[AArch64][GISel] Use Register instead of MCRegister for markPhysRegUsed in CallLowering.

For "returned" attribute arguments, the physical register is a
virtual register which shouldn't be stored in MCRegister. This
moves the conversion from Register to MCRegister into the derived
classes of IncomingArgHandler. The derived class ReturnedArgCallReturnHandler
does not use the register so no MCRegister is created in that case.

Author: topperc

llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp

@@ -207,14 +207,14 @@ struct IncomingArgHandler : public CallLowering::IncomingValueHandler {
   /// How the physical register gets marked varies between formal
   /// parameters (it's a basic-block live-in), and a call instruction
   /// (it's an implicit-def of the BL).
-  virtual void markPhysRegUsed(MCRegister PhysReg) = 0;
+  virtual void markPhysRegUsed(Register PhysReg) = 0;
 };
 
 struct FormalArgHandler : public IncomingArgHandler {
   FormalArgHandler(MachineIRBuilder &MIRBuilder, MachineRegisterInfo &MRI)
       : IncomingArgHandler(MIRBuilder, MRI) {}
 
-  void markPhysRegUsed(MCRegister PhysReg) override {
+  void markPhysRegUsed(Register PhysReg) override {
     MIRBuilder.getMRI()->addLiveIn(PhysReg);
     MIRBuilder.getMBB().addLiveIn(PhysReg);
   }
@@ -225,7 +225,7 @@ struct CallReturnHandler : public IncomingArgHandler {
                     MachineInstrBuilder MIB)
       : IncomingArgHandler(MIRBuilder, MRI), MIB(MIB) {}
 
-  void markPhysRegUsed(MCRegister PhysReg) override {
+  void markPhysRegUsed(Register PhysReg) override {
     MIB.addDef(PhysReg, RegState::Implicit);
   }
 
@@ -239,7 +239,7 @@ struct ReturnedArgCallReturnHandler : public CallReturnHandler {
                                MachineInstrBuilder MIB)
       : CallReturnHandler(MIRBuilder, MRI, MIB) {}
 
-  void markPhysRegUsed(MCRegister PhysReg) override {}
+  void markPhysRegUsed(Register PhysReg) override {}
 };
 
 struct OutgoingArgHandler : public CallLowering::OutgoingValueHandler {