>(x > 2)</tt></b>. Thus
1583pointers to subclasses of <tt>Expr</tt> can appear in the list of
1584statements in a block, and not just subclasses of <tt>Stmt</tt> that
1585refer to proper C statements.</p>
1586
1587<p>The terminator of block B4 is a pointer to the <tt>IfStmt</tt>
1588object in the AST. The pretty-printer outputs <b><tt>if
1589[B4.2]</tt></b> because the condition expression of the if-statement
1590has an actual place in the basic block, and thus the terminator is
1591essentially
1592<i>referring</i> to the expression that is the second statement of
1593block B4 (i.e., B4.2). In this manner, conditions for control-flow
1594(which also includes conditions for loops and switch statements) are
1595hoisted into the actual basic block.</p>
1596
Chris Lattner62fd2782008-11-22 21:41:31 +0000[diff] [blame]1597<!-- ===================== -->
1598<!-- <h4>Implicit Control-Flow</h4> -->
1599<!-- ===================== -->
Ted Kremenek8bc05712007-10-10 23:01:43 +0000[diff] [blame]1600
1601<!--
1602<p>A key design principle of the <tt>CFG</tt> class was to not require
1603any transformations to the AST in order to represent control-flow.
1604Thus the <tt>CFG</tt> does not perform any "lowering" of the
1605statements in an AST: loops are not transformed into guarded gotos,
1606short-circuit operations are not converted to a set of if-statements,
1607and so on.</p>
1608-->
Ted Kremenek17a295d2008-06-11 06:19:49 +0000[diff] [blame]1609
Chris Lattner7bad1992008-11-16 21:48:07 +0000[diff] [blame]1610
1611<!-- ======================================================================= -->
1612<h3 id="Constants">Constant Folding in the Clang AST</h3>
1613<!-- ======================================================================= -->
1614
1615<p>There are several places where constants and constant folding matter a lot to
1616the Clang front-end. First, in general, we prefer the AST to retain the source
1617code as close to how the user wrote it as possible. This means that if they
1618wrote "5+4", we want to keep the addition and two constants in the AST, we don't
1619want to fold to "9". This means that constant folding in various ways turns
1620into a tree walk that needs to handle the various cases.</p>
1621
1622<p>However, there are places in both C and C++ that require constants to be
1623folded. For example, the C standard defines what an "integer constant
1624expression" (i-c-e) is with very precise and specific requirements. The
1625language then requires i-c-e's in a lot of places (for example, the size of a
1626bitfield, the value for a case statement, etc). For these, we have to be able
1627to constant fold the constants, to do semantic checks (e.g. verify bitfield size
1628is non-negative and that case statements aren't duplicated). We aim for Clang
1629to be very pedantic about this, diagnosing cases when the code does not use an
1630i-c-e where one is required, but accepting the code unless running with
1631<tt>-pedantic-errors</tt>.</p>
1632
1633<p>Things get a little bit more tricky when it comes to compatibility with
1634real-world source code. Specifically, GCC has historically accepted a huge
1635superset of expressions as i-c-e's, and a lot of real world code depends on this
1636unfortuate accident of history (including, e.g., the glibc system headers). GCC
1637accepts anything its "fold" optimizer is capable of reducing to an integer
1638constant, which means that the definition of what it accepts changes as its
1639optimizer does. One example is that GCC accepts things like "case X-X:" even
1640when X is a variable, because it can fold this to 0.</p>
1641
1642<p>Another issue are how constants interact with the extensions we support, such
1643as __builtin_constant_p, __builtin_inf, __extension__ and many others. C99
1644obviously does not specify the semantics of any of these extensions, and the
1645definition of i-c-e does not include them. However, these extensions are often
1646used in real code, and we have to have a way to reason about them.</p>
1647
1648<p>Finally, this is not just a problem for semantic analysis. The code
1649generator and other clients have to be able to fold constants (e.g. to
1650initialize global variables) and has to handle a superset of what C99 allows.
