diff --git a/clang/include/clang/AST/OpenACCClause.h b/clang/include/clang/AST/OpenACCClause.h
index 7a1b17cc4e44e3..51db58d484a25f 100644
--- a/clang/include/clang/AST/OpenACCClause.h
+++ b/clang/include/clang/AST/OpenACCClause.h
@@ -191,8 +191,9 @@ using DeviceTypeArgument = std::pair<IdentifierInfo *, SourceLocation>;
 /// an identifier. The 'asterisk' means 'the rest'.
 class OpenACCDeviceTypeClause final
     : public OpenACCClauseWithParams,
-      public llvm::TrailingObjects<OpenACCDeviceTypeClause,
+      private llvm::TrailingObjects<OpenACCDeviceTypeClause,
                                    DeviceTypeArgument> {
+  friend TrailingObjects;
   // Data stored in trailing objects as IdentifierInfo* /SourceLocation pairs. A
   // nullptr IdentifierInfo* represents an asterisk.
   unsigned NumArchs;
@@ -377,7 +378,8 @@ class OpenACCClauseWithExprs : public OpenACCClauseWithParams {
 // Represents the 'devnum' and expressions lists for the 'wait' clause.
 class OpenACCWaitClause final
     : public OpenACCClauseWithExprs,
-      public llvm::TrailingObjects<OpenACCWaitClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCWaitClause, Expr *> {
+  friend TrailingObjects;
   SourceLocation QueuesLoc;
   OpenACCWaitClause(SourceLocation BeginLoc, SourceLocation LParenLoc,
                     Expr *DevNumExpr, SourceLocation QueuesLoc,
@@ -419,7 +421,8 @@ class OpenACCWaitClause final
 
 class OpenACCNumGangsClause final
     : public OpenACCClauseWithExprs,
-      public llvm::TrailingObjects<OpenACCNumGangsClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCNumGangsClause, Expr *> {
+  friend TrailingObjects;
 
   OpenACCNumGangsClause(SourceLocation BeginLoc, SourceLocation LParenLoc,
                         ArrayRef<Expr *> IntExprs, SourceLocation EndLoc)
@@ -449,7 +452,8 @@ class OpenACCNumGangsClause final
 
 class OpenACCTileClause final
     : public OpenACCClauseWithExprs,
-      public llvm::TrailingObjects<OpenACCTileClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCTileClause, Expr *> {
+  friend TrailingObjects;
   OpenACCTileClause(SourceLocation BeginLoc, SourceLocation LParenLoc,
                     ArrayRef<Expr *> SizeExprs, SourceLocation EndLoc)
       : OpenACCClauseWithExprs(OpenACCClauseKind::Tile, BeginLoc, LParenLoc,
@@ -503,7 +507,8 @@ class OpenACCClauseWithSingleIntExpr : public OpenACCClauseWithExprs {
 
 class OpenACCGangClause final
     : public OpenACCClauseWithExprs,
-      public llvm::TrailingObjects<OpenACCGangClause, Expr *, OpenACCGangKind> {
+      private llvm::TrailingObjects<OpenACCGangClause, Expr *, OpenACCGangKind> {
+  friend TrailingObjects;
 protected:
   OpenACCGangClause(SourceLocation BeginLoc, SourceLocation LParenLoc,
                     ArrayRef<OpenACCGangKind> GangKinds,
@@ -658,7 +663,8 @@ class OpenACCClauseWithVarList : public OpenACCClauseWithExprs {
 
 class OpenACCPrivateClause final
     : public OpenACCClauseWithVarList,
-      public llvm::TrailingObjects<OpenACCPrivateClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCPrivateClause, Expr *> {
+  friend TrailingObjects;
 
   OpenACCPrivateClause(SourceLocation BeginLoc, SourceLocation LParenLoc,
                        ArrayRef<Expr *> VarList, SourceLocation EndLoc)
@@ -680,7 +686,8 @@ class OpenACCPrivateClause final
 
 class OpenACCFirstPrivateClause final
     : public OpenACCClauseWithVarList,
-      public llvm::TrailingObjects<OpenACCFirstPrivateClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCFirstPrivateClause, Expr *> {
+  friend TrailingObjects;
 
   OpenACCFirstPrivateClause(SourceLocation BeginLoc, SourceLocation LParenLoc,
                             ArrayRef<Expr *> VarList, SourceLocation EndLoc)
@@ -702,7 +709,8 @@ class OpenACCFirstPrivateClause final
 
 class OpenACCDevicePtrClause final
     : public OpenACCClauseWithVarList,
-      public llvm::TrailingObjects<OpenACCDevicePtrClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCDevicePtrClause, Expr *> {
+  friend TrailingObjects;
 
   OpenACCDevicePtrClause(SourceLocation BeginLoc, SourceLocation LParenLoc,
                          ArrayRef<Expr *> VarList, SourceLocation EndLoc)
@@ -724,7 +732,8 @@ class OpenACCDevicePtrClause final
 
 class OpenACCAttachClause final
     : public OpenACCClauseWithVarList,
-      public llvm::TrailingObjects<OpenACCAttachClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCAttachClause, Expr *> {
+  friend TrailingObjects;
 
