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Misha Brukmanc1449e62008-12-10 23:07:02 +0000[diff] [blame]6 <title>LLVM Coding Standards</title>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]7</head>
8<body>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]9
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]10<h1>
Misha Brukmanc1449e62008-12-10 23:07:02 +0000[diff] [blame]11 LLVM Coding Standards
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]12</h1>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]13
14<ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]15 <li><a href="#introduction">Introduction</a></li>
Chris Lattner7ae36bb2001-07-23 20:40:41 +0000[diff] [blame]16 <li><a href="#mechanicalissues">Mechanical Source Issues</a>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]17 <ol>
18 <li><a href="#sourceformating">Source Code Formatting</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]19 <ol>
20 <li><a href="#scf_commenting">Commenting</a></li>
21 <li><a href="#scf_commentformat">Comment Formatting</a></li>
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]22 <li><a href="#scf_includes"><tt>#include</tt> Style</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]23 <li><a href="#scf_codewidth">Source Code Width</a></li>
24 <li><a href="#scf_spacestabs">Use Spaces Instead of Tabs</a></li>
25 <li><a href="#scf_indentation">Indent Code Consistently</a></li>
26 </ol></li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]27 <li><a href="#compilerissues">Compiler Issues</a>
28 <ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]29 <li><a href="#ci_warningerrors">Treat Compiler Warnings Like
30 Errors</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]31 <li><a href="#ci_portable_code">Write Portable Code</a></li>
Chris Lattner558f5d22010-11-30 19:20:40 +0000[diff] [blame]32 <li><a href="#ci_rtti_exceptions">Do not use RTTI or Exceptions</a></li>
Zhanyong Wancafe0b42010-11-23 05:03:07 +0000[diff] [blame]33 <li><a href="#ci_class_struct">Use of <tt>class</tt>/<tt>struct</tt> Keywords</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]34 </ol></li>
35 </ol></li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]36 <li><a href="#styleissues">Style Issues</a>
37 <ol>
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]38 <li><a href="#macro">The High-Level Issues</a>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]39 <ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]40 <li><a href="#hl_module">A Public Header File <b>is</b> a
41 Module</a></li>
Zhanyong Wancafe0b42010-11-23 05:03:07 +0000[diff] [blame]42 <li><a href="#hl_dontinclude"><tt>#include</tt> as Little as Possible</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]43 <li><a href="#hl_privateheaders">Keep "internal" Headers
44 Private</a></li>
Zhanyong Wancafe0b42010-11-23 05:03:07 +0000[diff] [blame]45 <li><a href="#hl_earlyexit">Use Early Exits and <tt>continue</tt> to Simplify
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]46 Code</a></li>
Zhanyong Wancafe0b42010-11-23 05:03:07 +0000[diff] [blame]47 <li><a href="#hl_else_after_return">Don't use <tt>else</tt> after a
48 <tt>return</tt></a></li>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]49 <li><a href="#hl_predicateloops">Turn Predicate Loops into Predicate
50 Functions</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]51 </ol></li>
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]52 <li><a href="#micro">The Low-Level Issues</a>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]53 <ol>
Zhanyong Wan7fcd4dc2010-12-02 05:10:07 +0000[diff] [blame]54 <li><a href="#ll_naming">Name Types, Functions, Variables, and Enumerators Properly</a></li>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]55 <li><a href="#ll_assert">Assert Liberally</a></li>
Zhanyong Wancafe0b42010-11-23 05:03:07 +0000[diff] [blame]56 <li><a href="#ll_ns_std">Do not use '<tt>using namespace std</tt>'</a></li>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]57 <li><a href="#ll_virtual_anch">Provide a virtual method anchor for
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]58 classes in headers</a></li>
Zhanyong Wancafe0b42010-11-23 05:03:07 +0000[diff] [blame]59 <li><a href="#ll_end">Don't evaluate <tt>end()</tt> every time through a
Chris Lattner0af39ea2009-06-30 06:13:23 +0000[diff] [blame]60 loop</a></li>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]61 <li><a href="#ll_iostream"><tt>#include &lt;iostream&gt;</tt> is
62 <em>forbidden</em></a></li>
Chris Lattner78ceb3a2010-12-10 00:54:03 +0000[diff] [blame]63 <li><a href="#ll_raw_ostream">Use <tt>raw_ostream</tt></a></li>
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]64 <li><a href="#ll_avoidendl">Avoid <tt>std::endl</tt></a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]65 </ol></li>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]66
67 <li><a href="#nano">Microscopic Details</a>
68 <ol>
69 <li><a href="#micro_spaceparen">Spaces Before Parentheses</a></li>
70 <li><a href="#micro_preincrement">Prefer Preincrement</a></li>
71 <li><a href="#micro_namespaceindent">Namespace Indentation</a></li>
72 <li><a href="#micro_anonns">Anonymous Namespaces</a></li>
73 </ol></li>
74
75
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]76 </ol></li>
77 <li><a href="#seealso">See Also</a></li>
78</ol>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]79
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]80<div class="doc_author">
Chris Lattner219bd292009-07-22 05:43:01 +0000[diff] [blame]81 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]82</div>
83
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]84
85<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]86<h2>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]87 <a name="introduction">Introduction</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]88</h2>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]89<!-- *********************************************************************** -->
90
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]91<div>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]92
93<p>This document attempts to describe a few coding standards that are being used
94in the LLVM source tree. Although no coding standards should be regarded as
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]95absolute requirements to be followed in all instances, coding standards can be
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]96useful.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]97
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]98<p>This document intentionally does not prescribe fixed standards for religious
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]99issues such as brace placement and space usage. For issues like this, follow
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]100the golden rule:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]101
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]102<blockquote>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]103
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]104<p><b><a name="goldenrule">If you are adding a significant body of source to a
105project, feel free to use whatever style you are most comfortable with. If you
106are extending, enhancing, or bug fixing already implemented code, use the style
107that is already being used so that the source is uniform and easy to
108follow.</a></b></p>
109
110</blockquote>
111
112<p>The ultimate goal of these guidelines is the increase readability and
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]113maintainability of our common source base. If you have suggestions for topics to
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]114be included, please mail them to <a
115href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]116
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]117</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]118
119<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]120<h2>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]121 <a name="mechanicalissues">Mechanical Source Issues</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]122</h2>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]123<!-- *********************************************************************** -->
124
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]125<div>
126
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]127<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]128<h3>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]129 <a name="sourceformating">Source Code Formatting</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]130</h3>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]131
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]132<div>
133
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]134<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]135<h4>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]136 <a name="scf_commenting">Commenting</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]137</h4>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]138
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]139<div>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]140
141<p>Comments are one critical part of readability and maintainability. Everyone
Chris Lattnerb927ca82009-07-12 00:10:24 +0000[diff] [blame]142knows they should comment, so should you. When writing comments, write them as
143English prose, which means they should use proper capitalization, punctuation,
144etc. Although we all should probably
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]145comment our code more than we do, there are a few very critical places that
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]146documentation is very useful:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]147
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]148<h5>File Headers</h5>
149
150<div>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]151
Reid Spencer669ed452007-07-09 08:04:31 +0000[diff] [blame]152<p>Every source file should have a header on it that describes the basic
153purpose of the file. If a file does not have a header, it should not be
154checked into Subversion. Most source trees will probably have a standard
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]155file header format. The standard format for the LLVM source tree looks like
156this:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]157
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]158<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]159<pre>
Chris Lattnerc49fcd12003-10-13 14:58:11 +0000[diff] [blame]160//===-- llvm/Instruction.h - Instruction class definition -------*- C++ -*-===//
Misha Brukman98117cd2009-01-02 16:58:42 +0000[diff] [blame]161//
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]162// The LLVM Compiler Infrastructure
163//
Chris Lattnerab2b10c2007-12-29 19:56:08 +0000[diff] [blame]164// This file is distributed under the University of Illinois Open Source
165// License. See LICENSE.TXT for details.
Misha Brukman98117cd2009-01-02 16:58:42 +0000[diff] [blame]166//
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]167//===----------------------------------------------------------------------===//
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]168//
169// This file contains the declaration of the Instruction class, which is the
170// base class for all of the VM instructions.
