1 files changed, 6 insertions, 0 deletions
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index a8b41ba..3603e9cd 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -11581,6 +11581,12 @@ QualType ASTContext::mergeTagDefinitions(QualType LHS, QualType RHS) {
   if (LangOpts.CPlusPlus || !LangOpts.C23)
     return {};
 
+  // Nameless tags are comparable only within outer definitions. At the top
+  // level they are not comparable.
+  const TagDecl *LTagD = LHS->castAsTagDecl(), *RTagD = RHS->castAsTagDecl();
+  if (!LTagD->getIdentifier() || !RTagD->getIdentifier())
+    return {};
+
   // C23, on the other hand, requires the members to be "the same enough", so
   // we use a structural equivalence check.
   StructuralEquivalenceContext::NonEquivalentDeclSet NonEquivalentDecls;