How To Release LLVM To The Public

Introduction

This document contains information about successfully releasing LLVM — including sub-projects: e.g., clang and compiler-rt — to the public. It is the Release Manager’s responsibility to ensure that a high quality build of LLVM is released.

If you’re looking for the document on how to test the release candidates and create the binary packages, please refer to the How To Validate a New Release instead.

Release Timeline

LLVM is released on a time based schedule — with major releases roughly every 6 months. In between major releases there may be dot releases. The release manager will determine if and when to make a dot release based on feedback from the community. Typically, dot releases should be made if there are large number of bug-fixes in the stable branch or a critical bug has been discovered that affects a large number of users.

Unless otherwise stated, dot releases will follow the same procedure as major releases.

The release process is roughly as follows:

  • Set code freeze and branch creation date for 6 months after last code freeze date. Announce release schedule to the LLVM community and update the website.

  • Create release branch and begin release process.

  • Send out release candidate sources for first round of testing. Testing lasts 7-10 days. During the first round of testing, any regressions found should be fixed. Patches are merged from mainline into the release branch. Also, all features need to be completed during this time. Any features not completed at the end of the first round of testing will be removed or disabled for the release.

  • Generate and send out the second release candidate sources. Only critical bugs found during this testing phase will be fixed. Any bugs introduced by merged patches will be fixed. If so a third round of testing is needed.

  • The release notes are updated.

  • Finally, release!

The release process will be accelerated for dot releases. If the first round of testing finds no critical bugs and no regressions since the last major release, then additional rounds of testing will not be required.

Release Process

Release Administrative Tasks

This section describes a few administrative tasks that need to be done for the release process to begin. Specifically, it involves:

  • Creating the release branch,

  • Setting version numbers, and

  • Tagging release candidates for the release team to begin testing.

Create Release Branch

Branch the Subversion trunk using the following procedure:

  1. Remind developers that the release branching is imminent and to refrain from committing patches that might break the build. E.g., new features, large patches for works in progress, an overhaul of the type system, an exciting new TableGen feature, etc.

  2. Verify that the current Subversion trunk is in decent shape by examining nightly tester and buildbot results.

  3. Create the release branch for llvm, clang, and other sub-projects, from the last known good revision. The branch’s name is release_XY, where X is the major and Y the minor release numbers. Use utils/release/tag.sh to tag the release.

  4. Advise developers that they may now check their patches into the Subversion tree again.

  5. The Release Manager should switch to the release branch, because all changes to the release will now be done in the branch. The easiest way to do this is to grab a working copy using the following commands:

    $ svn co https://llvm.org/svn/llvm-project/llvm/branches/release_XY llvm-X.Y

$ svn co https://llvm.org/svn/llvm-project/cfe/branches/release_XY clang-X.Y

$ svn co https://llvm.org/svn/llvm-project/test-suite/branches/release_XY test-suite-X.Y

Update LLVM Version

After creating the LLVM release branch, update the release branches’ CMakeLists.txt versions from ‘X.Ysvn’ to ‘X.Y’. Update it on mainline as well to be the next version (‘X.Y+1svn’).

In addition, the version numbers of all the Bugzilla components must be updated for the next release.

Tagging the LLVM Release Candidates

Tag release candidates using the tag.sh script in utils/release.

$ ./tag.sh -release X.Y.Z -rc $RC

The Release Manager may supply pre-packaged source tarballs for users. This can be done with the export.sh script in utils/release.

$ ./export.sh -release X.Y.Z -rc $RC

This will generate source tarballs for each LLVM project being validated, which can be uploaded to the website for further testing.

Build Clang Binary Distribution

Creating the clang binary distribution requires following the instructions here.

That process will perform both Release+Asserts and Release builds but only pack the Release build for upload. You should use the Release+Asserts sysroot, normally under final/Phase3/Release+Asserts/llvmCore-3.8.1-RCn.install/, for test-suite and run-time benchmarks, to make sure nothing serious has passed through the net. For compile-time benchmarks, use the Release version.

The minimum required version of the tools you’ll need are here

Release Qualification Criteria

A release is qualified when it has no regressions from the previous release (or baseline). Regressions are related to correctness first and performance second. (We may tolerate some minor performance regressions if they are deemed necessary for the general quality of the compiler.)

More specifically, Clang/LLVM is qualified when it has a clean test with all supported sub-projects included (make check-all), per target, and it has no regressions with the test-suite in relation to the previous release.

Regressions are new failures in the set of tests that are used to qualify each product and only include things on the list. Every release will have some bugs in it. It is the reality of developing a complex piece of software. We need a very concrete and definitive release criteria that ensures we have monotonically improving quality on some metric. The metric we use is described below. This doesn’t mean that we don’t care about other criteria, but these are the criteria which we found to be most important and which must be satisfied before a release can go out.

Official Testing

A few developers in the community have dedicated time to validate the release candidates and volunteered to be the official release testers for each architecture.

These will be the ones testing, generating and uploading the official binaries to the server, and will be the minimum tests necessary for the release to proceed.

This will obviously not cover all OSs and distributions, so additional community validation is important. However, if community input is not reached before the release is out, all bugs reported will have to go on the next stable release.

The official release managers are:

  • Major releases (X.0): Hans Wennborg

  • Stable releases (X.n): Tom Stellard

The official release testers are volunteered from the community and have consistently validated and released binaries for their targets/OSs. To contact them, you should email the release-testers@lists.llvm.org mailing list.