171//
172//===----------------------------------------------------------------------===//
173</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]174</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]175
Chris Lattnerab2b10c2007-12-29 19:56:08 +0000[diff] [blame]176<p>A few things to note about this particular format: The "<tt>-*- C++
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]177-*-</tt>" string on the first line is there to tell Emacs that the source file
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]178is a C++ file, not a C file (Emacs assumes <tt>.h</tt> files are C files by default).
179Note that this tag is not necessary in <tt>.cpp</tt> files. The name of the file is also
Misha Brukman69c58892004-07-28 22:37:57 +0000[diff] [blame]180on the first line, along with a very short description of the purpose of the
181file. This is important when printing out code and flipping though lots of
182pages.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]183
Chris Lattnerab2b10c2007-12-29 19:56:08 +0000[diff] [blame]184<p>The next section in the file is a concise note that defines the license
185that the file is released under. This makes it perfectly clear what terms the
186source code can be distributed under and should not be modified in any way.</p>
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]187
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]188<p>The main body of the description does not have to be very long in most cases.
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]189Here it's only two lines. If an algorithm is being implemented or something
190tricky is going on, a reference to the paper where it is published should be
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]191included, as well as any notes or "gotchas" in the code to watch out for.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]192
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]193</div>
194
195<h5>Class overviews</h5>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]196
Jim Laskeyf55914a2006-07-31 20:18:49 +0000[diff] [blame]197<p>Classes are one fundamental part of a good object oriented design. As such,
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]198a class definition should have a comment block that explains what the class is
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]199used for... if it's not obvious. If it's so completely obvious your grandma
200could figure it out, it's probably safe to leave it out. Naming classes
Misha Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]201something sane goes a long ways towards avoiding writing documentation.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]202
203
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]204<h5>Method information</h5>
205
206<div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]207
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]208<p>Methods defined in a class (as well as any global functions) should also be
Dan Gohman621a4152010-02-26 20:18:32 +0000[diff] [blame]209documented properly. A quick note about what it does and a description of the
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]210borderline behaviour is all that is necessary here (unless something
Dan Gohman621a4152010-02-26 20:18:32 +0000[diff] [blame]211particularly tricky or insidious is going on). The hope is that people can
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]212figure out how to use your interfaces without reading the code itself... that is
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]213the goal metric.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]214
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]215<p>Good things to talk about here are what happens when something unexpected
216happens: does the method return null? Abort? Format your hard disk?</p>
217
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]218</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]219
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]220</div>
221
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]222<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]223<h4>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]224 <a name="scf_commentformat">Comment Formatting</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]225</h4>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]226
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]227<div>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]228
229<p>In general, prefer C++ style (<tt>//</tt>) comments. They take less space,
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]230require less typing, don't have nesting problems, etc. There are a few cases
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]231when it is useful to use C style (<tt>/* */</tt>) comments however:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]232
233<ol>
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]234 <li>When writing C code: Obviously if you are writing C code, use C style
Misha Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]235 comments.</li>
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]236 <li>When writing a header file that may be <tt>#include</tt>d by a C source
237 file.</li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]238 <li>When writing a source file that is used by a tool that only accepts C
239 style comments.</li>
240</ol>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]241
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]242<p>To comment out a large block of code, use <tt>#if 0</tt> and <tt>#endif</tt>.
243These nest properly and are better behaved in general than C style comments.</p>
244
245</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]246
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]247<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]248<h4>
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]249 <a name="scf_includes"><tt>#include</tt> Style</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]250</h4>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]251
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]252<div>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]253
254<p>Immediately after the <a href="#scf_commenting">header file comment</a> (and
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]255include guards if working on a header file), the <a
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]256href="#hl_dontinclude">minimal</a> list of <tt>#include</tt>s required by the
257file should be listed. We prefer these <tt>#include</tt>s to be listed in this
258order:</p>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]259
260<ol>
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]261 <li><a href="#mmheader">Main Module Header</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]262 <li><a href="#hl_privateheaders">Local/Private Headers</a></li>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]263 <li><tt>llvm/*</tt></li>
264 <li><tt>llvm/Analysis/*</tt></li>
265 <li><tt>llvm/Assembly/*</tt></li>
Duncan Sands18d52f22010-09-29 20:09:55 +0000[diff] [blame]266 <li><tt>llvm/Bitcode/*</tt></li>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]267 <li><tt>llvm/CodeGen/*</tt></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]268 <li>...</li>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]269 <li><tt>Support/*</tt></li>
270 <li><tt>Config/*</tt></li>
271 <li>System <tt>#includes</tt></li>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]272</ol>
273
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]274<p>and each category should be sorted by name.</p>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]275
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]276<p><a name="mmheader">The "Main Module Header"</a> file applies to <tt>.cpp</tt> files
277which implement an interface defined by a <tt>.h</tt> file. This <tt>#include</tt>
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]278should always be included <b>first</b> regardless of where it lives on the file
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]279system. By including a header file first in the <tt>.cpp</tt> files that implement the
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]280interfaces, we ensure that the header does not have any hidden dependencies
281which are not explicitly #included in the header, but should be. It is also a
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]282form of documentation in the <tt>.cpp</tt> file to indicate where the interfaces it
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]283implements are defined.</p>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]284
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]285</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]286
287<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]288<h4>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]289 <a name="scf_codewidth">Source Code Width</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]290</h4>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]291
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]292<div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]293
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]294<p>Write your code to fit within 80 columns of text. This helps those of us who
295like to print out code and look at your code in an xterm without resizing
296it.</p>
297
Chris Lattner5822e9e2008-07-08 05:12:37 +0000[diff] [blame]298<p>The longer answer is that there must be some limit to the width of the code
299in order to reasonably allow developers to have multiple files side-by-side in
300windows on a modest display. If you are going to pick a width limit, it is
301somewhat arbitrary but you might as well pick something standard. Going with
30290 columns (for example) instead of 80 columns wouldn't add any significant
303value and would be detrimental to printing out code. Also many other projects
304have standardized on 80 columns, so some people have already configured their
305editors for it (vs something else, like 90 columns).</p>
306
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]307<p>This is one of many contentious issues in coding standards, but it is not up
Chris Lattner5822e9e2008-07-08 05:12:37 +0000[diff] [blame]308for debate.</p>
309
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]310</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]311
312<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]313<h4>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]314 <a name="scf_spacestabs">Use Spaces Instead of Tabs</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]315</h4>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]316
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]317<div>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]318
319<p>In all cases, prefer spaces to tabs in source files. People have different
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]320preferred indentation levels, and different styles of indentation that they
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]321like; this is fine. What isn't fine is that different editors/viewers expand
322tabs out to different tab stops. This can cause your code to look completely
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]323unreadable, and it is not worth dealing with.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]324
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]325<p>As always, follow the <a href="#goldenrule">Golden Rule</a> above: follow the
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]326style of existing code if you are modifying and extending it. If you like four
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]327spaces of indentation, <b>DO NOT</b> do that in the middle of a chunk of code
328with two spaces of indentation. Also, do not reindent a whole source file: it
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]329makes for incredible diffs that are absolutely worthless.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]330
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]331</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]332
333<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]334<h4>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]335 <a name="scf_indentation">Indent Code Consistently</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]336</h4>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]337
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]338<div>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]339
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]340<p>Okay, in your first year of programming you were told that indentation is
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]341important. If you didn't believe and internalize this then, now is the time.
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]342Just do it.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]343
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]344</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]345
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]346</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]347
348<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]349<h3>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]350 <a name="compilerissues">Compiler Issues</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]351</h3>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]352
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]353<div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]354
355<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]356<h4>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]357 <a name="ci_warningerrors">Treat Compiler Warnings Like Errors</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]358</h4>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]359
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]360<div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]361
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]362<p>If your code has compiler warnings in it, something is wrong &mdash; you
363aren't casting values correctly, your have "questionable" constructs in your
364code, or you are doing something legitimately wrong. Compiler warnings can
365cover up legitimate errors in output and make dealing with a translation unit
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]366difficult.</p>
367
368<p>It is not possible to prevent all warnings from all compilers, nor is it
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]369desirable. Instead, pick a standard compiler (like <tt>gcc</tt>) that provides
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]370a good thorough set of warnings, and stick to it. At least in the case of
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]371<tt>gcc</tt>, it is possible to work around any spurious errors by changing the
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]372syntax of the code slightly. For example, a warning that annoys me occurs when
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]373I write code like this:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]374
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]375<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]376<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]377if (V = getValue()) {
378 ...
