diff --git a/clang/include/clang/APINotes/APINotesManager.h b/clang/include/clang/APINotes/APINotesManager.h
index 98592438e90eab..05d7930d3a2e7f 100644
--- a/clang/include/clang/APINotes/APINotesManager.h
+++ b/clang/include/clang/APINotes/APINotesManager.h
@@ -10,6 +10,7 @@
 #define LLVM_CLANG_APINOTES_APINOTESMANAGER_H
 
 #include "clang/Basic/SourceLocation.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/PointerUnion.h"
@@ -41,7 +42,7 @@ class APINotesReader;
 /// external API notes files that correspond to a given header. Its primary
 /// operation is \c findAPINotes(), which finds the API notes reader that
 /// provides information about the declarations at that location.
-class APINotesManager {
+class CLANG_ABI APINotesManager {
   using ReaderEntry = llvm::PointerUnion<DirectoryEntryRef, APINotesReader *>;
 
   SourceManager &SM;
diff --git a/clang/include/clang/APINotes/APINotesReader.h b/clang/include/clang/APINotes/APINotesReader.h
index baf63340640242..58ee2857c7930f 100644
--- a/clang/include/clang/APINotes/APINotesReader.h
+++ b/clang/include/clang/APINotes/APINotesReader.h
@@ -16,6 +16,7 @@
 #define LLVM_CLANG_APINOTES_READER_H
 
 #include "clang/APINotes/Types.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/VersionTuple.h"
 #include <memory>
@@ -25,7 +26,7 @@ namespace api_notes {
 
 /// A class that reads API notes data from a binary file that was written by
 /// the \c APINotesWriter.
-class APINotesReader {
+class CLANG_ABI APINotesReader {
   class Implementation;
   std::unique_ptr<Implementation> Implementation;
 
diff --git a/clang/include/clang/APINotes/APINotesWriter.h b/clang/include/clang/APINotes/APINotesWriter.h
index 3cc16c3d959faf..b8b45a89dcfc8b 100644
--- a/clang/include/clang/APINotes/APINotesWriter.h
+++ b/clang/include/clang/APINotes/APINotesWriter.h
@@ -16,6 +16,7 @@
 #define LLVM_CLANG_APINOTES_WRITER_H
 
 #include "clang/APINotes/Types.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/VersionTuple.h"
 #include "llvm/Support/raw_ostream.h"
@@ -29,7 +30,7 @@ namespace api_notes {
 
 /// A class that writes API notes data to a binary representation that can be
 /// read by the \c APINotesReader.
-class APINotesWriter {
+class CLANG_ABI APINotesWriter {
   class Implementation;
   std::unique_ptr<Implementation> Implementation;
 
diff --git a/clang/include/clang/APINotes/APINotesYAMLCompiler.h b/clang/include/clang/APINotes/APINotesYAMLCompiler.h
index 9c24ed85b6a124..3954cf347e8244 100644
--- a/clang/include/clang/APINotes/APINotesYAMLCompiler.h
+++ b/clang/include/clang/APINotes/APINotesYAMLCompiler.h
@@ -9,6 +9,7 @@
 #ifndef LLVM_CLANG_APINOTES_APINOTESYAMLCOMPILER_H
 #define LLVM_CLANG_APINOTES_APINOTESYAMLCOMPILER_H
 
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/raw_ostream.h"
@@ -22,10 +23,10 @@ namespace api_notes {
 /// Parses the APINotes YAML content and writes the representation back to the
 /// specified stream.  This provides a means of testing the YAML processing of
 /// the APINotes format.
-bool parseAndDumpAPINotes(llvm::StringRef YI, llvm::raw_ostream &OS);
+CLANG_ABI bool parseAndDumpAPINotes(llvm::StringRef YI, llvm::raw_ostream &OS);
 
 /// Converts API notes from YAML format to binary format.
-bool compileAPINotes(llvm::StringRef YAMLInput, const FileEntry *SourceFile,
+CLANG_ABI bool compileAPINotes(llvm::StringRef YAMLInput, const FileEntry *SourceFile,
                      llvm::raw_ostream &OS,
                      llvm::SourceMgr::DiagHandlerTy DiagHandler = nullptr,
                      void *DiagHandlerCtxt = nullptr);
diff --git a/clang/include/clang/APINotes/Types.h b/clang/include/clang/APINotes/Types.h
index 89889910d1a073..574406586c4674 100644
--- a/clang/include/clang/APINotes/Types.h
+++ b/clang/include/clang/APINotes/Types.h
@@ -10,6 +10,7 @@
 #define LLVM_CLANG_APINOTES_TYPES_H
 
 #include "clang/Basic/Specifiers.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringRef.h"
 #include <climits>
@@ -49,7 +50,7 @@ enum class SwiftNewTypeKind {
 /// Describes API notes data for any entity.
 ///
 /// This is used as the base of all API notes.
-class CommonEntityInfo {
+class CLANG_ABI CommonEntityInfo {
 public:
   /// Message to use when this entity is unavailable.
   std::string UnavailableMsg;
@@ -132,7 +133,7 @@ inline bool operator!=(const CommonEntityInfo &LHS,
 }
 
 /// Describes API notes for types.
-class CommonTypeInfo : public CommonEntityInfo {
+class CLANG_ABI CommonTypeInfo : public CommonEntityInfo {
   /// The Swift type to which a given type is bridged.
   ///
   /// Reflects the swift_bridge attribute.
@@ -194,7 +195,7 @@ inline bool operator!=(const CommonTypeInfo &LHS, const CommonTypeInfo &RHS) {
 
 /// Describes API notes data for an Objective-C class or protocol or a C++
 /// namespace.
-class ContextInfo : public CommonTypeInfo {
+class CLANG_ABI ContextInfo : public CommonTypeInfo {
   /// Whether this class has a default nullability.
   LLVM_PREFERRED_TYPE(bool)
   unsigned HasDefaultNullability : 1;
@@ -301,7 +302,7 @@ inline bool operator!=(const ContextInfo &LHS, const ContextInfo &RHS) {
 }
 
 /// API notes for a variable/property.
-class VariableInfo : public CommonEntityInfo {
+class CLANG_ABI VariableInfo : public CommonEntityInfo {
   /// Whether this property has been audited for nullability.
   LLVM_PREFERRED_TYPE(bool)
   unsigned NullabilityAudited : 1;
@@ -358,7 +359,7 @@ inline bool operator!=(const VariableInfo &LHS, const VariableInfo &RHS) {
 }
 
 /// Describes API notes data for an Objective-C property.
-class ObjCPropertyInfo : public VariableInfo {
+class CLANG_ABI ObjCPropertyInfo : public VariableInfo {
   LLVM_PREFERRED_TYPE(bool)
   unsigned SwiftImportAsAccessorsSpecified : 1;
   LLVM_PREFERRED_TYPE(bool)
@@ -416,7 +417,7 @@ inline bool operator!=(const ObjCPropertyInfo &LHS,
 }
 
 /// Describes a function or method parameter.
-class ParamInfo : public VariableInfo {
+class CLANG_ABI ParamInfo : public VariableInfo {
   /// Whether noescape was specified.
   LLVM_PREFERRED_TYPE(bool)
   unsigned NoEscapeSpecified : 1;
@@ -486,7 +487,7 @@ inline bool operator!=(const ParamInfo &LHS, const ParamInfo &RHS) {
 }
 
 /// API notes for a function or method.
-class FunctionInfo : public CommonEntityInfo {
+class CLANG_ABI FunctionInfo : public CommonEntityInfo {
 private:
   static constexpr const uint64_t NullabilityKindMask = 0x3;
   static constexpr const unsigned NullabilityKindSize = 2;
@@ -606,7 +607,7 @@ inline bool operator!=(const FunctionInfo &LHS, const FunctionInfo &RHS) {
 }
 
 /// Describes API notes data for an Objective-C method.
-class ObjCMethodInfo : public FunctionInfo {
+class CLANG_ABI ObjCMethodInfo : public FunctionInfo {
 public:
   /// Whether this is a designated initializer of its class.
   LLVM_PREFERRED_TYPE(bool)
@@ -675,7 +676,7 @@ class EnumConstantInfo : public CommonEntityInfo {
 };
 
 /// Describes API notes data for a tag.
-class TagInfo : public CommonTypeInfo {
+class CLANG_ABI TagInfo : public CommonTypeInfo {
   LLVM_PREFERRED_TYPE(bool)
   unsigned HasFlagEnum : 1;
   LLVM_PREFERRED_TYPE(bool)
@@ -765,7 +766,7 @@ inline bool operator!=(const TagInfo &LHS, const TagInfo &RHS) {
 }
 
 /// Describes API notes data for a typedef.
-class TypedefInfo : public CommonTypeInfo {
+class CLANG_ABI TypedefInfo : public CommonTypeInfo {
 public:
   std::optional<SwiftNewTypeKind> SwiftWrapper;
 
diff --git a/clang/include/clang/ARCMigrate/ARCMT.h b/clang/include/clang/ARCMigrate/ARCMT.h
index 2b950e3d2cc2bf..dc078101e371ff 100644
--- a/clang/include/clang/ARCMigrate/ARCMT.h
+++ b/clang/include/clang/ARCMigrate/ARCMT.h
@@ -12,6 +12,7 @@
 #include "clang/ARCMigrate/FileRemapper.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Frontend/CompilerInvocation.h"
+#include "clang/Support/Compiler.h"
 
 namespace clang {
   class ASTContext;
@@ -37,7 +38,7 @@ namespace arcmt {
 /// the pre-migration ARC diagnostics.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool
+CLANG_ABI bool
 checkForManualIssues(CompilerInvocation &CI, const FrontendInputFile &Input,
                      std::shared_ptr<PCHContainerOperations> PCHContainerOps,
                      DiagnosticConsumer *DiagClient,
@@ -48,7 +49,7 @@ checkForManualIssues(CompilerInvocation &CI, const FrontendInputFile &Input,
 /// applies automatic modifications to source files to conform to ARC.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool
+CLANG_ABI bool
 applyTransformations(CompilerInvocation &origCI,
                      const FrontendInputFile &Input,
                      std::shared_ptr<PCHContainerOperations> PCHContainerOps,
@@ -65,7 +66,7 @@ applyTransformations(CompilerInvocation &origCI,
 /// the pre-migration ARC diagnostics.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool migrateWithTemporaryFiles(
+CLANG_ABI bool migrateWithTemporaryFiles(
     CompilerInvocation &origCI, const FrontendInputFile &Input,
     std::shared_ptr<PCHContainerOperations> PCHContainerOps,
     DiagnosticConsumer *DiagClient, StringRef outputDir,
@@ -75,7 +76,7 @@ bool migrateWithTemporaryFiles(
 /// migrateWithTemporaryFiles produced.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool getFileRemappings(std::vector<std::pair<std::string,std::string> > &remap,
+CLANG_ABI bool getFileRemappings(std::vector<std::pair<std::string,std::string> > &remap,
                        StringRef outputDir,
                        DiagnosticConsumer *DiagClient);
 
@@ -83,17 +84,17 @@ bool getFileRemappings(std::vector<std::pair<std::string,std::string> > &remap,
 /// info.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool getFileRemappingsFromFileList(
+CLANG_ABI bool getFileRemappingsFromFileList(
                         std::vector<std::pair<std::string,std::string> > &remap,
                         ArrayRef<StringRef> remapFiles,
                         DiagnosticConsumer *DiagClient);
 
 typedef void (*TransformFn)(MigrationPass &pass);
 
-std::vector<TransformFn> getAllTransformations(LangOptions::GCMode OrigGCMode,
+CLANG_ABI std::vector<TransformFn> getAllTransformations(LangOptions::GCMode OrigGCMode,
                                                bool NoFinalizeRemoval);
 
-class MigrationProcess {
+class CLANG_ABI MigrationProcess {
   CompilerInvocation OrigCI;
   std::shared_ptr<PCHContainerOperations> PCHContainerOps;
   DiagnosticConsumer *DiagClient;
@@ -107,7 +108,7 @@ class MigrationProcess {
                    DiagnosticConsumer *diagClient,
                    StringRef outputDir = StringRef());
 
-  class RewriteListener {
+  class CLANG_ABI RewriteListener {
   public:
     virtual ~RewriteListener();
 
diff --git a/clang/include/clang/ARCMigrate/ARCMTActions.h b/clang/include/clang/ARCMigrate/ARCMTActions.h
index 714f4b33db446b..50c6142078f5c8 100644
--- a/clang/include/clang/ARCMigrate/ARCMTActions.h
+++ b/clang/include/clang/ARCMigrate/ARCMTActions.h
@@ -11,12 +11,13 @@
 
 #include "clang/ARCMigrate/FileRemapper.h"
 #include "clang/Frontend/FrontendAction.h"
+#include "clang/Support/Compiler.h"
 #include <memory>
 
 namespace clang {
 namespace arcmt {
 
-class CheckAction : public WrapperFrontendAction {
+class CLANG_ABI CheckAction : public WrapperFrontendAction {
 protected:
   bool BeginInvocation(CompilerInstance &CI) override;
 
@@ -24,7 +25,7 @@ class CheckAction : public WrapperFrontendAction {
   CheckAction(std::unique_ptr<FrontendAction> WrappedAction);
 };
 
-class ModifyAction : public WrapperFrontendAction {
+class CLANG_ABI ModifyAction : public WrapperFrontendAction {
 protected:
   bool BeginInvocation(CompilerInstance &CI) override;
 
@@ -32,7 +33,7 @@ class ModifyAction : public WrapperFrontendAction {
   ModifyAction(std::unique_ptr<FrontendAction> WrappedAction);
 };
 
-class MigrateSourceAction : public ASTFrontendAction {
+class CLANG_ABI MigrateSourceAction : public ASTFrontendAction {
   FileRemapper Remapper;
 protected:
   bool BeginInvocation(CompilerInstance &CI) override;
@@ -40,7 +41,7 @@ class MigrateSourceAction : public ASTFrontendAction {
                                                  StringRef InFile) override;
 };
 
-class MigrateAction : public WrapperFrontendAction {
+class CLANG_ABI MigrateAction : public WrapperFrontendAction {
   std::string MigrateDir;
   std::string PlistOut;
   bool EmitPremigrationARCErrors;
@@ -55,7 +56,7 @@ class MigrateAction : public WrapperFrontendAction {
 };
 
 /// Migrates to modern ObjC syntax.
-class ObjCMigrateAction : public WrapperFrontendAction {
+class CLANG_ABI ObjCMigrateAction : public WrapperFrontendAction {
   std::string MigrateDir;
   unsigned    ObjCMigAction;
   FileRemapper Remapper;
diff --git a/clang/include/clang/ARCMigrate/FileRemapper.h b/clang/include/clang/ARCMigrate/FileRemapper.h
index afcee363516a21..3c9f706a75cf38 100644
--- a/clang/include/clang/ARCMigrate/FileRemapper.h
+++ b/clang/include/clang/ARCMigrate/FileRemapper.h
@@ -11,6 +11,7 @@
 
 #include "clang/Basic/FileEntry.h"
 #include "clang/Basic/LLVM.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
@@ -29,7 +30,7 @@ namespace clang {
 
 namespace arcmt {
 
-class FileRemapper {
+class CLANG_ABI FileRemapper {
   // FIXME: Reuse the same FileManager for multiple ASTContexts.
   std::unique_ptr<FileManager> FileMgr;
 
diff --git a/clang/include/clang/AST/APNumericStorage.h b/clang/include/clang/AST/APNumericStorage.h
index 95eddbcd86e839..ae634d46dfea2b 100644
--- a/clang/include/clang/AST/APNumericStorage.h
+++ b/clang/include/clang/AST/APNumericStorage.h
@@ -9,6 +9,7 @@
 #ifndef LLVM_CLANG_AST_APNUMERICSTORAGE_H
 #define LLVM_CLANG_AST_APNUMERICSTORAGE_H
 
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APInt.h"
 
@@ -23,7 +24,7 @@ class ASTContext;
 /// to allocate IntegerLiteral/FloatingLiteral nodes the memory associated with
 /// the APFloat/APInt values will never get freed. APNumericStorage uses
 /// ASTContext's allocator for memory allocation.
-class APNumericStorage {
+class CLANG_ABI APNumericStorage {
   union {
     uint64_t VAL;   ///< Used to store the <= 64 bits integer value.
     uint64_t *pVal; ///< Used to store the >64 bits integer value.
diff --git a/clang/include/clang/AST/APValue.h b/clang/include/clang/AST/APValue.h
index c4206b73b11562..fc6baf92a90202 100644
--- a/clang/include/clang/AST/APValue.h
+++ b/clang/include/clang/AST/APValue.h
@@ -14,6 +14,7 @@
 #define LLVM_CLANG_AST_APVALUE_H
 
 #include "clang/Basic/LLVM.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/APFixedPoint.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APSInt.h"
@@ -41,7 +42,7 @@ template <typename T> class BasicReaderBase;
   class QualType;
 
 /// Symbolic representation of typeid(T) for some type T.
-class TypeInfoLValue {
+class CLANG_ABI TypeInfoLValue {
   const Type *T;
 
 public:
@@ -119,7 +120,7 @@ namespace clang {
 /// APValue - This class implements a discriminated union of [uninitialized]
 /// [APSInt] [APFloat], [Complex APSInt] [Complex APFloat], [Expr + Offset],
 /// [Vector: N * APValue], [Array: N * APValue]
-class APValue {
+class CLANG_ABI APValue {
   typedef llvm::APFixedPoint APFixedPoint;
   typedef llvm::APSInt APSInt;
   typedef llvm::APFloat APFloat;
@@ -143,7 +144,7 @@ class APValue {
     AddrLabelDiff
   };
 
-  class LValueBase {
+  class CLANG_ABI LValueBase {
     typedef llvm::PointerUnion<const ValueDecl *, const Expr *, TypeInfoLValue,
                                DynamicAllocLValue>
         PtrTy;
@@ -179,11 +180,11 @@ class APValue {
 
     QualType getType() const;
 
-    friend bool operator==(const LValueBase &LHS, const LValueBase &RHS);
+    friend CLANG_ABI bool operator==(const LValueBase &LHS, const LValueBase &RHS);
     friend bool operator!=(const LValueBase &LHS, const LValueBase &RHS) {
       return !(LHS == RHS);
     }
-    friend llvm::hash_code hash_value(const LValueBase &Base);
+    friend CLANG_ABI llvm::hash_code hash_value(const LValueBase &Base);
     friend struct llvm::DenseMapInfo<LValueBase>;
 
   private:
@@ -205,7 +206,7 @@ class APValue {
   typedef llvm::PointerIntPair<const Decl *, 1, bool> BaseOrMemberType;
 
   /// A non-discriminated union of a base, field, or array index.
-  class LValuePathEntry {
+  class CLANG_ABI LValuePathEntry {
     static_assert(sizeof(uintptr_t) <= sizeof(uint64_t),
                   "pointer doesn't fit in 64 bits?");
     uint64_t Value;
@@ -237,7 +238,7 @@ class APValue {
       return llvm::hash_value(A.Value);
     }
   };
-  class LValuePathSerializationHelper {
+  class CLANG_ABI LValuePathSerializationHelper {
     const void *Ty;
 
   public:
@@ -274,7 +275,7 @@ class APValue {
     Vec &operator=(const Vec &) = delete;
     ~Vec() { delete[] Elts; }
   };
-  struct Arr {
+  struct CLANG_ABI Arr {
     APValue *Elts;
     unsigned NumElts, ArrSize;
     Arr(unsigned NumElts, unsigned ArrSize);
@@ -282,7 +283,7 @@ class APValue {
     Arr &operator=(const Arr &) = delete;
     ~Arr();
   };
-  struct StructData {
+  struct CLANG_ABI StructData {
     APValue *Elts;
     unsigned NumBases;
     unsigned NumFields;
@@ -291,7 +292,7 @@ class APValue {
     StructData &operator=(const StructData &) = delete;
     ~StructData();
   };
-  struct UnionData {
+  struct CLANG_ABI UnionData {
     const FieldDecl *Field;
     APValue *Value;
     UnionData();
@@ -702,7 +703,7 @@ class APValue {
 } // end namespace clang.
 
 namespace llvm {
-template<> struct DenseMapInfo<clang::APValue::LValueBase> {
+template<> struct CLANG_ABI DenseMapInfo<clang::APValue::LValueBase> {
   static clang::APValue::LValueBase getEmptyKey();
   static clang::APValue::LValueBase getTombstoneKey();
   static unsigned getHashValue(const clang::APValue::LValueBase &Base);
diff --git a/clang/include/clang/AST/ASTConcept.h b/clang/include/clang/AST/ASTConcept.h
index 00500e214f4ce6..59b0a8e9d96a9d 100644
--- a/clang/include/clang/AST/ASTConcept.h
+++ b/clang/include/clang/AST/ASTConcept.h
@@ -18,6 +18,7 @@
 #include "clang/AST/NestedNameSpecifier.h"
 #include "clang/AST/TemplateBase.h"
 #include "clang/Basic/SourceLocation.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/PointerUnion.h"
 #include "llvm/ADT/SmallVector.h"
@@ -32,7 +33,7 @@ struct PrintingPolicy;
 
 /// The result of a constraint satisfaction check, containing the necessary
 /// information to diagnose an unsatisfied constraint.
-class ConstraintSatisfaction : public llvm::FoldingSetNode {
+class CLANG_ABI ConstraintSatisfaction : public llvm::FoldingSetNode {
   // The template-like entity that 'owns' the constraint checked here (can be a
   // constrained entity or a concept).
   const NamedDecl *ConstraintOwner = nullptr;
@@ -84,7 +85,7 @@ using UnsatisfiedConstraintRecord =
 /// necessary information to diagnose an unsatisfied constraint.
 ///
 /// This is safe to store in an AST node, as opposed to ConstraintSatisfaction.
-struct ASTConstraintSatisfaction final :
+struct CLANG_ABI ASTConstraintSatisfaction final :
     llvm::TrailingObjects<ASTConstraintSatisfaction,
                           UnsatisfiedConstraintRecord> {
   std::size_t NumRecords;
@@ -121,7 +122,7 @@ struct ASTConstraintSatisfaction final :
 ///
 ///   template <std::derives_from<Expr> T> void dump();
 ///             ~~~~~~~~~~~~~~~~~~~~~~~ (in TemplateTypeParmDecl)
-class ConceptReference {
+class CLANG_ABI ConceptReference {
   // \brief The optional nested name specifier used when naming the concept.
   NestedNameSpecifierLoc NestedNameSpec;
 
diff --git a/clang/include/clang/AST/ASTConsumer.h b/clang/include/clang/AST/ASTConsumer.h
index 447f2592d23595..735c7e549f5cac 100644
--- a/clang/include/clang/AST/ASTConsumer.h
+++ b/clang/include/clang/AST/ASTConsumer.h
@@ -13,6 +13,7 @@
 #ifndef LLVM_CLANG_AST_ASTCONSUMER_H
 #define LLVM_CLANG_AST_ASTCONSUMER_H
 
+#include "clang/Support/Compiler.h"
 namespace clang {
   class ASTContext;
   class CXXMethodDecl;
@@ -31,7 +32,7 @@ namespace clang {
 /// ASTCons...
[truncated]

diff --git a/clang/include/clang/APINotes/APINotesManager.h b/clang/include/clang/APINotes/APINotesManager.h
index 98592438e90eab..05d7930d3a2e7f 100644
--- a/clang/include/clang/APINotes/APINotesManager.h
+++ b/clang/include/clang/APINotes/APINotesManager.h
@@ -10,6 +10,7 @@
 #define LLVM_CLANG_APINOTES_APINOTESMANAGER_H
 
 #include "clang/Basic/SourceLocation.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/PointerUnion.h"
@@ -41,7 +42,7 @@ class APINotesReader;
 /// external API notes files that correspond to a given header. Its primary
 /// operation is \c findAPINotes(), which finds the API notes reader that
 /// provides information about the declarations at that location.
-class APINotesManager {
+class CLANG_ABI APINotesManager {
   using ReaderEntry = llvm::PointerUnion<DirectoryEntryRef, APINotesReader *>;
 
   SourceManager &SM;
diff --git a/clang/include/clang/APINotes/APINotesReader.h b/clang/include/clang/APINotes/APINotesReader.h
index baf63340640242..58ee2857c7930f 100644
--- a/clang/include/clang/APINotes/APINotesReader.h
+++ b/clang/include/clang/APINotes/APINotesReader.h
@@ -16,6 +16,7 @@
 #define LLVM_CLANG_APINOTES_READER_H
 
 #include "clang/APINotes/Types.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/VersionTuple.h"
 #include <memory>
@@ -25,7 +26,7 @@ namespace api_notes {
 
 /// A class that reads API notes data from a binary file that was written by
 /// the \c APINotesWriter.
-class APINotesReader {
+class CLANG_ABI APINotesReader {
   class Implementation;
   std::unique_ptr<Implementation> Implementation;
 
diff --git a/clang/include/clang/APINotes/APINotesWriter.h b/clang/include/clang/APINotes/APINotesWriter.h
index 3cc16c3d959faf..b8b45a89dcfc8b 100644
--- a/clang/include/clang/APINotes/APINotesWriter.h
+++ b/clang/include/clang/APINotes/APINotesWriter.h
@@ -16,6 +16,7 @@
 #define LLVM_CLANG_APINOTES_WRITER_H
 
 #include "clang/APINotes/Types.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/VersionTuple.h"
 #include "llvm/Support/raw_ostream.h"
@@ -29,7 +30,7 @@ namespace api_notes {
 
 /// A class that writes API notes data to a binary representation that can be
 /// read by the \c APINotesReader.
-class APINotesWriter {
+class CLANG_ABI APINotesWriter {
   class Implementation;
   std::unique_ptr<Implementation> Implementation;
 
diff --git a/clang/include/clang/APINotes/APINotesYAMLCompiler.h b/clang/include/clang/APINotes/APINotesYAMLCompiler.h
index 9c24ed85b6a124..3954cf347e8244 100644
--- a/clang/include/clang/APINotes/APINotesYAMLCompiler.h
+++ b/clang/include/clang/APINotes/APINotesYAMLCompiler.h
@@ -9,6 +9,7 @@
 #ifndef LLVM_CLANG_APINOTES_APINOTESYAMLCOMPILER_H
 #define LLVM_CLANG_APINOTES_APINOTESYAMLCOMPILER_H
 
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/raw_ostream.h"
@@ -22,10 +23,10 @@ namespace api_notes {
 /// Parses the APINotes YAML content and writes the representation back to the
 /// specified stream.  This provides a means of testing the YAML processing of
 /// the APINotes format.
-bool parseAndDumpAPINotes(llvm::StringRef YI, llvm::raw_ostream &OS);
+CLANG_ABI bool parseAndDumpAPINotes(llvm::StringRef YI, llvm::raw_ostream &OS);
 
 /// Converts API notes from YAML format to binary format.
-bool compileAPINotes(llvm::StringRef YAMLInput, const FileEntry *SourceFile,
+CLANG_ABI bool compileAPINotes(llvm::StringRef YAMLInput, const FileEntry *SourceFile,
                      llvm::raw_ostream &OS,
                      llvm::SourceMgr::DiagHandlerTy DiagHandler = nullptr,
                      void *DiagHandlerCtxt = nullptr);
diff --git a/clang/include/clang/APINotes/Types.h b/clang/include/clang/APINotes/Types.h
index 89889910d1a073..574406586c4674 100644
--- a/clang/include/clang/APINotes/Types.h
+++ b/clang/include/clang/APINotes/Types.h
@@ -10,6 +10,7 @@
 #define LLVM_CLANG_APINOTES_TYPES_H
 
 #include "clang/Basic/Specifiers.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringRef.h"
 #include <climits>
@@ -49,7 +50,7 @@ enum class SwiftNewTypeKind {
 /// Describes API notes data for any entity.
 ///
 /// This is used as the base of all API notes.
-class CommonEntityInfo {
+class CLANG_ABI CommonEntityInfo {
 public:
   /// Message to use when this entity is unavailable.
   std::string UnavailableMsg;
@@ -132,7 +133,7 @@ inline bool operator!=(const CommonEntityInfo &LHS,
 }
 
 /// Describes API notes for types.
-class CommonTypeInfo : public CommonEntityInfo {
+class CLANG_ABI CommonTypeInfo : public CommonEntityInfo {
   /// The Swift type to which a given type is bridged.
   ///
   /// Reflects the swift_bridge attribute.
@@ -194,7 +195,7 @@ inline bool operator!=(const CommonTypeInfo &LHS, const CommonTypeInfo &RHS) {
 
 /// Describes API notes data for an Objective-C class or protocol or a C++
 /// namespace.
-class ContextInfo : public CommonTypeInfo {
+class CLANG_ABI ContextInfo : public CommonTypeInfo {
   /// Whether this class has a default nullability.
   LLVM_PREFERRED_TYPE(bool)
   unsigned HasDefaultNullability : 1;
@@ -301,7 +302,7 @@ inline bool operator!=(const ContextInfo &LHS, const ContextInfo &RHS) {
 }
 
