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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="#general">General Policies</a>
15 <li><a href="#informed">Stay Informed</a> </li>
16 <li><a href="#reviews">Code Reviews</a></li>
17 <li><a href="#testcases">Test Cases</a></li>
18 <li><a href="#quality">Quality</a></li>
19 <li><a href="#commitaccess">Obtaining Commit Access</a></li>
20 <li><a href="#newwork">Making a Major Change</a>
22 <li><a href="#incremental">Incremental Development</a></li>
24 <li><a href="#attribution">Attribution of Changes</a></li>
26 <li><a href="#patches">Patch Policies</a>
28 <li><a href="#p_form">Patch Form</a></li>
29 <li><a href="#p_submission">Patch Submission</a></li>
30 <li><a href="#p_aftersub">After Submission</a></li>
31 <li><a href="#p_aftercommit">After Commit</a></li>
33 <li><a href="#candl">Copyright and License</a>
35 <li><a href="#copyright">Copyright</a></li>
36 <li><a href="#license">License</a></li>
37 <li><a href="#devagree">Developer Agreements</a></li>
40 <div class="doc_author">Written by LLVM Oversight Team</div>
42 <!--=========================================================================-->
43 <div class="doc_section"><a name="introduction">Introduction</a></div>
44 <!--=========================================================================-->
45 <div class="doc_text">
46 <p>This document contains the LLVM Developer Policy which defines the
47 project's policy towards developers and their contributions. The intent of
48 this policy is to eliminate mis-communication, rework, and confusion that
49 might arise from the distributed nature of LLVM's development. By stating
50 the policy in clear terms, we hope each developer can know ahead of time
51 what to expect when making LLVM contributions.</p>
52 <p>This policy is also designed to accomplish the following objectives:</p>
54 <li>Attract both users and developers to the LLVM project.</li>
55 <li>Make life as simple and easy for contributors as possible.</li>
56 <li>Keep the top of tree CVS/SVN trees as stable as possible.</li>
59 <p>This policy is aimed at regular contributors to LLVM. People interested in
60 contributing one-off patches can do so in an informal way by sending them to
61 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
62 llvm-commits mailing list</a> and engaging another developer to see it through
67 <!--=========================================================================-->
68 <div class="doc_section"><a name="general">General Policies</a></div>
69 <!--=========================================================================-->
70 <div class="doc_text">
71 <p>This section contains policies that pertain generally to regular LLVM
72 developers. We always welcome <a href="#patches">random patches</a> from
73 people who do not routinely contribute to LLVM, but expect more from regular
74 contributors to keep the system as efficient as possible for everyone.
75 Regular LLVM developers are expected to meet the following obligations in
76 order for LLVM to maintain a high standard of quality.<p>
79 <!-- _______________________________________________________________________ -->
80 <div class="doc_subsection"> <a name="informed">Stay Informed</a> </div>
81 <div class="doc_text">
82 <p>Developers should stay informed by reading at least the
83 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a>
84 email list. If you are doing anything more than just casual work on LLVM,
85 it is suggested that you also subscribe to the
86 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
87 list and pay attention to changes being made by others.</p>
88 <p>We recommend that active developers register an email account with
89 <a href="http://llvm.org/bugs/">LLVM Bugzilla</a> and preferably subscribe to
90 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmbugs">llvm-bugs</a>
91 email list to keep track of bugs and enhancements occurring in LLVM.</p>
94 <!-- _______________________________________________________________________ -->
95 <div class="doc_subsection"> <a name="reviews">Code Reviews</a></div>
96 <div class="doc_text">
97 <p>LLVM has a code review policy. Code review is one way to increase the
98 quality of software. We generally follow these policies:</p>
100 <li>All developers are required to have significant changes reviewed
101 before they are committed to the repository.</li>
102 <li>Code reviews are conducted by email, usually on the llvm-commits
104 <li>Code can be reviewed either before it is committed or after. We expect
105 major changes to be reviewed before being committed, but smaller
106 changes (or changes where the developer owns the component) can be
107 reviewed after commit.</li>
108 <li>The developer responsible for a code change is also responsible for
109 making all necessary review-related changes.</li>
110 <li>Developers should participate in code reviews as both a reviewer and
111 a reviewee. We don't have a dedicated team of reviewers. If someone is
112 kind enough to review your code, you should return the favor for someone
117 <!-- _______________________________________________________________________ -->
118 <div class="doc_subsection"> <a name="testcases">Test Cases</a></div>
119 <div class="doc_text">
120 <p>Developers are required to create test cases for any bugs fixed and any new
121 features added. The following policies apply:</p>
123 <li>All feature and regression test cases must be added to the
124 <tt>llvm/test</tt> directory. The appropriate sub-directory should be
125 selected (see the <a href="TestingGuide.html">Testing Guide</a> for
127 <li>Test cases should be written in
128 <a href="LangRef.html">LLVM assembly language</a> unless the
129 feature or regression being tested requires another language (e.g. the
130 bug being fixed or feature being implemented is in the llvm-gcc C++
132 <li>Test cases, especially for regressions, should be reduced as much as
133 possible, by <a href="CommandGuide/html/bugpoint.html">bugpoint</a> or
134 manually. It is unacceptable
135 to place an entire failing program into <tt>llvm/test</tt> as this creates
136 a <i>time-to-test</i> burden on all developers. Please keep them short.</li>
137 <li>More extensive test cases (applications, benchmarks, etc.) should be
138 added to the <tt>llvm-test</tt> test suite. This test suite is for
139 coverage: not features or regressions.</li>
143 <!-- _______________________________________________________________________ -->
144 <div class="doc_subsection"> <a name="quality">Quality</a></div>
145 <div class="doc_text">
146 <p>The minimum quality standards that any change must satisfy before being
147 committed to the main development branch are:</p>
149 <li>Code must adhere to the
150 <a href="CodingStandards.html">LLVM Coding Standards</a>.</li>
151 <li>Code must compile cleanly (no errors, no warnings) on at least one
153 <li>Bug fixes and new features should <a href="#testcases">include a
154 testcase</a> so we know if the fix/feature ever regresses in the
156 <li>Code must pass the dejagnu (llvm/test) test suite.</li>
157 <li>The code must not cause regressions on a reasonable subset of llvm-test,
158 where "reasonable" depends on the contributor's judgement and the scope
159 of the change (more invasive changes require more testing). A reasonable
160 subset is "<tt>llvm-test/MultiSource/Benchmarks</tt>".</li>
162 <p>Additionally, the committer is responsible for addressing any problems
163 found in the future that the change is responsible for. For example:</p>
165 <li>The code should compile cleanly on all platforms.</li>
166 <li>The changes should not cause regressions in the <tt>llvm-test</tt>
167 suite including SPEC CINT2000, SPEC CFP2000, SPEC CINT2006, and
169 <li>The change set should not cause performance or correctness regressions
170 for the LLVM tools.</li>
171 <li>The changes should not cause performance or correctness regressions in
172 code compiled by LLVM on all applicable targets.</li>
173 <li>You are expected to address any <a href="http://llvm.org/bugs/">bugzilla
174 bugs</a> that result from your change.</li>
177 <p>We prefer for this to be handled before submission but understand that it's
178 not possible to test all of this for every submission. Our nightly testing
179 infrastructure normally finds these problems. A good rule of thumb is to
180 check the nightly testers for regressions the day after your change.</p>
182 <p>Commits that violate these quality standards (e.g. are very broken) may
183 be reverted. This is necessary when the change blocks other developers from
184 making progress. The developer is welcome to re-commit the change after
185 the problem has been fixed.</p>
188 <!-- _______________________________________________________________________ -->
189 <div class="doc_subsection">
190 <a name="commitaccess">Obtaining Commit Access</a></div>
191 <div class="doc_text">
194 We grant commit access to contributors with a track record of submitting high
195 quality patches. If you would like commit access, please send an email to the
196 <a href="mailto:llvm-oversight@cs.uiuc.edu">LLVM oversight group</a>.</p>
198 <p>If you have recently been granted commit access, these policies apply:</p>
200 <li>You are granted <i>commit-after-approval</i> to all parts of LLVM.
