MergedLoadStoreMotion pass

Merges equivalent loads on both sides of a hammock/diamond
and hoists into into the header.
Merges equivalent stores on both sides of a hammock/diamond
and sinks it to the footer.
Can enable if conversion and tolerate better load misses
and store operand latencies.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213396 91177308-0d34-0410-b5e6-96231b3b80d8