Gitiles
Code Review Sign In
gerrit-public.fairphone.software / toolchain / llvm-project / b8004d9b4c34a6d19be4ec658e331239b55c2f93 / . / llvm / docs / CodingStandards.html
blob: 7b05573703bca3531ae3a8432b6c9879e82fa4a9 [file] [log] [blame]
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
3<html>
4<head>
NAKAMURA Takumib8004d92011-10-31 11:21:59 +0000[diff] [blame^]5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]6 <link rel="stylesheet" href="llvm.css" type="text/css">
Misha Brukman6c2522a2008-12-10 23:07:02 +0000[diff] [blame]7 <title>LLVM Coding Standards</title>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]8</head>
9<body>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]10
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]11<h1>
Misha Brukman6c2522a2008-12-10 23:07:02 +0000[diff] [blame]12 LLVM Coding Standards
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]13</h1>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]14
15<ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]16 <li><a href="#introduction">Introduction</a></li>
Chris Lattner85014f42001-07-23 20:40:41 +0000[diff] [blame]17 <li><a href="#mechanicalissues">Mechanical Source Issues</a>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]18 <ol>
19 <li><a href="#sourceformating">Source Code Formatting</a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]20 <ol>
21 <li><a href="#scf_commenting">Commenting</a></li>
22 <li><a href="#scf_commentformat">Comment Formatting</a></li>
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]23 <li><a href="#scf_includes"><tt>#include</tt> Style</a></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]24 <li><a href="#scf_codewidth">Source Code Width</a></li>
25 <li><a href="#scf_spacestabs">Use Spaces Instead of Tabs</a></li>
26 <li><a href="#scf_indentation">Indent Code Consistently</a></li>
27 </ol></li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]28 <li><a href="#compilerissues">Compiler Issues</a>
29 <ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]30 <li><a href="#ci_warningerrors">Treat Compiler Warnings Like
31 Errors</a></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]32 <li><a href="#ci_portable_code">Write Portable Code</a></li>
Chris Lattner9db8e152010-11-30 19:20:40 +0000[diff] [blame]33 <li><a href="#ci_rtti_exceptions">Do not use RTTI or Exceptions</a></li>
Zhanyong Wan19b96fd2010-11-23 05:03:07 +0000[diff] [blame]34 <li><a href="#ci_class_struct">Use of <tt>class</tt>/<tt>struct</tt> Keywords</a></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]35 </ol></li>
36 </ol></li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]37 <li><a href="#styleissues">Style Issues</a>
38 <ol>
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]39 <li><a href="#macro">The High-Level Issues</a>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]40 <ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]41 <li><a href="#hl_module">A Public Header File <b>is</b> a
42 Module</a></li>
Zhanyong Wan19b96fd2010-11-23 05:03:07 +0000[diff] [blame]43 <li><a href="#hl_dontinclude"><tt>#include</tt> as Little as Possible</a></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]44 <li><a href="#hl_privateheaders">Keep "internal" Headers
45 Private</a></li>
Zhanyong Wan19b96fd2010-11-23 05:03:07 +0000[diff] [blame]46 <li><a href="#hl_earlyexit">Use Early Exits and <tt>continue</tt> to Simplify
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]47 Code</a></li>
Zhanyong Wan19b96fd2010-11-23 05:03:07 +0000[diff] [blame]48 <li><a href="#hl_else_after_return">Don't use <tt>else</tt> after a
49 <tt>return</tt></a></li>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]50 <li><a href="#hl_predicateloops">Turn Predicate Loops into Predicate
51 Functions</a></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]52 </ol></li>
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]53 <li><a href="#micro">The Low-Level Issues</a>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]54 <ol>
Zhanyong Wan4f3b26d2010-12-02 05:10:07 +0000[diff] [blame]55 <li><a href="#ll_naming">Name Types, Functions, Variables, and Enumerators Properly</a></li>
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]56 <li><a href="#ll_assert">Assert Liberally</a></li>
Zhanyong Wan19b96fd2010-11-23 05:03:07 +0000[diff] [blame]57 <li><a href="#ll_ns_std">Do not use '<tt>using namespace std</tt>'</a></li>
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]58 <li><a href="#ll_virtual_anch">Provide a virtual method anchor for
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]59 classes in headers</a></li>
Zhanyong Wan19b96fd2010-11-23 05:03:07 +0000[diff] [blame]60 <li><a href="#ll_end">Don't evaluate <tt>end()</tt> every time through a
Chris Lattner56c10942009-06-30 06:13:23 +0000[diff] [blame]61 loop</a></li>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]62 <li><a href="#ll_iostream"><tt>#include &lt;iostream&gt;</tt> is
63 <em>forbidden</em></a></li>
Chris Lattner02093e12010-12-10 00:54:03 +0000[diff] [blame]64 <li><a href="#ll_raw_ostream">Use <tt>raw_ostream</tt></a></li>
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]65 <li><a href="#ll_avoidendl">Avoid <tt>std::endl</tt></a></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]66 </ol></li>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]67
68 <li><a href="#nano">Microscopic Details</a>
69 <ol>
70 <li><a href="#micro_spaceparen">Spaces Before Parentheses</a></li>
71 <li><a href="#micro_preincrement">Prefer Preincrement</a></li>
72 <li><a href="#micro_namespaceindent">Namespace Indentation</a></li>
73 <li><a href="#micro_anonns">Anonymous Namespaces</a></li>
74 </ol></li>
75
76
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]77 </ol></li>
78 <li><a href="#seealso">See Also</a></li>
79</ol>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]80
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]81<div class="doc_author">
Chris Lattner9567fff2009-07-22 05:43:01 +0000[diff] [blame]82 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]83</div>
84
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]85
86<!-- *********************************************************************** -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]87<h2>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]88 <a name="introduction">Introduction</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]89</h2>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]90<!-- *********************************************************************** -->
91
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]92<div>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]93
94<p>This document attempts to describe a few coding standards that are being used
95in the LLVM source tree. Although no coding standards should be regarded as
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]96absolute requirements to be followed in all instances, coding standards can be
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]97useful.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]98
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]99<p>This document intentionally does not prescribe fixed standards for religious
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]100issues such as brace placement and space usage. For issues like this, follow
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]101the golden rule:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]102
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]103<blockquote>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]104
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]105<p><b><a name="goldenrule">If you are adding a significant body of source to a
106project, feel free to use whatever style you are most comfortable with. If you
107are extending, enhancing, or bug fixing already implemented code, use the style
108that is already being used so that the source is uniform and easy to
109follow.</a></b></p>
110
111</blockquote>
112
113<p>The ultimate goal of these guidelines is the increase readability and
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]114maintainability of our common source base. If you have suggestions for topics to
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]115be included, please mail them to <a
116href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]117
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]118</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]119
120<!-- *********************************************************************** -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]121<h2>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]122 <a name="mechanicalissues">Mechanical Source Issues</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]123</h2>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]124<!-- *********************************************************************** -->
125
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]126<div>
127
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]128<!-- ======================================================================= -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]129<h3>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]130 <a name="sourceformating">Source Code Formatting</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]131</h3>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]132
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]133<div>
134
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]135<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]136<h4>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]137 <a name="scf_commenting">Commenting</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]138</h4>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]139
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]140<div>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]141
142<p>Comments are one critical part of readability and maintainability. Everyone
Chris Lattnerbbe228b2009-07-12 00:10:24 +0000[diff] [blame]143knows they should comment, so should you. When writing comments, write them as
144English prose, which means they should use proper capitalization, punctuation,
145etc. Although we all should probably
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]146comment our code more than we do, there are a few very critical places that
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]147documentation is very useful:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]148
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]149<h5>File Headers</h5>
150
151<div>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]152
Reid Spencerc7f87f22007-07-09 08:04:31 +0000[diff] [blame]153<p>Every source file should have a header on it that describes the basic
154purpose of the file. If a file does not have a header, it should not be
155checked into Subversion. Most source trees will probably have a standard
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]156file header format. The standard format for the LLVM source tree looks like
157this:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]158
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]159<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]160<pre>
Chris Lattnere6f4e072003-10-13 14:58:11 +0000[diff] [blame]161//===-- llvm/Instruction.h - Instruction class definition -------*- C++ -*-===//
Misha Brukman02805a62009-01-02 16:58:42 +0000[diff] [blame]162//
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]163// The LLVM Compiler Infrastructure
164//
Chris Lattnerebf56662007-12-29 19:56:08 +0000[diff] [blame]165// This file is distributed under the University of Illinois Open Source
166// License. See LICENSE.TXT for details.
