When divisions operations are given as argument of explicitly truncated floor/ceil/round math function, then we only care about checking the remainder of the division, and no longer the infinity case. Math.floor(Inf) | 0 == Math.floor(0) | 0 This case also happens for MNop1 which is introduced in Bug 1000605 (attachment 8418084 [details] [diff] [review]), where we can remove the infinity check if the math function is directly truncated.