Avoid re-tagging of the index register in optimized byte array access.

runtime/vm/locations.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/locations.h"
 
 #include "vm/assembler.h"
 #include "vm/il_printer.h"
 #include "vm/intermediate_language.h"
 #include "vm/flow_graph_compiler.h"
@@ skipping 60 matching lines @@
 
 
 Location Location::FixedRegisterOrSmiConstant(Value* value, Register reg) {
   ConstantInstr* constant = value->definition()->AsConstant();
   return ((constant != NULL) && constant->value().IsSmi())
       ? Location::Constant(constant->value())
       : Location::RegisterLocation(reg);
 }
 
 
+Location Location::WritableRegisterOrSmiConstant(Value* value) {
+  ConstantInstr* constant = value->definition()->AsConstant();
+  return ((constant != NULL) && constant->value().IsSmi())
+      ? Location::Constant(constant->value())
+      : Location::WritableRegister();
+}
+
+
 Location Location::AnyOrConstant(Value* value) {
   ConstantInstr* constant = value->definition()->AsConstant();
   return (constant != NULL)
       ? Location::Constant(constant->value())
       : Location::Any();
 }
 
 
 Address Location::ToStackSlotAddress() const {
   const intptr_t index = stack_index();
@@ skipping 80 matching lines @@
 
   if (!out().IsInvalid()) {
     f->Print(" => ");
     out().PrintTo(f);
   }
 
   if (always_calls()) f->Print(" C");
 }
 
 }  // namespace dart