diff --git a/clang/include/clang/AST/OperationKinds.def b/clang/include/clang/AST/OperationKinds.def
index 8dd98730dff74..ef05072800f11 100644
--- a/clang/include/clang/AST/OperationKinds.def
+++ b/clang/include/clang/AST/OperationKinds.def
@@ -361,6 +361,9 @@ CAST_OPERATION(AddressSpaceConversion)
 // Convert an integer initializer to an OpenCL sampler.
 CAST_OPERATION(IntToOCLSampler)
 
+// Truncate a vector type by dropping elements from the end (HLSL only).
+CAST_OPERATION(HLSLVectorTruncation)
+
 //===- Binary Operations  -------------------------------------------------===//
 // Operators listed in order of precedence.
 // Note that additions to this should also update the StmtVisitor class,
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 935d94e38cc37..3f83dab879733 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -12112,6 +12112,9 @@ def err_hlsl_operator_unsupported : Error<
 def err_hlsl_param_qualifier_mismatch :
   Error<"conflicting parameter qualifier %0 on parameter %1">;
 
+def warn_hlsl_impcast_vector_truncation : Warning<
+  "implicit conversion truncates vector: %0 to %1">, InGroup<Conversion>;
+
 // Layout randomization diagnostics.
 def err_non_designated_init_used : Error<
   "a randomized struct can only be initialized with a designated initializer">;
diff --git a/clang/include/clang/Sema/Overload.h b/clang/include/clang/Sema/Overload.h
index 9b342c0916844..e4717dd5baf1e 100644
--- a/clang/include/clang/Sema/Overload.h
+++ b/clang/include/clang/Sema/Overload.h
@@ -195,6 +195,9 @@ class Sema;
     /// Fixed point type conversions according to N1169.
     ICK_Fixed_Point_Conversion,
 
+    /// HLSL vector truncation.
+    ICK_HLSL_Vector_Truncation,
+
     /// The number of conversion kinds
     ICK_Num_Conversion_Kinds,
   };
@@ -271,6 +274,12 @@ class Sema;
     /// pointer-to-member conversion, or boolean conversion.
     ImplicitConversionKind Second : 8;
 
+    /// Element - Between the second and third conversion a vector or matrix
+    /// element conversion may occur. If this is not ICK_Identity this
+    /// conversion is applied element-wise to each element in the vector or
+    /// matrix.
+    ImplicitConversionKind Element : 8;
+
     /// Third - The third conversion can be a qualification conversion
     /// or a function conversion.
     ImplicitConversionKind Third : 8;
@@ -367,7 +376,8 @@ class Sema;
     void setAsIdentityConversion();
 
     bool isIdentityConversion() const {
-      return Second == ICK_Identity && Third == ICK_Identity;
+      return Second == ICK_Identity && Element == ICK_Identity &&
+             Third == ICK_Identity;
     }
 
     ImplicitConversionRank getRank() const;
diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 8b10e28958326..cc0407131d793 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -1897,6 +1897,7 @@ bool CastExpr::CastConsistency() const {
   case CK_FixedPointToIntegral:
   case CK_IntegralToFixedPoint:
   case CK_MatrixCast:
+  case CK_HLSLVectorTruncation:
     assert(!getType()->isBooleanType() && "unheralded conversion to bool");
     goto CheckNoBasePath;
 
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 010010120cf6d..fcf8f6591a792 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -13980,6 +13980,7 @@ bool IntExprEvaluator::VisitCastExpr(const CastExpr *E) {
   case CK_FixedPointCast:
   case CK_IntegralToFixedPoint:
   case CK_MatrixCast:
+  case CK_HLSLVectorTruncation:
     llvm_unreachable("invalid cast kind for integral value");
 
   case CK_BitCast:
@@ -14818,6 +14819,7 @@ bool ComplexExprEvaluator::VisitCastExpr(const CastExpr *E) {
   case CK_FixedPointToIntegral:
   case CK_IntegralToFixedPoint:
   case CK_MatrixCast:
+  case CK_HLSLVectorTruncation:
     llvm_unreachable("invalid cast kind for complex value");
 
   case CK_LValueToRValue:
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 4a2f3caad6588..59a7fe8925001 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -5180,6 +5180,7 @@ LValue CodeGenFunction::EmitCastLValue(const CastExpr *E) {
   case CK_FixedPointToIntegral:
   case CK_IntegralToFixedPoint:
   case CK_MatrixCast:
+  case CK_HLSLVectorTruncation:
     return EmitUnsupportedLValue(E, "unexpected cast lvalue");
 
   case CK_Dependent:
diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index 22f55fe9aac90..d0d6202974fe9 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -933,6 +933,7 @@ void AggExprEmitter::VisitCastExpr(CastExpr *E) {
   case CK_BuiltinFnToFnPtr:
   case CK_ZeroToOCLOpaqueType:
   case CK_MatrixCast:
+  case CK_HLSLVectorTruncation:
 
   case CK_IntToOCLSampler:
   case CK_FloatingToFixedPoint:
@@ -1457,6 +1458,7 @@ static bool castPreservesZero(const CastExpr *CE) {
   case CK_MatrixCast:
   case CK_NonAtomicToAtomic:
   case CK_AtomicToNonAtomic:
+  case CK_HLSLVectorTruncation:
     return true;
 
   case CK_BaseToDerivedMemberPointer:
diff --git a/clang/lib/CodeGen/CGExprComplex.cpp b/clang/lib/CodeGen/CGExprComplex.cpp
index 9ddf0e763f139..176a7e00141f9 100644
--- a/clang/lib/CodeGen/CGExprComplex.cpp
+++ b/clang/lib/CodeGen/CGExprComplex.cpp
@@ -564,6 +564,7 @@ ComplexPairTy ComplexExprEmitter::EmitCast(CastKind CK, Expr *Op,
   case CK_FixedPointToIntegral:
   case CK_IntegralToFixedPoint:
   case CK_MatrixCast:
+  case CK_HLSLVectorTruncation:
     llvm_unreachable("invalid cast kind for complex value");
 
   case CK_FloatingRealToComplex:
diff --git a/clang/lib/CodeGen/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
index a054f38e860b7..75286dceb13a7 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -1225,6 +1225,7 @@ class ConstExprEmitter :
     case CK_IntegralToFixedPoint:
     case CK_ZeroToOCLOpaqueType:
     case CK_MatrixCast:
+    case CK_HLSLVectorTruncation:
       return nullptr;
     }
     llvm_unreachable("Invalid CastKind");
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index aa805f291d175..13526de3e7642 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -2408,6 +2408,12 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
                                 CE->getExprLoc());
 
