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Reid Spencer8d0ac692007-02-13 09:06:01 +00006 <title>LLVM Developer Policy</title>
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Reid Spencer8d0ac692007-02-13 09:06:01 +000010
NAKAMURA Takumi05d02652011-04-18 23:59:50 +000011<h1>LLVM Developer Policy</h1>
Reid Spencer8d0ac692007-02-13 09:06:01 +000012<ol>
Reid Spencer78bade22007-02-14 07:22:19 +000013 <li><a href="#introduction">Introduction</a></li>
Chris Lattner1ff20cd2007-02-19 06:05:58 +000014 <li><a href="#policies">Developer Policies</a>
Reid Spencer8d0ac692007-02-13 09:06:01 +000015 <ol>
Chris Lattner1653fec2007-02-19 05:57:29 +000016 <li><a href="#informed">Stay Informed</a></li>
17 <li><a href="#patches">Making a Patch</a></li>
Reid Spencer8d0ac692007-02-13 09:06:01 +000018 <li><a href="#reviews">Code Reviews</a></li>
Chris Lattnere268a402007-12-03 19:00:47 +000019 <li><a href="#owners">Code Owners</a></li>
Reid Spencer8d0ac692007-02-13 09:06:01 +000020 <li><a href="#testcases">Test Cases</a></li>
Chris Lattner1acdc952007-02-19 05:49:11 +000021 <li><a href="#quality">Quality</a></li>
22 <li><a href="#commitaccess">Obtaining Commit Access</a></li>
Chris Lattner1ff20cd2007-02-19 06:05:58 +000023 <li><a href="#newwork">Making a Major Change</a></li>
24 <li><a href="#incremental">Incremental Development</a></li>
Chris Lattnerc7d954e2007-02-19 05:43:04 +000025 <li><a href="#attribution">Attribution of Changes</a></li>
Reid Spencer8d0ac692007-02-13 09:06:01 +000026 </ol></li>
Chris Lattner793aa382007-02-19 06:19:16 +000027 <li><a href="#clp">Copyright, License, and Patents</a>
Reid Spencer78bade22007-02-14 07:22:19 +000028 <ol>
29 <li><a href="#copyright">Copyright</a></li>
30 <li><a href="#license">License</a></li>
Chris Lattner1ff20cd2007-02-19 06:05:58 +000031 <li><a href="#patents">Patents</a></li>
Reid Spencer78bade22007-02-14 07:22:19 +000032 </ol></li>
Reid Spencer8d0ac692007-02-13 09:06:01 +000033</ol>
Chris Lattner2ae49dd2007-02-19 06:24:23 +000034<div class="doc_author">Written by the LLVM Oversight Team</div>
Reid Spencer8d0ac692007-02-13 09:06:01 +000035
36<!--=========================================================================-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +000037<h2><a name="introduction">Introduction</a></h2>
Reid Spencer8d0ac692007-02-13 09:06:01 +000038<!--=========================================================================-->
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +000039<div>
Bill Wendling78c8fce2009-04-05 12:37:44 +000040<p>This document contains the LLVM Developer Policy which defines the project's
41 policy towards developers and their contributions. The intent of this policy
42 is to eliminate miscommunication, rework, and confusion that might arise from
43 the distributed nature of LLVM's development. By stating the policy in clear
44 terms, we hope each developer can know ahead of time what to expect when
Chris Lattnerb742ff02010-09-02 00:09:17 +000045 making LLVM contributions. This policy covers all llvm.org subprojects,
46 including Clang, LLDB, etc.</p>
Bill Wendling78c8fce2009-04-05 12:37:44 +000047<p>This policy is also designed to accomplish the following objectives:</p>
48
49<ol>
50 <li>Attract both users and developers to the LLVM project.</li>
51
52 <li>Make life as simple and easy for contributors as possible.</li>
53
54 <li>Keep the top of Subversion trees as stable as possible.</li>
55</ol>
Chris Lattnerc7d954e2007-02-19 05:43:04 +000056
Bill Wendling78c8fce2009-04-05 12:37:44 +000057<p>This policy is aimed at frequent contributors to LLVM. People interested in
58 contributing one-off patches can do so in an informal way by sending them to
59 the
60 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits
61 mailing list</a> and engaging another developer to see it through the
62 process.</p>
Reid Spencer8d0ac692007-02-13 09:06:01 +000063</div>
Reid Spencer8d0ac692007-02-13 09:06:01 +000064
65<!--=========================================================================-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +000066<h2><a name="policies">Developer Policies</a></h2>
Reid Spencer8d0ac692007-02-13 09:06:01 +000067<!--=========================================================================-->
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +000068<div>
Bill Wendling78c8fce2009-04-05 12:37:44 +000069<p>This section contains policies that pertain to frequent LLVM developers. We
70 always welcome <a href="#patches">one-off patches</a> from people who do not
71 routinely contribute to LLVM, but we expect more from frequent contributors
72 to keep the system as efficient as possible for everyone. Frequent LLVM
73 contributors are expected to meet the following requirements in order for
74 LLVM to maintain a high standard of quality.<p>
Reid Spencer8d0ac692007-02-13 09:06:01 +000075
76<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +000077<h3><a name="informed">Stay Informed</a></h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +000078<div>
Chris Lattnerb742ff02010-09-02 00:09:17 +000079<p>Developers should stay informed by reading at least the "dev" mailing list
80 for the projects you are interested in, such as
81 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a> for
82 LLVM, <a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">cfe-dev</a>
83 for Clang, or <a
84 href="http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev">lldb-dev</a>
85 for LLDB. If you are doing anything more than just casual work on LLVM, it
86 is suggested that you also subscribe to the "commits" mailing list for the
87 subproject you're interested in, such as
88 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>,
89 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits">cfe-commits</a>,
90 or <a href="http://lists.cs.uiuc.edu/mailman/listinfo/lldb-commits">lldb-commits</a>.
