diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 7f4b395..bc31d46 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -16,7 +16,6 @@
 #include "clang/AST/ASTConsumer.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/ASTLambda.h"
-#include "clang/AST/ASTMutationListener.h"
 #include "clang/AST/CXXInheritance.h"
 #include "clang/AST/CharUnits.h"
 #include "clang/AST/CommentDiagnostic.h"
@@ -1974,9 +1973,7 @@
         New->setTypeSourceInfo(OldTD->getTypeSourceInfo());
 
       // Make the old tag definition visible.
-      if (auto *Listener = getASTMutationListener())
-        Listener->RedefinedHiddenDefinition(Hidden, NewTag->getLocation());
-      Hidden->setHidden(false);
+      makeMergedDefinitionVisible(Hidden, NewTag->getLocation());
     }
   }
 
@@ -11311,8 +11308,8 @@
 /// \param IsTypeSpecifier \c true if this is a type-specifier (or
 /// trailing-type-specifier) other than one in an alias-declaration.
 ///
-/// \param SkipBody If non-null, will be set to true if the caller should skip
-/// the definition of this tag, and treat it as if it were a declaration.
+/// \param SkipBody If non-null, will be set to indicate if the caller should
+/// skip the definition of this tag and treat it as if it were a declaration.
 Decl *Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
                      SourceLocation KWLoc, CXXScopeSpec &SS,
                      IdentifierInfo *Name, SourceLocation NameLoc,
@@ -11323,7 +11320,7 @@
                      SourceLocation ScopedEnumKWLoc,
                      bool ScopedEnumUsesClassTag,
                      TypeResult UnderlyingType,
-                     bool IsTypeSpecifier, bool *SkipBody) {
+                     bool IsTypeSpecifier, SkipBodyInfo *SkipBody) {
   // If this is not a definition, it must have a name.
   IdentifierInfo *OrigName = Name;
   assert((Name != nullptr || TUK == TUK_Definition) &&
@@ -11633,6 +11630,10 @@
     }
   }
 
+  // If we have a known previous declaration to use, then use it.
+  if (Previous.empty() && SkipBody && SkipBody->Previous)
+    Previous.addDecl(SkipBody->Previous);
+
   if (!Previous.empty()) {
     NamedDecl *PrevDecl = Previous.getFoundDecl();
     NamedDecl *DirectPrevDecl =
@@ -11774,10 +11775,8 @@
                 // assume that this definition is identical to the hidden one
                 // we already have. Make the existing definition visible and
                 // use it in place of this one.
-                *SkipBody = true;
-                if (auto *Listener = getASTMutationListener())
-                  Listener->RedefinedHiddenDefinition(Hidden, KWLoc);
-                Hidden->setHidden(false);
+                SkipBody->ShouldSkip = true;
+                makeMergedDefinitionVisible(Hidden, KWLoc);
                 return Def;
               } else if (!IsExplicitSpecializationAfterInstantiation) {
                 // A redeclaration in function prototype scope in C isn't
@@ -13465,6 +13464,29 @@
                                   Val, EnumVal);
 }
 
+Sema::SkipBodyInfo Sema::shouldSkipAnonEnumBody(Scope *S, IdentifierInfo *II,
+                                                SourceLocation IILoc) {
+  if (!getLangOpts().Modules || !getLangOpts().CPlusPlus)
+    return SkipBodyInfo();
+
+  // We have an anonymous enum definition. Look up the first enumerator to
+  // determine if we should merge the definition with an existing one and
+  // skip the body.
+  NamedDecl *PrevDecl = LookupSingleName(S, II, IILoc, LookupOrdinaryName,
+                                         ForRedeclaration);
+  auto *PrevECD = dyn_cast_or_null<EnumConstantDecl>(PrevDecl);
+  NamedDecl *Hidden;
+  if (PrevECD &&
+      !hasVisibleDefinition(cast<NamedDecl>(PrevECD->getDeclContext()),
+                            &Hidden)) {
+    SkipBodyInfo Skip;
+    Skip.ShouldSkip = true;
+    Skip.Previous = Hidden;
+    return Skip;
+  }
+
+  return SkipBodyInfo();
+}
 
 Decl *Sema::ActOnEnumConstant(Scope *S, Decl *theEnumDecl, Decl *lastEnumConst,
                               SourceLocation IdLoc, IdentifierInfo *Id,