[clang][bytecode] Emit diagnostics from GetGlobalUnchecked

If the global is uninitialized.

Author: tbaederr

clang/lib/AST/ByteCode/Interp.h

@@ -1433,7 +1433,7 @@ bool GetGlobal(InterpState &S, CodePtr OpPC, uint32_t I) {
 template <PrimType Name, class T = typename PrimConv<Name>::T>
 bool GetGlobalUnchecked(InterpState &S, CodePtr OpPC, uint32_t I) {
   const Pointer &Ptr = S.P.getPtrGlobal(I);
-  if (!Ptr.isInitialized())
+  if (!CheckInitialized(S, OpPC, Ptr, AK_Read))
     return false;
   S.Stk.push<T>(Ptr.deref<T>());
   return true;

clang/test/AST/ByteCode/cxx11.cpp

@@ -194,3 +194,11 @@ namespace DynamicCast {
     int g : (S*)(void*)(sptr) == sptr;
   };
 }
+
+namespace GlobalInitializer {
+  extern int &g; // both-note {{here}}
+  struct S {
+    int G : g; // both-error {{constant expression}} \
+               // both-note {{initializer of 'g' is unknown}}
+  };
+}