Improve type optimization reusing the type argument vector of the instantiator

runtime/vm/object.h

 // Copyright (c) 2012, 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.
 
 #ifndef VM_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ skipping 4763 matching lines @@
   }
   void SetAt(intptr_t index, const Object& value) const {
     // TODO(iposva): Add storing NoGCScope.
     StorePointer(ObjectAddr(index), value.raw());
   }
 
   virtual RawAbstractTypeArguments* GetTypeArguments() const {
     return raw_ptr()->type_arguments_;
   }
   virtual void SetTypeArguments(const AbstractTypeArguments& value) const {
-    ASSERT(value.IsNull() || ((value.Length() == 1) && value.IsInstantiated()));
+    // An Array is raw or takes one type argument. However, its type argument
+    // vector may be longer than 1 due to a type optimization reusing the type
+    // argument vector of the instantiator.
+    ASSERT(value.IsNull() || ((value.Length() >= 1) && value.IsInstantiated()));
     StorePointer(&raw_ptr()->type_arguments_, value.raw());
   }
 
   virtual bool Equals(const Instance& other) const;
 
   static const intptr_t kBytesPerElement = kWordSize;
   static const intptr_t kMaxElements = kSmiMax / kBytesPerElement;
 
   static intptr_t type_arguments_offset() {
     return OFFSET_OF(RawArray, type_arguments_);
@@ skipping 107 matching lines @@
 
   void Add(const Object& value, Heap::Space space = Heap::kNew) const;
 
   void Grow(intptr_t new_capacity, Heap::Space space = Heap::kNew) const;
   RawObject* RemoveLast() const;
 
   virtual RawAbstractTypeArguments* GetTypeArguments() const {
     return raw_ptr()->type_arguments_;
   }
   virtual void SetTypeArguments(const AbstractTypeArguments& value) const {
-    ASSERT(value.IsNull() || ((value.Length() == 1) && value.IsInstantiated()));
+    // A GrowableObjectArray is raw or takes one type argument. However, its
+    // type argument vector may be longer than 1 due to a type optimization
+    // reusing the type argument vector of the instantiator.
+    ASSERT(value.IsNull() || ((value.Length() >= 1) && value.IsInstantiated()));
     const Array& contents = Array::Handle(data());
     contents.SetTypeArguments(value);
     StorePointer(&raw_ptr()->type_arguments_, value.raw());
   }
 
   virtual bool Equals(const Instance& other) const;
 
   static intptr_t type_arguments_offset() {
     return OFFSET_OF(RawGrowableObjectArray, type_arguments_);
   }
@@ skipping 782 matching lines @@
 
 
 RawObject* MegamorphicCache::GetTargetFunction(const Array& array,
                                                intptr_t index) {
   return array.At((index * kEntryLength) + kTargetFunctionIndex);
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_