[cfe-dev] llvmlab (phased buildmaster) is in production mode!

[Michael Gottesman]

Hello LLVM Dev and Clang Dev!

David Dean and I just finished bringing up a new build master on lab.llvm.org, llvmlab, which is located at the url http://lab.llvm.org:8013 and is in #llvm under the username llvmlab.

llvmlab is different than the current buildbot based continuous integration systems llvm uses; llvmlab is a phased builder based system. The high level details of the phased builder system are as follows:

1. Builders are grouped together into phases as sub builders. Each phase is a builder itself and triggers said grouped ``sub builders'' and assuming that all of the sub builders complete, triggers its successor phased builder if one exists. This creates a gating like effect.

2. All phases are gated together in a linear fashion, yielding via the linearity the phenomena that if an earlier phase does not succeed, then no later phases run. The key idea here is if we know that there is a fundamental issue with the compiler why try to build 20 compilers, when performing one quick build is all that is needed to ascertain such a fact? Also if we can not build a compiler successfully, why try to do LNT performance runs? This gets rid of pointless work, stops excessive emails from being sent out for 1 bad commit, and reduces cycle time especially if certain builds take significantly longer than others to fail.

3. Later phases do broader, longer lasting testing than earlier phases. Thus the 4 phases we currently have are:
	
	a. Phase 1 (sanity):          Phase 1 is a quick non-bootstrapped, non-lto compiler build, to check the ``basic sanity'' of the code base and build process. This generally takes 15-20 minutes to complete.
	b. Phase 2 (living on):      Phase 2 builds bootstrapped compilers for the different configurations that can be used for ``living on'', i.e. good enough for common compilation tasks. This is meant to cycle in up to an hour.
	c. Phase 3 (tree health):  Phase 3 runs performance tests, i.e., LNT (which are not live yet) as well as other compiler builds which take a longer amount of time (a full clang build with LTO enabled for instance).
	d. Phase 4 (validation):   Phase 4 runs longer running validation tests. Currently we have nothing in phase 4, but I am sure that will change = p.

4. Builders in later phases rely on outputs from earlier phases. If we are doing performance runs, why should we compile a new compiler for such a performance run? This is duplicated work! Instead the phased build system stores ``artifacts'', i.e., built compilers, in earlier phases and uses them as compilers for builds in later phases. Thus we could have 30 different Phase 3 LNT performance runs with different configurations all using the same compiler artifacts built in phase 2. This significantly deduplicates work yielding a decreased cycle time.

As time moves on we will be moving more and more builders to llvmlab including LNT performance builders and a builder which runs the libcxx test suite.

Michael

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