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16<div id="content">
17
18<h1>Clang Compiler User's Manual</h1>
19
20<ul>
21<li><a href="#intro">Introduction</a>
22 <ul>
23 <li><a href="#terminology">Terminology</a></li>
24 <li><a href="#basicusage">Basic Usage</a></li>
25 </ul>
26</li>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]27<li><a href="#commandline">Command Line Options</a>
28 <ul>
29 <li><a href="#cl_diagnostics">Options to Control Error and Warning
30 Messages</a></li>
31 </ul>
32</li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]33<li><a href="#general_features">Language and Target-Independent Features</a>
34 <ul>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]35 <li><a href="#diagnostics">Controlling Errors and Warnings</a>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]36 <ul>
37 <li><a href="#diagnostics_display">Controlling How Clang Displays Diagnostics</a></li>
38 <li><a href="#diagnostics_mappings">Diagnostic Mappings</a></li>
Chris Lattner67db8cd2010-05-30 23:42:51 +0000[diff] [blame]39 <li><a href="#diagnostics_categories">Diagnostic Categories</a></li>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]40 <li><a href="#diagnostics_commandline">Controlling Diagnostics via Command Line Flags</a></li>
41 <li><a href="#diagnostics_pragmas">Controlling Diagnostics via Pragmas</a></li>
Ted Kremenek2fb11eb2010-08-24 18:12:35 +0000[diff] [blame]42 <li><a href="#analyzer_diagnositics">Controlling Static Analyzer Diagnostics</a></li>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]43 </ul>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]44 </li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]45 <li><a href="#precompiledheaders">Precompiled Headers</a></li>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]46 <li><a href="#codegen">Controlling Code Generation</a></li>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]47 </ul>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]48</li>
49<li><a href="#c">C Language Features</a>
50 <ul>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]51 <li><a href="#c_ext">Extensions supported by clang</a></li>
52 <li><a href="#c_modes">Differences between various standard modes</a></li>
53 <li><a href="#c_unimpl_gcc">GCC extensions not implemented yet</a></li>
54 <li><a href="#c_unsupp_gcc">Intentionally unsupported GCC extensions</a></li>
55 <li><a href="#c_ms">Microsoft extensions</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]56 </ul>
57</li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]58<li><a href="#target_features">Target-Specific Features and Limitations</a>
59 <ul>
60 <li><a href="#target_arch">CPU Architectures Features and Limitations</a>
61 <ul>
62 <li><a href="#target_arch_x86">X86</a></li>
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]63 <li><a href="#target_arch_arm">ARM</a></li>
64 <li><a href="#target_arch_other">Other platforms</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]65 </ul>
66 </li>
67 <li><a href="#target_os">Operating System Features and Limitations</a>
68 <ul>
69 <li><a href="#target_os_darwin">Darwin (Mac OS/X)</a></li>
70 <li>Linux, etc.</li>
NAKAMURA Takumia75fdb22011-04-04 15:02:41 +0000[diff] [blame]71 <li><a href="#target_os_win32">Windows</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]72 </ul>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]73 </li>
74 </ul>
75</li>
76</ul>
77
78
79<!-- ======================================================================= -->
80<h2 id="intro">Introduction</h2>
81<!-- ======================================================================= -->
82
83<p>The Clang Compiler is an open-source compiler for the C family of programming
84languages, aiming to be the best in class implementation of these languages.
85Clang builds on the LLVM optimizer and code generator, allowing it to provide
86high-quality optimization and code generation support for many targets. For
87more general information, please see the <a href="http://clang.llvm.org">Clang
88Web Site</a> or the <a href="http://llvm.org">LLVM Web Site</a>.</p>
89
90<p>This document describes important notes about using Clang as a compiler for
91an end-user, documenting the supported features, command line options, etc. If
92you are interested in using Clang to build a tool that processes code, please
93see <a href="InternalsManual.html">the Clang Internals Manual</a>. If you are
94interested in the <a href="http://clang.llvm.org/StaticAnalysis.html">Clang
95Static Analyzer</a>, please see its web page.</p>
96
97<p>Clang is designed to support the C family of programming languages, which
98includes <a href="#c">C</a>, <a href="#objc">Objective-C</a>, <a
99href="#cxx">C++</a>, and <a href="#objcxx">Objective-C++</a> as well as many
100dialects of those. For language-specific information, please see the
101corresponding language specific section:</p>
102
103<ul>
104<li><a href="#c">C Language</a>: K&amp;R C, ANSI C89, ISO C90, ISO C94
105 (C89+AMD1), ISO C99 (+TC1, TC2, TC3). </li>
106<li><a href="#objc">Objective-C Language</a>: ObjC 1, ObjC 2, ObjC 2.1, plus
107 variants depending on base language.</li>
108<li><a href="#cxx">C++ Language Features</a></li>
109<li><a href="#objcxx">Objective C++ Language</a></li>
110</ul>
111
112<p>In addition to these base languages and their dialects, Clang supports a
113broad variety of language extensions, which are documented in the corresponding
114language section. These extensions are provided to be compatible with the GCC,
115Microsoft, and other popular compilers as well as to improve functionality
116through Clang-specific features. The Clang driver and language features are
117intentionally designed to be as compatible with the GNU GCC compiler as
118reasonably possible, easing migration from GCC to Clang. In most cases, code
119"just works".</p>
120
121<p>In addition to language specific features, Clang has a variety of features
122that depend on what CPU architecture or operating system is being compiled for.
Douglas Gregorcd5a5052009-11-09 15:15:41 +0000[diff] [blame]123Please see the <a href="#target_features">Target-Specific Features and
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]124Limitations</a> section for more details.</p>
125
126<p>The rest of the introduction introduces some basic <a
127href="#terminology">compiler terminology</a> that is used throughout this manual
128and contains a basic <a href="#basicusage">introduction to using Clang</a>
129as a command line compiler.</p>
130
131<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
132<h3 id="terminology">Terminology</h3>
133<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
134
135<p>Front end, parser, backend, preprocessor, undefined behavior, diagnostic,
136 optimizer</p>
137
138<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
139<h3 id="basicusage">Basic Usage</h3>
140<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
141
142<p>Intro to how to use a C compiler for newbies.</p>
143<p>
144compile + link
145
146compile then link
147
148debug info
149
150enabling optimizations
151
152picking a language to use, defaults to C99 by default. Autosenses based on
153extension.