 /// API notes for a variable/property.
-class VariableInfo : public CommonEntityInfo {
+class CLANG_ABI VariableInfo : public CommonEntityInfo {
   /// Whether this property has been audited for nullability.
   LLVM_PREFERRED_TYPE(bool)
   unsigned NullabilityAudited : 1;
@@ -358,7 +359,7 @@ inline bool operator!=(const VariableInfo &LHS, const VariableInfo &RHS) {
 }
 
 /// Describes API notes data for an Objective-C property.
-class ObjCPropertyInfo : public VariableInfo {
+class CLANG_ABI ObjCPropertyInfo : public VariableInfo {
   LLVM_PREFERRED_TYPE(bool)
   unsigned SwiftImportAsAccessorsSpecified : 1;
   LLVM_PREFERRED_TYPE(bool)
@@ -416,7 +417,7 @@ inline bool operator!=(const ObjCPropertyInfo &LHS,
 }
 
 /// Describes a function or method parameter.
-class ParamInfo : public VariableInfo {
+class CLANG_ABI ParamInfo : public VariableInfo {
   /// Whether noescape was specified.
   LLVM_PREFERRED_TYPE(bool)
   unsigned NoEscapeSpecified : 1;
@@ -486,7 +487,7 @@ inline bool operator!=(const ParamInfo &LHS, const ParamInfo &RHS) {
 }
 
 /// API notes for a function or method.
-class FunctionInfo : public CommonEntityInfo {
+class CLANG_ABI FunctionInfo : public CommonEntityInfo {
 private:
   static constexpr const uint64_t NullabilityKindMask = 0x3;
   static constexpr const unsigned NullabilityKindSize = 2;
@@ -606,7 +607,7 @@ inline bool operator!=(const FunctionInfo &LHS, const FunctionInfo &RHS) {
 }
 
 /// Describes API notes data for an Objective-C method.
-class ObjCMethodInfo : public FunctionInfo {
+class CLANG_ABI ObjCMethodInfo : public FunctionInfo {
 public:
   /// Whether this is a designated initializer of its class.
   LLVM_PREFERRED_TYPE(bool)
@@ -675,7 +676,7 @@ class EnumConstantInfo : public CommonEntityInfo {
 };
 
 /// Describes API notes data for a tag.
-class TagInfo : public CommonTypeInfo {
+class CLANG_ABI TagInfo : public CommonTypeInfo {
   LLVM_PREFERRED_TYPE(bool)
   unsigned HasFlagEnum : 1;
   LLVM_PREFERRED_TYPE(bool)
@@ -765,7 +766,7 @@ inline bool operator!=(const TagInfo &LHS, const TagInfo &RHS) {
 }
 
 /// Describes API notes data for a typedef.
-class TypedefInfo : public CommonTypeInfo {
+class CLANG_ABI TypedefInfo : public CommonTypeInfo {
 public:
   std::optional<SwiftNewTypeKind> SwiftWrapper;
 
diff --git a/clang/include/clang/ARCMigrate/ARCMT.h b/clang/include/clang/ARCMigrate/ARCMT.h
index 2b950e3d2cc2bf..dc078101e371ff 100644
--- a/clang/include/clang/ARCMigrate/ARCMT.h
+++ b/clang/include/clang/ARCMigrate/ARCMT.h
@@ -12,6 +12,7 @@
 #include "clang/ARCMigrate/FileRemapper.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Frontend/CompilerInvocation.h"
+#include "clang/Support/Compiler.h"
 
 namespace clang {
   class ASTContext;
@@ -37,7 +38,7 @@ namespace arcmt {
 /// the pre-migration ARC diagnostics.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool
+CLANG_ABI bool
 checkForManualIssues(CompilerInvocation &CI, const FrontendInputFile &Input,
                      std::shared_ptr<PCHContainerOperations> PCHContainerOps,
                      DiagnosticConsumer *DiagClient,
@@ -48,7 +49,7 @@ checkForManualIssues(CompilerInvocation &CI, const FrontendInputFile &Input,
 /// applies automatic modifications to source files to conform to ARC.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool
+CLANG_ABI bool
 applyTransformations(CompilerInvocation &origCI,
                      const FrontendInputFile &Input,
                      std::shared_ptr<PCHContainerOperations> PCHContainerOps,
@@ -65,7 +66,7 @@ applyTransformations(CompilerInvocation &origCI,
 /// the pre-migration ARC diagnostics.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool migrateWithTemporaryFiles(
+CLANG_ABI bool migrateWithTemporaryFiles(
     CompilerInvocation &origCI, const FrontendInputFile &Input,
     std::shared_ptr<PCHContainerOperations> PCHContainerOps,
     DiagnosticConsumer *DiagClient, StringRef outputDir,
@@ -75,7 +76,7 @@ bool migrateWithTemporaryFiles(
 /// migrateWithTemporaryFiles produced.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool getFileRemappings(std::vector<std::pair<std::string,std::string> > &remap,
+CLANG_ABI bool getFileRemappings(std::vector<std::pair<std::string,std::string> > &remap,
                        StringRef outputDir,
                        DiagnosticConsumer *DiagClient);
 
@@ -83,17 +84,17 @@ bool getFileRemappings(std::vector<std::pair<std::string,std::string> > &remap,
 /// info.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool getFileRemappingsFromFileList(
+CLANG_ABI bool getFileRemappingsFromFileList(
                         std::vector<std::pair<std::string,std::string> > &remap,
                         ArrayRef<StringRef> remapFiles,
                         DiagnosticConsumer *DiagClient);
 
 typedef void (*TransformFn)(MigrationPass &pass);
 
-std::vector<TransformFn> getAllTransformations(LangOptions::GCMode OrigGCMode,
+CLANG_ABI std::vector<TransformFn> getAllTransformations(LangOptions::GCMode OrigGCMode,
                                                bool NoFinalizeRemoval);
 
-class MigrationProcess {
+class CLANG_ABI MigrationProcess {
   CompilerInvocation OrigCI;
   std::shared_ptr<PCHContainerOperations> PCHContainerOps;
   DiagnosticConsumer *DiagClient;
@@ -107,7 +108,7 @@ class MigrationProcess {
                    DiagnosticConsumer *diagClient,
                    StringRef outputDir = StringRef());
 
-  class RewriteListener {
+  class CLANG_ABI RewriteListener {
   public:
     virtual ~RewriteListener();
 
diff --git a/clang/include/clang/ARCMigrate/ARCMTActions.h b/clang/include/clang/ARCMigrate/ARCMTActions.h
index 714f4b33db446b..50c6142078f5c8 100644
--- a/clang/include/clang/ARCMigrate/ARCMTActions.h
+++ b/clang/include/clang/ARCMigrate/ARCMTActions.h
@@ -11,12 +11,13 @@
 
 #include "clang/ARCMigrate/FileRemapper.h"
 #include "clang/Frontend/FrontendAction.h"
+#include "clang/Support/Compiler.h"
 #include <memory>
 
 namespace clang {
 namespace arcmt {
 
-class CheckAction : public WrapperFrontendAction {
+class CLANG_ABI CheckAction : public WrapperFrontendAction {
 protected:
   bool BeginInvocation(CompilerInstance &CI) override;
 
@@ -24,7 +25,7 @@ class CheckAction : public WrapperFrontendAction {
   CheckAction(std::unique_ptr<FrontendAction> WrappedAction);
 };
 
-class ModifyAction : public WrapperFrontendAction {
+class CLANG_ABI ModifyAction : public WrapperFrontendAction {
 protected:
   bool BeginInvocation(CompilerInstance &CI) override;
 
@@ -32,7 +33,7 @@ class ModifyAction : public WrapperFrontendAction {
   ModifyAction(std::unique_ptr<FrontendAction> WrappedAction);
 };
 
-class MigrateSourceAction : public ASTFrontendAction {
+class CLANG_ABI MigrateSourceAction : public ASTFrontendAction {
   FileRemapper Remapper;
 protected:
   bool BeginInvocation(CompilerInstance &CI) override;
@@ -40,7 +41,7 @@ class MigrateSourceAction : public ASTFrontendAction {
                                                  StringRef InFile) override;
 };
 
-class MigrateAction : public WrapperFrontendAction {
+class CLANG_ABI MigrateAction : public WrapperFrontendAction {
   std::string MigrateDir;
   std::string PlistOut;
   bool EmitPremigrationARCErrors;
@@ -55,7 +56,7 @@ class MigrateAction : public WrapperFrontendAction {
 };
 
 /// Migrates to modern ObjC syntax.
-class ObjCMigrateAction : public WrapperFrontendAction {
+class CLANG_ABI ObjCMigrateAction : public WrapperFrontendAction {
   std::string MigrateDir;
   unsigned    ObjCMigAction;
   FileRemapper Remapper;
diff --git a/clang/include/clang/ARCMigrate/FileRemapper.h b/clang/include/clang/ARCMigrate/FileRemapper.h
index afcee363516a21..3c9f706a75cf38 100644
--- a/clang/include/clang/ARCMigrate/FileRemapper.h
+++ b/clang/include/clang/ARCMigrate/FileRemapper.h
@@ -11,6 +11,7 @@
 
 #include "clang/Basic/FileEntry.h"
 #include "clang/Basic/LLVM.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
@@ -29,7 +30,7 @@ namespace clang {
 
 namespace arcmt {
 
-class FileRemapper {
+class CLANG_ABI FileRemapper {
   // FIXME: Reuse the same FileManager for multiple ASTContexts.
   std::unique_ptr<FileManager> FileMgr;
 
diff --git a/clang/include/clang/AST/APNumericStorage.h b/clang/include/clang/AST/APNumericStorage.h
index 95eddbcd86e839..ae634d46dfea2b 100644
--- a/clang/include/clang/AST/APNumericStorage.h
+++ b/clang/include/clang/AST/APNumericStorage.h
@@ -9,6 +9,7 @@
 #ifndef LLVM_CLANG_AST_APNUMERICSTORAGE_H
 #define LLVM_CLANG_AST_APNUMERICSTORAGE_H
 
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APInt.h"
 
@@ -23,7 +24,7 @@ class ASTContext;
 /// to allocate IntegerLiteral/FloatingLiteral nodes the memory associated with
 /// the APFloat/APInt values will never get freed. APNumericStorage uses
 /// ASTContext's allocator for memory allocation.
-class APNumericStorage {
+class CLANG_ABI APNumericStorage {
   union {
     uint64_t VAL;   ///< Used to store the <= 64 bits integer value.
     uint64_t *pVal; ///< Used to store the >64 bits integer value.
diff --git a/clang/include/clang/AST/APValue.h b/clang/include/clang/AST/APValue.h
index c4206b73b11562..fc6baf92a90202 100644
--- a/clang/include/clang/AST/APValue.h
+++ b/clang/include/clang/AST/APValue.h
@@ -14,6 +14,7 @@
 #define LLVM_CLANG_AST_APVALUE_H
 
 #include "clang/Basic/LLVM.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/APFixedPoint.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APSInt.h"
@@ -41,7 +42,7 @@ template <typename T> class BasicReaderBase;
   class QualType;
 
 /// Symbolic representation of typeid(T) for some type T.
-class TypeInfoLValue {
+class CLANG_ABI TypeInfoLValue {
   const Type *T;
 
 public:
@@ -119,7 +120,7 @@ namespace clang {
 /// APValue - This class implements a discriminated union of [uninitialized]
 /// [APSInt] [APFloat], [Complex APSInt] [Complex APFloat], [Expr + Offset],
 /// [Vector: N * APValue], [Array: N * APValue]
-class APValue {
+class CLANG_ABI APValue {
   typedef llvm::APFixedPoint APFixedPoint;
   typedef llvm::APSInt APSInt;
   typedef llvm::APFloat APFloat;
@@ -143,7 +144,7 @@ class APValue {
     AddrLabelDiff
   };
 
-  class LValueBase {
+  class CLANG_ABI LValueBase {
     typedef llvm::PointerUnion<const ValueDecl *, const Expr *, TypeInfoLValue,
                                DynamicAllocLValue>
         PtrTy;
@@ -179,11 +180,11 @@ class APValue {
 
     QualType getType() const;
 
-    friend bool operator==(const LValueBase &LHS, const LValueBase &RHS);
+    friend CLANG_ABI bool operator==(const LValueBase &LHS, const LValueBase &RHS);
     friend bool operator!=(const LValueBase &LHS, const LValueBase &RHS) {
       return !(LHS == RHS);
     }
-    friend llvm::hash_code hash_value(const LValueBase &Base);
+    friend CLANG_ABI llvm::hash_code hash_value(const LValueBase &Base);
     friend struct llvm::DenseMapInfo<LValueBase>;
 
   private:
@@ -205,7 +206,7 @@ class APValue {
   typedef llvm::PointerIntPair<const Decl *, 1, bool> BaseOrMemberType;
 
   /// A non-discriminated union of a base, field, or array index.
-  class LValuePathEntry {
+  class CLANG_ABI LValuePathEntry {
     static_assert(sizeof(uintptr_t) <= sizeof(uint64_t),
                   "pointer doesn't fit in 64 bits?");
     uint64_t Value;
@@ -237,7 +238,7 @@ class APValue {
       return llvm::hash_value(A.Value);
     }
   };
-  class LValuePathSerializationHelper {
+  class CLANG_ABI LValuePathSerializationHelper {
     const void *Ty;
 
   public:
@@ -274,7 +275,7 @@ class APValue {
     Vec &operator=(const Vec &) = delete;
     ~Vec() { delete[] Elts; }
   };
-  struct Arr {
+  struct CLANG_ABI Arr {
     APValue *Elts;
     unsigned NumElts, ArrSize;
     Arr(unsigned NumElts, unsigned ArrSize);
@@ -282,7 +283,7 @@ class APValue {
     Arr &operator=(const Arr &) = delete;
     ~Arr();
   };
-  struct StructData {
+  struct CLANG_ABI StructData {
     APValue *Elts;
     unsigned NumBases;
     unsigned NumFields;
@@ -291,7 +292,7 @@ class APValue {
     StructData &operator=(const StructData &) = delete;
     ~StructData();
   };
-  struct UnionData {
+  struct CLANG_ABI UnionData {
     const FieldDecl *Field;
     APValue *Value;
     UnionData();
@@ -702,7 +703,7 @@ class APValue {
 } // end namespace clang.
 
