diff --git a/clang/lib/AST/MicrosoftMangle.cpp b/clang/lib/AST/MicrosoftMangle.cpp
--- a/clang/lib/AST/MicrosoftMangle.cpp
+++ b/clang/lib/AST/MicrosoftMangle.cpp
@@ -3073,14 +3073,17 @@
 
 void MicrosoftCXXNameMangler::mangleType(const VectorType *T, Qualifiers Quals,
                                          SourceRange Range) {
-  const BuiltinType *ET = T->getElementType()->getAs<BuiltinType>();
-  assert(ET && "vectors with non-builtin elements are unsupported");
+  QualType EltTy = T->getElementType();
+  const BuiltinType *ET = EltTy->getAs<BuiltinType>();
+  const BitIntType *BitIntTy = EltTy->getAs<BitIntType>();
+  assert((ET || BitIntTy) &&
+         "vectors with non-builtin/_BitInt elements are unsupported");
   uint64_t Width = getASTContext().getTypeSize(T);
   // Pattern match exactly the typedefs in our intrinsic headers.  Anything that
   // doesn't match the Intel types uses a custom mangling below.
   size_t OutSizeBefore = Out.tell();
   if (!isa<ExtVectorType>(T)) {
-    if (getASTContext().getTargetInfo().getTriple().isX86()) {
+    if (getASTContext().getTargetInfo().getTriple().isX86() && ET) {
       if (Width == 64 && ET->getKind() == BuiltinType::LongLong) {
         mangleArtificialTagType(TTK_Union, "__m64");
       } else if (Width >= 128) {
@@ -3105,7 +3108,11 @@
     MicrosoftCXXNameMangler Extra(Context, Stream);
     Stream << "?$";
     Extra.mangleSourceName("__vector");
-    Extra.mangleType(QualType(ET, 0), Range, QMM_Escape);
+    if (ET)
+      Extra.mangleType(QualType(ET, 0), Range, QMM_Escape);
+    else
+      Extra.mangleType(QualType(BitIntTy, 0), Range, QMM_Escape);
+
     Extra.mangleIntegerLiteral(llvm::APSInt::getUnsigned(T->getNumElements()));
 
     mangleArtificialTagType(TTK_Union, TemplateMangling, {"__clang"});
diff --git a/clang/lib/Basic/Targets/DirectX.h b/clang/lib/Basic/Targets/DirectX.h
--- a/clang/lib/Basic/Targets/DirectX.h
+++ b/clang/lib/Basic/Targets/DirectX.h
@@ -63,6 +63,7 @@
   void getTargetDefines(const LangOptions &Opts,
                         MacroBuilder &Builder) const override;
 
+  bool hasBitIntType() const override { return true; }
   bool hasFeature(StringRef Feature) const override {
     return Feature == "directx";
   }
diff --git a/clang/lib/Headers/hlsl/hlsl_basic_types.h b/clang/lib/Headers/hlsl/hlsl_basic_types.h
--- a/clang/lib/Headers/hlsl/hlsl_basic_types.h
+++ b/clang/lib/Headers/hlsl/hlsl_basic_types.h
@@ -13,8 +13,8 @@
 
 #ifdef __HLSL_ENABLE_16_BIT
 // 16-bit integer.
-typedef unsigned short uint16_t;
-typedef short int16_t;
+typedef unsigned _BitInt(16) uint16_t;
+typedef _BitInt(16) int16_t;
 #endif
 
 // unsigned 32-bit integer.
diff --git a/clang/test/CodeGenHLSL/int16_t_add.hlsl b/clang/test/CodeGenHLSL/int16_t_add.hlsl
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGenHLSL/int16_t_add.hlsl
@@ -0,0 +1,24 @@
+// RUN: %clang_cc1 -finclude-default-header -x hlsl -triple \
+// RUN:   dxil-pc-shadermodel6.3-library %s -D__HLSL_ENABLE_16_BIT \
+// RUN:   -emit-llvm -disable-llvm-passes -O3 -o - | FileCheck %s
+
+// Make sure generate i16 add.
+// CHECK: add nsw i16 %
+int16_t add(int16_t a, int16_t b) {
+  return a + b;
+}
+// CHECK: define noundef <2 x i16> @
+// CHECK: add <2 x i16>
+int16_t2 add(int16_t2 a, int16_t2 b) {
+  return a + b;
+}
+// CHECK: define noundef <3 x i16> @
+// CHECK: add <3 x i16>
+int16_t3 add(int16_t3 a, int16_t3 b) {
+  return a + b;
+}
+// CHECK: define noundef <4 x i16> @
+// CHECK: add <4 x i16>
+int16_t4 add(int16_t4 a, int16_t4 b) {
+  return a + b;
+}