201 To get approval, submit a <a href="#patches">patch</a> to
202 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
203 llvm-commits</a>. When approved you may commit it yourself.</li>
204 <li>You are allowed to commit patches without approval which you think are
205 obvious. This is clearly a subjective decision. We simply expect you to
206 use good judgement. Examples include: fixing build breakage, reverting
207 obviously broken patches, documentation/comment changes, any other minor
209 <li>You are allowed to commit patches without approval to those portions
210 of LLVM that you have contributed or maintain (have been assigned
211 responsibility for), with the proviso that such commits must not break the
212 build. This is a "trust but verify" policy and commits of this nature are
213 reviewed after they are committed.</li>
214 <li>Multiple violations of these policies or a single egregious violation
215 may cause commit access to be revoked.</li>
220 <!-- _______________________________________________________________________ -->
221 <div class="doc_subsection"> <a name="newwork">Making a Major Change</a></div>
222 <div class="doc_text">
223 <p>When a developer begins a major new project with the aim of contributing
224 it back to LLVM, s/he should inform the community with an email to
225 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvm-dev</a>
226 email list, to the extent possible. The reason for this is to:
228 <li>keep the community informed about future changes to LLVM, </li>
229 <li>avoid duplication of effort by having multiple parties working on the
230 same thing and not knowing about it, and</li>
231 <li>ensure that any technical issues around the proposed work are
232 discussed and resolved before any significant work is done.</li>
235 <p>The design of LLVM is carefully controlled to ensure that all the pieces
236 fit together well and are as consistent as possible. If you plan to make a
237 major change to the way LLVM works or
238 a major new extension, it is a good idea to get consensus with the development
239 community before you start working on it.</p>
243 <!-- _______________________________________________________________________ -->
244 <div class="doc_subsubsection"> <a name="incremental">Incremental Development</a>
246 <div class="doc_text">
247 <p>Once the design of the new feature is finalized, the work itself should be
248 done as a series of incremental changes, not as a long-term development
249 branch. Long-term development branches have a number of drawbacks:</p>
252 <li>Branches must have mainline merged into them periodically. If the branch
253 development and mainline development occur in the same pieces of code,
254 resolving merge conflicts can take a lot of time.</li>
255 <li>Other people in the community tend to ignore work on branches.</li>
256 <li>Huge changes (produced when a branch is merged back onto mainline) are
257 extremely difficult to <a href="#reviews">code review</a>.</li>
258 <li>Branches are not routinely tested by our nightly tester
260 <li>Changes developed as monolithic large changes often don't work until the
261 entire set of changes is done. Breaking it down into a set of smaller
262 changes increases the odds that any of the work will be committed to the
263 main repository.</li>
267 To address these problems, LLVM uses an incremental development style and we
268 require contributors to follow this practice when making a large/invasive
269 change. Some tips:</p>
272 <li>Large/invasive changes usually have a number of secondary changes that
273 are required before the big change can be made (e.g. API cleanup, etc).