379}
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]380</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]381</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]382
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]383<p><tt>gcc</tt> will warn me that I probably want to use the <tt>==</tt>
384operator, and that I probably mistyped it. In most cases, I haven't, and I
385really don't want the spurious errors. To fix this particular problem, I
386rewrite the code like this:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]387
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]388<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]389<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]390if ((V = getValue())) {
391 ...
392}
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]393</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]394</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]395
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]396<p>which shuts <tt>gcc</tt> up. Any <tt>gcc</tt> warning that annoys you can
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]397be fixed by massaging the code appropriately.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]398
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]399<p>These are the <tt>gcc</tt> warnings that I prefer to enable:</p>
400
401<div class="doc_code">
402<pre>
403-Wall -Winline -W -Wwrite-strings -Wno-unused
404</pre>
405</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]406
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]407</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]408
409<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]410<h4>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]411 <a name="ci_portable_code">Write Portable Code</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]412</h4>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]413
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]414<div>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]415
416<p>In almost all cases, it is possible and within reason to write completely
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]417portable code. If there are cases where it isn't possible to write portable
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]418code, isolate it behind a well defined (and well documented) interface.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]419
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]420<p>In practice, this means that you shouldn't assume much about the host
Chris Lattner221b2392010-11-16 22:19:06 +0000[diff] [blame]421compiler, and Visual Studio tends to be the lowest common denominator.
422If advanced features are used, they should only be an implementation detail of
423a library which has a simple exposed API, and preferably be buried in
424libSystem.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]425
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]426</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]427
Reid Spencerb40df562004-09-23 16:03:48 +0000[diff] [blame]428<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]429<h4>
Chris Lattner558f5d22010-11-30 19:20:40 +0000[diff] [blame]430<a name="ci_rtti_exceptions">Do not use RTTI or Exceptions</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]431</h4>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]432<div>
Chris Lattner558f5d22010-11-30 19:20:40 +0000[diff] [blame]433
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]434<p>In an effort to reduce code and executable size, LLVM does not use RTTI
435(e.g. <tt>dynamic_cast&lt;&gt;</tt>) or exceptions. These two language features
436violate the general C++ principle of <i>"you only pay for what you use"</i>,
437causing executable bloat even if exceptions are never used in the code base, or
438if RTTI is never used for a class. Because of this, we turn them off globally
439in the code.</p>
Chris Lattner558f5d22010-11-30 19:20:40 +0000[diff] [blame]440
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]441<p>That said, LLVM does make extensive use of a hand-rolled form of RTTI that
442use templates like <a href="ProgrammersManual.html#isa"><tt>isa&lt;&gt;</tt>,
443<tt>cast&lt;&gt;</tt>, and <tt>dyn_cast&lt;&gt;</tt></a>. This form of RTTI is
444opt-in and can be added to any class. It is also substantially more efficient
445than <tt>dynamic_cast&lt;&gt;</tt>.</p>
Chris Lattner558f5d22010-11-30 19:20:40 +0000[diff] [blame]446
447</div>
448
449<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]450<h4>
Reid Spencerb40df562004-09-23 16:03:48 +0000[diff] [blame]451<a name="ci_class_struct">Use of <tt>class</tt> and <tt>struct</tt> Keywords</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]452</h4>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]453<div>
Misha Brukmanedcc78a2004-10-26 15:45:13 +0000[diff] [blame]454
455<p>In C++, the <tt>class</tt> and <tt>struct</tt> keywords can be used almost
456interchangeably. The only difference is when they are used to declare a class:
457<tt>class</tt> makes all members private by default while <tt>struct</tt> makes
458all members public by default.</p>
459
460<p>Unfortunately, not all compilers follow the rules and some will generate
461different symbols based on whether <tt>class</tt> or <tt>struct</tt> was used to
462declare the symbol. This can lead to problems at link time.</p>
463
464<p>So, the rule for LLVM is to always use the <tt>class</tt> keyword, unless
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]465<b>all</b> members are public and the type is a C++
466<a href="http://en.wikipedia.org/wiki/Plain_old_data_structure">POD</a> type, in
467which case <tt>struct</tt> is allowed.</p>
Misha Brukmanedcc78a2004-10-26 15:45:13 +0000[diff] [blame]468
Reid Spencerb40df562004-09-23 16:03:48 +0000[diff] [blame]469</div>
470
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]471</div>
472
473</div>
474
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]475<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]476<h2>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]477 <a name="styleissues">Style Issues</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]478</h2>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]479<!-- *********************************************************************** -->
480
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]481<div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]482
483<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]484<h3>
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]485 <a name="macro">The High-Level Issues</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]486</h3>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]487<!-- ======================================================================= -->
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]488
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]489<div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]490
491<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]492<h4>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]493 <a name="hl_module">A Public Header File <b>is</b> a Module</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]494</h4>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]495
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]496<div>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]497
498<p>C++ doesn't do too well in the modularity department. There is no real
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]499encapsulation or data hiding (unless you use expensive protocol classes), but it
500is what we have to work with. When you write a public header file (in the LLVM
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]501source tree, they live in the top level "<tt>include</tt>" directory), you are
502defining a module of functionality.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]503
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]504<p>Ideally, modules should be completely independent of each other, and their
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]505header files should only <tt>#include</tt> the absolute minimum number of
506headers possible. A module is not just a class, a function, or a
507namespace: <a href="http://www.cuj.com/articles/2000/0002/0002c/0002c.htm">it's
508a collection of these</a> that defines an interface. This interface may be
509several functions, classes, or data structures, but the important issue is how
510they work together.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]511
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]512<p>In general, a module should be implemented by one or more <tt>.cpp</tt>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]513files. Each of these <tt>.cpp</tt> files should include the header that defines
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]514their interface first. This ensures that all of the dependences of the module
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]515header have been properly added to the module header itself, and are not
516implicit. System headers should be included after user headers for a
517translation unit.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]518
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]519</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]520
521<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]522<h4>
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]523 <a name="hl_dontinclude"><tt>#include</tt> as Little as Possible</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]524</h4>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]525
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]526<div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]527
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]528<p><tt>#include</tt> hurts compile time performance. Don't do it unless you
529have to, especially in header files.</p>
530
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]531<p>But wait! Sometimes you need to have the definition of a class to use it, or
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]532to inherit from it. In these cases go ahead and <tt>#include</tt> that header
533file. Be aware however that there are many cases where you don't need to have
534the full definition of a class. If you are using a pointer or reference to a
535class, you don't need the header file. If you are simply returning a class
536instance from a prototyped function or method, you don't need it. In fact, for
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]537most cases, you simply don't need the definition of a class. And not
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]538<tt>#include</tt>'ing speeds up compilation.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]539
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]540<p>It is easy to try to go too overboard on this recommendation, however. You
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]541<b>must</b> include all of the header files that you are using &mdash; you can
542include them either directly or indirectly (through another header file). To
543make sure that you don't accidentally forget to include a header file in your
544module header, make sure to include your module header <b>first</b> in the
545implementation file (as mentioned above). This way there won't be any hidden
546dependencies that you'll find out about later.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]547
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]548</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]549
550<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]551<h4>
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]552 <a name="hl_privateheaders">Keep "Internal" Headers Private</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]553</h4>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]554
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]555<div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]556
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]557<p>Many modules have a complex implementation that causes them to use more than
558one implementation (<tt>.cpp</tt>) file. It is often tempting to put the
559internal communication interface (helper classes, extra functions, etc) in the
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]560public module header file. Don't do this!</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]561
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]562<p>If you really need to do something like this, put a private header file in
563the same directory as the source files, and include it locally. This ensures
564that your private interface remains private and undisturbed by outsiders.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]565
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]566<p>Note however, that it's okay to put extra implementation methods in a public
567class itself. Just make them private (or protected) and all is well.</p>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]568
569</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]570
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]571<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]572<h4>
Zhanyong Wancafe0b42010-11-23 05:03:07 +0000[diff] [blame]573 <a name="hl_earlyexit">Use Early Exits and <tt>continue</tt> to Simplify Code</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]574</h4>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]575
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]576<div>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]577
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]578<p>When reading code, keep in mind how much state and how many previous
579decisions have to be remembered by the reader to understand a block of code.
