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11 <div class="doc_title">LLVM Developer Policy</div>
13 <li><a href="#introduction">Introduction</a></li>
14 <li><a href="#policies">Developer Policies</a>
16 <li><a href="#informed">Stay Informed</a></li>
17 <li><a href="#patches">Making a Patch</a></li>
18 <li><a href="#reviews">Code Reviews</a></li>
19 <li><a href="#owners">Code Owners</a></li>
20 <li><a href="#testcases">Test Cases</a></li>
21 <li><a href="#quality">Quality</a></li>
22 <li><a href="#commitaccess">Obtaining Commit Access</a></li>
23 <li><a href="#newwork">Making a Major Change</a></li>
24 <li><a href="#incremental">Incremental Development</a></li>
25 <li><a href="#attribution">Attribution of Changes</a></li>
27 <li><a href="#clp">Copyright, License, and Patents</a>
29 <li><a href="#copyright">Copyright</a></li>
30 <li><a href="#license">License</a></li>
31 <li><a href="#patents">Patents</a></li>
32 <li><a href="#devagree">Developer Agreements</a></li>
35 <div class="doc_author">Written by the LLVM Oversight Team</div>
37 <!--=========================================================================-->
38 <div class="doc_section"><a name="introduction">Introduction</a></div>
39 <!--=========================================================================-->
40 <div class="doc_text">
41 <p>This document contains the LLVM Developer Policy which defines the project's
42 policy towards developers and their contributions. The intent of this policy
43 is to eliminate miscommunication, rework, and confusion that might arise from
44 the distributed nature of LLVM's development. By stating the policy in clear
45 terms, we hope each developer can know ahead of time what to expect when
46 making LLVM contributions.</p>
47 <p>This policy is also designed to accomplish the following objectives:</p>
50 <li>Attract both users and developers to the LLVM project.</li>
52 <li>Make life as simple and easy for contributors as possible.</li>
54 <li>Keep the top of Subversion trees as stable as possible.</li>
57 <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
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
65 <!--=========================================================================-->
66 <div class="doc_section"><a name="policies">Developer Policies</a></div>
67 <!--=========================================================================-->
68 <div class="doc_text">
69 <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>
77 <!-- _______________________________________________________________________ -->
78 <div class="doc_subsection"> <a name="informed">Stay Informed</a> </div>
79 <div class="doc_text">
80 <p>Developers should stay informed by reading at least the
81 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a> email
82 list. If you are doing anything more than just casual work on LLVM, it is
83 suggested that you also subscribe to the
84 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
85 list and pay attention to changes being made by others.</p>
87 <p>We recommend that active developers register an email account with
88 <a href="http://llvm.org/bugs/">LLVM Bugzilla</a> and preferably subscribe to
89 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmbugs">llvm-bugs</a>
90 email list to keep track of bugs and enhancements occurring in LLVM.</p>
93 <!-- _______________________________________________________________________ -->
94 <div class="doc_subsection"> <a name="patches">Making a Patch</a></div>
96 <div class="doc_text">
97 <p>When making a patch for review, the goal is to make it as easy for the
98 reviewer to read it as possible. As such, we recommend that you:</p>
101 <li>Make your patch against the Subversion trunk, not a branch, and not an old
102 version of LLVM. This makes it easy to apply the patch.</li>
104 <li>Similarly, patches should be submitted soon after they are generated. Old
105 patches may not apply correctly if the underlying code changes between the
106 time the patch was created and the time it is applied.</li>
108 <li>Patches should be made with this command:
109 <div class="doc_code">
114 or with the utility <tt>utils/mkpatch</tt>, which makes it easy to read
117 <li>Patches should not include differences in generated code such as the code
118 generated by <tt>autoconf</tt> or <tt>tblgen</tt>. The
119 <tt>utils/mkpatch</tt> utility takes care of this for you.</li>
122 <p>When sending a patch to a mailing list, it is a good idea to send it as an