   case CK_IntegralCast: {
+    if (E->getType()->isExtVectorType() && DestTy->isExtVectorType()) {
+      QualType SrcElTy = E->getType()->castAs<VectorType>()->getElementType();
+      return Builder.CreateIntCast(Visit(E), ConvertType(DestTy),
+                                   SrcElTy->isSignedIntegerOrEnumerationType(),
+                                   "conv");
+    }
     ScalarConversionOpts Opts;
     if (auto *ICE = dyn_cast<ImplicitCastExpr>(CE)) {
       if (!ICE->isPartOfExplicitCast())
@@ -2416,9 +2422,50 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
     return EmitScalarConversion(Visit(E), E->getType(), DestTy,
                                 CE->getExprLoc(), Opts);
   }
-  case CK_IntegralToFloating:
-  case CK_FloatingToIntegral:
-  case CK_FloatingCast:
+  case CK_IntegralToFloating: {
+    if (E->getType()->isVectorType() && DestTy->isVectorType()) {
+      // TODO: Support constrained FP intrinsics.
+      assert(!Builder.getIsFPConstrained() &&
+             "FP Constrained vector casts not supported yet.");
+      QualType SrcElTy = E->getType()->castAs<VectorType>()->getElementType();
+      if (SrcElTy->isSignedIntegerOrEnumerationType())
+        return Builder.CreateSIToFP(Visit(E), ConvertType(DestTy), "conv");
+      return Builder.CreateUIToFP(Visit(E), ConvertType(DestTy), "conv");
+    }
+    CodeGenFunction::CGFPOptionsRAII FPOptsRAII(CGF, CE);
+    return EmitScalarConversion(Visit(E), E->getType(), DestTy,
+                                CE->getExprLoc());
+  }
+  case CK_FloatingToIntegral: {
+    if (E->getType()->isVectorType() && DestTy->isVectorType()) {
+      // TODO: Support constrained FP intrinsics.
+      assert(!Builder.getIsFPConstrained() &&
+             "FP Constrained vector casts not supported yet.");
+      QualType DstElTy = DestTy->castAs<VectorType>()->getElementType();
+      if (DstElTy->isSignedIntegerOrEnumerationType())
+        return Builder.CreateFPToSI(Visit(E), ConvertType(DestTy), "conv");
+      return Builder.CreateFPToUI(Visit(E), ConvertType(DestTy), "conv");
+    }
+    CodeGenFunction::CGFPOptionsRAII FPOptsRAII(CGF, CE);
+    return EmitScalarConversion(Visit(E), E->getType(), DestTy,
+                                CE->getExprLoc());
+  }
+  case CK_FloatingCast: {
+    if (E->getType()->isVectorType() && DestTy->isVectorType()) {
+      // TODO: Support constrained FP intrinsics.
+      assert(!Builder.getIsFPConstrained() &&
+             "FP Constrained vector casts not supported yet.");
+      QualType SrcElTy = E->getType()->castAs<VectorType>()->getElementType();
+      QualType DstElTy = DestTy->castAs<VectorType>()->getElementType();
+      if (DstElTy->castAs<BuiltinType>()->getKind() <
+          SrcElTy->castAs<BuiltinType>()->getKind())
+        return Builder.CreateFPTrunc(Visit(E), ConvertType(DestTy), "conv");
+      return Builder.CreateFPExt(Visit(E), ConvertType(DestTy), "conv");
+    }
+    CodeGenFunction::CGFPOptionsRAII FPOptsRAII(CGF, CE);
+    return EmitScalarConversion(Visit(E), E->getType(), DestTy,
+                                CE->getExprLoc());
+  }
   case CK_FixedPointToFloating:
   case CK_FloatingToFixedPoint: {
     CodeGenFunction::CGFPOptionsRAII FPOptsRAII(CGF, CE);
@@ -2468,6 +2515,17 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
   case CK_IntToOCLSampler:
     return CGF.CGM.createOpenCLIntToSamplerConversion(E, CGF);
 
+  case CK_HLSLVectorTruncation: {
+    assert(DestTy->isVectorType() && "Expected dest type to be vector type");
+    Value *Vec = Visit(const_cast<Expr *>(E));
+    SmallVector<int, 16> Mask;
+    unsigned NumElts = DestTy->castAs<VectorType>()->getNumElements();
+    for (unsigned I = 0; I != NumElts; ++I)
+      Mask.push_back(I);
+
+    return Builder.CreateShuffleVector(Vec, Mask, "trunc");
+  }
+
   } // end of switch
 
   llvm_unreachable("unknown scalar cast");
diff --git a/clang/lib/Edit/RewriteObjCFoundationAPI.cpp b/clang/lib/Edit/RewriteObjCFoundationAPI.cpp
index 2e123e89b0036..22f2c47e1d6a1 100644
--- a/clang/lib/Edit/RewriteObjCFoundationAPI.cpp
+++ b/clang/lib/Edit/RewriteObjCFoundationAPI.cpp
@@ -1083,6 +1083,10 @@ static bool rewriteToNumericBoxedExpression(const ObjCMessageExpr *Msg,
     case CK_BooleanToSignedIntegral:
       llvm_unreachable("OpenCL-specific cast in Objective-C?");
 
+    case CK_HLSLVectorTruncation:
+      llvm_unreachable("HLSL-specific cast in Objective-C?");
+      break;
+
     case CK_FloatingToFixedPoint:
     case CK_FixedPointToFloating:
     case CK_FixedPointCast:
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index afe2673479e40..8e76338477444 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -15676,11 +15676,18 @@ static void CheckImplicitConversion(Sema &S, Expr *E, QualType T,
       if (S.SourceMgr.isInSystemMacro(CC))
         return;
       return DiagnoseImpCast(S, E, T, CC, diag::warn_impcast_vector_scalar);
+    } else if (S.getLangOpts().HLSL &&
+               Target->castAs<VectorType>()->getNumElements() <
+                   Source->castAs<VectorType>()->getNumElements()) {
+      // Diagnose vector truncation but don't return. We may also want to
+      // diagnose an element conversion.
+      DiagnoseImpCast(S, E, T, CC, diag::warn_hlsl_impcast_vector_truncation);
     }
 
     // If the vector cast is cast between two vectors of the same size, it is
-    // a bitcast, not a conversion.
-    if (S.Context.getTypeSize(Source) == S.Context.getTypeSize(Target))
+    // a bitcast, not a conversion, except under HLSL where it is a conversion.
+    if (!S.getLangOpts().HLSL &&
+        S.Context.getTypeSize(Source) == S.Context.getTypeSize(Target))
       return;
 
     Source = cast<VectorType>(Source)->getElementType().getTypePtr();
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index f2b89135af21c..801ce7b35ac47 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -4762,6 +4762,22 @@ Sema::PerformImplicitConversion(Expr *From, QualType ToType,
                              CK_ZeroToOCLOpaqueType,
                              From->getValueKind()).get();
     break;
+  case ICK_HLSL_Vector_Truncation: {
+    // Note: HLSL built-in vectors are ExtVectors. Since this truncates a vector
+    // to a smaller vector, this can only operate on arguments where the source
+    // and destination types are ExtVectors.
+    assert(From->getType()->isExtVectorType() && ToType->isExtVectorType() &&
+           "HLSL vector truncation should only apply to ExtVectors");
+    auto *FromVec = From->getType()->castAs<VectorType>();
+    auto *ToVec = ToType->castAs<VectorType>();
+    QualType ElType = FromVec->getElementType();
+    QualType TruncTy =
+        Context.getExtVectorType(ElType, ToVec->getNumElements());
+    From = ImpCastExprToType(From, TruncTy, CK_HLSLVectorTruncation,
+                             From->getValueKind())
+               .get();
+    break;
+  }
 
   case ICK_Lvalue_To_Rvalue:
   case ICK_Array_To_Pointer:
@@ -4774,6 +4790,76 @@ Sema::PerformImplicitConversion(Expr *From, QualType ToType,
     llvm_unreachable("Improper second standard conversion");
   }
 
