Revert "[MS] Don't expect vftables to be provided for extern template instantiations"

This reverts commit r273296, it broke the Windows self-host.

llvm-svn: 273305

2 files changed, 10 insertions, 13 deletions

diff --git a/clang/lib/AST/VTableBuilder.cpp b/clang/lib/AST/VTableBuilder.cpp
index 640fbf47aea..e43acc4de78 100644
--- a/clang/lib/AST/VTableBuilder.cpp
+++ b/clang/lib/AST/VTableBuilder.cpp
@@ -2545,13 +2545,14 @@ public:
         MostDerivedClassLayout(Context.getASTRecordLayout(MostDerivedClass)),
         WhichVFPtr(*Which),
         Overriders(MostDerivedClass, CharUnits(), MostDerivedClass) {
-    // Provide the RTTI component if RTTIData is enabled. If the vftable would
-    // be available externally, we should not provide the RTTI componenent. It
-    // is currently impossible to get available externally vftables with either
-    // dllimport or extern template instantiations, but eventually we may add a
-    // flag to support additional devirtualization that needs this.
+    // Only include the RTTI component if we know that we will provide a
+    // definition of the vftable.  We always provide the definition of
+    // dllimported classes.
     if (Context.getLangOpts().RTTIData)
-      HasRTTIComponent = true;
+      if (MostDerivedClass->hasAttr<DLLImportAttr>() ||
+          MostDerivedClass->getTemplateSpecializationKind() !=
+              TSK_ExplicitInstantiationDeclaration)
+        HasRTTIComponent = true;
 
     LayoutVFTable();
 
diff --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
index da9b7421879..38461446de5 100644
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -794,10 +794,6 @@ CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
       return DiscardableODRLinkage;
 
     case TSK_ExplicitInstantiationDeclaration:
-      // Explicit instantiations in MSVC do not provide vtables, so we must emit
-      // our own.
-      if (getTarget().getCXXABI().isMicrosoft())
-        return DiscardableODRLinkage;
       return shouldEmitAvailableExternallyVTable(*this, RD)
                  ? llvm::GlobalVariable::AvailableExternallyLinkage
                  : llvm::GlobalVariable::ExternalLinkage;
@@ -843,9 +839,9 @@ CodeGenVTables::GenerateClassData(const CXXRecordDecl *RD) {
 bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {
   assert(RD->isDynamicClass() && "Non-dynamic classes have no VTable.");
 
-  // We always synthesize vtables if they are needed in the MS ABI. MSVC doesn't
-  // emit them even if there is an explicit template instantiation.
-  if (CGM.getTarget().getCXXABI().isMicrosoft())
+  // We always synthesize vtables on the import side regardless of whether or
+  // not it is an explicit instantiation declaration.
+  if (CGM.getTarget().getCXXABI().isMicrosoft() && RD->hasAttr<DLLImportAttr>())
     return false;
 
   // If we have an explicit instantiation declaration (and not a