[Sema] Use MS ABI behavior for dllexport in Itanium

Similar to r284288, make the Itanium ABI follow MS ABI dllexport
semantics in the case of an explicit instantiation declaration followed
by a dllexport explicit instantiation definition.

Differential Revision: https://reviews.llvm.org/D26471

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@286419 91177308-0d34-0410-b5e6-96231b3b80d8

Author: smeenai

lib/Sema/SemaTemplate.cpp

@@ -7674,7 +7674,8 @@ Sema::ActOnExplicitInstantiation(Scope *S,
       Def->setTemplateSpecializationKind(TSK);
 
       if (!getDLLAttr(Def) && getDLLAttr(Specialization) &&
-          Context.getTargetInfo().getCXXABI().isMicrosoft()) {
+          (Context.getTargetInfo().getCXXABI().isMicrosoft() ||
+           Context.getTargetInfo().getTriple().isWindowsItaniumEnvironment())) {
         // In the MS ABI, an explicit instantiation definition can add a dll
         // attribute to a template with a previous instantiation declaration.
         // MinGW doesn't allow this.

test/CodeGenCXX/windows-itanium-dllexport.cpp

@@ -7,3 +7,19 @@ struct __declspec(dllexport) s {
 // CHECK: define {{.*}} dllexport {{.*}} @_ZN1saSERKS_
 // CHECK: define {{.*}} dllexport {{.*}} @_ZN1s1fEv
 
+template <class T>
+class c {
+  void f() {}
+};
+
+template class __declspec(dllexport) c<int>;
+
+// CHECK: define {{.*}} dllexport {{.*}} @_ZN1cIiEaSERKS0_
+// CHECK: define {{.*}} dllexport {{.*}} @_ZN1cIiE1fEv
+
+extern template class c<char>;
+template class __declspec(dllexport) c<char>;
+
+// CHECK: define {{.*}} dllexport {{.*}} @_ZN1cIcEaSERKS0_
+// CHECK: define {{.*}} dllexport {{.*}} @_ZN1cIcE1fEv
+