[SelectionDAGISel] Use MCRegister and Register for LiveInMap. NFC

This matches the MachineBasicBlock liveins used to populate it.

Author: topperc

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

@@ -673,7 +673,7 @@ bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
     TLI->insertCopiesSplitCSR(EntryMBB, Returns);
   }
 
-  DenseMap<unsigned, unsigned> LiveInMap;
+  DenseMap<MCRegister, Register> LiveInMap;
   if (!FuncInfo->ArgDbgValues.empty())
     for (std::pair<MCRegister, Register> LI : RegInfo->liveins())
       if (LI.second)
@@ -705,7 +705,7 @@ bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
       continue;
 
     // If Reg is live-in then update debug info to track its copy in a vreg.
-    DenseMap<unsigned, unsigned>::iterator LDI = LiveInMap.find(Reg);
+    DenseMap<MCRegister, Register>::iterator LDI = LiveInMap.find(Reg);
     if (LDI != LiveInMap.end()) {
       assert(!hasFI && "There's no handling of frame pointer updating here yet "
                        "- add if needed");