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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="#quality">Quality</a></li>
18 <li><a href="#testcases">Test Cases</a></li>
19 <li><a href="#c_new">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>
39 <li><a href="#terms">Terminology</a></li>
41 <div class="doc_author">Written by LLVM Oversight Team</div>
43 <!--=========================================================================-->
44 <div class="doc_section"><a name="introduction">Introduction</a></div>
45 <!--=========================================================================-->
46 <div class="doc_text">
47 <p>This document contains the LLVM Developer Policy which defines the
48 project's policy towards developers and their contributions. The intent of
49 this policy is to eliminate mis-communication, rework, and confusion that
50 might arise from the distributed nature of LLVM's development. By stating
51 the policy in clear terms, we hope each developer can know ahead of time
52 what to expect when making LLVM contributions.</p>
53 <p>This policy is also designed to accomplish the following objectives:</p>
55 <li>Attract both users and developers to the LLVM project.</li>
56 <li>Make life as simple and easy for contributors as possible.</li>
57 <li>Keep the top of tree CVS/SVN trees as stable as possible.</li>
60 <p>This policy is aimed at regular contributors to LLVM. People interested in
61 contributing one-off patches can do so in an informal way by sending them to
62 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
63 llvm-commits mailing list</a> and engaging another developer to see it through
68 <!--=========================================================================-->
69 <div class="doc_section"><a name="general">General Policies</a></div>
70 <!--=========================================================================-->
71 <div class="doc_text">
72 <p>This section contains policies that pertain generally to regular LLVM
73 developers. We always welcome <a href="#patches">random patches</a> from
74 people who do not routinely contribute to LLVM, but expect more from regular
75 contributors to keep the system as efficient as possible for everyone.
76 Regular LLVM developers are expected to meet the following obligations in
77 order for LLVM to maintain a high standard of quality.<p>
80 <!-- _______________________________________________________________________ -->
81 <div class="doc_subsection"> <a name="informed">Stay Informed</a> </div>
82 <div class="doc_text">
83 <p>Developers should stay informed by reading at least the
84 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a>
85 email list. If you are doing anything more than just casual work on LLVM,
86 it is suggested that you also subscribe to the
87 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
88 list and pay attention to changes being made by others.</p>
89 <p>We recommend that active developers register an email account with
90 <a href="http://llvm.org/bugs/">LLVM Bugzilla</a> and preferably subscribe to
91 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmbugs">llvm-bugs</a>
92 email list to keep track of bugs and enhancements occurring in LLVM.</p>
95 <!-- _______________________________________________________________________ -->
96 <div class="doc_subsection"> <a name="reviews">Code Reviews</a></div>
97 <div class="doc_text">
98 <p>LLVM has a code review policy. Code review is one way to increase the
99 quality of software. We generally follow these policies:</p>
101 <li>All developers are required to have significant changes reviewed
102 before they are committed to the repository.</li>
103 <li>Code reviews are conducted by email, usually on the llvm-commits
105 <li>Code can be reviewed either before it is committed or after. We expect
106 major changes to be reviewed before being committed, but smaller
107 changes (or changes where the developer owns the component) can be
108 reviewed after commit.</li>
109 <li>The developer responsible for a code change is also responsible for
110 making all necessary review-related changes.</li>
111 <li>Developers should participate in code reviews as both a reviewer and
