[C++20] [Modules] Correct the linkage for template instantiations in

named modules

Close #97313

In the previous patch (#75912),
I made an oversight that I ignored the templates in named module when
calculating the linkage for the vtables. In this patch, I tried to
correct the behavior by merging the logics to calculate the linkage with
key functions with named modules.

clang/lib/CodeGen/CGVTables.cpp

@@ -1079,33 +1079,38 @@ CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
   if (!RD->isExternallyVisible())
     return llvm::GlobalVariable::InternalLinkage;
 
-  // V-tables for non-template classes with an owning module are always
-  // uniquely emitted in that module.
-  if (RD->isInNamedModule())
-    return llvm::GlobalVariable::ExternalLinkage;
-
-  // We're at the end of the translation unit, so the current key
-  // function is fully correct.
-  const CXXMethodDecl *keyFunction = Context.getCurrentKeyFunction(RD);
-  if (keyFunction && !RD->hasAttr<DLLImportAttr>()) {
+  bool IsInNamedModule = RD->isInNamedModule();
+  // If the CXXRecordDecl are not in a module unit, we need to get
+  // its key function. We're at the end of the translation unit, so the current
+  // key function is fully correct.
+  const CXXMethodDecl *keyFunction =
+      IsInNamedModule ? nullptr : Context.getCurrentKeyFunction(RD);
+  if (IsInNamedModule || (keyFunction && !RD->hasAttr<DLLImportAttr>())) {
     // If this class has a key function, use that to determine the
     // linkage of the vtable.
     const FunctionDecl *def = nullptr;
-    if (keyFunction->hasBody(def))
+    if (keyFunction && keyFunction->hasBody(def))
       keyFunction = cast<CXXMethodDecl>(def);
 
-    switch (keyFunction->getTemplateSpecializationKind()) {
-      case TSK_Undeclared:
-      case TSK_ExplicitSpecialization:
+    bool IsExternalDefinition =
+        IsInNamedModule ? RD->shouldEmitInExternalSource() : !def;
+
+    TemplateSpecializationKind Kind =
+        IsInNamedModule ? RD->getTemplateSpecializationKind()
+                        : keyFunction->getTemplateSpecializationKind();
+
+    switch (Kind) {
+    case TSK_Undeclared:
+    case TSK_ExplicitSpecialization:
       assert(
-          (def || CodeGenOpts.OptimizationLevel > 0 ||
+          (IsInNamedModule || def || CodeGenOpts.OptimizationLevel > 0 ||
            CodeGenOpts.getDebugInfo() != llvm::codegenoptions::NoDebugInfo) &&
-          "Shouldn't query vtable linkage without key function, "
-          "optimizations, or debug info");
-      if (!def && CodeGenOpts.OptimizationLevel > 0)
+          "Shouldn't query vtable linkage without the class in module units, "
+          "key function, optimizations, or debug info");
+      if (IsExternalDefinition && CodeGenOpts.OptimizationLevel > 0)
         return llvm::GlobalVariable::AvailableExternallyLinkage;
 
-      if (keyFunction->isInlined())
+      if (keyFunction && keyFunction->isInlined())
         return !Context.getLangOpts().AppleKext
                    ? llvm::GlobalVariable::LinkOnceODRLinkage
                    : llvm::Function::InternalLinkage;
@@ -1124,7 +1129,7 @@ CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
 
       case TSK_ExplicitInstantiationDeclaration:
         llvm_unreachable("Should not have been asked to emit this");
-    }
+      }
   }
 
