This function consists of following steps:
1. Collect dependent memory accesses.
2. Analyze availability.
3. Perform fully redundancy elimination, or
4. Perform PRE, depending on the availability
Step 2, 3 and 4 are now moved to three helper routines.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181047 91177308-0d34-0410-b5e6-96231b3b80d8