+  if (SCS.Element != ICK_Identity) {
+    // If SCS.Element is not ICK_Identity the To and From types must be HLSL
+    // vectors or matrices.
+
+    // TODO: Support HLSL matrices.
+    assert((!From->getType()->isMatrixType() && !ToType->isMatrixType()) &&
+           "Element conversion for matrix types is not implemented yet.");
+    assert(From->getType()->isVectorType() && ToType->isVectorType() &&
+           "Element conversion is only supported for vector types.");
+    assert(From->getType()->getAs<VectorType>()->getNumElements() ==
+               ToType->getAs<VectorType>()->getNumElements() &&
+           "Element conversion is only supported for vectors with the same "
+           "element counts.");
+    QualType FromElTy = From->getType()->getAs<VectorType>()->getElementType();
+    unsigned NumElts = ToType->getAs<VectorType>()->getNumElements();
+    switch (SCS.Element) {
+    case ICK_Boolean_Conversion:
+      // Perform half-to-boolean conversion via float.
+      if (FromElTy->isHalfType()) {
+        QualType FPExtType = Context.getExtVectorType(FromElTy, NumElts);
+        From = ImpCastExprToType(From, FPExtType, CK_FloatingCast).get();
+        FromType = FPExtType;
+      }
+
+      From =
+          ImpCastExprToType(From, ToType, ScalarTypeToBooleanCastKind(FromElTy),
+                            VK_PRValue,
+                            /*BasePath=*/nullptr, CCK)
+              .get();
+      break;
+    case ICK_Integral_Promotion:
+    case ICK_Integral_Conversion:
+      if (ToType->isBooleanType()) {
+        assert(FromType->castAs<EnumType>()->getDecl()->isFixed() &&
+               SCS.Second == ICK_Integral_Promotion &&
+               "only enums with fixed underlying type can promote to bool");
+        From = ImpCastExprToType(From, ToType, CK_IntegralToBoolean, VK_PRValue,
+                                 /*BasePath=*/nullptr, CCK)
+                   .get();
+      } else {
+        From = ImpCastExprToType(From, ToType, CK_IntegralCast, VK_PRValue,
+                                 /*BasePath=*/nullptr, CCK)
+                   .get();
+      }
+      break;
+
+    case ICK_Floating_Promotion:
+    case ICK_Floating_Conversion:
+      From = ImpCastExprToType(From, ToType, CK_FloatingCast, VK_PRValue,
+                               /*BasePath=*/nullptr, CCK)
+                 .get();
+      break;
+    case ICK_Floating_Integral:
+      if (ToType->isRealFloatingType())
+        From =
+            ImpCastExprToType(From, ToType, CK_IntegralToFloating, VK_PRValue,
+                              /*BasePath=*/nullptr, CCK)
+                .get();
+      else
+        From =
+            ImpCastExprToType(From, ToType, CK_FloatingToIntegral, VK_PRValue,
+                              /*BasePath=*/nullptr, CCK)
+                .get();
+      break;
+    case ICK_Identity:
+    default:
+      llvm_unreachable("Improper element standard conversion");
+    }
+  }
+
   switch (SCS.Third) {
   case ICK_Identity:
     // Nothing to do.
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index b6de06464cd6f..0fd458837163e 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -6432,7 +6432,7 @@ void InitializationSequence::InitializeFrom(Sema &S,
   // For HLSL ext vector types we allow list initialization behavior for C++
   // constructor syntax. This is accomplished by converting initialization
   // arguments an InitListExpr late.
-  if (S.getLangOpts().HLSL && DestType->isExtVectorType() &&
+  if (S.getLangOpts().HLSL && Args.size() > 1 && DestType->isExtVectorType() &&
       (SourceType.isNull() ||
        !Context.hasSameUnqualifiedType(SourceType, DestType))) {
 
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 5c6d463bb895d..f7645422348b6 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -159,6 +159,7 @@ ImplicitConversionRank clang::GetConversionRank(ImplicitConversionKind Kind) {
       ICR_C_Conversion,
       ICR_C_Conversion_Extension,
       ICR_Conversion,
+      ICR_Conversion,
   };
   static_assert(std::size(Rank) == (int)ICK_Num_Conversion_Kinds);
   return Rank[(int)Kind];
@@ -199,6 +200,7 @@ static const char *GetImplicitConversionName(ImplicitConversionKind Kind) {
       "C specific type conversion",
       "Incompatible pointer conversion",
       "Fixed point conversion",
+      "HLSL vector truncation",
   };
   static_assert(std::size(Name) == (int)ICK_Num_Conversion_Kinds);
   return Name[Kind];
@@ -209,6 +211,7 @@ static const char *GetImplicitConversionName(ImplicitConversionKind Kind) {
 void StandardConversionSequence::setAsIdentityConversion() {
   First = ICK_Identity;
   Second = ICK_Identity;
+  Element = ICK_Identity;
   Third = ICK_Identity;
   DeprecatedStringLiteralToCharPtr = false;
   QualificationIncludesObjCLifetime = false;
@@ -227,11 +230,13 @@ void StandardConversionSequence::setAsIdentityConversion() {
 /// implicit conversions.
 ImplicitConversionRank StandardConversionSequence::getRank() const {
   ImplicitConversionRank Rank = ICR_Exact_Match;
-  if  (GetConversionRank(First) > Rank)
+  if (GetConversionRank(First) > Rank)
     Rank = GetConversionRank(First);
-  if  (GetConversionRank(Second) > Rank)
+  if (GetConversionRank(Second) > Rank)
     Rank = GetConversionRank(Second);
-  if  (GetConversionRank(Third) > Rank)
+  if (GetConversionRank(Element) > Rank)
+    Rank = GetConversionRank(Element);
+  if (GetConversionRank(Third) > Rank)
     Rank = GetConversionRank(Third);
   return Rank;
 }
@@ -1828,13 +1833,86 @@ bool Sema::IsFunctionConversion(QualType FromType, QualType ToType,
   return true;
 }
 
+/// Determine whether the conversion from FromType to ToType is a valid
+/// floating point conversion.
+///
+static bool IsFloatingPointConversion(Sema &S, QualType FromType,
+                                      QualType ToType) {
+  if (!FromType->isRealFloatingType() || !ToType->isRealFloatingType())
+    return false;
+  // FIXME: disable conversions between long double, __ibm128 and __float128
+  // if their representation is different until there is back end support
+  // We of course allow this conversion if long double is really double.
+
+  // Conversions between bfloat16 and float16 are currently not supported.
+  if ((FromType->isBFloat16Type() &&
+       (ToType->isFloat16Type() || ToType->isHalfType())) ||
+      (ToType->isBFloat16Type() &&
+       (FromType->isFloat16Type() || FromType->isHalfType())))
+    return false;
+
+  // Conversions between IEEE-quad and IBM-extended semantics are not
+  // permitted.
+  const llvm::fltSemantics &FromSem = S.Context.getFloatTypeSemantics(FromType);
+  const llvm::fltSemantics &ToSem = S.Context.getFloatTypeSemantics(ToType);
+  if ((&FromSem == &llvm::APFloat::PPCDoubleDouble() &&
+       &ToSem == &llvm::APFloat::IEEEquad()) ||
+      (&FromSem == &llvm::APFloat::IEEEquad() &&
+       &ToSem == &llvm::APFloat::PPCDoubleDouble()))
+    return false;
+  return true;
+}
+
+static bool IsVectorElementConversion(Sema &S, QualType FromType,
+                                      QualType ToType,
+                                      ImplicitConversionKind &ICK, Expr *From) {
+  if (S.Context.hasSameUnqualifiedType(FromType, ToType))
+    return true;
+
+  if (S.IsFloatingPointPromotion(FromType, ToType)) {
+    ICK = ICK_Floating_Promotion;
+    return true;
+  }
+
+  if (IsFloatingPointConversion(S, FromType, ToType)) {
+    ICK = ICK_Floating_Conversion;
+    return true;
+  }
+
+  if (ToType->isBooleanType() && FromType->isArithmeticType()) {
+    ICK = ICK_Boolean_Conversion;
+    return true;
+  }
+
+  if (S.IsIntegralPromotion(From, FromType, ToType)) {
+    ICK = ICK_Integral_Promotion;
+    return true;
+  }
+
+  if (FromType->isIntegralOrUnscopedEnumerationType() &&
+      ToType->isIntegralType(S.Context)) {
+    ICK = ICK_Integral_Conversion;
+    return true;
+  }
+
+  if ((FromType->isRealFloatingType() && ToType->isIntegralType(S.Context)) ||
+      (FromType->isIntegralOrUnscopedEnumerationType() &&
+       ToType->isRealFloatingType())) {
+    ICK = ICK_Floating_Integral;
+    return true;
+  }
+
+  return false;
+}
+
 /// Determine whether the conversion from FromType to ToType is a valid
 /// vector conversion.
 ///
 /// \param ICK Will be set to the vector conversion kind, if this is a vector
 /// conversion.
 static bool IsVectorConversion(Sema &S, QualType FromType, QualType ToType,
-                               ImplicitConversionKind &ICK, Expr *From,
+                               ImplicitConversionKind &ICK,
+                               ImplicitConversionKind &ElConv, Expr *From,
                                bool InOverloadResolution, bool CStyle) {
   // We need at least one of these types to be a vector type to have a vector
   // conversion.
@@ -1847,10 +1925,28 @@ static bool IsVectorConversion(Sema &S, QualType FromType, QualType ToType,
 
   // There are no conversions between extended vector types, only identity.
   if (ToType->isExtVectorType()) {
-    // There are no conversions between extended vector types other than the
-    // identity conversion.
-    if (FromType->isExtVectorType())
+    if (FromType->isExtVectorType()) {
+      // HLSL allows implicit truncation of vector types.
+      if (S.getLangOpts().HLSL) {
+        unsigned FromElts = FromType->getAs<VectorType>()->getNumElements();
+        unsigned ToElts = ToType->getAs<VectorType>()->getNumElements();
+        if (FromElts < ToElts)
+          return false;
+        if (FromElts == ToElts)
+          ICK = ICK_Identity;
+        else
+          ICK = ICK_HLSL_Vector_Truncation;
+
+        QualType FromElTy = FromType->getAs<VectorType>()->getElementType();
+        QualType ToElTy = ToType->getAs<VectorType>()->getElementType();
+        if (S.Context.hasSameUnqualifiedType(FromElTy, ToElTy))
+          return true;
+        return IsVectorElementConversion(S, FromElTy, ToElTy, ElConv, From);
+      }
+      // There are no conversions between extended vector types other than the
+      // identity conversion.
       return false;
+    }
 
     // Vector splat from any arithmetic type to a vector.
     if (FromType->isArithmeticType()) {
@@ -2056,6 +2152,7 @@ static bool IsStandardConversion(Sema &S, Expr* From, QualType ToType,
   // conversion.
   bool IncompatibleObjC = false;
   ImplicitConversionKind SecondICK = ICK_Identity;
+  ImplicitConversionKind ElementICK = ICK_Identity;
   if (S.Context.hasSameUnqualifiedType(FromType, ToType)) {
     // The unqualified versions of the types are the same: there's no
     // conversion to do.
@@ -2094,29 +2191,7 @@ static bool IsStandardConversion(Sema &S, Expr* From, QualType ToType,
     // Complex-real conversions (C99 6.3.1.7)
     SCS.Second = ICK_Complex_Real;
     FromType = ToType.getUnqualifiedType();
-  } else if (FromType->isRealFloatingType() && ToType->isRealFloatingType()) {
-    // FIXME: disable conversions between long double, __ibm128 and __float128
-    // if their representation is different until there is back end support
-    // We of course allow this conversion if long double is really double.
-
-    // Conversions between bfloat16 and float16 are currently not supported.
-    if ((FromType->isBFloat16Type() &&
-         (ToType->isFloat16Type() || ToType->isHalfType())) ||
-        (ToType->isBFloat16Type() &&
-         (FromType->isFloat16Type() || FromType->isHalfType())))
-      return false;
-
-    // Conversions between IEEE-quad and IBM-extended semantics are not
-    // permitted.
-    const llvm::fltSemantics &FromSem =
-        S.Context.getFloatTypeSemantics(FromType);
-    const llvm::fltSemantics &ToSem = S.Context.getFloatTypeSemantics(ToType);
-    if ((&FromSem == &llvm::APFloat::PPCDoubleDouble() &&
-         &ToSem == &llvm::APFloat::IEEEquad()) ||
-        (&FromSem == &llvm::APFloat::IEEEquad() &&
-         &ToSem == &llvm::APFloat::PPCDoubleDouble()))
-      return false;
-
+  } else if (IsFloatingPointConversion(S, FromType, ToType)) {
     // Floating point conversions (C++ 4.8).
     SCS.Second = ICK_Floating_Conversion;
     FromType = ToType.getUnqualifiedType();
@@ -2143,18 +2218,18 @@ static bool IsStandardConversion(Sema &S, Expr* From, QualType ToType,
                                          InOverloadResolution, FromType)) {
     // Pointer to member conversions (4.11).
     SCS.Second = ICK_Pointer_Member;
-  } else if (IsVectorConversion(S, FromType, ToType, SecondICK, From,
-                                InOverloadResolution, CStyle)) {
+  } else if (IsVectorConversion(S, FromType, ToType, SecondICK, ElementICK,
+                                From, InOverloadResolution, CStyle)) {
     SCS.Second = SecondICK;
+    SCS.Element = ElementICK;
     FromType = ToType.getUnqualifiedType();
   } else if (!S.getLangOpts().CPlusPlus &&
              S.Context.typesAreCompatible(ToType, FromType)) {
     // Compatible conversions (Clang extension for C function overloading)
     SCS.Second = ICK_Compatible_Conversion;
     FromType = ToType.getUnqualifiedType();
-  } else if (IsTransparentUnionStandardConversion(S, From, ToType,
-                                             InOverloadResolution,
-                                             SCS, CStyle)) {
+  } else if (IsTransparentUnionStandardConversion(
+                 S, From, ToType, InOverloadResolution, SCS, CStyle)) {
     SCS.Second = ICK_TransparentUnionConversion;
     FromType = ToType;
   } else if (tryAtomicConversion(S, From, ToType, InOverloadResolution, SCS,
@@ -2449,6 +2524,11 @@ bool Sema::IsIntegralPromotion(Expr *From, QualType FromType, QualType ToType) {
     return true;
   }
 
+  // In HLSL an rvalue of integral type can be promoted to an rvalue of a larger
+  // integral type.
+  if (Context.getLangOpts().HLSL)
+    return Context.getTypeSize(FromType) < Context.getTypeSize(ToType);
+
   return false;
 }
 
@@ -5042,6 +5122,7 @@ TryReferenceInit(Sema &S, Expr *Init, QualType DeclType,
                               : (RefConv & Sema::ReferenceConversions::ObjC)
                                     ? ICK_Compatible_Conversion
                                     : ICK_Identity;
+    ICS.Standard.Element = ICK_Identity;
     // FIXME: As a speculative fix to a defect introduced by CWG2352, we rank
     // a reference binding that performs a non-top-level qualification
     // conversion as a qualification conversion, not as an identity conversion.
@@ -5968,6 +6049,7 @@ static bool CheckConvertedConstantConversions(Sema &S,
   case ICK_C_Only_Conversion:
   case ICK_Incompatible_Pointer_Conversion:
   case ICK_Fixed_Point_Conversion:
+  case ICK_HLSL_Vector_Truncation:
     return false;
 
