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=====================
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LLVM Developer Policy
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=====================
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.. contents::
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:local:
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Introduction
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============
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This document contains the LLVM Developer Policy which defines the project's
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policy towards developers and their contributions. The intent of this policy is
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to eliminate miscommunication, rework, and confusion that might arise from the
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distributed nature of LLVM's development. By stating the policy in clear terms,
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we hope each developer can know ahead of time what to expect when making LLVM
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contributions. This policy covers all llvm.org subprojects, including Clang,
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LLDB, libc++, etc.
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This policy is also designed to accomplish the following objectives:
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#. Attract both users and developers to the LLVM project.
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#. Make life as simple and easy for contributors as possible.
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#. Keep the top of Subversion trees as stable as possible.
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#. Establish awareness of the project's :ref:`copyright, license, and patent
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policies <copyright-license-patents>` with contributors to the project.
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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 the
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`llvm-commits mailing list
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<http://lists.llvm.org/mailman/listinfo/llvm-commits>`_ and engaging another
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developer to see it through the process.
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Developer Policies
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==================
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This section contains policies that pertain to frequent LLVM developers. We
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always welcome `one-off patches`_ from people who do not routinely contribute to
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LLVM, but we expect more from frequent contributors to keep the system as
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efficient as possible for everyone. Frequent LLVM contributors are expected to
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meet the following requirements in order for LLVM to maintain a high standard of
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quality.
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Stay Informed
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-------------
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Developers should stay informed by reading at least the "dev" mailing list for
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the projects you are interested in, such as `llvm-dev
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<http://lists.llvm.org/mailman/listinfo/llvm-dev>`_ for LLVM, `cfe-dev
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<http://lists.llvm.org/mailman/listinfo/cfe-dev>`_ for Clang, or `lldb-dev
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<http://lists.llvm.org/mailman/listinfo/lldb-dev>`_ for LLDB. If you are
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doing anything more than just casual work on LLVM, it is suggested that you also
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subscribe to the "commits" mailing list for the subproject you're interested in,
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such as `llvm-commits
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<http://lists.llvm.org/mailman/listinfo/llvm-commits>`_, `cfe-commits
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<http://lists.llvm.org/mailman/listinfo/cfe-commits>`_, or `lldb-commits
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<http://lists.llvm.org/mailman/listinfo/lldb-commits>`_. Reading the
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"commits" list and paying attention to changes being made by others is a good
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way to see what other people are interested in and watching the flow of the
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project as a whole.
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We recommend that active developers register an email account with `LLVM
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Bugzilla <https://bugs.llvm.org/>`_ and preferably subscribe to the `llvm-bugs
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<http://lists.llvm.org/mailman/listinfo/llvm-bugs>`_ email list to keep track
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of bugs and enhancements occurring in LLVM. We really appreciate people who are
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proactive at catching incoming bugs in their components and dealing with them
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promptly.
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Please be aware that all public LLVM mailing lists are public and archived, and
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that notices of confidentiality or non-disclosure cannot be respected.
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.. _patch:
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.. _one-off patches:
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Making and Submitting a Patch
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-----------------------------
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When making a patch for review, the goal is to make it as easy for the reviewer
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to read it as possible. As such, we recommend that you:
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#. Make your patch against the Subversion trunk, not a branch, and not an old
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version of LLVM. This makes it easy to apply the patch. For information on
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how to check out SVN trunk, please see the `Getting Started
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Guide <GettingStarted.html#checkout>`_.
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#. Similarly, patches should be submitted soon after they are generated. Old
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patches may not apply correctly if the underlying code changes between the
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time the patch was created and the time it is applied.
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#. Patches should be made with ``svn diff``, or similar. If you use a
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different tool, make sure it uses the ``diff -u`` format and that it
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doesn't contain clutter which makes it hard to read.
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#. If you are modifying generated files, such as the top-level ``configure``
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script, please separate out those changes into a separate patch from the rest
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of your changes.
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Once your patch is ready, submit it by emailing it to the appropriate project's
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commit mailing list (or commit it directly if applicable). Alternatively, some
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patches get sent to the project's development list or component of the LLVM bug
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tracker, but the commit list is the primary place for reviews and should
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generally be preferred.
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When sending a patch to a mailing list, it is a good idea to send it as an
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*attachment* to the message, not embedded into the text of the message. This
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ensures that your mailer will not mangle the patch when it sends it (e.g. by
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making whitespace changes or by wrapping lines).
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*For Thunderbird users:* Before submitting a patch, please open *Preferences >
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Advanced > General > Config Editor*, find the key
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``mail.content_disposition_type``, and set its value to ``1``. Without this
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setting, Thunderbird sends your attachment using ``Content-Disposition: inline``
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rather than ``Content-Disposition: attachment``. Apple Mail gamely displays such
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a file inline, making it difficult to work with for reviewers using that
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program.
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When submitting patches, please do not add confidentiality or non-disclosure
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notices to the patches themselves. These notices conflict with the `LLVM
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License`_ and may result in your contribution being excluded.
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.. _code review:
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Code Reviews
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------------
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LLVM has a code review policy. Code review is one way to increase the quality of
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software. We generally follow these policies:
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#. All developers are required to have significant changes reviewed before they
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are committed to the repository.
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#. Code reviews are conducted by email on the relevant project's commit mailing
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list, or alternatively on the project's development list or bug tracker.
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#. Code can be reviewed either before it is committed or after. We expect major
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changes to be reviewed before being committed, but smaller changes (or
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changes where the developer owns the component) can be reviewed after commit.
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#. The developer responsible for a code change is also responsible for making
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all necessary review-related changes.
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#. Code review can be an iterative process, which continues until the patch is
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ready to be committed. Specifically, once a patch is sent out for review, it
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needs an explicit "looks good" before it is submitted. Do not assume silent
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approval, or request active objections to the patch with a deadline.
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Sometimes code reviews will take longer than you would hope for, especially for
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larger features. Accepted ways to speed up review times for your patches are:
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* Review other people's patches. If you help out, everybody will be more
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willing to do the same for you; goodwill is our currency.
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* Ping the patch. If it is urgent, provide reasons why it is important to you to
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get this patch landed and ping it every couple of days. If it is
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not urgent, the common courtesy ping rate is one week. Remember that you're
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asking for valuable time from other professional developers.
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* Ask for help on IRC. Developers on IRC will be able to either help you
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directly, or tell you who might be a good reviewer.
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* Split your patch into multiple smaller patches that build on each other. The
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smaller your patch, the higher the probability that somebody will take a quick
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look at it.
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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 return the
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favor for someone else. Note that anyone is welcome to review and give feedback
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on a patch, but only people with Subversion write access can approve it.
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There is a web based code review tool that can optionally be used
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for code reviews. See :doc:`Phabricator`.
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.. _code owners:
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Code Owners
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-----------
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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 combination
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of code review plus post-commit review for trusted maintainers. Having both is
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a great way for the project to take advantage of the fact that most people do
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the right thing most of the time, and only commit patches without pre-commit
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review when they are confident they are right.
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The trick to this is that the project has to guarantee that all patches that are
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committed are reviewed after they go in: you don't want everyone to assume
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someone else will review it, allowing the patch to go unreviewed. To solve this
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problem, we have a notion of an 'owner' for a piece of the code. The sole
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responsibility of a code owner is to ensure that a commit to their area of the
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code is appropriately reviewed, either by themself or by someone else. The list
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of current code owners can be found in the file
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`CODE_OWNERS.TXT <http://llvm.org/klaus/llvm/blob/master/CODE_OWNERS.TXT>`_
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in the root of the LLVM source tree.
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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 all
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patches that are committed are actually reviewed.
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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 opt-in,
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and anyone can choose to resign their "title" at any time. For now, we do not
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have an official policy on how one gets elected to be a code owner.
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.. _include a testcase:
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Test Cases
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----------
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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:
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* All feature and regression test cases are added to the ``llvm/test``
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directory. The appropriate sub-directory should be selected (see the
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:doc:`Testing Guide <TestingGuide>` for details).
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* Test cases should be written in :doc:`LLVM assembly language <LangRef>`.
