LLVM Developer Policy

This policy is aimed at frequent contributors to LLVM. People interested in + contributing one-off patches can do so in an informal way by sending them to + the + llvm-commits + mailing list and engaging another developer to see it through the + process.

This section contains policies that pertain generally to LLVM developers. -

LLVM Developers are expected to meet the following obligations in order - for LLVM to maintain a high standard of quality.

This section contains policies that pertain to frequent LLVM developers. We + always welcome one-off patches from people who do not + routinely contribute to LLVM, but we expect more from frequent contributors + to keep the system as efficient as possible for everyone. Frequent LLVM + contributors are expected to meet the following requirements in order for + LLVM to maintain a high standard of quality.

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 highly 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.

Developers should stay informed by reading at least the "dev" mailing list + for the projects you are interested in, such as + llvmdev for + LLVM, cfe-dev + for Clang, or lldb-dev + for LLDB. If you are doing anything more than just casual work on LLVM, it + is suggested that you also subscribe to the "commits" mailing list for the + subproject you're interested in, such as + llvm-commits, + cfe-commits, + or lldb-commits. + Reading the "commits" list and paying attention to changes being made by + others is a good way to see what other people are interested in and watching + the flow of the project as a whole.

+ +

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. We + really appreciate people who are proactive at catching incoming bugs in their + components and dealing with them promptly.

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: -

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

The design of LLVM is carefully controlled to ensure that all the pieces - fit together well. 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.

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:

+ +

Make your patch against the Subversion trunk, not a branch, and not an old + version of LLVM. This makes it easy to apply the patch. For information + on how to check out SVN trunk, please see the Getting Started Guide.
Similarly, patches should be submitted soon after they are generated. Old + patches may not apply correctly if the underlying code changes between the + time the patch was created and the time it is applied.
Patches should be made with svn diff, or similar. If you use + a different tool, make sure it uses the diff -u format and + that it doesn't contain clutter which makes it hard to read.
If you are modifying generated files, such as the top-level + configure script, please separate out those changes into + a separate patch from the rest of your changes.

+ +

When sending a patch to a mailing list, it is a good idea to send it as an + attachment to the message, not embedded into the text of the + message. This ensures that your mailer will not mangle the patch when it + sends it (e.g. by making whitespace changes or by wrapping lines).

+ +

For Thunderbird users: Before submitting a patch, please open + Preferences → Advanced → General → Config Editor, + find the key mail.content_disposition_type, and set its value to + 1. Without this setting, Thunderbird sends your attachment using + Content-Disposition: inline rather than Content-Disposition: + attachment. Apple Mail gamely displays such a file inline, making it + difficult to work with for reviewers using that program.

LLVM has a code review policy. Code review is an excellent way to ensure - high quality in the software. The following policies apply:

All developers are required to have any significant changes reviewed - before they are committed to the repository.
Code reviews are conducted by email.
Code can be reviewed either before it is committed or after.
The developer responsible for a code change is also responsible for - making all necessary review changes.
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.

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

LLVM uses an incremental development style and all developers are expected - to follow this practice. Incremental development is a big key to LLVM's - success and it is essential that developers submit incremental patches. The - following defines the incremental development approach:

The first task is to define the increment and get consensus (with the - LLVM development community) on what the end goal of the change is. Making - random small changes that go nowhere is not useful for anyone.
An increment is the smallest patch size necessary to effect one change - in LLVM.
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.

All developers are required to have significant changes reviewed before + they are committed to the repository.
Code reviews are conducted by email, usually on the llvm-commits + list.
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.
The developer responsible for a code change is also responsible for making + all necessary review-related changes.
Code review can be an iterative process, which continues until the patch + is ready to be committed.

+ +

Developers should participate in code reviews as both reviewers and + reviewees. If someone is kind enough to review your code, you should return + the favor for someone else. Note that anyone is welcome to review and give + feedback on a patch, but only people with Subversion write access can approve + it.

The minimum quality standards for any change to the main development - branch are:

Code must adhere to the - LLVM Coding Standards.
Code must compile cleanly (no errors, no warnings) on at least one - platform.
Code must pass the deja gnu (llvm/test) test suite.

Additionally, the committer is responsible for addressing all of the - following items (preferably before submission):

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 with LLVM on all applicable targets.

+ +

The LLVM Project relies on two features of its process to maintain rapid + development in addition to the high quality of its source base: the + combination of code review plus post-commit review for trusted maintainers. + Having both is a great way for the project to take advantage of the fact that + most people do the right thing most of the time, and only commit patches + without pre-commit review when they are confident they are right.

