[dllexport] Sort out emission order of delayed exported classes

Relands r260194 with a fix. If we have a template that transitions from
an extern template to an explicitly instantiated dllexport template, we
would add that class to the delayed exported class list without flushing
it.

For explicit instantiations, we can just flush the list of delayed
classes immediately. We don't have to worry about the bug fixed in
r260194 in this case because explicit instantiations can only occur at
file and namespace scope.

Fixes PR26490.

llvm-svn: 262056

clang/include/clang/Sema/Sema.h

@@ -5295,11 +5295,18 @@ public:
                             ArrayRef<CXXCtorInitializer*> MemInits,
                             bool AnyErrors);
 
+  /// \brief Check class-level dllimport/dllexport attribute. The caller must
+  /// ensure that referenceDLLExportedClassMethods is called some point later
+  /// when all outer classes of Class are complete.
   void checkClassLevelDLLAttribute(CXXRecordDecl *Class);
+
+  void referenceDLLExportedClassMethods();
+
   void propagateDLLAttrToBaseClassTemplate(
       CXXRecordDecl *Class, Attr *ClassAttr,
       ClassTemplateSpecializationDecl *BaseTemplateSpec,
       SourceLocation BaseLoc);
+
   void CheckCompletedCXXClass(CXXRecordDecl *Record);
   void ActOnFinishCXXMemberSpecification(Scope* S, SourceLocation RLoc,
                                          Decl *TagDecl,

clang/lib/Sema/SemaDeclCXX.cpp

@@ -9533,6 +9533,10 @@ void Sema::ActOnFinishCXXNonNestedClass(Decl *D) {
   if (RD && Context.getTargetInfo().getCXXABI().isMicrosoft())
     getDefaultArgExprsForConstructors(*this, RD);
 
+  referenceDLLExportedClassMethods();
+}
+
+void Sema::referenceDLLExportedClassMethods() {
   if (!DelayedDllExportClasses.empty()) {
     // Calling ReferenceDllExportedMethods might cause the current function to
     // be called again, so use a local copy of DelayedDllExportClasses.

clang/lib/Sema/SemaTemplate.cpp

@@ -7458,7 +7458,13 @@ Sema::ActOnExplicitInstantiation(Scope *S,
             getDLLAttr(Specialization)->clone(getASTContext()));
         A->setInherited(true);
         Def->addAttr(A);
+
+        // We reject explicit instantiations in class scope, so there should
+        // never be any delayed exported classes to worry about.
+        assert(DelayedDllExportClasses.empty() &&
+               "delayed exports present at explicit instantiation");
         checkClassLevelDLLAttribute(Def);
+        referenceDLLExportedClassMethods();
 
         // Propagate attribute to base class templates.
         for (auto &B : Def->bases()) {

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -1949,6 +1949,13 @@ Sema::InstantiateClass(SourceLocation PointOfInstantiation,
   bool MergeWithParentScope = !Instantiation->isDefinedOutsideFunctionOrMethod();
   LocalInstantiationScope Scope(*this, MergeWithParentScope);
 
+  // All dllexported classes created during instantiation should be fully
+  // emitted after instantiation completes. We may not be ready to emit any
+  // delayed classes already on the stack, so save them away and put them back
+  // later.
+  decltype(DelayedDllExportClasses) ExportedClasses;
+  std::swap(ExportedClasses, DelayedDllExportClasses);
+
   // Pull attributes from the pattern onto the instantiation.
   InstantiateAttrs(TemplateArgs, Pattern, Instantiation);
 
@@ -2034,6 +2041,9 @@ Sema::InstantiateClass(SourceLocation PointOfInstantiation,
   // default arg exprs for default constructors if necessary now.
   ActOnFinishCXXNonNestedClass(Instantiation);
 
+  // Put back the delayed exported classes that we moved out of the way.
+  std::swap(ExportedClasses, DelayedDllExportClasses);
+
   // Instantiate late parsed attributes, and attach them to their decls.
   // See Sema::InstantiateAttrs
   for (LateInstantiatedAttrVec::iterator I = LateAttrs.begin(),

clang/test/CodeGenCXX/dllexport-pr26549.cpp

@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 %s -fms-extensions -triple x86_64-windows-msvc -emit-llvm -o - | FileCheck %s
+
+template <typename> struct MessageT { };
+extern template struct MessageT<int>;
+
+// CHECK: define weak_odr dllexport {{.*}} %struct.MessageT* @"\01??4?$MessageT@H@@QEAAAEAU0@AEBU0@@Z"(
+template struct __declspec(dllexport) MessageT<int>;
+// Previously we crashed when this dllexport was the last thing in the file.
+// DO NOT ADD MORE TESTS AFTER THIS LINE!

clang/test/CodeGenCXX/dllexport.cpp

@@ -777,6 +777,17 @@ struct __declspec(dllexport) Baz {
 // M32-DAG: define weak_odr dllexport x86_thiscallcc dereferenceable(1) %"struct.InClassInits::Baz"* @"\01??4Baz@InClassInits@@QAEAAU01@ABU01@@Z"
 }
 
+// We had an issue where instantiating A would force emission of B's delayed
+// exported methods.
+namespace pr26490 {
+template <typename T> struct A { };
+struct __declspec(dllexport) B {
+  B(int = 0) {}
+  A<int> m_fn1() {}
+};
+// M32-DAG: define weak_odr dllexport x86_thiscallcc void @"\01??_FB@pr26490@@QAEXXZ"
+}
+
 
 //===----------------------------------------------------------------------===//
 // Classes with template base classes