GCC Development Plan

(Suggestions for changes to this plan are discussed on the GCC mailing list and approved or rejected by the GCC Steering Committee.)

Objectives

The goals of this policy are:

Higher-quality releases Support for more targets Continued encouragement of major infrastructure improvements More predictable release schedules More frequent releases

Rationale

Late in the GCC 2.x series and then GCC 3.x we struggled making consistent, high-quality releases for as wide a variety of targets as we would have liked. GCC 3.0 came late relative to original scheduling estimates and the time between the GCC 2.95 and GCC 3.0 releases was longer than everyone would have liked.

We think that more frequent releases on a consistent schedule serve our user communities better. In addition, a consistent schedule makes it possible for Release Managers to better understand what they are signing up for.

Development Methodology

Branches

The development of major changes shall be done on a branch. (Under some circumstances, development may be done in a private development tree, but the Steering Committee strongly encourages the use of a branch in the publicly accessible GCC development tree.)

Examples of major changes include:

A new C++ parser

A new memory allocation scheme for internal use in the compiler

A new optimization pass

There is no firm guideline for what constitutes a "major change" and what does not. If a developer is unsure, he or she should ask for guidance on the GCC mailing lists. In general, a change that has the potential to be extremely destabilizing should be done on a branch.

Changes may be merged from a development branch only after:

They meet the standards for any other check-in. For example, the code must be well-documented, and any user-visible changes, including command-line options, should be documented in the manual.

The branch has been validated on three different targets, each targeting a different microprocessor family. Validation should consist of bootstrapping the compiler (unless that is impossible for the microprocessor selected) and checking that there are no new regression test failures. It is acceptable to use a simulator for validation; the use of real hardware is not required.

Rationale

Making major improvements to the compiler is good. However, such changes are inevitably somewhat destabilizing. By using a branch, it is possible for people to test and improve the code, but without impacting other developers. By testing major changes more thoroughly than ordinary changes, we will help reduce the impact on other developers.

In addition, the presence of half-finished projects on the mainline presents a variety of problems when preparing for a release. If serious bugs remain, it may be impossible to do a release until the bugs are fixed, thereby impacting the release schedule. If functionality is present, but not robust (for example, command-line options that activate an optimization pass that does not work very well), then we can seriously confuse users.

Schedule

Development on our main branch will proceed in three stages.

Stage 1

During this period, changes of any nature may be made to the compiler. In particular, major changes may be merged from branches. Stage 1 is feature driven and will last at least four months. In order to avoid chaos, the Release Managers will ask for a list of major projects proposed for the coming release cycle before the start of this stage. They will attempt to sequence the projects in such a way as to cause minimal disruption. The Release Managers will not reject projects that will be ready for inclusion before the end of Stage 1. Similarly, the Release Managers have no special power to accept a particular patch or branch beyond what their status as maintainers affords. The role of the Release Managers is merely to attempt to order the inclusion of major features in an organized manner.

Stage 2

Stage 2 has been abandoned in favor of an extended feature driven Stage 1 since the development of GCC 4.4.

Stage 3

During this two-month period, the only (non-documentation) changes that may be made are changes that fix bugs or new ports which do not require changes to other parts of the compiler. New functionality may not be introduced during this period.

Stage 4

During this period, the only (non-documentation) changes that may be made are changes that fix regressions. Other important bugs like wrong-code, rejects-valid or build issues may be fixed as well. All changes during this period should be done with extra care on not introducing new regressions - fixing bugs at all cost is not wanted. Note that the same constraints apply to release branches. This period lasts until stage 1 opens for the next release.

Rationale

In order to produce releases on a regular schedule, we must ensure that the mainline is reasonably stable some time before we make the release. Therefore, more radical changes must be made earlier in the cycle, so that we have time to fix any problems that result.

In order to reach higher standards of quality, we must focus on fixing bugs; by working exclusively on bug-fixing through this stage and before branching for the release, we will have a higher quality source base as we prepare for a release.

Although maintaining a development branch, including merging new changes from the mainline, is somewhat burdensome, the absolute worst case is that such a branch will have to be maintained for a few months. During this period, the only mainline changes will be bug-fixes, so it is unlikely that many conflicts will occur.

Patch Reversion

If a patch is committed which introduces a regression on any target which the Steering Committee considers to be important and if:

the problem is reported to the original poster;

48 hours pass without the original poster or any other party indicating that a fix will be forthcoming in the very near future;

two people with write privileges to the affected area of the compiler determine that the best course of action is to revert the patch;

then they may revert the patch.

(The list of important targets will be revised at the beginning of each release cycle, if necessary, and is part of the release criteria.)

After the patch has been reverted, the poster may appeal the decision to the Steering Committee.

