Improved based on the review

Author: YexuanXiao

clang/include/clang/AST/ASTContext.h

@@ -258,7 +258,6 @@ class ASTContext : public RefCountedBase<ASTContext> {
   mutable llvm::FoldingSet<BitIntType> BitIntTypes;
   mutable llvm::ContextualFoldingSet<DependentBitIntType, ASTContext &>
       DependentBitIntTypes;
-  mutable llvm::FoldingSet<PredefinedSugarType> PredefinedSugarTypes;
   mutable llvm::FoldingSet<BTFTagAttributedType> BTFTagAttributedTypes;
   llvm::FoldingSet<HLSLAttributedResourceType> HLSLAttributedResourceTypes;
   llvm::FoldingSet<HLSLInlineSpirvType> HLSLInlineSpirvTypes;
@@ -278,6 +277,11 @@ class ASTContext : public RefCountedBase<ASTContext> {
   mutable llvm::ContextualFoldingSet<ArrayParameterType, ASTContext &>
       ArrayParameterTypes;
 
+  /// Store the unique Type corresponding to each Kind.
+  mutable std::array<Type *,
+                     llvm::to_underlying(PredefinedSugarType::Kind::Max)>
+      PredefinedSugarTypes;
+
   /// The set of nested name specifiers.
   ///
   /// This set is managed by the NestedNameSpecifier class.
@@ -1993,12 +1997,6 @@ class ASTContext : public RefCountedBase<ASTContext> {
                                                         bool IsDependent,
                                                         QualType Canon) const;
 
-  // The core language uses these types as the result types of some expressions,
-  // which are typically standard integer types and consistent with it's
-  // typedefs (if any).
-  QualType SizeType;       // __size_t
-  QualType SignedSizeType; // __signed_size_t
-  QualType PtrdiffType;    // __ptrdiff_t
 public:
   /// Return the unique reference to the type for the specified TagDecl
   /// (struct/union/class/enum) decl.

clang/include/clang/AST/Type.h

@@ -2266,7 +2266,10 @@ class alignas(TypeAlignment) Type : public ExtQualsTypeCommonBase {
     SignedSizeT,
 
     /// The "ptrdiff_t" type.
-    PtrdiffT
+    PtrdiffT,
+
+    // Indicates how many items the enum has.
+    Max
   };
 
   class PresefinedSugarTypeBitfields {
@@ -8060,7 +8063,7 @@ class DependentBitIntType final : public Type, public llvm::FoldingSetNode {
   }
 };
 
-class PredefinedSugarType final : public Type, public llvm::FoldingSetNode {
+class PredefinedSugarType final : public Type {
 public:
   friend class ASTContext;
   using Kind = PredefinedSugarKind;
@@ -8089,14 +8092,6 @@ class PredefinedSugarType final : public Type, public llvm::FoldingSetNode {
   static bool classof(const Type *T) {
     return T->getTypeClass() == PredefinedSugar;
   }
-
-  void Profile(llvm::FoldingSetNodeID &ID) const {
-    Profile(ID, llvm::to_underlying(getKind()));
-  }
-
-  static void Profile(llvm::FoldingSetNodeID &ID, unsigned KD) {
-    ID.AddInteger(KD);
-  }
 };
 
 /// A qualifier set is used to build a set of qualifiers.

clang/lib/AST/ASTContext.cpp

@@ -1516,16 +1516,6 @@ void ASTContext::InitBuiltinTypes(const TargetInfo &Target,
     MSGuidTagDecl = buildImplicitRecord("_GUID");
     getTranslationUnitDecl()->addDecl(MSGuidTagDecl);
   }
-
-  // size_t (C99TC3 6.5.3.4), signed size_t (C++23 5.13.2) and
-  // ptrdiff_t (C99TC3 6.5.6) Although these types are not built-in, they are
-  // part of the core language and are widely used.
-  // Using PredefinedSugarType makes these types as named sugar types rather
-  // than standard integer types, enabling better hints and diagnostics.
-  using Kind = PredefinedSugarType::Kind;
-  SizeType = getPredefinedSugarType(Kind::SizeT);
-  SignedSizeType = getPredefinedSugarType(Kind::SignedSizeT);
-  PtrdiffType = getPredefinedSugarType(Kind::PtrdiffT);
 }
 
 DiagnosticsEngine &ASTContext::getDiagnostics() const {
@@ -5232,24 +5222,27 @@ QualType ASTContext::getDependentBitIntType(bool IsUnsigned,
 
 QualType
 ASTContext::getPredefinedSugarType(PredefinedSugarType::Kind KD) const {
-  llvm::FoldingSetNodeID ID;
-  PredefinedSugarType::Profile(ID, llvm::to_underlying(KD));
 
