Run like: for i in `seq 1 10000`; do(DYLD_FRAMEWORK_PATH=./WebKitBuild/Release ./WebKitBuild/Release/jsc --useDollarVM=1 --useFTLJIT=false --useFunctionDotArguments=true --validateExceptionChecks=true --useDollarVM=true --maxPerThreadStackUsage=1572864 --airForceBriggsAllocator=true --useRandomizingExecutableIslandAllocation=true --forcePolyProto=true --useDataIC=true --useFTLJIT=true --thresholdForJITAfterWarmUp=10 --thresholdForJITSoon=10 --thresholdForOptimizeAfterWarmUp=20 --thresholdForOptimizeAfterLongWarmUp=20 --thresholdForOptimizeSoon=20 --thresholdForFTLOptimizeAfterWarmUp=20 --thresholdForFTLOptimizeSoon=20 --thresholdForOMGOptimizeAfterWarmUp=20 --thresholdForOMGOptimizeSoon=20 --maximumEvalCacheableSourceLength=150000 --useEagerCodeBlockJettisonTiming=true --repatchBufferingCountdown=0 --collectContinuously=true --useGenerationalGC=false --verifyGC=true --verboseVerifyGC=1 JSTests/stress/has-own-property-structure-for-in-loop-correctness.js); done Fails ~once every ~50,000 runs. I've only reproduced on x86.
<rdar://problem/81628046>