112 a reviewee. We don't have a dedicated team of reviewers. If someone is
113 kind enough to review your code, you should return the favor for someone
117 <!-- _______________________________________________________________________ -->
118 <div class="doc_subsection"> <a name="quality">Quality</a></div>
119 <div class="doc_text">
120 <p>The minimum quality standards that any change must satisfy before being
121 committed to the main development branch are:</p>
123 <li>Code must adhere to the
124 <a href="CodingStandards.html">LLVM Coding Standards</a>.</li>
125 <li>Code must compile cleanly (no errors, no warnings) on at least one
127 <li>Code must pass the deja gnu (llvm/test) test suite.</li>
128 <li>The code must not cause regressions on a reasonable subset of llvm-test,
129 where "reasonable" depends on the contributor's judgement and the scope
130 of the change (more invasive changes require more testing). A reasonable
131 subset is "<tt>llvm-test/MultiSource/Benchmarks</tt>".</li>
133 <p>Additionally, the committer is responsible for addressing any problems
134 found that the change is responsible for. For example:</p>
136 <li>The code should compile cleanly on all platforms.</li>
137 <li>The changes should not cause regressions in the <tt>llvm-test</tt>
138 suite including SPEC CINT2000, SPEC CFP2000, SPEC CINT2006, and
140 <li>The change set should not cause performance or correctness regressions
141 for the LLVM tools.</li>
142 <li>The changes should not cause performance or correctness regressions in
143 code compiled by LLVM on all applicable targets.</li>
144 <li>You are expected to address any <a href="http://llvm.org/bugs/">bugzilla
145 bugs</a> that result from your change.</li>
148 <p>We prefer for this to be handled before submission but understand that it's
149 not possible to test all of this for every submission. Our nightly testing
150 infrastructure normally finds these problems. A good rule of thumb is to
151 check the nightly testers for regressions the day after your change.</p>
153 <p>Commits that violate these quality standards (e.g. are very broken) may
154 be reverted. This is necessary when the change blocks other developers from
155 making progress. The developer is welcome to re-commit the change after
156 the problem has been fixed.</p>
159 <!-- _______________________________________________________________________ -->
160 <div class="doc_subsection"> <a name="testcases">Test Cases</a></div>
161 <div class="doc_text">
162 <p>Developers are required to create test cases for any bugs fixed and any new
163 features added. The following policies apply:</p>
165 <li>All feature and regression test cases must be added to the
166 <tt>llvm/test</tt> directory. The appropriate sub-directory should be
167 selected (see the <a href="TestingGuide.html">Testing Guide</a> for
169 <li>Test cases should be written in
170 <a href="LangRef.html">LLVM assembly language</a> unless the
171 feature or regression being tested requires another language (e.g. the
172 bug being fixed or feature being implemented is in the llvm-gcc C++
174 <li>Test cases, especially for regressions, should be reduced as much as
175 possible, by <a href="CommandGuide/html/bugpoint.html">bugpoint</a> or
176 manually. It is unacceptable
177 to place an entire failing program into <tt>llvm/test</tt> as this creates
178 a <i>time-to-test</i> burden on all developers. Please keep them short.</li>
179 <li>More extensive test cases (applications, benchmarks, etc.) should be
180 added to the <tt>llvm-test</tt> test suite. This test suite is for
181 coverage: not features or regressions.</li>
185 <!-- _______________________________________________________________________ -->
186 <div class="doc_subsection"> <a name="c_new">Obtaining Commit Access</a></div>
187 <div class="doc_text">
190 We grant commit access to contributors with a track record of submitting high
191 quality patches. If you would like commit access, please send an email to the
192 <a href="mailto:llvm-oversight@cs.uiuc.edu">LLVM oversight group</a>.</p>
194 <p>If you have recently been granted commit access, these policies apply:</p>
196 <li>You are granted <i>commit-after-approval</i> to all parts of LLVM.
197 To get approval, submit a <a href="#patches">patch</a> to
198 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
199 llvm-commits</a>. When approved you may commit it yourself.</li>
200 <li>You are allowed to commit patches without approval which you think are
201 obvious. This is clearly a subjective decision. We simply expect you to
202 use good judgement. Examples include: fixing build breakage, reverting
203 obviously broken patches, documentation/comment changes, any other minor
205 <li>You are allowed to commit patches without approval to those portions
206 of LLVM that you have contributed or maintain (have been assigned
207 responsibility for), with the proviso that such commits must not break the
208 build. This is a "trust but verify" policy and commits of this nature are
209 reviewed after they are committed.</li>
210 <li>Multiple violations of these policies or a single egregious violation
211 may cause commit access to be revoked.</li>
216 <!-- _______________________________________________________________________ -->
217 <div class="doc_subsection"> <a name="newwork">Making a Major Change</a></div>
218 <div class="doc_text">
219 <p>When a developer begins a major new project with the aim of contributing
220 it back to LLVM, s/he should inform the community with an email to
221 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvm-dev</a>
222 email list, to the extent possible. The reason for this is to:
224 <li>keep the community informed about future changes to LLVM, </li>
225 <li>avoid duplication of effort by having multiple parties working on the
226 same thing and not knowing about it, and</li>
227 <li>ensure that any technical issues around the proposed work are
228 discussed and resolved before any significant work is done.</li>
231 <p>The design of LLVM is carefully controlled to ensure that all the pieces
232 fit together well and are as consistent as possible. If you plan to make a
233 major change to the way LLVM works or
234 a major new extension, it is a good idea to get consensus with the development
235 community before you start working on it.</p>
239 <!-- _______________________________________________________________________ -->
240 <div class="doc_subsubsection"> <a name="incremental">Incremental Development</a>
242 <div class="doc_text">
243 <p>Once the design of the new feature is finalized, the work itself should be
244 done as a series of incremental changes, not as a long-term development
245 branch. Long-term development branches have a number of drawbacks:</p>
248 <li>Branches must have mainline merged into them periodically. If the branch
249 development and mainline development occur in the same pieces of code,
250 resolving merge conflicts can take a lot of time.</li>
251 <li>Other people in the community tend to ignore work on branches.</li>
252 <li>Huge changes (produced when a branch is merged back onto mainline) are
253 extremely difficult to <a href="#reviews">code review</a>.</li>
254 <li>Branches are not routinely tested by our nightly tester
256 <li>Changes developed as monolithic large changes often don't work until the
257 entire set of changes is done. Breaking it down into a set of smaller
258 changes increases the odds that any of the work will be committed to the
259 main repository.</li>
263 To address these problems, LLVM uses an incremental development style and we
264 require contributors to follow this practice when making a large/invasive
265 change. Some tips:</p>
268 <li>Large/invasive changes usually have a number of secondary changes that
269 are required before the big change can be made (e.g. API cleanup, etc).
270 These sorts of changes can often be done before the major change is done,
271 independently of that work.</li>
272 <li>The remaining inter-related work should be decomposed into unrelated
273 sets of changes if possible. Once this is done, define the first increment
274 and get consensus on what the end goal of the change is.</li>
275 <li>Increments can be stand alone (e.g. to fix a bug), or part of a planned
276 series of increments towards some development goal.</li>
277 <li>Increments should be kept as small as possible. This simplifies your
278 work (into a logical progression), simplifies code review and reduces the
279 chance that you will get negative feedback on the change. Small increments
280 also facilitate the maintenance of a high quality code base.</li>
281 <li>Often, an independent precursor to a big change is to add a new API and
282 slowly migrate clients to use the new API. Each change to use the new
283 API is often "obvious" and can be committed without review. Once the
284 new API is in place and used, it is often easy to replace the underlying
285 implementation of the API.</li>
288 <p>If you are interested in making a large change, and this scares you, please
289 make sure to first <a href="#newwork">discuss the change/gather
290 consensus</a> then feel free to ask about the best way to go about making
294 <!-- _______________________________________________________________________ -->
295 <div class="doc_subsection"><a name="attribution">Attribution of
297 <div class="doc_text">
