[[no_unique_address]] on non-class field is still potentially overlapping

This agrees with existing GCC behaviour: https://godbolt.org/z/Grr8r4sYr

Author: MitalAshok

clang/include/clang/AST/Decl.h

@@ -3177,9 +3177,10 @@ class FieldDecl : public DeclaratorDecl, public Mergeable<FieldDecl> {
   /// [[no_unique_address]] attribute.
   bool isZeroSize(const ASTContext &Ctx) const;
 
-  /// Determine if this field is of potentially-overlapping class type, that
+  /// Determine if this field is of potentially-overlapping type, that
   /// is, subobject with the [[no_unique_address]] attribute
-  bool isPotentiallyOverlapping() const;
+  /// If ClassOnly is true, the field also has to be of class type.
+  bool isPotentiallyOverlapping(bool ClassOnly = true) const;
 
   /// Get the kind of (C++11) default member initializer that this field has.
   InClassInitStyle getInClassInitStyle() const {

clang/lib/AST/Decl.cpp

@@ -4623,8 +4623,9 @@ bool FieldDecl::isZeroSize(const ASTContext &Ctx) const {
   });
 }
 
-bool FieldDecl::isPotentiallyOverlapping() const {
-  return hasAttr<NoUniqueAddressAttr>() && getType()->getAsCXXRecordDecl();
+bool FieldDecl::isPotentiallyOverlapping(bool ClassOnly) const {
+  return hasAttr<NoUniqueAddressAttr>() &&
+         (!ClassOnly || getType()->getAsCXXRecordDecl());
 }
 
 unsigned FieldDecl::getFieldIndex() const {

clang/lib/AST/RecordLayoutBuilder.cpp

@@ -2445,7 +2445,7 @@ static bool isItaniumPOD(const ASTContext &Context, const CXXRecordDecl *RD) {
         return true;
     }
 
-    return FD->isPotentiallyOverlapping();
+    return FD->isPotentiallyOverlapping(/*ClassOnly=*/false);
   };
 
   if (llvm::any_of(RD->fields(), IsDisqualifying))

clang/test/Layout/no-unique-address.cpp

@@ -1,5 +1,5 @@
-// RUN: %clang_cc1 -std=c++20 -fsyntax-only -triple x86_64-linux-gnu -fdump-record-layouts %s | FileCheck %s --check-prefixes=CHECK,NEW
-// RUN: %clang_cc1 -fclang-abi-compat=19.0 -std=c++20 -fsyntax-only -triple x86_64-linux-gnu -fdump-record-layouts %s | FileCheck %s --check-prefixes=CHECK,OLD
+// RUN: %clang_cc1 -DOLD_ABI=false -std=c++20 -fsyntax-only -triple x86_64-linux-gnu -fdump-record-layouts %s | FileCheck %s --check-prefixes=CHECK,NEW
+// RUN: %clang_cc1 -fclang-abi-compat=19.0 -DOLD_ABI=true -std=c++20 -fsyntax-only -triple x86_64-linux-gnu -fdump-record-layouts %s | FileCheck %s --check-prefixes=CHECK,OLD
 
 namespace Empty {
   struct A {};
@@ -269,3 +269,23 @@ namespace RepeatedVBase {
   // CHECK-NEXT:       | [sizeof=32, dsize=9, align=16,
   // CHECK-NEXT:       |  nvsize=9, nvalign=16]
 }
+
+namespace PotentiallyOverlappingNonClass {
+  struct A {
+    [[no_unique_address]] alignas(2) char x;
+  };
+  struct B : A {
+    char y;
+  };
+  static_assert(sizeof(B) == (OLD_ABI ? 4 : 2));
+  // CHECK:*** Dumping AST Record Layout
+  // CHECK:          0 | struct PotentiallyOverlappingNonClass::B
+  // CHECK-NEXT:     0 |   struct PotentiallyOverlappingNonClass::A (base)
+  // CHECK-NEXT:     0 |     char x
+  // NEW-NEXT:       1 |   char y
+  // NEW-NEXT:         | [sizeof=2, dsize=2, align=2,
+  // NEW-NEXT:         |  nvsize=2, nvalign=2]
+  // OLD-NEXT:       2 |   char y
+  // OLD-NEXT:         | [sizeof=4, dsize=3, align=2,
+  // OLD-NEXT:         |  nvsize=3, nvalign=2]
+}