Optimize LocalVarDescriptor objects for functions that have no local variables

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 375 matching lines @@
   static const Array& zero_array() {
     ASSERT(zero_array_ != NULL);
     return *zero_array_;
   }
 
   static const PcDescriptors& empty_descriptors() {
     ASSERT(empty_descriptors_ != NULL);
     return *empty_descriptors_;
   }
 
+  static const LocalVarDescriptors& empty_var_descriptors() {
+    ASSERT(empty_var_descriptors_ != NULL);
+    return *empty_var_descriptors_;
+  }
+
   // The sentinel is a value that cannot be produced by Dart code.
   // It can be used to mark special values, for example to distinguish
   // "uninitialized" fields.
   static const Instance& sentinel() {
     ASSERT(sentinel_ != NULL);
     return *sentinel_;
   }
   // Value marking that we are transitioning from sentinel, e.g., computing
   // a field value. Used to detect circular initialization.
   static const Instance& transition_sentinel() {
@@ skipping 257 matching lines @@
   // The static values below are read-only handle pointers for singleton
   // objects that are shared between the different isolates.
   static Object* null_object_;
   static Array* null_array_;
   static String* null_string_;
   static Instance* null_instance_;
   static TypeArguments* null_type_arguments_;
   static Array* empty_array_;
   static Array* zero_array_;
   static PcDescriptors* empty_descriptors_;
+  static LocalVarDescriptors* empty_var_descriptors_;
   static Instance* sentinel_;
   static Instance* transition_sentinel_;
   static Instance* unknown_constant_;
   static Instance* non_constant_;
   static Bool* bool_true_;
   static Bool* bool_false_;
   static Smi* smi_illegal_cid_;
   static LanguageError* snapshot_writer_error_;
   static LanguageError* branch_offset_error_;
 
@@ skipping 2409 matching lines @@
         sizeof(RawLocalVarDescriptors) + (len * kBytesPerElement));
   }
 
   static RawLocalVarDescriptors* New(intptr_t num_variables);
 
   static const char* KindToStr(intptr_t kind);
 
  private:
   FINAL_HEAP_OBJECT_IMPLEMENTATION(LocalVarDescriptors, Object);
   friend class Class;
+  friend class Object;
 };
 
 
 class PcDescriptors : public Object {
  public:
   void AddDescriptor(intptr_t index,
                      uword pc,
                      RawPcDescriptors::Kind kind,
                      int64_t deopt_id,
                      int64_t token_pos,  // Or deopt reason.
@@ skipping 4340 matching lines @@
 
 
 RawObject* MegamorphicCache::GetTargetFunction(const Array& array,
                                                intptr_t index) {
   return array.At((index * kEntryLength) + kTargetFunctionIndex);
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_