function f0(a1) { try{ Error.stackTraceLimit = a1; // put_by_id throw Error() } catch(e) { return e.stack; } } for (let v14 = 0; v14 < 2; v14++) { print(f0(v14)); } With the above script as input to JSC, run JSC with the following parameters: ./jsc test.js --useConcurrentJIT=0 JSC print two "undefined". The corrent result should be an "undefined" and a stackTrace. The problem may be in LLInt. The number of loops is 2. Therefore, LLInt will execute `put_by_id` twice, the first execution is slow_path, and `stackTraceLimit` in `globalObject` will be updated, but the slow_path is not used for the second time, and `stackTraceLimit` in `globalObject` is not updated. `getStackTrace` in Error.cpp will use `stackTraceLimit`, but stackTraceLimit is always 0, so two "undefined" are printed. Safari console also prints wrong result, V8 prints correct result.
<rdar://problem/108444270>