580Aim to reduce indentation where possible when it doesn't make it more difficult
581to understand the code. One great way to do this is by making use of early
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]582exits and the <tt>continue</tt> keyword in long loops. As an example of using
583an early exit from a function, consider this "bad" code:</p>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]584
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]585<div class="doc_code">
586<pre>
587Value *DoSomething(Instruction *I) {
588 if (!isa&lt;TerminatorInst&gt;(I) &amp;&amp;
589 I-&gt;hasOneUse() &amp;&amp; SomeOtherThing(I)) {
590 ... some long code ....
591 }
592
593 return 0;
594}
595</pre>
596</div>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]597
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]598<p>This code has several problems if the body of the '<tt>if</tt>' is large.
599When you're looking at the top of the function, it isn't immediately clear that
600this <em>only</em> does interesting things with non-terminator instructions, and
601only applies to things with the other predicates. Second, it is relatively
602difficult to describe (in comments) why these predicates are important because
603the <tt>if</tt> statement makes it difficult to lay out the comments. Third,
604when you're deep within the body of the code, it is indented an extra level.
605Finally, when reading the top of the function, it isn't clear what the result is
606if the predicate isn't true; you have to read to the end of the function to know
607that it returns null.</p>
Matthijs Kooijmaned58a972008-07-30 12:14:10 +0000[diff] [blame]608
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]609<p>It is much preferred to format the code like this:</p>
610
611<div class="doc_code">
612<pre>
613Value *DoSomething(Instruction *I) {
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]614 // Terminators never need 'something' done to them because ...
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]615 if (isa&lt;TerminatorInst&gt;(I))
616 return 0;
617
618 // We conservatively avoid transforming instructions with multiple uses
619 // because goats like cheese.
620 if (!I-&gt;hasOneUse())
621 return 0;
622
623 // This is really just here for example.
624 if (!SomeOtherThing(I))
625 return 0;
626
627 ... some long code ....
628}
629</pre>
630</div>
631
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]632<p>This fixes these problems. A similar problem frequently happens in <tt>for</tt>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]633loops. A silly example is something like this:</p>
634
635<div class="doc_code">
636<pre>
637 for (BasicBlock::iterator II = BB-&gt;begin(), E = BB-&gt;end(); II != E; ++II) {
638 if (BinaryOperator *BO = dyn_cast&lt;BinaryOperator&gt;(II)) {
639 Value *LHS = BO-&gt;getOperand(0);
640 Value *RHS = BO-&gt;getOperand(1);
641 if (LHS != RHS) {
642 ...
643 }
644 }
645 }
646</pre>
647</div>
648
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]649<p>When you have very, very small loops, this sort of structure is fine. But if
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]650it exceeds more than 10-15 lines, it becomes difficult for people to read and
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]651understand at a glance. The problem with this sort of code is that it gets very
652nested very quickly. Meaning that the reader of the code has to keep a lot of
653context in their brain to remember what is going immediately on in the loop,
654because they don't know if/when the <tt>if</tt> conditions will have elses etc.
655It is strongly preferred to structure the loop like this:</p>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]656
657<div class="doc_code">
658<pre>
659 for (BasicBlock::iterator II = BB-&gt;begin(), E = BB-&gt;end(); II != E; ++II) {
660 BinaryOperator *BO = dyn_cast&lt;BinaryOperator&gt;(II);
661 if (!BO) continue;
662
663 Value *LHS = BO-&gt;getOperand(0);
664 Value *RHS = BO-&gt;getOperand(1);
665 if (LHS == RHS) continue;
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]666
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]667 ...
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]668 }
669</pre>
670</div>
671
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]672<p>This has all the benefits of using early exits for functions: it reduces
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]673nesting of the loop, it makes it easier to describe why the conditions are true,
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]674and it makes it obvious to the reader that there is no <tt>else</tt> coming up
675that they have to push context into their brain for. If a loop is large, this
676can be a big understandability win.</p>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]677
678</div>
679
Chris Lattner9eb7e0a2009-07-28 22:54:04 +0000[diff] [blame]680<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]681<h4>
Zhanyong Wancafe0b42010-11-23 05:03:07 +0000[diff] [blame]682 <a name="hl_else_after_return">Don't use <tt>else</tt> after a <tt>return</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]683</h4>
Chris Lattner9eb7e0a2009-07-28 22:54:04 +0000[diff] [blame]684
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]685<div>
Chris Lattner9eb7e0a2009-07-28 22:54:04 +0000[diff] [blame]686
687<p>For similar reasons above (reduction of indentation and easier reading),
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]688please do not use '<tt>else</tt>' or '<tt>else if</tt>' after something that
689interrupts control flow &mdash; like <tt>return</tt>, <tt>break</tt>,
690<tt>continue</tt>, <tt>goto</tt>, etc. For example, this is <em>bad</em>:</p>
691
Chris Lattner9eb7e0a2009-07-28 22:54:04 +0000[diff] [blame]692<div class="doc_code">
693<pre>
694 case 'J': {
695 if (Signed) {
696 Type = Context.getsigjmp_bufType();
697 if (Type.isNull()) {
698 Error = ASTContext::GE_Missing_sigjmp_buf;
699 return QualType();
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]700 <b>} else {
Chris Lattner9eb7e0a2009-07-28 22:54:04 +0000[diff] [blame]701 break;
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]702 }</b>
Chris Lattner9eb7e0a2009-07-28 22:54:04 +0000[diff] [blame]703 } else {
704 Type = Context.getjmp_bufType();
705 if (Type.isNull()) {
706 Error = ASTContext::GE_Missing_jmp_buf;
707 return QualType();
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]708 <b>} else {
Chris Lattner9eb7e0a2009-07-28 22:54:04 +0000[diff] [blame]709 break;
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]710 }</b>
Chris Lattner9eb7e0a2009-07-28 22:54:04 +0000[diff] [blame]711 }
712 }
713 }
714</pre>
715</div>
716
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]717<p>It is better to write it like this:</p>
Chris Lattner9eb7e0a2009-07-28 22:54:04 +0000[diff] [blame]718
719<div class="doc_code">
720<pre>
721 case 'J':
722 if (Signed) {
723 Type = Context.getsigjmp_bufType();
724 if (Type.isNull()) {
725 Error = ASTContext::GE_Missing_sigjmp_buf;
726 return QualType();
727 }
728 } else {
729 Type = Context.getjmp_bufType();
730 if (Type.isNull()) {
731 Error = ASTContext::GE_Missing_jmp_buf;
732 return QualType();
733 }
734 }
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]735 <b>break;</b>
Chris Lattner9eb7e0a2009-07-28 22:54:04 +0000[diff] [blame]736</pre>
737</div>
738
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]739<p>Or better yet (in this case) as:</p>
Chris Lattner9eb7e0a2009-07-28 22:54:04 +0000[diff] [blame]740
741<div class="doc_code">
742<pre>
743 case 'J':
744 if (Signed)
745 Type = Context.getsigjmp_bufType();
746 else
747 Type = Context.getjmp_bufType();
748
749 if (Type.isNull()) {
750 Error = Signed ? ASTContext::GE_Missing_sigjmp_buf :
751 ASTContext::GE_Missing_jmp_buf;
752 return QualType();
753 }
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]754 <b>break;</b>
Chris Lattner9eb7e0a2009-07-28 22:54:04 +0000[diff] [blame]755</pre>
756</div>
757
758<p>The idea is to reduce indentation and the amount of code you have to keep
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]759track of when reading the code.</p>
Chris Lattner9eb7e0a2009-07-28 22:54:04 +0000[diff] [blame]760
761</div>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]762
763<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]764<h4>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]765 <a name="hl_predicateloops">Turn Predicate Loops into Predicate Functions</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]766</h4>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]767
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]768<div>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]769
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]770<p>It is very common to write small loops that just compute a boolean value.
771There are a number of ways that people commonly write these, but an example of
772this sort of thing is:</p>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]773
774<div class="doc_code">
775<pre>
776 <b>bool FoundFoo = false;</b>
777 for (unsigned i = 0, e = BarList.size(); i != e; ++i)
778 if (BarList[i]-&gt;isFoo()) {
779 <b>FoundFoo = true;</b>
780 break;
781 }
782
783 <b>if (FoundFoo) {</b>
784 ...