91 Reading the "commits" list and paying attention to changes being made by
92 others is a good way to see what other people are interested in and watching
93 the flow of the project as a whole.</p>
Bill Wendling78c8fce2009-04-05 12:37:44 +000094
95<p>We recommend that active developers register an email account with
96 <a href="http://llvm.org/bugs/">LLVM Bugzilla</a> and preferably subscribe to
97 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmbugs">llvm-bugs</a>
Chris Lattnerb742ff02010-09-02 00:09:17 +000098 email list to keep track of bugs and enhancements occurring in LLVM. We
99 really appreciate people who are proactive at catching incoming bugs in their
100 components and dealing with them promptly.</p>
Reid Spencer8d0ac692007-02-13 09:06:01 +0000101</div>
102
103<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000104<h3><a name="patches">Making a Patch</a></h3>
Chris Lattner1653fec2007-02-19 05:57:29 +0000105
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000106<div>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000107<p>When making a patch for review, the goal is to make it as easy for the
108 reviewer to read it as possible. As such, we recommend that you:</p>
Chris Lattner1653fec2007-02-19 05:57:29 +0000109
Bill Wendling78c8fce2009-04-05 12:37:44 +0000110<ol>
111 <li>Make your patch against the Subversion trunk, not a branch, and not an old
Chris Lattner9b96e802009-10-10 21:37:16 +0000112 version of LLVM. This makes it easy to apply the patch. For information
113 on how to check out SVN trunk, please see the <a
114 href="GettingStarted.html#checkout">Getting Started Guide</a>.</li>
Chris Lattner1653fec2007-02-19 05:57:29 +0000115
Bill Wendling78c8fce2009-04-05 12:37:44 +0000116 <li>Similarly, patches should be submitted soon after they are generated. Old
117 patches may not apply correctly if the underlying code changes between the
118 time the patch was created and the time it is applied.</li>
119
Dan Gohmanc1076ea2010-08-04 16:07:22 +0000120 <li>Patches should be made with <tt>svn diff</tt>, or similar. If you use
121 a different tool, make sure it uses the <tt>diff -u</tt> format and
122 that it doesn't contain clutter which makes it hard to read.</li>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000123
Dan Gohmanc1076ea2010-08-04 16:07:22 +0000124 <li>If you are modifying generated files, such as the top-level
125 <tt>configure</tt> script, please separate out those changes into
126 a separate patch from the rest of your changes.</li>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000127</ol>
Chris Lattner0cca50c2007-02-19 06:57:16 +0000128
Bill Wendling78c8fce2009-04-05 12:37:44 +0000129<p>When sending a patch to a mailing list, it is a good idea to send it as an
130 <em>attachment</em> to the message, not embedded into the text of the
131 message. This ensures that your mailer will not mangle the patch when it
132 sends it (e.g. by making whitespace changes or by wrapping lines).</p>
133
134<p><em>For Thunderbird users:</em> Before submitting a patch, please open
135 <em>Preferences &#8594; Advanced &#8594; General &#8594; Config Editor</em>,
136 find the key <tt>mail.content_disposition_type</tt>, and set its value to
137 <tt>1</tt>. Without this setting, Thunderbird sends your attachment using
138 <tt>Content-Disposition: inline</tt> rather than <tt>Content-Disposition:
139 attachment</tt>. Apple Mail gamely displays such a file inline, making it
140 difficult to work with for reviewers using that program.</p>
Chris Lattner1653fec2007-02-19 05:57:29 +0000141</div>
142
143<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000144<h3><a name="reviews">Code Reviews</a></h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000145<div>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000146<p>LLVM has a code review policy. Code review is one way to increase the quality
147 of software. We generally follow these policies:</p>
Chris Lattner0cca50c2007-02-19 06:57:16 +0000148
Bill Wendling78c8fce2009-04-05 12:37:44 +0000149<ol>