   case ICK_Lvalue_To_Rvalue:
@@ -6245,6 +6327,7 @@ Sema::EvaluateConvertedConstantExpression(Expr *E, QualType T, APValue &Value,
 static void dropPointerConversion(StandardConversionSequence &SCS) {
   if (SCS.Second == ICK_Pointer_Conversion) {
     SCS.Second = ICK_Identity;
+    SCS.Element = ICK_Identity;
     SCS.Third = ICK_Identity;
     SCS.ToTypePtrs[2] = SCS.ToTypePtrs[1] = SCS.ToTypePtrs[0];
   }
diff --git a/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp b/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
index 7e431f7e598c4..c3fc56ac30ee9 100644
--- a/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
+++ b/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
@@ -520,7 +520,8 @@ void ExprEngine::VisitCast(const CastExpr *CastE, const Expr *Ex,
       // Various C++ casts that are not handled yet.
       case CK_ToUnion:
       case CK_MatrixCast:
-      case CK_VectorSplat: {
+      case CK_VectorSplat:
+      case CK_HLSLVectorTruncation: {
         QualType resultType = CastE->getType();
         if (CastE->isGLValue())
           resultType = getContext().getPointerType(resultType);
diff --git a/clang/test/CodeGenHLSL/BasicFeatures/standard_conversion_sequences.hlsl b/clang/test/CodeGenHLSL/BasicFeatures/standard_conversion_sequences.hlsl
new file mode 100644
index 0000000000000..06e3cc5af87e1
--- /dev/null
+++ b/clang/test/CodeGenHLSL/BasicFeatures/standard_conversion_sequences.hlsl
@@ -0,0 +1,119 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-library -x hlsl -emit-llvm -disable-llvm-passes -o - %s | FileCheck %s
+
+// CHECK-LABEL: f3_to_d4
+// CHECK: [[f3:%.*]] = alloca <3 x float>
+// CHECK: [[d4:%.*]] = alloca <4 x double>
+// CHECK: store <3 x float> <float 1.000000e+00, float 1.000000e+00, float 1.000000e+00>, ptr [[f3]]
+// CHECK: [[vecf3:%.*]] = load <3 x float>, ptr [[f3]]
+// CHECK: [[vecf4:%.*]] = shufflevector <3 x float> [[vecf3]], <3 x float> poison, <4 x i32> <i32 0, i32 1, i32 2, i32 0>
+// CHECK: [[vecd4:%.*]] = fpext <4 x float> [[vecf4]] to <4 x double>
+// CHECK: store <4 x double> [[vecd4]], ptr [[d4]]
+void f3_to_d4() {
+  vector<float,3> f3 = 1.0;
+  vector<double,4> d4 = f3.xyzx;
+}
+
+// CHECK-LABEL: f3_to_f2
+// CHECK: [[f3:%.*]] = alloca <3 x float>
+// CHECK: [[f2:%.*]] = alloca <2 x float>
+// CHECK: store <3 x float> <float 2.000000e+00, float 2.000000e+00, float 2.000000e+00>, ptr [[f3]]
+// CHECK: [[vecf3:%.*]] = load <3 x float>, ptr [[f3]]
+// CHECK: [[vecf2:%.*]] = shufflevector <3 x float> [[vecf3]], <3 x float> poison, <2 x i32> <i32 0, i32 1>
+// CHECK: store <2 x float> [[vecf2]], ptr [[f2]]
+void f3_to_f2() {
+  vector<float,3> f3 = 2.0;
+  vector<float,2> f2 = f3;
+}
+
+// CHECK-LABEL: d4_to_f2
+// CHECK: [[d4:%.*]] = alloca <4 x double>
+// CHECK: [[f2:%.*]] = alloca <2 x float>
+// CHECK: store <4 x double> <double 3.000000e+00, double 3.000000e+00, double 3.000000e+00, double 3.000000e+00>, ptr [[d4]]
+// CHECK: [[vecd4:%.*]] = load <4 x double>, ptr [[d4]]
+// CHECK: [[vecd2:%.*]] = shufflevector <4 x double> [[vecd4]], <4 x double> poison, <2 x i32> <i32 0, i32 1>
+// CHECK: [[vecf2:%.*]] = fptrunc <2 x double> [[vecd2]] to <2 x float>
+// CHECK: store <2 x float> [[vecf2]], ptr [[f2]]
+void d4_to_f2() {
+  vector<double,4> d4 = 3.0;
+  vector<float,2> f2 = d4;
+}
+
+// CHECK-LABEL: f2_to_i2
+// CHECK: [[f2:%.*]] = alloca <2 x float>
+// CHECK: [[i2:%.*]] = alloca <2 x i32>
+// CHECK: store <2 x float> <float 4.000000e+00, float 4.000000e+00>, ptr [[f2]]
+// CHECK: [[vecf2:%.*]] = load <2 x float>, ptr [[f2]]
+// CHECK: [[veci2:%.*]] = fptosi <2 x float> [[vecf2]] to <2 x i32>
+// CHECK: store <2 x i32> [[veci2]], ptr [[i2]]
+void f2_to_i2() {
+  vector<float,2> f2 = 4.0;
+  vector<int,2> i2 = f2;
+}
+
+// CHECK-LABEL: d4_to_i2
+// CHECK: [[f4:%.*]] = alloca <4 x double>
+// CHECK: [[i2:%.*]] = alloca <2 x i32>
+// CHECK: store <4 x double> <double 5.000000e+00, double 5.000000e+00, double 5.000000e+00, double 5.000000e+00>, ptr [[d4]]
+// CHECK: [[vecd4:%.*]] = load <4 x double>, ptr [[d4]]
+// CHECK: [[vecd2:%.*]] = shufflevector <4 x double> [[vecd4]], <4 x double> poison, <2 x i32> <i32 0, i32 1>
+// CHECK: [[veci2]] = fptosi <2 x double> [[vecd2]] to <2 x i32>
+// CHECK: store <2 x i32> [[veci2]], ptr [[i2]]
+void d4_to_i2() {
+  vector<double,4> d4 = 5.0;
+  vector<int,2> i2 = d4;
+}
+
+// CHECK-LABEL: d4_to_l4
+// CHECK: [[d4:%.*]] = alloca <4 x double>
+// CHECK: [[l4:%.*]] = alloca <4 x i64>
+// CHECK: store <4 x double> <double 6.000000e+00, double 6.000000e+00, double 6.000000e+00, double 6.000000e+00>, ptr [[d4]]
+// CHECK: [[vecd4:%.*]] = load <4 x double>, ptr [[d4]]
+// CHECK: [[vecl4:%.*]] = fptosi <4 x double> [[vecd4]] to <4 x i64>
+// CHECK: store <4 x i64> [[vecl4]], ptr [[l4]]
+void d4_to_l4() {
+  vector<double,4> d4 = 6.0;
+  vector<long,4> l4 = d4;
+}
+
+
+// CHECK-LABEL: l4_to_i2
+// CHECK: [[l4:%.*]] = alloca <4 x i64>
+// CHECK: [[i2:%.*]] = alloca <2 x i32>
+// CHECK: store <4 x i64> <i64 7, i64 7, i64 7, i64 7>, ptr [[l4]]
+// CHECK: [[vecl4:%.*]] = load <4 x i64>, ptr [[l4]]
+// CHECK: [[vecl2:%.*]] = shufflevector <4 x i64> [[vecl4]], <4 x i64> poison, <2 x i32> <i32 0, i32 1>
+// CHECK: [[veci2:%.*]] = trunc <2 x i64> [[vecl2]] to <2 x i32>
+// CHECK: store <2 x i32> [[veci2]], ptr [[i2]]
+void l4_to_i2() {
+  vector<long, 4> l4 = 7;
+  vector<int,2> i2 = l4;
+}
+
+// CHECK-LABEL: i2_to_b2
+// CHECK: [[l2:%.*]] = alloca <2 x i32>
+// CHECK: [[b2:%.*]] = alloca i8
+// CHECK: store <2 x i32> <i32 8, i32 8>, ptr [[i2]]
+// CHECK: [[veci2:%.*]] = load <2 x i32>, ptr [[i2]]
+// CHECK: [[vecb2:%.*]] = icmp ne <2 x i32> [[veci2]], zeroinitializer
+// CHECK: [[vecb8:%.*]] = shufflevector <2 x i1> [[vecb2]], <2 x i1> poison, <8 x i32> <i32 0, i32 1, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+// CHECK: [[i8:%.*]] = bitcast <8 x i1> [[vecb8]] to i8
+// CHECK: store i8 [[i8]], ptr [[b2]]
+void i2_to_b2() {
+  vector<int, 2> i2 = 8;
+  vector<bool, 2> b2 = i2;
+}
+
+// CHECK-LABEL: d4_to_b2
+// CHECK: [[d4:%.*]] = alloca <4 x double>
+// CHECK: [[b2:%.*]] = alloca i8
+// CHECK: store <4 x double> <double 9.000000e+00, double 9.000000e+00, double 9.000000e+00, double 9.000000e+00>, ptr [[d4]]
+// CHECK: [[vecd4:%.*]] = load <4 x double>, ptr [[d4]]
+// CHECK: [[vecd2:%.*]] = shufflevector <4 x double> [[vecd4]], <4 x double> poison, <2 x i32> <i32 0, i32 1>
+// CHECK: [[vecb2:%.*]] = fcmp une <2 x double> [[vecd2]], zeroinitializer
+// CHECK: [[vecb8:%.*]] = shufflevector <2 x i1> [[vecb2]], <2 x i1> poison, <8 x i32> <i32 0, i32 1, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+// CHECK: [[i8:%.*]] = bitcast <8 x i1> [[vecb8]] to i8
+// CHECK: store i8 [[i8]], ptr [[b2]]
+void d4_to_b2() {
+  vector<double,4> d4 = 9.0;
+  vector<bool, 2> b2 = d4;
+}
diff --git a/clang/test/CodeGenHLSL/builtins/ScalarSwizzles.hlsl b/clang/test/CodeGenHLSL/builtins/ScalarSwizzles.hlsl
index d560d4b945fea..36f71f6860c06 100644
--- a/clang/test/CodeGenHLSL/builtins/ScalarSwizzles.hlsl
+++ b/clang/test/CodeGenHLSL/builtins/ScalarSwizzles.hlsl
@@ -85,7 +85,9 @@ float4 FillTwoPointFiveFloat(){
 // CHECK: [[vec1Ptr:%.*]] = alloca <1 x float>, align 4
 // CHECK: store <1 x float> <float 5.000000e-01>, ptr [[vec1Ptr]], align 4
 // CHECK: [[vec1:%.*]] = load <1 x float>, ptr [[vec1Ptr]], align 4
-// CHECK: [[vec1Ret:%.*]] = shufflevector <1 x float> [[vec1]], <1 x float> poison, <1 x i32> zeroinitializer
+// CHECK: [[el0:%.*]] = extractelement <1 x float> [[vec1]], i32 0
+// CHECK: [[vec1Splat:%.*]] = insertelement <1 x float> poison, float [[el0]], i64 0
+// CHECK: [[vec1Ret:%.*]] = shufflevector <1 x float> [[vec1Splat]], <1 x float> poison, <1 x i32> zeroinitializer
 // CHECK: ret <1 x float> [[vec1Ret]]
 vector<float, 1> FillOneHalfFloat(){
   return .5f.r;
@@ -113,32 +115,13 @@ float2 HowManyFloats(float V) {
 // up nicely too.
 
