[mono] Add mono calling convention to AArch64RegisterInfo::isArgumentRegister (#579)

This is a new case switch added in upstream 6e00a34

Author: lambdageek

llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp

@@ -687,6 +687,13 @@ bool AArch64RegisterInfo::isArgumentRegister(const MachineFunction &MF,
     if (STI.isTargetWindows())
       return HasReg(CC_AArch64_Win64PCS_ArgRegs, Reg);
     return HasReg(CC_AArch64_AAPCS_ArgRegs, Reg);
+  case CallingConv::Mono:
+    if (STI.isTargetDarwin())
+      return HasReg(CC_AArch64_Mono_DarwinPCS_ArgRegs, Reg);
+    else if (STI.isTargetWindows())
+      report_fatal_error("Unsupported calling convention.");
+    else
+      return HasReg(CC_AArch64_Mono_AAPCS_ArgRegs, Reg);
   }
 }