154
155using a makefile
156</p>
157
158
159<!-- ======================================================================= -->
160<h2 id="commandline">Command Line Options</h2>
161<!-- ======================================================================= -->
162
163<p>
164This section is generally an index into other sections. It does not go into
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]165depth on the ones that are covered by other sections. However, the first part
166introduces the language selection and other high level options like -c, -g, etc.
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]167</p>
168
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]169
170<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
171<h3 id="cl_diagnostics">Options to Control Error and Warning Messages</h3>
172<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
173
174<p><b>-Werror</b>: Turn warnings into errors.</p>
175<p><b>-Werror=foo</b>: Turn warning "foo" into an error.</p>
176<p><b>-Wno-error=foo</b>: Turn warning "foo" into an warning even if -Werror is
177 specified.</p>
178<p><b>-Wfoo</b>: Enable warning foo</p>
179<p><b>-Wno-foo</b>: Disable warning foo</p>
180<p><b>-w</b>: Disable all warnings.</p>
181<p><b>-pedantic</b>: Warn on language extensions.</p>
182<p><b>-pedantic-errors</b>: Error on language extensions.</p>
183<p><b>-Wsystem-headers</b>: Enable warnings from system headers.</p>
184
Chris Lattner0f0c9632010-04-07 20:49:23 +0000[diff] [blame]185<p><b>-ferror-limit=123</b>: Stop emitting diagnostics after 123 errors have
186 been produced. The default is 20, and the error limit can be disabled with
187 -ferror-limit=0.</p>
188
Douglas Gregor575cf372010-04-20 07:18:24 +0000[diff] [blame]189<p><b>-ftemplate-backtrace-limit=123</b>: Only emit up to 123 template instantiation notes within the template instantiation backtrace for a single warning or error. The default is 10, and the limit can be disabled with -ftemplate-backtrace-limit=0.</p>
190
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]191<!-- ================================================= -->
192<h4 id="cl_diag_formatting">Formatting of Diagnostics</h4>
193<!-- ================================================= -->
194
195<p>Clang aims to produce beautiful diagnostics by default, particularly for new
196users that first come to Clang. However, different people have different
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]197preferences, and sometimes Clang is driven by another program that wants to
198parse simple and consistent output, not a person. For these cases, Clang
199provides a wide range of options to control the exact output format of the
200diagnostics that it generates.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]201
202<dl>
203
204<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
205<dt id="opt_fshow-column"><b>-f[no-]show-column</b>: Print column number in
206diagnostic.</dt>
207<dd>This option, which defaults to on, controls whether or not Clang prints the
208column number of a diagnostic. For example, when this is enabled, Clang will
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]209print something like:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]210
211<pre>
212 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
213 #endif bad
214 ^
215 //
216</pre>
217
218<p>When this is disabled, Clang will print "test.c:28: warning..." with no
219column number.</p>
220</dd>
221
222<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
223<dt id="opt_fshow-source-location"><b>-f[no-]show-source-location</b>: Print
224source file/line/column information in diagnostic.</dt>
225<dd>This option, which defaults to on, controls whether or not Clang prints the
226filename, line number and column number of a diagnostic. For example,
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]227when this is enabled, Clang will print something like:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]228
229<pre>
230 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
231 #endif bad
232 ^
233 //
234</pre>
235
236<p>When this is disabled, Clang will not print the "test.c:28:8: " part.</p>
237</dd>
238
239<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
240<dt id="opt_fcaret-diagnostics"><b>-f[no-]caret-diagnostics</b>: Print source
241line and ranges from source code in diagnostic.</dt>
242<dd>This option, which defaults to on, controls whether or not Clang prints the
243source line, source ranges, and caret when emitting a diagnostic. For example,
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]244when this is enabled, Clang will print something like:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]245
246<pre>
247 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
248 #endif bad
249 ^
250 //
251</pre>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]252</dd>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]253<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Douglas Gregore8d44dd2010-07-09 16:31:58 +0000[diff] [blame]254<dt id="opt_fcolor_diagnostics"><b>-f[no-]color-diagnostics</b>: </dt>
255<dd>This option, which defaults to on when a color-capable terminal is
256 detected, controls whether or not Clang prints diagnostics in color.
257 When this option is enabled, Clang will use colors to highlight
258 specific parts of the diagnostic, e.g.,
Chris Lattner4e1c53d2011-01-24 03:47:34 +0000[diff] [blame]259 <pre>
260 <b><font color="black">test.c:28:8: <font color="magenta">warning</font>: extra tokens at end of #endif directive [-Wextra-tokens]</font></b>
261 #endif bad
262 <font color="green">^</font>
263 <font color="green">//</font>
Douglas Gregore8d44dd2010-07-09 16:31:58 +0000[diff] [blame]264</pre>
Chris Lattner4e1c53d2011-01-24 03:47:34 +0000[diff] [blame]265
266<p>When this is disabled, Clang will just print:</p>
267
268<pre>
269 test.c:2:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
270 #endif bad
271 ^
272 //
273</pre>
274</dd>
Douglas Gregore8d44dd2010-07-09 16:31:58 +0000[diff] [blame]275<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]276<dt id="opt_fdiagnostics-show-option"><b>-f[no-]diagnostics-show-option</b>:
277Enable <tt>[-Woption]</tt> information in diagnostic line.</dt>
278<dd>This option, which defaults to on,
279controls whether or not Clang prints the associated <A
280href="#cl_diag_warning_groups">warning group</a> option name when outputting
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]281a warning diagnostic. For example, in this output:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]282
283<pre>
284 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
285 #endif bad
286 ^
287 //
288</pre>
289
290<p>Passing <b>-fno-diagnostics-show-option</b> will prevent Clang from printing
291the [<a href="#opt_Wextra-tokens">-Wextra-tokens</a>] information in the
292diagnostic. This information tells you the flag needed to enable or disable the
293diagnostic, either from the command line or through <a
294href="#pragma_GCC_diagnostic">#pragma GCC diagnostic</a>.</dd>
295
Chris Lattner28a43a42010-05-05 01:35:28 +0000[diff] [blame]296<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
297<dt id="opt_fdiagnostics-show-category"><b>-fdiagnostics-show-category=none/id/name</b>:
298Enable printing category information in diagnostic line.</dt>
299<dd>This option, which defaults to "none",
300controls whether or not Clang prints the category associated with a diagnostic
301when emitting it. Each diagnostic may or many not have an associated category,
302if it has one, it is listed in the diagnostic categorization field of the
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]303diagnostic line (in the []'s).
Chris Lattner28a43a42010-05-05 01:35:28 +0000[diff] [blame]304
305<p>For example, a format string warning will produce these three renditions
306based on the setting of this option:</p>
307
308<pre>
309 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat]
310 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat<b>,1</b>]
311 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat<b>,Format String</b>]
312</pre>
313
314<p>This category can be used by clients that want to group diagnostics by
315category, so it should be a high level category. We want dozens of these, not
316hundreds or thousands of them.</p>
317</dd>
318
319
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]320
321<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
322<dt id="opt_fdiagnostics-fixit-info"><b>-f[no-]diagnostics-fixit-info</b>:
323Enable "FixIt" information in the diagnostics output.</dt>
324<dd>This option, which defaults to on, controls whether or not Clang prints the
325information on how to fix a specific diagnostic underneath it when it knows.
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]326For example, in this output:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]327
328<pre>
329 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
330 #endif bad
331 ^
332 //
333</pre>
334
335<p>Passing <b>-fno-diagnostics-fixit-info</b> will prevent Clang from printing
336the "//" line at the end of the message. This information is useful for users
337who may not understand what is wrong, but can be confusing for machine
338parsing.</p>
339</dd>
340
341<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]342<dt id="opt_fdiagnostics-print-source-range-info">
343<b>-f[no-]diagnostics-print-source-range-info</b>:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]344Print machine parsable information about source ranges.</dt>
345<dd>This option, which defaults to off, controls whether or not Clang prints
346information about source ranges in a machine parsable format after the
347file/line/column number information. The information is a simple sequence of
348brace enclosed ranges, where each range lists the start and end line/column
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]349locations. For example, in this output:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]350
351<pre>
352exprs.c:47:15:{47:8-47:14}{47:17-47:24}: error: invalid operands to binary expression ('int *' and '_Complex float')
353 P = (P-42) + Gamma*4;
354 ~~~~~~ ^ ~~~~~~~
355</pre>
356
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]357<p>The {}'s are generated by -fdiagnostics-print-source-range-info.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]358</dd>
359
Douglas Gregor4786c152010-08-19 20:24:43 +0000[diff] [blame]360<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
361<dt id="opt_fdiagnostics-parseable-fixits">
362<b>-fdiagnostics-parseable-fixits</b>:
363Print Fix-Its in a machine parseable form.</dt>
364<dd><p>This option makes Clang print available Fix-Its in a machine parseable format at the end of diagnostics. The following example illustrates the format:</p>
365
366<pre>
Douglas Gregorbf5e09d2010-08-20 03:17:33 +0000[diff] [blame]367 fix-it:"t.cpp":{7:25-7:29}:"Gamma"
Douglas Gregor4786c152010-08-19 20:24:43 +0000[diff] [blame]368</pre>
369
NAKAMURA Takumi44626362011-04-05 00:57:02 +0000[diff] [blame]370<p>The range printed is a half-open range, so in this example the characters at
371column 25 up to but not including column 29 on line 7 in t.cpp should be
372replaced with the string &quot;Gamma&quot;. Either the range or the replacement
373string may be empty (representing strict insertions and strict erasures,
374respectively). Both the file name and the insertion string escape backslash (as
375&quot;\\&quot;), tabs (as &quot;\t&quot;), newlines (as &quot;\n&quot;), double
376quotes(as &quot;\&quot;&quot;) and non-printable characters (as octal
377&quot;\xxx&quot;).</p>
Douglas Gregor4786c152010-08-19 20:24:43 +0000[diff] [blame]378</dd>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]379
380</dl>
381
382
383
384
385<!-- ===================================================== -->
386<h4 id="cl_diag_warning_groups">Individual Warning Groups</h4>
387<!-- ===================================================== -->
388
389<p>TODO: Generate this from tblgen. Define one anchor per warning group.</p>
390
391
392<dl>
393
394
395<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
396<dt id="opt_Wextra-tokens"><b>-Wextra-tokens</b>: Warn about excess tokens at
397 the end of a preprocessor directive.</dt>
398<dd>This option, which defaults to on, enables warnings about extra tokens at
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]399the end of preprocessor directives. For example:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]400
401<pre>
402 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
403 #endif bad
404 ^
405</pre>
406
407<p>These extra tokens are not strictly conforming, and are usually best handled
408by commenting them out.</p>
409
410<p>This option is also enabled by <a href="">-Wfoo</a>, <a href="">-Wbar</a>,
411 and <a href="">-Wbaz</a>.</p>
412</dd>
413
Jeffrey Yasskin21d07e42010-06-05 01:39:57 +0000[diff] [blame]414<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
415<dt id="opt_Wambiguous-member-template"><b>-Wambiguous-member-template</b>:
416Warn about unqualified uses of a member template whose name resolves
417to another template at the location of the use.</dt>
418<dd>This option, which defaults to on, enables a warning in the
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]419following code:
Jeffrey Yasskin21d07e42010-06-05 01:39:57 +0000[diff] [blame]420
421<pre>
422template&lt;typename T> struct set{};
423template&lt;typename T> struct trait { typedef const T& type; };
424struct Value {
425 template&lt;typename T> void set(typename trait&lt;T>::type value) {}
426};
427void foo() {
428 Value v;
429 v.set&lt;double>(3.2);
430}
431</pre>
432
433<p>C++ [basic.lookup.classref] requires this to be an error, but,
434because it's hard to work around, Clang downgrades it to a warning as
435an extension.</p>
436</dd>
437
Jeffrey Yasskin57d12fd2010-06-07 15:58:05 +0000[diff] [blame]438<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
439<dt id="opt_Wbind-to-temporary-copy"><b>-Wbind-to-temporary-copy</b>: Warn about
440an unusable copy constructor when binding a reference to a temporary.</dt>
441<dd>This option, which defaults to on, enables warnings about binding a
442reference to a temporary when the temporary doesn't have a usable copy
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]443constructor. For example:
Jeffrey Yasskin57d12fd2010-06-07 15:58:05 +0000[diff] [blame]444
445<pre>
446 struct NonCopyable {
447 NonCopyable();
448 private:
449 NonCopyable(const NonCopyable&);
450 };
451 void foo(const NonCopyable&);
452 void bar() {
453 foo(NonCopyable()); // Disallowed in C++98; allowed in C++0x.
454 }
455</pre>
456<pre>
457 struct NonCopyable2 {
458 NonCopyable2();
459 NonCopyable2(NonCopyable2&);
460 };
461 void foo(const NonCopyable2&);
462 void bar() {
463 foo(NonCopyable2()); // Disallowed in C++98; allowed in C++0x.
464 }
465</pre>
466
467<p>Note that if <tt>NonCopyable2::NonCopyable2()</tt> has a default
468argument whose instantiation produces a compile error, that error will
469still be a hard error in C++98 mode even if this warning is turned
470off.</p>
471
472</dd>
473
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]474</dl>
475
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]476<!-- ======================================================================= -->
477<h2 id="general_features">Language and Target-Independent Features</h2>
478<!-- ======================================================================= -->
479
480
481<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
482<h3 id="diagnostics">Controlling Errors and Warnings</h3>
483<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
484
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]485<p>Clang provides a number of ways to control which code constructs cause it to
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]486emit errors and warning messages, and how they are displayed to the console.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]487
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]488<h4 id="diagnostics_display">Controlling How Clang Displays Diagnostics</h4>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]489
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]490<p>When Clang emits a diagnostic, it includes rich information in the output,
491and gives you fine-grain control over which information is printed. Clang has
492the ability to print this information, and these are the options that control
493it:</p>
494
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]495<ol>
496<li>A file/line/column indicator that shows exactly where the diagnostic occurs
497 in your code [<a href="#opt_fshow-column">-fshow-column</a>, <a
498 href="#opt_fshow-source-location">-fshow-source-location</a>].</li>
499<li>A categorization of the diagnostic as a note, warning, error, or fatal
500 error.</li>
501<li>A text string that describes what the problem is.</li>
502<li>An option that indicates how to control the diagnostic (for diagnostics that
503 support it) [<a
504 href="#opt_fdiagnostics-show-option">-fdiagnostics-show-option</a>].</li>
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]505<li>A <a href="#diagnostics_categories">high-level category</a> for the
506 diagnostic for clients that want to group diagnostics by class (for
507 diagnostics that support it) [<a
Chris Lattner28a43a42010-05-05 01:35:28 +0000[diff] [blame]508 href="#opt_fdiagnostics-show-category">-fdiagnostics-show-category</a>].</li>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]509<li>The line of source code that the issue occurs on, along with a caret and
510 ranges that indicate the important locations [<a
511 href="opt_fcaret-diagnostics">-fcaret-diagnostics</a>].</li>
512<li>"FixIt" information, which is a concise explanation of how to fix the
513 problem (when Clang is certain it knows) [<a
514 href="opt_fdiagnostics-fixit-info">-fdiagnostics-fixit-info</a>].</li>
515<li>A machine-parsable representation of the ranges involved (off by
516 default) [<a
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]517 href="opt_fdiagnostics-print-source-range-info">-fdiagnostics-print-source-range-info</a>].</li>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]518</ol>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]519
520<p>For more information please see <a href="#cl_diag_formatting">Formatting of
521Diagnostics</a>.</p>
522
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]523
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]524<h4 id="diagnostics_mappings">Diagnostic Mappings</h4>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]525
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]526<p>All diagnostics are mapped into one of these 5 classes:</p>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]527
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]528<ul>
529<li>Ignored</li>
530<li>Note</li>
531<li>Warning</li>
532<li>Error</li>
533<li>Fatal</li>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]534</ul>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]535
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]536<h4 id="diagnostics_categories">Diagnostic Categories</h4>
537
538<p>Though not shown by default, diagnostics may each be associated with a
539 high-level category. This category is intended to make it possible to triage
540 builds that produce a large number of errors or warnings in a grouped way.
541</p>
542
543<p>Categories are not shown by default, but they can be turned on with the
544<a href="#opt_fdiagnostics-show-category">-fdiagnostics-show-category</a> option.
545When set to "<tt>name</tt>", the category is printed textually in the diagnostic
546output. When it is set to "<tt>id</tt>", a category number is printed. The
547mapping of category names to category id's can be obtained by running '<tt>clang
548 --print-diagnostic-categories</tt>'.
549</p>
550
551<h4 id="diagnostics_commandline">Controlling Diagnostics via Command Line
552 Flags</h4>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]553
554<p>-W flags, -pedantic, etc</p>
555
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]556<h4 id="diagnostics_pragmas">Controlling Diagnostics via Pragmas</h4>
557
558<p>Clang can also control what diagnostics are enabled through the use of
559pragmas in the source code. This is useful for turning off specific warnings
560in a section of source code. Clang supports GCC's pragma for compatibility
561with existing source code, as well as several extensions. </p>
562
563<p>The pragma may control any warning that can be used from the command line.
564Warnings may be set to ignored, warning, error, or fatal. The following
565example code will tell Clang or GCC to ignore the -Wall warnings:</p>
566
567<pre>
568#pragma GCC diagnostic ignored "-Wall"
569</pre>
570
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]571<p>In addition to all of the functionality provided by GCC's pragma, Clang
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]572also allows you to push and pop the current warning state. This is particularly
573useful when writing a header file that will be compiled by other people, because
574you don't know what warning flags they build with.</p>
575
576<p>In the below example
577-Wmultichar is ignored for only a single line of code, after which the
578diagnostics return to whatever state had previously existed.</p>
579
580<pre>
581#pragma clang diagnostic push
582#pragma clang diagnostic ignored "-Wmultichar"
583
584char b = 'df'; // no warning.