 // CHECK-LABEL: AllRighty
-// CHECK: [[XTmp:%.*]] = alloca <1 x double>, align 8
-// CHECK: [[YTmp:%.*]] = alloca <1 x double>, align 8
-// CHECK: [[ZTmp:%.*]] = alloca <1 x double>, align 8
-
-// CHECK: store <1 x double> <double 1.000000e+00>, ptr [[XTmp]], align 8
-// CHECK: [[XVec:%.*]] = load <1 x double>, ptr [[XTmp]], align 8
-// CHECK: [[XVec3:%.*]] = shufflevector <1 x double> [[XVec]], <1 x double> poison, <3 x i32> zeroinitializer
-// CHECK: [[XVal:%.*]] = extractelement <3 x double> [[XVec3]], i32 0
-// CHECK: [[XValF:%.*]] = fptrunc double [[XVal]] to float
-// CHECK: [[Vec3F1:%.*]] = insertelement <3 x float> poison, float [[XValF]], i32 0
-
-// CHECK: store <1 x double> <double 1.000000e+00>, ptr [[YTmp]], align 8
-// CHECK: [[YVec:%.*]] = load <1 x double>, ptr [[YTmp]], align 8
-// CHECK: [[YVec3:%.*]] = shufflevector <1 x double> [[YVec]], <1 x double> poison, <3 x i32> zeroinitializer
-// CHECK: [[YVal:%.*]] = extractelement <3 x double> [[YVec3]], i32 1
-// CHECK: [[YValF:%.*]] = fptrunc double [[YVal]] to float
-// CHECK: [[Vec3F2:%.*]] = insertelement <3 x float> [[Vec3F1]], float [[YValF]], i32 1
-
-// CHECK: store <1 x double> <double 1.000000e+00>, ptr [[ZTmp]], align 8
-// CHECK: [[ZVec:%.*]] = load <1 x double>, ptr [[ZTmp]], align 8
-// CHECK: [[ZVec3:%.*]] = shufflevector <1 x double> [[ZVec]], <1 x double> poison, <3 x i32> zeroinitializer
-// CHECK: [[ZVal:%.*]] = extractelement <3 x double> [[ZVec3]], i32 2
-// CHECK: [[ZValF:%.*]] = fptrunc double [[ZVal]] to float
-// CHECK: [[Vec3F3:%.*]] = insertelement <3 x float> [[Vec3F2]], float [[ZValF]], i32 2
-
-// ret <3 x float> [[Vec3F3]]
+// CHECK: [[Tmp:%.*]] = alloca <1 x double>, align 8
+// CHECK: store <1 x double> <double 1.000000e+00>, ptr [[Tmp]], align 8
+// CHECK: [[vec1:%.*]] = load <1 x double>, ptr [[Tmp]], align 8
+// CHECK: [[vec3:%.*]] = shufflevector <1 x double> [[vec1]], <1 x double> poison, <3 x i32> zeroinitializer
+// CHECK: [[vec3f:%.*]] = fptrunc <3 x double> [[vec3]] to <3 x float>
+// CHECK: ret <3 x float> [[vec3f]]
+
 float3 AllRighty() {
   return 1..rrr;
 }
diff --git a/clang/test/CodeGenHLSL/builtins/sqrt.hlsl b/clang/test/CodeGenHLSL/builtins/sqrt.hlsl
index 776269395a662..2c2a09617cf86 100644
--- a/clang/test/CodeGenHLSL/builtins/sqrt.hlsl
+++ b/clang/test/CodeGenHLSL/builtins/sqrt.hlsl
@@ -1,9 +1,6 @@
 // RUN: %clang_cc1 -std=hlsl2021 -finclude-default-header -x hlsl -triple \
 // RUN:   dxil-pc-shadermodel6.2-library %s -fnative-half-type \
 // RUN:   -emit-llvm -disable-llvm-passes -o - | FileCheck %s
-// RUN: %clang_cc1 -std=hlsl2021 -finclude-default-header -x hlsl -triple \
-// RUN:   dxil-pc-shadermodel6.2-library %s -emit-llvm -disable-llvm-passes \
-// RUN:   -o - | FileCheck %s --check-prefix=NO_HALF
 
 using hlsl::sqrt;
 
@@ -30,5 +27,3 @@ half sqrt_h(half x)
 
 // CHECK: define noundef half @"?sqrt_h@@YA$f16@$f16@@Z"(
 // CHECK: call half @llvm.sqrt.f16(half %0)
-// NO_HALF: define noundef float @"?sqrt_h@@YA$halff@$halff@@Z"(
-// NO_HALF: call float @llvm.sqrt.f32(float %0)
diff --git a/clang/test/SemaHLSL/BuiltIns/vector-constructors-erros.hlsl b/clang/test/SemaHLSL/BuiltIns/vector-constructors-erros.hlsl
index 73b5a192793e0..7f6bdc7e67836 100644
--- a/clang/test/SemaHLSL/BuiltIns/vector-constructors-erros.hlsl
+++ b/clang/test/SemaHLSL/BuiltIns/vector-constructors-erros.hlsl
@@ -18,5 +18,5 @@ void entry() {
   S s;
   float2 GettingStrange = float2(s, s); // expected-error{{no viable conversion from 'S' to 'float'}} expected-error{{no viable conversion from 'S' to 'float'}}
   S2 s2;
-  float2 EvenStranger = float2(s2); // expected-error{{no viable conversion from 'S2' to 'float'}} expected-error{{too few elements in vector initialization (expected 2 elements, have 1)}}
+  float2 EvenStranger = float2(s2); // expected-error{{cannot convert 'S2' to 'float2' (vector of 2 'float' values) without a conversion operator}}
 }
diff --git a/clang/test/SemaHLSL/OverloadResolutionBugs.hlsl b/clang/test/SemaHLSL/OverloadResolutionBugs.hlsl
new file mode 100644
index 0000000000000..135d6cf335c13
--- /dev/null
+++ b/clang/test/SemaHLSL/OverloadResolutionBugs.hlsl
@@ -0,0 +1,39 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-library -o - -fsyntax-only %s -verify
+// XFAIL: *
+
+// https://github.com/llvm/llvm-project/issues/81047
+
+// expected-no-diagnostics
+void Fn3(double2 D);
+void Fn3(float2 F);
+
+void Call3(half2 H) {
+  Fn3(H);
+}
+
+void Fn5(double2 D);
+
+void Call5(half2 H) {
+  Fn5(H);
+}
+
+void Fn4(int64_t2 L);
+void Fn4(int2 I);
+
+void Call4(int16_t H) {
+  Fn4(H);
+}
+
+// https://github.com/llvm/llvm-project/issues/81049
+
+// RUN: %clang_cc1 -std=hlsl2021 -finclude-default-header -x hlsl -triple \
+// RUN:   dxil-pc-shadermodel6.2-library %s -emit-llvm -disable-llvm-passes \
+// RUN:   -o - | FileCheck %s --check-prefix=NO_HALF
+
+half sqrt_h(half x)
+{
+  return sqrt(x);
+}
+
+// NO_HALF: define noundef float @"?sqrt_h@@YA$halff@$halff@@Z"(
+// NO_HALF: call float @llvm.sqrt.f32(float %0)
diff --git a/clang/test/SemaHLSL/Types/BuiltinVector/ScalarSwizzles.hlsl b/clang/test/SemaHLSL/Types/BuiltinVector/ScalarSwizzles.hlsl
index 4ffbcacf3f30c..a2e9a5f865ece 100644
--- a/clang/test/SemaHLSL/Types/BuiltinVector/ScalarSwizzles.hlsl
+++ b/clang/test/SemaHLSL/Types/BuiltinVector/ScalarSwizzles.hlsl
@@ -80,7 +80,7 @@ float4 FillTwoPointFiveFloat(){
 // initialze the returned vector.
 
