Re-write the address propagation code for pre-indexed loads/stores to take into account some previously misssed cases (PRE_DEC addressing mode, the offset and base address are swapped, etc). This should fix PR15581.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180609 91177308-0d34-0410-b5e6-96231b3b80d8