docs/DeveloperPolicy.html

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  10 <div class="doc_title">LLVM Developer Policy</div>
  11 <ol>
  12   <li><a href="#introduction">Introduction</a></li>
  13   <li><a href="#policies">Developer Policies</a>
  14   <ol>
  15     <li><a href="#informed">Stay Informed</a></li>
  16     <li><a href="#patches">Making a Patch</a></li>
  17     <li><a href="#reviews">Code Reviews</a></li>
  18     <li><a href="#testcases">Test Cases</a></li>
  19     <li><a href="#quality">Quality</a></li>
  20     <li><a href="#commitaccess">Obtaining Commit Access</a></li>
  21     <li><a href="#newwork">Making a Major Change</a></li>
  22     <li><a href="#incremental">Incremental Development</a></li>
  23     <li><a href="#attribution">Attribution of Changes</a></li>
  24   </ol></li>
  25   <li><a href="#clp">Copyright, License, and Patents</a>
  26   <ol>
  27     <li><a href="#copyright">Copyright</a></li>
  28     <li><a href="#license">License</a></li>
  29     <li><a href="#patents">Patents</a></li>
  30     <li><a href="#devagree">Developer Agreements</a></li>
  31   </ol></li>
  32 </ol>
  33 <div class="doc_author">Written by the LLVM Oversight Team</div>
  34
  35 <!--=========================================================================-->
  36 <div class="doc_section"><a name="introduction">Introduction</a></div>
  37 <!--=========================================================================-->
  38 <div class="doc_text">
  39   <p>This document contains the LLVM Developer Policy which defines the
  40   project's policy towards developers and their contributions. The intent of
  41   this policy is to eliminate mis-communication, rework, and confusion that
  42   might arise from the distributed nature of LLVM's development.  By stating
  43   the policy in clear terms, we hope each developer can know ahead of time
  44   what to expect when making LLVM contributions.</p>
  45   <p>This policy is also designed to accomplish the following objectives:</p>
  46   <ol>
  47     <li>Attract both users and developers to the LLVM project.</li>
  48     <li>Make life as simple and easy for contributors as possible.</li>
  49     <li>Keep the top of tree CVS/SVN trees as stable as possible.</li>
  50   </ol>
  51
  52   <p>This policy is aimed at frequent contributors to LLVM. People interested in
  53   contributing one-off patches can do so in an informal way by sending them to
  54   the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
  55   llvm-commits mailing list</a> and engaging another developer to see it through
  56   the process.</p>
  57
  58 </div>
  59
  60 <!--=========================================================================-->
  61 <div class="doc_section"><a name="policies">Developer Policies</a></div>
  62 <!--=========================================================================-->
  63 <div class="doc_text">
  64   <p>This section contains policies that pertain to frequent LLVM
  65   developers.  We always welcome <a href="#patches">one-off patches</a> from
  66   people who do not routinely contribute to LLVM, but we expect more from
  67   frequent contributors to keep the system as efficient as possible for
  68   everyone.
  69   Frequent LLVM contributors are expected to meet the following requirements in
  70   order for LLVM to maintain a high standard of quality.<p>
  71 </div>
  72
  73 <!-- _______________________________________________________________________ -->
  74 <div class="doc_subsection"> <a name="informed">Stay Informed</a> </div>
  75 <div class="doc_text">
  76   <p>Developers should stay informed by reading at least the
  77   <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a>
  78   email list.  If you are doing anything more than just casual work on LLVM,
  79   it is suggested that you also subscribe to the
  80   <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
  81   list and pay attention to changes being made by others.</p>
  82   <p>We recommend that active developers register an email account with
  83   <a href="http://llvm.org/bugs/">LLVM Bugzilla</a> and preferably subscribe to
  84   the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmbugs">llvm-bugs</a>
  85   email list to keep track of bugs and enhancements occurring in LLVM.</p>
  86 </div>
  87
  88 <!-- _______________________________________________________________________ -->
  89 <div class="doc_subsection"> <a name="patches">Making a Patch</a></div>
  90
  91 <div class="doc_text">
  92
  93 <p>When making a patch for review, the goal is to make it as easy for the
  94    reviewer to read it as possible.  As such, we recommend that you:</p>
  95   <ol>
  96     <li>Make your patch against the CVS HEAD (main development trunk),
  97         not a branch, and not an old version of LLVM.  This makes it easy to
  98         apply the patch.</li>
  99
 100     <li>Similarly, patches should be submitted soon after they are generated.