Note that no distinction is made between patches which are themselves buggy and patches that expose latent bugs elsewhere in the compiler.

Rationale

If an important platform is broken, then it will be difficult to prepare a release. If nobody volunteers to fix the problem, then we will have an unpleasant choice: delay the release, or release a compiler that we know to be worse than the previous release. Therefore, it is important that we be able to revert patches that cause problems. In addition, regressions on the mainline can impede the development of other improvements.

On the other hand, we want to encourage new development, and new development inevitably introduces new bugs. Therefore, it is important that decisions be made on a case-by-case basis, and that the proponent of a change have an opportunity to argue that the benefits of the change outweigh the costs. Therefore, the decision to revert requires two consenting parties, and such decisions may be appealed to the Steering Committee. However, during the appeal, the mainline will remain working, to avoid impeding other development.

Release Methodology

Schedule

At the conclusion of Stage 3, the trunk will go into release branch mode which allows documentation and regression fixes only. During this phase, the focus will be fixing any regressions from the previous release, so that each release is better than the one before.

At the point the trunk is in a state suitable for releasing a release branch will be created, a release candidate is made available and Stage 1 of the next release cycle starts. The decision on when this point is reached is up to the Release Managers. In particular at this point no P1 regressions are present on the trunk.

Rationale

While making releases on schedule is important, quality should not be subordinate to schedule. If a major platform is not adequately supported, but was well supported in a previous release, then we should address the problems. Presumably, this will not be unduly difficult, since we will have spent at least two months fixing bugs by the time the release would occur.

Bug-fix Releases

Bug-fix releases will be made two and four months after the initial release, as necessary.

Rationale

By waiting for two months to make a bug-fix release, we will be able to accumulate fixes for the most important problems, and avoid spending undue amounts of time on release testing and packaging.

Changes Appropriate for Bug-Fix Releases

As a general rule of thumb, bug-fix releases should contain fixes for regressions or serious bugs uncovered in the corresponding major release of GCC or those prior to it. When backporting patches from subsequent releases or from trunk, care should be taken to avoid making changes that cause previously accepted code to be rejected unless doing so would cause GCC to generate incorrect object code or code with undefined behavior.

Rationale

Users have an expectation of upgrading to a bug-fix GCC release without having to adjust their source code. Avoiding changes that reject code that was previously accepted makes this possible.

Version Numbering Scheme for GCC 5 and Up

Starting with GCC 5 we will bump the major version number for each release. The version number and DEV-PHASE will develop in the following way and on the following timeline:

Version DEV-PHASE When 5.0.0 (experimental) during active development of GCC 5 (stage 1 to 3) 5.0.1 (prerelease) during the stabilization period of GCC 5 6.0.0 (experimental) during active development of GCC 6 (stage 1 to 3) 5.1.0 for the first release from the GCC 5 branch 5.1.1 during development on the branch post the 5.1.0 release 5.2.0 for the second release from the GCC 5 branch 5.2.1 during development on the branch post the 5.2.0 release 6.0.1 (prerelease) during the stabilization period of GCC 6 ...

To summarize, the first release of GCC 5 will be GCC 5.1.0 while development snapshots will be GCC 5.0.0 and snapshots from the release branch GCC 5.n.1.

Rationale

This change allows to more easily identify GCC versions by giving each of the development phases distinctive versions. The change also takes advantage of the fact that previously the GCC major number carried little to no useful information.

Release Timeline

Here is a history of recent and a tentative timeline of upcoming stages of development, branch points, and releases:

