Improve key-function computation for templates. In particular:

  - All classes can have a key function; templates don't change that.
  non-template classes when computing the key function.
  - We always mark all of the virtual member functions of class
  template instantiations. 
  - The vtable for an instantiation of a class template has weak
  linkage. 

We could probably use available_externally linkage for vtables of
classes instantiated by explicit instantiation declarations (extern
templates), but GCC doesn't do this and I'm not 100% that the ABI
permits it.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@92753 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 16 insertions, 2 deletions

diff --git a/lib/CodeGen/CGVtable.cpp b/lib/CodeGen/CGVtable.cpp
index ba5a0c3543..ca148da956 100644
--- a/lib/CodeGen/CGVtable.cpp
+++ b/lib/CodeGen/CGVtable.cpp
@@ -1493,8 +1493,22 @@ void CGVtableInfo::MaybeEmitVtable(GlobalDecl GD) {
   llvm::GlobalVariable::LinkageTypes Linkage;
   if (RD->isInAnonymousNamespace() || !RD->hasLinkage())
     Linkage = llvm::GlobalVariable::InternalLinkage;
-  else if (KeyFunction && !MD->isInlined())
-    Linkage = llvm::GlobalVariable::ExternalLinkage;
+  else if (KeyFunction && !MD->isInlined()) {
+    switch (MD->getTemplateSpecializationKind()) {
+    case TSK_Undeclared:
+    case TSK_ExplicitSpecialization:
+      Linkage = llvm::GlobalVariable::ExternalLinkage;
+      break;
+
+    case TSK_ImplicitInstantiation:
+    case TSK_ExplicitInstantiationDeclaration:
+      // FIXME: could an explicit instantiation declaration imply
+      // available_externally linkage?
+    case TSK_ExplicitInstantiationDefinition:
+      Linkage = llvm::GlobalVariable::WeakODRLinkage;
+      break;
+    }
+  }
   else
     Linkage = llvm::GlobalVariable::WeakODRLinkage;