123 <em>attachment</em> to the message, not embedded into the text of the
124 message. This ensures that your mailer will not mangle the patch when it
125 sends it (e.g. by making whitespace changes or by wrapping lines).</p>
127 <p><em>For Thunderbird users:</em> Before submitting a patch, please open
128 <em>Preferences → Advanced → General → Config Editor</em>,
129 find the key <tt>mail.content_disposition_type</tt>, and set its value to
130 <tt>1</tt>. Without this setting, Thunderbird sends your attachment using
131 <tt>Content-Disposition: inline</tt> rather than <tt>Content-Disposition:
132 attachment</tt>. Apple Mail gamely displays such a file inline, making it
133 difficult to work with for reviewers using that program.</p>
136 <!-- _______________________________________________________________________ -->
137 <div class="doc_subsection"> <a name="reviews">Code Reviews</a></div>
138 <div class="doc_text">
139 <p>LLVM has a code review policy. Code review is one way to increase the quality
140 of software. We generally follow these policies:</p>
143 <li>All developers are required to have significant changes reviewed before
144 they are committed to the repository.</li>
146 <li>Code reviews are conducted by email, usually on the llvm-commits
149 <li>Code can be reviewed either before it is committed or after. We expect
150 major changes to be reviewed before being committed, but smaller changes
151 (or changes where the developer owns the component) can be reviewed after
154 <li>The developer responsible for a code change is also responsible for making
155 all necessary review-related changes.</li>
157 <li>Code review can be an iterative process, which continues until the patch
158 is ready to be committed.</li>
161 <p>Developers should participate in code reviews as both reviewers and
162 reviewees. If someone is kind enough to review your code, you should return
163 the favor for someone else. Note that anyone is welcome to review and give
164 feedback on a patch, but only people with Subversion write access can approve
168 <!-- _______________________________________________________________________ -->
169 <div class="doc_subsection"> <a name="owners">Code Owners</a></div>
170 <div class="doc_text">
172 <p>The LLVM Project relies on two features of its process to maintain rapid
173 development in addition to the high quality of its source base: the
174 combination of code review plus post-commit review for trusted maintainers.
175 Having both is a great way for the project to take advantage of the fact that
176 most people do the right thing most of the time, and only commit patches
177 without pre-commit review when they are confident they are right.</p>
179 <p>The trick to this is that the project has to guarantee that all patches that
180 are committed are reviewed after they go in: you don't want everyone to
181 assume someone else will review it, allowing the patch to go unreviewed. To
182 solve this problem, we have a notion of an 'owner' for a piece of the code.
183 The sole responsibility of a code owner is to ensure that a commit to their
184 area of the code is appropriately reviewed, either by themself or by someone
185 else. The current code owners are:</p>
188 <li><b>Anton Korobeynikov</b>: Exception handling, debug information, and
189 Windows codegen.</li>
191 <li><b>Duncan Sands</b>: llvm-gcc 4.2.</li>
193 <li><b>Evan Cheng</b>: Code generator and all targets.</li>
195 <li><b>Ted Kremenek</b>: Clang Static Analyzer.</li>
197 <li><b>Chris Lattner</b>: Everything else.</li>
200 <p>Note that code ownership is completely different than reviewers: anyone can
201 review a piece of code, and we welcome code review from anyone who is
202 interested. Code owners are the "last line of defense" to guarantee that all
203 patches that are committed are actually reviewed.</p>
205 <p>Being a code owner is a somewhat unglamorous position, but it is incredibly
206 important for the ongoing success of the project. Because people get busy,
207 interests change, and unexpected things happen, code ownership is purely
208 opt-in, and anyone can choose to resign their "title" at any time. For now,
209 we do not have an official policy on how one gets elected to be a code
213 <!-- _______________________________________________________________________ -->
214 <div class="doc_subsection"> <a name="testcases">Test Cases</a></div>
215 <div class="doc_text">
216 <p>Developers are required to create test cases for any bugs fixed and any new