 101     Old patches may not apply correctly if the underlying code changes between
 102     the time the patch was created and the time it is applied.</li>
 103
 104     <li>Patches should be made with this command:
 105     <pre>cvs diff -Ntdup -5</pre>
 106      or with the utility <tt>utils/mkpatch</tt>, which makes it easy to read the
 107      diff.</li>
 108
 109     <li>Patches should not include differences in generated code such as the
 110     code generated by <tt>flex</tt>, <tt>bison</tt> or <tt>tblgen</tt>. The
 111     <tt>utils/mkpatch</tt> utility takes care of this for you.</li>
 112
 113   </ol>
 114
 115   <p>When sending a patch to a mailing list, it is a good idea to send it as an
 116   <em>attachment</em> to the message, not embedded into the text of the
 117   message.  This ensures that your mailer will not mangle the patch when it
 118   sends it (e.g. by making whitespace changes or by wrapping lines).</p>
 119 </div>
 120
 121 <!-- _______________________________________________________________________ -->
 122 <div class="doc_subsection"> <a name="reviews">Code Reviews</a></div>
 123 <div class="doc_text">
 124   <p>LLVM has a code review policy. Code review is one way to increase the
 125   quality of software. We generally follow these policies:</p>
 126   <ol>
 127     <li>All developers are required to have significant changes reviewed
 128     before they are committed to the repository.</li>
 129     <li>Code reviews are conducted by email, usually on the llvm-commits
 130         list.</li>
 131     <li>Code can be reviewed either before it is committed or after.  We expect
 132         major changes to be reviewed before being committed, but smaller
 133         changes (or changes where the developer owns the component) can be
 134         reviewed after commit.</li>
 135     <li>The developer responsible for a code change is also responsible for
 136         making all necessary review-related changes.</li>
 137     <li>Code review can be an iterative process, which continues until the patch
 138         is ready to be committed.</li>
 139   </ol>
 140
 141   <p>Developers should participate in code reviews as both reviewers and
 142     reviewees. If someone is kind enough to review your code, you should
 143     return the favor for someone else.  Note that anyone is welcome to review
 144     and give feedback on a patch, but only people with CVS write access can
 145     approve it.</p>
 146
 147 </div>
 148
 149 <!-- _______________________________________________________________________ -->
 150 <div class="doc_subsection"> <a name="testcases">Test Cases</a></div>
 151 <div class="doc_text">
 152   <p>Developers are required to create test cases for any bugs fixed and any new
 153   features added.  Some tips for getting your testcase approved:</p>
 154   <ol>
 155     <li>All feature and regression test cases are added to the
 156     <tt>llvm/test</tt> directory. The appropriate sub-directory should be
 157     selected (see the <a href="TestingGuide.html">Testing Guide</a> for
 158     details).</li>
 159     <li>Test cases should be written in
 160     <a href="LangRef.html">LLVM assembly language</a> unless the
 161     feature or regression being tested requires another language (e.g. the
 162     bug being fixed or feature being implemented is in the llvm-gcc C++
 163     front-end, in which case it must be written in C++).</li>
 164     <li>Test cases, especially for regressions, should be reduced as much as
 165     possible, by <a href="Bugpoint.html">bugpoint</a> or
 166     manually. It is unacceptable
 167     to place an entire failing program into <tt>llvm/test</tt> as this creates
 168     a <i>time-to-test</i> burden on all developers. Please keep them short.</li>