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* Test cases, especially for regressions, should be reduced as much as possible,
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by :doc:`bugpoint <Bugpoint>` or manually. It is unacceptable to place an
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entire failing program into ``llvm/test`` as this creates a *time-to-test*
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burden on all developers. Please keep them short.
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Note that llvm/test and clang/test are designed for regression and small feature
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tests only. More extensive test cases (e.g., entire applications, benchmarks,
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etc) should be added to the ``llvm-test`` test suite. The llvm-test suite is
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for coverage (correctness, performance, etc) testing, not feature or regression
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testing.
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Quality
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-------
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The minimum quality standards that any change must satisfy before being
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committed to the main development branch are:
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#. Code must adhere to the `LLVM Coding Standards <CodingStandards.html>`_.
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#. Code must compile cleanly (no errors, no warnings) on at least one platform.
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#. Bug fixes and new features should `include a testcase`_ so we know if the
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fix/feature ever regresses in the future.
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#. Code must pass the ``llvm/test`` test suite.
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#. 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 of
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the change (more invasive changes require more testing). A reasonable subset
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might be something like "``llvm-test/MultiSource/Benchmarks``".
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Additionally, the committer is responsible for addressing any problems found in
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the future that the change is responsible for. For example:
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* The code should compile cleanly on all supported platforms.
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* The changes should not cause any correctness regressions in the ``llvm-test``
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suite and must not cause any major performance regressions.
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* The change set should not cause performance or correctness regressions for the
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LLVM tools.
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* The changes should not cause performance or correctness regressions in code
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compiled by LLVM on all applicable targets.
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* You are expected to address any `Bugzilla bugs <https://bugs.llvm.org/>`_ that
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result from your change.
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We prefer for this to be handled before submission but understand that it isn't
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possible to test all of this for every submission. Our build bots and nightly
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testing infrastructure normally finds these problems. A good rule of thumb is
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to check the nightly testers for regressions the day after your change. Build
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bots will directly email you if a group of commits that included yours caused a
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failure. You are expected to check the build bot messages to see if they are
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your fault and, if so, fix the breakage.
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Commits that violate these quality standards (e.g. are very broken) may be
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reverted. This is necessary when the change blocks other developers from making
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progress. The developer is welcome to re-commit the change after the problem has
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been fixed.
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.. _commit messages:
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Commit messages
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---------------
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Although we don't enforce the format of commit messages, we prefer that
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you follow these guidelines to help review, search in logs, email formatting
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and so on. These guidelines are very similar to rules used by other open source
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projects.
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Most importantly, the contents of the message should be carefully written to
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convey the rationale of the change (without delving too much in detail). It
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also should avoid being vague or overly specific. For example, "bits were not
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set right" will leave the reviewer wondering about which bits, and why they
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weren't right, while "Correctly set overflow bits in TargetInfo" conveys almost
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all there is to the change.
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Below are some guidelines about the format of the message itself:
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* Separate the commit message into title, body and, if you're not the original
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author, a "Patch by" attribution line (see below).
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* The title should be concise. Because all commits are emailed to the list with
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the first line as the subject, long titles are frowned upon. Short titles
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also look better in `git log`.
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* When the changes are restricted to a specific part of the code (e.g. a
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back-end or optimization pass), it is customary to add a tag to the
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beginning of the line in square brackets. For example, "[SCEV] ..."
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or "[OpenMP] ...". This helps email filters and searches for post-commit
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reviews.
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* The body, if it exists, should be separated from the title by an empty line.
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* The body should be concise, but explanatory, including a complete
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reasoning. Unless it is required to understand the change, examples,
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code snippets and gory details should be left to bug comments, web
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review or the mailing list.
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* If the patch fixes a bug in bugzilla, please include the PR# in the message.
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* `Attribution of Changes`_ should be in a separate line, after the end of
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the body, as simple as "Patch by John Doe.". This is how we officially
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handle attribution, and there are automated processes that rely on this
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format.
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* Text formatting and spelling should follow the same rules as documentation
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and in-code comments, ex. capitalization, full stop, etc.