585
586#pragma clang diagnostic pop
587</pre>
588
589<p>The push and pop pragmas will save and restore the full diagnostic state of
590the compiler, regardless of how it was set. That means that it is possible to
591use push and pop around GCC compatible diagnostics and Clang will push and pop
592them appropriately, while GCC will ignore the pushes and pops as unknown
593pragmas. It should be noted that while Clang supports the GCC pragma, Clang and
594GCC do not support the exact same set of warnings, so even when using GCC
595compatible #pragmas there is no guarantee that they will have identical behaviour
596on both compilers. </p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]597
Ted Kremenek2fb11eb2010-08-24 18:12:35 +0000[diff] [blame]598<h4 id="analyzer_diagnositics">Controlling Static Analyzer Diagnostics</h4>
599
600<p>While not strictly part of the compiler, the diagnostics from Clang's <a
601href="http://clang-analyzer.llvm.org">static analyzer</a> can also be influenced
602by the user via changes to the source code. This can be done in two ways:
603
604<ul>
605
606<li id="analyzer_annotations"><b>Annotations</b>: The static analyzer recognizes various GCC-style
607attributes (e.g., <tt>__attribute__((nonnull)))</tt>) that can either suppress
608static analyzer warnings or teach the analyzer about code invariants which
609enable it to find more bugs. While many of these attributes are standard GCC
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]610attributes, additional ones have been added to Clang to specifically support the
Ted Kremenek2fb11eb2010-08-24 18:12:35 +0000[diff] [blame]611static analyzer. Detailed information on these annotations can be found in the
612<a href="http://clang-analyzer.llvm.org/annotations.html">analyzer's
613documentation</a>.</li>
614
615<li><b><tt>__clang_analyzer__</tt></b>: When the static analyzer is using Clang
616to parse source files, it implicitly defines the preprocessor macro
617<tt>__clang_analyzer__</tt>. While discouraged, code can use this macro to
618selectively exclude code the analyzer examines. Here is an example:
619
620<pre>
621#ifndef __clang_analyzer__
622// Code not to be analyzed
623#endif
624</pre>
625
626In general, this usage is discouraged. Instead, we prefer that users file bugs
627against the analyzer when it flags false positives. There is also active
628discussion of allowing users in the future to selectively silence specific
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]629analyzer warnings (some of which can already be done using <a
Ted Kremenek2fb11eb2010-08-24 18:12:35 +0000[diff] [blame]630href="analyzer_annotations">annotations</a>).</li>
631
632</ul>
633
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]634<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
635<h3 id="precompiledheaders">Precompiled Headers</h3>
636<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
637
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]638<p><a href="http://en.wikipedia.org/wiki/Precompiled_header">Precompiled
639headers</a> are a general approach employed by many compilers to reduce
640compilation time. The underlying motivation of the approach is that it is
641common for the same (and often large) header files to be included by
642multiple source files. Consequently, compile times can often be greatly improved
643by caching some of the (redundant) work done by a compiler to process headers.
644Precompiled header files, which represent one of many ways to implement
645this optimization, are literally files that represent an on-disk cache that
646contains the vital information necessary to reduce some of the work
647needed to process a corresponding header file. While details of precompiled
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]648headers vary between compilers, precompiled headers have been shown to be
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]649highly effective at speeding up program compilation on systems with very large
650system headers (e.g., Mac OS/X).</p>
651
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]652<h4>Generating a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]653
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]654<p>To generate a PCH file using Clang, one invokes Clang with
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]655the <b><tt>-x <i>&lt;language&gt;</i>-header</tt></b> option. This mirrors the
656interface in GCC for generating PCH files:</p>
657
658<pre>
659 $ gcc -x c-header test.h -o test.h.gch
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]660 $ clang -x c-header test.h -o test.h.pch
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]661</pre>
662
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]663<h4>Using a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]664
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]665<p>A PCH file can then be used as a prefix header when a
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]666<b><tt>-include</tt></b> option is passed to <tt>clang</tt>:</p>
667
668<pre>
669 $ clang -include test.h test.c -o test
670</pre>
671
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]672<p>The <tt>clang</tt> driver will first check if a PCH file for <tt>test.h</tt>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]673is available; if so, the contents of <tt>test.h</tt> (and the files it includes)
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]674will be processed from the PCH file. Otherwise, Clang falls back to
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]675directly processing the content of <tt>test.h</tt>. This mirrors the behavior of
676GCC.</p>
677
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]678<p><b>NOTE:</b> Clang does <em>not</em> automatically use PCH files
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]679for headers that are directly included within a source file. For example:</p>
680
681<pre>
Chris Lattnere42ec542009-06-13 20:35:58 +0000[diff] [blame]682 $ clang -x c-header test.h -o test.h.pch
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]683 $ cat test.c
684 #include "test.h"
685 $ clang test.c -o test
686</pre>
687
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]688<p>In this example, <tt>clang</tt> will not automatically use the PCH file for
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]689<tt>test.h</tt> since <tt>test.h</tt> was included directly in the source file
690and not specified on the command line using <tt>-include</tt>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]691
Douglas Gregore650c8c2009-07-07 00:12:59 +0000[diff] [blame]692<h4>Relocatable PCH Files</h4>
693<p>It is sometimes necessary to build a precompiled header from headers that
694are not yet in their final, installed locations. For example, one might build a
695precompiled header within the build tree that is then meant to be installed
696alongside the headers. Clang permits the creation of "relocatable" precompiled
697headers, which are built with a given path (into the build directory) and can
698later be used from an installed location.</p>
699
700<p>To build a relocatable precompiled header, place your headers into a
701subdirectory whose structure mimics the installed location. For example, if you
702want to build a precompiled header for the header <code>mylib.h</code> that
703will be installed into <code>/usr/include</code>, create a subdirectory
704<code>build/usr/include</code> and place the header <code>mylib.h</code> into
705that subdirectory. If <code>mylib.h</code> depends on other headers, then
706they can be stored within <code>build/usr/include</code> in a way that mimics
707the installed location.</p>
708
709<p>Building a relocatable precompiled header requires two additional arguments.