   OpenACCAttachClause(SourceLocation BeginLoc, SourceLocation LParenLoc,
                       ArrayRef<Expr *> VarList, SourceLocation EndLoc)
@@ -746,7 +755,8 @@ class OpenACCAttachClause final
 
 class OpenACCDetachClause final
     : public OpenACCClauseWithVarList,
-      public llvm::TrailingObjects<OpenACCDetachClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCDetachClause, Expr *> {
+  friend TrailingObjects;
 
   OpenACCDetachClause(SourceLocation BeginLoc, SourceLocation LParenLoc,
                       ArrayRef<Expr *> VarList, SourceLocation EndLoc)
@@ -768,7 +778,8 @@ class OpenACCDetachClause final
 
 class OpenACCDeleteClause final
     : public OpenACCClauseWithVarList,
-      public llvm::TrailingObjects<OpenACCDeleteClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCDeleteClause, Expr *> {
+  friend TrailingObjects;
 
   OpenACCDeleteClause(SourceLocation BeginLoc, SourceLocation LParenLoc,
                       ArrayRef<Expr *> VarList, SourceLocation EndLoc)
@@ -790,7 +801,8 @@ class OpenACCDeleteClause final
 
 class OpenACCUseDeviceClause final
     : public OpenACCClauseWithVarList,
-      public llvm::TrailingObjects<OpenACCUseDeviceClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCUseDeviceClause, Expr *> {
+  friend TrailingObjects;
 
   OpenACCUseDeviceClause(SourceLocation BeginLoc, SourceLocation LParenLoc,
                          ArrayRef<Expr *> VarList, SourceLocation EndLoc)
@@ -812,7 +824,8 @@ class OpenACCUseDeviceClause final
 
 class OpenACCNoCreateClause final
     : public OpenACCClauseWithVarList,
-      public llvm::TrailingObjects<OpenACCNoCreateClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCNoCreateClause, Expr *> {
+  friend TrailingObjects;
 
   OpenACCNoCreateClause(SourceLocation BeginLoc, SourceLocation LParenLoc,
                         ArrayRef<Expr *> VarList, SourceLocation EndLoc)
@@ -834,7 +847,8 @@ class OpenACCNoCreateClause final
 
 class OpenACCPresentClause final
     : public OpenACCClauseWithVarList,
-      public llvm::TrailingObjects<OpenACCPresentClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCPresentClause, Expr *> {
+  friend TrailingObjects;
 
   OpenACCPresentClause(SourceLocation BeginLoc, SourceLocation LParenLoc,
                        ArrayRef<Expr *> VarList, SourceLocation EndLoc)
@@ -856,7 +870,8 @@ class OpenACCPresentClause final
 
 class OpenACCCopyClause final
     : public OpenACCClauseWithVarList,
-      public llvm::TrailingObjects<OpenACCCopyClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCCopyClause, Expr *> {
+  friend TrailingObjects;
 
   OpenACCCopyClause(OpenACCClauseKind Spelling, SourceLocation BeginLoc,
                     SourceLocation LParenLoc, ArrayRef<Expr *> VarList,
@@ -885,7 +900,8 @@ class OpenACCCopyClause final
 
 class OpenACCCopyInClause final
     : public OpenACCClauseWithVarList,
-      public llvm::TrailingObjects<OpenACCCopyInClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCCopyInClause, Expr *> {
+  friend TrailingObjects;
   bool IsReadOnly;
 
   OpenACCCopyInClause(OpenACCClauseKind Spelling, SourceLocation BeginLoc,
@@ -917,7 +933,8 @@ class OpenACCCopyInClause final
 
 class OpenACCCopyOutClause final
     : public OpenACCClauseWithVarList,
-      public llvm::TrailingObjects<OpenACCCopyOutClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCCopyOutClause, Expr *> {
+  friend TrailingObjects;
   bool IsZero;
 
   OpenACCCopyOutClause(OpenACCClauseKind Spelling, SourceLocation BeginLoc,
@@ -949,7 +966,8 @@ class OpenACCCopyOutClause final
 
 class OpenACCCreateClause final
     : public OpenACCClauseWithVarList,
-      public llvm::TrailingObjects<OpenACCCreateClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCCreateClause, Expr *> {
+  friend TrailingObjects;
   bool IsZero;
 
   OpenACCCreateClause(OpenACCClauseKind Spelling, SourceLocation BeginLoc,
@@ -981,7 +999,8 @@ class OpenACCCreateClause final
 
 class OpenACCReductionClause final
     : public OpenACCClauseWithVarList,
-      public llvm::TrailingObjects<OpenACCReductionClause, Expr *> {
+      private llvm::TrailingObjects<OpenACCReductionClause, Expr *> {
+  friend TrailingObjects;
   OpenACCReductionOperator Op;
 