217 features added. Some tips for getting your testcase approved:</p>
220 <li>All feature and regression test cases are added to the
221 <tt>llvm/test</tt> directory. The appropriate sub-directory should be
222 selected (see the <a href="TestingGuide.html">Testing Guide</a> for
225 <li>Test cases should be written in <a href="LangRef.html">LLVM assembly
226 language</a> unless the feature or regression being tested requires
227 another language (e.g. the bug being fixed or feature being implemented is
228 in the llvm-gcc C++ front-end, in which case it must be written in
231 <li>Test cases, especially for regressions, should be reduced as much as
232 possible, by <a href="Bugpoint.html">bugpoint</a> or manually. It is
233 unacceptable to place an entire failing program into <tt>llvm/test</tt> as
234 this creates a <i>time-to-test</i> burden on all developers. Please keep
238 <p>Note that llvm/test is designed for regression and small feature tests
239 only. More extensive test cases (e.g., entire applications, benchmarks, etc)
240 should be added to the <tt>llvm-test</tt> test suite. The llvm-test suite is
241 for coverage (correctness, performance, etc) testing, not feature or
242 regression testing.</p>
245 <!-- _______________________________________________________________________ -->
246 <div class="doc_subsection"> <a name="quality">Quality</a></div>
247 <div class="doc_text">
248 <p>The minimum quality standards that any change must satisfy before being
249 committed to the main development branch are:</p>
252 <li>Code must adhere to the <a href="CodingStandards.html">LLVM Coding
255 <li>Code must compile cleanly (no errors, no warnings) on at least one
258 <li>Bug fixes and new features should <a href="#testcases">include a
259 testcase</a> so we know if the fix/feature ever regresses in the
262 <li>Code must pass the dejagnu (<tt>llvm/test</tt>) test suite.</li>
264 <li>The code must not cause regressions on a reasonable subset of llvm-test,
265 where "reasonable" depends on the contributor's judgement and the scope of
266 the change (more invasive changes require more testing). A reasonable
267 subset might be something like
268 "<tt>llvm-test/MultiSource/Benchmarks</tt>".</li>
271 <p>Additionally, the committer is responsible for addressing any problems found
272 in the future that the change is responsible for. For example:</p>
275 <li>The code should compile cleanly on all supported platforms.</li>
277 <li>The changes should not cause any correctness regressions in the
278 <tt>llvm-test</tt> suite and must not cause any major performance
281 <li>The change set should not cause performance or correctness regressions for
284 <li>The changes should not cause performance or correctness regressions in
285 code compiled by LLVM on all applicable targets.</li>
287 <li>You are expected to address any <a href="http://llvm.org/bugs/">bugzilla
288 bugs</a> that result from your change.</li>
291 <p>We prefer for this to be handled before submission but understand that it
292 isn't possible to test all of this for every submission. Our build bots and
293 nightly testing infrastructure normally finds these problems. A good rule of
294 thumb is to check the nightly testers for regressions the day after your
295 change. Build bots will directly email you if a group of commits that
296 included yours caused a failure. You are expected to check the build bot
297 messages to see if they are your fault and, if so, fix the breakage.</p>
299 <p>Commits that violate these quality standards (e.g. are very broken) may be
300 reverted. This is necessary when the change blocks other developers from
301 making progress. The developer is welcome to re-commit the change after the
302 problem has been fixed.</p>
305 <!-- _______________________________________________________________________ -->
306 <div class="doc_subsection">
307 <a name="commitaccess">Obtaining Commit Access</a></div>
308 <div class="doc_text">
310 <p>We grant commit access to contributors with a track record of submitting high
311 quality patches. If you would like commit access, please send an email to
312 <a href="mailto:sabre@nondot.org">Chris</a> with the following
316 <li>The user name you want to commit with, e.g. "hacker".</li>
318 <li>The full name and email address you want message to llvm-commits to come
319 from, e.g. "J. Random Hacker <hacker@yoyodyne.com>".</li>
321 <li>A "password hash" of the password you want to use, e.g. "2ACR96qjUqsyM".
