In SS-1.0's 3d-raytrace, Scene.prototype.intersect() begins with the following loop: > var closest = null; > for (i = 0; i < this.triangles.length; i++) { > var triangle = this.triangles[i]; > var d = triangle.intersect(origin, dir, near, far); > if (d == null || d > far || d < near) > continue; > far = d; > closest = triangle; > } The comparisons are currently emitted as, respectively: LIsNullOrUndefined, LCompareV, and LCompareV. At the first LCompareV, the TypeSets contain the following: > lhs: Double, Int32, Null > rhs: Double, Int32, Null, Undefined However, it is impossible for |d|, |far|, or |near| to ever be Null at those locations. This prevents us from lowering the MCompare as LCompareD, which would be significantly faster.

Bug 824257 added some stuff for eliminating type barriers when they are only filtering out an impossible null/undefined value. I don't know how much of that logic can be reused here but the problems are similar.