785 }
786</pre>
787</div>
788
789<p>This sort of code is awkward to write, and is almost always a bad sign.
790Instead of this sort of loop, we strongly prefer to use a predicate function
791(which may be <a href="#micro_anonns">static</a>) that uses
Chris Lattner59fec6a2009-07-22 16:54:14 +0000[diff] [blame]792<a href="#hl_earlyexit">early exits</a> to compute the predicate. We prefer
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]793the code to be structured like this:</p>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]794
795<div class="doc_code">
796<pre>
797/// ListContainsFoo - Return true if the specified list has an element that is
798/// a foo.
799static bool ListContainsFoo(const std::vector&lt;Bar*&gt; &amp;List) {
800 for (unsigned i = 0, e = List.size(); i != e; ++i)
801 if (List[i]-&gt;isFoo())
802 return true;
803 return false;
804}
805...
806
807 <b>if (ListContainsFoo(BarList)) {</b>
808 ...
809 }
810</pre>
811</div>
812
813<p>There are many reasons for doing this: it reduces indentation and factors out
814code which can often be shared by other code that checks for the same predicate.
815More importantly, it <em>forces you to pick a name</em> for the function, and
816forces you to write a comment for it. In this silly example, this doesn't add
817much value. However, if the condition is complex, this can make it a lot easier
818for the reader to understand the code that queries for this predicate. Instead
Chris Lattner71d8f3b2009-07-22 16:30:39 +0000[diff] [blame]819of being faced with the in-line details of how we check to see if the BarList
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]820contains a foo, we can trust the function name and continue reading with better
821locality.</p>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]822
823</div>
824
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]825</div>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]826
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]827<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]828<h3>
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]829 <a name="micro">The Low-Level Issues</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]830</h3>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]831<!-- ======================================================================= -->
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]832
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]833<div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]834
835<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]836<h4>
837 <a name="ll_naming">
838 Name Types, Functions, Variables, and Enumerators Properly
839 </a>
840</h4>
Zhanyong Wan7fcd4dc2010-12-02 05:10:07 +0000[diff] [blame]841
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]842<div>
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]843
844<p>Poorly-chosen names can mislead the reader and cause bugs. We cannot stress
845enough how important it is to use <em>descriptive</em> names. Pick names that
846match the semantics and role of the underlying entities, within reason. Avoid
847abbreviations unless they are well known. After picking a good name, make sure
848to use consistent capitalization for the name, as inconsistency requires clients
849to either memorize the APIs or to look it up to find the exact spelling.</p>
Zhanyong Wan7fcd4dc2010-12-02 05:10:07 +0000[diff] [blame]850
Chris Lattner69ad7972010-12-10 00:52:35 +0000[diff] [blame]851<p>In general, names should be in camel case (e.g. <tt>TextFileReader</tt>
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]852and <tt>isLValue()</tt>). Different kinds of declarations have different
853rules:</p>
Zhanyong Wan7fcd4dc2010-12-02 05:10:07 +0000[diff] [blame]854
Chris Lattner69ad7972010-12-10 00:52:35 +0000[diff] [blame]855<ul>
Chris Lattner78ceb3a2010-12-10 00:54:03 +0000[diff] [blame]856<li><p><b>Type names</b> (including classes, structs, enums, typedefs, etc)
Chris Lattnerc5133092011-08-12 19:49:16 +0000[diff] [blame]857 should be nouns and start with an upper-case letter (e.g.
858 <tt>TextFileReader</tt>).</p></li>
859
860<li><p><b>Variable names</b> should be nouns (as they represent state). The
861 name should be camel case, and start with an upper case letter (e.g.
862 <tt>Leader</tt> or <tt>Boats</tt>).</p></li>
Chris Lattner69ad7972010-12-10 00:52:35 +0000[diff] [blame]863
Chris Lattner78ceb3a2010-12-10 00:54:03 +0000[diff] [blame]864<li><p><b>Function names</b> should be verb phrases (as they represent
Chris Lattner69ad7972010-12-10 00:52:35 +0000[diff] [blame]865 actions), and command-like function should be imperative. The name should
866 be camel case, and start with a lower case letter (e.g. <tt>openFile()</tt>
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]867 or <tt>isFoo()</tt>).</p></li>
Chris Lattner69ad7972010-12-10 00:52:35 +0000[diff] [blame]868
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]869<li><p><b>Enum declarations</b> (e.g. <tt>enum Foo {...}</tt>) are types, so
870 they should follow the naming conventions for types. A common use for enums
871 is as a discriminator for a union, or an indicator of a subclass. When an
872 enum is used for something like this, it should have a <tt>Kind</tt> suffix
873 (e.g. <tt>ValueKind</tt>).</p></li>
Chris Lattner69ad7972010-12-10 00:52:35 +0000[diff] [blame]874
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]875<li><p><b>Enumerators</b> (e.g. <tt>enum { Foo, Bar }</tt>) and <b>public member
876 variables</b> should start with an upper-case letter, just like types.
877 Unless the enumerators are defined in their own small namespace or inside a
878 class, enumerators should have a prefix corresponding to the enum
879 declaration name. For example, <tt>enum ValueKind { ... };</tt> may contain
880 enumerators like <tt>VK_Argument</tt>, <tt>VK_BasicBlock</tt>, etc.
881 Enumerators that are just convenience constants are exempt from the
882 requirement for a prefix. For instance:</p>
883
Zhanyong Wan7fcd4dc2010-12-02 05:10:07 +0000[diff] [blame]884<div class="doc_code">
885<pre>
886enum {
887 MaxSize = 42,
888 Density = 12
889};
890</pre>
891</div>
Chris Lattner69ad7972010-12-10 00:52:35 +0000[diff] [blame]892</li>
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]893
Chris Lattner69ad7972010-12-10 00:52:35 +0000[diff] [blame]894</ul>
895
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]896<p>As an exception, classes that mimic STL classes can have member names in
897STL's style of lower-case words separated by underscores (e.g. <tt>begin()</tt>,
898<tt>push_back()</tt>, and <tt>empty()</tt>).</p>
Chris Lattner69ad7972010-12-10 00:52:35 +0000[diff] [blame]899
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]900<p>Here are some examples of good and bad names:</p>
Zhanyong Wan7fcd4dc2010-12-02 05:10:07 +0000[diff] [blame]901
Zhanyong Wan7fcd4dc2010-12-02 05:10:07 +0000[diff] [blame]902<div class="doc_code">
903<pre>
904class VehicleMaker {
905 ...
Chris Lattner69ad7972010-12-10 00:52:35 +0000[diff] [blame]906 Factory&lt;Tire&gt; F; // Bad -- abbreviation and non-descriptive.
907 Factory&lt;Tire&gt; Factory; // Better.
908 Factory&lt;Tire&gt; TireFactory; // Even better -- if VehicleMaker has more than one
Zhanyong Wan7fcd4dc2010-12-02 05:10:07 +0000[diff] [blame]909 // kind of factories.
910};
911
912Vehicle MakeVehicle(VehicleType Type) {
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]913 VehicleMaker M; // Might be OK if having a short life-span.
914 Tire tmp1 = M.makeTire(); // Bad -- 'tmp1' provides no information.
Chris Lattner69ad7972010-12-10 00:52:35 +0000[diff] [blame]915 Light headlight = M.makeLight("head"); // Good -- descriptive.
Zhanyong Wan7fcd4dc2010-12-02 05:10:07 +0000[diff] [blame]916 ...