322 Note that you don't ever tell us what your password is, you just give it
323 to us in an encrypted form. To get this, run "htpasswd" (a utility that
324 comes with apache) in crypt mode (often enabled with "-d"), or find a web
325 page that will do it for you.</li>
328 <p>Once you've been granted commit access, you should be able to check out an
329 LLVM tree with an SVN URL of "https://username@llvm.org/..." instead of the
330 normal anonymous URL of "http://llvm.org/...". The first time you commit
331 you'll have to type in your password. Note that you may get a warning from
332 SVN about an untrusted key, you can ignore this. To verify that your commit
333 access works, please do a test commit (e.g. change a comment or add a blank
334 line). Your first commit to a repository may require the autogenerated email
335 to be approved by a mailing list. This is normal, and will be done when
336 the mailing list owner has time.</p>
338 <p>If you have recently been granted commit access, these policies apply:</p>
341 <li>You are granted <i>commit-after-approval</i> to all parts of LLVM. To get
342 approval, submit a <a href="#patches">patch</a> to
343 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>.
344 When approved you may commit it yourself.</li>
346 <li>You are allowed to commit patches without approval which you think are
347 obvious. This is clearly a subjective decision — we simply expect
348 you to use good judgement. Examples include: fixing build breakage,
349 reverting obviously broken patches, documentation/comment changes, any
350 other minor changes.</li>
352 <li>You are allowed to commit patches without approval to those portions of
353 LLVM that you have contributed or maintain (i.e., have been assigned
354 responsibility for), with the proviso that such commits must not break the
355 build. This is a "trust but verify" policy and commits of this nature are
356 reviewed after they are committed.</li>
358 <li>Multiple violations of these policies or a single egregious violation may
359 cause commit access to be revoked.</li>
362 <p>In any case, your changes are still subject to <a href="#reviews">code
363 review</a> (either before or after they are committed, depending on the
364 nature of the change). You are encouraged to review other peoples' patches
365 as well, but you aren't required to.</p>
368 <!-- _______________________________________________________________________ -->
369 <div class="doc_subsection"> <a name="newwork">Making a Major Change</a></div>
370 <div class="doc_text">
371 <p>When a developer begins a major new project with the aim of contributing it
372 back to LLVM, s/he should inform the community with an email to
373 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a>
374 email list, to the extent possible. The reason for this is to:
377 <li>keep the community informed about future changes to LLVM, </li>
379 <li>avoid duplication of effort by preventing multiple parties working on the
380 same thing and not knowing about it, and</li>
382 <li>ensure that any technical issues around the proposed work are discussed
383 and resolved before any significant work is done.</li>
386 <p>The design of LLVM is carefully controlled to ensure that all the pieces fit
387 together well and are as consistent as possible. If you plan to make a major
388 change to the way LLVM works or want to add a major new extension, it is a
389 good idea to get consensus with the development community before you start
392 <p>Once the design of the new feature is finalized, the work itself should be
393 done as a series of <a href="#incremental">incremental changes</a>, not as a
394 long-term development branch.</p>
397 <!-- _______________________________________________________________________ -->
398 <div class="doc_subsection"> <a name="incremental">Incremental Development</a>
400 <div class="doc_text">
401 <p>In the LLVM project, we do all significant changes as a series of incremental
402 patches. We have a strong dislike for huge changes or long-term development
403 branches. Long-term development branches have a number of drawbacks:</p>
406 <li>Branches must have mainline merged into them periodically. If the branch
407 development and mainline development occur in the same pieces of code,
408 resolving merge conflicts can take a lot of time.</li>
410 <li>Other people in the community tend to ignore work on branches.</li>
412 <li>Huge changes (produced when a branch is merged back onto mainline) are
