function write() {
  let m = /ab(c)?d/.exec("abd")
  return m
}
noInline(write)

let all = []
for(let i=0;i<300;i++){
  all.push(write())
}

let a = all[50]
let b = all[100]
print(Object.keys(a),a.length, describe(a))
print(Object.keys(b),b.length, describe(b))

With the above script as input to JSC, run JSC with the following parameters:
./jsc test.js --useConcurrentJIT=0

Variable a is the result for interpreter while b is the result for JIT. a.length == b.length, but Object.keys(a) != Object.keys(b).
There is a hole in b. This may be caused by strength reduction in DFG JIT.