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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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<head>
<title>LLVM Developer Policy</title>
<link rel="stylesheet" href="llvm.css" type="text/css">
</head>
<body>
<div class="doc_title">LLVM Developer Policy</div>
<ol>
<li><a href="#introduction">Introduction</a></li>
<li><a href="#policies">Developer Policies</a>
<ol>
<li><a href="#informed">Stay Informed</a></li>
<li><a href="#patches">Making a Patch</a></li>
<li><a href="#reviews">Code Reviews</a></li>
<li><a href="#testcases">Test Cases</a></li>
<li><a href="#quality">Quality</a></li>
<li><a href="#commitaccess">Obtaining Commit Access</a></li>
<li><a href="#newwork">Making a Major Change</a></li>
<li><a href="#incremental">Incremental Development</a></li>
<li><a href="#attribution">Attribution of Changes</a></li>
</ol></li>
<li><a href="#clp">Copyright, License, and Patents</a>
<ol>
<li><a href="#copyright">Copyright</a></li>
<li><a href="#license">License</a></li>
<li><a href="#patents">Patents</a></li>
<li><a href="#devagree">Developer Agreements</a></li>
</ol></li>
</ol>
<div class="doc_author">Written by the LLVM Oversight Team</div>
<!--=========================================================================-->
<div class="doc_section"><a name="introduction">Introduction</a></div>
<!--=========================================================================-->
<div class="doc_text">
<p>This document contains the LLVM Developer Policy which defines the
project's policy towards developers and their contributions. The intent of
this policy is to eliminate mis-communication, rework, and confusion that
might arise from the distributed nature of LLVM's development. By stating
the policy in clear terms, we hope each developer can know ahead of time
what to expect when making LLVM contributions.</p>
<p>This policy is also designed to accomplish the following objectives:</p>
<ol>
<li>Attract both users and developers to the LLVM project.</li>
<li>Make life as simple and easy for contributors as possible.</li>
<li>Keep the top of tree CVS/SVN trees as stable as possible.</li>
</ol>
<p>This policy is aimed at frequent contributors to LLVM. People interested in
contributing one-off patches can do so in an informal way by sending them to
the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
llvm-commits mailing list</a> and engaging another developer to see it through
the process.</p>
</div>
<!--=========================================================================-->
<div class="doc_section"><a name="policies">Developer Policies</a></div>
<!--=========================================================================-->
<div class="doc_text">
<p>This section contains policies that pertain to frequent LLVM
developers. We always welcome <a href="#patches">one-off patches</a> from
people who do not routinely contribute to LLVM, but we expect more from
frequent contributors to keep the system as efficient as possible for
everyone.
Frequent LLVM contributors are expected to meet the following requirements in
order for LLVM to maintain a high standard of quality.<p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"> <a name="informed">Stay Informed</a> </div>
<div class="doc_text">
<p>Developers should stay informed by reading at least the
<a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a>
email list. If you are doing anything more than just casual work on LLVM,
it is suggested that you also subscribe to the
<a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
list and pay attention to changes being made by others.</p>
<p>We recommend that active developers register an email account with
<a href="http://llvm.org/bugs/">LLVM Bugzilla</a> and preferably subscribe to
the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmbugs">llvm-bugs</a>
email list to keep track of bugs and enhancements occurring in LLVM.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"> <a name="patches">Making a Patch</a></div>
<div class="doc_text">
<p>When making a patch for review, the goal is to make it as easy for the
reviewer to read it as possible. As such, we recommend that you:</p>
<ol>
<li>Make your patch against the CVS HEAD (main development trunk),
not a branch, and not an old version of LLVM. This makes it easy to
apply the patch.</li>
<li>Similarly, patches should be submitted soon after they are generated.
