[MinGW] Produce a vtable and RTTI for dllexported classes without a key function

This matches what GCC does in these situations.

This fixes compiling Qt in debug mode. In release mode, references to
the vtable of this particular class ends up optimized away, but in debug
mode, the compiler creates references to the vtable, which is expected
to be dllexported from a different DLL. Make sure the dllexported
version actually ends up emitted.

Differential Revision: https://reviews.llvm.org/D55698

llvm-svn: 349256

2 files changed, 25 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 4a7ab11c715..d56c8803113 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -5528,6 +5528,9 @@ static void ReferenceDllExportedMembers(Sema &S, CXXRecordDecl *Class) {
     // declaration.
     return;
 
+  if (S.Context.getTargetInfo().getTriple().isWindowsGNUEnvironment())
+    S.MarkVTableUsed(Class->getLocation(), Class, true);
+
   for (Decl *Member : Class->decls()) {
     // Defined static variables that are members of an exported base
     // class must be marked export too.
diff --git a/clang/test/CodeGenCXX/dllexport-missing-key.cpp b/clang/test/CodeGenCXX/dllexport-missing-key.cpp
new file mode 100644
index 00000000000..90e736f6fad
--- /dev/null
+++ b/clang/test/CodeGenCXX/dllexport-missing-key.cpp
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -triple x86_64-windows-gnu -emit-llvm -std=c++11 -o - %s | FileCheck --check-prefix=GNU %s
+
+class __declspec(dllexport) QAbstractLayoutStyleInfo {
+public:
+  QAbstractLayoutStyleInfo() : m_isWindow(false) {}
+  virtual ~QAbstractLayoutStyleInfo() {}
+
+  virtual bool hasChangedCore() const { return false; }
+
+  virtual void invalidate() {}
+
+  virtual double windowMargin(bool orientation) const = 0;
+
+  bool isWindow() const { return m_isWindow; }
+
+protected:
+  bool m_isWindow;
+};
+
+// GNU-DAG: @_ZTV24QAbstractLayoutStyleInfo = weak_odr dso_local dllexport
+// GNU-DAG: @_ZTS24QAbstractLayoutStyleInfo = linkonce_odr
+// GNU-DAG: @_ZTI24QAbstractLayoutStyleInfo = linkonce_odr