[AMDGPU] Prevent Machine Copy Propagation from replacing live copy with the dead one

Differential revision: https://reviews.llvm.org/D38754

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@317884 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed