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5 <title>LLVM Developer Policy</title>
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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="#owners">Code Owners</a></li>
19 <li><a href="#testcases">Test Cases</a></li>
20 <li><a href="#quality">Quality</a></li>
21 <li><a href="#commitaccess">Obtaining Commit Access</a></li>
22 <li><a href="#newwork">Making a Major Change</a></li>
23 <li><a href="#incremental">Incremental Development</a></li>
24 <li><a href="#attribution">Attribution of Changes</a></li>
26 <li><a href="#clp">Copyright, License, and Patents</a>
28 <li><a href="#copyright">Copyright</a></li>
29 <li><a href="#license">License</a></li>
30 <li><a href="#patents">Patents</a></li>
31 <li><a href="#devagree">Developer Agreements</a></li>
34 <div class="doc_author">Written by the LLVM Oversight Team</div>
36 <!--=========================================================================-->
37 <div class="doc_section"><a name="introduction">Introduction</a></div>
38 <!--=========================================================================-->
39 <div class="doc_text">
40 <p>This document contains the LLVM Developer Policy which defines the
41 project's policy towards developers and their contributions. The intent of
42 this policy is to eliminate mis-communication, rework, and confusion that
43 might arise from the distributed nature of LLVM's development. By stating
44 the policy in clear terms, we hope each developer can know ahead of time
45 what to expect when making LLVM contributions.</p>
46 <p>This policy is also designed to accomplish the following objectives:</p>
48 <li>Attract both users and developers to the LLVM project.</li>
49 <li>Make life as simple and easy for contributors as possible.</li>
50 <li>Keep the top of Subversion trees as stable as possible.</li>
53 <p>This policy is aimed at frequent contributors to LLVM. People interested in
54 contributing one-off patches can do so in an informal way by sending them to
55 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
56 llvm-commits mailing list</a> and engaging another developer to see it through
61 <!--=========================================================================-->
62 <div class="doc_section"><a name="policies">Developer Policies</a></div>
63 <!--=========================================================================-->
64 <div class="doc_text">
65 <p>This section contains policies that pertain to frequent LLVM
66 developers. We always welcome <a href="#patches">one-off patches</a> from
67 people who do not routinely contribute to LLVM, but we expect more from
68 frequent contributors to keep the system as efficient as possible for
70 Frequent LLVM contributors are expected to meet the following requirements in
71 order for LLVM to maintain a high standard of quality.<p>
74 <!-- _______________________________________________________________________ -->
75 <div class="doc_subsection"> <a name="informed">Stay Informed</a> </div>
76 <div class="doc_text">
77 <p>Developers should stay informed by reading at least the
78 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a>
79 email list. If you are doing anything more than just casual work on LLVM,
80 it is suggested that you also subscribe to the
81 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
82 list and pay attention to changes being made by others.</p>
83 <p>We recommend that active developers register an email account with
84 <a href="http://llvm.org/bugs/">LLVM Bugzilla</a> and preferably subscribe to
85 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmbugs">llvm-bugs</a>
86 email list to keep track of bugs and enhancements occurring in LLVM.</p>
89 <!-- _______________________________________________________________________ -->
90 <div class="doc_subsection"> <a name="patches">Making a Patch</a></div>
92 <div class="doc_text">
94 <p>When making a patch for review, the goal is to make it as easy for the
95 reviewer to read it as possible. As such, we recommend that you:</p>
97 <li>Make your patch against the Subversion trunk, not a branch, and not an
98 old version of LLVM. This makes it easy to apply the patch.</li>
100 <li>Similarly, patches should be submitted soon after they are generated.