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* If the commit is a bug fix on top of another recently committed patch, or a
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revert or reapply of a patch, include the svn revision number of the prior
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related commit. This could be as simple as "Revert rNNNN because it caused
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PR#".
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For minor violations of these recommendations, the community normally favors
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reminding the contributor of this policy over reverting. Minor corrections and
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omissions can be handled by sending a reply to the commits mailing list.
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Obtaining Commit Access
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-----------------------
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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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`Chris <mailto:clattner@llvm.org>`_ with the following information:
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#. The user name you want to commit with, e.g. "hacker".
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#. The full name and email address you want message to llvm-commits to come
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from, e.g. "J. Random Hacker <hacker@yoyodyne.com>".
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#. 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 to
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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. Note that our system does not work with MD5
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hashes. These are significantly longer than a crypt hash - e.g.
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"``$apr1$vea6bBV2$Z8IFx.AfeD8LhqlZFqJer0``", we only accept the shorter crypt hash.
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Once you've been granted commit access, you should be able to check out an LLVM
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tree with an SVN URL of "https://username@llvm.org/..." instead of the normal
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anonymous URL of "http://llvm.org/...". The first time you commit you'll have
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to type in your password. Note that you may get a warning from SVN about an
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untrusted key; you can ignore this. To verify that your commit access works,
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please do a test commit (e.g. change a comment or add a blank line). Your first
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commit to a repository may require the autogenerated email to be approved by a
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mailing list. This is normal and will be done when the mailing list owner has
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time.
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If you have recently been granted commit access, these policies apply:
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#. You are granted *commit-after-approval* to all parts of LLVM. To get
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approval, submit a `patch`_ to `llvm-commits
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<http://lists.llvm.org/mailman/listinfo/llvm-commits>`_. When approved,
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you may commit it yourself.
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#. 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 to
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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.
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#. You are allowed to commit patches without approval to those portions of LLVM
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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.
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#. Multiple violations of these policies or a single egregious violation may
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cause commit access to be revoked.
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In any case, your changes are still subject to `code review`_ (either before or
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after they are committed, depending on the nature of the change). You are
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encouraged to review other peoples' patches as well, but you aren't required
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to do so.
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.. _discuss the change/gather consensus:
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Making a Major Change
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---------------------
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When a developer begins a major new project with the aim of contributing it back
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to LLVM, they should inform the community with an email to the `llvm-dev
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<http://lists.llvm.org/mailman/listinfo/llvm-dev>`_ email list, to the extent
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possible. The reason for this is to:
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#. keep the community informed about future changes to LLVM,
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#. avoid duplication of effort by preventing multiple parties working on the
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same thing and not knowing about it, and
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#. ensure that any technical issues around the proposed work are discussed and
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resolved before any significant work is done.
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The design of LLVM is carefully controlled to ensure that all the pieces fit
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together well and are as consistent as possible. If you plan to make a major
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change to the way LLVM works or want to add a major new extension, it is a good
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idea to get consensus with the development community before you start working on
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it.
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Once the design of the new feature is finalized, the work itself should be done
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as a series of `incremental changes`_, not as a long-term development branch.
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.. _incremental changes:
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Incremental Development
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-----------------------
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In the LLVM project, we do all significant changes as a series of incremental
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patches. We have a strong dislike for huge changes or long-term development
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branches. Long-term development branches have a number of drawbacks:
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#. 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.
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#. Other people in the community tend to ignore work on branches.
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#. Huge changes (produced when a branch is merged back onto mainline) are
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extremely difficult to `code review`_.
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#. Branches are not routinely tested by our nightly tester infrastructure.
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#. 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 main
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repository.
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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:
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* Large/invasive changes usually have a number of secondary changes that are
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required before the big change can be made (e.g. API cleanup, etc). These
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sorts of changes can often be done before the major change is done,
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independently of that work.