 // CHECK-LABEL: FillOneHalfFloat
-// CHECK: InitListExpr {{.*}} 'vector<float, 1>':'float __attribute__((ext_vector_type(1)))'
+// CHECK: ImplicitCastExpr {{.*}} 'vector<float, 1>':'float __attribute__((ext_vector_type(1)))' <VectorSplat>
 // CHECK-NEXT: ExtVectorElementExpr {{.*}} 'float' r
 // CHECK-NEXT: ImplicitCastExpr {{.*}} 'float __attribute__((ext_vector_type(1)))' <VectorSplat>
 // CHECK-NEXT: FloatingLiteral {{.*}} 'float' 5.000000e-01
@@ -113,31 +113,10 @@ int64_t4 HooBoy() {
 // list with float truncation casts.
 
 // CHECK-LABEL: AllRighty
-// CHECK: InitListExpr {{.*}} 'float3':'float __attribute__((ext_vector_type(3)))'
-
-// Vector element 0:
-// CHECK-NEXT: ImplicitCastExpr {{.*}} 'float' <FloatingCast>
-// CHECK-NEXT: ArraySubscriptExpr {{.*}} 'double'
-// CHECK-NEXT: ExtVectorElementExpr {{.*}} 'double __attribute__((ext_vector_type(3)))' rrr
-// CHECK-NEXT: ImplicitCastExpr {{.*}} 'double __attribute__((ext_vector_type(1)))' <VectorSplat>
-// CHECK-NEXT: FloatingLiteral {{.*}} 'double' 1.000000e+00
-// CHECK-NEXT: IntegerLiteral {{.*}} 'int' 0
-
-// Vector element 1:
-// CHECK-NEXT: ImplicitCastExpr {{.*}} 'float' <FloatingCast>
-// CHECK-NEXT: ArraySubscriptExpr {{.*}} 'double'
-// CHECK-NEXT: ExtVectorElementExpr {{.*}} 'double __attribute__((ext_vector_type(3)))' rrr
-// CHECK-NEXT: ImplicitCastExpr {{.*}} 'double __attribute__((ext_vector_type(1)))' <VectorSplat>
-// CHECK-NEXT: FloatingLiteral {{.*}} 'double' 1.000000e+00
-// CHECK-NEXT: IntegerLiteral {{.*}} 'int' 1
-
-// Vector element 2:
-// CHECK-NEXT: ImplicitCastExpr {{.*}} 'float' <FloatingCast>
-// CHECK-NEXT: ArraySubscriptExpr {{.*}} 'double'
+// CHECK: ImplicitCastExpr {{.*}} 'float3':'float __attribute__((ext_vector_type(3)))' <FloatingCast>
 // CHECK-NEXT: ExtVectorElementExpr {{.*}} 'double __attribute__((ext_vector_type(3)))' rrr
 // CHECK-NEXT: ImplicitCastExpr {{.*}} 'double __attribute__((ext_vector_type(1)))' <VectorSplat>
 // CHECK-NEXT: FloatingLiteral {{.*}} 'double' 1.000000e+00
-// CHECK-NEXT: IntegerLiteral {{.*}} 'int' 2
 