Misha Brukman02805a62009-01-02 16:58:42 +0000[diff] [blame]167//
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]168//===----------------------------------------------------------------------===//
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]169//
170// This file contains the declaration of the Instruction class, which is the
171// base class for all of the VM instructions.
172//
173//===----------------------------------------------------------------------===//
174</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]175</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]176
Chris Lattnerebf56662007-12-29 19:56:08 +0000[diff] [blame]177<p>A few things to note about this particular format: The "<tt>-*- C++
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]178-*-</tt>" string on the first line is there to tell Emacs that the source file
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]179is a C++ file, not a C file (Emacs assumes <tt>.h</tt> files are C files by default).
180Note that this tag is not necessary in <tt>.cpp</tt> files. The name of the file is also
Misha Brukman0d640e82004-07-28 22:37:57 +0000[diff] [blame]181on the first line, along with a very short description of the purpose of the
182file. This is important when printing out code and flipping though lots of
183pages.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]184
Chris Lattnerebf56662007-12-29 19:56:08 +0000[diff] [blame]185<p>The next section in the file is a concise note that defines the license
186that the file is released under. This makes it perfectly clear what terms the
187source code can be distributed under and should not be modified in any way.</p>
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]188
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]189<p>The main body of the description does not have to be very long in most cases.
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]190Here it's only two lines. If an algorithm is being implemented or something
191tricky is going on, a reference to the paper where it is published should be
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]192included, as well as any notes or "gotchas" in the code to watch out for.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]193
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]194</div>
195
196<h5>Class overviews</h5>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]197
Jim Laskey88b5e792006-07-31 20:18:49 +0000[diff] [blame]198<p>Classes are one fundamental part of a good object oriented design. As such,
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]199a class definition should have a comment block that explains what the class is
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]200used for... if it's not obvious. If it's so completely obvious your grandma
201could figure it out, it's probably safe to leave it out. Naming classes
Misha Brukman6d1686c2004-12-04 00:32:12 +0000[diff] [blame]202something sane goes a long ways towards avoiding writing documentation.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]203
204
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]205<h5>Method information</h5>
206
207<div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]208
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]209<p>Methods defined in a class (as well as any global functions) should also be
Dan Gohman42f56912010-02-26 20:18:32 +0000[diff] [blame]210documented properly. A quick note about what it does and a description of the
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]211borderline behaviour is all that is necessary here (unless something
Dan Gohman42f56912010-02-26 20:18:32 +0000[diff] [blame]212particularly tricky or insidious is going on). The hope is that people can
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]213figure out how to use your interfaces without reading the code itself... that is
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]214the goal metric.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]215
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]216<p>Good things to talk about here are what happens when something unexpected
217happens: does the method return null? Abort? Format your hard disk?</p>
218
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]219</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]220
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]221</div>
222
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]223<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]224<h4>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]225 <a name="scf_commentformat">Comment Formatting</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]226</h4>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]227
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]228<div>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]229
230<p>In general, prefer C++ style (<tt>//</tt>) comments. They take less space,
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]231require less typing, don't have nesting problems, etc. There are a few cases
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]232when it is useful to use C style (<tt>/* */</tt>) comments however:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]233
234<ol>
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]235 <li>When writing C code: Obviously if you are writing C code, use C style
Misha Brukman6d1686c2004-12-04 00:32:12 +0000[diff] [blame]236 comments.</li>
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]237 <li>When writing a header file that may be <tt>#include</tt>d by a C source
238 file.</li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]239 <li>When writing a source file that is used by a tool that only accepts C
240 style comments.</li>
241</ol>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]242
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]243<p>To comment out a large block of code, use <tt>#if 0</tt> and <tt>#endif</tt>.
244These nest properly and are better behaved in general than C style comments.</p>
245
246</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]247
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]248<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]249<h4>
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]250 <a name="scf_includes"><tt>#include</tt> Style</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]251</h4>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]252
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]253<div>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]254
255<p>Immediately after the <a href="#scf_commenting">header file comment</a> (and
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]256include guards if working on a header file), the <a
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]257href="#hl_dontinclude">minimal</a> list of <tt>#include</tt>s required by the
258file should be listed. We prefer these <tt>#include</tt>s to be listed in this
259order:</p>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]260
261<ol>
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]262 <li><a href="#mmheader">Main Module Header</a></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]263 <li><a href="#hl_privateheaders">Local/Private Headers</a></li>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]264 <li><tt>llvm/*</tt></li>
265 <li><tt>llvm/Analysis/*</tt></li>
266 <li><tt>llvm/Assembly/*</tt></li>
Duncan Sandse9da6db2010-09-29 20:09:55 +0000[diff] [blame]267 <li><tt>llvm/Bitcode/*</tt></li>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]268 <li><tt>llvm/CodeGen/*</tt></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]269 <li>...</li>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]270 <li><tt>Support/*</tt></li>
271 <li><tt>Config/*</tt></li>
272 <li>System <tt>#includes</tt></li>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]273</ol>
274
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]275<p>and each category should be sorted by name.</p>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]276
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]277<p><a name="mmheader">The "Main Module Header"</a> file applies to <tt>.cpp</tt> files
278which implement an interface defined by a <tt>.h</tt> file. This <tt>#include</tt>
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]279should always be included <b>first</b> regardless of where it lives on the file
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]280system. By including a header file first in the <tt>.cpp</tt> files that implement the
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]281interfaces, we ensure that the header does not have any hidden dependencies
282which are not explicitly #included in the header, but should be. It is also a
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]283form of documentation in the <tt>.cpp</tt> file to indicate where the interfaces it
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]284implements are defined.</p>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]285
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]286</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]287
288<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]289<h4>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]290 <a name="scf_codewidth">Source Code Width</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]291</h4>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]292
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]293<div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]294
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]295<p>Write your code to fit within 80 columns of text. This helps those of us who
296like to print out code and look at your code in an xterm without resizing
297it.</p>
298
Chris Lattnerfc12d2e2008-07-08 05:12:37 +0000[diff] [blame]299<p>The longer answer is that there must be some limit to the width of the code
300in order to reasonably allow developers to have multiple files side-by-side in
301windows on a modest display. If you are going to pick a width limit, it is
302somewhat arbitrary but you might as well pick something standard. Going with
30390 columns (for example) instead of 80 columns wouldn't add any significant
304value and would be detrimental to printing out code. Also many other projects
305have standardized on 80 columns, so some people have already configured their
306editors for it (vs something else, like 90 columns).</p>
307
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]308<p>This is one of many contentious issues in coding standards, but it is not up
Chris Lattnerfc12d2e2008-07-08 05:12:37 +0000[diff] [blame]309for debate.</p>
310
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]311</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]312
313<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]314<h4>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]315 <a name="scf_spacestabs">Use Spaces Instead of Tabs</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]316</h4>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]317
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]318<div>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]319
320<p>In all cases, prefer spaces to tabs in source files. People have different
Benjamin Kramer0f420382009-10-12 14:46:08 +0000[diff] [blame]321preferred indentation levels, and different styles of indentation that they
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]322like; this is fine. What isn't fine is that different editors/viewers expand
323tabs out to different tab stops. This can cause your code to look completely
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]324unreadable, and it is not worth dealing with.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]325
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]326<p>As always, follow the <a href="#goldenrule">Golden Rule</a> above: follow the
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]327style of existing code if you are modifying and extending it. If you like four
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]328spaces of indentation, <b>DO NOT</b> do that in the middle of a chunk of code
329with two spaces of indentation. Also, do not reindent a whole source file: it
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]330makes for incredible diffs that are absolutely worthless.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]331
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]332</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]333
334<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]335<h4>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]336 <a name="scf_indentation">Indent Code Consistently</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]337</h4>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]338
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]339<div>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]340
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]341<p>Okay, in your first year of programming you were told that indentation is
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]342important. If you didn't believe and internalize this then, now is the time.
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]343Just do it.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]344
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]345</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]346
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]347</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]348
349<!-- ======================================================================= -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]350<h3>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]351 <a name="compilerissues">Compiler Issues</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]352</h3>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]353
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]354<div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]355
356<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]357<h4>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]358 <a name="ci_warningerrors">Treat Compiler Warnings Like Errors</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]359</h4>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]360
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]361<div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]362
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]363<p>If your code has compiler warnings in it, something is wrong &mdash; you
364aren't casting values correctly, your have "questionable" constructs in your
365code, or you are doing something legitimately wrong. Compiler warnings can
366cover up legitimate errors in output and make dealing with a translation unit
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]367difficult.</p>
368
369<p>It is not possible to prevent all warnings from all compilers, nor is it
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]370desirable. Instead, pick a standard compiler (like <tt>gcc</tt>) that provides
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]371a good thorough set of warnings, and stick to it. At least in the case of
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]372<tt>gcc</tt>, it is possible to work around any spurious errors by changing the
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]373syntax of the code slightly. For example, a warning that annoys me occurs when
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]374I write code like this:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]375
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]376<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]377<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]378if (V = getValue()) {
379 ...
