[clang] [clang-repl] fix vtable symbol duplication error (closes #141039) (PR #185648)

[Vassil Vassilev via cfe-commits]

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@@ -1300,11 +1301,18 @@ void CodeGenModule::EmitDeferredVTables() {
   size_t savedSize = DeferredVTables.size();
 #endif
 
-  for (const CXXRecordDecl *RD : DeferredVTables)
+  for (const CXXRecordDecl *RD : DeferredVTables) {
+    // if a table has been emitted in an earlier PTU, but was also marked
+    // deferred, we should skip if the linkage is external
+    if (EmittedVTables.count(RD) &&
+        getVTableLinkage(RD) == llvm::GlobalValue::ExternalLinkage)
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vgvassilev wrote:

This is exactly what I was after. Thank you for the explanation.

We have two options:
  * Perhaps the most minimal change would be to remove from the list of DeferredVTables the strong symbols
  * Keep a the current patch.

@efriedma-quic, can you help me with deciding on this part?

https://github.com/llvm/llvm-project/pull/185648