+ +

The trick to this is that the project has to guarantee that all patches that + are committed are reviewed after they go in: you don't want everyone to + assume someone else will review it, allowing the patch to go unreviewed. To + solve this problem, we have a notion of an 'owner' for a piece of the code. + The sole responsibility of a code owner is to ensure that a commit to their + area of the code is appropriately reviewed, either by themself or by someone + else. The current code owners are:

+ +

Evan Cheng: Code generator and all targets.
Greg Clayton: LLDB.
Doug Gregor: Clang Frontend Libraries.
Howard Hinnant: libc++.
Anton Korobeynikov: Exception handling, debug information, and + Windows codegen.
Ted Kremenek: Clang Static Analyzer.
Chris Lattner: Everything not covered by someone else.
Duncan Sands: llvm-gcc 4.2.

+ +

Note that code ownership is completely different than reviewers: anyone can + review a piece of code, and we welcome code review from anyone who is + interested. Code owners are the "last line of defense" to guarantee that all + patches that are committed are actually reviewed.

+ +

Being a code owner is a somewhat unglamorous position, but it is incredibly + important for the ongoing success of the project. Because people get busy, + interests change, and unexpected things happen, code ownership is purely + opt-in, and anyone can choose to resign their "title" at any time. For now, + we do not have an official policy on how one gets elected to be a code + owner.

Developers are required to create test cases for regressions and new - features and include them with their changes. The following policies - apply:

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).
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 lvm-gcc C++ - front-end).
Test cases, especially for regressions, should be much as reduced 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. Keep them short!
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.

Developers are required to create test cases for any bugs fixed and any new + features added. Some tips for getting your testcase approved:

This section contains policies that pertain to submitting patches - to LLVM and committing code to the repository

When submitting a patch, developers must follow these rules:

Patches must be made against the CVS HEAD (main development trunk), - not a branch.
Patches should be made with this command:
```
-    cvs diff -Ntdup -5
```
or with the utility utils/mkpatch.
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.

Before a patch is submitted for review, it should be tested to ensure - that:

The patch must compile against the CVS HEAD cleanly (zero warnings, zero - errors).
All the llvm/test (Deja Gnu) tests must pass.
All the llvm-test tests must pass on at least one platform.

All feature and regression test cases are added to the + llvm/test directory. The appropriate sub-directory should be + selected (see the Testing Guide for + details).
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, in which case it must be written in + C++).
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.

+ +

Note that llvm/test and clang/test are designed for regression and small + feature tests only. More extensive test cases (e.g., entire applications, + benchmarks, etc) + should be added to the llvm-test test suite. The llvm-test suite is + for coverage (correctness, performance, etc) testing, not feature or + regression testing.

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

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.
Patches should be submitted by e-mail to the - - llvm-commits list.

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

+ +

Code must adhere to the LLVM Coding + Standards.
Code must compile cleanly (no errors, no warnings) on at least one + platform.
Bug fixes and new features should include a + testcase so we know if the fix/feature ever regresses in the + future.
Code must pass the llvm/test test suite.
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 might be something like + "llvm-test/MultiSource/Benchmarks".

+ +

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

+ +

The code should compile cleanly on all supported platforms.
The changes should not cause any correctness regressions in the + llvm-test suite and must not cause any major performance + regressions.
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 + isn't possible to test all of this for every submission. Our build bots and + 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. Build bots will directly email you if a group of commits that + included yours caused a failure. You are expected to check the build bot + messages to see if they are your fault and, if so, fix the breakage.

+ +

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.

After a patch has been submitted, these policies apply:

The patch is subject to review by anyone on the llvm-commits email list. -
Changes recommended by a reviewer should be incorporated into your - patch or you should explain why the reviewer is incorrect. This process - iterates until there are no more review comments.
If the submitter believes the review comment is in error, a response to - the - llvm-commits list should be made explaining why the recommendation - cannot be followed.

+ +

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 + Chris with the following + information:

+ +

The user name you want to commit with, e.g. "hacker".
The full name and email address you want message to llvm-commits to come + from, e.g. "J. Random Hacker <hacker@yoyodyne.com>".
A "password hash" of the password you want to use, e.g. "2ACR96qjUqsyM". + Note that you don't ever tell us what your password is, you just give it + to us in an encrypted form. To get this, run "htpasswd" (a utility that + comes with apache) in crypt mode (often enabled with "-d"), or find a web + page that will do it for you.

+ +

Once you've been granted commit access, you should be able to check out an + LLVM tree with an SVN URL of "https://username@llvm.org/..." instead of the + normal anonymous URL of "http://llvm.org/...". The first time you commit + you'll have to type in your password. Note that you may get a warning from + SVN about an untrusted key, you can ignore this. To verify that your commit + access works, please do a test commit (e.g. change a comment or add a blank + line). Your first commit to a repository may require the autogenerated email + to be approved by a mailing list. This is normal, and will be done when + the mailing list owner has time.

