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10 <div class="doc_title">LLVM Developer Policy</div>
12 <li><a href="#introduction">Introduction</a></li>
13 <li><a href="#policies">Developer Policies</a>
15 <li><a href="#informed">Stay Informed</a></li>
16 <li><a href="#patches">Making a Patch</a></li>
17 <li><a href="#reviews">Code Reviews</a></li>
18 <li><a href="#testcases">Test Cases</a></li>
19 <li><a href="#quality">Quality</a></li>
20 <li><a href="#commitaccess">Obtaining Commit Access</a></li>
21 <li><a href="#newwork">Making a Major Change</a></li>
22 <li><a href="#incremental">Incremental Development</a></li>
23 <li><a href="#attribution">Attribution of Changes</a></li>
25 <li><a href="#clp">Copyright, License, and Patents</a>
27 <li><a href="#copyright">Copyright</a></li>
28 <li><a href="#license">License</a></li>
29 <li><a href="#patents">Patents</a></li>
30 <li><a href="#devagree">Developer Agreements</a></li>
33 <div class="doc_author">Written by the LLVM Oversight Team</div>
35 <!--=========================================================================-->
36 <div class="doc_section"><a name="introduction">Introduction</a></div>
37 <!--=========================================================================-->
38 <div class="doc_text">
39 <p>This document contains the LLVM Developer Policy which defines the
40 project's policy towards developers and their contributions. The intent of
41 this policy is to eliminate mis-communication, rework, and confusion that
42 might arise from the distributed nature of LLVM's development. By stating
43 the policy in clear terms, we hope each developer can know ahead of time
44 what to expect when making LLVM contributions.</p>
45 <p>This policy is also designed to accomplish the following objectives:</p>
47 <li>Attract both users and developers to the LLVM project.</li>
48 <li>Make life as simple and easy for contributors as possible.</li>
49 <li>Keep the top of Subversion trees as stable as possible.</li>
52 <p>This policy is aimed at frequent contributors to LLVM. People interested in
53 contributing one-off patches can do so in an informal way by sending them to
54 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
55 llvm-commits mailing list</a> and engaging another developer to see it through
60 <!--=========================================================================-->
61 <div class="doc_section"><a name="policies">Developer Policies</a></div>
62 <!--=========================================================================-->
63 <div class="doc_text">
64 <p>This section contains policies that pertain to frequent LLVM
65 developers. We always welcome <a href="#patches">one-off patches</a> from
66 people who do not routinely contribute to LLVM, but we expect more from
67 frequent contributors to keep the system as efficient as possible for
69 Frequent LLVM contributors are expected to meet the following requirements in
70 order for LLVM to maintain a high standard of quality.<p>
73 <!-- _______________________________________________________________________ -->
74 <div class="doc_subsection"> <a name="informed">Stay Informed</a> </div>
75 <div class="doc_text">
76 <p>Developers should stay informed by reading at least the
77 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a>
78 email list. If you are doing anything more than just casual work on LLVM,
79 it is suggested that you also subscribe to the
80 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
81 list and pay attention to changes being made by others.</p>
82 <p>We recommend that active developers register an email account with
83 <a href="http://llvm.org/bugs/">LLVM Bugzilla</a> and preferably subscribe to
84 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmbugs">llvm-bugs</a>
85 email list to keep track of bugs and enhancements occurring in LLVM.</p>
88 <!-- _______________________________________________________________________ -->
89 <div class="doc_subsection"> <a name="patches">Making a Patch</a></div>
91 <div class="doc_text">
93 <p>When making a patch for review, the goal is to make it as easy for the
94 reviewer to read it as possible. As such, we recommend that you:</p>
96 <li>Make your patch against the Subversion trunk, not a branch, and not an
97 old version of LLVM. This makes it easy to apply the patch.</li>
99 <li>Similarly, patches should be submitted soon after they are generated.