1651Further, these clients can benefit from extended information. For example, we
1652know that "foo()||1" always evaluates to true, but we can't replace the
1653expression with true because it has side effects.</p>
1654
1655<!-- ======================= -->
1656<h4>Implementation Approach</h4>
1657<!-- ======================= -->
1658
1659<p>After trying several different approaches, we've finally converged on a
1660design (Note, at the time of this writing, not all of this has been implemented,
1661consider this a design goal!). Our basic approach is to define a single
1662recursive method evaluation method (<tt>Expr::Evaluate</tt>), which is
1663implemented in <tt>AST/ExprConstant.cpp</tt>. Given an expression with 'scalar'
1664type (integer, fp, complex, or pointer) this method returns the following
1665information:</p>
1666
1667<ul>
1668<li>Whether the expression is an integer constant expression, a general
1669 constant that was folded but has no side effects, a general constant that
1670 was folded but that does have side effects, or an uncomputable/unfoldable
1671 value.
1672</li>
1673<li>If the expression was computable in any way, this method returns the APValue
1674 for the result of the expression.</li>
1675<li>If the expression is not evaluatable at all, this method returns
1676 information on one of the problems with the expression. This includes a
1677 SourceLocation for where the problem is, and a diagnostic ID that explains
1678 the problem. The diagnostic should be have ERROR type.</li>
1679<li>If the expression is not an integer constant expression, this method returns
1680 information on one of the problems with the expression. This includes a
1681 SourceLocation for where the problem is, and a diagnostic ID that explains
1682 the problem. The diagnostic should be have EXTENSION type.</li>
1683</ul>
1684
1685<p>This information gives various clients the flexibility that they want, and we
1686will eventually have some helper methods for various extensions. For example,
1687Sema should have a <tt>Sema::VerifyIntegerConstantExpression</tt> method, which
1688calls Evaluate on the expression. If the expression is not foldable, the error
1689is emitted, and it would return true. If the expression is not an i-c-e, the
1690EXTENSION diagnostic is emitted. Finally it would return false to indicate that
1691the AST is ok.</p>
1692
1693<p>Other clients can use the information in other ways, for example, codegen can
1694just use expressions that are foldable in any way.</p>
1695
1696<!-- ========== -->
1697<h4>Extensions</h4>
1698<!-- ========== -->
1699
Chris Lattner552de0a2008-11-23 08:16:56 +0000[diff] [blame]1700<p>This section describes how some of the various extensions Clang supports
Chris Lattner7bad1992008-11-16 21:48:07 +0000[diff] [blame]1701interacts with constant evaluation:</p>
1702
1703<ul>
1704<li><b><tt>__extension__</tt></b>: The expression form of this extension causes
1705 any evaluatable subexpression to be accepted as an integer constant
1706 expression.</li>
Sylvestre Ledru2a700b12012-07-25 22:02:37 +0000[diff] [blame]1707<li><b><tt>__builtin_constant_p</tt></b>: This returns true (as an integer
Richard Smith8a0f1552011-12-09 03:40:28 +0000[diff] [blame]1708 constant expression) if the operand evaluates to either a numeric value
1709 (that is, not a pointer cast to integral type) of integral, enumeration,
1710 floating or complex type, or if it evaluates to the address of the first
1711 character of a string literal (possibly cast to some other type). As a
Chris Lattner28daa532008-12-12 06:55:44 +0000[diff] [blame]1712 special case, if <tt>__builtin_constant_p</tt> is the (potentially
1713 parenthesized) condition of a conditional operator expression ("?:"), only
Chris Lattner42b83dd2008-12-12 18:00:51 +0000[diff] [blame]1714 the true side of the conditional operator is considered, and it is evaluated
1715 with full constant folding.</li>
Chris Lattner7bad1992008-11-16 21:48:07 +0000[diff] [blame]1716<li><b><tt>__builtin_choose_expr</tt></b>: The condition is required to be an
1717 integer constant expression, but we accept any constant as an "extension of
1718 an extension". This only evaluates one operand depending on which way the
1719 condition evaluates.</li>
