This just in, it is a *bad idea* to use 'udiv' on an offset of

a pointer. A very bad idea. Let's not do that. Fixes PR14105.

Note that this wasn't *that* glaring of an oversight. Originally, these
routines were only called on offsets within an alloca, which are
intrinsically positive. But over the evolution of the pass, they ended
up being called for arbitrary offsets, and things went downhill...

llvm-svn: 166095