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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="#newwork">Starting New Work</a></li>
17 <li><a href="#reviews">Code Reviews</a></li>
18 <li><a href="#quality">Quality</a></li>
19 <li><a href="#testcases">Test Cases</a></li>
20 <li><a href="#c_new">Obtaining Commit Access</a></li>
21 <li><a href="#incremental">Incremental Development</a></li>
22 <li><a href="#attribution">Attribution</a></li>
24 <li><a href="#patches">Patch Policies</a>
26 <li><a href="#p_form">Patch Form</a></li>
27 <li><a href="#p_submission">Patch Submission</a></li>
28 <li><a href="#p_aftersub">After Submission</a></li>
29 <li><a href="#p_aftercommit">After Commit</a></li>
31 <li><a href="#candl">Copyright and License</a>
33 <li><a href="#copyright">Copyright</a></li>
34 <li><a href="#license">License</a></li>
35 <li><a href="#devagree">Developer Agreements</a></li>
37 <li><a href="#terms">Terminology</a></li>
39 <div class="doc_author">Written by LLVM Oversight Team</div>
41 <!--=========================================================================-->
42 <div class="doc_section"><a name="introduction">Introduction</a></div>
43 <!--=========================================================================-->
44 <div class="doc_text">
45 <p>This document contains the LLVM Developer Policy which defines the
46 project's policy towards developers and their contributions. The intent of
47 this policy is to eliminate mis-communication, rework, and confusion that
48 might arise from the distributed nature of LLVM's development. By stating
49 the policy in clear terms, we hope each developer can know ahead of time
50 what to expect when making LLVM contributions.</p>
51 <p>This policy is also designed to accomplish the following objectives:</p>
53 <li>Attract both users and developers to the LLVM project.</li>
54 <li>Make life as simple and easy for contributors as possible.</li>
55 <li>Keep the top of tree CVS/SVN trees as stable as possible.</li>
59 <!--=========================================================================-->
60 <div class="doc_section"><a name="general">General Policies</a></div>
61 <!--=========================================================================-->
62 <div class="doc_text">
63 <p>This section contains policies that pertain generally to regular LLVM
64 developers. We always welcome <a href="#patches">random patches</a> from
65 people who do not routinely contribute to LLVM, but expect more from regular
66 contributors to keep the system as efficient as possible for everyone.
67 Regular LLVM developers are expected to meet the following obligations in
68 order for LLVM to maintain a high standard of quality.<p>
71 <!-- _______________________________________________________________________ -->
72 <div class="doc_subsection"> <a name="informed">Stay Informed</a> </div>
73 <div class="doc_text">
74 <p>Developers should stay informed by reading at least the
75 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a>
76 email list. If you are doing anything more than just casual work on LLVM,
77 it is suggested that you also subscribe to the
78 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
79 list and pay attention to changes being made by others.</p>
80 <p>We recommend that active developers register an email account with
81 <a href="http://llvm.org/bugs/">LLVM Bugzilla</a> and preferably subscribe to
82 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmbugs">llvm-bugs</a>
83 email list to keep track of bugs and enhancements occurring in LLVM.</p>
86 <!-- _______________________________________________________________________ -->
87 <div class="doc_subsection"> <a name="newwork">Starting New Work</a></div>
88 <div class="doc_text">
89 <p>When a developer begins a major new project with the aim of contributing
90 it back to LLVM, s/he should inform the community with an email to
91 the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvm-dev</a>
92 email list, to the extent possible. The reason for this is to:
94 <li>keep the community informed about future changes to LLVM, </li>
95 <li>avoid duplication of effort by having multiple parties working on the
96 same thing and not knowing about it, and</li>
97 <li>ensure that any technical issues around the proposed work are
98 discussed and resolved before any significant work is done.</li>
100 <p>The design of LLVM is carefully controlled to ensure that all the pieces
101 fit together well and are as consistent as possible. If you plan to make a
102 major change to the way LLVM works or
103 a major new extension, it is a good idea to get consensus with the development
104 community before you start working on it.</p>
107 <!-- _______________________________________________________________________ -->
108 <div class="doc_subsection"> <a name="reviews">Code Reviews</a></div>
109 <div class="doc_text">
110 <p>LLVM has a code review policy. Code review is one way to increase the