380}
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]381</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]382</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]383
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]384<p><tt>gcc</tt> will warn me that I probably want to use the <tt>==</tt>
385operator, and that I probably mistyped it. In most cases, I haven't, and I
386really don't want the spurious errors. To fix this particular problem, I
387rewrite the code like this:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]388
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]389<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]390<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]391if ((V = getValue())) {
392 ...
393}
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]394</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]395</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]396
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]397<p>which shuts <tt>gcc</tt> up. Any <tt>gcc</tt> warning that annoys you can
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]398be fixed by massaging the code appropriately.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]399
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]400<p>These are the <tt>gcc</tt> warnings that I prefer to enable:</p>
401
402<div class="doc_code">
403<pre>
404-Wall -Winline -W -Wwrite-strings -Wno-unused
405</pre>
406</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]407
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]408</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]409
410<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]411<h4>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]412 <a name="ci_portable_code">Write Portable Code</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]413</h4>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]414
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]415<div>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]416
417<p>In almost all cases, it is possible and within reason to write completely
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]418portable code. If there are cases where it isn't possible to write portable
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]419code, isolate it behind a well defined (and well documented) interface.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]420
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]421<p>In practice, this means that you shouldn't assume much about the host
Chris Lattner44c22412010-11-16 22:19:06 +0000[diff] [blame]422compiler, and Visual Studio tends to be the lowest common denominator.
423If advanced features are used, they should only be an implementation detail of
424a library which has a simple exposed API, and preferably be buried in
425libSystem.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]426
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]427</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]428
Reid Spencerbf6439f2004-09-23 16:03:48 +0000[diff] [blame]429<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]430<h4>
Chris Lattner9db8e152010-11-30 19:20:40 +0000[diff] [blame]431<a name="ci_rtti_exceptions">Do not use RTTI or Exceptions</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]432</h4>
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]433<div>
Chris Lattner9db8e152010-11-30 19:20:40 +0000[diff] [blame]434
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]435<p>In an effort to reduce code and executable size, LLVM does not use RTTI
436(e.g. <tt>dynamic_cast&lt;&gt;</tt>) or exceptions. These two language features
437violate the general C++ principle of <i>"you only pay for what you use"</i>,
438causing executable bloat even if exceptions are never used in the code base, or
439if RTTI is never used for a class. Because of this, we turn them off globally
440in the code.</p>
Chris Lattner9db8e152010-11-30 19:20:40 +0000[diff] [blame]441
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]442<p>That said, LLVM does make extensive use of a hand-rolled form of RTTI that
443use templates like <a href="ProgrammersManual.html#isa"><tt>isa&lt;&gt;</tt>,
444<tt>cast&lt;&gt;</tt>, and <tt>dyn_cast&lt;&gt;</tt></a>. This form of RTTI is
445opt-in and can be added to any class. It is also substantially more efficient
446than <tt>dynamic_cast&lt;&gt;</tt>.</p>
Chris Lattner9db8e152010-11-30 19:20:40 +0000[diff] [blame]447
448</div>
449
450<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]451<h4>
Reid Spencerbf6439f2004-09-23 16:03:48 +0000[diff] [blame]452<a name="ci_class_struct">Use of <tt>class</tt> and <tt>struct</tt> Keywords</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]453</h4>
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]454<div>
Misha Brukmanf2499132004-10-26 15:45:13 +0000[diff] [blame]455
456<p>In C++, the <tt>class</tt> and <tt>struct</tt> keywords can be used almost
457interchangeably. The only difference is when they are used to declare a class:
458<tt>class</tt> makes all members private by default while <tt>struct</tt> makes
459all members public by default.</p>
460
461<p>Unfortunately, not all compilers follow the rules and some will generate
462different symbols based on whether <tt>class</tt> or <tt>struct</tt> was used to
463declare the symbol. This can lead to problems at link time.</p>
464
465<p>So, the rule for LLVM is to always use the <tt>class</tt> keyword, unless
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]466<b>all</b> members are public and the type is a C++
467<a href="http://en.wikipedia.org/wiki/Plain_old_data_structure">POD</a> type, in
468which case <tt>struct</tt> is allowed.</p>
Misha Brukmanf2499132004-10-26 15:45:13 +0000[diff] [blame]469
Reid Spencerbf6439f2004-09-23 16:03:48 +0000[diff] [blame]470</div>
471
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]472</div>
473
474</div>
475
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]476<!-- *********************************************************************** -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]477<h2>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]478 <a name="styleissues">Style Issues</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]479</h2>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]480<!-- *********************************************************************** -->
481
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]482<div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]483
484<!-- ======================================================================= -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]485<h3>
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]486 <a name="macro">The High-Level Issues</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]487</h3>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]488<!-- ======================================================================= -->
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]489
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]490<div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]491
492<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]493<h4>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]494 <a name="hl_module">A Public Header File <b>is</b> a Module</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]495</h4>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]496
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]497<div>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]498
499<p>C++ doesn't do too well in the modularity department. There is no real
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]500encapsulation or data hiding (unless you use expensive protocol classes), but it
501is what we have to work with. When you write a public header file (in the LLVM
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]502source tree, they live in the top level "<tt>include</tt>" directory), you are
503defining a module of functionality.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]504
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]505<p>Ideally, modules should be completely independent of each other, and their
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]506header files should only <tt>#include</tt> the absolute minimum number of
507headers possible. A module is not just a class, a function, or a
508namespace: <a href="http://www.cuj.com/articles/2000/0002/0002c/0002c.htm">it's
509a collection of these</a> that defines an interface. This interface may be
510several functions, classes, or data structures, but the important issue is how
511they work together.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]512
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]513<p>In general, a module should be implemented by one or more <tt>.cpp</tt>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]514files. Each of these <tt>.cpp</tt> files should include the header that defines
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]515their interface first. This ensures that all of the dependences of the module
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]516header have been properly added to the module header itself, and are not
517implicit. System headers should be included after user headers for a
518translation unit.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]519
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]520</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]521
522<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]523<h4>
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]524 <a name="hl_dontinclude"><tt>#include</tt> as Little as Possible</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]525</h4>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]526
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]527<div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]528
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]529<p><tt>#include</tt> hurts compile time performance. Don't do it unless you
530have to, especially in header files.</p>
531
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]532<p>But wait! Sometimes you need to have the definition of a class to use it, or
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]533to inherit from it. In these cases go ahead and <tt>#include</tt> that header
534file. Be aware however that there are many cases where you don't need to have
535the full definition of a class. If you are using a pointer or reference to a
536class, you don't need the header file. If you are simply returning a class
537instance from a prototyped function or method, you don't need it. In fact, for
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]538most cases, you simply don't need the definition of a class. And not
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]539<tt>#include</tt>'ing speeds up compilation.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]540
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]541<p>It is easy to try to go too overboard on this recommendation, however. You
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]542<b>must</b> include all of the header files that you are using &mdash; you can
543include them either directly or indirectly (through another header file). To
544make sure that you don't accidentally forget to include a header file in your
545module header, make sure to include your module header <b>first</b> in the
546implementation file (as mentioned above). This way there won't be any hidden
547dependencies that you'll find out about later.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]548
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]549</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]550
551<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]552<h4>
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]553 <a name="hl_privateheaders">Keep "Internal" Headers Private</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]554</h4>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]555
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]556<div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]557
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]558<p>Many modules have a complex implementation that causes them to use more than
559one implementation (<tt>.cpp</tt>) file. It is often tempting to put the
560internal communication interface (helper classes, extra functions, etc) in the
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]561public module header file. Don't do this!</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]562
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]563<p>If you really need to do something like this, put a private header file in
564the same directory as the source files, and include it locally. This ensures
565that your private interface remains private and undisturbed by outsiders.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]566
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]567<p>Note however, that it's okay to put extra implementation methods in a public
568class itself. Just make them private (or protected) and all is well.</p>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]569
570</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]571
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]572<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]573<h4>
Zhanyong Wan19b96fd2010-11-23 05:03:07 +0000[diff] [blame]574 <a name="hl_earlyexit">Use Early Exits and <tt>continue</tt> to Simplify Code</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]575</h4>
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]576
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]577<div>
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]578
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]579<p>When reading code, keep in mind how much state and how many previous
580decisions have to be remembered by the reader to understand a block of code.