 float3 AllRighty() {
   return 1..rrr;
diff --git a/clang/test/SemaHLSL/VectorOverloadResolution.hlsl b/clang/test/SemaHLSL/VectorOverloadResolution.hlsl
new file mode 100644
index 0000000000000..e07391f803f89
--- /dev/null
+++ b/clang/test/SemaHLSL/VectorOverloadResolution.hlsl
@@ -0,0 +1,30 @@
+// RUN: %clang_cc1 -triple dxil-unknown-shadermodel6.6-library -S -fnative-half-type -finclude-default-header -o - -ast-dump %s | FileCheck %s
+void Fn(double2 D);
+void Fn(half2 H);
+
+// CHECK: FunctionDecl {{.*}} Call 'void (float2)'
+// CHECK: CallExpr {{.*}}'void'
+// CHECK-NEXT: ImplicitCastExpr {{.*}} 'void (*)(double2)' <FunctionToPointerDecay>
+// CHECK-NEXT: DeclRefExpr {{.*}}'void (double2)' lvalue Function {{.*}} 'Fn' 'void (double2)'
+// CHECK-NEXT: ImplicitCastExpr {{.*}} 'double2':'double __attribute__((ext_vector_type(2)))' <FloatingCast>
+// CHECK-NEXT: ImplicitCastExpr {{.*}} 'float2':'float __attribute__((ext_vector_type(2)))' <LValueToRValue>
+// CHECK-NEXT: DeclRefExpr {{.*}} 'float2':'float __attribute__((ext_vector_type(2)))' lvalue ParmVar {{.*}} 'F' 'float2':'float __attribute__((ext_vector_type(2)))'
+
+void Call(float2 F) {
+  Fn(F);
+}
+
+void Fn2(int64_t2 L);
+void Fn2(int16_t2 S);
+
+// CHECK: FunctionDecl {{.*}} Call2 'void (int2)'
+// CHECK: CallExpr {{.*}} 'void'
+// CHECK-NEXT: ImplicitCastExpr {{.*}} 'void (*)(int64_t2)' <FunctionToPointerDecay>
+// CHECK-NEXT: DeclRefExpr {{.*}} 'void (int64_t2)' lvalue Function {{.*}} 'Fn2' 'void (int64_t2)'
+// CHECK-NEXT: ImplicitCastExpr {{.*}} 'int64_t2':'long __attribute__((ext_vector_type(2)))' <IntegralCast>
+// CHECK-NEXT: ImplicitCastExpr {{.*}} 'int2':'int __attribute__((ext_vector_type(2)))' <LValueToRValue>
+// CHECK-NEXT: DeclRefExpr {{.*}} 'int2':'int __attribute__((ext_vector_type(2)))' lvalue ParmVar {{.*}} 'I' 'int2':'int __attribute__((ext_vector_type(2)))'
+
+void Call2(int2 I) {
+  Fn2(I);
+}
diff --git a/clang/test/SemaHLSL/standard_conversion_sequences.hlsl b/clang/test/SemaHLSL/standard_conversion_sequences.hlsl
new file mode 100644
index 0000000000000..a0d398105f15d
--- /dev/null
+++ b/clang/test/SemaHLSL/standard_conversion_sequences.hlsl
@@ -0,0 +1,92 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-library -Wconversion -verify -o - %s
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-library -Wno-conversion -DNO_ERR -ast-dump %s | FileCheck %s
+
+void test() {
+  
+  // CHECK: VarDecl {{.*}} used f3 'vector<float, 3>':'float __attribute__((ext_vector_type(3)))' cinit
+  // CHECK-NEXt: ImplicitCastExpr {{.*}} 'vector<float, 3>':'float __attribute__((ext_vector_type(3)))' <VectorSplat>
+  // CHECK-NEXt: ImplicitCastExpr {{.*}} 'float' <FloatingCast>
+  // CHECK-NEXt: FloatingLiteral {{.*}} 'double' 1.000000e+00
+  vector<float,3> f3 = 1.0; // No warning for splatting to a vector from a literal.
+
+
+  // CHECK: VarDecl {{.*}} used d4 'vector<double, 4>':'double __attribute__((ext_vector_type(4)))' cinit
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<double, 4>':'double __attribute__((ext_vector_type(4)))' <FloatingCast>
+  // CHECK-NEXT: ExtVectorElementExpr {{.*}} 'float __attribute__((ext_vector_type(4)))' xyzx
+  // CHECK-NEXT: DeclRefExpr {{.*}} 'vector<float, 3>':'float __attribute__((ext_vector_type(3)))' lvalue Var {{.*}} 'f3' 'vector<float, 3>':'float __attribute__((ext_vector_type(3)))'
+  vector<double,4> d4 = f3.xyzx; // No warnings for promotion or explicit extension.
+
+  // CHECK: VarDecl {{.*}} used f2 'vector<float, 2>':'float __attribute__((ext_vector_type(2)))' cinit
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'float __attribute__((ext_vector_type(2)))' <HLSLVectorTruncation>
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<float, 3>':'float __attribute__((ext_vector_type(3)))' <LValueToRValue>
+  // CHECK-NEXT: DeclRefExpr {{.*}} 'vector<float, 3>':'float __attribute__((ext_vector_type(3)))' lvalue Var {{.*}} 'f3' 'vector<float, 3>':'float __attribute__((ext_vector_type(3)))'
+  // expected-warning@#f2{{implicit conversion truncates vector: 'vector<float, 3>' (vector of 3 'float' values) to 'float __attribute__((ext_vector_type(2)))' (vector of 2 'float' values)}}
+  vector<float,2> f2 = f3; // #f2
+
+  // CHECK: VarDecl {{.*}} f2_2 'vector<float, 2>':'float __attribute__((ext_vector_type(2)))' cinit
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<float, 2>':'float __attribute__((ext_vector_type(2)))' <FloatingCast>
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'double __attribute__((ext_vector_type(2)))' <HLSLVectorTruncation>
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<double, 4>':'double __attribute__((ext_vector_type(4)))' <LValueToRValue>
+  // CHECK-NEXT: DeclRefExpr {{.*}} 'vector<double, 4>':'double __attribute__((ext_vector_type(4)))' lvalue Var {{.*}} 'd4' 'vector<double, 4>':'double __attribute__((ext_vector_type(4)))'
+  // expected-warning@#f2_2{{implicit conversion truncates vector: 'vector<double, 4>' (vector of 4 'double' values) to 'vector<float, 2>' (vector of 2 'float' values)}}
+  // expected-warning@#f2_2{{implicit conversion loses floating-point precision: 'vector<double, 4>' (vector of 4 'double' values) to 'vector<float, 2>' (vector of 2 'float' values)}}
+  vector<float,2> f2_2 = d4; // #f2_2
+
+  // CHECK: VarDecl {{.*}} i2 'vector<int, 2>':'int __attribute__((ext_vector_type(2)))' cinit
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<int, 2>':'int __attribute__((ext_vector_type(2)))' <FloatingToIntegral>
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<float, 2>':'float __attribute__((ext_vector_type(2)))' <LValueToRValue>
+  // CHECK-NEXT: DeclRefExpr {{.*}} 'vector<float, 2>':'float __attribute__((ext_vector_type(2)))' lvalue Var {{.*}} 'f2' 'vector<float, 2>':'float __attribute__((ext_vector_type(2)))'
+  // expected-warning@#i2{{mplicit conversion turns floating-point number into integer: 'vector<float, 2>' (vector of 2 'float' values) to 'vector<int, 2>' (vector of 2 'int' values)}}
+  vector<int,2> i2 = f2; // #i2
+  
+  // CHECK: VarDecl {{.*}} i2_2 'vector<int, 2>':'int __attribute__((ext_vector_type(2)))' cinit
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<int, 2>':'int __attribute__((ext_vector_type(2)))' <FloatingToIntegral>
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'double __attribute__((ext_vector_type(2)))' <HLSLVectorTruncation>
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<double, 4>':'double __attribute__((ext_vector_type(4)))' <LValueToRValue>
+  // CHECK-NEXT: DeclRefExpr {{.*}} 'vector<double, 4>':'double __attribute__((ext_vector_type(4)))' lvalue Var {{.*}} 'd4' 'vector<double, 4>':'double __attribute__((ext_vector_type(4)))'
+  // expected-warning@#i2_2{{implicit conversion truncates vector: 'vector<double, 4>' (vector of 4 'double' values) to 'vector<int, 2>' (vector of 2 'int' values)}}
+  // expected-warning@#i2_2{{implicit conversion turns floating-point number into integer: 'vector<double, 4>' (vector of 4 'double' values) to 'vector<int, 2>' (vector of 2 'int' values)}}
+  vector<int,2> i2_2 = d4; // #i2_2
+
+
+  // CHECK: VarDecl {{.*}} used i64_4 'vector<long, 4>':'long __attribute__((ext_vector_type(4)))' cinit
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<long, 4>':'long __attribute__((ext_vector_type(4)))' <FloatingToIntegral>
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<double, 4>':'double __attribute__((ext_vector_type(4)))' <LValueToRValue>
+  // CHECK-NEXT: DeclRefExpr {{.*}} 'vector<double, 4>':'double __attribute__((ext_vector_type(4)))' lvalue Var {{.*}} 'd4' 'vector<double, 4>':'double __attribute__((ext_vector_type(4)))'
+  // expected-warning@#i64_4{{implicit conversion turns floating-point number into integer: 'vector<double, 4>' (vector of 4 'double' values) to 'vector<long, 4>' (vector of 4 'long' values)}}
+  vector<long,4> i64_4 = d4; // #i64_4
+
+  // CHECK: VarDecl {{.*}} used i2_3 'vector<int, 2>':'int __attribute__((ext_vector_type(2)))' cinit
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<int, 2>':'int __attribute__((ext_vector_type(2)))' <IntegralCast>
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'long __attribute__((ext_vector_type(2)))' <HLSLVectorTruncation>
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<long, 4>':'long __attribute__((ext_vector_type(4)))' <LValueToRValue>
+  // CHECK-NEXT: DeclRefExpr {{.*}} 'vector<long, 4>':'long __attribute__((ext_vector_type(4)))' lvalue Var {{.*}} 'i64_4' 'vector<long, 4>':'long __attribute__((ext_vector_type(4)))'
+  // expected-warning@#i2_3{{implicit conversion loses integer precision: 'vector<long, 4>' (vector of 4 'long' values) to 'vector<int, 2>' (vector of 2 'int' values)}}
+  // expected-warning@#i2_3{{implicit conversion truncates vector: 'vector<long, 4>' (vector of 4 'long' values) to 'vector<int, 2>' (vector of 2 'int' values)}}
+  vector<int,2> i2_3 = i64_4; // #i2_3
+
+  //CHECK: VarDecl {{.*}} b2 'vector<bool, 2>':'bool __attribute__((ext_vector_type(2)))' cinit
+  //CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<bool, 2>':'bool __attribute__((ext_vector_type(2)))' <IntegralToBoolean>
+  //CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<int, 2>':'int __attribute__((ext_vector_type(2)))' <LValueToRValue>
+  //CHECK-NEXT: DeclRefExpr {{.*}} 'vector<int, 2>':'int __attribute__((ext_vector_type(2)))' lvalue Var {{.*}} 'i2_3' 'vector<int, 2>':'int __attribute__((ext_vector_type(2)))'
+  vector<bool, 2> b2 = i2_3; // No warning for integer to bool conversion.
+
+  // CHECK: VarDecl {{.*}} b2_2 'vector<bool, 2>':'bool __attribute__((ext_vector_type(2)))' cinit
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<bool, 2>':'bool __attribute__((ext_vector_type(2)))' <FloatingToBoolean>
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'double __attribute__((ext_vector_type(2)))' <HLSLVectorTruncation>
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} 'vector<double, 4>':'double __attribute__((ext_vector_type(4)))' <LValueToRValue>
+  // CHECK-NEXT: DeclRefExpr {{.*}} 'vector<double, 4>':'double __attribute__((ext_vector_type(4)))' lvalue Var {{.*}} 'd4' 'vector<double, 4>':'double __attribute__((ext_vector_type(4)))'
+  // expected-warning@#b2_2{{implicit conversion truncates vector: 'vector<double, 4>' (vector of 4 'double' values) to 'vector<bool, 2>' (vector of 2 'bool' values)}}
+  // expected-warning@#b2_2{{implicit conversion turns floating-point number into integer: 'vector<double, 4>' (vector of 4 'double' values) to 'vector<bool, 2>' (vector of 2 'bool' values)}}
+  vector<bool, 2> b2_2 = d4; // #b2_2
+}
+
+#ifndef NO_ERR
+
+void illegal() {
+  // vector extension is illegal
+  vector<float,3> f3 = 1.0;
+  vector<float,4> f4 = f3; // expected-error{{cannot initialize a variable of type 'vector<[...], 4>' with an lvalue of type 'vector<[...], 3>'}}
+}
+
+#endif