 namespace llvm {
-template<> struct DenseMapInfo<clang::APValue::LValueBase> {
+template<> struct CLANG_ABI DenseMapInfo<clang::APValue::LValueBase> {
   static clang::APValue::LValueBase getEmptyKey();
   static clang::APValue::LValueBase getTombstoneKey();
   static unsigned getHashValue(const clang::APValue::LValueBase &Base);
diff --git a/clang/include/clang/AST/ASTConcept.h b/clang/include/clang/AST/ASTConcept.h
index 00500e214f4ce6..59b0a8e9d96a9d 100644
--- a/clang/include/clang/AST/ASTConcept.h
+++ b/clang/include/clang/AST/ASTConcept.h
@@ -18,6 +18,7 @@
 #include "clang/AST/NestedNameSpecifier.h"
 #include "clang/AST/TemplateBase.h"
 #include "clang/Basic/SourceLocation.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/PointerUnion.h"
 #include "llvm/ADT/SmallVector.h"
@@ -32,7 +33,7 @@ struct PrintingPolicy;
 
 /// The result of a constraint satisfaction check, containing the necessary
 /// information to diagnose an unsatisfied constraint.
-class ConstraintSatisfaction : public llvm::FoldingSetNode {
+class CLANG_ABI ConstraintSatisfaction : public llvm::FoldingSetNode {
   // The template-like entity that 'owns' the constraint checked here (can be a
   // constrained entity or a concept).
   const NamedDecl *ConstraintOwner = nullptr;
@@ -84,7 +85,7 @@ using UnsatisfiedConstraintRecord =
 /// necessary information to diagnose an unsatisfied constraint.
 ///
 /// This is safe to store in an AST node, as opposed to ConstraintSatisfaction.
-struct ASTConstraintSatisfaction final :
+struct CLANG_ABI ASTConstraintSatisfaction final :
     llvm::TrailingObjects<ASTConstraintSatisfaction,
                           UnsatisfiedConstraintRecord> {
   std::size_t NumRecords;
@@ -121,7 +122,7 @@ struct ASTConstraintSatisfaction final :
 ///
 ///   template <std::derives_from<Expr> T> void dump();
 ///             ~~~~~~~~~~~~~~~~~~~~~~~ (in TemplateTypeParmDecl)
-class ConceptReference {
+class CLANG_ABI ConceptReference {
   // \brief The optional nested name specifier used when naming the concept.
   NestedNameSpecifierLoc NestedNameSpec;
 
diff --git a/clang/include/clang/AST/ASTConsumer.h b/clang/include/clang/AST/ASTConsumer.h
index 447f2592d23595..735c7e549f5cac 100644
--- a/clang/include/clang/AST/ASTConsumer.h
+++ b/clang/include/clang/AST/ASTConsumer.h
@@ -13,6 +13,7 @@
 #ifndef LLVM_CLANG_AST_ASTCONSUMER_H
 #define LLVM_CLANG_AST_ASTCONSUMER_H
 
+#include "clang/Support/Compiler.h"
 namespace clang {
   class ASTContext;
   class CXXMethodDecl;
@@ -31,7 +32,7 @@ namespace clang {
 /// ASTCons...
[truncated]

diff --git a/clang/include/clang/APINotes/APINotesManager.h b/clang/include/clang/APINotes/APINotesManager.h
index 98592438e90eab..05d7930d3a2e7f 100644
--- a/clang/include/clang/APINotes/APINotesManager.h
+++ b/clang/include/clang/APINotes/APINotesManager.h
@@ -10,6 +10,7 @@
 #define LLVM_CLANG_APINOTES_APINOTESMANAGER_H
 
 #include "clang/Basic/SourceLocation.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/PointerUnion.h"
@@ -41,7 +42,7 @@ class APINotesReader;
 /// external API notes files that correspond to a given header. Its primary
 /// operation is \c findAPINotes(), which finds the API notes reader that
 /// provides information about the declarations at that location.
-class APINotesManager {
+class CLANG_ABI APINotesManager {
   using ReaderEntry = llvm::PointerUnion<DirectoryEntryRef, APINotesReader *>;
 
   SourceManager &SM;
diff --git a/clang/include/clang/APINotes/APINotesReader.h b/clang/include/clang/APINotes/APINotesReader.h
index baf63340640242..58ee2857c7930f 100644
--- a/clang/include/clang/APINotes/APINotesReader.h
+++ b/clang/include/clang/APINotes/APINotesReader.h
@@ -16,6 +16,7 @@
 #define LLVM_CLANG_APINOTES_READER_H
 
 #include "clang/APINotes/Types.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/VersionTuple.h"
 #include <memory>
@@ -25,7 +26,7 @@ namespace api_notes {
 
 /// A class that reads API notes data from a binary file that was written by
 /// the \c APINotesWriter.
-class APINotesReader {
+class CLANG_ABI APINotesReader {
   class Implementation;
   std::unique_ptr<Implementation> Implementation;
 
diff --git a/clang/include/clang/APINotes/APINotesWriter.h b/clang/include/clang/APINotes/APINotesWriter.h
index 3cc16c3d959faf..b8b45a89dcfc8b 100644
--- a/clang/include/clang/APINotes/APINotesWriter.h
+++ b/clang/include/clang/APINotes/APINotesWriter.h
@@ -16,6 +16,7 @@
 #define LLVM_CLANG_APINOTES_WRITER_H
 
 #include "clang/APINotes/Types.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/VersionTuple.h"
 #include "llvm/Support/raw_ostream.h"
@@ -29,7 +30,7 @@ namespace api_notes {
 
 /// A class that writes API notes data to a binary representation that can be
 /// read by the \c APINotesReader.
-class APINotesWriter {
+class CLANG_ABI APINotesWriter {
   class Implementation;
   std::unique_ptr<Implementation> Implementation;
 
diff --git a/clang/include/clang/APINotes/APINotesYAMLCompiler.h b/clang/include/clang/APINotes/APINotesYAMLCompiler.h
index 9c24ed85b6a124..3954cf347e8244 100644
--- a/clang/include/clang/APINotes/APINotesYAMLCompiler.h
+++ b/clang/include/clang/APINotes/APINotesYAMLCompiler.h
@@ -9,6 +9,7 @@
 #ifndef LLVM_CLANG_APINOTES_APINOTESYAMLCOMPILER_H
 #define LLVM_CLANG_APINOTES_APINOTESYAMLCOMPILER_H
 
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/raw_ostream.h"
@@ -22,10 +23,10 @@ namespace api_notes {
 /// Parses the APINotes YAML content and writes the representation back to the
 /// specified stream.  This provides a means of testing the YAML processing of
 /// the APINotes format.
-bool parseAndDumpAPINotes(llvm::StringRef YI, llvm::raw_ostream &OS);
+CLANG_ABI bool parseAndDumpAPINotes(llvm::StringRef YI, llvm::raw_ostream &OS);
 
 /// Converts API notes from YAML format to binary format.
-bool compileAPINotes(llvm::StringRef YAMLInput, const FileEntry *SourceFile,
+CLANG_ABI bool compileAPINotes(llvm::StringRef YAMLInput, const FileEntry *SourceFile,
                      llvm::raw_ostream &OS,
                      llvm::SourceMgr::DiagHandlerTy DiagHandler = nullptr,
                      void *DiagHandlerCtxt = nullptr);
diff --git a/clang/include/clang/APINotes/Types.h b/clang/include/clang/APINotes/Types.h
index 89889910d1a073..574406586c4674 100644
--- a/clang/include/clang/APINotes/Types.h
+++ b/clang/include/clang/APINotes/Types.h
@@ -10,6 +10,7 @@
 #define LLVM_CLANG_APINOTES_TYPES_H
 
 #include "clang/Basic/Specifiers.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringRef.h"
 #include <climits>
@@ -49,7 +50,7 @@ enum class SwiftNewTypeKind {
 /// Describes API notes data for any entity.
 ///
 /// This is used as the base of all API notes.
-class CommonEntityInfo {
+class CLANG_ABI CommonEntityInfo {
 public:
   /// Message to use when this entity is unavailable.
   std::string UnavailableMsg;
@@ -132,7 +133,7 @@ inline bool operator!=(const CommonEntityInfo &LHS,
 }
 
 /// Describes API notes for types.
-class CommonTypeInfo : public CommonEntityInfo {
+class CLANG_ABI CommonTypeInfo : public CommonEntityInfo {
   /// The Swift type to which a given type is bridged.
   ///
   /// Reflects the swift_bridge attribute.
@@ -194,7 +195,7 @@ inline bool operator!=(const CommonTypeInfo &LHS, const CommonTypeInfo &RHS) {
 
 /// Describes API notes data for an Objective-C class or protocol or a C++
 /// namespace.
-class ContextInfo : public CommonTypeInfo {
+class CLANG_ABI ContextInfo : public CommonTypeInfo {
   /// Whether this class has a default nullability.
   LLVM_PREFERRED_TYPE(bool)
   unsigned HasDefaultNullability : 1;
@@ -301,7 +302,7 @@ inline bool operator!=(const ContextInfo &LHS, const ContextInfo &RHS) {
 }
 
 /// API notes for a variable/property.
-class VariableInfo : public CommonEntityInfo {
+class CLANG_ABI VariableInfo : public CommonEntityInfo {
   /// Whether this property has been audited for nullability.
   LLVM_PREFERRED_TYPE(bool)
   unsigned NullabilityAudited : 1;
@@ -358,7 +359,7 @@ inline bool operator!=(const VariableInfo &LHS, const VariableInfo &RHS) {
 }
 
 /// Describes API notes data for an Objective-C property.
-class ObjCPropertyInfo : public VariableInfo {
+class CLANG_ABI ObjCPropertyInfo : public VariableInfo {
   LLVM_PREFERRED_TYPE(bool)
   unsigned SwiftImportAsAccessorsSpecified : 1;
   LLVM_PREFERRED_TYPE(bool)
@@ -416,7 +417,7 @@ inline bool operator!=(const ObjCPropertyInfo &LHS,
 }
 
 /// Describes a function or method parameter.
-class ParamInfo : public VariableInfo {
+class CLANG_ABI ParamInfo : public VariableInfo {
   /// Whether noescape was specified.
   LLVM_PREFERRED_TYPE(bool)
   unsigned NoEscapeSpecified : 1;
@@ -486,7 +487,7 @@ inline bool operator!=(const ParamInfo &LHS, const ParamInfo &RHS) {
 }
 
 /// API notes for a function or method.
-class FunctionInfo : public CommonEntityInfo {
+class CLANG_ABI FunctionInfo : public CommonEntityInfo {
 private:
   static constexpr const uint64_t NullabilityKindMask = 0x3;
   static constexpr const unsigned NullabilityKindSize = 2;
@@ -606,7 +607,7 @@ inline bool operator!=(const FunctionInfo &LHS, const FunctionInfo &RHS) {
 }
 
 /// Describes API notes data for an Objective-C method.
-class ObjCMethodInfo : public FunctionInfo {
+class CLANG_ABI ObjCMethodInfo : public FunctionInfo {
 public:
   /// Whether this is a designated initializer of its class.
   LLVM_PREFERRED_TYPE(bool)
@@ -675,7 +676,7 @@ class EnumConstantInfo : public CommonEntityInfo {
 };
 
 /// Describes API notes data for a tag.
-class TagInfo : public CommonTypeInfo {
+class CLANG_ABI TagInfo : public CommonTypeInfo {
   LLVM_PREFERRED_TYPE(bool)
   unsigned HasFlagEnum : 1;
   LLVM_PREFERRED_TYPE(bool)
@@ -765,7 +766,7 @@ inline bool operator!=(const TagInfo &LHS, const TagInfo &RHS) {
 }
 
 /// Describes API notes data for a typedef.
-class TypedefInfo : public CommonTypeInfo {
+class CLANG_ABI TypedefInfo : public CommonTypeInfo {
 public:
   std::optional<SwiftNewTypeKind> SwiftWrapper;
 
diff --git a/clang/include/clang/ARCMigrate/ARCMT.h b/clang/include/clang/ARCMigrate/ARCMT.h
index 2b950e3d2cc2bf..dc078101e371ff 100644
--- a/clang/include/clang/ARCMigrate/ARCMT.h
+++ b/clang/include/clang/ARCMigrate/ARCMT.h
@@ -12,6 +12,7 @@
 #include "clang/ARCMigrate/FileRemapper.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Frontend/CompilerInvocation.h"
+#include "clang/Support/Compiler.h"
 
 namespace clang {
   class ASTContext;
@@ -37,7 +38,7 @@ namespace arcmt {
 /// the pre-migration ARC diagnostics.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool
+CLANG_ABI bool
 checkForManualIssues(CompilerInvocation &CI, const FrontendInputFile &Input,
                      std::shared_ptr<PCHContainerOperations> PCHContainerOps,
                      DiagnosticConsumer *DiagClient,
@@ -48,7 +49,7 @@ checkForManualIssues(CompilerInvocation &CI, const FrontendInputFile &Input,
 /// applies automatic modifications to source files to conform to ARC.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool
+CLANG_ABI bool
 applyTransformations(CompilerInvocation &origCI,
                      const FrontendInputFile &Input,
                      std::shared_ptr<PCHContainerOperations> PCHContainerOps,
@@ -65,7 +66,7 @@ applyTransformations(CompilerInvocation &origCI,
 /// the pre-migration ARC diagnostics.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool migrateWithTemporaryFiles(
+CLANG_ABI bool migrateWithTemporaryFiles(
     CompilerInvocation &origCI, const FrontendInputFile &Input,
     std::shared_ptr<PCHContainerOperations> PCHContainerOps,
     DiagnosticConsumer *DiagClient, StringRef outputDir,
@@ -75,7 +76,7 @@ bool migrateWithTemporaryFiles(
 /// migrateWithTemporaryFiles produced.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool getFileRemappings(std::vector<std::pair<std::string,std::string> > &remap,
+CLANG_ABI bool getFileRemappings(std::vector<std::pair<std::string,std::string> > &remap,
                        StringRef outputDir,
                        DiagnosticConsumer *DiagClient);
 
@@ -83,17 +84,17 @@ bool getFileRemappings(std::vector<std::pair<std::string,std::string> > &remap,
 /// info.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool getFileRemappingsFromFileList(
+CLANG_ABI bool getFileRemappingsFromFileList(
                         std::vector<std::pair<std::string,std::string> > &remap,
                         ArrayRef<StringRef> remapFiles,
                         DiagnosticConsumer *DiagClient);
 
 typedef void (*TransformFn)(MigrationPass &pass);
 
-std::vector<TransformFn> getAllTransformations(LangOptions::GCMode OrigGCMode,
+CLANG_ABI std::vector<TransformFn> getAllTransformations(LangOptions::GCMode OrigGCMode,
                                                bool NoFinalizeRemoval);
 
