Using type feedback, eliminate store barriers for indexed stores.

runtime/vm/intermediate_language_x64.cc

 // 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.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/intermediate_language.h"
 
 #include "lib/error.h"
@@ skipping 933 matching lines @@
   // Note that index is Smi, i.e, times 4.
   ASSERT(kSmiTagShift == 1);
   Location index = locs()->in(1);
   FieldAddress field_address = index.IsConstant()
       ? FieldAddress(
           array,
           static_cast<int32_t>(
             Smi::Cast(index.constant()).Value() * kWordSize + sizeof(RawArray)))
       : FieldAddress(array, index.reg(), TIMES_4, sizeof(RawArray));
 
-  if (this->value()->NeedsStoreBuffer()) {
+  if (this->value()->NeedsStoreBuffer() && emit_store_barrier()) {
       Register value = locs()->in(2).reg();
     __ StoreIntoObject(array, field_address, value);
   } else {
     if (locs()->in(2).IsConstant()) {
       const Object& constant = locs()->in(2).constant();
       __ StoreObject(field_address, constant);
     } else {
       Register value = locs()->in(2).reg();
       __ StoreIntoObjectNoBarrier(array, field_address, value);
     }
@@ skipping 1340 matching lines @@
     __ j(ABOVE_EQUAL, deopt);
   }
 }
 
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_X64