   // -fapple-kext mode does not support weak linkage, so we must use

clang/test/Modules/pr97313.cppm

@@ -0,0 +1,118 @@
+// REQUIRES: !system-windows
+//
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/Base.cppm \
+// RUN:     -emit-module-interface -o %t/Base.pcm
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/Sub.cppm \
+// RUN:     -emit-module-interface -o %t/Sub.pcm -fprebuilt-module-path=%t
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/Sub.pcm \
+// RUN:     -emit-llvm -o %t/Sub.pcm -o - -fprebuilt-module-path=%t | \
+// RUN:     FileCheck %t/Sub.cppm
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/main.cpp \
+// RUN:     -emit-llvm -fprebuilt-module-path=%t -o - | FileCheck %t/main.cpp
+//
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/Mod.cppm \
+// RUN:     -emit-module-interface -o %t/Mod.pcm
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/Mod.pcm \
+// RUN:     -emit-llvm -o - | FileCheck %t/Mod.cppm
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/Use.cpp \
+// RUN:     -emit-llvm -fprebuilt-module-path=%t -o - | \
+// RUN:     FileCheck %t/Use.cpp
+
+//--- Base.cppm
+export module Base;
+
+export template <class>
+class Base
+{
+public:
+    constexpr Base();
+    constexpr virtual ~Base();
+};
+
+template <class X>
+constexpr Base<X>::Base() = default;
+
+template <class X>
+constexpr Base<X>::~Base() = default;
+
+//--- Sub.cppm
+export module Sub;
+export import Base;
+
+export class Sub : public Base<int>
+{
+};
+
+// CHECK: @_ZTIW4Base4BaseIiE = {{.*}}linkonce_odr
+
+//--- main.cpp
+import Sub;
+
+int main()
+{
+    Base<int> *b = new Sub();
+    delete b;
+}
+
+// CHECK: @_ZTIW4Base4BaseIiE = {{.*}}linkonce_odr
+
+//--- Mod.cppm
+export module Mod;
+
+export class NonTemplate {
+public:
+    virtual ~NonTemplate();
+};
+
+// CHECK: @_ZTIW3Mod11NonTemplate = {{.*}}constant
+
+export template <class C>
+class Template {
+public:
+    virtual ~Template();
+};
+
+export template<>
+class Template<char> {
+public:
+    virtual ~Template();
+};
+
+// CHECK: @_ZTIW3Mod8TemplateIcE = {{.*}}constant
+
+export template class Template<unsigned>;
+
+// CHECK: @_ZTIW3Mod8TemplateIjE = {{.*}}weak_odr
+
+export extern template class Template<double>;
+
+auto v = new Template<signed int>();
+
+// CHECK: @_ZTIW3Mod8TemplateIiE = {{.*}}linkonce_odr
+
+//--- Use.cpp
+import Mod;
+
+auto v1 = new NonTemplate();
+auto v2 = new Template<char>();
+auto v3 = new Template<unsigned>();
+auto v4 = new Template<double>();
+auto v5 = new Template<signed int>();
+auto v6 = new Template<NonTemplate>();
+
+// CHECK: @_ZTVW3Mod11NonTemplate = {{.*}}external
+// CHECK: @_ZTVW3Mod8TemplateIcE = {{.*}}external
+// CHECK: @_ZTVW3Mod8TemplateIjE = {{.*}}weak_odr
+// CHECK: @_ZTSW3Mod8TemplateIjE = {{.*}}weak_odr
+// CHECK: @_ZTIW3Mod8TemplateIjE = {{.*}}weak_odr
+// CHECK: @_ZTVW3Mod8TemplateIdE = {{.*}}external
+// CHECK: @_ZTVW3Mod8TemplateIiE = {{.*}}linkonce_odr
+// CHECK: @_ZTSW3Mod8TemplateIiE = {{.*}}linkonce_odr
+// CHECK: @_ZTIW3Mod8TemplateIiE = {{.*}}linkonce_odr
+// CHECK: @_ZTVW3Mod8TemplateIS_11NonTemplateE = {{.*}}linkonce_odr
+// CHECK: @_ZTSW3Mod8TemplateIS_11NonTemplateE = {{.*}}linkonce_odr
+// CHECK: @_ZTIW3Mod8TemplateIS_11NonTemplateE = {{.*}}linkonce_odr