Remove some redundant tests.

An empty list is not represented as a null pointer. Let TRI do its own
shortcuts.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157702 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/MachineInstr.cpp b/lib/CodeGen/MachineInstr.cpp
index 9cffc6d..59b0e65 100644
--- a/lib/CodeGen/MachineInstr.cpp
+++ b/lib/CodeGen/MachineInstr.cpp
@@ -1766,9 +1766,7 @@
       // There exists a super-register that's marked dead.
       if (RegInfo->isSuperRegister(IncomingReg, Reg))
         return true;
-      if (RegInfo->getSubRegisters(IncomingReg) &&
-          RegInfo->getSuperRegisters(Reg) &&
-          RegInfo->isSubRegister(IncomingReg, Reg))
+      if (RegInfo->isSubRegister(IncomingReg, Reg))
         DeadOps.push_back(i);
     }
   }