It fails in ~33% of the test runs with the following log: Exception: Error: FAIL: 'x' setter was not called. cached-prototype-setter.js:18:24 global code@cached-prototype-setter.js:19:3 It seems it is a DFG JIT bug, because it passes always with the same configuration and additional useDFGJIT=false
Just to document, I skipped it on AArch64 Linux: http://trac.webkit.org/changeset/182006/trunk/Source/JavaScriptCore/tests/stress/cached-prototype-setter.js
This failure isn't exhibited anymore. I'll close the bug once the skip directive is removed.