Recommit - [DSE]Enhance shorthening MemIntrinsic based on OverlapIntervals

Recommiting r275571 after fixing crash reported in PR28270.
Now we erase elements of IOL in deleteDeadInstruction().

Original Summary:
This change use the overlap interval map built from partial overwrite tracking to perform shortening MemIntrinsics.
Add test cases which was missing opportunities before.

llvm-svn: 276452