710First, pass the <code>--relocatable-pch</code> flag to indicate that the
711resulting PCH file should be relocatable. Second, pass
712<code>-isysroot /path/to/build</code>, which makes all includes for your
713library relative to the build directory. For example:</p>
714
715<pre>
716 # clang -x c-header --relocatable-pch -isysroot /path/to/build /path/to/build/mylib.h mylib.h.pch
717</pre>
718
719<p>When loading the relocatable PCH file, the various headers used in the PCH
720file are found from the system header root. For example, <code>mylib.h</code>
721can be found in <code>/usr/include/mylib.h</code>. If the headers are installed
722in some other system root, the <code>-isysroot</code> option can be used provide
723a different system root from which the headers will be based. For example,
724<code>-isysroot /Developer/SDKs/MacOSX10.4u.sdk</code> will look for
725<code>mylib.h</code> in
726<code>/Developer/SDKs/MacOSX10.4u.sdk/usr/include/mylib.h</code>.</p>
727
728<p>Relocatable precompiled headers are intended to be used in a limited number
729of cases where the compilation environment is tightly controlled and the
730precompiled header cannot be generated after headers have been installed.
731Relocatable precompiled headers also have some performance impact, because
732the difference in location between the header locations at PCH build time vs.
733at the time of PCH use requires one of the PCH optimizations,
734<code>stat()</code> caching, to be disabled. However, this change is only
735likely to affect PCH files that reference a large number of headers.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]736
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]737<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
738<h3 id="codegen">Controlling Code Generation</h3>
739<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
740
741<p>Clang provides a number of ways to control code generation. The options are listed below.</p>
742
743<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]744<dl>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]745<dt id="opt_fcatch-undefined-behavior"><b>-fcatch-undefined-behavior</b>: Turn
746on runtime code generation to check for undefined behavior.</dt>
747
748<dd>This option, which defaults to off, controls whether or not Clang
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]749adds runtime checks for undefined runtime behavior. If a check fails,
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]750<tt>__builtin_trap()</tt> is used to indicate failure.
751The checks are:
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]752<ul>
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]753<li>Subscripting where the static type of one operand is a variable
Mike Stump88b2a172009-12-16 03:25:12 +0000[diff] [blame]754 which is decayed from an array type and the other operand is
755 greater than the size of the array or less than zero.</li>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]756<li>Shift operators where the amount shifted is greater or equal to the
757 promoted bit-width of the left-hand-side or less than zero.</li>
Mike Stump8f6a3ed2009-12-16 03:18:14 +0000[diff] [blame]758<li>If control flow reaches __builtin_unreachable.
759<li>When llvm implements more __builtin_object_size support, reads and
760 writes for objects that __builtin_object_size indicates we aren't
761 accessing valid memory. Bit-fields and vectors are not yet checked.
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]762</ul>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]763</dd>
764
Nuno Lopesaa526242009-12-17 10:00:52 +0000[diff] [blame]765<dt id="opt_fno-assume-sane-operator-new"><b>-fno-assume-sane-operator-new</b>:
766Don't assume that the C++'s new operator is sane.</dt>
Nuno Lopesb23f20d2009-12-17 10:15:49 +0000[diff] [blame]767<dd>This option tells the compiler to do not assume that C++'s global new
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]768operator will always return a pointer that does not
Nuno Lopesaa526242009-12-17 10:00:52 +0000[diff] [blame]769alias any other pointer when the function returns.</dd>
Evan Chengfda026b2011-04-08 22:18:01 +0000[diff] [blame]770
Evan Cheng4cf4b592011-04-08 22:34:21 +0000[diff] [blame]771<dt id="opt_ftrap-function"><b>-ftrap-function=[name]</b>: Instruct code
Evan Chengfda026b2011-04-08 22:18:01 +0000[diff] [blame]772generator to emit a function call to the specified function name for
773<tt>__builtin_trap()</tt>.</dt>
774
775<dd>LLVM code generator translates <tt>__builtin_trap()</tt> to a trap
776instruction if it is supported by the target ISA. Otherwise, the builtin is
777translated into a call to <tt>abort</tt>. If this option is set, then the code
778generator will always lower the builtin to a call to the specified function
779regardless of whether the target ISA has a trap instruction. This option is
Chris Lattner02e266b2011-04-08 22:58:43 +0000[diff] [blame^]780useful for environments (e.g. deeply embedded) where a trap cannot be properly
781handled, or when some custom behavior is desired.</dd>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]782</dl>
Nuno Lopesaa526242009-12-17 10:00:52 +0000[diff] [blame]783
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]784<!-- ======================================================================= -->
785<h2 id="c">C Language Features</h2>
786<!-- ======================================================================= -->
787
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]788<p>The support for standard C in clang is feature-complete except for the C99
789floating-point pragmas.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]790
791<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]792<h3 id="c_ext">Extensions supported by clang</h3>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]793<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
794
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]795<p>See <a href="LanguageExtensions.html">clang language extensions</a>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]796
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]797<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
798<h3 id="c_modes">Differences between various standard modes</h3>
799<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]800
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]801<p>clang supports the -std option, which changes what language mode clang uses.
802The supported modes for C are c89, gnu89, c94, c99, gnu99 and various aliases
803for those modes. If no -std option is specified, clang defaults to gnu99 mode.
