When recording empty subobjects we should always look at the primary virtual base.

llvm-svn: 104464

clang/lib/AST/RecordLayoutBuilder.cpp

@@ -530,8 +530,15 @@ void ASTRecordLayoutBuilder::UpdateEmptyClassOffsets(const CXXRecordDecl *RD,
     UpdateEmptyClassOffsets(FD, Offset + FieldOffset);
   }
 
+  const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase();
+  
   if (UpdateVBases) {
     // FIXME: Update virtual bases.
+  } else if (PrimaryBase && Layout.getPrimaryBaseWasVirtual()) {
+    // We always want to update the offsets of a primary virtual base.
+    assert(Layout.getVBaseClassOffset(PrimaryBase) == 0 &&
+           "primary base class offset must always be 0!");
+    UpdateEmptyClassOffsets(PrimaryBase, Offset, /*UpdateVBases=*/false);
   }
 }
 

clang/test/SemaCXX/empty-class-layout.cpp

@@ -2,6 +2,8 @@
 
 #define SA(n, p) int a##n[(p) ? 1 : -1]
 
+namespace Test0 {
+
 struct A { int a; };
 SA(0, sizeof(A) == 4);
 
@@ -66,3 +68,19 @@ SA(11, sizeof(S7) == 8);
 struct S8 : Empty, A {
 };
 SA(12, sizeof(S8) == 4);
+
+}
+
+namespace Test1 {
+
+// Test that we don't try to place both A subobjects at offset 0.
+struct A { };
+class B { virtual void f(); };
+class C : A, virtual B { };
+struct D : virtual C { };
+struct E : virtual A { };
+class F : D, E { };
+
+SA(0, sizeof(F) == 24);
+
+}