100 Old patches may not apply correctly if the underlying code changes between
101 the time the patch was created and the time it is applied.</li>
103 <li>Patches should be made with this command:
104 <pre>svn diff -x -u</pre>
105 or with the utility <tt>utils/mkpatch</tt>, which makes it easy to read the
108 <li>Patches should not include differences in generated code such as the
109 code generated by <tt>flex</tt>, <tt>bison</tt> or <tt>tblgen</tt>. The
110 <tt>utils/mkpatch</tt> utility takes care of this for you.</li>
114 <p>When sending a patch to a mailing list, it is a good idea to send it as an
115 <em>attachment</em> to the message, not embedded into the text of the
116 message. This ensures that your mailer will not mangle the patch when it
117 sends it (e.g. by making whitespace changes or by wrapping lines).</p>
120 <!-- _______________________________________________________________________ -->
121 <div class="doc_subsection"> <a name="reviews">Code Reviews</a></div>
122 <div class="doc_text">
123 <p>LLVM has a code review policy. Code review is one way to increase the
124 quality of software. We generally follow these policies:</p>
126 <li>All developers are required to have significant changes reviewed
127 before they are committed to the repository.</li>
128 <li>Code reviews are conducted by email, usually on the llvm-commits
130 <li>Code can be reviewed either before it is committed or after. We expect
131 major changes to be reviewed before being committed, but smaller
132 changes (or changes where the developer owns the component) can be
133 reviewed after commit.</li>
134 <li>The developer responsible for a code change is also responsible for
135 making all necessary review-related changes.</li>
136 <li>Code review can be an iterative process, which continues until the patch
137 is ready to be committed.</li>
140 <p>Developers should participate in code reviews as both reviewers and
141 reviewees. If someone is kind enough to review your code, you should
142 return the favor for someone else. Note that anyone is welcome to review
143 and give feedback on a patch, but only people with Subversion write access
148 <!-- _______________________________________________________________________ -->
149 <div class="doc_subsection"> <a name="testcases">Test Cases</a></div>
150 <div class="doc_text">
151 <p>Developers are required to create test cases for any bugs fixed and any new
152 features added. Some tips for getting your testcase approved:</p>
154 <li>All feature and regression test cases are added to the
155 <tt>llvm/test</tt> directory. The appropriate sub-directory should be
156 selected (see the <a href="TestingGuide.html">Testing Guide</a> for
158 <li>Test cases should be written in
159 <a href="LangRef.html">LLVM assembly language</a> unless the
160 feature or regression being tested requires another language (e.g. the
161 bug being fixed or feature being implemented is in the llvm-gcc C++
162 front-end, in which case it must be written in C++).</li>
163 <li>Test cases, especially for regressions, should be reduced as much as
164 possible, by <a href="Bugpoint.html">bugpoint</a> or
165 manually. It is unacceptable
166 to place an entire failing program into <tt>llvm/test</tt> as this creates
167 a <i>time-to-test</i> burden on all developers. Please keep them short.</li>
170 <p>Note that llvm/test is designed for regression and small feature tests
171 only. More extensive test cases (e.g., entire applications, benchmarks,
172 etc) should be added to the <tt>llvm-test</tt> test suite. The llvm-test
173 suite is for coverage (correctness, performance, etc) testing, not feature
174 or regression testing.</p>
177 <!-- _______________________________________________________________________ -->
178 <div class="doc_subsection"> <a name="quality">Quality</a></div>
179 <div class="doc_text">
180 <p>The minimum quality standards that any change must satisfy before being
181 committed to the main development branch are:</p>
183 <li>Code must adhere to the
184 <a href="CodingStandards.html">LLVM Coding Standards</a>.</li>
185 <li>Code must compile cleanly (no errors, no warnings) on at least one
187 <li>Bug fixes and new features should <a href="#testcases">include a
188 testcase</a> so we know if the fix/feature ever regresses in the
190 <li>Code must pass the dejagnu (<tt>llvm/test</tt>) test suite.</li>
191 <li>The code must not cause regressions on a reasonable subset of llvm-test,
192 where "reasonable" depends on the contributor's judgement and the scope
193 of the change (more invasive changes require more testing). A reasonable
194 subset is "<tt>llvm-test/MultiSource/Benchmarks</tt>".</li>
196 <p>Additionally, the committer is responsible for addressing any problems
197 found in the future that the change is responsible for. For example:</p>
199 <li>The code should compile cleanly on all supported platforms.</li>
200 <li>The changes should not cause any correctness regressions in the
201 <tt>llvm-test</tt> suite and must not cause any major performance
203 <li>The change set should not cause performance or correctness regressions
204 for the LLVM tools.</li>
205 <li>The changes should not cause performance or correctness regressions in
206 code compiled by LLVM on all applicable targets.</li>
207 <li>You are expected to address any <a href="http://llvm.org/bugs/">bugzilla