804</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]805
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]806<p>Differences between all c* and gnu* modes:</p>
807<ul>
808<li>c* modes define "__STRICT_ANSI__".</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]809<li>Target-specific defines not prefixed by underscores, like "linux", are
810defined in gnu* modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]811<li>Trigraphs default to being off in gnu* modes; they can be enabled by the
812-trigraphs option.</li>
813<li>The parser recognizes "asm" and "typeof" as keywords in gnu* modes; the
814variants "__asm__" and "__typeof__" are recognized in all modes.</li>
Eli Friedmanb0ac5452009-05-16 23:17:30 +0000[diff] [blame]815<li>The Apple "blocks" extension is recognized by default in gnu* modes
816on some platforms; it can be enabled in any mode with the "-fblocks"
817option.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]818</ul>
819
820<p>Differences between *89 and *99 modes:</p>
821<ul>
822<li>The *99 modes default to implementing "inline" as specified in C99, while
823the *89 modes implement the GNU version. This can be overridden for individual
824functions with the __gnu_inline__ attribute.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]825<li>Digraphs are not recognized in c89 mode.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]826<li>The scope of names defined inside a "for", "if", "switch", "while", or "do"
827statement is different. (example: "if ((struct x {int x;}*)0) {}".)</li>
828<li>__STDC_VERSION__ is not defined in *89 modes.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]829<li>"inline" is not recognized as a keyword in c89 mode.</li>
830<li>"restrict" is not recognized as a keyword in *89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]831<li>Commas are allowed in integer constant expressions in *99 modes.</li>
832<li>Arrays which are not lvalues are not implicitly promoted to pointers in
833*89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]834<li>Some warnings are different.</li>
835</ul>
836
837<p>c94 mode is identical to c89 mode except that digraphs are enabled in
838c94 mode (FIXME: And __STDC_VERSION__ should be defined!).</p>
839
840<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
841<h3 id="c_unimpl_gcc">GCC extensions not implemented yet</h3>
842<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
843
844<p>clang tries to be compatible with gcc as much as possible, but some gcc
845extensions are not implemented yet:</p>
846
847<ul>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]848
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]849<li>clang does not support #pragma weak
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]850(<a href="http://llvm.org/bugs/show_bug.cgi?id=3679">bug 3679</a>). Due to
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]851the uses described in the bug, this is likely to be implemented at some
852point, at least partially.</li>
853
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]854<li>clang does not support code generation for local variables pinned to
855registers (<a href="http://llvm.org/bugs/show_bug.cgi?id=3933">bug 3933</a>).
856This is a relatively small feature, so it is likely to be implemented
857relatively soon.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]858
859<li>clang does not support decimal floating point types (_Decimal32 and
860friends) or fixed-point types (_Fract and friends); nobody has expressed
861interest in these features yet, so it's hard to say when they will be
862implemented.</li>
863
864<li>clang does not support nested functions; this is a complex feature which
865is infrequently used, so it is unlikely to be implemented anytime soon.</li>
866
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]867<li>clang does not support global register variables, this is unlikely
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]868to be implemented soon because it requires additional LLVM backend support.
869</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]870
871<li>clang does not support static initialization of flexible array
872members. This appears to be a rarely used extension, but could be
873implemented pending user demand.</li>
874
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]875<li>clang does not support __builtin_va_arg_pack/__builtin_va_arg_pack_len.
876This is used rarely, but in some potentially interesting places, like the
877glibc headers, so it may be implemented pending user demand. Note that
878because clang pretends to be like GCC 4.2, and this extension was introduced
879in 4.3, the glibc headers will not try to use this extension with clang at
880the moment.</li>
881
882<li>clang does not support the gcc extension for forward-declaring function
883parameters; this has not showed up in any real-world code yet, though, so it
884might never be implemented.</li>
885
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]886</ul>
887
888<p>This is not a complete list; if you find an unsupported extension
889missing from this list, please send an e-mail to cfe-dev. This list
890currently excludes C++; see <a href="#cxx">C++ Language Features</a>.
891Also, this list does not include bugs in mostly-implemented features; please
892see the <a href="http://llvm.org/bugs/buglist.cgi?quicksearch=product%3Aclang+component%3A-New%2BBugs%2CAST%2CBasic%2CDriver%2CHeaders%2CLLVM%2BCodeGen%2Cparser%2Cpreprocessor%2CSemantic%2BAnalyzer">
893bug tracker</a> for known existing bugs (FIXME: Is there a section for
894bug-reporting guidelines somewhere?).</p>
895
896<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
897<h3 id="c_unsupp_gcc">Intentionally unsupported GCC extensions</h3>
898<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
899
Eli Friedman0b326002009-06-12 20:11:05 +0000[diff] [blame]900<ul>
901
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]902<li>clang does not support the gcc extension that allows variable-length arrays
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]903in structures. This is for a few reasons: one, it is tricky
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]904to implement, two, the extension is completely undocumented, and three, the
Chris Lattnerb9d511c2010-10-28 02:20:32 +0000[diff] [blame]905extension appears to be rarely used. Note that clang <em>does</em> support
906flexible array members (arrays with a zero or unspecified size at the end of
907a structure).</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]908
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]909<li>clang does not support duplicate definitions of a function where one is
Daniel Dunbarc5f928c2009-06-04 18:37:52 +0000[diff] [blame]910inline. This complicates clients of the AST which normally can expect there is
911at most one definition for each function. Source code using this feature should
912be changed to define the inline and out-of-line definitions in separate
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]913translation units.</li>
Daniel Dunbarc5f928c2009-06-04 18:37:52 +0000[diff] [blame]914
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]915<li>clang does not have an equivalent to gcc's "fold"; this means that
916clang doesn't accept some constructs gcc might accept in contexts where a
917constant expression is required, like "x-x" where x is a variable, or calls
918to C library functions like strlen.</li>
919
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]920<li>clang does not support multiple alternative constraints in inline asm; this
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]921is an extremely obscure feature which would be complicated to implement
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]922correctly.</li>
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]923
924<li>clang does not support __builtin_apply and friends; this extension is
925extremely obscure and difficult to implement reliably.</li>
926
Eli Friedman0b326002009-06-12 20:11:05 +0000[diff] [blame]927</ul>
928
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]929<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
930<h3 id="c_ms">Microsoft extensions</h3>
931<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
932
933<p>clang has some experimental support for extensions from
934Microsoft Visual C++; to enable it, use the -fms-extensions command-line
Eli Friedmana1821b52009-06-08 06:21:03 +0000[diff] [blame]935option. This is the default for Windows targets. Note that the
936support is incomplete; enabling Microsoft extensions will silently drop
937certain constructs (including __declspec and Microsoft-style asm statements).