   OpenACCReductionClause(SourceLocation BeginLoc, SourceLocation LParenLoc,
diff --git a/clang/include/clang/AST/StmtOpenACC.h b/clang/include/clang/AST/StmtOpenACC.h
index e256a4b7c69eb5..a1903cd9e3a23a 100644
--- a/clang/include/clang/AST/StmtOpenACC.h
+++ b/clang/include/clang/AST/StmtOpenACC.h
@@ -127,11 +127,12 @@ class OpenACCAssociatedStmtConstruct : public OpenACCConstructStmt {
 /// the 'Kind'.
 class OpenACCComputeConstruct final
     : public OpenACCAssociatedStmtConstruct,
-      public llvm::TrailingObjects<OpenACCComputeConstruct,
-                                   const OpenACCClause *> {
+      private llvm::TrailingObjects<OpenACCComputeConstruct,
+                                    const OpenACCClause *> {
   friend class ASTStmtWriter;
   friend class ASTStmtReader;
   friend class ASTContext;
+  friend TrailingObjects;
   OpenACCComputeConstruct(unsigned NumClauses)
       : OpenACCAssociatedStmtConstruct(
             OpenACCComputeConstructClass, OpenACCDirectiveKind::Invalid,
@@ -189,7 +190,7 @@ class OpenACCComputeConstruct final
 /// Construct.
 class OpenACCLoopConstruct final
     : public OpenACCAssociatedStmtConstruct,
-      public llvm::TrailingObjects<OpenACCLoopConstruct,
+      private llvm::TrailingObjects<OpenACCLoopConstruct,
                                    const OpenACCClause *> {
   // The compute/combined construct kind this loop is associated with, or
   // invalid if this is an orphaned loop construct.
@@ -202,6 +203,7 @@ class OpenACCLoopConstruct final
   friend class OpenACCAssociatedStmtConstruct;
   friend class OpenACCCombinedConstruct;
   friend class OpenACCComputeConstruct;
+  friend TrailingObjects;
 
   OpenACCLoopConstruct(unsigned NumClauses);
 
@@ -245,8 +247,9 @@ class OpenACCLoopConstruct final
 // shared with both loop and compute constructs.
 class OpenACCCombinedConstruct final
     : public OpenACCAssociatedStmtConstruct,
-      public llvm::TrailingObjects<OpenACCCombinedConstruct,
+      private llvm::TrailingObjects<OpenACCCombinedConstruct,
                                    const OpenACCClause *> {
+  friend TrailingObjects;
   OpenACCCombinedConstruct(unsigned NumClauses)
       : OpenACCAssociatedStmtConstruct(
             OpenACCCombinedConstructClass, OpenACCDirectiveKind::Invalid,
@@ -297,8 +300,9 @@ class OpenACCCombinedConstruct final
 // and clauses, but is otherwise pretty simple.
 class OpenACCDataConstruct final
     : public OpenACCAssociatedStmtConstruct,
-      public llvm::TrailingObjects<OpenACCDataConstruct,
+      private llvm::TrailingObjects<OpenACCDataConstruct,
                                    const OpenACCClause *> {
+  friend TrailingObjects;
   OpenACCDataConstruct(unsigned NumClauses)
       : OpenACCAssociatedStmtConstruct(
             OpenACCDataConstructClass, OpenACCDirectiveKind::Data,
@@ -345,8 +349,9 @@ class OpenACCDataConstruct final
 // This class represents a 'enter data' construct, which JUST has clauses.
 class OpenACCEnterDataConstruct final
     : public OpenACCConstructStmt,
-      public llvm::TrailingObjects<OpenACCEnterDataConstruct,
+      private llvm::TrailingObjects<OpenACCEnterDataConstruct,
                                    const OpenACCClause *> {
+  friend TrailingObjects;
   OpenACCEnterDataConstruct(unsigned NumClauses)
       : OpenACCConstructStmt(OpenACCEnterDataConstructClass,
                              OpenACCDirectiveKind::EnterData, SourceLocation{},
@@ -382,8 +387,9 @@ class OpenACCEnterDataConstruct final
 // This class represents a 'exit data' construct, which JUST has clauses.
 class OpenACCExitDataConstruct final
     : public OpenACCConstructStmt,
-      public llvm::TrailingObjects<OpenACCExitDataConstruct,
+      private llvm::TrailingObjects<OpenACCExitDataConstruct,
                                    const OpenACCClause *> {
+  friend TrailingObjects;
   OpenACCExitDataConstruct(unsigned NumClauses)
       : OpenACCConstructStmt(OpenACCExitDataConstructClass,
                              OpenACCDirectiveKind::ExitData, SourceLocation{},
@@ -420,8 +426,9 @@ class OpenACCExitDataConstruct final
 // statement and clauses, but is otherwise pretty simple.
 class OpenACCHostDataConstruct final
     : public OpenACCAssociatedStmtConstruct,
-      public llvm::TrailingObjects<OpenACCHostDataConstruct,
+      private llvm::TrailingObjects<OpenACCHostDataConstruct,
                                    const OpenACCClause *> {
+  friend TrailingObjects;
   OpenACCHostDataConstruct(unsigned NumClauses)
       : OpenACCAssociatedStmtConstruct(
             OpenACCHostDataConstructClass, OpenACCDirectiveKind::HostData,