274 These sorts of changes can often be done before the major change is done,
275 independently of that work.</li>
276 <li>The remaining inter-related work should be decomposed into unrelated
277 sets of changes if possible. Once this is done, define the first increment
278 and get consensus on what the end goal of the change is.</li>
279 <li>Increments can be stand alone (e.g. to fix a bug), or part of a planned
280 series of increments towards some development goal.</li>
281 <li>Increments should be kept as small as possible. This simplifies your
282 work (into a logical progression), simplifies code review and reduces the
283 chance that you will get negative feedback on the change. Small increments
284 also facilitate the maintenance of a high quality code base.</li>
285 <li>Often, an independent precursor to a big change is to add a new API and
286 slowly migrate clients to use the new API. Each change to use the new
287 API is often "obvious" and can be committed without review. Once the
288 new API is in place and used, it is often easy to replace the underlying
289 implementation of the API.</li>
292 <p>If you are interested in making a large change, and this scares you, please
293 make sure to first <a href="#newwork">discuss the change/gather
294 consensus</a> then feel free to ask about the best way to go about making
298 <!-- _______________________________________________________________________ -->
299 <div class="doc_subsection"><a name="attribution">Attribution of
301 <div class="doc_text">
302 <p>We believe in correct attribution of contributions to
303 their contributors. However, we do not want the source code to be littered
304 with random attributions (this is noisy/distracting and revision control
305 keeps a perfect history of this anyway). As such, we follow these rules:</p>
307 <li>Developers who originate new files in LLVM should place their name at
308 the top of the file per the
309 <a href="CodingStandards.html#scf_commenting">Coding Standards</a>.</li>
310 <li>There should be only one name at the top of the file and it should be
311 the person who created the file.</li>
312 <li>Placing your name in the file does not imply <a
313 href="#candl">copyright</a>: it is only used to attribute the file to
314 its original author.</li>
315 <li>Developers should be aware that after some time has passed, the name at
316 the top of a file may become meaningless as maintenance/ownership of files
317 changes. Revision control keeps an accurate history of contributions.</li>
318 <li>Developers should maintain their entry in the
319 <a href="http://llvm.org/cvsweb/cvsweb.cgi/llvm/CREDITS.TXT?rev=HEAD&content-type=text/x-cvsweb-markup">CREDITS.txt</a>
320 file to summarize their contributions.</li>
321 <li>Commit comments should contain correct attribution of the person who
322 submitted the patch if that person is not the committer (i.e. when a
323 developer with commit privileges commits a patch for someone else).</li>
328 <!--=========================================================================-->
329 <div class="doc_section"><a name="patches">Patch Policies</a></div>
330 <!--=========================================================================-->
332 <div class="doc_text">
333 <p>This section describes policies that apply to developers who regularly
334 contribute code to LLVM. As usual, we often accept small patches and
335 contributions that do not follow this policy. In this case, one of the
336 regular contributors has to get the code in shape.</p>
339 <!-- _______________________________________________________________________ -->
340 <div class="doc_subsection"> <a name="p_form">Patch Form</a></div>
341 <div class="doc_text">
342 <p>When submitting a patch, developers must follow these rules:</p>
344 <li>Patches must be made against the CVS HEAD (main development trunk),
346 <li>Patches should be made with this command:
347 <pre>cvs diff -Ntdup -5</pre>
348 or with the utility <tt>utils/mkpatch</tt>.</li>
349 <li>Patches should not include differences in generated code such as the
350 code generated by <tt>flex</tt>, <tt>bison</tt> or <tt>tblgen</tt>. The
351 <tt>utils/mkpatch</tt> utility takes care of this for you.</li>
352 <li>Contributions must not knowingly infringe on any patents. To the best of
353 our knowledge, LLVM is free of any existing patent violations and it is our
354 intent to keep it that way.</li>
358 <!-- _______________________________________________________________________ -->
359 <div class="doc_subsection"> <a name="p_submission">Patch Submission</a></div>
360 <div class="doc_text">
361 <p>When a patch is ready to be submitted, these policies apply:</p>
363 <li>Patches should be submitted immediately after they are generated. Stale
364 patches may not apply correctly if the underlying code changes between the
365 time the patch was created and the time it is applied.</li>
366 <li>Patches should be submitted by e-mail to the
367 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
368 llvm-commits</a> list.</li>
372 <!-- _______________________________________________________________________ -->
373 <div class="doc_subsection"> <a name="p_aftersub">After Submission</a></div>
374 <div class="doc_text">
375 <p>After a patch has been submitted, these policies apply:</p>
377 <li>The patch is subject to review by anyone on the
378 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
380 <li>Changes recommended by a reviewer should be incorporated into your
381 patch or you should explain why the reviewer is incorrect.
382 <li>Changes to the patch must be re-submitted to the
383 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
385 <li>This process iterates until all review issues have been addressed.</li>
389 <!-- _______________________________________________________________________ -->
390 <div class="doc_subsection"> <a name="p_aftercommit">After Commit</a></div>
391 <div class="doc_text">
392 <p>After a patch has been committed, these policies apply:</p>
394 <li>The patch is subject to further review by anyone on the llvm-commits
396 <li>The patch submitter is responsible for all aspects of the patch per
397 the <a href="quality">quality policy</a> above.</li>
398 <li>If the patch is discovered to not meet the
399 <a href="quality">quality policy</a> standards within a reasonable time
400 frame (24 hours), it may be subject to reversal.</li>
404 <!--=========================================================================-->
405 <div class="doc_section"><a name="candl">Copyright and License</a></div>
406 <!--=========================================================================-->
408 <div class="doc_text">
409 <p>We address here the issues of copyright and license for the LLVM project.