-  void *InsertPos = nullptr;
-  if (PredefinedSugarType *Existing =
-          PredefinedSugarTypes.FindNodeOrInsertPos(ID, InsertPos))
-    return QualType(Existing, 0);
+  auto Target = PredefinedSugarTypes[llvm::to_underlying(KD)];
+  if (Target != nullptr)
+    return QualType(Target, 0);
 
   using Kind = PredefinedSugarType::Kind;
 
   auto getCanonicalType = [](const ASTContext &Ctx, Kind KDI) -> QualType {
     switch (KDI) {
+      // size_t (C99TC3 6.5.3.4), signed size_t (C++23 5.13.2) and
+      // ptrdiff_t (C99TC3 6.5.6) Although these types are not built-in, they
+      // are part of the core language and are widely used. Using
+      // PredefinedSugarType makes these types as named sugar types rather than
+      // standard integer types, enabling better hints and diagnostics.
     case Kind::SizeT:
       return Ctx.getFromTargetType(Ctx.Target->getSizeType());
     case Kind::SignedSizeT:
       return Ctx.getFromTargetType(Ctx.Target->getSignedSizeType());
     case Kind::PtrdiffT:
       return Ctx.getFromTargetType(Ctx.Target->getPtrDiffType(LangAS::Default));
+    case Kind::Max:;
     }
     llvm_unreachable("unexpected kind");
   };
@@ -5258,7 +5251,7 @@ ASTContext::getPredefinedSugarType(PredefinedSugarType::Kind KD) const {
       PredefinedSugarType(KD, &Idents.get(PredefinedSugarType::getName(KD)),
                           getCanonicalType(*this, static_cast<Kind>(KD)));
   Types.push_back(New);
-  PredefinedSugarTypes.InsertNode(New, InsertPos);
+  Target = New;
   return QualType(New, 0);
 }
 
@@ -6842,19 +6835,25 @@ QualType ASTContext::getTagDeclType(const TagDecl *Decl) const {
 /// getSizeType - Return the unique type for "size_t" (C99 7.17), the result
 /// of the sizeof operator (C99 6.5.3.4p4). The value is target dependent and
 /// needs to agree with the definition in <stddef.h>.
-QualType ASTContext::getSizeType() const { return SizeType; }
+QualType ASTContext::getSizeType() const {
+  return getPredefinedSugarType(PredefinedSugarType::Kind::SizeT);
+}
 
 CanQualType ASTContext::getCanonicalSizeType() const {
   return getFromTargetType(Target->getSizeType());
 }
 
 /// Return the unique signed counterpart of the integer type
 /// corresponding to size_t.
-QualType ASTContext::getSignedSizeType() const { return SignedSizeType; }
+QualType ASTContext::getSignedSizeType() const {
+  return getPredefinedSugarType(PredefinedSugarType::Kind::SignedSizeT);
+}
 
 /// getPointerDiffType - Return the unique type for "ptrdiff_t" (C99 7.17)
 /// defined in <stddef.h>. Pointer - pointer requires this (C99 6.5.6p9).
-QualType ASTContext::getPointerDiffType() const { return PtrdiffType; }
+QualType ASTContext::getPointerDiffType() const {
+  return getPredefinedSugarType(PredefinedSugarType::Kind::PtrdiffT);
+}
 
 /// Return the unique unsigned counterpart of "ptrdiff_t"
 /// integer type. The standard (C11 7.21.6.1p7) refers to this type

clang/lib/AST/FormatString.cpp

@@ -362,6 +362,8 @@ static bool namedTypeToLengthModifierKind(ASTContext &Ctx, QualType QT,
     case Kind::PtrdiffT:
       K = LengthModifier::AsPtrDiff;
       return true;
+    case Kind::Max:
+      llvm_unreachable("unexpected kind");
     }
   }
   return false;

clang/lib/AST/Type.cpp

@@ -5631,6 +5631,7 @@ StringRef PredefinedSugarType::getName(Kind KD) {
     return "__signed_size_t";
   case Kind::PtrdiffT:
     return "__ptrdiff_t";
+  case Kind::Max:;
   }
   llvm_unreachable("unexpected kind");
 }

clang/lib/Sema/TreeTransform.h

@@ -1278,8 +1278,6 @@ class TreeTransform {
   QualType RebuildDependentBitIntType(bool IsUnsigned, Expr *NumBitsExpr,
                                       SourceLocation Loc);
 
-  QualType RebuildPredefinedSugarType(PredefinedSugarType::Kind K);
-
   /// Build a new template name given a nested name specifier, a flag
   /// indicating whether the "template" keyword was provided, and the template
   /// that the template name refers to.
@@ -7253,16 +7251,7 @@ QualType TreeTransform<Derived>::TransformDependentBitIntType(
 template <typename Derived>
 QualType TreeTransform<Derived>::TransformPredefinedSugarType(
     TypeLocBuilder &TLB, PredefinedSugarTypeLoc TL) {
-  const PredefinedSugarType *EIT = TL.getTypePtr();
-  QualType Result = TL.getType();
-
-  if (getDerived().AlwaysRebuild()) {
-    Result = getDerived().RebuildPredefinedSugarType(EIT->getKind());
-  }
-
-  PredefinedSugarTypeLoc NewTL = TLB.push<PredefinedSugarTypeLoc>(Result);
-  NewTL.setNameLoc(TL.getNameLoc());
-  return Result;
+  llvm_unreachable("This type does not need to be transformed.");
 }
 
   /// Simple iterator that traverses the template arguments in a
@@ -17446,12 +17435,6 @@ QualType TreeTransform<Derived>::RebuildDependentBitIntType(
   return SemaRef.BuildBitIntType(IsUnsigned, NumBitsExpr, Loc);
 }
 
-template <typename Derived>
-QualType TreeTransform<Derived>::RebuildPredefinedSugarType(
-    PredefinedSugarType::Kind K) {
-  return SemaRef.Context.getPredefinedSugarType(K);
-}
-
 template<typename Derived>
 TemplateName
 TreeTransform<Derived>::RebuildTemplateName(CXXScopeSpec &SS,