111 quality of software. We generally follow these policies:</p>
113 <li>All developers are required to have significant changes reviewed
114 before they are committed to the repository.</li>
115 <li>Code reviews are conducted by email, usually on the llvm-commits
117 <li>Code can be reviewed either before it is committed or after. We expect
118 major changes to be reviewed before being committed, but smaller
119 changes (or changes where the developer owns the component) can be
120 reviewed after commit.</li>
121 <li>The developer responsible for a code change is also responsible for
122 making all necessary review-related changes.</li>
123 <li>Developers should participate in code reviews as both a reviewer and
124 a reviewee. We don't have a dedicated team of reviewers. If someone is
125 kind enough to review your code, you should return the favor for someone
129 <!-- _______________________________________________________________________ -->
130 <div class="doc_subsection"> <a name="quality">Quality</a></div>
131 <div class="doc_text">
132 <p>The minimum quality standards that any change must satisfy before being
133 committed to the main development branch are:</p>
135 <li>Code must adhere to the
136 <a href="CodingStandards.html">LLVM Coding Standards</a>.</li>
137 <li>Code must compile cleanly (no errors, no warnings) on at least one
139 <li>Code must pass the deja gnu (llvm/test) test suite.</li>
140 <li>The code must not cause regressions on a reasonable subset of llvm-test,
141 where "reasonable" depends on the contributor's judgement and the scope
142 of the change (more invasive changes require more testing). A reasonable
143 subset is "<tt>llvm-test/MultiSource/Benchmarks</tt>".</li>
145 <p>Additionally, the committer is responsible for addressing any problems
146 found that the change is responsible for. For example:</p>
148 <li>The code should compile cleanly on all platforms.</li>
149 <li>The changes should not cause regressions in the <tt>llvm-test</tt>
150 suite including SPEC CINT2000, SPEC CFP2000, SPEC CINT2006, and
152 <li>The change set should not cause performance or correctness regressions
153 for the LLVM tools.</li>
154 <li>The changes should not cause performance or correctness regressions in
155 code compiled by LLVM on all applicable targets.</li>
156 <li>You are expected to address any <a href="http://llvm.org/bugs/">bugzilla
157 bugs</a> that result from your change.</li>
160 <p>We prefer for this to be handled before submission but understand that it's
161 not possible to test all of this for every submission. Our nightly testing
162 infrastructure normally finds these problems. A good rule of thumb is to
163 check the nightly testers for regressions the day after your change.</p>
165 <p>Commits that violate these quality standards (e.g. are very broken) may
166 be reverted. This is necessary when the change blocks other developers from
167 making progress. The developer is welcome to re-commit the change after
168 the problem has been fixed.</p>
171 <!-- _______________________________________________________________________ -->
172 <div class="doc_subsection"> <a name="testcases">Test Cases</a></div>
173 <div class="doc_text">
174 <p>Developers are required to create test cases for any bugs fixed and any new
175 features added. The following policies apply:</p>
177 <li>All feature and regression test cases must be added to the
178 <tt>llvm/test</tt> directory. The appropriate sub-directory should be
179 selected (see the <a href="TestingGuide.html">Testing Guide</a> for
181 <li>Test cases should be written in
182 <a href="LangRef.html">LLVM assembly language</a> unless the
183 feature or regression being tested requires another language (e.g. the
184 bug being fixed or feature being implemented is in the llvm-gcc C++
186 <li>Test cases, especially for regressions, should be reduced as much as
187 possible, by <a href="CommandGuide/html/bugpoint.html">bugpoint</a> or
188 manually. It is unacceptable
189 to place an entire failing program into <tt>llvm/test</tt> as this creates
190 a <i>time-to-test</i> burden on all developers. Please keep them short.</li>
191 <li>More extensive test cases (applications, benchmarks, etc.) should be
192 added to the <tt>llvm-test</tt> test suite. This test suite is for
193 coverage: not features or regressions.</li>
197 <!-- _______________________________________________________________________ -->
198 <div class="doc_subsection"> <a name="c_new">Obtaining Commit Access</a></div>
199 <div class="doc_text">
202 We grant commit access to contributors with a track record of submitting high
203 quality patches. If you would like commit access, please send an email to the
204 <a href="mailto:llvm-oversight@cs.uiuc.edu">LLVM oversight group</a>.</p>
206 <p>If you have recently been granted commit access, these policies apply:</p>
208 <li>You are granted <i>commit-after-approval</i> to all parts of LLVM.
209 To get approval, submit a <a href="#patches">patch</a> to
210 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
211 llvm-commits</a>. When approved you may commit it yourself.</li>
212 <li>You are allowed to commit patches without approval which you think are
213 obvious. This is clearly a subjective decision. We simply expect you to
214 use good judgement. Examples include: fixing build breakage, reverting
215 obviously broken patches, documentation/comment changes, any other minor
217 <li>You are allowed to commit patches without approval to those portions
218 of LLVM that you have contributed or maintain (have been assigned
219 responsibility for), with the proviso that such commits must not break the
220 build. This is a "trust but verify" policy and commits of this nature are
221 reviewed after they are committed.</li>
222 <li>Multiple violations of these policies or a single egregious violation
223 may cause commit access to be revoked.</li>
228 <!-- _______________________________________________________________________ -->
229 <div class="doc_subsection"> <a name="incremental">Incremental Development</a>
231 <div class="doc_text">
232 <p>When making a large change to LLVM, we use a incremental style of
233 development instead of having long-term development branches. Long-term
234 development branches have a number of drawbacks:</p>
237 <li>Branches must have mainline merged into them periodically. If the branch
238 development and mainline development occur in the same pieces of code,
239 resolving merge conflicts can take a lot of time.</li>
240 <li>Other people in the community tend to ignore work on branches.</li>
241 <li>Huge changes (produced when a branch is merged back onto mainline) are
242 extremely difficult to <a href="#reviews">code review</a>.</li>
243 <li>Branches are not routinely tested by our nightly tester
245 <li>Changes developed as monolithic large changes often don't work until the
246 entire set of changes is done. Breaking it down into a set of smaller
247 changes increases the odds that any of the work will be committed to the
248 main repository.</li>
252 To address these problems, LLVM uses an incremental development style and we
253 require contributors to follow this practice when making a large/invasive
254 change. Some tips:</p>
257 <li>Large/invasive changes usually have a number of secondary changes that
258 are required before the big change can be made (e.g. API cleanup, etc).
259 These sorts of changes can often be done before the major change is done,
260 independently of that work.</li>
261 <li>The remaining inter-related work should be decomposed into unrelated
262 sets of changes if possible. Once this is done, define the first increment
263 and get consensus on what the end goal of the change is.</li>
264 <li>Increments can be stand alone (e.g. to fix a bug), or part of a planned
265 series of increments towards some development goal.</li>
266 <li>Increments should be kept as small as possible. This simplifies your
267 work (into a logical progression), simplifies code review and reduces the
268 chance that you will get negative feedback on the change. Small increments
269 also facilitate the maintenance of a high quality code base.</li>
270 <li>Often, an independent precursor to a big change is to add a new API and
271 slowly migrate clients to use the new API. Each change to use the new
272 API is often "obvious" and can be committed without review. Once the
273 new API is in place and used, it is often easy to replace the underlying
274 implementation of the API.</li>
277 <p>If you are interested in making a large change, and this scares you, please
278 make sure to first <a href="#newwork">discuss the change/gather
279 consensus</a> then feel free to ask about the best way to go about making
283 <!-- _______________________________________________________________________ -->
284 <div class="doc_subsection"><a name="attribution">Attribution</a></div>
285 <div class="doc_text">
286 <p>We believe in correct attribution of contributions to
287 their contributors. However, we do not want the source code to be littered
288 with random attributions (this is noisy/distracting and revision control
289 keeps a perfect history of this anyway). As such, we follow these rules:</p>
291 <li>Developers who originate new files in LLVM should place their name at
292 the top of the file per the
293 <a href="CodingStandards.html#scf_commenting">Coding Standards</a>.</li>
294 <li>There should be only one name at the top of the file and it should be
295 the person who created the file.</li>