581Aim to reduce indentation where possible when it doesn't make it more difficult
582to understand the code. One great way to do this is by making use of early
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]583exits and the <tt>continue</tt> keyword in long loops. As an example of using
584an early exit from a function, consider this "bad" code:</p>
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]585
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]586<div class="doc_code">
587<pre>
588Value *DoSomething(Instruction *I) {
589 if (!isa&lt;TerminatorInst&gt;(I) &amp;&amp;
590 I-&gt;hasOneUse() &amp;&amp; SomeOtherThing(I)) {
591 ... some long code ....
592 }
593
594 return 0;
595}
596</pre>
597</div>
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]598
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]599<p>This code has several problems if the body of the '<tt>if</tt>' is large.
600When you're looking at the top of the function, it isn't immediately clear that
601this <em>only</em> does interesting things with non-terminator instructions, and
602only applies to things with the other predicates. Second, it is relatively
603difficult to describe (in comments) why these predicates are important because
604the <tt>if</tt> statement makes it difficult to lay out the comments. Third,
605when you're deep within the body of the code, it is indented an extra level.
606Finally, when reading the top of the function, it isn't clear what the result is
607if the predicate isn't true; you have to read to the end of the function to know
608that it returns null.</p>
Matthijs Kooijmanca4ffaa2008-07-30 12:14:10 +0000[diff] [blame]609
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]610<p>It is much preferred to format the code like this:</p>
611
612<div class="doc_code">
613<pre>
614Value *DoSomething(Instruction *I) {
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]615 // Terminators never need 'something' done to them because ...
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]616 if (isa&lt;TerminatorInst&gt;(I))
617 return 0;
618
619 // We conservatively avoid transforming instructions with multiple uses
620 // because goats like cheese.
621 if (!I-&gt;hasOneUse())
622 return 0;
623
624 // This is really just here for example.
625 if (!SomeOtherThing(I))
626 return 0;
627
628 ... some long code ....
629}
630</pre>
631</div>
632
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]633<p>This fixes these problems. A similar problem frequently happens in <tt>for</tt>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]634loops. A silly example is something like this:</p>
635
636<div class="doc_code">
637<pre>
638 for (BasicBlock::iterator II = BB-&gt;begin(), E = BB-&gt;end(); II != E; ++II) {
639 if (BinaryOperator *BO = dyn_cast&lt;BinaryOperator&gt;(II)) {
640 Value *LHS = BO-&gt;getOperand(0);
641 Value *RHS = BO-&gt;getOperand(1);
642 if (LHS != RHS) {
643 ...
644 }
645 }
646 }
647</pre>
648</div>
649
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]650<p>When you have very, very small loops, this sort of structure is fine. But if
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]651it exceeds more than 10-15 lines, it becomes difficult for people to read and
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]652understand at a glance. The problem with this sort of code is that it gets very
653nested very quickly. Meaning that the reader of the code has to keep a lot of
654context in their brain to remember what is going immediately on in the loop,
655because they don't know if/when the <tt>if</tt> conditions will have elses etc.
656It is strongly preferred to structure the loop like this:</p>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]657
658<div class="doc_code">
659<pre>
660 for (BasicBlock::iterator II = BB-&gt;begin(), E = BB-&gt;end(); II != E; ++II) {
661 BinaryOperator *BO = dyn_cast&lt;BinaryOperator&gt;(II);
662 if (!BO) continue;
663
664 Value *LHS = BO-&gt;getOperand(0);
665 Value *RHS = BO-&gt;getOperand(1);
666 if (LHS == RHS) continue;
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]667
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]668 ...
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]669 }
670</pre>
671</div>
672
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]673<p>This has all the benefits of using early exits for functions: it reduces
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]674nesting of the loop, it makes it easier to describe why the conditions are true,
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]675and it makes it obvious to the reader that there is no <tt>else</tt> coming up
676that they have to push context into their brain for. If a loop is large, this
677can be a big understandability win.</p>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]678
679</div>
680
Chris Lattner14abb832009-07-28 22:54:04 +0000[diff] [blame]681<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]682<h4>
Zhanyong Wan19b96fd2010-11-23 05:03:07 +0000[diff] [blame]683 <a name="hl_else_after_return">Don't use <tt>else</tt> after a <tt>return</tt></a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]684</h4>
Chris Lattner14abb832009-07-28 22:54:04 +0000[diff] [blame]685
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]686<div>
Chris Lattner14abb832009-07-28 22:54:04 +0000[diff] [blame]687
688<p>For similar reasons above (reduction of indentation and easier reading),
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]689please do not use '<tt>else</tt>' or '<tt>else if</tt>' after something that
690interrupts control flow &mdash; like <tt>return</tt>, <tt>break</tt>,
691<tt>continue</tt>, <tt>goto</tt>, etc. For example, this is <em>bad</em>:</p>
692
Chris Lattner14abb832009-07-28 22:54:04 +0000[diff] [blame]693<div class="doc_code">
694<pre>
695 case 'J': {
696 if (Signed) {
697 Type = Context.getsigjmp_bufType();
698 if (Type.isNull()) {
699 Error = ASTContext::GE_Missing_sigjmp_buf;
700 return QualType();
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]701 <b>} else {
Chris Lattner14abb832009-07-28 22:54:04 +0000[diff] [blame]702 break;
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]703 }</b>
Chris Lattner14abb832009-07-28 22:54:04 +0000[diff] [blame]704 } else {
705 Type = Context.getjmp_bufType();
706 if (Type.isNull()) {
707 Error = ASTContext::GE_Missing_jmp_buf;
708 return QualType();
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]709 <b>} else {
Chris Lattner14abb832009-07-28 22:54:04 +0000[diff] [blame]710 break;
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]711 }</b>
Chris Lattner14abb832009-07-28 22:54:04 +0000[diff] [blame]712 }
713 }
714 }
715</pre>
716</div>
717
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]718<p>It is better to write it like this:</p>
Chris Lattner14abb832009-07-28 22:54:04 +0000[diff] [blame]719
720<div class="doc_code">
721<pre>
722 case 'J':
723 if (Signed) {
724 Type = Context.getsigjmp_bufType();
725 if (Type.isNull()) {
726 Error = ASTContext::GE_Missing_sigjmp_buf;
727 return QualType();
728 }
729 } else {
730 Type = Context.getjmp_bufType();
731 if (Type.isNull()) {
732 Error = ASTContext::GE_Missing_jmp_buf;
733 return QualType();
734 }
735 }
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]736 <b>break;</b>
Chris Lattner14abb832009-07-28 22:54:04 +0000[diff] [blame]737</pre>
738</div>
739
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]740<p>Or better yet (in this case) as:</p>
Chris Lattner14abb832009-07-28 22:54:04 +0000[diff] [blame]741
742<div class="doc_code">
743<pre>
744 case 'J':
745 if (Signed)
746 Type = Context.getsigjmp_bufType();
747 else
748 Type = Context.getjmp_bufType();
749
750 if (Type.isNull()) {
751 Error = Signed ? ASTContext::GE_Missing_sigjmp_buf :
752 ASTContext::GE_Missing_jmp_buf;
753 return QualType();
754 }
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]755 <b>break;</b>
Chris Lattner14abb832009-07-28 22:54:04 +0000[diff] [blame]756</pre>
757</div>
758
759<p>The idea is to reduce indentation and the amount of code you have to keep
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]760track of when reading the code.</p>
Chris Lattner14abb832009-07-28 22:54:04 +0000[diff] [blame]761
762</div>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]763
764<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]765<h4>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]766 <a name="hl_predicateloops">Turn Predicate Loops into Predicate Functions</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]767</h4>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]768
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]769<div>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]770
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]771<p>It is very common to write small loops that just compute a boolean value.
772There are a number of ways that people commonly write these, but an example of
773this sort of thing is:</p>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]774
775<div class="doc_code">
776<pre>
777 <b>bool FoundFoo = false;</b>
778 for (unsigned i = 0, e = BarList.size(); i != e; ++i)
779 if (BarList[i]-&gt;isFoo()) {
780 <b>FoundFoo = true;</b>
781 break;
782 }
783
784 <b>if (FoundFoo) {</b>
785 ...
786 }
787</pre>
788</div>
789
790<p>This sort of code is awkward to write, and is almost always a bad sign.
