[X86] Teach the expansion of copy instructions how to do proper liveness.

When the simple analysis provided by MachineBasicBlock::computeRegisterLiveness
fails, fall back on the LivePhysReg utility.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267623 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed