diff --git a/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp b/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp
--- a/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp
+++ b/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp
@@ -1380,6 +1380,7 @@
   default:
     llvm_unreachable("Unsupported calling convention");
   case CallingConv::C:
+  case CallingConv::Fast:
     break;
   }