791Instead of this sort of loop, we strongly prefer to use a predicate function
792(which may be <a href="#micro_anonns">static</a>) that uses
Chris Lattnerd63f12372009-07-22 16:54:14 +0000[diff] [blame]793<a href="#hl_earlyexit">early exits</a> to compute the predicate. We prefer
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]794the code to be structured like this:</p>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]795
796<div class="doc_code">
797<pre>
798/// ListContainsFoo - Return true if the specified list has an element that is
799/// a foo.
800static bool ListContainsFoo(const std::vector&lt;Bar*&gt; &amp;List) {
801 for (unsigned i = 0, e = List.size(); i != e; ++i)
802 if (List[i]-&gt;isFoo())
803 return true;
804 return false;
805}
806...
807
808 <b>if (ListContainsFoo(BarList)) {</b>
809 ...
810 }
811</pre>
812</div>
813
814<p>There are many reasons for doing this: it reduces indentation and factors out
815code which can often be shared by other code that checks for the same predicate.
816More importantly, it <em>forces you to pick a name</em> for the function, and
817forces you to write a comment for it. In this silly example, this doesn't add
818much value. However, if the condition is complex, this can make it a lot easier
819for the reader to understand the code that queries for this predicate. Instead
Chris Lattner611a1882009-07-22 16:30:39 +0000[diff] [blame]820of being faced with the in-line details of how we check to see if the BarList
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]821contains a foo, we can trust the function name and continue reading with better
822locality.</p>
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]823
824</div>
825
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]826</div>
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]827
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]828<!-- ======================================================================= -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]829<h3>
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]830 <a name="micro">The Low-Level Issues</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]831</h3>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]832<!-- ======================================================================= -->
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]833
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]834<div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]835
836<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]837<h4>
838 <a name="ll_naming">
839 Name Types, Functions, Variables, and Enumerators Properly
840 </a>
841</h4>
Zhanyong Wan4f3b26d2010-12-02 05:10:07 +0000[diff] [blame]842
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]843<div>
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]844
845<p>Poorly-chosen names can mislead the reader and cause bugs. We cannot stress
846enough how important it is to use <em>descriptive</em> names. Pick names that
847match the semantics and role of the underlying entities, within reason. Avoid
848abbreviations unless they are well known. After picking a good name, make sure
849to use consistent capitalization for the name, as inconsistency requires clients
850to either memorize the APIs or to look it up to find the exact spelling.</p>
Zhanyong Wan4f3b26d2010-12-02 05:10:07 +0000[diff] [blame]851
Chris Lattner77c8cc82010-12-10 00:52:35 +0000[diff] [blame]852<p>In general, names should be in camel case (e.g. <tt>TextFileReader</tt>
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]853and <tt>isLValue()</tt>). Different kinds of declarations have different
854rules:</p>
Zhanyong Wan4f3b26d2010-12-02 05:10:07 +0000[diff] [blame]855
Chris Lattner77c8cc82010-12-10 00:52:35 +0000[diff] [blame]856<ul>
Chris Lattner02093e12010-12-10 00:54:03 +0000[diff] [blame]857<li><p><b>Type names</b> (including classes, structs, enums, typedefs, etc)
Chris Lattner30e697e2011-08-12 19:49:16 +0000[diff] [blame]858 should be nouns and start with an upper-case letter (e.g.
859 <tt>TextFileReader</tt>).</p></li>
860
861<li><p><b>Variable names</b> should be nouns (as they represent state). The
862 name should be camel case, and start with an upper case letter (e.g.
863 <tt>Leader</tt> or <tt>Boats</tt>).</p></li>
Chris Lattner77c8cc82010-12-10 00:52:35 +0000[diff] [blame]864
Chris Lattner02093e12010-12-10 00:54:03 +0000[diff] [blame]865<li><p><b>Function names</b> should be verb phrases (as they represent
Chris Lattner77c8cc82010-12-10 00:52:35 +0000[diff] [blame]866 actions), and command-like function should be imperative. The name should
867 be camel case, and start with a lower case letter (e.g. <tt>openFile()</tt>
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]868 or <tt>isFoo()</tt>).</p></li>
Chris Lattner77c8cc82010-12-10 00:52:35 +0000[diff] [blame]869
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]870<li><p><b>Enum declarations</b> (e.g. <tt>enum Foo {...}</tt>) are types, so
871 they should follow the naming conventions for types. A common use for enums
872 is as a discriminator for a union, or an indicator of a subclass. When an
873 enum is used for something like this, it should have a <tt>Kind</tt> suffix
874 (e.g. <tt>ValueKind</tt>).</p></li>
Chris Lattner77c8cc82010-12-10 00:52:35 +0000[diff] [blame]875
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]876<li><p><b>Enumerators</b> (e.g. <tt>enum { Foo, Bar }</tt>) and <b>public member
877 variables</b> should start with an upper-case letter, just like types.
878 Unless the enumerators are defined in their own small namespace or inside a
879 class, enumerators should have a prefix corresponding to the enum
880 declaration name. For example, <tt>enum ValueKind { ... };</tt> may contain
881 enumerators like <tt>VK_Argument</tt>, <tt>VK_BasicBlock</tt>, etc.
882 Enumerators that are just convenience constants are exempt from the
883 requirement for a prefix. For instance:</p>
884
Zhanyong Wan4f3b26d2010-12-02 05:10:07 +0000[diff] [blame]885<div class="doc_code">
886<pre>
887enum {
888 MaxSize = 42,
889 Density = 12
890};
891</pre>
892</div>
Chris Lattner77c8cc82010-12-10 00:52:35 +0000[diff] [blame]893</li>
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]894
Chris Lattner77c8cc82010-12-10 00:52:35 +0000[diff] [blame]895</ul>
896
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]897<p>As an exception, classes that mimic STL classes can have member names in
898STL's style of lower-case words separated by underscores (e.g. <tt>begin()</tt>,
899<tt>push_back()</tt>, and <tt>empty()</tt>).</p>
Chris Lattner77c8cc82010-12-10 00:52:35 +0000[diff] [blame]900
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]901<p>Here are some examples of good and bad names:</p>
Zhanyong Wan4f3b26d2010-12-02 05:10:07 +0000[diff] [blame]902
Zhanyong Wan4f3b26d2010-12-02 05:10:07 +0000[diff] [blame]903<div class="doc_code">
904<pre>
905class VehicleMaker {
906 ...
Chris Lattner77c8cc82010-12-10 00:52:35 +0000[diff] [blame]907 Factory&lt;Tire&gt; F; // Bad -- abbreviation and non-descriptive.
908 Factory&lt;Tire&gt; Factory; // Better.
909 Factory&lt;Tire&gt; TireFactory; // Even better -- if VehicleMaker has more than one
Zhanyong Wan4f3b26d2010-12-02 05:10:07 +0000[diff] [blame]910 // kind of factories.
911};
912
913Vehicle MakeVehicle(VehicleType Type) {
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]914 VehicleMaker M; // Might be OK if having a short life-span.
915 Tire tmp1 = M.makeTire(); // Bad -- 'tmp1' provides no information.
Chris Lattner77c8cc82010-12-10 00:52:35 +0000[diff] [blame]916 Light headlight = M.makeLight("head"); // Good -- descriptive.
Zhanyong Wan4f3b26d2010-12-02 05:10:07 +0000[diff] [blame]917 ...