1720<li><b><tt>__builtin_classify_type</tt></b>: This always returns an integer
1721 constant expression.</li>
1722<li><b><tt>__builtin_inf,nan,..</tt></b>: These are treated just like a
1723 floating-point literal.</li>
1724<li><b><tt>__builtin_abs,copysign,..</tt></b>: These are constant folded as
1725 general constant expressions.</li>
Richard Smith8a0f1552011-12-09 03:40:28 +0000[diff] [blame]1726<li><b><tt>__builtin_strlen</tt></b> and <b><tt>strlen</tt></b>: These are
1727 constant folded as integer constant expressions if the argument is a string
1728 literal.</li>
Chris Lattner7bad1992008-11-16 21:48:07 +0000[diff] [blame]1729</ul>
1730
1731
Jeffrey Yasskin28dadd62011-01-28 23:41:54 +0000[diff] [blame]1732<!-- ======================================================================= -->
1733<h2 id="Howtos">How to change Clang</h2>
1734<!-- ======================================================================= -->
Chris Lattner7bad1992008-11-16 21:48:07 +0000[diff] [blame]1735
Jeffrey Yasskin28dadd62011-01-28 23:41:54 +0000[diff] [blame]1736<!-- ======================================================================= -->
1737<h3 id="AddingAttributes">How to add an attribute</h3>
1738<!-- ======================================================================= -->
1739
1740<p>To add an attribute, you'll have to add it to the list of attributes, add it
1741to the parsing phase, and look for it in the AST scan.
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]1742<a href="http://llvm.org/viewvc/llvm-project?view=rev&amp;revision=124217">r124217</a>
Jeffrey Yasskin28dadd62011-01-28 23:41:54 +0000[diff] [blame]1743has a good example of adding a warning attribute.</p>
1744
1745<p>(Beware that this hasn't been reviewed/fixed by the people who designed the
1746attributes system yet.)</p>
1747
1748<h4><a
1749href="http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/Attr.td?view=markup">include/clang/Basic/Attr.td</a></h4>
1750
1751<p>Each attribute gets a <tt>def</tt> inheriting from <tt>Attr</tt> or one of
1752its subclasses. <tt>InheritableAttr</tt> means that the attribute also applies
1753to subsequent declarations of the same name.</p>
1754
1755<p><tt>Spellings</tt> lists the strings that can appear in
1756<tt>__attribute__((here))</tt> or <tt>[[here]]</tt>. All such strings
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]1757will be synonymous. If you want to allow the <tt>[[]]</tt> C++11
Jeffrey Yasskin28dadd62011-01-28 23:41:54 +0000[diff] [blame]1758syntax, you have to define a list of <tt>Namespaces</tt>, which will
1759let users write <tt>[[namespace:spelling]]</tt>. Using the empty
1760string for a namespace will allow users to write just the spelling
1761with no "<tt>:</tt>".</p>
1762
1763<p><tt>Subjects</tt> restricts what kinds of AST node to which this attribute
1764can appertain (roughly, attach).</p>
1765
1766<p><tt>Args</tt> names the arguments the attribute takes, in order. If
1767<tt>Args</tt> is <tt>[StringArgument&lt;"Arg1">, IntArgument&lt;"Arg2">]</tt>
1768then <tt>__attribute__((myattribute("Hello", 3)))</tt> will be a valid use.</p>
1769
1770<h4>Boilerplate</h4>
1771
Jeffrey Yasskin28dadd62011-01-28 23:41:54 +0000[diff] [blame]1772<p>Write a new <tt>HandleYourAttr()</tt> function in <a
1773href="http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclAttr.cpp?view=markup">lib/Sema/SemaDeclAttr.cpp</a>,
1774and add a case to the switch in <tt>ProcessNonInheritableDeclAttr()</tt> or
1775<tt>ProcessInheritableDeclAttr()</tt> forwarding to it.</p>
1776
1777<p>If your attribute causes extra warnings to fire, define a <tt>DiagGroup</tt>
1778in <a
1779href="http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticGroups.td?view=markup">include/clang/Basic/DiagnosticGroups.td</a>
1780named after the attribute's <tt>Spelling</tt> with "_"s replaced by "-"s. If
1781you're only defining one diagnostic, you can skip <tt>DiagnosticGroups.td</tt>
1782and use <tt>InGroup&lt;DiagGroup&lt;"your-attribute">></tt> directly in <a
1783href="http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?view=markup">DiagnosticSemaKinds.td</a></p>
1784
1785<h4>The meat of your attribute</h4>
1786
1787<p>Find an appropriate place in Clang to do whatever your attribute needs to do.