938</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]939
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]940<ul>
Douglas Gregord3b227d2010-12-14 16:21:49 +0000[diff] [blame]941<li>clang allows setting _MSC_VER with -fmsc-version=. It defaults to 1300 which
Michael J. Spencerdae4ac42010-10-21 05:21:48 +0000[diff] [blame]942is the same as Visual C/C++ 2003. Any number is supported and can greatly affect
943what Windows SDK and c++stdlib headers clang can compile. This option will be
944removed when clang supports the full set of MS extensions required for these
945headers.</li>
946
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]947<li>clang does not support the Microsoft extension where anonymous
Daniel Dunbar869e0542009-05-13 00:23:53 +0000[diff] [blame]948record members can be declared using user defined typedefs.</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]949
Daniel Dunbar9375ed12009-05-13 21:40:49 +0000[diff] [blame]950<li>clang supports the Microsoft "#pragma pack" feature for
951controlling record layout. GCC also contains support for this feature,
952however where MSVC and GCC are incompatible clang follows the MSVC
953definition.</li>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]954</ul>
Daniel Dunbar9375ed12009-05-13 21:40:49 +0000[diff] [blame]955
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]956<!-- ======================================================================= -->
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]957<h2 id="target_features">Target-Specific Features and Limitations</h2>
958<!-- ======================================================================= -->
959
960
961<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
962<h3 id="target_arch">CPU Architectures Features and Limitations</h3>
963<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
964
965<!-- ======================== -->
966<h4 id="target_arch_x86">X86</h4>
967<!-- ======================== -->
Daniel Dunbarbcaf7aa2010-09-19 19:26:59 +0000[diff] [blame]968
969<p>The support for X86 (both 32-bit and 64-bit) is considered stable on Darwin
970(Mac OS/X), Linux, FreeBSD, and Dragonfly BSD: it has been tested to correctly
971compile many large C, C++, Objective-C, and Objective-C++ codebases.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]972
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]973<p>On x86_64-mingw32, passing i128(by value) is incompatible to Microsoft x64
974calling conversion. You might need to tweak WinX86_64ABIInfo::classify()
975in lib/CodeGen/TargetInfo.cpp.</p>
NAKAMURA Takumia75fdb22011-04-04 15:02:41 +0000[diff] [blame]976
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]977<!-- ======================== -->
978<h4 id="target_arch_arm">ARM</h4>
979<!-- ======================== -->
Daniel Dunbarbcaf7aa2010-09-19 19:26:59 +0000[diff] [blame]980
981<p>The support for ARM (specifically ARMv6 and ARMv7) is considered stable on
982Darwin (iOS): it has been tested to correctly compile many large C, C++,
Bob Wilson4ea8dfa2011-01-10 17:55:14 +0000[diff] [blame]983Objective-C, and Objective-C++ codebases. Clang only supports a limited number
984of ARM architectures. It does not yet fully support ARMv5, for example.</p>
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]985
986<!-- ======================== -->
987<h4 id="target_arch_other">Other platforms</h4>
988<!-- ======================== -->
989clang currently contains some support for PPC and Sparc; however, significant
990pieces of code generation are still missing, and they haven't undergone
991significant testing.
992
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]993<p>clang contains limited support for the MSP430 embedded processor, but both
994the clang support and the LLVM backend support are highly experimental.
995
996<p>Other platforms are completely unsupported at the moment. Adding the
997minimal support needed for parsing and semantic analysis on a new platform
998is quite easy; see lib/Basic/Targets.cpp in the clang source tree. This level
999of support is also sufficient for conversion to LLVM IR for simple programs.
1000Proper support for conversion to LLVM IR requires adding code to
1001lib/CodeGen/CGCall.cpp at the moment; this is likely to change soon, though.
1002Generating assembly requires a suitable LLVM backend.
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]1003
1004<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
1005<h3 id="target_os">Operating System Features and Limitations</h3>
1006<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
1007
1008<!-- ======================================= -->
1009<h4 id="target_os_darwin">Darwin (Mac OS/X)</h4>
1010<!-- ======================================= -->
1011
1012<p>No __thread support, 64-bit ObjC support requires SL tools.</p>
1013
NAKAMURA Takumia75fdb22011-04-04 15:02:41 +0000[diff] [blame]1014<!-- ======================================= -->
1015<h4 id="target_os_win32">Windows</h4>
1016<!-- ======================================= -->
1017
1018<p>Experimental supports are on Cygming.</p>
1019
1020<h5>Cygwin</h5>
1021
1022<p>Clang works on Cygwin-1.7.</p>
1023
1024<h5>MinGW32</h5>
1025
1026<p>Clang works on some mingw32 distributions.
1027Clang assumes directories as below;</p>
1028
1029<ul>
1030<li><tt>C:/mingw/include</tt></li>
1031<li><tt>C:/mingw/lib</tt></li>
1032<li><tt>C:/mingw/lib/gcc/mingw32/4.[3-5].0/include/c++</tt></li>
1033</ul>
1034
1035<p>On MSYS, a few tests might fail. It is due to <a href="http://llvm.org/bugs/show_bug.cgi?id=8520">Bug 8520</a> and is fixed in <a href="http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110314/118106.html">LLVM's r127724</a>.</p>
1036
1037<h5>MinGW-w64</h5>
1038
1039<p>For x32(i686-w64-mingw32), it is not supported yet.</p>
1040
1041<p>For x64(x86_64-w64-mingw32), <a href="http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110321/118499.html">an essential patch(LLVM's r128206)</a> would be needed. It is incompatible to <a href="http://tdm-gcc.tdragon.net/development">TDM-GCC</a> due to the definiton of symbol &quot;<code>___chkstk</code>&quot;. Clang assumes as below;<p>
1042
1043<ul>
1044<li><tt>C:/mingw/x86_64-w64-mingw32/include</tt></li>
1045<li><tt>C:/mingw/x86_64-w64-mingw32/include/c++/4.5.[23]</tt></li>
1046<li>GCC driver &quot;gcc.exe&quot; to build x86_64-w64-mingw32 binary.</li>
1047</ul>
1048
1049<p><a href="http://llvm.org/bugs/show_bug.cgi?id=8833">Some tests might fail</a>
1050on x64.</p>
1051
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]1052</div>
1053</body>
1054</html>