Sped up hashCode by removing megamorphic call to _identityHashCode.

runtime/lib/object.cc

 // Copyright (c) 2011, 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/bootstrap_natives.h"
 
 #include "lib/invocation_mirror.h"
 #include "vm/code_patcher.h"
 #include "vm/exceptions.h"
 #include "vm/heap.h"
@@ skipping 21 matching lines @@
 
 
 DEFINE_NATIVE_ENTRY(Object_equals, 1) {
   // Implemented in the flow graph builder.
   UNREACHABLE();
   return Object::null();
 }
 
 
 DEFINE_NATIVE_ENTRY(Object_getHash, 1) {
-  const Instance& instance = Instance::CheckedHandle(arguments->NativeArgAt(0));
+  // Please note that no handle is created for the argument.
+  // This is safe since the argument is only used in a tail call.
+  // The performance benefit is more than 5% when using hashCode.

[siva, 2016/07/08 22:12:10]

Maybe add:

ASSERT(arguments->NativeArgAt(0)->IsDartInstance());

[bakster, 2016/07/08 22:15:11]

Done.

   Heap* heap = isolate->heap();
-  return Smi::New(heap->GetHash(instance.raw()));
+  return Smi::New(heap->GetHash(arguments->NativeArgAt(0)));
 }
 
 
 DEFINE_NATIVE_ENTRY(Object_setHash, 2) {
   const Instance& instance = Instance::CheckedHandle(arguments->NativeArgAt(0));
   GET_NON_NULL_NATIVE_ARGUMENT(Smi, hash, arguments->NativeArgAt(1));
   Heap* heap = isolate->heap();
   heap->SetHash(instance.raw(), hash.Value());
   return Object::null();
 }
@@ skipping 274 matching lines @@
 
 DEFINE_NATIVE_ENTRY(Internal_inquireIs64Bit, 0) {
 #if defined(ARCH_IS_64_BIT)
   return Bool::True().raw();
 #else
   return Bool::False().raw();
 #endif  // defined(ARCH_IS_64_BIT)
 }
 
 }  // namespace dart