296 <li>Placing your name in the file does not imply <a
297 href="#candl">copyright</a>: it is only used to attribute the file to
298 its original author.</li>
299 <li>Developers should be aware that after some time has passed, the name at
300 the top of a file may become meaningless as maintenance/ownership of files
301 changes. Revision control keeps an accurate history of contributions.</li>
302 <li>Developers should maintain their entry in the
303 <a href="http://llvm.org/cvsweb/cvsweb.cgi/llvm/CREDITS.TXT?rev=HEAD&content-type=text/x-cvsweb-markup">CREDITS.txt</a>
304 file to summarize their contributions.</li>
305 <li>Commit comments should contain correct attribution of the person who
306 submitted the patch if that person is not the committer (i.e. when a
307 developer with commit privileges commits a patch for someone else).</li>
312 <!--=========================================================================-->
313 <div class="doc_section"><a name="patches">Patch Policies</a></div>
314 <!--=========================================================================-->
316 <div class="doc_text">
317 <p>This section describes policies that apply to developers who regularly
318 contribute code to LLVM. As usual, we often accept small patches and
319 contributions that do not follow this policy. In this case, one of the
320 regular contributors has to get the code in shape.</p>
323 <!-- _______________________________________________________________________ -->
324 <div class="doc_subsection"> <a name="p_form">Patch Form</a></div>
325 <div class="doc_text">
326 <p>When submitting a patch, developers must follow these rules:</p>
328 <li>Patches must be made against the CVS HEAD (main development trunk),
330 <li>Patches should be made with this command:
331 <pre>cvs diff -Ntdup -5</pre>
332 or with the utility <tt>utils/mkpatch</tt>.</li>
333 <li>Patches should not include differences in generated code such as the
334 code generated by <tt>flex</tt>, <tt>bison</tt> or <tt>tblgen</tt>. The
335 <tt>utils/mkpatch</tt> utility takes care of this for you.</li>
336 <li>Contributions must not knowingly infringe on any patents. To the best of
337 our knowledge, LLVM is free of any existing patent violations and it is our
338 intent to keep it that way.</li>
342 <!-- _______________________________________________________________________ -->
343 <div class="doc_subsection"> <a name="p_submission">Patch Submission</a></div>
344 <div class="doc_text">
345 <p>When a patch is ready to be submitted, these policies apply:</p>
347 <li>Patches should be submitted immediately after they are generated. Stale
348 patches may not apply correctly if the underlying code changes between the
349 time the patch was created and the time it is applied.</li>
350 <li>Patches should be submitted by e-mail to the
351 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
352 llvm-commits</a> list.</li>
356 <!-- _______________________________________________________________________ -->
357 <div class="doc_subsection"> <a name="p_aftersub">After Submission</a></div>
358 <div class="doc_text">
359 <p>After a patch has been submitted, these policies apply:</p>
361 <li>The patch is subject to review by anyone on the
362 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
364 <li>Changes recommended by a reviewer should be incorporated into your
365 patch or you should explain why the reviewer is incorrect.
366 <li>Changes to the patch must be re-submitted to the
367 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
369 <li>This process iterates until all review issues have been addressed.</li>
373 <!-- _______________________________________________________________________ -->
374 <div class="doc_subsection"> <a name="p_aftercommit">After Commit</a></div>
375 <div class="doc_text">
376 <p>After a patch has been committed, these policies apply:</p>
378 <li>The patch is subject to further review by anyone on the llvm-commits
380 <li>The patch submitter is responsible for all aspects of the patch per
381 the <a href="quality">quality policy</a> above.</li>
382 <li>If the patch is discovered to not meet the
383 <a href="quality">quality policy</a> standards within a reasonable time
384 frame (24 hours), it may be subject to reversal.</li>
388 <!--=========================================================================-->
389 <div class="doc_section"><a name="candl">Copyright and License</a></div>
390 <!--=========================================================================-->
392 <div class="doc_text">
393 <p>We address here the issues of copyright and license for the LLVM project.
