6610906: inexplicable IncompatibleClassChangeError

Summary: dependency check must treat polymorphic interfaces consistently
Reviewed-by: kvn, never, sgoldman

src/share/vm/code/dependencies.cpp

@@ -882,6 +882,14 @@ klassOop ClassHierarchyWalker::find_witness_in(DepChange& changes,
   // Must not move the class hierarchy during this check:
   assert_locked_or_safepoint(Compile_lock);
 
+  int nof_impls = instanceKlass::cast(context_type)->nof_implementors();
+  if (nof_impls > 1) {
+    // Avoid this case: *I.m > { A.m, C }; B.m > C
+    // %%% Until this is fixed more systematically, bail out.
+    // See corresponding comment in find_witness_anywhere.
+    return context_type;
+  }
+
   assert(!is_participant(new_type), "only old classes are participants");
   if (participants_hide_witnesses) {
     // If the new type is a subtype of a participant, we are done.

src/share/vm/code/nmethod.cpp

@@ -1971,7 +1971,7 @@ void nmethod::print_dependencies() {
     if (ctxk != NULL) {
       Klass* k = Klass::cast(ctxk);
       if (k->oop_is_instance() && ((instanceKlass*)k)->is_dependent_nmethod(this)) {
-        tty->print("   [nmethod<=klass]%s", k->external_name());
+        tty->print_cr("   [nmethod<=klass]%s", k->external_name());
       }
     }
     deps.log_dependency();  // put it into the xml log also