413 extremely difficult to <a href="#reviews">code review</a>.</li>
415 <li>Branches are not routinely tested by our nightly tester
418 <li>Changes developed as monolithic large changes often don't work until the
419 entire set of changes is done. Breaking it down into a set of smaller
420 changes increases the odds that any of the work will be committed to the
421 main repository.</li>
424 <p>To address these problems, LLVM uses an incremental development style and we
425 require contributors to follow this practice when making a large/invasive
426 change. Some tips:</p>
429 <li>Large/invasive changes usually have a number of secondary changes that are
430 required before the big change can be made (e.g. API cleanup, etc). These
431 sorts of changes can often be done before the major change is done,
432 independently of that work.</li>
434 <li>The remaining inter-related work should be decomposed into unrelated sets
435 of changes if possible. Once this is done, define the first increment and
436 get consensus on what the end goal of the change is.</li>
438 <li>Each change in the set can be stand alone (e.g. to fix a bug), or part of
439 a planned series of changes that works towards the development goal.</li>
441 <li>Each change should be kept as small as possible. This simplifies your work
442 (into a logical progression), simplifies code review and reduces the
443 chance that you will get negative feedback on the change. Small increments
444 also facilitate the maintenance of a high quality code base.</li>
446 <li>Often, an independent precursor to a big change is to add a new API and
447 slowly migrate clients to use the new API. Each change to use the new API
448 is often "obvious" and can be committed without review. Once the new API
449 is in place and used, it is much easier to replace the underlying
450 implementation of the API. This implementation change is logically
451 separate from the API change.</li>
454 <p>If you are interested in making a large change, and this scares you, please
455 make sure to first <a href="#newwork">discuss the change/gather consensus</a>
456 then ask about the best way to go about making the change.</p>
459 <!-- _______________________________________________________________________ -->
460 <div class="doc_subsection"><a name="attribution">Attribution of
462 <div class="doc_text">
463 <p>We believe in correct attribution of contributions to their contributors.
464 However, we do not want the source code to be littered with random
465 attributions "this code written by J. Random Hacker" (this is noisy and
466 distracting). In practice, the revision control system keeps a perfect
467 history of who changed what, and the CREDITS.txt file describes higher-level
468 contributions. If you commit a patch for someone else, please say "patch
469 contributed by J. Random Hacker!" in the commit message.</p>
471 <p>Overall, please do not add contributor names to the source code.</p>
474 <!--=========================================================================-->
475 <div class="doc_section">
476 <a name="clp">Copyright, License, and Patents</a>
478 <!--=========================================================================-->
480 <div class="doc_text">
481 <p>This section addresses the issues of copyright, license and patents for the
482 LLVM project. Currently, the University of Illinois is the LLVM copyright
483 holder and the terms of its license to LLVM users and developers is the
484 <a href="http://www.opensource.org/licenses/UoI-NCSA.php">University of
485 Illinois/NCSA Open Source License</a>.</p>
487 <div class="doc_notes">
488 <p style="text-align:center;font-weight:bold">NOTE: This section deals with
489 legal matters but does not provide legal advice. We are not lawyers, please
490 seek legal counsel from an attorney.</p>
494 <!-- _______________________________________________________________________ -->
495 <div class="doc_subsection"><a name="copyright">Copyright</a></div>
496 <div class="doc_text">
497 <p>For consistency and ease of management, the project requires the copyright
498 for all LLVM software to be held by a single copyright holder: the University
499 of Illinois (UIUC).</p>
501 <p>Although UIUC may eventually reassign the copyright of the software to
502 another entity (e.g. a dedicated non-profit "LLVM Organization") the intent
503 for the project is to always have a single entity hold the copyrights to LLVM