150 <li>All developers are required to have significant changes reviewed before
151 they are committed to the repository.</li>
152
153 <li>Code reviews are conducted by email, usually on the llvm-commits
154 list.</li>
155
156 <li>Code can be reviewed either before it is committed or after. We expect
157 major changes to be reviewed before being committed, but smaller changes
158 (or changes where the developer owns the component) can be reviewed after
159 commit.</li>
160
161 <li>The developer responsible for a code change is also responsible for making
162 all necessary review-related changes.</li>
163
164 <li>Code review can be an iterative process, which continues until the patch
165 is ready to be committed.</li>
166</ol>
167
168<p>Developers should participate in code reviews as both reviewers and
169 reviewees. If someone is kind enough to review your code, you should return
170 the favor for someone else. Note that anyone is welcome to review and give
171 feedback on a patch, but only people with Subversion write access can approve
172 it.</p>
Reid Spencer8d0ac692007-02-13 09:06:01 +0000173</div>
Reid Spencer8d0ac692007-02-13 09:06:01 +0000174
175<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000176<h3><a name="owners">Code Owners</a></h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000177<div>
Chris Lattnere268a402007-12-03 19:00:47 +0000178
Bill Wendling78c8fce2009-04-05 12:37:44 +0000179<p>The LLVM Project relies on two features of its process to maintain rapid
180 development in addition to the high quality of its source base: the
181 combination of code review plus post-commit review for trusted maintainers.
182 Having both is a great way for the project to take advantage of the fact that
183 most people do the right thing most of the time, and only commit patches
184 without pre-commit review when they are confident they are right.</p>
Chris Lattnere268a402007-12-03 19:00:47 +0000185
Bill Wendling78c8fce2009-04-05 12:37:44 +0000186<p>The trick to this is that the project has to guarantee that all patches that
187 are committed are reviewed after they go in: you don't want everyone to
188 assume someone else will review it, allowing the patch to go unreviewed. To
189 solve this problem, we have a notion of an 'owner' for a piece of the code.
190 The sole responsibility of a code owner is to ensure that a commit to their
191 area of the code is appropriately reviewed, either by themself or by someone
192 else. The current code owners are:</p>
Chris Lattnere268a402007-12-03 19:00:47 +0000193
Bill Wendling78c8fce2009-04-05 12:37:44 +0000194<ol>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000195 <li><b>Evan Cheng</b>: Code generator and all targets.</li>
196
Chris Lattner5ce89812010-09-23 17:27:54 +0000197 <li><b>Greg Clayton</b>: LLDB.</li>
198
199 <li><b>Doug Gregor</b>: Clang Frontend Libraries.</li>
200
201 <li><b>Howard Hinnant</b>: libc++.</li>
Chris Lattneraf5bd672009-09-16 05:36:07 +0000202
Chris Lattnerb2030432009-09-16 05:37:13 +0000203 <li><b>Anton Korobeynikov</b>: Exception handling, debug information, and
204 Windows codegen.</li>
205
Chris Lattnerf86a7782009-09-16 05:42:12 +0000206 <li><b>Ted Kremenek</b>: Clang Static Analyzer.</li>
207
Chris Lattner941f4cd2009-09-16 05:36:54 +0000208 <li><b>Chris Lattner</b>: Everything not covered by someone else.</li>
Chris Lattneraf5bd672009-09-16 05:36:07 +0000209
John McCall74699fd2011-08-02 01:38:19 +0000210 <li><b>John McCall</b>: Clang LLVM IR generation.</li>
211
Evan Chengb7676132011-10-07 17:26:38 +0000212 <li><b>Jakob Olesen</b>: Register allocators and TableGen.</li>
213
Chris Lattnerb0387f92011-09-23 22:46:43 +0000214 <li><b>Duncan Sands</b>: dragonegg and llvm-gcc 4.2.</li>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000215</ol>
Chris Lattnere268a402007-12-03 19:00:47 +0000216
Bill Wendling78c8fce2009-04-05 12:37:44 +0000217<p>Note that code ownership is completely different than reviewers: anyone can
218 review a piece of code, and we welcome code review from anyone who is
219 interested. Code owners are the "last line of defense" to guarantee that all