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* 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.
|
|
|
|
* 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.
|
|
|
|
* 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.
|
|
|
|
* 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.
|
|
|
|
If you are interested in making a large change, and this scares you, please make
|
|
sure to first `discuss the change/gather consensus`_ then ask about the best way
|
|
to go about making the change.
|
|
|
|
Attribution of Changes
|
|
----------------------
|
|
|
|
When contributors submit a patch to an LLVM project, other developers with
|
|
commit access may commit it for the author once appropriate (based on the
|
|
progression of code review, etc.). When doing so, it is important to retain
|
|
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 Hacker" (this is noisy and distracting). In practice, the revision
|
|
control system keeps a perfect history of who changed what, and the CREDITS.txt
|
|
file describes higher-level contributions. If you commit a patch for someone
|
|
else, please follow the attribution of changes in the simple manner as outlined
|
|
by the `commit messages`_ section. Overall, please do not add contributor names
|
|
to the source code.
|
|
|
|
Also, don't commit patches authored by others unless they have submitted the
|
|
patch to the project or you have been authorized to submit them on their behalf
|
|
(you work together and your company authorized you to contribute the patches,
|
|
etc.). The author should first submit them to the relevant project's commit
|
|
list, development list, or LLVM bug tracker component. If someone sends you
|
|
a patch privately, encourage them to submit it to the appropriate list first.
|
|
|
|
|
|
.. _IR backwards compatibility:
|
|
|
|
IR Backwards Compatibility
|
|
--------------------------
|
|
|
|
When the IR format has to be changed, keep in mind that we try to maintain some
|
|
backwards compatibility. The rules are intended as a balance between convenience
|
|
for llvm users and not imposing a big burden on llvm developers:
|
|
|
|
* The textual format is not backwards compatible. We don't change it too often,
|
|
but there are no specific promises.
|
|
|
|
* Additions and changes to the IR should be reflected in
|
|
``test/Bitcode/compatibility.ll``.
|
|
|
|
* The current LLVM version supports loading any bitcode since version 3.0.
|
|
|
|
* After each X.Y release, ``compatibility.ll`` must be copied to
|
|
``compatibility-X.Y.ll``. The corresponding bitcode file should be assembled
|
|
using the X.Y build and committed as ``compatibility-X.Y.ll.bc``.
|
|
|
|
* Newer releases can ignore features from older releases, but they cannot
|
|
miscompile them. For example, if nsw is ever replaced with something else,
|
|
dropping it would be a valid way to upgrade the IR.
|
|
|
|
* Debug metadata is special in that it is currently dropped during upgrades.
|
|
|
|
* Non-debug metadata is defined to be safe to drop, so a valid way to upgrade
|
|
it is to drop it. That is not very user friendly and a bit more effort is
|
|
expected, but no promises are made.
|
|
|
|
C API Changes
|
|
----------------
|
|
|
|
* Stability Guarantees: The C API is, in general, a "best effort" for stability.
|
|
This means that we make every attempt to keep the C API stable, but that
|
|
stability will be limited by the abstractness of the interface and the
|
|
stability of the C++ API that it wraps. In practice, this means that things
|
|
like "create debug info" or "create this type of instruction" are likely to be
|
|
less stable than "take this IR file and JIT it for my current machine".
|
|
|
|
* Release stability: We won't break the C API on the release branch with patches
|
|
that go on that branch, with the exception that we will fix an unintentional
|
|
C API break that will keep the release consistent with both the previous and
|
|
next release.
|
|
|
|
* Testing: Patches to the C API are expected to come with tests just like any
|
|
other patch.
|
|
|
|
* Including new things into the API: If an LLVM subcomponent has a C API already
|
|
included, then expanding that C API is acceptable. Adding C API for
|
|
subcomponents that don't currently have one needs to be discussed on the
|
|
mailing list for design and maintainability feedback prior to implementation.
|
|
|
|
* Documentation: Any changes to the C API are required to be documented in the
|
|
release notes so that it's clear to external users who do not follow the
|
|
project how the C API is changing and evolving.
|
|
|
|
New Targets
|
|
-----------
|
|
|
|
LLVM is very receptive to new targets, even experimental ones, but a number of
|
|
problems can appear when adding new large portions of code, and back-ends are
|
|
normally added in bulk. We have found that landing large pieces of new code
|
|
and then trying to fix emergent problems in-tree is problematic for a variety
|
|
of reasons.