101 Old patches may not apply correctly if the underlying code changes between
102 the time the patch was created and the time it is applied.</li>
104 <li>Patches should be made with this command:
105 <div class="doc_code"><pre>svn diff -x -u</pre></div>
106 or with the utility <tt>utils/mkpatch</tt>, which makes it easy to read the
109 <li>Patches should not include differences in generated code such as the
110 code generated by <tt>autoconf</tt> or <tt>tblgen</tt>. The
111 <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>
119 <p><em>For Thunderbird users:</em> Before submitting a patch, please open
120 <em>Preferences → Advanced → General → Config Editor</em>,
121 find the key <tt>mail.content_disposition_type</tt>, and set its value to
122 <tt>1</tt>. Without this setting, Thunderbird sends your attachment using
123 <tt>Content-Disposition: inline</tt> rather than <tt>Content-Disposition:
124 attachment</tt>. Apple Mail gamely displays such a file inline, making it
125 difficult to work with for reviewers using that program.</p>
128 <!-- _______________________________________________________________________ -->
129 <div class="doc_subsection"> <a name="reviews">Code Reviews</a></div>
130 <div class="doc_text">
131 <p>LLVM has a code review policy. Code review is one way to increase the
132 quality of software. We generally follow these policies:</p>
134 <li>All developers are required to have significant changes reviewed
135 before they are committed to the repository.</li>
136 <li>Code reviews are conducted by email, usually on the llvm-commits
138 <li>Code can be reviewed either before it is committed or after. We expect
139 major changes to be reviewed before being committed, but smaller
140 changes (or changes where the developer owns the component) can be
141 reviewed after commit.</li>
142 <li>The developer responsible for a code change is also responsible for
143 making all necessary review-related changes.</li>
144 <li>Code review can be an iterative process, which continues until the patch
145 is ready to be committed.</li>
148 <p>Developers should participate in code reviews as both reviewers and
149 reviewees. If someone is kind enough to review your code, you should
150 return the favor for someone else. Note that anyone is welcome to review
151 and give feedback on a patch, but only people with Subversion write access
156 <!-- _______________________________________________________________________ -->
157 <div class="doc_subsection"> <a name="owners">Code Owners</a></div>
158 <div class="doc_text">
160 <p>The LLVM Project relies on two features of its process to maintain rapid
161 development in addition to the high quality of its source base: the
162 combination of code review plus post-commit review for trusted maintainers.
163 Having both is a great way for the project to take advantage of the fact
164 that most people do the right thing most of the time, and only commit
165 patches without pre-commit review when they are confident they are
168 <p>The trick to this is that the project has to guarantee that all patches
169 that are committed are reviewed after they go in: you don't want everyone
170 to assume someone else will review it, allowing the patch to go unreviewed.
171 To solve this problem, we have a notion of an 'owner' for a piece of the
172 code. The sole responsibility of a code owner is to ensure that a commit
173 to their area of the code is appropriately reviewed, either by themself or
174 by someone else. The current code owners are:</p>
177 <li><b>Anton Korobeynikov</b>: Exception handling, debug information, and
178 Windows codegen.</li>
179 <li><b>Duncan Sands</b>: llvm-gcc 4.2.</li>
180 <li><b>Evan Cheng</b>: Code generator and all targets.</li>
181 <li><b>Chris Lattner</b>: Everything else.</li>
184 <p>Note that code ownership is completely different than reviewers: anyone can
185 review a piece of code, and we welcome code review from anyone who is
186 interested. Code owners are the "last line of defense" to guarantee that
187 all patches that are committed are actually reviewed.</p>
189 <p>Being a code owner is a somewhat unglamorous position, but it is incredibly
190 important for the ongoing success of the project. Because people get busy,
191 interests change, and unexpected things happen, code ownership is purely
192 opt-in, and anyone can choose to resign their "title" at any time. For now,
193 we do not have an official policy on how one gets elected to be a code
200 <!-- _______________________________________________________________________ -->
201 <div class="doc_subsection"> <a name="testcases">Test Cases</a></div>
202 <div class="doc_text">
203 <p>Developers are required to create test cases for any bugs fixed and any new
204 features added. Some tips for getting your testcase approved:</p>
206 <li>All feature and regression test cases are added to the
207 <tt>llvm/test</tt> directory. The appropriate sub-directory should be
208 selected (see the <a href="TestingGuide.html">Testing Guide</a> for
210 <li>Test cases should be written in