918}
919</pre>
920</div>
921
922</div>
923
924
925<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]926<h4>
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]927 <a name="ll_assert">Assert Liberally</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]928</h4>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]929
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]930<div>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]931
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]932<p>Use the "<tt>assert</tt>" macro to its fullest. Check all of your
Benjamin Kramer0f420382009-10-12 14:46:08 +0000[diff] [blame]933preconditions and assumptions, you never know when a bug (not necessarily even
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]934yours) might be caught early by an assertion, which reduces debugging time
935dramatically. The "<tt>&lt;cassert&gt;</tt>" header file is probably already
936included by the header files you are using, so it doesn't cost anything to use
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]937it.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]938
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]939<p>To further assist with debugging, make sure to put some kind of error message
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]940in the assertion statement, which is printed if the assertion is tripped. This
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]941helps the poor debugger make sense of why an assertion is being made and
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]942enforced, and hopefully what to do about it. Here is one complete example:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]943
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]944<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]945<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]946inline Value *getOperand(unsigned i) {
947 assert(i &lt; Operands.size() &amp;&amp; "getOperand() out of range!");
948 return Operands[i];
949}
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]950</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]951</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]952
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]953<p>Here are more examples:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]954
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]955<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]956<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]957assert(Ty-&gt;isPointerType() &amp;&amp; "Can't allocate a non pointer type!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]958
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]959assert((Opcode == Shl || Opcode == Shr) &amp;&amp; "ShiftInst Opcode invalid!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]960
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]961assert(idx &lt; getNumSuccessors() &amp;&amp; "Successor # out of range!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]962
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]963assert(V1.getType() == V2.getType() &amp;&amp; "Constant types must be identical!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]964
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]965assert(isa&lt;PHINode&gt;(Succ-&gt;front()) &amp;&amp; "Only works on PHId BBs!");
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]966</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]967</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]968
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]969<p>You get the idea.</p>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]970
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]971<p>Please be aware that, when adding assert statements, not all compilers are aware of
Nick Lewyckyfb75d422008-05-31 23:54:55 +0000[diff] [blame]972the semantics of the assert. In some places, asserts are used to indicate a piece of
973code that should not be reached. These are typically of the form:</p>
974
975<div class="doc_code">
976<pre>
Dan Gohman8ef44982008-11-24 17:18:39 +0000[diff] [blame]977assert(0 &amp;&amp; "Some helpful error message");
Nick Lewyckyfb75d422008-05-31 23:54:55 +0000[diff] [blame]978</pre>
979</div>
980
981<p>When used in a function that returns a value, they should be followed with a return
982statement and a comment indicating that this line is never reached. This will prevent
983a compiler which is unable to deduce that the assert statement never returns from
984generating a warning.</p>
985
986<div class="doc_code">
987<pre>
Dan Gohman8ef44982008-11-24 17:18:39 +0000[diff] [blame]988assert(0 &amp;&amp; "Some helpful error message");
Nick Lewyckyfb75d422008-05-31 23:54:55 +0000[diff] [blame]989// Not reached
990return 0;
991</pre>
992</div>
993
Chris Lattner8a7f4da2010-11-12 00:19:41 +0000[diff] [blame]994<p>Another issue is that values used only by assertions will produce an "unused
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]995value" warning when assertions are disabled. For example, this code will
996warn:</p>
Chris Lattner8a7f4da2010-11-12 00:19:41 +0000[diff] [blame]997
998<div class="doc_code">
999<pre>
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1000unsigned Size = V.size();
1001assert(Size &gt; 42 &amp;&amp; "Vector smaller than it should be");
Chris Lattner8a7f4da2010-11-12 00:19:41 +0000[diff] [blame]1002
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1003bool NewToSet = Myset.insert(Value);
1004assert(NewToSet &amp;&amp; "The value shouldn't be in the set yet");
Chris Lattner8a7f4da2010-11-12 00:19:41 +0000[diff] [blame]1005</pre>
1006</div>
1007
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1008<p>These are two interesting different cases. In the first case, the call to
Chris Lattner8a7f4da2010-11-12 00:19:41 +0000[diff] [blame]1009V.size() is only useful for the assert, and we don't want it executed when
1010assertions are disabled. Code like this should move the call into the assert
1011itself. In the second case, the side effects of the call must happen whether
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1012the assert is enabled or not. In this case, the value should be cast to void to
1013disable the warning. To be specific, it is preferred to write the code like
1014this:</p>
Chris Lattner8a7f4da2010-11-12 00:19:41 +0000[diff] [blame]1015
1016<div class="doc_code">
1017<pre>
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1018assert(V.size() &gt; 42 &amp;&amp; "Vector smaller than it should be");
Chris Lattner8a7f4da2010-11-12 00:19:41 +0000[diff] [blame]1019
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1020bool NewToSet = Myset.insert(Value); (void)NewToSet;
1021assert(NewToSet &amp;&amp; "The value shouldn't be in the set yet");
Chris Lattner8a7f4da2010-11-12 00:19:41 +0000[diff] [blame]1022</pre>
1023</div>
1024
1025
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1026</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1027
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]1028<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1029<h4>
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1030 <a name="ll_ns_std">Do Not Use '<tt>using namespace std</tt>'</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1031</h4>
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]1032
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]1033<div>
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1034
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]1035<p>In LLVM, we prefer to explicitly prefix all identifiers from the standard
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]1036namespace with an "<tt>std::</tt>" prefix, rather than rely on
1037"<tt>using namespace std;</tt>".</p>
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]1038
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]1039<p> In header files, adding a '<tt>using namespace XXX</tt>' directive pollutes
Misha Brukman586a15c2008-12-11 19:37:04 +0000[diff] [blame]1040the namespace of any source file that <tt>#include</tt>s the header. This is
1041clearly a bad thing.</p>
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]1042
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]1043<p>In implementation files (e.g. <tt>.cpp</tt> files), the rule is more of a stylistic
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]1044rule, but is still important. Basically, using explicit namespace prefixes
1045makes the code <b>clearer</b>, because it is immediately obvious what facilities
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1046are being used and where they are coming from. And <b>more portable</b>, because
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]1047namespace clashes cannot occur between LLVM code and other namespaces. The
1048portability rule is important because different standard library implementations
1049expose different symbols (potentially ones they shouldn't), and future revisions
1050to the C++ standard will add more symbols to the <tt>std</tt> namespace. As
1051such, we never use '<tt>using namespace std;</tt>' in LLVM.</p>
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]1052
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]1053<p>The exception to the general rule (i.e. it's not an exception for
1054the <tt>std</tt> namespace) is for implementation files. For example, all of
1055the code in the LLVM project implements code that lives in the 'llvm' namespace.
Chris Lattnereebbbeb2010-11-17 19:47:20 +0000[diff] [blame]1056As such, it is ok, and actually clearer, for the <tt>.cpp</tt> files to have a
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1057'<tt>using namespace llvm;</tt>' directive at the top, after the
Chris Lattnereebbbeb2010-11-17 19:47:20 +0000[diff] [blame]1058<tt>#include</tt>s. This reduces indentation in the body of the file for source
1059editors that indent based on braces, and keeps the conceptual context cleaner.
1060The general form of this rule is that any <tt>.cpp</tt> file that implements
1061code in any namespace may use that namespace (and its parents'), but should not
1062use any others.</p>
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]1063
1064</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1065
1066<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1067<h4>
1068 <a name="ll_virtual_anch">
1069 Provide a Virtual Method Anchor for Classes in Headers
1070 </a>
1071</h4>
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]1072
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]1073<div>
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]1074
1075<p>If a class is defined in a header file and has a v-table (either it has
1076virtual methods or it derives from classes with virtual methods), it must
1077always have at least one out-of-line virtual method in the class. Without
Misha Brukman586a15c2008-12-11 19:37:04 +0000[diff] [blame]1078this, the compiler will copy the vtable and RTTI into every <tt>.o</tt> file
1079that <tt>#include</tt>s the header, bloating <tt>.o</tt> file sizes and
1080increasing link times.</p>
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]1081
1082</div>
1083
Chris Lattner56c10942009-06-30 06:13:23 +0000[diff] [blame]1084<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1085<h4>
Nick Lewycky9d0e8b62011-02-20 02:03:04 +0000[diff] [blame]1086 <a name="ll_end">Don't evaluate <tt>end()</tt> every time through a loop</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1087</h4>
Chris Lattner56c10942009-06-30 06:13:23 +0000[diff] [blame]1088
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]1089<div>
Chris Lattner56c10942009-06-30 06:13:23 +0000[diff] [blame]1090
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1091<p>Because C++ doesn't have a standard "<tt>foreach</tt>" loop (though it can be
1092emulated with macros and may be coming in C++'0x) we end up writing a lot of
1093loops that manually iterate from begin to end on a variety of containers or
1094through other data structures. One common mistake is to write a loop in this
1095style:</p>
Chris Lattner56c10942009-06-30 06:13:23 +0000[diff] [blame]1096
1097<div class="doc_code">
1098<pre>
1099 BasicBlock *BB = ...
1100 for (BasicBlock::iterator I = BB->begin(); I != <b>BB->end()</b>; ++I)
1101 ... use I ...
1102</pre>
1103</div>
1104
1105<p>The problem with this construct is that it evaluates "<tt>BB->end()</tt>"
1106every time through the loop. Instead of writing the loop like this, we strongly
1107prefer loops to be written so that they evaluate it once before the loop starts.
1108A convenient way to do this is like so:</p>
1109
1110<div class="doc_code">
1111<pre>
1112 BasicBlock *BB = ...
1113 for (BasicBlock::iterator I = BB->begin(), E = <b>BB->end()</b>; I != E; ++I)
1114 ... use I ...