|
|
|
|
For these reasons, new targets are *always* added as *experimental* until
|
|
they can be proven stable, and later moved to non-experimental. The difference
|
|
between both classes is that experimental targets are not built by default
|
|
(need to be added to -DLLVM_TARGETS_TO_BUILD at CMake time).
|
|
|
|
The basic rules for a back-end to be upstreamed in **experimental** mode are:
|
|
|
|
* Every target must have a :ref:`code owner<code owners>`. The `CODE_OWNERS.TXT`
|
|
file has to be updated as part of the first merge. The code owner makes sure
|
|
that changes to the target get reviewed and steers the overall effort.
|
|
|
|
* There must be an active community behind the target. This community
|
|
will help maintain the target by providing buildbots, fixing
|
|
bugs, answering the LLVM community's questions and making sure the new
|
|
target doesn't break any of the other targets, or generic code. This
|
|
behavior is expected to continue throughout the lifetime of the
|
|
target's code.
|
|
|
|
* The code must be free of contentious issues, for example, large
|
|
changes in how the IR behaves or should be formed by the front-ends,
|
|
unless agreed by the majority of the community via refactoring of the
|
|
(:doc:`IR standard<LangRef>`) **before** the merge of the new target changes,
|
|
following the :ref:`IR backwards compatibility`.
|
|
|
|
* The code conforms to all of the policies laid out in this developer policy
|
|
document, including license, patent, and coding standards.
|
|
|
|
* The target should have either reasonable documentation on how it
|
|
works (ISA, ABI, etc.) or a publicly available simulator/hardware
|
|
(either free or cheap enough) - preferably both. This allows
|
|
developers to validate assumptions, understand constraints and review code
|
|
that can affect the target.
|
|
|
|
In addition, the rules for a back-end to be promoted to **official** are:
|
|
|
|
* The target must have addressed every other minimum requirement and
|
|
have been stable in tree for at least 3 months. This cool down
|
|
period is to make sure that the back-end and the target community can
|
|
endure continuous upstream development for the foreseeable future.
|
|
|
|
* The target's code must have been completely adapted to this policy
|
|
as well as the :doc:`coding standards<CodingStandards>`. Any exceptions that
|
|
were made to move into experimental mode must have been fixed **before**
|
|
becoming official.
|
|
|
|
* The test coverage needs to be broad and well written (small tests,
|
|
well documented). The build target ``check-all`` must pass with the
|
|
new target built, and where applicable, the ``test-suite`` must also
|
|
pass without errors, in at least one configuration (publicly
|
|
demonstrated, for example, via buildbots).
|
|
|
|
* Public buildbots need to be created and actively maintained, unless
|
|
the target requires no additional buildbots (ex. ``check-all`` covers
|
|
all tests). The more relevant and public the new target's CI infrastructure
|
|
is, the more the LLVM community will embrace it.
|
|
|
|
To **continue** as a supported and official target:
|
|
|
|
* The maintainer(s) must continue following these rules throughout the lifetime
|
|
of the target. Continuous violations of aforementioned rules and policies
|
|
could lead to complete removal of the target from the code base.
|
|
|
|
* Degradation in support, documentation or test coverage will make the target as
|
|
nuisance to other targets and be considered a candidate for deprecation and
|
|
ultimately removed.
|
|
|
|
In essences, these rules are necessary for targets to gain and retain their
|
|
status, but also markers to define bit-rot, and will be used to clean up the
|
|
tree from unmaintained targets.
|
|
|
|
.. _copyright-license-patents:
|
|
|
|
Copyright, License, and Patents
|
|
===============================
|
|
|
|
.. note::
|
|
|
|
This section deals with legal matters but does not provide legal advice. We
|
|
are not lawyers --- please seek legal counsel from an attorney.
|
|
|
|
This section addresses the issues of copyright, license and patents for the LLVM
|
|
project. The copyright for the code is held by the individual contributors of
|
|
the code and the terms of its license to LLVM users and developers is the
|
|
`University of Illinois/NCSA Open Source License
|
|
<http://www.opensource.org/licenses/UoI-NCSA.php>`_ (with portions dual licensed
|
|
under the `MIT License <http://www.opensource.org/licenses/mit-license.php>`_,
|
|
see below). As contributor to the LLVM project, you agree to allow any
|
|
contributions to the project to licensed under these terms.