917}
918</pre>
919</div>
920
921</div>
922
923
924<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]925<h4>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]926 <a name="ll_assert">Assert Liberally</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]927</h4>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]928
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]929<div>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]930
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]931<p>Use the "<tt>assert</tt>" macro to its fullest. Check all of your
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]932preconditions and assumptions, you never know when a bug (not necessarily even
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]933yours) might be caught early by an assertion, which reduces debugging time
934dramatically. The "<tt>&lt;cassert&gt;</tt>" header file is probably already
935included by the header files you are using, so it doesn't cost anything to use
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]936it.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]937
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]938<p>To further assist with debugging, make sure to put some kind of error message
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]939in the assertion statement, which is printed if the assertion is tripped. This
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]940helps the poor debugger make sense of why an assertion is being made and
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]941enforced, and hopefully what to do about it. Here is one complete example:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]942
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]943<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]944<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]945inline Value *getOperand(unsigned i) {
946 assert(i &lt; Operands.size() &amp;&amp; "getOperand() out of range!");
947 return Operands[i];
948}
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]949</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]950</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]951
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]952<p>Here are more examples:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]953
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]954<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]955<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]956assert(Ty-&gt;isPointerType() &amp;&amp; "Can't allocate a non pointer type!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]957
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]958assert((Opcode == Shl || Opcode == Shr) &amp;&amp; "ShiftInst Opcode invalid!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]959
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]960assert(idx &lt; getNumSuccessors() &amp;&amp; "Successor # out of range!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]961
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]962assert(V1.getType() == V2.getType() &amp;&amp; "Constant types must be identical!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]963
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]964assert(isa&lt;PHINode&gt;(Succ-&gt;front()) &amp;&amp; "Only works on PHId BBs!");
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]965</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]966</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]967
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]968<p>You get the idea.</p>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]969
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]970<p>Please be aware that, when adding assert statements, not all compilers are aware of
Nick Lewyckyf4408e82008-05-31 23:54:55 +0000[diff] [blame]971the semantics of the assert. In some places, asserts are used to indicate a piece of
972code that should not be reached. These are typically of the form:</p>
973
974<div class="doc_code">
975<pre>
Dan Gohmanf0032762008-11-24 17:18:39 +0000[diff] [blame]976assert(0 &amp;&amp; "Some helpful error message");
Nick Lewyckyf4408e82008-05-31 23:54:55 +0000[diff] [blame]977</pre>
978</div>
979
980<p>When used in a function that returns a value, they should be followed with a return
981statement and a comment indicating that this line is never reached. This will prevent
982a compiler which is unable to deduce that the assert statement never returns from
983generating a warning.</p>
984
985<div class="doc_code">
986<pre>
Dan Gohmanf0032762008-11-24 17:18:39 +0000[diff] [blame]987assert(0 &amp;&amp; "Some helpful error message");
Nick Lewyckyf4408e82008-05-31 23:54:55 +0000[diff] [blame]988// Not reached
989return 0;
990</pre>
991</div>
992
Chris Lattner97928d12010-11-12 00:19:41 +0000[diff] [blame]993<p>Another issue is that values used only by assertions will produce an "unused
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]994value" warning when assertions are disabled. For example, this code will
995warn:</p>
Chris Lattner97928d12010-11-12 00:19:41 +0000[diff] [blame]996
997<div class="doc_code">
998<pre>
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]999unsigned Size = V.size();
1000assert(Size &gt; 42 &amp;&amp; "Vector smaller than it should be");
Chris Lattner97928d12010-11-12 00:19:41 +0000[diff] [blame]1001
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1002bool NewToSet = Myset.insert(Value);
1003assert(NewToSet &amp;&amp; "The value shouldn't be in the set yet");
Chris Lattner97928d12010-11-12 00:19:41 +0000[diff] [blame]1004</pre>
1005</div>
1006
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1007<p>These are two interesting different cases. In the first case, the call to
Chris Lattner97928d12010-11-12 00:19:41 +0000[diff] [blame]1008V.size() is only useful for the assert, and we don't want it executed when
1009assertions are disabled. Code like this should move the call into the assert
1010itself. In the second case, the side effects of the call must happen whether
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1011the assert is enabled or not. In this case, the value should be cast to void to
1012disable the warning. To be specific, it is preferred to write the code like
1013this:</p>
Chris Lattner97928d12010-11-12 00:19:41 +0000[diff] [blame]1014
1015<div class="doc_code">
1016<pre>
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1017assert(V.size() &gt; 42 &amp;&amp; "Vector smaller than it should be");
Chris Lattner97928d12010-11-12 00:19:41 +0000[diff] [blame]1018
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1019bool NewToSet = Myset.insert(Value); (void)NewToSet;
1020assert(NewToSet &amp;&amp; "The value shouldn't be in the set yet");
Chris Lattner97928d12010-11-12 00:19:41 +0000[diff] [blame]1021</pre>
1022</div>
1023
1024
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1025</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1026
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]1027<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1028<h4>
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1029 <a name="ll_ns_std">Do Not Use '<tt>using namespace std</tt>'</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1030</h4>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]1031
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1032<div>
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1033
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]1034<p>In LLVM, we prefer to explicitly prefix all identifiers from the standard
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]1035namespace with an "<tt>std::</tt>" prefix, rather than rely on
1036"<tt>using namespace std;</tt>".</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]1037
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]1038<p> In header files, adding a '<tt>using namespace XXX</tt>' directive pollutes
Misha Brukman2d33c542008-12-11 19:37:04 +0000[diff] [blame]1039the namespace of any source file that <tt>#include</tt>s the header. This is
1040clearly a bad thing.</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]1041
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]1042<p>In implementation files (e.g. <tt>.cpp</tt> files), the rule is more of a stylistic
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]1043rule, but is still important. Basically, using explicit namespace prefixes
1044makes the code <b>clearer</b>, because it is immediately obvious what facilities
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1045are being used and where they are coming from. And <b>more portable</b>, because
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]1046namespace clashes cannot occur between LLVM code and other namespaces. The
1047portability rule is important because different standard library implementations
1048expose different symbols (potentially ones they shouldn't), and future revisions
1049to the C++ standard will add more symbols to the <tt>std</tt> namespace. As
1050such, we never use '<tt>using namespace std;</tt>' in LLVM.</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]1051
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]1052<p>The exception to the general rule (i.e. it's not an exception for
1053the <tt>std</tt> namespace) is for implementation files. For example, all of
1054the code in the LLVM project implements code that lives in the 'llvm' namespace.
Chris Lattnereddd9692010-11-17 19:47:20 +0000[diff] [blame]1055As such, it is ok, and actually clearer, for the <tt>.cpp</tt> files to have a
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1056'<tt>using namespace llvm;</tt>' directive at the top, after the
Chris Lattnereddd9692010-11-17 19:47:20 +0000[diff] [blame]1057<tt>#include</tt>s. This reduces indentation in the body of the file for source
1058editors that indent based on braces, and keeps the conceptual context cleaner.
1059The general form of this rule is that any <tt>.cpp</tt> file that implements
1060code in any namespace may use that namespace (and its parents'), but should not
1061use any others.</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]1062
1063</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1064
1065<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1066<h4>
1067 <a name="ll_virtual_anch">
1068 Provide a Virtual Method Anchor for Classes in Headers
1069 </a>
1070</h4>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]1071
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1072<div>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]1073
1074<p>If a class is defined in a header file and has a v-table (either it has
1075virtual methods or it derives from classes with virtual methods), it must
1076always have at least one out-of-line virtual method in the class. Without
Misha Brukman2d33c542008-12-11 19:37:04 +0000[diff] [blame]1077this, the compiler will copy the vtable and RTTI into every <tt>.o</tt> file
1078that <tt>#include</tt>s the header, bloating <tt>.o</tt> file sizes and
1079increasing link times.</p>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]1080
1081</div>
1082
Chris Lattner0af39ea2009-06-30 06:13:23 +0000[diff] [blame]1083<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1084<h4>
Nick Lewycky7ac01992011-02-20 02:03:04 +0000[diff] [blame]1085 <a name="ll_end">Don't evaluate <tt>end()</tt> every time through a loop</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1086</h4>
Chris Lattner0af39ea2009-06-30 06:13:23 +0000[diff] [blame]1087
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1088<div>
Chris Lattner0af39ea2009-06-30 06:13:23 +0000[diff] [blame]1089
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1090<p>Because C++ doesn't have a standard "<tt>foreach</tt>" loop (though it can be
1091emulated with macros and may be coming in C++'0x) we end up writing a lot of
1092loops that manually iterate from begin to end on a variety of containers or
1093through other data structures. One common mistake is to write a loop in this
1094style:</p>
Chris Lattner0af39ea2009-06-30 06:13:23 +0000[diff] [blame]1095
1096<div class="doc_code">
1097<pre>
1098 BasicBlock *BB = ...
1099 for (BasicBlock::iterator I = BB->begin(); I != <b>BB->end()</b>; ++I)
1100 ... use I ...
1101</pre>
1102</div>
1103
1104<p>The problem with this construct is that it evaluates "<tt>BB->end()</tt>"
1105every time through the loop. Instead of writing the loop like this, we strongly
1106prefer loops to be written so that they evaluate it once before the loop starts.