220 patches that are committed are actually reviewed.</p>
Chris Lattnere268a402007-12-03 19:00:47 +0000221
Bill Wendling78c8fce2009-04-05 12:37:44 +0000222<p>Being a code owner is a somewhat unglamorous position, but it is incredibly
223 important for the ongoing success of the project. Because people get busy,
224 interests change, and unexpected things happen, code ownership is purely
225 opt-in, and anyone can choose to resign their "title" at any time. For now,
226 we do not have an official policy on how one gets elected to be a code
227 owner.</p>
Chris Lattnere268a402007-12-03 19:00:47 +0000228</div>
229
Chris Lattnere268a402007-12-03 19:00:47 +0000230<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000231<h3><a name="testcases">Test Cases</a></h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000232<div>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000233<p>Developers are required to create test cases for any bugs fixed and any new
234 features added. Some tips for getting your testcase approved:</p>
235
236<ol>
237 <li>All feature and regression test cases are added to the
238 <tt>llvm/test</tt> directory. The appropriate sub-directory should be
239 selected (see the <a href="TestingGuide.html">Testing Guide</a> for
240 details).</li>
241
242 <li>Test cases should be written in <a href="LangRef.html">LLVM assembly
243 language</a> unless the feature or regression being tested requires
244 another language (e.g. the bug being fixed or feature being implemented is
245 in the llvm-gcc C++ front-end, in which case it must be written in
246 C++).</li>
247
248 <li>Test cases, especially for regressions, should be reduced as much as
249 possible, by <a href="Bugpoint.html">bugpoint</a> or manually. It is
250 unacceptable to place an entire failing program into <tt>llvm/test</tt> as
251 this creates a <i>time-to-test</i> burden on all developers. Please keep
252 them short.</li>
253</ol>
Chris Lattner0cca50c2007-02-19 06:57:16 +0000254
Chris Lattnerb742ff02010-09-02 00:09:17 +0000255<p>Note that llvm/test and clang/test are designed for regression and small
256 feature tests only. More extensive test cases (e.g., entire applications,
257 benchmarks, etc)
Bill Wendling78c8fce2009-04-05 12:37:44 +0000258 should be added to the <tt>llvm-test</tt> test suite. The llvm-test suite is
259 for coverage (correctness, performance, etc) testing, not feature or
260 regression testing.</p>
Reid Spencer8d0ac692007-02-13 09:06:01 +0000261</div>
262
Chris Lattner450f40a2007-02-19 03:50:31 +0000263<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000264<h3><a name="quality">Quality</a></h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000265<div>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000266<p>The minimum quality standards that any change must satisfy before being
267 committed to the main development branch are:</p>
268
269<ol>
270 <li>Code must adhere to the <a href="CodingStandards.html">LLVM Coding
271 Standards</a>.</li>
272
273 <li>Code must compile cleanly (no errors, no warnings) on at least one
274 platform.</li>
275
276 <li>Bug fixes and new features should <a href="#testcases">include a
277 testcase</a> so we know if the fix/feature ever regresses in the
278 future.</li>
279
Chris Lattnerb742ff02010-09-02 00:09:17 +0000280 <li>Code must pass the <tt>llvm/test</tt> test suite.</li>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000281
282 <li>The code must not cause regressions on a reasonable subset of llvm-test,
283 where "reasonable" depends on the contributor's judgement and the scope of
284 the change (more invasive changes require more testing). A reasonable
285 subset might be something like
286 "<tt>llvm-test/MultiSource/Benchmarks</tt>".</li>
287</ol>
288
289<p>Additionally, the committer is responsible for addressing any problems found
290 in the future that the change is responsible for. For example:</p>
291
292<ul>
293 <li>The code should compile cleanly on all supported platforms.</li>
294
295 <li>The changes should not cause any correctness regressions in the
296 <tt>llvm-test</tt> suite and must not cause any major performance
297 regressions.</li>
298
299 <li>The change set should not cause performance or correctness regressions for
300 the LLVM tools.</li>
301
302 <li>The changes should not cause performance or correctness regressions in
303 code compiled by LLVM on all applicable targets.</li>
304
305 <li>You are expected to address any <a href="http://llvm.org/bugs/">bugzilla
306 bugs</a> that result from your change.</li>
307</ul>
Chris Lattner39582bd2007-02-19 05:47:13 +0000308
Bill Wendling78c8fce2009-04-05 12:37:44 +0000309<p>We prefer for this to be handled before submission but understand that it
Chris Lattnerd7f10d32009-08-01 19:25:25 +0000310 isn't possible to test all of this for every submission. Our build bots and
311 nightly testing infrastructure normally finds these problems. A good rule of
312 thumb is to check the nightly testers for regressions the day after your
313 change. Build bots will directly email you if a group of commits that
314 included yours caused a failure. You are expected to check the build bot
315 messages to see if they are your fault and, if so, fix the breakage.</p>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000316
317<p>Commits that violate these quality standards (e.g. are very broken) may be
318 reverted. This is necessary when the change blocks other developers from
319 making progress. The developer is welcome to re-commit the change after the
320 problem has been fixed.</p>
Chris Lattner39582bd2007-02-19 05:47:13 +0000321</div>
322
323<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000324<h3><a name="commitaccess">Obtaining Commit Access</a></h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000325<div>
Chris Lattner450f40a2007-02-19 03:50:31 +0000326
Bill Wendling78c8fce2009-04-05 12:37:44 +0000327<p>We grant commit access to contributors with a track record of submitting high
328 quality patches. If you would like commit access, please send an email to
329 <a href="mailto:sabre@nondot.org">Chris</a> with the following
330 information:</p>
Chris Lattnerbebcdabd82007-12-03 00:36:20 +0000331
332<ol>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000333 <li>The user name you want to commit with, e.g. "hacker".</li>
334
Chris Lattnerbebcdabd82007-12-03 00:36:20 +0000335 <li>The full name and email address you want message to llvm-commits to come
Bill Wendling78c8fce2009-04-05 12:37:44 +0000336 from, e.g. "J. Random Hacker &lt;hacker@yoyodyne.com&gt;".</li>
337
Chris Lattnerbebcdabd82007-12-03 00:36:20 +0000338 <li>A "password hash" of the password you want to use, e.g. "2ACR96qjUqsyM".
339 Note that you don't ever tell us what your password is, you just give it
340 to us in an encrypted form. To get this, run "htpasswd" (a utility that
341 comes with apache) in crypt mode (often enabled with "-d"), or find a web
342 page that will do it for you.</li>
343</ol>
344
345<p>Once you've been granted commit access, you should be able to check out an
346 LLVM tree with an SVN URL of "https://username@llvm.org/..." instead of the
347 normal anonymous URL of "http://llvm.org/...". The first time you commit
348 you'll have to type in your password. Note that you may get a warning from
349 SVN about an untrusted key, you can ignore this. To verify that your commit
350 access works, please do a test commit (e.g. change a comment or add a blank
351 line). Your first commit to a repository may require the autogenerated email
352 to be approved by a mailing list. This is normal, and will be done when
353 the mailing list owner has time.</p>
Chris Lattner450f40a2007-02-19 03:50:31 +0000354
355<p>If you have recently been granted commit access, these policies apply:</p>
Chris Lattnerbebcdabd82007-12-03 00:36:20 +0000356
Chris Lattner450f40a2007-02-19 03:50:31 +0000357<ol>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000358 <li>You are granted <i>commit-after-approval</i> to all parts of LLVM. To get
359 approval, submit a <a href="#patches">patch</a> to
360 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>.