|
|
|
|
Copyright
|
|
---------
|
|
|
|
The LLVM project does not require copyright assignments, which means that the
|
|
copyright for the code in the project is held by its respective contributors who
|
|
have each agreed to release their contributed code under the terms of the `LLVM
|
|
License`_.
|
|
|
|
An implication of this is that the LLVM license is unlikely to ever change:
|
|
changing it would require tracking down all the contributors to LLVM and getting
|
|
them to agree that a license change is acceptable for their contribution. Since
|
|
there are no plans to change the license, this is not a cause for concern.
|
|
|
|
As a contributor to the project, this means that you (or your company) retain
|
|
ownership of the code you contribute, that it cannot be used in a way that
|
|
contradicts the license (which is a liberal BSD-style license), and that the
|
|
license for your contributions won't change without your approval in the
|
|
future.
|
|
|
|
.. _LLVM License:
|
|
|
|
License
|
|
-------
|
|
|
|
We intend to keep LLVM perpetually open source and to use a liberal open source
|
|
license. **As a contributor to the project, you agree that any contributions be
|
|
licensed under the terms of the corresponding subproject.** All of the code in
|
|
LLVM is available under the `University of Illinois/NCSA Open Source License
|
|
<http://www.opensource.org/licenses/UoI-NCSA.php>`_, which boils down to
|
|
this:
|
|
|
|
* You can freely distribute LLVM.
|
|
* You must retain the copyright notice if you redistribute LLVM.
|
|
* Binaries derived from LLVM must reproduce the copyright notice (e.g. in an
|
|
included readme file).
|
|
* You can't use our names to promote your LLVM derived products.
|
|
* There's no warranty on LLVM at all.
|
|
|
|
We believe this fosters the widest adoption of LLVM because it **allows
|
|
commercial products to be derived from LLVM** 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
|
|
`License <http://www.opensource.org/licenses/UoI-NCSA.php>`_ if further
|
|
clarification is needed.
|
|
|
|
In addition to the UIUC license, the runtime library components of LLVM
|
|
(**compiler_rt, libc++, and libclc**) are also licensed under the `MIT License
|
|
<http://www.opensource.org/licenses/mit-license.php>`_, which does not contain
|
|
the binary redistribution clause. As a user of these runtime libraries, it
|
|
means that you can choose to use the code under either license (and thus don't
|
|
need the binary redistribution clause), and as a contributor to the code that
|
|
you agree that any contributions to these libraries be licensed under both
|
|
licenses. We feel that this is important for runtime libraries, because they
|
|
are implicitly linked into applications and therefore should not subject those
|
|
applications to the binary redistribution clause. This also means that it is ok
|
|
to move code from (e.g.) libc++ to the LLVM core without concern, but that code
|
|
cannot be moved from the LLVM core to libc++ without the copyright owner's
|
|
permission.
|
|
|
|
Note that the LLVM Project does distribute dragonegg, **which is
|
|
GPL.** This means that anything "linked" into dragonegg must itself be compatible
|
|
with the GPL, and must be releasable under the terms of the GPL. This implies
|
|
that **any code linked into dragonegg and distributed to others may be subject to
|
|
the viral aspects of the GPL** (for example, a proprietary code generator linked
|
|
into dragonegg 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 GPL-containing subprojects are kept in separate SVN repositories whose
|
|
LICENSE.txt files specifically indicate that they contain GPL code.
|
|
|
|
We have no plans to change the license of LLVM. If you have questions or
|
|
comments about the license, please contact the `LLVM Developer's Mailing
|
|
List <mailto:llvm-dev@lists.llvm.org>`_.
|
|
|
|
Patents
|
|
-------
|
|
|
|
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).
|
|
|
|
When contributing code, we expect contributors to notify us of any potential for
|
|
patent-related trouble with their changes (including from third parties). 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 `LLVM Foundation Board of Directors <mailto:board@llvm.org>`_ for more
|
|
details.
|