208 bugs</a> that result from your change.</li>
211 <p>We prefer for this to be handled before submission but understand that it
212 isn't possible to test all of this for every submission. Our nightly
214 infrastructure normally finds these problems. A good rule of thumb is to
215 check the nightly testers for regressions the day after your change.</p>
217 <p>Commits that violate these quality standards (e.g. are very broken) may
218 be reverted. This is necessary when the change blocks other developers from
219 making progress. The developer is welcome to re-commit the change after
220 the problem has been fixed.</p>
223 <!-- _______________________________________________________________________ -->
224 <div class="doc_subsection">
225 <a name="commitaccess">Obtaining Commit Access</a></div>
226 <div class="doc_text">
229 We grant commit access to contributors with a track record of submitting high
230 quality patches. If you would like commit access, please send an email to the
231 <a href="mailto:llvm-oversight@cs.uiuc.edu">LLVM oversight group</a>.</p>
233 <p>If you have recently been granted commit access, these policies apply:</p>
235 <li>You are granted <i>commit-after-approval</i> to all parts of LLVM.
236 To get approval, submit a <a href="#patches">patch</a> to
237 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
238 llvm-commits</a>. When approved you may commit it yourself.</li>
239 <li>You are allowed to commit patches without approval which you think are
240 obvious. This is clearly a subjective decision — we simply expect you
241 to use good judgement. Examples include: fixing build breakage, reverting
242 obviously broken patches, documentation/comment changes, any other minor
244 <li>You are allowed to commit patches without approval to those portions
245 of LLVM that you have contributed or maintain (i.e., have been assigned
246 responsibility for), with the proviso that such commits must not break the
247 build. This is a "trust but verify" policy and commits of this nature are
248 reviewed after they are committed.</li>
249 <li>Multiple violations of these policies or a single egregious violation
250 may cause commit access to be revoked.</li>
253 <p>In any case, your changes are still subject to <a href="#reviews">code
254 review</a> (either before or after they are committed, depending on the nature
255 of the change). You are encouraged to review other peoples' patches as well,
256 but you aren't required to.</p>
260 <!-- _______________________________________________________________________ -->
261 <div class="doc_subsection"> <a name="newwork">Making a Major Change</a></div>
262 <div class="doc_text">
263 <p>When a developer begins a major new project with the aim of contributing
264 it back to LLVM, s/he should inform the community with an email to
265 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a>
266 email list, to the extent possible. The reason for this is to:
268 <li>keep the community informed about future changes to LLVM, </li>
269 <li>avoid duplication of effort by preventing multiple parties working on
270 the same thing and not knowing about it, and</li>
271 <li>ensure that any technical issues around the proposed work are
272 discussed and resolved before any significant work is done.</li>
275 <p>The design of LLVM is carefully controlled to ensure that all the pieces
276 fit together well and are as consistent as possible. If you plan to make a
277 major change to the way LLVM works or want to add a major new extension, it
278 is a good idea to get consensus with the development
279 community before you start working on it.</p>
281 <p>Once the design of the new feature is finalized, the work itself should be
282 done as a series of <a href="#incremental">incremental changes</a>, not as
283 a long-term development branch.</p>
287 <!-- _______________________________________________________________________ -->
288 <div class="doc_subsection"> <a name="incremental">Incremental Development</a>
290 <div class="doc_text">
291 <p>In the LLVM project, we do all significant changes as a series of
292 incremental patches. We have a strong dislike for huge changes or
293 long-term development branches. Long-term development branches have a
294 number of drawbacks:</p>
297 <li>Branches must have mainline merged into them periodically. If the branch
298 development and mainline development occur in the same pieces of code,
299 resolving merge conflicts can take a lot of time.</li>
300 <li>Other people in the community tend to ignore work on branches.</li>
301 <li>Huge changes (produced when a branch is merged back onto mainline) are
302 extremely difficult to <a href="#reviews">code review</a>.</li>
303 <li>Branches are not routinely tested by our nightly tester
305 <li>Changes developed as monolithic large changes often don't work until the
306 entire set of changes is done. Breaking it down into a set of smaller
307 changes increases the odds that any of the work will be committed to the
308 main repository.</li>
312 To address these problems, LLVM uses an incremental development style and we
313 require contributors to follow this practice when making a large/invasive
314 change. Some tips:</p>
317 <li>Large/invasive changes usually have a number of secondary changes that
318 are required before the big change can be made (e.g. API cleanup, etc).
319 These sorts of changes can often be done before the major change is done,
320 independently of that work.</li>
321 <li>The remaining inter-related work should be decomposed into unrelated
322 sets of changes if possible. Once this is done, define the first increment
323 and get consensus on what the end goal of the change is.</li>
325 <li>Each change in the set can be stand alone (e.g. to fix a bug), or part
326 of a planned series of changes that works towards the development goal.</li>
328 <li>Each change should be kept as small as possible. This simplifies your
329 work (into a logical progression), simplifies code review and reduces the
330 chance that you will get negative feedback on the change. Small increments
331 also facilitate the maintenance of a high quality code base.</li>
333 <li>Often, an independent precursor to a big change is to add a new API and
334 slowly migrate clients to use the new API. Each change to use the new
335 API is often "obvious" and can be committed without review. Once the
336 new API is in place and used, it is much easier to replace the
337 underlying implementation of the API. This implementation change is
338 logically separate from the API change.</li>
341 <p>If you are interested in making a large change, and this scares you, please
342 make sure to first <a href="#newwork">discuss the change/gather
343 consensus</a> then ask about the best way to go about making
347 <!-- _______________________________________________________________________ -->
348 <div class="doc_subsection"><a name="attribution">Attribution of
350 <div class="doc_text">
351 <p>We believe in correct attribution of contributions to
352 their contributors. However, we do not want the source code to be littered
353 with random attributions (this is noisy/distracting and revision control
354 keeps a perfect history of this anyway). As such, we follow these rules:</p>
356 <li>Developers who originate new files in LLVM should place their name at
357 the top of the file per the
358 <a href="CodingStandards.html#scf_commenting">Coding Standards</a>.</li>
359 <li>There should be only one name at the top of the file and it should be
360 the person who created the file.</li>
361 <li>Placing your name in the file does not imply <a
362 href="#clp">copyright</a>: it is only used to attribute the file to
363 its original author.</li>
364 <li>Developers should be aware that after some time has passed, the name at
365 the top of a file may become meaningless as maintenance/ownership of files
366 changes. Despite this, once set, the attribution of a file never changes.
367 Revision control keeps an accurate history of contributions.</li>
368 <li>Developers should maintain their entry in the
369 <a href="http://llvm.org/svn/llvm-project/llvm/trunk/CREDITS.TXT">CREDITS.txt</a>
370 file to summarize their contributions.</li>
371 <li>Commit comments should contain correct attribution of the person who
372 submitted the patch if that person is not the committer (i.e. when a
373 developer with commit privileges commits a patch for someone else).</li>
379 <!--=========================================================================-->
380 <div class="doc_section">
381 <a name="clp">Copyright, License, and Patents</a>
383 <!--=========================================================================-->
385 <div class="doc_text">
386 <p>This section addresses the issues of copyright, license and patents for
388 Currently, the University of Illinois is the LLVM copyright holder and the
389 terms of its license to LLVM users and developers is the
390 <a href="http://www.opensource.org/licenses/UoI-NCSA.php">University of
391 Illinois/NCSA Open Source License</a>.</p>
393 <div class="doc_notes">
394 <p><b>NOTE: This section deals with legal matters but does not provide
395 legal advice. We are not lawyers, please seek legal counsel from an
400 <!-- _______________________________________________________________________ -->
401 <div class="doc_subsection"><a name="copyright">Copyright</a></div>
402 <div class="doc_text">
404 <p>For consistency and ease of management, the project requires the
405 copyright for all LLVM software to be held by a single copyright holder:
406 the University of Illinois (UIUC).</p>
409 Although UIUC may eventually reassign the copyright of the software to another
410 entity (e.g. a dedicated non-profit "LLVM Organization", or something)
411 the intent for the project is to always have a single entity hold the
412 copyrights to LLVM at any given time.</p>
414 <p>We believe that having a single copyright
415 holder is in the best interests of all developers and users as it greatly
416 reduces the managerial burden for any kind of administrative or technical
417 decisions about LLVM. The goal of the LLVM project is to always keep the code
418 open and <a href="#license">licensed under a very liberal license</a>.</p>
421 <!-- _______________________________________________________________________ -->
422 <div class="doc_subsection"><a name="license">License</a></div>
423 <div class="doc_text">
424 <p>We intend to keep LLVM perpetually open source
425 and to use a liberal open source license. The current license is the
426 <a href="http://www.opensource.org/licenses/UoI-NCSA.php">
427 University of Illinois/NCSA Open Source License</a>, which boils
430 <li>You can freely distribute LLVM.</li>
431 <li>You must retain the copyright notice if you redistribute LLVM.</li>
432 <li>Binaries derived from LLVM must reproduce the copyright notice.</li>
433 <li>You can't use our names to promote your LLVM derived products.</li>
434 <li>There's no warranty on LLVM at all.</li>
437 <p>We believe this fosters the widest adoption of LLVM because it <b>allows
438 commercial products to be derived from LLVM</b> with few restrictions and
439 without a requirement for making any derived works also open source (i.e.
440 LLVM's license is not a "copyleft" license like the GPL). We suggest that you
441 read the <a href="http://www.opensource.org/licenses/UoI-NCSA.php">License</a>
442 if further clarification is needed.</p>
444 <p>Note that the LLVM Project does distribute llvm-gcc, <b>which is GPL.</b>
445 This means that anything "linked" into llvm-gcc must itself be compatible
446 with the GPL, and must be releasable under the terms of the GPL. This implies
447 that <b>any code linked into llvm-gcc and distributed to others may be subject
448 to the viral aspects of the GPL</b> (for example, a proprietary code generator
449 linked into llvm-gcc must be made available under the GPL). This is not a
450 problem for code already distributed under a more liberal license (like the
451 UIUC license), and does not affect code generated by llvm-gcc. It may be a
452 problem if you intend to base commercial development on llvm-gcc without
453 redistributing your source code.</p>
455 <p>We have no plans to change the license of LLVM. If you have questions
456 or comments about the license, please contact the <a
457 href="mailto:llvm-oversight@cs.uiuc.edu">LLVM Oversight Group</a>.</p>
461 <!-- _______________________________________________________________________ -->
462 <div class="doc_subsection"><a name="patents">Patents</a></div>
463 <div class="doc_text">
465 <p>To the best of our knowledge, LLVM does not infringe on any patents (we have
466 actually removed code from LLVM in the past that was found to infringe).
467 Having code in LLVM that infringes on patents would violate an important
468 goal of the project by making it hard or impossible to reuse the code for
469 arbitrary purposes (including commercial use).</p>
471 <p>When contributing code, we expect contributors to notify us of any potential
472 for patent-related trouble with their changes. If you own the rights to a
473 patent and would like to contribute code to LLVM that relies on it, we
474 require that you sign an agreement that allows any other user of LLVM to
475 freely use your patent. Please contact the <a
476 href="mailto:llvm-oversight@cs.uiuc.edu">oversight group</a> for more
481 <!-- _______________________________________________________________________ -->
482 <div class="doc_subsection"><a name="devagree">Developer Agreements</a></div>
483 <div class="doc_text">
484 <p>With regards to the LLVM copyright and licensing, developers agree to
485 assign their copyrights to UIUC for any contribution made so that
486 the entire software base can be managed by a single copyright holder. This
487 implies that any contributions can be licensed under the license that the
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