diff --git a/llvm/lib/AsmParser/LLLexer.cpp b/llvm/lib/AsmParser/LLLexer.cpp
--- a/llvm/lib/AsmParser/LLLexer.cpp
+++ b/llvm/lib/AsmParser/LLLexer.cpp
@@ -595,6 +595,7 @@
   KEYWORD(arm_aapcs_vfpcc);
   KEYWORD(aarch64_vector_pcs);
   KEYWORD(aarch64_sve_vector_pcs);
+  KEYWORD(msp430_builtincc);
   KEYWORD(msp430_intrcc);
   KEYWORD(avr_intrcc);
   KEYWORD(avr_signalcc);
diff --git a/llvm/lib/AsmParser/LLParser.cpp b/llvm/lib/AsmParser/LLParser.cpp
--- a/llvm/lib/AsmParser/LLParser.cpp
+++ b/llvm/lib/AsmParser/LLParser.cpp
@@ -2005,6 +2005,7 @@
 ///   ::= 'arm_aapcs_vfpcc'
 ///   ::= 'aarch64_vector_pcs'
 ///   ::= 'aarch64_sve_vector_pcs'
+///   ::= 'msp430_builtincc'
 ///   ::= 'msp430_intrcc'
 ///   ::= 'avr_intrcc'
 ///   ::= 'avr_signalcc'
@@ -2054,6 +2055,7 @@
   case lltok::kw_aarch64_sve_vector_pcs:
     CC = CallingConv::AArch64_SVE_VectorCall;
     break;
+  case lltok::kw_msp430_builtincc:CC = CallingConv::MSP430_BUILTIN; break;
   case lltok::kw_msp430_intrcc:  CC = CallingConv::MSP430_INTR; break;
   case lltok::kw_avr_intrcc:     CC = CallingConv::AVR_INTR; break;
   case lltok::kw_avr_signalcc:   CC = CallingConv::AVR_SIGNAL; break;
diff --git a/llvm/lib/AsmParser/LLToken.h b/llvm/lib/AsmParser/LLToken.h
--- a/llvm/lib/AsmParser/LLToken.h
+++ b/llvm/lib/AsmParser/LLToken.h
@@ -143,6 +143,7 @@
   kw_arm_aapcs_vfpcc,
   kw_aarch64_vector_pcs,
   kw_aarch64_sve_vector_pcs,
+  kw_msp430_builtincc,
   kw_msp430_intrcc,
   kw_avr_intrcc,
   kw_avr_signalcc,
diff --git a/llvm/lib/IR/AsmWriter.cpp b/llvm/lib/IR/AsmWriter.cpp
--- a/llvm/lib/IR/AsmWriter.cpp
+++ b/llvm/lib/IR/AsmWriter.cpp
@@ -367,6 +367,7 @@
   case CallingConv::AArch64_SVE_VectorCall:
     Out << "aarch64_sve_vector_pcs";
     break;
+  case CallingConv::MSP430_BUILTIN:Out << "msp430_builtincc"; break;
   case CallingConv::MSP430_INTR:   Out << "msp430_intrcc"; break;
   case CallingConv::AVR_INTR:      Out << "avr_intrcc "; break;
   case CallingConv::AVR_SIGNAL:    Out << "avr_signalcc "; break;
diff --git a/llvm/test/Bitcode/compatibility.ll b/llvm/test/Bitcode/compatibility.ll
--- a/llvm/test/Bitcode/compatibility.ll
+++ b/llvm/test/Bitcode/compatibility.ll
@@ -486,6 +486,10 @@
 ; CHECK: declare amdgpu_hs void @f.cc93()
 declare amdgpu_hs void @f.amdgpu_hs()
 ; CHECK: declare amdgpu_hs void @f.amdgpu_hs()
+declare cc94 void @f.cc94()
+; CHECK: declare msp430_builtincc void @f.cc94()
+declare msp430_builtincc void @f.msp430_builtincc()
+; CHECK: declare msp430_builtincc void @f.msp430_builtincc()
 declare cc95 void @f.cc95()
 ; CHECK: declare amdgpu_ls void @f.cc95()
 declare amdgpu_ls void @f.amdgpu_ls()
diff --git a/llvm/utils/vim/syntax/llvm.vim b/llvm/utils/vim/syntax/llvm.vim
--- a/llvm/utils/vim/syntax/llvm.vim
+++ b/llvm/utils/vim/syntax/llvm.vim
@@ -105,6 +105,7 @@
       \ minsize
       \ module
       \ monotonic
+      \ msp430_builtincc
       \ msp430_intrcc
       \ musttail
       \ naked
diff --git a/llvm/utils/vscode/llvm/syntaxes/ll.tmLanguage.yaml b/llvm/utils/vscode/llvm/syntaxes/ll.tmLanguage.yaml
--- a/llvm/utils/vscode/llvm/syntaxes/ll.tmLanguage.yaml
+++ b/llvm/utils/vscode/llvm/syntaxes/ll.tmLanguage.yaml
@@ -202,6 +202,7 @@
             \\bminsize\\b|\
             \\bmodule\\b|\
             \\bmonotonic\\b|\
+            \\bmsp430_builtincc\\b|\
             \\bmsp430_intrcc\\b|\
             \\bmusttail\\b|\
             \\bnaked\\b|\