1115</pre>
1116</div>
1117
1118<p>The observant may quickly point out that these two loops may have different
1119semantics: if the container (a basic block in this case) is being mutated, then
1120"<tt>BB->end()</tt>" may change its value every time through the loop and the
1121second loop may not in fact be correct. If you actually do depend on this
Chris Lattner6ad089c2009-06-30 06:20:03 +0000[diff] [blame]1122behavior, please write the loop in the first form and add a comment indicating
Chris Lattner56c10942009-06-30 06:13:23 +0000[diff] [blame]1123that you did it intentionally.</p>
1124
1125<p>Why do we prefer the second form (when correct)? Writing the loop in the
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1126first form has two problems. First it may be less efficient than evaluating it
1127at the start of the loop. In this case, the cost is probably minor &mdash; a
1128few extra loads every time through the loop. However, if the base expression is
1129more complex, then the cost can rise quickly. I've seen loops where the end
Chris Lattner56c10942009-06-30 06:13:23 +0000[diff] [blame]1130expression was actually something like: "<tt>SomeMap[x]->end()</tt>" and map
Chris Lattner67f2a4ac2009-06-30 06:27:54 +0000[diff] [blame]1131lookups really aren't cheap. By writing it in the second form consistently, you
Chris Lattner56c10942009-06-30 06:13:23 +0000[diff] [blame]1132eliminate the issue entirely and don't even have to think about it.</p>
1133
Chris Lattner6ad089c2009-06-30 06:20:03 +0000[diff] [blame]1134<p>The second (even bigger) issue is that writing the loop in the first form
Chris Lattner56c10942009-06-30 06:13:23 +0000[diff] [blame]1135hints to the reader that the loop is mutating the container (a fact that a
1136comment would handily confirm!). If you write the loop in the second form, it
1137is immediately obvious without even looking at the body of the loop that the
1138container isn't being modified, which makes it easier to read the code and
1139understand what it does.</p>
1140
1141<p>While the second form of the loop is a few extra keystrokes, we do strongly
1142prefer it.</p>
1143
1144</div>
1145
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]1146<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1147<h4>
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1148 <a name="ll_iostream"><tt>#include &lt;iostream&gt;</tt> is Forbidden</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1149</h4>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1150
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]1151<div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1152
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1153<p>The use of <tt>#include &lt;iostream&gt;</tt> in library files is
1154hereby <b><em>forbidden</em></b>. The primary reason for doing this is to
1155support clients using LLVM libraries as part of larger systems. In particular,
1156we statically link LLVM into some dynamic libraries. Even if LLVM isn't used,
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1157the static constructors are run whenever an application starts up that uses the
1158dynamic library. There are two problems with this:</p>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1159
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1160<ol>
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1161 <li>The time to run the static c'tors impacts startup time of applications
1162 &mdash; a critical time for GUI apps.</li>
1163
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1164 <li>The static c'tors cause the app to pull many extra pages of memory off the
1165 disk: both the code for the static c'tors in each <tt>.o</tt> file and the
1166 small amount of data that gets touched. In addition, touched/dirty pages
1167 put more pressure on the VM system on low-memory machines.</li>
1168</ol>
1169
1170<p>Note that using the other stream headers (<tt>&lt;sstream&gt;</tt> for
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1171example) is not problematic in this regard &mdash;
1172just <tt>&lt;iostream&gt;</tt>. However, <tt>raw_ostream</tt> provides various
1173APIs that are better performing for almost every use than <tt>std::ostream</tt>
1174style APIs. <b>Therefore new code should always
Chris Lattner5db2ff52009-08-23 21:53:47 +0000[diff] [blame]1175use <a href="#ll_raw_ostream"><tt>raw_ostream</tt></a> for writing, or
1176the <tt>llvm::MemoryBuffer</tt> API for reading files.</b></p>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1177
1178</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1179
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1180
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1181<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1182<h4>
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]1183 <a name="ll_raw_ostream">Use <tt>raw_ostream</tt></a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1184</h4>
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]1185
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]1186<div>
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]1187
1188<p>LLVM includes a lightweight, simple, and efficient stream implementation
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1189in <tt>llvm/Support/raw_ostream.h</tt>, which provides all of the common
1190features of <tt>std::ostream</tt>. All new code should use <tt>raw_ostream</tt>
1191instead of <tt>ostream</tt>.</p>
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]1192
1193<p>Unlike <tt>std::ostream</tt>, <tt>raw_ostream</tt> is not a template and can
1194be forward declared as <tt>class raw_ostream</tt>. Public headers should
1195generally not include the <tt>raw_ostream</tt> header, but use forward
1196declarations and constant references to <tt>raw_ostream</tt> instances.</p>
1197
1198</div>
1199
1200
1201<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1202<h4>
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]1203 <a name="ll_avoidendl">Avoid <tt>std::endl</tt></a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1204</h4>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]1205
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]1206<div>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1207
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1208<p>The <tt>std::endl</tt> modifier, when used with <tt>iostreams</tt> outputs a
1209newline to the output stream specified. In addition to doing this, however, it
1210also flushes the output stream. In other words, these are equivalent:</p>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]1211
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]1212<div class="doc_code">
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]1213<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]1214std::cout &lt;&lt; std::endl;
1215std::cout &lt;&lt; '\n' &lt;&lt; std::flush;
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]1216</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]1217</div>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]1218
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1219<p>Most of the time, you probably have no reason to flush the output stream, so
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]1220it's better to use a literal <tt>'\n'</tt>.</p>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]1221
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1222</div>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]1223
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]1224</div>
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]1225
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1226<!-- ======================================================================= -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1227<h3>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1228 <a name="nano">Microscopic Details</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1229</h3>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1230<!-- ======================================================================= -->
1231
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]1232<div>
1233
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1234<p>This section describes preferred low-level formatting guidelines along with
1235reasoning on why we prefer them.</p>
1236
1237<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1238<h4>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1239 <a name="micro_spaceparen">Spaces Before Parentheses</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1240</h4>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1241
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]1242<div>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1243
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]1244<p>We prefer to put a space before an open parenthesis only in control flow
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1245statements, but not in normal function call expressions and function-like
1246macros. For example, this is good:</p>
1247
1248<div class="doc_code">
1249<pre>
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1250<b>if (</b>x) ...
1251<b>for (</b>i = 0; i != 100; ++i) ...
1252<b>while (</b>llvm_rocks) ...
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1253
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1254<b>somefunc(</b>42);
1255<b><a href="#ll_assert">assert</a>(</b>3 != 4 &amp;&amp; "laws of math are failing me");
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1256
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1257a = <b>foo(</b>42, 92) + <b>bar(</b>x);
1258</pre>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1259</div>
1260
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1261<p>and this is bad:</p>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1262
1263<div class="doc_code">
1264<pre>
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1265<b>if(</b>x) ...
1266<b>for(</b>i = 0; i != 100; ++i) ...
1267<b>while(</b>llvm_rocks) ...
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1268
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1269<b>somefunc (</b>42);
1270<b><a href="#ll_assert">assert</a> (</b>3 != 4 &amp;&amp; "laws of math are failing me");
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1271
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1272a = <b>foo (</b>42, 92) + <b>bar (</b>x);
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1273</pre>
1274</div>
1275
1276<p>The reason for doing this is not completely arbitrary. This style makes
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1277control flow operators stand out more, and makes expressions flow better. The
1278function call operator binds very tightly as a postfix operator. Putting a
1279space after a function name (as in the last example) makes it appear that the
1280code might bind the arguments of the left-hand-side of a binary operator with
1281the argument list of a function and the name of the right side. More
1282specifically, it is easy to misread the "a" example as:</p>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1283
1284<div class="doc_code">
1285<pre>
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1286a = foo <b>(</b>(42, 92) + bar<b>)</b> (x);
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1287</pre>
1288</div>
1289
Bill Wendling510504a2010-12-21 03:31:05 +0000[diff] [blame]1290<p>when skimming through the code. By avoiding a space in a function, we avoid
1291this misinterpretation.</p>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1292
1293</div>
1294
1295<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1296<h4>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1297 <a name="micro_preincrement">Prefer Preincrement</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1298</h4>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1299
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]1300<div>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1301
1302<p>Hard fast rule: Preincrement (<tt>++X</tt>) may be no slower than
1303postincrement (<tt>X++</tt>) and could very well be a lot faster than it. Use
1304preincrementation whenever possible.</p>
1305
1306<p>The semantics of postincrement include making a copy of the value being
1307incremented, returning it, and then preincrementing the "work value". For
1308primitive types, this isn't a big deal... but for iterators, it can be a huge
1309issue (for example, some iterators contains stack and set objects in them...
