Array indexes can overflow in some situations

[msullivan]

In some situations, array indexes that should be out of bounds may overflow to in bounds array indexes. This can happen due if the index type is wider than the platform int size and gets truncated or if the multiplication by the element size overflows.

[eholk]

What's the failure mode here? Does it just crash with an array out of bounds error? If so, that doesn't seem unreasonable to me.

[msullivan]

No, the failure mode is that it will successfully index into the array at a wrapped around index, which is almost certainly not what we want.

[catamorphism]

Seems to me like an instance of a much more general problem, so I opened #6012 and am closing this.