In machine code, you can't just replaceRegWith() the same way you can
replaceAllUsesWith() in IR. Virtual registers may have different
register classes that need to be merged first.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142201 91177308-0d34-0410-b5e6-96231b3b80d8