-class MigrationProcess {
+class CLANG_ABI MigrationProcess {
   CompilerInvocation OrigCI;
   std::shared_ptr<PCHContainerOperations> PCHContainerOps;
   DiagnosticConsumer *DiagClient;
@@ -107,7 +108,7 @@ class MigrationProcess {
                    DiagnosticConsumer *diagClient,
                    StringRef outputDir = StringRef());
 
-  class RewriteListener {
+  class CLANG_ABI RewriteListener {
   public:
     virtual ~RewriteListener();
 
diff --git a/clang/include/clang/ARCMigrate/ARCMTActions.h b/clang/include/clang/ARCMigrate/ARCMTActions.h
index 714f4b33db446b..50c6142078f5c8 100644
--- a/clang/include/clang/ARCMigrate/ARCMTActions.h
+++ b/clang/include/clang/ARCMigrate/ARCMTActions.h
@@ -11,12 +11,13 @@
 
 #include "clang/ARCMigrate/FileRemapper.h"
 #include "clang/Frontend/FrontendAction.h"
+#include "clang/Support/Compiler.h"
 #include <memory>
 
 namespace clang {
 namespace arcmt {
 
-class CheckAction : public WrapperFrontendAction {
+class CLANG_ABI CheckAction : public WrapperFrontendAction {
 protected:
   bool BeginInvocation(CompilerInstance &CI) override;
 
@@ -24,7 +25,7 @@ class CheckAction : public WrapperFrontendAction {
   CheckAction(std::unique_ptr<FrontendAction> WrappedAction);
 };
 
-class ModifyAction : public WrapperFrontendAction {
+class CLANG_ABI ModifyAction : public WrapperFrontendAction {
 protected:
   bool BeginInvocation(CompilerInstance &CI) override;
 
@@ -32,7 +33,7 @@ class ModifyAction : public WrapperFrontendAction {
   ModifyAction(std::unique_ptr<FrontendAction> WrappedAction);
 };
 
-class MigrateSourceAction : public ASTFrontendAction {
+class CLANG_ABI MigrateSourceAction : public ASTFrontendAction {
   FileRemapper Remapper;
 protected:
   bool BeginInvocation(CompilerInstance &CI) override;
@@ -40,7 +41,7 @@ class MigrateSourceAction : public ASTFrontendAction {
                                                  StringRef InFile) override;
 };
 
-class MigrateAction : public WrapperFrontendAction {
+class CLANG_ABI MigrateAction : public WrapperFrontendAction {
   std::string MigrateDir;
   std::string PlistOut;
   bool EmitPremigrationARCErrors;
@@ -55,7 +56,7 @@ class MigrateAction : public WrapperFrontendAction {
 };
 
 /// Migrates to modern ObjC syntax.
-class ObjCMigrateAction : public WrapperFrontendAction {
+class CLANG_ABI ObjCMigrateAction : public WrapperFrontendAction {
   std::string MigrateDir;
   unsigned    ObjCMigAction;
   FileRemapper Remapper;
diff --git a/clang/include/clang/ARCMigrate/FileRemapper.h b/clang/include/clang/ARCMigrate/FileRemapper.h
index afcee363516a21..3c9f706a75cf38 100644
--- a/clang/include/clang/ARCMigrate/FileRemapper.h
+++ b/clang/include/clang/ARCMigrate/FileRemapper.h
@@ -11,6 +11,7 @@
 
 #include "clang/Basic/FileEntry.h"
 #include "clang/Basic/LLVM.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
@@ -29,7 +30,7 @@ namespace clang {
 
 namespace arcmt {
 
-class FileRemapper {
+class CLANG_ABI FileRemapper {
   // FIXME: Reuse the same FileManager for multiple ASTContexts.
   std::unique_ptr<FileManager> FileMgr;
 
diff --git a/clang/include/clang/AST/APNumericStorage.h b/clang/include/clang/AST/APNumericStorage.h
index 95eddbcd86e839..ae634d46dfea2b 100644
--- a/clang/include/clang/AST/APNumericStorage.h
+++ b/clang/include/clang/AST/APNumericStorage.h
@@ -9,6 +9,7 @@
 #ifndef LLVM_CLANG_AST_APNUMERICSTORAGE_H
 #define LLVM_CLANG_AST_APNUMERICSTORAGE_H
 
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APInt.h"
 
@@ -23,7 +24,7 @@ class ASTContext;
 /// to allocate IntegerLiteral/FloatingLiteral nodes the memory associated with
 /// the APFloat/APInt values will never get freed. APNumericStorage uses
 /// ASTContext's allocator for memory allocation.
-class APNumericStorage {
+class CLANG_ABI APNumericStorage {
   union {
     uint64_t VAL;   ///< Used to store the <= 64 bits integer value.
     uint64_t *pVal; ///< Used to store the >64 bits integer value.
diff --git a/clang/include/clang/AST/APValue.h b/clang/include/clang/AST/APValue.h
index c4206b73b11562..fc6baf92a90202 100644
--- a/clang/include/clang/AST/APValue.h
+++ b/clang/include/clang/AST/APValue.h
@@ -14,6 +14,7 @@
 #define LLVM_CLANG_AST_APVALUE_H
 
 #include "clang/Basic/LLVM.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/APFixedPoint.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APSInt.h"
@@ -41,7 +42,7 @@ template <typename T> class BasicReaderBase;
   class QualType;
 
 /// Symbolic representation of typeid(T) for some type T.
-class TypeInfoLValue {
+class CLANG_ABI TypeInfoLValue {
   const Type *T;
 
 public:
@@ -119,7 +120,7 @@ namespace clang {
 /// APValue - This class implements a discriminated union of [uninitialized]
 /// [APSInt] [APFloat], [Complex APSInt] [Complex APFloat], [Expr + Offset],
 /// [Vector: N * APValue], [Array: N * APValue]
-class APValue {
+class CLANG_ABI APValue {
   typedef llvm::APFixedPoint APFixedPoint;
   typedef llvm::APSInt APSInt;
   typedef llvm::APFloat APFloat;
@@ -143,7 +144,7 @@ class APValue {
     AddrLabelDiff
   };
 
-  class LValueBase {
+  class CLANG_ABI LValueBase {
     typedef llvm::PointerUnion<const ValueDecl *, const Expr *, TypeInfoLValue,
                                DynamicAllocLValue>
         PtrTy;
@@ -179,11 +180,11 @@ class APValue {
 
     QualType getType() const;
 
-    friend bool operator==(const LValueBase &LHS, const LValueBase &RHS);
+    friend CLANG_ABI bool operator==(const LValueBase &LHS, const LValueBase &RHS);
     friend bool operator!=(const LValueBase &LHS, const LValueBase &RHS) {
       return !(LHS == RHS);
     }
-    friend llvm::hash_code hash_value(const LValueBase &Base);
+    friend CLANG_ABI llvm::hash_code hash_value(const LValueBase &Base);
     friend struct llvm::DenseMapInfo<LValueBase>;
 
   private:
@@ -205,7 +206,7 @@ class APValue {
   typedef llvm::PointerIntPair<const Decl *, 1, bool> BaseOrMemberType;
 
   /// A non-discriminated union of a base, field, or array index.
-  class LValuePathEntry {
+  class CLANG_ABI LValuePathEntry {
     static_assert(sizeof(uintptr_t) <= sizeof(uint64_t),
                   "pointer doesn't fit in 64 bits?");
     uint64_t Value;
@@ -237,7 +238,7 @@ class APValue {
       return llvm::hash_value(A.Value);
     }
   };
-  class LValuePathSerializationHelper {
+  class CLANG_ABI LValuePathSerializationHelper {
     const void *Ty;
 
   public:
@@ -274,7 +275,7 @@ class APValue {
     Vec &operator=(const Vec &) = delete;
     ~Vec() { delete[] Elts; }
   };
-  struct Arr {
+  struct CLANG_ABI Arr {
     APValue *Elts;
     unsigned NumElts, ArrSize;
     Arr(unsigned NumElts, unsigned ArrSize);
@@ -282,7 +283,7 @@ class APValue {
     Arr &operator=(const Arr &) = delete;
     ~Arr();
   };
-  struct StructData {
+  struct CLANG_ABI StructData {
     APValue *Elts;
     unsigned NumBases;
     unsigned NumFields;
@@ -291,7 +292,7 @@ class APValue {
     StructData &operator=(const StructData &) = delete;
     ~StructData();
   };
-  struct UnionData {
+  struct CLANG_ABI UnionData {
     const FieldDecl *Field;
     APValue *Value;
     UnionData();
@@ -702,7 +703,7 @@ class APValue {
 } // end namespace clang.
 
 namespace llvm {
-template<> struct DenseMapInfo<clang::APValue::LValueBase> {
+template<> struct CLANG_ABI DenseMapInfo<clang::APValue::LValueBase> {
   static clang::APValue::LValueBase getEmptyKey();
   static clang::APValue::LValueBase getTombstoneKey();
   static unsigned getHashValue(const clang::APValue::LValueBase &Base);
diff --git a/clang/include/clang/AST/ASTConcept.h b/clang/include/clang/AST/ASTConcept.h
index 00500e214f4ce6..59b0a8e9d96a9d 100644
--- a/clang/include/clang/AST/ASTConcept.h
+++ b/clang/include/clang/AST/ASTConcept.h
@@ -18,6 +18,7 @@
 #include "clang/AST/NestedNameSpecifier.h"
 #include "clang/AST/TemplateBase.h"
 #include "clang/Basic/SourceLocation.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/PointerUnion.h"
 #include "llvm/ADT/SmallVector.h"
@@ -32,7 +33,7 @@ struct PrintingPolicy;
 
 /// The result of a constraint satisfaction check, containing the necessary
 /// information to diagnose an unsatisfied constraint.
-class ConstraintSatisfaction : public llvm::FoldingSetNode {
+class CLANG_ABI ConstraintSatisfaction : public llvm::FoldingSetNode {
   // The template-like entity that 'owns' the constraint checked here (can be a
   // constrained entity or a concept).
   const NamedDecl *ConstraintOwner = nullptr;
@@ -84,7 +85,7 @@ using UnsatisfiedConstraintRecord =
 /// necessary information to diagnose an unsatisfied constraint.
 ///
 /// This is safe to store in an AST node, as opposed to ConstraintSatisfaction.
-struct ASTConstraintSatisfaction final :
+struct CLANG_ABI ASTConstraintSatisfaction final :
     llvm::TrailingObjects<ASTConstraintSatisfaction,
                           UnsatisfiedConstraintRecord> {
   std::size_t NumRecords;
@@ -121,7 +122,7 @@ struct ASTConstraintSatisfaction final :
 ///
 ///   template <std::derives_from<Expr> T> void dump();
 ///             ~~~~~~~~~~~~~~~~~~~~~~~ (in TemplateTypeParmDecl)
-class ConceptReference {
+class CLANG_ABI ConceptReference {
   // \brief The optional nested name specifier used when naming the concept.
   NestedNameSpecifierLoc NestedNameSpec;
 
diff --git a/clang/include/clang/AST/ASTConsumer.h b/clang/include/clang/AST/ASTConsumer.h
index 447f2592d23595..735c7e549f5cac 100644
--- a/clang/include/clang/AST/ASTConsumer.h
+++ b/clang/include/clang/AST/ASTConsumer.h
@@ -13,6 +13,7 @@
 #ifndef LLVM_CLANG_AST_ASTCONSUMER_H
 #define LLVM_CLANG_AST_ASTCONSUMER_H
 
+#include "clang/Support/Compiler.h"
 namespace clang {
   class ASTContext;
   class CXXMethodDecl;
@@ -31,7 +32,7 @@ namespace clang {
 /// ASTCons...
[truncated]

diff --git a/clang/include/clang/APINotes/APINotesManager.h b/clang/include/clang/APINotes/APINotesManager.h
index 98592438e90eab..05d7930d3a2e7f 100644
--- a/clang/include/clang/APINotes/APINotesManager.h
+++ b/clang/include/clang/APINotes/APINotesManager.h
@@ -10,6 +10,7 @@
 #define LLVM_CLANG_APINOTES_APINOTESMANAGER_H
 
 #include "clang/Basic/SourceLocation.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/PointerUnion.h"
@@ -41,7 +42,7 @@ class APINotesReader;
 /// external API notes files that correspond to a given header. Its primary
 /// operation is \c findAPINotes(), which finds the API notes reader that
 /// provides information about the declarations at that location.
-class APINotesManager {
+class CLANG_ABI APINotesManager {
   using ReaderEntry = llvm::PointerUnion<DirectoryEntryRef, APINotesReader *>;
 
   SourceManager &SM;
diff --git a/clang/include/clang/APINotes/APINotesReader.h b/clang/include/clang/APINotes/APINotesReader.h
index baf63340640242..58ee2857c7930f 100644
--- a/clang/include/clang/APINotes/APINotesReader.h
+++ b/clang/include/clang/APINotes/APINotesReader.h
@@ -16,6 +16,7 @@
 #define LLVM_CLANG_APINOTES_READER_H
 
 #include "clang/APINotes/Types.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/VersionTuple.h"
 #include <memory>
@@ -25,7 +26,7 @@ namespace api_notes {
 
 /// A class that reads API notes data from a binary file that was written by
 /// the \c APINotesWriter.
-class APINotesReader {
+class CLANG_ABI APINotesReader {
   class Implementation;
   std::unique_ptr<Implementation> Implementation;
 
diff --git a/clang/include/clang/APINotes/APINotesWriter.h b/clang/include/clang/APINotes/APINotesWriter.h
index 3cc16c3d959faf..b8b45a89dcfc8b 100644
--- a/clang/include/clang/APINotes/APINotesWriter.h
+++ b/clang/include/clang/APINotes/APINotesWriter.h
@@ -16,6 +16,7 @@
 #define LLVM_CLANG_APINOTES_WRITER_H
 
 #include "clang/APINotes/Types.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/VersionTuple.h"
 #include "llvm/Support/raw_ostream.h"
@@ -29,7 +30,7 @@ namespace api_notes {
 
 /// A class that writes API notes data to a binary representation that can be
 /// read by the \c APINotesReader.
-class APINotesWriter {
+class CLANG_ABI APINotesWriter {
   class Implementation;
   std::unique_ptr<Implementation> Implementation;
 
diff --git a/clang/include/clang/APINotes/APINotesYAMLCompiler.h b/clang/include/clang/APINotes/APINotesYAMLCompiler.h
index 9c24ed85b6a124..3954cf347e8244 100644
--- a/clang/include/clang/APINotes/APINotesYAMLCompiler.h
+++ b/clang/include/clang/APINotes/APINotesYAMLCompiler.h
@@ -9,6 +9,7 @@
 #ifndef LLVM_CLANG_APINOTES_APINOTESYAMLCOMPILER_H
 #define LLVM_CLANG_APINOTES_APINOTESYAMLCOMPILER_H
 
