Support explicit instantiation of function templates and members of class

templates when only the declaration is in scope. This requires deferring the
instantiation to be lazy, and ensuring the definition is required for that
translation unit. We re-use the existing pending instantiation queue,
previously only used to track implicit instantiations which were required to be
lazy. Fixes PR7979.

A subsequent change will rename *PendingImplicitInstantiations to
*PendingInstatiations for clarity given its broader role.

llvm-svn: 112037

clang/lib/Sema/SemaTemplate.cpp

@@ -5071,8 +5071,7 @@ Sema::DeclResult Sema::ActOnExplicitInstantiation(Scope *S,
     // Instantiate static data member.
     Prev->setTemplateSpecializationKind(TSK, D.getIdentifierLoc());
     if (TSK == TSK_ExplicitInstantiationDefinition)
-      InstantiateStaticDataMemberDefinition(D.getIdentifierLoc(), Prev, false,
-                                            /*DefinitionRequired=*/true);
+      InstantiateStaticDataMemberDefinition(D.getIdentifierLoc(), Prev);
     
     // FIXME: Create an ExplicitInstantiation node?
     return (Decl*) 0;
@@ -5179,8 +5178,7 @@ Sema::DeclResult Sema::ActOnExplicitInstantiation(Scope *S,
   Specialization->setTemplateSpecializationKind(TSK, D.getIdentifierLoc());
   
   if (TSK == TSK_ExplicitInstantiationDefinition)
-    InstantiateFunctionDefinition(D.getIdentifierLoc(), Specialization, 
-                                  false, /*DefinitionRequired=*/true);
+    InstantiateFunctionDefinition(D.getIdentifierLoc(), Specialization);
  
   // C++0x [temp.explicit]p2:
   //   If the explicit instantiation is for a member function, a member class 

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -2040,8 +2040,12 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
         Diag(PatternDecl->getLocation(), 
              diag::note_explicit_instantiation_here);
       Function->setInvalidDecl();
+    } else if (Function->getTemplateSpecializationKind()
+                 == TSK_ExplicitInstantiationDefinition) {
+      PendingImplicitInstantiations.push_back(
+        std::make_pair(Function, PointOfInstantiation));
     }
-      
+
     return;
   }
 
@@ -2176,8 +2180,12 @@ void Sema::InstantiateStaticDataMemberDefinition(
            diag::err_explicit_instantiation_undefined_member)
         << 2 << Var->getDeclName() << Var->getDeclContext();
       Diag(Def->getLocation(), diag::note_explicit_instantiation_here);
-    }    
-    
+    } else if (Var->getTemplateSpecializationKind()
+                 == TSK_ExplicitInstantiationDefinition) {
+      PendingImplicitInstantiations.push_back(
+        std::make_pair(Var, PointOfInstantiation));
+    }
+
     return;
   }
 
@@ -2714,8 +2722,10 @@ void Sema::PerformPendingImplicitInstantiations(bool LocalOnly) {
                                             Function->getLocation(), *this,
                                             Context.getSourceManager(),
                                            "instantiating function definition");
-
-      InstantiateFunctionDefinition(/*FIXME:*/Inst.second, Function, true);
+      bool DefinitionRequired = Function->getTemplateSpecializationKind() ==
+                                TSK_ExplicitInstantiationDefinition;
+      InstantiateFunctionDefinition(/*FIXME:*/Inst.second, Function, true,
+                                    DefinitionRequired);
       continue;
     }
 