The official testers list is in the file RELEASE_TESTERS.TXT, in the LLVM repository.

Community Testing

Once all testing has been completed and appropriate bugs filed, the release candidate tarballs are put on the website and the LLVM community is notified.

We ask that all LLVM developers test the release in any the following ways:

  1. Download llvm-X.Y, llvm-test-X.Y, and the appropriate clang binary. Build LLVM. Run make check and the full LLVM test suite (make TEST=nightly report).

  2. Download llvm-X.Y, llvm-test-X.Y, and the clang sources. Compile everything. Run make check and the full LLVM test suite (make TEST=nightly report).

  3. Download llvm-X.Y, llvm-test-X.Y, and the appropriate clang binary. Build whole programs with it (ex. Chromium, Firefox, Apache) for your platform.

  4. Download llvm-X.Y, llvm-test-X.Y, and the appropriate clang binary. Build your programs with it and check for conformance and performance regressions.

  5. Run the release process, if your platform is different than that which is officially supported, and report back errors only if they were not reported by the official release tester for that architecture.

We also ask that the OS distribution release managers test their packages with the first candidate of every release, and report any new errors in Bugzilla. If the bug can be reproduced with an unpatched upstream version of the release candidate (as opposed to the distribution’s own build), the priority should be release blocker.

During the first round of testing, all regressions must be fixed before the second release candidate is tagged.

In the subsequent stages, the testing is only to ensure that bug fixes previously merged in have not created new major problems. This is not the time to solve additional and unrelated bugs! If no patches are merged in, the release is determined to be ready and the release manager may move onto the next stage.

Reporting Regressions

Every regression that is found during the tests (as per the criteria above), should be filled in a bug in Bugzilla with the priority release blocker and blocking a specific release.

To help manage all the bugs reported and which ones are blockers or not, a new “[meta]” bug should be created and all regressions blocking that Meta. Once all blockers are done, the Meta can be closed.

If a bug can’t be reproduced, or stops being a blocker, it should be removed from the Meta and its priority decreased to normal. Debugging can continue, but on trunk.

Merge Requests

You can use any of the following methods to request that a revision from trunk be merged into a release branch:

  1. Use the utils/release/merge-request.sh script which will automatically file a bug requesting that the patch be merged. e.g. To request revision 12345 be merged into the branch for the 5.0.1 release: llvm.src/utils/release/merge-request.sh -stable-version 5.0 -r 12345 -user bugzilla@example.com

  2. Manually file a bug with the subject: “Merge r12345 into the X.Y branch”, enter the commit(s) that you want merged in the “Fixed by Commit(s)” and mark it as a blocker of the current release bug. Release bugs are given aliases in the form of release-x.y.z, so to mark a bug as a blocker for the 5.0.1 release, just enter release-5.0.1 in the “Blocks” field.

  3. Reply to the commit email on llvm-commits for the revision to merge and cc the release manager.

Release Patch Rules

Below are the rules regarding patching the release branch:

  1. Patches applied to the release branch may only be applied by the release manager, the official release testers or the code owners with approval from the release manager.

  2. During the first round of testing, patches that fix regressions or that are small and relatively risk free (verified by the appropriate code owner) are applied to the branch. Code owners are asked to be very conservative in approving patches for the branch. We reserve the right to reject any patch that does not fix a regression as previously defined.

  3. During the remaining rounds of testing, only patches that fix critical regressions may be applied.

  4. For dot releases all patches must maintain both API and ABI compatibility with the previous major release. Only bug-fixes will be accepted.

Merging Patches

The utils/release/merge.sh script can be used to merge individual revisions into any one of the llvm projects. To merge revision $N into project $PROJ, do:

  1. svn co https://llvm.org/svn/llvm-project/$PROJ/branches/release_XX $PROJ.src

  2. $PROJ.src/utils/release/merge.sh --proj $PROJ --rev $N

  3. Run regression tests.

  4. cd $PROJ.src. Run the svn commit command printed out by merge.sh in step 2.

Release Final Tasks

The final stages of the release process involves tagging the “final” release branch, updating documentation that refers to the release, and updating the demo page.

Update Documentation

Review the documentation and ensure that it is up to date. The “Release Notes” must be updated to reflect new features, bug fixes, new known issues, and changes in the list of supported platforms. The “Getting Started Guide” should be updated to reflect the new release version number tag available from Subversion and changes in basic system requirements. Merge both changes from mainline into the release branch.

Tag the LLVM Final Release

Tag the final release sources using the tag.sh script in utils/release.

$ ./tag.sh -release X.Y.Z -final

Update the LLVM Demo Page

The LLVM demo page must be updated to use the new release. This consists of using the new clang binary and building LLVM.

Update the LLVM Website

The website must be updated before the release announcement is sent out. Here is what to do:

  1. Check out the www module from Subversion.

  2. Create a new sub-directory X.Y in the releases directory.

  3. Commit the llvm, test-suite, clang source and binaries in this new directory.

  4. Copy and commit the llvm/docs and LICENSE.txt files into this new directory. The docs should be built with BUILD_FOR_WEBSITE=1.

  5. Commit the index.html to the release/X.Y directory to redirect (use from previous release).

  6. Update the releases/download.html file with the new release.

  7. Update the releases/index.html with the new release and link to release documentation.

  8. Finally, update the main page (index.html and sidebar) to point to the new release and release announcement. Make sure this all gets committed back into Subversion.

Announce the Release

Send an email to the list announcing the release, pointing people to all the relevant documentation, download pages and bugs fixed.