410 The object of the copyright and license is the LLVM source code and
412 Currently, the University of Illinois is the LLVM copyright holder and the
413 terms of its license to LLVM users and developers is the
414 <a href="http://www.opensource.org/licenses/UoI-NCSA.php">University of
415 Illinois/NCSA Open Source License</a>.
417 <div class="doc_notes">
418 <p><b>NOTE: This section deals with legal matters but does not provide
419 official legal advice. We are not lawyers, please seek legal counsel from an
425 <!-- _______________________________________________________________________ -->
426 <div class="doc_subsection"><a name="copyright">Copyright</a></div>
427 <div class="doc_text">
429 <p>For consistency and ease of management, the project requires the
430 copyright for all LLVM software to be held by a single copyright holder:
431 the University of Illinois (UIUC).</p>
434 Although UIUC may eventually reassign the copyright of the software to another
435 entity (e.g. a dedicated non-profit "LLVM Organization", or something)
436 the intent for the project is to always have a single entity hold the
437 copyrights to LLVM at any given time.</p>
439 <p>We believe that having a single copyright
440 holder is in the best interests of all developers and users as it greatly
441 reduces the managerial burden for any kind of administrative or technical
442 decisions about LLVM. The goal of the LLVM project is to always keep the code
443 open and <a href="#license">licensed under a very liberal license</a>.</p>
446 <!-- _______________________________________________________________________ -->
447 <div class="doc_subsection"><a name="license">License</a></div>
448 <div class="doc_text">
449 <p>We intend to keep LLVM perpetually open source
450 and to use a liberal open source license. The current license is the
451 <a href="http://www.opensource.org/licenses/UoI-NCSA.php">
452 University of Illinois/NCSA Open Source License</a>, which boils
455 <li>You can freely distribute LLVM.</li>
456 <li>You must retain the copyright notice if you redistribute LLVM.</li>
457 <li>Binaries derived from LLVM must reproduce the copyright notice.</li>
458 <li>You can't use our names to promote your LLVM derived products.</li>
459 <li>There's no warranty on LLVM at all.</li>
462 <p>We believe this fosters the widest adoption of LLVM because it <b>allows
463 commercial products to be derived from LLVM</b> with few restrictions and
464 without a requirement for making any derived works also open source (i.e.
465 LLVM's license is not a "copyleft" license like the GPL). We suggest that you
466 read the <a href="http://www.opensource.org/licenses/UoI-NCSA.php">License</a>
467 if further clarification is needed.</p>
469 <p>Note that the LLVM Project does distribute some code that includes GPL
470 software (notably, llvm-gcc which is based on the GCC GPL source base).
471 This means that anything "linked" into to llvm-gcc must itself be compatible
472 with the GPL, and must be releasable under the terms of the GPL. This implies
473 that you <b>any code linked into llvm-gcc and distributed may be subject to
474 the viral aspects of the GPL</b>. This is not a problem for the main LLVM
475 distribution (which is already licensed under a more liberal license), but may
476 be a problem if you intend to do commercial development without redistributing
477 your source code.</p>
479 <p>We have no plans to change the license of LLVM. If you have questions
480 or comments about the license, please contact the <a
481 href="mailto:llvm-oversight@cs.uiuc.edu">LLVM Oversight Group</a>.</p>
484 <!-- _______________________________________________________________________ -->
485 <div class="doc_subsection"><a name="devagree">Developer Agreements</a></div>
486 <div class="doc_text">
487 <p>With regards to the LLVM copyright and licensing, developers agree to
488 assign their copyrights to UIUC for any contribution made so that
489 the entire software base can be managed by a single copyright holder. This
490 implies that any contributions can be licensed under the license that the
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