298 <p>We believe in correct attribution of contributions to
299 their contributors. However, we do not want the source code to be littered
300 with random attributions (this is noisy/distracting and revision control
301 keeps a perfect history of this anyway). As such, we follow these rules:</p>
303 <li>Developers who originate new files in LLVM should place their name at
304 the top of the file per the
305 <a href="CodingStandards.html#scf_commenting">Coding Standards</a>.</li>
306 <li>There should be only one name at the top of the file and it should be
307 the person who created the file.</li>
308 <li>Placing your name in the file does not imply <a
309 href="#candl">copyright</a>: it is only used to attribute the file to
310 its original author.</li>
311 <li>Developers should be aware that after some time has passed, the name at
312 the top of a file may become meaningless as maintenance/ownership of files
313 changes. Revision control keeps an accurate history of contributions.</li>
314 <li>Developers should maintain their entry in the
315 <a href="http://llvm.org/cvsweb/cvsweb.cgi/llvm/CREDITS.TXT?rev=HEAD&content-type=text/x-cvsweb-markup">CREDITS.txt</a>
316 file to summarize their contributions.</li>
317 <li>Commit comments should contain correct attribution of the person who
318 submitted the patch if that person is not the committer (i.e. when a
319 developer with commit privileges commits a patch for someone else).</li>
324 <!--=========================================================================-->
325 <div class="doc_section"><a name="patches">Patch Policies</a></div>
326 <!--=========================================================================-->
328 <div class="doc_text">
329 <p>This section describes policies that apply to developers who regularly
330 contribute code to LLVM. As usual, we often accept small patches and
331 contributions that do not follow this policy. In this case, one of the
332 regular contributors has to get the code in shape.</p>
335 <!-- _______________________________________________________________________ -->
336 <div class="doc_subsection"> <a name="p_form">Patch Form</a></div>
337 <div class="doc_text">
338 <p>When submitting a patch, developers must follow these rules:</p>
340 <li>Patches must be made against the CVS HEAD (main development trunk),
342 <li>Patches should be made with this command:
343 <pre>cvs diff -Ntdup -5</pre>
344 or with the utility <tt>utils/mkpatch</tt>.</li>
345 <li>Patches should not include differences in generated code such as the
346 code generated by <tt>flex</tt>, <tt>bison</tt> or <tt>tblgen</tt>. The
347 <tt>utils/mkpatch</tt> utility takes care of this for you.</li>
348 <li>Contributions must not knowingly infringe on any patents. To the best of
349 our knowledge, LLVM is free of any existing patent violations and it is our
350 intent to keep it that way.</li>
354 <!-- _______________________________________________________________________ -->
355 <div class="doc_subsection"> <a name="p_submission">Patch Submission</a></div>
356 <div class="doc_text">
357 <p>When a patch is ready to be submitted, these policies apply:</p>
359 <li>Patches should be submitted immediately after they are generated. Stale
360 patches may not apply correctly if the underlying code changes between the
361 time the patch was created and the time it is applied.</li>
362 <li>Patches should be submitted by e-mail to the
363 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
364 llvm-commits</a> list.</li>
368 <!-- _______________________________________________________________________ -->
369 <div class="doc_subsection"> <a name="p_aftersub">After Submission</a></div>
370 <div class="doc_text">
371 <p>After a patch has been submitted, these policies apply:</p>
373 <li>The patch is subject to review by anyone on the
374 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
376 <li>Changes recommended by a reviewer should be incorporated into your
377 patch or you should explain why the reviewer is incorrect.
378 <li>Changes to the patch must be re-submitted to the
379 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
381 <li>This process iterates until all review issues have been addressed.</li>
385 <!-- _______________________________________________________________________ -->
386 <div class="doc_subsection"> <a name="p_aftercommit">After Commit</a></div>
387 <div class="doc_text">
388 <p>After a patch has been committed, these policies apply:</p>
390 <li>The patch is subject to further review by anyone on the llvm-commits
392 <li>The patch submitter is responsible for all aspects of the patch per
393 the <a href="quality">quality policy</a> above.</li>
394 <li>If the patch is discovered to not meet the
395 <a href="quality">quality policy</a> standards within a reasonable time
396 frame (24 hours), it may be subject to reversal.</li>
400 <!--=========================================================================-->
401 <div class="doc_section"><a name="candl">Copyright and License</a></div>
402 <!--=========================================================================-->
404 <div class="doc_text">
405 <p>We address here the issues of copyright and license for the LLVM project.