1107A convenient way to do this is like so:</p>
1108
1109<div class="doc_code">
1110<pre>
1111 BasicBlock *BB = ...
1112 for (BasicBlock::iterator I = BB->begin(), E = <b>BB->end()</b>; I != E; ++I)
1113 ... use I ...
1114</pre>
1115</div>
1116
1117<p>The observant may quickly point out that these two loops may have different
1118semantics: if the container (a basic block in this case) is being mutated, then
1119"<tt>BB->end()</tt>" may change its value every time through the loop and the
1120second loop may not in fact be correct. If you actually do depend on this
Chris Lattner09bc65e2009-06-30 06:20:03 +0000[diff] [blame]1121behavior, please write the loop in the first form and add a comment indicating
Chris Lattner0af39ea2009-06-30 06:13:23 +0000[diff] [blame]1122that you did it intentionally.</p>
1123
1124<p>Why do we prefer the second form (when correct)? Writing the loop in the
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1125first form has two problems. First it may be less efficient than evaluating it
1126at the start of the loop. In this case, the cost is probably minor &mdash; a
1127few extra loads every time through the loop. However, if the base expression is
1128more complex, then the cost can rise quickly. I've seen loops where the end
Chris Lattner0af39ea2009-06-30 06:13:23 +0000[diff] [blame]1129expression was actually something like: "<tt>SomeMap[x]->end()</tt>" and map
Chris Lattnera44f87f2009-06-30 06:27:54 +0000[diff] [blame]1130lookups really aren't cheap. By writing it in the second form consistently, you
Chris Lattner0af39ea2009-06-30 06:13:23 +0000[diff] [blame]1131eliminate the issue entirely and don't even have to think about it.</p>
1132
Chris Lattner09bc65e2009-06-30 06:20:03 +0000[diff] [blame]1133<p>The second (even bigger) issue is that writing the loop in the first form
Chris Lattner0af39ea2009-06-30 06:13:23 +0000[diff] [blame]1134hints to the reader that the loop is mutating the container (a fact that a
1135comment would handily confirm!). If you write the loop in the second form, it
1136is immediately obvious without even looking at the body of the loop that the
1137container isn't being modified, which makes it easier to read the code and
1138understand what it does.</p>
1139
1140<p>While the second form of the loop is a few extra keystrokes, we do strongly
1141prefer it.</p>
1142
1143</div>
1144
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]1145<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1146<h4>
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1147 <a name="ll_iostream"><tt>#include &lt;iostream&gt;</tt> is Forbidden</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1148</h4>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1149
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1150<div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1151
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1152<p>The use of <tt>#include &lt;iostream&gt;</tt> in library files is
1153hereby <b><em>forbidden</em></b>. The primary reason for doing this is to
1154support clients using LLVM libraries as part of larger systems. In particular,
1155we statically link LLVM into some dynamic libraries. Even if LLVM isn't used,
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1156the static constructors are run whenever an application starts up that uses the
1157dynamic library. There are two problems with this:</p>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1158
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1159<ol>
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1160 <li>The time to run the static c'tors impacts startup time of applications
1161 &mdash; a critical time for GUI apps.</li>
1162
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1163 <li>The static c'tors cause the app to pull many extra pages of memory off the
1164 disk: both the code for the static c'tors in each <tt>.o</tt> file and the
1165 small amount of data that gets touched. In addition, touched/dirty pages
1166 put more pressure on the VM system on low-memory machines.</li>
1167</ol>
1168
1169<p>Note that using the other stream headers (<tt>&lt;sstream&gt;</tt> for
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1170example) is not problematic in this regard &mdash;
1171just <tt>&lt;iostream&gt;</tt>. However, <tt>raw_ostream</tt> provides various
1172APIs that are better performing for almost every use than <tt>std::ostream</tt>
1173style APIs. <b>Therefore new code should always
Chris Lattner983c5922009-08-23 21:53:47 +0000[diff] [blame]1174use <a href="#ll_raw_ostream"><tt>raw_ostream</tt></a> for writing, or
1175the <tt>llvm::MemoryBuffer</tt> API for reading files.</b></p>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1176
1177</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1178
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1179
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1180<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1181<h4>
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]1182 <a name="ll_raw_ostream">Use <tt>raw_ostream</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1183</h4>
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]1184
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1185<div>
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]1186
1187<p>LLVM includes a lightweight, simple, and efficient stream implementation
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1188in <tt>llvm/Support/raw_ostream.h</tt>, which provides all of the common
1189features of <tt>std::ostream</tt>. All new code should use <tt>raw_ostream</tt>
1190instead of <tt>ostream</tt>.</p>
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]1191
1192<p>Unlike <tt>std::ostream</tt>, <tt>raw_ostream</tt> is not a template and can
1193be forward declared as <tt>class raw_ostream</tt>. Public headers should
1194generally not include the <tt>raw_ostream</tt> header, but use forward
1195declarations and constant references to <tt>raw_ostream</tt> instances.</p>
1196
1197</div>
1198
1199
1200<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1201<h4>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]1202 <a name="ll_avoidendl">Avoid <tt>std::endl</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1203</h4>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]1204
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1205<div>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1206
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1207<p>The <tt>std::endl</tt> modifier, when used with <tt>iostreams</tt> outputs a
1208newline to the output stream specified. In addition to doing this, however, it
1209also flushes the output stream. In other words, these are equivalent:</p>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]1210
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]1211<div class="doc_code">
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]1212<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]1213std::cout &lt;&lt; std::endl;
1214std::cout &lt;&lt; '\n' &lt;&lt; std::flush;
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]1215</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]1216</div>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]1217
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1218<p>Most of the time, you probably have no reason to flush the output stream, so
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]1219it's better to use a literal <tt>'\n'</tt>.</p>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]1220
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1221</div>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]1222
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1223</div>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]1224
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1225<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1226<h3>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1227 <a name="nano">Microscopic Details</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1228</h3>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1229<!-- ======================================================================= -->
1230
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1231<div>
1232
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1233<p>This section describes preferred low-level formatting guidelines along with
1234reasoning on why we prefer them.</p>
1235
1236<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1237<h4>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1238 <a name="micro_spaceparen">Spaces Before Parentheses</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1239</h4>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1240
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1241<div>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1242
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]1243<p>We prefer to put a space before an open parenthesis only in control flow
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1244statements, but not in normal function call expressions and function-like
1245macros. For example, this is good:</p>
1246
1247<div class="doc_code">
1248<pre>
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1249<b>if (</b>x) ...
1250<b>for (</b>i = 0; i != 100; ++i) ...
1251<b>while (</b>llvm_rocks) ...
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1252
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1253<b>somefunc(</b>42);
1254<b><a href="#ll_assert">assert</a>(</b>3 != 4 &amp;&amp; "laws of math are failing me");
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1255
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1256a = <b>foo(</b>42, 92) + <b>bar(</b>x);
1257</pre>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1258</div>
1259
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1260<p>and this is bad:</p>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1261
1262<div class="doc_code">
1263<pre>
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1264<b>if(</b>x) ...
1265<b>for(</b>i = 0; i != 100; ++i) ...
1266<b>while(</b>llvm_rocks) ...
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1267
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1268<b>somefunc (</b>42);
1269<b><a href="#ll_assert">assert</a> (</b>3 != 4 &amp;&amp; "laws of math are failing me");
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1270
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1271a = <b>foo (</b>42, 92) + <b>bar (</b>x);
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1272</pre>
1273</div>
1274
1275<p>The reason for doing this is not completely arbitrary. This style makes
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1276control flow operators stand out more, and makes expressions flow better. The
1277function call operator binds very tightly as a postfix operator. Putting a
1278space after a function name (as in the last example) makes it appear that the
1279code might bind the arguments of the left-hand-side of a binary operator with
1280the argument list of a function and the name of the right side. More
1281specifically, it is easy to misread the "a" example as:</p>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1282
1283<div class="doc_code">
1284<pre>
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1285a = foo <b>(</b>(42, 92) + bar<b>)</b> (x);
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1286</pre>
1287</div>
1288
Bill Wendlingb8602032010-12-21 03:31:05 +0000[diff] [blame]1289<p>when skimming through the code. By avoiding a space in a function, we avoid
1290this misinterpretation.</p>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1291
1292</div>
1293
1294<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1295<h4>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1296 <a name="micro_preincrement">Prefer Preincrement</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1297</h4>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1298
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1299<div>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1300
1301<p>Hard fast rule: Preincrement (<tt>++X</tt>) may be no slower than
1302postincrement (<tt>X++</tt>) and could very well be a lot faster than it. Use
1303preincrementation whenever possible.</p>
1304
1305<p>The semantics of postincrement include making a copy of the value being
1306incremented, returning it, and then preincrementing the "work value". For
1307primitive types, this isn't a big deal... but for iterators, it can be a huge
1308issue (for example, some iterators contains stack and set objects in them...