1788Check for the attribute's presence using <tt>Decl::getAttr&lt;YourAttr>()</tt>.</p>
1789
1790<p>Update the <a href="LanguageExtensions.html">Clang Language Extensions</a>
1791document to describe your new attribute.</p>
Chris Lattner7bad1992008-11-16 21:48:07 +0000[diff] [blame]1792
Douglas Gregor1f634c62011-09-30 21:32:37 +0000[diff] [blame]1793<!-- ======================================================================= -->
1794<h3 id="AddingExprStmt">How to add an expression or statement</h3>
1795<!-- ======================================================================= -->
1796
1797<p>Expressions and statements are one of the most fundamental constructs within a
1798compiler, because they interact with many different parts of the AST,
1799semantic analysis, and IR generation. Therefore, adding a new
1800expression or statement kind into Clang requires some care. The following list
1801details the various places in Clang where an expression or statement needs to be
1802introduced, along with patterns to follow to ensure that the new
1803expression or statement works well across all of the C languages. We
1804focus on expressions, but statements are similar.</p>
1805
1806<ol>
1807 <li>Introduce parsing actions into the parser. Recursive-descent
1808 parsing is mostly self-explanatory, but there are a few things that
1809 are worth keeping in mind:
1810 <ul>
1811 <li>Keep as much source location information as possible! You'll
1812 want it later to produce great diagnostics and support Clang's
1813 various features that map between source code and the AST.</li>
1814 <li>Write tests for all of the "bad" parsing cases, to make sure
1815 your recovery is good. If you have matched delimiters (e.g.,
1816 parentheses, square brackets, etc.), use
Douglas Gregor4a8dfb52011-10-12 16:37:45 +0000[diff] [blame]1817 <tt>Parser::BalancedDelimiterTracker</tt> to give nice diagnostics when
Douglas Gregor1f634c62011-09-30 21:32:37 +0000[diff] [blame]1818 things go wrong.</li>
1819 </ul>
1820 </li>
1821
1822 <li>Introduce semantic analysis actions into <tt>Sema</tt>. Semantic
1823 analysis should always involve two functions: an <tt>ActOnXXX</tt>
1824 function that will be called directly from the parser, and a
1825 <tt>BuildXXX</tt> function that performs the actual semantic
1826 analysis and will (eventually!) build the AST node. It's fairly
1827 common for the <tt>ActOnCXX</tt> function to do very little (often
1828 just some minor translation from the parser's representation to
1829 <tt>Sema</tt>'s representation of the same thing), but the separation
1830 is still important: C++ template instantiation, for example,
1831 should always call the <tt>BuildXXX</tt> variant. Several notes on
1832 semantic analysis before we get into construction of the AST:
1833 <ul>
1834 <li>Your expression probably involves some types and some
1835 subexpressions. Make sure to fully check that those types, and the
1836 types of those subexpressions, meet your expectations. Add
1837 implicit conversions where necessary to make sure that all of the
1838 types line up exactly the way you want them. Write extensive tests
1839 to check that you're getting good diagnostics for mistakes and
1840 that you can use various forms of subexpressions with your
1841 expression.</li>
1842 <li>When type-checking a type or subexpression, make sure to first
1843 check whether the type is "dependent"
1844 (<tt>Type::isDependentType()</tt>) or whether a subexpression is
1845 type-dependent (<tt>Expr::isTypeDependent()</tt>). If any of these
1846 return true, then you're inside a template and you can't do much
1847 type-checking now. That's normal, and your AST node (when you get
1848 there) will have to deal with this case. At this point, you can
1849 write tests that use your expression within templates, but don't
1850 try to instantiate the templates.</li>
1851 <li>For each subexpression, be sure to call
1852 <tt>Sema::CheckPlaceholderExpr()</tt> to deal with "weird"
1853 expressions that don't behave well as subexpressions. Then,
1854 determine whether you need to perform
1855 lvalue-to-rvalue conversions
1856 (<tt>Sema::DefaultLvalueConversion</tt>e) or
1857 the usual unary conversions
1858 (<tt>Sema::UsualUnaryConversions</tt>), for places where the
1859 subexpression is producing a value you intend to use.</li>
1860 <li>Your <tt>BuildXXX</tt> function will probably just return
1861 <tt>ExprError()</tt> at this point, since you don't have an AST.