 169   </ol>
 170
 171   <p>Note that llvm/test is designed for regression and small feature tests
 172     only. More extensive test cases (e.g., entire applications, benchmarks,
 173     etc) should be added to the <tt>llvm-test</tt> test suite.  The llvm-test
 174     suite is for coverage (correctness, performance, etc) testing, not feature
 175     or regression testing.</p>
 176 </div>
 177
 178 <!-- _______________________________________________________________________ -->
 179 <div class="doc_subsection"> <a name="quality">Quality</a></div>
 180 <div class="doc_text">
 181   <p>The minimum quality standards that any change must satisfy before being
 182     committed to the main development branch are:</p>
 183   <ol>
 184     <li>Code must adhere to the
 185     <a href="CodingStandards.html">LLVM Coding Standards</a>.</li>
 186     <li>Code must compile cleanly (no errors, no warnings) on at least one
 187     platform.</li>
 188     <li>Bug fixes and new features should <a href="#testcases">include a
 189         testcase</a> so we know if the fix/feature ever regresses in the
 190         future.</li>
 191     <li>Code must pass the dejagnu (<tt>llvm/test</tt>) test suite.</li>
 192     <li>The code must not cause regressions on a reasonable subset of llvm-test,
 193         where "reasonable" depends on the contributor's judgement and the scope
 194         of the change (more invasive changes require more testing). A reasonable
 195         subset is "<tt>llvm-test/MultiSource/Benchmarks</tt>".</li>
 196   </ol>
 197   <p>Additionally, the committer is responsible for addressing any problems
 198   found in the future that the change is responsible for.  For example:</p>
 199   <ul>
 200     <li>The code should compile cleanly on all supported platforms.</li>
 201     <li>The changes should not cause any correctness regressions in the
 202        <tt>llvm-test</tt> suite and must not cause any major performance
 203        regressions.</li>
 204     <li>The change set should not cause performance or correctness regressions
 205     for the LLVM tools.</li>
 206     <li>The changes should not cause performance or correctness regressions in
 207     code compiled by LLVM on all applicable targets.</li>
 208     <li>You are expected to address any <a href="http://llvm.org/bugs/">bugzilla
 209     bugs</a> that result from your change.</li>
 210   </ul>
 211
 212   <p>We prefer for this to be handled before submission but understand that it
 213      isn't possible to test all of this for every submission.  Our nightly
 214      testing
 215      infrastructure normally finds these problems.  A good rule of thumb is to
 216      check the nightly testers for regressions the day after your change.</p>
 217
 218   <p>Commits that violate these quality standards (e.g. are very broken) may
 219     be reverted. This is necessary when the change blocks other developers from
 220     making progress. The developer is welcome to re-commit the change after
 221     the problem has been fixed.</p>
 222 </div>
 223
 224 <!-- _______________________________________________________________________ -->
 225 <div class="doc_subsection">
 226   <a name="commitaccess">Obtaining Commit Access</a></div>
 227 <div class="doc_text">
 228
 229 <p>
 230 We grant commit access to contributors with a track record of submitting high
 231 quality patches.  If you would like commit access, please send an email to the
 232 <a href="mailto:llvm-oversight@cs.uiuc.edu">LLVM oversight group</a>.</p>
 233
 234 <p>If you have recently been granted commit access, these policies apply:</p>
 235 <ol>
 236   <li>You are granted <i>commit-after-approval</i> to all parts of LLVM.