... former releases ... | +-- GCC 3.0 branch created ------+ | (Feb 12 2001) \ | v v GCC 3.0 release (Jun 18 2001) New development plan announced \ | (Jul 18 2001) v | GCC 3.0.1 release (Aug 20 2001) | \ v v GCC 3.1 Stage 1 (ended Oct 15 2001) GCC 3.0.2 release (Oct 25 2001) | \ v v GCC 3.1 Stage 2 (ended Dec 19 2001) GCC 3.0.3 release (Dec 20 2001) | \ v v GCC 3.1 Stage 3 (ended Feb 26 2002) GCC 3.0.4 release (Feb 20 2002) | +-- GCC 3.1 branch created ------+ | \ | v v GCC 3.1 release (May 15 2002) GCC 3.2 Stage 1 (ended Jun 22 2002) \ | v | GCC 3.1.1 release (Jul 25 2002) | \ v v New development plan announced Branch renamed to GCC 3.2 to | (Jul 14 2002) accommodate for C++ ABI fixes | (C++ binary incompatible with | GCC 3.1, see release info) | \ | v | GCC 3.2 release (Aug 14 2002) | \ | v | GCC 3.2.1 release (Nov 19 2002) | \ | v | GCC 3.2.2 release (Feb 05 2003) | \ | v | GCC 3.2.3 release (April 22 2003) v GCC 3.3 Stage 2 (ends Aug 15 2002) | v GCC 3.3 Stage 3 (ends Oct 15 2002) | +-- GCC 3.3 branch created ------+ | (Dec 14 2002) \ | v | GCC 3.3 release (May 13 2003) | \ v v GCC 3.4 Stage 1 (ends July 4 2003) GCC 3.3.1 release (Aug 8 2003) | \ v v GCC 3.4 Stage 2 (ends October 15 2003) GCC 3.3.2 release (Oct 17 2003) | \ v v GCC 3.4 Stage 3 GCC 3.3.3 release (Feb 14 2004) | \ | v | GCC 3.3.4 release (May 31 2004) | \ | v | GCC 3.3.5 release (Sep 30 2004) | \ | v | GCC 3.3.6 release (May 03 2005) | +-- GCC 3.4 branch created ------+ | (Jan 16 2004) \ | v Tree SSA infrastructure GCC 3.4.0 release (Apr 18 2004) merged to mainline (May 17 2004) \ | v v GCC 3.4.1 release (Jul 1 2004) GCC 4.0 Stage 2 \ | v v GCC 3.4.2 release (Sep 6 2004) GCC 4.0 Stage 3 \ | v | GCC 3.4.3 release (Nov 4 2004) | \ | v | GCC 3.4.4 release (May 18 2005) | \ | v | GCC 3.4.5 release (Nov 30 2005) | \ | v | GCC 3.4.6 release (Mar 06 2006) | +-- GCC 4.0 branch created ------+ | (Feb 25 2005) \ v v GCC 4.1 Stage 1 (ends April 25 2005) GCC 4.0.0 release (Apr 20 2005) | \ v v GCC 4.1 Stage 2 (ends July 8 2005) GCC 4.0.1 release (Jul 7 2005) | \ v v GCC 4.1 Stage 3 GCC 4.0.2 release (Sep 28 2005) | \ | v | GCC 4.0.3 release (Mar 10 2006) | \ | v | GCC 4.0.4 release (Jan 31 2007) | +-- GCC 4.1 branch created ------+ | (Nov 18 2005) \ v v GCC 4.2 Stage 1 (ends Jan 18 2006) GCC 4.1.0 release (Feb 28 2006) | \ v v GCC 4.2 Stage 2 (ends Mar 18 2006) GCC 4.1.1 release (May 24 2006) | \ v v GCC 4.2 Stage 3 GCC 4.1.2 release (Feb 13 2007) | | +-- GCC 4.2 branch created ------+ | \ v v GCC 4.3 Stage 1 (starts 2006-10-20) GCC 4.2.0 release (2007-05-13) | \ v v GCC 4.3 Stage 2 (starts 2007-01-20) GCC 4.2.1 release (2007-07-18) | \ v v GCC 4.3 Stage 3 (starts 2007-09-12) GCC 4.2.2 release (2007-10-07) | \ | v | GCC 4.2.3 release (2008-02-01) | \ | v | GCC 4.2.4 release (2008-05-19) | | +-- GCC 4.3 branch created ------+ | \ v v GCC 4.4 Stage 1 (starts 2008-02-18) GCC 4.3.0 release (2008-03-05) | \ | v | GCC 4.3.1 release (2008-06-06) | \ | v v GCC 4.3.2 release (2008-08-27) GCC 4.4 Stage 3 (starts 2008-09-01) \ | v | GCC 4.3.3 release (2009-01-24) | \ | v | GCC 4.3.4 release (2009-08-04) | \ | v | GCC 4.3.5 release (2010-05-22) | \ | v | GCC 4.3.6 release (2011-06-27) | +-- GCC 4.4 branch created ------+ | \ v v GCC 4.5 Stage 1 (starts 2009-03-27) GCC 4.4.0 release (2009-04-21) | \ | v | GCC 4.4.1 release (2009-07-22) GCC 4.5 Stage 3 (starts 2009-10-01) \ | v | GCC 4.4.2 release (2009-10-15) | \ | v | GCC 4.4.3 release (2010-01-21) | \ | v | GCC 4.4.4 release (2010-04-29) | \ | v | GCC 4.4.5 release (2010-10-01) | \ | v | GCC 4.4.6 release (2011-04-16) | \ | v | GCC 4.4.7 release (2012-03-13) | +-- GCC 4.5 branch created ------+ | \ v v GCC 4.6 Stage 1 (starts 2010-04-06) GCC 4.5.0 release (2010-04-14) | \ | v | GCC 4.5.1 release (2010-07-31) GCC 4.6 Stage 3 (starts 2010-11-03) \ | v | GCC 4.5.2 release (2010-12-16) | \ | v | GCC 4.5.3 release (2011-04-28) | \ | v | GCC 4.5.4 release (2012-07-02) | +-- GCC 4.6 branch created ------+ | \ v v GCC 4.7 Stage 1 (starts 2011-03-14) GCC 4.6.0 release (2011-03-25) | \ | v | GCC 4.6.1 release (2011-06-27) | \ | v | GCC 4.6.2 release (2011-10-26) GCC 4.7 Stage 3 (starts 2011-11-08) \ | v | GCC 4.6.3 release (2012-03-01) | \ | v | GCC 4.6.4 release (2013-04-12) | +-- GCC 4.7 branch created ------+ | \ v v GCC 4.8 Stage 1 (starts 2012-03-02) GCC 4.7.0 release (2012-03-22) | \ | v | GCC 4.7.1 release (2012-06-14) | \ | v | GCC 4.7.2 release (2012-09-20) GCC 4.8 Stage 3 (starts 2012-11-06) \ | v | GCC 4.7.3 release (2013-04-11) | \ | v | GCC 4.7.4 release (2014-06-12) | +-- GCC 4.8 branch created ------+ | \ v v GCC 4.9 Stage 1 (starts 2013-03-16) GCC 4.8.0 release (2013-03-22) | \ | v | GCC 4.8.1 release (2013-05-31) | \ | v | GCC 4.8.2 release (2013-10-16) | \ GCC 4.9 Stage 3 (starts 2013-11-22) v | GCC 4.8.3 release (2014-05-22) | \ | v | GCC 4.8.4 release (2014-12-19) | \ | v | GCC 4.8.5 release (2015-06-23) +-- GCC 4.9 branch created ------+ | \ v v GCC 4.10 Stage 1 (starts 2014-04-11) GCC 4.9.0 release (2014-04-22) | \ | v | GCC 4.9.1 release (2014-07-16) New GCC versioning scheme announced \ | (2014-08-13) v | GCC 4.9.2 release (2014-10-30) | \ GCC 5 Stage 1 v | GCC 4.9.3 release (2015-06-26) GCC 5 Stage 3 (starts 2014-11-16) \ | v GCC 5 Stage 4 (starts 2015-01-17) GCC 4.9.4 release (2016-08-03) | +-- GCC 5 branch created --------+ | \ v v GCC 6 Stage 1 (starts 2015-04-12) GCC 5.1 release (2015-04-22) | \ | v | GCC 5.2 release (2015-07-16) GCC 6 Stage 3 (starts 2015-11-15) \ | v GCC 6 Stage 4 (starts 2016-01-20) GCC 5.3 release (2015-12-04) | \ | v | GCC 5.4 release (2016-06-03) | \ | v | GCC 5.5 release (2017-10-10) +-- GCC 6 branch created --------+ | \ v v GCC 7 Stage 1 (starts 2016-04-15) GCC 6.1 release (2016-04-27) | \ | v | GCC 6.2 release (2016-08-22) GCC 7 Stage 3 (starts 2016-11-14) \ | v | GCC 6.3 release (2016-12-21) GCC 7 Stage 4 (starts 2017-01-20) \ | v | GCC 6.4 release (2017-07-04) | \ | v | GCC 6.5 release (2018-10-26) +-- GCC 7 branch created --------+ | \ | v GCC 8 Stage 1 (starts 2017-04-20) GCC 7.1 release (2017-05-02) | \ | v | GCC 7.2 release (2017-08-14) GCC 8 Stage 3 (starts 2017-11-18) \ | v GCC 8 Stage 4 (starts 2018-01-15) GCC 7.3 release (2018-01-25) | \ | v | GCC 7.4 release (2018-12-06) | \ | v | GCC 7.5 release (2019-11-14) +-- GCC 8 branch created --------+ | \ | v GCC 9 Stage 1 (starts 2018-04-25) GCC 8.1 release (2018-05-02) | \ | v | GCC 8.2 release (2018-07-26) GCC 9 Stage 3 (starts 2018-11-12) \ | v GCC 9 Stage 4 (starts 2019-01-07) GCC 8.3 release (2019-02-22) | \ | v | GCC 8.4 release (2020-03-04) | +-- GCC 9 branch created --------+ | \ | v GCC 10 Stage 1 (starts 2019-04-25) GCC 9.1 release (2019-05-03) | \ | v | GCC 9.2 release (2019-08-12) GCC 10 Stage 3 (starts 2019-11-17) \ | v GCC 10 Stage 4 (starts 2020-01-13) GCC 9.3 release (2020-03-12) | | +-- GCC 10 branch created -------+ | \ | v GCC 11 Stage 1 (starts 2020-04-30) GCC 10.1 release (2020-05-07) | \ | v | GCC 10.2 release (2020-06-23) v