1310copying an iterator could invoke the copy ctor's of these as well). In general,
1311get in the habit of always using preincrement, and you won't have a problem.</p>
1312
1313</div>
1314
1315<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1316<h4>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1317 <a name="micro_namespaceindent">Namespace Indentation</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1318</h4>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1319
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]1320<div>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1321
1322<p>
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]1323In general, we strive to reduce indentation wherever possible. This is useful
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1324because we want code to <a href="#scf_codewidth">fit into 80 columns</a> without
1325wrapping horribly, but also because it makes it easier to understand the code.
1326Namespaces are a funny thing: they are often large, and we often desire to put
1327lots of stuff into them (so they can be large). Other times they are tiny,
1328because they just hold an enum or something similar. In order to balance this,
1329we use different approaches for small versus large namespaces.
1330</p>
1331
1332<p>
1333If a namespace definition is small and <em>easily</em> fits on a screen (say,
1334less than 35 lines of code), then you should indent its body. Here's an
1335example:
1336</p>
1337
1338<div class="doc_code">
1339<pre>
Chris Lattnerd63f12372009-07-22 16:54:14 +0000[diff] [blame]1340namespace llvm {
1341 namespace X86 {
1342 /// RelocationType - An enum for the x86 relocation codes. Note that
1343 /// the terminology here doesn't follow x86 convention - word means
1344 /// 32-bit and dword means 64-bit.
1345 enum RelocationType {
1346 /// reloc_pcrel_word - PC relative relocation, add the relocated value to
1347 /// the value already in memory, after we adjust it for where the PC is.
1348 reloc_pcrel_word = 0,
1349
1350 /// reloc_picrel_word - PIC base relative relocation, add the relocated
1351 /// value to the value already in memory, after we adjust it for where the
1352 /// PIC base is.
1353 reloc_picrel_word = 1,
1354
1355 /// reloc_absolute_word, reloc_absolute_dword - Absolute relocation, just
1356 /// add the relocated value to the value already in memory.
1357 reloc_absolute_word = 2,
1358 reloc_absolute_dword = 3
1359 };
1360 }
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1361}
1362</pre>
1363</div>
1364
1365<p>Since the body is small, indenting adds value because it makes it very clear
1366where the namespace starts and ends, and it is easy to take the whole thing in
1367in one "gulp" when reading the code. If the blob of code in the namespace is
Chris Lattner8defde02010-11-17 17:14:55 +0000[diff] [blame]1368larger (as it typically is in a header in the <tt>llvm</tt> or <tt>clang</tt> namespaces), do not
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1369indent the code, and add a comment indicating what namespace is being closed.
1370For example:</p>
1371
1372<div class="doc_code">
1373<pre>
1374namespace llvm {
1375namespace knowledge {
1376
1377/// Grokable - This class represents things that Smith can have an intimate
1378/// understanding of and contains the data associated with it.
1379class Grokable {
1380...
1381public:
1382 explicit Grokable() { ... }
1383 virtual ~Grokable() = 0;
1384
1385 ...
1386
1387};
1388
1389} // end namespace knowledge
1390} // end namespace llvm
1391</pre>
1392</div>
1393
1394<p>Because the class is large, we don't expect that the reader can easily
1395understand the entire concept in a glance, and the end of the file (where the
1396namespaces end) may be a long ways away from the place they open. As such,
1397indenting the contents of the namespace doesn't add any value, and detracts from
1398the readability of the class. In these cases it is best to <em>not</em> indent
1399the contents of the namespace.</p>
1400
1401</div>
1402
1403<!-- _______________________________________________________________________ -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1404<h4>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1405 <a name="micro_anonns">Anonymous Namespaces</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1406</h4>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1407
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]1408<div>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1409
Chris Lattnerd63f12372009-07-22 16:54:14 +0000[diff] [blame]1410<p>After talking about namespaces in general, you may be wondering about
1411anonymous namespaces in particular.
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1412Anonymous namespaces are a great language feature that tells the C++ compiler
1413that the contents of the namespace are only visible within the current
1414translation unit, allowing more aggressive optimization and eliminating the
1415possibility of symbol name collisions. Anonymous namespaces are to C++ as
1416"static" is to C functions and global variables. While "static" is available
1417in C++, anonymous namespaces are more general: they can make entire classes
1418private to a file.</p>
1419
1420<p>The problem with anonymous namespaces is that they naturally want to
1421encourage indentation of their body, and they reduce locality of reference: if
1422you see a random function definition in a C++ file, it is easy to see if it is
1423marked static, but seeing if it is in an anonymous namespace requires scanning
1424a big chunk of the file.</p>
1425
1426<p>Because of this, we have a simple guideline: make anonymous namespaces as
1427small as possible, and only use them for class declarations. For example, this
1428is good:</p>
1429
1430<div class="doc_code">
1431<pre>
1432<b>namespace {</b>
1433 class StringSort {
1434 ...
1435 public:
1436 StringSort(...)
1437 bool operator&lt;(const char *RHS) const;
1438 };
1439<b>} // end anonymous namespace</b>
1440
1441static void Helper() {
1442 ...
1443}
1444
1445bool StringSort::operator&lt;(const char *RHS) const {
1446 ...
1447}
1448
1449</pre>
1450</div>
1451
1452<p>This is bad:</p>
1453
1454
1455<div class="doc_code">
1456<pre>
1457<b>namespace {</b>
1458class StringSort {
1459...
1460public:
1461 StringSort(...)
1462 bool operator&lt;(const char *RHS) const;
1463};
1464
1465void Helper() {
1466 ...
1467}
1468
1469bool StringSort::operator&lt;(const char *RHS) const {
1470 ...
1471}
1472
1473<b>} // end anonymous namespace</b>
1474
1475</pre>
1476</div>
1477
1478
1479<p>This is bad specifically because if you're looking at "Helper" in the middle
1480of a large C++ file, that you have no immediate way to tell if it is local to
1481the file. When it is marked static explicitly, this is immediately obvious.
1482Also, there is no reason to enclose the definition of "operator&lt;" in the
Chris Lattnerd63f12372009-07-22 16:54:14 +0000[diff] [blame]1483namespace just because it was declared there.
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1484</p>
1485
1486</div>
1487
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]1488</div>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1489
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]1490</div>
Chris Lattner6720d7e2009-07-22 05:40:54 +0000[diff] [blame]1491
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1492<!-- *********************************************************************** -->
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1493<h2>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1494 <a name="seealso">See Also</a>
NAKAMURA Takumifc8d9302011-04-18 23:59:50 +0000[diff] [blame]1495</h2>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1496<!-- *********************************************************************** -->
1497
NAKAMURA Takumiaa3d6242011-04-23 00:30:22 +0000[diff] [blame]1498<div>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1499
1500<p>A lot of these comments and recommendations have been culled for other
1501sources. Two particularly important books for our work are:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1502
1503<ol>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1504
Chris Lattnerf9f08bf2007-11-09 21:49:08 +0000[diff] [blame]1505<li><a href="http://www.amazon.com/Effective-Specific-Addison-Wesley-Professional-Computing/dp/0321334876">Effective
1506C++</a> by Scott Meyers. Also
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]1507interesting and useful are "More Effective C++" and "Effective STL" by the same
1508author.</li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1509
Chris Lattnerf9f08bf2007-11-09 21:49:08 +0000[diff] [blame]1510<li>Large-Scale C++ Software Design by John Lakos</li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1511
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1512</ol>
1513
1514<p>If you get some free time, and you haven't read them: do so, you might learn
Misha Brukman6d1686c2004-12-04 00:32:12 +0000[diff] [blame]1515something.</p>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1516
1517</div>
1518
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]1519<!-- *********************************************************************** -->
1520
1521<hr>
Misha Brukmand4f290a2004-05-12 18:37:22 +0000[diff] [blame]1522<address>
1523 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman86242e12008-12-11 17:34:48 +0000[diff] [blame]1524 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukmand4f290a2004-05-12 18:37:22 +0000[diff] [blame]1525 <a href="http://validator.w3.org/check/referer"><img
Misha Brukman86242e12008-12-11 17:34:48 +0000[diff] [blame]1526 src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1527
Misha Brukmand4f290a2004-05-12 18:37:22 +0000[diff] [blame]1528 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
NAKAMURA Takumica46f5a2011-04-09 02:13:37 +0000[diff] [blame]1529 <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1530 Last modified: $Date$
Misha Brukmand4f290a2004-05-12 18:37:22 +0000[diff] [blame]1531</address>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]1532
1533</body>
1534</html>