Old patches may not apply correctly if the underlying code changes between
the time the patch was created and the time it is applied.</li>
<li>Patches should be made with this command:
<pre>cvs diff -Ntdup -5</pre>
or with the utility <tt>utils/mkpatch</tt>, which makes it easy to read the
diff.</li>
<li>Patches should not include differences in generated code such as the
code generated by <tt>flex</tt>, <tt>bison</tt> or <tt>tblgen</tt>. The
<tt>utils/mkpatch</tt> utility takes care of this for you.</li>
</ol>
<p>When sending a patch to a mailing list, it is a good idea to send it as an
<em>attachment</em> to the message, not embedded into the text of the
message. This ensures that your mailer will not mangle the patch when it
sends it (e.g. by making whitespace changes or by wrapping lines).</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"> <a name="reviews">Code Reviews</a></div>
<div class="doc_text">
<p>LLVM has a code review policy. Code review is one way to increase the
quality of software. We generally follow these policies:</p>
<ol>
<li>All developers are required to have significant changes reviewed
before they are committed to the repository.</li>
<li>Code reviews are conducted by email, usually on the llvm-commits
list.</li>
<li>Code can be reviewed either before it is committed or after. We expect
major changes to be reviewed before being committed, but smaller
changes (or changes where the developer owns the component) can be
reviewed after commit.</li>
<li>The developer responsible for a code change is also responsible for
making all necessary review-related changes.</li>
<li>Code review can be an iterative process, which continues until the patch
is ready to be committed.</li>
</ol>
<p>Developers should participate in code reviews as both reviewers and
reviewees. If someone is kind enough to review your code, you should
return the favor for someone else. Note that anyone is welcome to review
and give feedback on a patch, but only people with CVS write access can
approve it.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"> <a name="testcases">Test Cases</a></div>
<div class="doc_text">
<p>Developers are required to create test cases for any bugs fixed and any new
features added. Some tips for getting your testcase approved:</p>
<ol>
<li>All feature and regression test cases are added to the
<tt>llvm/test</tt> directory. The appropriate sub-directory should be
selected (see the <a href="TestingGuide.html">Testing Guide</a> for
details).</li>
<li>Test cases should be written in
<a href="LangRef.html">LLVM assembly language</a> unless the
feature or regression being tested requires another language (e.g. the
bug being fixed or feature being implemented is in the llvm-gcc C++
front-end, in which case it must be written in C++).</li>
<li>Test cases, especially for regressions, should be reduced as much as
possible, by <a href="CommandGuide/html/bugpoint.html">bugpoint</a> or
manually. It is unacceptable
to place an entire failing program into <tt>llvm/test</tt> as this creates
a <i>time-to-test</i> burden on all developers. Please keep them short.</li>
</ol>
<p>Note that llvm/test is designed for regression and small feature tests
only. More extensive test cases (e.g., entire applications, benchmarks,
etc) should be added to the <tt>llvm-test</tt> test suite. The llvm-test
suite is for coverage (correctness, performance, etc) testing, not feature
or regression testing.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"> <a name="quality">Quality</a></div>
<div class="doc_text">
<p>The minimum quality standards that any change must satisfy before being
committed to the main development branch are:</p>
<ol>
<li>Code must adhere to the
<a href="CodingStandards.html">LLVM Coding Standards</a>.</li>
<li>Code must compile cleanly (no errors, no warnings) on at least one
platform.</li>
<li>Bug fixes and new features should <a href="#testcases">include a
testcase</a> so we know if the fix/feature ever regresses in the
future.</li>
<li>Code must pass the dejagnu (<tt>llvm/test</tt>) test suite.</li>
<li>The code must not cause regressions on a reasonable subset of llvm-test,
where "reasonable" depends on the contributor's judgement and the scope
of the change (more invasive changes require more testing). A reasonable
subset is "<tt>llvm-test/MultiSource/Benchmarks</tt>".</li>
</ol>
<p>Additionally, the committer is responsible for addressing any problems
found in the future that the change is responsible for. For example:</p>
<ul>
<li>The code should compile cleanly on all supported platforms.</li>
<li>The changes should not cause any correctness regressions in the
<tt>llvm-test</tt> suite and must not cause any major performance
regressions.</li>
<li>The change set should not cause performance or correctness regressions
for the LLVM tools.</li>
<li>The changes should not cause performance or correctness regressions in
code compiled by LLVM on all applicable targets.</li>
<li>You are expected to address any <a href="http://llvm.org/bugs/">bugzilla
bugs</a> that result from your change.</li>
</ul>
<p>We prefer for this to be handled before submission but understand that it
isn't possible to test all of this for every submission. Our nightly
testing
infrastructure normally finds these problems. A good rule of thumb is to
check the nightly testers for regressions the day after your change.</p>
<p>Commits that violate these quality standards (e.g. are very broken) may
be reverted. This is necessary when the change blocks other developers from
making progress. The developer is welcome to re-commit the change after
the problem has been fixed.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection">
<a name="commitaccess">Obtaining Commit Access</a></div>
<div class="doc_text">
<p>
We grant commit access to contributors with a track record of submitting high
quality patches. If you would like commit access, please send an email to the
<a href="mailto:llvm-oversight@cs.uiuc.edu">LLVM oversight group</a>.</p>
<p>If you have recently been granted commit access, these policies apply:</p>
<ol>
<li>You are granted <i>commit-after-approval</i> to all parts of LLVM.
To get approval, submit a <a href="#patches">patch</a> to
<a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
llvm-commits</a>. When approved you may commit it yourself.</li>
<li>You are allowed to commit patches without approval which you think are
obvious. This is clearly a subjective decision &mdash; we simply expect you
to use good judgement. Examples include: fixing build breakage, reverting
obviously broken patches, documentation/comment changes, any other minor
changes.</li>
<li>You are allowed to commit patches without approval to those portions
of LLVM that you have contributed or maintain (i.e., have been assigned
responsibility for), with the proviso that such commits must not break the
build. This is a "trust but verify" policy and commits of this nature are
reviewed after they are committed.</li>
<li>Multiple violations of these policies or a single egregious violation
may cause commit access to be revoked.</li>
</ol>
<p>In any case, your changes are still subject to <a href="#reviews">code
review</a> (either before or after they are committed, depending on the nature
of the change). You are encouraged to review other peoples' patches as well,
but your aren't required to.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"> <a name="newwork">Making a Major Change</a></div>
<div class="doc_text">
<p>When a developer begins a major new project with the aim of contributing
it back to LLVM, s/he should inform the community with an email to
the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a>
email list, to the extent possible. The reason for this is to:
<ol>
<li>keep the community informed about future changes to LLVM, </li>
<li>avoid duplication of effort by preventing multiple parties working on
the same thing and not knowing about it, and</li>
<li>ensure that any technical issues around the proposed work are
discussed and resolved before any significant work is done.</li>
</ol>
<p>The design of LLVM is carefully controlled to ensure that all the pieces
fit together well and are as consistent as possible. If you plan to make a
major change to the way LLVM works or want to add a major new extension, it
is a good idea to get consensus with the development
community before you start working on it.</p>
<p>Once the design of the new feature is finalized, the work itself should be
done as a series of <a href="#incremental">incremental changes</a>, not as
a long-term development branch.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"> <a name="incremental">Incremental Development</a>
</div>
<div class="doc_text">
<p>In the LLVM project, we do all significant changes as a series of
incremental patches. We have a strong dislike for huge changes or
long-term development branches. Long-term development branches have a
number of drawbacks:</p>
<ol>
<li>Branches must have mainline merged into them periodically. If the branch
development and mainline development occur in the same pieces of code,
resolving merge conflicts can take a lot of time.</li>
<li>Other people in the community tend to ignore work on branches.</li>
<li>Huge changes (produced when a branch is merged back onto mainline) are
extremely difficult to <a href="#reviews">code review</a>.</li>
<li>Branches are not routinely tested by our nightly tester
infrastructure.</li>
<li>Changes developed as monolithic large changes often don't work until the
entire set of changes is done. Breaking it down into a set of smaller
changes increases the odds that any of the work will be committed to the
main repository.</li>
</ol>
<p>
To address these problems, LLVM uses an incremental development style and we
require contributors to follow this practice when making a large/invasive
change. Some tips:</p>
<ul>
<li>Large/invasive changes usually have a number of secondary changes that
are required before the big change can be made (e.g. API cleanup, etc).
These sorts of changes can often be done before the major change is done,
independently of that work.</li>
<li>The remaining inter-related work should be decomposed into unrelated
sets of changes if possible. Once this is done, define the first increment
and get consensus on what the end goal of the change is.</li>
<li>Each change in the set can be stand alone (e.g. to fix a bug), or part
of a planned series of changes that works towards the development goal.</li>
<li>Each change should be kept as small as possible. This simplifies your
work (into a logical progression), simplifies code review and reduces the
chance that you will get negative feedback on the change. Small increments
also facilitate the maintenance of a high quality code base.</li>
<li>Often, an independent precursor to a big change is to add a new API and
slowly migrate clients to use the new API. Each change to use the new
API is often "obvious" and can be committed without review. Once the
new API is in place and used, it is much easier to replace the
underlying implementation of the API. This implementation change is
logically separate from the API change.</li>
</ul>
<p>If you are interested in making a large change, and this scares you, please
make sure to first <a href="#newwork">discuss the change/gather
consensus</a> then ask about the best way to go about making
the change.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"><a name="attribution">Attribution of
Changes</a></div>
<div class="doc_text">
<p>We believe in correct attribution of contributions to
their contributors. However, we do not want the source code to be littered
with random attributions (this is noisy/distracting and revision control
keeps a perfect history of this anyway). As such, we follow these rules:</p>
<ol>
<li>Developers who originate new files in LLVM should place their name at
the top of the file per the
<a href="CodingStandards.html#scf_commenting">Coding Standards</a>.</li>
<li>There should be only one name at the top of the file and it should be
the person who created the file.</li>
<li>Placing your name in the file does not imply <a
href="#clp">copyright</a>: it is only used to attribute the file to
its original author.</li>
<li>Developers should be aware that after some time has passed, the name at
the top of a file may become meaningless as maintenance/ownership of files
changes. Despite this, once set, the attribution of a file never changes.
Revision control keeps an accurate history of contributions.</li>
<li>Developers should maintain their entry in the
<a href="http://llvm.org/cvsweb/cvsweb.cgi/llvm/CREDITS.TXT?rev=HEAD&amp;content-type=text/x-cvsweb-markup">CREDITS.txt</a>
file to summarize their contributions.</li>
<li>Commit comments should contain correct attribution of the person who
submitted the patch if that person is not the committer (i.e. when a
developer with commit privileges commits a patch for someone else).</li>
</ol>
</div>
<!--=========================================================================-->
<div class="doc_section">
<a name="clp">Copyright, License, and Patents</a>
</div>
<!--=========================================================================-->
<div class="doc_text">
<p>This section addresses the issues of copyright, license and patents for
the LLVM project.
Currently, the University of Illinois is the LLVM copyright holder and the
terms of its license to LLVM users and developers is the
<a href="http://www.opensource.org/licenses/UoI-NCSA.php">University of
Illinois/NCSA Open Source License</a>.</p>
<div class="doc_notes">
<p><b>NOTE: This section deals with legal matters but does not provide
legal advice. We are not lawyers, please seek legal counsel from an
attorney.</b></p>
</div>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"><a name="copyright">Copyright</a></div>
<div class="doc_text">
<p>
<p>For consistency and ease of management, the project requires the
copyright for all LLVM software to be held by a single copyright holder:
the University of Illinois (UIUC).</p>
<p>
Although UIUC may eventually reassign the copyright of the software to another
entity (e.g. a dedicated non-profit "LLVM Organization", or something)
the intent for the project is to always have a single entity hold the
copyrights to LLVM at any given time.</p>
<p>We believe that having a single copyright
holder is in the best interests of all developers and users as it greatly
reduces the managerial burden for any kind of administrative or technical
decisions about LLVM. The goal of the LLVM project is to always keep the code
open and <a href="#license">licensed under a very liberal license</a>.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"><a name="license">License</a></div>
<div class="doc_text">
<p>We intend to keep LLVM perpetually open source
and to use a liberal open source license. The current license is the
<a href="http://www.opensource.org/licenses/UoI-NCSA.php">
University of Illinois/NCSA Open Source License</a>, which boils
down to this:</p>
<ul>
<li>You can freely distribute LLVM.</li>
<li>You must retain the copyright notice if you redistribute LLVM.</li>
<li>Binaries derived from LLVM must reproduce the copyright notice.</li>
<li>You can't use our names to promote your LLVM derived products.</li>
<li>There's no warranty on LLVM at all.</li>
</ul>
<p>We believe this fosters the widest adoption of LLVM because it <b>allows
commercial products to be derived from LLVM</b> with few restrictions and
without a requirement for making any derived works also open source (i.e.
LLVM's license is not a "copyleft" license like the GPL). We suggest that you
read the <a href="http://www.opensource.org/licenses/UoI-NCSA.php">License</a>
if further clarification is needed.</p>
<p>Note that the LLVM Project does distribute llvm-gcc, <b>which is GPL.</b>
This means that anything "linked" into llvm-gcc must itself be compatible
with the GPL, and must be releasable under the terms of the GPL. This implies
that <b>any code linked into llvm-gcc and distributed to others may be subject
to the viral aspects of the GPL</b> (for example, a proprietary code generator
linked into llvm-gcc must be made available under
the GPL). This is not a problem for the main LLVM
distribution (which is already licensed under a more liberal license), but may
be a problem if you intend to base commercial development on llvm-gcc without
redistributing your source code.</p>
<p>We have no plans to change the license of LLVM. If you have questions
or comments about the license, please contact the <a
href="mailto:llvm-oversight@cs.uiuc.edu">LLVM Oversight Group</a>.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"><a name="patents">Patents</a></div>
<div class="doc_text">
<p>To the best of our knowledge, LLVM does not infringe on any patents (we have
actually removed code from LLVM in the past that was found to infringe).
Having code in LLVM that infringes on patents would violate an important
goal of the project by making it hard or impossible to reuse the code for
arbitrary purposes (including commercial use).</p>
<p>When contributing code, we expect contributors to notify us of any potential
for patent-related trouble with their changes. If you own the rights to a
patent and would like to contribute code to LLVM that relies on it, we
require that you sign an agreement that allows any other user of LLVM to
freely use your patent. Please contact the <a
href="mailto:llvm-oversight@cs.uiuc.edu">oversight group</a> for more
details.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"><a name="devagree">Developer Agreements</a></div>
<div class="doc_text">
<p>With regards to the LLVM copyright and licensing, developers agree to
assign their copyrights to UIUC for any contribution made so that
the entire software base can be managed by a single copyright holder. This
implies that any contributions can be licensed under the license that the
project uses.</p>
</div>
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