Merge day is Tuesday, 2-Sep, so this is semi-urgent. Presumably just needs an early abort if arr.mapPar isn't supported. https://tbpl.mozilla.org/php/getParsedLog.php?id=46644860&tree=Try

Looking at the other jit-tests that use mapPar, I guess we'd just want to do this? -run(range(0, 1024), function (i) { var a = []; a.length = i; }); +if (getBuildConfiguration().parallelJS) + run(range(0, 1024), function (i) { var a = []; a.length = i; });

Try says this works.

Comment on attachment 8478224 [details] [diff] [review] only run the test if ParallelJS is supported Review of attachment 8478224 [details] [diff] [review]: ----------------------------------------------------------------- wfm

OK that makes no sense was test only.

but makes me think bug 1055034 is the regressor.