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:
This policy is aimed at regular contributors to LLVM. People interested in contributing one-off patches can do so in an informal way by sending them to the llvm-commits mailing list and engaging another developer to see it through the process.
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 making a patch for review, the goal is to make it as easy for the reviewer to read it as possible. As such, we recommend that you:
cvs diff -Ntdup -5or with the utility utils/mkpatch, which makes it easy to read the diff.
LLVM has a code review policy. Code review is one way to increase the quality of software. We generally follow these policies:
Developers are required to create test cases for any bugs fixed and any new features added. The following policies apply:
The minimum quality standards that any change must satisfy before being committed to the main development branch are:
Additionally, the committer is responsible for addressing any problems found in the future that the change is responsible for. For example:
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.
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:
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:
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.
Once the design of the new feature is finalized, the work itself should be done as a series of incremental changes, not as a long-term development branch.
In the LLVM project, we do all significant changes as a series of incremental patches. We have a strong dislike for huge changes or long-term development branches. Long-term development branches have a number of drawbacks:
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:
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:
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.
NOTE: This section deals with legal matters but does not provide official legal advice. We are not lawyers, please seek legal counsel from an attorney.
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:
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.
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 the one of the goals of the project by making it hard or impossible to reuse the code for arbitrary purposes.
When contributing code, we expect contributors to notify us of any potential for patent-related trouble with their changes. If you own the rights to a patent and would like to contribute code to LLVM that relies on it, we require that you sign an agreement that allows any other user of LLVM to freely use your patent. Please contact the oversight group for more details.
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.