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/raw_ostream.h"
@@ -22,10 +23,10 @@ namespace api_notes {
 /// Parses the APINotes YAML content and writes the representation back to the
 /// specified stream.  This provides a means of testing the YAML processing of
 /// the APINotes format.
-bool parseAndDumpAPINotes(llvm::StringRef YI, llvm::raw_ostream &OS);
+CLANG_ABI bool parseAndDumpAPINotes(llvm::StringRef YI, llvm::raw_ostream &OS);
 
 /// Converts API notes from YAML format to binary format.
-bool compileAPINotes(llvm::StringRef YAMLInput, const FileEntry *SourceFile,
+CLANG_ABI bool compileAPINotes(llvm::StringRef YAMLInput, const FileEntry *SourceFile,
                      llvm::raw_ostream &OS,
                      llvm::SourceMgr::DiagHandlerTy DiagHandler = nullptr,
                      void *DiagHandlerCtxt = nullptr);
diff --git a/clang/include/clang/APINotes/Types.h b/clang/include/clang/APINotes/Types.h
index 89889910d1a073..574406586c4674 100644
--- a/clang/include/clang/APINotes/Types.h
+++ b/clang/include/clang/APINotes/Types.h
@@ -10,6 +10,7 @@
 #define LLVM_CLANG_APINOTES_TYPES_H
 
 #include "clang/Basic/Specifiers.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringRef.h"
 #include <climits>
@@ -49,7 +50,7 @@ enum class SwiftNewTypeKind {
 /// Describes API notes data for any entity.
 ///
 /// This is used as the base of all API notes.
-class CommonEntityInfo {
+class CLANG_ABI CommonEntityInfo {
 public:
   /// Message to use when this entity is unavailable.
   std::string UnavailableMsg;
@@ -132,7 +133,7 @@ inline bool operator!=(const CommonEntityInfo &LHS,
 }
 
 /// Describes API notes for types.
-class CommonTypeInfo : public CommonEntityInfo {
+class CLANG_ABI CommonTypeInfo : public CommonEntityInfo {
   /// The Swift type to which a given type is bridged.
   ///
   /// Reflects the swift_bridge attribute.
@@ -194,7 +195,7 @@ inline bool operator!=(const CommonTypeInfo &LHS, const CommonTypeInfo &RHS) {
 
 /// Describes API notes data for an Objective-C class or protocol or a C++
 /// namespace.
-class ContextInfo : public CommonTypeInfo {
+class CLANG_ABI ContextInfo : public CommonTypeInfo {
   /// Whether this class has a default nullability.
   LLVM_PREFERRED_TYPE(bool)
   unsigned HasDefaultNullability : 1;
@@ -301,7 +302,7 @@ inline bool operator!=(const ContextInfo &LHS, const ContextInfo &RHS) {
 }
 
 /// API notes for a variable/property.
-class VariableInfo : public CommonEntityInfo {
+class CLANG_ABI VariableInfo : public CommonEntityInfo {
   /// Whether this property has been audited for nullability.
   LLVM_PREFERRED_TYPE(bool)
   unsigned NullabilityAudited : 1;
@@ -358,7 +359,7 @@ inline bool operator!=(const VariableInfo &LHS, const VariableInfo &RHS) {
 }
 
 /// Describes API notes data for an Objective-C property.
-class ObjCPropertyInfo : public VariableInfo {
+class CLANG_ABI ObjCPropertyInfo : public VariableInfo {
   LLVM_PREFERRED_TYPE(bool)
   unsigned SwiftImportAsAccessorsSpecified : 1;
   LLVM_PREFERRED_TYPE(bool)
@@ -416,7 +417,7 @@ inline bool operator!=(const ObjCPropertyInfo &LHS,
 }
 
 /// Describes a function or method parameter.
-class ParamInfo : public VariableInfo {
+class CLANG_ABI ParamInfo : public VariableInfo {
   /// Whether noescape was specified.
   LLVM_PREFERRED_TYPE(bool)
   unsigned NoEscapeSpecified : 1;
@@ -486,7 +487,7 @@ inline bool operator!=(const ParamInfo &LHS, const ParamInfo &RHS) {
 }
 
 /// API notes for a function or method.
-class FunctionInfo : public CommonEntityInfo {
+class CLANG_ABI FunctionInfo : public CommonEntityInfo {
 private:
   static constexpr const uint64_t NullabilityKindMask = 0x3;
   static constexpr const unsigned NullabilityKindSize = 2;
@@ -606,7 +607,7 @@ inline bool operator!=(const FunctionInfo &LHS, const FunctionInfo &RHS) {
 }
 
 /// Describes API notes data for an Objective-C method.
-class ObjCMethodInfo : public FunctionInfo {
+class CLANG_ABI ObjCMethodInfo : public FunctionInfo {
 public:
   /// Whether this is a designated initializer of its class.
   LLVM_PREFERRED_TYPE(bool)
@@ -675,7 +676,7 @@ class EnumConstantInfo : public CommonEntityInfo {
 };
 
 /// Describes API notes data for a tag.
-class TagInfo : public CommonTypeInfo {
+class CLANG_ABI TagInfo : public CommonTypeInfo {
   LLVM_PREFERRED_TYPE(bool)
   unsigned HasFlagEnum : 1;
   LLVM_PREFERRED_TYPE(bool)
@@ -765,7 +766,7 @@ inline bool operator!=(const TagInfo &LHS, const TagInfo &RHS) {
 }
 
 /// Describes API notes data for a typedef.
-class TypedefInfo : public CommonTypeInfo {
+class CLANG_ABI TypedefInfo : public CommonTypeInfo {
 public:
   std::optional<SwiftNewTypeKind> SwiftWrapper;
 
diff --git a/clang/include/clang/ARCMigrate/ARCMT.h b/clang/include/clang/ARCMigrate/ARCMT.h
index 2b950e3d2cc2bf..dc078101e371ff 100644
--- a/clang/include/clang/ARCMigrate/ARCMT.h
+++ b/clang/include/clang/ARCMigrate/ARCMT.h
@@ -12,6 +12,7 @@
 #include "clang/ARCMigrate/FileRemapper.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Frontend/CompilerInvocation.h"
+#include "clang/Support/Compiler.h"
 
 namespace clang {
   class ASTContext;
@@ -37,7 +38,7 @@ namespace arcmt {
 /// the pre-migration ARC diagnostics.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool
+CLANG_ABI bool
 checkForManualIssues(CompilerInvocation &CI, const FrontendInputFile &Input,
                      std::shared_ptr<PCHContainerOperations> PCHContainerOps,
                      DiagnosticConsumer *DiagClient,
@@ -48,7 +49,7 @@ checkForManualIssues(CompilerInvocation &CI, const FrontendInputFile &Input,
 /// applies automatic modifications to source files to conform to ARC.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool
+CLANG_ABI bool
 applyTransformations(CompilerInvocation &origCI,
                      const FrontendInputFile &Input,
                      std::shared_ptr<PCHContainerOperations> PCHContainerOps,
@@ -65,7 +66,7 @@ applyTransformations(CompilerInvocation &origCI,
 /// the pre-migration ARC diagnostics.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool migrateWithTemporaryFiles(
+CLANG_ABI bool migrateWithTemporaryFiles(
     CompilerInvocation &origCI, const FrontendInputFile &Input,
     std::shared_ptr<PCHContainerOperations> PCHContainerOps,
     DiagnosticConsumer *DiagClient, StringRef outputDir,
@@ -75,7 +76,7 @@ bool migrateWithTemporaryFiles(
 /// migrateWithTemporaryFiles produced.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool getFileRemappings(std::vector<std::pair<std::string,std::string> > &remap,
+CLANG_ABI bool getFileRemappings(std::vector<std::pair<std::string,std::string> > &remap,
                        StringRef outputDir,
                        DiagnosticConsumer *DiagClient);
 
@@ -83,17 +84,17 @@ bool getFileRemappings(std::vector<std::pair<std::string,std::string> > &remap,
 /// info.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool getFileRemappingsFromFileList(
+CLANG_ABI bool getFileRemappingsFromFileList(
                         std::vector<std::pair<std::string,std::string> > &remap,
                         ArrayRef<StringRef> remapFiles,
                         DiagnosticConsumer *DiagClient);
 
 typedef void (*TransformFn)(MigrationPass &pass);
 
-std::vector<TransformFn> getAllTransformations(LangOptions::GCMode OrigGCMode,
+CLANG_ABI std::vector<TransformFn> getAllTransformations(LangOptions::GCMode OrigGCMode,
                                                bool NoFinalizeRemoval);
 
-class MigrationProcess {
+class CLANG_ABI MigrationProcess {
   CompilerInvocation OrigCI;
   std::shared_ptr<PCHContainerOperations> PCHContainerOps;
   DiagnosticConsumer *DiagClient;
@@ -107,7 +108,7 @@ class MigrationProcess {
                    DiagnosticConsumer *diagClient,
                    StringRef outputDir = StringRef());
 
-  class RewriteListener {
+  class CLANG_ABI RewriteListener {
   public:
     virtual ~RewriteListener();
 
diff --git a/clang/include/clang/ARCMigrate/ARCMTActions.h b/clang/include/clang/ARCMigrate/ARCMTActions.h
index 714f4b33db446b..50c6142078f5c8 100644
--- a/clang/include/clang/ARCMigrate/ARCMTActions.h
+++ b/clang/include/clang/ARCMigrate/ARCMTActions.h
@@ -11,12 +11,13 @@
 
 #include "clang/ARCMigrate/FileRemapper.h"
 #include "clang/Frontend/FrontendAction.h"
+#include "clang/Support/Compiler.h"
 #include <memory>
 
 namespace clang {
 namespace arcmt {
 
-class CheckAction : public WrapperFrontendAction {
+class CLANG_ABI CheckAction : public WrapperFrontendAction {
 protected:
   bool BeginInvocation(CompilerInstance &CI) override;
 
@@ -24,7 +25,7 @@ class CheckAction : public WrapperFrontendAction {
   CheckAction(std::unique_ptr<FrontendAction> WrappedAction);
 };
 
-class ModifyAction : public WrapperFrontendAction {
+class CLANG_ABI ModifyAction : public WrapperFrontendAction {
 protected:
   bool BeginInvocation(CompilerInstance &CI) override;
 
@@ -32,7 +33,7 @@ class ModifyAction : public WrapperFrontendAction {
   ModifyAction(std::unique_ptr<FrontendAction> WrappedAction);
 };
 
-class MigrateSourceAction : public ASTFrontendAction {
+class CLANG_ABI MigrateSourceAction : public ASTFrontendAction {
   FileRemapper Remapper;
 protected:
   bool BeginInvocation(CompilerInstance &CI) override;
@@ -40,7 +41,7 @@ class MigrateSourceAction : public ASTFrontendAction {
                                                  StringRef InFile) override;
 };
 
-class MigrateAction : public WrapperFrontendAction {
+class CLANG_ABI MigrateAction : public WrapperFrontendAction {
   std::string MigrateDir;
   std::string PlistOut;
   bool EmitPremigrationARCErrors;
@@ -55,7 +56,7 @@ class MigrateAction : public WrapperFrontendAction {
 };
 
 /// Migrates to modern ObjC syntax.
-class ObjCMigrateAction : public WrapperFrontendAction {
+class CLANG_ABI ObjCMigrateAction : public WrapperFrontendAction {
   std::string MigrateDir;
   unsigned    ObjCMigAction;
   FileRemapper Remapper;
diff --git a/clang/include/clang/ARCMigrate/FileRemapper.h b/clang/include/clang/ARCMigrate/FileRemapper.h
index afcee363516a21..3c9f706a75cf38 100644
--- a/clang/include/clang/ARCMigrate/FileRemapper.h
+++ b/clang/include/clang/ARCMigrate/FileRemapper.h
@@ -11,6 +11,7 @@
 
 #include "clang/Basic/FileEntry.h"
 #include "clang/Basic/LLVM.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
@@ -29,7 +30,7 @@ namespace clang {
 
 namespace arcmt {
 
-class FileRemapper {
+class CLANG_ABI FileRemapper {
   // FIXME: Reuse the same FileManager for multiple ASTContexts.
   std::unique_ptr<FileManager> FileMgr;
 
diff --git a/clang/include/clang/AST/APNumericStorage.h b/clang/include/clang/AST/APNumericStorage.h
index 95eddbcd86e839..ae634d46dfea2b 100644
--- a/clang/include/clang/AST/APNumericStorage.h
+++ b/clang/include/clang/AST/APNumericStorage.h
@@ -9,6 +9,7 @@
 #ifndef LLVM_CLANG_AST_APNUMERICSTORAGE_H
 #define LLVM_CLANG_AST_APNUMERICSTORAGE_H
 
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APInt.h"
 
@@ -23,7 +24,7 @@ class ASTContext;
 /// to allocate IntegerLiteral/FloatingLiteral nodes the memory associated with
 /// the APFloat/APInt values will never get freed. APNumericStorage uses
 /// ASTContext's allocator for memory allocation.
-class APNumericStorage {
+class CLANG_ABI APNumericStorage {
   union {
     uint64_t VAL;   ///< Used to store the <= 64 bits integer value.
     uint64_t *pVal; ///< Used to store the >64 bits integer value.
diff --git a/clang/include/clang/AST/APValue.h b/clang/include/clang/AST/APValue.h
index c4206b73b11562..fc6baf92a90202 100644
--- a/clang/include/clang/AST/APValue.h
+++ b/clang/include/clang/AST/APValue.h
@@ -14,6 +14,7 @@
 #define LLVM_CLANG_AST_APVALUE_H
 
 #include "clang/Basic/LLVM.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/APFixedPoint.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APSInt.h"
@@ -41,7 +42,7 @@ template <typename T> class BasicReaderBase;
   class QualType;
 
 /// Symbolic representation of typeid(T) for some type T.
-class TypeInfoLValue {
+class CLANG_ABI TypeInfoLValue {
   const Type *T;
 
 public:
@@ -119,7 +120,7 @@ namespace clang {
 /// APValue - This class implements a discriminated union of [uninitialized]
 /// [APSInt] [APFloat], [Complex APSInt] [Complex APFloat], [Expr + Offset],
 /// [Vector: N * APValue], [Array: N * APValue]
-class APValue {
+class CLANG_ABI APValue {
   typedef llvm::APFixedPoint APFixedPoint;
   typedef llvm::APSInt APSInt;
   typedef llvm::APFloat APFloat;
@@ -143,7 +144,7 @@ class APValue {
     AddrLabelDiff
   };
 
-  class LValueBase {
+  class CLANG_ABI LValueBase {
     typedef llvm::PointerUnion<const ValueDecl *, const Expr *, TypeInfoLValue,
                                DynamicAllocLValue>
         PtrTy;
@@ -179,11 +180,11 @@ class APValue {
 
     QualType getType() const;
 
-    friend bool operator==(const LValueBase &LHS, const LValueBase &RHS);
+    friend CLANG_ABI bool operator==(const LValueBase &LHS, const LValueBase &RHS);
     friend bool operator!=(const LValueBase &LHS, const LValueBase &RHS) {
       return !(LHS == RHS);
     }
-    friend llvm::hash_code hash_value(const LValueBase &Base);
+    friend CLANG_ABI llvm::hash_code hash_value(const LValueBase &Base);
     friend struct llvm::DenseMapInfo<LValueBase>;
 
   private:
@@ -205,7 +206,7 @@ class APValue {
   typedef llvm::PointerIntPair<const Decl *, 1, bool> BaseOrMemberType;
 
   /// A non-discriminated union of a base, field, or array index.
-  class LValuePathEntry {
+  class CLANG_ABI LValuePathEntry {
     static_assert(sizeof(uintptr_t) <= sizeof(uint64_t),
                   "pointer doesn't fit in 64 bits?");
     uint64_t Value;
@@ -237,7 +238,7 @@ class APValue {
       return llvm::hash_value(A.Value);
     }
   };
-  class LValuePathSerializationHelper {
+  class CLANG_ABI LValuePathSerializationHelper {
     const void *Ty;
 
   public:
@@ -274,7 +275,7 @@ class APValue {
     Vec &operator=(const Vec &) = delete;
     ~Vec() { delete[] Elts; }
   };
-  struct Arr {
+  struct CLANG_ABI Arr {
     APValue *Elts;
     unsigned NumElts, ArrSize;
     Arr(unsigned NumElts, unsigned ArrSize);
@@ -282,7 +283,7 @@ class APValue {
     Arr &operator=(const Arr &) = delete;
     ~Arr();
   };
-  struct StructData {
+  struct CLANG_ABI StructData {
     APValue *Elts;
     unsigned NumBases;
     unsigned NumFields;
@@ -291,7 +292,7 @@ class APValue {
     StructData &operator=(const StructData &) = delete;
     ~StructData();
   };
-  struct UnionData {
+  struct CLANG_ABI UnionData {
     const FieldDecl *Field;
     APValue *Value;
     UnionData();
@@ -702,7 +703,7 @@ class APValue {
 } // end namespace clang.
 
 namespace llvm {
-template<> struct DenseMapInfo<clang::APValue::LValueBase> {
+template<> struct CLANG_ABI DenseMapInfo<clang::APValue::LValueBase> {
   static clang::APValue::LValueBase getEmptyKey();
   static clang::APValue::LValueBase getTombstoneKey();
   static unsigned getHashValue(const clang::APValue::LValueBase &Base);
diff --git a/clang/include/clang/AST/ASTConcept.h b/clang/include/clang/AST/ASTConcept.h
index 00500e214f4ce6..59b0a8e9d96a9d 100644
--- a/clang/include/clang/AST/ASTConcept.h
+++ b/clang/include/clang/AST/ASTConcept.h
@@ -18,6 +18,7 @@
 #include "clang/AST/NestedNameSpecifier.h"
 #include "clang/AST/TemplateBase.h"
 #include "clang/Basic/SourceLocation.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/PointerUnion.h"
 #include "llvm/ADT/SmallVector.h"
@@ -32,7 +33,7 @@ struct PrintingPolicy;
 
 /// The result of a constraint satisfaction check, containing the necessary
 /// information to diagnose an unsatisfied constraint.
-class ConstraintSatisfaction : public llvm::FoldingSetNode {
+class CLANG_ABI ConstraintSatisfaction : public llvm::FoldingSetNode {
   // The template-like entity that 'owns' the constraint checked here (can be a
   // constrained entity or a concept).
   const NamedDecl *ConstraintOwner = nullptr;
@@ -84,7 +85,7 @@ using UnsatisfiedConstraintRecord =
 /// necessary information to diagnose an unsatisfied constraint.
 ///
 /// This is safe to store in an AST node, as opposed to ConstraintSatisfaction.
-struct ASTConstraintSatisfaction final :
+struct CLANG_ABI ASTConstraintSatisfaction final :
     llvm::TrailingObjects<ASTConstraintSatisfaction,
                           UnsatisfiedConstraintRecord> {
   std::size_t NumRecords;
@@ -121,7 +122,7 @@ struct ASTConstraintSatisfaction final :
 ///
 ///   template <std::derives_from<Expr> T> void dump();
 ///             ~~~~~~~~~~~~~~~~~~~~~~~ (in TemplateTypeParmDecl)
-class ConceptReference {
+class CLANG_ABI ConceptReference {
   // \brief The optional nested name specifier used when naming the concept.
   NestedNameSpecifierLoc NestedNameSpec;
 
diff --git a/clang/include/clang/AST/ASTConsumer.h b/clang/include/clang/AST/ASTConsumer.h
index 447f2592d23595..735c7e549f5cac 100644
--- a/clang/include/clang/AST/ASTConsumer.h
+++ b/clang/include/clang/AST/ASTConsumer.h
@@ -13,6 +13,7 @@
 #ifndef LLVM_CLANG_AST_ASTCONSUMER_H
 #define LLVM_CLANG_AST_ASTCONSUMER_H
 
+#include "clang/Support/Compiler.h"
 namespace clang {
   class ASTContext;
   class CXXMethodDecl;
@@ -31,7 +32,7 @@ namespace clang {
 /// ASTCons...
[truncated]

diff --git a/clang/include/clang/APINotes/APINotesManager.h b/clang/include/clang/APINotes/APINotesManager.h
index 98592438e90eab..05d7930d3a2e7f 100644
--- a/clang/include/clang/APINotes/APINotesManager.h
+++ b/clang/include/clang/APINotes/APINotesManager.h
@@ -10,6 +10,7 @@
 #define LLVM_CLANG_APINOTES_APINOTESMANAGER_H
 
 #include "clang/Basic/SourceLocation.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/PointerUnion.h"
@@ -41,7 +42,7 @@ class APINotesReader;
 /// external API notes files that correspond to a given header. Its primary
 /// operation is \c findAPINotes(), which finds the API notes reader that
 /// provides information about the declarations at that location.
-class APINotesManager {
+class CLANG_ABI APINotesManager {
   using ReaderEntry = llvm::PointerUnion<DirectoryEntryRef, APINotesReader *>;
 
   SourceManager &SM;
diff --git a/clang/include/clang/APINotes/APINotesReader.h b/clang/include/clang/APINotes/APINotesReader.h
index baf63340640242..58ee2857c7930f 100644
--- a/clang/include/clang/APINotes/APINotesReader.h
+++ b/clang/include/clang/APINotes/APINotesReader.h
@@ -16,6 +16,7 @@
 #define LLVM_CLANG_APINOTES_READER_H
 
 #include "clang/APINotes/Types.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/VersionTuple.h"
 #include <memory>
@@ -25,7 +26,7 @@ namespace api_notes {
 
 /// A class that reads API notes data from a binary file that was written by
 /// the \c APINotesWriter.
-class APINotesReader {
+class CLANG_ABI APINotesReader {
   class Implementation;
   std::unique_ptr<Implementation> Implementation;
 
diff --git a/clang/include/clang/APINotes/APINotesWriter.h b/clang/include/clang/APINotes/APINotesWriter.h
index 3cc16c3d959faf..b8b45a89dcfc8b 100644
--- a/clang/include/clang/APINotes/APINotesWriter.h
+++ b/clang/include/clang/APINotes/APINotesWriter.h
@@ -16,6 +16,7 @@
 #define LLVM_CLANG_APINOTES_WRITER_H
 
 #include "clang/APINotes/Types.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/VersionTuple.h"
 #include "llvm/Support/raw_ostream.h"
@@ -29,7 +30,7 @@ namespace api_notes {
 
 /// A class that writes API notes data to a binary representation that can be
 /// read by the \c APINotesReader.
-class APINotesWriter {
+class CLANG_ABI APINotesWriter {
   class Implementation;
   std::unique_ptr<Implementation> Implementation;
 
diff --git a/clang/include/clang/APINotes/APINotesYAMLCompiler.h b/clang/include/clang/APINotes/APINotesYAMLCompiler.h
index 9c24ed85b6a124..3954cf347e8244 100644
--- a/clang/include/clang/APINotes/APINotesYAMLCompiler.h
+++ b/clang/include/clang/APINotes/APINotesYAMLCompiler.h
@@ -9,6 +9,7 @@
 #ifndef LLVM_CLANG_APINOTES_APINOTESYAMLCOMPILER_H
 #define LLVM_CLANG_APINOTES_APINOTESYAMLCOMPILER_H
 
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/raw_ostream.h"
@@ -22,10 +23,10 @@ namespace api_notes {
 /// Parses the APINotes YAML content and writes the representation back to the
 /// specified stream.  This provides a means of testing the YAML processing of
 /// the APINotes format.
-bool parseAndDumpAPINotes(llvm::StringRef YI, llvm::raw_ostream &OS);
+CLANG_ABI bool parseAndDumpAPINotes(llvm::StringRef YI, llvm::raw_ostream &OS);
 
 /// Converts API notes from YAML format to binary format.
-bool compileAPINotes(llvm::StringRef YAMLInput, const FileEntry *SourceFile,
+CLANG_ABI bool compileAPINotes(llvm::StringRef YAMLInput, const FileEntry *SourceFile,
                      llvm::raw_ostream &OS,
                      llvm::SourceMgr::DiagHandlerTy DiagHandler = nullptr,
                      void *DiagHandlerCtxt = nullptr);
diff --git a/clang/include/clang/APINotes/Types.h b/clang/include/clang/APINotes/Types.h
index 89889910d1a073..574406586c4674 100644
--- a/clang/include/clang/APINotes/Types.h
+++ b/clang/include/clang/APINotes/Types.h
@@ -10,6 +10,7 @@
 #define LLVM_CLANG_APINOTES_TYPES_H
 
 #include "clang/Basic/Specifiers.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringRef.h"
 #include <climits>
@@ -49,7 +50,7 @@ enum class SwiftNewTypeKind {
 /// Describes API notes data for any entity.
 ///
 /// This is used as the base of all API notes.
-class CommonEntityInfo {
+class CLANG_ABI CommonEntityInfo {
 public:
   /// Message to use when this entity is unavailable.
   std::string UnavailableMsg;
@@ -132,7 +133,7 @@ inline bool operator!=(const CommonEntityInfo &LHS,
 }
 
 /// Describes API notes for types.
-class CommonTypeInfo : public CommonEntityInfo {
+class CLANG_ABI CommonTypeInfo : public CommonEntityInfo {
   /// The Swift type to which a given type is bridged.
   ///
   /// Reflects the swift_bridge attribute.
@@ -194,7 +195,7 @@ inline bool operator!=(const CommonTypeInfo &LHS, const CommonTypeInfo &RHS) {
 
 /// Describes API notes data for an Objective-C class or protocol or a C++
 /// namespace.
-class ContextInfo : public CommonTypeInfo {
+class CLANG_ABI ContextInfo : public CommonTypeInfo {
   /// Whether this class has a default nullability.
   LLVM_PREFERRED_TYPE(bool)
   unsigned HasDefaultNullability : 1;
@@ -301,7 +302,7 @@ inline bool operator!=(const ContextInfo &LHS, const ContextInfo &RHS) {
 }
 
 /// API notes for a variable/property.
-class VariableInfo : public CommonEntityInfo {
+class CLANG_ABI VariableInfo : public CommonEntityInfo {
   /// Whether this property has been audited for nullability.
   LLVM_PREFERRED_TYPE(bool)
   unsigned NullabilityAudited : 1;
@@ -358,7 +359,7 @@ inline bool operator!=(const VariableInfo &LHS, const VariableInfo &RHS) {
 }
 
 /// Describes API notes data for an Objective-C property.
-class ObjCPropertyInfo : public VariableInfo {
+class CLANG_ABI ObjCPropertyInfo : public VariableInfo {
   LLVM_PREFERRED_TYPE(bool)
   unsigned SwiftImportAsAccessorsSpecified : 1;
   LLVM_PREFERRED_TYPE(bool)
@@ -416,7 +417,7 @@ inline bool operator!=(const ObjCPropertyInfo &LHS,
 }
 
 /// Describes a function or method parameter.
-class ParamInfo : public VariableInfo {
+class CLANG_ABI ParamInfo : public VariableInfo {
   /// Whether noescape was specified.
   LLVM_PREFERRED_TYPE(bool)
   unsigned NoEscapeSpecified : 1;
@@ -486,7 +487,7 @@ inline bool operator!=(const ParamInfo &LHS, const ParamInfo &RHS) {
 }
 
 /// API notes for a function or method.
-class FunctionInfo : public CommonEntityInfo {
+class CLANG_ABI FunctionInfo : public CommonEntityInfo {
 private:
   static constexpr const uint64_t NullabilityKindMask = 0x3;
   static constexpr const unsigned NullabilityKindSize = 2;
@@ -606,7 +607,7 @@ inline bool operator!=(const FunctionInfo &LHS, const FunctionInfo &RHS) {
 }
 
 /// Describes API notes data for an Objective-C method.
-class ObjCMethodInfo : public FunctionInfo {
+class CLANG_ABI ObjCMethodInfo : public FunctionInfo {
 public:
   /// Whether this is a designated initializer of its class.
   LLVM_PREFERRED_TYPE(bool)
@@ -675,7 +676,7 @@ class EnumConstantInfo : public CommonEntityInfo {
 };
 
 /// Describes API notes data for a tag.
-class TagInfo : public CommonTypeInfo {
+class CLANG_ABI TagInfo : public CommonTypeInfo {
   LLVM_PREFERRED_TYPE(bool)
   unsigned HasFlagEnum : 1;
   LLVM_PREFERRED_TYPE(bool)
@@ -765,7 +766,7 @@ inline bool operator!=(const TagInfo &LHS, const TagInfo &RHS) {
 }
 
