LLVM Developer Policy

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:

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

- -

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 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 miscommunication, 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:

+ +

Attract both users and developers to the LLVM project.
Make life as simple and easy for contributors as possible.
Keep the top of Subversion trees as stable as possible.

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.

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 this command: +
+
```
+svn diff
+
```
+
+ or with the utility utils/mkpatch, which makes it easy to read + the diff.
Patches should not include differences in generated code such as the code + generated by autoconf or tblgen. The + utils/mkpatch utility takes care of this for you.

+ +

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 one way to increase the - quality of software. We generally follow these policies:

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.
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:

+ +

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 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.
Doug Gregor: Clang Basic, Lex, Parse, and Sema Libraries.
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 any bugs fixed and any new - features added. 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 llvm-gcc C++ - front-end).
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.
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:

+ +

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 is 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.

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 dejagnu (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 is "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 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.

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 dejagnu (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'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 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.

-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.

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 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 (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.
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.

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 technical issues around the proposed work are - discussed and resolved before any significant work is done.

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 - a major new extension, it is a good idea to get consensus with the development - community before you start working on it.

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.

Incremental Development +

Incremental Development

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. 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.
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.

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:

- -

Attribution of -Changes

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:

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: it is only used to attribute the file to - its original 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. Revision control keeps an accurate history of contributions.
Developers should maintain their entry in the - CREDITS.txt - file to summarize their contributions.
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).

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.

Patch Policies

Huge changes (produced when a branch is merged back onto mainline) are + extremely difficult to code review.

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.

Branches are not routinely tested by our nightly tester + infrastructure.

Patch Form

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.
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.

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:

- -

Patch Submission

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.

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.

After Submission

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. -
Changes to the patch must be re-submitted to the - llvm-commits - email list.
This process iterates until all review issues have been addressed.

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 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).

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.

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

+ +

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 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 (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.

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.

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 Oversight Group.

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.