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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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"http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<title>LLVM Developer Policy</title>
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<link rel="stylesheet" href="llvm.css" type="text/css">
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</head>
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<body>
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<div class="doc_title">LLVM Developer Policy</div>
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<ol>
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<li><a href="#introduction">Introduction</a></li>
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<li><a href="#policies">Developer Policies</a>
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<ol>
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<li><a href="#informed">Stay Informed</a></li>
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<li><a href="#patches">Making a Patch</a></li>
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<li><a href="#reviews">Code Reviews</a></li>
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<li><a href="#owners">Code Owners</a></li>
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<li><a href="#testcases">Test Cases</a></li>
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<li><a href="#quality">Quality</a></li>
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<li><a href="#commitaccess">Obtaining Commit Access</a></li>
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<li><a href="#newwork">Making a Major Change</a></li>
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<li><a href="#incremental">Incremental Development</a></li>
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<li><a href="#attribution">Attribution of Changes</a></li>
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</ol></li>
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<li><a href="#clp">Copyright, License, and Patents</a>
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<ol>
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<li><a href="#copyright">Copyright</a></li>
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<li><a href="#license">License</a></li>
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<li><a href="#patents">Patents</a></li>
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<li><a href="#devagree">Developer Agreements</a></li>
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</ol></li>
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</ol>
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<div class="doc_author">Written by the LLVM Oversight Team</div>
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<!--=========================================================================-->
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<div class="doc_section"><a name="introduction">Introduction</a></div>
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<!--=========================================================================-->
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<div class="doc_text">
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<p>This document contains the LLVM Developer Policy which defines the
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project's policy towards developers and their contributions. The intent of
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this policy is to eliminate mis-communication, rework, and confusion that
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might arise from the distributed nature of LLVM's development. By stating
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the policy in clear terms, we hope each developer can know ahead of time
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what to expect when making LLVM contributions.</p>
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<p>This policy is also designed to accomplish the following objectives:</p>
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<ol>
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<li>Attract both users and developers to the LLVM project.</li>
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<li>Make life as simple and easy for contributors as possible.</li>
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<li>Keep the top of Subversion trees as stable as possible.</li>
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</ol>
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<p>This policy is aimed at frequent contributors to LLVM. People interested in
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contributing one-off patches can do so in an informal way by sending them to
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the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
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llvm-commits mailing list</a> and engaging another developer to see it through
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the process.</p>
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</div>
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<!--=========================================================================-->
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<div class="doc_section"><a name="policies">Developer Policies</a></div>
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<!--=========================================================================-->
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<div class="doc_text">
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<p>This section contains policies that pertain to frequent LLVM
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developers. We always welcome <a href="#patches">one-off patches</a> from
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people who do not routinely contribute to LLVM, but we expect more from
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frequent contributors to keep the system as efficient as possible for
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everyone.
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Frequent LLVM contributors are expected to meet the following requirements in
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order for LLVM to maintain a high standard of quality.<p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"> <a name="informed">Stay Informed</a> </div>
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<div class="doc_text">
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<p>Developers should stay informed by reading at least the
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<a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a>
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email list. If you are doing anything more than just casual work on LLVM,
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it is suggested that you also subscribe to the
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<a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">llvm-commits</a>
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list and pay attention to changes being made by others.</p>
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<p>We recommend that active developers register an email account with
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<a href="http://llvm.org/bugs/">LLVM Bugzilla</a> and preferably subscribe to
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the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmbugs">llvm-bugs</a>
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email list to keep track of bugs and enhancements occurring in LLVM.</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"> <a name="patches">Making a Patch</a></div>
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<div class="doc_text">
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<p>When making a patch for review, the goal is to make it as easy for the
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reviewer to read it as possible. As such, we recommend that you:</p>
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<ol>
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<li>Make your patch against the Subversion trunk, not a branch, and not an
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old version of LLVM. This makes it easy to apply the patch.</li>
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<li>Similarly, patches should be submitted soon after they are generated.
