[clang] [C++20] [Modules] [Itanium ABI] Generate the vtable in the module unit of dynamic classes (PR #75912)

[David Blaikie via cfe-commits]

================
@@ -1483,10 +1483,15 @@ void ASTDeclWriter::VisitCXXRecordDecl(CXXRecordDecl *D) {
   if (D->isThisDeclarationADefinition())
     Record.AddCXXDefinitionData(D);
 
-  // Store (what we currently believe to be) the key function to avoid
-  // deserializing every method so we can compute it.
-  if (D->isCompleteDefinition())
-    Record.AddDeclRef(Context.getCurrentKeyFunction(D));
+  if (D->isCompleteDefinition()) {
+    if (D->getOwningModule() && D->getOwningModule()->isInterfaceOrPartition())
+      Writer.ModularCodegenDecls.push_back(Writer.GetDeclRef(D));
+    else {
+      // Store (what we currently believe to be) the key function to avoid
----------------
dwblaikie wrote:

This seems like a serialization optimization that'd be separate/good to go in its own PR (make it easier to see what the change is, how it's tested, etc) separate from this one?

https://github.com/llvm/llvm-project/pull/75912