Bug 1492663 upgraded those builds to clang 7, and bug 1503330 brought them back to clang 6 because of speedometer regressions. Bisecting llvm trunk between clang 6 and 7 identified the regression as caused by https://github.com/llvm-mirror/llvm/commit/031332e78887f4658e2d7a2f7541827c2ca9baf5 . I filed this as https://bugs.llvm.org/show_bug.cgi?id=39717 but it's entirely possible it won't be changed. However, we can disable the outliner manually on clang 7, allowing to upgrade again. No amount of squinting makes me see an actual regression on arm, only aarch64, so we'll upgrade both.

It's enabled by default as of clang 7 with -Oz on aarch64 (that is, afaict, the only platform where it's enabled), and regresses our performance on speedometer.

Bug 1492663 upgraded those builds to clang 7, and bug 1503330 brought them back to clang 6 because of speedometer regressions. With the previous change, the regression doesn't happen any more, allowing to upgrade again. Depends on D12394

Pushed by mh@glandium.org: https://hg.mozilla.org/integration/autoland/rev/6f3303d415f7 Disable the machine outliner on Android. r=dmajor https://hg.mozilla.org/integration/autoland/rev/8540104bb0bd Switch Android builds to clang 7 again. r=dmajor

https://hg.mozilla.org/mozilla-central/rev/6f3303d415f7 https://hg.mozilla.org/mozilla-central/rev/8540104bb0bd