@@ -2734,9 +2744,12 @@ void Sema::PerformPendingImplicitInstantiations(bool LocalOnly) {
     case TSK_Undeclared:
       assert(false && "Cannot instantitiate an undeclared specialization.");
     case TSK_ExplicitInstantiationDeclaration:
-    case TSK_ExplicitInstantiationDefinition:
     case TSK_ExplicitSpecialization:
-      continue;  // No longer need implicit instantiation.
+      continue;  // No longer need to instantiate this type.
+    case TSK_ExplicitInstantiationDefinition:
+      // We only need an instantiation if the pending instantiation *is* the
+      // explicit instantiation.
+      if (Var != Var->getMostRecentDeclaration()) continue;
     case TSK_ImplicitInstantiation:
       break;
     }
@@ -2746,7 +2759,10 @@ void Sema::PerformPendingImplicitInstantiations(bool LocalOnly) {
                                           "instantiating static data member "
                                           "definition");
 
-    InstantiateStaticDataMemberDefinition(/*FIXME:*/Inst.second, Var, true);
+    bool DefinitionRequired = Var->getTemplateSpecializationKind() ==
+                              TSK_ExplicitInstantiationDefinition;
+    InstantiateStaticDataMemberDefinition(/*FIXME:*/Inst.second, Var, true,
+                                          DefinitionRequired);
   }
 }
 

clang/test/CXX/temp/temp.spec/temp.explicit/p3.cpp

@@ -2,8 +2,9 @@
 
 // A declaration of a function template shall be in scope at the point of the 
 // explicit instantiation of the function template.
-template<typename T> void f0(T) { }
+template<typename T> void f0(T);
 template void f0(int); // okay
+template<typename T> void f0(T) { }
 
 // A definition of the class or class template containing a member function 
 // template shall be in scope at the point of the explicit instantiation of 
@@ -47,3 +48,27 @@ template X2<int>::X2(); // expected-error{{not an instantiation}}
 template X2<int>::X2(const X2&); // expected-error{{not an instantiation}}
 template X2<int>::~X2(); // expected-error{{not an instantiation}}
 template X2<int> &X2<int>::operator=(const X2<int>&); // expected-error{{not an instantiation}}
+
+
+// A definition of a class template is sufficient to explicitly
+// instantiate a member of the class template which itself is not yet defined.
+namespace PR7979 {
+  template <typename T> struct S {
+    void f();
+    static void g();
+    static int i;
+    struct S2 {
+      void h();
+    };
+  };
+
+  template void S<int>::f();
+  template void S<int>::g();
+  template int S<int>::i;
+  template void S<int>::S2::h();
+
+  template <typename T> void S<T>::f() {}
+  template <typename T> void S<T>::g() {}
+  template <typename T> int S<T>::i;
+  template <typename T> void S<T>::S2::h() {}
+}

clang/test/CodeGenCXX/explicit-instantiation.cpp

@@ -1,5 +1,8 @@
 // RUN: %clang_cc1 -emit-llvm -triple i686-pc-linux-gnu -o - %s | FileCheck %s
 
+// This check logically is attached to 'template int S<int>::i;' below.
+// CHECK: @_ZN1SIiE1iE = weak global i32
+
 template<typename T, typename U, typename Result>
 struct plus {
   Result operator()(const T& t, const U& u) const;
@@ -12,3 +15,31 @@ Result plus<T, U, Result>::operator()(const T& t, const U& u) const {
 
 // CHECK: define weak_odr i32 @_ZNK4plusIillEclERKiRKl
 template struct plus<int, long, long>;
+
+// Check that we emit definitions from explicit instantiations even when they
+// occur prior to the definition itself.
+template <typename T> struct S {
+  void f();
+  static void g();
+  static int i;
+  struct S2 {
+    void h();
+  };
+};
+
+// CHECK: define weak_odr void @_ZN1SIiE1fEv
+template void S<int>::f();
+
+// CHECK: define weak_odr void @_ZN1SIiE1gEv
+template void S<int>::g();
+
+// See the check line at the top of the file.
+template int S<int>::i;
+
+// CHECK: define weak_odr void @_ZN1SIiE2S21hEv
+template void S<int>::S2::h();
+
+template <typename T> void S<T>::f() {}
+template <typename T> void S<T>::g() {}
+template <typename T> int S<T>::i;
+template <typename T> void S<T>::S2::h() {}