Fix a really annoying "bug" introduced in r165941. The change from that

Fix a really annoying "bug" introduced in r165941. The change from that
revision makes no sense. We cannot use the address space of the *post
indexed* type to conclude anything about a *pre indexed* pointer type's
size. More importantly, this index can never be over a pointer. We are
indexing over arrays and vectors here.

Of course, I have no test case here. Neither did the original patch. =/

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166091 91177308-0d34-0410-b5e6-96231b3b80d8