1309copying an iterator could invoke the copy ctor's of these as well). In general,
1310get in the habit of always using preincrement, and you won't have a problem.</p>
1311
1312</div>
1313
1314<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1315<h4>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1316 <a name="micro_namespaceindent">Namespace Indentation</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1317</h4>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1318
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1319<div>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1320
1321<p>
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]1322In general, we strive to reduce indentation wherever possible. This is useful
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1323because we want code to <a href="#scf_codewidth">fit into 80 columns</a> without
1324wrapping horribly, but also because it makes it easier to understand the code.
1325Namespaces are a funny thing: they are often large, and we often desire to put
1326lots of stuff into them (so they can be large). Other times they are tiny,
1327because they just hold an enum or something similar. In order to balance this,
1328we use different approaches for small versus large namespaces.
1329</p>
1330
1331<p>
1332If a namespace definition is small and <em>easily</em> fits on a screen (say,
1333less than 35 lines of code), then you should indent its body. Here's an
1334example:
1335</p>
1336
1337<div class="doc_code">
1338<pre>
Chris Lattner59fec6a2009-07-22 16:54:14 +0000[diff] [blame]1339namespace llvm {
1340 namespace X86 {
1341 /// RelocationType - An enum for the x86 relocation codes. Note that
1342 /// the terminology here doesn't follow x86 convention - word means
1343 /// 32-bit and dword means 64-bit.
1344 enum RelocationType {
1345 /// reloc_pcrel_word - PC relative relocation, add the relocated value to
1346 /// the value already in memory, after we adjust it for where the PC is.
1347 reloc_pcrel_word = 0,
1348
1349 /// reloc_picrel_word - PIC base relative relocation, add the relocated
1350 /// value to the value already in memory, after we adjust it for where the
1351 /// PIC base is.
1352 reloc_picrel_word = 1,
1353
1354 /// reloc_absolute_word, reloc_absolute_dword - Absolute relocation, just
1355 /// add the relocated value to the value already in memory.
1356 reloc_absolute_word = 2,
1357 reloc_absolute_dword = 3
1358 };
1359 }
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1360}
1361</pre>
1362</div>
1363
1364<p>Since the body is small, indenting adds value because it makes it very clear
1365where the namespace starts and ends, and it is easy to take the whole thing in
1366in one "gulp" when reading the code. If the blob of code in the namespace is
Chris Lattner684cf812010-11-17 17:14:55 +0000[diff] [blame]1367larger (as it typically is in a header in the <tt>llvm</tt> or <tt>clang</tt> namespaces), do not
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1368indent the code, and add a comment indicating what namespace is being closed.
1369For example:</p>
1370
1371<div class="doc_code">
1372<pre>
1373namespace llvm {
1374namespace knowledge {
1375
1376/// Grokable - This class represents things that Smith can have an intimate
1377/// understanding of and contains the data associated with it.
1378class Grokable {
1379...
1380public:
1381 explicit Grokable() { ... }
1382 virtual ~Grokable() = 0;
1383
1384 ...
1385
1386};
1387
1388} // end namespace knowledge
1389} // end namespace llvm
1390</pre>
1391</div>
1392
1393<p>Because the class is large, we don't expect that the reader can easily
1394understand the entire concept in a glance, and the end of the file (where the
1395namespaces end) may be a long ways away from the place they open. As such,
1396indenting the contents of the namespace doesn't add any value, and detracts from
1397the readability of the class. In these cases it is best to <em>not</em> indent
1398the contents of the namespace.</p>
1399
1400</div>
1401
1402<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1403<h4>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1404 <a name="micro_anonns">Anonymous Namespaces</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1405</h4>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1406
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1407<div>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1408
Chris Lattner59fec6a2009-07-22 16:54:14 +0000[diff] [blame]1409<p>After talking about namespaces in general, you may be wondering about
1410anonymous namespaces in particular.
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1411Anonymous namespaces are a great language feature that tells the C++ compiler
1412that the contents of the namespace are only visible within the current
1413translation unit, allowing more aggressive optimization and eliminating the
1414possibility of symbol name collisions. Anonymous namespaces are to C++ as
1415"static" is to C functions and global variables. While "static" is available
1416in C++, anonymous namespaces are more general: they can make entire classes
1417private to a file.</p>
1418
1419<p>The problem with anonymous namespaces is that they naturally want to
1420encourage indentation of their body, and they reduce locality of reference: if
1421you see a random function definition in a C++ file, it is easy to see if it is
1422marked static, but seeing if it is in an anonymous namespace requires scanning
1423a big chunk of the file.</p>
1424
1425<p>Because of this, we have a simple guideline: make anonymous namespaces as
1426small as possible, and only use them for class declarations. For example, this
1427is good:</p>
1428
1429<div class="doc_code">
1430<pre>
1431<b>namespace {</b>
1432 class StringSort {
1433 ...
1434 public:
1435 StringSort(...)
1436 bool operator&lt;(const char *RHS) const;
1437 };
1438<b>} // end anonymous namespace</b>
1439
1440static void Helper() {
1441 ...
1442}
1443
1444bool StringSort::operator&lt;(const char *RHS) const {
1445 ...
1446}
1447
1448</pre>
1449</div>
1450
1451<p>This is bad:</p>
1452
1453
1454<div class="doc_code">
1455<pre>
1456<b>namespace {</b>
1457class StringSort {
1458...
1459public:
1460 StringSort(...)
1461 bool operator&lt;(const char *RHS) const;
1462};
1463
1464void Helper() {
1465 ...
1466}
1467
1468bool StringSort::operator&lt;(const char *RHS) const {
1469 ...
1470}
1471
1472<b>} // end anonymous namespace</b>
1473
1474</pre>
1475</div>
1476
1477
1478<p>This is bad specifically because if you're looking at "Helper" in the middle
1479of a large C++ file, that you have no immediate way to tell if it is local to
1480the file. When it is marked static explicitly, this is immediately obvious.
1481Also, there is no reason to enclose the definition of "operator&lt;" in the
Chris Lattner59fec6a2009-07-22 16:54:14 +0000[diff] [blame]1482namespace just because it was declared there.
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1483</p>
1484
1485</div>
1486
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1487</div>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1488
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1489</div>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame]1490
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1491<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1492<h2>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1493 <a name="seealso">See Also</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1494</h2>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1495<!-- *********************************************************************** -->
1496
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1497<div>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1498
1499<p>A lot of these comments and recommendations have been culled for other
1500sources. Two particularly important books for our work are:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1501
1502<ol>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1503
Chris Lattner788ee282007-11-09 21:49:08 +0000[diff] [blame]1504<li><a href="http://www.amazon.com/Effective-Specific-Addison-Wesley-Professional-Computing/dp/0321334876">Effective
1505C++</a> by Scott Meyers. Also
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]1506interesting and useful are "More Effective C++" and "Effective STL" by the same
1507author.</li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1508
Chris Lattner788ee282007-11-09 21:49:08 +0000[diff] [blame]1509<li>Large-Scale C++ Software Design by John Lakos</li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1510
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1511</ol>
1512
1513<p>If you get some free time, and you haven't read them: do so, you might learn
Misha Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]1514something.</p>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1515
1516</div>
1517
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1518<!-- *********************************************************************** -->
1519
1520<hr>
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]1521<address>
1522 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]1523 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]1524 <a href="http://validator.w3.org/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]1525 src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1526
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]1527 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
NAKAMURA Takumib9a33632011-04-09 02:13:37 +0000[diff] [blame]1528 <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1529 Last modified: $Date$
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]1530</address>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1531
1532</body>
1533</html>