[HLSL] Vector standard conversions (#71098)

HLSL supports vector truncation and element conversions as part of
standard conversion sequences. The vector truncation conversion is a C++
second conversion in the conversion sequence. If a vector truncation is
in a conversion sequence an element conversion may occur after it before
the standard C++ third conversion.

Vector element conversions can be boolean conversions, floating point or
integral conversions or promotions.

[HLSL Draft
Specification](https://microsoft.github.io/hlsl-specs/specs/hlsl.pdf)

---------

Co-authored-by: Aaron Ballman <aaron@aaronballman.com>

13 files changed, 289 insertions, 42 deletions

diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 8b10e28..cc04071 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 0100101..fcf8f65 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 4a2f3ca..59a7fe8 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 22f55fe..d0d6202 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 9ddf0e7..176a7e0 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 a054f38..75286dc 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -1225,6 +1225,7 @@ public:
     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 aa805f29..13526de 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 2e123e8..22f2c47e 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 afe2673..8e76338 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 f2b8913..801ce7b 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 b6de064..0fd4588 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 5c6d463..f764542 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;
 }
@@ -1829,12 +1834,85 @@ bool Sema::IsFunctionConversion(QualType FromType, QualType ToType,
 }
 
 /// 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 7e431f7..c3fc56a 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);