fixes #7392 (#7395)

compiler/ccgexprs.nim

@@ -2044,6 +2044,7 @@ proc upConv(p: BProc, n: PNode, d: var TLoc) =
       if t.kind notin {tyVar, tyLent} or not p.module.compileToCpp:
         r = "(*$1)" % [r]
       t = skipTypes(t.lastSon, abstractInst)
+    discard getTypeDesc(p.module, t)
     if not p.module.compileToCpp:
       while t.kind == tyObject and t.sons[0] != nil:
         add(r, ".Sup")

tests/ccgbugs/mymodule.nim

@@ -1,7 +1,9 @@
 type
   MyRefObject* = ref object
     s: string
-
+  
+  BaseObj* = ref object of RootObj
+  ChildObj* = ref object of BaseObj
 
 proc newMyRefObject*(s: string): MyRefObject =
   new(result)

tests/ccgbugs/tforward_decl_only.nim

@@ -27,3 +27,8 @@ proc f(foo: ptr Foo, foo2: ptr Foo2): cint =
   if foo2 != nil: {.emit: [result, " = ", foo2[], ".b;"].}
 
 discard f(nil, nil)
+
+
+# bug #7392
+var x1: BaseObj
+var x2 = ChildObj(x1)