394 The object of the copyright and license is the LLVM source code and
396 Currently, the University of Illinois is the LLVM copyright holder and the
397 terms of its license to LLVM users and developers is the
398 <a href="http://www.opensource.org/licenses/UoI-NCSA.php">University of
399 Illinois/NCSA Open Source License</a>.
401 <div class="doc_notes">
402 <p><b>NOTE: This section deals with legal matters but does not provide
403 official legal advice. We are not lawyers, please seek legal counsel from an
409 <!-- _______________________________________________________________________ -->
410 <div class="doc_subsection"><a name="copyright">Copyright</a></div>
411 <div class="doc_text">
413 <p>For consistency and ease of management, the project requires the
414 copyright for all LLVM software to be held by a single copyright holder:
415 the University of Illinois (UIUC).</p>
418 Although UIUC may eventually reassign the copyright of the software to another
419 entity (e.g. a dedicated non-profit "LLVM Organization", or something)
420 the intent for the project is to always have a single entity hold the
421 copyrights to LLVM at any given time.</p>
423 <p>We believe that having a single copyright
424 holder is in the best interests of all developers and users as it greatly
425 reduces the managerial burden for any kind of administrative or technical
426 decisions about LLVM. The goal of the LLVM project is to always keep the code
427 open and <a href="#license">licensed under a very liberal license</a>.</p>
430 <!-- _______________________________________________________________________ -->
431 <div class="doc_subsection"><a name="license">License</a></div>
432 <div class="doc_text">
433 <p>We intend to keep LLVM perpetually open source
434 and to use a liberal open source license. The current license is the
435 <a href="http://www.opensource.org/licenses/UoI-NCSA.php">
436 University of Illinois/NCSA Open Source License</a>, which boils
439 <li>You can freely distribute LLVM.</li>
440 <li>You must retain the copyright notice if you redistribute LLVM.</li>
441 <li>Binaries derived from LLVM must reproduce the copyright notice.</li>
442 <li>You can't use our names to promote your LLVM derived products.</li>
443 <li>There's no warranty on LLVM at all.</li>
446 <p>We believe this fosters the widest adoption of LLVM because it <b>allows
447 commercial products to be derived from LLVM</b> with few restrictions and
448 without a requirement for making any derived works also open source (i.e.
449 LLVM's license is not a "copyleft" license like the GPL). We suggest that you
450 read the <a href="http://www.opensource.org/licenses/UoI-NCSA.php">License</a>
451 if further clarification is needed.</p>
453 <p>Note that the LLVM Project does distribute some code that includes GPL
454 software (notably, llvm-gcc which is based on the GCC GPL source base).
455 This means that anything "linked" into to llvm-gcc must itself be compatible
456 with the GPL, and must be releasable under the terms of the GPL. This implies
457 that you <b>any code linked into llvm-gcc and distributed may be subject to
458 the viral aspects of the GPL</b>. This is not a problem for the main LLVM
459 distribution (which is already licensed under a more liberal license), but may
460 be a problem if you intend to do commercial development without redistributing
461 your source code.</p>
463 <p>We have no plans to change the license of LLVM. If you have questions
464 or comments about the license, please contact the <a
465 href="mailto:llvm-oversight@cs.uiuc.edu">LLVM Oversight Group</a>.</p>
468 <!-- _______________________________________________________________________ -->
469 <div class="doc_subsection"><a name="devagree">Developer Agreements</a></div>
470 <div class="doc_text">
471 <p>With regards to the LLVM copyright and licensing, developers agree to
472 assign their copyrights to UIUC for any contribution made so that
473 the entire software base can be managed by a single copyright holder. This
474 implies that any contributions can be licensed under the license that the
479 <!--=========================================================================-->
480 <div class="doc_section"><a name="terms">Terminology</a></div>
481 <!--=========================================================================-->
482 <div class="doc_text">
483 <p>So that the policies defined in this document are clear, we define some
486 <dt><a name="t_change">Change</a></dt>
487 <dd>Any modification to LLVM including documentation, tests, build system,
488 etc. either in <a href="#t_patch">patch</a> or
489 <a href="#t_commit">commit</a> form.</dd>
490 <dt><a name="t_commit">Commit</a><dt>
491 <dd>A <a href="t_change">change</a> submitted directly to LLVM software
492 repository via the <tt>cvs commit</tt> command.</dd>
493 <dt><a name="t_developer">Developer</a></dt>
494 <dd>Anyone who submits a <a href="#t_change">change</a> to LLVM.</dd>
495 <dt><a name="t_inrement">Increment</a></dt>
496 <dd>A <a href="#t_change">change</a> or set of changes, whether by
497 <a href="#t_patch">patch</a> or <a href="#t_commit">commit</a>, that are
498 related by a single common purpose. Increments are atomic as they
499 leave LLVM in a stable state (both compiling and working properly).</dd>
500 <dt><a name="t_patch">Patch</a></dt>
501 <dd>A <a href="#t_change">change</a> submitted by email in patch (diff)
502 format generated by the <tt>cvs diff</tt> command.</dd>
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