+ +

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

+ +

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.
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.
You are allowed to commit patches without approval to those portions of + LLVM that you have contributed or maintain (i.e., have been assigned + responsibility for), with the proviso that such commits must not break the + build. This is a "trust but verify" policy and commits of this nature are + reviewed after they are committed.
Multiple violations of these policies or a single egregious violation may + cause commit access to be revoked.

+ +

In any case, your changes are still subject to code + review (either before or after they are committed, depending on the + nature of the change). You are encouraged to review other peoples' patches + as well, but you aren't required to.

After a patch has been committed, these policies apply:

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

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 llvmdev + email list, to the extent possible. The reason for this is to: + +

keep the community informed about future changes to LLVM,
avoid duplication of effort by preventing multiple parties working on the + same thing and not knowing about it, and
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 want to add a major new extension, it is a + good idea to get consensus with the development community before you start + working on it.

+ +

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.

Commit access to the repository is granted according to this policy:

Commit access is not granted to anyone unless they specifically ask for - it.
Requests for commit access must be sent to the - LLVM Oversight Group.
Granting commit access is at the sole discretion of the LLVM Oversight - Group.

Submitting patches to LLVM via the patch policy above will greatly - increase the chance that your request for commit access is granted. Getting - to know the members of the LLVM community (email, IRC, in person contact, - etc.) will also increase your chances.

- +

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:

+ +

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.
Other people in the community tend to ignore work on branches.
Huge changes (produced when a branch is merged back onto mainline) are + extremely difficult to code review.
Branches are not routinely tested by our nightly tester + infrastructure.
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.
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.

For those who have recently obtained commit access, the following policies - apply:

You are granted commit-after-approval to all parts of LLVM. - To get approval, submit a patch to - llvm-commits - per the patch policies above. When approved you may commit it - yourself.
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.
You are granted commit-without-approval to those portions of LLVM - that you own (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.
Commits that violate the quality standards may - be reverted. This is necessary when the change blocks other developers from - making progress. The developers is welcome to re-commit the change after - the problem has been fixed.
Multiple violations of these policies or a single egregious violation - may cause commit access to be revoked.

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 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 say "patch + contributed by J. Random Hacker!" in the commit message.

+ +

Overall, please do not add contributor names to the source code.

We address here the issues of copyright and license for the LLVM project. - The object of the copyright and license is the LLVM source 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. -

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 + University of + Illinois/NCSA Open Source License.

The LLVM project believes in correct attribution of contributions to - their contributors, as follows:

Developers who originate new files in LLVM should place their name at - the top of the file per the - Coding Standards.
There should be only one name at the top of the file and it should be - the person who created the file.
Placing your name in the file does not imply copyright but does - correctly attribute the file to its author.
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.
Developers should submit or commit patches to the - CREDITS.txt - file to summarize their contributions.
Commit comments should contain correct attribution of the person who s - submitted the patch if that person is not the committer (i.e. when a - developer with commit privileges commits a patch for someone else).

However, for consistency and ease of management, the project requires the - copyright for all LLVM software to be held by a single copyright holder. - Although UIUC may assign the copyright of the software to another entity, - the intent for the project is to always have a single entity hold the copy - rights to LLVM at any given time. -

Having multiple copyright holders for various portions of LLVM is - problematic in the management of the software. 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 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 licensing decisions will be made by the LLVM Oversight Group. Any - issues, comments or suggestions with the licensing should be sent to the - LLVM Oversight Group.

The LLVM Oversight Group intends to keep LLVM perpetually open source - and to use liberal open source licenses. The current license is the - University of Illinois Open Source License (see LICENSE.TXT), 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. We - suggest that you read the - License if - further clarification is needed.

With regards to the LLVM copyright and licensing, developers agree to:

assign their copy rights to UIUC for any contribution made so that - the entire software base can be managed by a single copyright holder.
allow their contribution(s) to be licensed as open source by the then - current license chosen by the LLVM Oversight Group.

We intend to keep LLVM perpetually open source and to use a liberal open + source license. All of the code in LLVM is available under 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 (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 + if further clarification is needed.

+ +

In addition to the UIUC license, the runtime library components of LLVM + (compiler_rt and libc++) are also licensed under the MIT license, + 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 llvm-gcc, which is GPL. + 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 any code linked into llvm-gcc and distributed to others may + be subject to the viral aspects of the GPL (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.

+ +

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.

This section contains some notes on policy topics that need to be - resolved and incorporated into the main body of the document above.

When to open a new bug and when to re-use an existing one. For example - PR1158. If the same assertion happens do you open a new bug or reopen - 1158?

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. 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 oversight group for more + details.

Contents