Revert "Use MachineInstr::readsWritesVirtualRegister to determine if a register is read."

This reverts r104322. I think it was causing miscompilations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@104323 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed