[clang][Interp] Fix DeclRefExprs of void-typed dummy pointers

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -3795,6 +3795,8 @@ bool ByteCodeExprGen<Emitter>::VisitDeclRefExpr(const DeclRefExpr *E) {
   if (std::optional<unsigned> I = P.getOrCreateDummy(D)) {
     if (!this->emitGetPtrGlobal(*I, E))
       return false;
+    if (E->getType()->isVoidType())
+      return true;
     // Convert the dummy pointer to another pointer type if we have to.
     if (PrimType PT = classifyPrim(E); PT != PT_Ptr) {
       if (!this->emitDecayPtr(PT_Ptr, PT, E))

clang/test/AST/Interp/c.c

@@ -278,3 +278,9 @@ void addrlabelexpr(void) {
  a0: ;
   static void *ps[] = { &&a0 }; // pedantic-warning {{use of GNU address-of-label extension}}
 }
+
+extern void cv2;
+void *foo5 (void)
+{
+  return &cv2; // pedantic-warning{{address of an expression of type 'void'}}
+}