 237   To get approval, submit a <a href="#patches">patch</a> to
 238   <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
 239   llvm-commits</a>.  When approved you may commit it yourself.</li>
 240   <li>You are allowed to commit patches without approval which you think are
 241   obvious. This is clearly a subjective decision &mdash; we simply expect you
 242   to use good judgement.  Examples include: fixing build breakage, reverting
 243   obviously broken patches, documentation/comment changes, any other minor
 244   changes.</li>
 245   <li>You are allowed to commit patches without approval to those portions
 246   of LLVM that you have contributed or maintain (i.e., have been assigned
 247   responsibility for), with the proviso that such commits must not break the
 248   build.  This is a "trust but verify" policy and commits of this nature are
 249   reviewed after they are committed.</li>
 250   <li>Multiple violations of these policies or a single egregious violation
 251   may cause commit access to be revoked.</li>
 252 </ol>
 253
 254 <p>In any case, your changes are still subject to <a href="#reviews">code
 255 review</a> (either before or after they are committed, depending on the nature
 256 of the change).  You are encouraged to review other peoples' patches as well,
 257 but you aren't required to.</p>
 258
 259 </div>
 260
 261 <!-- _______________________________________________________________________ -->
 262 <div class="doc_subsection"> <a name="newwork">Making a Major Change</a></div>
 263 <div class="doc_text">
 264   <p>When a developer begins a major new project with the aim of contributing
 265   it back to LLVM, s/he should inform the community with an email to
 266   the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a>
 267   email list, to the extent possible. The reason for this is to:
 268   <ol>
 269     <li>keep the community informed about future changes to LLVM, </li>
 270     <li>avoid duplication of effort by preventing multiple parties working on
 271      the same thing and not knowing about it, and</li>
 272     <li>ensure that any technical issues around the proposed work are
 273     discussed and resolved before any significant work is done.</li>
 274   </ol>
 275
 276   <p>The design of LLVM is carefully controlled to ensure that all the pieces
 277   fit together well and are as consistent as possible. If you plan to make a
 278   major change to the way LLVM works or want to add a major new extension, it
 279   is a good idea to get consensus with the development
 280   community before you start working on it.</p>
 281
 282   <p>Once the design of the new feature is finalized, the work itself should be
 283      done as a series of <a href="#incremental">incremental changes</a>, not as
 284      a long-term development branch.</p>
 285
 286 </div>
 287
 288 <!-- _______________________________________________________________________ -->
 289 <div class="doc_subsection"> <a name="incremental">Incremental Development</a>
 290 </div>
 291 <div class="doc_text">
 292   <p>In the LLVM project, we do all significant changes as a series of
 293      incremental patches.  We have a strong dislike for huge changes or
 294      long-term development branches.  Long-term development branches have a
 295      number of drawbacks:</p>
 296
 297    <ol>
 298    <li>Branches must have mainline merged into them periodically.  If the branch
 299        development and mainline development occur in the same pieces of code,
 300        resolving merge conflicts can take a lot of time.</li>
 301    <li>Other people in the community tend to ignore work on branches.</li>
 302    <li>Huge changes (produced when a branch is merged back onto mainline) are
 303        extremely difficult to <a href="#reviews">code review</a>.</li>
 304    <li>Branches are not routinely tested by our nightly tester
 305        infrastructure.</li>
 306    <li>Changes developed as monolithic large changes often don't work until the
 307        entire set of changes is done.  Breaking it down into a set of smaller
 308        changes increases the odds that any of the work will be committed to the
 309        main repository.</li>
 310    </ol>
 311
 312   <p>
 313   To address these problems, LLVM uses an incremental development style and we
 314   require contributors to follow this practice when making a large/invasive
 315   change.  Some tips:</p>
 316
 317   <ul>
 318     <li>Large/invasive changes usually have a number of secondary changes that
 319      are required before the big change can be made (e.g. API cleanup, etc).
