Improve upper bound finalization in VM and fix #25122.

runtime/vm/class_finalizer.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/class_finalizer.h"
 
 #include "vm/code_generator.h"
 #include "vm/flags.h"
 #include "vm/heap.h"
 #include "vm/isolate.h"
@@ skipping 1251 matching lines @@
   const intptr_t num_type_params = cls.NumTypeParameters();
   TypeParameter& type_param = TypeParameter::Handle();
   AbstractType& bound = AbstractType::Handle();
   const TypeArguments& type_params =
       TypeArguments::Handle(cls.type_parameters());
   ASSERT((type_params.IsNull() && (num_type_params == 0)) ||
          (type_params.Length() == num_type_params));
   for (intptr_t i = 0; i < num_type_params; i++) {
     type_param ^= type_params.TypeAt(i);
     bound = type_param.bound();
-    if (bound.IsFinalized() || bound.IsBeingFinalized()) {
+    // Bound may be finalized, but not canonical yet.
+    if (bound.IsCanonical() || bound.IsBeingFinalized()) {
       // A bound involved in F-bounded quantification may form a cycle.
       continue;
     }
     bound = FinalizeType(cls, bound, kCanonicalize);
     type_param.set_bound(bound);
   }
 }
 
 
 void ClassFinalizer::ResolveAndFinalizeMemberTypes(const Class& cls) {
@@ skipping 941 matching lines @@
   }
   // Finalize super class.
   Class& super_class = Class::Handle(cls.SuperClass());
   if (!super_class.IsNull()) {
     FinalizeTypesInClass(super_class);
   }
   // Finalize type parameters before finalizing the super type.
   FinalizeTypeParameters(cls);  // May change super type.
   super_class = cls.SuperClass();
   ASSERT(super_class.IsNull() || super_class.is_type_finalized());
-  ResolveUpperBounds(cls);
+  // Only resolving rather than finalizing the upper bounds here would result in
+  // instantiated type parameters of the super type to temporarily have
+  // unfinalized bounds. It is more efficient to finalize them early.
+  FinalizeUpperBounds(cls);
   // Finalize super type.
   AbstractType& super_type = AbstractType::Handle(cls.super_type());
   if (!super_type.IsNull()) {
     // In case of a bound error in the super type in production mode, the
     // finalized super type will have a BoundedType as type argument for the
     // out of bound type argument.
     // It should not be a problem if the class is written to a snapshot and
     // later executed in checked mode. Note that the finalized type argument
     // vector of any type of the base class will contain a BoundedType for the
     // out of bound type argument.
@@ skipping 92 matching lines @@
     // 'ResolveAndFinalizeMemberTypes(cls)' has not been called yet, unfinalized
     // member types could choke the snapshotter.
     ASSERT(Array::Handle(cls.functions()).Length() == 0);
   }
 }
 
 
 void ClassFinalizer::FinalizeClass(const Class& cls) {
   Thread* thread = Thread::Current();
   HANDLESCOPE(thread);
+  ASSERT(cls.is_type_finalized());
   if (cls.is_finalized()) {
     return;
   }
   if (FLAG_trace_class_finalization) {
     THR_Print("Finalize %s\n", cls.ToCString());
   }
   if (cls.is_patch()) {
     // The fields and functions of a patch class are copied to the
     // patched class after parsing. There is nothing to finalize.
     ASSERT(Array::Handle(cls.functions()).Length() == 0);
@@ skipping 846 matching lines @@
   ASSERT(fields_array.Length() == ByteBuffer::NumberOfFields());
   field ^= fields_array.At(0);
   ASSERT(field.Offset() == ByteBuffer::data_offset());
   name ^= field.name();
   expected_name ^= String::New("_data");
   ASSERT(String::EqualsIgnoringPrivateKey(name, expected_name));
 #endif
 }
 
 }  // namespace dart