We have detected a build metrics regression from push: https://hg.mozilla.org/integration/autoland/pushloghtml?changeset=ef52b30f64606d6e0c2f2781b37812f8bb5ae179 As author of one of the patches included in that push, we need your help to address this regression. Regressions: 7% build times summary linux64 asan asan-fuzzing taskcluster-c4.4xlarge 1,198.96 -> 1,286.27 You can find links to graphs and comparison views for each of the above tests at: https://treeherder.mozilla.org/perf.html#/alerts?id=7652 On the page above you can see an alert for each affected platform as well as a link to a graph showing the history of scores for this test. There is also a link to a treeherder page showing the jobs in a pushlog format. To learn more about the regressing test(s), please see: https://developer.mozilla.org/en-US/docs/Mozilla/Performance/Automated_Performance_Testing_and_Sheriffing/Build_Metrics

:rforbes Could you take a look over this build time regression and estimate a fix time for it?

:rforbes is on PTO. In bug 1376978, we switched the compiler from Clang 3.9 to Clang 4.0. It is well possible that this increases the build time, though I don't see what we could do about that. The changeset does nothing else besides the compiler switch.

There's not much we can do here except profile compiler invocations and report performance regressions upstream. Sometimes compilers get faster. Sometimes they get slower. Often when they get slower it is for a good reason. FWIW, bug 1376968 decreased the compile time substantially, offsetting this loss.

Thanks for the feedback. This is reasonable to accept, so I'm marking it as WONTFIX.