 320      These sorts of changes can often be done before the major change is done,
 321      independently of that work.</li>
 322     <li>The remaining inter-related work should be decomposed into unrelated
 323     sets of changes if possible.  Once this is done, define the first increment
 324     and get consensus on what the end goal of the change is.</li>
 325
 326     <li>Each change in the set can be stand alone (e.g. to fix a bug), or part
 327     of a planned series of changes that works towards the development goal.</li>
 328
 329     <li>Each change should be kept as small as possible. This simplifies your
 330     work (into a logical progression), simplifies code review and reduces the
 331     chance that you will get negative feedback on the change. Small increments
 332     also facilitate the maintenance of a high quality code base.</li>
 333
 334     <li>Often, an independent precursor to a big change is to add a new API and
 335         slowly migrate clients to use the new API.  Each change to use the new
 336         API is often "obvious" and can be committed without review.  Once the
 337         new API is in place and used, it is much easier to replace the
 338         underlying implementation of the API.  This implementation change is
 339         logically separate from the API change.</li>
 340   </ul>
 341
 342   <p>If you are interested in making a large change, and this scares you, please
 343      make sure to first <a href="#newwork">discuss the change/gather
 344      consensus</a> then ask about the best way to go about making
 345      the change.</p>
 346 </div>
 347
 348 <!-- _______________________________________________________________________ -->
 349 <div class="doc_subsection"><a name="attribution">Attribution of
 350 Changes</a></div>
 351 <div class="doc_text">
 352   <p>We believe in correct attribution of contributions to
 353   their contributors.  However, we do not want the source code to be littered
 354   with random attributions (this is noisy/distracting and revision control
 355   keeps a perfect history of this anyway).  As such, we follow these rules:</p>
 356   <ol>
 357     <li>Developers who originate new files in LLVM should place their name at
 358     the top of the file per the
 359     <a href="CodingStandards.html#scf_commenting">Coding Standards</a>.</li>
 360     <li>There should be only one name at the top of the file and it should be
 361     the person who created the file.</li>
 362     <li>Placing your name in the file does not imply <a
 363         href="#clp">copyright</a>: it is only used to attribute the file to
 364         its original author.</li>
 365     <li>Developers should be aware that after some time has passed, the name at
 366     the top of a file may become meaningless as maintenance/ownership of files
 367     changes.  Despite this, once set, the attribution of a file never changes.
 368     Revision control keeps an accurate history of contributions.</li>
 369     <li>Developers should maintain their entry in the
 370     <a href="http://llvm.org/cvsweb/cvsweb.cgi/llvm/CREDITS.TXT?rev=HEAD&amp;content-type=text/x-cvsweb-markup">CREDITS.txt</a>
 371     file to summarize their contributions.</li>
 372     <li>Commit comments should contain correct attribution of the person who
 373     submitted the patch if that person is not the committer (i.e. when a
 374     developer with commit privileges commits a patch for someone else).</li>
 375   </ol>
 376 </div>
 377
 378
 379
 380 <!--=========================================================================-->
 381 <div class="doc_section">
 382   <a name="clp">Copyright, License, and Patents</a>
 383 </div>
 384 <!--=========================================================================-->
 385
 386 <div class="doc_text">
 387   <p>This section addresses the issues of copyright, license and patents for
 388   the LLVM project.
 389   Currently, the University of Illinois is the LLVM copyright holder and the
 390   terms of its license to LLVM users and developers is the
 391   <a href="http://www.opensource.org/licenses/UoI-NCSA.php">University of
 392     Illinois/NCSA Open Source License</a>.</p>
 393
 394 <div class="doc_notes">
 395   <p><b>NOTE: This section deals with legal matters but does not provide
 396   legal advice.  We are not lawyers, please seek legal counsel from an
 397   attorney.</b></p>
 398 </div>
 399 </div>
 400
 401 <!-- _______________________________________________________________________ -->
 402 <div class="doc_subsection"><a name="copyright">Copyright</a></div>
 403 <div class="doc_text">
 404   <p>
 405   <p>For consistency and ease of management, the project requires the
 406   copyright for all LLVM software to be held by a single copyright holder:
 407   the University of Illinois (UIUC).</p>
 408
 409   <p>
 410   Although UIUC may eventually reassign the copyright of the software to another
 411   entity (e.g. a dedicated non-profit "LLVM Organization", or something)
 412   the intent for the project is to always have a single entity hold the
 413   copyrights to LLVM at any given time.</p>
 414
 415   <p>We believe that having a single copyright
 416   holder is in the best interests of all developers and users as it greatly
 417   reduces the managerial burden for any kind of administrative or technical
 418   decisions about LLVM.  The goal of the LLVM project is to always keep the code
 419   open and <a href="#license">licensed under a very liberal license</a>.</p>
 420 </div>
 421
 422 <!-- _______________________________________________________________________ -->
 423 <div class="doc_subsection"><a name="license">License</a></div>
 424 <div class="doc_text">
 425   <p>We intend to keep LLVM perpetually open source
 426   and to use a liberal open source license. The current license is the
 427   <a href="http://www.opensource.org/licenses/UoI-NCSA.php">
 428     University of Illinois/NCSA Open Source License</a>, which boils
 429   down to this:</p>
 430   <ul>
 431     <li>You can freely distribute LLVM.</li>
 432     <li>You must retain the copyright notice if you redistribute LLVM.</li>
 433     <li>Binaries derived from LLVM must reproduce the copyright notice.</li>
 434     <li>You can't use our names to promote your LLVM derived products.</li>
 435     <li>There's no warranty on LLVM at all.</li>
 436   </ul>
 437
 438   <p>We believe this fosters the widest adoption of LLVM because it <b>allows
 439   commercial products to be derived from LLVM</b> with few restrictions and
 440   without a requirement for making any derived works also open source (i.e.
 441   LLVM's license is not a "copyleft" license like the GPL). We suggest that you
 442   read the <a href="http://www.opensource.org/licenses/UoI-NCSA.php">License</a>
 443   if further clarification is needed.</p>
 444
 445   <p>Note that the LLVM Project does distribute llvm-gcc, <b>which is GPL.</b>
 446   This means that anything "linked" into llvm-gcc must itself be compatible
 447   with the GPL, and must be releasable under the terms of the GPL.  This implies
 448   that <b>any code linked into llvm-gcc and distributed to others may be subject
 449   to the viral aspects of the GPL</b> (for example, a proprietary code generator
 450   linked into llvm-gcc must be made available under the GPL).  This is not a
 451   problem for code already distributed under a more liberal license (like the
 452   UIUC license), and does not affect code generated by llvm-gcc.  It may be a
 453   problem if you intend to base commercial development on llvm-gcc without
 454   redistributing your source code.</p>
 455
 456   <p>We have no plans to change the license of LLVM.  If you have questions
 457     or comments about the license, please contact the <a
 458     href="mailto:llvm-oversight@cs.uiuc.edu">LLVM Oversight Group</a>.</p>
 459
 460 </div>
 461
 462 <!-- _______________________________________________________________________ -->
 463 <div class="doc_subsection"><a name="patents">Patents</a></div>
 464 <div class="doc_text">
 465
 466 <p>To the best of our knowledge, LLVM does not infringe on any patents (we have
 467    actually removed code from LLVM in the past that was found to infringe).
 468    Having code in LLVM that infringes on patents would violate an important
 469    goal of the project by making it hard or impossible to reuse the code for
 470    arbitrary purposes (including commercial use).</p>
 471
 472 <p>When contributing code, we expect contributors to notify us of any potential
 473    for patent-related trouble with their changes.  If you own the rights to a
 474    patent and would like to contribute code to LLVM that relies on it, we
 475    require that you sign an agreement that allows any other user of LLVM to
 476    freely use your patent.  Please contact the <a
 477    href="mailto:llvm-oversight@cs.uiuc.edu">oversight group</a> for more
 478    details.</p>
 479 </div>
 480
 481
 482 <!-- _______________________________________________________________________ -->
 483 <div class="doc_subsection"><a name="devagree">Developer Agreements</a></div>
 484 <div class="doc_text">
 485   <p>With regards to the LLVM copyright and licensing, developers agree to
 486   assign their copyrights to UIUC for any contribution made so that
 487   the entire software base can be managed by a single copyright holder.  This
 488   implies that any contributions can be licensed under the license that the
 489   project uses.</p>
 490 </div>
 491
 492 <!-- *********************************************************************** -->
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