 /// Describes API notes data for a typedef.
-class TypedefInfo : public CommonTypeInfo {
+class CLANG_ABI TypedefInfo : public CommonTypeInfo {
 public:
   std::optional<SwiftNewTypeKind> SwiftWrapper;
 
diff --git a/clang/include/clang/ARCMigrate/ARCMT.h b/clang/include/clang/ARCMigrate/ARCMT.h
index 2b950e3d2cc2bf..dc078101e371ff 100644
--- a/clang/include/clang/ARCMigrate/ARCMT.h
+++ b/clang/include/clang/ARCMigrate/ARCMT.h
@@ -12,6 +12,7 @@
 #include "clang/ARCMigrate/FileRemapper.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Frontend/CompilerInvocation.h"
+#include "clang/Support/Compiler.h"
 
 namespace clang {
   class ASTContext;
@@ -37,7 +38,7 @@ namespace arcmt {
 /// the pre-migration ARC diagnostics.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool
+CLANG_ABI bool
 checkForManualIssues(CompilerInvocation &CI, const FrontendInputFile &Input,
                      std::shared_ptr<PCHContainerOperations> PCHContainerOps,
                      DiagnosticConsumer *DiagClient,
@@ -48,7 +49,7 @@ checkForManualIssues(CompilerInvocation &CI, const FrontendInputFile &Input,
 /// applies automatic modifications to source files to conform to ARC.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool
+CLANG_ABI bool
 applyTransformations(CompilerInvocation &origCI,
                      const FrontendInputFile &Input,
                      std::shared_ptr<PCHContainerOperations> PCHContainerOps,
@@ -65,7 +66,7 @@ applyTransformations(CompilerInvocation &origCI,
 /// the pre-migration ARC diagnostics.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool migrateWithTemporaryFiles(
+CLANG_ABI bool migrateWithTemporaryFiles(
     CompilerInvocation &origCI, const FrontendInputFile &Input,
     std::shared_ptr<PCHContainerOperations> PCHContainerOps,
     DiagnosticConsumer *DiagClient, StringRef outputDir,
@@ -75,7 +76,7 @@ bool migrateWithTemporaryFiles(
 /// migrateWithTemporaryFiles produced.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool getFileRemappings(std::vector<std::pair<std::string,std::string> > &remap,
+CLANG_ABI bool getFileRemappings(std::vector<std::pair<std::string,std::string> > &remap,
                        StringRef outputDir,
                        DiagnosticConsumer *DiagClient);
 
@@ -83,17 +84,17 @@ bool getFileRemappings(std::vector<std::pair<std::string,std::string> > &remap,
 /// info.
 ///
 /// \returns false if no error is produced, true otherwise.
-bool getFileRemappingsFromFileList(
+CLANG_ABI bool getFileRemappingsFromFileList(
                         std::vector<std::pair<std::string,std::string> > &remap,
                         ArrayRef<StringRef> remapFiles,
                         DiagnosticConsumer *DiagClient);
 
 typedef void (*TransformFn)(MigrationPass &pass);
 
-std::vector<TransformFn> getAllTransformations(LangOptions::GCMode OrigGCMode,
+CLANG_ABI std::vector<TransformFn> getAllTransformations(LangOptions::GCMode OrigGCMode,
                                                bool NoFinalizeRemoval);
 
-class MigrationProcess {
+class CLANG_ABI MigrationProcess {
   CompilerInvocation OrigCI;
   std::shared_ptr<PCHContainerOperations> PCHContainerOps;
   DiagnosticConsumer *DiagClient;
@@ -107,7 +108,7 @@ class MigrationProcess {
                    DiagnosticConsumer *diagClient,
                    StringRef outputDir = StringRef());
 
-  class RewriteListener {
+  class CLANG_ABI RewriteListener {
   public:
     virtual ~RewriteListener();
 
diff --git a/clang/include/clang/ARCMigrate/ARCMTActions.h b/clang/include/clang/ARCMigrate/ARCMTActions.h
index 714f4b33db446b..50c6142078f5c8 100644
--- a/clang/include/clang/ARCMigrate/ARCMTActions.h
+++ b/clang/include/clang/ARCMigrate/ARCMTActions.h
@@ -11,12 +11,13 @@
 
 #include "clang/ARCMigrate/FileRemapper.h"
 #include "clang/Frontend/FrontendAction.h"
+#include "clang/Support/Compiler.h"
 #include <memory>
 
 namespace clang {
 namespace arcmt {
 
-class CheckAction : public WrapperFrontendAction {
+class CLANG_ABI CheckAction : public WrapperFrontendAction {
 protected:
   bool BeginInvocation(CompilerInstance &CI) override;
 
@@ -24,7 +25,7 @@ class CheckAction : public WrapperFrontendAction {
   CheckAction(std::unique_ptr<FrontendAction> WrappedAction);
 };
 
-class ModifyAction : public WrapperFrontendAction {
+class CLANG_ABI ModifyAction : public WrapperFrontendAction {
 protected:
   bool BeginInvocation(CompilerInstance &CI) override;
 
@@ -32,7 +33,7 @@ class ModifyAction : public WrapperFrontendAction {
   ModifyAction(std::unique_ptr<FrontendAction> WrappedAction);
 };
 
-class MigrateSourceAction : public ASTFrontendAction {
+class CLANG_ABI MigrateSourceAction : public ASTFrontendAction {
   FileRemapper Remapper;
 protected:
   bool BeginInvocation(CompilerInstance &CI) override;
@@ -40,7 +41,7 @@ class MigrateSourceAction : public ASTFrontendAction {
                                                  StringRef InFile) override;
 };
 
-class MigrateAction : public WrapperFrontendAction {
+class CLANG_ABI MigrateAction : public WrapperFrontendAction {
   std::string MigrateDir;
   std::string PlistOut;
   bool EmitPremigrationARCErrors;
@@ -55,7 +56,7 @@ class MigrateAction : public WrapperFrontendAction {
 };
 
 /// Migrates to modern ObjC syntax.
-class ObjCMigrateAction : public WrapperFrontendAction {
+class CLANG_ABI ObjCMigrateAction : public WrapperFrontendAction {
   std::string MigrateDir;
   unsigned    ObjCMigAction;
   FileRemapper Remapper;
diff --git a/clang/include/clang/ARCMigrate/FileRemapper.h b/clang/include/clang/ARCMigrate/FileRemapper.h
index afcee363516a21..3c9f706a75cf38 100644
--- a/clang/include/clang/ARCMigrate/FileRemapper.h
+++ b/clang/include/clang/ARCMigrate/FileRemapper.h
@@ -11,6 +11,7 @@
 
 #include "clang/Basic/FileEntry.h"
 #include "clang/Basic/LLVM.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
@@ -29,7 +30,7 @@ namespace clang {
 
 namespace arcmt {
 
-class FileRemapper {
+class CLANG_ABI FileRemapper {
   // FIXME: Reuse the same FileManager for multiple ASTContexts.
   std::unique_ptr<FileManager> FileMgr;
 
diff --git a/clang/include/clang/AST/APNumericStorage.h b/clang/include/clang/AST/APNumericStorage.h
index 95eddbcd86e839..ae634d46dfea2b 100644
--- a/clang/include/clang/AST/APNumericStorage.h
+++ b/clang/include/clang/AST/APNumericStorage.h
@@ -9,6 +9,7 @@
 #ifndef LLVM_CLANG_AST_APNUMERICSTORAGE_H
 #define LLVM_CLANG_AST_APNUMERICSTORAGE_H
 
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APInt.h"
 
@@ -23,7 +24,7 @@ class ASTContext;
 /// to allocate IntegerLiteral/FloatingLiteral nodes the memory associated with
 /// the APFloat/APInt values will never get freed. APNumericStorage uses
 /// ASTContext's allocator for memory allocation.
-class APNumericStorage {
+class CLANG_ABI APNumericStorage {
   union {
     uint64_t VAL;   ///< Used to store the <= 64 bits integer value.
     uint64_t *pVal; ///< Used to store the >64 bits integer value.
diff --git a/clang/include/clang/AST/APValue.h b/clang/include/clang/AST/APValue.h
index c4206b73b11562..fc6baf92a90202 100644
--- a/clang/include/clang/AST/APValue.h
+++ b/clang/include/clang/AST/APValue.h
@@ -14,6 +14,7 @@
 #define LLVM_CLANG_AST_APVALUE_H
 
 #include "clang/Basic/LLVM.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/APFixedPoint.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APSInt.h"
@@ -41,7 +42,7 @@ template <typename T> class BasicReaderBase;
   class QualType;
 
 /// Symbolic representation of typeid(T) for some type T.
-class TypeInfoLValue {
+class CLANG_ABI TypeInfoLValue {
   const Type *T;
 
 public:
@@ -119,7 +120,7 @@ namespace clang {
 /// APValue - This class implements a discriminated union of [uninitialized]
 /// [APSInt] [APFloat], [Complex APSInt] [Complex APFloat], [Expr + Offset],
 /// [Vector: N * APValue], [Array: N * APValue]
-class APValue {
+class CLANG_ABI APValue {
   typedef llvm::APFixedPoint APFixedPoint;
   typedef llvm::APSInt APSInt;
   typedef llvm::APFloat APFloat;
@@ -143,7 +144,7 @@ class APValue {
     AddrLabelDiff
   };
 
-  class LValueBase {
+  class CLANG_ABI LValueBase {
     typedef llvm::PointerUnion<const ValueDecl *, const Expr *, TypeInfoLValue,
                                DynamicAllocLValue>
         PtrTy;
@@ -179,11 +180,11 @@ class APValue {
 
     QualType getType() const;
 
-    friend bool operator==(const LValueBase &LHS, const LValueBase &RHS);
+    friend CLANG_ABI bool operator==(const LValueBase &LHS, const LValueBase &RHS);
     friend bool operator!=(const LValueBase &LHS, const LValueBase &RHS) {
       return !(LHS == RHS);
     }
-    friend llvm::hash_code hash_value(const LValueBase &Base);
+    friend CLANG_ABI llvm::hash_code hash_value(const LValueBase &Base);
     friend struct llvm::DenseMapInfo<LValueBase>;
 
   private:
@@ -205,7 +206,7 @@ class APValue {
   typedef llvm::PointerIntPair<const Decl *, 1, bool> BaseOrMemberType;
 
   /// A non-discriminated union of a base, field, or array index.
-  class LValuePathEntry {
+  class CLANG_ABI LValuePathEntry {
     static_assert(sizeof(uintptr_t) <= sizeof(uint64_t),
                   "pointer doesn't fit in 64 bits?");
     uint64_t Value;
@@ -237,7 +238,7 @@ class APValue {
       return llvm::hash_value(A.Value);
     }
   };
-  class LValuePathSerializationHelper {
+  class CLANG_ABI LValuePathSerializationHelper {
     const void *Ty;
 
   public:
@@ -274,7 +275,7 @@ class APValue {
     Vec &operator=(const Vec &) = delete;
     ~Vec() { delete[] Elts; }
   };
-  struct Arr {
+  struct CLANG_ABI Arr {
     APValue *Elts;
     unsigned NumElts, ArrSize;
     Arr(unsigned NumElts, unsigned ArrSize);
@@ -282,7 +283,7 @@ class APValue {
     Arr &operator=(const Arr &) = delete;
     ~Arr();
   };
-  struct StructData {
+  struct CLANG_ABI StructData {
     APValue *Elts;
     unsigned NumBases;
     unsigned NumFields;
@@ -291,7 +292,7 @@ class APValue {
     StructData &operator=(const StructData &) = delete;
     ~StructData();
   };
-  struct UnionData {
+  struct CLANG_ABI UnionData {
     const FieldDecl *Field;
     APValue *Value;
     UnionData();
@@ -702,7 +703,7 @@ class APValue {
 } // end namespace clang.
 
 namespace llvm {
-template<> struct DenseMapInfo<clang::APValue::LValueBase> {
+template<> struct CLANG_ABI DenseMapInfo<clang::APValue::LValueBase> {
   static clang::APValue::LValueBase getEmptyKey();
   static clang::APValue::LValueBase getTombstoneKey();
   static unsigned getHashValue(const clang::APValue::LValueBase &Base);
diff --git a/clang/include/clang/AST/ASTConcept.h b/clang/include/clang/AST/ASTConcept.h
index 00500e214f4ce6..59b0a8e9d96a9d 100644
--- a/clang/include/clang/AST/ASTConcept.h
+++ b/clang/include/clang/AST/ASTConcept.h
@@ -18,6 +18,7 @@
 #include "clang/AST/NestedNameSpecifier.h"
 #include "clang/AST/TemplateBase.h"
 #include "clang/Basic/SourceLocation.h"
+#include "clang/Support/Compiler.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/PointerUnion.h"
 #include "llvm/ADT/SmallVector.h"
@@ -32,7 +33,7 @@ struct PrintingPolicy;
 
 /// The result of a constraint satisfaction check, containing the necessary
 /// information to diagnose an unsatisfied constraint.
-class ConstraintSatisfaction : public llvm::FoldingSetNode {
+class CLANG_ABI ConstraintSatisfaction : public llvm::FoldingSetNode {
   // The template-like entity that 'owns' the constraint checked here (can be a
   // constrained entity or a concept).
   const NamedDecl *ConstraintOwner = nullptr;
@@ -84,7 +85,7 @@ using UnsatisfiedConstraintRecord =
 /// necessary information to diagnose an unsatisfied constraint.
 ///
 /// This is safe to store in an AST node, as opposed to ConstraintSatisfaction.
-struct ASTConstraintSatisfaction final :
+struct CLANG_ABI ASTConstraintSatisfaction final :
     llvm::TrailingObjects<ASTConstraintSatisfaction,
                           UnsatisfiedConstraintRecord> {
   std::size_t NumRecords;
@@ -121,7 +122,7 @@ struct ASTConstraintSatisfaction final :
 ///
 ///   template <std::derives_from<Expr> T> void dump();
 ///             ~~~~~~~~~~~~~~~~~~~~~~~ (in TemplateTypeParmDecl)
-class ConceptReference {
+class CLANG_ABI ConceptReference {
   // \brief The optional nested name specifier used when naming the concept.
   NestedNameSpecifierLoc NestedNameSpec;
 
diff --git a/clang/include/clang/AST/ASTConsumer.h b/clang/include/clang/AST/ASTConsumer.h
index 447f2592d23595..735c7e549f5cac 100644
--- a/clang/include/clang/AST/ASTConsumer.h
+++ b/clang/include/clang/AST/ASTConsumer.h
@@ -13,6 +13,7 @@
 #ifndef LLVM_CLANG_AST_ASTCONSUMER_H
 #define LLVM_CLANG_AST_ASTCONSUMER_H
 
+#include "clang/Support/Compiler.h"
 namespace clang {
   class ASTContext;
   class CXXMethodDecl;
@@ -31,7 +32,7 @@ namespace clang {
 /// ASTCons...
[truncated]