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

[Chuanqi Xu via cfe-commits]

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@@ -6853,6 +6853,13 @@ void CodeGenModule::EmitTopLevelDecl(Decl *D) {
         if (ES->hasExternalDefinitions(D) == ExternalASTSource::EK_Never)
           DI->completeUnusedClass(*CRD);
     }
+    // If we're emitting a dynamic class from the importable module we're
+    // emitting, we always need to emit the virtual table according to the ABI
+    // requirement.
+    if (CRD->getDefinition() && CRD->isDynamicClass() &&
+        CRD->isInCurrentModuleUnit())
+      EmitVTable(CRD);
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ChuanqiXu9 wrote:

Yes, this can happen with the two phase compilation of modules (https://clang.llvm.org/docs/StandardCPlusPlusModules.html#how-to-produce-a-bmi). Which will compile a `.cppm` file to a `.pcm` file, and we will compile the `.pcm` file the `.o` file.

The one phase compilation can also happen for modules.

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