The current check in CombineToPreIndexedLoadStore is too
conversative, preventing a pre-indexed store when the base pointer
is a predecessor of the value being stored. Instead, we should check
the pointer operand of the store.
Differential Revision: https://reviews.llvm.org/D56719
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@351933 91177308-0d34-0410-b5e6-96231b3b80d8