406 The object of the copyright and license is the LLVM source code and
408 Currently, the University of Illinois is the LLVM copyright holder and the
409 terms of its license to LLVM users and developers is the
410 <a href="http://www.opensource.org/licenses/UoI-NCSA.php">University of
411 Illinois/NCSA Open Source License</a>.
413 <div class="doc_notes">
414 <p><b>NOTE: This section deals with legal matters but does not provide
415 official legal advice. We are not lawyers, please seek legal counsel from an
421 <!-- _______________________________________________________________________ -->
422 <div class="doc_subsection"><a name="copyright">Copyright</a></div>
423 <div class="doc_text">
425 <p>For consistency and ease of management, the project requires the
426 copyright for all LLVM software to be held by a single copyright holder:
427 the University of Illinois (UIUC).</p>
430 Although UIUC may eventually reassign the copyright of the software to another
431 entity (e.g. a dedicated non-profit "LLVM Organization", or something)
432 the intent for the project is to always have a single entity hold the
433 copyrights to LLVM at any given time.</p>
435 <p>We believe that having a single copyright
436 holder is in the best interests of all developers and users as it greatly
437 reduces the managerial burden for any kind of administrative or technical
438 decisions about LLVM. The goal of the LLVM project is to always keep the code
439 open and <a href="#license">licensed under a very liberal license</a>.</p>
442 <!-- _______________________________________________________________________ -->
443 <div class="doc_subsection"><a name="license">License</a></div>
444 <div class="doc_text">
445 <p>We intend to keep LLVM perpetually open source
446 and to use a liberal open source license. The current license is the
447 <a href="http://www.opensource.org/licenses/UoI-NCSA.php">
448 University of Illinois/NCSA Open Source License</a>, which boils
451 <li>You can freely distribute LLVM.</li>
452 <li>You must retain the copyright notice if you redistribute LLVM.</li>
453 <li>Binaries derived from LLVM must reproduce the copyright notice.</li>
454 <li>You can't use our names to promote your LLVM derived products.</li>
455 <li>There's no warranty on LLVM at all.</li>
458 <p>We believe this fosters the widest adoption of LLVM because it <b>allows
459 commercial products to be derived from LLVM</b> with few restrictions and
460 without a requirement for making any derived works also open source (i.e.
461 LLVM's license is not a "copyleft" license like the GPL). We suggest that you
462 read the <a href="http://www.opensource.org/licenses/UoI-NCSA.php">License</a>
463 if further clarification is needed.</p>
465 <p>Note that the LLVM Project does distribute some code that includes GPL
466 software (notably, llvm-gcc which is based on the GCC GPL source base).
467 This means that anything "linked" into to llvm-gcc must itself be compatible
468 with the GPL, and must be releasable under the terms of the GPL. This implies
469 that you <b>any code linked into llvm-gcc and distributed may be subject to
470 the viral aspects of the GPL</b>. This is not a problem for the main LLVM
471 distribution (which is already licensed under a more liberal license), but may
472 be a problem if you intend to do commercial development without redistributing
473 your source code.</p>
475 <p>We have no plans to change the license of LLVM. If you have questions
476 or comments about the license, please contact the <a
477 href="mailto:llvm-oversight@cs.uiuc.edu">LLVM Oversight Group</a>.</p>
480 <!-- _______________________________________________________________________ -->
481 <div class="doc_subsection"><a name="devagree">Developer Agreements</a></div>
482 <div class="doc_text">
483 <p>With regards to the LLVM copyright and licensing, developers agree to
484 assign their copyrights to UIUC for any contribution made so that
485 the entire software base can be managed by a single copyright holder. This
486 implies that any contributions can be licensed under the license that the
491 <!--=========================================================================-->
492 <div class="doc_section"><a name="terms">Terminology</a></div>
493 <!--=========================================================================-->
494 <div class="doc_text">
495 <p>So that the policies defined in this document are clear, we define some
498 <dt><a name="t_change">Change</a></dt>
499 <dd>Any modification to LLVM including documentation, tests, build system,
500 etc. either in <a href="#t_patch">patch</a> or
501 <a href="#t_commit">commit</a> form.</dd>
502 <dt><a name="t_commit">Commit</a><dt>
503 <dd>A <a href="t_change">change</a> submitted directly to LLVM software
504 repository via the <tt>cvs commit</tt> command.</dd>
505 <dt><a name="t_developer">Developer</a></dt>
506 <dd>Anyone who submits a <a href="#t_change">change</a> to LLVM.</dd>
507 <dt><a name="t_inrement">Increment</a></dt>
508 <dd>A <a href="#t_change">change</a> or set of changes, whether by
509 <a href="#t_patch">patch</a> or <a href="#t_commit">commit</a>, that are
510 related by a single common purpose. Increments are atomic as they
511 leave LLVM in a stable state (both compiling and working properly).</dd>
512 <dt><a name="t_patch">Patch</a></dt>
513 <dd>A <a href="#t_change">change</a> submitted by email in patch (diff)
514 format generated by the <tt>cvs diff</tt> command.</dd>
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