Turn some insert_subreg, extract_subreg, subreg_to_reg into implicit_defs.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78151 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/LowerSubregs.cpp

@@ -119,6 +119,7 @@ bool LowerSubregsInstructionPass::LowerExtract(MachineInstr *MI) {
          "Extract supperg source must be a physical register");
   assert(TargetRegisterInfo::isPhysicalRegister(DstReg) &&
          "Extract destination must be in a physical register");
+  assert(SrcReg && "invalid subregister index for register");
 
   DOUT << "subreg: CONVERTING: " << *MI;