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Old patches may not apply correctly if the underlying code changes between
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the time the patch was created and the time it is applied.</li>
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<li>Patches should be made with this command:
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<pre>svn diff -x -u</pre>
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or with the utility <tt>utils/mkpatch</tt>, which makes it easy to read the
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diff.</li>
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<li>Patches should not include differences in generated code such as the
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code generated by <tt>flex</tt>, <tt>bison</tt> or <tt>tblgen</tt>. The
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<tt>utils/mkpatch</tt> utility takes care of this for you.</li>
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</ol>
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<p>When sending a patch to a mailing list, it is a good idea to send it as an
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<em>attachment</em> to the message, not embedded into the text of the
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message. This ensures that your mailer will not mangle the patch when it
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sends it (e.g. by making whitespace changes or by wrapping lines).</p>
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<p><em>For Thunderbird users:</em> Before submitting a patch, please open
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<em>Preferences → Advanced → General → Config Editor</em>,
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find the key <tt>mail.content_disposition_type</tt>, and set its value to
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<tt>1</tt>. Without this setting, Thunderbird sends your attachment using
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<tt>Content-Disposition: inline</tt> rather than <tt>Content-Disposition:
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attachment</tt>. Apple Mail gamely displays such a file inline, making it
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difficult to work with for reviewers using that program.</p>
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</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"> <a name="reviews">Code Reviews</a></div>
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<div class="doc_text">
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<p>LLVM has a code review policy. Code review is one way to increase the
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quality of software. We generally follow these policies:</p>
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<ol>
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<li>All developers are required to have significant changes reviewed
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before they are committed to the repository.</li>
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<li>Code reviews are conducted by email, usually on the llvm-commits
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list.</li>
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<li>Code can be reviewed either before it is committed or after. We expect
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major changes to be reviewed before being committed, but smaller
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changes (or changes where the developer owns the component) can be
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reviewed after commit.</li>
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<li>The developer responsible for a code change is also responsible for
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making all necessary review-related changes.</li>
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<li>Code review can be an iterative process, which continues until the patch
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is ready to be committed.</li>
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</ol>
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<p>Developers should participate in code reviews as both reviewers and
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reviewees. If someone is kind enough to review your code, you should
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return the favor for someone else. Note that anyone is welcome to review
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and give feedback on a patch, but only people with Subversion write access
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can approve it.</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"> <a name="owners">Code Owners</a></div>
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<div class="doc_text">
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<p>The LLVM Project relies on two features of its process to maintain rapid
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development in addition to the high quality of its source base: the
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combination of code review plus post-commit review for trusted maintainers.
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Having both is a great way for the project to take advantage of the fact
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that most people do the right thing most of the time, and only commit
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patches without pre-commit review when they are confident they are
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right.</p>
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<p>The trick to this is that the project has to guarantee that all patches
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that are committed are reviewed after they go in: you don't want everyone
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to assume someone else will review it, allowing the patch to go unreviewed.
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To solve this problem, we have a notion of an 'owner' for a piece of the
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code. The sole responsibility of a code owner is to ensure that a commit
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to their area of the code is appropriately reviewed, either by themself or
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by someone else. The current code owners are:</p>
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<ol>
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<li><b>Anton Korobeynikov</b>: Exception handling, debug information, and
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Windows codegen.</li>
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<li><b>Duncan Sands</b>: llvm-gcc 4.2.</li>
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<li><b>Evan Cheng</b>: Code generator and all targets.</li>
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<li><b>Chris Lattner</b>: Everything else.</li>
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</ol>
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<p>Note that code ownership is completely different than reviewers: anyone can
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review a piece of code, and we welcome code review from anyone who is
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interested. Code owners are the "last line of defense" to guarantee that
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all patches that are committed are actually reviewed.</p>
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<p>Being a code owner is a somewhat unglamorous position, but it is incredibly
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important for the ongoing success of the project. Because people get busy,
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interests change, and unexpected things happen, code ownership is purely
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opt-in, and anyone can choose to resign their "title" at any time. For now,
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we do not have an official policy on how one gets elected to be a code
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owner.
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</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"> <a name="testcases">Test Cases</a></div>
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<div class="doc_text">
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<p>Developers are required to create test cases for any bugs fixed and any new
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features added. Some tips for getting your testcase approved:</p>
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<ol>
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<li>All feature and regression test cases are added to the
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<tt>llvm/test</tt> directory. The appropriate sub-directory should be
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selected (see the <a href="TestingGuide.html">Testing Guide</a> for
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details).</li>
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<li>Test cases should be written in
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<a href="LangRef.html">LLVM assembly language</a> unless the
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feature or regression being tested requires another language (e.g. the
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bug being fixed or feature being implemented is in the llvm-gcc C++
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front-end, in which case it must be written in C++).</li>
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<li>Test cases, especially for regressions, should be reduced as much as
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possible, by <a href="Bugpoint.html">bugpoint</a> or
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manually. It is unacceptable
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to place an entire failing program into <tt>llvm/test</tt> as this creates
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a <i>time-to-test</i> burden on all developers. Please keep them short.</li>
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</ol>
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<p>Note that llvm/test is designed for regression and small feature tests
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only. More extensive test cases (e.g., entire applications, benchmarks,
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etc) should be added to the <tt>llvm-test</tt> test suite. The llvm-test
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suite is for coverage (correctness, performance, etc) testing, not feature
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or regression testing.</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"> <a name="quality">Quality</a></div>
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<div class="doc_text">
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<p>The minimum quality standards that any change must satisfy before being
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committed to the main development branch are:</p>
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<ol>
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<li>Code must adhere to the
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<a href="CodingStandards.html">LLVM Coding Standards</a>.</li>
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<li>Code must compile cleanly (no errors, no warnings) on at least one
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platform.</li>
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<li>Bug fixes and new features should <a href="#testcases">include a
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testcase</a> so we know if the fix/feature ever regresses in the
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future.</li>
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<li>Code must pass the dejagnu (<tt>llvm/test</tt>) test suite.</li>
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<li>The code must not cause regressions on a reasonable subset of llvm-test,
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where "reasonable" depends on the contributor's judgement and the scope
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of the change (more invasive changes require more testing). A reasonable
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subset is "<tt>llvm-test/MultiSource/Benchmarks</tt>".</li>
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</ol>
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<p>Additionally, the committer is responsible for addressing any problems
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found in the future that the change is responsible for. For example:</p>
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<ul>
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<li>The code should compile cleanly on all supported platforms.</li>
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<li>The changes should not cause any correctness regressions in the
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<tt>llvm-test</tt> suite and must not cause any major performance
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regressions.</li>
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<li>The change set should not cause performance or correctness regressions
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for the LLVM tools.</li>
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<li>The changes should not cause performance or correctness regressions in
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code compiled by LLVM on all applicable targets.</li>
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<li>You are expected to address any <a href="http://llvm.org/bugs/">bugzilla
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bugs</a> that result from your change.</li>
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</ul>
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<p>We prefer for this to be handled before submission but understand that it
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isn't possible to test all of this for every submission. Our nightly
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testing
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infrastructure normally finds these problems. A good rule of thumb is to
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check the nightly testers for regressions the day after your change.</p>
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<p>Commits that violate these quality standards (e.g. are very broken) may
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be reverted. This is necessary when the change blocks other developers from
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making progress. The developer is welcome to re-commit the change after
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the problem has been fixed.</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection">
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<a name="commitaccess">Obtaining Commit Access</a></div>
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<div class="doc_text">
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<p>
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We grant commit access to contributors with a track record of submitting high
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quality patches. If you would like commit access, please send an email to
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<a href="mailto:sabre@nondot.org">Chris</a> with the following information:</p>
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<ol>
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<li>The user name you want to commit with, e.g. "sabre".</li>
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<li>The full name and email address you want message to llvm-commits to come
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from, e.g. "Chris Lattner <sabre@nondot.org>".</li>
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<li>A "password hash" of the password you want to use, e.g. "2ACR96qjUqsyM".
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Note that you don't ever tell us what your password is, you just give it
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to us in an encrypted form. To get this, run "htpasswd" (a utility that
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comes with apache) in crypt mode (often enabled with "-d"), or find a web
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page that will do it for you.</li>
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</ol>
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<p>Once you've been granted commit access, you should be able to check out an
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LLVM tree with an SVN URL of "https://username@llvm.org/..." instead of the
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normal anonymous URL of "http://llvm.org/...". The first time you commit
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you'll have to type in your password. Note that you may get a warning from
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SVN about an untrusted key, you can ignore this. To verify that your commit
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access works, please do a test commit (e.g. change a comment or add a blank
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line). Your first commit to a repository may require the autogenerated email
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to be approved by a mailing list. This is normal, and will be done when
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the mailing list owner has time.</p>
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<p>If you have recently been granted commit access, these policies apply:</p>
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<ol>
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<li>You are granted <i>commit-after-approval</i> to all parts of LLVM.
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To get approval, submit a <a href="#patches">patch</a> to
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<a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits">
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llvm-commits</a>. When approved you may commit it yourself.</li>
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<li>You are allowed to commit patches without approval which you think are
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obvious. This is clearly a subjective decision — we simply expect you
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to use good judgement. Examples include: fixing build breakage, reverting
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obviously broken patches, documentation/comment changes, any other minor
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changes.</li>
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<li>You are allowed to commit patches without approval to those portions
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of LLVM that you have contributed or maintain (i.e., have been assigned
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responsibility for), with the proviso that such commits must not break the
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build. This is a "trust but verify" policy and commits of this nature are
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reviewed after they are committed.</li>
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<li>Multiple violations of these policies or a single egregious violation
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may cause commit access to be revoked.</li>
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</ol>
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<p>In any case, your changes are still subject to <a href="#reviews">code
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review</a> (either before or after they are committed, depending on the nature
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of the change). You are encouraged to review other peoples' patches as well,
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but you aren't required to.</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"> <a name="newwork">Making a Major Change</a></div>
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<div class="doc_text">
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<p>When a developer begins a major new project with the aim of contributing
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it back to LLVM, s/he should inform the community with an email to
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the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev</a>
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email list, to the extent possible. The reason for this is to:
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<ol>
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<li>keep the community informed about future changes to LLVM, </li>
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<li>avoid duplication of effort by preventing multiple parties working on
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the same thing and not knowing about it, and</li>
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<li>ensure that any technical issues around the proposed work are
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discussed and resolved before any significant work is done.</li>
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</ol>
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<p>The design of LLVM is carefully controlled to ensure that all the pieces
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fit together well and are as consistent as possible. If you plan to make a
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major change to the way LLVM works or want to add a major new extension, it
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is a good idea to get consensus with the development
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community before you start working on it.</p>
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<p>Once the design of the new feature is finalized, the work itself should be
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done as a series of <a href="#incremental">incremental changes</a>, not as
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a long-term development branch.</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"> <a name="incremental">Incremental Development</a>
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</div>
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<div class="doc_text">
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<p>In the LLVM project, we do all significant changes as a series of
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incremental patches. We have a strong dislike for huge changes or
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long-term development branches. Long-term development branches have a
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number of drawbacks:</p>
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<ol>
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<li>Branches must have mainline merged into them periodically. If the branch
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development and mainline development occur in the same pieces of code,
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resolving merge conflicts can take a lot of time.</li>
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<li>Other people in the community tend to ignore work on branches.</li>
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<li>Huge changes (produced when a branch is merged back onto mainline) are
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extremely difficult to <a href="#reviews">code review</a>.</li>
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<li>Branches are not routinely tested by our nightly tester
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infrastructure.</li>
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<li>Changes developed as monolithic large changes often don't work until the
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entire set of changes is done. Breaking it down into a set of smaller
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changes increases the odds that any of the work will be committed to the
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main repository.</li>
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</ol>
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<p>
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To address these problems, LLVM uses an incremental development style and we
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require contributors to follow this practice when making a large/invasive
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change. Some tips:</p>
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<ul>
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<li>Large/invasive changes usually have a number of secondary changes that
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are required before the big change can be made (e.g. API cleanup, etc).
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These sorts of changes can often be done before the major change is done,
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independently of that work.</li>
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<li>The remaining inter-related work should be decomposed into unrelated
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sets of changes if possible. Once this is done, define the first increment
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and get consensus on what the end goal of the change is.</li>
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<li>Each change in the set can be stand alone (e.g. to fix a bug), or part
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of a planned series of changes that works towards the development goal.</li>
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<li>Each change should be kept as small as possible. This simplifies your
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work (into a logical progression), simplifies code review and reduces the
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chance that you will get negative feedback on the change. Small increments
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also facilitate the maintenance of a high quality code base.</li>
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<li>Often, an independent precursor to a big change is to add a new API and
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slowly migrate clients to use the new API. Each change to use the new
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API is often "obvious" and can be committed without review. Once the
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new API is in place and used, it is much easier to replace the
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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 code written by J Random Guy" (this is noisy
|
|
and distracting. In practice, the revision control system keeps a perfect
|
|
history of who change what, and the CREDITS.txt file describes higher-level
|
|
contributions.</p>
|
|
|
|
<p>Overall, please do not add contributor names to the source base.</p>
|
|
</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")
|
|
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 (e.g.
|
|
in an included readme file).</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 code already distributed under a more liberal license (like the
|
|
UIUC license), and does not affect code generated by llvm-gcc. It 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 or your employer
|
|
own the rights to a
|
|
patent and would like to contribute code to LLVM that relies on it, we
|
|
require that
|
|
the copyright owner 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>
|
|
|
|
<p>When contributing code, you also affirm that you are legally entitled to
|
|
grant this copyright, personally or on behalf of your employer. If the code
|
|
belongs to some other entity, please raise this issue with the oversight
|
|
group before the code is committed.</p>
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<hr>
|
|
<address>
|
|
<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
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src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
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Written by the
|
|
<a href="mailto:llvm-oversight@cs.uiuc.edu">LLVM Oversight Group</a><br>
|
|
<a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
|
|
Last modified: $Date$
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</address>
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