361 When approved you may commit it yourself.</li>
362
Chris Lattner450f40a2007-02-19 03:50:31 +0000363 <li>You are allowed to commit patches without approval which you think are
Bill Wendling78c8fce2009-04-05 12:37:44 +0000364 obvious. This is clearly a subjective decision &mdash; we simply expect
365 you to use good judgement. Examples include: fixing build breakage,
366 reverting obviously broken patches, documentation/comment changes, any
367 other minor changes.</li>
368
369 <li>You are allowed to commit patches without approval to those portions of
370 LLVM that you have contributed or maintain (i.e., have been assigned
371 responsibility for), with the proviso that such commits must not break the
372 build. This is a "trust but verify" policy and commits of this nature are
373 reviewed after they are committed.</li>
374
375 <li>Multiple violations of these policies or a single egregious violation may
376 cause commit access to be revoked.</li>
Chris Lattner450f40a2007-02-19 03:50:31 +0000377</ol>
Chris Lattner0cca50c2007-02-19 06:57:16 +0000378
379<p>In any case, your changes are still subject to <a href="#reviews">code
Bill Wendling78c8fce2009-04-05 12:37:44 +0000380 review</a> (either before or after they are committed, depending on the
381 nature of the change). You are encouraged to review other peoples' patches
382 as well, but you aren't required to.</p>
Chris Lattner450f40a2007-02-19 03:50:31 +0000383</div>
384
385<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000386<h3><a name="newwork">Making a Major Change</a></h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000387<div>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000388<p>When a developer begins a major new project with the aim of contributing it
389 back to LLVM, s/he should inform the community with an email to
390 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a>
391 email list, to the extent possible. The reason for this is to:
392
393<ol>
394 <li>keep the community informed about future changes to LLVM, </li>
395
396 <li>avoid duplication of effort by preventing multiple parties working on the
397 same thing and not knowing about it, and</li>
398
399 <li>ensure that any technical issues around the proposed work are discussed
400 and resolved before any significant work is done.</li>
401</ol>
Chris Lattnerc7d954e2007-02-19 05:43:04 +0000402
Bill Wendling78c8fce2009-04-05 12:37:44 +0000403<p>The design of LLVM is carefully controlled to ensure that all the pieces fit
404 together well and are as consistent as possible. If you plan to make a major
405 change to the way LLVM works or want to add a major new extension, it is a
406 good idea to get consensus with the development community before you start
407 working on it.</p>
Chris Lattnerc7d954e2007-02-19 05:43:04 +0000408
Bill Wendling78c8fce2009-04-05 12:37:44 +0000409<p>Once the design of the new feature is finalized, the work itself should be
410 done as a series of <a href="#incremental">incremental changes</a>, not as a
411 long-term development branch.</p>
Chris Lattnerc7d954e2007-02-19 05:43:04 +0000412</div>
413
414<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000415<h3><a name="incremental">Incremental Development</a></h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000416<div>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000417<p>In the LLVM project, we do all significant changes as a series of incremental
418 patches. We have a strong dislike for huge changes or long-term development
419 branches. Long-term development branches have a number of drawbacks:</p>
420
421<ol>
422 <li>Branches must have mainline merged into them periodically. If the branch
423 development and mainline development occur in the same pieces of code,
424 resolving merge conflicts can take a lot of time.</li>
425
426 <li>Other people in the community tend to ignore work on branches.</li>
427
428 <li>Huge changes (produced when a branch is merged back onto mainline) are
429 extremely difficult to <a href="#reviews">code review</a>.</li>
430
431 <li>Branches are not routinely tested by our nightly tester
432 infrastructure.</li>
433
434 <li>Changes developed as monolithic large changes often don't work until the
435 entire set of changes is done. Breaking it down into a set of smaller
436 changes increases the odds that any of the work will be committed to the
437 main repository.</li>
438</ol>
Chris Lattner450f40a2007-02-19 03:50:31 +0000439
Bill Wendling78c8fce2009-04-05 12:37:44 +0000440<p>To address these problems, LLVM uses an incremental development style and we
441 require contributors to follow this practice when making a large/invasive
442 change. Some tips:</p>
443
444<ul>
445 <li>Large/invasive changes usually have a number of secondary changes that are
446 required before the big change can be made (e.g. API cleanup, etc). These
447 sorts of changes can often be done before the major change is done,
448 independently of that work.</li>
449
450 <li>The remaining inter-related work should be decomposed into unrelated sets
451 of changes if possible. Once this is done, define the first increment and
452 get consensus on what the end goal of the change is.</li>
453
454 <li>Each change in the set can be stand alone (e.g. to fix a bug), or part of
455 a planned series of changes that works towards the development goal.</li>
456
457 <li>Each change should be kept as small as possible. This simplifies your work
458 (into a logical progression), simplifies code review and reduces the
459 chance that you will get negative feedback on the change. Small increments
460 also facilitate the maintenance of a high quality code base.</li>
461
462 <li>Often, an independent precursor to a big change is to add a new API and
463 slowly migrate clients to use the new API. Each change to use the new API
464 is often "obvious" and can be committed without review. Once the new API
465 is in place and used, it is much easier to replace the underlying
466 implementation of the API. This implementation change is logically
467 separate from the API change.</li>
468</ul>
Chris Lattner450f40a2007-02-19 03:50:31 +0000469
Bill Wendling78c8fce2009-04-05 12:37:44 +0000470<p>If you are interested in making a large change, and this scares you, please
471 make sure to first <a href="#newwork">discuss the change/gather consensus</a>
472 then ask about the best way to go about making the change.</p>
Chris Lattner450f40a2007-02-19 03:50:31 +0000473</div>
474
475<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000476<h3><a name="attribution">Attribution of Changes</a></h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000477<div>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000478<p>We believe in correct attribution of contributions to their contributors.
