This document contains the LLVM Developer Policy which defines the project's policy towards developers and their contributions. The intent of this policy is to eliminate mis-communication, rework, and confusion that might arise from the distributed nature of LLVM's development. By stating the policy in clear terms, we hope each developer can know ahead of time what to expect when making LLVM contributions.

This policy is also designed to accomplish the following objectives:

1. Attract both users and developers to the LLVM project.
2. Make life as simple and easy for contributors as possible.
3. Keep the top of tree CVS/SVN trees as stable as possible.

This section contains policies that pertain generally to regular LLVM developers. We always welcome random patches from people who do not routinely contribute to LLVM, but expect more from regular contributors to keep the system as efficient as possible for everyone. Regular LLVM developers are expected to meet the following obligations in order for LLVM to maintain a high standard of quality.

Developers should stay informed by reading at least the llvmdev email list. If you are doing anything more than just casual work on LLVM, it is suggested that you also subscribe to the llvm-commits list and pay attention to changes being made by others.

We recommend that active developers register an email account with LLVM Bugzilla and preferably subscribe to the llvm-bugs email list to keep track of bugs and enhancements occurring in LLVM.

When a developer begins a major new project with the aim of contributing it back to LLVM, s/he should inform the community with an email to the llvm-dev email list, to the extent possible. The reason for this is to:

1. keep the community informed about future changes to LLVM,
2. avoid duplication of effort by having multiple parties working on the same thing and not knowing about it, and
3. ensure that any technical issues around the proposed work are discussed and resolved before any significant work is done.

The design of LLVM is carefully controlled to ensure that all the pieces fit together well and are as consistent as possible. If you plan to make a major change to the way LLVM works or a major new extension, it is a good idea to get consensus with the development community before you start working on it.

LLVM has a code review policy. Code review is one way to increase the quality of software. We generally follow these policies:

1. All developers are required to have significant changes reviewed before they are committed to the repository.
2. Code reviews are conducted by email, usually on the llvm-commits list.
3. Code can be reviewed either before it is committed or after. We expect major changes to be reviewed before being committed, but smaller changes (or changes where the developer owns the component) can be reviewed after commit.
4. The developer responsible for a code change is also responsible for making all necessary review-related changes.
5. Developers should participate in code reviews as both a reviewer and a reviewee. We don't have a dedicated team of reviewers. If someone is kind enough to review your code, you should return the favor for someone else.

The minimum quality standards that any change must satisfy before being committed to the main development branch are:

1. Code must adhere to the LLVM Coding Standards.
2. Code must compile cleanly (no errors, no warnings) on at least one platform.
3. Code must pass the deja gnu (llvm/test) test suite.
4. The code must not cause regressions on a reasonable subset of llvm-test, where "reasonable" depends on the contributor's judgement and the scope of the change (more invasive changes require more testing). A reasonable subset is "llvm-test/MultiSource/Benchmarks".

Additionally, the committer is responsible for addressing any problems found that the change is responsible for. For example:

• The code should compile cleanly on all platforms.
• The changes should not cause regressions in the llvm-test suite including SPEC CINT2000, SPEC CFP2000, SPEC CINT2006, and SPEC CFP2006.
• The change set should not cause performance or correctness regressions for the LLVM tools.
• The changes should not cause performance or correctness regressions in code compiled by LLVM on all applicable targets.
• You are expected to address any bugzilla bugs that result from your change.

We prefer for this to be handled before submission but understand that it's not possible to test all of this for every submission. Our nightly testing infrastructure normally finds these problems. A good rule of thumb is to check the nightly testers for regressions the day after your change.

Commits that violate these quality standards (e.g. are very broken) may be reverted. This is necessary when the change blocks other developers from making progress. The developer is welcome to re-commit the change after the problem has been fixed.

Developers are required to create test cases for any bugs fixed and any new features added. The following policies apply:

1. All feature and regression test cases must be added to the llvm/test directory. The appropriate sub-directory should be selected (see the Testing Guide for details).
2. Test cases should be written in LLVM assembly language unless the feature or regression being tested requires another language (e.g. the bug being fixed or feature being implemented is in the llvm-gcc C++ front-end).
3. Test cases, especially for regressions, should be reduced as much as possible, by bugpoint or manually. It is unacceptable to place an entire failing program into llvm/test as this creates a time-to-test burden on all developers. Please keep them short.
4. More extensive test cases (applications, benchmarks, etc.) should be added to the llvm-test test suite. This test suite is for coverage: not features or regressions.

We grant commit access to contributors with a track record of submitting high quality patches. If you would like commit access, please send an email to the LLVM oversight group.

If you have recently been granted commit access, these policies apply:

1. You are granted commit-after-approval to all parts of LLVM. To get approval, submit a patch to llvm-commits. When approved you may commit it yourself.
2. You are allowed to commit patches without approval which you think are obvious. This is clearly a subjective decision. We simply expect you to use good judgement. Examples include: fixing build breakage, reverting obviously broken patches, documentation/comment changes, any other minor changes.
3. You are allowed to commit patches without approval to those portions of LLVM that you have contributed or maintain (have been assigned responsibility for), with the proviso that such commits must not break the build. This is a "trust but verify" policy and commits of this nature are reviewed after they are committed.
4. Multiple violations of these policies or a single egregious violation may cause commit access to be revoked.

