[DA] Improve alias checking in dependence analysis

Improve the alias analysis to account for cases where we
know that src/dst pairs cannot alias due to things like
TBAA. As we know they are noalias, we know no dependency
can occur. Also fixes issues around the size parameter
to AA being incorrect.

Differential Revision: https://reviews.llvm.org/D42381

llvm-svn: 329692