479 However, we do not want the source code to be littered with random
480 attributions "this code written by J. Random Hacker" (this is noisy and
481 distracting). In practice, the revision control system keeps a perfect
482 history of who changed what, and the CREDITS.txt file describes higher-level
483 contributions. If you commit a patch for someone else, please say "patch
484 contributed by J. Random Hacker!" in the commit message.</p>
Chris Lattnerab2b10c2007-12-29 19:56:08 +0000485
Bill Wendling78c8fce2009-04-05 12:37:44 +0000486<p>Overall, please do not add contributor names to the source code.</p>
Chris Lattner450f40a2007-02-19 03:50:31 +0000487</div>
488
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000489</div>
490
Reid Spencer8d0ac692007-02-13 09:06:01 +0000491<!--=========================================================================-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000492<h2>
Chris Lattner793aa382007-02-19 06:19:16 +0000493 <a name="clp">Copyright, License, and Patents</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000494</h2>
Reid Spencer78bade22007-02-14 07:22:19 +0000495<!--=========================================================================-->
Chris Lattner450f40a2007-02-19 03:50:31 +0000496
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000497<div>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000498<p>This section addresses the issues of copyright, license and patents for the
Chris Lattner5d8f43f2011-09-22 18:54:31 +0000499 LLVM project. The copyright holder for the code is held by the individual
500 contributors of the code and the terms of its license to LLVM users and
501 developers is the
Bill Wendling78c8fce2009-04-05 12:37:44 +0000502 <a href="http://www.opensource.org/licenses/UoI-NCSA.php">University of
503 Illinois/NCSA Open Source License</a>.</p>
Reid Spencer78bade22007-02-14 07:22:19 +0000504
505<div class="doc_notes">
Bill Wendling78c8fce2009-04-05 12:37:44 +0000506<p style="text-align:center;font-weight:bold">NOTE: This section deals with
507 legal matters but does not provide legal advice. We are not lawyers, please
508 seek legal counsel from an attorney.</p>
Reid Spencer78bade22007-02-14 07:22:19 +0000509</div>
Reid Spencer78bade22007-02-14 07:22:19 +0000510
511<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000512<h3><a name="copyright">Copyright</a></h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000513<div>
Chris Lattner305915b2008-05-20 20:06:53 +0000514
Chris Lattnerc226fc82010-09-27 21:17:15 +0000515<p>The LLVM project does not require copyright assignments, which means that the
516 copyright for the code in the project is held by its respective contributors
517 who have each agreed to release their contributed code under the terms of the
518 <a href="#license">LLVM License</a>.</p>
519
520<p>An implication of this is that the LLVM license is unlikely to ever change:
521 changing it would require tracking down all the contributors to LLVM and
522 getting them to agree that a license change is acceptable for their
523 contribution. Since there are no plans to change the license, this is not a
524 cause for concern.</p>
525
526<p>As a contributor to the project, this means that you (or your company) retain
527 ownership of the code you contribute, that it cannot be used in a way that
528 contradicts the license (which is a liberal BSD-style license), and that the
529 license for your contributions won't change without your approval in the
530 future.</p>
531
Reid Spencer78bade22007-02-14 07:22:19 +0000532</div>
Chris Lattner450f40a2007-02-19 03:50:31 +0000533
Reid Spencer78bade22007-02-14 07:22:19 +0000534<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000535<h3><a name="license">License</a></h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000536<div>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000537<p>We intend to keep LLVM perpetually open source and to use a liberal open
Chris Lattnerac139f12010-11-16 21:32:53 +0000538 source license. All of the code in LLVM is available under the
Bill Wendling78c8fce2009-04-05 12:37:44 +0000539 <a href="http://www.opensource.org/licenses/UoI-NCSA.php">University of
Dan Gohman621a4152010-02-26 20:18:32 +0000540 Illinois/NCSA Open Source License</a>, which boils down to this:</p>
Chris Lattner450f40a2007-02-19 03:50:31 +0000541
Bill Wendling78c8fce2009-04-05 12:37:44 +0000542<ul>
543 <li>You can freely distribute LLVM.</li>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000544 <li>You must retain the copyright notice if you redistribute LLVM.</li>
Chris Lattnerac139f12010-11-16 21:32:53 +0000545 <li>Binaries derived from LLVM must reproduce the copyright notice (e.g. in an
546 included readme file).</li>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000547 <li>You can't use our names to promote your LLVM derived products.</li>
Bill Wendling78c8fce2009-04-05 12:37:44 +0000548 <li>There's no warranty on LLVM at all.</li>
549</ul>
550
551<p>We believe this fosters the widest adoption of LLVM because it <b>allows
552 commercial products to be derived from LLVM</b> with few restrictions and
553 without a requirement for making any derived works also open source (i.e.
