diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -1460,6 +1460,11 @@
   let Documentation = [Undocumented];
 }
 
+def MSP430Builtin : DeclOrTypeAttr, TargetSpecificAttr<TargetMSP430> {
+  let Spellings = [Clang<"msp430_builtin">];
+  let Documentation = [Undocumented];
+}
+
 def Mips16 : InheritableAttr, TargetSpecificAttr<TargetMips32> {
   let Spellings = [GCC<"mips16">];
   let Subjects = SubjectList<[Function], ErrorDiag>;
diff --git a/clang/include/clang/Basic/Specifiers.h b/clang/include/clang/Basic/Specifiers.h
--- a/clang/include/clang/Basic/Specifiers.h
+++ b/clang/include/clang/Basic/Specifiers.h
@@ -286,6 +286,7 @@
     CC_PreserveMost, // __attribute__((preserve_most))
     CC_PreserveAll,  // __attribute__((preserve_all))
     CC_AArch64VectorCall, // __attribute__((aarch64_vector_pcs))
+    CC_MSP430Builtin, // __attribute__((msp430_builtin))
   };
 
   /// Checks whether the given calling convention supports variadic
diff --git a/clang/lib/AST/ItaniumMangle.cpp b/clang/lib/AST/ItaniumMangle.cpp
--- a/clang/lib/AST/ItaniumMangle.cpp
+++ b/clang/lib/AST/ItaniumMangle.cpp
@@ -2854,6 +2854,7 @@
   case CC_OpenCLKernel:
   case CC_PreserveMost:
   case CC_PreserveAll:
+  case CC_MSP430Builtin:
     // FIXME: we should be mangling all of the above.
     return "";
 
diff --git a/clang/lib/AST/Type.cpp b/clang/lib/AST/Type.cpp
--- a/clang/lib/AST/Type.cpp
+++ b/clang/lib/AST/Type.cpp
@@ -3115,6 +3115,7 @@
   case CC_Swift: return "swiftcall";
   case CC_PreserveMost: return "preserve_most";
   case CC_PreserveAll: return "preserve_all";
+  case CC_MSP430Builtin: return "msp430_builtin";
   }
 
   llvm_unreachable("Invalid calling convention.");
@@ -3529,6 +3530,7 @@
   case attr::IntelOclBicc:
   case attr::PreserveMost:
   case attr::PreserveAll:
+  case attr::MSP430Builtin:
     return true;
   }
   llvm_unreachable("invalid attr kind");
diff --git a/clang/lib/AST/TypePrinter.cpp b/clang/lib/AST/TypePrinter.cpp
--- a/clang/lib/AST/TypePrinter.cpp
+++ b/clang/lib/AST/TypePrinter.cpp
@@ -940,6 +940,9 @@
     case CC_PreserveAll:
       OS << " __attribute__((preserve_all))";
       break;
+    case CC_MSP430Builtin:
+      OS << " __attribute__((msp430_builtin))";
+      break;
     }
   }
 
@@ -1635,6 +1638,9 @@
   case attr::ArmSveVectorBits:
     OS << "arm_sve_vector_bits";
     break;
+  case attr::MSP430Builtin:
+    OS << "msp430_builtin";
+    break;
   }
   OS << "))";
 }
diff --git a/clang/lib/Basic/Targets/MSP430.h b/clang/lib/Basic/Targets/MSP430.h
--- a/clang/lib/Basic/Targets/MSP430.h
+++ b/clang/lib/Basic/Targets/MSP430.h
@@ -96,6 +96,16 @@
     // FIXME: implement
     return TargetInfo::CharPtrBuiltinVaList;
   }
+
+  CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
+    switch (CC) {
+      default:
+        return CCCR_Warning;
+      case CC_C:
+      case CC_MSP430Builtin:
+        return CCCR_OK;
+    }
+  }
 };
 
 } // namespace targets
diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -65,6 +65,7 @@
   case CC_PreserveMost: return llvm::CallingConv::PreserveMost;
   case CC_PreserveAll: return llvm::CallingConv::PreserveAll;
   case CC_Swift: return llvm::CallingConv::Swift;
+  case CC_MSP430Builtin: return llvm::CallingConv::MSP430_BUILTIN;
   }
 }
 
@@ -239,6 +240,9 @@
   if (D->hasAttr<PreserveAllAttr>())
     return CC_PreserveAll;
 
+  if (D->hasAttr<MSP430BuiltinAttr>())
+    return CC_MSP430Builtin;
+
   return CC_C;
 }
 