When making a large change to LLVM, we use a incremental style of development instead of having long-term development branches. Long-term development branches have a number of drawbacks:

1. Branches must have mainline merged into them periodically. If the branch development and mainline development occur in the same pieces of code, resolving merge conflicts can take a lot of time.
2. Other people in the community tend to ignore work on branches.
3. Huge changes (produced when a branch is merged back onto mainline) are extremely difficult to code review.
4. Branches are not routinely tested by our nightly tester infrastructure.
5. Changes developed as monolithic large changes often don't work until the entire set of changes is done. Breaking it down into a set of smaller changes increases the odds that any of the work will be committed to the main repository.

To address these problems, LLVM uses an incremental development style and we require contributors to follow this practice when making a large/invasive change. Some tips:

• Large/invasive changes usually have a number of secondary changes that are required before the big change can be made (e.g. API cleanup, etc). These sorts of changes can often be done before the major change is done, independently of that work.
• 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.
• Increments can be stand alone (e.g. to fix a bug), or part of a planned series of increments towards some development goal.
• Increments 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 often easy to replace the underlying implementation of the API.

If you are interested in making a large change, and this scares you, please make sure to first discuss the change/gather consensus then feel free to ask about the best way to go about making the change.

We believe in correct attribution of contributions to their contributors. However, we do not want the source code to be littered with random attributions (this is noisy/distracting and revision control keeps a perfect history of this anyway). As such, we follow these rules:

1. Developers who originate new files in LLVM should place their name at the top of the file per the Coding Standards.
2. There should be only one name at the top of the file and it should be the person who created the file.
3. Placing your name in the file does not imply copyright: it is only used to attribute the file to its original author.
4. Developers should be aware that after some time has passed, the name at the top of a file may become meaningless as maintenance/ownership of files changes. Revision control keeps an accurate history of contributions.
5. Developers should maintain their entry in the CREDITS.txt file to summarize their contributions.
6. Commit comments should contain correct attribution of the person who submitted the patch if that person is not the committer (i.e. when a developer with commit privileges commits a patch for someone else).

This section describes policies that apply to developers who regularly contribute code to LLVM. As usual, we often accept small patches and contributions that do not follow this policy. In this case, one of the regular contributors has to get the code in shape.

When submitting a patch, developers must follow these rules:

1. Patches must be made against the CVS HEAD (main development trunk), not a branch.
2. Patches should be made with this command:

   cvs diff -Ntdup -5

   or with the utility utils/mkpatch.
3. Patches should not include differences in generated code such as the code generated by flex, bison or tblgen. The utils/mkpatch utility takes care of this for you.
4. Contributions must not knowingly infringe on any patents. To the best of our knowledge, LLVM is free of any existing patent violations and it is our intent to keep it that way.

When a patch is ready to be submitted, these policies apply:

1. Patches should be submitted immediately after they are generated. Stale patches may not apply correctly if the underlying code changes between the time the patch was created and the time it is applied.
2. Patches should be submitted by e-mail to the llvm-commits list.

After a patch has been submitted, these policies apply:

1. The patch is subject to review by anyone on the llvm-commits email list.
2. Changes recommended by a reviewer should be incorporated into your patch or you should explain why the reviewer is incorrect.
3. Changes to the patch must be re-submitted to the llvm-commits email list.
4. This process iterates until all review issues have been addressed.

After a patch has been committed, these policies apply:

1. The patch is subject to further review by anyone on the llvm-commits email list.
2. The patch submitter is responsible for all aspects of the patch per the quality policy above.
3. If the patch is discovered to not meet the quality policy standards within a reasonable time frame (24 hours), it may be subject to reversal.

We address here the issues of copyright and license for the LLVM project. The object of the copyright and license is the LLVM source code and documentation. Currently, the University of Illinois is the LLVM copyright holder and the terms of its license to LLVM users and developers is the University of Illinois/NCSA Open Source License.

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).

Although UIUC may eventually reassign the copyright of the software to another entity (e.g. a dedicated non-profit "LLVM Organization", or something) the intent for the project is to always have a single entity hold the copyrights to LLVM at any given time.

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 licensed under a very liberal license.

We intend to keep LLVM perpetually open source and to use a liberal open source license. The current license is the University of Illinois/NCSA Open Source License, 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.
• 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 if further clarification is needed.

Note that the LLVM Project does distribute some code that includes GPL software (notably, llvm-gcc which is based on the GCC GPL source base). This means that anything "linked" into to llvm-gcc must itself be compatible with the GPL, and must be releasable under the terms of the GPL. This implies that you any code linked into llvm-gcc and distributed may be subject to the viral aspects of the GPL. This is not a problem for the main LLVM distribution (which is already licensed under a more liberal license), but may be a problem if you intend to do commercial development without redistributing your source code.

We have no plans to change the license of LLVM. If you have questions or comments about the license, please contact the LLVM Oversight Group.

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.

So that the policies defined in this document are clear, we define some terms here.

Change

Any modification to LLVM including documentation, tests, build system, etc. either in patch or commit form.

Commit

A change submitted directly to LLVM software repository via the cvs commit command.

Developer

Anyone who submits a change to LLVM.

Increment

A change or set of changes, whether by patch or commit, that are related by a single common purpose. Increments are atomic as they leave LLVM in a stable state (both compiling and working properly).

Patch

A change submitted by email in patch (diff) format generated by the cvs diff command.