1862 That's perfectly fine, and shouldn't impact your testing.</li>
1863 </ul>
1864 </li>
1865
1866 <li>Introduce an AST node for your new expression. This starts with
1867 declaring the node in <tt>include/Basic/StmtNodes.td</tt> and
1868 creating a new class for your expression in the appropriate
1869 <tt>include/AST/Expr*.h</tt> header. It's best to look at the class
1870 for a similar expression to get ideas, and there are some specific
1871 things to watch for:
1872 <ul>
1873 <li>If you need to allocate memory, use the <tt>ASTContext</tt>
1874 allocator to allocate memory. Never use raw <tt>malloc</tt> or
1875 <tt>new</tt>, and never hold any resources in an AST node, because
1876 the destructor of an AST node is never called.</li>
1877
1878 <li>Make sure that <tt>getSourceRange()</tt> covers the exact
1879 source range of your expression. This is needed for diagnostics
1880 and for IDE support.</li>
1881
1882 <li>Make sure that <tt>children()</tt> visits all of the
1883 subexpressions. This is important for a number of features (e.g., IDE
1884 support, C++ variadic templates). If you have sub-types, you'll
1885 also need to visit those sub-types in the
1886 <tt>RecursiveASTVisitor</tt>.</li>
1887
1888 <li>Add printing support (<tt>StmtPrinter.cpp</tt>) and dumping
1889 support (<tt>StmtDumper.cpp</tt>) for your expression.</li>
1890
1891 <li>Add profiling support (<tt>StmtProfile.cpp</tt>) for your AST
1892 node, noting the distinguishing (non-source location)
1893 characteristics of an instance of your expression. Omitting this
1894 step will lead to hard-to-diagnose failures regarding matching of
1895 template declarations.</li>
1896 </ul>
1897 </li>
1898
1899 <li>Teach semantic analysis to build your AST node! At this point,
1900 you can wire up your <tt>Sema::BuildXXX</tt> function to actually
1901 create your AST. A few things to check at this point:
1902 <ul>
1903 <li>If your expression can construct a new C++ class or return a
1904 new Objective-C object, be sure to update and then call
1905 <tt>Sema::MaybeBindToTemporary</tt> for your just-created AST node
1906 to be sure that the object gets properly destructed. An easy way
1907 to test this is to return a C++ class with a private destructor:
1908 semantic analysis should flag an error here with the attempt to
1909 call the destructor.</li>
1910 <li>Inspect the generated AST by printing it using <tt>clang -cc1
1911 -ast-print</tt>, to make sure you're capturing all of the
1912 important information about how the AST was written.</li>
1913 <li>Inspect the generated AST under <tt>clang -cc1 -ast-dump</tt>
1914 to verify that all of the types in the generated AST line up the
1915 way you want them. Remember that clients of the AST should never
1916 have to "think" to understand what's going on. For example, all
1917 implicit conversions should show up explicitly in the AST.</li>
1918 <li>Write tests that use your expression as a subexpression of
1919 other, well-known expressions. Can you call a function using your
1920 expression as an argument? Can you use the ternary operator?</li>
1921 </ul>
1922 </li>
1923
1924 <li>Teach code generation to create IR to your AST node. This step
1925 is the first (and only) that requires knowledge of LLVM IR. There
1926 are several things to keep in mind:
1927 <ul>
1928 <li>Code generation is separated into scalar/aggregate/complex and
1929 lvalue/rvalue paths, depending on what kind of result your
1930 expression produces. On occasion, this requires some careful
1931 factoring of code to avoid duplication.</li>
1932
1933 <li><tt>CodeGenFunction</tt> contains functions
1934 <tt>ConvertType</tt> and <tt>ConvertTypeForMem</tt> that convert
1935 Clang's types (<tt>clang::Type*</tt> or <tt>clang::QualType</tt>)
1936 to LLVM types.