211 <a href="LangRef.html">LLVM assembly language</a> unless the
212 feature or regression being tested requires another language (e.g. the
213 bug being fixed or feature being implemented is in the llvm-gcc C++
214 front-end, in which case it must be written in C++).</li>
215 <li>Test cases, especially for regressions, should be reduced as much as
216 possible, by <a href="Bugpoint.html">bugpoint</a> or
217 manually. It is unacceptable
218 to place an entire failing program into <tt>llvm/test</tt> as this creates
219 a <i>time-to-test</i> burden on all developers. Please keep them short.</li>
222 <p>Note that llvm/test is designed for regression and small feature tests
223 only. More extensive test cases (e.g., entire applications, benchmarks,
224 etc) should be added to the <tt>llvm-test</tt> test suite. The llvm-test
225 suite is for coverage (correctness, performance, etc) testing, not feature
226 or regression testing.</p>
229 <!-- _______________________________________________________________________ -->
230 <div class="doc_subsection"> <a name="quality">Quality</a></div>
231 <div class="doc_text">
232 <p>The minimum quality standards that any change must satisfy before being
233 committed to the main development branch are:</p>
235 <li>Code must adhere to the
236 <a href="CodingStandards.html">LLVM Coding Standards</a>.</li>
237 <li>Code must compile cleanly (no errors, no warnings) on at least one
239 <li>Bug fixes and new features should <a href="#testcases">include a
240 testcase</a> so we know if the fix/feature ever regresses in the
242 <li>Code must pass the dejagnu (<tt>llvm/test</tt>) test suite.</li>
243 <li>The code must not cause regressions on a reasonable subset of llvm-test,
244 where "reasonable" depends on the contributor's judgement and the scope
245 of the change (more invasive changes require more testing). A reasonable
246 subset might be something like
247 "<tt>llvm-test/MultiSource/Benchmarks</tt>".</li>
249 <p>Additionally, the committer is responsible for addressing any problems
250 found in the future that the change is responsible for. For example:</p>
252 <li>The code should compile cleanly on all supported platforms.</li>
253 <li>The changes should not cause any correctness regressions in the
254 <tt>llvm-test</tt> suite and must not cause any major performance
256 <li>The change set should not cause performance or correctness regressions
257 for the LLVM tools.</li>
258 <li>The changes should not cause performance or correctness regressions in
259 code compiled by LLVM on all applicable targets.</li>
260 <li>You are expected to address any <a href="http://llvm.org/bugs/">bugzilla
261 bugs</a> that result from your change.</li>
264 <p>We prefer for this to be handled before submission but understand that it
265 isn't possible to test all of this for every submission. Our nightly
267 infrastructure normally finds these problems. A good rule of thumb is to
268 check the nightly testers for regressions the day after your change.</p>
270 <p>Commits that violate these quality standards (e.g. are very broken) may
271 be reverted. This is necessary when the change blocks other developers from
272 making progress. The developer is welcome to re-commit the change after
273 the problem has been fixed.</p>
276 <!-- _______________________________________________________________________ -->
277 <div class="doc_subsection">
278 <a name="commitaccess">Obtaining Commit Access</a></div>
279 <div class="doc_text">
282 We grant commit access to contributors with a track record of submitting high
283 quality patches. If you would like commit access, please send an email to
284 <a href="mailto:sabre@nondot.org">Chris</a> with the following information:</p>
287 <li>The user name you want to commit with, e.g. "sabre".</li>
288 <li>The full name and email address you want message to llvm-commits to come
289 from, e.g. "Chris Lattner <sabre@nondot.org>".</li>
290 <li>A "password hash" of the password you want to use, e.g. "2ACR96qjUqsyM".
291 Note that you don't ever tell us what your password is, you just give it
292 to us in an encrypted form. To get this, run "htpasswd" (a utility that
293 comes with apache) in crypt mode (often enabled with "-d"), or find a web
294 page that will do it for you.</li>
297 <p>Once you've been granted commit access, you should be able to check out an
298 LLVM tree with an SVN URL of "https://username@llvm.org/..." instead of the
299 normal anonymous URL of "http://llvm.org/...". The first time you commit
300 you'll have to type in your password. Note that you may get a warning from
301 SVN about an untrusted key, you can ignore this. To verify that your commit
302 access works, please do a test commit (e.g. change a comment or add a blank
303 line). Your first commit to a repository may require the autogenerated email
304 to be approved by a mailing list. This is normal, and will be done when
305 the mailing list owner has time.</p>
307 <p>If you have recently been granted commit access, these policies apply:</p>
310 <li>You are granted <i>commit-after-approval</i> to all parts of LLVM.
