There is also the possibility of performing pointer arithmetic with two pointers, one just before the 2GB boundary and one just after it. Thus mixing IV and UV math.

Whether deriving offsets in structs, or extracting or manipulating sub-strings, I'm not at all convinced that there are not places within the Perl sources themselves where such manipulations are done, that work only because most 32-bit Perls run limited to 2GB.

Certainly, when I was playing with 32-bit perl made /largeaddressaware and with /3GB set, I saw enough weirdness and crashes to give up on the idea of using that instead of a 64-bit Perl in order to get access to my full complement of ram.