1937 Use the former for values, and the later for memory locations:
1938 test with the C++ "bool" type to check this. If you find
1939 that you are having to use LLVM bitcasts to make
1940 the subexpressions of your expression have the type that your
1941 expression expects, STOP! Go fix semantic analysis and the AST so
1942 that you don't need these bitcasts.</li>
1943
1944 <li>The <tt>CodeGenFunction</tt> class has a number of helper
1945 functions to make certain operations easy, such as generating code
1946 to produce an lvalue or an rvalue, or to initialize a memory
1947 location with a given value. Prefer to use these functions rather
1948 than directly writing loads and stores, because these functions
1949 take care of some of the tricky details for you (e.g., for
1950 exceptions).</li>
1951
1952 <li>If your expression requires some special behavior in the event
1953 of an exception, look at the <tt>push*Cleanup</tt> functions in
1954 <tt>CodeGenFunction</tt> to introduce a cleanup. You shouldn't
1955 have to deal with exception-handling directly.</li>
1956
1957 <li>Testing is extremely important in IR generation. Use <tt>clang
1958 -cc1 -emit-llvm</tt> and <a
1959 href="http://llvm.org/cmds/FileCheck.html">FileCheck</a> to verify
1960 that you're generating the right IR.</li>
1961 </ul>
1962 </li>
1963
1964 <li>Teach template instantiation how to cope with your AST
1965 node, which requires some fairly simple code:
1966 <ul>
1967 <li>Make sure that your expression's constructor properly
1968 computes the flags for type dependence (i.e., the type your
1969 expression produces can change from one instantiation to the
1970 next), value dependence (i.e., the constant value your expression
1971 produces can change from one instantiation to the next),
Douglas Gregord1cb2dc2011-10-14 00:54:15 +0000[diff] [blame]1972 instantiation dependence (i.e., a template parameter occurs
Douglas Gregor1f634c62011-09-30 21:32:37 +0000[diff] [blame]1973 anywhere in your expression), and whether your expression contains
1974 a parameter pack (for variadic templates). Often, computing these
1975 flags just means combining the results from the various types and
1976 subexpressions.</li>
1977
1978 <li>Add <tt>TransformXXX</tt> and <tt>RebuildXXX</tt> functions to
1979 the
1980 <tt>TreeTransform</tt> class template in <tt>Sema</tt>.
1981 <tt>TransformXXX</tt> should (recursively) transform all of the
1982 subexpressions and types
1983 within your expression, using <tt>getDerived().TransformYYY</tt>.
1984 If all of the subexpressions and types transform without error, it
1985 will then call the <tt>RebuildXXX</tt> function, which will in
1986 turn call <tt>getSema().BuildXXX</tt> to perform semantic analysis
1987 and build your expression.</li>
1988
1989 <li>To test template instantiation, take those tests you wrote to
1990 make sure that you were type checking with type-dependent
1991 expressions and dependent types (from step #2) and instantiate
1992 those templates with various types, some of which type-check and
1993 some that don't, and test the error messages in each case.</li>
1994 </ul>
1995 </li>
1996
1997 <li>There are some "extras" that make other features work better.
1998 It's worth handling these extras to give your expression complete
1999 integration into Clang:
2000 <ul>
2001 <li>Add code completion support for your expression in
2002 <tt>SemaCodeComplete.cpp</tt>.</li>
2003
2004 <li>If your expression has types in it, or has any "interesting"
2005 features other than subexpressions, extend libclang's
2006 <tt>CursorVisitor</tt> to provide proper visitation for your
2007 expression, enabling various IDE features such as syntax
2008 highlighting, cross-referencing, and so on. The
2009 <tt>c-index-test</tt> helper program can be used to test these
2010 features.</li>
2011 </ul>
2012 </li>
2013</ol>
2014
Ted Kremenek17a295d2008-06-11 06:19:49 +0000[diff] [blame]2015</div>
2016</body>
Douglas Gregor2e1cd422008-11-17 14:58:09 +0000[diff] [blame]2017</html>