554 LLVM's license is not a "copyleft" license like the GPL). We suggest that you
555 read the <a href="http://www.opensource.org/licenses/UoI-NCSA.php">License</a>
556 if further clarification is needed.</p>
Chris Lattnerac139f12010-11-16 21:32:53 +0000557
558<p>In addition to the UIUC license, the runtime library components of LLVM
559 (<b>compiler_rt and libc++</b>) are also licensed under the <a
560 href="http://www.opensource.org/licenses/mit-license.php">MIT license</a>,
561 which does not contain the binary redistribution clause. As a user of these
562 runtime libraries, it means that you can choose to use the code under either
563 license (and thus don't need the binary redistribution clause), and as a
564 contributor to the code that you agree that any contributions to these
565 libraries be licensed under both licenses. We feel that this is important
566 for runtime libraries, because they are implicitly linked into applications
567 and therefore should not subject those applications to the binary
568 redistribution clause. This also means that it is ok to move code from (e.g.)
569 libc++ to the LLVM core without concern, but that code cannot be moved from
570 the LLVM core to libc++ without the copyright owner's permission.
571</p>
572
Bill Wendling78c8fce2009-04-05 12:37:44 +0000573<p>Note that the LLVM Project does distribute llvm-gcc, <b>which is GPL.</b>
574 This means that anything "linked" into llvm-gcc must itself be compatible
575 with the GPL, and must be releasable under the terms of the GPL. This
576 implies that <b>any code linked into llvm-gcc and distributed to others may
577 be subject to the viral aspects of the GPL</b> (for example, a proprietary
578 code generator linked into llvm-gcc must be made available under the GPL).
579 This is not a problem for code already distributed under a more liberal
580 license (like the UIUC license), and does not affect code generated by
581 llvm-gcc. It may be a problem if you intend to base commercial development
582 on llvm-gcc without redistributing your source code.</p>
583
584<p>We have no plans to change the license of LLVM. If you have questions or
585 comments about the license, please contact the
Chris Lattnerac139f12010-11-16 21:32:53 +0000586 <a href="mailto:llvmdev@cs.uiuc.edu">LLVM Developer's Mailing List</a>.</p>
Reid Spencer78bade22007-02-14 07:22:19 +0000587</div>
Chris Lattner1ff20cd2007-02-19 06:05:58 +0000588
589<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000590<h3><a name="patents">Patents</a></h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000591<div>
Chris Lattnerb87fb2a2007-02-19 06:13:50 +0000592<p>To the best of our knowledge, LLVM does not infringe on any patents (we have
593 actually removed code from LLVM in the past that was found to infringe).
Bill Wendling78c8fce2009-04-05 12:37:44 +0000594 Having code in LLVM that infringes on patents would violate an important goal
595 of the project by making it hard or impossible to reuse the code for
Chris Lattnerd0742ce2007-02-19 06:15:33 +0000596 arbitrary purposes (including commercial use).</p>
Chris Lattnerb87fb2a2007-02-19 06:13:50 +0000597
598<p>When contributing code, we expect contributors to notify us of any potential
Bill Wendling78c8fce2009-04-05 12:37:44 +0000599 for patent-related trouble with their changes. If you or your employer own
600 the rights to a patent and would like to contribute code to LLVM that relies
601 on it, we require that the copyright owner sign an agreement that allows any
602 other user of LLVM to freely use your patent. Please contact
603 the <a href="mailto:llvm-oversight@cs.uiuc.edu">oversight group</a> for more
Chris Lattnerb87fb2a2007-02-19 06:13:50 +0000604 details.</p>
Chris Lattner1ff20cd2007-02-19 06:05:58 +0000605</div>
606
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000607</div>
608
Reid Spencer8d0ac692007-02-13 09:06:01 +0000609<!-- *********************************************************************** -->
610<hr>
611<address>
612 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000613 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Reid Spencer8d0ac692007-02-13 09:06:01 +0000614 <a href="http://validator.w3.org/check/referer"><img
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Chris Lattnerd0742ce2007-02-19 06:15:33 +0000616 Written by the
Reid Spencer3eedbd32007-02-14 07:57:48 +0000617 <a href="mailto:llvm-oversight@cs.uiuc.edu">LLVM Oversight Group</a><br>
NAKAMURA Takumib9a33632011-04-09 02:13:37 +0000618 <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
Reid Spencer8d0ac692007-02-13 09:06:01 +0000619 Last modified: $Date$
620</address>
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