311 To get approval, submit a <a href="#patches">patch</a> to
312 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
313 llvm-commits</a>. When approved you may commit it yourself.</li>
314 <li>You are allowed to commit patches without approval which you think are
315 obvious. This is clearly a subjective decision — we simply expect you
316 to use good judgement. Examples include: fixing build breakage, reverting
317 obviously broken patches, documentation/comment changes, any other minor
319 <li>You are allowed to commit patches without approval to those portions
320 of LLVM that you have contributed or maintain (i.e., have been assigned
321 responsibility for), with the proviso that such commits must not break the
322 build. This is a "trust but verify" policy and commits of this nature are
323 reviewed after they are committed.</li>
324 <li>Multiple violations of these policies or a single egregious violation
325 may cause commit access to be revoked.</li>
328 <p>In any case, your changes are still subject to <a href="#reviews">code
329 review</a> (either before or after they are committed, depending on the nature
330 of the change). You are encouraged to review other peoples' patches as well,
331 but you aren't required to.</p>
335 <!-- _______________________________________________________________________ -->
336 <div class="doc_subsection"> <a name="newwork">Making a Major Change</a></div>
337 <div class="doc_text">
338 <p>When a developer begins a major new project with the aim of contributing
339 it back to LLVM, s/he should inform the community with an email to
340 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a>
341 email list, to the extent possible. The reason for this is to:
343 <li>keep the community informed about future changes to LLVM, </li>
344 <li>avoid duplication of effort by preventing multiple parties working on
345 the same thing and not knowing about it, and</li>
346 <li>ensure that any technical issues around the proposed work are
347 discussed and resolved before any significant work is done.</li>
350 <p>The design of LLVM is carefully controlled to ensure that all the pieces
351 fit together well and are as consistent as possible. If you plan to make a
352 major change to the way LLVM works or want to add a major new extension, it
353 is a good idea to get consensus with the development
354 community before you start working on it.</p>
356 <p>Once the design of the new feature is finalized, the work itself should be
357 done as a series of <a href="#incremental">incremental changes</a>, not as
358 a long-term development branch.</p>
362 <!-- _______________________________________________________________________ -->
363 <div class="doc_subsection"> <a name="incremental">Incremental Development</a>
365 <div class="doc_text">
366 <p>In the LLVM project, we do all significant changes as a series of
367 incremental patches. We have a strong dislike for huge changes or
368 long-term development branches. Long-term development branches have a
369 number of drawbacks:</p>
372 <li>Branches must have mainline merged into them periodically. If the branch
373 development and mainline development occur in the same pieces of code,
374 resolving merge conflicts can take a lot of time.</li>
375 <li>Other people in the community tend to ignore work on branches.</li>
376 <li>Huge changes (produced when a branch is merged back onto mainline) are
377 extremely difficult to <a href="#reviews">code review</a>.</li>
378 <li>Branches are not routinely tested by our nightly tester
380 <li>Changes developed as monolithic large changes often don't work until the
381 entire set of changes is done. Breaking it down into a set of smaller
382 changes increases the odds that any of the work will be committed to the
383 main repository.</li>
387 To address these problems, LLVM uses an incremental development style and we
388 require contributors to follow this practice when making a large/invasive
389 change. Some tips:</p>
392 <li>Large/invasive changes usually have a number of secondary changes that
393 are required before the big change can be made (e.g. API cleanup, etc).
394 These sorts of changes can often be done before the major change is done,
395 independently of that work.</li>
396 <li>The remaining inter-related work should be decomposed into unrelated
397 sets of changes if possible. Once this is done, define the first increment
398 and get consensus on what the end goal of the change is.</li>
400 <li>Each change in the set can be stand alone (e.g. to fix a bug), or part
401 of a planned series of changes that works towards the development goal.</li>
403 <li>Each change should be kept as small as possible. This simplifies your
404 work (into a logical progression), simplifies code review and reduces the
405 chance that you will get negative feedback on the change. Small increments
406 also facilitate the maintenance of a high quality code base.</li>
408 <li>Often, an independent precursor to a big change is to add a new API and
409 slowly migrate clients to use the new API. Each change to use the new
410 API is often "obvious" and can be committed without review. Once the
411 new API is in place and used, it is much easier to replace the
412 underlying implementation of the API. This implementation change is
413 logically separate from the API change.</li>
416 <p>If you are interested in making a large change, and this scares you, please
417 make sure to first <a href="#newwork">discuss the change/gather
418 consensus</a> then ask about the best way to go about making
422 <!-- _______________________________________________________________________ -->
423 <div class="doc_subsection"><a name="attribution">Attribution of
425 <div class="doc_text">
426 <p>We believe in correct attribution of contributions to
427 their contributors. However, we do not want the source code to be littered
428 with random attributions "this code written by J Random Guy" (this is noisy
429 and distracting). In practice, the revision control system keeps a perfect
430 history of who changed what, and the CREDITS.txt file describes higher-level