504 at any given time.</p>
506 <p>We believe that having a single copyright holder is in the best interests of
507 all developers and users as it greatly reduces the managerial burden for any
508 kind of administrative or technical decisions about LLVM. The goal of the
509 LLVM project is to always keep the code open and <a href="#license">licensed
510 under a very liberal license</a>.</p>
513 <!-- _______________________________________________________________________ -->
514 <div class="doc_subsection"><a name="license">License</a></div>
515 <div class="doc_text">
516 <p>We intend to keep LLVM perpetually open source and to use a liberal open
517 source license. The current license is the
518 <a href="http://www.opensource.org/licenses/UoI-NCSA.php">University of
519 llinois/NCSA Open Source License</a>, which boils down to this:</p>
522 <li>You can freely distribute LLVM.</li>
524 <li>You must retain the copyright notice if you redistribute LLVM.</li>
526 <li>Binaries derived from LLVM must reproduce the copyright notice (e.g. in
527 an included readme file).</li>
529 <li>You can't use our names to promote your LLVM derived products.</li>
531 <li>There's no warranty on LLVM at all.</li>
534 <p>We believe this fosters the widest adoption of LLVM because it <b>allows
535 commercial products to be derived from LLVM</b> with few restrictions and
536 without a requirement for making any derived works also open source (i.e.
537 LLVM's license is not a "copyleft" license like the GPL). We suggest that you
538 read the <a href="http://www.opensource.org/licenses/UoI-NCSA.php">License</a>
539 if further clarification is needed.</p>
541 <p>Note that the LLVM Project does distribute llvm-gcc, <b>which is GPL.</b>
542 This means that anything "linked" into llvm-gcc must itself be compatible
543 with the GPL, and must be releasable under the terms of the GPL. This
544 implies that <b>any code linked into llvm-gcc and distributed to others may
545 be subject to the viral aspects of the GPL</b> (for example, a proprietary
546 code generator linked into llvm-gcc must be made available under the GPL).
547 This is not a problem for code already distributed under a more liberal
548 license (like the UIUC license), and does not affect code generated by
549 llvm-gcc. It may be a problem if you intend to base commercial development
550 on llvm-gcc without redistributing your source code.</p>
552 <p>We have no plans to change the license of LLVM. If you have questions or
553 comments about the license, please contact the
554 <a href="mailto:llvm-oversight@cs.uiuc.edu">LLVM Oversight Group</a>.</p>
557 <!-- _______________________________________________________________________ -->
558 <div class="doc_subsection"><a name="patents">Patents</a></div>
559 <div class="doc_text">
560 <p>To the best of our knowledge, LLVM does not infringe on any patents (we have
561 actually removed code from LLVM in the past that was found to infringe).
562 Having code in LLVM that infringes on patents would violate an important goal
563 of the project by making it hard or impossible to reuse the code for
564 arbitrary purposes (including commercial use).</p>
566 <p>When contributing code, we expect contributors to notify us of any potential
567 for patent-related trouble with their changes. If you or your employer own
568 the rights to a patent and would like to contribute code to LLVM that relies
569 on it, we require that the copyright owner sign an agreement that allows any
570 other user of LLVM to freely use your patent. Please contact
571 the <a href="mailto:llvm-oversight@cs.uiuc.edu">oversight group</a> for more
575 <!-- _______________________________________________________________________ -->
576 <div class="doc_subsection"><a name="devagree">Developer Agreements</a></div>
577 <div class="doc_text">
578 <p>With regards to the LLVM copyright and licensing, developers agree to assign
579 their copyrights to UIUC for any contribution made so that the entire
580 software base can be managed by a single copyright holder. This implies that
581 any contributions can be licensed under the license that the project
584 <p>When contributing code, you also affirm that you are legally entitled to
585 grant this copyright, personally or on behalf of your employer. If the code
586 belongs to some other entity, please raise this issue with the oversight
587 group before the code is committed.</p>
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