[DAG] Add canMergeStoresTo predicate checks. NFCI.

Propagate canMergeStoresTo checks to missing cases in StoreMerge.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@303668 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed