The code that eliminated additional coalescable copies in
removeCopyByCommutingDef() used MergeValueNumberInto() which internally
may merge A into B or B into A. In this case A and B had different Def
points, so we have to reset ValNo.Def to the intended one after merging.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225503 91177308-0d34-0410-b5e6-96231b3b80d8