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -1230,6 +1230,7 @@
     return llvm::dwarf::DW_CC_LLVM_PreserveAll;
   case CC_X86RegCall:
     return llvm::dwarf::DW_CC_LLVM_X86RegCall;
+  // TODO case CC_MSP430Builtin:
   }
   return 0;
 }
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -4459,6 +4459,9 @@
   case ParsedAttr::AT_PreserveAll:
     D->addAttr(::new (S.Context) PreserveAllAttr(S.Context, AL));
     return;
+  case ParsedAttr::AT_MSP430Builtin:
+    D->addAttr(::new (S.Context) MSP430BuiltinAttr(S.Context, AL));
+    return;
   default:
     llvm_unreachable("unexpected attribute kind");
   }
@@ -4624,6 +4627,9 @@
   case ParsedAttr::AT_PreserveAll:
     CC = CC_PreserveAll;
     break;
+  case ParsedAttr::AT_MSP430Builtin:
+    CC = CC_MSP430Builtin;
+    break;
   default: llvm_unreachable("unexpected attribute kind");
   }
 
@@ -7252,6 +7258,7 @@
   case ParsedAttr::AT_PreserveMost:
   case ParsedAttr::AT_PreserveAll:
   case ParsedAttr::AT_AArch64VectorPcs:
+  case ParsedAttr::AT_MSP430Builtin:
     handleCallConvAttr(S, D, AL);
     break;
   case ParsedAttr::AT_Suppress:
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -124,7 +124,8 @@
   case ParsedAttr::AT_Pcs:                                                     \
   case ParsedAttr::AT_IntelOclBicc:                                            \
   case ParsedAttr::AT_PreserveMost:                                            \
-  case ParsedAttr::AT_PreserveAll
+  case ParsedAttr::AT_PreserveAll:                                             \
+  case ParsedAttr::AT_MSP430Builtin
 
 // Function type attributes.
 #define FUNCTION_TYPE_ATTRS_CASELIST                                           \
@@ -7248,6 +7249,8 @@
     return createSimpleAttr<PreserveMostAttr>(Ctx, Attr);
   case ParsedAttr::AT_PreserveAll:
     return createSimpleAttr<PreserveAllAttr>(Ctx, Attr);
+  case ParsedAttr::AT_MSP430Builtin:
+    return createSimpleAttr<MSP430BuiltinAttr>(Ctx, Attr);
   }
   llvm_unreachable("unexpected attribute kind!");
 }
diff --git a/clang/test/CodeGen/msp430-cc-builtin.c b/clang/test/CodeGen/msp430-cc-builtin.c
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGen/msp430-cc-builtin.c
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -triple msp430 -emit-llvm < %s | FileCheck %s
+
+__attribute__((msp430_builtin)) int f(long long x, long long y);
+
+__attribute__((msp430_builtin)) int g(long long x, long long y) {
+  return (int)42;
+}
+// CHECK: define cc94 {{(dso_local )?}}i16 @g(i64 %x, i64 %y)
+
+int caller()
+{
+  return f(0, 0);
+// CHECK: call cc94 i16 @f
+}
+
+// CHECK: declare cc94 {{(dso_local )?}}i16 @f(i64, i64)
diff --git a/clang/test/Sema/attr-msp430.c b/clang/test/Sema/attr-msp430.c
--- a/clang/test/Sema/attr-msp430.c
+++ b/clang/test/Sema/attr-msp430.c
@@ -11,3 +11,6 @@
 
 __attribute__((interrupt(0))) void f6(void);
 __attribute__((interrupt(63))) void f7(void);
+
+__attribute__((msp430_builtin)) int t2; // expected-warning {{'msp430_builtin' only applies to function types; type here is 'int'}}
+__attribute__((msp430_builtin)) void f8(long long a, long long b);
diff --git a/clang/tools/libclang/CXType.cpp b/clang/tools/libclang/CXType.cpp
--- a/clang/tools/libclang/CXType.cpp
+++ b/clang/tools/libclang/CXType.cpp
@@ -666,6 +666,7 @@
       TCALLINGCONV(Swift);
       TCALLINGCONV(PreserveMost);
       TCALLINGCONV(PreserveAll);
+    case CC_MSP430Builtin: return CXCallingConv_Unexposed;
     case CC_SpirFunction: return CXCallingConv_Unexposed;
     case CC_OpenCLKernel: return CXCallingConv_Unexposed;
       break;
diff --git a/llvm/lib/Target/MSP430/MSP430ISelLowering.cpp b/llvm/lib/Target/MSP430/MSP430ISelLowering.cpp
--- a/llvm/lib/Target/MSP430/MSP430ISelLowering.cpp
+++ b/llvm/lib/Target/MSP430/MSP430ISelLowering.cpp
@@ -573,6 +573,7 @@
     report_fatal_error("Unsupported calling convention");
   case CallingConv::C:
   case CallingConv::Fast:
+  case CallingConv::MSP430_BUILTIN:
     return LowerCCCArguments(Chain, CallConv, isVarArg, Ins, dl, DAG, InVals);
   case CallingConv::MSP430_INTR:
     if (Ins.empty())