431 contributions. If you commit a patch for someone else, please say "patch
432 contributed by J Random Guy!" in the commit message.</p>
434 <p>Overall, please do not add contributor names to the source code.</p>
439 <!--=========================================================================-->
440 <div class="doc_section">
441 <a name="clp">Copyright, License, and Patents</a>
443 <!--=========================================================================-->
445 <div class="doc_text">
446 <p>This section addresses the issues of copyright, license and patents for
448 Currently, the University of Illinois is the LLVM copyright holder and the
449 terms of its license to LLVM users and developers is the
450 <a href="http://www.opensource.org/licenses/UoI-NCSA.php">University of
451 Illinois/NCSA Open Source License</a>.</p>
453 <div class="doc_notes">
454 <p style="text-align:center;font-weight:bold">NOTE: This section
455 deals with legal matters but does not provide legal advice. We are not
456 lawyers, please seek legal counsel from an attorney.</p>
460 <!-- _______________________________________________________________________ -->
461 <div class="doc_subsection"><a name="copyright">Copyright</a></div>
462 <div class="doc_text">
464 <p>For consistency and ease of management, the project requires the
465 copyright for all LLVM software to be held by a single copyright holder:
466 the University of Illinois (UIUC).</p>
469 Although UIUC may eventually reassign the copyright of the software to another
470 entity (e.g. a dedicated non-profit "LLVM Organization")
471 the intent for the project is to always have a single entity hold the
472 copyrights to LLVM at any given time.</p>
474 <p>We believe that having a single copyright
475 holder is in the best interests of all developers and users as it greatly
476 reduces the managerial burden for any kind of administrative or technical
477 decisions about LLVM. The goal of the LLVM project is to always keep the code
478 open and <a href="#license">licensed under a very liberal license</a>.</p>
482 <!-- _______________________________________________________________________ -->
483 <div class="doc_subsection"><a name="license">License</a></div>
484 <div class="doc_text">
485 <p>We intend to keep LLVM perpetually open source
486 and to use a liberal open source license. The current license is the
487 <a href="http://www.opensource.org/licenses/UoI-NCSA.php">
488 University of Illinois/NCSA Open Source License</a>, which boils
491 <li>You can freely distribute LLVM.</li>
492 <li>You must retain the copyright notice if you redistribute LLVM.</li>
493 <li>Binaries derived from LLVM must reproduce the copyright notice (e.g.
494 in an included readme file).</li>
495 <li>You can't use our names to promote your LLVM derived products.</li>
496 <li>There's no warranty on LLVM at all.</li>
499 <p>We believe this fosters the widest adoption of LLVM because it <b>allows
500 commercial products to be derived from LLVM</b> with few restrictions and
501 without a requirement for making any derived works also open source (i.e.
502 LLVM's license is not a "copyleft" license like the GPL). We suggest that you
503 read the <a href="http://www.opensource.org/licenses/UoI-NCSA.php">License</a>
504 if further clarification is needed.</p>
506 <p>Note that the LLVM Project does distribute llvm-gcc, <b>which is GPL.</b>
507 This means that anything "linked" into llvm-gcc must itself be compatible
508 with the GPL, and must be releasable under the terms of the GPL. This implies
509 that <b>any code linked into llvm-gcc and distributed to others may be subject
510 to the viral aspects of the GPL</b> (for example, a proprietary code generator
511 linked into llvm-gcc must be made available under the GPL). This is not a
512 problem for code already distributed under a more liberal license (like the
513 UIUC license), and does not affect code generated by llvm-gcc. It may be a
514 problem if you intend to base commercial development on llvm-gcc without
515 redistributing your source code.</p>
517 <p>We have no plans to change the license of LLVM. If you have questions
518 or comments about the license, please contact the <a
519 href="mailto:llvm-oversight@cs.uiuc.edu">LLVM Oversight Group</a>.</p>
523 <!-- _______________________________________________________________________ -->
524 <div class="doc_subsection"><a name="patents">Patents</a></div>
525 <div class="doc_text">
527 <p>To the best of our knowledge, LLVM does not infringe on any patents (we have
528 actually removed code from LLVM in the past that was found to infringe).
529 Having code in LLVM that infringes on patents would violate an important
530 goal of the project by making it hard or impossible to reuse the code for
531 arbitrary purposes (including commercial use).</p>
533 <p>When contributing code, we expect contributors to notify us of any potential
534 for patent-related trouble with their changes. If you or your employer
536 patent and would like to contribute code to LLVM that relies on it, we
538 the copyright owner sign an agreement that allows any other user of LLVM to
539 freely use your patent. Please contact the <a
540 href="mailto:llvm-oversight@cs.uiuc.edu">oversight group</a> for more
545 <!-- _______________________________________________________________________ -->
546 <div class="doc_subsection"><a name="devagree">Developer Agreements</a></div>
547 <div class="doc_text">
548 <p>With regards to the LLVM copyright and licensing, developers agree to
549 assign their copyrights to UIUC for any contribution made so that
550 the entire software base can be managed by a single copyright holder. This
551 implies that any contributions can be licensed under the license that the
554 <p>When contributing code, you also affirm that you are legally entitled to
555 grant this copyright, personally or on behalf of your employer. If the code
556 belongs to some other entity, please raise this issue with the oversight
557 group before the code is committed.</p>
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